Plasma interactions with aminoacid (l-alanine) as a basis of fundamental processes in plasma medicine

Plasma interactions with l-alaine have been studied as a basis of fundamental processes in plasma medicine. The plasma interactions with l-alaine have been examined for investigations of molecular degradations induced by direct exposures with Ar plasma and exposures with UV–VUV photons emitted from the Ar plasma via chemical bonding states analyses using X-ray photoelectron spectroscopy (XPS). The direct Ar-plasma exposure resulted in significant degradations of COOH group and CNH₂ group. Separate experiments via irradiation with photons in UV and VUV regions from the Ar plasma showed that the molecular degradation via irradiation with photons in VUV region was much more significant than via irradiation with photons in UV region. These experiments have indicated that the causality of the molecular degradation of the l-alanine during the Ar plasma exposure is considered to be significant in the following order; ions > VUV photons > UV photons ～ meta-stable radicals. Furthermore, the exposure with Ar–O₂ mixture plasma resulted in insignificant change in the XPS C1s spectra for variation of the exposure time ranging from 30 s to 300 s, indicating that the surface etching process is much more considerable than the chemical degradation process.     

Correlation of ZnO thin film surface properties with conductivity

Technological demands for the fabrication of nanostructured active coatings provide renewed motivation for understanding the properties that control the morphology of the thin film surface. With decreasing structure size, the issues of finite size and shape effects become non-negligible including issues of stability against decay and structural rearrangement. The surface of the wide band gap semiconductor ZnO is known to be very active, with a wide variety of absorption and chemisorptions phenomena taking place. These processes can alter the charge carrier distribution in the sub-surface region and locally change the doping levels. There is a limited amount of literature dedicated to systematic and detailed studies on the surface evolution with growth parameters and their effect on the ZnO surface conductivity under reduction/oxidation. Therefore, this work focuses on the analysis of the thin ZnO film surface properties by studying specific surface parameters such as amplitude related parameters (average roughness, the root mean square), mixed parameters (surface area ratio), functional parameters for characterizing bearing and fluid retention (skewness), and spatial parameters (the fractal dimensions) as they correlate with the film conductivity changes under subsequent exposure to UV light (as reductor factor) and ozone (as surface oxidant agent). All ZnO thin films of different thicknesses were grown by the dc planar magnetron sputtering technique under the same sputtering conditions. PACS 68.37.Ps; 73.25.+I; 73.50.-h; 73.50.Pz     

Optical and magneto-optical resonances in nanocorrugated ferromagnetic films

We report here on optical and magneto-optical spectra investigations of nanostructured Co and Ni films deposited on top of polymethyl methacrylate (PMMA) colloidal crystal. Resonant peculiarities have been observed in both spectra; their positions are scaled with the PMMA sphere diameter and depend on incident angle. Asymmetry of the resonance lineshapes as well as change of the direction of magneto-optical rotation has been observed. Both the surface plasmon resonance and the interference between reflections from the colloidal crystal and from the nanostructured film should be considered to explain the obtained results.     

Effects of 1064 nm laser on the structural and optical properties of nanostructured TiO2 thin film

TiO₂ thin film has been widely used as photoelectrode in dye-sensitized solar cells. It can also be used in quantum dot synthesized solar cells. Study of its effects in different spectrum of light is important for its use in solar cells. We have reported effects of 1064 nm laser on the surface morphology, structural and optical properties of nanostructured TiO₂ thin film deposited on glass substrates using sol-gel spin coating technique. Q-Switched Nd:YAG pulsed laser at various power densities is used in this study. Surface morphology of the film is investigated using X-ray diffraction (XRD) and atomic force microscopy technique. The XRD pattern of as deposited TiO₂ thin film is amorphous and after laser exposure it became TiO₂ anatase structure. Atomic force microscopy of the crystalline TiO₂ thin film shows that the grain size increases by increasing laser power density. The calculations of the band gap are carried out from UV/Visible spectroscopy measurements with JASCO spectrometer. For laser power density of 25 MW/cm² there is an increase in the transmission and it decreases at the value of 38 MW/cm² and band gap decreases with increasing laser power density. Photoluminescence spectra of the crystalline TiO₂ thin film indicate two broad peaks in the range of 415 and 463 nm, one for band gap peak (415 nm) and other for oxygen defect during film deposition process.     

