P11

BL-5

XPS study on the boron-doped amorphous carbon films
Yuji Muraokaa, Kota Matusob, Takanori Wakitaa and Takayoshi Yokoyaa
aResearch Institute for Interdisciplinary Science, Okayama University,
3-1-1 Tsushima-naka, Tsushima, Kita-ku, Okayama 700-8530, Japanb
Graduate School of Natural Science and Technology, Okayama University,
3-1-1 Tsushima-naka, Tsushima, Kita-ku, Okayama 700-8530, Japan
Keywords: XPS, Boron dope, Amorphous carbon, Film

Heavily boron (B)-doped amorphous carbon, which is called as B-doped Q-carbon, shows thesuperconductivity with a superconducting transition temperature of 55K [1,2]. Since B-doped Q carbon is
the first example of amorphous semiconductor showing the superconductivity, much efforts have been
devoted to preparing this material. However, preparation of this material is quite difficult because of its
metastable form achieved by the nano-second pulsed laser annealing to the B-doped amorphous carbon
precursors. So far, B-doped Q-carbon has not yet been reproduced. One of important studies related to thepreparation of B-doped Q-carbon is to characterize the B-doped amorphous carbon precursors. Especially,
the chemical states of B-doped amorphous carbon may affect the formation of the B-doped Q-carbon. In thisstudy, we investigate the chemical states of carbon and boron atoms in the B-doped amorphous carbon
precursors with different nominal boron content by means of an X-ray photoemission spectroscopy.
The B-doped amorphous carbon precursors were fabricated by a pulsed laser deposition method with aKrF excimer laser (  = 248nm). Single crystal Al2O3(0001) substates were used for the film deposition. Thedeposition was performed under the vacuum condition of 3.0 x 10-6 Pa. Nominal boron content in the films
was varied by changing the B/C ration in the target materials. The film thickness of the obtained precursor
films was 200 to 300 nm. X-ray photoemission spectroscopy (XPS) measurements were carried out on thebeamline BL-5, at the Hiroshima Synchrotron Radiation Center in Hiroshima University with nonmonochromatic Mg K X-ray source (h = 1253.6 eV). C 1s and B 1s core-level spectra were measured
under an ultrahigh vacuum of ~10-7 Pa using a VSW hemispherical analyzer. The total energy resolution was
about 1.8 eV. The binding energy of the films was corrected using the peak position of molybdenum spectra.
Before measurements, the films were annealed at 100 °C under ultrahigh vacuum (~10 -6 Pa) for 1 h toclean the film surface.
Figure 1 shows the C 1s core-level spectra of B-doped amorphous carbon films with different B content.
The peak at 285 eV is observed for the non-doped films. This peak position shifts toward lower binding
energy side with increasing boron content. Figure 2 shows the B 1s core-level spectra of B-doped amorphous
carbon films with different B content. The peak structure appears as the nominal boron content is increased,indicating that boron atoms are present in the films. The B/C ratio of the films is estimated from the peakarea ratio of C 1s and B 1s spectra to be 0-0.27. The peak position is located at 189 eV, which originatesfrom B0 states [3]. This indicates that most of boron atoms exist as an elemental state in the films. The reasonfor the shit of the C 1s spectra with increasing B content is probably due to the surface bending effect. It will
be interesting to see how the chemical states of carbon and boron atoms change after pulsed laser annealing.
Our present results provide an important starting point for obtaining the B-doped Q-carbon.

C 1s

B1s

B content

B/C

Intensity (a.u.)

Intensity (a.u.)

large

0.27
0.18

0.04

00
290

288

286

284

282

280

194

192

190

188

186

184

Binding Energy (eV)Binding Energy (eV)FIGURE 1. C 1s core-level spectra ofFIGURE 2. B 1s core-level spectra ofboron-doped amorphous carbon films
with different boron content.

boron-doped amorphous carbon films
with different boron content.

REFERENCES
1. A. Bhaumik, R. Sachan, and J. Narayan, ACS Nano. 11, 5351-5357 (2017).
2. A. Bhaumik, R. Sachan, S. Gupta, and J. Narayan, ACS Nano. 11, 11915-11922 (2017).
3. W. G. Shin, H. J. Jung, H. G. Sung, H. S. Hyun, and Y. Sohn, Ceram. Int. 40, 11511-11517 (2014).