Mitsuhiro Katayama

Coaxial impact-collision ion scattering spectroscopy (CAICISS): A novel method for surface structure analysis

Abstract A novel low-energy ion scattering spectrometer, in which an ion source and an energy analyzer are arranged coaxially so that the experimental scattering angle is just 180°, has been constructed. This mode of low-energy ion scattering spectroscopy, which we call coaxial impact-collision ion scattering spectroscopy (CAICISS), has several advantages. For example, CAICISS is suitable for in situ observation of various surface processes (e.g., epitaxial film growth at semiconductor surfaces) because of its geometrical simplicity. Preliminary experiments using the CAICISS apparatus have been made for a Au/Si(111) surface.

Hydrogen interaction with clean and modified silicon surfaces

The present report deals with the main aspects of the interaction of hydrogen with the atomically clean crystalline silicon surfaces and submonolayer metal/silicon interfaces. After a brief presentation of the experimental techniques applied nowadays in the hydrogen/silicon interaction studies, the main recent results obtained in this field are reviewed. For the case of clean silicon surfaces, hydrogen interaction is shown to change greatly their structure and properties. The main regularities of the hydrogenation of silicon and the features of the processes on the hydrogen-adsorbed silicon surfaces (chemical reactions, metal film growth, silicon and germanium epitaxy) are discussed. The atomic hydrogen interaction with the metal/silicon submonolayer interfaces results in most cases in the agglomeration of the two-dimensional metal layers into the three-dimensional metal islands. The application of this process for the structural investigations is demonstrated. The feasibility of the selective deposition and extraction of H atoms by a tip of scanning tunneling microscope is shown to open wide opportunities for nanostructure fabrication.

Efficient field emission from an individual aligned carbon nanotube bundle enhanced by edge effect

The authors report on the field emission from an aligned carbon nanotube (CNT) bundle grown by thermal chemical vapor deposition. The CNT bundle showed a low-threshold electric field of 2.0V∕μm that produced a current density of 10mA∕cm2, sustainable evolution of current density up to 2.8A∕cm2 at 2.9V∕μm, and good emission stability without degradation for 200h of continuous dc emission. By calculating the electric-field distribution, it was found that the electric field was significantly higher at the edge of the CNT bundle than at the center. The excellent field-emission properties of the aligned CNT bundle were attributed to the edge effect and the high-density structure.

Single-Walled Carbon Nanotube Thin-Film Sensor for Ultrasensitive Gas Detection

We demonstrated a gas sensor fabricated by growing a single-walled carbon nanotube (SWNT) thin film directly on a conventional sensor substrate. NO2 and Cl2 were detected down to the ppb level under room-temperature operation with a fast response. Using an electrical breakdown technique, gas response sensitivity was improved by an order of magnitude. The relationship between gas concentration and sensor response was derived based on the Langmuir adsorption isotherm, predicting a detection limit of 8 ppb for NO2. The SWNT thin-film gas sensor exhibits merits over other types of sensors by virtue of its simplicity in fabrication and feasible application.

Recent developments in low-energy ion scattering spectroscopy (ISS) for surface structural analysis

Abstract Recent years have seen significant progress in low-energy ion scattering spectroscopy (ISS) for surface structural analysis. They include the development of impact-collision ion scattering spectroscopy (ICISS) to make quantitative surface structural analysis possible and the use of alkali ions rather than noble-gas ions in ICISS (ALICISS) to avoid the ambiguity of ion neutralization probability. The latest progress is the development of coaxial impact-collision ion scattering spectroscopy (CAICISS) in which a pulsed-beam ion source and a time-of-flight energy analyzer are arranged coaxially so as to take the experimental scattering angle just at 180°. Various characteristics of CAICISS, which are due to (a) the 180° experimental scattering angle, (b) the time-of-flight mode for the energy analysis, and (c) the use of an acceleration tube for scattered ions, are discussed.

Family of the metal-induced Si(111)3×1 reconstructions with a top Si atom density of 4/3 monolayer

Abstract Using scanning tunneling microscopy (STM), the common features and peculiarities of the Si(111)3×1 reconstructions induced by Na, Ag, Ca, and Mg have been studied. From the quantitative consideration of the Si mass transport occurring at the 7×7→3×1 transformation, the top Si atom density has been found, and it appears to be the same, 4/3 monolayer, for all surface structures under consideration. A thorough examination of the numerous high-resolution STM images of Si(111)3×1–Na surfaces reveals that all 3×1 domains have a unique orientation with respect to the Si(111) substrate. The recently proposed double-π-bonded chain and honeycomb chain-channel models appear to be the only models that fit these experimental findings properly.

Ultra-Low-Threshold Field Electron Emission from Pillar Array of Aligned Carbon Nanotube Bundles

We observed the field electron emission of the technologically useful current density of 10 mA/cm2 at an extremely low threshold electric field (Eth) of 1.0 V/µm, from an array of pillars of aligned carbon nanotube bundles, which were grown on a Si substrate by thermal chemical vapor deposition. Adjusting the distance between the neighboring pillars (R) and the pillar height (H) to the optimal condition (R/H = 2) can effectually enhance the field concentration, resulting in a highly efficient electron emission. The obtained Eth is 1/2–1/3 times lower than the best values that have been reported to date.

Multiframe x-ray imaging system for temporally and spatially resolved measurements of imploding inertial confinement fusion targets

A compact and simple multiframe x‐ray imaging system was developed in order to monitor the implosion of spherical targets in inertial confinement fusion research. Time intervals between consecutive frames can be adjusted flexibly, and the maximum number of adjacent frames is 20 for an overall duration of 1.4 ns. Each frame is recorded with a temporal resolution of 83±20 ps, a spatial resolution of 10 lp/mm at a modulation transfer function of 20%, and an intensity dynamic range of 103. A proximity focused image intensifier with two microchannel plates allows to obtain a gain of 105. Measured temporal response and gain characteristics could be reproduced by a simple Monte Carlo calculation.

Surface hydroxyl formation on vacuum-annealed TiO2(110)

The change in surface composition and structure of a rutile TiO2(110) surface during thermal annealing in an ultrahigh vacuum was studied by coaxial impact–collision ion scattering spectroscopy and time-of-flight elastic recoil detection analysis. When the clean TiO2(110) surface with a 1×1 bridging-oxygen-rows structure was obtained by annealing at 730 °C, about one monolayer of hydrogen atoms still resided on the surface. These hydrogen atoms were assigned to surface hydroxyls as an ingredient of the TiO2(110)1×1 structure, which was formed in the self-restoration process of surface oxygen vacancy defects by dissociative adsorption of water molecules during thermal annealing.

Electronic Transport in Multiwalled Carbon Nanotubes Contacted with Patterned Electrodes

The electrical conductance of 0:8 � 5-mm-long multiwalled carbon nanotubes (MWCNT) was measured at room temperature in a multiprobe scanning tunneling microscope (STM)-scanning electron microscope (SEM) system and a conventional prober system, by bringing the MWCNTs into contact with patterned metal electrodes. The contact resistance between the CNTs and metal electrodes was sufficiently small. The conductance was proportional to A=L (and also to B=L, within our experimental error), where A, B, and L are the cross section, circumference, and length of CNTs. This indicates the occurrence of diffusive transport. A nonlinear current-voltage characteristic was obtained; the conductance increased steeply with current. A multiprobe STM-SEM system was very useful for measuring individual CNTs. [DOI: 10.1143/JJAP.43.L1081]