Guolei Liu

A self-powered UV photodetector based on TiO2 nanorod arrays

Large-area vertical rutile TiO2 nanorod arrays (TNAs) were grown on F/SnO2 conductive glass using a hydrothermal method at low temperature. A self-powered ultraviolet (UV) photodetector based on TiO2 nanorod/water solid–liquid heterojunction is designed and fabricated. These nanorods offer an enlarged TiO2/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. A photosensitivity of 0.025 A/W and a quick response time were observed. At the same time, a high photosensitivity in a wide range of wavelength was also demonstrated. This TNA/water UV detector can be a particularly suitable candidate for practical applications for its high photosensitivity, fast response, excellent spectral selectivity, uncomplicated low-cost fabrication process, and environment-friendly feature.

High TC ferromagnetism of Zn(1−x)CoxO diluted magnetic semiconductors grown by oxygen plasma-assisted molecular beam epitaxy

Co-doped wurtzite ZnO [Zn(1−x)CoxO] thin films have been grown on Al2O3(0001) substrates by using oxygen plasma-assisted molecular beam epitaxy at the low growth temperature of 450°C. The epitaxial films of Co concentration at 0⩽x⩽0.12 are single crystalline, which were examined by reflection high energy electron diffraction and x-ray diffraction. Both of optical transmission spectrum and in situ. x-ray photoelectron spectroscopy studies confirmed the incorporation of Co2+ cations into wurtzite ZnO lattice. Magnetic measurements revealed that the Zn(1−x)CoxO thin films are ferromagnetic with Curie temperature TC above room temperature, and the ferromagnetism shows intrinsic characteristic.

High-performance self-powered UV photodetectors based on TiO2 nano-branched arrays

Nano-branched TiO2 arrays were fabricated on fluorine-doped tin oxide (FTO) glass by a facile two-step chemical synthesis process. Self-powered UV photodetectors based on photoelectrochemical cells (PECs) were assembled using these TiO2 nano-branched arrays as photoanodes. These visible-blind self-powered UV photodetectors exhibit high sensitivity and high-speed photoresponse. Compared with photodetectors based on bare TiO2 nanorod arrays, TiO2 nano-branched arrays show drastically improved photodetecting performance as photoanodes. The photosensitivity increases from 0.03 to 0.22 A W(-1) when optimized nano-branched TiO2 arrays are used, corresponding to an incident photon-to-current conversion efficiency higher than 77%. The UV photodetectors also exhibit excellent spectral selectivity and fast response (0.05 s decay time). The improved performance is attributed to a markedly enlarged TiO2/electrolyte contact area and good electron conductivity in the one-dimensional, well-aligned TiO2 nanorod trunk.

High temperature ferromagnetism and perpendicular magnetic anisotropy in Fe-doped In2O3 films

High temperature ferromagnetism and perpendicular magnetic anisotropy were observed in Fe-doped In2O3 magnetic semiconductor films deposited on R-cut sapphire by pulse laser deposition. The films show a Curie temperature as high as 927K. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.77 and a coercivity of 680Oe is demonstrated. Extensive microstructure, composition, and magnetic studies indicate that Fe element incorporates into the indium oxide lattice by substituting the position of indium atoms, which suggests the observed ferromagnetism is intrinsic rather than from Fe clusters or any other magnetic impurity phases.

Electronic structure of Fe-doped In2O3 magnetic semiconductor with oxygen vacancies: Evidence for F-center mediated exchange interaction

Based on the first-principles calculations, the electronic structure and magnetic properties of Fe-doped In2O3 were theoretically investigated. The presence of the predominating defects in oxide, i.e., oxygen vacancies, can lead to strong ferromagnetic coupling between the nearest neighboring Fe cations. Spin density and band-projected charge distribution in the vicinity of the oxygen vacancies reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Fe:3d and Fe:4s electrons trapped in oxygen vacancies. Such results provide direct evidence for the F-center mediated exchange interaction in oxide-based magnetic semiconductors.

ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector

ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode.

Electronic structure and magnetic properties of Fe 0.125 Sn 0.875 O 2

The electronic structure of Fe-doped

Magnetic and transport properties of homogeneous MnxGe1−x ferromagnetic semiconductor with high Mn concentration

{\mathrm{SnO}}_{2}

Transformation of electrical transport from variable range hopping to hard gap resistance in Zn1−xFexO1−v magnetic semiconductor films

is systematically investigated by means of first-principles calculations. A ferrimagnetic exchange interaction between the dopants, which is rarely found in dilute magnetic semiconductors, is predicted for the ground doping configuration in which two Fe ions are adjacently substituting the Sn sites in a distorted rutile structure. Spin density results reveal the direct exchange interaction between

Self-powered solid-state photodetector based on TiO2 nanorod/spiro-MeOTAD heterojunction

\mathrm{O}\phantom{\rule{0.3em}{0ex}}2p