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1.	Munch Roager, Henrik, et al. (author) Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: A randomised cross-over trial 2019 In: Gut. - : BMJ. - 1468-3288 .- 0017-5749. ; 68:1, s. 83-93 Journal article (peer-reviewed)abstract Objective T o investigate whether a whole grain diet alters the gut microbiome and insulin sensitivity, as well as biomarkers of metabolic health and gut functionality. Design 60 Danish adults at risk of developing metabolic syndrome were included in a randomised cross-over trial with two 8-week dietary intervention periods comprising whole grain diet and refined grain diet, separated by a washout period of =6 weeks. The response to the interventions on the gut microbiome composition and insulin sensitivity as well on measures of glucose and lipid metabolism, gut functionality, inflammatory markers, anthropometry and urine metabolomics were assessed. Results 50 participants completed both periods with a whole grain intake of 179±50 g/day and 13±10 g/day in the whole grain and refined grain period, respectively. Compliance was confirmed by a difference in plasma alkylresorcinols (p<0.0001). Compared with refined grain, whole grain did not significantly alter glucose homeostasis and did not induce major changes in the faecal microbiome. Also, breath hydrogen levels, plasma short-chain fatty acids, intestinal integrity and intestinal transit time were not affected. The whole grain diet did, however, compared with the refined grain diet, decrease body weight (p<0.0001), serum inflammatory markers, interleukin (IL)-6 (p=0.009) and C-reactive protein (p=0.003). The reduction in body weight was consistent with a reduction in energy intake, and IL-6 reduction was associated with the amount of whole grain consumed, in particular with intake of rye. Conclusion C ompared with refined grain diet, whole grain diet did not alter insulin sensitivity and gut microbiome but reduced body weight and systemic lowgrade inflammation.
2.	Ciechonski, Rafal, et al. (author) In-situ treatment of GaN epilayers in hot-wall MOCVD Other publication (other academic/artistic)
3.	Pedersen, Henrik, 1981-, et al. (author) Chloride-based SiC epitaxial growth 2009 In: Materials Science Forum Vols. 615-617. - : Trans Tech Publications. ; , s. 89- Conference paper (peer-reviewed)abstract Some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors or/and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the Cl/Si-ratio has on the growth have been studied. MTS is showed to be the most efficient precursor; the growth can be hindered by to much chlorine in the gas mixture. The Cl/Si-ratio is also found to be a process parameter that affects the amount of incorporated nitrogen in the epilayers.
4.	Stenberg, Pontus, 1984-, et al. (author) Matching precursor kinetics to afford a more robust CVD chemistry: a case study of the C chemistry for silicon carbide using SiF4 as Si precursor 2017 In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 5, s. 5818-5823 Journal article (peer-reviewed)abstract Chemical Vapor Deposition (CVD) is one of the technology platforms forming the backbone of the semiconductor industry and is vital in the production of electronic devices. To upscale a CVD process from the lab to the fab, large area uniformity and high run-to-run reproducibility are needed. We show by a combination of experiments and gas phase kinetics modeling that the combinations of Si and C precursors with the most well-matched gas phase chemistry kinetics gives the largest area of of homoepitaxial growth of SiC. Comparing CH4, C2H4 and C3H8 as carbon precursors to the SiF4 silicon precursor, CH4 with the slowest kinetics renders the most robust CVD chemistry with large area epitaxial growth and low temperature sensitivity. We further show by quantum chemical modeling how the surface chemistry is impeded by the presence of F in the system which limits the amount of available surface sites for the C to adsorb.
5.	Beyer, Franziska, 1980-, et al. (author) Defects in 4H-SiC Layers Grown by Chloride-based Epitaxy 2009 In: Materials Science Forum Vols. 615-617. - : Trans Tech Publications. ; , s. 373- Conference paper (peer-reviewed)abstract Chloride-based 4H-SiC epitaxial layers were investigated by DLTS, MCTS and PL. The DLTS spectra of the as grown samples showed dominance of the Z1/2 and the EH6/7 peaks. For growth rates exceeding 100 µm/h, an additional peak occurred in the DLTS spectra which can be assigned to the UT1 defect. The shallow and the deep boron complexes as well as the HS1 defect are observed in MCTS measurements. The PL spectra are completely dominated by the near band gap (NBG) emission. No luminescence from donor-acceptor pair occurred. The PL line related to the D1 centre was weakly observed. In the NBG region nitrogen bound exciton (N-BE) and free exciton (FE) related lines could be seen. The addition of chlorine in the growth process gives the advantage of high growth rates without the introduction of additional defects.
6.	Beyer, Franziska, et al. (author) Defects in low-energy electron-irradiated n-type 4H-SiC 2010 In: Physica Scripta, vol. T141. - : IOP Publishing. ; , s. 014006- Conference paper (peer-reviewed)abstract The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation increased the DLTS signals of the intrinsic defects Z(1/2) and EH6/7 and introduced the frequently observed defects EH1 and EH3. After the M-center is annealed out at about 650K without bias and at about 575K with bias applied to the sample during the annealing process, a new bistable defect in the low temperature range of the DLTS spectrum, the EB-center, evolves. Since low-energy irradiation affects mainly the carbon atoms in SiC, the M-center and the newly discovered EB-center are most probably carbon-related intrinsic defects.
7.	Blomqvist, A., et al. (author) Understanding the catalytic effects of H2S on CVD-growth of α-alumina : Thermodynamic gas-phase simulations and density functional theory 2011 In: Proceedings of the 38th International Conference on Metallurgical Coatings and Thin Films (ICMCTF) — ICMCTF 2011. - : Elsevier BV. ; 206:7, s. 1771-1779 Conference paper (peer-reviewed)abstract The catalytic effect of H2S on the AlCl3/H2/CO2/HCl chemical vapor deposition (CVD) process has been investigated on an atomistic scale. We apply a combined approach with thermodynamic modeling and density functional theory and show that H2S acts as mediator for the oxygenation of the Al-surface which will in turn increase the growth rate of Al2O3. Furthermore we suggest surface terminations for the three investigated surfaces. The oxygen surface is found to be hydrogenated, in agreement with a number of previous works. The aluminum surfaces are Cl-terminated in the studied CVD-process. Furthermore, we find that the AlClO molecule is a reactive transition state molecule which interacts strongly with the aluminum and oxygen surfaces.
8.	Bombarda, F., et al. (author) Runaway electron beam control 2019 In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1 Journal article (peer-reviewed)
9.	Carlsson, Patrick, 1975-, et al. (author) Photo-EPR Studies on Low-Energy Electron-irradiated 4H-SiC 2009 In: Materials Science Forum, Vols. 615-617. - Materials Science Forum Vols. 615-617 : Trans Tech Publications. - 9780878493340 ; , s. 401-404 Conference paper (peer-reviewed)abstract Photoexcitation electron paramagnetic resonance (photo-EPR) was used to determine deep levels related to the carbon vacancy (VC) in 4H-SiC. High-purity free-standing n-type 4H-SiC epilayers with concentration of intrinsic defects (except the photo-insensitive SI1 center) below the detection limit of EPR were irradiated with low-energy (200 keV) electrons to create mainly VC and defects related to the C sublattice. The simultaneous observation of and signals, their relative intensity changes and the absence of other defects in the sample provide a more straight and reliable interpretation of the photo-EPR results. The study suggests that the (+\|0) level of VC is located at ~EC–1.77 eV in agreement with previously reported results and its single and double acceptor levels may be at ~ EC–0.8 eV and ~ EC–1.0 eV, respectively.
10.	Choolakkal, Arun Haridas, 1992- (author) Conformal chemical vapor deposition of boron carbide thin films 2023 Licentiate thesis (other academic/artistic)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.
