Search

Amorphous carbon nitride (a-CN x ) deposited by reactive sputtering shows deformation, photoconductive behavior, and thermal radiation by visible light irradiation. In this study, we investigated these photoresponse behaviors of a-CN x . To obtain films with different bonding structures, the films were deposited at various temperatures from 473 to 873 K. A reduction in N/C ratio led to a decrease in C–N bonding fraction and an increase in graphite component. The optical band gaps decreased with increasing temperature. Under white light illumination, the surface temperature of a-CN x increased with the narrowing of the band gap owing to the conversion of photon energy primarily into thermal energy. On the photoconductivity and deformation, a nonlinear relationship to the band gap energy was observed. In addition, both these photoresponses showed opposite trends in relation to the deposition temperature. The photoinduced deformation was suppressed by increasing the graphite component and decreasing the C–N bonding fraction.

Amorphous carbon nitride (a-CN x ) films show photoinduced deformation under visible light illumination. To investigate the effect of nitrogen on this deformation, we compared the deformation of a-CN x films with that of nitrogen-free amorphous carbon films. The films were deposited on a rectangular ultrathin Si substrate to obtain the amount of deformation estimated from the bending curvature of the substrate. The amount of photoinduced deformation was increased by nitrogen incorporation. In the case of a nitrogen concentration (N/C) of 0.3, the deformation was under the detection limit of our apparatus. By detailed analysis of chemical bonding states, the amount of deformation was found to increase with increasing N/C ratio and N–sp3C/N–sp2C ratio, which increased with increasing nitrogen content. Furthermore, from the results of Fourier transform infrared spectroscopy, it is found that the photoinduced deformation occurred through the formation of triple bonds as the termination structures related to nitrogen and chain bonds.

Electrical behaviors of amorphous carbon nitride (a-CNx) films following exposure to various gas species were investigated. The a-CNx film was prepared by reactive RF magnetron sputtering at 873 K. The resistivity of the film was measured in flowing He, N2, O2, Ar, and CO2. Regardless of gas species, the electrical resistivity of the a-CNx film dropped rapidly following gas injection and recovered in the evacuation process. This phenomenon is closely related to the changes in the film microstructure and electrical state. The response time in the adsorption process decreased with increasing gas pressure. The variation range of the electrical resistivity changed depending on the gas species.

The effects of thermal history on the electrical properties of amorphous carbon nitride (a-CNx) films were investigated. a-CNx films were prepared by reactive RF magnetron sputtering at 873 K. The temperature dependence of electrical conductivity was measured in the temperature range from 300 to 473 K in a vacuum chamber. Sample heating was repeated nine times. The initial conductivity increased markedly after the first process, which is probably caused by eliminating nitrogen atoms from the film surface. In spite of the same thermal history, conductivity hysteresis was observed by repeating all the processes.

The effects of chemical bonding states on the electrical properties of hydrogen-free amorphous carbon nitride (a-CN x ) films were reported. a-CN x films were prepared by reactive RF magnetron sputtering at various deposition temperatures. The electrical conductivity of the a-CN x films increased with increasing deposition temperature because of the predominant sp2C–C bonding sites. Their conductivity increased by almost one order of magnitude with a 25% decrease in the fraction of the N-sp3C bonding state. It was found that the fraction of the N-sp2C bonding state strongly contributed to the increase in the electrical conductivity. Nitrogen incorporation led to an increase in the sp3C–C bonding fraction in the films; as a result, the conductivity of the a-CN x films was found to be lower than that of the a-C films deposited under the same conditions.

The electrical properties of amorphous carbon nitride (a-CN x ) films have been investigated in terms of the nitrogen concentration (N/C) and chemical bonding states in the films. The films were deposited by the reactive rf magnetron sputtering method. Nitrogen concentration and chemical bonding states in the films were controlled by regulating the deposition temperature. C–C networks in the films changed to those having a graphite like structure with decreasing N/C, as deduced by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, the N–sp2C bonding state becomes more predominant. These results indicate the contributions of the N–sp2C component to the decrease in electrical resistivity and increase in photoconductivity.

