| 1. |
- Baloch, Ramen Munir, et al.
(författare)
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Indoor air pollution, physical and comfort parameters related to schoolchildren's health : Data from the European SINPHONIE study
- 2020
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Ingår i: Science of the Total Environment. - : ELSEVIER. - 0048-9697 .- 1879-1026. ; 739
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Tidskriftsartikel (refereegranskat)abstract
- Substantial knowledge is available on the association of the indoor school environment and its effect among schoolchildren. In the same context, the SINPHONIE (School indoor pollution and health: Observatory network in Europe) conducted a study to collect data and determine the distribution of several indoor air pollutants (IAPs), physical and thermal parameters and their association with eye, skin, upper-, lower respiratory and systemic disorder symptoms during the previous three months. Finally, data from 115 schools in 54 European cities from 23 countries were collected and included 5175 schoolchildren using a harmonized and standardized protocol. The association between exposures and the health outcomes were examined using logistic regression models on the environmental stressors assessed in classroom while adjusting for several confounding factors; a VOC (volatile organic compound) score defined as the sum of the number of pollutants to which the children were highly exposed (concentration > median of the distribution) in classroom was also introduced to evaluate the mul tiexposu re - outcome association. Schoolchildren while adjusting for several confounding factors. Schoolchildren exposed to above or equal median concentration of PM2.5, benzene, limonene, ozone and radon were at significantly higher odds of suffering from upper, lower airways, eye and systemic disorders. Increased odds were also observed for any symptom (sick school syndrome) among schoolchildren exposed to concentrations of limonene and ozone above median values. Furthermore, the risks for upper and lower airways and systemic disorders significantly increased with the VOCs score. Results also showed that increased ventilation rate was significantly associated with decreased odds of suffering from eye and skin disorders whereas similar association was observed between temperature and upper airways symptoms. The present study provides evidence that exposure to IAPs in schools is associated with various health problems in children. Further investigations are needed to confirm our findings. (C) 2020 Elsevier B.V. All rights reserved.
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| 2. |
- Charatsidou, Elina, et al.
(författare)
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Proton irradiation-induced cracking and microstructural defects in UN and (U,Zr)N composite fuels
- 2024
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Ingår i: Journal of Materiomics. - : Elsevier. - 2352-8478 .- 2352-8486. ; 10:4, s. 906-918
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Tidskriftsartikel (refereegranskat)abstract
- Proton irradiation with a primary ion energy of 2 MeV was used to simulate radiation damage in UN and (U,Zr)N fuel pellets. The pellets, nominally at room temperature, were irradiated to peak levels of 0.1, 1, 10 dpa and 100.0 dpa resulting in a peak hydrogen concentration of at most 90 at. %. Microstructure and mechanical properties of the samples were investigated and compared before and after irradiation. The irradiation induced an increase in hardness, whereas a decrease in Young’s modulus was observed for both samples. Microstructural characterization revealed irradiation-induced cracking, initiated in the bulk of the material, where the peak damage was deposited, propagating towards the surface. Additionally, transmission electron microscopy was used to study irradiation defects. Dislocation loops and fringes were identified and observed to increase in density with increasing dose levels. The high density of irradiation defects and hydrogen implanted are proposed as the main cause of swelling and consequent sample cracking, leading simultaneously to increased hardening and a decrease in Young's modulus.
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| 3. |
- Dévai, Gergely, et al.
(författare)
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Efficient Code Generation from the High-level Domain-specific Language Feldspar for DSPs
- 2010
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Ingår i: ODES-8: 8th Workshop on Optimizations for DSP and Embedded Systems, workshop associated with IEEE/ACM International Symposium on Code Generation and Optimization (CGO).
