M. Morita

Bio: M. Morita is an academic researcher. The author has contributed to research in topics: Ultrapure water & Oxide. The author has an hindex of 2, co-authored 3 publications receiving 918 citations.

Growth of native oxide on a silicon surface

Abstract: The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n +‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure waterdrops and chemical binding energy. These chemical bond structures for native oxide filmsgrown in air and in ultrapure water are also discussed.

Control Factor of Native Oxide Growth on Silicon in Air or in Ultrapure Water

Abstract: Native silicon (Si) oxide growth on Si (100) wafers in air and in ultrapure water at room temperature requires coexistence of water and oxygen in the air and ultrapure water ambients. The growth rate data on n‐, n+‐, and p+‐Si (100) in air indicate layer‐by‐layer growth of an oxide. The growth rate on n‐Si (100) in ultrapure water may be governed by a parabolic law. For native oxide growth in ultrapure water, the number of Si atoms dissolved in ultrapure water is over one order of magnitude larger than the number of Si atoms contained in the grown native oxide film. The structural difference between the native oxide film in air and in ultrapure water is also discussed.

Electroluminescence in metal-oxide-semiconductor tunnel diodes with a crystalline silicon/silicon dioxide quantum well

Abstract: We investigated electroluminescence (EL) in metal-oxide-semiconductor (MOS) diodes with an indium tin oxide (ITO) film/ultrathin silicon dioxide (SiO 2 ) film/ultrathin crystalline-silicon (Si) layer/buried SiO 2 layer/Si substrate structure at a negative voltage applied to the ITO film. The EL peak shifted toward higher energy with decreasing Si-layer thickness. The dependence of the EL-peak energy on the Si-layer thickness shows that the EL is due to one-dimensional quantum confinement. Characterization of the MOS diodes suggested that electrons tunneling through the ultrathin SiO 2 film from the conduction band (CB) of the ITO film are injected into higher energy states in the CB of the ultrathin Si layer with a negative voltage applied to the ITO film, and the tunneling electrons radiatively recombine with holes accumulated near the Si/SiO 2 interface in the ultrathin Si layer. • Quantum confinement-induced electroluminescence peaks were observed. • Peaks shifted toward higher energy with decreasing quantum well thickness. • Electroluminescence was excited by injecting tunneling electrons into a quantum well. • Electrons were injected into high-energy states in a silicon conduction band.

Hydrogen Electrocatalysis by Carbon Supported Pt and Pt Alloys An In Situ X-Ray Absorption Study

Abstract: In situ x-ray absorption spectroscopy (XAS) in 1 M HC1O4 was used to examine the electronic and structural effects of hydrogen adsorption on carbon supported Pt (Pt/C) and Pt alloyed with first row transition metals (Cr, Mn, Fe, Co, and Ni). In the case of Pt/C, potential excursions from the double layer region (0.54 V vs. RHE) to 0.0 V caused significant changes in the XAS spectra whereas none was observed for the alloys. The L, and L2 x-ray absorption near edge structure indicated the generation of empty electronic states in the vicinity of the Fermi level due to adsorption of hydrogen, and the L, extended x-ray absorption fine structure indicated an increase in the coordination number of the first Pt-Pt

A Physically Transient Form of Silicon Electronics

Abstract: A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example.

Demonstration of Magnetic Dipole Resonances of Dielectric Nanospheres in the Visible Region

Abstract: Strong resonant light scattering by individual spherical Si nanoparticles is experimentally demonstrated, revealing pronounced resonances associated with the excitation of magnetic and electric modes in these nanoparticles. It is shown that the low-frequency resonance corresponds to the magnetic dipole excitation. Due to high permittivity, the magnetic dipole resonance is observed in the visible spectral range for Si nanoparticles with diameters of ∼200 nm, thereby opening a way to the realization of isotropic optical metamaterials with strong magnetic responses in the visible region.

Growth of native oxide on a silicon surface

Abstract: The control factors controlling the growth of native silicon oxide on silicon (Si) surfaces have been identified. The coexistence of oxygen and water or moisture is required for growth of native oxide both in air and in ultrapure water at room temperature. Layer‐by‐layer growth of native oxide films occurs on Si surfaces exposed to air. Growth of native oxides on n‐Si in ultrapure water is described by a parabolic law, while the native oxide film thickness on n +‐Si in ultrapure water saturates at 10 A. The native oxide growth on n‐Si in ultrapure water is continuously accompanied by a dissolution of Si into the water and degrades the atomic flatness at the oxide‐Si interface, producing a rough oxide surface. A dissolution of Si into the water has not been observed for the Si wafer having surface covered by the native oxide grown in air. Native oxides grown in air and in ultrapure de‐ionized water have been demonstrated experimentally to exhibit remarkable differences such as contact angles of ultrapure waterdrops and chemical binding energy. These chemical bond structures for native oxide filmsgrown in air and in ultrapure water are also discussed.

Modification of hydrogen-passivated silicon by a scanning tunneling microscope operating in air

Abstract: The chemical modification of hydrogen‐passivated n‐Si (111) surfaces by a scanning tunneling microscope (STM) operating in air is reported. The modified surface regions have been characterized by STM spectroscopy, scanning electron microscopy (SEM), time‐of‐flight secondary‐ion mass spectrometry (TOF SIMS), and chemical etch/Nomarski microscopy. Comparison of STM images with SEM, TOF SIMS, and optical information indicates that the STM contrast mechanism of these features arises entirely from electronic structure effects rather than from topographical differences between the modified and unmodified substrate. No surface modification was observed in a nitrogen ambient. Direct writing of features with 100 nm resolution was demonstrated. The permanence of these features was verified by SEM imaging after three months storage in air. The results suggest that field‐enhanced oxidation/diffusion occurs at the tip‐substrate interface in the presence of oxygen.