| 1. |
- Alkaissi, Hammoudi, 1983-
(författare)
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Identification of candidate genes involved in Mercury Toxicokinetics and Mercury Induced Autoimmunity
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BACKGROUND: Autoimmune diseases require the involvement and activation of immune cells and occur when the body builds up an immune response against its own tissues. This process takes place due to the inability to distinguish self-antigen from foreign antigen. Systemic autoimmunity represents an important cause of morbidity and mortality in humans. The mechanisms triggering autoimmune responses are complex and involve a network of genetic factors. Genome wide association study (GWAS) is a powerful method, used to identify genetic risk factors in numerous diseases, such as systemic autoimmune diseases. The goal of GWAS is to identify these genetic risk factors in order to make predictions about who is at risk and investigate the biological process of disease susceptibility. There are several valuable mouse models to investigate the underlying mechanisms causing systemic autoimmune diseases in which mercury induced autoimmunity (HgIA) is a well- established and relevant model. HgIA in mice includes development of autoantibodies, immune complex glomerulonephritis, lymphocyte proliferation, hypergammaglobulinemia and polyclonal B cell activation. In humans, mercury exposure accumulates with considerable concentrations in kidney, liver, and brain. Toxicokinetics of Hg has been studied extensively but the key for inter-individual variation in humans are largely unclear. Differences in accumulation of renal Hg between inbred mouse strains suggest a genetic inter-strain variation regulating retention or/and excretion of Hg.OBJECTIVES: To find loci and candidate genes associated with phenotypes involved in the development of autoimmunity and find candidate genes involved in the regulation of renal Hg excretion.METHODS: MHC II (H-2s) mice were paired (A.SW x B10.S) to obtain F2 offspring exposed to 2.0 or 4.0 mg Hg in drinking water for 6 weeks. Mercury induced autoimmune phenotypes were studied with immunofluorescence (anti-nucleolar antibodies (ANoA)), ELISA anti-DNP/anti-ssDNA (polyclonal B cell activation), anti-chromatin antibodies (ACA) (4.0 mg Hg), and serum IgG1 concentrations. Mercury accumulation in kidney was performed previously and data was included as phenotype. F2 mice exposed to 2.0 mg Hg were genotyped with microsatellites for genome-wide scan with Ion Pair Reverse Phase High Performance Liquid Chromatography (IP RP HPLC). F2 mice exposed to 4.0 mg Hg were genotyped with single nucleotide polymorphisms for genomewide scan with SNP&SEQ technology platform. Quantitative trait loci (QTL) was established with R/QTL. Denaturing HPLC, next generation sequencing, conserved region analysis and genetic mouse strain comparison were used for haplotyping and fine mapping on QTLs associated with Hg concentration in kidney, development of ANoA and serum IgG1 hypergammaglobulinemia. Candidate genes (Pprc1, Bank1 and Nfkb1) verified by additional QTL were further investigated by real time polymerase chain reaction. Genes involved in the intracellular signaling together with candidate genes were included for gene expression analysis.RESULTS: F2 mice exposed to 2.0 mg Hg had low or no development of autoantibodies and showed no significant difference in polyclonal B cell activation in the B10.S and F2 strains. F2 mice exposed to 4.0 mg Hg developed autoantibodies and significantly increased IgG1 concentration and polyclonal B cell activation (anti-DNP). QTL analysis showed a logarithm of odds ratio (LOD) score between 2.9 – 4.36 on all serological phenotypes exposed to 4.0 mg Hg, and a LOD score of 5.78 on renal Hg concentration. Haplotyping and fine mapping associated the development of ANoA with Bank1 (B-cell scaffold protein with ankyrin repeats 1) and Nfkb1 (nuclear factor kappa B subunit 1). The serum IgG1 concentration was associated with a locus on chromosome 3, in which Rxfp4 (Relaxin Family Peptide/INSL5 Receptor 4) is a potential candidate gene. The renal Hg concentration was associated with Pprc1 (Peroxisome Proliferator-Activated Receptor Gamma, Co-activator-Related). Gene expression analysis revealed that the more susceptible A.SW strain expresses significantly higher levels of Nfkb1, Il6 and Tnf than the less susceptible B10.S strain. The A.SW strain expresses significantly lower levels of Pprc1 and cascade proteins than the B10.S strain. Development of ACA was associated with chromosomes 3, 6, 7 and 16 (LOD 3.1, 3.2, 3.4 and 6.8 respectively). Polyclonal B cell activation was associated with chromosome 2 with a LOD score of 2.9.CONCLUSIONS: By implementing a GWAS on HgIA in mice, several QTLs were discovered to be associated with the development of autoantibodies, polyclonal B cell activation and hypergammaglobulinemia. This thesis plausibly supports Bank1 and Nfkb1 as key regulators for ANoA development and HgIA seems to be initiated by B cells rather than T cells. GWAS on renal mercury excretion plausibly supports Pprc1 as key regulator and it seems that this gene has a protective role against Hg.
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| 2. |
- Halim, Joseph, 1985-
(författare)
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Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.
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| 3. |
- Olsson, Hans
(författare)
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Stage T1 Urinary Bladder Carcinoma : Investigation of A Population-Based Cohort
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Approximately 2 300 new cases of urinary bladder carcinoma (UBC) are diagnosed every year in Sweden. This type of cancer is characterized as a long-standing disease with a high risk of recurrence and progression from an indolent to a more aggressive course. UBC occurs in a non-muscle-invasive form (stages Ta and T1), which is treated mainly with local resection and BCG instillation, and a muscle-invasive form (stage ≥ T2), for which the treatment of choice is irradiation or cystectomy.The aim of the research underlying this thesis was to explore the factors involved in tumor development and progression, and to find prognostic markers for recurrence and progression in patients with primary stage T1 urothelial carcinoma of the bladder (UCB).Tumor tissue in archived paraffin blocks from patients diagnosed with that type of malignancy was used in the four studies that were conducted. This was a population-based project, because all of the patients had been reported to the cancer center in the Southeast Healthcare Region in Sweden from 1992 to 2001. The follow-up time was comparable long in the cases included and was intended to be at least 10 years.The hospital records were reviewed to gather information on clinical characteristics of the tumors, such as size and multiplicity, as well as treatment modalities, recurrence and/or progression, and eventual death from UBC. The original tumor slides were re-evaluated. These two initial activities yielded a study population comprising 211 well-characterized patients with primary T1 UCB. Some of the originally selected patients were excluded due to missing paraffin blocks or poor quality of the tumor material, the latter being particularly important in the genetic analyses conducted in the fourth study.Ordinary light microscopy was performed to evaluate specific tumor characteristics, such as lymphovascular tumor infiltration, and for T1 sub-staging. Immunohistochemistry was carried out to, among other things, analyze cell cycle regulators. Furthermore, pyrosequencing, single-strand conformation analysis (SSCA), and Sanger sequencing were conducted in the fourth study to assess mutations in the p53 gene and murine double minute 2 SNP309 promoter polymorphism. Statistical analyses to estimate the risk of tumor recurrence and progression were carried out in all four investigations.Conclusions: This population-based cohort of patients with well-characterized T1 tumors of the urinary bladder showed high rates of recurrence (80%) and progression (39%), and the aggressiveness is underlined by the fact that 32% died from the disease. Lymphovascular tumor infiltration and abnormal immunohistochemical staining for p16 were found to be associated with tumor progression, and in the future analysis of these parameters might be used in treatment decisions regarding T1 bladder tumors. No other clinical or pathological variable or cell cycle regulator was associated with progression, and none of the genetic analyses conducted in the current studies were helpful in predicting outcome or explaining the mechanisms of tumor development.
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| 4. |
- Bergh Johannesson, Kerstin, 1949-
(författare)
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Traumatic Exposure, Bereavement and Recovery among Survivors and Close Relatives after Disasters
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- International studies of disasters indicate the risk for developing posttraumatic stress reactions among survivors is high. Modern life implicates increased traveling. During the last decades a large number of Swedish citizens were confronted with disasters taking place outside of their country. The prevalence of trauma reactions in a population that does not normally experience natural disasters, but are able to return to a community unaffected by the catastrophe, is not well studied. In addition, the effects of bereavement after traumatic circumstances have not been satisfactorily explored. Longitudinal studies on the effects of natural disasters are underrepresented and there are few studies investigating the course of recovery after traumatic exposure. The aim for this thesis was to examine long-term post-traumatic stress reactions, mental health, and complicated grief after disaster exposure and traumatic bereavement. Data from returned questionnaires were analysed from bereaved Italian and Swedish relatives 18 months after the Linate airplane disaster 2001, and at 14 months and three years from Swedish travelers returning from Southeast Asia after the 2004 tsunami disaster, and from home staying bereaved relatives within the second year after the tsunami disaster. The main outcome measures were GHQ-12, IES-R and Inventory of Complicated Grief. The findings indicated many survivors were resilient and had ability to recover, but severe exposure to a disaster had considerable impact on psychological distress. Life threat was associated with higher levels of post-traumatic stress reactions, and increased the risk for affected mental health and suicidal ideation. Loss in combination with severe life threat exposure indicated a further increased risk of posttraumatic stress reactions and for complicated grief; this should be considered a substantial risk factor for general mental health. Loss of close relatives, especially loss of children, was associated with higher levels of posttraumatic stress and created a greater risk for complicated grief. Many survivors recovered over time; however, severe exposure and traumatic loss appeared to slow the recovery process. The findings have implications for government and health agencies, regarding the importance of knowledge and awareness of these risks for health, and for organizational structure, training, and accessibility of support and adequate treatment.
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| 5. |
- Buchholt, Kristina, 1978-
(författare)
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Nanostructured materials for gas sensing applications
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis I have investigated the use of nanostructured films as sensing and contact layers for field effect gas sensors in order to achieve high sensitivity, selectivity, and long term stability of the devices in corrosive environments at elevated temperatures. Electrochemically synthesized Pd and Au nanoparticles deposited as sensing layers on capacitive field effect devices were found to give a significant response to NOx with small, or no responses to H2, NH3, and C3H6. Pt nanoparticles incorporated in a TiC matrix are catalytically active, but the agglomeration and migration of the Pt particles towards the substrate surface reduces the activity of the sensing layer. Magnetron sputtered epitaxial films from the Ti-Si-C and the Ti-Ge-C systems were grown on 4H-SiC substrates in order to explore their potential as high temperature stable ohmic contact materials to SiC based field effect gas sensors. Ti3SiC2 thin films deposited on 4H-SiC substrates were found to yield ohmic contacts to n-type SiC after a high temperature rapid thermal anneal at 950 ºC. Investigations on the growth mode of Ti3SiC2 thin films with varying Si content on 4H-SiC substrates showed the growth to be lateral step-flow with the propagation of steps with a height as small as half a unit cell. The amount of Si present during deposition leads to differences in surface faceting of the films and Si-supersaturation conditions gives growth of Ti3SiC2 films with the presence of TiSi2 crystallites. Current-voltage measurements of the as-deposited Ti3GeC2 films indicate that this material is also a promising candidate for achieving long term stable contact layers to 4H-SiC for operation at elevated temperatures in corrosive environments. Further investigations into the Ti-Ge-C system showed that the previously unreported solid solutions of (Ti,V)2GeC, (Ti,V)3GeC2 and (Ti,V)4GeC3 can be synthesized, and it was found that the growth of these films is affected by the nature of the substrate.
