CHEMICAL INTERACTION IN ION-IMPLANTED AMORPHOUS SIO2 AND APPLICATION TO FORMATION AND MODIFICATION OF NANOSIZE COLLOID PARTICLES

Ion-solid chemistry approached from structural defects produced by implantation is summarized for implanted amorphous SiO2 (a-SiO2). The primary factor controlling the chemical interaction of implanted ions with substrate structure is the electronegative nature of implants. Implants with electropositive nature (M) pull oxygens out from the silica network structure to form M-O bonds, leaving Si-Si bonds at concentrations comparable to those of the implant, whereas implants (A) with electronegative nature react chemically with Si atoms to form Si-A bonds, forming O-2 molecules and peroxy radicals. Implants with weak chemical reactivity occur in a neutral state such as diatomic molecules and elementary colloids. The importance of Si-Si bonds as an active intermediate in dual implantation is stressed illustrating the formation of Si-N bonds. The effectiveness of ion implantation as a tool to fabricate nanosize colloids embedded in glass is demonstrated and a criterion of colloid formation in a-SiO2 by implantation established. The morphology and optical absorptions of Cu colloid particles have been found to be modified by subsequent implantation of F ions, and the mechanism is considered on the basis of ion-solid chemistry. Formation of and nature of nanosize colloids of a-phosphorus and a novel approach to synthesize Ge nanocrystals are briefly described.