Chemistry and structure of GaAs surfaces cleaned by sulfur annealing

A new method for cleaning and passivating GaAs surfaces, sulfur annealing, is proposed. The GaAs surfaces are exposed to sulfur atoms generated by an Ag/AgI/Ag₂S/Pt electrochemical cell at elevated substrate temperatures without arsenic beam irradiation. The chemistry and structure of the GaAs surfaces cleaned by sulfur annealing are studied by synchrotron radiation photoemission spectroscopy and low energy electron diffraction (LEED). The S 2p and Ga 3d spectra indicate that Ga---S bonds are formed on the GaAs surfaces where no oxides remain. 4 × 1 and 2 × 1 LEED patterns were observed for the surfaces with an average sulfur layer thickness of 0.15 nm and 0.24 nm respectively. The surface band bending is found to be reduced by 0.2–0.3 eV for the sulfur-annealed surfaces, but slightly increased for the conventionally cleaned surfaces with arsenic beam irradiation. We conclude that the surface cleaning and the submonolayer sulfur passivation can be attained simultaneously by sulfur annealing without arsenic beam irradiation. The method is promising for pre-cleaning the GaAs surfaces before semiconductor crystal growth and thin film deposition.     

The Empirical Studies on IT Management Effectiveness in Japan: 2000, 2002 and the Future

Many corporate senior managers have not been fully convinced of successful IT management over a period of decades. In order to clarify the mechanism of IT management in companies, we conducted the surveys on IT management in 2000 and 2002. Through the surveys and analyses, we found the causal structure in IT management, developed IT Management Effectiveness as a new measurement tool, published ranking lists of high scored companies, and analyzed characteristics of industry/sizes of respondents and so on. Based on the surveys and researches so far, we would suggest future works, such as comparison of Japanese companies with overseas companies, time series analyses.     

Macromolecular complexes consisting of poly(aluminum chloride), [2-(diethylamino)ethyl]dextran hydrochloride,and potassium poly(vinyl sulfate)

The mixture of poly(aluminum chloride) (PAC) and [2-(diethylamino)ethyl]dextran hydrochloride (EA) were allowed to react with potassium poly(vinyl sulfate) (PVSK) to form many different water-insoluble macromolecular complexes (MCs) in aqueous solution at various hydrogen ion concentrations. According to elemental analyses, IR spectroscopy, and solubilities of MCs, molecular structures of each MC depend on [H⁺]. It is suggested that the MCs obtained at pH 1.0 are products consisting of EA, PVSK, and aluminum aquo-complex having coordination water whereas the MCs at pH 4.0 are higher molecular products consisting of EA, PVSK, and basic aluminum maltidentate complex. This result is attributable to change with [H⁺] in the degree of dissociation and conformation of EA, PVSK, and the dissociation of hydrated coordination of PAC. MC membranes were made by casting solutions of all kinds of MCs, and active, selective transport phenomena through a membrane of the MC prepared in a solution of pH 1.0 HCl were investigated under various conditions. Transport ratio of Na⁺ and the electric potential difference between the left and right sides of the membrane were measured, with a result that the higher value the membrane potential difference was long allowed to maintain, the higher the transport ratio became. According to this result, the driving force of transport is dependent on the membrane potential, Donnan potential, and diffusion potential, between both sides of the membrane. The Cl^? exclusion (Donnan exclusion), however, is small due to the small cation-exchange capacity, so that the membrane potential difference is caused to decrease rather rapidly by Cl^? permeation. It was also suggested that the affinity of the carrier and both the chemical and physical properties of the MC membrane controlled the selective transport through the membrane.     

Developmental signalling: a careful balancing act

Embryos of arthropods and chordates are patterned along the dorso-ventral axis by a gradient of secreted morphogens of the Bmp4/Dpp family. This gradient now appears to be shaped by the opposing activities of Bmp-sequestering proteins, on the one hand, and Bmp-releasing metalloproteases, on the other.     

Atom Electronics: A proposal of nano-scale devices based on atom/molecule switching

This paper describes the possibility of atom/molecule switching devices, which are candidates to supersede the present metal-oxide-semiconductor (MOS) devices and to establish the new era of Atom Electronics. They are Atom Relay Transistors (ART) and Molecular Single Electron Switching (MOSES) devices, with total dimensions of a few nm and an operation speed of more than Tera (10¹²) Hz. Using these devices, it is estimated that a supercomputer, with 10⁷ gates of logic circuit and 10⁹ bits of memory, would be integrated in an area 200 μm square and operating at more than Tera (10¹²) Hz. ART and MOSES devices are evaluated on the basis of the characteristics necessary for information processing integrated circuit devices, together with other nano scale devices, and are found to be the most promising candidates that supersede the present metal oxide semiconductor (MOS) devices for information processing in the next decade. This paper also describes several technologies which could contribute to the establishment of Atom Electronics, including beam assisted scanning tunneling microscope (BASTM) which makes it possible to observe insulator surfaces, micromachine scanning tunneling microscope (μ-STM) by which the vacuum tunneling gap is successfully observed and the Needle Formation and Tip Imaging (NFTI) method which makes possible the in-situ evaluation of the tip apex of an STM.     

A Multivariate Analysis of Risk Factors for Cerebrovascular Disease in Hisayama,Kyushu Island,Japan

Behaviormetrika - A multivariate analysis of risk factors for cerebrovascular disease (CVD) has been applied to 78 CVD cases in 1,419 residents during a six-year follow-up period in Hisayama,...     

Theoretical Studies on the Inverse Problem in Electrocardiography and the Uniqueness of the Solution

This paper focuses on the theoretical formulation of the inverse problem in electrocardiography under a general inhomogeneous and anisotropic configuration of the torso conductor. The following points are especially considered: 1) derivation of the Fredholm integral equation of the first kind which relates epicardial to body surface potentials, 2) specification of the conditions which its kernel must satisfy, 3) general solution method for the inverse problem by using the vector space theory, taking into consideration the ill condition of this inverse problem, and 4) proof of the uniqueness of the epicardial potentials.     

Application of catastrophe theory to power systems

In recent publications dealing with nonlinear systems, nonlinearities existing in the systems under study have drawn much attention. Studies on the effects of nonlinearities in power systems are becoming an increasingly important part of the research on system stability. It is probable that heretofore undiscovered phenomena caused by the nonlinearities involved in load flow equations, generator swing equations and characteristics of control equipments and loads, etc., may be found. This paper presents a new Catastrophe Theory application to nonlinear power systems. Making use of the concept of Duffing's equation, it is shown that a Catastrophe Theory analogy can be used to interpret unstable phenomena caused by system nonlinearities from the viewpoint of oscillations. When considering system nonlinearities due to poor combinations of system parameters and periodic disturbances, there may exist the characteristic “jumps” in system ates that correspond to slow (quasi-dynamic) changes of the frequencies of periodic disturbances. With this Catastrophe Theory approach, a system bifurcation set can be identified to assess the unstable phenomena of power systems.