Sol–gel broadband anti-reflective single-layer silica films with high laser damage threshold

A simple processing of preparing broadband anti-reflective single-layer silica films is presented in this article. By adding polyvinylpyrrolidone (PVP) into reactant mixture, PVP-containing SiO₂ sol was obtained under base catalyzed hydrolysis and condensation of tetraethoxysilane. The spin-coating films and the dip-coating films were deposited on one side and two sides of quartz substrates. The anti-reflection band is 315 nm wide for dip-coating film and 559 nm wide for spin-coating film and the transmittance reached to 99.95 and 95.92% for dip-coating film and spin-coating film, respectively. By a Nd:YAG lasers the laser damage threshold of as-deposited films was measured at 1064 nm wavelength (1 ns pulse). It ranged from 24 to 33 J/cm² with an average of 28.7 J/cm². Compared to SiO₂ sol without PVP, not only was the anti-reflection band broadened but the anti-reflection and laser damage threshold were retained.     

Counter-ion effect of merocyanine J aggregates: formation and structural change upon chemical and thermal treatments

The counter-ion effect of the J aggregate of a merocyanine dye having a long alkyl chain was investigated with monomolecular films on water and with Langmuir-Blodgett films. As the counter-ions, various amines as well as Ba²⁺, Ca²⁺ and Co²⁺ were employed. The destruction and restoration of the J aggregate were also discussed in relation to the structure.     

The spontaneous formation of a J-like aggregate in Langmuir-Blodgett films of a squarylium dye

The physical properties of chalcogenide-containing squarylium (SQ) dyes with long alkyl chains were examined. The SQ dyes were deposited as Y-type films. The SQ dye of a 6-methylselenazole derivative spontaneously forms a J-like aggregate in Langmuir-Blodgett films at ambient conditions.     

Corrosion of tin in citric acid solution and the effect of some inorganic anions

The corrosion behaviour of tin in different concentrations of citric acid solutions (0.3–1.0 M, pH=1.8) was studied at 30 °C by potentiodynamic technique. The E/I profiles exhibit an active passive behaviour. The active dissolution involves one anodic peak A associated with a dissolution of the metals as Sn(II) species. The passivity is due to the formation of thin film of SnO₂ and or Sn(OH)₄ on the anode surface. The cathodic sweep shows a small peak C related to the reduction of the passive film. The peak current density I_p of peak A increases with increasing both acid concentration and sweep rate.

The effects of adding increasing concentrations of Na₂CrO₄, NaMoO₄, NaNO₃ and NaNO₂ on the corrosion of tin in 0.5 M citric acid at 30 °C were investigated. Both CrO₄²⁻ and MoO₄²⁻ ions inhibit the corrosion of tin and the extent of inhibition enhances with their concentrations. Addition of either NO₃⁻ or NO₂⁻ accelerates the corrosion of tin. NO₃⁻ ions are more aggressive than NO₂⁻ ions.     

Surface acoustic wave sensors incorporating Langmuir-Blodgett films

Acoustoelectric devices offer many attractive features for applications as physical and chemical sensors. Surface acoustic wave (SAW) oscillators are of particular importance owing to their high sensitivity. This paper describes the use of Langmuir-Blodgett (LB) films as gas absorbent layers on the surface of SAW devices.

Areal densities of standard LB film forming materials were measured and found to agree with those obtained from pressure-area isotherms. Sensors incorporating ω-tricosenoic acid and docosylamine overlayers were examined and their responses to alkanoic acids reported.

The room temperature chemiresponse of a SAW device coated with monolayers of tetra-4-tert butyl silicon phthalocyanine dichloride showed response and recovery times comparable with those reported for other phthalocyanine-based sensors operated at much higher temperatures. The detection limit of the LB film device was found to be 40 ppb NO₂ in dry air at an operating frequency of 98.6 MHz and an ambient temperature of 22°C. The frequency change was shown to be entirely due to the mass of gas absorbed by the film.     

Degradation of azo dye acid red B on manganese dioxide in the absence and presence of ultrasonic irradiation

Degradation of azo dye acid red B (ARB) on MnO₂ in the absence and presence of ultrasonic irradiation (sonication) has been investigated. The effect of initial pH, anions (Cl⁻, NO₃⁻, SO₄²⁻), and saturated gas (argon/oxygen) has been studied. The experimental results show that decolorization of the dye on MnO₂ is highly pH dependent, with increasing decolorization efficiencies at decreasing pH values. The SO₄²⁻ and NO₃⁻ ions are observed to suppress the adsorption of ARB on MnO₂ dramatically, suggesting competitive nature with the dye. Sonication accelerates decolorization and mineralization of the dye. And oxygen used as saturated gas is more favorable for mineralization of the dye than argon. The average particle diameter of MnO₂ decreases from 47.5 to 3.19 μm after sonication.     

