| 1. |
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| 2. |
- Engberg, David L. J., 1986-, et al.
(författare)
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Atom probe tomography field evaporation characteristics and compositional corrections of ZrB2
- 2019
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of stoichiometric ZrB2.0 and B over-stoichiometric ZrB2.5 thin films has been studied using atom probe tomography (APT), X-ray diffraction, and transmission electron microscopy. Both films consist of columnar ZrB2 grains with AlB2-type crystal structure. The narrow stoichiometry range of ZrB2 results in the presence of separate disordered B-rich boundaries even in ZrB2.0. At higher average B content, specifically ZrB2.5, the formation of a continuous network around the sides of the ZrB2 columns is promoted. In addition, the APT field evaporation characteristics of ZrB2 and its influence on the measured local composition has been studied and compared to the average composition from elastic recoil detection analysis (ERDA). Differences in the measured average compositions of the two techniques are explained by the APT detector dead-time/space. A new pile-up pairs correction procedure based on co-evaporation correlation data was thus employed here for the APT data and compared with the 10B-method (the B equivalence of the 13C-method), as well as the combination of both methods. In ZrB2.0, all of the applied compositional correction methods were found to reduce the compositional difference when appropriate isotopic abundances were used. In ZrB2.5, the inhomogeneity of the film likely increased the local APT composition to such an extent that even conservative correction procedures overestimated the B content compared to the ERDA reference. The strengths of the pile-up pairs correction compared the 10B and the combined methods are higher precision, due to it being less dependent on the accuracy of estimated isotopic abundances, and that the correction itself is not dependent on careful background correction of the mass spectrum.
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| 3. |
- Hänninen, Tuomas, 1988-, et al.
(författare)
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Silicon carbonitride thin films deposited by reactive high power impulse magnetron sputtering
- 2018
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 335, s. 248-256
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous silicon carbonitride thin films for biomedical applications were deposited in an industrial coating unit from a silicon target in different argon/nitrogen/acetylene mixtures by reactive high power impulse magnetron sputtering (rHiPIMS). The effects of acetylene (C2H2) flow rate, substrate temperature, substrate bias voltage, and HiPIMS pulse frequency on the film properties were investigated. Low C2H2 flow rates (<10 sccm) resulted in silicon nitride-like film properties, seen from a dense morphology when viewed in cross-sectional scanning electron microscopy, a hardness up to ∼22 GPa as measured by nanoindentation, and Si-N bonds dominating over Si-C bonds in X-ray photoelectron spectroscopy core-level spectra. Higher C2H2 flows resulted in increasingly amorphous carbon-like film properties, with a granular appearance of the film morphology, mass densities below 2 g/cm3 as measured by X-ray reflectivity, and a hardness down to 4.5 GPa. Increasing substrate temperatures and bias voltages resulted in slightly higher film hardnesses and higher compressive residual stresses. The film H/E ratio showed a maximum at film carbon contents ranging between 15 and 30 at.% and at elevated substrate temperatures from 340 °C to 520 °C.
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| 4. |
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| 5. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Compositional dependence of epitaxial Tin+1SiCn MAX-phase thin films grown from a Ti3SiC2 compound target
- 2019
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:2
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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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| 6. |
- Choolakkal, Arun Haridas, 1992-
(författare)
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Conformal chemical vapor deposition of boron carbide thin films
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The sustainability goals of the modern world and the fascinating properties of sub-micron scale materials promote development of materials in thin film form. Thin films are materials that have thicknesses ranging from sub-nanometer to several micrometers, synthesized by various deposition techniques. They are used for diverse applications, such as light emitting diodes, solar cells, semiconductor chips, etc. The primary objective of this research project is to develop a chemical vapor deposition (CVD) process for conformal boron carbide thin films. Since boron carbide is a promising neutron converter material for solid-state neutron detectors, the process was validated by depositing on prototype detector chips. In this study, triethylboron (TEB) was used as single source CVD precursor to deposit boron carbide thin films. The initial experiments focused on low reaction rate deposition by depositing in a kinetically limited regime. The films deposited at ≤450 °C in 8:1 aspect ratio micro-trench structures were highly conformal and show a stoichiometry of about B5.2C. We attribute this observed conformality to the slow reaction kinetics of the TEB at the low deposition temperature enabling the diffusive transport of the precursor molecule down the trench. The depositions carried out on the prototype detector-chips show promising results. We expand our studies to investigate a new strategy with the prospect of improving the step coverage at higher temperatures for better film properties. We hypothesize that adding a suitable heavier molecule, diffusion additive, with an appropriate partial pressure can enhance the step coverage by pushing the lighter precursor molecule via competitive co-diffusion. It was tested by adding Xe gas to the boron carbide CVD from TEB. The result shows that with this diffusion additive the step coverage was improved from 0.71 to 0.97. From our experimental results, we suggest a competitive diffusion model that can be adapted to other CVD processes to enhance the film step coverage. The CVD process is further validated by depositing onto carbon nanotube membranes. The initial results show that the process was able to afford evenly deposition around the individual nanotubes in the carbon nanotube membrane. Raman spectroscopy measurements show a similar D-band to G-band intensity ratio before and after the deposition indicating that no defects were induced in the nanotubes.
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| 7. |
- Eklund, Per, 1977-, et al.
(författare)
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Ta4AlC3 : Phase determination, polymorphism and deformation
- 2007
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 55:14, s. 4723-4729
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Tidskriftsartikel (refereegranskat)abstract
- Ta4AlC3, a new member of the Mn+1AXn-phase family, has been synthesized and characterized (n = 1-3, M = early transition metal, A = A-group element, and X = C and/or N). Phase determination by Rietveld refinement of synchrotron X-ray diffraction data shows that Ta4AlC3 belongs to the P63/mmc space group with a and c lattice parameters of 3.10884 ± 0.00004 Å and 24.0776 ± 0.0004 Å, respectively. This is shown to be the α-polymorph of Ta4AlC3, with the same structure as Ti4AlN3. Lattice imaging by high-resolution transmission electron microscopy demonstrates the characteristic MAX-phase stacking of α-Ta4AlC3. Three modes of mechanical deformation of α-Ta4AlC3 are observed: lattice bending, kinking and delamination. © 2007.
