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1.
The electrical properties and interface chemistry of Cr/6H-SiC(0 0 0 1) contacts have been studied by current-sensing atomic force microscopy (CS-AFM) and X-ray photoelectron spectroscopy (XPS). Cr layers were vapor deposited under ultrahigh vacuum onto both ex situ etched in H2 and in situ Ar+ ion-bombarded samples. The Cr/SiC contacts are electrically non-uniform. Both the measured I-V characteristics and the modeling calculations enabled to estimate changes of the Schottky barrier height caused by Ar+ bombardment. Formation of ohmic nano-contacts on Ar+-bombarded surfaces was observed.  相似文献   

2.
Electron energy loss spectra (ELS) have been obtained from polycrystalline Cr and Cr2O3 before and after surface reduction by 2 keV Ar+ bombardment. The primary electron energy used in the ELS measurements was systematically varied from 100 to 1150 eV in order to distinguish surface versus bulk loss processes. Two predominant loss features in the ELS spectra obtained from Cr metal at 9.0 and 23.0 eV are assigned to the surface and bulk plasmon excitations, respectively, and a number of other features arising from single electron transitions from both the bulk and surface Cr 3d bands to higher-lying states in the conduction band are also present. The ELS spectra obtained from Cr2O3 exhibit features that originate from both interband transitions and charge-transfer transitions between the Cr and O ions as well as the bulk plasmon at 24.4 eV. The ELS feature at 4.0 eV arises from a charge-transfer transition between the oxygen and chromium ions in the two surface layers beneath the chemisorbed oxygen layer, and the ELS feature at 9.8 eV arises from a similar transition involving the chemisorbed oxygen atoms. The intensity of the ELS peak at 9.8 eV decreases after Ar+ sputtering due to the removal of chemisorbed oxygen atoms. Sputtering also increases the number of Cr2+ states on the surface, which in turn increases the intensity of the 4.0 eV feature. Furthermore, the ELS spectra obtained from the sputtered Cr2O3 surface exhibit features characteristic of both Cr0 and Cr2O3, indicating that Ar+ sputtering reduces Cr2O3. The fact that neither the surface- nor the bulk-plasmon features of Cr0 can be observed in the ELS spectra obtained from sputtered Cr2O3 while the loss features due to Cr0 interband transitions are clearly present indicates that Cr0 atoms form small clusters lacking a bulk metallic nature during Ar+ bombardment of Cr2O3.  相似文献   

3.
Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm2 at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm2, respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr2O3 started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm2 after annealing up to a temperature of 600 °C.  相似文献   

4.
CrNx films were deposited on stainless steel and Si (1 1 1) substrates via medium frequency magnetron sputtering in a N2 + Ar mixed atmosphere. The influence of N2 content on the deposition rate, composition, microstructure, mechanical and tribological properties of the as-deposited films was investigated by means of the X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), nanoindentation and tribometer testing. It was found that the N atomic concentration increased and the phase transformed from a mixture of Cr2N + Cr(N) to single-phase Cr2N, and then Cr2N + CrN to pure CrN phase with the increase of N2 content. The Cr 2p3/2 and N 1s of XPS spectra also confirmed the evolution of phase. Accordingly, all films exhibited a typical columnar structure which lies in the zone T of Thornton Model. The mixed Cr2N and Cr(N) phases showed low hardness and high friction coefficient. Cr2N possessed higher hardness than CrN while CrN exhibited lower friction coefficient.  相似文献   

5.
The structure and electronic properties of epitaxial grown CeO2(1 1 1) thin films before and after Ar+ bombardment have been comprehensively studied with synchrotron radiation photoemission spectroscopy (SRPES). Ar+ bombardment of the surface causes a new emission appearing at 1.6 eV above the Fermi edge which is related to the localized Ce 4f1 orbital in the reduced oxidation state Ce3+. Under the condition of the energy of Ar ions being 1 keV and a constant current density of 0.5 μA/cm2, the intensity of the reduced state Ce3+ increases with increasing time of sputtering and reaches a constant value after 15 min sputtering, which corresponds to the surface being exposed to 2.8 × 1015 ions/cm2. The reduction of CeO2 is attributed to a preferential sputtering of oxygen from the surface. As a result, Ar+ bombardment leads to a gradual buildup of an, approximately 0.69 nm thick, sputtering altered layer. Our studies have demonstrated that Ar+ bombardment is an effective method for reducing CeO2 to CeO2−x and the degree of the reduction is related to the energy and amount of Ar ions been exposed to the CeO2 surface.  相似文献   

