Shuxian Zhuang

An AES, UPS and HREELS study of the oxidation and reaction of NB(110)

Abstract The oxidation of Nb(110) upon oxygen adsorption has been investigated using AES, UPS and HREELS. For low and medium exposures of oxygen, two new loss features at 720 and ∼950 cm −1 develop, which are assigned to NbO and NbONb stretching vibrations, respectively. When oxygen exposure is high, a broad and strong loss peak at 600–900 cm −1 appears, which is due to bulk-like NbONb stretching vibrations, the changes in the vibrational spectroscopy suggest that, with increasing oxidation of the surface, NbO 4 tetrahedra transform into NbO 6 octahedra. Experiments involving methanol adsorption further confirm these results concerning the process of oxidation.

Preparation and adsorption properties of Mo2N model catalyst

Abstract Mo(100)c(2×2)-N, as a model surface for the real Mo2N catalyst, was prepared. The adsorption of CO and 15NO on this model surface were studied by high-resolution electron energy loss spectroscopy (HREELS). It was found that CO and 15NO not only could be adsorbed on the top of the Mo sites but also could react with surface N sites to form surface NCO and N2O species, respectively. This indicated that both the Mo atoms and N atoms of the surface are all active for CO and 15NO adsorption.

The adsorption and reaction of cyclohexanone on the Pt(111) surface

Abstract The interaction of cyclohexanone with the Pt(111) surface has been investigated by HREELS and TDS. At 160 K, the chemisorption of cyclohexanone induces a “red-shift” of the C O stretch band and a decrease in work function. Heating the sample from 220 to 370 K leads to complete disappearance of the dominant CH 2 rocking band at 720 cm −1 and the C O stretching band at 1650 cm −1 , indicating the dehydrogenation of the entire adlayer to form intermediate species. Strong bands of the dehydrogenated species appear at 860 and 3000 cm −1 which is different from phenoxy on Pt(111). Above ∼ 380K, the dehydrogenated species is decomposed to form hydrocarbon fragments and C O which directly desorbs into the vacuum.

Interaction of chlorine with a Co50Ni50(111) surface

Abstract The adsorption and desorption of chlorine on a Co50Ni50(111) surface have been investigated by AES, XPS, UPS and work function measurements between 300 and 913 K. While the initial sticking probability is almost independent of the adsorption temperature, the saturation coverage of chlorine was found to be strongly temperature dependent. At 300 K a nickel enrichment was observed on the clean surface. Heating the clean surface leads to a continuous decrease in the surface concentration of Ni. Between 500 and 913 K, chlorine adsorption induces an additional segregation of Ni with a pronounced maximum near 700 K due to the preferential reaction-desorption of CoCl2. The various chlorine induced effects on the Co50Ni50(111) surface are discussed in terms of the ionic radius of the adsorbate and the heats of formation and vaporization, respectively, of the surface chlorides formed.

The interaction of coadsorbed Cl and CO on Ni(110)

Abstract The influence of preadsorbed chlorine on the adsorption behavior of CO on Ni(110) has been studied using AES, photoemission and work function measurements. It is found that the presence of chlorine causes a drastic reduction of the CO adsorption rate and capacity on the Ni(110) surface. Cl presaturation of the Ni(110) surface completely blocks the CO sticking. Conversely, chlorine displaces preadsorbed CO. At constant total coverage, increasing Cl precoverage causes the 1π level of coadsorbed CO to shift to higher binding energy, while the 5σ level slightly moves towards lower binding energy. These findings together with the decrease in the average dipole moment of CO induced by coadsorbed chlorine indicate the reduced CO-Ni coupling and are in line with the poisonous character of electronegative surface additives in heterogeneous catalysis.