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| 6. |
- Fashandi, Hossein, 1984-
(författare)
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Novel Layered and 2D Materials for Functionality Enhancement of Contacts and Gas Sensors
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chemical gas sensors are widely-used electronic devices for detecting or measuring the density levels of desired gas species. In this study, materials with established or potential applications for gas sensors are treated. For the case of high-temperature applications (≈ 600 °C), semiconductor-based gas sensors suffer from rapid oxidation of the metallic ohmic contacts, the same cause-of-failure as for the general case of high-temperature semiconductor electronics. 4H-SiC is an ideal semiconductor for high-temperature applications. Ti3SiC2 is a known ohmic contact to 4H-SiC with the known two-step synthesis process of post-annealing of pre-deposited Ti/Al multilayers or sputter-deposition of Ti3SiC2 films at > 900 °C. Here, sputter-deposition of Ti on 4H-SiC at > 900 °C is presented as a novel single-step method for the synthesis of Ti3SiC2 ohmic contacts, based on a concurrent reaction between sputter-deposited Ti and 4HSiC. Ti3SiC2, similar to any other known ohmic contact, degrade rapidly in high-temperature oxidizing ambient. To try to overcome this obstacle, noble metal diffusion into Ti3SiC2 has been s studied with the goal to retain ohmic properties of Ti3SiC2 and harnessing oxidation resistivity of noble metals. A novel exchange intercalation between Ti3SiC2 and Au is discovered which results in the almost complete exchange of Si with Au giving rise to novel Ti3AuC2 and Ti3Au2C2. Ti3IrC2 is also synthesized through exchange intercalation of Ir into Ti3Au2C2. All the aforementioned phases showed ohmic properties to 4H-SiC. This technique is also studied based on Ti2AlC and Ti3AlC2 resulting in the synthesis of novel Ti2Au2C and Ti3Au2C2, respectively. Using Ti3AuC2 and an Au/IrOx capping layer, an ohmic contact was manufactured, which maintained ohmic properties and showed no structural defects after 1000 h of aging at 600 °C air.Ti3SiC2 is a member of a large family of materials known as Mn+1AXn phases. While exchange reactions of Si (or Al) planes in Ti3SiC2 (Ti2AlC and Ti3AlC2) is presented here, a world-wide research already exists on chemical removal of the same atomic planes from different Mn+1AXn phases and the synthesis of Mn+1Xn sheets known as MXenes. I performed a theoretical study regarding simulation of electronic and structural properties of more than120 different possible MXene phases. The results show that some MXene phases, when terminated by particular gas species, turn into Dirac materials. That is, they possess massless Dirac fermions with different properties compared to graphene such as higher number of Dirac points at the Fermi level, giant spin orbit splitting, and preserved 2D-type electronic properties by extending the dimensionality. The general substantial change of the electronic properties of MXenes under different gas adsorption configurations stands out and can thus be harnessed for sensing applications.Growth of monolayer iron oxide on porous Pt sensing layers is another novel approach used in this study for applying the unique properties of 2D materials for gas sensors. A low temperature shift in CO oxidation characteristics is presented. The approach is similar to that previously reported using bulk single crystal Pt substrate, the latter being an unrealistic model for sensors and catalysts. Monolayer-coated Pt sensing layers were fabricated as the metal component of a metal oxide semiconductor (MOS) capacitor device, whereby the electrical response of the MOS device could be used to map out the catalytic properties of the sensing layer. The monolayer-coated Pt surface showed to be stable with retained improved catalytic properties for > 200 h. The MOS device measurements are here utilized as a handy method for in-situ monitoring of the surface chemical properties of the monolayer-coated Pt and the approach is highly functional for use and characterization of monolayer coatings of widely used sensingor catalytic layers.
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| 7. |
- Halim, Joseph, 1985-
(författare)
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Synthesis and transport properties of 2D transition metal carbides (MXenes)
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the isolation and characterization of graphene, there has been a growing interest in 2D materials owing to their unique properties compared to their 3D counterparts. Recently, a family of 2D materials of early transition metal carbides and nitrides, labelled MXenes, has been discovered (Ti2CTz, Ti3C2Tz, Mo2TiC2Tz, Ti3CNTz, Ta4C3Tz, Ti4N3Tz among many others), where T stands for surface-terminating groups (O, OH, and F). MXenes are mostly produced by selectively etching A layers (where A stands for group A elements, mostly groups 13 and 14) from the MAX phases. The latter are a family of layered ternary carbides and/or nitrides and have a general formula of Mn+1AXn (n = 1-3), where M is a transition metal and X is carbon and/or nitrogen. The produced MXenes have a conductive carbide core and a non-conductive O-, OH- and/or F-terminated surface, which allows them to work as electrodes for energy storage applications, such as Li-ion batteries and supercapacitors.Prior to this work, MXenes were produced in the form of flakes of lateral dimension of about 1 to 2 microns; such dimensions and form are not suitable for electronic characterization and applications. I have synthesized various MXenes (Ti3C2Tz, Ti2CTz and Nb2CTz) as epitaxial thin films, a more suitable form for electronic and photonic applications. These films were produced by HF, NH4HF2 or LiF + HCl etching of magnetron sputtered epitaxial Ti3AlC2, Ti2AlC, and Nb2AlC thin films. For transport properties of the Ti-based MXenes, Ti2CTz and Ti3C2Tz, changing n from 1 to 2 resulted in an increase in conductivity but had no effect on the transport mechanism (i.e. both Ti3C2Tx and Ti2CTx were metallic). In order to examine whether the electronic properties of MXenes differ when going from a few layers to a single flake, similar to graphene, the electrical characterization of a single Ti3C2Tz flake with a lateral size of about 10 μm was performed. These measurements, the first for MXene, demonstrated its metallic nature, along with determining the nature of the charge carriers and their mobility. This indicates that Ti3C2Tz is inherently of 2D nature independent of the number of stacked layers, unlike graphene, where the electronic properties change based on the number of stacked layers.Changing the transition metal from Ti to Nb, viz. comparing Ti2CTz and Nb2CTz thin films, the electronic properties and electronic conduction mechanism differ. Ti2CTz showed metallic-like behavior (resistivity increases with increasing temperature) unlike Nb2CTz where the conduction occurs via variable range hopping mechanism (VRH) - where resistivity decreases with increasing temperature.Furthermore, these studies show the synthesis of pure Mo2CTz in the form of single flakes and freestanding films made by filtering Mo2CTz colloidal suspensions. Electronic characterization of free-standing films made from delaminated Mo2CTz flakes was investigated, showing that a VRH mechanism prevails at low temperatures (7 to ≈ 60 K). Upon vacuum annealing, the room temperature, RT, conductivity of Mo2CTx increased by two orders of magnitude. The conduction mechanism was concluded to be VRH most likely dominated by hopping within each flake.Other Mo-based MXenes, Mo2TiC2Tz and Mo2Ti2C3Tz, showed VRH mechanism at low temperature. However, at higher temperatures up to RT, the transport mechanism was not clearly understood. Therefore, a part of this thesis was dedicated to further investigating the transport properties of Mo-based MXenes. This includes Mo2CTz, out-of-plane ordered Mo2TiC2Tz and Mo2Ti2C3Tz, and vacancy ordered Mo1.33CTz. Magneto-transport of free-standing thin films of the Mo-based MXenes were studied, showing that all Mo-based MXenes have two transport regimes: a VRH mechanism at lower temperatures and a thermally activated process at higher temperatures. All Mo-based MXenes except Mo1.33CTz show that the electrical transport is dominated by inter-flake transfer. As for Mo1.33CTz, the primary electrical transport mechanism is more likely to be intra-flake.The synthesis of vacancy ordered MXenes (Mo1.33CTz and W1.33CTz) raised the question of possible introduction of vacancies in all MXenes. Vacancy ordered MXenes are produced by selective etching of Al and (Sc or Y) atoms from the parent 3D MAX phases, such as (Mo2/3Sc1/3)2AlC, with in-plane chemical ordering of Mo and Sc. However, not all quaternary parent MAX phases form the in-plane chemical ordering of the two M metals; thus the synthesis of the vacancy-ordered MXenes is restricted to a very limited number of MAX phases. I present a new method to obtain MXene flakes with disordered vacancies that may be generalized to all quaternary MAX phases. As proof of concept, I chose Nb-C MXene, as this 2D material has shown promise in several applications, including energy storage, photothermal cell ablation and photocatalysts for hydrogen evolution. Starting from synthetizing (Nb2/3Sc1/3)2AlC quaternary solid solution and etching both the Sc and Al atoms resulted in Nb1.33C material with a large number of vacancies and vacancy clusters. This method may be applicable to other quaternary or higher MAX phases wherein one of the transition metals is more reactive than the other, and it could be of vital importance in applications such as catalysis and energy storage.
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| 8. |
- Lai, Chung-Chuan
(författare)
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Phase Formation of Nanolaminated Transition Metal Carbide Thin Films
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research on inherently nanolaminated transition metal carbides is inspired by their unique properties combining metals and ceramics, such as higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining the metallic conductivity. The interesting properties are related to their laminated structure, composed of transition-metalcarbide layers interleaved by non-transition-metal (carbide) layers. These materials in thin-film form are particularly interesting for potential applications such as protective coatings and electrical contacts. The goal of this work is to explore nanolaminated transition metal carbides from the aspects of phase formation and crystal growth during thin-film synthesis. This was realized by studying phases in select material systems synthesized from two major approaches, namely, fromdirect-deposition and post-deposition treatment.The first approach was used in studies on the Mo-Ga-C and Zr-Al-C systems. In the former system, intriguing properties have been predicted for the 3D phases and their 2D derivatives (socalled MXenes), while in the latter system, the phases are interesting for nuclear applications. In this work, the discovery of a new Mo-based nanolaminated ternary carbide, Mo2Ga2C, is evidenced from thin-film and bulk processes. Its structure was determined using theoretical and experimental techniques, showing that Mo2Ga2C has Ga double-layers in simple hexagonal stacking between adjacent Mo2C layers, and therefore is structurally very similar to Mo2GaC, except for the additional Ga layers. For the Zr-Al-C system, the optimization of phase composition and structure of Zr2Al3C4 in a thin-film deposition process was studied by evaluating the effect of deposition parameters. I concluded that the formation of Zr2Al3C4 is favored with a plasma flux overstoichiometric in Al, and with a minimum lattice-mismatch to the substrates. Consequently, epitaxial Zr2Al3C4 thin film of high quality were deposited on 4H-SiC(001) substrates at 800 °C.With the approach of post-deposition treatment, the studies were focused on a new method of thermally-induced selective substitution reaction of Au for the non-transition-metal layers in nanolaminated carbides. Here, the reaction mechanism has been explored in Al-containing (Ti2AlCand Ti3AlC2) and Ga-containing (Mo2GaC and Mo2Ga2C) phases. The Al and Ga in these phases were selectively replaced by Au while the carbide layers remained intact, resulting in the formation of new layered phases, Ti2Au2C, Ti3Au2C2, Mo2AuC, and Mo2(Au1-xGax)2C, respectively. The substitution reaction was explained by fast outward diffusion of the Al or Ga being attracted to the surface Au, in combination with back-filling of Au, which is chemically inert to the carbide layers,to the vacancies.The substitution reaction was further applied to Ga-containing nanolaminated carbides, (Cr0.5Mn0.5)2GaC and Mo2GaC, motivated by development of novel magnetic nanolaminates. The former experiment resulted in the formation of (Cr0.5Mn0.5)2AuC, where the retained (Cr0.5Mn0.5)2C layers allowed a comparative study on the magnetic properties under the exchange of Ga for Au. After Au substitution, reduction in the Curie temperature and the saturation magnetization were observed, showing a weakened magnetic exchange interaction of the magnetic (Cr0.5Mn0.5)2 Clayers across the Au. In the Mo2GaC case, an Fe-containing MAX phase, Mo2AC with 50 at.% of Fe on the A site, was synthesized through selective substitution of Au-Fe alloy for the Ga layers, showing the first direct evidence for Fe in the MAX-phase structure. The substitution of Fe did not take place on another Mo2GaC sample tested for Fe exchange only, indicating the essential role of Au in catalyzing the Fe-substitution reaction.The knowledge gained from this thesis work contributes to improved approaches for attaining thin films of nanolaminated transition metal carbides with desired phase composition and crystal quality. The reports on the new nanolaminated phases through exchange interactions are likely to expand the family of nanolaminated carbides and advance their properties, and trigger more studies on related (quasi-) 2D materials.
