Credit: © 2007 ACS

Semiconductor nanowires could have applications in a wide range of technologies including optics, biosensing, data storage and quantum computing (see pages 622 and 626). However, disorder can lead to the formation of quantum dots and other defects that compromise the performance of the nanowires. These defects have now been imaged with a scanning probe microscope by Robert Westervelt and co-workers at Harvard University, Delft University of Technology and Philips Research Laboratories (Nano Lett. 7, 2559–2562; 2007).

Measurements of the conductance of indium arsenide nanowires at liquid-helium temperatures reveal the signature of a Coulomb blockade — a phenomenon that is often observed in quantum dots. Now Westervelt and co-workers have used a scanning probe microscope to image electron flow through the nanowires and investigate the effects of the quantum dots in more detail. The three figures show the conductance as a function of the position of the probe tip. Quantum dots are located at the centre of the rings of high conductance (shown in green and white), which move outwards as the tip voltage is increased from left to right. The ability to image the electronic properties of nanowires in this way should lead to improvements in device performance.