Modulation of refractive index and thickness of poly(methyl methacrylate) thin films with UV irradiation and heat treatment

This paper reports changes in refractive index and thickness of spin-coated poly(methyl methacrylate) (PMMA) thin films upon irradiation by a conventional high-pressure mercury UV lamp. Significant increase in refractive index and reduction in thickness are detected. Index modulations of greater than 0.01 are achieved in the thin films after 4 min of irradiation. The thickness reduction of an irradiated PMMA film is consistent with its weight loss. This is caused by the escape of the volatile molecules generated during the irradiation process. A slight increase in the refractive index is also found in the film, heat-treated above its glass transition temperature (Tg). This thermal effect is detected in the UV irradiation process. We propose three possible aliphatic structures that are formed during the photochemical reaction and may exist in the main chain of irradiated PMMA after the irradiation. Their refractive indices in aggregate state are greater than that of PMMA based on an evaluation using the Lorentz-Lorenz equation. This is suggested to be an important reason for the refractive index increase in the UV-irradiated PMMA films. A UV-irradiated film, heat-treated above its Tg, has a rough surface with many tiny holes as illustrated by atomic force microscopy. These holes are attributed to the evaporation of the small molecules generated during the irradiation process.     

Femtosecond laser nanostructuring of silver film

In this paper, we report an evolution of surface morphology of silver film irradiated by a 1 kHz femtosecond laser. By SEM observations, it is noted that different nanostructures with respective surface features depend highly on the number of pulses and the laser fluence. Especially when the laser fluence is below the threshold fluence of film breakdown, a textured nanostructure including many nanobumps and nanocavities will appear on the surface of silver film. In order to determine an optimal regime for nanostructuring silver film and to further study the underlying mechanism, we perform a quantitative analysis of laser fluence and pulse number. The results show that this nanostructure formation should be due to a sequential process of laser melting, vapor bubbles bursting, heat stress confinement, and subsequent material redistribution. As a potential application, we find this nanostructured silver film can be used as the active substrate for surface enhanced Raman scattering effect.     

Surface segregational behaviour studied as an effect of thickness by SIMS and AFM in annealed PS-PMMA blend and block copolymer thin films

The surface behaviour of a two-phase polymer mixture depends on the chemical structure of the polymer components, the interaction between the two polymers and the processing conditions. The microscopic morphology and the surface composition need to be known in order to fully utilize the thin film properties. The technique of static time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to obtain the molecular surface composition of thin films of blends and block copolymers. The depth profiling tool of Nano-SIMS, a dynamic SIMS technique, helps to provide the chemical mapping of the surface in 2D and 3D. The surface morphology is investigated using AFM. Thin films of PS and PMMA diblock copolymers with molecular weight of 12K-12K and 10K-10K and blends of PS/PMMA (10K/10K) for thicknesses ranging from 5 nm to 50 nm are examined. For the blends, the ToF-SIMS spectra for all the thicknesses show the same behaviour of a high increase of PMMA on the surface after annealing. Nano-SIMS images reveal the formation of nanostructures on the annealed surfaces and AFM studies show these nanostructures to be droplets having distinct phase shift from the surrounding matrix. The droplet dimensions increase with the increase of the thickness of the film but the absolute intensity from the ToF-SIMS spectra for all the annealed films remains almost the same. For the copolymers, the ToF-SIMS spectra show that there is a decrease of PMMA on the surface for the annealed films when compared to the as-cast ones. AFM morphology reveals that, for different thicknesses, annealing induces different topographical features like droplets, holes, spinodal patterns, etc. but with no distinct phase shift between the patterns and the surrounding matrix. The two different copolymers of comparable molecular weight are found to exhibit very different topography even when the thickness of the films remained the same. The surface composition from the ToF-SIMS data, however, was not found to vary even when the topography was completely different.     

