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1.
Atomic oxygen coverages of up to 1.2 ML may be cleanly adsorbed on the Au(111) surface by exposure to O 3 at 300 K. We have studied the adsorbed oxygen layer by AES, XPS, HREELS, LEED, work function measurements and TPD. A plot of the O(519 eV)/Au(239 eV) AES ratio versus coverage is nearly linear, but a small change in slope occurs at ΘO=0.9 ML. LEED observations show no ordered superlattice for the oxygen overlayer for any coverage studied. One-dimensional ordering of the adlayer occurs at low coverages, and disordering of the substrate occurs at higher coverages. Adsorption of 1.0 ML of oxygen on Au(111) increases the work function by +0.80 eV, indicating electron transfer from the Au substrate into an oxygen adlayer. The O(1s) peak in XPS has a binding energy of 530.1 eV, showing only a small (0.3 eV) shift to a higher binding energy with increasing oxygen coverage. No shift was detected for the Au 4f 7/2 peak due to adsorption. All oxygen is removed by thermal desorption of O 2 to leave a clean Au(111) surface after heating to 600 K. TPD spectra initially show an O 2 desorption peak at 520 K at low ΘO, and the peak shifts to higher temperatures for increasing oxygen coverages up to ΘO=0.22 ML. Above this coverage, the peak shifts very slightly to higher temperatures, resulting in a peak at 550 K at ΘO=1.2 ML. Analysis of the TPD data indicates that the desorption of O 2 from Au(111) can be described by first-order kinetics with an activation energy for O 2 desorption of 30 kcal mol −1 near saturation coverage. We estimate a value for the Au–O bond dissociation energy D(Au–O) to be 56 kcal mol −1. 相似文献
2.
Mo, Au and their coadsorbed layers were produced on nearly stoichiometric and oxygen-deficient titania surfaces by physical vapor deposition (PVD) and characterized by low energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM). The behavior of Au/Mo bimetallic layers was studied at different relative metal coverages and sample temperatures. STM data indicated clearly that the deposition of Au on the Mo-covered stoichiometric TiO2(1 1 0) surface results in an enhanced dispersion of gold at 300 K. The mean size of the Au nanoparticles formed at 300 K on the Mo-covered TiO2(1 1 0) was significantly less than on the Mo-free titania surface (2 ± 0.5 nm and 4 ± 1 nm, respectively). Interestingly, the deposition of Mo at 300 K onto the stoichiometric TiO2(1 1 0) surface covered by Au nanoparticles of 3–4 nm (0.5 ML) also resulted in an increased dispersity of gold. The driving force for the enhanced wetting at 300 K is that the Au–Mo bond energy is larger than the Au–Au bond energy in 3D gold particles formed on stoichiometric titania. In contrast, 2D gold nanoparticles produced on ion-sputtered titania were not disrupted in the presence of Mo at 300 K, indicating a considerable kinetic hindrance for breaking of the strong Au-TiOx bond. The annealing of the coadsorbed layer formed on a strongly reduced surface to 740 K did not cause a decrease in the wetting of titania surface by gold. The preserved dispersion of Au at higher temperatures is attributed to the presence of the oxygen-deficient sites of titania, which were retained through the reaction of molybdenum with the substrate. Our results suggest that using a Mo-load to titania, Au nanoparticles can be produced with high dispersion and high thermal stability, which offers the fabrication of an effective Au catalyst. 相似文献
3.
The preferential sputtering of S from bulk MoS 2 standard samples exposed to 3 keV Ar + ion bombardment has been studied by XPS. The MoS x stoichiometry decreases from MoS 2 to MoS 1.12 with a concomitant reduction in the Mo 3d 5/2 binding energy from 229.25 to 228.35 eV. The altered layer extends to a depth of 3.8 nm and is proposed to consist of a single amorphous MoS x phase in which Mo has a varying number of nearest neighbour S atoms. Using peak positions alone it is possible to determine the MoS x stoichiometry to an accuracy of x±0.1 from a plot of MoS x stoichiometry against (Mo 3d 5/2–S 2p 3/2) binding energy. The results are of strong current interest for coating analysis applications as MoS 2 is a compound capable of providing low friction properties when incorporated into hard coatings. 相似文献
4.
