Large-area graphene synthesis and its application to interface-engineered field effect transistors

This article reviews recent advances in the large-area synthesis of graphene sheets and the applications of such sheets to graphene-based transistors. Graphene is potentially useful in a wide range of practical applications that could benefit from its exceptional electrical, optical, and mechanical properties. Tremendous effort has been devoted to overcoming several fundamental limitations of graphene, such as a zero band gap and a low direct current conductivity-to-optical conductivity ratio. The intrinsic properties of graphene depend on the synthetic and transfer route, and this dependence has been intensively investigated. Several representative reports describing the application of graphene as a channel and electrode material for use in flexible transparent transistor devices are discussed. A fresh perspective on the optimization of graphene as a 2D framework for crystalline organic semiconductor growth is introduced, and its effects on transistor performance are discussed. This critical review provides insights and a new perspective on the development of high-quality large-area graphene and the optimization of graphene-based transistors.     

ZnO hedgehog-like structures for control cell cultivation

Growth of biocompatible zinc oxide hedgehog-like structures on glass substrates using hydrothermal method at low temperature is demonstrated. The as-grown samples are characterized by scanning electron microscopy and Raman spectroscopy. The optical absorption of the as-grown ZnO microstructures measured with photothermal deflection spectroscopy showed very low optical absorption and strong scattering making ZnO microrods an ideal diffuser in the visible and near IR regions. In addition, the effect of ZnO microstructures on the cultivation of osteosarcoma cells (SAOS-2) is presented. During the 48 h cultivation period, no toxic effect of ZnO as a chemical agent on SAOS-2 cells was observed.     

Optical metamaterials at near and mid-IR range fabricated by nanoimprint lithography

Two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure for the near-IR range was a metal/dielectric/metal stack “fishnet” structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 μm. In the mid-IR range, the metamaterial was an ordered array of fourfold symmetric L-shaped resonators (LSRs) that showed both a dipole plasmon resonance resulting in negative permittivity and a magnetic resonance with negative permeability near wavelengths of 3.7 μm and 5.25 μm, respectively. The optical properties of both metamaterials are in agreement with theoretical predictions. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the nanoimprint lithography as a low-cost, high-throughput fabrication approach. PACS 42.25.Bs; 81.16.Nd; 42.70.-a; 81.07.-b     

Micromagnetic studies of cobalt microbars fabricated by nanoimprint lithography and electrodeposition

Micromagnetic and macromagnetic switching properties of cobalt bars with six different aspect ratios produced by electrodeposition of cobalt into patterns defined by nanoimprint lithography were studied. It was found that microbars in the demagnetized state formed configurations with closed magnetic flux. Magnetization along the long axis of the microbars resulted in a single-domain state of magnetization for microbars of all aspect ratios. In the remanent state, magnetization in microbars with smaller aspect ratios resumed the vortex configuration. Individual remanent curves, as well as the net remanent curve, were extracted from magnetic force microscopy images for microbars with all aspect ratios, and their agreement with the macroscopic magnetization measurements is discussed.     

Large-area wafer bonding of GaAs using hydrogen and ultrahigh vacuum atmospheres

Uniform direct or fusion wafer bonding of GaAs wafers up to 4 inch in diameter was achieved by means of two methods: (i) pre-heating, bonding at elevated temperatures and post-annealing in a H₂ atmosphere (gas environmental hot bonding) and (ii) bonding inside an UHV apparatus at temperatures as low as 150 °C after cleaning with atomic hydrogen. Both methods yield atomically abrupt interfaces as shown by cross-sectional TEM and by imaging the screw-dislocation network formed at low angles of twist between the wafers. At large twist angles, additional "step" dislocations arising from bonding across surface steps could be clearly imaged. The problem of occasionally occuring microvoids, probably arising due to insufficient pre-cleaning or at excessive post-annealing, is addressed. Both bonding procedures neither need mechanical loading of the wafers nor channel-patterning of the surfaces.     

Large-area back-illuminated InGaAs/InP photodiodes for use at 1 to 1.6 μm wavelength

Back-illuminated PIN photodiodes with active areas 1 mm in diameter have been made from LPE-grown InGaAs/InP. The diodes have photoresponse, leakage and stability properties which suggest that they may be superior to germanium photodiodes for many general-purpose long-wavelength applications.     