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| 9. |
- Clifford, Jenny, 1980-
(författare)
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Gold allergy : In vitro studies using peripheralblood mononuclear cells
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Positive patch test reactions to gold are commonly seen in dermatology clinics, but it is veryunusual for the patients to actually have any clinical symptoms. It is also common with irritantreactions that are not linked to adaptive immunity. Therefore, a deeper understanding of themechanisms underlying allergic contact dermatitis (ACD) reaction, and the search for acomplementing diagnostic tool, is important.In paper I we included three subject groups; one with morphologically positive patch testreactions to gold sodium thiosulphate (GSTS, the gold salt used in patch testing), one withnegative patch tests, and one with irritant reactions to gold. Blood samples were collected andexamined regarding the proliferation rate and which cytokines were secreted after culturingwith GSTS. We saw that the cultured lymphocytes from the allergic donors proliferated at asignificantly higher rate than the two other subject groups, and that the cells secreted cytokinesof both Th1 (Interferon (IFN) -g and Interleukin (IL) -2) and Th2 (IL-13 and IL-10) types. Theallergic donors secreted significantly higher levels of IFN-g, IL-2 and IL-13 than the two othersubject groups. Both the negative and irritant subject groups showed suppressed levels of thecytokines as compared with the unstimulated cultures, demonstrating the immunosuppressingeffects of gold.We also examined whether any of the analyzed markers, alone or combined, could be usedas an aid for diagnosing ACD to gold. We found that the IFN-g assay yielded the highestsensitivity (81.8 %) and specificity (82.1 %), and also identified 87.5 % of the irritant group asnon-allergic.In paper II we decided to investigate what cell types and subsets that reacted to the goldstimulation. We analyzed proliferation rate and expression of CD45RA, CD45R0, cutaneouslymphocyte-associated antigen (CLA) and the chemokine receptors CXCR3, CCR4 andCCR10. Similar to what has previously been published about nickel (Ni) allergy, the cells fromthe gold-allergic subjects that reacted to the GSTS stimulation expressedCD3+CD4+CD45R0+CLA+. However, contrary to findings in studies on Ni-reactive cells, wesaw no differences between allergic and non-allergic subjects regarding any of the chemokine receptors studied.In conclusion, we found that analysis of IFN-g might be a useful complement to patchtesting, possibly of interest in avoiding the need for repeated tests to rule out irritant reactions.We also saw that the cells that proliferated in response to gold were memory T-cells expressingCD4 and CLA, the marker for skin-homing. However, these cells did not express elevatedlevels of any of the chemokine receptors analyzed, showing that there are both similarities anddifferences between the mechanisms for Ni allergy and gold allergy.
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| 10. |
- Ding, Haoming, et al.
(författare)
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Synthesis of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N by A-site replacement reaction in molten salts
- 2019
-
Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 7:12, s. 510-516
-
Tidskriftsartikel (refereegranskat)abstract
- New MAX phases Ti2(AlxCu1−x)N and Nb2CuC were synthesized by A-site replacement by reacting Ti2AlN and Nb2AlC, respectively, with CuCl2 or CuI molten salt. X-ray diffraction, scanning electron microscopy, and atomically resolved scanning transmission electron microscopy showed complete A-site replacement in Nb2AlC, which lead to the formation of Nb2CuC. However, the replacement of Al in Ti2AlN phase was only close to complete at Ti2(Al0.1Cu0.9)N. Density-functional theory calculations corroborated the structural stability of Nb2CuC and Ti2CuN phases. Moreover, the calculated cleavage energy in these Cu-containing MAX phases are weaker than in their Al-containing counterparts.The preparation of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N were realized by A-site replacement in Ti2AlN and Nb2AlN, respectively.
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| 11. |
- Frodelius, Jenny, 1978-
(författare)
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Thick and Thin Ti2AlC Coatings
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Thesis explores the deposition techniques of magnetron sputtering and high velocity oxy-fuel (HVOF) spraying for Ti2AlC as a promising high-temperature material. Magnetron sputtering aims at producing thin (≤1 μm) Ti2AlC films of high crystal quality for use as a model system in understanding the material’s basic properties. HVOF is a new method for deposition of thick (≥200 μm) coatings by spraying Ti2AlC powder, with the aim of transferring the good bulk properties to coatings. The oxidation behavior of Ti2AlC coatings has been investigated for temperatures up to 1200 °C in air. As-deposited Ti2AlC(0001) thin films decompose into TiC during vacuum annealing at 700 °C by out-diffusion of Al as shown by x-ray diffraction analysis. The release of Al starts already at 500 °C in ambient air as driven by aluminum oxide formation on the film surface where the oxide initially forms clusters as observed by electron microscopy. While sputtering from a Ti2AlC target is simpler than by using different elemental targets, the resulting film composition differs from the target stoichiometry. This is due to differences in energy and angular distribution of the sputtered species and evaporation of Al at substrate temperatures above 700 °C. The composition can be compensated for by adding Ti to bind the Al and obtain phase-pure Ti2AlC coatings. For HVOF, I demonstrate how the total gas flow of a H2/O2 mixture (441-953 liter/min) and the powder grain size (30-56 μm) determine the thickness, density, and microstructure of the coatings. High gas flow and small grain size yield thick coatings of 210 μm with a low porosity of 2-8 % and a tensile stress of ≥80 MPa. A fraction of the Ti2AlC powder decomposes during spraying into TiC, Ti3AlC2, and Ti-Al alloys. The coatings also contain as much as 25 at.% O since the powder partly oxidizes during the spraying process. Increasing the powder size and decreasing the total gas flow yield a higher amount of Ti2AlC, but produces thinner coatings with lower cohesion. Post-annealing of the coatings at 900 °C in vacuum increases the Ti2AlC content due to a reversible phase transformation of the as-sprayed material. The high oxygen content, however, hinders the coating to completely transform into Ti2AlC and deteriorates its oxidation resistance. The work thus offers insights to the key parameters for optimizing Ti2AlC coating processing.
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| 12. |
- Kerdsongpanya, Sit, 1985-
(författare)
-
Design of Transition-Metal Nitride Thin Films for Thermoelectrics
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermoelectric devices are one of the promising energy harvesting technologies, because of their ability to convert heat (temperature gradient) to electricity by the Seebeck effect. Furthermore, thermoelectric devices can be used for cooling or heating by the inverse effect (Peltier effect). Since this conversion process is clean, with no emission of greenhouse gases during the process, this technology is attractive for recovering waste heat in automobiles or industries into usable electricity. However, the conversion efficiency of such devices is rather low due to fundamental materials limitations manifested through the thermoelectric figure of merit (ZT). Thus, there is high demand on finding materials with high ZT or strategies to improve ZT of materials.In this thesis, I discuss the basics of thermoelectrics and how to improve ZT of materials, including present-day strategies. Based on these ideas, I propose a new class of materials for thermoelectric applications: transition-metal nitrides, mainly ScN, CrN and their solid solutions. Here, I employed both experimental and theoretical methods to synthesize and study their thermoelectric properties. My study envisages ways for improving the thermoelectric figure of merit of ScN and possible new materials for thermoelectric applications.The results of my studies show that ScN is a promising thermoelectric material since it exhibits high thermoelectric power factor 2.5x10-3 Wm-1K-2 at 800 K, due to low metallic-like electrical resistivity while retained relatively large Seebeck coefficient. My studies on thermal conductivity of ScN also suggest a possibility to control thermal conductivity by tailoring the microstructure of ScN thin films. Furthermore, my theoretical studies on effects of impurities and stoichiometry on the electronic structure of ScN suggest the possibly to improve ScN ZT by stoichiometry tuning and doping. For CrN and Cr1-xScxN solid solution thin films, the results show that the power factor of CrN (8x10-4 Wm-1K-2 at 770 K) can be retained for the solid solution Cr0.92Sc0.08N. Finally, density functional theory was used to enable a systematic predictionbased strategy for optimizing ScN thermoelectric properties via phase stability of solid solutions. Sc1-xGdxN and Sc1-xLuxN are stabilized as disordered solid solutions, while in the Sc-Nb-N and Sc-Ta-N systems, the inherently layered ternary structures ScNbN2 and ScTaN2 are stable.
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| 13. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
-
Chemical Reactivity and Alteration of Pyrite Mineral in the Kubi Gold Concession in Ghana
- 2024
-
Ingår i: Mining, Metallurgy & Exploration. - : Springer. - 2524-3462 .- 2524-3470.
-
Tidskriftsartikel (refereegranskat)abstract
- Pyrite is the most common among the group of sulfide minerals in the Earth and abundant in most geological settings. This gangue mineral in association with garnet, hematite, magnetite, and other sulfide minerals acts as an indicator mineral in the Kubi concession of the Asante Gold corporation in Ghana. X-ray diffraction (XRD), air annealing in a furnace, energy-dispersive x-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the crystal structure, identify individual elements, permanence, transformation, and chemical/electronic properties of such pyrite. The study aims to identify individual elements and to gain an understanding of the surface reaction mechanisms, as well as the properties of precipitated pyrite particles observed during the hydrothermal formation of the ore deposit. XRD shows that pristine and annealed samples contain some hematite and quartz besides pyrite. Results from air annealing indicate that the relationship between pyrite and hematite-magnetite is controlled by temperature. EDX reveals that the sample has O and C as contaminants, while XPS in addition reveals Ba, Au, P, Al, and N. These elements are attributed to pyrite that bonds metallically or covalently to neighboring ligands/impurity minerals such as oxides, chalcogenide sulfides, as well as the gangue alteration minerals of magnetite and hematite in the pyrite sample.These findings suggest that during the hydrothermal flow regime, pyrite, pathfinder elements, and impurity minerals/metals were in contact with quartz minerals before undergoing hematite transformation, which thus becomes an indicator mineral in the Kubi gold concession.