11.	Damas, Giane, et al. (author) Thermal decomposition of trimethylindium and indium trisguanidinate precursors for InN growth: An ab initio and kinetic modeling study 2023 In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 158:17 Journal article (peer-reviewed)abstract Indium nitride (InN) is an interesting material for future electronic and photonic-related applications, as it combines high electron mobility and low-energy band gap for photoabsorption or emission-driven processes. In this context, atomic layer deposition techniques have been previously employed for InN growth at low temperatures (typically <350 °C), reportedly yielding crystals with high quality and purity. In general, this technique is assumed to not involve any gas phase reactions as a result from the time-resolved insertion of volatile molecular sources into the gas chamber. Nonetheless, such temperatures could still favor the precursor decomposition in the gas phase during the In half-cycle, therefore altering the molecular species that undergoes physisorption and, ultimately, driving the reaction mechanism to pursue other pathways. Thence, we herein evaluate the thermal decomposition of relevant In precursors in the gas phase, namely, trimethylindium (TMI) and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato) indium (III) (ITG), by means of thermodynamic and kinetic modeling. According to the results, at T = 593 K, TMI should exhibit partial decomposition of ∼8% after 400 s to first generate methylindium and ethane (C2H6), a percentage that increases to ∼34% after 1 h of exposure inside the gas chamber. Therefore, this precursor should be present in an intact form to undergo physisorption during the In half-cycle of the deposition (<10 s). On the other hand, the ITG decomposition starts already at the temperatures used in the bubbler, in which it slowly decomposes as it is evaporated during the deposition process. At T = 300 °C, the decomposition is a fast process that reaches 90% completeness after 1 s and where equilibrium, at which almost no ITG remains, is achieved before 10 s. In this case, the decomposition pathway is likely to occur via elimination of the carbodiimide ligand. Ultimately, these results should contribute for a better understanding of the reaction mechanism involved in the InN growth from these precursors.
12.	Damas, Giane, et al. (author) Understanding indium nitride thin film growth under ALD conditions by atomic scale modelling : From the bulk to the In-rich layer 2022 In: Applied Surface Science. - Amsterdam, Netherlands : Elsevier. - 0169-4332 .- 1873-5584. ; 592 Journal article (peer-reviewed)abstract In recent decades, indium nitride (InN) has been attracting a great deal of attention for its potential applicability in the field of light-emitting diodes (LEDs) and high-frequency electronics. However, the contribution from adsorption- and reaction- related processes at the atomic scale level to the InN growth has not yet been unveiled, limiting the process optimization that is essential to achieve highly crystalline and pure thin films. In this report, we investigate the reaction pathways that are involved in the crystal growth of InN thin film in atomic layer deposition (ALD) techniques from trimethylindium (TMI) and ammonia (NH3) precursors. To accomplish this task, we use a solid-state approach to perform the ab-initio calculations within the Perdew–Burke–Ernzerhof functional (PBE) level of theory. The results clarify the activation role from the N-rich layer to decrease the barrier for the first TMI precursor dissociation from Δ‡H= +227 kJ/mol, in gas phase, to solely +16 kJ/mol, in the surface environment. In either case, the subsequent CH3 release is found to be thermo- and kinetically favored with methylindium (MI) formed at the hcp site and ethane (C2H6) as the byproduct. In the following step, the TMI physisorption at a nearby occupied hcp site promotes the sequential hydrogen removal from the N-rich layer at the minimum energy cost of Δ‡H < +105 kJ/mol with methane (CH4) release. An alternative mechanism involving the production of CH4 is also feasible upon dissociation in gas phase. Furthermore, the high concentration of CH3 radicals, from precursor dissociation, might be the origin of the carbon impurities in this material under the experimental conditions of interest. Finally, the passivation methodology is not found to affect the evaluation of the surface-related processes, whereas the inclusion of spin-polarization is demonstrated to be essential to the proper understanding of the reaction mechanism.
13.	Deminskyi, Petro, 1987-, et al. (author) Atomic layer deposition of InN using trimethylindium and ammonia plasma 2019 In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 37:2 Journal article (peer-reviewed)abstract Indium nitride (InN) is a low bandgap, high electron mobility semiconductor material of interest to optoelectronics and telecommunication. Such applications require the deposition of uniform crystalline InN thin films on large area substrates, with deposition temperatures compatible with this temperature-sensitive material. As conventional chemical vapor deposition (CVD) struggles with the low temperature tolerated by the InN crystal, the authors hypothesize that a time-resolved, surface-controlled CVD route could offer a way forward for InN thin film deposition. In this work, the authors report atomic layer deposition of crystalline, wurtzite InN thin films using trimethylindium and ammonia plasma on Si(100). They found a narrow atomic layer deposition window of 240-260 degrees C with a deposition rate of 0.36 A/cycle and that the flow of ammonia into the plasma is an important parameter for the crystalline quality of the film. X-ray diffraction measurements further confirmed the polycrystalline nature of InN thin films. X-ray photoelectron spectroscopy measurements show nearly stoichiometric InN with low carbon level (amp;lt;1 at. %) and oxygen level (amp;lt;5 at. %) in the film bulk. The low carbon level is attributed to a favorable surface chemistry enabled by the NH3 plasma. The film bulk oxygen content is attributed to oxidation upon exposure to air via grain boundary diffusion and possibly by formation of oxygen containing species in the plasma discharge. Published by the AVS.
14.	Henry, Anne, 1959-, et al. (author) Growth of 4H-SiC Epitaxial Layers on 4° Off-axis Si-face substrates 2009 In: Materials Science Forum, Vols. 615-617. - : Trans Tech Publications. - 9780878493340 ; , s. 81-84 Conference paper (peer-reviewed)abstract CVD growth of epitaxial layers with a mirror like surface grown on 75 mm diameter 4° off-axis 4H SiC substrates is demonstrated. The effect of the C/Si ratio, temperature and temperature ramp up conditions is studied in detail. A low C/Si ratio of 0.4 and a temperature of 1530 °C is the best combination to avoid step bunching and triangular defects on the epitaxial layers. Using a low growth rate (about 3 µm/h) 6 μm thick, n-type doped epilayers were grown on 75 mm diameter wafers resulting in an RMS value of 0.7 nm and good reproducibility. 20 μm thick epitaxial layers with a background doping in the low 1014 cm-3 were grown with a mirror-like, defect-free surface. Preliminary results when using higher Si/H2 ratio (up to 0.4 %) and HCl addition are also presented: growth rate of 28 μm/h is achieved while keeping a smooth morphology.
15.	Henry, Anne, 1959-, et al. (author) Thick epilayers for power devices 2007 In: Materials Science Forum, vol. 556-557. - : Trans Tech Publications. ; , s. 47- Conference paper (peer-reviewed)abstract Growth of thick epitaxial SiC layers needed for high power devices is presented for horizontal hot-wall CVD (HWCVD) reactors. We demonstrate thickness of epilayer of 100 μm and more with good morphology, low-doping with no doping variation through the whole thick layer and reasonable carrier lifetime which mainly depends on the substrate quality. Typical epidefects are described and their density can dramatically be reduced when choosing correctly the growth conditions as well as the polishing of the surface prior to the growth. The control of the doping and thickness uniformities as well as the run-to-run reproducibility is also presented. Various characterization techniques such as optical microscopy, AFM, reflectance, CV, PL and minority carrier lifetime have been used. Results of high-voltage SiC Schottky power devices are presented.
16.	Huang, Jing-Jia, 1990-, et al. (author) Growth of silicon carbide multilayers with varying preferred growth orientation 2022 In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 447 Journal article (peer-reviewed)abstract SiC multilayer coatings were deposited via thermal chemical vapor deposition (CVD) using silicon tetrachloride (SiCl4) and various hydrocarbons under identical growth conditions, i.e. at 1100 °C and 10 kPa. The coatings consisted of layers whose preferred growth orientation alternated between random and highly 〈111〉-oriented. The randomly oriented layers were prepared with either methane (CH4) or ethylene (C2H4) as carbon precursor, whereas the highly 〈111〉-oriented layers were grown utilizing toluene (C7H8) as carbon precursor. In this work, we demonstrated how to fabricate multilayer coatings with different growth orientations by merely switching between hydrocarbons. Moreover, the success in depositing multilayer coatings on both flat and structured graphite substrates has strengthened the assumption proposed in our previous study that the growth of highly 〈111〉-oriented SiC coatings using C7H8 was primarily driven by chemical surface reactions.
