The visibility and stability of GaSe nanoflakes of about 50 layers on SiO2/Si wafers

Abstract

GaSe nanoflakes on silicon substrates covered by SiO2 films are prepared by mechanical exfoliation from the bulk Bridgman-grown GaSe crystals using a scotch tape. The thickness of SiO2 films on Si substrates providing the highest optical contrast for observation of GaSe flakes is estimated by taking into account the spectral sensitivity of a commercial CMOS camera and broadband visible light illumination. According to our estimations, the optimal SiO2 thickness is [Formula: see text]126 nm for the visualization of GaSe flakes of 1–3 layers and [Formula: see text]100 nm for the flakes of 40–70 layers. The obtained nanoflakes are investigated by optical and atomic force microscopy and Raman spectroscopy. The observed spectral positions of the Raman peaks are in agreement with the positions of the peaks known for bulk and nanolayered GaSe samples. It is found that the 50 nm thick flakes are stable but are covered by oxide structures with lateral size about 100 nm and height [Formula: see text]5 nm after [Formula: see text]9 months exposure to ambient atmosphere.