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| 14. |
- Palisaitis, Justinas
(författare)
-
Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate Thesis covers experimental and theoretical investigations of the bulk plasmon response to different compositions and strain states of group III-nitride materials. Investigated materials were grown using magnetron sputtering epitaxy and metal organic chemical vapour deposition and studied by Rutherford backscattering spectrometry, X-ray diffraction, electron microscopy and electron energy loss spectroscopy (EELS).It is shown that low-loss EELS is a powerful method for a fast compositional determination in AlxIn1-xN system. The bulk plasmon energy of the investigated material system follows a linear relation with respect to lattice parameter and composition in unstrained layers.Furthermore, the effect of strain on the bulk plasmon peak position has been investigated by using low-loss EELS in group III-nitrides. We experimentally determine the AlN bulk plasmon peak shift of 0.156 eV per 1% volume change. The AlN peak shift was corroborated by full potential calculations (Wein2k), which reveal that the bulk plasmon peak position of III-nitrides varies near linearly with unit cell volume variations.Finally, self-assembled ternary Al1-xInxN nanorod arrays with variable In concentration have been realized onto c-plane sapphire substrates by ultra-high-vacuum magnetron sputtering epitaxy with Ti0.21Zr0.79N or VN seed layer assistance. The nanorods exhibit hexagonal cross-sections with preferential growth along the Al1-xInxN c-axis. A coaxial rod structure with higher In concentration in the core was observed by scanning transmission electron microscopy in combination with low-loss EELS.
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| 15. |
- Pališaitis, Justinas, 1983-
(författare)
-
Valence Electron Energy Loss Spectroscopy of III-Nitride Semiconductors
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctorate thesis covers both experimental and theoretical investigations of the optical responses of the group III-nitrides (AlN, GaN, InN) and their ternary alloys. The goal of this research has been to explore the usefulness of valence electron energy loss spectroscopy (VEELS) for materials characterization of group III-nitride semiconductors at the nanoscale. The experiments are based on the evaluation of the bulk plasmon characteristics in the low energy loss part of the EEL spectrum since it is highly dependent on the material’s composition and strain. This method offers advantages as being fast, reliable, and sensitive. VEELS characterization results were corroborated with other experimental methods like X-ray diffraction and Rutherford backscattering spectrometry as well as full-potential calculations (Wien2k). Investigated III-nitride structures were grown using magnetron sputtering epitaxy and metal organic chemical vapor deposition techniques.Initially, it was demonstrated that EELS in the valence region is a powerful method for a fast compositional analysis of the Al1-xInxN (0≤x≤1) system. The bulk plasmon energy follows a linear relation with respect to the lattice parameter and composition in Al1-xInxN layers. Furthermore, the effect of strain on valence EELS was investigated. It was experimentally determined that the AlN bulk plasmon peak experiences a shift of 0.156 eV per 1% volume change at constant composition. The experimental results were corroborated by full-potential calculations, which showed that the bulk plasmon peak position varies nearly linearly with the unit-cell volume, at least up to 3% volume change.Employing the bulk plasmon energy loss, compositional characterization was also applied to confined structures, such as nanorods and quantum wells (QWs). Compositional profiling of spontaneously formed AlInN nanorods with varying In concentration was realized in cross-sectional and plan-view geometries. It was established that the structures exhibit a core-shell structure, where the In concentration in the core is higher than in the shell. The growth of InGaN/GaN multiple QWs with respect to composition and interface homogeneities was investigated. It was found that at certain compositions and thicknesses of QWs, where phase separation does not occur due to spinodal decomposition. Instead, QWs develop quantum dot like features inside the well as a consequence of Stranski-Krastanov-type growth mode, and delayed In incorporation into the structure.The thermal stability and degradation mechanisms of Al1-xInxN (0≤x≤1) films with different In contents, stacked in a multilayer sample, and different periodicity Al1-xInxN/AlN multilayer films, was investigated by performing a thermal annealing in combination with VEELS mapping in-situ. It was concluded that the In content in the Al1-xInxN layer determines the thermal stability and decomposition path. Finally, the phase separation by spinodal decomposition of different periodicity AlInN/AlN layers, with a starting composition inside the miscibility gap, was explored.
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| 16. |
- Serban, Alexandra, 1988-
(författare)
-
Magnetron Sputter Epitaxy of Group III-Nitride Semiconductor Nanorods
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The III-nitride semiconductors family includes gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and related ternary and quaternary alloys. The research interest on this group of materials is sparked by the direct bandgaps, and excellent physical and chemical properties. Moreover, the ternary alloys (InGaN, InAlN and AlGaN) present the advantage of bandgap tuning, giving access to the whole visible spectrum, from near infrared into deep ultraviolet wavelengths. The intrinsic properties of III-nitride materials can be combined with characteristical features of nanodimension and geometry in nanorod structures. Moreover, nanorods offer the advantage of avoiding problems arising from the lack of native substrates, like lattice and thermal expansion, film – substrate mismatch.The growth and characterization of group III-nitride semiconductos nanorods, namely InAlN and GaN nanorods, is presented in this thesis. All the nanostructures were grown by employing direct-current reactive magnetron sputter epitaxy. InxAl1−xN self-assembled, core-shell nanorods on Si(111) substrates were demonstrated. A comprehensive study of temperature effect upon the morphology and composition of the nanorods was realized. The radial nanorod heterostructure consists of In-rich cores surrounded by Al-rich shells with different thicknesses. The spontaneous formation of core-shell nanorods is suggested to originate from phase separation due to spinodal decomposition. As the growth temperature increase, In desorption is favored, resulting in thicker Al-rich shells and larger nanorod diameters.Both self-assembled and selective-area grown GaN nanorods are presented. Self-assembled growth of GaN nanorods on cost-effective substrates offers a cheaper alternative and simplifies device processing. Successful growth of high- quality GaN (exhibiting strong bandedge emission and high crystalline quality) on conductive templates/substrates such as Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti is supported by the possibility to be used as electrodes when integrated in optoelectronic devices.The self-assembled growth leads to mainly random nucleation, resulting in nanorods with large varieties of diameters, heights and densities within a single growth run. This translates into non-uniform properties and complicates device processing. These problems can be circumvented by employing selective-area growth. Pre-patterned substrates by nano-sphere lithography resulted in GaN nanorods with controlled length, diameter, shape, and density. Well-faceted c-axis oriented GaN nanorods were grown directly onto the native SiOx layer inside nano-opening areas, exhibiting strong bandedge emission at room- temperature and single-mode lasing. Our studies on the growth mechanism revealed a different growth behavior when compared with selective-area grown GaN nanorods by MBE and MOCVD. The time-dependent growth series helped define a comprehensive growth mechanism from the initial thin wetting layer formed inside the openings, to the well-defined, uniform, hexagonal NRs resulted from the coalescence of multiple initial nuclei.
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| 17. |
- Tengstrand, Olof, 1983-
(författare)
-
Transition metal carbide nanocomposite and amorphous thin films
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact resistance and high mechanical strength. Electrical contacts are one example of application that has been of special interest in this thesis. Since some industrially important substrates used in electrical contacts soften at higher temperature, all films were deposited with dc magnetron sputtering at a low substrate temperature (200-350 °C).I show that the electrical resistivity and mechanical properties of composites consisting of nanocrystalline NbC grains (nc-NbC) in a matrix of amorphous C (a-C) depend strongly on the amount of amorphous C. The best combination of hardness (23 GPa) and electrical resistivity (260 μΩ*cm) are found in films with ~15 at.% a-C phase. This is a higher hardness and lower resistivity than measured for the more well studied Ti-C system if deposited under similar conditions. The better results can be explained by a thinner matrix of amorphous C phase in the case of NbC. The nc-NbC/a-C is therefore interesting as a material in electrical contacts.Si can be added to further control the structure and thereby the properties of binary Me-C systems. There are however, different opinions in the literature of whether Si is incorporated on the Ti or C site in the cubic NaCl (B1) structure of TiC. In order to understand how Si is incorporated in a Me-Si-C material I use a model system of epitaxial TiCx (x ~0.7). In this model system a few atomic percent of Si can be incorporated in the cubic TiC structure. The experimental results together with theoretical stability calculations suggest that the Si is positioned at the C sites forming Ti(Si,C)x. The calculation further shows a strong tendency for Si segregation, which is seen at higher Si contents in the experiments, where Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy.If Si is added to an Nb-C nanocomposite, it hinders the grain growth and thus a reduced size of the NbC grains is observed. The Si segregates to the amorphous matrix forming a-SiC. At the same time the resistivity increases and the hardness is reduced. With even higher amounts of Si (>25 at.%) into the Nb-Si-C material, grain growth is no longer possible and the material becomes amorphous. In order to separate between effects from the addition of Si and the choice of transition metal I compare the Nb-Si-C system to already published results for the Zr-Si-C system. I find that the hardness of the material depends on the amount of strong Si-C bonds rather than the type of transition metal. The reduced elastic modulus is, however, dependent on the choice of transition metal. I therefore suggest that it is possible to make Me-Si-C films with high wear resistance by an appropriate choice of transition metal and composition.Electron microscopy was of importance for determining amorphous structures of Nb-Si-C and Zr-Si-C at high Si contents. However, the investigations were obstructed by electron beam induced crystallization. Further investigations show that the energy transferred from the beam electrons to C and Si atoms in the material is enough to cause atomic displacements. The displacements cause volume fluctuations and thereby enhance the mobility of all the atoms in the material. The result is formation of MeC grains, which are stable to further irradiation.Finally, I have studied substitution of Ge for Si in a ternary system looking at Nb-Ge-C thin films. I show that the films consist of nc-NbC/a-C/a-Ge and that Ge in a similar way to Si decreases the size of the crystalline NbC grains. However, a transition to a completely amorphous material is not seen even at high Ge contents (~30 at.%). Another dissimilarity is that while Si bonds to C and forms a matrix of a-SiC, Ge tends to bond to Ge.
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| 18. |
- Bakhit, Babak, 1983-, et al.
(författare)
-
Age hardening in superhard ZrB2-rich Zr1-xTaxBy thin films
- 2021
-
Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 191, s. 120-125
-
Tidskriftsartikel (refereegranskat)abstract
- We recently showed that sputter-deposited Zr1-xTaxBy thin films have hexagonal AlB2-type columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. As-deposited layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we study the mechanical properties of ZrB2.4, Zr0.8Ta0.2B1.8, and Zr0.7Ta0.3B1.5 films annealed in Ar atmosphere as a function of annealing temperature Ta up to 1200 °C. In-situ and ex-situ nanoindentation analyses reveal that all films undergo age hardening up to Ta = 800 °C, with the highest hardness achieved for Zr0.8Ta0.2B1.8 (45.5±1.0 GPa). The age hardening, which occurs without any phase separation or decomposition, can be explained by point-defect recovery that enhances chemical bond density. Although hardness decreases at Ta > 800 °C due mainly to recrystallization, column coarsening, and planar defect annihilation, all layers show hardness values above 34 GPa over the entire Ta range.
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| 19. |
- Bakhit, Babak, 1983-, et al.
