Richard Coull

Spray Deposition of Highly Transparent, Low‐Resistance Networks of Silver Nanowires over Large Areas

A method to produce scalable, low-resistance, high-transparency, percolating networks of silver nanowires by spray coating is presented. By optimizing the spraying parameters, networks with a sheet resistance of R(s) ≈ 50 Ω □(-1) at a transparency of T = 90% can be produced. The critical processing parameter is shown to be the spraying pressure. Optimizing the pressure reduces the droplet size resulting in more uniform networks. High uniformity leads to a low percolation exponent, which is essential for low-resistance, high-transparency films.

Very thin transparent, conductive carbon nanotube films on flexible substrates

We investigate the morphological, electrical, and optical properties of carbon nanotube thin films, focusing on films with transmittance, T>90%. For films with T≈90% we measure sheet resistance of Rs 90%. Thus, while reducing t can give T>99%, the corresponding Rs increases to >40 kΩ/◻. Acid treatment improves the conductivity by doping, giving properties such as T≈98% for Rs≈10 kΩ/◻.

Spray deposition of Silver Nanowire transparent conductive networks

We investigate Silver Nanowire (AgNW) networks, deposited by spray coating, on a flexible plastic substrate, for application as transparent electrodes for Indium Tin Oxide (ITO) replacement. We demonstrate that the network performance is controlled by the size distribution of the droplets impinging the substrate. Droplet size distribution can be controlled by tuning the spray pressure. Under the most favorable conditions, we achieve networks with typical transmittance T~90% and sheet resistance Rs~50Ω/□, and Rs~1kΩ/□ at T~94%.

Carbon Nanotube network based sensors

We demonstrate three types of sensors based on spray-deposited Carbon Nanotube (CNT) networks on flexible substrates: humidity sensors, dew-point sensors and time-temperature indicators. The presence of Sodium Dodecylsulphate (SDS) significantly increases the sensitivity of the film resistance of CNT networks to changes of relative humidity. We observe up to a 3% change in film resistance in the 30-75% range of relative humidity, with a non-linear relationship. When these SDS-impregnated CNT films are cooled to the dew-point of air, with the temperature of the film monitored, the associated increase in sheet resistance can be used to establish the dew-point temperature. We use acid-doped CNT networks as time-temperature indicators, exploiting the de-doping of the CNT networks at higher temperature. We observe an increase in film resistance of such networks at temperatures higher than 50°C. The rate of the resistance increase follows the Arrhenius law. The extent of the resistance increase ranges from ~30%at 50°C to >;300% at 100°C.