| 1. |
- Birch, Jens, et al.
(author)
-
Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window
- 2002
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 68:3, s. 275-282
-
Journal article (peer-reviewed)abstract
- Cr/Sc multilayer X-ray mirrors intended for normal incidence reflection in the water window wavelength range, lambda=[2.4-4.4 nm], have been grown by ion-assisted sputter deposition and characterized using soft and hard X-ray reflectivity. By extracting low-energy ions, with energies, E-ion, ranging from 9 to 113 eV and with ion-to-metal flux ratios, Phi, between 0.76 and 23.1, from the sputtering plasma to the growing film, the nano-structure of the multilayer interfaces could be modified. A significantly increased soft X-ray reflectivity, using lambda = 3.374 nm, for Cr/Sc multilayers with layer thicknesses in the range 0.4-2.8 nm, was obtained when high ion-to-metal flux ratios, Phi(Cr) = 7.1 and Phi(Sc) = 23.1, and low energy ions, E-ion = 9eV, were used. An experimental reflectivity of 5.5% was obtained at 76degrees for a multilayer with 400 bi-layers. Simulations of the reflectivity data showed that the interface widths are < 0.425 nm. It could be concluded that roughness of low spatial frequency is reduced at lower ion energies than the high spatial frequency which was eliminated at the expense of intermixing at the interfaces at higher ion energies. The predicted performance of normal incidence multilayer mirrors grown at optimum conditions and designed for lambda = 3.374 and 3.115 nm indicates possible reflectivities of 6.5% and 14%, respectively.
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| 2. |
- CHAKAROV, DV, et al.
(author)
-
WATER-ADSORPTION ON GRAPHITE(0001)
- 1995
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In: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1109-1112
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Journal article (peer-reviewed)abstract
- Wafer adsorption on the clean graphite (0001) surface has been studied by high-resolution electron-energy-loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). At 85 K H2O adsorbs non-dissociatively forming hydrogen-bonded aggregates. The structure and the growth mode of water clusters depend on the substrate temperature and the coverage. At all coverages, above a few per cent of a monolayer (ML), the desorption is characterized by zero-order kinetics, while the HREEL spectra reveal a threshold coverage approximately 1 ML when the average co-ordination of the H2O molecules changes. Isothermal measurements of the desorption rate and HREELS measurements at elevated temperatures suggest an irreversible phase transition from amorphous to crystalline ice at approximately 135 K.
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| 3. |
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| 4. |
- Donchev, V., et al.
(author)
-
High-temperature excitons in GaAs quantum wells embedded in AlAs/GaAs superlattices
- 2000
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 58:2, s. 478-484
-
Journal article (peer-reviewed)abstract
- Photoluminescence (PL) spectra of GaAs quantum wells embedded in short-period AlAs/GaAs superlattices have been measured at 2 K and at room temperature. Two approaches have been applied in order to investigate the mechanisms of radiative recombination in these structures. In the first one, we studied the excitation density dependence of the PL intensity. In the second approach a line-shape analysis of the PL spectra is performed by means of a statistical model, which includes both free exciton, and free carrier recombinations. The fit based on this model reproduces with high accuracy the experimental spectra and allows to assess the relative contributions of excitons and free carriers to the radiative recombination process. The results of both approaches indicate the predominance of free excitons in the radiative recombination at room temperature.
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| 5. |
- Ehiasarian, A.P., et al.
(author)
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Influence of high power densities on the composition of pulsed magnetron plasmas
- 2002
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 65:2, s. 147-154
-
Journal article (peer-reviewed)abstract
- The application of high power pulses with peak voltage of -2 kV and peak power density of 3 kWcm-2 to magnetron plasma sources is a new development in sputtering technology. The high power is applied to ordinary magnetron cathodes in pulses with short duration of typically some tens of microseconds in order to avoid a glow-to-arc transition. High plasma densities are obtained which have been predicted to initiate self-sputtering. This study concerns Cr and Ti cathodes and presents evidence of multiply charged metal ions as well as of Ar ions in the dense plasma region of the high power pulsed magnetron discharge and a substantially increased metal ion production compared to continuous magnetron sputtering. The average degree of ionisation of the Cr metal deposition flux generated in the plasma source was 30% at a distance of 50 cm. Deposition rates were maintained comparable to conventional magnetron sputtering due to the low pressure of operation of the pulsed discharge - typically 0.4 Pa (3mTorr) of Ar pressure was used. Observations of the current-voltage characteristics of the discharge confirmed two modes of operation of the plasma source representing conventional pulsed sputtering at low powers (0.2 kWcm-2) and pulsed self-sputtering at higher powers (3 kWcm-2). The optical emission from the various species in the plasma showed an increase in metal ion-to-neutral ratio with increasing power. The time evolution within a pulse of the optical emission from Ar0, Cr0, Cr1+, and Cr2+ showed that at low powers Cr and Ar excitation develops simultaneously. However, at higher powers a distinct transition from Ar to Cr plasma within the duration of the pulse was observed. The time evolution of the discharge at higher powers is discussed. © 2002 Elsevier Science Ltd. All rights reserved.