The interaction of CO 2 with Cs-promoted Fe(110) at 85 K as well as temperature-dependent reactions between 100 and 700 K have been studied by means of ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Several surface species could be detected at 85 K, i.e. carbon monoxide (CO), carbonate (CO n−3), physisorbed linear carbon dioxide (CO lin2) and very small amounts of oxidic oxygen (O ox). An oxalate species (C 2O m−4) could not be identified definitively, but from comparison with the literature there is evidence that C 2O m−4 is present. Increasing the temperature after saturation with CO 2 leads to a complicated reaction behaviour. CO 2 either desorbs or dissociates into CO and CO n−3 or forms C 2O m−4 at temperatures between 85 and 160 K. Above 160 K C 2O m−4, decomposes in parallel reactions into CO 2, CO n−3 and CO. Above 320 K, adsorbed CO either desorbs into the gas phase or dissociates into C and O. In the temperature region between 500 and 700 K a recombination of C and O to CO and the desorption of Cs take place. As in the case of Fe(110)/K+CO 2, at high alkali coverages two carbonate species could be detected which dissociate upon heating at different temperatures. The system Fe(110)/Cs+CO 2 is proved to be very similar to the system Fe(110)/K+CO 2. 相似文献
5.
The adsorption and electron-stimulated desorption of CCl 4 on Ru(0001) have been studied at 100 K using a variety of surface analytical techniques, including thermal desorption spectroscopy, Auger electron spectroscopy, low-energy ion scattering, and mass and angle-resolved electron-stimulated desorption (ESDIAD). CC1 4 is found to dissociate partially for fractional monolayer coverages, and to adsorb molecularly above a coverage of 13%. Upon electron bombardment, Cl + ions are found to desorb with their angular distribution directed along the surface normal; this implies that CC1 4 orients with one C-C1 bond normal to the surface. The total yield of Cl + increases linearly with increasing molecular CC1 4 coverage up to one monolayer, which implies that Cl + stems mainly from molecular CCl 4 and that interadsorbate quenching is not significantly affecting the desorption yield. Beyond a coverage of 1 ML, the Cl + yield continues to increase, and starts leveling off after 2 ML. We estimate the yield from a thick layer of CCl 4 to be of the order of 3 × 10 −8 ions/electron. The angular distribution of the desorbing Cl + ions widens with increasing CCl 4 exposure. Besides Cl +, higher mass fragments of CCl 4, such as CCl +, CCl 2+ and CCl 3+ are also found to desorb from multilayers upon electron bombardment. 相似文献
6.
Sm 3(Fe, Mo) 29N x nitride has been synthesized at 823 K for 2.5 h by gas phase reaction under 1 atm of nitrogen. The nitride retains the structure of parent compound. The unit cell volume of the nitride is 4.7% greater than that of the parent compound. Introduction of nitrogen leads to an increase of Curie temperature Tc from 445 K for the parent to 704 K for the nitride, and an increase of saturation magnetization Ms from 135 A m 2/kg for the parent to 152 A m 2/kg for the nitride at 4.2 K, and from 107 A m 2/kg for the parent to 137 A m 2/kg for the nitride at 300 K. The nitride exhibits uniaxial anisotropy with an anisotropy field Ba of 20.5 T at 4.2 K and 14.6 T at 300 K. 相似文献
8.
The educed Gd atoms in the X-structure (Th 6Mn 23-type) of Gd(Fe 1−xMn x) 2 were magnetically investigated by comparing with Gd 6(Fe 1−yMn y) 23 whose structure is Th 6Mn 23-type. The magnetic properties of Gd(Fe 1−xMn x) 2 (0.4≤ x≤0.7) were observed to be quite similar to those of Gd 6(Fe 1−yMn y) 23 (0.4≤ y≤0.7). 相似文献
9.
The adsorption of CO and CO 2 on K-predosed Pd{1 1 0} at room temperature has been examined via reflection–absorption infrared spectroscopy (RAIRS). CO 2 adsorbs on 0.37 ML K-predosed Pd{1 1 0} with high sticking probability and a reactive chemisorbed intermediate, CO 2−, is detected in RAIRS at room temperature. Reaction of this species ultimately yields carbonate. The same high K precoverage induces dissociation of CO at low CO exposure. Carbonate is detected at higher CO exposure and is probably produced via stepwise oxidation of molecularly adsorbed CO. In contrast at low K precoverage (0.11 ML), CO remains intact but the C–O bond is considerably weakened with respect to CO chemisorbed on clean Pd{1 1 0}. These findings illustrate a dual promoter mechanism of K in the adsorption and reaction of CO or CO 2 at high K coverage. The alkali metal induces dissociation of these molecules and directly participates in the formation of a surface compound, K 2CO 3. 相似文献
10.
