Photon Factory Activity Report 2014 #32 (2015) B

BL-27A/2013G524

Depth analysis of the surface of Mg2Si crystals with XAS and XPS
Hiroyuki Yamamoto, Takehiro Nojima and Fumitaka Esaka*
Japan Atomic Energy Agency, Ibaraki 319-1195, Japan
1 Introduction
In order to develop silicon-based electronic devices,
metal silicides are widely studied. Information of thesurface chemical states of metal silicides is important toobtain homo-epitaxial films with excellent quality. X-ray
photoelectron spectroscopy (XPS) is commonly used toelucidate surface chemical states of solids. Here, nondestructive depth analysis is possible by changing
excitation X-ray energy [1,2]. However, peakassignments in XPS are often difficult due to insufficientchemical shifts. In this case, the analysis with X-ray
absorption spectroscopy (XAS) would give useful
information on the peak assignments.
In this work, depth analysis of surface chemical statesof Mg2Si crystals is carried by XPS. Depth analysis isalso performed in XAS measurement with total electronyield (T.E.Y.) and partial electron yield (P.E.Y.) modes.
2 Experiment
The Mg2Si crystals were prepared from Mg2Si ingots
grown by a modified vertical Bridgman method [3]. Thecleaved surface of the Mg2Si crystal was measured withXPS and XAS. The measurement was performed at thebeam line 27A. In the XPS measurements, excitationenergies ranging from 2100 to 3300 eV were used. The Si
K-edge XAS spectra were obtained with T.E.Y. andP.E.Y. modes.
3 Results and Discussion
The Si 1s XPS spectra of the cleaved surface of theMg2Si crystal measured with the excitation energies of2100 and 3300 eV show significant change as shown inFig. 1. The peak at 1836.8 eV is dominant in the spectrum
measured with the energy of 3300 eV, which is assignedto Mg2Si structure. In contrast, The peak (1841.4 eV)
attributed to SiO structure is dominant in the spectrum
measured with the energy of 2100 eV. The use of thelower excitation energy enables us to obtain information
on shallower surface. Therefore, the result indicates that
SiO is formed on the surface of the Mg2Si crystal. Here,no peak assigned to SiO2 structure is observed in Fig. 1.
Figure 2 shows the Si K-edge XAS spectra of thecleaved surface of the Mg2Si crystal. In the spectrum
obtained with the P.E.Y. mode, a peak at 1843.7 eV isdominant, compared to the spectrum obtained with T.E.Y.
mode. The peak can be assigned to SiO structure. Since
the electrons with the energy of around 50 eV wereobtained in this measurement, the P.E.Y. spectrum gives
the information on shallower region of the Mg2Si surface.
Therefore, Fig. 2 indicates the formation of SiO on thesurface of the Mg2Si crystal, which is consistent with thatof XPS analysis.

Fig. 1: Si 1s XPS spectra of a Mg2Si crystal measured
with the excitation X-ray energies of 2100 and 3300 eV.

Fig. 2: Si K-edge XAS spectra of a Mg2Si crystal
obtained with P.E.Y. and T.E.Y. modes.
Acknowledgement
This work was supported by the Grant-in-Aid for
Scientific Research (C) (No.25410160), JSPS. The
authors would like to acknowledge Prof. H. Udono andMr. N. Hori for sample preparation of Mg2Si crystals.
References[1] F. Esaka et al., Appl. Surf. Sci. 256, 3155 (2010).
[2] F. Esaka et al., Appl. Surf. Sci. 257, 2950 (2011).
[3] H. Udono et al., J. Phys. Chem. Solids 74, 311 (2013).
* esaka.fumitaka@jaea.go.jp