17.	Huang, Jing-Jia, 1990- (author) Surface-Controlled Chemical Vapor Deposition of Silicon Carbide 2022 Doctoral thesis (other academic/artistic)abstract Polycrystalline cubic silicon carbide, 3C-SiC, has long been investigated in the field of hard coating materials. The typical synthesis method for 3C-SiC coatings is thermal chemical vapor deposition (CVD) using either multicomponent precursors, e.g. methyltrichlorosilane, or a combination of single component precursors, e.g. silane and propane. In this thesis, the fabrication of polycrystalline SiC coatings has been explored from the new aspects on the basis of thermal CVD utilizing silicon tetrachloride (SiCl4) and various hydrocarbons, i.e. toluene (C7H8), methane (CH4) and ethylene (C2H4) as the precursors. The goal of this thesis is to control the surface chemistry in the SiCl4-based SiC CVD and has been accomplished by the following three different approaches: In the first approach to control the surface chemistry of SiC CVD, the difference in the adsorption energy of aromatic and aliphatic hydrocarbons on different SiC crystal planes was utilized. Under identical deposition conditions, a highly <111>-oriented 3C-SiC coating was deposited using C7H8 as the carbon precursor, whereas using CH4 resulted in a randomly oriented 3C-SiC. The results from quantum chemical calculation showed that the active film forming carbon species, i.e. C6H6 in the C7H8 process and CH3 in both C7H8 and CH4 processes, behaved differently when they adsorbed on the 3C-SiC (111) and (110) planes. CH3 is strongly chemisorbed on both planes, while C6H6 is chemisorbed on the (111) plane, but only physiosorbed on the other. The significant difference in the adsorption energy of CH3 and C6H6 on the (111) and (110) planes therefore explains the resulting highly <111>-oriented 3C-SiC from the C7H8 process. Furthermore, the ability to deposit 3C-SiC coatings with alternating highly <111>- and randomly oriented layers by merely switching the carbon precursor between C7H8 and CH4 or C2H4 in a single CVD deposition has further proven that the effect of aromatic hydrocarbons on the preferred growth orientation of 3C-SiC was controlled primarily by the surface chemistry. The second approach to the surface-controlled SiC CVD was based on the reduction of surface reaction probability (β) for conformal film growth via low-temperature, low-pressure CVD, which was originally proposed by Abelson and Girolami. Their strategies in reducing β, including lowering the temperature and increasing the precursor partial pressure, were successfully adapted to the SiC CVD growth using SiCl4 and C2H4 as the precursors in this thesis, where an elevated temperature and a moderate pressure were used. Moreover, the addition of Cl species as a growth inhibitor to the process further reduced the β, leading to a superconformal SiC growth. The third approach employed in this thesis for the SiC growth was pulsed CVD. Instead of a continuous and simultaneous SiCl4 and C2H4 flow, the precursors were pulsed alternately into the chamber with each precursor pulse being separated by a H2 purge. In this precursor delivery mode, the gas phase reactions between SiCl4 and C2H4 were avoided and hence the SiC growth was mostly controlled by the surface chemistry. Altering the pulse durations of the precursors led to a variation of growth per cycle (GPC), which was explained by a two-step mechanism. During the SiCl4 pulse, a thin layer of Si is deposited, which is carburized by carbon species produced during the C2H4 pulse. Additionally, the separation of precursor pulses should lead to a large increase in the surface coverage of Cl species, further enhancing the inhibition effect and resulting in a superconformal SiC growth. By using this approach, superconformal SiC coatings were achieved at temperatures where conventional CVD only yielded nonconformal SiC coatings. The observed decline in coating conformality with an elongated purge implied that more surface Cl species were replaced by H during the H2 purge and consequently the inhibition effect was diminished.
18.	Imam, Mewlude, 1983- (author) CVD Chemistry of Organoborons for Boron-Carbon Thin Film Depositions 2017 Doctoral thesis (other academic/artistic)abstract Boron-carbon thin films enriched with 10B are potential neutron converting layers for 10B-based solid state neutron detectors given the good neutron absorption cross section of 10B atoms in thin films. The common neutron-transparent base material, Al (melting point 660 °C), limits the deposition temperature and the use of chlorinated precursors forming corrosive by-products such as HCl. Therefore, the organoborons triethylboron B(C2H5)3 (TEB) and trimethylboron B(CH3)3 (TMB) are evaluated as precursors for CVD of BxC films. In order to get a complete understanding of the CVD behaviour of these precursors for deposition of boron containing films, both thermal CVD and plasma CVD of BxC films have been demonstrated. A gas phase chemical mechanism at the corresponding thermal CVD conditions was proposed by quantum chemical calculations while chemical mechanism in the plasma was suggested based on plasma composition obtained from Optical emission spectroscopy (OES).The behaviours of TEB and TMB in thermal CVD are investigated by depositing BxC films in both H2 and Ar atmospheres, respectively. Films deposited using TEB within a temperature window of 600 – 1000 °C are X-ray amorphous with 2.5 ≤ x ≤ 4.5. The impurity level of H is less than 1 at. % above 600 °C. Calculations predict that the gas phase reactions are dominated by β-hydride eliminations of C2H4 to yield BH3. In addition, a complementary bimolecular reaction path based on H2 assisted C2H6 elimination to BH3 is also present at lower temperatures in the presence of hydrogen molecules. As for films deposited with TMB, dense, amorphous, boron rich (B/C = 1.5-3) films are obtained at 1000 °C in both H2 and Ar atmosphere. The quantum chemical calculations suggest that the TMB molecule is mainly decomposed by unimolecular α- elimination of CH4 complemented by H2 assisted elimination of CH4.Plasma CVD of BxC thin films has been studied using both TMB and TEB as single-source precursors in an Ar plasma at temperatures lower than that allowed by thermal CVD. The effect of plasma power, TMB/TEB and Ar gas flow on film composition and morphology are investigated. The highest B/C ratio of 1.9 is found for films deposited at highest plasma power (2400 W) and high TMB flow (7 sccm). The H content in the films stays almost constant at 15±5 at. %. The B-C bonding is dominant in the films while small amounts of C-C and B-O exist, likely due to formation of amorphous carbon and surface oxidation. Film density is determined as 2.16±0.01 g/cm3 and the internal compressive stresses are measured to be less than 400 MPa. OES shows that TMB is decomposed to mainly atomic H, C2, BH, and CH. A plasma chemical model for decomposition of the TMB is constructed using a combination of film and plasma composition. It is suggested that the decomposition of TMB starts with dehydrogenation of the methyl groups followed by breakage of the B-C bonds to form the CH radicals. This bond breaking is at least partly assisted by hydrogen in forming the BH radicals.When films are deposited using TEB flow of 5 and 7 sccm, the B/C ratio is found to be plasma power dependent while the carbon content is almost not affected. The highest B/C ratio of 1.7 is obtained at the highest power applied (2400 W) and attributed to better dissociation of TEB at higher plasma power. The H content in the films is within 14-20 at. %. The density of films is increased to 2.20 g/cm3 with increasing plasma power and attributed to a higher energetic surface bombardment during deposition. The oxygen content in the film is reduced to less than 1 at. % with increasing plasma power due to the densification of the films preventing surface oxidation upon air exposure. Plasma composition from OES shows that the TEB molecules are also dissociated mainly to BH, CH, C2 and H. A plasma chemical model where the first ethyl group is split off by β-hydrogen elimination to form C2H4, which is further dehydrogenated to C2H2 and forms C2 and CH is suggested. The BH species is assumed to be formed by the dehydrogenation of remaining ethyl groups and breakage of the remaining B-C bonds to form BH.
