H.B. Pan

The electronic structure and spectral properties of ZnO and its defects

The electronic structure of ZnO and its defects, which include intrinsic point defects and their complexes, have been calculated using full-potential linear Muffin-tin orbital method. According to our calculation data, the positions of the defect state levels have been determined in the energy band of ZnO. Based on the results above, we analysis the mechanism of the absorption and emission spectra of ZnO and discuss the effects of the electronic structure of complete ZnO and its defects on the spectral properties.

XRD and PES Studies of the Bi2Sr2Ca1−xPrxCu2O8+δ System

The Bi2Sr2CaCu2O8+δ system samples doped with Pr on Ca sites were synthesized. Resistivity measurements, x-ray powder diffraction, and photoemission experiments were performed. The experiment results show that Pr ions entered the lattice and chemical environment plays a major role in the shift of core-level spectra and valence-band spectra.

Studies of Mg overlayer on GaAs(100) surface treated by CH3CSNH2

Abstract 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.

Substitution effect of Sn for Cu in the Bi2Sr2CaCu2-xSnxO8+δ system

The Bi2Sr2CaCu2O8+δ system samples doped with Sn on Cu sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction and photoemission experiments have been performed. Suppression of superconductivity in the Sn-doped Bi2Sr2CaCu2O8+δ system has been observed. X-ray photoemission measurements show that Sn ion enters the lattice. Our results reveal that Sn ions are mostly in bivalent states.

INTERFACE FORMATION AND INTERACTION OF FE OVERLAYER ON S-PASSIVATED GAAS(100)

Abstract 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.

Interfaces of Mg and MgOx films with GaAs(100) substrate studied by synchrotron radiation photoemission

Abstract 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 chemistry, structure and stability of CH3CSNH2 passivated GaAs(100) surfaces

Abstract 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.

Substitution Effect of Pr for Ca in Bi2Sr2CaCu2O8+δ System

The Bi2Sr2CaCu2O8+δ system samples doped with Pr on Ca sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction, and photoemission experiments have been performed. Both X-ray diffraction and photoemission measurements show that Pr ion enters the lattice with a valence higher than 3+, which supports the hole-filling mechanism of the suppression of superconductivity.

An unexpected electronic structure of Gd

Abstract 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.

Studies of Mn/ZnO (0001̄) Interfacial Formation and Electronic Properties with Synchrotron Radiation

The initial growth, interfacial reaction and Fermi level movement of Mn on the O‐terminated Zn (000 1) surface have been investigated by using synchrotron radiation photoelectron spectroscopy (SRPES) and X‐ray photoemission (XPS). Mn is found to be grown on the surface in the layer‐by‐layer (Frank‐van der Merwe) mode and be quite stable on the O‐terminated surface at room temperature. With increasing the coverage of Mn, a downward Fermi level movement in band structure measurement of SRPES is observed and the resultant Schottky Barrier Height (SBH) is calculated to be about 1.1eV. Annealing behavior of the interface is investigated and we find that annealing at 600 °C induces a pronounced Mn‐Zn atoms exchange reaction at the interface.