Weitian Wang

Anomalous electrical transport characteristics of orthorhombic HoMnO3/Nb-doped SrTiO3 epitaxial heterojunctions

Orthorhombic HoMnO3 films with c-axis and a-axis orientations were prepared epitaxially on Nb-1.0 wt %-doped SrTiO3 single crystal substrates by using pulsed laser deposition technique to fabricate all-oxide heterojunctions. The temperature dependent current-voltage measurements display diodelike rectifying behaviors, and the forward current was perfectly fitted using the thermionic emission model. An anomalous increase in the reverse-bias current with decreasing temperature was observed in c-axis-oriented HoMnO3/Nb-doped SrTiO3 junctions, which was not found in a-axis-oriented ones. The tunneling through the junction, which depends on the effective barrier height at the interface, was used to explain the results.

Dielectric properties of a-axis-oriented orthorhombic HoMnO3 thin films

Orthorhombic HoMnO3 films were prepared epitaxially on Nb-doped SrTiO3 (110) single crystal substrates by using pulsed laser deposition technique. The films showed perfectly a-axis crystallographic orientations and were well aligned with the substrates. The complex dielectric properties of HoMnO3 films were measured as functions of temperature (77–250 K) and frequency (100 Hz–100 kHz). Thermally activated dielectric relaxations were found, and the respective peaks shifted to higher temperatures as the measuring frequency increased. The frequency dependence of dielectric properties was ascribed to the universal dielectric response models, and the hopping conductivity and the dipolar effects induced by the charge carriers were used to explain the results.

Guiding modes of semi-infinite nanowire and their dispersion character

Conventionally, the optical properties of finite semiconductor nanowires have been understood and explained in terms of an infinite nanowire. This work describes completely different photonic modes for a semi-finite nanowire based on a rigorous theoretical method, and the implications for the finite one. First, the special eigenvalue problem charactered by the end results in a distinctive mode spectrum for the semi-infinite dielectric nanowire. Meanwhile, the results show hybrid degenerate modes away from cutoff frequency, and transverse electric–transverse magnetic (TE–TM) degeneracy. Second, accompanying a different mode spectrum, a semi-finite nanowire also shows a distinctive dispersion relation compared to an infinite nanowire. Taking a semi-infinite, ZnO nanowire as an example, we find that the ω−kz space is not continuous in the interested photon energy window, implying that there is no uniform polariton dispersion relation for semi-infinite nanowire. Our method is shown correct through a field-reconstruction for a thin ZnO nanowire (55 nm in radius) and position determination of FP modes for a ZnO nanowire (200 nm in diameter). The results are of great significance to correctly understand the guiding and lasing mechanisms of semiconductor nanowires.

Thermionic and Frenkel-Poole emission effects in orthorhombic HoMnO3/Nb-doped SrTiO3 epitaxial heterojunctions

Metastable orthorhombic HoMnO3 thin films with c-axis orientation were deposited epitaxially on (001) orientated Nb-1.0 wt. %-doped SrTiO3 single crystal substrates using a pulsed laser deposition technique to fabricate all-oxide p-n heterojunctions. The temperature dependent current-voltage measurements display diodelike rectifying behaviors in the temperature range of 80–260 K, and the forward current was perfectly fitted using the thermionic emission model. However, at a given reverse bias, the junction current increases with decreasing temperature, which suggests that the leakage mechanism is not just thermally limited current. This anomalous electrical transport behavior was explained by the Frenkel-Poole emission assisted tunneling through the junction.

Novel spin-electronic properties of BC7 sheets induced by strain

Based on first-principles calculations, the authors have investigated the electronic and magnetic properties of BC7 sheets with different planar strains. It is found that metal–semiconductor transition appears at the biaxial strain of 15.5%, and the sheets are characteristic of spin-polarized semiconductor with a zero band-gap. The band-gap rapidly increases with strain, and reaches a maximum value of 0.60 eV at the strain of 20%. Subsequently, the band-gap decreases until the strain reaches up to 22% and shows a semiconductor-half metal transformation. It will further present metal properties until the strain is up to the maximum value of 35%. The magnetic moments also have some changes induced by biaxial strain. The numerical analysis shows that the two-dimensional distortions have great influences on the magnetic moments. The novel spin-electronic properties make BC7 sheets have potential applications in future spintronic nanodevices.

A DFT STUDY ON THE ELECTRONIC CHARACTER OF P700

This density functional study is devoted to the long debated electronic nature of P700+. We found that P700+ is intrinsically a dimer of chlorophyll molecules. The unpaired electron spin distributes equally over two chlorophyll molecule halves in the bare P700+, while the dressed P700+ shows the spin density asymmetry mainly coming from the H-bond donated to 131-keto-O of one half. The experimental contradictions on the electronic nature of P700+ are also discussed.

Purcell factor for a cylindrical nanocavity: ab initio analytical approach: comment

In a recent paper [J. Opt. Soc. Am. B29, 1799 (2012)], to construct the electromagnetic fields of the confined point dipole inside a dielectric cavity, the scattering-superposition method is used incorrectly, and the boundary conditions also are not satisfied. Therefore, the Purcell factor obtained in this paper must be misleading.