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Konferensbidrag (refereegranskat)abstract
- Software for digital signal processors (DSPs) is traditionally highly hardware-dependent and hence porting it to new processors usually requires significant design effort. In this paper we present Feldspar (Functional Embedded Language for DSP and Parallelism), an embedded, high-level, domain-specific language for DSP algorithm design and the compilation techniques we developed for generating C code from specifications written in Feldspar. While Feldspar allows description of algorithms on specification level, we show that with the right set of abstractions and transformations this high level, functional specification can be transformed into C code that is comparable or better than reference, hand-crafted C language implementations. The Feldspar compiler is highly modular and plugin-based, hence future hardware-specific plugins will enable automatic generation of efficient, hardware-specific code. This approach enables the encapsulation of knowledge of hardware completely in the compiler and thus allows description of algorithms in completely hardware-independent, portable manner.
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| 4. |
- El Jamal, Ghada, et al.
(författare)
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A scalable, resource-efficient process for synthesis of self-supporting germanium nanomembranes
- 2024
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Ingår i: Materials Science in Semiconductor Processing. - : Elsevier. - 1369-8001 .- 1873-4081. ; 172
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Tidskriftsartikel (refereegranskat)abstract
- The design of self-supporting membranes is gaining high interest in a broad range of applications, from nanodevices, optoelectronics, sensing, separation, and catalysis. In this report, we demonstrate a synthesis pathway for high quality ultrathin self-supporting germanium membranes using a highly scalable and resource-efficient process. We discuss the process flow, the compatibility between the materials and the processing chemicals, the important details for achieving the pure membranes and potential anomalies related to the etching process. Comprehensive characterization using SEM, EDX, TEM and nuclear microprobe analysis is employed for revealing the physical and structural properties of the synthesized membranes. The outcome of the fabrication process is large-area Ge nanomembranes with extremely flat and clean surfaces.
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| 5. |
- Gangaprasad Rao, Smita, et al.
(författare)
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Low temperature epitaxial growth of Cantor-nitride thin films by magnetic field assisted magnetron sputtering
- 2023
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 41:5
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature epitaxial growth of multicomponent alloy-based thin films remains an outstanding challenge in materials science and is important for established fundamental properties of these complex materials. Here, Cantor nitride (CrMnFeCoNi)N thin films were epitaxially grown on MgO(100) substrates at low deposition temperature by magnetic-field-assisted dc-magnetron sputtering, a technique where a magnetic field is applied to steer the dense plasma to the substrate thereby influencing the flux of Ar-ions bombarding the film during growth. Without ion bombardment, the film displayed textured growth. As the ion flux was increased, the films exhibited epitaxial growth. The epitaxial relationship between film and substrate was found to be cube on cube (001)film parallel to(001)MgO, [100]film parallel to[100]MgO. The epitaxy was retained up to a thickness of approximately similar to 100 nm after which the growth becomes textured with a 002 out-of-plane orientation. The elastic constants determined by Brillouin inelastic light scattering were found to be C-11 = 320 GPa, C-12 = 125 GPa, and C-44 = 66 GPa, from which the polycrystalline Young's modulus was calculated as 204 GPa and Poisson's ratio = 0.32, whereas available elastic properties still remained very scarce.
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| 6. |
- Gangaprasad Rao, Smita, et al.
(författare)
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Phase formation in CrFeCoNi nitride thin films
- 2023
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical highentropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, Delta G of (CrFeCoNi)(1-x)N-x solid solutions has a maximum at x = 0.20-0.25, and AG becomes lower when x < 0.20 and x > 0.25. Thin films of (CrFeCoNi)1-xNx (0.14 >= x <= 0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x <= 0.22 and the stabilization of the NaCl B1 structure when x > 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics. The results from the study further aid in making correlations between the observed mechanical properties and the crystal structure of the films.
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| 7. |
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| 8. |
- Karakatsanis, A., et al.