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| 6. |
- Engstrom, C., et al.
(author)
-
Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil
- 2000
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 56:2, s. 107-113
-
Journal article (peer-reviewed)abstract
- An original design and solution to the problem of magnetic field interactions in a vacuum chamber between two unbalanced magnetron sputtering sources and a solenoid coil serving to increase plasma density in near substrate position, is presented. By changing the solenoid coil current strength and direction, plasma growth conditions in an argon discharge and Ti-magnetron cathodes were found to vary in a broad region. Langmuir probe analysis shows that an increase in the coil current from 0 to 6 A caused plasma and substrate floating potentials to change from -7 to -30 V and from +1 to -10 V, respectively, as well as increasing the ion densities to a biased substrate from 0.2 to 5.2 mA cm-2 for each of the magnetrons. By using a ferro-powder magnetic field model, as well as finite element method analysis, we demonstrate the interference of the three magnetic fields - those of the two magnetrons and the solenoid coil. X-ray diffraction and transmission electron microscopy were used to study the microstructure and morphology of Ti-films grown under different ion bombardment conditions. At low Ar-ion-to-Ti-atom arrival rate ratios, Jion/Jn to approximately 1.5, at the substrate, variations of the ion energy, Eion, from 8 to 70 eV has only a minor effect on the microstructure and film preferred crystallographic orientation, resulting in an open/porous structure with defect-rich grains. At a higher Jion/Jn value of approximately 20, films with a well-defined dense structure were deposited at ion energies of 80 eV. The increase in ion flux also resulted in changes of the Ti film preferred orientation, from an (0 0 0 2) preferred orientation to a mixture of (0 0 0 2) and (1 0 1¯ 1) orientations.
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| 7. |
- Eriksson, Mats, 1963-, et al.
(author)
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The water-forming reaction on thin, SiO2 supported, palladium films
- 1990
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 41:1-3, s. 137-138
-
Journal article (peer-reviewed)abstract
- The water-forming reaction has been studied on thin Pd films, evaporated on planar SiO2 substrates. The nominal film thickness varied between 5 and 100 Å. The studies were performed in uhv by means of mass spectrometry, UPS and work function measurements in the temperature range 323–523 K. The film structure was also studied with TEM. The results are compared with previous measurements on 1000 Å, thick, homogeneous Pd films. The structure of the thin Pd films changed dramatically during cyclic H2 and O2 exposures, from that of a continuous film with cracks to that of drop-like metal particles. These structural changes are not observed on the thick (1000 Å) Pd films. Even though there are large structural changes, the water-forming reaction looks qualitatively the same as on a thick Pd film. The total water production however, decreases with decreasing film thickness. We believe that some minor qualitative differences in the water-forming reaction for different nominal Pd film thicknesses, are due to the increasing PdSiO2 boundary as the thickness is reduced.
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| 8. |
- Fogelberg, J., et al.
(author)
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A hydrogen sensitive palladium metal-oxide-semiconductor device as sensor for dissociating NO in H2-atmospheres
- 1990
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 41, s. 705-
-
Journal article (peer-reviewed)abstract
- A Pd-MOS structure can be used as a sensitive analytical tool in the study of dissociating oxygen containing molecules. Nitric oxide has been studied as a test case. Initially NO adsorbs very effectively and dissociatively on polycrystalline Pd at temperatures above 473 K. At this temperature H2O, N2O and N2 desorbs during an NO exposure in a hydrogen background. After such exposure the surface is probably left with only residual nitrogen atoms adsorbed on the surface. Below 390 K the dissociation probability is insignificant.
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| 9. |
- Jonsson, Lars, et al.
(author)
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Controlled topography production - True 3D simulation and experiment
- 1995
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 46, s. 971-975
-
Journal article (peer-reviewed)abstract
- A true 3D computer program, named DINESE, has been developed to simulate the evolution of real 3D structures during erosion and deposition. It is based on the generalized Huygens reconstruction formalism of surface evolution and can predict the evolution of any surface of the form z = f(x,y) resulting from any erosion or deposition process. True 3D computer simulations of a number of cases are presented and compared with experiment. The powers of the simulation method are further demonstrated by a series of sequential predictive simulations resulting in a desired topography which is then verified experimentally under the same sequence of conditions. Specifically, the evolution of different Si3N4 structures during ion beam etching with Ar ions under different erosion conditions has been studied both numerically and experimentally.
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| 10. |
- Mankefors, S., et al.
(author)
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Theoretical investigation of soft x-ray emission from a Si(100) layer buried in GaAs
- 1998
-
In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 49:3, s. 181-184
-
Journal article (peer-reviewed)abstract
- Calculations of the soft x-ray emission spectrum have been carried out on a buried Si(100) layer in GaAs and compared with experimental data. We find that Si occupies Ga- as well as As-sites and that the local density of states is different for these two cases.
