A novel method to mass-produce PDMS stamps based on nanoimprint

Soft lithography is a low-cost and convenient method for the forming and manufacturing of micro/ nanostructures compared to the traditional optical lithography. In soft lithography, poly（dimethylsiloxane） （PDMS） stamps with relief structures have been widely used to transfer patterns. The traditional fabrication approach of PDMS stamps is time-consuming since the master has been occupied during the curing process. By adding and repeating fast nanoimprint step, many intermediate polymeric molds can be produced from the master and these molds can then be employed to replicate more PDMS stamps while the time used is close to that of the common way. We demonstrated this idea by three masters which were made by the DEM （Deepetching, Electroforming and Microreplicating） and FIB （Focused Ion Beam） techniques. The photos show that the patterns on the PMDS stamps successfully duplicated patterns on the origin masters.     

Atomistic structural change of silicon surface under a nanoparticle collision

As the dimensions of the semiconductor device com-ponents shrink, a profound understanding of the mi-cro/nanomachining of monocrystalline silicon surface isbecoming essential. Molecular dynamics (MD) simulationis a powerful tool for the study of the processing mecha-nism of silicon surfaces. The MD simulations of nano-cutting[1,2], nano-grinding[3,4], as well as nano-indenta-tion[5,6] have been studied intensively. It is shown that theamorphous phase transformation and the plastic flow in-si…     

Hydrogen Bonding in Hydrogenated Amorphous Germanium

Thin films of hydrogenated amorphous germanium (a-Ge:H) were prepared by radio frequency glow discharge deposition at various substrate temperatures. The hydrogen distribution and bonding structure in a-Ge:H were discussed based on infrared absorption data. The correlation between infrared absorption spectra and hydrogen effusion measurements was used to determine the proportionality constant for each vibration mode of the Ge-H bonds. The results reveal that the bending mode appearing at 835 cm^-1 is associated with the Ge-H2 (dihydride) groups on the internal surfaces of voids. While 1880 cm^-1 is assigned to vibrations of Ge-H (monohydride) groups in the bulk, the 2000 cm^-1 stretching mode is attributed to Ge-H and Ge-H2 bonds located on the surfaces of voids. For films associated with bending modes in the infrared spectra, the proportionality constant values of the stretching modes near 1880 and 2000 cm^-1 are found to be lower than those of films which had no correspondina bending modes.     

Bi-Spectrum Scattering Model for Dielectric Randomly Rough Surface

The bistatic scattering model is often used for remote microwave sensing. The bi-spectrum model (BSM) for conducting surfaces was used to develop a scattering model for dielectric randomly rough surfaces to estimate their bistatic scattering coefficients. The model for dielectric rough surfaces differs from the BSM for a conducting surface by including Fresnell reflection and transmission from dielectric rough surfaces. The bistatic scattering coefficients were defined to satisfy the reciprocal theorem. Values calculated using the BSM for dielectric randomly rough surfaces compare well with those of the integral equation model (IEM) and with experimental data, showing that the BSM accuracy is acceptable and its range of validity is similar to that of IEM while the BSM expression is simpler than that of IEM。     

PL Emission and Shape of Silicon Quantum Dots

The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.     

Imprint Lithography at Room Temperature with Novolak Resin and Its Application

1 Results Imprint lithography[1] has attracted considerable attention from the viewpoint of low cost fabrication,because light exposure systems are not required. Up to now,polymethylmethacrylate (PMMA) films and hard molds were often used in imprint lithography.In this paper,we report on the successful demonstration of imprint lithography using novolak resin (OFPR-800),which is more suitable than PMMA for dry etching,and a soft mold such as a soft polyester sheet,which has a two-dimensional (2D) square grating with a pitch of 1 000 nm and a height of 300 nm. By combining pressing and successive developing of OFPR-800,a 2D square grating on the soft mold was successfully transferred onto OFPR-800.Schematic of an imprint apparatus is illustrated in Fig.1,and atomic force micrographs (AFMs) of the soft mold and the patterned OFPR-800 are shown in Fig.2.     

Field emission characteristics of ZnO nanotetrapods and the effect of thermal annealing in hydrogen

Large-scale tetrapod-like ZnO nanostructures have been synthesized using a thermal chemical vapor deposition method on a silicon substrate. The high-purity nanotetrapods show sharp tips geometry with a wurtzite structure. The field emission properties of the uniform ZnO nanostructural material are investigated at different anode-cathode distances. The turn-on field for the ZnO nanotetrapods is found to be about 3.7 V/μm at a current density of 1 μA/cm^2. The field emission behavior obeys Fowler-Nordheim relationship. More importantly, the field emission properties are improved after annearing in hydrogen, and therefore high emission current and low turn-on field are obtained. These results indicate that tetrapod-like ZnO nanostructures are a promising candidate for cold cathode emitters.     