(författare)
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Delayed Sentinel Lymph Node Dissection in Patients with a Preoperative Diagnosis of Ductal Cancer In Situ by Preoperative Injection with Superparamagnetic Iron Oxide (SPIO) Nanoparticles: The SentiNot Study
- 2023
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Ingår i: Annals of Surgical Oncology. - : Springer Science and Business Media LLC. - 1068-9265 .- 1534-4681. ; 30:7, s. 4064-4072
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundDifficulty in preoperatively assessing the risk for occult invasion or surgery that precludes future accurate axillary mapping in patients with ductal cancer in situ (DCIS) account for overutilization of SLND.MethodsProspective, multicenter, cohort study, including women with any DCIS planned for mastectomy or DCIS grade 2 and > 20 mm, any DCIS grade 3, any mass-forming DCIS and any planned surgery. Patients received an interstitial SPIO injection during breast surgery, but no upfront SLND was performed. If invasion was identified on final pathology, delayed SLND (d-SLND) was performed separately with the coadministration of isotope +/- blue dye (BD). Study outcomes were proportion of upfront SLNDs that were avoided, detection rates during d-SLND, and impact on healthcare costs.ResultsIn total, 78.7% of study participants (N = 254, mean age 60 years, mean DCIS size 37.8 mm) avoided upfront SLND. On d-SLND (median 28 days, range 9-46), SPIO outperformed Tc-99 with (98.2% vs. 63.6%, p < 0.001) or without BD (92.7% vs. 50.9%, p < 0.001) and had higher nodal detection rate (86.9% vs. 32.3%, p < 0.001) and with BD (93.9% vs. 41.4%, p < 0.001). Only 27.9% of all SLNs retrieved were concordant for Tc-99 and SPIO. Type of breast procedure (WLE vs. oncoplastic BCT vs. mastectomy) affected these outcomes and accounted for the low performance of Tc-99 (p < 0.001). d-SLND resulted in a 28.1% total cost containment for women with pure DCIS on final pathology (4190 vs. 5828 USD, p < 0.001).ConclusionsMarking the SLN with SPIO may avoid overtreatment and allow for accurate d-SLND in patients with DCIS.
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| 9. |
- Kevei, Eva, et al.
(författare)
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Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE.
- 2006
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 140:3, s. 933-45
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Tidskriftsartikel (refereegranskat)abstract
- The circadian system of Arabidopsis (Arabidopsis thaliana) includes feedback loops of gene regulation that generate 24-h oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LIGHT, OXYGEN, VOLTAGE (LOV)/Period-ARNT-Sim (PAS) domain was unique in retaining wild-type responses to red light both for the circadian period and for control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously described partner proteins Arabidopsis S-phase kinase-related protein 1, TIMING OF CAB EXPRESSION 1, and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly discovered components of the circadian system, although current approaches have saturated mutations at some loci.
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| 10. |
- McCarthy, Brian D., et al.
(författare)
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Elemental Depth Profiling of Intact Metal-Organic Framework Single Crystals by Scanning Nuclear Microprobe
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:44, s. 18626-18634
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Tidskriftsartikel (refereegranskat)abstract
- The growing field of MOF-catalyst composites often relies on postsynthetic modifications for the installation of active sites. In the resulting MOFs, the spatial distribution of the inserted catalysts has far-reaching ramifications for the performance of the system and thus needs to be precisely determined. Herein, we report the application of a scanning nuclear microprobe for accurate and nondestructive depth profiling of individual UiO-66 and UiO-67 (UiO = Universitetet i Oslo) single crystals. Initial optimization work using native UiO-66 crystals yielded a microbeam method which avoided beam damage,y while subsequent analysis of Zr/Hf mixed-metal UiO-66 crystals demonstrated the potential of the method to obtain high-resolution depth profiles. The microbeam method was further used to analyze the depth distribution of postsynthetically introduced organic moieties, revealing either core-shell or uniform incorporation can be obtained depending on the size of the introduced molecule, as well as the number of carboxylate binding groups. Finally, the spatial distribution of platinum centers that were postsynthetically installed in the bpy binding pockets of UiO-67-bpy (bpy = 5,5'dicarboxyy-2,2'-bipyridine) was analyzed by microbeam and contextualized. We expect that the method presented herein will be applicable for characterizing a wide variety of MOFs subjected to postsynthetic modifications and provide information crucial for their optimization as functional materials.
