The damage from ion irradiation is usually an undesirable phenomenon unless one is pre-amorphizing a material, such as Si, prior to doping.  However, recent experiments on electron and ion irradiation of various nanostructures demonstrated the ability to tailor the structure and properties of nanosystems with high precision.

A sponge-like structure can be formed within the amorphous phase of Ge during ion implantation with heavy ions at room temperature [1]. We report here the formation and self-organization of nanoscale structures during ion beam implantation of 300 keV Ge in bulk Ge and thin Ge films. A random honeycomb structure consisting of voids (pores 5-50 nm wide) surrounded by amorphous Ge has been observed and studied in details by combining several morphological and structural analyses (SEM, AFM, TEM, RBS).

Electrical characterization, scanning tunnelling microscopy and surface photovoltage spectroscopy have been performed to investigate the charge carrier transport in the honeycomb material. P-type conductivity related to surface states has been observed. Moreover, the honeycomb Ge is stable upon annealing treatments at 600°C in N2 and O2 gas flow. The porous structure provides an enormous surface-area-to-weight ratio, so it can be a promising active nano-structured layer for applications such as low cost chemical and biochemical-sensing devices or electrodes in Li batteries.

[1] I. H. Wilson, J. Appl. Phys., 53, 1698 (1982).