Self-assembly of chiral amphiphiles with π-conjugated tectons

Self-assembly of chiral amphiphiles with π-conjugated tectons into one-dimensional helical nanostructures offers great potential applications in the biological,physical,and material sciences.In this review,the recent development of supramolecular self-assembly of chiral amphiphiles with π-conjugated tectons has been discussed on the basis of experimental exploration by elegantly utilizing cooperative noncovalent forces such as π-π stacking,hydrophobic interaction,hydrogen bond and electrostatic interaction,and the potential applications of these self-assembled helical nanostructures in chiral recognition,asymmetric catalysis,electrical conduction,switchable interfaces and soft template for the fabrication of one-dimensional hard materials are described by a representative example.Meanwhile,some scientific and technical challenges in the development of supramolecular self-assembly of chiral amphiphiles with π-conjugated tectons are also presented.It is hoped that this review can summarize the strategies for self-assembling soft nanomaterials by using chiral amphiphiles with π-conjugated tectons,and also as a guideline for design functional nanomaterials for various potential applications.     

Sliding mode identifier for parameter uncertain nonlinear dynamic systems with nonlinear input

This paper presents a sliding mode(SM) based identifier to deal with the parameter idenfification problem for a class of parameter uncertain nonlinear dynamic systems with input nonlinearity. A sliding mode controller (SMC) is used to ensure the global reaching condition of the sliding mode for the nonlinear system;an identifier is designed to identify the uncertain parameter of the nonlinear system. A numerical example is studied to show the feasibility of the SM controller and the asymptotical convergence of the identifier.     

Rod-shaped Au@PtCu nanostructures with enhanced peroxidase-like activity and their ELISA application

Pt and its based alloy nanoparticles （NPs） have been reported to demonstrate novel enzyme-like activities. Varying composition is very important to realize the opti- mization of their functions through the tuning of electronic structure. In this paper, our effort is focused in this direction by tailoring the electronic structure of Pt NPs via alloying with copper. Using gold nanorod （Au NR） as core, a simple method to prepare PtCu alloy shell is developed （termed as Au@PtCu NR）. The introduction of copper could result in endcap-preferred growth mode owing to the lattice mismatch between alloy shell and the Au core. The variation in the electronic structure changes the substrate affinity, and enhanced affinity was found for H202. Besides, the designed Au@PtCu nanostructures have realized spatial separation of catalytic and recognition sites. Binding of recognition antibodies had negligible effect on their catalytic activity. Based on their peroxidase- like activity, a highly sensitive detection of human immunoglobulin G （IgG） was demonstrated in a direct enzyme-linked immunosorbent assay （ELISA） mode. The detection limit can be as low as 90 pg/mL.     

Human Body Modeling and Posture Simulating Based on 3D Surface Scan Data

This paper presents a new approach for modeling the human body by considering the motion state and the shape of whole body. The body model consists of a skeleton kinematic model and a surface model. The former is used to determine the posture of the body, and the latter is used to generate the body shape according to the given posture. The body surface is reconstructed with multi-segment B-spline surfaces based on the 3D scan data from a real human body. Using only a few joints parameters and the original surface scan data, the various body postures and the shape can be generated easily. The model has a strong potential of being used for ergonomic design, garment design, virtual reality environment, as well as creating human animation, etc.     

A Preliminary Study on Soft Tissue Cutting in Virtual Surgery Simulation

A method for simulation of cutting virtual soft tissue objects made of tetrahedron elements is developed. A linear isotropic elastic model is used for the soft tissue material properties and a tensor-mass model chosen for the physical deformation. The Verlet leapfrog method is used to perform time integration in solving the dynamic equations. Cutting is simulated by simply removing the tetrahedron elements that are intersected with the virtual scalpel. By making use of the spatial coherence, collision detection between soft tissue objects and the virtual scalpel is sped up. To facilitate the simulation, the soft tissue object is represented by linked lists of vertices, edges and tetra elements with pointers to the related neighboring features. The established software framework can serve as a base for the future development. Results of virtual experiments are shown and discussed. Possible future directions are also given.     

Improved ethanol, acetone and H2 sensing performances of micro-sensors based on loose ZnO nanofibers

Both one-dimensional nanostructures and porous nanostructures are benefit to the sensing enhancement of semiconducting functional materials.The present paper shows an effective route to combining the advantages of these two nanostructures for a novel type of ZnO nanomaterials.Basically,a pore-forming material is employed in an electrospinning method,and the products are characterized by X-ray powder diffraction(XRD),energy dispersive X-ray spectroscopy(EDX),and transmission electron microscopy(TEM).The obtained materials are loose ZnO nanofibers,which own both porous and one-dimensional nanostructures.Micro-sensors are fabricated by sputtering and etching techniques,and the as-prepared nanofibers are used as the functional materials in them.The sensors show improved sensing properties both in sensitivity and response-speeds.The sensitivity is enhanced from 4 to 8 and the response time is shortened from 14 to 10 s when the sensors are exposed to 100 μL/L ethanol at 260℃.Similar results are also observed in acetone and H2 sensing tests.These enhancements are based on the one-dimensional and porous nanostructures of the nanofibers.     

