Credit: © 2007 Nature Materials

The integration of semiconducting nanowires with flexible materials could lead to new advances in wearable electronic devices for monitoring hazardous chemicals. With the wet-transfer methods currently used to deliver arrays of nanowires onto plastic substrates, however, it is difficult to retain highly ordered patterns. Now, James Heath and co-workers1 at the California Institute of Technology have developed a dry-transfer method to 'print' arrays of nanowires onto flexible plastic films.

Heath and co-workers first make an array of parallel 18-nm-wide silicon nanowires by etching into a silicon-on-insulator wafer. A silicon-based polymer (PDMS) 'stamp' is then pressed on top of the wafer and peeled off, bringing the nanowires with it. A plastic substrate coated with an epoxy resin is brought into contact with the PDMS stamp and the epoxy layer is hardened on exposure to heat and ultraviolet light. The PDMS stamp is slowly peeled away, leaving the nanowires on the plastic substrate. 'Before and after' comparison images taken with a scanning electron microscope show that the nanowires remain largely intact, with a few broken lines arising from shear forces during peeling.

The transferred wires can be made into field-effect transistors, exhibiting large on–off current ratios and low power consumption. Heath and co-workers also demonstrate a 'nano-electronic nose' — an array of sensor nanowires with individual chemical-detecting functions — to detect organic solvent vapours at low concentrations.