Takashi Ikuno

Preparation of Alkyl-Modified Silicon Nanosheets by Hydrosilylation of Layered Polysilane (Si6H6)

Alkyl-modified crystalline silicon nanosheets 2 were synthesized and maintained the crystal structure of a Si(111) plane, in which the dangling silicon bond is stabilized by capping with the alkyl group. 2 was characterized using UV-vis, Fourier transform-infrared, and X-ray photoelectron spectroscopies; X-ray diffraction; and X-ray absorption near edge structure analysis. A model structure is proposed that has a periodicity through the nanosheet surface.

SnS thin film solar cells with Zn1−xMgxO buffer layers

The conduction band offset (CBO) of SnS as the light absorbing layer and Zn1−xMgxO as the buffer layer in SnS thin film solar cells has been optimized to improve the solar cell conversion efficiency. We controlled the CBO experimentally by varying the Mg content (x) of the Zn1−xMgxO layer. The optimum CBO value range for improved solar cell performance was determined to be from −0.1 to 0 eV. A SnS thin film solar cell sample with the optimum CBO value exhibited conversion efficiency of approximately 2.1%.

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.

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]

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.

SiC nanofibers grown by high power microwave plasma chemical vapor deposition

Silicon carbide (SiC) nanofibers have been synthesized on Si substrates covered by Ni thin films using high power microwave chemical vapor deposition (CVD). Characterization using transmission electron microscopy (TEM) combined with electron energy-dispersive X-ray spectroscopy (EDX) revealed that the resultant fibrous nanostructures were assigned to β-SiC with high crystallinity. The formation of SiC nanofibers can be explained by the vapor liquid solid (VLS) mechanism in which precipitation of SiC occurs from the supersaturated Ni nanoparticle containing Si and C.

Formation of Vertically Aligned Carbon Nanotubes by Dual-RF-Plasma Chemical Vapor Deposition

The dual-RF-plasma chemical vapor deposition (dual-RF CVD) technique was examined for the formation of large areas of vertically aligned multiwalled carbon nanotubes (MWNTs). Two RF powers, Pdischarge (Pdis) and Psubstrate (Psub), were used for the dissociation of methane gas and control of the energy of positive ions impinging on the substrates, respectively. The Psub is necessary for the formation of MWNTs, without which a foil-like carbon nanostructured film was deposited. The positive ion bombardment works to suppress the deposition of amorphous carbon films and foil-like carbon nanostructures. Formation of MWNTs was observed within an area of 25 cm2 under the experimental setup. A threshold temperature between 500 to 540°C was defined for the formation of vertically aligned MWNTs.

Ultrasensitive Ozone Detection Using Single-Walled Carbon Nanotube Networks

We demonstrated ultrasensitive detection of ozone using single-walled carbon nanotube (SWNT) networks directly grown on a conventional sensor substrate. Ozone was detected down to the ppb level (~6 ppb) at room-temperature operation with a fast response. Using an electrical breakdown technique, gas sensitivity was improved. This result clearly indicates that owing to its high sensitivity, simplicity in fabrication and compact size, an SWNT sensor provides a feasible route to ultrasensitive ozone detection surpassing existing methods.

Thermally driven nanomechanical deflection of hybrid nanowires

We observed thermally induced nanomechanical deflection of a hybrid inorganic nanowire (NW) synthesized by pulsed-laser deposition, the structure of which is a carbon nanotube template sandwiched by aluminum oxide and tungsten oxide thin layers. The hybrid NW was gradually bent at a specimen temperature ranging from room temperature to 800 °C, due to the different coefficients of thermal expansion of the coated layers. This mechanical deflection exhibited repeatability.

Low Temperature Synthesis of Aligned Carbon Nanotubes by Inductively Coupled Plasma Chemical Vapor Deposition Using Pure Methane

Inductively coupled plasma chemical vapor deposition combined with substrate biasing using pure methane was applied to low-temperature synthesis of carbon nanotubes. We found that the resultant carbon nanotubes were crystalline even at a growth temperature of 500°C. The growth mechanism of the crystallized carbon nanotubes was discussed in terms of the moderate etching of carbon deposit by hydrogen species dissociated from methane in inductively coupled plasma.