We have reported the fabrication of amorphous carbon nitride, a-CN x , films with a graded band gap structure to improve their photoconductivity and their structural, optical, and electrical properties are studied. In this study, two different structured a-CN x films with graded band gap structures were compared with single-layered a-CN x films. One of the graded band gap structure films consists of four stacked layers with different band gaps (multilayered film), and the other film consists of one layer with a gradually changed band gap (graded-layered film). All of the a-CN x films are prepared by the reactive radio frequency magnetron sputtering method using a graphite target in pure nitrogen gas. The ratio of photo- and dark-conductivity, σp/σd, of the multilayered film is quite low. In contrast, the σp/σd value of the graded-layered a-CN x film is about 11 times larger than that of the single-layered film and 80 times larger than that of the multilayered film.

Glow curves and energy spectra of thermally stimulated exoelectrons are reported for several BaTiO3 ceramics, including pure ceramics, which have a negative temperature coefficient (NTC) of resistivity, and positive temperature coefficient (PTC) ceramics. The surface potentials of these materials are measured at temperatures up to 250°C in air. Glow peaks are not easily observed in pure BaTiO3 ceramics excited by X-rays. However, several glow peaks are readily detected between 40°C and 250°C in PTC ceramics, with especially strong emissions occurring in the semiconductor region below 100°C. Distinct glow peaks are not observed in the same temperature region in the NTC ceramics. These results could be related to the facts that the surface of the PTC ceramics was charged positively and that the potential increased with increasing temperatures.

A new method for the measurement of the differential energy distribution of exoelectrons by using a retarding potential has been developed in which the retarding voltage changes at the center of each channel of a multichannel analyzer. Within the first half interval of a channel, input pulses are added; within the second half interval, the input pulses are subtracted from the previously accumulated data. A differential energy distribution can be obtained after one scan of the retarding voltage. Using this method, differential energy distributions have been measured for thermally stimulated exoelectrons from a LiF single crystal and a BeO ceramics excited by UV light in an ultra-high vacuum.

To reduce the power consumption of a PLZT light shutter and the driving voltage change of it with the environmental temperature, we investigated the relation between halfwave voltage and temperature in various PLZT compositions. Compositions which showed a memory effect at room temperature showed large transverse quadratic electro-optic coefficients at temperatures higher than room temperature. We found these compositions required less power when the PLZT was kept at the higher temperature. A shutter consisting ofa PLZT with the composition 7.3/65/35 and an ITO heater showed low power consumption and a stable driving voltage when the PLZT was held at 100°C by the heater.

We have prepared a 110 K superconducting phase as the dominant phase in the BiSrCaCu2O x ceramic by sintering at 865±5°C for 900 h in air. This superconductor has a resistance T c of 109.3 K and a structure containing stacking faults, as suggested by the broadened X-ray diffraction pattern. The volume fraction of the 110 K phase is as large as 28% by dc susceptibility measurements.

A new light-valve video projector using a PLZT light shutter linear array has been developed. A beam from a Xenon light source passes through the PLZT linear array and the resulting modulated beam is scanned vertically by a movable mirror and projected on the screen. PLZT shutters in the array are modulated with analog signals sampled from the video signal. Each shutter maintains its light intensity for the horizontal scanning period of 63.5 microseconds. The floating driving method can be used to maintain the driving voltage at the specified level because the PLZT light shutters have a memory effect similar to a capacitor. The PLZT shutters are separated from each other to eliminate crosstalk caused by stray capacity. The shutter array is made using the cutting method, which is described in detail.

The exoelectron emission from stainless steel (types 304 and 430) has been investigated in an ultra-high vacuum system. A strong emission was detected at low and high temperatures for both samples. The intensity of exoelectrons emitted from color-treated film was weaker than that from bright annealed film. Samples from which bright annealed films had been removed, however, showed the strongest intensity at low and high temperature peaks. The mean energies at peak temperatures were measured by means of a retarding-field method. The mean energy obtained at high temperatures was lower than that at low temperatures. The this results shows that the exoelectron emission phenomenon can be used for monitoring the oxide films used to cover engineering-type materials.