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| 8. |
- Emmerlich, Jens, 1974-, et al.
(författare)
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Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:9, s. 4817-4826
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900 °C. This process allows composition control to synthesize Mn + 1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and/or N; n = 1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (105), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700 °C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25 µ cm was measured. The Young's modulus, ascertained by nanoindentation, yielded a value of 343–370 GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30 GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.
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| 9. |
- Emmerlich, Jens, 1974-, et al.
(författare)
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Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films
- 2008
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Ingår i: Wear. - Amsterdam, Netherlands : Elsevier. - 0043-1648 .- 1873-2577. ; 264:11-12, s. 914-919
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Tidskriftsartikel (refereegranskat)abstract
- Ti3SiC2(0 0 0 1) thin films prepared by magnetron sputtering were investigated for their response to tribomechanical strain induced during ball-on-disk experiments with 6 mm alumina balls and scratch tests with a 1 μm cono-spherical diamond tip. Normal loads of 100 μN to 0.24 N were applied resulting in a friction coefficient of 0.1 for the low loads. With higher applied normal loads, the friction coefficient increased up to 0.8. Analysis of the wear tracks using atomic force microscopy, scanning electron microscopy, and Raman spectroscopy revealed excessive debris resulting in third-body abrasion and fast wear. The formation of the debris can be explained by the generation of subsurface delamination cracks on basal planes. Subsequent kink formation obstructs the ball movement which results in the removal of the kinked film parts.
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| 10. |
- Hänninen, Tuomas, 1988-
(författare)
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Silicon Nitride Based Coatings Grown by Reactive Magnetron Sputtering
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon nitride and silicon nitride-based ceramics have several favorable material properties, such as high hardness and good wear resistance, which makes them important materials for the coating industry. This thesis focuses the synthesis of silicon nitride, silicon oxynitride, and silicon carbonitride thin films by reactive magnetron sputtering. The films were characterized based on their chemical composition, chemical bonding structure, and mechanical properties to link the growth conditions to the film properties. Silicon nitride films were synthesized by reactive high power impulse magnetron sputtering (HiPIMS) from a Si target in Ar/N2 atmospheres, whereas silicon oxynitride films were grown by using nitrous oxide as the reactive gas. Silicon carbonitride was synthesized by two different methods. The first method was using acetylene (C2H2) in addition to N2 in a Si HiPIMS process and the other was co-sputtering of Si and C, using HiPIMS for Si and direct current magnetron sputtering (DCMS) for graphite targets in an Ar/N2 atmosphere. Langmuir probe measurements were carried out for the silicon nitride and silicon oxynitride processes and positive ion mass spectrometry for the silicon nitride processes to gain further understanding on the plasma conditions during film growth. The target current and voltage waveforms of the reactive HiPIMS processes were evaluated.The main deposition parameter affecting the nitrogen concentration of silicon nitride films was found to be the nitrogen content in the plasma. Films with nitrogen contents of 50 at.% were deposited at N2/Ar flow ratios of 0.3 and above. These films showed Si-N as the dominating component in Si 2p X-ray photoelectron spectroscopy (XPS) core level spectra and Si–Si bonds were absent. The substrate temperature and target power were found to affect the nitrogen content to a lower extent. The residual stress and hardness of the films were found to increase with the film nitrogen content. Another factors influencing the coating stress were the process pressure, negative substrate bias, substrate temperature, and HiPIMS pulse energy. Silicon nitride coatings with good adhesion and low levels of compressive residual stress were grown by using a pressure of 600 mPa, a substrate temperature below 200 °C, pulse energies below 2.5 Ws, and negative bias voltages up to 100 V.The elemental composition of silicon oxynitride films was shown to depend on the target power settings as well as on the nitrous oxide flow rate. Silicon oxide-like films were synthesized under poisoned target surface conditions, whereas films deposited in the transition regime between poisoned and metallic conditions showed higher nitrogen concentrations. The nitrogen content of the films deposited in the transition region was controlled by the applied gas flow rate. The applied target power did not affect the nitrogen concentration in the transition regime, while the oxygen content increased at decreasing target powers. The chemical composition of the films was shown to range from silicon-rich to effectively stoichiometric silicon oxynitrides, where no Si–Si contributions were found in the XPS Si 2p core level spectra. The film optical properties, namely the refractive index and extinction coefficient, were shown to depend on the film chemical bonding, with the stoichiometric films displaying optical properties falling between those of silicon oxide and silicon nitride.The properties of silicon carbonitride films were greatly influenced by the synthesis method. The films deposited by HiPIMS using acetylene as the carbon source showed silicon nitride-like mechanical properties, such as a hardness of ~ 20 GPa and compressive residual stresses of 1.7 – 1.9 GPa, up to film carbon contents of 30 at.%. At larger film carbon contents the films had increasingly amorphous carbon-like properties, such as densities below 2 g/cm3 and hardnesses below 10 GPa. The films with more than 30 at.% carbon also showed columnar morphologies in cross-sectional scanning electron microscopy, whereas films with lower carbon content showed dense morphologies. Due to the use of acetylene the carbonitride films contained hydrogen, up to ~ 15 at.%. The co-sputtered silicon carbonitride films showed a layered SiNx/CNx structure. The hardness of these films increased with the film carbon content, reaching a maximum of 18 GPa at a film carbon content of 12 at.%. Comparatively hard and low stressed films were grown by co-sputtering using a C target power of 1200 W for a C content around 12 at.%, a negative substrate bias less than 100 V, and a substrate temperature up to 340 °C.
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| 11. |
- Högberg, Hans, 1968-, et al.
