Nanoscale porosity in polymer films: fabrication and therapeutic applications

This review focuses on current developments in the field of nanostructured bulk polymers and their application in bioengineering and therapeutic sciences. In contrast to well-established nanoscale materials, such as nanoparticles and nanofibers, bulk nanostructured polymers combine nanoscale structure in a macroscopic construct, which enables unique application of these materials. Contemporary fabrication and processing techniques capable of producing nanoporous polymer films are reviewed. Focus is placed on techniques capable of sub-100 nm features since this range approaches the size scale of biological components, such as proteins and viruses. The attributes of these techniques are compared, with an emphasis on the characteristic advantages and limitations of each method. Finally, application of these materials to biofiltration, immunoisolation, and drug delivery are reviewed.     

Nanoscale rapid melting and crystallization of semiconductor thin films

The current study details nanosecond laser-based rapid melting and crystallization of thin amorphous silicon (a-Si) films at the nanoscale using two different optical near-field processing schemes. Both apertureless and tapered fiber near-field scanning optical microscope probes were utilized to deliver highly confined irradiation on the target surface. The various modification regimes produced as a result of the rapid a-Si melting and crystallization transformations were shown to critically depend on the applied laser fluence. Consequently, the crystallized pattern morphology and feature size could be finely controlled. High energy density was observed to impart ablation surrounded by a narrow melt ring. At much lower incident laser energy density, single nanostructures with a lateral dimension of approximately 90 nm were defined.     

Electrochemical fabrication of nanoporous polypyrrole thin films

Polypyrrole thin films with pores in nanometer scale were synthesized by direct electrochemical oxidation of pyrrole in a mixed electrolyte of isopropyl alcohol, boron trifluoride diethyl etherate, sodium dodecylsulfonate and poly(ethylene glycol) using well-aligned ZnO nanowires arrays as templates. The thin films exhibit high conductivity of ca. σ_rt ∼ 20.5  s/cm and can be driven to bend during redox processes in 1.0  M lithium perchlorate aqueous solution. The movement rate of an actuator based on this nanoporous film was measured to be over 90°/s at a driving potential of 0.8  V (vs. Ag/AgCl).     

Physics,fabrication, and characterization of thin films

Superconducting tunnel junctions as well as transition edge thermometers could benefit from high quality thin films. We point out the important features of various cryo detectors and show where high purity, or even epitaxially grown films are advantageous for detector performance. Some fabrication methods are discussed and methods of film characterization introduced. Photolithography has proven necessary to fabricate the complex structure of the present cryo detectors.     

Nanoscale domain switching behaviour in polycrystalline ferroelectric thin films

We report on the nanoscale domain switching behaviour in polycrystalline tetragonal perovskite lead zirconate titanate (PZT) ferroelectric thin films investigated via piezoresponse force microscopy (PFM). Local domain structures were imaged as a function of varying biasing conditions and spatial location of the tip within 50-100?nm sized grains. Nanoscale piezoresponse images provided direct visual evidence of the complex interplay between electrical and mechanical fields in a polycrystalline system, which causes effects such as correlated switching between the grain of interest and neighbouring grains, ferroelastic domain switching, inhomogeneous piezostrain profiles and domain pinning on very minute length scales. Detailed investigations on mechanisms which induce such domain behaviour are presented.     

Surface fabrication of nanostructured thin films: a top-down chemical strategy

A chemical corrosion strategy has been successfully designed to synthesize nanostructured Nb2O5 nanocone and nanorod films on niobium surface in the presence of fluoride ions containing solution. The synthesis of Nb2O5 films via this chemical route is based on a solution-phase epitaxy growth process on niobium substrate. In the growth process, niobium foil is introduced into a reaction solution system, which can act as the reactant to provide niobium source and the substrate to support nanostructured film growth. Nb2O5 films with controllable nanostructures can be selectively obtained on the surface of niobium foil with different manipulations. The possible formation mechanism and influence factors have been investigated. This synthetic method shows that some advantages compared with those available methods, such as e.g., the use of simple equipment, low temperature reaction, low cost, and no need for the use of metal catalyst.     

铌酸锶钡薄膜制备及椭偏光谱研究

用溶胶-凝胶法成功地制备出了退火温度分别为500、600、700、800、900℃的铌酸锶钡(SBN)薄膜;对制备出SBN薄膜分别进行了椭偏光谱测量研究,得到了不同退火SBN薄膜椭偏光谱参数曲线;并对测得的椭偏光谱进行了数值反演计算,得到了不同退火温度的SBN薄膜的光学常数谱.结果发现SBN薄膜的折射率和消光系数都随着退火温度的增高而增大.     