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| 11. |
- Nagy, Gyula, et al.
(författare)
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Ion-beam assisted synthesis and thermal oxidation of TiN thin films combined with in-situ, depth-resolved characterization using MeV ions
- 2024
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 482
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Tidskriftsartikel (refereegranskat)abstract
- We present an in-situ, depth-resolved and non-destructive approach to assess the chemical composition of titanium nitride (TiN) thin films during synthesis and controlled oxidation. Ion beam assisted deposition was used to deposit a TiN sample of approximately 120 nm thickness. The chemical composition was characterized in the deposition environment using non-destructive Rutherford/Elastic Backscattering Spectrometry (RBS/EBS), with a depth resolution of ca. 25 nm. The high sensitivity of the measurements to the non-metallic species was ensured by the use of elastic resonances. Analysis revealed a few percent oxygen incorporated in the films due to residual gases during growth. After deposition, the TiN film was exposed to oxygen at step-wise increasing temperatures, and the composition of the film was analyzed after every annealing step. The measurements provide a direct proof of inward oxidation with associated concentration gradients, starting with oxygen absorption without significant nitrogen release when using moderate annealing temperatures (250 -310 degrees C), where the oxygen content tends to saturation. At 710 degrees C, above the oxidation onset temperature, atomic composition data indicate N loss parallel to the O uptake. However, ex-situ transmission electron microscopy showed no evidence of any oxide phase, implying that oxidation starts without crystallite formation.
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| 12. |
- Nagy, Gyula, et al.
(författare)
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The scanning light ion microprobe in Uppsala - Status in 2022
- 2022
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 533, s. 66-69
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Tidskriftsartikel (refereegranskat)abstract
- The Scanning Light Ion Microprobe in Uppsala (SLIM-UP) was originally installed during 1989/90. Since then, the microprobe has undergone several minor and major modifications. The present configuration is a re-build of the SLIM-UP, that is now connected to the 5 MV tandem Pelletron (R) accelerator of the Tandem Laboratory, Uppsala University. We give an overview of the present status of the Uppsala microprobe facility, including a detailed description of the components and a recent resolution test. In addition, we present the most recent technical developments whereby, the system is able to quickly image large area samples, to reliably identify individual microparticles, and to analyse them separately. Optimal parameters for a certain system can be found by simple test measurements on dummy samples. Our test scenario comprises of Fe particles embedded in a light matrix, representing human tissue. We found a good compromise between the required analysis time and particle detection efficiency.
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| 13. |
- Tran, Tuan, et al.
(författare)
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Enabling tailored nanoporous germanium by quantifying the evolution of structural properties during self-irradiation
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 663
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Tidskriftsartikel (refereegranskat)abstract
- Porous materials are essential for a wide range of applications in energy storage, catalysis, and environmental solutions. Material fabrication methods which can tailor the porous structures in a deterministic manner are highly valuable for the development of the field. In this paper, we use ion irradiation to synthesize large-scale germanium (Ge)-based porous structures. We furthermore demonstrate the structure to consist of pores interconnected by ultra-small channels that effectively allow transport of gaseous molecules throughout the whole network. Aside qualitative assessment of the evolution of the structure, the combination of transmission electron microscopy, microbeam Rutherford backscattering spectrometry and a Ge-on-Si sample design enables the quantification of properties such as mass density and sputtering yields during the evolution of porosity. We find progression of pore formation from the surface with a constant rate with increasing dose at otherwise constant density of the porous phase. Proximity to the substrate terminates pore formation well before reaching the interface with higher doses, eventually inducing a depth-independent densification of the porous structure. Experimental evidence challenges vacancy clustering as a commonly referred-to mechanism for pore-formation. Instead, relaxation in structurally weakened, i.e. near-surface volumes of the material by micro-explosions can conclusively explain all observations. The porous germanium synthesized in our approach is considered more resilient at high temperature and strong pH conditions than polymeric and hybrid materials, indicating great potential for applications in such environments.
