Swaminathan Parasuraman

In a DC magnetron sputtering system, the deposition rate is significantly affected by the sputtering power and working pressure, and the precise nature of this dependence varies from machine to machine. An understanding of the effect of sputtering parameters on the deposition rate is required before undertaking further studies. To do so, we have carried out a design of experiments study on the optimization of deposition process parameters using a Taguchi design methodology. Taking an example of silver (Ag) deposited on silicon (100) substrates using the DC magnetron sputtering method, we use a Taguchi L9 design to reduce the experimental design space from 27 to 9 combinations. The attributes of the Ag thin films were quantified with respect to surface roughness (Ra), thickness (t), and sheet resistance (R s). The objectives of this study are 3-fold: establishing the effect of sputtering process parameters, namely the power and working pressure, on the deposition rate for the system under consideration; optimizing the sputtering process parameters within the chosen design space to ensure the formation of smooth conductive films using Taguchi analysis and response surface models; and analyzing the effect of annealing on the thin film characteristics. We found that the deposition rate increases with increasing the sputtering power. The highest deposition rate for the maximum power considered (25 W) was achieved at an intermediate working pressure of 6.1 × 10−3 mbar. The lowest deposition rate was obtained for the minimum power (5 W) and the highest working pressure (8.5 × 10−3 mbar) considered. For the given substrate–material system, we also found that the critical thickness below which the deposited films are non-conductive was 16 nm, which agrees with the existing literature.

We report on the anti-reflection characteristics of silica nanopillars fabricated using bimetallic copper-silver nanoparticles as an etch mask. The particles were formed by dewetting and their size and shape were controlled by the film thickness and annealing conditions. Our results showed that annealing of a copper-silver film results in formation of segregated bimetallic nanoparticles. Using these bimetallic nanoparticles as a mask for reactive ion etching produced dual diameter nanopillars, compared to single diameter nanopillars for monometallic nanoparticles. The height and shape of the nanopillars were controlled by the initial film thickness, annealing temperature, and etching parameters. The fabricated silica nanopillars showed a reduction in reflectance as compared to the bare substrate in the UV–Vis-NIR range, and dual diameter nanopillars were better as compared to single diameter nanopillars. Increasing etch duration resulted in increase in pillar height and a further reduction in reflectance. These silica nanopillar structures can be used as anti-reflection coatings.

We report on the effect of added silver on the solid state dewetting behavior of copper thin films, grown by thermal evaporation. The films were annealed under different conditions, conventional furnace annealing in air and argon and rapid thermal annealing in nitrogen. Our results show that for all annealing conditions, addition of silver to copper films suppresses the dewetting when compared to pure copper films. Fully dewet silver–copper films produce roughly spherical nanoparticles, with the amount of silver controlling the particle areal density and size distribution. This provides an additional parameter for controlled synthesis of nanoparticles by a bottom–up approach.

Metal nanowire-based conducting networks, primarily based on silver nanowires (Ag NWs), show promise for flexible transparent conducting electrodes. The synthesis of high aspect ratio Ag NWs is the key to accomplishing good optoelectronic performance. Among the various synthesis routes available, the one-pot polyol method is widely used. It is based on the reduction of silver nitrate (AgNO3) by a polyol, typically ethylene glycol, in the presence of polyvinylpyrrolidone (PVP) and ferric chloride. The present work provides a systematic study of the role of PVP to AgNO3 weight ratio on the physical dimensions (length, diameter, and aspect ratio) of the Ag NWs and the role of NW concentration and spin coating speed on the optoelectronic properties (transparency and conductivity) of the NW-based network.