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1.
Low density (˜μ A/ cm2) 0.48 and 1.0 keV electron beams have been used to create surface defects on a TiO 2(110) surface. These electron-beam induced defects were examined primarily by X-ray photoelectron spectroscopy (XPS) with supporting ultraviolet photoemission spectroscopy (UPS). Glancing and normal emission XPS spectra of nearly defect-free surfaces revealed that Ti atoms on the surface were similar to the bulk Ti, while some surface oxygen atoms were different from the bulk oxygen. XPS of Ti 2 p3/2 was used to quantify the defect concentration and to examine the defect electronic structure. Based on our calculation of defect concentrations and the comparison of our results with results and models from the literature, we conclude that oxygen vacancies induced by electron beams in the current study are mostly from the bridging oxygen sites, in agreement with the previous work. A range of defect concentrations with similar electronic structure, mainly composed of Ti 3+, have been induced by low-density electron beams. Beam energy and exposure were the experimental variables. The rates of defect formation at low beam exposure were beam-energy dependent, with a faster growth rate at 0.48 keV than at 1.0 keV. These defects were similar to those by thermal annealing in vacuum, but a higher concentration of defects could be obtained with longer beam exposure. However, the e-beam induced defects were different from those produced by Ar + ion bombardment since both this and previous studies have found defects produced by Ar + ion bombardment to be complex, with a variety of different local environments where oxygen and titanium surface atoms coexist. 相似文献
2.
The strong interaction between Pt and TiO 2 under oxidizing atmosphere was studied by means of X-ray photoelectron spectroscopy (XPS) and Ar + sputtering test. The results obtained show that under oxidizing atmosphere Pt 0 atoms can thermally diffuse into TiO 2 lattice and be oxidized to Pt 2+ to substitute for Ti 4+ or form the interstitial ions at 673 K. 相似文献
3.
Compositional changes induced by 3.5 keV Ar + sputtering in TiO 2, NiO, NiTiO 3 and a (TiO 2 + NiO) mixture have been quantitatively studied by XPS. Although all the samples show important changes in their stoichiometry, the extent of the decomposition depends on the compound. The stability of Ti 4+ appears to be enhanced by the presence of Nisu2+ cations which, on the other hand, are more easily reduced to Ni 0 than in pure NiO. To explain these results a redox solid state reaction between the intermediate phases formed during sputtering is proposed, which tends to preserve the most stable phases. 相似文献
4.
The lasing action of titanium-doped chrysoberyl crystal (Ti:BeAl 204) is related to the crystal-field levels of Ti 3+ ions at the mirror sites, for which two kinds of energy-level diagrams were suggested under different local symmetries. To ascertain which one is reasonabk, first-principle calculations are performed on the energy levels of Ti 3+ ions with four cluster models. The study supports the energy-level.diagram suggested by Sugimoto et al. under C, symmetry, but disfavors that proposed by Chiba et al. under D 2h symmetry. Moreover, the results indicate that the impurity will introduce some local lattice distortion within Cs symmetry and a reasonable distorted geometrical configuration of cluster (TiO 6) 9- is proposed, with which experimental data can be satisfactorily explained and for which various electronic properties are further presented. 相似文献
5.
以钛酸四丁酯、无水乙醇、冰醋酸为原料,在室温下用溶胶-凝胶法制备得到二氧化钛及其掺Fe样品的湿凝胶,室温放置2天后,100 ℃干燥得到干凝胶,在500 ℃下焙烧得到二氧化钛及其掺Fe的粉末状样品. 利用X射线衍射、电子顺磁共振等测试手段对样品进行分析,结果显示所得样品均为锐钛矿,Fe被引入了二氧化钛晶格中,Ti 3+氧化中心信号强度随Fe掺杂量的增加而增强,峰值向磁场减小方向小幅偏移. 在不同测试温度下, 含Fe量为0.1%的Fe-TiO 2样品中Ti 3+氧化中心信号强度随温度升高而增强,峰值也向磁场减小方向小幅偏移. 根据电子顺磁共振理论以及二氧化钛在空气中与O 2的反应解释了这些现象. 相似文献
6.
A study of the magnetic and microstructural properties of the M-type Ti 4+-doped Barium hexaferrite according to the stoichiometric formulation BaFe (12−(4/3)x)Ti xO 19 with x=0, 0.6, 0.8 and 1.0, has been reported. The XRD and magnetic analysis show a variation of the host lattice parameters and a decrease in the values of remnant magnetization and magnetic anisotropy with Ti 4+ content. The behavior of magnetic properties of materials is explained by the combined effect of the coherent rotation of the magnetic domains and the replacements of Fe 3+ by Ti 4+ ions in the octahedral and tetrahedral sites. 相似文献
7.
Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) has been used to probe the non-dissociative adsorption of N 2 on an atomically clean Pt(111) single crystal. In contradiction to a previous IRAS study of nitrogen adsorption on a Pt(111) foil at 120 K, no nitrogen infrared (IR) band was observed on a fully annealed Pt(111) surface at 90 K. Following Ar + ion bombardment, adsorption of nitrogen at 90 K produces an intense IR band at 2222 cm −1 attributed to the N---N stretching mode of molecular nitrogen adsorbed on defect sites produced by ion bombardment. Annealing the Ar + ion sputtered surface to a temperature above 750 K completely suppresses the adsorption of nitrogen at 90 K. Based on these and other results, we postulate that nitrogen adsorbs at 90 K mainly on monovacancies on platinum. We suggest that this specific adsorption occurs by sigma donation from nitrogen to the base of monovacancy sites which possess a low d-electron density compared to surface Pt atoms. 相似文献
8.
Partial electron density plots were calculated for a model SrTiO 3(100) surface with √5 × √5 ordered oxygen vacancy to examine why the bright spots of the scanning tunneling microscopy (STM) images of SrTiO 3(100) observed in ultrahigh vacuum (UHV) correspond to the oxygen vacancy sites. Possible dependence of the image on the polarity and magnitude of the bias voltage was also discussed on the basis of partial electron density plot calculations. Our study strongly suggests that the UHV STM imaging involves the lowest-lying d-block level of every two Ti 3+ centers adjacent to an oxygen vacancy, the tip-sample distance involved in the UHV STM experiments is substantially larger than that involved in typical ambient-condition STM imaging, and the Ti 4+ and Ti 3+ sites of SrTiO 3(100) are reconstructed. 相似文献
9.
The reaction of CO 2 and H 2O to form bicarbonate (HCO −3) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO 2(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO 2 only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti 4+ sites (TPD peak at 137 K) typical of the nearly perfect TiO 2(110) surface. Vibrational HREELS indicates that CO 2 is linearly bound at the latter sites with a νa(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H 2O to bridging OH groups which recombine to liberate H 2O in TPD at 490 K. No evidence for a reaction between CO 2 and H 2O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO 2 adsorption is blocked by the presence of preadsorbed H 2O, adsorbed CO 2 is displaced by postdosed H 2O, and there is little or no evidence for bicarbonate formation in either case. However, when CO 2 and H 2O are simultaneously dosed, a new CO 2 TPD state is observed at 213 K, and the 166 K state associated with CO 2 at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO 2 TPD state to a bicarbonate species. The 213 K CO 2 TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO 2+H 2O exposure. Sticking coefficient measurements suggest that CO 2 adsorption at 110 K is precursor-mediated, as is known to be the case for H 2O adsorption on TiO 2(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H 2O–CO 2 van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO 2 and H 2O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO 2, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution. 相似文献
10.
In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O + ions through discontinuous Au films adsorbed on TiO 2(110). A low energy (< 10 eV) O + ion beam is generated via electron stimulated desorption when an Au-dosed TiO 2(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO 2(110). As the Au coverage increases, the formation of Au clusters on TiO 2(110) blocks a fraction of the TiO 2 surface and the O + yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O + signal decreases at a faster rate than the TiO 2 open area fraction. We attribute the attenuation of the O + yield for high Au coverages mainly to blocking of O + by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O + and neighboring Au clusters. 相似文献
11.
The oxygen ion conductivity of Y 2O 3---Nb 2O 5 with a fluorite-like structure was studied. Substitutional solid solutions of Nb 2 O 5 in Y 2O 3 lattice formed the defect fluorite phase and remarkably enhanced the oxygen ion conductivity. Doping with tetravalent cations, especially Ti 4+ or Ce 4+, in yttria-niobia oxide is effective in enhancing the oxygen ion conductivity. Although the n-type semiconducting property appeared below PO2 = 10 −18 atm at 1243 K, the yttria-niobia mixed oxide doped with Ce 4+, Ti 4+, and Zr 4+ stably exhibited oxygen-ion conduction in the wide range of oxygen partial pressures studied. 相似文献
12.