Nanoscale control of exchange bias with BiFeO3 thin films

We demonstrate a direct correlation between the domain structure of multiferroic BiFeO3 thin films and exchange bias of Co 0.9Fe 0.1/BiFeO3 heterostructures. Two distinct types of interactions - an enhancement of the coercive field ( exchange enhancement) and an enhancement of the coercive field combined with large shifts of the hysteresis loop ( exchange bias) - have been observed in these heterostructures, which depend directly on the type and crystallography of the nanoscale ( approximately 2 nm) domain walls in the BiFeO3 film. We show that the magnitude of the exchange bias interaction scales with the length of 109 degrees ferroelectric domain walls in the BiFeO 3 thin films which have been probed via piezoresponse force microscopy and X-ray magnetic circular dichroism.     

Advanced fabrication and characterization of epitaxial ferroelectric thin films and multilayers

Understanding the behavior of ferroelectrics on the nanoscale level requires the production of materials of the highest quality and advanced characterization techniques for probing the fascinating properties of these systems with reduced dimensions. Here we give an overview of our recent achievements in this area, which includes the detailed study of the suppression of ferroelectricity in PbTiO3 thin films, the fabrication of PbTiO3/SrTiO3 superlattices in which ferroelectricity shows some surprising behavior, and finally the manipulation of nanoscale ferroelectric domains using the atomic force microscope which leads to the precise analysis of domain wall creep and roughness in Pb(Zr,Ti)O3 thin films.     

Nanoscale structuration and optical properties of thin gold films on textured FTO

In this work, we propose a methodology to synthesize metallic nanoparticles on textured Fluorine Tin Oxide (FTO) surface by laser irradiations of deposited Au films. In particular, the breakup of the Au films into nanoparticles (NPs) is observed as a consequence of the melting and solidification processes induced by laser irradiations. The mean Au NPs size and surface density evolution are analyzed as a function of the laser fluence. Optical characterizations of the glass/FTO/Au NPs multilayer show, in the absorption spectra, plasmonic peaks due to the Au NPs and an improvement of the light absorption efficiency from the sample with larger Au NPs. The simulated trends of the ratio between the scattering and absorption cross section suggest that the absorption efficiency dominates over the scattering efficiency in the spectral range between 200 and 600 nm. The simulation shows that, by varying the NPs radius from about 18 to 24 nm, the radiation-scattered intensity remains symmetric in forward and reverse directions. These results indicate that the surface coverage size distribution of Au NPs is the key parameter to correlate the structural and optical properties of the glass/FTO/Au NPs multilayer. Furthermore, electrical characterizations highlight a reduction in the sheet resistance of the textured FTO due to the presence of the NPs. We compare these results with those obtained for the same systems when standard furnace annealing processes are used to obtain the Au NPs on the textured FTO surface.     

Nanoscale thermal-mechanical probe determination of 'softening transitions' in thin polymer films

We report a quantitative study of the softening behavior of glassy polystyrene (PS) films at length scales on the order of 100?nm using nano-thermomechanometry (nano-TM), an emerging scanning probe technique in which a highly doped silicon atomic force microscopy (AFM) tip is resistively heated on the surface of a polymer film. The apparent 'softening temperature' T(s) of the film is found to depend on the logarithm of the square root of the thermal ramping rate R. This relation allows us to estimate a quasi-equilibrium (or zero rate) softening transition temperature T(s0) by extrapolation. We observe marked shifts of T(s0) with decreasing film thickness, but the nature of these shifts, and even their sign, depend strongly on both the thermal and mechanical properties of the supporting substrate. Finite element simulations suggest that thin PS films on rigid substrates with large thermal conductivities lead to increasing T(s0) with decreasing film thickness, whereas softer, less thermally conductive substrates promote reductions in T(s0). Experimental observations on a range of substrates confirm this behavior and indicate a complicated interplay between the thermal and mechanical properties of the thin PS film and the substrate. This study directly points to relevant factors for quantitative measurements of thermophysical properties of materials at the nanoscale using this nano-TM based method.     

锂磷氧氮电解质薄膜制备与性能研究

首次采用355nm脉冲激光沉积(PLD)法在N2压强26.6Pa、激光能量密度15J/cm2、靶-基片距离5cm、基片温度为室温条件下制备了室温离子电导率为1.6×10-6S/cm、厚度均匀、无针孔、无裂缝的非晶态LiPON电解质薄膜。考察了反应气氛压强、激光能量密度对LiPON薄膜电化学性能的影响,并利用台阶仪、XPS、EDX、SEM等分析方法对薄膜进行表征。     

Thermal stability of gold-PS nanocomposites thin films

Low-temperature transmission electron microscopy (TEM) studies were performed on polystyrene (PS, M _w = 234 K) — Au nanoparticle composite thin films that were annealed up to 350°C under reduced pressure conditions. The composite thin films were prepared by wet chemical approach and the samples were then subsequently spin-coated on a carbon-coated copper grid for TEM measurements. TEM measurements were performed at liquid nitrogen temperatures to reduce the electron-beam-induced radiation damage. The results showed a marginal increase in Au nanoparticle diameter (2.3 nm–3.6 nm) and more importantly, an improved thermal stability of the polystyrene (PS) composite film much above its glass transition temperature.     

