12-02 :: February/March 2012

nanotimes News in Brief

59

When a thin layer of gold anneals on top of a silicon wafer coated with native silicon oxide, randomly distributed pools of eutectic alloy quickly form – and then go through a rapid series of strange changes, leaving behind bare silicon-dioxide circles surrounded by debris. Each denuded circle reveals a perfect square at its center. The area shown is about 107 by 155μm. © LBL

The rapid growth and evolution of the strange circles at 600˚ C (1,112° F) is caught in successive frames under an elec- tron microscope (structures at right are already in place as the sequence begins). Underlying a thin layer of gold (mottled gray), a weak spot opens in the silicon dioxide barrier, allowing pure silicon in the substrate to react with the gold. A pool of molten eutectic quickly spreads (dark gray). When it becomes large enough, surface tension ruptures the liquid, pulling the eutectic aside to surround a cleared zone of silicon dioxide, now barren except for a central square of gold and silicon. Time from first to last frame is just 2.8 seconds; the area covered in each image is about 40 by 80μm. © LBL