Direct evidence is presented that vapor-phase crystal growth is induced on solid surfaces bombarded with inert-gas ions. Surface cones formed on AlGaAs/GaAs superlattice targets exposed to a few keV Ar + ions were characterized as polycrystalline cone tips protruding beyond the original target surface. Fine particles were also found to grow in close vicinity to the cone evolution sites, thus demonstrating that target atoms ejected from the impact area condensed into polycrystalline cone tips and particles, as a result of an enhanced particle supply to the projected areas. Since this finding is not within the current knowledge of ion-solid interactions, a new theoretical approach is required for its interpretation. 相似文献
13.
Clean and K-covered Ni surfaces are bombarded with low energy (10–500 eV) beams of He +, Ne +, Ar 2+, and Kr + ions, and the emitted ion yield is measured as a function of beam energy. The apparent threshold energies for K + and Ni + emission are proportional to the ionic binding energies of K + and Ni + to the Ni surface. From comparison of the ion and neutral yield curves, it is suggested that these ions are emitted via momentum transfer collisions similar to neutral sputtering. 相似文献
14.
The dominant Ti 3+ trapped electron center in flux-grown RbTiOPO 4 (RTP) crystals has been characterized using electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR). This center is produced during an X-ray irradiation at room temperature when a Ti 4+ ion traps an electron and becomes a Ti 3+ ion, and is best studied in the 30–40 K range. The EPR spectrum contains a three-line hyperfine pattern from two nearly equivalent neighboring 31P nuclei, along with hyperfine lines from the 47Ti and 49Ti nuclei. The g matrix, determined from the angular dependence of the EPR spectrum, has principal values of 1.819, 1.889, and 1.947. Hyperfine matrices for four 31P nuclei are obtained from the angular dependence of the ENDOR spectrum. The proposed model for this defect is a Ti 3+ ion adjacent to an oxygen vacancy at an OT position. Analogies are made to a similar Ti 3+ center in KTiOPO 4 (KTP) crystals. 相似文献
15.
The temperature effects on sub-monolayers of V deposited at the TiO 2(001) surface have been studied by ultraviolet and X-ray photoelectron spectroscopies, UPS and XPS, from 300 up to 623 K. V coverages, Θv, between 0.2 and 0.7 monolayers (ML) were deposited by an e-beam evaporator at 300 K. The V 2p3/2 core line region exhibits two well-defined components whose relative intensity depends on Θv. These two components, assigned to different oxidation states of V, are correlated with two features, with a dominant V 3d character, detected within the TiO2(001) band gap of the UPS valence band spectra. UPS and XPS measurements performed after in-situ thermal treatments show unambiguous and reproducible changes of these spectral components. After annealing at 623 K only the higher binding energy component is present in the V 2p3/2 spectra; the Ti 2p core lines recover the typical symmetry of the clean and stoichiometric TiO2(001) surface and the higher binding energy feature only is detected in the TiO2 band gap. These data suggest that, within the volume probed by XPS and UPS, Ti ions have a mainly d0 configuration, while V has a single and stable open-shell configuration, as revealed by the significant intensity detected within the TiO2 band gap. These annealing-induced changes are due, as suggested by the O 1s/Ti 2p core line intensity trend, to an oxygen diffusion from the TiO2 bulk to the surface. Finally, a detailed analysis of the data indicates that different V/TiO2(001) interfaces exhibit different behaviours after annealing treatments, depending on Θv. For Θv = 0.7 ML, V interdiffuses into the TiO2 sub-surface layers, whereas for Θv = 0.2 ML it remains at the surface. This finding is consistent with a rearrangement of V atoms. which under annealing occupy first the energetically most favorable surface sites (Θv = 0.2 ML) before interdiffusing into the TiO2 lattice (Θv = 0.7 ML). 相似文献
16.
