Masato Nakao

Preparation and Piezoresistive Properties of Polycrystalline SnO2 Films

Tin oxide thin films were deposited by dc magnetron sputtering in a gas mixture of Ar and O2 using a target containing antimony. The films were characterized using X-ray diffraction. The films showed preferred orientation in a or plane. The properties of films depended on the substrate temperature and the gas flow ratio of Ar/O2. The piezoresistive properties of these films have been measured using a conventional cantilever method. The gauge factor was measured to be around negative 5–20 at room temperature, which is comparable to the gauge factor of polycrystalline silicon films.

Preparation of carbon nanofibers by hot filament-assisted sputtering

Abstract Crystalline carbon thin films containing carbon nanofibers were obtained by using a hot filament-assisted sputtering system. Pure argon gas was employed as the sputtering gas. The crystal structure of the carbon thin films was investigated by XRD, XPS, TEM and TED. XPS profiles show the compositions of the films, which consisted of over 90% carbon atoms. From the results of observations using TEM and TED, it was revealed that the crystalline carbon films consisted of nanocrystal grains and nanofibers. To determine the valence state (sp 3 , sp 2 and sp hybridization) of the carbon atoms in the films, laser raman spectra were examined and it was found that the films showed three Raman bands at 1581, 1368 and 1979 cm −1 . The first two peaks belong to polycrystalline graphite and the last peak corresponds to carbyne, one of the allotropes of carbon.

Preparation and properties of boron thin films

Abstract Boron thin films were deposited by pyrolysis of decaborane. The substrate was heated up to 1200 °C by infrared irradiation from a halogen lamp. The films were characterized by electron beam diffraction, XPS and electrical measurements. Spots and rings were observed in the electron beam diffraction patterns, which indicates that the films consist of α-rhombohedral boron. The activation energy of the conductivity was 0.1–0.3 eV from R.T. to 500 °C and 1.0–1.4 eV above 500 °C. This demonstrates that infrared radiation is an effective method in obtaining high quality boron films via the pyrolysis of decaborane.

Y-Ba-Cu-O Thin Films Formed on Alumina Ceramic Substrates Coated with Yttria Stabilized Zirconia Layer

Y–Ba–Cu–O thin films have been deposited by DC magnetron sputtering on alumina ceramic substrate coated with yttria stabilized zirconia layer (YSZ). The YSZ layer acted as the buffer layer between the alumina ceramic substrate and the Y–Ba–Cu–O thin film. The temperatures of superconducting onset and zero resistance were 95 K and 47 K, respectively.

Characterization of Nitride Layer on 6H-SiC Prepared by High-Temperature Nitridation in NH3

The nitride layers were prepared by direct thermal nitridation of 6H-SiC substrates at 1200–1570°C in a NH3 atmosphere. The layer was characterized by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman scattering spectroscopy. The thickness of the nitride layers prepared at lower than 1400°C was estimated to be less than 10 nm. The higher nitridation temperature resulted in the formation of a thicker surface layer. XPS measurement showed that the surface layer was composed of N, Si, C and O. Peaks corresponding to α-Si3N4 were detected in the Raman spectra and the XRD patterns of the sample prepared at higher than 1500°C, indicating the crystallization of the nitrided layer.

Highly preferred crystalline carbon thin films obtained by DC magnetron sputtering with a hot filament

Abstract Highly preferred crystalline carbon thin films were obtained easily at relatively low substrate temperatures using a newly developed DC magnetron sputtering system with a hot filament. The crystal structure of the carbon films was investigated by X-ray diffraction, FE-SEM and TED analysis. X-ray diffraction analysis of the films prepared at substrate temperatures from 600 to 700°C and with the filament temperature up to 2000°C revealed very strong diffraction peaks at 2 θ = 40.22° corresponding to chaoite (220) which are identical to that of carbyne, one of the carbon allotropes. FE-SEM images showed that a great number of microcrystallites of about 60 nm diameter exist on the surface of the film. TED patterns showed a (220) preferred orientation which coincided with the X-ray results.

