Noboru Kutsuwada

Sharp optical emission from CuInSe2 thin films grown by molecular beam epitaxy

Optical properties of CuInSe2 (CIS) films grown on (001) GaAs by molecular beam epitaxy (MBE) have been investigated by means of low temperature photoluminescence (PL) spectroscopy. Distinct emission lines including a bandedge emission were observed reproducibly from Cu-rich films, indicating high crystalline quality. Such well-defined PL spectra have made possible the extensive characterization of radiative recombination processes through the intrinsic defects in this material; some of the emission lines were attributed to phonon replicas with a phonon energy of 28–29 meV for the first time. PL spectra were found to be very sensitive to the MBE growth parameters such as substrate temperature, suggesting dominant defects in CIS epitaxial films can be controlled by varying the growth conditions.

Molecular Beam Epitaxial Growth and Properties of CuInSe2

CuInSe2 (CIS) films with Cu/In ratios (γ) ranging from 0.81 to 1.81 have been grown by molecular beam epitaxy on (001)-oriented GaAs substrates at a substrate temperature of Ts=450°C. It is found that Cu-rich films tend to become Se-poor, and In-rich films tend to become Se-rich. X-ray diffraction patterns obtained from these films have shown the peaks with respect to CIS {n00} planes, clearly indicating epitaxial growth. Optical properties of the CIS films have been characterized by means of photoluminescence (PL) spectroscopy at 2 K. Many distinct emission lines including a band edge emission were present on PL spectra obtained from Cu-rich films. A broad emission (λ~1.45 µm) appeared at γ=1.04, then became dominant with further decreasing γ.

Photoluminescence properties of CuInSe2 grown by molecular beam epitaxy

Abstract Photoluminescence (PL) properties of CuInSe 2 thin films with Cu/In ratio ranging from 0.81 to 1.81 grown by molecular beam epitaxy have been investigated for photovoltaic applications. The PL spectra of Cu-rich CuInSe 2 epitaxial films unlike those of polycrystalline CuInSe 2 showed well-defined emission lines, suggesting that high quality CuInSe 2 epitaxial films have been grown. Such fine PL spectra made the identification possible of phono replicas, in other words, the separation of such phonon replicas from substantive emmissions. PL properties are found to be very sensitive to the growth parameters such as Cu/In ratio and substrate temperature. A broad peak at λ ∼ 1.45 μm becomes dominant in In-rich films, and excitation power dependence of such a broad emission indicated a pair-type radiative recombination, most likely the emission due to donor-acceptor pair or their complex.

Optimization of quantization table based on visual characteristics in DCT image coding

Abstract The DCT (Discrete Cosine Transform) based coding process of full color images is standardized by the JPEG (Joint Photographic Expert Group). The JPEG method is applied widely, for example a color facsimile. The quantization table in the JPEG coding influences image quality. However, detailed research is not accomplished sufficiently about a quantization table. Therefore, we study the relations between quantization table and image quality. We examine first the influence to image quality given by quantization table. Quantization table is grouped into four bands by frequency. When each value of bands is changed, the merit and demerit of color image are examined. At the present time, we analyze the deterioration component of a color image. We study the relationship between the quantization table and the restoration image. Color image is composed of continuoustone level and we evaluate the deterioration component visually. We also analyze it numerically. An analysis method using the 2-D FFT (Fast Fourier Transform) can catch a change of a color image data by a quantization table change. On the basis of these results, we propose a quantization table using Fibonacci numbers.

MEASUREMENT OF VAN DER WAALS FORCE OF TONER ADHESION EMPLOYING A LINEARLY INCREASING ELECTRIC FIELD AND DETERMINING THE TONER JUMPING VOLTAGE

ABSTRACT Both van der Waals and electrostatic forces of adhesion between toners and substrates play an important role in electrophotography processes employed in copying machines and laser printers. We report here a method of estimating van der Waals forces of adhesion between various substrates and toners of different particle sizes. The method involves the measurement of the detachment force and the resultant current caused by toner jumping between two closely-spaced conducting parallel plates. Conducting toners are first sprayed on the top surface of the bottom plate; the voltage across the two plates is then ramped at a constant rate. When the electrostatic force of detachment exceeds the forces of adhesion between the toners and substrate, there is a significant increase of current between the two parallel plates. The particles jump from the bottom plate and reach the upper electrode. Upon reaching the upper electrode, the initial induced charge is lost and the particles acquire electrostatic charge ...

Direct measurement of toner particle size

The distribution of particle size in an electrophotographic toner has a marked influence on the images formed by the plain paper copier. The authors present a method for the direct measurement of toner particle size using an optical microscope in combination with an image processor. The Nexus 6400 image processing system is used, assisted by a minicomputer, allowing a large number of toner particles to be measured in a short time. The distribution of particle size for four types of shattered toner on the market has been measured by this system, and the median effective diameter for over 1000 particles has been determined to be near 14-16 mu m from the typical cumulative distribution. The experimental results are compared with previous results obtained by an applied Millikan method and a laser Doppler method.<<ETX>>

Image quality improvement by pre- and post-processing in DCT coding

Coding for full-color still-image is standardized internationally by JPEG (Joint Photographic Experts Group). The coding method is used in wide area applications. In many cases, continuous-tone images are accompanied by characters. So improvements of JPEG coding by pre and post processing are investigated in mixed images. In this process, we use sharpening before JPEG coding as a pre-processing, and we use smoothing after JPEG coding as a post- processing. In both pre and post processing, the degree of emphasis is controlled by a weighting factor and the quality is compared between processed and unprocessed images. As a result of this process, it is confirmed that the processed image is better than an unprocessed image in quality.

Formation and evaluation of images obtained by the toner jet printing technology (III)

Various nonimpact printing methods used printers are in general use. We have investigated an imaging method using the Toner Jet in which a visible direct image is obtained using an electrostatic field to make the toner stick to the paper. Images obtained from the Toner Jet are of equal quality to those obtained by an electrophotographic method. We have confirmed that the Toner Jet method will be an effective nonimpact printing method in the near future.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Numerical simulation of toner jet method for nonimpact printing

The toner jet method has been previously proposed to perform electrophotographic nonimpact printing easily. To clarify the fundamental properties of this method, the jet behavior of toner is studied through simulation on a personal computer. The mesh electrode is assumed to be inserted halfway between the development roller and the paper-back electrode. This is done to control the locus and the distribution path of toner from the magnetic development roller electrode to the electrode on the back of the paper receiver. The electric field applied between the magnetic development roller and the paper-back electrode is higher than the field between the mesh electrode and the magnetic development roller. The locus and the distribution of toner particles developed on the paper are simulated by changing the applied voltage in each row and each column of the mesh electrode. It is assumed that the jet behavior of toner particles from the magnetic development roller to paper is controllable. In conclusion, the useful role of the mesh electrode in the image quality of the toner jet method is suggested.

Formation and evaluation of image obtained by the toner-jet printing technology

Various nonimpact printing methods used printers are in general use. We have investigated an imaging method using the Toner Jet in which a visible direct image is obtained using an electrostatic field to make the toner stick to the paper. Images obtained from the Toner Jet are of equal quality to those obtained by an electrophotographic method. We have confirmed that the Toner Jet method will be an effective nonimpact printing method in the near future.