Formation of micro-/nano-structures on the surface of Cr thin films by electron beam irradiation

Electron beam (EB)-induced deformations of the surface of thin Cr films on soda-lime glass and Si substrates were studied using atomic force microscopy. The thickness of the Cr films was within the range 20 to 500 nm. The thin films were irradiated with a 30 keV EB in the vacuum chamber of a scanning electron microscope. The EB current was within the range 10 pA to 15 nA, and the irradiation time was within the range 30 s to 10 min. The lateral size of the deformations was typically at the micrometre scale, while their vertical size was at the sub-micron and nanometre scales. Depressions of up to 80 nm deep and bulges of up to 700 nm high were observed. Irradiated areas were wet etched using K3[Fe(CN)6] in an alkaline solution. It was observed that EB irradiation can significantly decrease the etching rate and that wet etching can increase the height to width ratio of EB-induced deformations on Cr thin films. Possible physical mechanisms for formation of these deformations are discussed.