19.	Kalered, Emil, 1988- (author) Quantum chemical studies of deposition and catalytic surface reactions 2018 Doctoral thesis (other academic/artistic)abstract Quantum chemical calculations have been used to model chemical reactions in epitaxial growth of silicon carbide by chemical vapor deposition (CVD) processes and to study heterogeneous catalytic reactions for methanol synthesis. CVD is a common method to produce high-quality materials and e.g. thin films in the semiconductor industry, and one of the many usages of methanol is as a promising future renewable and sustainable energy carrier. To optimize the chemical processes it is essential to understand the reaction mechanisms. A comprehensive theoretical model for the process is therefore desired in order to be able to explore various variables that are difficult to investigate in situ. In this thesis reaction paths and reaction energies are computed using quantum chemical calculations. The quantum-chemical results can subsequently be used as input for thermodynamic, kinetic and computational fluid dynamics modelling in order to obtain data directly comparable with the experimental observations.For the CVD process, the effect of halogen addition to the gas mixture is studied by modelling the adsorption and diffusion of SiH2, SiCl2 and SiBr2 on the (0001̅) 4H-SiC surface. SiH2 was found to bind strongest to the surface and SiBr2 binds slightly stronger than the SiCl2 molecule. The diffusion barrier is shown to be lower for SiH2 than for SiBr2 and SiCl2 which have similar barriers. SiBr2 and SiCl2 are found to have similar physisorption energies and bind stronger than the SiH2 molecule. Gibbs free-energy calculations also indicate that the SiC surface is not fully hydrogen terminated at CVD conditions since missing-neighboring pair of surface hydrogens is found to be common. Calculations for the (0001) surface show that SiCl, SiCl2, SiHCl, SiH, and SiH2 likely adsorb on a methylene site, but the processes are thermodynamically less favorable than their reverse reactions. However, the adsorbed products may be stabilized by subsequent surface reactions to form a larger structure. The formation of these larger structures is found to be fast enough to compete with the desorption processes. Also the Gibbs free energies for adsorption of Si atoms, SiX, SiX2, and SiHX where X is F or Br are presented. Adsorption of Si atoms is shown to be the most thermodynamically favorable reaction followed by SiX, SiHX, and SiX2, X being a halide. The results in this study suggest that the major Si contributors in the SiC–CVD process are Si atoms, SiX and SiH.Methanol can be synthesized from gaseous carbon dioxide and hydrogen using solid metal-metal oxide mixtures acting as heterogeneous catalysts. Since a large surface area of the catalyst enhances the speed of the heterogeneous reaction, the use of nanoparticles (NP) is expected to be advantageous due to the NPs’ large area to surface ratio. The plasma-induced creation of copper NPs is investigated. One important element during particle growth is the charging process where the variation of the work function (W) with particle size is a key quantity, and the variation becomes increasingly pronounced at smaller NP sizes. The work functions are computed for a set of NP charge numbers, sizes and shapes, using copper as a case study. A derived analytical expression for W is shown to give quite accurate estimates provided that the diameter of the NP is larger than about a nanometer and that the NP has relaxed to close to a spherical shape. For smaller sizes W deviates from the approximative expression, and also depends on the charge number. Some consequences of these results for NP charging process are outlined.Key reaction steps in the methanol synthesis reaction mechanism using a Cu/ZrO2 nanoparticle catalyst is investigated. Two different reaction paths for conversion of CO2 to CO is studied. The two paths result in the same complete reaction 2 CO2 → 2 CO + O2 where ZrO2 (s) acts as a catalyst. The highest activation energies are significantly lower compared to that of the gas phase reaction. The presence of oxygen vacancies at the surface appear to be decisive for the catalytic process to be effective. Studies of the reaction kinetics show that when oxygen vacancies are present on the ZrO2 surface, carbon monoxide is produced within a microsecond. The IR spectra of CO2 and H2 interacting with ZrO2 and Cu under conditions that correspond to the catalyzed CH3OH production process is also studied experimentally and compared to results from the theoretical computations. Surface structures and gas-phase molecules are identified through the spectral lines by matching them to specific vibrational modes from the literature and from the new computational results. Several surface structures are verified and can be used to pin point surface structures in the reaction path. This gives important information that help decipher how the reaction mechanism of the CO2 conversion and ultimately may aid to improve the methanol synthesis process.
20.	Klasson, Anna, 1973-, et al. (author) Cell tracking with novel contrast agents fromed by gadolinium oxide nanoparticels 2005 In: ESMRMB,2005. Conference paper (peer-reviewed)
21.	Käll, Per-Olov, 1947-, et al. (author) Synthesis, Characterisation and Molecular Functionalisation of Gd2O3 Nanocrystals 2004 In: NAN:-8,2004. Conference paper (other academic/artistic)abstract
22.	Leone, Stefano, 1978-, et al. (author) Growth of Thick 4H-SiC Epitaxial Layers on On-axis Si-Face Substrates with HCl Addition 2009 In: Materials Science Forum, Vols. 615-617. - : Trans Tech Publications. ; , s. 93-96 Conference paper (peer-reviewed)abstract Homoepitaxial growth of 4H-SiC on on-axis Si-face substrates is reported using hydrogen chloride together with silane and ethylene. In this study, the main process parameters, such as temperature, Cl/Si ratio, C/Si ratio, Si/H2 ratio and ramp up conditions, were studied in detail to understand their effects on the growth mechanisms. Two different optimal epitaxial growth conditions were found. Silicon rich conditions and a high Cl/Si ratio were the key parameters to grow thick homoepitaxial layers with a very low background doping concentration and a growth rate higher than 20 μm/h.
23.	Leone, Stefano, 1978-, et al. (author) High growth rate of 4H-SiC epilayers grown on on-axis substrates with different chlorinated precursors 2010 In: Crystal Growth & Design. - : American Chemical Society. - 1528-7483 .- 1528-7505. ; 10:12, s. 5334-5340 Journal article (peer-reviewed)abstract The epitaxial growth of 4H-SiC on on-axis substrates is a very important process to develop in order to accelerate the development and improve the performance of bipolar SiC based power devices, but until now, only relatively low growth rate processes have been demonstrated. The aim of this study is to demonstrate a high growth rate deposition process of high quality 4H-SiC epilayers on on-axis substrates, free of 3C-SiC inclusions. Previous studies showed that silicon-rich gas-phase conditions (prior to, and during the deposition process) and/or high Cl/Si ratios were vital in order to avoid 3C-SiC inclusions in the epitaxial layers when growing on on-axis substrates. This study combines the knowledge of surface pre-treatment with the chloride-based chemistry developed for off-axis growth. Two different precursor approaches were used, one adopting the standard precursors (silane and ethylene) with addition of hydrogen chloride (HCl), and the other based on the molecule methyltrichlorosilane (CH3SiCl3 or MTS). In this study we will show that using a MTS-based CVD process in combination with proper in situ silane etching and accurate optimisation of the other process parameters (temperature, C/Si and Cl/Si ratio) results in homoepitaxial growth of high purity and high quality 4H-SiC layers on on-axis Si-face substrates at a growth rate of 100 μm/h. Additionally, a higher efficiency of the MTS precursor chemistry was found and discussed.
24.	Leone, Stefano, et al. (author) Homoepitaxial growth of 4H-SiC on on-axis Si-face substrates using chloride-based CVD 2009 Conference paper (peer-reviewed)abstract The homoepitaxial chloride-based CVD growth is demonstrated on Si-face on-axis 4HSiC substrates. The use of chloride-based CVD has allowed growth of 100% 4H-SiC epitaxial layers with a growth rate of 20μm/h, thus about seven times higher than with standard precursors. It was also found that chlorine etches preferentially the 3C-SiC inclusions that tends to nucleate on Siface on-axis substrates. Therefore the Cl/Si ratio is a fundamental process parameter to optimize.
25.	Leone, Stefano, et al. (author) Improved morphology for epitaxial growth on 4° off-axis 4H-SiC substrates 2009 In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 311:12, s. 3265-3272 Journal article (peer-reviewed)abstract A process optimization of the growth of SiC epilayers on 4° off-axis 4H-SiC substrates is reported. Process parameters such as growth temperature, C/Si-ratio and temperature ramp up conditions are optimized for the standard non-chlorinated growth in order to grow smooth epilayers without step-bunching and triangular defects. The growth of 6 μm thick n-type doped epitaxial layers on 75 mm diameter wafers is demonstrated as well as that of 20 μm thick layer. The optimized process was then transferred to a chloride-based process and a growth rate 28 μm/h was achieved without morphology degradation. A low growth temperature and a low C/Si ratio are the key parameters to reduce both the step-bunching and the formation of triangular defects.
26.	Mpofu, Pamburayi, et al. (author) Thermal atomic layer deposition of In2O3 thin films using a homoleptic indium triazenide precursor and water 2022 In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:12, s. 4712-4719 Journal article (peer-reviewed)abstract Indium oxide (In2O3) is an important transparent conducting material widely used in optoelectronic applications. Herein, we study the deposition of In2O3 by thermal atomic layer deposition (ALD) using our recently reported indium(iii) triazenide precursor and H2O. A temperature interval with self-limiting growth was found between similar to 270 and 385 degrees C with a growth per cycle of similar to 1.0 angstrom. The deposited films were polycrystalline cubic In2O3 with In : O ratios of 1 : 1.2, and low levels of C and no detectable N impurities. The transmittance of the films was found to be >70% in visible light and the resistivity was found to be 0.2 m omega cm. The high growth rates, low impurities, high optical transmittance, and low resistivity of these films give promise to this process being used for ALD of In2O3 films for future microelectronic displays.
