UC Berkeley

The fabrication and structural characterization of ion beam synthesized Ge and Ge-Au nanoclusters embedded in silica is presented. The theory of nanocluster size distribution from ion beam synthesis is discussed and a processing route to narrow the size distribution is investigated. Transmission electron microscopy is used to determine the size distribution of ion beam synthesized Ge nanoclusters embedded in silica. It is demonstrated that implantation at room temperature, liquid nitrogen (LN₂) or ramping temperature, i.e., half dose at LN₂ temperature immediately followed by half dose at increasing temperature until room temperature is reached, results in a narrow size distribution of particles. However, it is determined that post-growth thermal annealing broadens the size distribution regardless of the implantation condition. High resolution transmission electron microscopy is used to evaluate the crystallinity of the nanoclusters before and after thermal annealing.

Ge-Au nanoclusters embedded in silica are fabricated by co-sputtering Au and silica followed by Ge implantation and thermal annealing. Scanning transmission electron microscopy, Raman spectroscopy, and synchrotron X-ray diffraction are used to demonstrate a reversible phase transition in the system. The bi-lobe structure observed after annealing is switched to a homogeneously mixed structure using a 30 ns UV laser pulse. The structure is switched back to bi-lobe by heating at 80 ºC. The bi-lobe/homogeneously mixed switching can be performed at least 10 times. The phases present in the bi-lobe and homogeneously mixed structures are evaluated by synchrotron X-ray diffraction. The melting behavior of the Ge-Au nanoclusters is explored by in-situ transmission electron microscopy.