Defomable surface modeling based on dual subdivision

Based on dual Doo-Sabin subdivision and the corresponding parameterization, a modeling technique of deformable surfaces is presented in this paper. In the proposed model, all the dynamic parameters are computed in a unified way for both non-defective and defective subdivision matrices, and central differences are used to discretize the Lagrangian dynamics equation instead of backward differences. Moreover, a local scheme is developed to solve the dynamics equation approximately, thus the order of the linear equation is reduced greatly. Therefore, the proposed model is more efficient and faster than the existing dynamic models. It can be used for deformable surface design, interactive surface editing, medical imaging and simulation.     

Covalent electron density analysis and surface energy calculation of gold with the empirical electron surface model

Based on the empirical electron surface model (EESM), the covalent electron density of dangling bonds (CEDDB) was calculated for various crystal planes of gold, and the surface energy was calculated further. Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface. The calculated surface energy is in agreement with experimental and other theoretical values. The calculated surface energy of the close-packed (111) surface has the lowest surface energy, which agrees with the theoretical prediction. Also, it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces. Therefore, CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.     

Design of an air-slot mode-gap nanocavity in a two dimensional photonic crystal slab

We present a novel and simple design of an air-slot mode-gap photonic crystal(PC) nanocavity by introducing a linear air slot to the center of a line-defect waveguide in a two dimensional triangular-lattice silicon PC slab.A high quality factor(Q factor) of 8.42*105 and an ultrasmall mode volume of 0.998 cubic wavelength are achieved in an optimized air-slot nanocavity which is a suitable choice for the strong matter-field interaction in free space.The high Q cavities with ultrasmall mode volume are important for applications such as quantum computation and nonlinear optics.     

Polycrystalline Silicon Gettered by Porous Silicon and Heavy Phosphorous Diffusion

The biggest barrier for photovoltaic (PV) utilization is its high cost, so the key for scale PV utilization is to further decrease the cost of solar cells. One way to improve the efficiency, and therefore lower the cost, is to increase the minority carrier lifetime by controlling the material defects. The main defects in grain boundaries of polycrystaUine silicon gettered by porous silicon and heavy phosphorous diffusion have been studied. The porous silicon was formed on the two surfaces of wafers by chemical etching. Phosphorous was then diffused into the wafers at high temperature (900℃). After the porous silicon and diffusion layers were removed, the minority carrier lifetime was measured by photo-conductor decay. The results show that the lifetime‘s minority carriers are increased greatly after such treatment.     

Sliding Mode Control Approach for Electrically Controllable Clutch of AMT Based on the Feedback Linearization

A sliding mode control approach based on the feedback linearization is proposed for the electrically controllable clutch of AMT vehicles. The nonlinear dynamic model for the hydraulic actuator associated with clutch is established. By means of the exact feedback linearization procedure of differential geometry, an equivalent, fully controllable and linear model is derived via a homomorphic transformation for the AMT clutch system. Furthermore, a sliding mode control is introduced to improve robustness. The tracking tests are performed using the sliding mode control on a Santana LX passenger car, and the experimental results prove that this nonlinear controller is of fine robustness and high degree of tracking accuracy.     

Fabrication of high aspect ratio microfiber arrays that mimic gecko foot hairs

In nature, geckos have developed complex adhesion structures capable of smart adhesion, which is the ability to cling to different smooth and rough surfaces, even ceilings, and detach at will. The hierarchical structure of gecko foot hairs consists of microscale setae, branches and nanoscale spatulae, which contributes to their strong adhesion on different surfaces. In this paper, we propose a simple and low-cost method for fabricating two-level high aspect ratio microfiber arrays that mimic gecko foot hairs. SU-8 photoresist was used and single-level SU-8 microfiber arrays were obtained by a thick film photolithography process. Single-level polydimethyl-siloxane (PDMS) microfiber arrays were also obtained by a micromolding process and the master template for this process was fabricated using inductively coupled plasma (ICP) technology. Using the silicon mold with deep-hole arrays as a substrate, an SU-8 layer with microhole arrays was added to it using thick film photolithography and it formed a double stack mold from which the two-level hierarchical PDMS microfiber arrays were replicated. Water contact angle tests showed that the two-level hierarchical structures are extremely hydrophobic (about 148.5° compared with the Tokay gecko’s 160°).     

Complex microstructure fabrication by integrating silicon anisotropic etching and UV-LIGA technology

A fabrication method which integrates silicon anisotropic etching micromachining with UV-LIGA technology to make complex microstructures is presented.This proposod combined process enables the fabrication of high-aspect-ratio and three-dimensional(3D)microstmctures,which cannot be fabricated by silicon bulk micromachining or UV-LIGA alone.To demonstrate this combined method.the 100μm thick SU-8 micro gears were fabricated on the silicon convex square structure.which is 100μm×100μm×80μm in dimension.In the subsequent micro hot embossing process,a novel type of plastics polyethylene terephtalate glycol(PETG)Was tried for use.Through optimizing process parameters,PETG shows the potential of being used as plastic replica in micro-electro-mechanical system(MEMS).This fabrication technology provides a new option for the increasing need of functionality,quality and economy of MEMS.