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The adsorption of K on the n-GaAs(I 0 0) surface was investigated by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (SR-PES). The Ga3d and As3d core level was measured for clean and K adsorbed GaAs(I 0 0) surface. The adsorption of K induced chemical reaction between K and As, and the K-As reactant formed when the K coverage theta > I ML. The chemical reaction between K and Ga did not occur, but Ga atoms were exchanged by K atoms. From the data of band bending, the Schottky barrier is 0.70 eV. The Fermi-level pinning was not caused by defect levels. The probable reason is that the dangling bonds of surface Ga atoms were filled by the outer-shell electrons of K atoms, forming a half-filled surface state. The Fermi-level pinning was caused by this half-filled surface state. (c) 2004 Elsevier B.V. All rights reserved.

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.

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.

We have produced epitaxial Fe overlayers on S-passivated GaAs(100) surfaces by CH3CSNH2 treatment. The correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces was investigated by changing the annealing temperature of the surface prior to growth. The results show that the magnetization of Fe overlayers is crucially determined by the GaxS chemical bonds and by the presence of excess As after the anneals. A comparative investigation of the magnetization has been performed on both S-passivated and clean GaAs(100). It is confirmed that S-passivation on GaAs surfaces can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer.

Synchrotron radiation photoelectron spectroscopy (SRPES) has been applied to surface analysis of indium tin oxide (ITO) thin films. Several different components of In and Sn were observed at the clean ITO surface. By comparing the chemical compositions of the film before and after vacuum annealing, the contents of In 2 O 3− x and Sn 3 O 4 were found to be the major factors influencing the electrical conductivity and optical transparency of the film.

An organic sulfide, CH 3 CSNH 2 treated sulfur-passivated GaAs(100), has been studied using synchrotron radiation photo-emission spectroscopy (SRPES), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The SRPES and AES measurements show that the treatment removes the GaAs surface oxide layer and forms sulfides of Ga and As on the surface. The thermal stability and surface structure of the passivated samples at different temperatures have also been studied. We found that the surface sulfides are also gradually removed and a clean, ordered and thus Fermi level unpinning surface can finally be achieved. Surface restructuring can be observed from the GaAs(100)–S (2×1) pattern between 260 and 450°C to the (4×1) pattern without S between 460 and 550°C.

We have studied the interface formation and electronic structure of an Fe overlayer deposited on S-passivated GaAs(100). In the first stage of deposition, Fe clusters were formed near S atoms. Compared to Fe/GaAs(100), the sulfur passivation weakens the reaction between As and Fe. It is beneficial to the magnetism at the interface. A magnetic ordering feature could be found at higher coverage due to large exchange splitting.

Interface formation between Co with GaAs(100) and S-passivated GaAs(100) by CH 3 CSNH 2 treatment has been studied with synchrotron radiation photoemission. Strong interface disruption and reaction occurs between the overlayer with GaAs(100) even at low Co coverage (∼0.2 nm), while the reaction is much weaker on S/GaAs(100); a stable interface forms at a coverage of 1 nm and 0.8 nm, respectively. For S-passivated GaAs(100), Ga atoms bonded with S at the surface exchange with Co atoms and cause the formation of Co–S bonding, the amount of As bonded with Co is much less than that on GaAs(100), no segregated As appears at the surface of Co overlayer, in contrast with the case of Co/GaAs(100), indicating that S-passivation on GaAs(100) is an effective way of inhibiting the interdiffusion of As and Ga through the overlayer.

Using photoelectron spectroscopies we studied the growth process of SiC on n-Si(111) by polyimide Langmuir–Blodgett (LB) film. The polyimide pyrolyzes when heated, and leaves a skeleton of carbon atoms on the film surface, which remains the structure of LB films before pyrolysis. At about 800°C, if the polyimide LB film is thin, the substrate Si will outdiffuse quickly and form a Si layer on top of the film. At 1000°C, the Si from Si–O reacts with carbon from pyrolysis to form SiC. From the results we suggest that the LB film thickness is an important factor in the growth of good quality single crystalline SiC films.

Contradictory results are obtained when Gd is deposited on S–GaP(100) and GaAs(100) substrates, respectively. The Gd4f spectra from Gd/S–GaP show single peaks with binding energy 8.3 eV at a thickness of 0.9 nm. However, the Gd4f spectra from Gd/GaAs evolve from a narrow peak into a two-featured structure with an increment of Gd. At a thickness of 2.33 nm, one feature centers at 10.3 eV binding energy, and another at 8.0 eV. We confidently exclude the contribution of contamination in these unexpected results and a new phase is supposed.

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.

Dipping of GaAs (1 0 0) wafers in S2Cl2 or S2Cl2 + CCl4 solution has been previously found effective to passivating the GaAs surface. Application of synchrotron radiation photoelectron spectroscopy (SRPES) to such a surface reveals the presence of various S-containing species on the surface. Although bulk-like AsxSy phases prevail on the as-treated surface, annealing of the sample to above 150°C results in a thorough transfer of S atoms from AsS to GaS, indicating that steady passivation is associated with the presence of GaS bonds at the surface.

The growth and electronic structure of the Cr/InP(100) interface are studied by synchrotron radiation photoemission. At the first stage of growth, Cr atoms cover the whole InP surface. With increasing Cr coverage, Cr reacts strongly with the substrate and creates a disruptive interface. The electronic structure of the ultrathin Cr film is found to be different from that of bulk Cr film, and the possibility that magnetic ordering exists in the ultrathin overlayer of Cr is proposed.