Preparation and properties of the SmOx/Rh(100) model surface

The preparation of SmOx/Rh(100) and CO adsorption on this model surface have been investigated with Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption spectroscopy (TDS). The oxygen adsorption on the SmRh alloy surface leads to the aggregation of Sm on the surface. The thermal treatment of this oxidized surface induces the further agglomeration of SmOx on the Rh(100) surface. Compared with CO TDS on the clean Rh(100) surface, three additional CO desorption peaks can be observed at 176, 331 and 600 K on the SmOx/Rh(100) surface. The CO desorption peak at 176 K may originate from CO adsorbed on SmOx islands, while the appearance of the CO adsorption peaks at 331 and 600 K, depending on the oxidation state of Sm, is attributed to CO species located at the interface of SmOx/Rh(100).

Photoemission study on the growth and stability of Gd cluster films over Ni(110) surface

Abstract The growth of Gd films on a Ni(110) surface was studied by synchrotron radiation photoemission spectroscopy (SRPES) and XPS techniques. The results showed that at a thickness below 0.20 nm Gd4f exhibited a single-peak feature indicating that the Gd film grows in layer-by-layer mode. When the Gd coverage is larger than 0.20 nm, however, the Gd4f peak evolves into a double-peak feature with 2.3 eV separation at 2.00 nm. A similar phenomenon was observed in the Gd4d XPS spectra. It is suggested that the double-peak structure of Gd4f is attributed to Gd clusters which might exhibit different electronic states from Gd metal owing to their special structures. Anneal treatment induced the collapse of Gd clusters and uniform spread of Gd over the Ni(110) surface, implying that Gd clusters are unstable thermodynamically.

The adsorption of chlorine on an Fe64Ni36(100) surface

Chlorine adsorption on an Fe 64 Ni 36 (100) surface at 300 K has been studied by AES, XPS, UPS and work-function measurements. Chlorine dissociatively adsorbs on the surface and the uptake curve consists of two stages: an initial rapid chemisorption followed by a slow further uptake. ΔO and UPS provide the evidence of a Cl monolayer formed on Fe 64 Ni 36 (100) up to saturation. Chlorine adsorption induces the preferential oxidation of surface Fe atoms and the segregation of Fe to the Fe 64 Ni 36 (100) surface at high temperatures. Chlorine preadsorption on the surface strongly reduces or completely suppresses any further uptake of oxygen above a certain chlorine coverage

Oxidation of Gd–Ni composite and Gd cluster films grown on Ni(110) surface studied by photoemission

Abstract Soft X-ray synchrotron radiation photoemission (SRPES) and XPS were used to study the interaction of oxygen with Gd–Ni composite and Gd cluster films grown on Ni(110) surface. Different oxidation manners were found for the two kinds of films. Over the Gd–Ni composite film, the adsorption of oxygen resulted in the segregation and oxidation of Gd component, and chemisorbed O − and lattice oxygen were detected. For the Gd cluster film, with the increase of oxygen exposure the oxidation states of Gd were developed between the two peaks of the Gd4f double-peak at the expense of attenuation of HBE peak. Only one O1s XPS peak at 529.6 eV was detected in the range of 0–50 L exposure.

Synchrotron radiation photoemission study on growth of gadolinium film over Ni(110) surface

The growth of Gd film on Ni (110) surface was studied by synchrotron radiation photoemission spectroscopy and XPS techniques. It is revealed that in the coverage range of 0–0.22 nm Gd4f core level showed a single-peak structure, therefore Gd film grows over Ni(110) in the layer-by-layer mode. However, when Gd coverage was larger than 0.22 nm the Gd4f peak turned gradually into double-peak and a double-peak structure with 2.3 eV separation was formed at 1.51 nm, meanwhile similar phenomenon was observed in the Gd4d XPS spectra. It is suggested that the double-peak structure of Gd4f was derived from the growth of Gd film in cluster mode and the Gd atomic clusters may exhibit different electronic states from Gd metal owing to their special structures. The Gd4f double-peak e-volved into a single-peak on annealing at 600 K, implying that Gd clusters are thermodynamically unstable.