Nano-cluster engineering: A combined ion implantation and ionizing radiation

During room temperature implantation, after reaching the threshold implantation dose, some of the implanted species will tend to spontaneously form nanoclusters. Similarly, there is a threshold implantation dose of the implanted species in a layer of the host material such that during high temperature annealing the nanoclusters nucleate before the implanted material dissolves in the host material. We present the results of our investigation of producing nanoclusters of Au, Ag and Cu ions in silica at fluences of two orders of magnitude less than what is traditionally used. This is accomplished by first implanting these metal ions into silica, then subsequently bombarding the silica with MeV Si ions (post implantation bombardment). The size of the nanoclusters, ranging from 1 to 10 nanometers, are controlled by the implantation dose and by the total electronic energy deposited by each post implantation bombarding ion in the implanted layer. With the use of an indirect measurement method, such as optical absorption spectrophotometry (non-destructive), and a direct method, such as transmission electron microscopy (destructive), we will show how, and at what concentrations, metallic ions nucleate to form nanoclusters by irradiation assisted nucleation at a dose below that needed for spontaneous nanocluster formation.