组合方法筛选新型发光材料

结合作者课题组开展的工作,简要介绍了组合方法在发光材料研究中的应用.包括:适用于发光材料库合成的组合溶液喷射和原位掩模薄膜顺序沉积技术;应用于发光材料库高通量筛选的照相术、组合扫描光谱和组合真空紫外发光表征系统.列举了组合方法在稀土聚合物敏化发光材料、真空紫外发光材料和长余辉发光材料等研究中的应用.     

Removal of doped poly(methylmetacrylate) from tungsten and titanium substrates by femto- and nanosecond laser cleaning

The influence of different laser pulse lengths on the removal of a polymer layer from metal substrates was investigated. As model systems, doped poly(methylmetacrylate) (PMMA) on titanium and tungsten substrates were selected.The ablation threshold and irradiation spot morphology of titanium and tungsten were compared for femtosecond (fs) and nanosecond (ns) laser irradiation and different pulse numbers. Nanosecond laser treatment resulted in a non-homogeneous surface morphology for both titanium and tungsten substrates. Femtosecond irradiation of tungsten revealed a homogeneous ablation spot with little changes in the surface morphology. For titanium, the formation of columnar structures within the irradiation spot was observed.Two different dopant concentrations were used for PMMA to achieve an equal linear absorption coefficient for the femto- and nanosecond laser wavelengths of 790 and 1064 nm. The best results were achieved for the removal of doped PMMA by femtosecond laser irradiation, where only a minimal modification of the metal surface was detected. In the case of nanosecond laser exposure, a pronounced change of the structure was observed, suggesting that damage-free cleaning of the selected metal may only be possible using femtosecond laser pulses. Different experimental parameters, such as laser fluence, pulse repetition rate and sample speed were also investigated to optimize the cleaning quality of doped PMMA from tungsten substrates with femtosecond laser pulses.     

A novel approach to enhancement of surface properties of CdO films by using surfactant: dextrin

We studied the effect of an organic surfactant, dextrin, concentration on structural, morphological and optical properties of nanostructured CdO films deposited on glass substrates by using an easy and low-cost SILAR method. Microstructures of the nanostructured CdO films were optimized by adjusting dextrin concentration. XRD, SEM and UV–Vis Spectroscopy were used to study phase structure, surface morphology and optical properties of CdO films. Furthermore, effects of dextrin concentration on the surface roughness characteristics of CdO samples were reported. The results showed that the presence of organic surfactant highly affected the physical properties of CdO nanomaterials.     

Fabrication of an integrated optical Mach-Zehnder interferometer based on refractive index modification of polymethylmethacrylate by krypton fluoride excimer laser radiation

It is known that deep ultraviolet (UV) radiation induces a refractive index increase in the surface layer of polymethylmethacrylate (PMMA) samples. This effect can be used for the fabrication of integrated optical waveguides. PMMA is of considerable interest for bio and chemical sensing applications because it is biocompatible and can be micromachined by several methods, e.g. structuring by photolithography, ablation and hot embossing. In the presented work direct UV irradiation of a common PMMA substrate by a krypton fluoride excimer laser beam through a contact mask has been used to write integrated optical Mach-Zehnder interferometers (MZI). MZI are used as sensitive bio and chemical sensors. The aim was to determine contact mask design and laser irradiation parameters for fabricating single-mode MZI for the infrared region from 1.30 μm to 1.62 μm. Straight and curved waveguides have been generated and characterized to determine the optical losses. The generation of channel waveguide structures has been optimized by a two step irradiation process to minimize the lithographic writing time and optical loss. By flood exposure to UV laser radiation in the first step the optical absorption of PMMA can be increased in the irradiated region. The required refractive index profile is then achieved with a second lithographic irradiation. The spectral behaviour of an unbalanced, integrated optical MZI fabricated by this excimer laser based contact mask method is shown for the first time. Further the optical intensity at the output port of a MZI has been measured while the optical path length difference was tuned by creating a temperature difference between the two arms of the MZI.     