27.	Nadhom, Hama, 1986- (author) Area Selective Chemical Vapor Deposition of Metallic Films using Plasma Electrons as Reducing Agents 2021 Doctoral thesis (other academic/artistic)abstract Metallic films are used to improve optical, chemical, mechanical, magnetic, and electrical properties and are therefore of high importance in many applications, from electronics and catalysis, environmental protection and health, to wearable and flexible electronic materials. Many of these applications, however, require that the metal films are deposited uniformly on topographically complex surfaces and structures. Some form of chemical vapor deposition (CVD) where the deposition is governed by the surface chemistry is needed for uniform film deposition on topographically complex surfaces. Furthermore, area selective deposition (ASD) has gained large considerations lately, where films deposited only on specified areas of the substrate, and not on others, simplifies the processing significantly and opens the way for less complex fabrication of, for instance, nanoscaled electronics. ASD occurs when the surface chemical reactions are disabled on selected areas of the substrate. Since the metal centers in CVD precursor molecules typically have a positive valence, a reductive surface chemistry is required to form a metallic film. This is usually done by using a second precursor, i.e., a molecular reducing agent. The negative standard reduction potential of the first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) means that CVD of these metals requires either very high temperatures or very powerful molecular reducing agents. This thesis describes a new low temperature CVD method for depositing metallic films where instead free electrons in a plasma discharge are utilized to reduce the metal centers of chemisorbed precursor molecules. By applying a positive bias voltage to the substrate holder, the plasma electrons are attracted to the substrate for electron-precursor interactions. This was demonstrated by successfully depositing iron, cobalt, and nickel films from their corresponding metallocene precursors. The electrical resistivity of the substrate and the polarity of the substrate bias were shown to play an important role in depositing metallic films with this CVD approach. The experimental results show that films deposited, with +40 V bias voltage, on silver substrates contain substantially higher metal concentration compare to films deposited on silicon substrates. Deposition on electrically insulating silicon dioxide substrates however yielded no detectable amount of metal atoms on the substrate surface. This indicates that electron current through the substrate is essential to grow metal films in this CVD process. The effect of the electrical resistivity of the substrate was studied for ASD. The new CVD method is shown to be inherently area selective from the surface electrical resistivity by depositing iron from ferrocene on silicon dioxide substrate partially coated with silver. No, or very small, detectable amount of metal atoms could be found on areas with high resistivity, whereas several hundred nm thick iron films are deposited on areas with low resistivity. The only heating of the substrate emanates from the electric current from the plasma through the substrate holder, resulting in a slight heating to 35–50 °C, depending on the substrate bias voltage. This was regarded as the deposition temperature. Such low deposition temperature was exploited to achieve ASD by a masking approach with different temperature sensitive materials such as polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polystyrene (PS), Parafilm, Kapton tape, Scotch tape, and office paper. These materials were used to mask area of the substrate in the new CVD method as demonstrated by depositing iron from ferrocene on partially masked silver substrates. All initial experiments rendered only a phenomenological understanding of the new CVD process. Therefore, a quartz crystal microbalance (QCM) system was modified, by the addition of a positive bias voltage, and used to further understand the chemical and physical processes controlling the deposition process. The results show that differences in film deposition with different deposition parameters, such as plasma power and bias voltage, can be observed using the new QCM approach where the QCM crystal indeed works as a substrate in our new CVD process. In summary, a new CVD concept has been developed for metallic thin films. This method uses the free plasma electrons as reducing agents and can also be utilized for ASD of metal thin films. This
28.	Nadhom, Hama, 1986-, et al. (author) Area Selective Deposition of Metals from the Electrical Resistivity of the Substrate 2021 In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:17, s. 4130-4133 Journal article (peer-reviewed)abstract Area selective deposition (ASD) of films only on desired areas of the substrate opens for less complex fabrication of nanoscaled electronics. We show that a newly developed CVD method, where plasma electrons are used as the reducing agent in deposition of metallic thin films, is inherently area selective from the electrical resistivity of the substrate surface. When depositing iron with the new CVD method, no film is deposited on high-resistivity SiO2 surfaces whereas several hundred nanometers thick iron films are deposited on areas with low resistivity, obtained by adding a thin layer of silver on the SiO2 surface. On the basis of such a scheme, we show how to use the electric resistivity of the substrate surface as an extension of the ASD toolbox for metal-on-metal deposition.
29.	Ojamäe, Lars, 1964-, et al. (author) IR and quantum-chemical studies of carboxylic acid and glycine adsorption on rutile TiO2 nanoparticles 2006 In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 296:1, s. 71-78 Journal article (peer-reviewed)abstract Nanocrystalline TiO2 powders of the rutile polymorph, synthesized by a sol–gel method, were treated with water solutions containing, respectively, formic, acetic, and citric acid and glycine in order to study the adsorption properties of these organic species. The samples were characterized by FTIR, Raman, powder XRD, and TEM. It was found that HCOOH, CH3COOH and HOC(COOH)(CH2COOH)2—but not NH2CH2COOH—adsorbed onto TiO2. The adsorption of HCOOH, CH3COOH and NH2CH2COOH onto the (110) surface of rutile was also studied by quantum-chemical periodic density functional theory (DFT) calculations. The organic molecules were from the computations found to adsorb strongly to the surfaces in a bridge-coordinating mode, where the two oxygens of the deprotonated carboxylic acid bind to two surface titanium ions. Surface relaxation is found to influence adsorption geometries and energies significantly. The results from DFT calculations and ab initio molecular-dynamics simulations of formic acid adsorption onto TiO2 are compared and match well with the experimental IR measurements, supporting the bridge-binding geometry of carboxylic-acid adsorption on the TiO2 nanoparticles.
30.	Pedersen, Annie, 1981, et al. (author) Circulating neurofilament light in ischemic stroke: temporal profile and outcome prediction 2019 In: Journal of Neurology. - : Springer Science and Business Media LLC. - 0340-5354 .- 1432-1459. ; 266:11, s. 2796-2806 Journal article (peer-reviewed)abstract Background and purpose Neurofilament light chain (NfL) is a marker of neuroaxonal damage. We aimed to study associations between serum NfL (sNfL) concentrations at different time points after ischemic stroke and outcomes. Methods We prospectively included ischemic stroke cases (n=595, mean age 59 years, 64% males) and assessed outcomes by both the modified Rankin Scale (mRS) and the NIH stroke scale (NIHSS) at 3 months and by mRS at 2 years. In a subsample, long-term (7-year) outcomes were also assessed by both mRS and NIHSS. We used the ultrasensitive single-molecule array assay to measure sNfL in the acute phase (range 1–14, median 4 days), after 3 months and 7 years in cases and once in controls (n=595). Results Acute-phase sNfL increased by the time to blood-draw and highest concentrations were observed at 3 months post-stroke. High sNfL associated to stroke severity and poor outcomes, and both associations were strongest for 3-month sNfL. After adjusting for age, previous stroke, stroke severity, and day of blood draw, 3-month sNfL was significantly associated to both outcomes at all time points (p<0.01 throughout). For all main etiological subtypes, both acute phase and 3-month sNfL were significantly higher than in controls, but the dynamics of sNfL differed by stroke subtype. Conclusions The results from this study inform on sNfL in ischemic stroke and subtypes over time, and show that sNfL predicts short- and long-term neurological and functional outcomes. Our findings suggest a potential utility of sNfL in ischemic stroke outcome prediction.
31.	Pedersen, Henrik, 1981-, et al. (author) Acceptor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD 2009 In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 311:13, s. 3364-3370 Journal article (peer-reviewed)abstract A systematic p-type doping study has been performed on 4H- and 6H-SiC epilayers grown at high growth rate using chloride-based chemical vapor deposition. The effect of temperature, pressure, growth rate, C/Si-, Cl/Si ratio and dopant flow on the incorporation of the acceptor atoms aluminum and boron has been studied. The C/Si-ratio on the aluminum incorporation has similar behavior to what has been reported for the standard non-chlorinated low-growth rate process, while no clear effect of C/Si-ratio was observed for the boron incorporation. A higher Cl/Si-ratio seems to lead to lower aluminum and boron incorporation either due to more effective silicon supply at high Cl/Si ratio or due to removal of dopant atoms from the surface by chlorine. The doping concentration is stable to the variations in silicon molar fraction, growth pressure and growth temperature for the aluminum doped layers. Also p-type doping with gallium was tested.