Large-area metallic photonic crystal fabrication with interference lithography and dry etching

Large-area one-dimensional periodic metallic structures were fabricated on a waveguide layer with interference lithography and dry etching. As narrow as 115-nm gold nanowires were obtained with a period of 395 nm, covering a homogeneous area as large as 5 × 5 mm². Extinction measurements demonstrate the strong coupling between waveguide mode and gold-particle plasmon resonance. We demonstrate good agreement with a scattering-matrix theory. The dispersion of the metallic photonic crystals was obtained by angle-resolved measurements. This method represents a simple and low-cost way to fabricate large-area metallic photonic crystals.     

Fabrication of molecular-electronic circuits by nanoimprint lithography at low temperatures and pressures

We have utilized a modified version of thermal nanoimprint lithography to fabricate a rewritable, nonvolatile, molecular memory device with a density of 6.4 Gbit/cm². It has the advantages of a relatively low operating temperature of (70 °C) and pressure of (<500 psi or 4.5 MPa), both of which are critical to preserving the integrity of the molecular layer. The architecture of the circuit was based on an 8×8 crossbar structure, with an active molecular layer sandwiched between the top and bottom electrodes. A liftoff process was utilized to produce the top and bottom electrodes made of Pt/Ti bilayers. The active molecular layer was deposited by the Languir–Blodgett technique. We utilized a new class of nanoimprint resist formulated by dissolving a polymer in its monomer. The formulation we used, was poly(benzyl methacrylate), dissolved in benzyl methacrylate with t-butyl peroxy 2-ethylhexanoate added as a self-initiator (8:90:2 by weight). The new resist allowed us to achieve Pt/Ti lines of 40 nm in width and 130 nm in pitch. PACS 86.65.+h; 81.16.Nd; 81.16.Rf     

Large-area In2O3 ordered pore arrays and their photoluminescence properties

Large-area In₂O₃ ordered pore arrays were prepared on glass and silicon substrates by the sol–gel technique based on colloidal monolayer spheres. The morphologies of such arrays are determined by precursor concentration used and colloidal sphere size, and are thus controllable. It has been shown that the formed ordered pore arrays consist of In₂O₃ polycrystallites. The photoluminescence measurement of the In₂O₃ ordered pore arrays shows that there is a strong photoluminescence band in the blue-green region centered around 465 nm, which does not exist in the bulk materials. Further experiments reveal that this peak originates from the oxygen deficiencies in In₂O₃ skeletons. This polydomain ordered pore-structured array could be of great potential for Si-based integrated nanophotonics and optoelectronic devices of the next generation, in addition to new gas sensors. PACS  01.30.-y; 78.20.-e; 78.55.-m; 78.55.Et     

超声对细胞膜通透性的影响及应用

适当参数的超声，使细胞膜发生可以修复的损伤，使细胞膜的通透性提高，从而使细胞内的物流释放到细胞外，细胞外的物质进入细胞内，这一现象可以用于释放代谢产物或中间产物，基因转导，强化化学方法治疗肿瘤等方面。     

Large-area pulsed laser deposition of YBCO thin films: homogeneity and surface

YBCO thin films and buffer layers are deposited by a special PLD setup with an 8-cm line focus on cylindrical targets and substrate scanning perpendicular to it. Different kinds of substrates (SrTiO₃, MgO, LaAlO₃, Y-ZrO₂and sapphire) as large as 7᎜ cm² were coated with YBCO. Two important aspects of the presented PLD setup will be discussed in detail: the method of substrate heating and the variation of the angle between the incident laser beam and the target surface ("wobbling"). The surface of the target material has been investigated by SEM. The influence of target "wobbling" on the time stability of the plasma will be discussed. The homogeneity of the deposited YBCO films with respect to structural and electrical properties has been investigated by XRD, RBS/channeling, and spatially resolved inductive measurements of T_c and j_c. The values of j_c on 7᎜ cm²in situ buffered sapphire substrates are 2.0 MA/cm² at (77 K, 0 T) with a j_c variation of less than ᆨ%.     

