Pan Hai-Bin

Electronic structure of ZnO and its defects

The electronic structure of ZnO and its native point defects has been calculated using full potential linear Muffin-tin orbital ( FP-LMTO) method for the first time. The results show that Zn3d electrons play an important role in the bonding of ZnO. Vacant Zn (Vzn) and interstitial O (Oi) produce the shallow acceptor levels at 0.3 eV and 0.4 eV above the top of the valence band (VB), while interstitial Zn (Zni) produces a shallow donor level at 0.5 eV bellow the bottom of the conduction band (CB). However, Vacant O (Vo) produces a deep donor level at 1.3 eV below the bottom of CB. On the basis of these results, we confirm that Zni is the main factor to induce the native n-type conductivity in ZnO

Native Point Defect States in ZnO

The native point defect states in ZnO have been calculated by using a full-potential linear muffin-tin orbital method. The results show that Zn vacancy and O interstitial produce the shallow acceptor levels above the valence band. The O vacancy produces a deep donor level, while Zn interstitial produces a shallow donor level, both below the conduction band. The Zn interstitial is the main factor which induces the native n-type conductivity in ZnO.

A FP–LMTO study on the native shallow donor in ZnO

Abstract First-principle calculations are performed on ZnO:V O , ZnO:V Zn and ZnO:Zn I using a FP–LMTO (full potential linear muffin-tin orbital) method. The results prove that the Zn I is the dominant donor in ZnO, and V Zn , a shallow acceptor, while V O is a deep donor.

Enhancement of fluorescence and Raman spectroscopies of undoped C60 film

The spectroscopic characteristics of C60 films deposited on different substrates have been investigated at room temperature. We find that the fluorescence of C60 film is enhanced by the presence of a rough silver surface and also by oxygen under excitation at 5145 A (2.41 eV) at room temperature. The enhancement of the fluorescence on the rough silver surface is mainly due to an appropriate work function of the silver surface and an external electromagnetic field induced by laser irradiation, which leads to a resonant coupling with the C60 molecular dipole. The fluorescence enhancement by oxygen is interpreted as resulting from the strong reduction in symmetry of C60 from Ih to C2v or lower due to photooxygenation of the C60 molecules. This also results in larger Jahn-Teller distortions. The kinetics of the photochemical reactions between oxygen and C60 have also been obtained with an observed rate constant of magnitude about 1.6 × 10−2s−1 by monitoring the changes of the fluorescence and Raman spectra with the irradiation time.

Epitaxial Growth of Graphene on 6H-SiC (0001) by Thermal Annealing

An epitaxial graphene (EG) layer is successfully grown on a Si-terminated 6H-SiC (0001) substrate by the method of thermal annealing in an ultrahigh vacuum molecular beam epitaxy chamber. The structure and morphology of the EG sample are characterized by reflection high energy diffraction (RHEED), Raman spectroscopy and atomic force microscopy (AFM). Graphene diffraction streaks can be seen in RHEED. The G and 2D peaks of graphene are clearly observed in the Raman spectrum. The AFM results show that the graphene nominal thickness is about 4−10 layers.

X-Ray Photoelectron Spectroscopy and Reflection High Energy Electron Diffraction of Epitaxial Growth SiC on Si(100) Using C60 and Si

The formation of silicon carbide upon deposition of C60 and Si on Si(100) surface at 850°C is studied via x-ray photoelectron spectroscopy and reflection high energy electron diffraction (RHEED). The C 1s, O 1s and Si 2p core-level spectra and the RHEED patterns indicate the formation of 3C–SiC.

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers–Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.

Electronic structure studies of Bi2Sr2CaCu2-xSnxO8+? system

Photoemission measurements have been carried out for Bi2Sr2CaCu2-xSnxO8+? system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence band. From the experiment, we can deduce that the shifts of all core levels and valence bands may involve some other mechanisms, such as electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.

A new method to enhance the magnetism of Fe overlayer on GaAs(100): sulfur passivation using CH3CSNH2

Ferromagnetic resonance (FMR) has been used to investigat the magnetism of Fe overlayer on S-passivated GaAs(100) pretreated by CH3CSNH2. Comparing with the magnetism of Fe overlayer on clean GaAs(100), we find that sulfur passivation can prevent As diffusion into Fe overlayer and weaken the interaction of As and Fe. It results in enhancing the magnetism of Fe overlayer on GaAs(100). We also investigate the effects of the pre-annealing of S- passivated GaAs(100) substrate on the magnetism of Fe overlayers. The results show that the maximum effective magnetization can be obtained at annealing temperature of 400 °C. According to the experimental results of synchrotron radiation photoemission, it can be explained by the change of chemical composition and surface structure of the passivation layer on GaAs(100) surface after the annealing.

Study of iron overlayer on sulphur passivated GaAs(100) by synchrotron radiation photoemission

We have studied the interface electronic structures and the chemical reaction of the Fe overlayer deposited on S-passivated GaAs(100). The chemical bond and electronic structure are different from Fe/GaAs, and the reaction between As and Fe is weakened by S atoms. This is beneficial to the magnetism in the interface. In the first stage of deposition, Fe clusters is form near S atoms due to the large electronegativity of S. The S atoms remain at the interface with Fe coverage. Magnetic ordering feature is found at a coverage higher than 0.6 nm. According to the large exchange splitting in valence band spectra, we suggest that Fe phase transition from bcc to fcc occurs with increasing coverage.