32.	Pedersen, Henrik, 1981- (author) Chloride-based Silicon Carbide CVD 2008 Doctoral thesis (other academic/artistic)abstract Silicon carbide (SiC) is a promising material for high power and high frequency devices due to its wide bandgap, high break down field and high thermal conductivity. The most established technique for growth ofepitaxial layers of SiC is chemical vapor deposition (CVD) at around 1550 °C using silane, SiH4, and lighthydrocarbons e g propane, C3H8, or ethylene, C2H4, as precursors heavily diluted in hydrogen. For high-voltagedevices made of SiC thick (> 100 μm), low doped epilayers are needed. Normal growth rate in SiC epitaxy is~ 5 μm/h, rendering long growth times for such SiC device structures. The main problem when trying to achievehigher growth rate by increasing the precursor flows is the formation of aggregates in the gas phase; for SiCCVD these aggregates are mainly silicon droplets and their formation results in saturation of the growth ratesince if the gas flow does not manage to transport these droplets out of the growth zone, they will eventuallycome in contact with the crystal surface and thereby creating very large defects on the epilayer making theepilayer unusable. To overcome this problem, high temperature- as well as low pressure processes have beendeveloped where the droplets are either dissolved by the high temperature or transported out of the susceptor bythe higher gas flow. A different approach is to use chloride-based epitaxy that uses the idea that the silicondroplets can be dissolved by presence of species that bind stronger to silicon than silicon itself. An appropriatecandidate to use is chlorine since it forms strong bonds to silicon and chlorinated compounds of high purity canbe purchased. In this thesis the chloride-based CVD process is studied by using first a single molecule precursor,methyltrichlorosilane (MTS) that contributes with silicon, carbon and chlorine to the process. Growth of SiCepilayers from MTS is explored in Paper 1 where growth rates up to 104 μm/h are reported together withmorphology studies, doping dependence of growth rate and the influence of the C/Si- and Cl/Si-ratios on thegrowth rate and doping. In Paper 2 MTS is used for the growth of 200 μm thick epilayers at a growth rate of 100μm/h, the epilayers are shown to be of very high crystalline quality and the growth process stable. The growthcharacteristics of the chloride-based CVD process, is further studied in Paper 3, where the approach to add HClgas to the standard precursors silane and ethylene is used as well as the MTS approach. A comparison betweenliterature data of growth rates for different approaches is done and it is found that a precursor molecule withdirect Si-Cl bonds should be more efficient for the growth process. Also the process stability and growth ratedependence on C/Si- and Cl/Si are further studied. In Paper 4 the standard growth process for growth on 4° offaxis substrates is improved in order to get better morphology of the epilayers. It is also shown that the optimizedprocess conditions can be transferred to a chloride-based process and a high growth rate of 28 μm/h wasachieved, using the HCl-approach, while keeping the good morphology. In Paper 5 chloride-based CVD growthon on-axis substrates is explored using both the HCl- and MTS-approaches. The incorporation of dopants in SiCepilayers grown by the chloride-based CVD process is studied in Papers 6 and 7 using the HCl-approach. InPaper 6 the incorporation of the donor atoms nitrogen and phosphorus is studied and in Paper 7 theincorporation of the acceptor atoms boron and aluminum. The incorporation of dopants is found to follow thetrends seen in the standard growth process but it is also found that the Cl/Si-ratio can affect the amount ofincorporated dopants.
33.	Pedersen, Henrik, 1981-, et al. (author) Donor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD 2009 In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 311:5, s. 1321-1327 Journal article (peer-reviewed)abstract A systematic n-type doping study has been performed on 4H- and 6H-SiC epilayers grown at high growth rate using chloride-based CVD. The effect of temperature, pressure, growth rate, C/Si-, Cl/Si ratio and dopant flow on the incorporation of the nitrogen and phosphorus donor atoms have been investigated. It is found that the effect of the C/Si-ratio on the incorporation of nitrogen or phosphorus atoms is similar to what has been reported for the standard low growth rate process without addition of chlorine. The Cl/Si-ratio seems to affect the nitrogen incorporation at growth rates higher than 65 μm/h. The doping concentration is stable against variations in growth rate, growth pressure and growth temperature for the nitrogen doped layers.
34.	Pedersen, Henrik, 1981- (author) Experimental and quantum-chemical studies of the surface interactions between organic molecules and nanocrystals of (a) RE2O3 (RE = Y or Gd); and (b) TiOb2 2005 Licentiate thesis (other academic/artistic)abstract The increasing interest for using nanocrystals in bio-medical and optical applications has highlighted the need of molecular functionalisation of nanocrystals. Knowledge of how to attach molecules to the nanocrystal surface is a key factor. This thesis focuses on the surface interactions between nanocrystals of (a) RE2O3 (RE = Y or Gd); and (b) TiO2 and organic molecules, which have been studied experimentally and by quantum-chemical calculations with the intent to elucidate the chemisorption characteristics such as adsorption geometries and energies.(a) RE2O3 nanocrystal synthesis was performed by a colloidal method based on polyols and by a rapid combustion method. The products were experimentally characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR), Raman, and X-ray photoelectron spectroscopy (XPS). By quantum chemical calculations the chemisorption of formic acid, DEG, water and TMOS at the surface of RE12O18 clusters was studied. From comparison between calculated and experimental vibrational spectra, the binding mode for formic acid on RE2O3 was inferred to be of bridge or bidentate type. XPS and IR showed that DEG chemisorbs on the particle surface and experimental IR spectra of DEG chemisorbed on RE2O3 were consistent with an adsorption mode where the hydroxyl groups are deprotonated according to the quantum-chemical computations.(b) Synthesis of single-phase rutile TiO2 nanocrystals was done by a sol-gel method and the nanocrystals was subsequently functionalized by organic acids and glycine. Quantum-chemical studies indicate that formic- and acetic acid adsorbs in a bridge or monodentate binding mode, while glycine is suggested to adsorb as a zwitterion with bridge bonded carboxylic group and a hydrogen bonded amino group. However, spectroscopic data showed that the amino acid, unlike the other acids did not adsorb on TiO2 under the given experimental conditions.
35.	Pedersen, Henrik, 1981-, et al. (author) Growth and Photoluminescence study of Aluminium doped SiC epitaxial layers 2007 In: Materials Science Forum, Vols. 556-557. - : Trans Tech Publications. ; , s. 97- Conference paper (peer-reviewed)
36.	Pedersen, Henrik, 1981-, et al. (author) Growth characteristics of chloride-based SiC epitaxial growth 2008 In: Physica status solidi (RRL) - Rapid Research Letters. - : Wiley InterScience. - 1862-6270 .- 1862-6254. ; 2:6, s. 278-280 Journal article (peer-reviewed)abstract In this study some aspects of the chloride-based CVD growth process have been investigated by using both the approach to add HCl to the standard precursors and by using the single molecule precursor methyltrichlorosilane (MTS). The efficiency of the process for different precursors, the growth rate stability and the effect that the C/Si and Cl/Si ratios have on the growth are studied. It is found that MTS is the most efficient precursor and that the growth becomes carbon limited at C/Si < 1.
37.	Pedersen, Henrik, 1981-, et al. (author) Towards Biocompatibility of RE2O3 Nanocrystals − Water and Organic Molecules Chemisorbed on Gd2O3 and Y2O3 Nanocrystals Studied by Quantum-Chemical Computations 2006 In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 6:9, s. 2004-2008 Journal article (peer-reviewed)abstract Nanocrystals of Gd2O3/Y2O3 and their interaction with water, formic acid, diethylene glycol (DEG), and tetramethoxy silane (TMOS) have been studied by quantum-chemical calculations at the B3LYP level using solvent-coated clusters of gadolinia and yttria. Adsorption energies, surface geometries, electronic structures, and excitation spectra were calculated. The results concerning adsorption strengths and superparamagnetic high-spin states can provide insight into the design of molecular-capped RE2O3 nanocrystals to be used in vivo.
