ABSTRACT
Silver nanowire (AgNW) networks have attracted particular attention as transparent conductive films (TCF) due to their high conductivity, flexibility, transparency, and large scale processing compatible synthesis. As-prepared AgNW percolating networks typically suffer from high contact resistance, requiring additional post-synthetic processing. In this report, large area irradiation with 200 ns short intense pulsed ion beam (IPIB) was used to anneal and enhance the conductivity of AgNW network, deposited on temperature-sensitive polyethylene terephthalate (PET) substrate. A TCF sheet resistance shows irradiation dose dependence, decreasing by four orders of magnitude and reaching a value of 70 Ω/sq without damaging the polymer substrate, which retained a transparency of 94%. The IPIB irradiation fused AgNW network into the PET substrate, resulting in a great adhesion enhancement. Heat transfer simulations show that the heat originates at the near-surface layer of the TCF and lasts an ultra-short period of time. Obtained experimental and simulation results indicate that the irradiation with IPIBs opens new perspectives in the low-temperature annealing of nanomaterials deposited on temperature-sensitive substrates.
ABSTRACT
In this report, an improvement of the electrical performance and stability of a silver nanowire (AgNW) transparent conductive coating (TCC) is presented. The TCC stability against oxidation is achieved by coating the AgNWs with a polyvinyl alcohol (PVA) layer. As a result, a UV/ozone treatment has not affected the morphology of the AgNWs network and the PVA protection layer, unlike non-passivated TCC, which showed severe degradation. The irradiation with an intense pulsed ion beam (IPIB) of 200 ns duration and a current density of 30 A/cm2 is used to increase the conductivity of the AgNWs network without degradation of the temperature-resistant PVA coating and decrease in the TCC transparency. Simulations have shown that, although the sample temperature reaches high values, the ultra-high heating and cooling rates, together with local annealing, enable the delicate thermal processing. The developed coatings and irradiation strategies are used to prepare and enhance the performance of AgNW-based transparent heaters. A single irradiation pulse increases the operating temperature of the transparent heater from 92 to 160 °C at a technologically relevant voltage of 12 V. The proposed technique shows a great promise in super-fast, low-temperature annealing of devices with temperature-sensitive components.
ABSTRACT
As one of the highest mobility semiconductor materials, carbon nanotubes (CNTs) have been extensively studied for use in field effect transistors (FETs). To fabricate surround-gate FETs- which offer the best switching performance-deposition of conformal, weakly-interacting dielectric layers is necessary. This is challenging due to the chemically inert surface of CNTs and a lack of nucleation sites-especially for defect-free CNTs. As a result, a technique that enables integration of uniform high-k dielectrics, while preserving the CNT's exceptional properties is required. In this work, we show a method that enables conformal atomic layer deposition (ALD) of high-k dielectrics on defect-free CNTs. By depositing a thin Ti metal film, followed by oxidation to TiO2 under ambient conditions, a nucleation layer is formed for subsequent ALD deposition of Al2O3. The technique is easy to implement and is VLSI-compatible. We show that the ALD coatings are uniform, continuous and conformal, and Raman spectroscopy reveals that the technique does not induce defects in the CNT. The resulting bilayer TiO2/Al2O3 thin-film shows an improved dielectric constant of 21.7 and an equivalent oxide thickness of 2.7 nm. The electrical properties of back-gated and top-gated devices fabricated using this method are presented.
