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1.
The effect of bromine methanol (BM) etching and NH4F/H2O2 passivation on the Schottky barrier height between Au contact and semi-insulated (SI) p-Cd1−xZnxTe (x ≈ 0.09-0.18) was studied through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Near-infrared (NIR) spectroscopy technique was utilized to determine the Zn concentration. X-ray photoelectron spectroscopy (XPS) for surface composition analysis showed that BM etched sample surface left a Te0-rich layer, however, which was oxidized to TeO2 and the surface [Te]/([Cd] + [Zn]) ratio restored near-stoichiometry after NH4F/H2O2 passivation. According to I-V measurement, barrier height was 0.80 ± 0.02-0.85 ± 0.02 eV for Au/p-Cd1−xZnxTe with BM etching, however, it increased to 0.89 ± 0.02-0.93 ± 0.02 eV with NH4F/H2O2 passivation. Correspondingly, it was about 1.34 ± 0.02-1.43 ± 0.02 eV and 1.41 ± 0.02-1.51 ± 0.02 eV by C-V method.  相似文献   

2.
Sessile drop experiments of Ni and Ni(2at.%Al) were conducted under controlled working conditions, at 1500°C, P(O2) 10–9 Torr. It is shown that Al and oxygen atoms engaged in the capillary driven mass transport at the interface have a significant impact on the surface/interface thermodynamics. The surface energy of liquid Ni determined from experiments in which Ni comes into contact with Al2O3 is significantly lower than that of high purity Ni, due to the segregation of Al. The free energy of segregation of Al to the free surface of Ni ( G S) was found to range from –164 to –152 kJ/mol, indicating a relatively strong tendency for segregation of Al to the free surface of Ni(Al). It is proposed that an Al(O)-rich liquid layer forms adjacent to the Ni-Al2O3 interface, which improves interfacial adhesion. In the Ni(Al)-Al2O3 system, an increase in the Al content of the alloy leads to the improvement of both wetting and adhesion of the alloy on the ceramic, correlating with the improvement in the interface strength after solidification.  相似文献   

3.
Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 °C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current-voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current-voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 °C. The surface of Au and Ti/Au contacts annealed at 900 °C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 °C. X-ray diffraction examinations showed, that new Ti2N, Au2Ga and Ga3Ti2 interface phases formed in Ti/Au contact at 900 °C, new Ti2N phase formed in Ti/Al contact at 700 and 900 °C, as well as new AlN interface phase developed in Ti/Al contact at 900 °C.  相似文献   

4.
Au nanoclusters have been deposited on Si(0 0 1) surfaces by sputtering of a metallic Au target using an Ar plasma. Different wet and dry treatments of the Si(0 0 1) surface, including dipping in HF solution and exposure to H2 and N2 plasmas, have been applied and the effects of these treatments on the Au nanoparticles/Si interface, the Au nanoclusters aspect ratio and the surface plasmon resonance (SPR) energy and amplitude are investigated exploiting spectroscopic ellipsometry and atomic force microscopy. It is found that the Au nanoclusters aspect ratio depends on the extent of the Au-Si intermixing. The thicker the Au-Si interface layer, the larger the Au nanoparticles aspect ratio and the red-shift of the SPR peak. Furthermore, SiO2 and the H2 plasma treatment inhibit the Si-Au intermixing, while HF-dipping and the N2 plasma treatment favour Au-Si intermixing, yielding silicide formation which increases the Si wetting by Au.  相似文献   