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| 11. |
- Philipps, V., et al.
(author)
-
Erosion and redeposition of wall material in controlled fusion devices
- 2002
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 67:04-mar, s. 399-408
-
Journal article (peer-reviewed)abstract
- Processes of erosion and redeposition and their impact on plasma facing materials in devices for magnetically confined fusion are discussed. Volatile molecules formed in the erosion process are partly pumped out but the majority of species released from the wall components returns to the surface causing the modification of its morphology. Prompt redeposition and redeposition after global transport reduce the gross erosion at any surface. Detailed analysis shows that erosion and deposition can coexist on otherwise erosion-dominated surfaces due to local inhomogenities. The erosion yield of redeposited material of sub-monolayer thickness significantly differs from that observed for thick targets. On deposition dominated areas one observes the formation of thick co-deposits containing a mixture of trapped fuel atoms (hydrogen isotopes) and species removed originally from the wall. This leads to a large and long-term fuel accumulation (tritium inventory) in a device. Reduced mechanical integrity of such layers stimulates their flaking and peeling-off if a critical thickness has been reached. This, in turn, results in the formation of hydrogen-rich dust particles.
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| 12. |
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| 13. |
- Rubel, M., et al.
(author)
-
Deuterium interaction with silicon-graphite materials exposed to the tokamak plasma
- 1994
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 45:4, s. 429-434
-
Journal article (peer-reviewed)abstract
- Silicon-containing composites are considered as plasma facing materials in controlled fusion devices. Comparative studies of deuterium interaction with carbon based substrates were performed for graphite-silicon mixtures (5-50 wt% of Si), carbon fibres and isotropic graphite. Both virgin and deuterium treated surfaces were characterized by means of several surface sensitive techniques. The substrates were exposed to the deuterium plasma in the TEXTOR tokamak, in a magnetron or in a hollow cathode. The uptake, retention and release of deuterium were investigated. Migration of deuterium from the plasma deposited layer to the bulk of the substrates was found for the graphite-silicon mixtures. The structure of the deuterium-containing deposits was studied using atomic force microscopy. The initial stage of bubble formation was observed on the surfaces exposed to the tokamak plasma
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| 14. |
- Rubel, Marek J., et al.
(author)
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Ion beam analysis methods in the studies of plasma facing materials in controlled fusion devices
- 2003
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 70:03-feb, s. 423-428
-
Journal article (peer-reviewed)abstract
- Application of ion beam analysis techniques in the studies of material transport and fuel inventory in the controlled fusion devices is exemplified. Enhanced proton scattering on the carbon isotopes C-12(p,p)C-12, C-13(p,p)C-13 and secondary ion mass spectrometry allowed for determination of carbon erosion and re-deposition on the wall components following the experiments with a tracer ((CH4)-C-13) injection into the plasma edge at the TEXTOR tokamak. For the assessment of the deuterium fuel accumulation in the plasma facing components depth profiling by means of nuclear reaction analysis, He-3(d,p)He-4, was performed. Advantages and limitations of those nuclear methods in solving experimental problems are addressed.
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| 15. |
- Shao, Yidong, et al.
(author)
-
Water adsorption on Ge(100) : a computational study
- 1991
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 42:4, s. 313-319
-
Journal article (peer-reviewed)abstract
- Cluster calculations simulating water dissociation on Ge(100) are presented. We evaluate the electronic structure of molecular water and dissociation products (OH, O, H) in a LCAO-X scheme. Ge 3d core level shifts were approximated by the ionization potentials (IPs) of nonbonding a2 orbitals. Finally, we discuss the nomenclature of hydroxyl groups ligated to different adsorbents. The germanium-adsorbate atomic distance and not simply the perpendicular position above the first Ge(100) layer was found to be the most important chemisorption parameter. This illustrates the importance of directional bonding and contrasts adsorption on metals. Adsorption at open bridge sites will give significantly less perturbation than adsorption at terminal sites. Major perturbations at the former site require movement of substrate atoms to accommodate the necessary short GeO distances. Our calculations suggest that (i) some water dissociation occurs already at 100 K, (ii) two different hydroxyl species are present at the surface, and (iii) one of the hydroxyl ligands is akin to adsorbed oxygen.
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| 16. |
- Shtinkov, N., et al.