(författare)
-
Self-organized columnar Zr0.7Ta0.3B1.5 core/shell-nanostructure thin films
- 2020
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 401
-
Tidskriftsartikel (refereegranskat)abstract
- We recently showed that Zr1−xTaxBy thin films have columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. Layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we determine the atomic-scale nanostructure of sputter-deposited columnar Zr0.7Ta0.3B1.5 thin films. The columns, 95 ± 17 Å, are core/shell nanostructures in which 80 ± 15-Å cores are crystalline hexagonal-AlB2-structure Zr-rich stoichiometric Zr1−xTaxB2. The shell structure is a narrow dense, disordered region that is Ta-rich and highly B-deficient. The cores are formed under intense ion mixing via preferential Ta segregation, due to the lower formation enthalpy of TaB2 than ZrB2, in response to the chemical driving force to form a stoichiometric compound. The films with unique combination of nanosized crystalline cores and dense metallic-glass-like shells provide excellent mechanical properties.
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| 20. |
- Boo, Sofia
(författare)
-
Lärares arbete med individanpassning : Strategier och dilemman i klassrummet
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major challenge for teachers in crowded classrooms is to adapt the teaching to different pupil’s needs and abilities. Previous research shows that learning for pupils in the Swedish primary school has somewhat become an individual project. An increase in the individual work has been at the expense of whole class teaching. This has had a negative impact on pupils' academic performance. However, previous research also indicates that individual adaptation may affect results positively when the teacher is active, has knowledge of pupil’s needs and abilities and also a willingness to meet them.In the last few versions of the Swedish curriculum it is mentioned that teaching should be adjusted based on each pupil's abilities and needs. The purpose of this study is to investigate, describe and analyze how today's teachers in primary school (grades 1-6) handle individual adaptation in teaching, what strategies they use and what dilemmas that occurs. The study focuses on how work is carried out in practice. Qualitative interviews and participant observations are used in the data collection.This study has been conducted in two parts. The first part addresses five teachers and their classes in four different schools. In the second part the study has been extended with one of the above teachers whose classroom work was followed during a period of seven weeks. The results show that teachers are working hard to find methods that promote communication and interaction. They use different strategies to adapt teaching to each student. Individual work is still present but does not dominate the classroom work. Teachers individualize teaching by variation and interaction, by working together with tasks, with active relationship-oriented work and through continuous adjustments in the moment. The study also shows that teachers face several dilemmas when they individualize teaching in the classroom. One dilemma is among the ideal adaptation that teachers have a vision of, versus the time- and efficiencydriven adaptation that is possible to accomplish in the classroom. There is a tension between overall ideal images and teachers' practical everyday reality.
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| 21. |
- Chang, Jui-Che, et al.
(författare)
-
Domain epitaxial growth of Ta3N5 film on c-plane sapphire substrate
- 2022
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 443
-
Tidskriftsartikel (refereegranskat)abstract
- Tritantalum pentanitride (Ta3N5) semiconductor is a promising material for photoelectrolysis of water with high efficiency. Ta3N5 is a metastable phase in the complex system of TaN binary compounds. Growing stabilized single-crystal Ta3N5 films is correspondingly challenging. Here, we demonstrate the growth of a nearly single-crystal Ta3N5 film with epitaxial domains on c-plane sapphire substrate, Al2O3(0001), by magnetron sputter epitaxy. Introduction of a small amount ~2% of O2 into the reactive sputtering gas mixed with N2 and Ar facilitates the formation of a Ta3N5 phase in the film dominated by metallic TaN. In addition, we indicate that a single-phase polycrystalline Ta3N5 film can be obtained with the assistance of a Ta2O5 seed layer. With controlling thickness of the seed layer smaller than 10 nm and annealing at 1000 °C, a crystalline β phase Ta2O5 was formed, which promotes the domain epitaxial growth of Ta3N5 films on Al2O3(0001). The mechanism behind the stabilization of the orthorhombic Ta3N5 structure resides in its stacking with the ultrathin seed layer of orthorhombic β-Ta2O5, which is energetically beneficial and reduces the lattice mismatch with the substrate.
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| 22. |
- Chang, Jui-Che, et al.
(författare)
-
HiPIMS-grown AlN buffer for threading dislocation reduction in DC-magnetron sputtered GaN epifilm on sapphire substrate
- 2023
-
Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 217
-
Tidskriftsartikel (refereegranskat)abstract
- Gallium nitride (GaN) epitaxial films on sapphire (Al2O3) substrates have been grown using reactive magnetron sputter epitaxy with a liquid Ga target. Threading dislocations density (TDD) of sputtered GaN films was reduced by using an inserted high-quality aluminum nitride (AlN) buffer layer grown by reactive high power impulse magnetron sputtering (R-HiPIMS) in a gas mixture of Ar and N2. After optimizing the Ar/N2 pressure ratio and deposition power, a high-quality AlN film exhibiting a narrow full-width at half-maximum (FWHM) value of the double-crystal x-ray rocking curve (DCXRC) of the AlN(0002) peak of 0.086° was obtained by R-HiPIMS. The mechanism giving rise the observed quality improvement is attributed to the enhancement of kinetic energy of the adatoms in the deposition process when operated in a transition mode. With the inserted HiPIMS-AlN as a buffer layer for direct current magnetron sputtering (DCMS) GaN growth, the FWHM values of GaN(0002) and (10 1‾ 1) XRC decrease from 0.321° to 0.087° and from 0.596° to 0.562°, compared to the direct growth of GaN on sapphire, respectively. An order of magnitude reduction from 2.7 × 109 cm−2 to 2.0 × 108 cm−2 of screw-type TDD calculated from the FWHM of the XRC data using the inserted HiPIMS-AlN buffer layer demonstrates the improvement of crystal quality of GaN. The result of TDD reduction using the HiPIMS-AlN buffer was also verified by weak beam dark-field (WBDF) cross-sectional transmission electron microscopy (TEM).
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| 23. |
- Edström, Daniel, 1986-, et al.
(författare)
-
Mechanical properties of VMoNO as a function of oxygen concentration : Toward development of hard and tough refractory oxynitrides
- 2019
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:6
-
Tidskriftsartikel (refereegranskat)abstract
- Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl-structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem that may compromise material properties and performance. Here, the authors explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx solid solutions as a function of the oxygen concentration x. Elastic constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, the authors' results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile. Published by the AVS.
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| 24. |
- Eklund, Per, 1977-
(författare)
-
Multifunctional nanostructured Ti-Si-C thin films
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis, I have investigated multifunctional nanostructured Ti-Si-C thin films synthesized by magnetron sputtering in the substrate-temperature range from room temperature to 900 °C. The studies cover high-temperature growth of Ti3SiC2 and Ti4SiC3, low-temperature growth of Ti-Si-C nanocomposites, and Ti-Si-C-based multi¬layers, as well as their electrical, mechanical, and thermal-stability properties. Ti3SiC2 and Ti4SiC3 were synthesized homoepitaxially onto bulk Ti3SiC2 from individual sputtering targets and heteroepitaxially onto Al2O3(0001) substrates from a Ti3SiC2 target at substrate temperatures of 700 – 900 °C. In the latter case, the film composition exhibits excess C compared to the nominal target composition due to differences between species in angular and energy distribution and gas-phase scattering processes. Ti buffering is shown to compensate for this excess C. The electrical-resistivity values of Ti3SiC2 and Ti4SiC3 thin films were measured to 21-32 uOhmcm and ~50 uOhmcm, respectively. The good conductivity is because the presence of Si layers enhances the relative strength of the metallic Ti-Ti bonds. The higher density of Si layers in Ti3SiC2 than in Ti4SiC3 explains why Ti3SiC2 is the better conductor of the two. Ti3SiC2 thin films are shown to be thermally stable up to 1000 – 1100 °C. Annealing at higher temperature results in decomposition of Ti3SiC2 by Si out-diffusion to the surface with subsequent evaporation. Above 1200 °C, TiCx layers recrystallized. Nanocomposites comprising nanocrystalline (nc-)TiC in an amorphous (a-)SiC matrix phase were deposited at substrate temperatures in the range 100 – 300 °C. These nc-TiC/a-SiC films exhibit low contact resistance in electrical contacts and a ductile deformation behavior due to rotation and gliding of nc-TiC grains in the matrix. The ductile mechanical properties of nc-TiC/a-SiC are actually more similar to those of Ti3SiC2, which is very ductile due to kinking and delamination, than to those of the brittle TiC. Epitaxial TiC/SiC multilayers deposited at ~550 °C were shown to contain cubic SiC layers up to a thickness of ~2 nm. Thicker SiC layers gives a-SiC due to the corresponding increase in interfacial strain energy leading to loss of coherent-layer growth. Nanoindentation of epitaxial Ti3SiC2/TiC0.67 nanolaminates showed inhibition of kink-band formation in Ti3SiC2, as the lamination with the less ductile TiC effectively hindered this mechanism.
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| 25. |
- Fallqvist, Amie
(författare)
-
Aberration-Corrected Analytical Electron Microscopy of Transition Metal Nitride and Silicon Nitride Multilayers
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two multilayer thin films have been studied: TiN/SiNx and ZrN/SiNx. A double-corrected transmission electron microscope (TEM) was utilized for imaging and spectroscopy. Imaging was carried out in scanning mode (STEM) for all samples. Energy dispersive X-ray (EDX) spectrometry was used for chemical mapping of the ZrN/SiNx samples and electron energy loss spectrometry (EELS) for atomic coordination of the nitrogen in the TiN/SiNx samples.In the TiN/SiNx multilayer the structure of the epitaxially stabilized cubic SiNx was investigated. The high-resolution STEM images were compared with image simulations of SiNx in B1 (sodium chloride) and B3 (zinc blende) configurations and were found to be most similar to the B1 configuration. Core-loss EEL spectra were compared with calculated spectra and corroborated a resemblance with the B1 configuration.The ZrN/SiNx multilayers were initially believed to show a similarity to TiN/SiNx but further investigations with STEM showed that the SiNx is amorphous. For samples deposited at 800 °C a SiNx layer thickness ≤6 Å the SiNx forms precipitates at grain boundaries and surface defects of the ZrN resulting in a columnar distribution of the SiNx, which was further revealed by EDX. For such samples the ZrN grows by epitaxial lateral overgrowth. For samples deposited at 800 °C but with a SiNx layer thickness of 6 Å the SiNx starts to form more laterally extending layers and for thicknesses ≥8 Å the SiNx grows into continuous, amorphous layers causing the following ZrN layers to assume a polycrystalline microstructure. The transition from epitaxial ZrN with columnar, amorphous SiNx, to multilayers of polycrystalline ZrN and amorphous SiNx layers appears at an even smaller thickness of SiNx if the deposition temperature is lowered, which is explained by the lowered adatom mobility.
