NANOHOLES ON SILICON SURFACE CREATED BY ELECTRON-IRRADIATION UNDER ULTRAHIGH-VACUUM ENVIRONMENT

We have found that a novel structure is formed in a thin silicon cryst al. Uniform-intensity electron irradiation in an ultrahigh vacuum envi ronment (1.0 X 10(-7) Pa) introduces an array of holes 2 to 3 nm in di ameter and several nanometers deep at the electron exit surfaces. The holes are distributed in average 6 nm apart. The irradiation temperatu re is needed to be below 300 degrees C. The formation of the holes occ urs regardless of the surfaces, i.e., {111} and {110}. It is suggested that the phenomenon is attributed to the spinodal instability involvi ng the surface vacancies accumulated by electron irradiation.