(författare)
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Epitaxial Ti2GeC, Ti3GeC2, and Ti4GeC3 MAX-phase thin films grown by magnetron sputtering
- 2005
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 20:4, s. 779-782
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Tidskriftsartikel (refereegranskat)abstract
- We have grown single-crystal thin films of Ti2GeC and Ti3GeC2 and a new phase Ti4GeC3, as well as two new intergrown MAX-structures, Ti5Ge2C3 and Ti7Ge2C5. Epitaxial films were grown on Al2O3(0001) substrates at 1000 °C using direct current magnetron sputtering. X-ray diffraction shows that Ti–Ge–C MAX-phases require higher deposition temperatures in a narrower window than their Ti–Si–C correspondences do, while there are similarities in phase distribution. Nanoindentation reveals a Young’s modulus of 300 GPa, lower than that of Ti3SiC2. Four-point probe measurements yield resistivity values of 50–200 μΩcm. The lowest value is obtained for phase-pure Ti3GeC2(0001) films.
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| 12. |
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| 13. |
- Högberg, Hans, 1968-, et al.
(författare)
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Growth and characterization of MAX-phase thin films
- 2005
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 193, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- We report that magnetron sputtering can be applied to synthesize MAX-phase films of several systems including Ti–Si–C, Ti–Ge–C, Ti–Al–C, and Ti–Al–N. In particular, epitaxial films of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, Ti3AlC2, Ti2AlC, and Ti2AlN as well as the newly discovered thin film phases Ti4SiC3, Ti4GeC3 and intergrown structures can be deposited at 900–1000 °C on Al2O3(0001) and MgO(111) pre-seeded with TiC or Ti(Al)N. From XTEM and AFM we suggest a growth and nucleation model where MAX-phase nucleation is initiated at surface steps or facets on the seed layer and followed by lateral growth. Differences between the growth behavior of the systems with respect to phase distribution and phase stabilities are discussed. Characterization of mechanical properties for Tin+1Si–Cn films with nanoindentation show decreased hardness from about 25 to 15 GPa upon penetration of the basal planes with characteristic large plastic deformation with pile up dependent on the choice of MAX material. This is explained by cohesive delamination of the basal planes and kink band formation, in agreement with the observations made for bulk material. Measurements of the electrical resistivity for Ti–Si–C and Ti–Al–N films with four-point probe technique show values of 30 and 39 μΩ cm, respectively, comparable to bulk materials.
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| 14. |
- Lundberg, Hans, et al.
(författare)
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Towards a Conceptual Model for Heritagepreneurship and Regional Development
- 2016
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Ingår i: Tourism and Culture in the Age of Innovation. - Cham : Springer. - 9783319275284 - 9783319275277 ; , s. 23-40
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Konferensbidrag (refereegranskat)abstract
- In this text, we present a conceptual model for discussing and analysing what happens when culture, in the form of heritage, and regional development, in the form of entrepreneurship, is juxtaposed (=heritagepreneurship). By comparing case studies from Mexican and South West Scandinavian regions our ambition is to elucidate potentials and limits in different ways of working with regional development using heritage as a mean.Our case studies showed that heritage becomes staged, enacted, and perceived in very differing ways depending on the ways memories are embraced, constructed or repressed in the heritagepreneurship process. Different meanings thereby give different societal effects, influencing the heritagepreneurship process.The strategies used in these case studies tend to be located “in the extremes”, from unconscious ignorance or a conscious effort to forget, to efforts to provide full attention and an active awareness of what has happened. We believe that more nuanced strategies for more long-term sustainable heritagepreneurship and regional development are located in-between these extremes.
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| 15. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121, s. 25750-25758
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Tidskriftsartikel (refereegranskat)abstract
- The variation in local atomic structure and chemical bonding of ZrHx (x=0.15, 0.30, 1.16) magnetron sputtered thin films are investigated by Zr K-edge (1s) X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies. A chemical shift of the Zr K-edge towards higher energy with increasing hydrogen content is observed due to charge-transfer and an ionic or polar covalent bonding component between the Zr 4d and the H 1s states with increasing valency for Zr. We find an increase in the Zr-Zr bond distance with increasing hydrogen content from 3.160 Å in the hexagonal closest-packed metal (a-phase) to 3.395 Å in the understoichiometric d-ZrHx film (CaF2-type structure) with x=1.16 that largely resembles that of bulk d-ZrH2. For yet lower hydrogen contents, the structures are mixed a- and d-phases, while sufficient hydrogen loading (x>1) yields a pure δ-phase that is understoichiometric, but thermodynamically stable. The change in the hydrogen content and strain is discussed in relation to the corresponding change of bond lengths, hybridizations, and trends in electrical resistivity.
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| 16. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy
- 2018
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 649, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk α-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk α-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible 11, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material. For the bulk α-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to α-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 Å, c=3.520 Å) in comparison to the bulk target material (a=3.175 Å, c=3.540 Å) while in hexagonal closest-packed metal (α-phase, a=3.254 Å, c=5.147 Å). The modelled coordination numbers show that the EXAFS spectra of the epitaxial ZrB2 film is highly anisotropic with strong in-plane contribution, while the bulk target material is more isotropic. The Zr-B distance in the film of 2.539 Å is in agreement with the calculated value from XRD data of 2.542 Å. This is slightly shorter compared to that in the ZrB2 compound target 2.599 Å, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.
