We demonstrated that single-walled carbon nanotubes (SWCNTs) grew from Ir catalysts by an alcohol catalytic chemical vapor deposition (ACCVD) method using a gas source-type CVD system. At an ethanol pressure of 1×10−1 Pa at 800°C, vertically aligned SWCNTs (VA-SWCNTs) were grown on SiO2/Si substrates. As the growth time became longer, the VA-SWCNT became thicker, and it reached almost 5 μm for a growth time of 180 min. The Raman spectroscopy results showed that the diameters of the grown SWCNTs were mainly distributed below 1.1 nm, indicating that the SWCNTs grown from Ir catalysts had small diameters compared with those from other metal catalysts.

Growth of single-walled carbon nanotube (SWCNT) was achieved by an alcohol catalytic chemical vapor deposition (CVD) mechanism that was conducted in a high vacuum using Ru catalysts. By optimizing the ethanol pressure, SWCNTs can grow in a wide range of temperature between 500 °C and 900 °C. Both the yield and crystalline quality of SWCNTs reached their maxima at 700 °C. Significantly, the SWCNT growth was achieved even at 450 °C, which was much lower than the growth temperatures that were required for SWCNT growth using Ru catalysts previously. Raman measurements exhibited that the diameter distribution of the SWCNTs that were grown at 450 °C was quite narrow and (11, 4) nanotubes were dominant. The observations of transmission electron microscope (TEM) suggested that the size of the Ru particles were larger than the diameter of SWCNT. Such a relation was similar to the relation observed in the growth of SWCNTs using Pt catalysts.

Growth of single-walled carbon nanotube (SWCNT) was achieved by an alcohol catalytic chemical vapor deposition (CVD) mechanism that was conducted in a high vacuum using Ru catalysts. By optimizing the ethanol pressure, SWCNTs can grow in a wide range of temperature between 500 °C and 900 °C. Both the yield and crystalline quality of SWCNTs reached their maxima at 700 °C. Significantly, the SWCNT growth was achieved even at 450 °C, which was much lower than the growth temperatures that were required for SWCNT growth using Ru catalysts previously. Raman measurements exhibited that the diameter distribution of the SWCNTs that were grown at 450 °C was quite narrow and (11, 4) nanotubes were dominant. The observations of transmission electron microscope (TEM) suggested that the size of the Ru particles were larger than the diameter of SWCNT. Such a relation was similar to the relation observed in the growth of SWCNTs using Pt catalysts.

In situ X-ray absorption near edge structure (XANES) measurements were conducted to elucidate the chemical states of Co and Ni catalysts during single-walled carbon nanotube (SWCNT) growth via chemical vapor deposition (CVD). XANES spectra indicated that both Co and Ni catalysts partially oxidized before heating. It was found that Co catalysts formed carbides during the SWCNT growth. In contrast, Ni catalysts remained metallic state even after the SWCNT growth had begun. These results indicate that during SWCNT growth, carbon atoms dissolve into Co particles, whereas for Ni particles, they diffuse on the surface region. It was concluded that the growth mechanisms of SWCNTs formed by CVD differed for either Co or Ni catalyst.

We carried out single-walled carbon nanotube (SWCNT) growth using a Rh catalyst on Al2O3 buffer layers that were prepared by three different methods based on electron beam (EB) evaporation: native oxidation of Al layer deposited by EB ([EB(Al)+NO]-Al2O3 layer); thermal oxidation of Al layer deposited by EB ([EB(Al)+TO]-Al2O3 layer); EB deposition of Al2O3 layer ([EB(Al2O3)]-Al2O3 layer). SWCNT yield was the largest for the [EB(Al2O3)]-Al2O3 layer, while SWCNTs were not grown on the [EB(Al)+NO]- Al2O3 layer. Transmission electron spectroscopy showed that most of Rh particle sizes were distributed between 1.0 and 2.6 nm on the [EB(Al)+NO]- Al2O3 and [EB(Al2O3)]- Al2O3 layers, while they were distributed between 1.8 and 4.2 nm on the [EB(Al)+TO]- Al2O3 layer. This result indicates that surface migration of Rh catalysts was suppressed on the [EB(Al2O3)]- Al2O3 layer, resulting in the largest SWCNT yield. On the other hand, enlargement of Rh catalyst particles occurred on the [EB(Al)+TO]- Al2O3 layer, leading to the reduction of SWCNT yield. Taking into account our previous study, inward diffusion of Rh catalysts into the Al2O3 buffer layer inhibited SWCNT growth on the [EB(Al)+NO]- Al2O3 layer, although enlargement of Rh particle size was suppressed. We also carried out ultra-violet photoemission measurements for Rh catalysts on the [EB(Al)+TO]- Al2O3 and [EB(Al2O3)]- Al2O3 layers and investigated the electronic states of Rh catalysts on them.