Chemical stability of doped ZnO thin films

We present the results of a chemical etching stability study carried out on ZnO thin films doped with several elements deposited by spray pyrolysis. Prior to the etching, a structural study was done by X-ray diffraction and the texture of the samples was obtained by scanning electron microscopy. The samples were etched employing a solution of dilute hydrochloric acid. The etching rates obtained for the different samples depend on the dopant element and our results confirm that films doped with Cr present the highest stability against chemical etching.     

Doping-free fabrication of silicon thin films for schottky solar cell

Thin film Schottky solar cells were fabricated without doping processes, which may provide an alternative approach to the conventional thin film solar cells in the n-i-p configuration. A thin Co layer was coated on a substrate, which worked as a back contact metal and then Si film was grown above it. Deposition condition may modulate the Si film structure to be a fully amorphous Si (a-Si) or a mixing of microcrystalline Si (mc-Si) and a-Si. A thin Au layer was deposited above the grown Si films, which formed a Schottky junction. Two types of Schottky solar cells were prepared on a fully a-Si film and a mixing of mc-Si and a-Si film. Under one sun illumination, the mixing of mc-Si and a-Si device provided 35% and 68.4% enhancement in the open circuit voltage and fill factor compared to that of the amorphous device.     

Taguchi design for fabrication of high-performance as-deposited Fe-Sm-O thin films

The Taguchi experimental design was used in this study to obtain optimal conditions for which as-deposited Fe-Sm-O thin films with both good soft magnetic properties and high electrical resistivity could be fabricated by r.f. magnetron sputtering method. The factors considered were the number of Sm₂O₃ chips, sputtering power and time, base vacuum, Ar work pressure, and O₂ partial pressure. The results showed that the optimal conditions were as follows: four Sm₂O₃ chips sputtering power of 350 W, sputtering time of 10 min, base vacuum of 2.6×10^-4Pa, work pressure of 0.2 Pa and O₂ content in Ar of 5%. The thin film fabricated at those conditions had the composition of Fe_75.3Sm_4.3O_20.4. The properties of as-deposited Fe_75.3Sm_4.3O_20.4 thin film were: saturation magnetization of 16.3 kG, coercivity of 0.9 Oe, effective permeability of 2200 in the range of 0.5–100 MHz, and electrical resistivity of 190 cm. The percentage contribution of each factor to electrical resistivity, soft magnetic properties such as magnetic permeability, coercivity and saturation magnetization were also calculated.     

Multilayer optical thin films for use at terahertz frequencies: method of fabrication

A new method of fabricating multilayer optical coatings used at terahertz frequencies has been developed. Using plasma-enhanced chemical-vapor deposition, a multilayer antireflection coating for germanium optics at terahertz frequencies was fabricated. The coating consists of amorphous silicon and silicon-oxide layers. The transmittance and structure of the coating were experimentally investigated. The transmittance spectrum of the coating on the Ge substrate shows a wideband antireflection behavior in the 40-120 cm(-1) region.     

基于计算机辅助的光学薄膜优化设计方法

概述了光学薄膜优化设计的发展和光学薄膜优化设计的原理。详细介绍了当前光学薄膜优化设计中几种常用方法并分析了它们的优缺点，最后预测了光学优化设计方法以后的发展趋势。     

Nanoscale patterning of Zr-Al-Cu-Ni metallic glass thin films deposited by magnetron sputtering

Completely glassy thin films of Zr-Al-Cu-Ni exhibiting a large super-cooled liquid region (deltaTx = 95 K), very smooth surface (Ra = 0.65 nm), and an extremely high value of Vicker's hardness (Hv = 940), as compared to bulk Zr-Al-Cu-Ni metallic glass, were deposited by radiofrequency magnetron sputtering. Nanoscale patterning ability of Zr-Al-Cu-Ni metallic glass thin films was demonstrated by a focused ion beam etching. The capability to write nanometer-scale patterns (line width approximately 12 nm) opens up a variety of possibilities for fabricating nanomolds for imprint lithography, and a wide range of two- or three-dimensional components for future nanoelectromechanical systems.