Palladium overlayers deposited on TiO 2(110) by metal vapour deposition have been investigated using LEED, XPS and FT-RAIRS of adsorbed CO. Low coverages of palladium (<3 ML) deposited at 300 K adsorb CO exclusively in a bridged configuration with a band (B 1 at 1990 cm −1) characteristic of CO adsorption on Pd(110) and Pd(100) surfaces. When annealed to 500 K, XPS and LEED indicate the nucleation of Pd particles on which CO adsorbs predominantly as a strongly bound linear species which we associate with edge sites on the Pd particles (L* band at 2085 cm −1). Both bridged and linear CO bands are exhibited as increases in reflectivity at the resonant frequency, indicating the retention of small particle size during the annealing process. Palladium overlayers of intermediate coverages (10–20 ML) deposited at 300 K undergo some nucleation during growth, and adsorbed CO exhibits both absorption and transmission bands in the B 1 (1990 cm −1) and B 2 (1940 cm −1) regions. The latter is associated with the formation of Pd(111) facets. Highly dispersed Pd particles are produced on annealing at 500 K. This is evidenced by the dominance of transmission bands for adsorbed CO and a significant concentration of edge sites, which accommodate the strongly bound linear species at 300 K. Adsorption of CO at low temperature also allows the identification of the constituent faces of Pd and the conversion of Pd(110)/(100) facets to Pd(111) facets during the annealing process. High coverages of palladium (100 ML) produce only absorption bands in FT-RAIRS of adsorbed CO associated with the Pd facets, but annealing these surfaces also shows a conversion to Pd(111) facets. LEED indicates that at coverages above 10 ML, the palladium particles exhibit (111) facets parallel to the substrate and aligned with the TiO 2(110) unit cell, and that this ordering in the particles is enhanced by annealing. 相似文献
17.
A complete understanding of the electrical and optical properties of all the Ti-related levels is deduced from a number of different characterization techniques performed on several types of Ti-doped GaP materials (n-type, p-type and semi-insulating) grown by LEC. The Ti 3+ /Ti 4+ donor level and the Ti 2+ /Ti 3+ acceptor level are found at Ev + 0.92 and about Ec - 0.56 eV, respectively. Likewise, a comprehensive scheme of the two internal transitions 3T 2→ 3A 2 of the Ti 2+ charge state and 2T 2→ 2E of the Ti 3+ charge state is given. 相似文献
18.
In order to obtain a comprehensive understanding of both thermodynamics and kinetics of water dissociation on TiO 2, the reactions between liquid water and perfect and defective rutile TiO 2 (110) surfaces were investigated using ab initio molecular dynamics simulations. The results showed that the free-energy barrier (~4.4 kcal/mol) is too high for a spontaneous dissociation of water on the perfect rutile (110) surface at a low temperature. The most stable oxygen vacancy (V o1) on the rutile (110) surface cannot promote the dissociation of water, while other unstable oxygen vacancies can significantly enhance the water dissociation rate. This is opposite to the general understanding that V o1 defects are active sites for water dissociation. Furthermore, we reveal that water dissociation is an exothermic reaction, which demonstrates that the dissociated state of the adsorbed water is thermodynamically favorable for both perfect and defective rutile (110) surfaces. The dissociation adsorption of water can also increase the hydrophilicity of TiO 2. 相似文献
19.
First-principles calculations based on density functional theory and the pseudopotential method have been used to investigate the energetics of H 2O adsorption on the (110) surface of TiO 2 and SnO 2. Full relaxation of all atomic positions is performed on slab systems with periodic boundary conditions, and cases of full and half coverage are studied. Both molecular and dissociative (H 2O→OH −+H −) adsorption are treated, and allowance is made for relaxation of the adsorbed species to unsymmetrica configurations. It is found that for both TiO 2 and SnO 2 an unsymmetrical dissociated configuration is the most stable. The symmetrical molecularly adsorbed configuration is unstable with respect to lowering of symmetry, and is separated from the fully dissociated configuration by at most a very small energy barrier. The calculated dissociative adsorption energies for TiO 2 and SnO 2 are in reasonable agreement with the results of thermal desorption experiments. Calculated total and local electronic densities of states for dissociatively and molecularly adsorbed configurations are presented, and their relation with experimental UPS spectra is discussed. 相似文献
20.
First-principles calculations based on density functional theory in the generalised gradient approximation, together with pseudopotentials and plane-wave basis sets, have been used to investigate the energetics of oxygen adsorption on stoichiometric and weakly and strongly reduced SnO 2(1 1 0) surfaces. It is shown that, if the surface species formed by oxygen adsorption are restricted to be charge neutral, then oxygen cannot be exothermically adsorbed from the gas phase on the stoichiometric surface. A variety of molecular and dissociative modes of adsorption are examined on the reduced surface produced by removing all bridging oxygens and on the weakly reduced surface that results from removal of only a fraction of these oxygens, with the adsorbed species being in both the singlet and the triplet states, and we identify a number of modes not discussed before in the literature. We use the calculated adsorption energies to propose a tentative assignment of these adsorption modes to the peaks observed in temperature programmed desorption experiments on the SnO 2 and TiO 2(1 1 0) surfaces. 相似文献
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