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| 17. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Electronic Structure of ß-Ta Films from X-ray Photoelectron Spectroscopy and First-principles Calculations
- 2019
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 470, s. 607-612
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and chemical bonding of ß-Ta synthesized as a thin 001-oriented film (space group P 21m) is investigated by 4f core level and valence band X-ray photoelectron spectroscopy and compared to α-Ta bulk. For the b-phase, the 4f7/2 peak is located at 21.91 eV and with the 4f5/2 at 23.81 eV which is 0.16 eV higher compared to the corresponding 4f peaks of the a-Ta reference. We suggest that this chemical shift originates from higher resistivity and tensile strain in the ß-Ta film. Furthermore, the 5d-5s states at the bottom of the valence band are shifted by 0.75 eV towards higher binding energy in ß-Ta compared to α-Ta. This is a consequence of the lower number of nearest neighbors with four in ß-Ta compared to eight in the α-Ta phase. The difference in the electronic structures, spectral line shapes of the valence band and the energy positions of the Ta 4f, 5p core-levels of b-Ta versus a-Ta are discussed in relation to calculated states of ß-Ta and α-Ta. In particular, the lower number of states at the Fermi level of ß-Ta (0.557 states/eV/atom) versus α-Ta (1.032 states/eV/atom) that according to Mott’s law should decrease the conductivity in metals and affect the stability by charge redistribution in the valence band. This is experimentally supported from resistivity measurements of the film yielding a value of ~170 µW cm in comparison to α-Ta bulk with a reported value of ~13.1 µW cm.
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| 18. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Reactive magnetron sputtering of tungsten target in krypton/trimethylboron atmosphere
- 2019
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 688
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Tidskriftsartikel (refereegranskat)abstract
- W-B-C films were deposited on Si(100) substrates held at elevated temperature by reactive sputtering from a W target in Kr/trimethylboron (TMB) plasmas. Quantitative analysis by Xray photoelectron spectroscopy (XPS) shows that the films are W-rich between ~ 73 and ~ 93 at.% W. The highest metal content is detected in the film deposited with 1 sccm TMB. The C and B concentrations increase with increasing TMB flow to a maximum of ~18 and ~7 at.%, respectively, while the O content remains nearly constant at 2-3 at.%. Chemical bonding structure analysis performed after samples sputter-cleaning reveals C-W and B-W bonding and no detectable W-O bonds. During film growth with 5 sccm TMB and 500 o C or with 10 sccm TMB and 300-600 o C thin film X-ray diffraction shows the formation of cubic 100-oriented WC1-x with a possible solid solution of B. Lower flows and lower growth temperatures favor growth of W and W2C, respectively. Depositions at 700 and 800 o C result in the formation of WSi2 due to a reaction with the substrate. At 900 o C, XPS analysis shows ~96 at.% Si in the film due to Si interdiffusion. Scanning electron microscopy images reveal a fine-grained microstructure for the deposited WC1-x films. Nanoindentation gives hardness values in the range from ~23 to ~31 GPa and reduced elastic moduli between ~220 and 280 GPa in the films deposited at temperatures lower than 600 o C. At higher growth temperatures the hardness decreases by a factor of 3 to 4 following the formation of WSi2 at 700-800 o C and Si-rich surface at 900 o C.
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| 19. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Review of Transition-Metal Diboride Thin Films
- 2022
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 196
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Forskningsöversikt (refereegranskat)abstract
- We review the thin film growth, chemistry, and physical properties of Group 4-6 transition-metal diboride (TMB2) thin films with AlB2-type crystal structure (Strukturbericht designation C32). Industrial applications are growing rapidly as TMB2 begin competing with conventional refractory ceramics like carbides and nitrides, including pseudo-binaries such as Ti1-xAlxN. The TMB2 crystal structure comprises graphite-like honeycombed atomic sheets of B interleaved by hexagonal close-packed TM layers. From the C32 crystal structure stems unique properties including high melting point, hardness, and corrosion resistance, yet limited oxidation resistance, combined with high electrical conductivity. We correlate the underlying chemical bonding, orbital overlap, and electronic structure to the mechanical properties, resistivity, and high-temperature properties unique to this class of materials. The review highlights the importance of avoiding contamination elements (like oxygen) and boron segregation on both the target and substrate sides during sputter deposition, for better-defined properties, regardless of the boride system investigated. This is a consequence of the strong tendency for B to segregate to TMB2 grain boundaries for boron-rich compositions of the growth flux. It is judged that sputter deposition of TMB2 films is at a tipping point towards a multitude of applications for TMB2 not solely as bulk materials, but also as protective coatings and electrically conducting high-temperature stable thin films.
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| 20. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Arrhenius-type temperature dependence of the chemical desorption processes active during deposition of fullerene-like carbon nitride thin films
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 569:1-3
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Tidskriftsartikel (refereegranskat)abstract
- The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CNx) thin solid films by reactive magnetron sputtering of a carbon target in a N2-containing atmosphere. The desorption of mainly C2N2 was suppressed by decreasing the substrate temperature for various N2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N 2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N 2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed C xNy species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N 2 in the discharge, while the obtained activation energies of 0.05-0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed C xNy species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption. © 2004 Elsevier B.V. All rights reserved.
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| 21. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Cryogenic deposition of carbon nitride thin solid films by reactive magnetron sputtering, Suppression of the chemical desorption processes
- 2005
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 478:1-2, s. 34-41
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured fullerene-like carbon nitride (FL CNx) is commonly grown by reactive magnetron sputtering of carbon in a nitrogen-containing atmosphere. The film structure formation for this technique is presumably due to the existence of preformed molecular CxNy (x,y≤2) species in the deposition flux, which act as growth templates and enhance the selectivity of chemical desorption processes. In the present study, the extent of the desorption processes and the implications on the resulting film have been investigated in detail, addressing in particular the structure evolution and the origin of the incorporated nitrogen. This was studied by varying the N2-fraction in the discharge from 0 to 1 and the substrate temperature from 600 °C (873 K) down to minus 130 °C (143 K). The results show that the incorporation rate of carbon and nitrogen into the film increases substantially with an increased N2-content in the plasma and decreasing substrate temperature, thus indicating that the chemistry and magnitude of the arriving flux is substantially altered with the N2-fraction in the discharge. It is concluded that the chemically activated desorption in conjunction with the varying chemistry of the film-forming flux affects the sensitive structural balance, determined by incorporation and desorption of film forming CxNy (x,y≤2) species.
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| 22. |
- Nilsson, Pernilla, 1969-, et al.
