R.F. sputtered thin films for integrated optical components

The attenuation in waveguides operating at optical frequencies has been examined for a range of materials and fabrication techniques. The factors governing the operation of planar and topographically defined waveguides have been discussed in an attempt to determine the effect of the dielectric material indices; some of the limitations of the materials have been reviewed with particular reference to the modifications induced by thin film deposition.The technique of r.f. sputtering has been used to fabricate planar guides from glasses and metal oxides. The difficulties encountered and the results achieved have been presented in some detail.Measurements of the optical indices of the thin films were made by probing with a guided wave; the technique has been explained from first principles.     

Dip-coated hydrotungstite thin films as humidity sensors

Thin films of a hydrated phase of tungsten oxide, viz. hydrotungstite, have been prepared on glass substrates by dipcoating method using ammonium tungstate precursor solution. X-ray diffraction shows the films to have a strongb — axis orientation. The resistance of the films is observed to be sensitive to the humidity content of the ambient, indicating possible applications of these films for humidity sensing. A homemade apparatus designed to measure the d.c. electrical resistance in response to exposure to controlled pulses of a sensing gas has been employed to evaluate the sensitivity of the hydrotungstite films towards humidity.     

Sprayed ZnO thin films for ethanol sensors

The electrical characteristics of ZnO thin films prepared by spray pyrolysis, have been studied for ethanol sensors. The sensitivities of the films are measured at various temperatures and concentrations of ethanol. It is observed that the sensitivity increases with increasing working temperature. At higher ethanol concentrations, the sensitivity increases more rapidly with increasing temperature. Further, the films show fast response and recovery times at higher working temperatures. The sensing mechanism of the films towards ethanol vapour has been explained.     

Sensitivity of the surface microwave impedance of superconducting thin films to modulated optical radiation

A theoretical analysis is made of the photosensitivity of the component of the microwave surface impedance of high-temperature superconducting films exposed to intensity-modulated optical excitation. The results agree with the experimental data. Pis’ma Zh. Tekh. Fiz. 25, 50–56 (February 12, 1999)     

Deposition of optical thin films by ion beam sputtering

The use of sputtering from diode or magnetron sources has been investigated thoroughly in the last few years in order to replace traditional evaporation methods for optical thin film deposition. The kinetic energy of sputtered materials, higher than that of evaporated atoms, is one of the most important causes of the superior adherence, hardness and mechanical stability of sputtered thin films. Present technology evolution is tending to develop new techniques, allowing higher and more controllable energies of materials impinging on the substrate. In the ion beam sputter deposition (IBSD) technique the working pressure in the deposition chamber may be lower than 10^-2 Pa, so thermalization of sputtered materials is avoided and the energies of depositing atoms are higher than in plasma sputtering, where thermalization takes place. This work describes the investigations carried out for realizing optical treatments by means of IBSD. The apparatus used for this study is described with details of the experiments carried out and the results obtained in the deposition of TiO₂, Y₂O₃, Al₂O₃, SiO₂ and ZnS. The films are characterized optically, mechanically and for the determination of the damage threshold from 1064 nm laser radiation.     

Nonlinear problems of heating thin films by optical radiation

We consider thin films deposited on a transparent substrate and heated by the absorption of optical radiation. We derive relations which are convenient for comparing calculated and experimental data.     

Plasma deposited thin films suitable as moisture sensors

Plasma polymerized thin films from a mixture of hexamethyldisiloxane (HMDSO) and ammonia (NH₃) deposited directly onto a microdielectrometer chip have been evaluated as moisture sensors. Microdielectrometry was chosen as the measuring technique because of its fast response and real time detection capability. The sheet resistance of the plasma polymerized film was found to decrease by eight orders of magnitude with an increase in relative humidity from 0 to 92%. The moisture effect on the sheet resistance was also found to be reversible. The composition and structure of the films deposited from various mixtures of HMDSO/NH₃ have been elucidated by Electron Spectroscopy for Chemical Analysis (ESCA) and infrared spectroscopy.     

