Preparation and characterization of B-C-N hybrid thin films

Uddin, M. N.*; Shimoyama, Iwao; Sekiguchi, Tetsuhiro; Nath, K. G.*; Baba, Yuji; Nagano, Masamitsu*

JAEA-Research 2006-034, 72 Pages, 2006/06

JAEA-Research-2006-034.pdf:4.05MB

no abstracts in English

Substitution effect on orientation of organosilicon compounds (CH)SiX (X = F, Cl, Br, I, NCO) as studied using NEXAFS spectroscopy

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.*; Uddin, M. N.*

Journal of Physics; Condensed Matter, 17(36), p.5453 - 5466, 2005/09

https://doi.org/10.1088/0953-8984/17/36/002

The orientation nature of multilayer organosilicon compounds has been investigated by measuring the dependence of the Si K-shell near-edge X-ray absorption fine structures (NEXAFS) on the polarization angle. Two approaches helped to elucidate the orientation mechanism: the substitution effect and the deposition-rate dependence. The orientation angles of Si-X bond axes were obtained for trimethylsilyl halides, (CH)SiX (X =F Cl Br I NCO, condensed on Cu(111) at a low (82 K) temperature: the angles are 60, 73, 61, 55, and 55 degrees with respect to the surface normal, for X =F, Cl, Br, I, and NCO, respectively. Chloride (X =Cl) produces the most parallel tilt angle. The specific orientation nature of chloride is attributed to its strong dipole moment as well as the regular tetrahedron shape of the molecule. The molecular volumes calculated verify this view. Furthermore, deposition rates are found to greatly influence the growth manner: namely, high deposition rates led to a slightly perpendicular orientation of Si-X bond axis.

B-C-N hybrid synthesis by high-temperature ion implantation

Uddin, M. N.; Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Nath, K. G.; Nagano, Masamitsu*

Applied Surface Science, 241(1-2), p.246 - 249, 2005/01

https://doi.org/10.1016/j.apsusc.2004.09.040

Recently, much attention has been given on the synthesis and characterization of graphite-like B-C-N hybrid. Since graphite-like B-C-N hybrid may have semiconducting property, this material is interesting for applications to electronic and luminescent devices. In order to synthesize this material, borazine ion plasma was implanted in graphite at room temperature (RT) and 600 C. An ultrahigh vacuum (UHV) chamber with base pressure 10 Pa was used for the experiment. The X-ray photoelectron spectroscopy (XPS) study suggested that B atoms in the deposited films are in a wide variety of atomic environment such as BC3, BN3 and B-C-N hybrid. The ratios of these coordinations strongly depend on the temperature during the ion implantation. It was found that the B-C-N hybrid is predominantly synthesized by the implantation at 600 C where the surface [B]/([B]+[C]+[N]) ratio ranges from 0.1 to 0.35. The results imply that it is possible to control the composition of B-C-N hybrid by changing the fluence of the ion plasma and the temperature of graphite during ion implantation.

Detection of desorbed ions from the top surface using angle-dependent detector

Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Hirao, Norie*; Nath, K. G.*; Uddin, M. N.*

no journal, , 

We have constructed a novel rotatable time-of-flight (TOF) mass detector for desorbed fragment-ions produced by irradiation of synchrotron radiation (SR). This makes the best use of advantages in synchrotron, including variable X-ray energy, linear polarization, and pulsed capability. The detector allows us to measure excitation-energy dependences of desorbing ion yields from solid surfaces in a variety of incident angles of X-ray beams. We propose that this angle-dependent technique provides insights into orientation of chemical bonds lying at the top surface. The present paper reports our recent findings that the mass-patterns and yields of desorbed ions drastically depend on the incident angles less than 10 degrees. The results suggest that direct desorption mechanism prevails in extremely small angles and indirect desorption mechanism induced through collision excitation by secondary electrons is suppressed.

Coordination and configuration analysis of local structures of B-C-N hybrid thin films

Shimoyama, Iwao; Uddin, M. N.*; Baba, Yuji; Sekiguchi, Tetsuhiro; Nagano, Masamitsu*

no journal, , 

Graphite-like B-C-N hybrids have been expected to control a wide variety of electronic properties from metal to insulator. However, since most B-C-N hybrids have complex structure including various unknown chemical bonding states, the local structures have not been clarified yet. In order to clarify the chemical bonding states of this material, we measured near-edge X-ray absorption fine structure (NEXAFS) of B-C-N hybrid thin films. B-C-N hybrid thin films were synthesized by ion beam deposition of borazine on a graphite substrate, and the composition was controlled by ion fluence. Some * peaks were observed in B and N K-edge NEXAFS spectra, and relative intensities of the peaks depended on ion fluence and polarization. Electronic structures of some model clusters are calculated by a molecular orbital theory, and compared with NEXAFS spectra. From the experimental and theoretical results, we discuss some models of local structures.

Formation of fullerene-like structures by B and N doping in graphite

Shimoyama, Iwao; Uddin, M. N.*; Baba, Yuji; Sekiguchi, Tetsuhiro; Nagano, Masamitsu*

no journal, , 

B-C-N hybrid has medium composition between semi-metallic graphite and insulating hexagonal boron nitride, and has been theoretically predicted that semiconducting property is obtained depending on composition and atomic arrangement. Since the structure of the products has not been clarified well, we used near edge X-ray absorption fine structure (NEXAFS) to analyze local structure of B-C-N hybrid. Samples were prepared by ion beam deposition method with borazine gas as a precursor. B and N K-edges NEXAFS spectra were measured for some samples which had different compositions, and showed plural peaks which have different polarization dependences. This result suggests that distorted plane structures were formed at B and N sites. We calculated partial density of states (PDOS) for some model clusters by an ab initio molecular orbital calculation, and proposed that distorted plane structures consist of pentagons and hexagons which is termed as fullerene-like structure.

Formation of fullerene-like structure by low-energy ion beam doping

Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Uddin, M. N.*; Nagano, Masamitsu*

no journal, , 

Carbon alloys formed by B and N dopings is expected for some applications, e.g., catalyst and semiconductor. However, the relationship between doping and material properties is not clear enough because of complicated structures around dopant atoms due to various chemical conditions between ternary system of B, C, and N. We measured polarization dependence of near-edge X-ray absorption fine structure (NEXAFS) to investigate configuration of local structure around dopant atoms in BN co-doped graphite. B and N K-edge NEXAFS spectra showed graphite-like polarization dependence and some * peaks in the spectra showed different magnitude of polarization dependence. This indicates existence of local structures which have distorted planar configuration. We propose a fullerene-like structure for the distorted planar configuration based on comparison of structure stability calculated by a molecular orbital theory with model clusters.

Local structure change by B and N dopings in graphite

Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Uddin, M. N.*; Nagano, Masamitsu*

no journal, , 

Carbon alloys formed by heteroatom doping is expected for some applications, e.g., catalyst and semiconductor. However, the relationship between doping and material properties is not clear enough because of complicated structures around dopant atoms due to various chemical conditions between dopant and carbon atoms. We measured polarization dependence of near-edge X-ray absorption fine structure (NEXAFS) to investigate configuration of local structure around dopant atoms in BN co-doped graphite. B and N K-edge NEXAFS spectra showed graphite-like polarization dependence and some * peaks in the spectra showed different magnitude of polarization dependence. This indicates existence of local structures which have distorted planar configuration. We propose a fullerene-like structure for the distorted planar configuration based on comparison of structure stability calculated by a molecular orbital theory with model clusters.