(författare)
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Distribuerad case-metodik i ingenjörsutbildningen
- 2009
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Ingår i: Den 2:a Utvecklingskonferensen för Sveriges ingenjörsutbildningar. - Lund : Lunds Tekniska Högskola, Genombrottet. ; , s. 71-73, s. 71-73
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper is based on a project in which an academic developer worked as a critical friend for a group of engineering in order to stimulate their collaboration and their reflection on their own teaching and learning as a way of developing their scholarship of teaching. The project was built on collaboration between three different universities, Halmstad, Örebro and Skövde and reports on how teachers, as well as the students collaborative learning experiences.
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| 23. |
- Nyman, Johan, 1992-
(författare)
-
Cathodic arc deposition of metal-rich Cr-based coatings
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood and wood-based products have always been key components in the development of human civilization. Nowadays most wood harvesting is done using chainsaws, and their efficient operation helps promote worker safety and reduce emissions. An important factor for efficient operation is the sharpness of the chain – a sharper chain requires less energy for cutting and reduces the risk of dangerous kickback. To reduce the rate of wear and prolong the life of the chains, they are protected by a hard chrome coating. The production of this coating involves compounds in which Cr atoms are in the toxic and carcinogenic hexavalent state. The deposited coatings contain no toxic compounds, however. Consequently, there is a need to develop replacement processes which can produce equally well-performing coatings.In this thesis I investigate the process of cathodic arc deposition of coatings for this purpose. Cathodic arc deposition is a well-established technique for tool coatings, free of toxic compounds. Specifically, elemental Cr coatings, and Cr-rich Cr-N, Cr-C, and Cr-C-N coatings are studied.For the study on elemental Cr, focus is put on the impact of substrate bias on the growth and coating properties. This is important in cathodic arc deposition as the evaporated species are ionized to a high degree. I show that an increasing substrate bias increases the temperature of the substrate and compressive stress of the coatings while decreasing the growth rate because of resputtering. The texture also changes from a preferential [110]- to [100]-orientation, and the hardness is lower than for typical hard chrome coatings.For alloying with N or C, using N2 and C2H2, respectively, the N-/Ccontent is shown to decrease with increasing bias. This process is attributed to preferential resputtering, and ceases at a critical partial pressure, different for N and C, at which point there is no observed difference in N- or C- content at different bias. The incorporation strongly affects the microstructure of the coatings. For N, there is a transition from a columnar structure to a featureless appearance at high N-content, while for C a mixed amorphous/crystalline structure appears at high C-content. For both C and N, the change in microstructure is accompanied by a large increase in hardness, which almost doubles when the alloying concentration reaches ~7 at.%.In a fourth study, combined C- and N-alloying is investigated. Here it is seen that the preferential resputtering persists for N, but for C there is a linear increase in content with partial pressure of C2H2 for all bias levels. This results in the coatings containing more C than N, with a structure like that of Cr-C. At the highest alloying level, a new structure appears which is not seen for the Cr-N and Cr-C studies, consisting of small, elongated grains and columns.In a fifth study, synchrotron-based X-ray adsorption spectroscopy is used to provide structural information about the coatings that is difficult to access with X-ray diffraction. The measurements show that Cr2N and Cr3C2 are the predominant phases forming alongside bcc Cr and reveal changes in bond orientations and strengths at differing alloying concentrations.
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| 24. |
- Nyman, Johan, 1992-, et al.
(författare)
-
Substrate bias effects on cathodic arc deposited Cr coatings
- 2023
-
Ingår i: Results in Materials. - 2590-048X. ; 19
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the effects of substrate bias on cathodic arc deposition of Cr coatings without external substrate heating at four different substrate bias levels, floating, −30, −50, and −70 V. After 10 min of deposition, the substrate temperature reaches 180, 210, 230, and 260 °C for floating potential, −30, −50, and −70 V, respectively. Time-of-flight energy elastic recoil detection analysis shows that all grown coatings are of high purity, with no coating containing more than 0.2 at.% of C and/or O. Increasing the substrate bias also reduces the number of macroparticles, steers the texture from preferred [110]- to [100]-orientation and induces a residual compressive stress of ∼450 MPa in the coatings. The hardness of the coatings remains at a constant 7.5 GPa irrespective of the substrate bias. The four-point probe resistivity of the grown coatings is 15–17 μΩcm regardless of substrate bias, close to the 12.9 μΩcm of bulk Cr.
