1. Introduction
High aspect ratio semiconductor nanostructures have started to have a profound effect on the design and performance of many types of devices, including batteries, solar cells, detectors and thermoelectric systems. For example, it has been demonstrated recently that using silicon (Si) nanowires as the anode in a lithium battery could enhance the battery charge capacity and promote a longer battery life. This is attributed to the large strain accommodation capacity of the nanoscale dimension thus resilience to pulverization upon lithium insertion and extraction, and efficient 1-dimensional carrier transport along the nanowires. For thermoelectric applications, a 100-fold reduction of thermal conductivity has been found in rough Si nanowires leading to an enhanced figure-of-merit ZT of 0.6 at room temperature. Using Si nanowire arrays for solar cell applications has also been demonstrated with promising results, owing to the high anti-reflectivity hence better absorption efficiency.