Temperature and Chemical Sensors Based on FIB-Written Carbon Nanowires

Carbon nanowires written by focused ion beam on diamond surface are novel nanostructures with interesting electronic properties. In this communication, carbon nanowire structures working as temperature and chemical sensors are reported. The sensor structures were made as arrays of carbon nanowires written by a 30 keV ${\rm Ga}^{+}$ focused ion beam on polycrystalline CVD diamond films. The electronic structure of a carbon nanowire array is discussed as multiple unipolar heterodiodes graphite-diamond-graphite (G-D-G). The energy barrier of the G-D-G diodes has been found of a value 0.25 eV. The structures exhibited changes in conductance when measured at different temperatures or when put in proximity of some volatile liquids. This temperature and chemical sensitivity is explained by the activation of the charge carrier flow over the G-D barrier caused by temperature or by the charge of the analyte molecules adsorbed on the surface of the structure. The temperature response of the sensors in the range from 40 to 140$~^{\circ}{\rm C}$ is exponential at a rate of 0.11 ${\rm dB}/^{\circ}{\rm C}$. The chemical sensitivity has been found selective and particularly pronounced for water vapor. The advantages of the novel carbon nanowire sensors are their blindness to visible light, compatibility with carbon nanotechnology, simplicity and reproducibility of fabrication. The all-carbon nature of the sensors implies their applicability in medicine and biology.