(author)
-
Effect of non-abrupt interfaces in AlAs/GaAs superlattices with embedded GaAs quantum wells
- 2000
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 58:2, s. 561-567
-
Journal article (peer-reviewed)abstract
- In the present paper, we investigate the effect of the non-abrupt interfaces on the electronic and optical properties of short-period AlAs/GaAs superlattices with embedded GaAs quantum wells. The lateral disorder and the component interdiffusion at the interfaces are averaged over the layer planes and are effectively represented by a diffusion concentration profile in the growth direction. The diffusion length LD is used as a parameter characterizing the degree of interface broadening. The electronic structure calculations are made using the sp3s* spin-dependent empirical tight-binding Hamiltonian, the virtual crystal approximation, and the surface Green function matching method. The dependencies of the lowest electron (E1), heavy hole (HH1), and light hole (LH1) bound states on the diffusion length are calculated for LD from 0 to 4 monolayers. It is found that the energies of the transitions (E1-HH1) and (E1-LH1) increase as LD increases. The results obtained are compared with photoluminescence data for MBE-grown samples. It is found that the degree of interface broadening depends on the growth temperature and on the sample geometry. The diffusion lengths calculated from the experimental data follow the expected trends, revealing a good qualitative agreement between theory and experiment.
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| 17. |
- TJERNBERG, O, et al.
(author)
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ANGLE-RESOLVED PHOTOEMISSION ON NIO - ON THE NATURE OF THE VALENCE-BAND
- 1995
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 46:8-10, s. 1215-1218
-
Journal article (peer-reviewed)abstract
- Angle resolved photoelectron spectroscopy has been performed on the valence band of NiO at the National Swedish Laboratory for Synchrotron Radiation. Normal emission spectra have been recorded for photon energies between 17 and 140 eV in order to study the electronic structure of the valence band. The experimentally determined band structure has been compared with a local density augmented plane wave band structure calculation. Signs of the influence of antiferromagnetic ordering are found and the general agreement between experimental and theoretical oxygen derived bands indicates strong hybridization between Ni 3d and O 2p orbitals.
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| 18. |
- Toneva, A, et al.
(author)
-
FeSi2 thin films investigated by X-ray photoelectron and infrared spectroscopy
- 2000
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 58:2-3, s. 420-427
-
Journal article (peer-reviewed)abstract
- Thin films of iron silicide prepared by ion-beam and by electron-beam evaporation of iron on silicon substrates and following rapid thermal processing are investigated. Low-energy argon ion sputtering of surface layer is used for depth profile XPS analysis. The Si2p, Fe2p3/2, O1s and C1s electron spectra are recorded. On the basis of established binding energies and infrared transmission spectra (200–600 cm−1) conclusion are made about the effect of the annealing temperature and duration on the chemical bond type and phase composition of the iron silicide films.
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| 19. |
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| 20. |
- Wronkowska, A.A., et al.
(author)
-
Characterisation of Cd1-xMgxSe solid solutions by spectroscopic ellipsometry
- 2001
-
In: Vacuum. - 0042-207X .- 1879-2715. ; 63:1-2, s. 233-239
-
Conference paper (other academic/artistic)abstract
- Optical properties of bulk Cd1-xMgxSe mixed crystals, grown from a CdSe, Mg, and Se melt by the Bridgman method, are presented. The alloys have a wurtzite type structure in the investigated range of composition, i.e. for 0 = x = 0.4. Measurements of the complex pseudo-dielectric function, = + ie2(?)>, were performed at room temperature in the photon energy range of 1.25-4.5 eV, using a computer-controlled variable angle of incidence ellipsometer. The spectral dependence of the effective refractive index and the absorption coefficient were also derived. The structure observed in the dielectric functions, attributed to the interband transitions E0, E0 + ?0 and E1, have been analysed by fitting the and d2/d?2 spectra to the damped harmonic oscillator and critical-point line shapes, respectively. For all critical points, the energy increases with increasing Mg concentration. The ellipsometric results of a fundamental band-gap shift due to Mg content are compared with the rate of increase of the excitonic energy, derived from photoluminescence spectra. © 2001 Elsevier Science Ltd.
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| 21. |
- Abbasi, Mazhar Ali, et al.
(author)
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Anions effect on the low temperature growth of ZnO nanostructures
- 2012
-
In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 86:12, s. 1998-2001
-
Journal article (peer-reviewed)abstract
- Seed mediated aqueous chemical growth (ACG) route was used for the growth of ZnO nanostructures on Si substrate in four different growth mediums. The growth medium has shown to affect the morphology and the size of the different nanostructures. We observed that the medium containing zinc nitrate anions yields the nanorods, in a medium containing zinc acetate anions nano-candles are obtained. While in a medium containing zinc chloride anions ZnO nano-discs were obtained and in a medium containing zinc sulfate anions nano-flakes are achieved. Growth in these different mediums has also shown effect on the optical emission characteristics of the different ZnO nanostructures.
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| 22. |
- Alberdi, Alberto, et al.
