Key Engineering Materials Vols. 609-610

Abstract: In this paper, resistance switching devices with Au/SnO₂/Al sandwich structure were fabricated. The prepared devices showed a reliable unipolar resistance switching characteristic. The forming voltage of SnO₂-based resistance devices increased with increasing film thicknesses, while SnO₂ film thickness had little influence on set and reset voltages. When the SnO₂ film thickness was 46 nm, the device showed steady and reliable conversion under voltage sweeping and the ratio between high and low resistance states was higher than 10², which can basically satisfy the requirements for practical application.

Abstract: Ag-doping TiO₂ nanotubes (Ag-TNTs) were synthesized. A double junction is proposed, involving a Schottky junction and p-n junction (denoted as Ag-p-n junction) occurring between the Ag particles and the nanotube surface, as well as forming inside TiO₂ nanotubes, respectively. The strongly built-in electric field of the junctions promotes the separation of photo-holes and photoelectrons, enhancing the photocatalytic efficiency. Ag-TNTs were characterized by XRD and TEM. XRD results indicated that a mixture of anatase and rutile phases. The presence of a new peak at 271 cm¹ was revealed by Raman spectral analysis of Ag-TNTs.

Abstract: Highly monodispersed ZnO nanorods have been synthesized by the hydrothermal approach with polyacrylamide (PAM) as the template and zinc acetate as the zinc source. Most of these synthesized ZnO rods have diameters of 30 nm~200 nm and lengths of 80 nm~15 μm. The structural characterization of ZnO nanorods was carried out by XRD, TG, FTIR, TEM and SEM. nanoZnO rods can be prepared merely by one step reaction using little template. It indicated that this method can be applied to the commercialization of rod-like ZnO preparation technology.

Abstract: The Ti-48at%Al composite powder was synthesized by high energy ball milling. The properties of the composite particles, such as medium diameter,Phase ,microstructure and components, were respectively investigated . Results show that, the phase evolution process can be described by: Ti+ Al fcc Ti (Al),TiAl,TiAl₃,Ti₃AlTiAl₃,Ti₃Alamorphous phase. After milling 3 hours, Fcc Ti (Al) solid solution, TiAl, TiAl₃, Ti₃Al were found. After milling 9 hours, the amorphous phase of Ti - 48 at % Al were produced. The element distribution of the mechanically alloyed Ti-48at%Al powder was close to the initial design composition after 5 h milling, but this distribution was inhomogeneous. Medium diameter (D₅₀) of Ti-48at%Al composite powder achieved the minimal size 9.56 μm after milling for 5hours.

Abstract: Dip-pen nanolithography (DPN), based on atomic force microscope (AFM) system, is an effective method for nanoscale science and engineering, and the potential applications of DPN will be shown in the field of nanomechanics, nanomaterials, nanobiotechnology, nanomedicine. And the novel combined-dynamic mode DPN (CDDPN), rather than mostly used contact mode DPN or tapping mode DPN, becomes the important tool for the fabrication of nanodots with the direct-writing method of depositing the ink onto the hard silicon surface at the predetermined position, which is presented in the corresponding experiments. In addition, the size of nanodots gradually decreases in the diameter with the increase of the number of nanodots in the case of AFM tip dipping in ink once. However, the size in height does not monotonically reduce as the reduction of the ink, which is affected by the interaction among the relative humidity, AFM tip, substrate material, surface roughness, etc. For the better nanolithography quality of the nanodot, the nanolithography process, under the optimized process parameters, is accomplished once without the intermediate scan imaging process as much as possible.

Abstract: A freestanding sensor-based 3ω method was employed to measure the effective thermal conductivity of porous polymethacrylimide (PMI) foams with different densities at different temperatures. Experimental data showed that within the measuring temperature range, the effective thermal conductivity increased with temperature. Moreover, the formation mechanism of the relationship between the effective thermal conductivity and temperature was analyzed in this paper.