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| 25. |
- Nzulu, Gabriel Kofi, 1974-
(författare)
-
Characterization of Pathfinders and Indicators of Gold
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research on natural minerals and their chemical bonding to economically critical raw materials is a viable industrially relevant research area due to its increasing demand. Meeting demands requires fast, robust, and efficient techniques to explore new ore deposits and continuous operation of active mines as well as recycling. One of the most critical metals is gold which occurs in three main types of ore deposits: i) hydrothermal quartz veins and related deposits in metamorphic and igneous rocks; ii) volcanic-exhalative sulfide deposits, and iii) consolidated to unconsolidated placer deposits. Gold is commonly found as disseminated grains in quartz veins in pyrite and other sulfides or as rounded grains, flakes or nuggets in deposits in riverbanks, in contact with metamorphic or hypothermal deposits (e.g., skarns) or epithermal deposits such as volcanic fumaroles. Pathfinder elements and indicator minerals provide means to explore large areas for their potential mineral commodities such as gold, diamond, base metals, platinum group of elements, and rare earth elements by narrowing the search area to reduce exploration costs. The recent technological advancement in obtaining rapid geochemical results using field portable analytical devices as alternatives to the old approach where collected field samples are carried to the laboratory calls for further investigation to explore other techniques in mineral and metal exploration.In this Thesis, I investigate the properties of artisanal small-scale gold mining concentrate, outcrop, bulk Au, and drill hole samples from the Kubi Gold Project of the Asante Gold Corporation near Dunkwa-on-Offin in the Central Region of Ghana with a materials science perspective. X-ray diffraction (XRD) is used to identify SiO2 (quartz), Fe3O4 (magnetite), garnet, pyrite (FeS2), periclase (MgO), arsenopyrites, pyrrhotite, biotite, titanium oxide, and Fe2O3 (hematite) as the main indicator minerals in the mining site with less significant contributions from chalcopyrite, iridosmine, scheelite, tetradymite, gypsum, and a few other sulfates. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) indicate that Fe, Ag, Al, N, O, Si, Hg, C, Ba, P, Ca, Mg, Na, Mn, Cl, S, K, and Ti are important host elements that form alloys with Au or are inherent in the sediment at the concession site. The results also indicate that Si and Ag are in strong co-occurrence with Au due to their eutectic qualities, while N, C, and O occur due to their attraction to Si. Also, the XPS results indicate that the relationship between Au and pathfinder elements or indicator minerals depends on the d-orbital of Au and other elements that possess octahedral or tetrahedral geometry to split into two states, eg and t2g that can acquire either higher or lower energy depending on the geometry and are responsible for the covalent, metallic, and ionic states of Au with other ligands. From the air anneal furnace (AAF) and differential scanning calorimetry (DSC), I investigated the transformations in quartz and pyrite minerals that alter to hematite minerals. The quartz samples are observed to transform from α-quartz to β-quartz and finally to cristobalite while the pyrite transforms to magnetite and later to hematite. These findings suggest that during the hydrothermal flow regime impurity materials are trapped by voids and faults and can be altered at different depositional stages by oxidation and reduction processes. Results from the scanning electron microscopy (SEM) revealed the presence of carbonates in fracture zones in the quartz, pyrite, and almandine-type garnet mineral in gabbroic rocks.The findings indicate that, from the top of the oxide zone, grains within sediments are seen to be controlled by quartz, and hematite, the bedrock consists of pyrite and pyrrhotite, and the orebody contains garnet, arsenopyrite, periclase, and biotite as pathfinder minerals within the concession area. Therefore, the Au mineralogy of the alluvial environment that is mined by artisanal small-scale miners is traced from the chemical weathering reaction of garnet minerals from the orebody that produces fractions of other indicator minerals as by-products in the Kubi mining area. These findings also indicate that primary geochemical dispersion evolving from the crystallization of magma and hydrothermal liquids are the main attributes and constitute the identification of indicator minerals and pathfinding elements in this mineralogical study area.Furthermore, the findings suggest that XRD, XPS, TEM, and EDX could be combined in other mineralogical laboratories to aid in identifying indicator minerals of Au and the location of ore bodies, to increase the knowledge in this field, and reduce environmental and exploration costs.
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| 26. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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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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| 27. |
- Nzulu, Gabriel K., et al.
(författare)
-
Elucidating Pathfinding Elements from the Kubi Gold Mine in Ghana
- 2021
-
Ingår i: Minerals. - : MDPI. - 2075-163X. ; 11:9
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) are applied to investigate the properties of fine-grained concentrates on artisanal, small-scale gold mining samples from the Kubi Gold Project of the Asante Gold Corporation near Dunwka-on-Offinin the Central Region of Ghana. Both techniques show that the Au-containing residual sediments are dominated by the host elements Fe, Ag, Al, N, O, Si, Hg, and Ti that either form alloys with gold or with inherent elements in the sediments. For comparison, a bulk nugget sample mainly consisting of Au forms an electrum, i.e., a solid solution with Ag. Untreated (impure) sediments, fine-grained Au concentrate, coarse-grained Au concentrate, and processed ore (Au bulk/nugget)samples were found to contain clusters of O, C, N, and Ag, with Au concentrations significantly lower than that of the related elements. This finding can be attributed to primary geochemical dispersion, which evolved from the crystallization of magma and hydrothermal liquids as well as the migration of metasomatic elements and the rapid rate of chemical weathering of lateralization in secondary processes. The results indicate that Si and Ag are strongly concomitant with Au because of their eutectic characteristics, while N, C, and O follow alongside because of their affinity to Si. These non-noble elements thus act as pathfinders for Au ores in the exploration area. This paper further discusses relationships between gold and sediments of auriferous lodes as key to determining indicator minerals of gold in mining sites.
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| 28. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
-
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
-
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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| 29. |
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| 30. |
- Schnitter, Claudia, 1989-, et al.
(författare)
-
Epitaxial Growth of Magnetron-Sputtered ZrB2 Films on Si(100) Substrates
- 2022
-
Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-V C H Verlag GMBH. - 1862-6300 .- 1862-6319. ; 219:21
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial growth of ZrB2 films on Si(100) substrates at 900 degrees C is demonstrated using direct-current magnetron sputter deposition from sintered ZrB2 targets. This case of epitaxial growth is structurally more challenging than on Si(111), 4 H-SiC(001), and Al2O3(001). From pole figure measurements, two epitaxial relationships are determined: A) in-plane: ZrB 2 [ 001 ] parallel to Si [ 110 ] and ZrB 2 [ 110 ] parallel to Si [ 110 ] , out-of-plane: ZrB 2 ( 100 ) parallel to Si ( 100 ) , and B) in-plane: ZrB 2 [ 1 2 over bar 1 ] parallel to Si [ 110 ] and the same multiply rotated 90 degrees around the 102 axis, out of plane: ZrB 2 ( 102 ) parallel to Si ( 100 ) . From full width at half maximum (FWHM) values from rocking curve measurements (omega-scans) of the 100 and 102 peaks, a measure of epitaxial quality for these two preferred orientations is obtained. Both omega-scans and theta/2 theta diffractograms show higher quality for the A-type with a FWHM value of 2.00 degrees compared with 4.97 degrees for the B-type. The film composition is found to be ZrB2.3 from time-of-flight elastic recoil detection analysis. The B-type crystallographic relationship ZrB 2 ( 102 ) parallel to Si ( 100 ) and ZrB 2 [ 1 2 over bar 0 ] parallel to Si [ 110 ] has not been previously reported.