(author)
-
Tribological behavior of nanocomposite coatings based on fullerene-like structures
- 2011
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 85:12, s. 1087-1092
-
Journal article (peer-reviewed)abstract
- This paper presents a new group of nanocomposite coatings based on integrating inorganic fullerene-like material (IFLM) structures into conventional coating matrices. Such coatings have been developed within the scope of the European funded FOREMOST project (FP6-NMP3-CT-2005-515840). Regarding the synthesis of these nanocomposite coatings based on fullerene-like components, two alternative routes were explored: introducing preformed IFLMs into the coating deposition process or forming the fullerene-like components in situ during the coating deposition process. Both methods have been demonstrated to be technically feasible, depending on the nature of the coating matrix or the desired fullerene-like structure. These new materials allow some independent control of tribological properties usually known as antagonists (very high load bearing capacity with a very low friction coefficient). In the case of unidirectional movement, under dry conditions, the best coatings developed in FOREMOST displayed a coefficient of friction in air within the range 0.04-0.10, depending on the degree of humidity and the test conditions. Pure sliding laboratory tests indicate that for some industrial applications fullerene-like nanocomposite coatings can give significant reductions in wear and friction coefficient when compared to similar coatings without fullerene-like components. The lubrication mechanisms through which these fullerene-like structures improve friction and prevent wear are also discussed in this paper.
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| 23. |
- Ali, Sharafat, et al.
(author)
-
Novel transparent Mg-Si-O-N thin films with high hardness and refractive index
- 2016
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 131, s. 1-4
-
Journal article (peer-reviewed)abstract
- There is an increasing demand for glass materials with better mechanical and optical properties for display and electronic applications. This paper describes the deposition of novel thin films of Mg-Si-O-N onto float glass substrates. Amorphous thin films in the Mg-Si-O-N system with high nitrogen and magnesium contents were deposited by reactive RF magnetron co-sputtering from Mg and Si targets in Ar/N2/O2 gas mixtures. The thin films studied span an unprecedented range of compositions up to 45 at% Mg and 80 at% N out of cations and anions respectively. Thin films in the Mg-Si-O-N system were found to be homogeneous and transparent in the visible region. Mechanical properties like hardness (H) and reduced elastic modulus (Er) show high values, up to 21 GPa and 166 GPa respectively. The refractive index (1.87-2.00) increases with increasing magnesium and nitrogen contents.
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| 24. |
- Alouhmy, M., et al.
(author)
-
Effects of hydrogen implantation on the magnetocaloric properties of amorphous FeZr films
- 2021
-
In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 186
-
Journal article (peer-reviewed)abstract
- We report on the effects of H-implantation on the magnetic and magnetocaloric properties of amorphous FeZr films. Arrott plots reveal a second order ferromagnetic to paramagnetic phase transition for the as-grown and H-implanted films, with an increase in T-C from 160 to 200 K upon implantation. The maximum change in magnetic entropy (-Delta S-M) increases from 0.66 to 0.77J/kgK for a field change mu 0 Delta H = 1.5T, as well as the relative cooling power (RCP) values were improved from 84.5 to 108.6J/kg. This improvement was attributed to the increase in magnetization and chemical inhomogeneity induced by the implantation process. The increase in the chemical inhomogeneity was supported by the determination of the local exponent n extracted from the slope of Ln(-Delta S-M) as a function of Ln(mu 0H), which is line with the simulated depth profile of hydrogen atoms through the FeZr film.
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| 25. |
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| 26. |
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| 27. |
- Andersson, Matilda, et al.
(author)
-
Deposition and characterization of magnetron sputtered amorphous Cr-C films
- 2012
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 86:9, s. 1408-1416
-
Journal article (peer-reviewed)abstract
- Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 degrees C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young's modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp(2)/sp(3) ratio of the a-C phase.
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| 28. |
- Askari, SJ, et al.
(author)
-
Two-step growth of high-quality nano-diamond films using CH 4/H 2 gas mixture
- 2007
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 81:5, s. 713-717
-
Journal article (peer-reviewed)abstract
- Diamond films with fine grain size and good quality were successfully deposited on pure titanium substrate using a novel two-step growth technique in microwave plasma-assisted chemical vapor deposition (MWPCVD) system. The films were grown with varying the methane (CH4) concentration at the stage of bias-enhanced nucleation (BEN) and nano-diamond film deposition. It was found that nano-diamond nuclei were formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. Nano-diamond film deposition on pure titanium was always very hard due to the high diffusion coefficient of carbon in Ti, the big difference between thermal expansion coefficients of diamond and Ti, the complex nature of the interlayer created during diamond deposition, and the difficulty in achieving very high nucleation density. A smooth and well-adhered nano-diamond film was successfully obtained on pure Ti substrate. Detailed experimental results on the synthesis, characterization and successful deposition of the nano-diamond film on pure Ti are discussed
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| 29. |
- Atanassov, A, et al.
(author)
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Grazing incident asymmetric X-ray diffraction of beta-FeSi2 layers, produced by ion beam synthesis
- 2004
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76:02-Mar, s. 277-280
-
Journal article (peer-reviewed)abstract
- The crystal structure of beta-FeSi2 phase, prepared by ion beam synthesis (IBS) method, followed by rapid thermal annealing (RTA) is investigated by grazing incident asymmetric X-ray diffraction (GIAXRD). The X-ray spectra, obtained at different grazing angles, indicated that the beta-FeSi2 phase is formed in the whole implantation range. From the comparison of the reflections intensities ratios, it is found that in the metal-deficient regions, where the beta-FeSi2 phase is present in the form of precipitates, the crystallites orientation is influenced by the one of the silicon substrates, while the orientation in the metal-rich region is different and depends on the annealing temperature. (C) 2004 Elsevier Ltd. All rights reserved.
