[en] We have studied epitaxial crystal growth of Si_1-xGe_x films on silicon substrates at 550 .deg. C by low pressure chemical vapor deposition. In a low PH₃ partial pressure region such as below 1.25x10^-3 Pa, both the phosphorus and carrier concentrations increased with increasing PH₃ partial pressure, but the deposition rate and the Ge fraction remained constant. In a higher PH₃ partial pressure region, the deposition rate, the phosphorus concentration, and the carrier concentration decreased, while the Ge fraction increased. These suggest that high surface coverage of phosphorus suppresses both SiH₄ and GeH₄ adsorption/reactions on the surfaces, and its suppression effect on SiH₄ is actually much stronger than on GeH₄. In particular, epitaxial crystal growth is largely controlled by surface coverage effect of phosphorus in a higher PH₃ partial pressure region

[en] We have used a variational wave function for hydrogenic impurities in cylindrical quantum wires to calculate the dependence of the photoionization cross section of such impurities on the photon energy. The calculation has been performed using the infinite well model. The transition takes place between the impurity level associated with the ground subband and the free particle state in the free excited state for hydrogenic impurities at the center of a cylindrical quantum wire. The result is presented for various wire radii at the center of a cylindrical quantum wire. We see that the peak value initially increases with increasing wire size, reaching a maximum value and then decreasing with a further increase in wire size, because the binding energy increases with decreasing wire radius. This peak value occurs when the photon energy is larger than the difference between the final and initial state energies of the impurity

[en] The vertically aligned uniformed carbon nanotubes (CNTs) on a large area of Ni deposited Si substrates were grown by thermal chemical vapor deposition using C₂H₂ gas. The diameter of CNTs is as small as about 60 nm and the length is about 50 μm. High-resolution TEM analysis reveals that the CNTs have multi-walls with good crystallinity and there are some defects on the wall surface. The base growth model is suitable to bamboo-shaped CNTs using thermal chemical vapor deposition

[en] We fabricated point emitters using a multiwalled carbon nanotube (MWCNT) yarn which was treated by ethylene glycol. The point emitter showed a very high emission current of 3.01 mA (current density of 1.1 x 10⁸ A cm^-2) and good emission stability of over 20 h. We attributed the excellent field emission properties to a large field enhancement factor caused by the large aspect ratio of the sharp tip of the point emitter and the tight bonding of neighboring MWCNTs due to the ethylene glycol treatment. We investigated the field enhancement factor according to the gap between the anode and the emitter tip at a macroscopic gap regime. The measured field enhancement factor of the MWCNT point emitter was in good agreement with theoretical models.

[en] A lipase from Pseudomonas cepacia was immobilized onto single walled carbon nanotubes (SWNTs) in two different ways in each of two solvent systems (buffer and ionic liquid). The most efficient immobilization was achieved in ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIM-BF4). In this procedure, carbon nanotubes were first functionalized noncovalently with 1-pyrenebutyric acid N-hydroxysuccinimide ester and then subject to the coupling reaction with the lipase in ionic liquid. The resulting immobilized enzyme displayed the highest activity in the transesterification of 1-phenylethyl alcohol in the presence of vinyl acetate in toluene

[en] The improved field emission stability of thin multiwalled carbon nanotube (thin-MWCNT) emitters using a tip sonication process has been investigated. The thin-MWCNTs showed short lengths and many open tips after the tip sonication treatment. The field emission properties of the thin-MWCNT emitters were investigated. Field emission stability dramatically increased as the tip sonication time increased. In particular, field emission current at an acceleration condition was quite stable and showed no degradation for over 19 h after tip sonication treatment of 30 min. Tip sonication could effectively cut CNTs short and regulate the length of CNTs. Therefore, field emission stability was significantly improved during a long period of operation because many shortened thin-MWCNTs could participate in field emission after the treatment.

[en] In situ potassium (K)-doped single-walled carbon nanotube (SWCNT) was synthesized using a hydrogen arc-discharge method. X-ray photoelectron spectroscopy analysis showed that the K-doped SWCNTs consisted of 0.12% K mass composition. The K-doped SWCNTs showed the lower turn-on electric field of 2.0 V/μm at a current density of 10^-9 A/cm² and the higher emission current density of 3.0 mA/cm² at an applied field of 4.6 V/μm compared with the undoped SWCNTs. The improved field emission performance of K-doped SWCNTs was mainly attributed to the decreased work function and the increased density of state near the Fermi energy

[en] Hole patterns were fabricated on SiO₂/Si substrate by a conventional lithography method using photoresist, and iron was deposited on substrate by RF sputtering. We have synthesized vertically-aligned carbon nanotubes which were selectively grown on the iron-deposited hole patterns by thermal chemical vapor deposition of C₂H₂ gas at 750 ∼ 850 .deg. C. The carbon nanotubes selectively grown on hole patterns are applicable to a field emission display of triode type. We confirmed the growth of the carbon nanotubes using electron microscopy

[en] Vertically aligned double-walled carbon nanotube (VA-DWCNT) arrays were synthesized by point-arc microwave plasma chemical vapor deposition on Cr/n-Si and SiO₂/n-Si substrates. The outer tube diameters of VA-DWCNTs are in the range of 2.5-3.8 nm, and the average interlayer spacing is approximately 0.42 nm. The field emission properties of these VA-DWCNTs were studied. It was found that a VA-DWCNT array grown on a Cr/n-Si substrate had better field emission properties as compared with a VA-DWCNT array grown on a SiO₂/n-Si substrate and randomly oriented DWCNTs, showing a turn-on field of about 0.85 V μm^-1 at the emission current density of 0.1 μA cm^-2 and a threshold field of 1.67 V μm^-1 at the emission current density of 1.0 mA cm^-2. The better field emission performance of the VA-DWCNT array was mainly attributed to the vertical alignment of DWCNTs on the Cr/n-Si substrate and the low contact resistance between CNTs and the Cr/n-Si substrate

[en] Single-walled carbon nanotubes (SWCNTs) are promising materials as active channels for flexible transistors owing to their excellent electrical and mechanical properties. However, flexible SWCNT transistors have never been realized on paper substrates, which are widely used, inexpensive, and recyclable. In this study, we fabricated SWCNT thin-film transistors on photo paper substrates. The devices exhibited a high on/off current ratio of more than 10⁶ and a field-effect mobility of approximately 3 cm²/V·s. The proof-of-concept demonstration indicates that SWCNT transistors on flexible paper substrates could be applied as low-cost and recyclable flexible electronics