5.
X-ray photoelectron spectroscopy (XPS) has been used to characterize the oxidation of a clean Ni(Pt)Si surface under two distinct conditions: exposure to a mixed flux of atomic and molecular oxygen (O + O2; PO+O2 = 5 × 10−6 Torr) and pure molecular oxygen (O2; PO2 = 10−5 Torr) at ambient temperatures. Formation of the clean, stoichiometric (nickel monosilicide) phase under vacuum conditions results in the formation of a surface layer enriched in PtSi. Oxidation of this surface in the presence of atomic oxygen initially results in formation of a silicon oxide overlayer. At higher exposures, kinetically limited oxidation of Pt results in Pt silicate formation. No passivation of oxygen uptake of the sample is observed for total O + O2 exposure <8 × 104 L, at which point the average oxide/silicate overlayer thickness is 23 (3) Å (uncertainty in the last digit in parentheses). In contrast, exposure of the clean Ni(Pt)Si surface to molecular oxygen only (maximum exposure: 5 × 105 L) results in slow growth of a silicon oxide overlayer, without silicate formation, and eventual passivation at a total average oxide thickness of 8(1) Å, compared to a oxide average thickness of 17(2) Å (no silicate formation) for the as-received sample (i.e., exposed to ambient.) The aggressive silicon oxidation by atomic oxygen, results in Ni-rich silicide formation in the substrate and the kinetically limited oxidation of the Pt.  相似文献   

6.
The effect of alloy surface roughness, achieved by different degrees of surface polishing, on the development of protective alumina layer on Fe-10 at.% Al alloys containing 0, 5, and 10 at.% Cr was investigated during oxidation at 1000 °C in 0.1 MPa oxygen. For alloys that are not strong Al2O3 formers (Fe-10Al and Fe-5Cr-10Al), the rougher surfaces increased Fe incorporation into the overall surface layer. On the Fe-10Al, more iron oxides were formed in a uniform layer of mixed aluminum- and iron-oxides since the layer was thicker. On the Fe-5Cr-10Al, more iron-rich nodules developed on an otherwise thin Al2O3 surface layer. These nodules nucleated preferentially along surface scratch marks but not on alloy grain boundaries. For the strong Al2O3-forming Fe-10Cr-10Al alloy, protective alumina surface layers were observed regardless of the surface roughness. These results indicate that the formation of a protective Al2O3 layer on Fe-Cr-Al surfaces is not dictated by Al diffusion to the surface. More cold-worked surfaces caused an enhanced Fe diffusion, hence produced more Fe-rich oxides during the early stage of oxidation.  相似文献   

7.
Jooho Kim  Bruce E. Koel 《Surface science》2006,600(19):4622-4632
Nanosized gold particles supported on reducible metal oxides have been reported to show high catalytic activity toward CO oxidation at low temperature. This has generated great scientific and technological interest, and there have been many proposals to explain this unusual activity. One intriguing explanation that can be tested is that of Nørskov and coworkers [Catal. Lett. 64 (2000) 101] who suggested that the “unusually large catalytic activity of highly-dispersed Au particles may in part be due to high step densities on the small particles and/or strain effects due to the mismatch at the Au-support interface”. In particular, their calculations indicated that the Au(2 1 1) stepped surface would be much more reactive towards O2 dissociative adsorption and CO adsorption than the Au(1 1 1) surface. We have now studied the adsorption of O2 and O3 (ozone) on an Au(2 1 1) stepped surface. We find that molecular oxygen (O2) was not activated to dissociate and produce oxygen adatoms on the stepped Au(2 1 1) surface even under high-pressure (700 Torr) conditions with the sample at 300-450 K. Step sites do bind oxygen adatoms more tightly than do terrace sites, and this was probed by using temperature programmed desorption (TPD) of O2 following ozone (O3) exposures to produce oxygen adatoms up to a saturation coverage of θO = 0.90 ML. In the low-coverage regime (θO ? 0.15 ML), the O2 TPD peak at 540 K, which does not shift with coverage, is attributed to oxygen adatoms that are bound at the steps on the Au(2 1 1) surface. At higher coverages, an additional lower temperature desorption peak that shifts from 515 to 530 K at saturation coverage is attributed to oxygen adsorbed on the (1 1 1) terrace sites of the Au(2 1 1) surface. Although the desorption kinetics are likely to be quite complex, a simple Redhead analysis gives an estimate of the desorption activation energy, Ed, for the step-adsorbed oxygen of 34 kcal/mol and that for oxygen at the terraces near saturation coverage of 33 kcal/mol, values that are similar to others reported on Au surfaces. Low Energy Electron Diffraction (LEED) indicates an oxygen-induced step doubling on the Au(2 1 1) surface at low-coverages (θO = 0.08-0.17 ML) and extensive disruption of the 2D ordering at the surface for saturation coverages of oxygen (θO ? 0.9 ML). Overall, our results indicate that unstrained step sites on Au(2 1 1) surfaces of dispersed Au nanoparticles do not account for the novel reactivity of supported Au catalysts for CO oxidation.  相似文献   