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| 30. |
- Azarov, A. Yu., et al.
(author)
-
Structural damage in ZnO bombarded by heavy ions
- 2010
-
In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 84:8, s. 1058-1061
-
Journal article (peer-reviewed)abstract
- The effect of implantation parameters on damage build-up in ZnO bombarded with Bi and Er ions is studied by Rutherford backscattering/channelling spectrometry. The results show that the damage accumulation behaviour in ZnO is different dramatically from that in other semiconductors. In particular, a variation of implantation parameters, such as collision cascade density, sample temperature and ion flux, has only a minor influence on the damage accumulation in the crystal bulk for the case of such heavy ions. Moreover, an intermediate damage peak, between the surface and bulk defect peaks, is observed for all the irradiation conditions studied. The cascade density affects the behaviour of this intermediate peak with increasing ion dose.
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| 31. |
- Bakhit, Babak, 1983-, et al.
(author)
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Dense Ti0.67Hf0.33B1.7 thin films grown by hybrid HfB2-HiPIMS/TiB2-DCMS co-sputtering without external heating
- 2021
-
In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 186
-
Journal article (peer-reviewed)abstract
- There is a need for developing synthesis techniques that allow the growth of high-quality functional films at low substrate temperatures to minimize energy consumption and enable coating temperature-sensitive substrates. A typical shortcoming of conventional low-temperature growth strategies is insufficient atomic mobility, which leads to porous microstructures with impurity incorporation due to atmosphere exposure, and, in turn, poor mechanical properties. Here, we report the synthesis of dense Ti0.67Hf0.33B1.7 thin films with a hardness of ∼41.0 GPa grown without external heating (substrate temperature below ∼100 °C) by hybrid high-power impulse and dc magnetron co-sputtering (HfB2-HiPIMS/TiB2-DCMS) in pure Ar on Al2O3(0001) substrates. A substrate bias potential of −300 V is synchronized to the target-ion-rich portion of each HiPIMS pulse. The limited atomic mobility inherent to such desired low-temperature deposition is compensated for by heavy-mass ion (Hf+) irradiation promoting the growth of dense Ti0.67Hf0.33B1.7.
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| 32. |
- Bakhit, Babak, 1983-, et al.
(author)
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Multifunctional ZrB2-rich Zr1-xCrxBy thin films with enhanced mechanical, oxidation, and corrosion properties
- 2021
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 185
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Journal article (peer-reviewed)abstract
- Refractory transition-metal (TM) diborides have high melting points, excellent hardness, and good chemical stability. However, these properties are not sufficient for applications involving extreme environments that require high mechanical strength as well as oxidation and corrosion resistance. Here, we study the effect of Cr addition on the properties of ZrB2-rich Zr1-xCrxBy thin films grown by hybrid high-power impulse and dc magnetron co-sputtering (Cr-HiPIMS/ZrB2-DCMS) with a 100-V Cr-metal-ion synchronized potential. Cr metal fraction, x = Cr/(Zr+Cr), is increased from 0.23 to 0.44 by decreasing the power Pzrb2 applied to the DCMS ZrB2 target from 4000 to 2000 W, while the average power, pulse width, and frequency applied to the HiPIMS Cr target are maintained constant. In addition, y decreases from 2.18 to 1.11 as a function of Pzrb2, as a result of supplying Cr to the growing film and preferential B resputtering caused by the pulsed Cr-ion flux. ZrB2.18, Zr0.77Cr0.23B1.52, Zr0.71Cr0.29B1.42, and Zr0.68Cr0.32B1.38 2 films have hexagonal AlB2 crystal structure with a columnar nanostructure, while Zr0.64Cr0.36B1.30 and Zr0.56Cr0.44B1.11 are amorphous. All films show hardness above 30 GPa. Zr0.56Cr0.44B1.11 alloys exhibit much better toughness, wear, oxidation, and corrosion resistance than ZrB2.18. This combination of properties makes Zr0.56Cr0.44B1.11 ideal candidates for numerous strategic applications.
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| 33. |
- Baránková, Hana, et al.
