Shojiro Komatsu

Boron nitride nanotubes, webs, and coexisting amorphous phase formed by the plasma jet method

Boron nitride (BN) nanotubes were prepared by a high-temperature plasma jet method. While the BN nanotubes were found in quantity on the surface of a BN sintered disk, amorphous BN webs were found dominant in the water-cooled collector. These structures were studied on the basis of transmission electron microscopy observations. One of them was composed of 21 layers grown coaxially with a regular spacing of 0.34 nm and their tip ends were terminated with parallel bases of the coaxial cylindrical shapes. The diameter of the innermost tube was 0.6 nm and this dimension is in fairly good agreement with the diameters of the smallest BN fullerenes.

Effect of the excitation wavelength on Raman scattering of microcrystalline diamond prepared in a low pressure inductively coupled plasma

Microcrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma. The bonding in the films obtained were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelengths. 514 nm excited Raman spectra exhibit peaks at ∼1355 and ∼1580 cm−1 corresponding to sp2 bonding, and a peak at ∼1150 cm−1 assigned to sp3 bonding. The 1332 cm−1 diamond peak due to zone center optical phonon mode with F2g symmetry clearly appears and the peak at ∼1580 cm−1 is remarkably enhanced with 325 nm excitation. In 244 nm excited Raman scattering, the peak at 1332 cm−1 is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra are discussed in terms of resonant Raman scattering due to the electronic π–π* transition in sp2-bonded carbon with 514 nm (2.4 eV) excitation, and the possible enhancement of the peak due to the sp3-bonded carbon with 325 (3.8 eV) and 244 nm (5.1 eV) excitations.

Influence of atomic hydrogen on the growth reactions of amorphous boron films in a low-pressure B2H6+He+H2 plasma

The activation energy (E) of the growth reactions of boron films in plasma‐assisted chemical vapor deposition from B2H6+He+H2 at a pressure of 300 Pa was measured at a range of substrate temperature from 750 to 1200 K. It was found that the E decreases continuously from 1.83 to 0.54 kcal/mol and then increases up to 4.97 kcal/mol with the increase of partial pressure of atomic hydrogen ([H]). The continuous change of E is supposed to be due to the transition of the dominant rate determining growth reaction, which is accompanied with the change of the composition of adsorbed layer on a film surface. The variation of E as a function of [H] can be explained with a kinetic model proposed here, in which the E of the growth reaction through BH3 is assigned to 1.83 kcal/mol, that through BH2 to 0.54 kcal/mol, and E of migration of BH2 on the film surface covered with hydrogen is related to be 4.97 kcal/mol.

Growth steps and etch pits appearing on {100} planes of diamonds prepared by combustion-flame deposition method

Abstract The growth steps and etch pits were observed on {100} planes of diamonds prepared by C2H2-O2 combustion-flame deposition method. The direction of the growth steps and the edges of the etch pits were both parallel to 〈110〉. They are in good agreement with the (2X1) surface reconstruction hypothesis, which suggests that the surface dangling bonds under these growing conditions are not terminated with hydrogen.

Transition from thermal‐ to electron‐impact decomposition of diborane in plasma‐enhanced chemical vapor deposition of boron films from B2H6+He

The apparent reaction orders for the growth of boron films in plasma‐enhanced chemical vapor deposition from B2 H6 + He were measured as a function of the plasma power, which ranged from 0.4 to 1.6 kW. The conditions were as follows: substrate temperature, 890 °C; pressure, 200 Pa; and total flowrate of gases, 200 sccm. It was found that the reaction order (n) makes a transition from 1/2 to 1 at 900 W with an increase of the plasma power, and which accompanied a corresponding morphological transition. On the basis of a simple kinetic model, the observed reaction‐order transition is related with a transition from thermal‐ to electron‐impact decomposition of diborane occurring at 900 W: the n of 1/2 observed at the power range below 900 W is attributed to a pyrolysis‐dominant growth mechanism in which the association of two BH3 into B2 H6 cannot be neglected, whereas the n of 1 observed at the power range above 900 W is related to a growth mechanism in which the electron‐impact dissociation of diborane is d...

Sp2 bonding distributions in nanocrystalline diamond particles by electron energy loss spectroscopy

Nanocrystalline diamond particles with 200–500 nm in diameter have been prepared in a 13.56 MHz low pressure inductively coupled CH4/CO/H2 plasma. The chemical bonding map was investigated by electron energy loss spectroscopy (EELS). The EEL spectrum shows a peak at 290 eV due to σ* states and the energy loss near-edge structure is similar to that of diamond. A slight peak appears at ∼285 eV corresponding to π* states. The mapping of sp2 states by π* peak reveals that sp2-bonded carbons are identified around the 20–50 nm subgrains of nanocrystalline diamond particles at approximately 1 nm resolution.