8.
The atomic arrangement and distribution of oxides (Cr2O3, NiCr2O4 and NiO) on the sprayed-NiCoCrAlY coating after oxidation are analyzed. The formation and the growth model of Ni-Cr oxide phases are discussed according to the matching relationship between atoms. The outline character and a scale of spinel NiCr2O4 are discussed. The results show that Cr atoms can form two close-packed arrangements in the crystal plane of Cr2O3 perpendicular to 〈0 0 1〉 orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni3Al in {1 1 1} crystal face. This suggests that Ni/Ni3Al is the substrate for Cr2O3 to grow along 〈0 0 1〉 direction. The lattice mismatch between Cr2O3 and Ni/Ni3Al is less than that of Al2O3, which indicates that Cr2O3 is easier to form than Al2O3 during the oxidation process. The atomic spacing in another close-packed arrangement of Cr2O3 perpendicular to 〈0 0 1〉 orientation is approximately equal to that of Ni or Cr in the plane of NiCr2O4 and NiO perpendicular to 〈1 1 1〉 orientation. So Cr2O3 can be the substrate for NiCr2O4 and NiO to grow in the 〈0 0 1〉 direction. NiCr2O4 and NiO can grow directly along the 〈1 1 1〉 orientation on each other. NiCr2O4 can grow outward in the planes of Cr2O3 perpendicular to 〈0 0 1〉 and grow inward along 〈1 1 1〉 orientation of NiO.  相似文献   

9.
The annealing temperature dependence of contact resistance and layer stability of ZrB2/Ti/Au and Ni/Au/ZrB2/Ti/Au Ohmic contacts on p-GaN is reported. The as-deposited contacts are rectifying and transition to Ohmic behavior for annealing at ≥750 °C, a significant improvement in thermal stability compared to the conventional Ni/Au Ohmic contact on p-GaN, which is stable only to <600 °C. A minimum specific contact resistance of ∼2 × 10−3 Ω cm−2 was obtained for the ZrB2/Ti/Au after annealing at 800 °C while for Ni/Au/ZrB2/Ti/Au the minimum value was 10−4 Ω cm−2 at 900 °C. Auger Electron Spectroscopy profiling showed significant Ti, Ni and Zr out diffusion at 750 °C in the Ni/Au/ZrB2/Ti/Au while the Ti and Zr intermix at 900 °C in the ZrB2/Ti/Au. These boride-based contacts show promise for contacts to p-GaN in high temperature applications.  相似文献   

10.
The growth and oxidation of a thin film of Ni3Al grown on Ni(1 0 0) were studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy (EELS). At 300 K, a 12 Å thick layer of aluminium was deposited on a Ni(1 0 0) surface and subsequently annealed to 1150 K resulting in a thin film of Ni3Al which grows with the (1 0 0) plane parallel to the (1 0 0) surface of the substrate. Oxidation at 300 K of Ni3Al/Ni(1 0 0) until saturation leads to the growth of an aluminium oxide layer consisting of different alumina phases. By annealing up to 1000 K, a well ordered film of the Al2O3 film is formed which exhibits in the EEL spectra Fuchs-Kliewer phonons at 420, 640 and 880 cm−1. The LEED pattern of the oxide shows a twelvefold ring structure. This LEED pattern is explained by two domains with hexagonal structure which are rotated by 90° with respect to each other. The lattice constant of the hexagonal structure amounts to ∼2.87 Å. The EELS data and the LEED pattern suggest that the γ-Al2O3 phase is formed which grows with the (1 1 1) plane parallel to the Ni(1 0 0) surface.  相似文献   