(author)
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Effect of the electrode material on the atmospheric plasma conversion of NO in air mixtures
- 2010
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 84:12, s. 1385-1388
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Journal article (peer-reviewed)abstract
- Non-thermal atmospheric pressure plasma is widely used for conversion of hazardous gases. Results from different laboratories confirm importance of energy non-equilibrium in the plasma where dominant energy carriers are electrons and a dominant chemistry is based on formation and interactions of radicals. Because of rather high electric fields required for generation and sustaining of air discharges at atmospheric pressure many plasma systems were found rather to create a lot of NO instead of removing it. A widely supported way to clean NO and NO2 from air mixtures is a plasma assisted catalytic reduction where the cold plasma is combined with the solid-state catalyst. In an ideal case the plasma acts as an oxidation catalyst where an atomic oxygen from air oxidizes NO to NO2 and the solid-state catalysts are then capable to convert all NO2 to N-2 and O-2. In most cases it is also necessary to involve auxiliary gases, e.g., propylene, to make the process efficient enough. This work introduces an original cold plasma system based on atmospheric hollow cathodes generated by a nanopulse DC power with controllable voltage and pulse frequency. The system was optimized in both the geometry and the applied power. However, the material of electrodes was found to be the most important factor affecting the plasma performance and consequently the chemical kinetics. A 100% conversion of NO to NO2 was achieved with a graphite electrode, without using any auxiliary gas and without catalyst. Plasma performance and conversion efficiency are compared for several electrode materials.
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| 34. |
- Baránková, Hana, et al.
(author)
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Optimization and performance of atmospheric Fused Hollow Cathodes
- 2013
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 87, s. 128-131
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Journal article (peer-reviewed)abstract
- Experimental results on the atmospheric hollow cathode plasma generation and performance, using a special configuration with tunable wall separations, are presented. The influence of the gas and type of the power used for generation on the optimum size of the cathode slit is investigated. The experimental results are in agreement with the hollow cathode model. The plasma source/plasma reactor design is of utmost importance for control of plasma-chemical kinetics. An example of the atmospheric hollow cathode plasma application for the NOx conversion is given. The energy consumption and plasma characteristics are discussed.
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| 35. |
- Barankova, Hana, et al.
(author)
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Reactive Deposition of TiN Films by Magnetron with Magnetized Hollow Cathode Enhanced Target
- 2018
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 152, s. 123-127
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Journal article (peer-reviewed)abstract
- Magnetized Hollow Cathode Activated Magnetron in which the target is coupled with the hollow cathode magnetized by the magnetic field of the magnetron was tested in the reactive process of TiN deposition. Increased deposition rate compared to the Ti metal deposition rate was confirmed. The depositions as well as optical measurements were performed at several pressures in the reactor. The results of the TiN reactive deposition are presented and discussed, including the TiN deposition in pure nitrogen.
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| 36. |
- Bardos, Ladislav, et al.
(author)
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Plasma processes at atmospheric and low pressures
- 2008
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In: Vacuum. - Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom : Elsevier Ltd. - 0042-207X .- 1879-2715. ; 83:3, s. 522-527
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Journal article (peer-reviewed)abstract
- In the last few decades there has been an intense development in non-equilibrium ("cold") plasma surface processing systems at atmospheric pressure. This new trend is stimulated mainly to decrease equipment costs by avoiding expensive pumping systems of conventional low-pressure plasma devices. This work summarizes physical and practical limitations where atmospheric plasmas cannot compete with low-pressure plasma and vice-versa. As the processing conditions for atmospheric plasma are rather different from reduced pressure systems in many cases these conditions may increase final equipment costs substantially. In this work we briefly review the main principles, advantages and drawbacks of atmospheric plasma for a better understanding of the capabilities and limitations of the atmospheric plasma processing technology compared with conventional low-pressure plasma processing. 2008 Elsevier Ltd. All rights reserved.
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| 37. |
- Bardos, Ladislav, et al.
(author)
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Radio frequency powered spiral hollow cathodes
- 2020
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In: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 175
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Journal article (peer-reviewed)abstract
- Potential usage of the radio frequency (RF) spiral hollow electrodes in comparison with the compact hollow cathodes was examined for coating and other surface processing treatments. Most properties were found similar to the compact RF hollow cathodes. The non-conventional shapes of spiral hollow cathodes can be suitable for the inner coating in narrow tubes and pipes. Small diameter spiral cathodes can generate focused high-density ion flux capable of rapid etching of the substrate.
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| 38. |
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| 39. |
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| 40. |
- Batool, S S, et al.
(author)
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Silica nanofibers based impedance type humidity detector prepared on glass substrate
- 2013
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In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 87, s. 1-6
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Journal article (peer-reviewed)abstract
- Impedance type relative humidity detector is fabricated by depositing electrospun silica nanofibers on glass substrate. The silica nanofibers with an average diameter similar to 150 nm and length similar to 100 mu m were used. Thermogravimetric and differential scanning calorimetric analysis confirm that the accurate annealing temperature is 500 degrees C for complete removal of PVP. Humidity detecting devices were fabricated by defining titanium electrodes on top of the silica nanofibers. The performance of silica nanofibers humidity detectors was tested by AC electrical measurements at 40-90% relative humidity. The response and the recovery times were 5 s and 3 s, respectively, between 40% and 90% relative humidity. Contribution of dipoles, space charge polarization, relaxation of these dipoles and low frequency dispersion phenomenon were observed during impedance measurements.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
- Beshkova, M., et al.