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
11.
New Pb based layered superconducting cuprates (Pb 0.5Cd 0.5)(Sr 0.9R 0.1) 2(R′ 0.7Ce 0.3) 2Cu 2O y with (R,R′) = (Eu,Gd), (Eu,Dy) and (Nd,Gd), have been successfully synthesized. The structure of (Pb,Cd)(Sr,Eu) 2(Gd,Ce) 2Cu 2O y is determined using XRD data. The X-ray powder diffraction pattern can be indexed by the tetragonal structure with lattice parameters a = 3.8250 Å, C = 29.2235 Å and a space group of I4/mmm. The effects of synthesis conditions on (Pb,Cd)(Sr,Eu) 2(Gd,Ce) 2Cu 2O y are studied and a Tc(onset) of 26 K is obtained by resistance measurements. It is isostructural to the superconductor (Pb,Cu)(Sr,Eu) 2(Eu,Ce) 2Cu 2O y. 相似文献
12.
In this work, luminescence properties of β-(Ga 1−xIn x) 2O 3 solid solutions were investigated with the purpose of making the new thermoluminophors for ultraviolet (UV) dosimetry. The doping of aliovalent cation admixture (Mg, Mo) in the β-Ga 2O 3 ceramic sample brings about the appearance of high-temperature thermoluminescence glow peaks with a maximum at 395 and 435 K. The maximum of the thermoluminophor photosensitivity shifts when the composition of solid solution changes. 相似文献
13.
The misfit layer compounds (LaS) 1.14(NbS 2) n ( n=1, 2) and [(Pb,Sb)S] 1.14NbS 2 were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In these compounds the NaCl-type double MS (M=La, Pb, Sb) layers (Q layers) alternate with the NbS 2 layers (H layers) made up of NbS 6 trigonal prisms. It was possible to record AFM and STM images for only the H layers for (LaS) 1.14(NbS 2) n, but for both the H- and Q-layers for [(Pb,Sb)S] 1.14NbS 2. Partial and total electron density plots of the H and Q layers were calculated to interpret the observed STM and AFM images. The bright spots in the STM and AFM images of the H layer correspond to S atoms, and those of the Q layer to Pb and Sb atoms. The STM images for the Q layers of [(Pb,Sb)S] 1.14NbS 2 suggest that a short-range ordering of the Pb and Sb atoms occurs in the (Pb,Sb)S sheets of the Q layer. 相似文献
14.
The absorption specta of CO laser radiation by 3ν 3 overtone bands of 238UF 6 and 235UF 6 has been measured using photoacoustic spectroscopic techniques. For the two temperatures 250 K and 290 K, measured absorption coefficients and cross-sections of the 3ν 3 band of 235UF 6 are reported for the first time. 相似文献
15.
Diffusion of dysprosium on the (1 1 1) facet of a tungsten micromonocrystal was investigated by means of spectral analysis of field emission current fluctuations. The experimental spectral density functions of the current fluctuations were analysed by using Gesley and Swanson’s theoretical spectral density function, which enables to determine the surface diffusion coefficient D for dysprosium. Derived from the temperature dependence of D, the diffusion activation energy E is presented for some Dy coverages θ(1 1 1). In the temperature range 400–600 K, the E first drops from 1.25 eV per atom at θ (111)≈0.25 ML to 0.48 eV per atom at θ (111)≈1 ML (corresponding to the minimum of the work function of the system), then increases to 1.03 eV per atom at θ (111)≈1.3 ML. The results are discussed from the aspects of the substrate structure and interaction in the adsorbed layer. 相似文献
16.