Single-walled carbon nanotube (SWCNT) growth from Pt catalysts by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD), was investigated. Raman results showed that the diameters of SWCNTs grown from Pt were below 1.2 nm, while transmission electron microscopy (TEM) showed that the diameters of most Pt catalyst particles were above 1.2 nm. This suggests that SWCNT diameters were smaller than Pt catalysts particles. X-ray photoelectron spectroscopy measurements showed that reduction of Pt particles occurred during the SWCNT growth. Based on these experimental data, growth mechanism of SWCNTs was discussed.

The mechanism for the precipitation of multilayer graphene was investigated with respect to the use of an Al2O3 barrier layer and Au capping layer. The Al2O3 barrier layer suppresses the dissolution of carbon into the catalyst, especially at low temperature, and assists a decrease in the density of graphene nuclei. On the other hand, the Au capping layer is beneficial to weaken the strong binding between the catalyst and the graphene carbon atoms, and enhances the surface migration of precipitated carbon adatoms. A combination of the Al2O3 barrier layer and Au capping layer is useful for the synthesis of high-quality graphene with large grains. On a sample with both layers annealed for 60 min, the area of 5-layer graphene islands is as large as 10 μm, and covers 60% of the entire surface. The Raman D/G band intensity ratio of 0.024 indicates the precipitated graphene is high quality.

Single-walled carbon nanotube (SWCNT) growth were carried out on SiO2/Si substrates using Pt catalysts at different temperatures, from 400°C to 700°C, under various ethanol pressures by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD). Raman measurements showed that the optimal ethanol pressure decreased as the growth temperature was reduced, and that SWCNTs grew even at 400°C by optimizing the ethanol pressure to 1×10-5 Pa in a high vacuum system. Compared to the SWCNTs grown from Co catalysts, the diameters of SWCNTs grown from Pt were smaller, irrespective of the growth temperature. In addition, both the SWCNT diameter and the distribution became narrower by reducing the growth temperature and we obtained small-diameter SWCNTs of which the diameters were less than 1 nm using Pt catalysts.

Aluminum oxide (Al2Ox) buffer layers were employed to grow single-walled carbon nanotubes (SWNTs) at 400°C using an alcohol gas source and a Co catalyst. By optimizing the thickness of the aluminum oxide layer, the SWNT yield was enhanced by a factor of several times. In addition, SWNT growth at 350°C was realized on the Al2Ox buffer layer by this method. Raman measurements at various excitation wavelengths suggest that a Al2Ox buffer layer preferentially enhances the growth of SWNTs with larger diameters (>1 nm).

We studied the effects of annealing in H2O2 on the morphologies and structures of “as grown” high-density, well-aligned multi-walled carbon nanotube (MWNT) films formed by surface decomposition of SiC. After annealing in H2O2 solution at 100°C for 3 h, the G/D ratio increased from 1.44 to 2.33, the FWHM of the G band peak became narrower, and a D′ shoulder peak appeared. Transmission electron microscopy (TEM) revealed that the dispersion of MWNTs in dimethylformamide (DMF) solution was improved, suggesting that film impurities were reduced and that damage to the MWNTs was negligible. After annealing for 9 h, the G/D ratio decreased to 1.57, and exfoliation of some MWNTs was observed. In addition, several functional groups such as carboxylic (-COOH) and hydroxyl (-OH) were formed on the surface of the MWNTs. From these results, we conclude that annealing in H2O2 under proper conditions can effectively purify “as grown” MWNT films formed by surface decomposition of SiC.