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| 26. |
- Havarinasab, Said, 1964-
(författare)
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Effect of thimerosal on the murine immune system : especially induction of systemic autoimmunity
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The organic mercury compound ethylmercurithiosalicylate (thimerosal), an antiseptic and a preservative, has recently raised public health concern due to its presence in vaccines globally. Thimerosal dissociates in the body to thiosalicylate and ethyl mercury (EtHg), which is partly converted to inorganic mercuric mercury (Hg2+). The immunosuppressive, immunostimulatory, and de novo autoimmunogen effect of thimerosal in mice, as well as the accelerating/aggravating effect on spontaneous systemic autoimmunity including dose-response aspects were the subject of this thesis.Thimerosal perorally (590 μg Hg/kg body weight (bw)/day) to genetically susceptible (H-2s) mice caused immunosuppression during the first week with reduction of the total number of splenocytes, T- and B-cells. The suppression lasted 2 weeks for CD4+ cells, but was superseded by a strong immunostimulation/proliferation including T- as well as B-cells, and polyclonal B-cell activation (PBA). Antinuclear antibodies targeting the 34-kDa nucleolar protein fibrillarin (AFA) appeared after 10 days, followed by renal mesangial and systemic vessel wall immune-complex (IC) deposits. The Lowest Observed Adverse Effect Level (LOAEL) was in the order AFA = glomerular and splenic vessel wall deposits < hyperimmunoglobulinemia < PBA. The LOAEL for AFA was 118 μg Hg/kg bw/day. The LOAEL for the different parameters of this thimerosal-induced systemic autoimmune condition (HgIA) was 3-11-fold higher compared with HgIA induced by HgCl2. The thimerosal-induced HgIA shared with HgCl2 a significant dose-response relationship, and requirement for: T-cells, the costimulatory factor CD28, the IFN-γ/IFN-γ-receptor pathway,but not IL-4. The mRNA expression in lymph nodes of IL-2, IFN-γ, IL-4, and IL-15 was significantly increased but not delayed compared with HgCl2.Treatment with the ubiquitous organic Hg compound methyl Hg using equimolar doses of Hg (533 μg Hg/kg bw/day) caused a transient immunosuppression, followed by a weak immunostimulation and AFA. The IgG AFA isotypes induced by the organic Hg compounds MeHg and EtHg were stable and dominated by a Th1-like pattern over a broad time- and dose range. Treatment with inorganic HgCl2 caused a dose- and time-dependent pattern of IgG AFA isotypes. Low doses favored a Th1-like pattern, a high dose a balanced or Th2-like pattern. Middle-range doses showed initially a Th1-like pattern which gradually evolved into a balanced or Th2-like pattern. The qualitative difference in IgG AFA isotypes between organic and inorganic Hg may be due to differences in activation and/or suppression of T-helper cell subsets or factors influencing the Th1/Th2-function. Speciation of the renal Hg2+ concentration and comparison with the threshold dose for induction of AFA by HgCl2 showed that even with the lowest doses of thimerosal and MeHg used in this thesis, the AFA response might from a dose threshold point of view have been caused by conversion of the organic Hg species to Hg2+.Primary treatment with inorganic Hg (HgCl2) accelerates/aggravates murine systemic autoimmunity, both spontaneous (genetic) and induced by other means. This capacity was assessed for thimerosal over a broad dose range using the (NZB X NZW)F1 hybrid mouse model. Significantly increased antinuclear antibodies (ANA) was seen after 4-7 weeks treatment (LOAEL 147 μg Hg/kg bw/day), and the response was dose-dependent up to 13 weeks. Renal mesangial and systemic vessel walls deposits similar to those in de novo HgIA were present after 7 weeks treatment. Twenty-two to 25 weeks treatment with thimerosal caused, in a dose-dependent fashion (LOAEL 295 μg Hg/kg bw/day), relocalization of the spontaneously developing glomerular IC deposits from the capillary vessel walls to the mesangium, which attenuated histological kidney damage and proteinuria, and increased survival. Thimerosal caused systemic vessel wall IC-deposits over a broad dose range: the Low Observed Adverse Effect Level (LOAEL) for renal and splenic vessel wall IC deposits was 18 and 9 μg Hg/kg bw/day, respectively. The No Observed Adverse Effect Level (NOAEL) could not be determined for the latter, since deposits were present even with the lowest dose used.Thimerosal causes in genetically susceptible mice an initial, transient immunosuppression which is superseded by a strong immunostimulation and systemic autoimmunity, sharing many characteristics with the HgIA induced by inorganic HgCl2. The IgG AFA isotype pattern is however qualitatively different, and the threshold dose substantially higher. In contrast, long-term treatment with thimerosal induces systemic vessel wall IC-deposits also using doses below those needed to induce HgIA de novo in H-2s mice.
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| 27. |
- Kerdsongpanya, Sit
(författare)
-
Scandium Nitride Thin Films for Thermoelectrics
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermoelectric devices are one of the promising energy harvesting technologies, since they can convert heat (i.e. a temperature gradient) to electricity. This result leads us to use them to harvest waste heat from heat engines or in power plants to generate usable electricity. Moreover, thermoelectric devices can also perform cooling. The conversion process is clean, with no emission of greenhouse gases during the process. However, the converting efficiency of thermoelectrics is very low because of the materials limitations of the thermoelectric figure of merit (ZTm). Thus, there is high demand to maximize the ZTm.I have discovered that ScN has high power factor 2.5 mW/(mK2) at 800 K, due to low metalliclike electrical resistivity (∼3.0 μΩm) with retained relatively large Seebeck coefficient of -86 μV/K. The ScN thin films were grown by reactive dc magnetron sputtering from Sc targets. For ScN, X-ray diffraction, supported by transmission electron microscopy, show that we can obtain epitaxial ScN(111) on Al2O3(0001). We also reported effects on thermoelectric properties of ScN with small changes in the composition with the power factor changing one order of magnitude depending on e.g. oxygen, carbon and fluorine content which were determined by elastic recoil detection analysis. The presence of impurities may influence the electronic density of states or Fermi level (EF) which could yield enhancement of power factor.Therefore, the effects of defects and impurities on the electronic density of states of scandium nitride were investigated using first-principles calculations with general gradient approximation and hybrid functionals for the exchange correlation energy. Our results show that for Sc and N vacancies can introduce asymmetric peaks in the density of states close to the Fermi level. We also find that the N vacancy states are sensitive to total electron concentration of the system due to their possibility for spin polarization. Substitutional point defects shift the Fermi level in the electronic band according to their valence but do not introduce sharp features. The energetics and electronic structure of defect pairs are also studied. By using hybrid functionals, a correct description of the open band gap of scandium nitride is obtained, in contrast to regular general gradient approximation. Our results envisage ways for improving the thermoelectric figure of merit of ScN by electronic structure engineering through stoichiometry tuning and doping.
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| 28. |
- Khatibi, Ali, 1982-
(författare)
-
Deposition and Phase Transformations of Ternary Al-Cr-O Thin Films
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the ternary Al-Cr-O system. (Al1-xCrx)2O3 solid solution thin films with 0.62 gas mixture. As-deposited and annealed (Al1-xCrx)2O3 thin films were analyzed by x-ray diffraction, elastic recoil detection analysis, scanning electron microscopy, transmission electron microscopy, and nanoindentation. (Al1-xCrx)2O3 showed to have face centered cubic structure with lattice parameter of 4.04 Å, which is in contrast to the typical corundum structure reported for these films. The as-deposited films exhibited hardness of ~ 26 GPa and elastic modulus of 220-235 GPa. Phase transformation from cubic to corundum (Al0.32Cr0.68)2O3 starts at 925 °C. Annealing at 1000 °C resulted in complete phase transformation, while no precipitates of alumina and chromia were observed. Studies on kinetics of phase transformation showed a two-step thermally activated process; phase transformation and grain growth with the apparent activation energies 213±162 and 945±27 kJ/mol, respectively.
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| 29. |
- Khatibi, Ali, 1982-
(författare)
-
Growth and Heat Treatment Studies of Al-Cr-O and Al-Cr-O-N Thin Films
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum oxide based thin films are applied on cutting tool inserts as a top layer to protect the underlying nitride or carbide functional layer from the harsh working environment in terms of abrasive and chemical wear under thermal and pressure load. This Thesis explores the synthesis and characterization of the next generations of multifunctional wear-resistant thin film coatings in the form of Al-Cr-O and Al-Cr-O-N compounds. The experiments include the deposition of oxide films by reactive magnetron sputtering and cathodic arc evaporation as well as investigation of structural and mechanical properties in as-deposited and annealed states. Ternary (Al1-xCrx)2+yO3-y films were deposited on Si(001) and WC-Co substrates kept at 400-575 °C from elemental Al and Cr or alloyed Al/Cr cathodes in Ar/O2, O2/N2, and pure O2 atmospheres. Also, quaternary (Al1-xCrx)2+z(O1-yNy)3-z films were deposited at substrate temperature of ~400 °C on WC-Co substrates in O2/N2 atmosphere. X-ray diffraction and analytical electron microscopy combined with ab initio calculations showed the existence of a new face centered cubic (Al,Cr)2O3 phase with 33% vacancies on the metallic Al/Cr sites. Increasing the temperature during annealing of these metastable cubic films resulted in phase transformation to corundum solid solution in the temperature range of 900-1100 °C. The apparent activation energy of this phase transformation process was calculated as 380-480 kJ/mol by using the Johnson-Mehl-Avrami model. The mechanical properties of the cubic and corundum oxide films were measured in terms of nanoindentation hardness and metal cutting performance. The cubic and corundum films showed hardness values of 26-28 GPa and 28-30 GPa, respectively. The oxynitride solid solution films showed to be predominantly cubic Al-Cr-N and cubic-(Al,Cr)2O3 and secondary corundum-(Al,Cr)2O3 with a hardness of ~30 GPa, slightly higher than Al-rich ternary oxides. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.
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| 30. |
- Landälv, Ludvig, 1982-, et al.
(författare)
-
Influence of Si doping and O-2 flow on arc-deposited (Al,Cr)(2)O-3 coatings
- 2019
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 37:6
-
Tidskriftsartikel (refereegranskat)abstract
- (Al,Cr)(2)O-3 coatings with Al/( Al + Cr) = 0.5 or Al = 70 at. %, doped with 0, 5, or 10 at. % Si, were deposited on hard metal and Si(100) substrates to elucidate the influence of Si on the resulting coatings. The chemical analysis of the coatings showed between 3.3 and 7.4 at. % metal fraction Si incorporated into all studied coatings depending on cathode Si composition. The incorporated Si content does not change significantly with different oxygen flows covering a wide range of deposition conditions from low to high O-2 flow during growth. The addition of Si promotes the metastable B1-like cubic structure over the thermodynamically stable corundum structure. The hardness determined by nanoindentation of the as-deposited coatings is slightly reduced upon Si incorporation as well as upon increased Al content. Si is found enriched in droplets but can also be found at a lower content, evenly spread, without visible segregation at the similar to 5 nm scale, in the actual oxide coating. The positive effect of improved cathode erosion upon Si incorporation has to be balanced against the promotion of the metastable B1-like structure, having lower room temperature hardness and inferior thermal stability compared to the corundum structure. Published by the AVS.
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| 31. |
- Landälv, Ludvig, 1982-, et al.
(författare)
-
Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings
- 2019
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 688
-
Tidskriftsartikel (refereegranskat)abstract
- Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.
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| 32. |
- Landälv, Ludvig, 1982-, et al.