6.
H.Y. Hu 《Applied Surface Science》2008,254(24):8029-8034
The chemical structure and site location of sulfur atoms on n-GaAs (1 0 0) surface treated by bombardment of S+ ions over their energy range from 10 to 100 eV have been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. The formation of Ga-S and As-S species on the S+ ion bombarded n-GaAs surface is observed. An apparent donor doping effect is observed for the n-GaAs by the 100 eV S+ ion bombardment. It is found that the S+ ions with higher energy are more effective in the formation of Ga-S species, which assists the n-GaAs (1 0 0) surface in reconstruction into an ordered (1 × 1) structure upon subsequent annealing. The treatment is further extended to repair Ar+ ion damaged n-GaAs (1 0 0) surface. It is found that after a n-GaAs (1 0 0) sample is damaged by 150 eV Ar+ ion bombardment, and followed by 50 eV S+ ion treatment and subsequent annealing process, finally an (1 × 1) ordering GaAs (1 0 0) surface with low surface states is obtained.  相似文献   

7.
CrSiN coatings were deposited on stainless steel (Grade: SA304) and silicon Si(1 0 0) substrates, with varying argon-nitrogen gas proportions and deposition temperature, using reactive magnetron sputtering technique in the present work. The influence of sputtering (Ar) and reactive gas proportions (N2) and temperature on the structural properties of the CrSiN coating was investigated. A small amount of silicon content (3.67 at.% Si) plays a crucial role in addition to the nitrogen content for the formation of different phases in the CrSiN coatings as observed in the present work. For example, the coating with comparatively low nitrogen content, 40% N2, during deposition, formed a crystalline structure consisting of nano-crystalline CrN which is separated by an amorphous SiN phase, as evident from X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of CrN(1 1 1) and Cr2N(1 1 1) phases has occurred at 30% N2 with 3.67% Si content, which transformed in to CrN(1 1 1) and CrN(2 0 0) with increase in N2 content but with same Si content. The surface topography and morphology of the coatings were analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), respectively. A less columnar growth is observed in CrSiN coatings deposited at low argon content, Ar:N2 (20:80), and with 3.67 at.% Si in the coatings. However, it becomes dense with increase in nitrogen content and temperature. The XRD analysis showed that the intensity of a dominating peak (1 1 1) is decreasing from (80:20) to (60:40) argon:nitrogen environment. With a further increase of nitrogen content, from (60:40), in the sputtering gas mixture, to (40:60) argon-nitrogen, there is a sudden increase in (1 1 1) peak and above (40:60), the peak reduction rate is very slow than the previous one. The (1 1 1) and (2 0 0) peak intensity variations are very limited due to high nitrogen content, above 50%, and considerable amount of Si atoms, 3.67 at.%, present in the CrN coatings.  相似文献   

8.
Amorphous Ge1−xCrx thin films are deposited on (1 0 0)Si by using a thermal evaporator. Amorphous phase is obtained when Cr concentration is lower than 30.7 at%. The electrical resistivities are 1.89×10−3–0.96×102 Ω cm at 300 K, and decrease with Cr concentration. The Ge1−xCrx thin films are p-type. The hole concentrations are 5×1016–7×1021 cm−3 at 300 K, and increase with Cr concentration. Magnetizations are 7.60–1.57 emu/cm3 at 5 K in the applied field of 2 T. The magnetizations decrease with Cr concentration and temperature. Magnetization characteristics show that the Ge1−xCrx thin films are paramagnetic.  相似文献   

