Jieqiong Zhang

Interface control and leakage current conduction mechanism in HfO2 film prepared by pulsed laser deposition

The N2 atmosphere postannealing is introduced to improve the interfacial quality and the dielectric properties of HfO2 films prepared by pulsed laser deposition. The disappearance of interface layer between HfO2 film and Si substrate and the decrease of leakage current densities after annealing are further confirmed by high-resolution cross-sectional transmission electron microscopy investigation and electrical measurement. Electric conduction analysis results show that the dominant leakage current conduction mechanisms of the annealed HfO2 film are the Schottky emission at low electric field, the trap-assisted tunneling, and space-charge-limited current at high electric field for the gate and substrate injections, respectively.

Synthesis and photoelectrochemical response of CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes

A continuous and compact CdS quantum dot-sensitive layer was synthesized on TiO2 nanorods by successive ionic layer adsorption and reaction (SILAR) and subsequent thermal annealing. The thickness of the CdS quantum dot layer was tuned by SILAR cycles, which was found to be closely related to light absorption and carrier transformation. The CdS quantum dot-sensitized TiO2 nanorod array photoelectrodes were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet–visible absorption spectroscopy, and photoelectrochemical property measurement. The optimum sample was fabricated by SILAR in 70 cycles and then annealed at 400°C for 1 h in air atmosphere. A TiO2/CdS core-shell structure was formed with a diameter of 35 nm, which presented an improvement in light harvesting. Finally, a saturated photocurrent of 3.6 mA/cm2 was produced under the irradiation of AM1.5G simulated sunlight at 100 mW/cm2. In particular, the saturated current density maintained a fixed value of approximately 3 mA/cm2 without decadence as time passed under the light conditions, indicating the steady photoelectronic property of the photoanode.

Preparation and photoluminescence of undoped ZnTiO3 thin films

ZnTiO3 thin films were prepared by radio frequency cosputtering of ZnO and TiO2. It was found the as-prepared film is amorphous and the cubic phase ZnTiO3 films form after annealing at temperature above 500 °C. The absorption spectra indicate that the optical band gap of the crystalline ZnTiO3 film is about 3.70 eV. A strong photoluminescence band centered at 355 nm consisting of two emission peaks was observed in 800 °C annealed ZnTiO3 thin film, and the peak positions of these two emission move to short wavelength with increasing annealing temperature. It was found the emission peak at ultraviolet zone is resulted from O2− vacancy and that in the blue zone is attributed to Zn2+ vacancy.

Evidence of interface conversion and electrical characteristics improvement of ultra-thin HfTiO films upon rapid thermal annealing

Ultra-thin HfTiO films were grown on Si substrate and subjected to rapid thermal annealing at 400 °C, 500 °C, 600 °C, and 700 °C in nitrogen ambient. The interface of the as deposited film is formed by SiOx and silicate, but after annealing at 600 °C, interfacial SiOx completely converted into silicate. The film annealed at 600 °C has the highest k value of 45.9, the smallest equivalent oxide thickness of 0.8 nm with the physical thickness of 9.4 nm, the lowest leakage current density of 3.1 × 10−6 A/cm−2 at bias voltage of −1 V, which shows excellent electrical properties.

Study on Composition Distribution and Ferromagnetism of Monodisperse FePt Nanoparticles.

Monodisperse FePt nanoparticles with size of 4.5 and 6.0 nm were prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in benzylether. The crystallography structure, size, and composition of the FePt nanoparticles were examined by X-ray diffraction and transmission electron microscopy. Energy dispersive X-ray spectrometry measurements of individual particles indicate a broad compositional distribution in both the 4.5 and 6 nm FePt nanoparticles. The effects of compositional distribution on the phase-transition and magnetic properties of the FePt nanoparticles were investigated.

Structure and electrical properties of sputtered TiO2/ZrO2 bilayer composite dielectrics upon annealing in nitrogen

The high-k dielectric TiO2/ZrO2 bilayer composite film was prepared on a Si substrate by radio frequency magnetron sputtering and post annealing in N2 at various temperatures in the range of 573 K to 973 K. Transmission electron microscopy observation revealed that the bilayer film fully mixed together and had good interfacial property at 773 K. Metal-oxide-semiconductor capacitors with high-k gate dielectric TiO2/ZrO2/p-Si were fabricated using Pt as the top gate electrode and as the bottom side electrode. The largest property permittivity of 46.1 and a very low leakage current density of 3.35 × 10-5 A/cm2 were achieved for the sample of TiO2/ZrO2/Si after annealing at 773 K.

Fe-Pt Alloy Nanowire Arrays Prepared by Pulse DC Electrodeposition

Highly ordered Fe-Pt nanowire arrays were fabricated using anodic aluminum oxide templates by pulse DC electrodeposition. The influences of pulse ratio and frequency on the microstructural and magnetical properties of Fe-Pt nanowire arrays have been studied. The composition of Fe-Pt nanowires can be adjusted by pulse ratio and the crystallization of wires can be modified by pulse frequency. By choosing an optimal pulse ratio and pulse frequency, the Fe-Pt nanowire arrays with out-of plane coercivity up to 1620 Oe can be achieved. Annealing of Fe-Pt nanowire arrays could improve the crystallinity of wires and accordingly enhance the coercivity.

(001) oriented L10 FePt/B4C multilayer thin films on naturally oxidized Si substrate

(001) oriented FePt/B4C multilayer thin films with high perpendicular coercivity (≥9.7 kOe) were prepared on naturally oxidized Si substrates by magnetron sputtering and thereafter annealing. Effect of FePt layer thickness on the texture parameter of the (001) orientation, chemical ordering, and magnetic properties has been studied. It was found that the texture parameter of (001) orientation increases while the degree of chemical ordering decreases with the decrease of FePt layer thickness. The coercivity drops with the decrease of layer thickness due to the low degree of chemical ordering. The results of δM plots analysis show that intergrain exchange coupling action weakens in response to the decrease of layer thickness and thus decreases the remanence ratio.

ZnO nanorod multilayer film prepared by hydrothermal growth and its application in dye sensitised solar cells

Abstract ZnO nanorod multilayer film was hydrothermal fabricated on fluorine-doped SnO2-coated glass (FTO) substrate using the sol–gel method from a ZnO seed layer. Such a multilayer film has micrometre scale arms linking with ZnO nanorod arrays vertical to the FTO substrate. It provides a large surface area for dye adsorption and a rapid pathway for electron transport along the nanorod channel. The sensitised solar cell based on the optimised ZnO nanorod multilayer film with thickness of 56.7 μm reaches a power conversion efficiency (PCE) of 1.8%.

Influence of Source and Drain Electrodes on Device Performance of ZnO Thin Film Transistors

In this study, thin film transistors (TFT) with ZnO as the channel layer and HfO2 as the gate dielectric were fabricated by radio frequency magnetron sputtering. The electrical properties of the TFT devices related to the Al and Au electrodes were investigated. From the drain current (IDS) vs the drain-source voltage (VDS) curve of the TFT, IDS can reach 0.3 mA for Al electrodes at the gate voltage (VGS) = 14 V and VDS = 10 V, while it is 0.13 mA for Au. From the transfer properties curve, the former yields a threshold voltage of 3 V, and a sub-threshold swing of 1.78 V/decade; while the latter has 4 V and 1.88 V/decade, respectively. The result indicates that the electrical properties of TFT device with Al electrodes are better than Au. The smaller work function with the Al electrodes is the key to TFT devices (Al: 4.28 eV < Au: 5.1 eV).