Improvement in mechanical and optical properties of vapour chopped vacuum evaporated PANI/PMMA composite thin film

PANI/PMMA composite was synthesized by emulsion polymerization pathway and the composite thin film was obtained by vacuum evaporation. The effect of vapour chopping and varying PMMA concentration was also studied. The FTIR spectra showed that the PANI/PMMA composite thin film deposited as a short chain oligomers. Increase in transmittance and decrease in refractive index was obtained with increasing concentration of PMMA, which further increased the adhesion and decreased intrinsic stress. The vapour chopping improved its optical as well as mechanical properties and produced smoother surface morphology. Increase of PMMA made the film more amorphous and does not change its band gap.     

Chemical alteration of poly(vinyl fluoride) Tedlar induced by exposure to vacuum ultraviolet radiation

In this study the chemical alteration of poly(vinyl fluoride) Tedlar^® by vacuum ultraviolet radiation (VUV) (115-400 nm) has been examined using X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 0.34 decreases to 0.17 after a 2-h exposure. The F/C atom ratio is further reduced to a steady-state value of approximately 0.04 after a 24-h exposure. Similarly, the O/C atom ratio is reduced from 0.08 to 0.05 and then to 0.02 during these two exposures. As the F and O are removed by VUV exposure, the C concentration increases from 70.5 to 82.0 and then to 94.6 at.% thus forming a graphitic or amorphous carbon-like layer which erodes more slowly than the virgin Tedlar surface. Exposure of the VUV-damaged surface to O₂ results in chemisorption of O, indicating that reactive sites are formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen but a subsequent exposure to air at atmospheric conditions causes a three-fold increase in O chemisorbed at the surface. Comparison of XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (∼5 eV) atomic oxygen (AO) are similar.     

真空紫外辐射对碳/环氧复合材料性能的影响

 介绍了真空紫外线的模拟和射流式真空紫外辐射模拟设备的工作原理、技术参数及特点,并利用该设备及其它分析手段对环氧树脂浇铸体(EP648)和碳/环氧复合材料(C/E648)在真空紫外线辐照作用下的出气、质量损失率、层间剪切强度和表面状态的变化进行了研究。试验结果表明：真空紫外线辐照导致材料产生明显的出气效应,质量损失率呈现先递增后趋于平缓的趋势;17 280esh辐照剂量下,EP648的质量损失是C/E648的3.4倍,C/E648的层间剪切强度与辐照前相比下降了13.3%;环氧树脂破损较重,而碳纤维表面状态基本完好,并对内部的环氧树脂起到一定的保护作用。     

Bump formation on a glass surface with a transparent coating using femtosecond laser processing

The morphology of a glass surface having a transparent coating processed with focused femtosecond laser pulses is investigated. The transparent coating is formed of poly-methyl methacrylate (PMMA). When the glass was coated with a PMMA film with a thickness of 2.8 μm, bumps were formed over a wide range of axial focus positions. The same laser pulse energy produced cavities when processing bare glass with no coating. The bumps were formed as a result of suppressing material emission from the glass surface by a shielding effect of plasma generated by ablation of the PMMA film and by physical blocking of the PMMA film. A thinner film with a thickness of 0.7 μm produced a reduced shielding effect, forming an exploded bump with a small pit at its center and debris around the periphery. PACS 44.10.+i; 61.80.Ba; 79.20.Ds     

Improvement in thermo mechanical and optical properties of in situ synthesized PMMA/TiO2 nanocomposite

In this paper, transparent thin films of nano titania filled Poly(methyl methacrylate) (PMMA) composites were synthesized by solvent casting method using tetra hydro furan as a solvent, with in situ nonaqueous ‘sol-gel’ transformation involving the mixing of titanium isopropoxide (as sol-gel precursor) and methanol. The present research work is focused at studying the effect of titania loading on optical and mechanical behavior of transparent nano hybrid thin films. The effect of nano Titanium dioxide (TiO₂) loading on PMMA morphology was studied by using a scanning electron microscope (SEM). Bowl shaped structures were obtained in pure PMMA thin film, which were deformed on incorporation of TiO₂ nanoparticles. This nanocomposite exhibits enhanced optical and mechanical properties. The peak of UV absorption is blue shifted to 261 and 266?nm with the incorporation of TiO₂. At this wavelength, the absorption is increased up to approximately 397%. The nanocomposites exhibit increased tensile strength up to 40% and modulus up to 16%. Tg of PMMA increased from 84.8 to 86.7?°C on adding 1.25% TiO₂ nanoparticles.     