Fabrication and applications of ultraflexible nanostructures using dielectric heating-assisted nanoimprint on PVC films

We developed dielectric heating-assisted nanoimprint method for rapid fabrication of ultraflexible nanostructures. Using spin-coating polyvinyl-chloride (PVC) film on the glass slide, the dielectric heating on PVC film helped the pattern transfer from the mold to PVC film in few seconds. Various kinds of nanostructures were successfully made on PVC films with about 20-μm thickness. We demonstrated the applications of ultraflexible metallic nanostructures for bending measurement using surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) on the curved surfaces. For measuring bending angles using SPR on capped nanowire arrays, the minimum detection angle was 2.4 × 10⁻³ degree under 0.02 nm wavelength resolution. For SERS measurement, the nanorod arrays on a curved substrate can increase SERS signals for two times as compared to planar SERS substrate.     

Surface adhesion and demolding force dependence on resist composition in ultraviolet nanoimprint lithography

Demolding, the process to separate stamp from molded resist, is most critical to the success of ultraviolet nanoimprint lithography (UV-NIL). In the present study we investigated adhesion and demolding force in UV-NIL for different compositions of a model UV-curable resist system containing a base (either tripropyleneglycol diacrylate with shorter oligomer length or polypropyleneglycol diacrylate with longer oligomer length), a cross-linking agent (trimethylolpropane triacrylate) and a photoinitiator (Irgacure 651). The demolding force was measured using a tensile test machine with homemade fixtures after imprinting the UV resist on a silicon stamp. While decreasing the cross-linking agent content from 49 to 0 wt% has little effect on the resist surface energy, it reduces the resist's elastic modulus drastically. The decrease in elastic modulus results in a decreased adhesion force at the resist/stamp interface thereby facilitating the demolding. The decrease in elastic modulus and, therefore, demolding force by lowering the cross-linking agent content was markedly less pronounced in tripropyleneglycol diacrylate-based resists due to its shorter oligomer length. These general findings will be useful in designing new resists for UV-NIL process.     

An application of cell theory to molecular models of n-alkane solids

Solid phase properties for hard sphere chain molecular models of n-alkanes are calculated using the cell theory, and a numerical method for implementation of cell theory for chain molecules is described. Good agreement with Monte Carlo simulations for solid phase properties is obtained from the theory. By using cell theory for the solid phase and an equation of state for the fluid phase, solid-phase equilibrium can be calculated. The predictions are in quite good agreement with Monte Carlo simulation results. Cell theory is used to assess the impact of an approximate treatment used in earlier work for the effect of the temperature dependence of the molecular flexibility upon the solid phase properties of a hard chain model with a realistic torsional potential.     

The application with protocatechualdehyde to improve anticoagulant activity and cell affinity of silk fibroin

Protocatechualdehyde (PCA) is one of the effective ingredients extracted from Danshen (Radix Salviae Miltiorrhizae) and was employed to modify the silk fibroin (SF) by graft polymerization and surface adsorption. The surface composition of modified SF was characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometer. The anticoagulant activity of modified SF was assessed by in vitro coagulation test and platelet adhesion measurement. The endothelial cell affinity was evaluated by a parallel plate flow chamber. The test results indicated that with the introduction of PCA into SF, the anticoagulant activity has been improved obviously. And the SF surface composition altered by PCA, but did not disturb its β-sheet conformation. Moreover, the adsorbed PCA on SF surface can enhance the endothelial cell affinity.     

大面积高深宽比硅微通道板阵列制作

利用光辅助电化学刻蚀方法,在厚度为425μm的5英寸硅片上,制作成深宽比达50以上的微通道板阵列结构.理论分析了影响微孔阵列形貌形成的关键因素,并结合实验条件,通过调整刻蚀电压值和根据莱曼模型修正实验电流值得到理想的孔壁形貌.结果表明,相比于目前在硅基上制作高深宽微结构的几种技术,光辅助电化学刻蚀方法能够实现孔壁光滑、面积大和深宽比高的微通道板阵列结构的低成本制作.