Abstract: BaTiO₃ crystal film has the very high electro-optic effect, so it has important research value for thin film waveguide electro-optic modulators. In this work, BPM software is used to simulate the single-mode condition of ridge waveguide at first, then BaTiO₃ film waveguide structure is designed with suitable film thickness.BaTiO₃ waveguide thin films are grown by pulsed laser deposition on single crystal MgO substrate. The BaTiO₃ thin-film crystalline structures grown at different temperature sand different laser powers were analyzed by using X ray diffraction , which showed the BaTiO₃ films have a priority crystallization direction and good crystallization quality at 750°C grown temperature. For the optimally-designed waveguide structures, the PECVD technique and ICP plasma etching method are employed to coat and etch Si₃N₄ films, respectively. Through the optimization of main process parameters, 60 sccm reaction gas flow and 150 nm/min etching speed are finally selected to create the ridge waveguides, and consequently, the surface roughness of Si₃N₄ film waveguide reaches 2.3 nm.

Abstract: This paper presents an experimental investigation of microstructure and piezoresistive properties of phosphorus-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The phosphorus-doped nc-Si:H thin films (5% doping ratio of PH₃ to SiH₄) were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The microstructure and surface morphology of the deposited thin films was characterized and analyzed with Raman spectroscopy and atomic force microscopy (AFM), respectively. The piezoresistive properties of the deposited thin films were investigated with a designed four-point bending-based evaluation system. In addition, the influence of temperature on the piezoresistive properties of these thin films was evaluated with the temperature coefficient of resistance (TCR) measurements from room temperature up to 80°C. The experimental results show that phosphorus-doped nc-Si:H thin films prepared by PECVD technique are a two-phase material that constitutes of nanocrystalline silicon and amorphous silicon, and they present a granular structure composed of homogeneously scattered nanoclusters formed by nanocrystalline silicon grains (6nm). Moreover, phosphorus-doped nc-Si:H thin films exhibit negative GF at room temperature and show good thermal stability from room temperature up to 80°C, and the value of GF and TCR is about-31 and-509ppm/°C, respectively. These features could make phosphorus-doped nc-Si:H thin films act as a promising material for piezoresistive-based MEMS sensor.

Abstract: The different layers of graphene were prepared by liquid ultrasonic direct exfoliation. The dispersion stability of graphene in water under different ultrasonic time, the antifriction Performance, and the elements and morphology of the wear surface are investigated. The wear mechanism of graphene solution was preliminarily discussed. The results indicate that graphene with thickness of 10nm-150nm can be produced by ultrasonic peeling expanded graphite and the dispersion stability of graphene aqueous is best when sonicating for 3h. The antifriction property and wear mechanism of graphene aqueous vary with the graphene content. When graphene content is 0.01wt%, the antifriction performance of graphene aqueous was optimum and its wear mechanism was abrasive wear.

Abstract: 1:1 MMT/In composite nanopowders were prepared by nanoMMT and nanoIn modified with coupling agent KH550, and the nano-MMT/In lubricating oil dispersion system was prepared by 150N base opl containing 3 mass fraction of nano-MMT/In composite powders, and then took the dispersion effect by laser particle size analyzer ,TEM and IR. The anti-wear and friction-reducing behaviors of that lubricating oil dispersion system were observed on the MMU-10G abrasive-wear tester with 45^#steel tribo-pair, the morphology and the element of the worn surfaces were analyzed by SEM and EDX. The results showed that the grain size of the modified nano-MMT/In was smaller than the one without modification, and the modified nano-MMT/In had the good dispersion in the system; compare with the one in base oil system, the average friction coefficient of sample of 45^#steel tribo-pair in nano-MMT/In additive lubricating oil system had declined by 27.5%, and the total wear mass loss had declined by 63%; The surface of sample after friction had created the self-repairing film that contain the characteristic element of MMT and In, that phenomenon was caused by the interaction of nano-MMT and nano-In.