11.
The use of a TiB2 diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25-950 °C) dependence of ohmic contact characteristics using a Ni/Au/TiB2/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500 °C . A minimum specific contact resistivity of ∼3 × 10−4 Ω cm−2 was obtained after annealing over a broad range of temperatures (800-950 °C for 60 s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB2 at 800 °C. By 900 °C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB2 diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500 °C.  相似文献   

12.
The effects of O2 plasma pretreatment on the properties of Ga-doped ZnO films on PET substrate were studied. Ga-doped ZnO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesion of PET substrate, O2 plasma pretreatment process was used prior to GZO sputtering. With increasing O2 plasma treatment time, the contact angle decreases and the RMS surface roughness increases significantly. The transmittance of GZO films on PET substrate in a wavelength of 550 nm was 70-84%. With appropriate O2 plasma treatment, the resistivity of GZO films on PET substrate was 3.4 × 10−3 Ω cm.  相似文献   

13.
We have designed a promising contact scheme to p-GaN. Au/NiOx layers with a low concentration of O in NiOx are deposited on p-GaN by reactive dc magnetron sputtering and annealed in N2 and in a mixture of O2 + N2 to produce low resistivity ohmic contacts. Annealing has been studied of NiOx layers with various contents of oxygen upon the electrical properties of Au/NiOx/p-GaN. It has been found that the Au/NiOx/p-GaN structure with a low content of oxygen in NiOx layer provides a low resistivity ohmic contact even after subsequent annealing in N2 or O2 + N2 ambient at 500 °C for 2 min.Auger depth profiles and transmission electron microscopy (TEM) micrographs reveal that while annealing in O2 + N2 ambient results in reconstruction of the initial deposited Au/NiOx/p-GaN contact structure into a Au/p-NiO/p-GaN structure, annealing in N2 brings about reconstruction into Au/p-NiO/p-GaN and Ni/p-NiO/p-GaN structures. Hence, in both cases, after annealing in N2 as well as in O2 + N2 ambient, the ohmic properties of the contacts are determined by creation of a thin oxide layer (p-NiO) on the metal/p-GaN interface. Higher contact resistivities in the samples annealed in O2 + N2 ambient are most likely caused by a smaller effective area of the contact due to creation of voids.  相似文献   

14.
Aluminum and ceramic (Al2O3) coatings were deposited onto the polymer substrate by air plasma spray (APS) to improve the mechanical properties of the polymer surface. The effect of spray parameters (current and spray distance in this paper) on the phase composition, microstructure and mechanical properties was investigated. Shear adhesion strength between the coatings and the substrates was also examined. The results indicate that the deposition parameters have a significant effect on the phase composition, microstructure and mechanical properties of as-spayed coatings. The maximum shear adhesion strength of the bond coats was 5.21 MPa with the current of 180 A and 190 mm spray distance.  相似文献   

15.
X-ray photoelectron spectroscopy was applied to study the hydroxylation of α-Al2O3 (0 0 0 1) surfaces and the stability of surface OH groups. The evolution of interfacial chemistry of the α-Al2O3 (0 0 0 1) surfaces and metal/α-Al2O3 (0 0 0 1) interfaces are well illustrated via modifications of the surface O1s spectra. Clean hydroxylated surfaces are obtained through water- and oxygen plasma treatment at room temperature. The surface OH groups of the hydroxylated surface are very sensitive to electron beam illumination, Ar+ sputtering, UHV heating, and adsorption of reactive metals. The transformation of a hydroxylated surface to an Al-terminated surface occurs by high temperature annealing or Al deposition.  相似文献   