The design and construction of a VUV Ar-arc source and a VUV monochromator

The design and construction of a VUV source and a VUV monochromator is reported. The reliability of the VUV source suggests that it can be used as a VUV high radiance transfer secondary standard. A VUV window is used to isolate the high pressure argon-arc source from the VUV monochromator. The spectrum is therefore limited by the transmission cut-off of the window. Alternatively, a differential pump could be used to extend the wavelength range to the extreme UV and eliminate the uncertainties associated with the aging effects of the VUV window. The apparatus is to be used to measure the VUV spectra of certain glass samples.We wish to acknowledge the financial support by SERC under research grant number GR/E 01973.     

一维纳米氧化锌自驱动紫外探测器的构建与性能研究

本文通过化学气相沉积法制备了ZnO纳米材料, 利用扫描电镜、光致发光谱、X衍射光谱及拉曼光谱等方法对制备的材料进行了表征. 基于制备的单根ZnO线分别构建了三种不同结构的紫外探测器件: Ag-ZnO-Ag肖特基型、PEDOT:PSS/n-ZnO结型和p-Si/n-ZnO结型紫外探测器, 并对器件的性能进行了研究. 结果表明: 三种不同结构的器件都表现出良好的整流特性, 对紫外线均有明显的光响应; 在零偏压下, 都有明显的自驱动特性. 三种器件中, p-Si/n-ZnO型紫外探测器性能最为优异: 在零偏压下, 暗电流约在1.2×10^-3 nA, 光电流在5.4 nA左右, 光暗电流比为4.5×10³, 上升和下降时间分别为0.7 s和1 s. 通过三类器件性能比较, 表明无机p-Si更适合与ZnO构建pn结型自驱动紫外探测器.     

Core-level electronic properties of nanostructured NiO coatings

Nanostructured NiO films with different thicknesses were grown on nanoporous alumina membrane substrates by reactive evaporation of Ni in an oxygen atmosphere. The reactive deposition process was assisted by a low energy oxygen ion-beam in order to increase the NiO input into the pores. Surface morphology and structure of the films were analyzed by SEM and XPS. SEM observations reveal a well adhered film of NiO on the substrate. This film appears to be uniform and presents a rather irregular nanostructured morphology, built of NiO clusters with sizes ranging between 5 and 30 nm. The core-level electronic properties of this nanostructured NiO film result to be similar to those of an ultrathin film about one monolayer thick. This behaviour can be explained by the large surface to volume ratio of both systems.     

一种自支撑金纳米薄膜的制备、结构和氮吸附特性

以一种新的硅微米/纳米结构复合体系——硅纳米孔柱阵列作为还原性衬底，采用浸渍技术制备出一种自支撑的金纳米薄膜，并对其表面形貌和结构进行了表征.实验表明，金纳米薄膜的制备过程是一个自终止过程.当硅纳米孔柱阵列被耗尽后，浸渍溶液中Au³⁺的还原反应将自行终止；同时，所形成的金纳米薄膜自动与衬底脱离并成为一种自支撑薄膜.薄膜的形成机理被归因于硅纳米孔柱阵列所具有的高的表面活性和还原性.用能量弥散x射线谱对薄膜表面化学成分分析的结果表明，如此制备的金纳米薄膜具有很强的氮吸附和氮储存能力.这一特性有可能在气体传感器、空气分离和氮纯化以及氮化合物的膜合成器等技术领域得到应用. 关键词： 自支撑金纳米薄膜 硅纳米孔柱阵列 浸渍技术