38.	Pedersen, Henrik, 1981-, et al. (author) Very high crystalline quality of thick 4H-SiC epilayers grown from methyltrichlorosilane (MTS) 2008 In: Physica status solidi (RRL) - Rapid Research Letters. - : Wiley InterScience. - 1862-6254 .- 1862-6270. ; 2:4, s. 188-190 Journal article (peer-reviewed)abstract 200 µm thick 4H-SiC epilayers have been grown by chloride-based chemical-vapor deposition using methyltrichlorosilane (MTS) as single precursor. The very high crystalline quality of the grown epilayer is demonstrated by high resolution X-Ray Diffraction rocking curve with a full-width-half-maximum value of only 9 arcsec. The high quality of the epilayer is further shown by low temperature photoluminescence showing strong free exciton and nitrogen bound exciton lines. The very high crystalline quality achieved for the thick epilayer grown in just two hours at 1600 °C suggests that MTS is a suitable precursor molecule for SiC bulk growth.
39.	Pedersen, Henrik, 1981-, et al. (author) Very high epitaxial growth rate of SiC using MTS as chloride-based precursor 2007 In: Surface and Coatings Technology, Volume 201, Issue 22-23 SPEC. ISS.. - : Elsevier. ; , s. 8931- Conference paper (peer-reviewed)abstract
40.	Pedersen, Henrik, 1981-, et al. (author) Very high growth rate of 4H-SiC epilayers using the chlorinated precursor methyltrichlorosilane (MTS) 2007 In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 307:2, s. 334-340 Journal article (peer-reviewed)abstract The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall chemical vapour deposition (CVD) reactor with growth rates higher than 100 μm/h. The addition of chlorinated species to the gas mixture prevents silicon nucleation in the gas phase, thus allowing higher input flows of the precursors resulting in much higher growth rate than that of standard silicon carbide (SiC) epitaxial growth using only silane, SiH4, and hydrocarbons as precursors. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate, morphology, and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor. The growth rate dropped for C/Si<1 but was constant for C/Si>1. Further, the growth rate decreased with lower Cl/Si ratio. This study shows that MTS is a promising precursor for homoepitaxial growth of SiC within the concept of chloride-based SiC growth.
41.	Rouf, Polla, 1993-, et al. (author) Epitaxial GaN using Ga(NMe2)3 and NH3 plasma by Atomic Layer Deposition 2020 In: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 8:25, s. 8457-8465 Journal article (peer-reviewed)abstract Low temperature deposition of high-quality epitaxial GaN is crucial for its integration in electronic applications. Chemical vapor deposition at approximately 800 °C using SiC with an AlN buffer layer or nitridized sapphire as substrate is used to facilitate the GaN growth. Here, we present a low temperature atomic layer deposition (ALD) process using tris(dimethylamido)gallium(III) with NH3 plasma. The ALD process shows self-limiting behaviour between 130–250 °C with a growth rate of 1.4 Å per cycle. The GaN films produced were crystalline on Si (100) at all deposition temperatures with a near stochiometric Ga/N ratio with low carbon and oxygen impurities. When GaN was deposited on 4H-SiC, the films grew epitaxially without the need for an AlN buffer layer, which has never been reported before. The bandgap of the GaN films was measured to be ∼3.42 eV and the Fermi level showed that the GaN was unintentionally n-type doped. This study shows the potential of ALD for GaN-based electronic devices.
42.	Rouf, Polla, 1993- (author) Time-resolved CVD of Group 13-Nitrides 2021 Doctoral thesis (other academic/artistic)abstract Group 13 nitrides (AlN, GaN and InN) and their alloys are semiconductor materials with a wide bandgap span covering from UV down to IR range. Their excellent electronic properties make them extremely attractive materials for light emitting diodes (LEDs) and different kind of transistor structures, especially high electron mobility transistors (HEMTs). These materials are routinely deposited by chemical vapor deposition (CVD) at high temperatures. The most sought-after material among the group 13 nitrides is InN due to its high electron mobility making it extremely useful in transistor structures. InN needs to be deposited at low temperatures as it decomposes at high temperatures. This does not only limit the deposition temperature for InN growth but also for all the other materials that will be deposited on top of InN. In this thesis the deposition of group 13 nitrides is investigated by low temperature atomic layer deposition (ALD) via both a thermal and plasma route. This was conducted by both process development and by improving the deposition chemistry by developing new precursors. Carbon impurities is one of the greater challenges when using the standard aluminum precursor trimethylaluminum (TMA) in ALD due to the strong Al–C bonds in the molecule. An in-situ removal of carbon impurities was investigated by introducing a cleaning pulse, after the TMA pulse. The cleaning pulse consisted of an H2, N2 or Ar gas pulse perpendicular to the surface. The introduction of the cleaning pulse reduced the carbon impurity in the AlN film from 3 at% down to under 1 at%. This made it possible to deposit AlN at higher temperature to obtain better crystalline quality and on the same time reduce the impurity levels. Kinetic simulations showed that the cleaning pulse cleans the surface from desorbed methyl groups resulting in a suppressed reabsorption pathway. To further reduce carbon impurities, the strong M–C bonded precursors was replaced with a M–N bonded one. The precursor used were tris(dimethylamido)gallium together with ammonia (NH3) plasma to deposit GaN. The precursor showed ALD behavior and the resulting GaN film possessed significantly lower carbon impurities compared to M-C bonded precursor at low deposition temperatures. This precursor could also produce epitaxial GaN directly on 4H-SiC without a need of a seed layer. To further investigate the precursor impact on deposition chemistry and ultimately the film quality, three indium precursors were evaluated, indium(III)guanidinate, indium(III)amidinate and indium(III)formamidinate. All three precursors have more or less the same structure, only difference being the size of the substituent on the endocyclic carbon position (-NMe2, -Me and -H respectively). Experimental results showed that smaller groups on the endocyclic carbon position improved the InN film quality in terms of crystallinity, morphology, stoichiometry and optical properties. Density functional theory (DFT) calculations showed that smaller moieties on the endocyclic position will lead to less surface and steric repulsion with the exocyclic position. As the size is decreased the exocyclic groups can fold up closer towards the endocyclic position leading to elongated metal-ligand bonds which will result in easier removal of the ligand for the upcoming NH3 plasma pulse. From these results a new ligand was developed to further improve the deposition chemistry where the endocyclic carbon atom in the ligand backbone of the foramidinate ligand was replaced by a N atom to form a triazenide ligand (iPr–N–N=N–iPr). The triazenide ligand possess no moiety on the endocyclic position compared to the ligands used previously and hence should result in improved material quality if extrapolated from our previous study. The ligand was placed on indium and gallium forming In(III)triazenide and Ga(III)triazenide respectively. Both precursors showed excellent thermal properties making them good ALD precursors. Their use for depositing InN and GaN was investigated with NH3plasma. The resulting films showed excellent quality where no carbon could be detected for either InN nor GaN using XPS and ERDA. Both InN and GaN showed epitaxial growth behavior on 4H-SiC at deposition temperature of 350 °C, a factor of three lower deposition temperature compared to CVD. Interestingly, several linear growth regimes (ALD windows) upon changing the temperature were observed, two and three for InN and GaN respectively. This indicated that the precursors decomposed upon increasing the temperature to form smaller fragments which increased the growth rate but on the same time the smaller precursor fragments saturated the surface. This was further confirmed by DFT calculations. The In(III)triazenide and Ga(III)triazenide was further used to deposit the ternary InGaN phase. A new method was developed where both precursors were mixed in the bubbler and co-sublimed into the reactor via a single pulse. The composition of the films could be tuned via bubbler temperature, deposition temperature and premixed ratio of the precursors in the bubbler. Near In0.5Ga0.5N could be obtained at low deposition temperatures confirmed by both XPS, ERDA and bandgap measurement. Deposition at 350 °C on 4H-SiC resulted in epitaxial In1-xGaxN without a need of a seed layer.
