Indium-tin-oxide single-nanowire gas sensor fabricated via laser writing and subsequent etching

We report on the design and nanofabrication of a single nanowire (NW) indium-tin-oxide (ITO) gas sensor and on test results obtained with an oxidizing and a reducing gas. As a novel fabrication approach, direct laser writing and a subsequent etching process on sputtered ITO thin-film layers is applied. For this technique a near-infrared Ti: sapphire laser with sub-15 fs pulses and a repetition rate of 85 MHz is used. NWs for gas sensors are realized in two versions with a thickness of 125 +/- 25 nm; one with 350 nm in width and 90 mu m in length the other with 700 nm in width and 200 mu m in length. The sensors are exposed to nitrogen dioxide (NO2) in synthetic air with concentrations from 1 ppm to 50 ppm showing a significant change in resistance (up to 15.8%), whereas the reaction to 2000 ppm carbon monoxide (CO) turns out to be negligible (0.05%). At ambient temperature, the sensor exhibits integrating dosimeter-like behavior with relaxation times of more than 20 h. By self-heating, the NW can be reset to its initial condition, thus enabling a new dosimeter run at room-temperature. When the sensors are operated in self-heating mode, a conventional behavior is observed, enabling the detection of NO2 concentrations down to about 1 ppm at a stationary temperature below 200 degrees C. (C) 2015 Elsevier B.V. All rights reserved.