| 1. |
- Marinova, Ts., et al.
(författare)
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Nickel based ohmic contacts on SiC
- 1997
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Ingår i: Materials Science and Engineering B. - 0921-5107. ; 46:1-3, s. 223-226
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Tidskriftsartikel (refereegranskat)abstract
- We have compared the chemical and structural properties of Ni/SiC and Ni2Si/SiC interfaces. In the case of Ni/SiC, the contact formation is initiated by the dissociation of SiC, due to the strong reactivity of nickel at 950 °C. Ni2Si is formed and carbon accumulates, both at the interface and throughout the metal layer. At the interface, many Kirkendall voids are observed by TEM. Despite this poor interface morphology, low contact resistances have been measured. But the presence of carbon in the contact layer and at the interface is a potential source of contact degradation at high temperature. In the case of Ni/Si multilayers evaporated on SiC instead of pure Ni, the contact formation is preceded by Ni and Si mutual diffusion in the deposited layer yielding Ni2Si. Therefore, a smaller amount of carbon is released from SiC. Low carbon segregation, abrupt interface and low contact resistance characterize this contact. The thermal stability of Ni2Si contacts is illustrated with ageing experiments carried out at 500 °C.
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| 2. |
- Radnoczi, G., et al.
(författare)
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Structure of DC sputtered Si-C-N thin films
- 2003
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 440:1-2, s. 41-44
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Tidskriftsartikel (refereegranskat)abstract
- Si-C-N films of maximum 65 at.% of Si and maximum 40 at.% of N were prepared by reactive magnetron sputtering and their fine structure was investigated by high-resolution transmission electron microscopy. For compositions, where C-C and C-N bonds prevail, the films had anisotropic structure on the atomic scale, composed of curved graphitic layers, aligned parallel to the substrate normal. An isotropic structure was detected in the middle of the compositional triangle. On a larger scale, a columnar morphology, aligned in the direction of the deposition flux was formed in films containing more than 15 at.% of Si. Singular or simultaneous appearance of the above structures depended on film composition. © 2003 Elsevier B.V. All rights reserved.
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| 3. |
- Riascos, Henry, 1999-, et al.
(författare)
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Structure and properties of pulsed-laser deposited carbon nitride thin films
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 497:1-2, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride (CNx) thin films were deposited on silicon (100) and (111) substrates at 300 °C by laser ablation of a graphite target using a pulsed Nd:YAG laser in a nitrogen atmosphere. The composition and structural properties of the films were investigated as functions of gas pressure and laser fluence. X-ray photoelectron spectroscopy (XPS) revealed a strong dependence of the amount of structurally incorporated nitrogen upon gas pressure. A maximum was observed at the highest laser fluence of 10 J/cm2 and at an intermediate pressure of 4 Pa. Further analyses of the XPS N 1s core level spectra of the CNx films, exhibiting the highest elasticity in nanoindentation experiments, revealed a typical double-peak arrangement; most pronounced for the highest laser fluence at low pressures. These two peak components indicate that the nitrogen bonded onto a graphitic structure dominates over the two-fold coordinated pyridine-like bonding configuration. This favors the growth of intersecting corrugated graphene structures that may be considered to have “fullerene-like” microstructures. Additionally, Fourier Transformed Infrared Spectroscopy analyses of films deposited at different pressures show the presence of 2229 and 2273 cm− 1 stretching peaks associated with CN triple bonds (CN) of nitriles and isocyanides, 1640 cm− 1 and 1545 cm− 1 associated with the CC and CN and a peak at 1730 cm− 1, which is connected to the CO carbonyls groups. Films grown at 0.66 Pa revealed the strongest CN peak.
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| 4. |
- Birch, J., et al.
