Kenjiro Oura

Smooth and high-rate reactive ion etching of diamond

Diamond surfaces with patterned Al masks were etched by a reactive ion etching (RIE) system under conditions that the RF power was 100-280 W, the CF 4 /O 2 ratio was 0-12.5% and the gas pressure 2-40 Pa. It was found that the roughness of the etched diamond surface decreased with an increase in the CF 4 /O 2 ratio, although this reduced the selective etching ratio of diamond against Al. The gas pressure also affected the surface roughness and the etching anisotropy. The etching rate of diamond considerably increased upon a small addition of CF 4 in O 2 . Based on these results, we were successful in an anisotropic etching of diamond at a very high rate (∼9.5 μm/h) with a smooth etched surface (R a < 0.4 nm), a high selective etching ratio of diamond vs. Al, and a high aspect ratio (the height/diameter was ∼8 for array structures and ∼25 for exceptional cases) by choosing appropriate etching conditions.

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.

LEED-AES study of the AuSi(100) system

Abstract The system Au/Si(100) has been studied using LEED and AES. Au films grow as Au(111) | Si(100) having six azimuthally rotated orientations at low deposition temperatures below 50°C after the formation of intermediate gold suicide layers. Crystalline gold silicide thin layers are formed on the Au(111) film after heat treatment at 100–400°C. Two types of suicide LEED pattern observed seem to have no correlation with crystallographic data reported on quenched alloy films. Heat treatment over 450°C leads to agglomeration of the film, producing a series of Au-induced superstructures. Heat treatment of the Au film over 1000°C regenerates the clean Si surface accompanied with many etch pits.

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.

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.

Atomic Arrangement of the Si(111)-√3×√3-Ag Structure Derived from Low-Energy Ion-Scattering Spectroscopy

Si(111)-√3×√3-Ag surface structure has been studied by low-energy ion-scattering spectroscopy using neon ions with an energy of 500 eV, combined with LEED-AES. It has been proposed that Ag atoms giving rise to the √3 structure are slightly embedded below the outermost Si layer, including consequent displacements of the substrate Si atoms.

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]

Highly Sensitive Detection of Carbon Monoxide at Room Temperature Using Platinum-Decorated Single-Walled Carbon Nanotubes

We demonstrated highly sensitive detection of carbon monoxide (CO) down to 1 ppm at room temperature using platinum-decorated single-walled carbon nanotubes (Pt-SWNTs). The obtained sensitivity to CO was 3–4 orders higher than the values reported for functionalized SWNTs, and was achieved by the controlled deposition of Pt nanoparticles on SWNTs. For 1–10 ppm of CO, the sensor response linearly increased with CO concentration, affording the quantitative detection of CO in a low-concentration range. Furthermore, Pt-SWNTs exhibited detection selectivity to CO against H2. The sensing mechanism was attributed to electron donation to the SWNTs as a result of CO oxidation on the Pt catalyst surface.

Coating carbon nanotubes with inorganic materials by pulsed laser deposition

Using pulsed laser deposition (PLD), coaxial coating of carbon nanotubes (CNTs) with various inorganic materials (e.g., ZrOx,HfOx,AlOx,ZnOx, and Au) has been performed. The morphology and crystallinity of the coated layers were found to differ according to the materials used even at the same deposition temperature. For oxide materials, the deposits exhibited a uniform layer structure the composition of which was precisely controlled, while for Au, well-crystallized Au nanoparticles were observed on the CNT surface densely. Moreover, not only a single layer but also multiple layers were sequentially coated on CNTs by repeating PLD.