9.
Surface ions generated by electron stimulated desorption from mass spectrometer ion source grids are frequently observed, but often misidentified. For example, in the case of mass 19, the source is often assumed to be surface fluorine, but since the metal oxide on grid surfaces has been shown to form water and hydroxides, a more compelling case can be made for the formation of hydronium. Further, fluorine is strongly electronegative, so it is rarely generated as a positive ion. A commonly used metal for ion source grids is 316L stainless steel. Thermal vacuum processing by bakeout or radiation heating from the filament typically alters the surface composition to predominantly Cr2O3. X-ray photoelectron spectral shoulders on the O 1s and Cr 2p3/2 peaks can be attributed to adsorbed water and hydroxides, the intensity of which can be substantially increased by hydrogen dosing. On the other hand, the sub-peak intensities are substantially reduced by heating and/or by electron bombardment. Electron bombardment diode measurements show an initial work function increase corresponding to predominant hydrogen desorption (H2) and a subsequent work function decrease corresponding to predominant oxygen desorption (CO). The fraction of hydroxide concentration on the surface was determined from X-ray photoelectron spectroscopy and from the deconvolution of temperature desorption spectra. Electron stimulated desorption yields from the surface show unambiguous H3O+ peaks that can be significantly increased by hydrogen dosing. Time of flight secondary ion mass spectrometry sputter yields show small signals of H3O+, as well as its constituents (H+, O+ and OH+) and a small amount of fluorine as F, but no F+ or F+ complexes (HF+, etc.). An electron stimulated desorption cross-section of σ+ ∼ 1.4 × 10−20 cm2 was determined for H3O+ from 316L stainless steel for hydrogen residing in surface chromium hydroxide.  相似文献   

10.
We report the evolution of photoluminescence (PL) of Si nanocrystals (nc-Si) embedded in a matrix of SiO2 during Ar+ ion bombardment. The integrated intensity of nc-Si PL falls down drastically before the Ar+ ion fluence of 1015 ions cm−2, and then decreases slowly with the increasing ion fluence. At the meantime, the PL peak position blueshifts steadily before the fluence of 1015 ions cm−2, and then changes in an oscillatory manner. Also it is found that the nc-Si PL of the Ar+-irradiated sample can be partly recovered after annealing at 800 °C in nitrogen, but can be almost totally recovered after annealing in oxygen. The results confirm that the ion irradiation-induced defects are made up of oxygen vacancies, which absorb light strongly. The oscillatory peak shift of nc-Si can be related to a size-distance distribution of nc-Si in SiO2.  相似文献   

11.
To study the ion sputtering rates of W-, Ti- and Cr-carbides, trilayer structures comprising C-graphite (59 nm)/WC (50 nm)/W (38 nm), C-graphite (56 nm)/TiC (40 nm)/Ti (34 nm) and C-graphite (46 nm)/C3C2 (60 nm)/Cr (69 nm) with a tolerance ±2% were sputter deposited onto smooth silicon substrates. Their precise structural and compositional characterization by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) revealed that the WC and Cr3C2 layers were amorphous, while the TiC layer had a polycrystalline structure. The ion sputtering rates of all three carbides, amorphous carbon and polycrystalline Cr, Ti and W layers were determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence of two symmetrically inclined 1 keV Ar+ ion beams in the range between 22° and 82°. The sputtering rates were calculated from the known thicknesses of the layers and the sputtering times necessary to remove the individual layers. It was found that the sputtering rates of carbides, C-graphite and metals were strongly angle dependent. For the carbides in the range between 36° and 62° the highest ion sputtering rate was found for Cr3C2 and the lowest for TiC, while the values of the sputtering rates for WC were intermediate. The normalized sputtering yields calculated from the experimentally obtained data for all three carbides followed the trend of theoretical results obtained by calculation of the transport of ions in solids by the SRIM code. The sputtering yields are also presented in terms of atoms/ion. Our experimental data for two ion incidence angles of 22° and 49° and reported values of other authors for C-graphite and metals are mainly inside the estimated error of about ±20%. The influence of the ion-induced surface topography on the measured sputtering yields was estimated from the atomic force microscope (AFM) measurements at the intermediate points of the corresponding layers on the crater walls formed during depth profiling.  相似文献   

