Shoji Furukawa

Three-Dimensional Quantum Well Effects in Ultrafine Silicon Particles

The mostly crystallized Si:H having a wide optical band gap and showing a visible photoluminescence at room temperature, has been fabricated by means of a planar magnetron rf sputtering technique in hydrogen gas onto a low temperature (about 100 K) substrate. The materials consist of very small crystalline silicon particles (average diameters: 2–5 nm) surrounded by =SiH2 groups. The observed macroscopic physical properties are explained by the three-dimensional quantum size effects in the ultrafine silicon particles.

Estimation of localized state distribution profiles in undoped and doped a-Si:H by measuring space-charge-limited current

Abstract The characteristic temperature which characterizes the localized states of amorphous silicon-hydrogen (a-Si:H) has been obtained by measuring space-charge-limited (SCL) currents in planar structure gap cells for undoped and nitrogen doped films. The SCL current is confirmed by measuring the critical voltage as a function of electrode gap spacing. The characteristic temperature obtained is 1060 ± 150 K for undoped a-Si:H films. The value of nitrogen doped film prepared under the condition of 0.4% N2 gas partial pressure becomes less than 400 K.

Structure and orientation of polydimethylsilane films

Abstract The structure of polydimethylsilane crystals has been determined by use of X-ray diffraction measurements and a theoretical diffraction pattern. The crystal structure obtained is monoclinic ( a = 0.745 nm , b = 0.724 nm , c = 0.389 nm , and γ = 67.1°), in which the primitive translation vector c correspinds to the period of a one-dimensional silicon backbone having an all-trans conformation. The orientation of the evaporated film, as well as the source-melted film, can be well explained by the obtained crystal structure. The abrupt change in the stack perpendicular to the chain direction, by which the twin-like X-ray pattern is observed in the rocking curve, is also explained quite naturally by the present structural model.

SAW humidity sensor using dielectric hygroscopic polymer film

A surface acoustic wave (SAW) sensor for measurement of humidity is described. SAW devices have the ability to directly respond to the inertial mass and elastic mechanical properties of materials in contact with the device surface. Feature enables them to directly sense mass and mechanical properties of their environment. In this paper, we show a new SAW humidity sensor that uses the changes in the film permittivity rather than the mass. A dual SAW delay line fabricated on a piezoelectric substrate was coated with cellulose acetate. For a 128° YX LiNbO3 substrate, the hygroscopic polymer-coating caused a SAW velocity change of 0.33 m/s per 10% relative humidity. The response was linear in the range from 10% to 70% in relative humidity. The results suggest that the SAW humidity sensor using the dielectric interaction with the SAW electric field is quite promising

Structure and orientation control of organopolysilanes and their application to electronic devices

Abstract Molecular structure and packing of various organopolysilanes having symmetrical side-chains of alkyl substituents, such as poly(di-methyl silane), poly(di-ethyl silane), poly(di-propyl silane), poly(di-butyl silane), poly(di-pentyl silane), and poly(di-hexyl silane), are examined, and the method of orientation control of the polysilane thin film is proposed. The application of the evaporated film to the electro-luminescent device is also demonstrated.

Optical properties in binary Si: H alloy from disilane

Abstract Binary Si: H alloy films having a wide optical band gap have been prepared by r.f. glow discharge of disilane. The optical band gap and the infrared absorption spectrum have been measured for those binary alloy films. The infrared absorption strength for 850 cm -1 peak and the vibrational freqcencies for all absorption peaks are increased with an increase in the optical band gap. This sugests the (SiH 2 ) n group formation in a wide optical gap film.

Crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane)

The crystal structures of poly(di-n-butyl silane) and poly(di-n-pentyl silane) have been determined by comparing the experimental X-ray diffraction pattern with the theoretical pattern. The side-chain conformation is mostly determined by the intramolecular steric hindrance as well as the van der Waals interaction between the side chains. The Si backbone conformation of both crystals is a 7/3 helix, which is mainly determined by the intramolecular van der Waals interaction between the nearest-neighbour side chains. On the other hand. The Si backbone conformation of both crystals after a pressure treatment of 1500 MPa is all trans, which is caused by the van der Waals interaction between the side chains attached to the second-nearest-neighbour Si atoms; In all cases, one of the two C-Si-C-C groups in Si(C4H9)2 or Si(C5H11)2 is an essentially trans conformation. Whereas the other C-C-Si-C group has a cis-like conformation, which is different from that generally accepted.

Orientation of films prepared by the evaporation of poly(dimethyl silane)

This paper describes highly oriented films prepared by the evaporation of poly(dimethyl silane). The specimens are prepared at various evaporation speeds and substrate temperatures. The polymer is divided into species of about 2 nm length on the evaporation heater, and the species recrystallize on the substrate. The structure and orientation of the films are investigated using wide-angle X-ray diffraction and ultraviolet absorption methods. The substrates used are single-crystal silicon (100) for the X-ray diffraction measurement and fused silica for the ultraviolet absorption measurement. The polymer exhibits the same orientation on both substrates. It is found that most of the silicon chains are perpendicular to the substrate surface in the film prepared under the condition whose growth rate is lower than 20 nm min-1. On increasing the substrate temperature, the number of silicon chains whose orientation is normal to the substrate surface increases.

Humidity Sensor Using Surface Acoustic Wave Delay Line with Hygroscopic Dielectric Film

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. SAW technology is increasingly being used in sensors. The majority of the work reported on SAW sensors to date has studied the effect of mass loading. In this paper, we propose a new SAW humidity sensor that uses the changes in the film permittivity rather than the mass. A 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with cellulose acetate. This hygroscopic polymer coating caused a SAW velocity change of 0.36 m/s per 10% relative humidity. The response was linear in the range from 10% to 80% in relative humidity.

Passive strain sensor using SH-SAW reflective delay line

A shear horizontal-mode surface acoustic wave (SH-SAW) has the unique characteristic of complete reflection at a free edge normal to the direction of propagation, making it possible to construct a reflective delay line. A passive SAW strain sensor based on such a reflective delay line is presented. The reflective delay line is constructed on a 36° YX LiTaO 3 substrate. The SH-SAW velocity is shown to provide a reliable measure of the strain of a propagation surface, and incorporation of an oscillator circuit is demonstrated to allow wireless remote monitoring of strain using this sensor.