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| 31. |
- Schnitter, Claudia, 1989-
(författare)
-
Epitaxial thin films of group 4 transition metal diborides
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Group 4 transition metal diboride films were deposited epitaxially onto different substrates, typically at 900 °C, using direct-current magnetron sputtering from compound targets of ZrB2, TiB2, and HfB2. Epitaxial ZrB2 has been deposited on Al2O3(0001), 4H-SiC(0001), and Si(100) describing the epitaxial relationships on Si(100) for the first time, where two relationships were observed from pole-figure analysis, namely A) in-plane: ZrB2[001] ∥ Si[110] and ZrB2[110] ∥ Si[110], out-of-plane: ZrB2(100) ∥ Si(100), and B) in-plane: ZrB2[11] ∥ Si[110] and the same rotated 90° around the 102 axis, out-of- plane: ZrB2(102) ∥ Si(100). Composition analysis by time-of-flight elastic recoil detection analysis revealed typically B-rich ZrB2 and TiB2, and stoichiometric to Hf-rich HfB2. For ZrB2, the application of an additional external magnetic field during growth influenced the B-to-Zr ratio towards being stoichiometric. Rocking curve measurements of ZrB2 deposited onto Si(100) reveal a higher crystal order in the 100-oriented domains, compared to the 102-oriented domains. In ZrB2 films annealed to temperatures in the range of 1100-1500 °C, rocking curve measurements of the symmetric 001 reflection as well as the asymmetric 101 reflection reveal increased order with increased temperature. This phenomenon occurred at lower temperature when the annealing was performed in H2 compared to Ar.The morphology in plan-view transmission electron microscopy reflects the composition of the film: TiB2.5 has B-rich areas around the grain boundaries, forming an almost continuous network around the grains. ZrBx films with x between 2.0 and 2.3 also contain B-rich regions, though to a smaller extent and mostly in areas where more than two grains adjoin each other. In Hf-rich HfB1.8, no B-rich areas were observed. Scanning transmission electron micrographs and a combination of B electron energy loss spectroscopy and energy dispersive X-ray analysis Hf distribution maps revealed Hf-rich areas in a close-to single crystalline matrix. The hardness of epitaxial HfB2 films is reported to 33 and 36 GPa for films deposited onto Al2O3 and SiC, respectively. These values are slightly higher than reported for bulk HfB2. ZrB2 films on SiC decrease in hardness to 38, 37, and 30 GPa, upon annealing in Ar up to 1100, 1300, and 1500 °C, respectively. In summary, the knowledge is expanded about epitaxially grown group 4 transition metal diborides in terms of their Chemical composition, crystallographic orientations, microstructure, electrical and mechanical properties, as well as their response to heat treatment.
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| 32. |
- 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
-
Ingår i: Energies. - Basel, Switzerland : MDPI AG. - 1996-1073. ; 10:9
-
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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| 33. |
- Sharma, Sachin, 1994-
(författare)
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Phase Evolution of Boron Nitride and Carbide during Chemical Vapor Deposition
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films of Boron Nitride (BN) and Boron Carbide (BC) possess properties that make them attractive for various applications. Epitaxially grown BN exhibits potential for optoelectronic devices, as piezoelectric materials, and graphene technology. Epitaxial BC is a semiconductor that could allow bandgap tuning and has potential applications in thermoelectric and optoelectronic devices. Both BN and BC material systems, generally deposited using chemical vapour deposition (CVD), are limited by the lack of control in depositing epitaxial films. In my thesis work, I have studied the evolution of various crystal phases of BN and BC and the factors that affect them during their CVD processes. I deposited and compared the growth of BN on Al2O3 (0001), (11 2 over bar 0), (1 1 over bar 02) and (10 1 over bar 0) substrates and used two organoboranes as boron precursors. Only Al2O3(11 2 over bar 0) and Al2O3 (0001) rendered crystalline films while the BN growth on the remaining substrates was X-ray amorphous. Furthermore, the less investigated Al2O3(11 2 over bar 0) had better crystalline quality versus the commonly used Al2O3 (0001). To further understand this, I studied crystalline BN thin films on an atomic scale and with a time evolution approach, uncovering the influence of carbon on hexagonal BN (h-BN). I showed that h-BN nucleates on both substrates but then either polytype transforms to rhombohedral-BN (r-BN) in stages, turns to less ordered turbostratic-BN or is terminated. An increase in local carbon content is the cause of these changes in epitaxial BN films during CVD. From the time evolution, we studied the effect of Al2O3 modification on h-BN nucleation during CVD. The interaction between boron and carbon during BN growth motivated studies also on the BxC materials. BxC was deposited using CVD at different temperatures on 4H-SiC(0001) (Si-face) and 4H-SiC(000 1 over bar) (C-face) substrates. Epitaxial rhombohedral-B4C (r-B4C) grew at 1300 °C on the C-face while the films deposited on the Si-face were polycrystalline. Comparing the initial nucleation layers on both 4H-SiC substrates on an atomic scale we showed that no interface phenomena are affecting epitaxial r-B4C growth conditions. We suggest that the difference in surface energy on the two substrate surfaces is the most plausible reason for the differences in epitaxial r-B4C growth conditions. In this thesis work, I identify the challenges and propose alternative routes to synthesise epitaxial BN and B4C materials using CVD. This fundamental materials science work enhances the understanding of growing these material systems epitaxially and in doing so furthers their development.