Local structure of metal ions in arachidate Langmuir-Blodgett film

The fluorescence extended X-ray absorption fine structures near the Ba-L₃ edge of a Ba-arachidate (CH₃(CH₂)₁₈COO₂Ba) Langmuir-Blodgett film are investigated by using polarized X-rays from a synchrotron radiation source. From the analysis of the observed spectra for different incident angles, the absorption-site geometries are obtained. The distance from the Ba ion to the nearest neighbor oxygen atoms, lying almost in the Ba plane, is found to be 0.278 nm. Taking account of the reported structural data, a local structure model around the Ba ion is proposed.     

Electric-field-induced migration of chemisorbed gas molecules on a sensitive film—a new chemical sensor

Thin films of sputtered In₂O₃ were exposed to a continuous flow of N₂, pure synthetic air and synthetic air contaminated with NO₂, NH₃ and H₂ while an electric field step function of 76 V/cm was applied. After the field parallel to the surface was switched on, large changes in the ratio between the film resistance close to the negative contact and the overall film resistance were observed. During the electric pulse different time-dependent behaviors were observed depending on the film ambient. This effect is attributed to migration phenomena on the surface and allows to build a new class of chemical sensors. It might, with this technology, be possible to distinguish different gases by means of the same sensitive film.     

Yttrium oxide film deposition by a Langmuir-Blodgett processing technique and its incorpiration into oxide scales by substrate oxidation

Thin films (about 10 nm) of Y₂O₃ have been deposited by a Langmuir-Blodgett processing technique onto a variety of substrates: type 304 stainless steel, low carbon steel, titanium, zirconium and silicon. The substrates were afterwards oxidized in air at 800, 1000 (304 steel), 400 (low C steel), 500 (Ti), 450 (Zr) and 1000 (Si) °C. The effects of the film on the oxide scale thickness and the interaction between Y₂O₃ and the oxide of the substrate have been studied by ion backscattering. In stainless steel, the Y₂O₃ film reduces the oxidation rate by orders of magnitude and Y is distributed throughout the oxide scalw (1–10 at.% level). In other substrates, the effect on oxidation rate was less pronounced, but changes in the visual appearance often took place. The Y₂O₃ incorporation varied for the different substrates, and Y₂O₃ remained as a surface film in the cases of Ti and Si. Such films exhibited good adherence and could not be removed by wiping. The potential use of metal oxide thin films for surface analysis standards and diffusion marker studies is discussed.     

电沉积氧化锌纳米柱的带隙和近带边发射蓝移

用电化学沉积方法制备了ZnO纳米柱阵列。在Zn(NO₃)₂基础电解液中加入新电解质并引入NH₄NO₃ 和Ga(NO₃)₃,实现了对ZnO纳米柱阵列的带隙、近带边发射、斯托克斯位移、直径、密度等物理性质的设计和裁剪。可在63~77 nm操控纳米柱的直径。增加电解液中的Ga(NO₃)₃浓度,阵列的密度可降低到7.0×10⁹ /cm²。新加入电解液中的盐类使ZnO纳米柱的带隙蓝移~50 meV并使光致发光图谱中的近带边发射蓝移53~73 meV以及斯托克斯位移蓝移23 meV,表明可对其非辐射复合进行抑制设计和裁剪。     

基于ZIF8/rGO的高性能NO2室温传感器

二氧化氮气体是一种常见的大气污染物, 对自然环境和人类健康造成严重的危害, 开发检测该类有毒有害气体的高效检测设备势在必行。新型复合薄膜气体传感器可以在常温下对二氧化氮进行高选择性、高灵敏度检测, 为自然环境和人类健康保驾护航。本工作采用化学沉淀法和超声法制备了多孔、高比表面积的ZIF8/还原氧化石墨烯(ZIF8/rGO)复合材料, 以此为气敏材料构建NO₂传感器, 并系统研究了其在室温下对NO₂的气敏性能, 进一步探讨了ZIF8/rGO气敏传感器感应NO₂的可能机理。气敏实验结果表明：ZIF8/rGO气敏传感器对50×10^-6 NO₂的响应达到34.77%, 是纯rGO气敏传感器的3.2倍。ZIF8/rGO传感器在4个可逆循环测试中表现出较好的可重复性, RSD(Relative Standard Deviation)为3.9%。此外, ZIF8/rGO传感器表现出优秀的长期稳定性(RSD为2.5%)、选择性和低的检出限(3.8×10^-8)。室温下灵敏感应NO₂的气敏性能主要归因于ZIF8的多孔结构和超大的比表面积以及rGO的优越性能。本工作将为ZIF8/rGO作为气敏材料检测有毒有害的NO₂气体提供新思路。     