The magnetic phase diagram of La 2(Cu 1−xZn x)O 4 has been determined from zero-field muon-spin-rotation (ZF-μSR) data taken at LAMPF for 0 ≤ x ≤ 0.10. Antiferromagnetic onset temperatures follow TN( x) from susceptibility measurements on the same samples. However, the order becomes long range, as evidenced by a well-defined internal magnetic field, only at temperatures well below TN. Extrapolation of our results yields TN → 0 K at x = 0.11 for a single (Cu 1−xZn x)O 2 plane, and comparison with YBa 2(Cu 1−xZn x) 3O 6 implies identical disruption of magnetism by Zn doping in the single- and double-plane systems. 相似文献
17.
用多体势结合分子动力学计算了L1 2型NiAl 3, L1 2型Ni 3Al, L1 0型NiAl和B 2 型NiAl的晶格常数, 结合能以及合金形成热; 分析了结构性点缺陷在上述四种合金中的存在形式; 在此基础上研究了合金化元素Mo, Ta, W在Ni xAl 1-x( x=0.25,0.5,0.75)中的择优占位行为. 计算结果表明: 对于四种结构的Ni-Al合金, 偏离理想化学配比时,主要的结构缺陷形式是反位置; 根据占位能最小化, 第三组元元素Mo, Ta, W在上述四种Ni-Al中都显著优先占据Al格位.
关键词:
多体势
Ni-Al合金
占位 相似文献
18.
Phase evolution in the Bi---Sr---Ca---Cu---Al---O system was studied. Two Al-containing phases BiSr 1.5Ca 0.5Al 2O z and (Sr 1−xCa x) 3Al 2O 6 ( x = 0.4 − 0.45) were determined to be chemically compatible with Bi 2.18Sr 2CaCu 2O 8+x (Bi-2212) at temperatures of the samples processing. The phase equilibria in the title system were investigated above the solidus temperature. The BiSr 1.5Ca 0.5Al 2O z was found to be in equilibrium only with the melt and the (Sr 1−xCa x) 3Al 2O 6 phase. This latter aluminate equilibrated with Ca,Sr cuprates, CaO, the Cu-free phase, and the liquid. The melting and solidification in Bi-2212, doped with the aluminate, corresponded to the reversible reaction Bi-2212 + BiSr 1.5Ca 0.5Al 2O z ↔ (Sr 1−xCa x) 3Al 2O 6 + liquid. Two sets of superconducting composite materials with initial compositions Bi-2212 + nBiSr 1.5Ca 0.5Al 2O z and Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 were prepared by solidification from the partial melt. The former material was composed mostly of large Bi-2212 lamellas separated by the BiSr 1.5Ca 0.5Al 2O z phase, which destroyed superconducting links between Bi-2212 grains. The latter material consisted of a Bi-2212 polycrystalline matrix with high concentration of small (ca. 3 μm) grains of (Sr 1−xCa x) 3Al 2O 6 imbedded in Bi-2212 lamellas. The Bi-2212 + m(Sr 1−xCa x) 3Al 2O 6 materials displayed a trend to enhance flux pinning at T = 60 K with the increase of aluminate phase content. 相似文献
19.
Anomalous magnetotransport phenomena have been observed in θ-(BEDT-TTF) 2I 3 crystals at temperatures below 15 K. The magnetoresistance M : (1) is a linear function of the magnetic field H, (2) is not affected by the angle between the electric current and the magnetic field, (3) but depends on the magnetic field orientation with respect to the crystal axis. Magnetoresistance is expressed as M = ( aH2a + bH2b + cH2c) 0-3/2/ H in terms of H = ( Ha, Hb, Hc), the zero field resistivity 0, and parameters a, b, and c which are independent of temperature and magnetic field. We have found that b a > c. Magnetoresistance up to 40 is observed for H = 7 T along the b-axis at T = 1.5K. 相似文献
20.
High field magnetization measurements have been performed to examine the existence of itinerant metamagnetism in exchange-enhanced systems related to YCo 2 together with Fe 1−x Co xSi. In the Y(Co −xFe x) 2 system, the meta magnetism inherent in YCo 2 has been observed in 0.04 x0.07. The transition is not as sharp as in the Y(Co 1−xAl x) 2 system. Other exchange-enhanced paramagnets Y(Co −xCu x) 2 and Y 1−xLa xCo x2 and weakly itinerant ferromagnet Fe 1−xCo xSi exhibit no metamagnetic transition up to 430 kOe. 相似文献
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