(författare)
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Growth and structural characterization of single-crystal (001) oriented Mo V superlattices
- 1990
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Ingår i: Vacuum. - 0042-207X. ; 41:4-6, s. 1231-1233
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Tidskriftsartikel (refereegranskat)abstract
- Dual target magnetron sputtering has been used to grow single-crysal MoV superlattice structures (SLS) with modulation wavelengths λ ranging from 0.6 to 17.7 nm on (001) oriented MgO substrates held at temperatures Ts between 600 and 900°C. High resolution cross-sectional transmission electron microscopy (HRXTEM) images and comparisions between experimental and calculated X-ray diffraction (XRD) spectra show that SLS with an interface sharpness of ±1 monolayer (±0.15 nm) could be grown for λ ⩽ 4.9 nm and Ts ⩽ 700°C whereas interdiffusion broadened the interfaces for higher Ts values. This interface sharpness was also verified by growing SLS with λ = 0.6 nm (one unit cell of Mo and one of V) which exhibited strong superlattice satellites in both XRD and selected area electron diffraction (SAED), and contrast from the individual layers was also observed in HRXTEM images. For λ > 4.9 nm, HRXTEM images showed non-uniform layers and the XRD peak width (FWHM) increased by 250%.
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| 5. |
- Birch, J., et al.
(författare)
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Structural characterization of precious-mean quasiperiodic Mo/V single-crystal superlattices grown by dual-target magnetron sputtering
- 1990
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Ingår i: Physical Review B. - 1098-0121. ; 41:15, s. 10398-10407
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Tidskriftsartikel (refereegranskat)abstract
- A class of quasiperiodic superlattice structures, which can be generated by the concurrent inflation rule A→AmB and B→A (where m=positive integer), has been studied both theoretically and experimentally. Given that the ratios between the thicknesses of the two superlattice building blocks, A and B, are chosen to be γ(m)=[m+(m2+4)1/2]/2 (known as the ‘‘precious means’’), then the x-ray- and electron-diffraction peak positions are analytically found to be located at the wave vectors q=2πΛ−1r[γ(m)]k, where r and k are integers and Λ is an average superlattice wavelength. The analytically obtained results have been compared to experimental results from single-crystalline Mo/V superlattice structures, generated with m=1, 2, and 3. The superlattices were grown by dual-target dc-magnetron sputtering on MgO(001) substrates kept at 700 °C. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) showed that the analytical model mentioned above predicts the peak positions of the experimental XRD and SAED spectra with a very high accuracy. Furthermore, numerical calculations of the diffraction intensities based on a kinematical model of diffraction showed good agreement with the experimental data for all three cases. In addition to a direct verification of the quasiperiodic modulation, both conventional and high-resolution cross-sectional transmission electron microscopy (XTEM) showed that the superlattices are of high crystalline quality with sharp interfaces. Based on lattice resolution images, the width of the interfaces was determined to be less than two (002) lattice-plane spacings (≊0.31 nm).
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| 6. |
- Broitman, E., et al.
(författare)
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Carbon nitride films on orthopedic substrates
- 2000
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Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 9:12, s. 1984-1991
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and tribological properties of carbon nitride (CN(X)) films deposited on orthopedic substrates are presented. CN(X) films were prepared by d.c. reactive magnetron sputtering from a graphite target in N2/Ar plasma. Films were grown on Ni and ZrO2 substrates to a thickness of ~1 µm at a total pressure of 3 mtorr and a substrate temperature of 250°C. High-resolution transmission electron microscopy (HRTEM) shows dense and homogeneous films, with 'fullerene-like' micro-structures consisting of curved, frequently intersecting, and highly in-plane oriented basal lattice planes. Nanoindentation measurements revealed a change in the mechanical properties of films treated with three different biological solutions. Spectroscopic analysis confirmed a change in the chemical structure of the treated films. The friction coefficients of CN(X) films against high speed steel (HSS), ZrO2 and Ultra-High Molecular Weight Polyethylene (UHMWPE) balls were evaluated by ball-on-disk tests in dry and lubricated conditions. In the case of dry sliding against a HSS ball, the steady state friction coefficient values are 0.22 for the film on the Ti substrate and 0.26 for the film on the ZrO2 substrate. The friction coefficients under human serum lubrication conditions were below 0.18 for the ZrO2 and UHMWPE balls. An increase in wettability of human plasma on CN(X) films was observed compared to the