固体激光用Nd:Lu2O3透明陶瓷的制备和光学性能研究

Nd:Lu2O3材料由于具有高热导率、低声子能量和优异的光学特性而成为非常有前景的高功率固体激光器用的增益介质.但Lu2O3单晶的熔点超过2400℃,难以生长,而Lu2O3陶瓷既能在低温下制备,又具有与晶体相当的光学性质和激光性能从而备受关注.本研究制备了高透明的Nd:Lu2O3陶瓷并对其光学性质和激光性能进行探究.以...     

Selective Formation of Size-Controlled Silicon Nanocrystals by Photosynthesis in SiO Nanoparticle Thin Film

The SiO_x thin film with a thickness of about 1 mum was formed on a GaAs substrate by bar-coating with the organic solution of the SiO_x nanoparticles (~40 nm). The as-formed SiO_x thin film consists of the SiO_x nanoparticles; thus the thin film is macroscopically discontinuous and is referred to as a nanoparticle thin film. Although there were no silicon (Si) nanocrystals in the as-formed SiO_x nanoparticle thin film, Si nanocrystals were observed by Raman scattering measurement after the thin film was exposed to the laser beam. The growth of Si nanocrystals by laser irradiation is referred to as photosynthesis. The photosynthesis of Si nanocrystals is found to be a self-limiting process. After the average size reaches a certain value, further increase of irradiation time or laser power does not increase the average size. The photosynthesis is similar to the thermal synthesis of Si nanocrystals from SiO_x but much faster and low-temperature growth of Si nanocrystals from SiO _x. Furthermore, the laser irradiation makes nanoparticles larger by merging. This suggests a possibility of low-temperature formation of a Si-nanocrystal array embedded in a SiO₂ thin film. Such a structure has many potential device applications     

Enhancement of the dielectric properties of Pb(La,Ti)O3 thin films fabricated by pulsed laser deposition

PLT thin films with a thickness of 600 nm were grown by pulsed laser deposition (PLD) using different laser wavelengths of 355, 532 and 1064 nm, respectively. We have systematically investigated the variation of grain sizes depending on the process condition. A two-step process to grow (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) films was adopted and verified to be useful to enlarge the grain size of the film and to enhance leakage current characteristics. Structural and electrical properties including dielectric constant, ferroelectric characteristics, and leakage current of PLT thin films were shown to be strongly influenced by grain size.     

The properties of conducting tetracyanoquinodimethane Langmuir-Blodgett films: A study using acoustoelectric devices

Results are presented for Langmuir-Blodgett films of a pyridinium tetracyanoquinodimethane molecular system suitably engineered for deposition with a Langmuir trough. Piezoelectric substrates have been used to demonstrate the reproducibility of the thin film coating procedure, to establish their electrical conductivity and to evaluate their potential use as sensors. The data obtained using surface acoustic wave devices are particularly interesting. They yield a conductivity surface acoustic wave devices are particularly interesting. They yield a conductivity of 0.5 μ^-1 cm^-1 for the charge transfer complex and demonstrate the potential of the devices as a sensor of NO₂, with a detection limit of 10 ppb.     

Integrated circuit microsensor for selectively detecting nitrogen dioxide and diisopropyl methylphosphonate

A novel gas-sensitive microsensor, known as the interdiginatated gate electrode field effect transistor (IGEFET), was realized by selectively decositing a chemically-active, electron-beam evaporated copper phthalocyanine (CuPc) thin film onto an integrated circuit (IC). When isothermally operated at 150 °C, the microsensor can selectively and reversibly detect parts-per-billion concentration levels of nitrogen dioxide (NO₂) and diisopropyl methylphosphonate (DIMP). The selectivity feature of the microsensor was established by operating it with a 5 V peak amplitude, 2 μs duration, 1000 Hz repetition frequency pulse, and then analyzing its time- and frequency-domain responses. The envelopes associated with the normalized-difference Fourier transform magnitude spectra, and their derivatives, reveal features which unambiguously distinguish the NO₂ and DIMP challenge gas responses. Furthermore, the area beneath each response envelope may correspondingly be interpreted as the microsensor's sensitivity for a specific challenge gas concentration. Scanning electron microscopy (SEM) was used to characterize the morphology of the CuPc thin film. Additionally, infrared (IR) spectroscopy was employed to verify the - and β-phases of the sublimed CuPc thin films and to study the NO₂- and DIMP-CuPc interactions.     