Highly Oriented Crystalline Carbon Thin Films Obtained by DC Magnetron Sputtering with a Hot Filament

Highly orientated crystalline carbon thin films were prepared easily at relatively low substrate temperatures using a DC magnetron sputtering system with a hot filament. The crystal structure of the carbon films was investigated by X-ray diffraction and RHEED analysis, and FE-SEM. X-ray diffraction analysis of the films prepared at substrate temperatures from 600° C to 700° C and with the filament temperature up to 2000° C revealed very strong diffraction peaks at 2θ=40.22 degrees corresponding to chaoite (220) which are identical to that of carbyne, one of the carbon allotropes. FE-SEM images showed that a great number of microcrystallites of about 60 nm diameter exist on the surface of the film. RHEED patterns showed a preferred orientation which coincided with the X-ray results.

Preparation of Carbon Films by Hot-Filament-Assisted Sputtering for Field Emission Cathode

Carbon thin films on a silicon substrate were prepared by DC magnetron sputtering method with a tungsten hot filament. In order to investigate the effects of the hot filament on film properties, the carbon thin films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and electron emission measurements. The tungsten atoms were evaporated from the hot filament and incorporated in the carbon film. The field emission measurement showed that the incorporation of tungsten was effective in reducing the turn-on voltage. The value of the turn-on voltage was 3.0 V/µm for the sample prepared with a tungsten filament heated at the temperature of 2000°C. The intentional insertion of a tungsten layer between the carbon film and the substrate was effective in obtaining a carbon film with a low turn-on voltage for the field emission.

SEM and TEM observation of carbon nano-fibers prepared by hot filament assisted sputtering

Abstract Carbon films were prepared by hot filament assisted sputtering. Pure argon was used as the sputtering gas. The substrate temperature was 600 °C and the filament temperature was about 2000 °C. Sample was inhomogeneous. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images showed that some part of films consisted of carbon nano fibers (not hollow but solid). Amorphous and polycrystalline phases were also detected by these measurements. No tube structure was observed by high resolution TEM. The diameter of the fiber was 10–30 nm.

X-Ray Photoelectron Spectroscopy of Nitride Layer on SiC by Thermal Nitridation Using NH3

Nitride layers were grown on a SiC surface by thermal nitridation using a mixed gas of NH3 and N2. The thermal nitridation was carried out at 1000°C and 1090 °C under the atmospheric pressure. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface layer. The peaks from Si2p, C1s, N1s and O1s were observed in the XPS spectra. These peaks showed that the surface layer consisted of Si, N, C and O. The thickness of the surface layer was estimated at less than 10 nm. Introduction Because of its electrical and physical properties, silicon carbide (SiC) is a very attractive semiconductor for high-temperature, high-power and high-frequency devices [1]. The thermal oxides on SiC also give its significant advantage over other compound semiconductors [2]. However, the generation of CO2 during oxidization is one of the reasons for the poor interface characteristics of SiO2/SiC structure. Employing a nitridation could keep the SiC surface away from this problem. In addition, the products formed by the SiC nitridation are silicon nitride (Si3N4) and carbon nitride (C3N4), which are both excellent insulators. The nitridation of the gate oxide is effective to improve the quality of the SiO2/SiC interface [3]. It is also reported that the silicon nitride layer was grown directly on the Si surface by thermal nitridation [4] [5]. However, no paper has been reported about the direct thermal nitridation of the SiC surface for applying to MIS devices. In this work, the nitride layer was grown on the SiC surface by direct thermal nitridation using a mixed gas of NH3 and N2. Experimental The nitride layer was formed on n-type 6H-SiC (CREE Research, one-sided mirror, 0.32 Ωcm) by direct thermal nitridation. The thermal nitridation was carried out at temperatures from 1000 to 1090 °C using NH3 in a quartz tube. The NH3 gas was diluted to 10% with N2, and the purity of the gas was higher than 99.999%. The gas flow rate was 100 sccm. Before the nitridation, the quartz tube was evacuated by an oil rotary pump to reduce the residual oxygen. Argon gas was flowed through the tube until the furnace temperature increased to the set point. The values of the temperatures shown in this paper were the measured temperatures of the resistance furnace. In order to obtain the flat and clean surface of the SiC substrate, the substrates were thermally oxidized for 2 hours at 1000 °C in wet oxygen and were etched in a hydrofluoric acid as pretreatment. X-ray photoelectron spectroscopy (XPS: Shimazu ESCA850, Mg (Kα)) was used to characterize the nitride layer. The cross-sectional image of the layer was observed by the high resolution transmission electron microscopy (HRTEM: JEOL JEM2010). Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1549-1552 doi:10.4028/www.scientific.net/MSF.457-460.1549