12.
Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr2O3 using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and bc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr2O3). A second phase, namely θ-(Al,Cr)2O3, was revealed by XRD in the sample containing 9.60 wt% Cr2O3. The structure of mullites was refined by the Rietveld method, location of Cr3+ was performed by the EPR spectroscopy. At low chromium doping level (Cr2O3 content less than ∼5 wt%) Cr3+ ions were substituted for Al3+ in the AlO6 octahedra of the mullite structure (M1 site). For higher doping level, Cr3+ ions were additionally substituted for Al3+ in the AlO6 octahedra of the second phase [θ-(Al,Cr)2O3 at 1400 °C, or α-(Al,Cr)2O3 at 1600 °C] which segregated in the system. Substitution of Cr3+ for Al3+ on M1 site in the mullite structure resulted in increase of average distances in (M1)O6 octahedron and decrease of average distances in T*O4 tetrahedron, while average distances in TO4 tetrahedron stayed almost constant.  相似文献   

13.
Compositionally gradient CrNx coatings were fabricated using arc ion plating by gradually increasing N2 flow rate during the deposition process. The effect of substrate bias, ranging from 0 to −250 V, on film microstructure and mechanical properties were systematically investigated with XRD, SEM, HRTEM, nanoindentation, adhesion and wear tests. The results show that substrate bias has an important influence on film microstructure and mechanical properties of gradient CrNx coatings. The coatings mainly crystallized in the mixture of hexagonal Cr2N, bcc Cr and fcc rock-salt CrN phases. N2 flow rate change during deposition results in phase changes in order of Cr, Cr + Cr2N, Cr2N, Cr2N + CrN, and CrN, respectively, along thickness direction. Phase fraction and preferred orientation in CrNx coatings vary with substrate bias, exerting an effective influence on film hardness. With the increasing of bias, film microstructure evolves from an apparent columnar structure to a highly dense one. The maximum hardness of 39.1 GPa was obtained for the coatings deposited at a bias of −50 V with a friction coefficient of 0.55. It was also found that adhesion property and wear resistance of gradient CrNx coatings were better than that of homogeneous CrN coatings.  相似文献   

14.
Low-temperature neutron diffraction measurements were carried out on a powder sample of the compound La0.75Sr0.25CrO3 in order to elucidate its magnetic structure. Rietveld analysis of the neutron diffraction data, as a function of temperature, showed that it possesses a G-type antiferromagnetic alignment of Cr spins at all temperatures below 300 K. Down to the lowest achievable temperature, viz. 17 K, the Cr site moments were found to be the weighted average of the 75% Cr3+ and 25% Cr4+ spin-only ionic moments. At 17 K, the Cr site moment was 2.71(5) μB/Cr ion. There is no observable change in the Cr–O bond lengths as a function of temperature. The tilt angles of the CrO6 octahedra marginally increase with decreasing temperature.  相似文献   

15.
A passive film was formed on electroless Ni-P coating (ENPC) in a bath of K2Cr2O7 30 g/l. XPS and electrochemical methods were employed to analyze its chemical compositions and corrosion behaviors. The potentiodynamic polarization tests indicated the corrosion current of the passivated sample was 1/30 that of as-plated ENPC. The XPS analysis illustrated the film comprised Cr, Ni and O. The film thickness was evaluated to be a few nanometers according to the sputtering rate of Ar+ ion. High-resolution XPS spectra suggested that the detected Cr in film was in the form of trivalent compounds, Cr2O3 and Cr(OH)3.  相似文献   

16.
Using a field emission gun based scanning electron microscopy, we report the formation of nanodots on the InP surfaces after bombardment by 100 keV Ar+ ions under off-normal ion incidence (30° and 60° with respect to the surface normal) condition in the fluence range of 1 × 1016 to 1 × 1018 ions cm−2. Nanodots start forming after a threshold fluence of about 1 × 1017 ions cm−2. It is also seen that although the average dot diameter increases with fluence the average number of dots decreases with increasing fluence. Formation of such nanostructured features is attributed due to ion-beam sputtering. X-ray photoelectron spectroscopy analysis of the ion sputtered surface clearly shows In enrichment of the sputtered InP surface. The observation of growth of nanodots on the Ar+-ion sputtered InP surface under the present experimental condition matches well with the recent simulation results based on an atomistic model of sputter erosion.  相似文献   