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| 34. |
- Souqui, Laurent, 1991-
(författare)
-
Chemical vapour deposition of sp2-hybridised B-C-N materials from organoborons
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films of sp2-BN are promising materials for graphene and deep-UV optoelectronics. They are typically deposited by thermally activated chemical vapour deposition (CVD) from triethylboron (TEB) and ammonia (NH3) at 1500 °C, albeit in a narrow process window. The aim of this thesis is to establish a better understanding for and to develop CVD of sp2-BN, BxC and BCxNy further. This has been done by fundamental studies of the gas phase and surface chemistries of the organoboron precursor trimethylboron (TMB), studying new substrate materials and by studying plasma CVD.From previous experience with TEB, TMB has been investigated as an alternative precursor. From a study on the gas phase chemistry of TMB in argon and hydrogen ambient, BxC films can be deposited from 600 °C at 5000 Pa and the B/C ratio reaches 3 at susceptor temperatures of 1000 °C. Supporting calculations show that TMB dissociates mainly by α-elimination of CH4 in both ambient, although H2-assisted elimination also occurs in hydrogen ambient. Furthermore, we have demonstrated deposition of BxC films in features with high aspect ratios (up to 2000:1) at 700°C and 5000 Pa, which are much higher temperature and pressure conditions compared to most surface-controlled CVD processes. This was enabled from competitive adsorption of radicals from TMB and H2 on the growing surface. Deposition of sp2-BN from TMB and NH3 was performed between 1200 °C – 1485 °C. The use of TMB instead of TEB allowed for the deposition of epitaxial rhombohedral-BN (r-BN) on nitridated sapphire from 1300 °C and in a wider process window (3000 to 9000 Pa, NH3/TEB from 321 to 1286) and three times higher deposition rate, but at a cost of a higher carbon contamination. The epitaxial relationships are ? − ??(0001) ∥ ? − ???(0001) ∥ ? − ??2?3(0001) out-of-plane and in-plane ? − ??(1120) ∥ ? − ???(1120) ∥ ? − ??2?3(1000) and ? − ??(1120) ∥ ? − ???(1120) ∥ ? − ??2?3(1̅ 000), as determined by φ-scan measurements.For growth on silicon, we studied the feasibility of depositing sp2-BN at 1300 °C, 7000 Pa, and NH3/TEB = 321. Pre-treatments from TEB and NH3 were applied in order to stabilise the silicon surface. It resulted in the growth of amorphous boron nitride (a-BN), regardless of the pretreatment. We brought into light a memory effect involving boron carbide and silane (SiH4) that permitted the growth of orientated crystalline or turbostratic BN grains on the silicon surface, as determined by X-ray diffraction and scanning electron microscopy images. In contrast to the temperature sensitive Si substrate, epitaxial zirconium diboride (ZrB2) templates were studied as a conductive alternative high- substrate to the sapphire (insulator) and silicon carbide (wide bandgap semiconductor). φ-scan measurements showed that r-BN grows with the epitaxial relationship: ? − ??(0001) ∥ ??????−1(111) ∥ ???2(0001) ∥ ???(0001) and ? − ??(1120) ∥ ??????−1(220) ∥ ???2(1120) ∥ ???(1120). The coverage of the surface by epitaxial r-BN grains is found to increase with upon silane exposure prior to growth.In addition, microwave-plasma-activated CVD was studied as an alternative deposition technique. sp2-BCxNy films were deposited from TEB and an Ar-N2 plasma in an approach similar to a 23- factorial design. We observed the effects of the absorbed microwave power, the total gas flow and the N/Ar ratio on the growth rate, composition and morphology. Two deposition regimes were found whether nitrogen or argon is the main gas. The films showed high boron and nitrogen (up to 46 and 41 at. %, respectively) contents and the composition was found not to vary significantly with the deposition parameters. The morphology of the film evolves from granular films to nanosheets. The use of plasma enabled using optical emission spectroscopy to get insight into the deposition chemistry. The relative permittivity κ of the sp2-BCxNy films could be varied between 3 and 35. A strong correlation was found between carbon content and increase of κ.
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| 35. |
- Souqui, Laurent, 1991-, et al.
(författare)
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Texture evolution in rhombohedral boron carbide films grown on 4H-SiC(0001) and 4H-SiC(0001) substrates by chemical vapor deposition
- 2022
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:41, s. 15974-15982
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Tidskriftsartikel (refereegranskat)abstract
- Boron carbide in its rhombohedral form (r-BxC), commonly denoted B4C or B13C2, is a well-known hard material, but it is also a potential semiconductor material. We deposited r-BxC by chemical vapor deposition between 1100 degrees C and 1500 degrees C from triethylboron in H-2 on 4H-SiC(0001) and 4H-SiC(0001). We show, using ToF-ERDA, that pure B4C was grown at 1300 degrees C, furthermore, using XRD that graphite forms above 1400 degrees C. The films deposited above 1300 degrees C on 4H-SiC(0001) were found to be epitaxial, with the epitaxial relationships B4C(0001)[1010]||4H-SiC(0001)[1010] obtained from pole figure measurements. In contrast, the films deposited on 4H-SiC(0001) were polycrystalline. We suggest that the difference in growth mode is explained by the difference in the ability of the different surfaces of 4H-SiC to act as carbon sources in the initial stages of the film growth.
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| 36. |
- Trinh, David, 1981-, et al.
(författare)
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Coated Insert
- 2006
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Patent (populärvet., debatt m.m.)
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| 37. |
- Wilhelmsson, O., et al.
(författare)
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Structural, electrical and mechanical characterization of magnetron-sputtered V-Ge-C thin films
- 2008
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 56:11, s. 2563-2569
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Tidskriftsartikel (refereegranskat)abstract
- V2GeC MAX-phase thin films were deposited by DC magnetron sputter epitaxy in the temperature range 450-850 °C. The MAX-phase nucleates directly on (0 0 0 l)-oriented sapphire-wafer substrates without the need for a seed layer. The films contain, however, a small fraction of binary vanadium carbide (VCx) inclusions. X-ray diffraction analysis furthermore shows that these inclusions partly consist of the ordered superstructure V8C7. The amount of Ge in the films decreases at higher temperatures, which can be attributed to Ge evaporation. At temperatures below 450 °C the films consist of polycrystalline Ge and an X-ray amorphous carbide phase attributed to VCx or V2C. No MAX-phase was observed in this temperature region. The electrical and mechanical properties of the films were characterized. © 2008 Acta Materialia Inc.
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