A novel structure was found in thin crystals. Uniform-intensity electron irradiation under ultra-high vacuum (10-7Pa) introduced an array of holes which were 2 to 3nm in diameter and were several nm deep at the electron exit surfaces. The holes were distributed an average of 6nm apart. The irradiation temperature had to be below 300C, and hole formation occurred regardless of the surface: {111} or {110}. It was suggested that the phenomenon was due to a spinodal instability which involved surface vacancies that accumulated during electron irradiation.

S.Takeda, K.Koto, S.Iijima, T.Ichihashi: Physical Review Letters, 1997, 79[16], 2994-7