Formation and optical properties of nanometer-sized amorphous arsenic clusters embedded in amorphous SiO2 by ion implantation

Nanometer-sized amorphous arsenic colloid particles embedded in SiO2 glasses were prepared by ion implantation of As+ ions to a dose of 2 x 10(17) cm(-2) at an acceleration voltage of 300 kV. X-ray photoelectron spectroscopy of As 3p(3/2) levels revealed that approximately 70% of implanted As exists in a neutral state. The formation of amorphous clusters with diameter of 3-6 nm was observed by transmission electron microscopy, These particles were identified as amorphous (a-) arsenic by resonance Raman scattering measurements. The optical band gap determined from a Tauc plot was 1.7 eV, which is larger by similar to 0.5 eV than that of bulk a-As. A red shift of similar to 0.05 eV in the optical band gap was observed upon band-gap light illumination. This shift was tentatively ascribed to photo-induced polymerization of As-4 molecules, which are partially contained in the clusters. The nonlinear optical susceptibility, chi((3)), measured by degenerate four-wave mixing using a XeCl-pumped dye laser (pulse duration: 20 ns) was 4 x 10(-8) esu. There results were compared with those for P-implanted SiO2 glasses.