Chemical gas sensor application of open-pore mesoporous thin films based on integrated optical polarimetric interferometry

Chemical gas sensors that employ integrated optical polarimetric interferometry were fabricated by the sol-gel synthesis of transparent mesoporous thin films of TiO2-P2O5 nanocomposite on tapered layers of TiO2 sputtered on tin-diffused glass waveguides. Atomic force microscopy images of the mesoporous thin film clearly show the open pore mouths on the film surface that favor rapid diffusion and adsorption of gas-phase analytes within the entire film. Adsorption of gas and vapor induces changes (Deltan) in the refractive index of the mesoporous thin film that lead to shifts in the phase difference between the fundamental transverse electric and magnetic modes simultaneously excited in the glass waveguide via single-beam incidence. Upon exposure to NH3 gas at concentrations as low as 100 ppb in dry air at room temperature, the sensor exhibits a reversible change in the phase difference with the response and recovery times of less than 60 and 90 s, respectively. It is unexpected that the sensor is unresponsive to either NO2 or C6H6 vapor, leading to a somewhat selective sensitivity to NH3. Determination of Deltan was carried out with a combination of the experimental results and the theoretical calculations. The sensor design represents a novel, effective, and easily accessible approach to mesoporous thin-film-based integrated optical chemical sensors.     

光学材料和光学薄膜的光热表征(英文)

光热技术用来测量样品的光学和热特性。简要介绍了光热技术及其在光学薄膜测量和钛蓝宝石激光晶体表征中的应用。光热技术可以提供纯光学光谱学所无法提供的、类似光-热能量转换效率之类的信息。光热技术已被用作质量测试和改善现代光学制造的有用工具。     

Photothermal measurements on optical thin films

An overview of the application of the photothermal technique for optical as well as thermophysical characterizations of thin films is given. The peculiarities of this technique are discussed in some detail, and selected important results are pointed out. Emphasis is placed on the influence of both residual absorption and randomly distributed inhomogeneities in thin films on their laser-damage resistance.     

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.     

双靶溅射法制备M-SmS光学薄膜的研究

为了制备难以直接获得的金属相SmS,以Sm和Sm2S3为靶材,采用双靶子溅射系统,于单晶Si基板上直接获得了常温常压下稳定存在的M-SmS微晶薄膜,并采用XRD分析、内应力和RBS成分测试等手段对M-SmS的形成机理进行了研究.结果表明:M-SmS薄膜的形成是由于薄膜中存在压应力,压应力的形成与薄膜基板温度、薄膜沉积速率、薄膜中Sm元素过量以及基板之间膨胀系数的差异有关.     

Miniaturized acceleration sensors with in-plane polarized piezoelectric thin films produced by micromachining

Miniaturized acceleration sensors employing piezoelectric thin films were fabricated through batch micromachining with silicon and silicon-on-insulator (SOI) wafers. The acceleration sensors comprised multiple suspension beams supporting a central seismic mass. Ferroelectric (Pb,La)(Zr,Ti) O(3) (PLZT) thin films were coated and in-plane polarized on the surfaces of the suspension beams for realizing electromechanical conversion through the piezoelectric effect. Interdigital electrodes were formed on the PLZT films and connected in parallel. Finite element analyses were conducted for the stress and strain distributions, providing guidance to the structural design, including optimizing electrode positioning for collecting the electrical output constructively. Uniformity of the beam thickness and sample consistency were significantly improved by using SOI wafers instead of silicon wafers. The measurement results showed that all the sensor samples had fundamental resonances of symmetric out-of-plane vibration mode at frequencies in the range of 8 to 35 kHz, depending on the sample dimensions. These sensors exhibited stable electrical outputs in response to acceleration input, achieving a high signal-to-noise ratio without any external amplifier or signal conditioning.     

Sensitivity of optical sensors based on laser-excited surface-plasmon waves.

We investigate the effect of the divergence of a Gaussian laser beam on the resonance curve and the sensitivity of optical sensors based on surface-plasmon resonance (SPR). For He-Ne laser beams it is found that, for beams with a waist radius of less than 300 mum, the SPR-curve characteristics differ appreciably from the case in which a plane wave is considered. Simple expressions for the sensitivity of (bio)chemical sensors are given. A simple Lorentzian model is used to estimate the maximum possible sensitivity when a multilayer system is used to enhance the resonance peak. It was found that the sensitivity can reach its highest value when the width of the SPR curve is equal to the laser-beam divergence. The results could be particularly important when a SPR curve is used to measure the absolute value of the refractive index of a sample or the dielectric constant and the thickness of a metal layer.     

