Lucas Augusto Moisés

We present a study of an anomalous electrical behavior observed in SnO2 memristor devices based on nanowire networks previously studied by our group. This behavior shows strongly depend on the surface–environment interaction of the nanowires. To enhance/evidence it, we built a device based on a single microwire with higher interaction to ambient air. This device proved to be a memristor in cyclic voltammetry. Based on the literature and voltammetry data, we propose a model to describe that behavior based on the formation/rupture of surface conductive paths formed by water molecules adsorbed in oxygen vacancies and the changes caused by these dynamics in the device's equivalent circuit. We also enhance the behavior in nanowire networks, producing devices with a higher exposure level of the nanowires to the environment. Additionally, these network devices showed potential for application in resistive memories, with an ON/OFF ratio of 22.2 and retention of 1400 s.

Transparent Conductive Oxides (TCOs) have been widely used as sensors for various hazardous gases. Among the most studied TCOs is SnO₂, due to tin being an abundant material in nature, and therefore being accessible for moldable-like nanobelts. Sensors based on SnO₂ nanobelts are generally quantified according to the interaction of the atmosphere with its surface, changing its conductance. The present study reports on the fabrication of a nanobelt-based SnO₂ gas sensor, in which electrical contacts to nanobelts are self-assembled, and thus the sensors do not need any expensive and complicated fabrication processes. The nanobelts were grown using the vapor–solid–liquid (VLS) growth mechanism with gold as the catalytic site. The electrical contacts were defined using testing probes, thus the device is considered ready after the growth process. The sensorial characteristics of the devices were tested for the detection of CO and CO₂ gases at temperatures from 25 to 75 °C, with and without palladium nanoparticle deposition in a wide concentration range of 40–1360 ppm. The results showed an improvement in the relative response, response time, and recovery, both with increasing temperature and with surface decoration using Pd nanoparticles. These features make this class of sensors important candidates for CO and CO₂ detection for human health.