orthopedic surfaces, which could enhance the retention of synovial fluid on those surfaces, improving the lubrication of the bearings of total joint arthroplasty components during function. (C) 2000 Elsevier Science B.V. All rights reserved.The mechanical and tribological properties of carbon nitride (CNX) films deposited on orthopedic substrates are presented. CNX films were prepared by d.c. reactive magnetron sputtering from a graphite target in N2/Ar plasma. Films were grown on Ni and ZrO2 substrates to a thickness of approximately 1 µm at a total pressure of 3 mtorr and a substrate temperature of 250 °C. High-resolution transmission electron microscopy (HRTEM) shows dense and homogeneous films, with `fullerene-like' microstructures consisting of curved, frequently intersecting, and highly in-plane oriented basal lattice planes. Nanoindentation measurements revealed a change in the mechanical properties of films treated with three different biological solutions. Spectroscopic analysis confirmed a change in the chemical structure of the treated films. The friction coefficients of CNX films against high speed steel (HSS), ZrO2 and Ultra-High Molecular Weight Polyethylene (UHMWPE) balls were evaluated by ball-on-disk tests in dry and lubricated conditions. In the case of dry sliding against a HSS ball, the steady state friction coefficient values are 0.22 for the film on the Ti substrate and 0.26 for the film on the ZrO2 substrate. The friction coefficients under human serum lubrication conditions were below 0.18 for the ZrO2 and UHMWPE balls. An increase in wettability of human plasma on CNX films was observed compared to the orthopedic surfaces, which could enhance the retention of synovial fluid on those surfaces, improving the lubrication of the bearings of total joint arthroplasty components during function.
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| 7. |
- Broitman, E., et al.
(författare)
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Electrical and optical properties of CNx(0=x=0.25) films deposited by reactive magnetron sputtering
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:2, s. 1184-1190
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Tidskriftsartikel (refereegranskat)abstract
- The electrical and optical properties of carbon-nitride CNx films (O=x=0.25) deposited by unbalanced reactive magnetron sputtering from a graphite target in mixed Ar/N2 discharges at a substrate temperature of 350°C have been investigated. Pure C films exhibit a dark conductivity at room temperature of 250 O-1 cm-1, which grows up to 250 O-1 cm-1 for CNx films with N content of 20%. For CNx films, temperature-dependent conductivity measurements suggest that two electron conduction processes exist in the investigated temperature range 130
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| 8. |
- Pecz, B, et al.
(författare)
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Structural investigation of SiC epitaxial layers grown under microgravity and on-ground conditions
- 1999
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 357:2, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- Thick 4H-, and 6H-SiC epitaxial layers have been grown by LPE from Si-Sc-C solvent at microgravity conditions during a space experiment, as well as on-ground. The samples are characterised by cross-sectional TEM and HRXRD. Layers grown at microgravity are relatively defect free, although their surfaces are always stepped. Control samples grown on-ground have similar surface appearance, but contain scandium carbide precipitates, nanopipes, micropipes and/or cavities as verified by TEM. However, none of the aforementioned defects was traced in the layers grown at microgravity conditions. So, samples grown at space microgravity conditions are superior in their defect structure to those ones grown on the ground. The defects called nanopipes can be described as empty pipes of about 200 nm diameter traversing the layer in the [0001] (growth) direction. The steps in the microgravity and on-ground samples have facets of {104} type crystallographic planes both in 6H-, and 4H-SiC. We suggest, that those facets are formed and preferred during growth due to a possible mechanism of decreasing the high energy of the growing Si terminated (0001) surface. (C) 1999 Elsevier Science S.A. All rights reserved.
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| 9. |
- Pecz, B, et al.
(författare)
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Structure of SiC layers grown by LPE in microgravity and on-ground conditions
- 1999
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Ingår i: Institute of Physics Conference Series. - 0951-3248 .- 2154-6630. ; :164, s. 243-246
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Tidskriftsartikel (refereegranskat)abstract
- High quality, hexagonal SiC layers have been grown in microgravity conditions and on-ground as well. The surface of the layers is always stepped. The dislocation density of the layers is increased closer to the surface. Scandium carbide precipitates, nanopipes and cavities were found in the SiC layers grown on-ground, but none of them were traced in the layers grown under microgravity conditions.
