Search

Very-high-frequency (VHF) magnetron sputtering is an important method to deposit the polycrystalline films at low temperature. To increase the plasma density, ion flux and to control the ion energy, the inductively coupled plasma (ICP) and substrate bias co-assisted VHF magnetron sputtering was developed. The plasma properties of this system were measured by a Langmuir probe and a retarding field energy analyzer. In the VHF magnetron sputtering, the ICP discharge can increase the plasma density effectively but has a small influence on the ion energy and ion flux; the substrate bias can increase the plasma density and ion flux more effectively but result in the divergence of ion energy. When the ICP discharge and substrate bias are simultaneously applied, the divergence of ion energy can be suppressed, while the high plasma density (2.6 × 10 17 m − 3 ) and ion flux (4.3 × 10 20 m − 2 ⋅ s − 1 ) can be remained. Therefore, the ICP and substrate bias co-assisted VHF magnetron sputtering is a possible way to deposit the polycrystalline films at low temperature with a higher growth rate.

The plasma property of a hybrid ICP/sputtering discharge driven by 13.56 MHz/60 MHz power sources was investigated by Langmuir probe measurement. For the pure sputtering discharge, the low electron density and ion flux, the rise of floating potential and plasma potential with increasing power, as well as the bi-Maxwellian distribution of electron energy distributions (EEDFs) were obtained. The assistance of ICP discharge led to the effective increases of electron density and ion flux, the suppression of rise of floating potential and plasma potential, as well as the change of EEDFs from bi-Maxwellian distribution into Maxwellian distribution. The increase of electron density and ion flux, and the EEDFs evolution were related to the effective electron heating by the induced electric field.

The aggregation behavior of silicone oil polymers exposed to Ar plasmas was investigated. A reptation aggregation related to the viscosity of silicone oil was found. The viscosity dependence η ∼ Lb on the reptation length L with b = 3.37 in the viscous coefficient range of 20 and 500 mm2 · s−1 was obtained. The formation of reptation aggregation is thought to relate to the gradient viscosity in the vertical direction due to crosslinking and formation of SiO network at the surfaces of silicone oils induced by energetic ions bombardment and the vacuum-ultraviolet irradiation, as well as the temperature gradient in vertical direction induced by energetic ions bombardment.

The growing demand for compact point-of-care medical devices and portable instruments for on-site environmental sampling has stimulated intense research on flexible sensors that can be miniaturized and function under considerable physical deformation. We report a new type of flexible electrochemical biosensors based on free-standing graphene paper carrying binary nanocomposites of PtAu alloy and MnO 2 . The coral-like PtAu–MnO 2 nanocomposites are grown on the substrate through one-step template-free electrodeposition, leading to an intimate contact between the PtAu alloy and MnO 2 matrix. The flexible electrode exhibits a unique set of structural and electrochemical properties such as better uniformity, larger active surface areas, and faster electron transfer in comparison with the control electrode prepared by tandem growth of MnO 2 network and PtAu alloy in two steps. In nonenzymatic amperometric glucose detection, the PtAu–MnO 2 binary nanostructure-decorated graphene paper has shown greatly enhanced sensing performance such as wide liner range (0.1 mM to 30.0 mM), high sensitivity (58.54 μA cm −2 mM −1 ), low detection limit (0.02 mM, S / N =3), satisfactory selectivity, excellent reproducibility and stability, and tolerability to mechanical stress. The strategy of co-growth of metal and metal oxides on freestanding carbon substrates opens new possibility to develop high-performance flexible electrochemical sensors.

With the fluorocarbon plasma pre-etching silicon carbide (SiC), a method to prepare few-layer graphene at lower temperature (950 °C) by thermal decomposition of SiC was developed. The graphene phase has been found by the X-ray photoelectron spectroscopy and Raman spectroscopy measurement. The planar sheet of carbon atoms was also observed by atomic force microscopy. The results demonstrate that few-layer graphene can form on SiC substrate at low temperature.

Polycrystalline BaTiO3/SrTiO3 (BT/ST) multilayer thin films were fabricated via pulsed-laser deposition onto Pt/Ti/SiO2/Si substrates. The dielectric constant of the multilayer films was obviously enhanced and the dielectric loss was almost the same as that of the pure BaTiO3 and SrTiO3 thin films. A dielectric constant of 721 at 10 kHz was observed for a stacking periodicity of 60 nm at room temperature and the corresponding dielectric loss was maintained below 0.04. The study indicates that there are some differences between the multilayer films and the pure films in electrical properties. The mechanism of dielectric enhancement of the multilayer thin films was discussed.

