Changing semiconductors into flexible membranes

University of Wisconsin-Madison researchers have demonstrated a way to release thin membranes of semiconductors from a substrate and transfer them to new surfaces-an advance that could unite the properties of silicon and many other materials, including diamond, metal and even plastic.

Led by materials science and engineering graduate student Michelle Roberts, the team reports in the April 9 issue of Nature Materials that the freed membranes, just tens of nanometers thick, retain all the properties of silicon in wafer form. Yet, the nanomembranes are flexible, and by varying the thicknesses of the silicon and silicon-germanium layers composing them, scientists can make membrane shapes ranging from flat to curved to tubular.

Most importantly, the technique stretches the nanomembranes in a predictable and easily controlled manner, says materials science and engineering professor Max Lagally, who is Roberts' advisor. In silicon that is stretched, or under tensile strain, current flows faster-a fact engineers already exploit to help control silicon's conductivity and produce speedier electronics. Strain also becomes important whenever different materials are integrated.

The new technique makes tuning the strain of materials simpler, while avoiding the defects that normally result. In addition, Lagally says: "We're no longer held to a rigid rock of material. We now have the ability to transfer the membranes to anything we want. So, there are some really novel things we can do".........