Ji Mingrong

Valency and adsorption characteristics of a sulphided MoO3/γ-Al2O3 methanation catalyst

Abstract The sulphur-to-molybdenum ratio and the activity of the methanation reaction as a function of sulphiding time were measured on a sulphided MoO3/γ-Al2O3 catalyst. The sulphur-to-molybdenum atomic ratio of catalyst samples did not increase after 2 h of sulphidation at 400°C, whereas the activity of methanation was constant after 6 h of sulphidation. X-ray photoelectron spectroscopic (XPS) measurements showed that most of the Mo6+ was easily reduced to Mo4+ and the valency of most of the sulphur was −2 during the sulphidation process in a CS2 H2 stream at 400°C. Mo5+ was only detected by XPS under very mild sulphidation conditions and in samples with a lower content. A small amount of high-valency sulphur was detected that vanished with prolonged sulphidation. No change in the valency of molybdenum or sulphur was observed after reaction for 8 h. Low-temperature oxygen chemisorption and the adsorption and temperature-programmed desorption (TPD) of hydrogen were investigated. A linear correlation was observed between the methane production rate and oxygen uptake. The oxygen uptake with different pretreatments showed that carbon monoxide and hydrogen were not adsorbed on the same sites on the catalyst surface. Probably carbon monoxide was adsorbed on the coordinatively unsaturated molybdenum sites whereas hydrogen was adsorbed on sulphur sites. The TPD spectra of hydrogen indicated that it had two adsorption states, i.e., molecular adsorption and atomic adsorption. Only atomic adsorption was detected when the adsorption temperatures were above 300°C. The mechanism of the methanation reaction on molybdenum catalysts is discussed.

High-Tc superconductivities and electronic structures of some (BaxY1−x)CuO3 species by x-ray photoelectron spectroscopy

Abstract The electronic structures of a set of species (BaxY1−x)CuO3 have been investigated by means of X-ray photoelectron spectroscopy. The mid-point transition temperature Tc correlated monotonically with the density of states at the Fermi level. Evidence was found for the existence of a low valence state of barium, Ba+2−σ in these ceramics, the ratio Ba+2−σ/ Ba+2 being very likely of great importance to the theoretical understanding of their superconductivity.

Oxygen adsorption on the Co50Ni50(111) surface

Abstract Oxygen adsorption on the Co 50 Ni 50 (111) surface at RT has been studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The uptake rate and the work function variations show the different stages of linear initial adsorption, oxide nucleation and oxide thickening. Chemisorption of oxygen induced a segregation of cobalt. Heating at 327°C caused a further cobalt segregation which reduced Ni 2+ to Ni 0 and finally islands of cobalt oxide were formed.

Study of Ti/InP interfaces by PES

Abstract The interface of Ti/InP(110) was studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). It is evident that deposition of Ti on the surface of InP(110) at room temperature introduced a break of the In-P bond and a diffusion of In atoms into the Ti film. The interaction of Ti and P occurred at a temperature of 350°C.

Photoemission and work function measurement of Cl adsorption on GaAs(110)

The changes of work function of GaAs(110) after various chlorine exposures are obtained from UPS. It is shown that when more Cl was adsorbed, the work function increased which may be caused by the changes of the ionisation energy.

Influence of oxygen content on super-conductivity of Bi-system material

The sample with nominal composition Bi1.8Pb0.35Sr2Ca2Cu3Oy was prepared by solid state reaction method. Through the measurements of resistivity, dc. susceptibility, and the analysis of x-ray diffraction and Energy Dispersive x-ray (EDX) microanalysis, we found that: (1) there is only one superconducting transition with transition temperature near 110K, its zero-resistance temperature (Tce) is as high as 106.5K, the diffraction pattern is similar to that of 2223 single phase (110K), but the cation ratio of Bi:Pb:Sr:Ca:Cu is near 25.8:5.74:18.43:19.53:30.50, i.e., Bi2.5Pb0.5Sr2Ca2Cu3. We suppose that the 3223 phase is caused by intergrowth in the sample; (2) like the 1-2-3 phase material, the superconductivity of Bi-system is sensitive to oxygen content. We suppose that different oxygen content in the same crystal structure leads to the change of electronic structure, and so to great difference in the superconductivity.

X-ray photoelectron spectroscopy study of the single phase high-Tc superconductor YBa2Cu3O9-δ

X-ray Photoelectron Spectroscopy (XPS) was employed to study the single phase high-Tc superconductor YBa2Cu3O9-δ. Comparison of the observed valence band spectrum with the theoretical spectrum of Mattheiss is given. The core level spectrum of Ba 3d5/2 was examined. The results of Y2Cu2O5 and Y2BaCuO5 are also reported.

Photoemission of the Oxidation of Cerium Overlayers on GaSb(110) Surface

We have used x-ray photoelectron spectroscopy to study the oxidation of cerium overlayers on a semiconductor GaSb(110) surface. A GaSb(110) sample covered with 10 monolayers Ce was used to adsorb oxygen. When the exposure of O2 was up to 50 L, the oxide of cerium, Ce2O3, began to change into unstable CeO2. The dissociation of CeO2 resulted in strong oxidation of the substrate. The main products are Ga2O3, Sb2O3, and then Sb2O5. After annealing, a part of the oxygen atoms transferred from cerium dioxide toward Ga and Sb.

Structure and properties of the La-doped Bi-2201 system

In this article, the influence of La substitution for Sr on structure and physical properties of the 2201 phase is studied. First, the crystal microstructure of the Bi2.1Sr1.9-xLaxCuOy (0 ≤ x ≤ 1.0) is characterized by means of x-ray diffraction and electron diffraction analyses, it is discovered that in the La-doped 2201 system with increasing La content the 2201 phase undergoes tetragnoal-orthorhombic-monoclinic structural transition. With this phase transition, the modulation vector of the 2201 phase transforms from incommensurate to commensurate, and the period of the modulation wave decreases. Secondly, the superconductivity of this system is analyzed systematically. The results of the resistivity measurement show that the appropriate amount of La doping can raise the superconducting transition temperature (Tc) of the 2201 phase, with x=0.2, Tc reaches as high as 25 K. However the excessive doping of La (x ≥ 0.3) leads the 2201 phase to transit from metal to insulator and the superconductivity disappears. The measurement of thermoelectric power (TEP) of this system shows that with increasing La content the TEP value also increases gradually. But the interesting point is that the transition from positive to negative in TEP occurs for x=0.2 sample. In addition, the electronic structure and oxygen content of this system are also studied. Based on these, we analyze the relation between the microstructure, electronic structure of the La-doped 2201 phase and its superconductivity, indicating that the type of element substitution with higher valence, together with the microstructural distortion induced by the substitution affects the electronic states of Cu 3d seriously, that is, changes the degree of coulomb correlation of Cu 3d electrons, thus resulting in the transition of the type of carrier of this system and the decrease of hole carrier concentration, as well as the corresponding variation of the superconductivity of La-doped 2201 phase.

The cooperative effect of electronic structures in high Tc superconductor YBa2Cu3O7−δ system

Different temperature quenched YBa 2 Cu 3 O 7−δ samples have been investigated by means of X-ray photoelectron spectroscopy(XPS). The binding energy shift and the shape variation of Y3d and Ba3d 5/2 show some correlation with superconductivity of the samples. It is suggested that the superconductivity of Y-based oxides may come from the cooperative effect of the components other than from the CuO 2 layers or Cu-O chains only.