Field ion microscopy of silicon

The 〈111〉 oriented silicon whiskers were investigated using field ion microscopy (FIM) and atom-probe FIM. We studied a strong effect of light illumination on the field ion image. By illuminating the emitter surface with infrared light, the image quality is improved markedly. We show that this observation is likely to result from the increase of the surface electric field provided by the sharp resistivity drop at the surface oxide layer through photoconductivity effect. Another interesting finding is the anomalous field evaporation of a silicon tip in vacuum. Surface Si atoms evaporate randomly forming clusters of Si atoms instead of evaporating one by one from the surface kink sites. We conclude that this is due to the unique bonding geometry of the tetrahedral crystal structure and due to the field penetration in the near-surface bulk.