16.
Adsorption of CO molecules and Pb atoms on the Ni(1 1 1) and Ni3Al(1 1 1) substrates is studied theoretically within an ab initio density-functional-theory approach. Stable adsorption sites and the corresponding adsorption energies are first determined for stoichiometric surfaces. The three-fold hollow sites (fcc for Pb and hcp for CO) are found most favourable on both substrates. Next, the effect of surface alloying by a substitution of selected topmost substrate atoms by Pb or Ni atoms on the adsorption characteristics is investigated. When the surface Al atoms of the Ni3Al(1 1 1) substrate are replaced by Ni atoms, the Pb and CO adsorption energies approach those for a pure Ni(1 1 1) substrate. The Pb alloying has a more substantial effect. On the Ni3Al(1 1 1) substrate, it reduces considerably adsorption energy of CO. On the Ni(1 1 1) substrate, CO binding strengthens slightly upon the formation of the Ni(1 1 1)p(2×2)-Pb surface alloy, whereas it weakens drastically when the Ni(1 1 1)-Pb surface alloy is formed.  相似文献   

17.
The characteristics of Ni/Si(1 0 0) solid-state reaction with Al addition (Ni/Al/Si(1 0 0), Ni/Al/Ni/Si(1 0 0) and Al/Ni/Si(1 0 0)) is studied. Ni and Al films were deposited on Si(1 0 0) substrate by ion beam sputtering. The solid-state reaction between metal films and Si was performed by rapid thermal annealing. The sheet resistance of the formed silicide film was measured by four-point probe method. The X-ray diffraction (XRD) was employed to detect the phases in the silicide film. The Auger electron spectroscopy was applied to reveal the element profiles in depth. The influence of Al addition on the Schottky barrier heights of the formed silicide/Si diodes was investigated by current-voltage measurements. The experimental results show that NiSi forms even with the addition of Al, although the formation temperature correspondingly changes. It is revealed that Ni silicidation is accompanied with Al diffusion in Ni film toward the film top surface and Al is the dominant diffusion species in Ni/Al system. However, no NixAly phase is detected in the films and no significant Schottky barrier height modulation by the addition of Al is observed.  相似文献   

18.
The radiation effects induced effects by electron beam (EB) treatment on the catalytic activity of Ni/γ-Al2O3 were studied for the carbon dioxide reforming of methane with different EB energy and absorbed radiation dose. Transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to determine the change in structure and surface states of Ni/γ-Al2O3 catalyst before and after the EB treatment. Higher energy EB treatment is useful for increasing the proportion of the active sites (such as Ni0 and NiAl2O4-phase) on the surface. The increase of Ni/Al-ratio indicates that the Ni dispersion on the surface increased with the EB-treatment, resulting in an increase of the active sites, which leads to improving the catalytic activity. XPS measurement also showed a decrease of the surface carbon with EB dose. The maximum 20% increase in the conversion of CO2/CH4-mixture into CO/H2 gas was observed for the catalyst treated with 2 MeV energy and 600 kGy dose of EB relative to untreated.  相似文献   

19.
Au/GaN/n-GaAs structure has been fabricated by the electrochemically anodic nitridation method for providing an evidence of achievement of stable electronic passivation of n-doped GaAs surface. The change of the electronic properties of the GaAs surface induced by the nitridation process has been studied by means of current-voltage (I-V) characterizations on Schottky barrier diodes (SBDs) shaped on gallium nitride/gallium arsenide structure. Au/GaN/n-GaAs Schottky diode that showed rectifying behavior with an ideality factor value of 2.06 and barrier height value of 0.73 eV obeys a metal-interfacial layer-semiconductor (MIS) configuration rather than an ideal Schottky diode due to the existence of GaN at the Au/GaAs interfacial layer. The formation of the GaN interfacial layer for the stable passivation of gallium arsenide surface is investigated through calculation of the interface state density Nss with and without taking into account the series resistance Rs. While the interface state density calculated without taking into account Rs has increased exponentially with bias from 2.2×1012 cm−2 eV−1 in (Ec−0.48) eV to 3.85×1012 cm−2 eV−1 in (Ec−0.32) eV of n-GaAs, the Nss obtained taking into account the series resistance has remained constant with a value of 2.2×1012 cm−2 eV−1 in the same interval. This has been attributed to the passivation of the n-doped GaAs surface with the formation of the GaN interfacial layer.  相似文献   

20.
The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (1 1 1) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along (1 1 1) direction and (1 1 1) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have low γus/γI value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have large γus/γI value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.  相似文献   

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