ETCHING TECHNIQUE FOR TRANSMISSION ELECTRON-MICROSCOPY OBSERVATION OFNANOSTRUCTURE OF VISIBLE LUMINESCENT POROUS SILICON

We present a special configuration for the electrochemical etching of silicon, in which thin samples suitable for direct transmission electr on microscopy observation are produced. This technique allows the obse rvation of images of an irregular matrix of pores and individual colum nlike structures with a approximately 15 angstrom cross-sectional diam eter. These images show that the preferential etching directions are t he projections of the {100} planes on the (111) plane for the etched [ 111]-oriented silicon. The large pore ( > 50 nm diam) axis orientation is independent of the preferential etching direction and is parallel to the etching current direction.