Osamu Suekane

Static Friction Force of Carbon Nanotube Surfaces

To elucidate forces providing high mechanical strength during formation of carbon nanotube (CNT) yarns and sheets, internanotube static friction force was investigated using a transmission electron microscope with a nanomanipulation system. Results show that the static friction force depends strongly on the CNT surface state. That force between two as-grown CNTs grown by chemical vapor deposition is much larger than that for highly crystalline CNTs. The as-grown CNT surfaces generally have amorphous carbon and defects. For CNT yarns and sheets, the frictional force attributable to surface roughness, rather than the van der Waals force, affects interactions among CNTs.

Current-induced curing of defective carbon nanotubes

Defective carbon nanotubes (CNTs) were cured using current-induced thermal excitation. The original straight position of a CNT with an artificially induced plastic bend was restored using an applied current of 2.4μA∕nm. That current is nearly equivalent to the current causing sublimation of CNTs. Thermal excitation cures CNTs with defects of pentagons and heptagons. Such cured CNTs have high crystallinity, as confirmed by applying the second process to them to induce an artificial plastic bend and to recover their straight position. That curing phenomenon was also confirmed using a sample of a one-turn coiled CNT with pentagons and heptagons.

Effect of Morphology on Field Emission Properties of Carbon Nanocoils and Carbon Nanotubes

Helical carbon nanocoils exhibit excellent field emission properties, and are thus expected to be applicable as electron emitters in field emission displays. We have synthesized carbon nanocoils with different diameters by the catalytic thermal decomposition of acetylene using iron–indium–tin–oxide catalysts. It is found that the turn-on voltage is decreased by decreasing the average diameter of the grown carbon nanocoils. The turn-on voltage of as low as 30 V at the electrode gap of 130 µm was achieved when the coil diameter is decreased to 60 nm. The calculation for the concentration of the electric field on the coil surface has been performed using a finite element method. It is found that the strength of the electric field around the top ring of a coil is increased with the decrease of the tubular diameter of the coil and has a similar value as that at the tip of a carbon nanotube, suggesting that the efficiency of the field emission from nanocoils would be higher than that from nanotubes. These results can explain the high stability of field emission from carbon nanocoils.

Rapid Growth of Vertically Aligned Carbon Nanotubes

100-?m-long vertically aligned multiwall carbon nanotubes were grown in 1 s. A thermal chemical vapor deposition method at 700?C was used with a catalyst of iron films and a carbon source gas of acetylene diluted with helium. This study revealed a novel rapid growth mode that appears in the beginning of chemical vapor deposition when the rate of increase in the concentration of carbon source gas is high at the substrate. This new growth mode, which precedes a normal growth mode, provides well-crystallized and straight nanotubes.

Scanning tunneling miscroscopy study of InAs islands grown on GaAs(001) substrates

Scanning tunneling microscopy (STM) connected to molecular beam epitaxy (MBE) has been used to investigate InAs islands and wetting layers (WLs) on GaAs(001) substrates. STM results reveal that the size and density of InAs islands depend strongly both on the growth temperature and growth rate of InAs. With increasing the growth temperature, the island density becomes lower and the size larger. With increasing the growth rate, the island density becomes higher and the size smaller. Moreover, it is found that two-step growth by varying the growth temperature under a fixed growth rate results in the bimodal distribution of the InAs island-size. These results indicate that controlling the growth temperature and growth rate makes it possible to control the size distribution of InAs islands as well as the size and density of InAs islands.

Growth Temperature Dependence of InAs Islands Grown on GaAs (001) Substrates

Scanning tunneling microscopy (STM) in conjunction with molecular beam epitaxy has been used to investigate InAs islands and wetting layers on GaAs(001) substrates. STM results reveal that the size, density and shape of InAs islands strongly depend on the growth temperature of InAs. With increasing the growth temperature, the island density decreases, the size increases, and the shape becomes round rather than elliptical. In the photoluminescence (PL) results, a PL peak shift is observed with increasing InAs growth temperature. This shift agrees with the STM observation that larger islands are grown at higher growth temperatures. The change in the size and density of islands can be explained in terms of a critical nucleus in heterogeneous nucleation. These results indicate that controlling the growth temperature makes it possible to control the size, density and shape of InAs islands.

Scanning tunneling microscopy study of GaAs overgrowth on InAs islands formed on GaAs(001)

Self-assembled InAs quantum dots by utilizing islanding in a Stranski-Krastanov mode are expected to have tremendous potential for electronic and optical applications. So far, shapes of InAs islands (dots) formed on GaAs[001] have been intensively examined with the use of reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and cross-sectional STM. There are some discrepancies between STM and XSTM results, i.e., considerable differences in shape between before and after GaAs overgrowth on islands. In this paper, STM and RHEED have been used to investigate the overgrowth of GaAs capping layers on InAs islands formed on GaAs[001] substrates. In particular, we focus on how the overgrowth of GaAs on InAs islands proceeds and whether or not the overgrowth of GaAs brings about changes in the shape of InAs islands.

Scanning tunneling microscopy study of GaAs overgrowth on InAs islands formed on GaAs[001]

Self-assembled InAs quantum dots by utilizing islanding in a Stranski-Krastanov mode are expected to have tremendous potential for electronic and optical applications. So far, shapes of InAs islands (dots) formed on GaAs[001] have been intensively examined with the use of reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and cross-sectional STM. There are some discrepancies between STM and XSTM results, i.e., considerable differences in shape between before and after GaAs overgrowth on islands. In this paper, STM and RHEED have been used to investigate the overgrowth of GaAs capping layers on InAs islands formed on GaAs[001] substrates. In particular, we focus on how the overgrowth of GaAs on InAs islands proceeds and whether or not the overgrowth of GaAs brings about changes in the shape of InAs islands.

Growth temperature dependence of InAs islands grown on GaAs [001] substrates

Scanning tunneling microscopy (STM) connected to molecular beam epitaxy (MBE) has been used to investigate InAs islands and wetting layers (WLs) on GaAs[001] substrates. STM results reveal that the size and density of InAs islands strongly depend on the growth temperature. The density of InAs islands decreases and their size increases with increasing growth temperature. From photoluminescence (PL) results, a PL peak shift is observed with increasing InAs growth temperature. This shift agrees with the results of the STM observation that larger islands are grown at higher growth temperature.