(author)
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Device applications of epitaxial graphene on silicon carbide
- 2016
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In: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 128, s. 186-197
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Research review (peer-reviewed)abstract
- Graphene has become an extremely hot topic due to its intriguing material properties allowing for ground-breaking fundamental research and applications. It is one of the fastest developing materials during the last several years. This progress is also driven by the diversity of fabrication methods for graphene of different specific properties, size, quantity and cost. Graphene grown on SiC is of particular interest due to the possibility to avoid transferring of free standing graphene to a desired substrate while having a large area SiC (semi-insulating or conducting) substrate ready for device processing. Here, we present a review of the major current explorations of graphene on SiC in electronic devices, such as field effect transistors (FET), radio frequency (RF) transistors, integrated circuits (IC), and sensors. The successful role of graphene in the metrology sector is also addressed. Typical examples of graphene on SiC implementations are illustrated and the drawbacks and promises are critically analyzed. (C) 2016 Elsevier Ltd. All rights reserved.
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| 45. |
- Beshkova, Milena, et al.
(author)
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Low-pressure sublimation epitaxy of AlN films - growth and characterization
- 2004
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In: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 76, s. 143-146
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Journal article (peer-reviewed)abstract
- Epitaxial layers of aluminum nitride have been grown at temperatures 1900-2400degreesC on 10 x 10 mm(2) 4H-SiC substrate via sublimation recondensation in an RF heated graphite furnace. The source material was polycrystalline sintered AlN. A maximum growth rate of about 100 mum/h was achieved at 2400degreesC and seed to source distance of 1 mm. The surface morphology reflects the hexagonal symmetry of the seed suggesting an epitaxial growth. This was confirmed by X-ray diffraction (XRD). The spectra showed very strong and well-defined (0002) reflection position at around 36.04degrees in symmetric Theta-2Thetascans for all samples. Micro-Raman spectroscopy reveals that the films have a wurtzite structure. It is evidenced by the appearance of the A(1) (TO) (at 601 cm(-1)) and E-2((2)) (at 651 cm(-1)) lines in the spectra. Secondary-ion mass spectroscopy (SIMS) results showed a low concentration of carbon incorporation in the AlN films. A correlation between the growth conditions and properties of the AlN layers was established.
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| 46. |
- Beshkova, Milena, et al.
(author)
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Properties and potential applications of two-dimensional AlN
- 2020
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In: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 176
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Research review (peer-reviewed)abstract
- The success of Graphene has triggered the research interest in other stable, single and few-atom-thick layers of van der Waals materials, which can possess attractive and technologically useful properties. Other complex structures, such as boron nitride, MXenes and metal chalcogenides have been successfully synthesized as layered materials showing advanced properties. Here, after an introduction briefing novel 2D materials, we focus on 2D AlN and present a review covering theoretical considerations on the stability of an infinite hexagonal AlN (h-AlN) sheet, differences that occur in the electronic structure between bulk AlN and single layer and discuss possible methods of tuning their electronic and magnetic properties by manipulating the surface and strain using DFT (density functional theory) computations. We address potential applications of 2D-AlN with an emphasis on gas sensing for CO2, CO, H-2, O-2, NO and NO2 in the presence of NH3. Further, we discuss some growth strategies of AlN single layer and few layers on different substrates. 2D AlN layers and nanotubes with ultrawide bandgap (9.20-9.60 eV) which shows a great potential to support innovative and front-end development of deep-ultraviolet optoelectronic devices are illustrated.
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| 47. |
- Beshkova, Milena, et al.
(author)
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Sublimation epitaxy of 3C-SiC grown at Si- and C-rich conditions
- 2012
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In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 86:10, s. 1595-1599
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Journal article (peer-reviewed)abstract
- 3C-SiC layers have been grown by using sublimation epitaxy at a source temperature of 2000 degrees C, under vacuum conditions (andlt;10(-5) mbar) on well oriented (on-axis) 6H-SiC (0001) substrates. Close space sublimation growth geometry has been used in a RF-heated furnace employing high-purity graphite crucible with a possibility to change the growth environment from Si vapor-rich to C vapor-rich. The optical microscopy in transmission mode reveals continuous 3C-domains for 3C-SiC with less than 0.4% 6H-inclusions for the layer grown at Si-rich conditions, and separate 3C-SiC domains for the layer grown at C-rich conditions. The type of 6H-inclusions for layers with continuous domain structure investigated by Atomic Force Microscopy (AFM) is discussed. 2Theta-omega scan shows 0006 and 111 peaks coming from the substrate and the layer, respectively with a higher intensity of the 111 peak for 3C-SiC grown at Si-rich conditions which is related with the continuous character of the 3C-SiC domains.
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| 48. |
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| 49. |
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| 50. |
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