17.
A Ti-rich oxide, (Ti0.50Zr0.26Mg0.14Cr0.10)∑=1.0O1.81, was synthesized at 8.8 GPa and 1600 °C using a multi-anvil apparatus. Its crystal structure at ambient conditions and compressibility up to 10.58 GPa were determined with single-crystal X-ray diffraction. This high-pressure phase is isomorphous with cubic zirconia (fluorite-type) with space group Fm3¯m and unit-cell parameters a=4.8830(5) Å and V=116.43(4) Å3. Like stabilized cubic zirconia, the structure of (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 is also relaxed, with all O atoms displaced from the (, , ) position along 〈1 0 0〉 by 0.319 Å and all cations from the (0, 0, 0) position along 〈1 1 1〉 by 0.203 Å. No phase transformation was detected within the experimental pressure range. Fitting the high-pressure data (V vs. P) to a third-order Birch-Murnaghan EOS yields K0=164(4) GPa, K′=4.3(7), and V0=116.38(3) Å3. The bulk modulus of (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 is significantly lower than that (202 GPa) determined experimentally for cubic TiO2 or that (~210 GPa) estimated for cubic ZrO2. This study demonstrates that cubic TiO2 may also be obtained by introducing various dopants, similar to the way cubic zirconia is stabilized below 2370 °C. Furthermore, (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 has the greatest ratio of Ti4+ content vs. vacant O2− sites of all doped cubic zirconia samples reported thus far, making it a more promising candidate for the development of electrolytes in solid oxide fuel cells.  相似文献   

18.
The H2 reduced NiFe2−xCrxO4 can be used to decompose CO2 to C repeatedly. A series of nanocrystalline Ni-ferrite doping different contents of Cr3+ were synthesized by mixed ions co-precipitation method and characterized by XRD, BET and TEM. The results showed that their crystallite sizes were 1-2 nm and BET surface area changed from 220 to 285 m2/g. The evaluation of the activity and stability indicated that Ni-ferrite with 4 wt% Cr3+ dopant could be used repeatedly as many as 60 times and was transformed to FeyNi1−y (0<y<1) alloy and Fe5C2 gradually during the cycle decomposition of CO2 to carbon, especially for no Cr3+ sample. After the 60th reaction, although NiFe2O4 phase just remained 2.1 wt%, the decomposition activity of Ni-ferrite with 4 wt% Cr3+ was still 60% of initial activity. This fact suggests that nanocrystalline FeyNi1−y (0<y<1) alloy from the cycle reaction can contribute to the decomposition of CO2. The results from scanning electron microscopy (SEM), TEM and XRD show that the deposited carbon from CO2 decomposition consisted of amorphous, crystallite and carbon nanotubes.  相似文献   

19.
The aim of the present study is to demonstrate the feasibility to form well-ordered nanoholes on InP(1 0 0) surfaces by low Ar+ ion sputtering process in UHV conditions from anodized aluminum oxide (AAO) templates. This process is a promising approach in creating ordered arrays of surface nanostructures with controllable size and morphology. To follow the Ar+ ion sputtering effects on the AAO/InP surfaces, X-ray photoelectron spectroscopy (XPS) was used to determine the different surface species. In4d and P2p core level spectra were recorded on different InP(1 0 0) surfaces after ions bombardment. XPS results showed the presence of metallic indium on both smooth InP(1 0 0) and AAO/InP(1 0 0) surfaces. Finally, we showed that this experiment led to the formation of metallic In dropplets about 10 nm in diameter on nanoholes patterned InP surface while the as-received InP(1 0 0) surface generated metallic In about 60 nm in diameter.  相似文献   

20.
Compositional and chemical changes in TiO2 and Ph, Ni, Al and Ba titanates induced by bombardment with Ar+ and O 2 + ons of different energies have been studied quantitatively by XPS. An increase of preferential loss of oxygen and, in case of PbTiO3, of lead has been observed when increasing the Ar+ ion energy from 3.5 to 10 keV. Because of oxygen loss, Ti4+ species reduce to Ti3+ and Ti2+. In addition, the loss of oxygen from PbTiO3 and NiTiO3 leads to the metallic state of nickel and lead, whereas aluminium and barium in Al2TiO5 and BaTiO3 maintain their chemical state (i.e., Al3+ and Ba2+). Bombardment with OZ ions of PbTiO3 and NiTiO3 leads to a partial reduction of Pb and Ni. This metallization and the preferential loss of lead are more efficient at higher ion energies for both, O 2 + and Ar+ bombardment. The results are discussed in terms of chemical stabilities and the possibility of oxygen diffusion in the bombarded oxides.  相似文献   

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