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| 10. |
- Radnoczi, G., et al.
(författare)
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Defect formation in al-doped SI(100) films grown by molecular-beam epitaxy and solid-phase epitaxy
- 1989
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Ingår i: Institute of Physics Conference Series. - 0951-3248. ; :100, s. 235-240
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Tidskriftsartikel (refereegranskat)abstract
- Aluminium doped Si layers grown either by solid phase epitaxy (SPE) or molecular beam epitaxy (MBE) have been investigated over wide ranges of Al fluxes (J(Al) = 1 x 10(10)-3 x 10(13) cm-2s-1) and growth temperatures (T(s) = 500-900-degrees-C), using RHEED, LEED and AES during growth and cross section TEM of the as-deposited layers. For MBE growth, defect free films could be grown almost in the whole interval of J(Al) and T(s). In the SPE case Al is completely incorporated in the amorphous films. Upon crystallization dislocations and stacking faults/twins, as well as small voids are formed. For all concentrations and annealing temperatures TEM shows similar defect structures.
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| 11. |
- Radnóczi, G. Z., et al.
(författare)
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Growth of highly curved Al1-xinxN nanocrystals
- 2005
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:7
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Tidskriftsartikel (refereegranskat)abstract
- A materials structure is reported that is characterized by high lattice curvature assigned to a compositional gradient. The phenomenon occurs for physical vapour deposition of Al1-xInxN epitaxial thin films with directional fluxes of Al and In at kinetically limited growth conditions. According to our growth model unit cells are incorporated on the growth surfaces of emerging whiskers (nanowires) with a continuously varying lattice parameter depending on their position with respect to Al- and In-rich sides of the whisker. Such curved crystals are effectively quenched solid solutions. We present a description of this generic, self-assembled curved crystal structure and its implications. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 12. |
- Seppänen, Timo, et al.
(författare)
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Magnetron sputter epitaxy of wurtzite Al1-x Inx N (0.1
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:8, s. 083503-
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Tidskriftsartikel (refereegranskat)abstract
- Ternary wurtzite Al1-x Inx N thin films with compositions throughout the miscibility gap have been grown onto seed layers of TiN and ZrN by magnetron sputter epitaxy (MSE) using dual reactive direct current magnetron sputter deposition under ultra high vacuum conditions. The film compositions were calculated using Vegard's law from lattice parameters determined by x-ray diffraction (XRD). XRD showed that single-phase Al1-x Inx N alloy films in the wurtzite structure with [0.10 TiN,ZrN <110>. At higher substrate temperatures almost pure AlN was formed. The microstructure of the films was also investigated by high-resolution electron microscopy. A columnar growth mode with epitaxial column widths from 10 to 200 nm was observed. Rocking curve full-width-at-half-maximum measurements revealed highly stressed lattices for growth onto TiN at 600°C. Pseudobinary MSE growth phase field diagrams for Al1-x Inx N onto ZrN and TiN were established for substrate temperatures up to 1000°C. Large regimes for single-phase solid solutions were thus identified with In being the diffusing species. © 2005 American Institute of Physics.
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| 13. |
- Valcheva, E., et al.
(författare)
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Growth-induced defects in AlN/GaN superlattices with different periods
- 2003
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526.
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Konferensbidrag (refereegranskat)abstract
- MOCVD-grown AlN/GaN superlattices (SL) with different thickness of the well and barrier are investigated by transmission electron microscopy in low-magnification and high-resolution modes. Growth-induced defects are observed in some places causing different degree of disturbances of the regularity of the SLs. The SL grown with a thickness of the AlN barrier higher than the critical thickness hc for coherent growth reveals 2D growth of AlN platelets that give rise to cusps or irregularities at the interfaces. The SL with thickness of the GaN and AlN layers lower than hc is coherently grown. There is some evidence of dot-like structures formation in separate areas due to the large strain field present. © 2003 Elsevier B.V. All rights reserved.
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