Haijie Qian

Electronic structure of antimonene grown on Sb2Te3 (111) and Bi2Te3 substrates

We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi2Te3 and Sb2Te3 substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi2Te3 are flatter than on Sb2Te3, which attributes to Bi2Te3 substrate lattice constants lager than Sb2Te3. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.

Highly efficient charge transfer from a trans-ruthenium bipyridine complex to nanocrystalline TiO2 particles

trans-Di(isothiocyanato)-[N-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) acts as a very efficient charge-transfer sensitizer for nanocrystalline TiO2 films. The incident photon-to-electron conversion efficiency (IPCE) for the dye-coated TiO2 film exceeded 80% in the wavelength domain between 400 and 600 nm. A sandwich-type regenerative solar cell fabricated from a 10 μm thick TiO2 film sensitized with this dye generated a short-circuit photocurrent of 19.6 mA cm−2 and an open-circuit photovoltage of 720 mV in simulated AM1.5 solar light (924 W m−2) with an overall power conversion efficiency of 8.6%.

Electronic structure of BiFe 1-x Mn x O 3 thin films investigated by X-ray absorption spectroscopy

Multiferroic polycrystalline BiFe1-xMnxO3 (0 ≤ x ≤ 0.3) thin films have been prepared on the Pt(111)/Ti/SiO2/Si(100) substrates by pulsed laser deposition method. The influence of Mn substitution on the electronic structure and magnetic properties has been studied. X-ray diffraction spectroscopy shows that Mn substitution slightly modulates crystal structure of the BiFe1-xMnxO3 system within the same structural phase. According to Fe L edge X ray absorption spectroscopy, Fe ions are found to be formally trivalent for doping amount x in BiFe1-xMnxO3. The enhanced magnetization by increasing Mn content is attributed to an alternation degree of hybridization between Fe 3d-O 2p and Mn 3d-O 2p orbitals, basing on the carefully examined Fe L and O K edge X-ray absorption spectroscopy. The crystal structural and the electronic structural results show a causal relation between them by demonstrating intrinsic mutual dependence between respective variations.

Growth and characterization of SrMoO3 thin films

Highly conductive SrMoO3 thin films with good crystallinity and smooth surface were grown on SrTiO3 (0 0 1) substrates by pulsed laser deposition. The effects of substrate temperature and oxygen pressure on the structure, surface morphology, and electrical properties were studied. In the range of substrate temperatures from 560 degreesC to 640 degreesC and oxygen pressure from 10 (-3) to 10 (-4) Pa studied in our experiments, high-quality SrMoO3 thin films were produced. Beyond the top temperature or oxygen pressure limit, SrMoO4 appears as an impurity phase. High-resolution transmission electron microscopy (HRTEM) study shows that the SrMoO3 film has high-quality crystallinity and an epitaxial nature. The root-mean-square surface roughness of the film deposited at 2.5 x 10 (-4) Pa is 3.9 Angstrom. The films exhibit metallic conduction, which results from the delocalized electrons from Mo. X-ray photoelectron spectroscopy (XPS) measurements characterized its core level spectra and the valence band

Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy

Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films.PACS: 81; 81.05.Dz; 81.15.Hi.

Charge transfer dynamics of 3,4,9,10-perylene-tetracarboxylic-dianhydride molecules on Au(111) probed by resonant photoemission spectroscopy

Charge transfer dynamics across the lying-down 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) organic semiconductor molecules on Au(111) interface has been investigated using the core-hole clock implementation of resonant photoemission spectroscopy. It is found that the charge transfer time scale at the PTCDA∕Au(111) interface is much larger than the C 1s core-hole lifetime of 6 fs, indicating weak electronic coupling between PTCDA and the gold substrate due to the absence of chemical reaction and∕or bonding.

Aluminium doping induced enhancement of p–d coupling in ZnO

Valence-band type Auger lines in Al doped and undoped ZnO were comparatively studied with the corresponding core level x-ray photoelectron spectrography (XPS) spectra as references. Then the shift trend of energy levels in the valence band was that p and p-s-d states move upwards but e and p-d states downwards with increasing Al concentration. The decreased energy of the Zn 3d state is larger than the increased energy of the 0 2p state, indicating the lowering of total energy. This may indicate that Al doping could induce the enhancement of p-d coupling in ZnO, which originates from stronger Al-O hybridization. The shifts of these states and the mechanism were confirmed by valence band XPS spectra and 0 K-edge x-ray absorption spectrography (XAS) spectra. Finally, some previously reported phenomena are explained based on the Al doping induced enhancement of p-d coupling.

Supercritical synthesis and characterization of SWNT-based one dimensional nanomaterials

The present study developed a novel, fast and efficient method to synthesize one dimensional nanotube-based materials via supercritical reactions and supercritical fluids. It was proved that supercritical organic fluids were good media to take materials into the nanocavity, not only as solvents but also as reaction agents. Different kinds of metals (Ni, Cu, Ag) and fullerenes (C(60), C(70), C(78), C(84), Gd@C(82), Er@C(82), Ho@C(82), Y@C(82)) were successfully inserted into nanotubes with small diameters by this technique, with various supercritical fluids such as C(2)H(5)OH, CH(3)OH or C(6)H(5)CH(3). The filling rates were proved to be more than 90%. The high filling efficiency and the properties of the as-generated materials were characterized by TEM, Raman, EDS and XPS. In principle, this technique can be applied to construct new types of nanomaterials, if we choose the appropriate supercritical reaction and fluid in the CNTs.

Correlation between electronic structure and magnetic properties of Fe-doped ZnO films

Fe-doped ZnO films with different Fe concentrations that display ferromagnetism at room temperature have been prepared by plasma assisted molecular beamepitaxy (p-MBE) techniques. Synchrotron-based measurements of photoemission spectroscopy (PES), x-ray absorption spectroscopy (XAS), resonant photoemission spectroscopy (RPES), and superconducting quantum interference device (SQUID) were performed to investigate the electronic structure and magnetic properties of the films. It was found by Fe 2p PES and XAS that the dominant valence state of Fe ions is Fe3+ and that the configuration of Fe ions varies from tetrahedral sites to octahedral sites as the Fe concentration increases. Results of RPES indicate that the electronic states related to Fe2+ also exist near the Fermi level and that the distribution of Fe 3d electronic states in the valence band varies with different Fe concentrations. Correlations of the magnetic properties with the electronic structure of Fe-ZnO films have established that the electronic states related to Fe2+ and localized defects like Zn vacancies play an important role for ferromagnetism of Fe-ZnO films, while Fe3+ ions at octahedral sites destabilize the ferromagnetic interactions