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| 14. |
- Whitlow, Harry J., et al.
(författare)
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Dynamic Analysis of major elements in biological tissue validating quantification of trace life elements in MeV ion beam microscopy
- 2024
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 554
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Tidskriftsartikel (refereegranskat)abstract
- MeV ion microprobe measurements of the lesser and trace life element concentrations in biological tissues are challenging because of complex spatial inhomogeneities in these types of samples. Measurements on ex vivo tissue sections require determination of the matrix element composition and the tissue section thickness. For these reasons, in this work, we adapted the Dynamic Analysis approach known from literature, to interpret the MeV ion microscopy data to determine concentrations of H, C, O, and N as well as the thickness of different tissue regions in Non Human Primate (NHP) mesenteric lymph node section. The results showed no strong variations of the matrix element contents regardless of section thickness variations in the tissue. The matrix information was used to quantify total-Ca molarities and a significant ∼30 mM Ca concentration hotspot was observed at the edge of sinus structure in the mesenteric lymph node as compared to the 3-4 mM total-Ca levels in the surrounding tissues. Thus, MeV ion microprobe imaging combined with dynamic analysis comprise a novel chemometric approach paving a way for quantitative analysis of similarly complicated animal and plant biological tissue sections.
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| 15. |
- Whitlow, Harry J., et al.
(författare)
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Micro-Particle Induced X-ray Emission Study of Lead-Free and Lead-Based Solders and Interactions with Copper Wires
- 2023
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 220:10
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Tidskriftsartikel (refereegranskat)abstract
- Pb-free electrical solders, such as Cu-Sn alloys, work well for reflow soldering under tightly controlled conditions. Hand soldering, however, often results in poor quality joints compared to conventional Pb-Sn solders. To investigate this under realistic workshop conditions, micro-particle induced X-ray emission (micro-PIXE) with 2 MeV protons has been employed. Commercial flux-cored Cu-Sn and Pb-Sn solder wires are studied. Solder blobs under two cooling conditions as well as tinning Restriction of Hazardous Substances (RoHS)-compliant and legacy component wires are investigated. The results show that the long heating and slow cooling of Cu-Sn solder blobs lead to formation of an acicular precipitate that can be ascribed to Cu-6 Sn-5. Pb-Sn solder under the same conditions shows phase separation with regions of high Sn and regions with high Pb. In the case of rapidly cooled blobs where a shiny surface is produced, no phase separation in either solder is observed. Tinning of RoHS-compliant and legacy Cu component wires with the two solders produce significantly different interfacial depth profiles with varying degrees of grading, indicative of intermetallic phase formation.
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| 16. |
- Whitlow, Harry J., et al.
(författare)
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Proton beam induced degradation of Pioloform & REG; (polyvinyl butyral (PVB)) support films used for analysis of biomedical tissue sections
- 2023
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 539, s. 136-140
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Tidskriftsartikel (refereegranskat)abstract
- Pioloform & REG;, an often used support film for ion microprobe research is a terpolymer of polyvinyl butyral (PVB) and 18 mass % polyvinyl alcohol (PVA). Simultaneous off-axis Scanning Transmission Ion Microscopy (OA-STIM) and Elastic Backscattering Spectrometry (EBS) measurements have been used to measure the evolution of the C, H and O contents for an increasing proton fluence. The results showed that the composition at zero proton-fluence was in close agreement with the theoretical atomic composition. This strongly suggests OA-STIM measurements. With increasing proton fluences preferential loss of H and O was observed from the films.
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| 17. |
- Whitlow, Harry J., et al.