It has been reported that carbon nanotubes (CNTs) were formed through the decomposition of SiC(000-1) surfaces by heating in a vacuum. By this growth technique, well aligned zigzag-type CNTs can be selectively formed without any catalysts and the diameters of the CNTs are fairly uniform. Moreover, this growth technique has an advantage in fabrication of CNT devices, since CNTs grow into the inside of SiC, facilitating the application of semiconductor process. So far, we have reported that ambient oxygen enhances the CNT growth rate [1]. However, the optimum oxygen pressure has never been investigated enough. It has also been reported that SiO2 layer is formed on SiC surface after annealing under high oxygen pressure [2]. In this study, we investigated the relation between surface oxide formation and CNT growth under various annealing conditions. After HF etching, 6H-SiC(000-1) (Carbon-face) samples were introduced into an ultra-high vacuum (UHV) chamber and annealed at various temperatures between 800 and 1250°C. During the annealing, oxygen partial pressure was controlled by supply of oxygen gas. The oxygen pressure was set between 10-4 and 1 Pa. For comparison, we also annealed several samples under UHV (10-6 Pa). Scanning tunneling microscopy (STM) observation and X-ray photoelectron spectroscopy (XPS) measurements were carried out to analyze their surface structures and chemical species. It was observed that the surface decomposition of SiC had occurred after annealing at 800°C under UHV, and carbon nanocaps were formed on the SiC surface at 1200°C, which subsequently transformed into CNTs. When oxygen pressure was below 10-2 Pa, the nanocap formation was observed between 1150 and 1200°C irrespective of oxygen pressure. However, at 1 Pa of oxygen pressure, SiO2 layer was observed on the SiC surface after annealing at 1200°C and no carbon nanocaps were observed. These results indicate that it is necessary to anneal SiC below 1 Pa to form CNT, although the presence of oxygen enhances CNT formation below 10-3 Pa. The boundary between the active oxidation and the passive oxidation in SiC oxidation estimated from our results was well consistent with previous studies for SiC oxidation under higher oxygen pressure (>1 Pa)[2]. From our results, in order to grow CNT effectively, it is important to minutely control oxygen pressure.

Conventional alcohol catalytic chemical vapor deposition (ACCVD) growth of carbon nanotubes (CNTs) have been carried out under ambient gases from 103 to105 Pa. These ambient gas pressures have prevented in situ observations using an electron beam during CNT growth, such as scanning electron microscopy (SEM), scanning tunneling microscopy (STM). Therefore, in order to realize the in situ observations and to clarify the growth mechanism of nanotube, CNT growth in a high vacuum is essential. In addition, the effects of residual gases also may be avoided in the growth under high vacuum. In this study, we carried out CNT growth under high vacuum using an alcohol gas source in an ultrahigh vacuum (UHV) chamber and we achieved CNT growth below 400°C without any excitation processes of carbon source. After deposition of Co catalyst of 1 nm in thickness on SiO2/Si substrate, ethanol gas was supplied to the substrate surface through a stainless steel nozzle in the UHV chamber. The growth temperature was monitored by a pyrometer during the growth, and set between 350 and 900°C. The supply of ethanol gas was controlled by monitoring an ambient pressure, which was varied from 1 ∼10-1 to 1 ∼10-4 Pa. The grown CNTs were characterized by SEM and Raman spectroscopy. The G/Si intensity ratio reached its maximum at 700°C, when the pressure was 1 ∼10-1 Pa. The maximum point of the G/Si peak intensity shifted to a lower temperature as the growth pressure decreased. When the pressure was 1 ∼10-4 Pa, the G/Si intensity ratio reached its maximum at 400°C, at which clear RBM peaks were observed in the Raman spectrum. From the RBM peaks, the CNT diameters were estimated to be between 0.9 to 1.7 nm, and CNTs of 1.2-1.4 nm in diameter were dominant at 1 ∼10-1 Pa, whereas thinner CNTs (diameter is below 1.0 nm) were increased with the reduction of the pressure. Our largest G/D ratio was about 40 for the sample grown at 1 ∼10-1 Pa, which is considerably larger than the reported value for the CNTs grown under low pressure. From these results, we conclude that the reduction of the growth pressure lowers the growth temperature. This technique can be applied to in situ observation, and may also be useful for low temperature growth of CNTs, which opens new possibilities for the fabrication of CNT based nanodevices.