Polycrystalline BaTiO3/SrTiO3 multilayered thin films have been prepared on Pt/Ti/SiO2/Si substrates by a sol–gel processing. The X-ray diffraction (XRD) patterns and Auger electron spectroscopy (AES) indicate that the multilayered thin films were formed. The dielectric constant of the multilayered films was significantly enhanced and the dielectric loss was almost the same as that of the uniform BaTiO3 and SrTiO3 thin films. A dielectric constant of 660 at 1 kHz was observed for a stacking periodicity of 66 nm at room temperature and the corresponding dielectric loss was maintained below 0.05. The study indicates that there are some differences between the multilayered films and the uniform films in the dielectric constant–frequency relation and capacitance–voltage characteristics. The report also analyzes the mechanism of dielectric enhancement of the multilayered thin films prepared by the sol–gel process.

Dielectric enhancement was observed in polycrystalline BaTiO3/Ba0.6Sr0.4TiO3 multilayered thin films deposited layer-by-layer on Pt/Ti/SiO2/Si substrates via pulsed laser deposition. The dielectric constant of the films was enhanced more than four times with the decrease of the individual layer thickness down to 30 nm, while the dielectric loss was kept at a low level comparable to that of the solid solution Ba0.8Sr0.2TiO3 thin films. The Maxwell-Wagner model is proposed to explain the experimental data, which can predict both the dielectric enhancement and frequency dependence when the individual layer thickness is more than 40 nm.

The deposition of nitrogen-containing carbon films on silicon substrates at atmospheric pressure and low temperature has been carried out by electrolysis of methanol and ammonia solutions. Amorphous carbon films containing about 8% nitrogen were obtained. The observed C–N vibration bonds by Raman and FTIR spectroscopy and the chemical states by XPS of C and N atoms indicate that the carbon and nitrogen are sp 2 and sp 3 chemically bonded in the films. Schemes for film growth in the liquid phase were suggested.

High transmittance, low resistivity, and c-axis highly oriented ZnO:Al thin films on glass substrate were obtained by laser ablation at different deposition conditions. These films were deposited with an excimer (KrF) laser beam of λ = 248 nm operated under the conditions of 7.0 J cm−2 energy density and 5 Hz repetition rate. The electrical and optical properties were found to depend on substrate temperature and doping ratio of Al. From electrical and optical analyses we observed that the carrier concentration, optical transmittance and optical energy gap the ZnO:Al transparent conductive oxides increased when the deposition temperature is raised from 200°C to 300°C. X-ray diffraction analyses showed that the crystallinity of the film became better with increasing temperature, and indicated that the crystallinity of the film determined its electrical and optical properties. The film prepared at 300°C using a target of doping ratio of 1.5% Al2O3 is strongly c-axis-oriented polycrystalline, and has a low resistivity of 9.0 × 10−4cm, a carrier concentration of 5.8 × 1020 cm−3 and a transmittance of about 90% in the visible range. However, the crystallinity of the film prepared at 500°C became poor, and its resistivity also became higher.

The leakage characteristics and dielectric properties of Pt/(Ba,Sr)TiO3/Pt thin-film capacitors were found to be remarkably sensitive to the postannealing temperature in oxygen and nitrogen atmosphere. High leakage currents and low-frequency dielectric relaxation were found in as-deposited capacitors after they had been postannealed in nitrogen at 550 °C and subsequently annealed in oxygen at 350 °C. Such results are related to the mobile oxygen ions and oxygen vacancies accumulated in the (Ba,Sr)TiO3 films. The chemical process of the formation of charged oxygen ions during postannealing is proposed.

We report the successful fabrication of (Er3+, Yb3+)-co-doped ZnO transparent hybrid materials by controlling compositions and crystallization. The singly precipitated ZnO nanocrystals were preferentially oriented along the c-axis on the glass surface, leading to an intense luminescence at the bandgap energy of ZnO. The Er3+ and Yb3+ ions assembled around the low-phonon-energy ZnO nanocrystals, achieving an enhanced two-photon upconversion emission in the visible region. In addition, the glass ceramic exhibited typical paramagnetism with antiferromagnetic interactions. The multifunctional combination in such a low-cost, easily shapable and environmentally friendly bulk material may find a wide range of device applications.