43.	Rönnby, Karl, 1991- (author) A Study of Group 13-Nitride Atomic Layer Deposition : Computational Chemistry Modelling of Atomistic Deposition Processes 2023 Doctoral thesis (other academic/artistic)abstract The crystalline solids aluminium nitride (AlN), gallium nitride (GaN) and indium nitride (InN), together with their alloys, are of huge interest in the semiconductor industry. Their bandgaps span an extensive range from 6.0 eV for AlN to 0.7 eV for InN, with GaN in between at a bandgap of 3.6 eV. Thus, with bandgap tuning from infrared (IR) to ultraviolet (UV) they are well suited for photoelectric applications such as light emitting diodes (LED). The higher bandgaps of AlN and GaN compared to that of silicon (1.1 eV) makes them suitable for high power applications while the high electron mobility of InN makes it attractive for high frequency transistors. Since aluminium, gallium, and indium belong to group 13, their nitrides are termed group 13-nitrides (13Ns). The deposition techniques chemical vapor deposition (CVD) and atomic layer deposition (ALD) can be used to produce thin films upon a substrate through reactions by suitable precursor molecules in the gas phase or at the surface. These techniques have successfully deposited thin films of 13Ns using commercially available precursors, e.g., trimethyl aluminium (TMA), trimethyl gallium (TMG) and trimethyl indium (TMI) as metal precursor and ammonia (NH3) as nitrogen precursor. However, the chemistry between these precursors is not well developed, as evidenced by the large nonstoichiometric ratio between the metal and nitrogen precursors, in the order of 1:100-1:105. This is not sustainable for mass production of these materials, as significant amounts of precursor gas are wasted and must either be cleaned from the exhaust or be released into the atmosphere. In my thesis, the gas phase decomposition and the surface adsorption of these precursors and alternatives are investigated by computational approaches. Gas phase decomposition of ammonia is investigated by kinetic modelling at relevant temperature and pressures. At these conditions, a very small fraction of the initial ammonia molecules can decompose within the expected residence time for the gases in the process. The conclusion is that the low reactivity of ammonia is intrinsic and is not due to decomposition into unreactive nitrogen and hydrogen gas. Methylamines as alternative nitrogen precursors are explored for CVD of GaN. Although these are more reactive in the gas phase, their lower surface reactivity compared to ammonia limits their use as a replacement for ammonia in 13N CVD. The origin of the surface reactivity of ammonia in thermal ALD of AlN and GaN, in comparison to the lack of reactivity on InN, is explored. Comparing GaN and InN surface chemistry, the surface adsorption process on InN is less favourable than on GaN as well as being many orders of magnitude slower, indicating that the lack of any reported thermal ALD process on InN arises from the low reactivity of ammonia towards the InN surface. The resulting surface terminations after ammonia dosing determines how the metal precursors adsorb and react. A series of nitrogen rich surface terminations of the 13Ns is investigated by density functional theory (DFT) modelling and their stability and prevalence at different temperature and pressures are determined from statistical thermodynamics. At low temperatures the surfaces are terminated by hydrogen bonding amino groups while at high temperatures the surface is bare, with the transition temperature between the two structures decreasing from AlN to GaN to InN. TMA can adsorb onto the amino terminated surface and loses ligands by decomposing. Subsequent TMA molecules are found to decompose in two ways depending on how close it adsorbed to an already adsorbed and decomposed molecule. A suitable alternative class of metal precursor for 13N ALD are molecules with nitrogen to metal bonds, such as formamidinates, amidinates, trisguanidinates, or triazenides. Ammonia will have an easier process to break the weaker metal nitrogen bond compared to a metal carbon bond. The gas phase decomposition of a trisguanidinate precursor is investigated but it is shown to be likely to decompose during volatilization, limiting its use as an InN ALD precursor. My thesis consists of detailed atomistic simulations of the deposition of AlN, GaN and InN thin films. The simulations in cooperation with experimental work are used to elucidate the detailed atomistic mechanisms occurring during the process. It gives insight into the shortcomings of the current processes and precursors and can be used as a basis for how to improve them, rendering the 13N a suitable material in a sustainable large-scale production for a variety of semiconductor applications.
44.	Rönnby, Karl, 1991-, et al. (author) On the limitations of thermal atomic layer deposition of InN using ammonia 2023 In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 41:2 Journal article (peer-reviewed)abstract Chemical vapor deposition of indium nitride (InN) is severely limited by the low thermal stability of the material, and, thus, low-temperature deposition processes such as atomic layer deposition (ALD) are needed to deposit InN films. The two chemically and structurally closely related materials—aluminum nitride and gallium nitride (GaN)—can be deposited by both plasma and thermal ALD, with ammonia (NH3) as a nitrogen precursor in thermal processes. InN, however, can only be deposited using plasma ALD, indicating that there might be a limitation to thermal ALD with NH3 for InN. We use quantum-chemical density functional theory calculations to compare the adsorption process of NH3 on GaN and InN to investigate if differences in the process could account for the lack of thermal ALD of InN. Our findings show a similar reactive adsorption mechanism on both materials, in which NH3 could adsorb onto a vacant site left by a desorbing methyl group from the surfaces. The difference in energy barrier for this adsorption indicates that the process is many magnitudes slower on InN compared to GaN. Slow kinetics would hinder NH3 from reactively adsorbing onto InN in the timeframe of the ALD growth process and, thus, limit the availability of a thermal ALD process.
45.	Samii, Rouzbeh, 1986- (author) Group 11–14 Triazenides : Synthesis, characterization, and thermal evaluation for use in chemical vapor deposition 2022 Doctoral thesis (other academic/artistic)abstract Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are corner-stone techniques for depositing thin films in semi-conductor manufacturing. To deposit semiconductor grade materials, these techniques rely on high-performance precursors. This thesis covers synthesis, characterization, and evaluation of 1,3-dialkyltriazenides of group 11–14 metals as precursors for CVD and ALD. Triazenides had previously not been used as precursors for ALD, nor any other CVD process. The gallium and indium triazenides were used for ALD of indium- and gallium nitride and yielded materials of superior quality over other precursors. The success of these precursors sparked subsequent investigation into triazenides of zinc, and the group 11- and 14 metals. These triazenides showed high volatility and thermal stability making them highly interesting as CVD and ALD precursors.
46.	Sharma, Sachin, 1994- (author) Phase Evolution of Boron Nitride and Carbide during Chemical Vapor Deposition 2024 Doctoral thesis (other academic/artistic)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.
47.	Souqui, Laurent, 1991- (author) Chemical vapour deposition of sp2-hybridised B-C-N materials from organoborons 2019 Doctoral thesis (other academic/artistic)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.
48.	Souqui, Laurent, 1991-, et al. (author) Texture evolution in rhombohedral boron carbide films grown on 4H-SiC(0001) and 4H-SiC(0001) substrates by chemical vapor deposition 2022 In: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 51:41, s. 15974-15982 Journal article (peer-reviewed)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.
49.	Stefansson, Hreinn, et al. (author) Homozygosity for R47H in TREM2 and the Risk of Alzheimer's Disease 2024 In: New England Journal of Medicine. - : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 390:23, s. 2217-2219 Journal article (other academic/artistic)
50.	Vryonidis, Efstathios, 1989-, et al. (author) Pathways to Identify Electrophiles In Vivo Using Hemoglobin Adducts : Hydroxypropanoic Acid Valine Adduct and Its Possible Precursors 2022 In: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 35:12, s. 2227-2240 Journal article (peer-reviewed)abstract Analytical methods and tools for the characterization of the human exposome by untargeted mass spectrometry approaches are advancing rapidly. Adductomics methods have been developed for untargeted screening of short-lived electrophiles, in the form of adducts to proteins or DNA, in vivo. The identification of an adduct and its precursor electrophile in the blood is more complex than that of stable chemicals. The present work aims to illustrate procedures for the identification of an adduct to N-terminal valine in hemoglobin detected with adductomics, and pathways for the tracing of its precursor and possible exposure sources. Identification of the adduct proceeded via preparation and characterization of standards of adduct analytes. Possible precursor(s) and exposure sources were investigated by measurements in blood of adduct formation by precursors in vitro and adduct levels in vivo. The adduct was identified as hydroxypropanoic acid valine (HPA-Val) by verification with a synthesized reference. The HPA-Val was measured together with other adducts (from acrylamide, glycidamide, glycidol, and acrylic acid) in human blood (n = 51, schoolchildren). The HPA-Val levels ranged between 6 and 76 pmol/g hemoglobin. The analysis of reference samples from humans and rodents showed that the HPA-Val adduct was observed in all studied samples. No correlation of the HPA-Val level with the other studied adducts was observed in humans, nor was an increase in tobacco smokers observed. A small increase was observed in rodents exposed to glycidol. The formation of the HPA-Val adduct upon incubation of blood with glycidic acid (an epoxide) was shown. The relatively high adduct levels observed in vivo in relation to the measured reactivity of the epoxide, and the fact that the epoxide is not described as naturally occurring, suggest that glycidic acid is not the only precursor of the HPA-Val adduct identified in vivo. Another endogenous electrophile is suspected to contribute to the in vivo HPA-Val adduct level.

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