Solid State Phenomena Vols. 121-123

Abstract: This paper presents a novel valance intersubband laser based on Si-based Si-Ge superlattices grown on a relaxed Si0.5Ge0.5 buffer layer. Effective mass theory is used to calculate the inplane valence subband dispersion of Si-Ge superlattices within 6×6 Kane model. Analysis of the inplane energy dispersion shows that the light-hole effective mass is inverted at off zone center region. The laser structure can be designed with a simple quantum cascade scheme. Our calculation shows that with the electrical pump, it is possible to achieve population inversion between the two subbands at local k space where the light-hole effective mass is inverted. Optical gain of the order 100/cm can be achieved with a pumping current density 10 kA/cm2.

Abstract: Nano-imprinting technology, currently developing as an alternative technology for photolithography, is mostly dealing with photo resist materials for etching barrier. In other words, the materials imprinted are used as the barriers for wet etching or RIE (reactive ion etching), and then are removed after all. Thus, most materials developed for nano-imprinting technology have relatively low Tg(<100oC), in case of solids or have a low viscosity before curing in order to fill the gap of the stamp. Such materials could not be suitable for the structures that require relatively high temperature process ability, high modulus or high durability. Epoxy is one of candidates that meet such requirements for the structures. However, it has not been reported about imprinting on epoxy materials. In this paper, nano-imprinting technology was developed to fabricate the microstructures. Instead of thermoplastic imprint resin, solid phase epoxy films, which is thermoset polymer, were imprinted with SAM (self assembly monolayer) coated quartz and silicon stamps. Feature size of stamp varies from 150nm to 1 μm and height was 300nm for quartz stamp and 3μm for Si stamp.

Abstract: The quantum transmission characteristic of three-terminal C60 molecular bridge is investigated theoretically by using Green's function approach based on tight-binding theory with only one π orbital per carbon atom inside C60 molecule. The transmission spectra that electrons transport through the C60 molecular bridge from one terminal to the other two terminals are obtained. The electronic current distributions inside the molecular bridge are calculated and shown in graphical analogy by the current density method based on Fisher-Lee formula at the energy points E=±0.42, ±1.06 and ±1.5, respectively, where the transmission probabilities appear peaks. We found that the transmission spectra are related to the incident electronic energy, and depend on C60 molecular levels strongly. We also found that the electrons transport through the C60 molecular bridge symmetrically, and the multi-point switching properties depend on the energy. That the current distributions in the C60 molecular bridge agree well with Kirchhoff quantum current momentum conservation law is shown.

Abstract: We developed a method to fabricate bent fiber probe: heated pulling combined with chemical etching. Based on sampling theory, the resolving power of SNOM relates to the size of the probe tip. If the apex of the probe is smaller, the resolution ability of SNOM is higher. At the same time it can collect more near-field information through bigger cone angle of probe. Through improving the operation and optimizing the parameters of the heated-pulling instrument, we can obtain the probe with bent angle fiber varying from 120-150 degree, the cone angle varying from 40-90 degree and the apex diameter less than 100nm. With this new brush shape of probe, the collecting efficiency for near-field light is improved. That is to say that more near-field information is obtained. The successful ratio of the produce is more than 70%.

Abstract: The high-frequency capability of carbon nanotube field-effect transistors is investigated by simulating the small-signal performance of a device with negative-barrier Schottky contacts for the source and drain, and with a small, ungated region of nanotube between the end contacts and the edge of the wrap-around gate electrode. The overall structure is shown to exhibit resonant behaviour, which leads to a significant bias dependence of the small-signal capacitances and transconductance. This could lead to high-frequency figures of merit (fT and fmax) in the terahertz regime.

Abstract: Photoacid generators (PAGs) have been widely used as a key component in a chemically amplified photoresist system. The PAG monomer containing an arylsulfonium triflate group was synthesized and was polymerized with benzyl methacrylates. The molecular weight and the content of PAG were controlled to improve thermal stability and sensitivity for atomic force microscope lithography. The fabrication of anodization patterns, which can be enhanced by addition of PAG unit to resist, was achieved at the low bias voltage and the high speed of AFM patterning. The physical properties of resists and lithographic factors affecting the high speed AFM lithography will be discussed.

Abstract: In this paper it had been observed experimentally that hydrogen adsorption on nano-structure sp2-bonded amorphous carbon film, which was produced on ceramic substrate by microwave plasma chemical vapor deposition system, could improve its field emission property. Considering that surface morphology is not significantly varied with hydrogen adsorption, we suggested that hydrogen adsorption on the film surface mainly lowered the work function of emitter surface. For confirmation of the above suggestion, theoretical calculation was performed to investigate work functions of graphite (0001) surfaces with different hydrogen chemisorption sites at 1/2 H coverage by using first principles method based on DFT-GGA. An asymmetric slab supercell approach with periodic boundaries had been employed to model the graphite (0 0 0 1) surface. The calculation results were in agreement with experimental conclusion.

Abstract: Solid lipid nanoparticles(SLN) appear a promising approach as a drug system for topical application. The solid lipid matrices allow protection of incorporated active ingredients against chemical and physical degradation. This paper deals with controllable preparation of solid lipid nanoparticles based on the phase behaviors of hot microemulsions. The pseudoternary phase diagram for the system of glyceryl monostearate(GMS)/ mixed surfactants (polyoxyethylene(40) stearate(S-40) and poloxamer 188 (F-68))/ water was obtained at 60 °C using self-made apparatus with temperature control. The mass ratios of glyceryl monostearate(GMS), mixed surfactants and water were determined according to the region of w/o hot microemulsion. It was shown that the size of TP-SLN increased slightly with the increasing of concentration of TP, polydispersity index was approximately 0.5, encapsulation efficiency decreased distinctly. The percutaneous absorption experiment of tea polyphenols loaded SLN through the rabbit skin were conducted using self-made Franz diffusion cell in vitro. The transdermal penetration was sustained.

Abstract: Hardening of blood vessels has steeply increased every year, and implantation stent was used to solve that the conditions of illness. However, in-stent restenosis continues to make problem. To overcome the problem of in-stent restenosis, the concept of local delivery of antiproliferative or immunosuppressive drugs has been introduced into interventional cardiology. Local drug delivery system was demonstrated by using drug-eluting stents coated with nanoporous anodic aluminum oxide (AAO) used for controlled drug release. Effects of diameter and depth of AAO on the diffusion characteristics of drug were investigated. 2-deoxyadenosine was tested. AAO pore diameter and depth showed image by SEM and characterization of diffusion of drug from the AAO nanoporous pore diameter and depth was carried out using by HPLC (high performance liquid chromatography).