(författare)
-
Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)(2)O-3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum
- 2019
-
Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 34:22, s. 3735-3746
-
Tidskriftsartikel (refereegranskat)abstract
- The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at similar to 750-800 degrees C, followed by decomposition of the alpha-Cr2O3 structure in conjunction with bcc-Cr formation, starting at similar to 950 degrees C. The resulting coating after annealing to 1140 degrees C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at similar to 750 degrees C. The resulting coating after annealing to 975 degrees C is a mixture of t-ZrO2 and alpha-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with alpha-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 degrees C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.
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| 33. |
- Landälv, Ludvig, 1982-, et al.
(författare)
-
Structural evolution in reactive RF magnetron sputtered (Cr,Zr)2O3 coatings during annealing
- 2017
-
Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 131, s. 543-552
-
Tidskriftsartikel (refereegranskat)abstract
- Reactive RF-magnetron sputtering is used to grow Cr0.28Zr0.10O0.61 coatings at 500 degrees C. Coatings are annealed at 750 degrees C, 810 degrees C, and 870 degrees C. The microstructure evolution of the pseudobinary oxide compound is characterized through high resolution state of the art HRSTEM and HREDX-maps, revealing the segregation of Cr and Zr on the nm scale. The as-deposited coating comprises cc-(Cr,Zr)(2)O-3 solid solution with a Zr-rich (Zr,Cr)O-x. amorphous phase. After annealing to 750 degrees C tetragonal ZrO2 nucleates and grows from the amorphous phase. The ZrO2 phase is stabilized in its tetragonal structure at these fairly low annealing temperatures, possibly due to the small grain size (below 30 nm). Correlated with the nucleation and growth of the tetragonal-ZrO2 phase is an increase in hardness, with a maximum hardness after annealing to 750 degrees C, followed by a decrease in hardness upon coarsening, bcc metallic Cr phase formation and loss of oxygen, during annealing to 870 degrees C. The observed phase segregation opens up future design routes for pseudobinary oxides with tunable microstructural and mechanical properties. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 34. |
- Landälv, Ludvig, 1982-
(författare)
-
Thin Film and Plasma Characterization of PVD Oxides
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The state-of-the-art tools for machining metals are primarily based on a metal-ceramic composite(WC-Co) coated with different combinations of carbide, nitride and oxide coatings. Combinations of these coating materials are optimized to withstand specific wear conditions. Oxide coatings are especially desired because of their possible high hot hardness, chemical inertness with respect to the workpiece, and their low friction.This thesis deals with process and coating characterization of new oxide coatings deposited by physical vapor deposition (PVD) techniques, focusing on the Cr-Zr-O and Al-Cr-Si-O systems.The thermal stability of α-Cr0.28Zr0.10O0.61 deposited by reactive radio frequency (RF)-magnetron sputtering at 500 °C was investigated after annealing up to 870 °C. The annealed samples showed transformation of α-(Cr,Zr)2O3 and amorphous ZrOx-rich areas into tetragonal ZrO2 and bcc Cr. The instability of the α-(Cr,Zr)2O3 is surprising and possibly related to the annealing being done under vacuum, facilitating the loss of oxygen. The stabilization of the room temperature metastable tetragonal ZrO2 phase, due to surface energy effects, may prove to be useful for metal cutting applications. The observed phase segregation of α-(Cr,Zr)2O3 and formation of tetragonal ZrO2 with corresponding increase in hardness for this pseudo-binary oxide system also opens up design routes for pseudo-binary oxides with tunable microstructural and mechanical properties.The inherent difficulties of depositing insulating oxide films with PVD, demanding a closed circuit, makes the investigation of process stability an important part of this research. In this context, we investigated the influence of adding small amount of Si in Al-Cr cathode on plasma characteristics ,process parameters, and coating properties. Si was chosen here due to a previous study showing improved erosion behavior of Al-Cr-Si over pure Al-Cr cathode without Si incorporation in the coating.This work shows small improvements in cathode erosion and process stability (lower pressure and cathode voltage) when introducing 5 at % Si in the Al70Cr30-cathode. This also led to fewer droplets at low cathode current and intermediate O2 flow. A larger positive effect on cathode erosion was observed with respect to cleaning the cathode from oxide contamination by increasing cathode current with 50%. However, higher cathode current also resulted in increased amount of droplets in the coating which is undesirable. Through plasma analysis the presence of volatile SiO species could be confirmed but the loss of Si through volatile SiO species was negligible, since the coating composition matched the cathode composition. The positive effect of added Si on the process stability at the cathode surface should be weighed against Si incorporation in the coating. This incorporation may or may not be beneficial for the final application since literature states that Si promotes the metastable γ-phase over the thermodynamically stable α-phase of pure Al2O3, contrary to the effect of Cr, which stabilizes the α-phase.
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| 35. |
- Lauridsen, Jonas, 1983-
(författare)
-
TiC-based nanocomposite coatings as electrical contacts
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Thesis concerns the advanced surface engineering of novel TiC-based nanocomposite and AgI electrical contact materials. The objective is to make industrially applicable coatings that are electrically conductive and wear-resistant, and have a low coefficient of friction. I have studied electrical contact systems consisting of a Cu substrate with a Ni diffusion barrier and loading support, and a conductive top coating. The contact systems were characterized by x-ray diffraction and photoelectron spectroscopy, analytical electron microscopy, ion beam analysis, nanoindentation, resistivity, and contact resistance measurements. Nc-TiC/a-C/SiC nanocomposite coatings consisting of nanocrystalline (nc) TiC embedded in an amorphous (a) matrix of C/SiC were deposited by magnetron sputtering with rates as high as 16 μm/h. These coatings have a contact resistance comparable with Ag at high loads (~800 N) and a resistivity of 160-770 μΩcm. The electrical properties of the contact can be improved by adding Ag to make nc-Ag/nc-TiC/a-SiC nanocomposites. It is possible to tailor the size and distribution of the Ag grains by varying the fraction of amorphous matrix, so as to achieve good conductivity in all directions in the coatings. Ti-Si-C-Ag coatings have a contact resistance that is one magnitude larger than Ag at lower loads (~1 N), and a resistivity of 77-142 μΩcm. The conductivity of the matrix phase can be increased by substituting Ge, Sn or Cu for Si, which also reduces the Ag grain growth. This yields coatings with a contact resistance twice as high as Ag at loads of 1 N, and a resistivity 274-1013 μΩcm. The application of a conductive top layer of Ag-Pd upon a Ti-Si-C-Ag:Pd coating can further reduce the contact resistance. For barrier materials against Cu interdiffusion, it is shown that conventional electroplating of Ni can be replaced with sputtering of Ni or Ti layers. This is an advantage since both contact and barrier layers can now be deposited in and by the same deposition process. For Ti-B-C coatings deposited by magnetron sputtering, I demonstrate promising electrical properties in a materials system otherwise known for its good mechanical properties. In coatings of low B concentration, the B is incorporated into the TiC phase, probably by enrichment on the TiC{111} planes. The corresponding disturbance of the cubic symmetry results in a rhombohedral TiC:B structure. Finally, it is shown that AgI coatings consisting of weakly agglomerated AgI grains function as solid lubricant on Ag contacts. In an Ag sliding electrical contact, AgI decreases the friction coefficient from ~1.2 to ~0.4. After a few hundred operations, AgI grains have deagglomerated and Ag from the underlying layer is exposed on the surface and the contact resistance decreases to < 100 μΩ.
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| 36. |
- Magnuson, Martin, 1965-, et al.
(författare)
-
Compositional dependence of epitaxial Tin+1SiCn MAX-phase thin films grown from a Ti3SiC2 compound target
- 2019
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:2
-
Tidskriftsartikel (refereegranskat)abstract
- The authors investigate sputtering of a Ti3SiC2 compound target at temperatures ranging from RT (no applied external heating) to 970 °C as well as the influence of the sputtering power at 850 °C for the deposition of Ti3SiC2 films on Al2O3(0001) substrates. Elemental composition obtained from time-of-flight energy elastic recoil detection analysis shows an excess of carbon in all films, which is explained by differences in the angular distribution between C, Si, and Ti, where C scatters the least during sputtering. The oxygen content is 2.6 at. % in the film deposited at RT and decreases with increasing deposition temperature, showing that higher temperatures favor high purity films. Chemical bonding analysis by x-ray photoelectron spectroscopy shows C–Ti and Si–C bonding in the Ti3SiC2 films and Si–Si bonding in the Ti3SiC2 compound target. X-ray diffraction reveals that the phases Ti3SiC2, Ti4SiC3, and Ti7Si2C5 can be deposited from a Ti3SiC2 compound target at substrate temperatures above 850 °C and with the growth of TiC and the Nowotny phase Ti5Si3Cx at lower temperatures. High-resolution scanning transmission electron microscopy shows epitaxial growth of Ti3SiC2, Ti4SiC3, and Ti7Si2C5 on TiC at 970 °C. Four-point probe resistivity measurements give values in the range ∼120 to ∼450 μΩ cm and with the lowest values obtained for films containing Ti3SiC2, Ti4SiC3, and Ti7Si2C5.
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| 37. |
- Malyshev, O. B., et al.
(författare)
-
Preface
- 2022
-
Ingår i: Vacuum. - Oxford, United Kingdom : Elsevier. - 0042-207X .- 1879-2715. ; 197
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 38. |
- Martinsson, Klara, 1977-
(författare)
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Fcγ-receptors in systemic autoimmune conditions : lessons from murine mercury-induced autoimmunity
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we investigated the role of activating (FcγRI, FcγRIII) and inhibitory (FcγRIIB) Fcγ-receptors on systemic autoimmunity using two mouse strains, DBA/1 (H-2q) and BALB/c mice (H-2d), susceptible to induction of autoimmunity by mercury (Hg).Fc-receptors for IgG (FcγR) link cellular and humoral immune responses, control the balance between activating and inhibitory immune responses and are important in the development of several autoimmune diseases. Mercury induces a T cell-dependent autoimmune condition, Hg-induced autoimmunity (HgIA) in genetically (H-2s,q,f,t2) susceptible mice characterized in its fullblown type by lymphoproliferation, hypergammaglobulinemia, systemic immune-complex (IC) deposits and antinucleolar antibodies (ANoA). All manifestations in HgIA are dependent on the presence of IFN-γ.Hg-treated BALB/c mice lacking activating FcγRs (FcγRI, FcγIII and FcεRI) showed significantly higher levels of both IgG1- and IgG2a-CIC whereas renal mesangial and vessel wall IC deposits were severely delayed and reduced/abolished, compared to mice without mutations (wild type, wt). Wt mice developed modest levels of IgG1- and IgG2a-CIC followed by a distinct formation of IC deposits in the renal glomerular mesangium, as well in renal and splenic vessel walls. Compared to wt mice, the mice lacking the inhibitory FcγRIIB showed similar titres of IC deposits in the renal mesangium, whereas vessel wall IC deposits were reduced.DBA/1 mice deficient for the FcRγ-chain (lack of the activating receptors FcγRI, FcγIII and FcεRI) or FcγRIII and treated with Hg showed a delayed and attenuated IgG1, IgG2a and IgG2b ANoA response compared to wt mice.Increasing the Hg dose or prolonging the treatment time could not override the attenuated ANoA response seen in FcγRIII mice. Female Hg-treated FcγRIIB mice showed a significant increase of IgG2b ANoA development compared to wt mice.The total serum IgG1 response due to treatment with Hg was attenuated in both BALB/c mice lacking the Fcγ-chain, and in DBA/1 mice lacking either the Fcγ- chain or specifically the FcγRIII compared to wt mice. This indicates that FcγRIII is the receptor important for the in HgIA characteristic serum IgG1 response. On the other hand, Hg-treated FcγRIIB deficient BALB/c and DBA/1 mice showed an increase of both serum IgG1 and IgE compared to wt mice.The cytokine profile in DBA/1 wt mice treated with Hg revealed a more marked Th1 profile compared to FcγRIII deficient mice. In contrast, the total Th2 and Th17 profile increased in both wt and FcγRIII deficient mice. However, during Hg treatment IL-21 mRNA expression was significantly reduced in FcγRIII deficient mice compared with wt mice. The increased Th1 profile in the wt mice could not be attributed to an increase of IFN-γ secretion from the major IFN-γ cell source, NK cells.We conclude that FcγRIII are important for the formation of IC deposits as shown by the delayed and reduced formation of IC deposits and the high levels of CIC in mice lacking FcγRIII. The expression of FcγRIII is also of importance for the rapidity and final strength of the ANoA response probably due to a reduced expression of Th1 cytokines and inflammatory factors. The ANoA response is modestly counter-regulated by FcγRIIB. The increase of serum IgG1 in HgIA is dependent on FcγRIII which is likely to be mediated by the low expression of IL- 21 in mice deficient for FcγRIII. In contrast, lack of FcγRIIB increases both the serum IgG1 and IgE response.