Self-consistent optical constants of SiC thin films

The optical constants of ion-beam-sputtered SiC films have been measured by ellipsometry in the 190 to 950 nm range. The set of data has been extended both toward shorter and longer wavelengths with data in the literature, along with inter- and extrapolations, in order to obtain a self-consistent set of data by means of Kramers-Kr?nig analysis. All data correspond to films that were deposited by sputtering on nonheated substrates, and hence they are expected to be amorphous. A bandgap of 1.9 eV for the films was fitted from the obtained optical constants. A good global accuracy of the data was estimated through the use of various sum rules. The consistent dataset includes the visible to the extreme ultraviolet (EUV); this large spectrum of characterization will enable the design of multilayer coatings that combine a high reflectance in parts of the EUV with desired performance at a secondary range, such as the visible. To our knowledge, this paper provides the first compilation of the optical constants of amorphous SiC films.     

Micromachined piezoelectric force sensors based on PZT thin films

A micromachined lead zirconate titanate (PZT) force sensor for scanning force microscope (SFM) is conceptualized by its piezoelectricity. The fabrication procedure is interpreted, and mechanical characteristics of the micromachined PZT force sensors with various lengths are studied in this paper. A compact SFM is constructed by using the piezoelectric PZT sensor. A very clear image is taken by this SFM. The current study of the micromachined PZT force sensor can be considered as a breakthrough of design of SFM as well as a good example of integrated piezoelectric microdevices     

氢敏元件的种类及半导体薄膜材料在其中的应用

随着氢燃料电池技术在汽车应用中的日益完善,对高性能氢敏元件的需求也更加迫切。本文介绍了采用不同工作原理制备的氢敏元件的种类,着重描述了半导体薄膜材料的工作原理和改性途径,并针对我国目前研究较少的Ga2O3新型薄膜材料进行了较为详细的综合论述。     

Titanium dioxide thin films for high temperature gas sensors

Titanium dioxide (TiO₂) thin film gas sensors were fabricated via the sol-gel method from a starting solution of titanium isopropoxide dissolved in methoxyethanol. Spin coating was used to deposit the sol on electroded aluminum oxide (Al₂O₃) substrates forming a film 1 μm thick. The influence of crystallization temperature and operating temperature on crystalline phase, grain size, electronic conduction activation energy, and gas sensing response toward carbon monoxide (CO) and methane (CH₄) was studied. Pure anatase phase was found with crystallization temperatures up to 800 °C, however, rutile began to form by 900 °C. Grain size increased with increasing calcination temperature. Activation energy was dependent on crystallite size and phase. Sensing response toward CO and CH₄ was dependent on both calcination and operating temperatures. Films crystallized at 650 °C and operated at 450 °C showed the best selectivity toward CO.     

Infrared absorption enhancement of C60 by overlaying thin silver island films

Normal-incidence infrared absorption has been observed for silver overlaid C(60) thin films formed on surface-oxidized Si(111) substrates as a function of the silver or C(60) film thickness. The absorption spectra exhibit bands at 1429 and 1180 cm(-1) due, respectively, to the infrared active T(lu) (4) and T(lu) (3) modes of C(60) in multi-layers. Additionally, two bands appear at 1442 and 1370 cm(-1). The former band is caused by activation of the infrared inactive (Raman active) A(g) (2) mode via electron transfer from the silver to adsorbed C(60), and the latter is assigned to the T(1u) (4) mode red-shifted by the charge transfer. These bands are all enhanced in intensity dependent either upon the silver or C(60) thickness, i.e., the largest absorption enhancement is obtained for 25-monolayers-thick silver and 12-nm-thick C(60). Under atomic force microprobe inspection, the average size and height of the islands in the overlaid 25-monolayers-thick silver change with underlying C(60) film thickness. The influence of the C(60) film structure upon the silver film and in turn the absorption intensity is strongly suggested.