(författare)
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Sequestration of Ca in simian nasal mucosa : Determination of Ca molarity in ex vivo tissue by simultaneous off-axis Scanning Transmission Ion Microscopy, Particle Induced X-Ray Emission and Elastic Backscattering Spectrometry
- 2023
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 539, s. 152-161
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Tidskriftsartikel (refereegranskat)abstract
- A technique to determine the molar concentration of elements in ex vivo tissue sections by Particle Induced X-ray Emission (PIXE) has been developed. The method is based on simultaneous off-axis scanning transmission ion microscopy (OA-STIM) and Elastic Backscattering Spectrometry (EBS) measurement of the sample thickness and major element (H, C, N, O) composition. The method was applied to determine the molarity of localised Ca concentration hot-spots in the outer epithelium tissue of nasal mucosa of a rhesus macaque subject infected with simian immunodeficiency virus (SIV). The results show Ca sequestration in concentration hot-spots and outer epithelial tissue that significantly exceeded the Ca concentration in the surrounding tissues. This may originate from mineralisation and/or Ca enhancement in goblet cells.
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| 18. |
- Zubayer, Anton, et al.
(författare)
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Reflective, polarizing, and magnetically soft amorphous neutron optics with 11B-enriched B4C
- 2024
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 10:7
-
Tidskriftsartikel (refereegranskat)abstract
- The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. However, state-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that, by incorporating (B4C)-B-11 into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering, and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 militesla). This approach offers prospects for substantial improvement in polarizing neutron optics with nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.
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| 19. |
- Öhman, Sebastian, 1991-, et al.
(författare)
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Circumventing Thermodynamic Constraints in Nucleation-Controlled Crystallization of Al2TiO5-Based Chemical Vapor Deposition Coatings
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:11, s. 5151-5164
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation is a fundamental part in most syntheses of ceramic materials. Yet, few techniques enable control of this step, which would offer possibilities to attain full-scale kinetic selectivity of the syntheses to reach novel compounds with unique properties. Herein, we present a nucleation-controlled crystallization pathway to synthesize coatings of aluminum titanate (Al2TiO5)─renowned for its low-to-negative thermal expansion─at significantly reduced temperatures than conventional solid-state techniques. Based on a kinetic study using in situ X-ray diffraction, detailed mechanistic insights into the crystallization process and phase evolutions within the Al–Ti–O system are obtained. The lowest activation energies for crystallization are given when the Al–Ti ratio is close-to-stoichiometric or Ti-enriched. Along with these compositions’ similar kinetics at the earliest stages of the transformation, a joint nucleation behavior is discovered, revealing the elemental role of titanium in nucleating the main Al2TiO5 phase. Based on classical nucleation theory, we deduce the significant influence of the configurational entropy (Sconfig) when crystallization occurs in the nucleation-controlled domain. Finally, peculiar transition features are observed in the Al-enriched regime during annealing at intermediate temperatures, whose causes are ascribed to the presence of secondary nucleation events and possibilities of structural relaxations in the amorphous matrixes when crystallizing.
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| 20. |
- Öhman, Sebastian, 1991-, et al.
(författare)
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Role of Oxygen in Vacancy-Induced Phase Formation and Crystallization of Al2TiO5-Based Chemical Vapor-Deposited Coatings
- 2023
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:13, s. 6456-6465
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen is a commonly overlooked element influencing the properties of many metal oxides. By combining several analytical in situ techniques and theoretical calculations, we demonstrate that oxygen plays a vital part in the phase formation and crystallization of Al2TiO5-based chemical vapor-deposited coatings. Rutherford backscattering spectrometry (RBS) corroborates a polymorphic transformation during crystallization. Subsequent hard X-ray photoelectron spectroscopy (HAXPES) shows that crystallization occurs through a displacive (diffusionless) mechanism. Coupled with theoretical calculations, the crystallization and co-formation of Al2TiO5, Al6Ti2O13, and Al16Ti5O34 are suggested to be driven by the migration of oxygen ions and their corresponding vacancies.
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