Naotake Toyama

A (23×213) surface phase in the 6H–SiC(0001) surface studied by scanning tunneling microscopy

The structure of Si-rich 6H–SiC(0001) surfaces has been investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction. We observed a surface phase with (−2  4 26) periodicity (designated as (23×213) for convenience), coexisting with the known stable (3×3) phase, in a surface obtained by annealing the (3×3) surface at 800 °C. A structural model containing eight Si adatoms per unit cell on the Si adlayer is proposed, which is consistent with the present STM images and with the extension of the (3×3) model structure.

AN STM OBSERVATION OF THE INITIAL PROCESS OF GRAPHITIZATION AT THE 6H-SiC(000¯1) SURFACE

We applied scanning tunneling microscopy (STM) as well as low-energy electron diffraction (LEED) to analyze the initial process of graphitization at

ArF-Excimer-Laser Annealing of 3C-SiC Films

{\rm 6H \mbox-SiC}(000{\bar 1})

Optical emission spectroscopy of ArF‐laser‐irradiated disilane‐acetylene mixtures for 3C‐SiC epitaxial growth

surfaces. After annealing a

Kinetic model for photochemical processes of laser chemical vapor deposition of SiC

{\rm 6H \mbox-SiC}(000{\bar 1})

Laser‐energy dependence of optical emission from radicals and atoms in laser‐induced chemical‐vapor deposition of SiC

surface at 1200°C, there appeared many domains with a single graphite layer in the STM image. Each graphite domain was azimuthally disordered to each other. Many large and small domains with various periodicities were observed in the STM image taken after annealing the surface at temperatures higher than 1300°C. These STM images can be explained as Moire patterns due to different combinations of two graphite layers. In a LEED pattern azimuthally rotated graphite 1 × 1 spots are observed together with the fundamental 6H-SiC(0001)(1 × 1) spots, in consistent with the STM result.

Growth control of carbon nanotubes on silicon carbide surfaces using the laser irradiation effect

Boron-doped 3C-SiC films grown by thermal chemical vapor deposition (CVD) at 950°C using an infrared lamp were annealed using an ArF excimer laser (193 nm). The crystal quality was studied using reflection high-energy electron diffraction (RHEED), and the surface morphology was studied using a scanning electron microscope (SEM). It was demonstrated that both the crystal quality and the surface morphology were improved after irradiation of three laser pulses with an energy density of 1.4–1.6 J/cm2 per pulse.

STM and LEED observation of hydrogen adsorption on the 6H–SiC(0 0 0 1)3×3 surface

A mixture of Si2H6 and C2H2 was used for deposition of SiC by ArF‐excimer‐laser chemical vapor deposition. Optical emission spectroscopy was employed to study the radicals CH, C2, SiH, and Si atoms in the photolyzed gas. The line intensities were measured changing the disilane/acetylene flow ratio. The concentrations of excited CH and C2 were very low without disilane, however they rapidly increased with the addition of disilane. This is attributed to the reactions of silicon‐based radicals with C2H2 or C2H to form CH and C2. A measurement on the deposition rates of the films agreed well with the result.

Influence of surface structure modifications on the growth of carbon-nanotubes on the SiC(0001¯) surfaces

The photochemical processes in a mixture of Si2H6 and C2H2 irradiated with an ArF excimer laser (193 nm) are analyzed numerically using rate equations. The simulation includes 19 processes of photolysis, chemical reactions, and optical emission. The densities of radicals, excited atoms, etc. have been calculated as a function of time. The dependence of SiH* intensity on the laser energy is quadratic up to 10 mJ and shows saturation above 40 mJ. The Si* and C2* intensities are proportional to the 1.3–1.7 power of the laser energy. The C2* emission intensity of Si2H6/C2H2 mixture is higher than that of pure C2H2. These calculated results agree with the results of optical emission spectroscopy experiments. The reactions of Si* with C2H2 and C2H contribute to the increase in C2* emission and in the deposition rate when Si2H6 is added to C2H2.

STM and LEED Analysis of Reconstructions on the 6H-SiC (0001) Surface

Optical emission spectroscopy has been employed to study the photolysis and the subsequent reaction processes of the mixture of Si2H6 and C2H2 irradiated with a 193 nm ArF excimer laser. The emission intensities of SiH*, Si*, and C2* were measured as a function of the laser energy up to 80 mJ (∼0.43 J/cm2). The formation processes of the radicals and atoms were estimated from the dependence of these intensities on the laser energy. The dependence of the SiH* intensity in the low‐energy region up to 10 mJ was quadratic and revealed two‐step processes. The dependence of the intensities of Si* and C2* was the 1.3–1.6 power of the laser energy, which revealed the saturation of the processes. The intensity of C2* increased when Si2H6 was added to C2H2. The origin of this increase is the production of the carbon‐based radicals by the collisions of Si* with C2H2 and C2H.