Surface and step reconstructions on {100} and {111} planes of diamonds prepared by combustion‐flame deposition

The growth steps were observed on both {100} and {111} planes of diamonds prepared by a combustion‐flame deposition method using C2H2‐O2. The etch pits on {100} planes of diamonds were also observed with a scanning electron microscope. The orientations of both growth steps and etch pits on {100} planes were parallel to 〈110〉, whereas the step directions on {111} planes were [112]‐oriented and the lateral growth rate was the slowest in the [112] direction. The former is described with the hypothesis of so‐called (2×1) surface reconstruction, and the latter is successfully explained by a step reconstruction model. The occurrence of the surface reconstruction would indicate that not only atomic hydrogen but also OH radicals and atomic oxygen, which adequately exist in the diamond growing region in a flame, prevent the surface from being passivated or adsorbed by impinging atoms and/or radicals under the growing conditions.

High‐pressure phases of boron nitride grown by laser‐assisted plasma chemical vapor deposition from BCl3+NH3+H2+Ar

By using a newly designed collimated plasma beam reactor, plasma‐enhanced chemical vapor deposition from BCl3+NH3+H2+Ar with the surface irradiated by a 193‐nm excimer laser at a pressure of 2.8 Torr and substrate temperatures of 500–900 °C yielded BN films with the following texture as revealed by transmission electron diffractometry (TED), transmission electron microscopy, scanning electron microscopy, and Fourier‐transformed infrared spectroscopy: (1) a thin‐film part which consists of 10‐nm‐sized crystallites with a sp2‐bonded structure grown on the substrate, namely, a sp2 100 A layer; (2) polycrystalline parts with cBN or wBN structure, depending on the condition, embedded in a sp2 100 A layer; (3) crystallites, though found infrequently, grown to be much larger than the sp2 100 A layer thickness. The TED pattern of the polycrystalline wBN was particularly in agreement with the standard data.

First-Principles Study of BN, SiC, and AlN Polytypes

We calculated the electronic and lattice properties of BN, SiC, and AlN polytypes. The calculated polytypes are 2H, 3C (= 3H), 4H, 5H, and 6H. These polytypes are s p 3 -bonded compounds. The 6H polytype has two crystal structures as ABCACB and ABCBCB stacking sequences. The lattice properties were optimized automatically by the first-principles molecular dynamics (FPMD) method. Most calculated electronic band structures of these polytypes are non-metallic and their band gaps are indirect. The most stable BN, SiC and AlN polytypes are 3C-BN, 4H-SiC, and 2H-AlN, respectively. The calculated total energies of BN polytypes are in the order of 3C < 6H(ABCACB) < 5H < 4H < 6H(ABCBCB) < 2H. The calculated total energies of SiC polytypes are in the order of 4H < 6H(ABCACB) < 3C < 5H < 6H(ABCBCB) < 2H. The calculated total energies of AlN polytypes are in the order of 2H < 6H(ABCBCB) < 4H < 5H < 6H(ABCACB) < 3C. The total energies and energetical stabilities of the BN and AlN polytypes are related to hexagonality ...

Langmuir probe measurements in a low pressure inductively coupled plasma used for diamond deposition

The characterization of 13.56 MHz low pressure inductively coupled plasmas used for diamond deposition has been performed with a Langmuir probe. The plasma potential (Vp), electron temperature (Te), electron density (Ne), ion density (Ni), and electron energy distribution function (EEDF) were measured in a CH4/H2 plasma with 10–50 mTorr of the gas pressure at 1 kW of the plasma power, and were compared with those of an Ar plasma. We found that the Vp, Ne, and Ni have a similar radial distribution, which has a peak at the center axis and decreases outward in the radial direction, while the Te is almost constant within the radius of 20 mm and slightly decreases toward the chamber wall. It was also found that with increasing pressure the Vp and the Te decrease, whereas the Ne increases, except for a CH4/H2 plasma at 50 mTorr. The transition from a Maxwellian distribution to a Druyveysten distribution was observed at 10 mTorr in the EEDFs of Ar plasmas, while it occurred at 20 mTorr in CH4/H2 plasmas. The EED...