T. Katsuno

Highly photoconductive amorphous carbon nitride films prepared by cyclic nitrogen radical sputtering

We report on the growth of amorphous carbon nitride films (a-CNx) showing the highest conductivity to date. The films were prepared using a layer-by-layer method (a-CNx:LL), by the cyclical nitrogen radical sputtering of a graphite radical, alternated with a brief hydrogen etch. The photosensitivity S of these films is 105, defined as the ratio of the photoconductivity σp to the dark conductivity σd and is the highest value reported thus far. We believe that the carriers generated by the monochromatic light (photon energy 6.2eV) in the a-CNx:LL films are primarily electrons, with the photoconductivity shown to increase with substrate deposition temperature.

Observation and analysis of percolation behavior in carbon microcoils/silicone-rubber composite sheets

The electrical properties of carbon microcoils (CMCs)/ silicone-rubber composites were studied on the changes in the values of the electrical parameters (impedance, phase angle, resistance, and capacitance) as a function of the CMC content in the matrix, using an impedance analyzer in the frequency range from 40to200kHz. Percolation paths were observed at a 3wt% CMC content in the matrix. The properties of the composites were separated at the percolation threshold. The capacitance with a small value was dominant at CMC content less than 3wt%, and the resistance was dominant at CMC content higher than 3wt%.

Characterization of low dielectric constant amorphous carbon nitride films

Amorphous carbon nitride (a-CNx) films have rather high resistivity and low dielectric constants that could be applied as low dielectric constant materials. Several properties of a-CNx films including interactions with metal electrodes are studied and discussed using data from the frequency dependence of capacitance, Raman and photoluminescence spectra.

The effect of hydrogen- and oxygen-plasma treatments on dielectric properties of amorphous carbon nitride films

Abstract Amorphous carbon nitride (a-CN x ) films made by a reactive sputtering of a carbon target with nitrogen plasma shows high resistivity and high electrical breakdown field. Therefore, a-CN x is a good material as a dielectric material. In this paper, the effects of hydrogen-plasma and oxygen-plasma treatment to the dielectric properties of a-CN x films were studied, discussed and compared. A cyclic process of the deposition of a thin a-CN x film and hydrogen- and oxygen-plasma treatment, which is called the layer-by-layer process (LL), were used to make LLa-CN x and LLa-CN x O y films, respectively. Comparing the results of capacitance made of a-CN x , LLa-CN x , and LLa-CN x O y the most effective treatment to get smaller dielectric constant materials at present was to use hydrogen plasma treatment.

Response time of photoconductivity of amorphous carbon nitride films prepared by a nitrogen radical sputter method

Abstract Amorphous carbon nitride a-CN X films prepared by a nitrogen radical sputter method have been studied and found as good material applicable as photoconductive devices from 2 up to ultraviolet 6.2 eV. Especially a-CN X made by the layer-by-layer method, LLa-CN X , shows photoconductivity larger than that of usual a-CN X . It is interesting to observe the response time τ of photoconductivity for LLa-CN X films, because response time τ is an important factor to design a device. The value of response time τ for the light-on experiments is found in 160 μs or less under the light source of 6 eV. Dependence of photoconductivity for LLa-CN X on preparation conditions is also studied. LLa-CN X prepared at higher substrate temperature T S shows large photoconductivity than that made at lower T S . The results are discussed with data of X-ray Photoelectron Spectroscopy (XPS) and Electron Spin Resonance (ESR).

Internal stress of amorphous carbon nitride films

We have studied the characteristics of amorphous carbon nitride (a-CNx) films as low dielectric constant materials for ultralarge scale integration. In this article the initial internal stress of a-CNx films is studied and discussed. The stress in a single-layer film on a substrate is determined using the measured radius of curvature and Stoney’s equation. a-CNx films are prepared by a reactive radio frequency magnetron sputtering on the ultrathin quartz glass substrates. It is observed that the internal stress in a-CNx depends mainly on the substrate temperature increasing from about 10 to 50 MPa of compressive nature. These values are about one tenth of that for hydrogenated amorphous silicon (a-Si:H) prepared by a plasma-enhanced chemical vapor deposition.

New preparation method of diamond like carbon: the layer-by-layer method

Abstract A new method––the layer-by-layer method––is used to prepare diamond like carbon (DLC) films. The layer-by-layer method is a cyclic process for the deposition of DLC by a rf magnetron sputtering using Ar gas and with alternate the atomic hydrogen treatment, which samples are called LL-DLC. A DLC sample without atomic hydrogen treatment and an atomic-hydrogen-treated DLC sample are prepared to compare with LL-DLC. LL-DLC samples are prepared with the substrate temperature from RT to 400 °C. The data of the electrical conductivity including Fermi level E F , optical energy gap E O4 , X-ray photoelectron spectroscopy, sp 3 fraction obtained by Raman spectra, infrared absorption coefficient spectra and atomic force microscope are used to characterize these DLC films. These results are also discussed comparing with amorphous carbon nitride a-CN X and the layer-by-layer prepared amorphous carbon nitride LLa-CN X .

Amorphous carbon nitride deposition by nitrogen radical sputtering C+N+O+H

Abstract Amorphous carbon nitride films a-CNx were prepared by a nitrogen radical sputtering of a carbon target. A-CNx films were treated by atomic hydrogen or by an oxygen plasma, using a layer-by-layer method, forming LLa-CNx or LLa-CNxOy. These a-CNx films show large photosensitivity, high resistivity and low dielectric constants. Possible applications are also discussed briefly.

Properties of amorphous carbon nitride a-CNx films prepared by the layer-by-layer method

Amorphous carbon nitride a-CNx films prepared by a nitrogen radical sputter method show high photosensitivity PS=σp/σd, which is the ratio of photoconductivity σp and dark-electrical conductivity σd. In particular, PS of a-CNx prepared by a layer-by-layer LLa-CNx method, is large compared with that of usual a-CNx. The layer-by-layer LL method, is a cyclic process of a deposition by a nitrogen radical sputter and an atomic hydrogen treatment. It is very important to find clearly the reason for the change of properties by LL method. Therefore, we studied and discussed the characteristics of LLa-CNx comparing with those of a-CNx using the results of X-ray photoelectron spectroscopy, electron spin resonance and optical transmittance spectra.

Detection of heavy ions for cancer therapy using amorphous carbon nitride a-CNX films prepared by a nitrogen radical sputter method

Abstract Secondary-electron (SE) yields from amorphous carbon nitride (a-CN X ) films on Al foil were measured by using fully-stripped and fixed-velocity (6 MeV/n) heavy ion beams, C 6+ . The purpose of our research is to study the characteristics of a-CN X films for the application to heavy particle detectors. a-CN X films were prepared by a nitrogen radical sputter method, and were deposited on one side of an Al foil. SE yields from both surfaces of forward and backward ( Q F , Q B ) by the impact of 6 MeV/n C 6+ ions were independently measured. When a-CN X film was on the backside of the Al foil in the beam direction, the SE yield ( Q B ) from a-CN X was significantly larger than Q F from the Al surface side. This was an unexpected result from the well-known knowledge. Comparing the SE yields between the Al surface side with the backward of a-CN X and the pure Al foil (without a-CN X ), Q B from a-CN X was significantly larger than Al, suggesting a promising possibility of a-CN X for the application of a new detector; meanwhile Q F from Al (with a-CN X ) was smaller than that from the pure Al by a factor of 3.4. We found the latter phenomenon can be explained by a decrease in a vacuum level of a-CN X film side.