应力对蓝宝石衬底上生长二氧化钒薄膜结构和光电性能的调控

利用脉冲激光沉积技术在蓝宝石衬底上生长不同厚度的VO₂薄膜, 对薄膜的结构、表面形貌和光电性能进行研究。结果表明: 所沉积的VO₂薄膜为具有单晶性能、表面平整的单斜晶相的VO₂薄膜, 相变前后, 方块电阻的变化可达到3~4个数量级, 在波长为2500 nm的透过率变化最高可达56%, 优化的可视透过率(T_lum)和太阳能调节率( ∆T_sol )为43.2%和8.7%。薄膜受到的应力对VO₂薄膜有重要影响, 可以通过调节薄膜的厚度对VO₂薄膜光电性能实现调控。当VO₂薄膜厚度较小时, 薄膜受到拉应力, 拉应力能使相变温度显著降低, 金属-绝缘体转变性能(MIT)不但与载流子浓度的变化相关, 而且还受载流子迁移率变化的影响;当VO₂薄膜厚度较大时, 薄膜受到压应力, VO₂薄膜的相变温度接近块体VO₂的相变温度, MIT转变主要来自于载流子浓度在相变前后的变化, 其载流子迁移率几乎不变。     

Growth, thermal and optical properties of Yb:GdYAl3(BO3)4 crystal

Single crystal of Yb:GdYAl₃(BO₃)₄(Yb:GdYAB) has been grown by the flux method. The structure of Yb:GdYAB crystal has been determined by X-ray diffraction analysis. The experiment show that the crystal has the same structure as that of YAl₃(BO₃)₄ crystal and its unit cell constants have been measured to be a = 9.30146 Å, c = 7.24164 Å, Vol = 542.59 Å³. The absorption and fluorescence spectrum of Yb:GdYAl₃(BO₃)₄ crystal have also been measured at room temperature. In the absorption spectra, there are two absorption bands at 938 nm and 974 nm, respectively, which is suitable for InGaAs diode laser pumping. In the fluorescence spectra, there are two fluorescence peaks at 992 and 1040 nm. The thermal properties of Yb:GdYAl₃(BO₃)₄ crystal have been studied for the first time. The thermal expansion coefficient along c-axis is almost 5.4 times larger than that along a-axis. The specific heat of the crystal has been measured to be 0.77 J/g °C at room temperature. The calculated thermal conductivity is 5.26 Wm⁻¹ K⁻¹ along a-direction.     

Improvement of Interface in SiC Particle-Reinforced Al-Li Composite by Sol-Gel Coating Technique

This paper describes a study to investigate an improvement of the interface in SiC particle-reinforced Al-Li composite by coating the SiC particle with metallic oxide film. A coating method utilizing a sol-gel technique produced fine SiC powders covered with SiO₂, TiO₂, or ZrO₂ metallic oxide film. The film thickness was not affected by the hydrolysis time of the sol solution under a dry argon atmosphere. The average thickness of the SiO₂, TiO₂ and ZrO₂ films was about 10 nm, 8 nm and 27 nm, respectively. In metallic oxide coated SiC particle-reinforced Al-Li composite, TEM observation showed that the coating film was not damaged by fabrication processing, and that the formation of Al⁴C³ at the interface between the matrix and reinforcement was controlled by the coating film. The tensile strength and elongation of the extruded TiO₂, coated sample increased by 12% and 24%, respectively, compared with the non-coated sample.     

Study on the concentration of an enzyme immobilized by Langmuir-Blodgett films

Urease is an enzyme which decomposes urea into NH₃ and CO₂. We can produce a urea sensor by immobilizing urease on the pH sensor, and the Langmuir-Blodgett (LB) method has been expected to be useful as one of the immobilizing methods. We have measured for the first time the amount of urease adsorbed onto the LB film and shown that the relationship between the amount of adsorbed urease and the concentration in the solution can be expressed by an equation similar to the Langmuir adsorption isotherm.