EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Few years ago we demonstrated the use of site-selective synthesis of nanowires on top micromembranes as an energy-efficient and low cost methodology for their integration [1]. For this, micromembranes, which contained surface interdigitate microelectrodes and buried heaters, when the latter were biased, promoted the decomposition of the chemical precursor and the growth of the nanowires. In this way, we achieved the growth of Ge and SnO2 nanowires and we showed their efficient use as resistive gas sensors.
Here we will present the latest advances in this methodology to further control the growth and miniaturise the gas sensors. For this, we have developed a site-selective spatially localised growth of nanowires consisting in fabricated narrow gold stripes on top of the micromembranes, obtained through electron beam lithography and lift-off processes. In this way, the area on top of the heated micromembranes in which the growth of the nanowires is achieved can be controlled. The growth of SnO2 nanowires has been successfully achieved on continuous stripes of 100x10 and 100x1 micrometre2 , or containing a micrometre-sized gap.
The fabricated nanowire-containing devices behave as chemoresistors in the presence of some industrially-relevant gases, like CO and NO2. Their relative resistance change in the presence of the gases is almost independent on the size of the continuous stripes, but that a huge improvement of the response, about 200-fold, is observed when the growth in the gapped gold stripe. This improvement can be related to the fact that the current path across the gap occurs through few bridging nanowires in opposition to a dense network in continuous stripes. The results will be discussed based on the observed nanowire morphology and the contribution of the different charge conducting mechanisms.

[1] S. Barth et al., Chem. Comm. 48, 4734 (2000)