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| 39. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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Pathfinder elements and indicator minerals of Au from the Kubi Gold ore deposits in Ghana
- 2023
-
Ingår i: Environmental Earth Sciences. - : Springer. - 1866-6280 .- 1866-6299. ; 82:16
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Tidskriftsartikel (refereegranskat)abstract
- The Au mineralization in the Kubi Gold Mining Area in the Birimian of Ghana is associated with garnet (about 85 vol.%), magnetite, pyrrhotite, arsenopyrite, and sulfide minerals, as well as quartz with gold and calcite. These minerals and the included elements can act as indicator minerals or pathfinder elements. For the present work, we collected samples from drill holes at different depths, from the alluvial zone (0–45 m) to the ore zone (75–100 m). The distributions of minerals and elements in the rocks that act as indicator minerals and pathfinder elements in the concession area were investigated along the drill hole cross sections. X-ray diffraction shows that the samples contain garnet, pyrite, periclase, and quartz as the main indicator minerals. By energy-dispersive X-ray spectroscopy, Fe, Mg, Al, S, O, Mn, Na, Cu, Si, and K are identified as corresponding pathfinder elements. The results indicate that the Au mineralization in the Kubi Mine area correlates mostly with the occurrence of garnet, pyrite, goethite, and kaolinite in the host rocks, which show towards the surface increasingly hematitic and limonitic alteration in form of Fe(oxy-)hydroxides.
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| 40. |
- Serban, Alexandra, 1988-, et al.
(författare)
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Magnetron Sputter Epitaxy of High-Quality GaN Nanorods on Functional and Cost-Effective Templates/Substrates
- 2017
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Ingår i: Energies. - Basel, Switzerland : MDPI AG. - 1996-1073. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.
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| 41. |
- Serban, Elena Alexandra, 1988-
(författare)
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Self-Assembled and Selective-Area Growth of Group III-Nitride Semiconductor Nanorods by Magnetron Sputter Epitaxy
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The III-nitride semiconductor family includes gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), and the related ternary and quaternary alloys. The research interest on this group of materials is sparked by the direct bandgaps, and excellent physical and chemical properties. Moreover, the ternary alloys (InGaN, InAlN and AlGaN) present the advantage of bandgap tuning, giving access to the whole visible spectrum, from near infrared into deep ultraviolet wavelengths. The intrinsic properties of III-nitride materials can be combined with characteristic features of nanodimension and geometry in nanorod structures. Moreover, nanorods offer the advantage of avoiding problems arising from the lack of native substrates with film/substrate lattice and thermal expansion mismatch.The growth and characterization of group III-nitride semiconductor nanorods, namely InAlN and GaN nanorods, is presented in this Thesis. All the nanostructures were grown by employing direct-current reactive magnetron sputter epitaxy. The results include the growth and study of both self-assembled and site-controlled grown nanorods.InxAl1−xN self-assembled, core-shell nanorods on Si(111) substrates were demonstrated. A comprehensive study of temperature effect upon the morphology and composition of the nanorods was realized. The radial nanorod heterostructure consists of In-rich cores surrounded by Al-rich shells with different thicknesses. The spontaneous formation of core-shell nanorods is suggested to originate from phase separation due to spinodal decomposition. As the growth temperature increases, In desorption is favored, resulting in thicker Al-rich shells and larger nanorod diameters. Moreover, the in-plane crystallographic relationship of the nanorods and substrate was modified from a fiber-textured to an epitaxial growth by removing the native SiOx layer from the substrate.Self-assembled growth of GaN nanorods on cost-effective substrates offers a cheaper alternative and simplifies device processing. Successful growth of high-quality GaN (exhibiting strong bandedge emission and high crystalline quality) on conductive templates/substrates such as Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti is supported by the possibility to be used as electrodes when integrated in optoelectronic devices. The influence of growth temperature upon the resulting size and optical properties of the nanorods was investigated. By applying a kinetic model, average diffusion length was calculated in correlation with growth temperature in order to explain the nanorods’ morphology evolution.The self-assembled growth leads to random nucleation, resulting in nanorods with large varieties of diameters, heights and densities within a single growth run. This translates into non-uniform properties and complicates device processing. These problems can be circumvented by employing selective-area growth. Pre-patterned substrates by nanosphere lithography resulted in GaN nanorods with controlled length, diameter, shape, and density. Well-faceted caxis oriented GaN nanorods were grown directly onto the native SiOx layer inside opening areas exhibiting strong bandedge emission at room-temperature and single-mode lasing. The time-dependent growth series helped define a comprehensive growth mechanism from the initial thin wetting layer formed inside the openings, to the well-defined, uniform, hexagonal nanorods resulted from the coalescence of multiple initial nuclei.Although nanosphere lithography is a fast and cheap patterning method, it does not offer the control on the size, position or density. The growth parameters were transferred onto focused ion beam lithography - patterned substrates which offers more control on the design. Focused ion beam lithography optimization included tailoring of the milling current (2-50 pA) and milling time (5-50 s). The patterning process optimisation enabled the minimization of mask and substrate damage, the key to attain uniform, welldefined, single, and straight nanorods. Destruction of the mask results in selective-area growth failure, while damage of the substrate surface promotes inclined nanorods grown into the openings, owning to random oriented nucleation. At lower growth temperatures (950 °C) nanostructures resulted from the coalescence of multiple, tilted, and irregular nanorods are observed. The tilting of the nanorods is reduced when increasing the growth temperature to 980 °C resulting in single and straight nanorods. The partial pressure of the Ar/N2 working gas was also varied for achieving selectivity and single nanorods, and study the growth behaviour. By increasing the amount of Ar in the working gas from 0 to 50%, we observe a transition of the target from a nitridized to metallic-state, affecting the sputtering conditions of the GaN nanorods. The change in the sputtering and deposition conditions influences the growth selectivity, coalescence, and growth rates. By balancing these effects, the selective growth of faceted, single nanorods was achieved.
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| 42. |
- Serban, Elena Alexandra, 1988-, et al.
(författare)
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Site-controlled growth of GaN nanorod arrays by magnetron sputter epitaxy
- 2018
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 660, s. 950-955
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst-free GaN nanorod regular arrays have been realized by reactive magnetron sputter epitaxy. Two nanolithographic methods, nanosphere lithography (NSL) and focused ion beam lithography (FIBL), were applied to pattern Si substrates with TiNx masks. The growth temperature was optimized for achieving selectivity and well-faceted nanorods grown onto the NSL-patterned substrates. With increasing temperature from 875 to 985 °C, we observe different growth behaviors and associate them with selective insensitive, diffusion-dominated, and desorption-dominated zones. To further achieve site-specific and diameter control, these growth parameters were transferred onto FIBL-patterned substrates. Further investigation into the FIBL process through tailoring of milling current and time in combination with varying nanorod growth temperature, suggests that minimization of mask and substrate damage is the key to attain uniform, well-defined, single, and straight nanorods. Destruction of the mask results in selective area growth failure, while damage of the substrate surface promotes inclined nanorods grown into the openings, owning to random oriented nucleation.
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| 43. |
- Tengstrand, Olof
(författare)
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Me-Si-C (Me= Nb, Ti or Zr) : Nanocomposite and Amorphous Thin Films
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates thin films of the transition metal carbide systems Ti-Si-C, Nb-Si-C, and Zr-Si-C, deposited at a low substrate temperature (350 °C) with dc magnetron sputtering in an Ar discharge. Both the electrical and mechanical properties of these systems are highly affected by their structure. For Nb-Si-C, both the ternary Nb-Si-C and the binary Nb-C are studied. I show pure NbC films to consist of crystalline NbC grains embedded in a matrix of amorphous carbon. The best combination of hardness and electrical resistivity are for ~15 at.% a-C phase. The properties of nc-NbC/a-C are similar to films consisting of nc-TiC/a-C. I further show that in a model system of epitaxial TiCx (x ~0.7) up to 5 at.% Si can be incorporated. At higher Si content, Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy. Higher amounts of Si into the Nb-Si-C and Zr-Si-C systems make them become amorphous. These amorphous structures are unstable under electron irradiation were they crystallize. I show that the cause of crystallization is driven by atomic displacement events.
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| 44. |
- Thörnberg, Jimmy, et al.
(författare)
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Microstructure and materials properties of understoichiometric TiBx thin films grown by HiPIMS
- 2020
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 404
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Tidskriftsartikel (refereegranskat)abstract
- TiBx thin films with a B content of 1.43 <= x <= 2.70 were synthesized using high-power impulse magnetron sputtering (HiPIMS) and direct-current magnetron sputtering (DCMS). HiPIMS allows compositions ranging from understoichiometric to overstoichiometric dense TiBx thin films with a B/Ti ratio between 1.43 and 2.06, while DCMS yields overstoichiometric TiBx films with a B/Ti ratio ranging from 2.20 to 2.70. Excess B in overstoichiometric TiBx thin films from DCMS results in a hardness up to 37.7 +/- 0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase interlacing stoichiometric TiB2 columnar structures. We furthermore show that understoichiometric TiB1.43 thin films synthesized by HiPIMS, where the deficiency of B is found to be accommodated by Ti-rich planar defects, exhibit a superior hardness of 43.9 +/- 0.9 GPa. The apparent fracture toughness and thermal conductivity of understoichiometric TiB1.43 HiPIMS films are 4.2 +/- 0.1 MPa root m and 2.46 +/- 0.22 W/(m.K), respectively, as compared to corresponding values for overstoichiometric TiB2.70 DCMS film samples of 3.1 +/- 0.1 MPa root m and 4.52 +/- 0.45 W/(mK). This work increases the fundamental understanding of understoichiometric TiBx thin films and their materials properties, and shows that understoichiometric films have properties matching or going beyond those with excess B.
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