presented in VUV-12, San Francisco, Aug 1998.

Desorption of the Excimer from the Surface of Solid Neon Initiated by Excitons

Takashi Adachi1, Akira Hayama1, Takato Hirayama1,
Ichiro Arakawa1, Koichiro Mitsuke2 and Makoto Sakurai2
1Department of Physics, Gakushuin University, Toshima, Tokyo 171-8588,Japan
2Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444-8585, Japan

Desorption of various kinds of particles can occur when the surface of rare gas solids is electronically excited. This phenomena, which is called desorption induced by electronic transitions (DIET) has been extensively studied in these 10 years. Though desorption of an excited dimer (excimer) from solid Ne, Ar, and Kr, it has theoretically been predicted but has not experimentally been confirmed only for Ar[1]. In our previous work, we reported the emission which seems to be originated from the Ne excimer (Ne2*) after desorption from the surface[2]. In the present study, we have measured the spatial distribution of the emission from the excited particles desorbed from the surface of the Ne solid and confirmed the desorption of Ne2*.

Electron and photon stimulated desorption (ESD and PSD) experiments have been carried out at Gakushuin University and at beam line BL5B at UVSOR in Institute for Molecular Science, Okazaki, respectively. Both the experimental apparatus were installed in ultrahigh-vacuum chambers with a base pressure of 7x10-9 Pa. Ne gas was deposited on the surface of Cu(111) or Pt(111) attached to a liquid helium cryostat at the temperature of 6K. The thickness of a Ne film was typically a few hundreds atomic layers. A pinhole-camera equipped with a micro channel plate (MCP) and a two dimensional position sensitive detector was used to obtain the image of spatial distribution of VUV emission from the desorbed Ne2* in vacuum.

In the ESD experiments, we found the luminescence whose radiative lifetime was of the order of 10-5 sec. This value is in good agreement with the lifetime of 6.62microsec reported for Ne2*(3Su) [3]. Deexcitation of excited atoms may be another possible origin of luminescence. It is, however, known that the lifetime of excited atoms are of the order of 10-9 sec for optically allowed transitions and of 1 sec for forbidden ones. Therefore, we attributed the observed emission to the deexcitaion of desorbed excimers. In the PSD experiments using monochromatic VUV light, we measured the dependence of the desorption yield of excimers on incident wavelength, which is shown in figure 1. Position of each peak corresponds to the excitaion creation energies of the bulk and surface excitons. These results show that the desorption of the excimer is apparently initiated by exciton creation.


Figure 1. Dependence of excimer desorption yield on the incident wavelength. Position of each peak corresponds to the exciton creation energies of the surface (S1. S') and the bulk (B1, B2) excitons.

1. C.T.Reimann et al., Phys. Rev. B45, 43 (1992).
2. E.V.Savchenko et al., Surf. Sci, 390, 261 (1997).
3. T.Oka et al., J. Chem. Phys. 61, 4740 (1974).