We have focused to grow cubic GaN (c-GaN) on Si(100) substrates using boronmonophosphide(BP) buffer crystals. We have successfully grown BP crystals by MOVPE technique with electrically n-type and thickness deviation is within several % along 2inch wafer under undoped conditions. The electrical conductivity is less than 0.5mohm∙cm. We have preliminary grown GaN by RF-MBE technique, before we carry out mass-producing MOVPE on larger diameter Si substrates. It has been found the cubic type GaN has been successfully grown on the substrates by measuring X-ray diffraction. The crystal quality and defect generation were observed by TEM. It has been found that there are much more dislocations than 109cm-2 generated at GaN/BP interface.

Formation process of nanosized cap structures on a thermally treated 6H-SiC(000-1) substrate was investigated using atomic-resolution ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). After formation of clusters of carobon particles 1-2 nanometer in diameter at 1150°C, these nanoparticles merged, forming nanosized cap structures. Hexagonal carbon networks, partly composed of pentagons, were clearly observed on the surface of the cap structures for a sample annealed above 1200°C. A model for the formation of carbon nanocaps on 6H-SiC(000-1) was proposed.

A nitridation mask on a GaAs surface was prepared using RF-MBE and its machinability by STM lithography was studied. A 5.2 nm thick crystal-like layer was formed at 350°C, and was modified by STM at a sample bias of ±80V with good size reliability, which was sufficiently fine for realizing dislocation-free heteroepitaxial growth of GaAs / Si. The mask was maintained up to 620°C under As flux exposure at 1.5 × 10−4 Pa.

The Structural properties of Europium (Eu) doped GaN and its relation with optical properties were studied. Concentration quenching of the intensity of the Eu related luminescence observed when Eu concentration exceeds 3 at.%. In situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were carried out to study this luminescence quenching and it was discovered that there is close relationship between the luminescence intensity at 622 nm and structural properties. The cause of the concentration quenching is likely related to the polycrystalline growth as well as to the EuN formation.

The surface nitridation of GaAs substrate under various conditions were performed and its surface morphology was studied by using atomic force microscope. The RMS roughness of the surfaces was closely related to formation of the particles which was formed by As evaporation and subsequent Ga migration, which was enhanced by higher substrate temperature.

Beam induced lateral epitaxy (BILE) on truncated ridges was applied to the heteroepitaxial growth of GaAs on a Si substrate. A GaAs buffer layer was formed on the Si substrate, and then this GaAs/Si template was used as a substrate for the BILE process. As a result, overgrown regions of GaAs of widths as large as 6.5 μm were grown laterally from the sides of the truncated ridges. The growth regions had a flat, smooth top surface consisting of a (111) facet. Although stacking faults from the GaAs/Si template remained in the growth region, which are unfavorable for device applications, the lateral grown region has no dislocations. Thus, the BILE method is useful for reducing dislocations in heteroepitaxy.

We developed a new technique of epitaxial lateral growth without using oxide masks called beam induced lateral epitaxy (BILE). In this technique, molecular beams are directed at a nearly glancing angle with respect to a substrate that has pre-fabricated truncated ridges. By using BILE we grew GaAs laterally from the side of ridges on a GaAs substrate. The growth behavior of BILE strongly depended on both incident angle of the Ga beam and the crystal orientation of the truncated ridges. The formation of facets on the lateral growth front controlled the grown shape of the layers. By using a (111) B substrate with BILE, we grew a smooth, flat (111) B facet on the top of the layer.