Soft-X-ray photoemission spectroscopy was used to characterize the Gd/GaAs(100)-interface formation at room temperature. At low Gd coverage (

Some progresses of the photoemission study on metal/semiconductor interfaces with synchrotron radiation at NSRL are reviewed in this paper. The possibility that the magnetic ordering exists in the ultra-thin overlayer of Mn on semiconductor surface is proposed. The formation of interface for Sm/Si(100)2×1 and its thermal evolution have been investigated. For alkali and alkali-earth metal doped C 60 the doping effect and the interaction between doping and C 60 have been studied. Finally, the interface formation and the band offsets of Ge/ZnS(111) and Ge/ZnSe(100) are discussed in the text.

A new sulfur passivation method for GaAs, CH 3 CSNH 2 treatment, has been developed. By Synchrotron Radiation Photoemission Spectroscopy(SRPES), the chemical states and electronic aspects of the passivated surfaces are investigated. It is found that the oxide layer of the GaAs is effectively removed, and Sulfur atoms bond both to Ga and As atom at room temperature. In addition, the behavior of Mg deposited on the passivated surfaces with and without annealing has been investigated. It is found that Ga atoms can be exchanged from GaS bond, and diffuse into Mg overlayer, but the sulfur atoms remain at the interfaces. At higher Mg coverage, a MgGa alloy may be formed due to excess Mg atoms reacting with Ga atoms at the overlayer.

The formation and electronic structure of Mn/Cd0.96Zn0.04Te(111) have been investigated by photoemission with synchrotron radiation. It is determined that Mn grows on Mn/Cd0.96Zn0.04Te(111) in a two-dimensional mode at early stage. The possibility that the magnetic ordering state exists in the ultra-thin Mn film is proposed. With increasing Mn coverage, Mn atoms interdiffuse to the substrate and the exchange reaction between Mn and Cd is observed. The features of the spectra show that the Cd1−xMnxTe phase is formed at the interface. At high coverage of Mn, bulk α-Mn becomes dominant

Synchrotron Radiation Photoemission Spectroscopy (SRPES) has been used to investigate the chemical states and electronic states of a [NH 4 ] 2 S x treated GaSb(100) surface. We have found that the oxides of Ga and Sb are removed and the sulfides of Ga and Sb are formed on the surface. After sulfurized GaSb(100) was annealed, the SbS bond is broken to form elemental Sb, while the GaS bonds terminate the surface; these results imply that ammonia sulfide has a passivating role for GaSb. At room temperature (RT), deposited Mg on passivated surface has been also investigated. It is found that Ga atoms can be exchanged by Mg atoms and diffuse into Mg overlayer. Moreover, the Schottky barrier height of the Mg overlayer on the sulfurized GaSb surface was determined to be about 0.3eV.

Using photoemission spectroscopy, we have studied the adsorption of Sm on C60 film. At the first stage of Sm adsorption, the C60 valence band shifts to the high binding energy side. The maximum shift is about 0.4 eV. In the meantime, there appears a new structure at the upper side of the highest occupied molecule orbit (HOMO) band, which comes from the hybrid of the Sm 4f5 state and C60 HOMO band. As Sm coverage increases the Sm electron is in a kind of Sm2+ state due to the forming of Sm cluster on the surface.

The adsorption of K on the n-type GaAs(100) and p-type InP(100) surfaces were investigated with core-level and valence-band photoemission using synchrotron radiation. The characteristics of both interfaces were similar to each other in many ways. It was found that the chemical reaction between the adsorbate K and the anions of the substrates were occurred with the K adsorption, and the interface reactants were K As and K P compounds, respectively. However, there was no chemical reaction between K and the cations of the substrate, but the cations could be exchanged by K atoms and segregated to the surfaces. From the data of band bending on K/GaAs(100) and K/InP(100), the Schottky barrier heights were about 0.72 eV and 0.75 eV, respectively. We believe that the Fermi-level pinning may be caused by half-filled sates rather than by defect levels. These states are formed by the outer-shell electrons of K atoms that fill the empty states of the dangling bonds of the surface cations exchanged by the K atoms.

A new sulfur passivation method for GaAs by using CH3CSNH2 has been developed. Its passivation mechanics have been studied. The sulfide passivation layer can prevent deposited Mg and Fe from diffusing into or reacting with GaAs substrate. It is illustrated that sulfur passivation is beneficial to the enhancement of the magnetism of Fe overlayer on GaAs surface.

The interaction of ultrathin Mg and MgOx films with the GaAs(100) semiconductor substrate was investigated using synchrotron radiation photoemission. The results showed that strong interaction existed between Mg and GaAs leading to the formation of an interface more than 11 A, while negligible interaction and interdiffusion took place between the MgOx overlayer and the substrate. Different Mg:O 2 ratio during the deposition gave rise to the formation of MgOx with different compositions and properties.

The effects of exposure of molecular nitrogen and oxygen on p-type InP(100) surfaces modified by potassium overlayers were studied by core level and valence band (VB) photoemission using synchrotron radiation. On the K pre-covered surface, the potassium coverage enhanced the nitrogen and oxygen sticking coefficients dramatically. As far as the process of nitrogen adsorption is concerned, nitrogen atoms react mainly with P atoms rather than not react directly with indium atoms. Two kinds of nitride complexes, InPX x and InPN x + y were formed at the K-precovered InP(100) surface. In case of oxygen adsorption, O may bond with K and produce the peroxides O 2 2− and superoxides O 2 − . Following this a few kinds of phosphate phases, In(PO 4 ) x , were formed on the surface. In comparison with InP(110) surface, we found that the oxidation and nitridation promotion for the InP(100) surface was much stronger. The reasons may be the number of surface defects as well as the polarity of the InP(100) surface.