The effect of size and shape of gold nanoparticles on thin film properties

Abstract

This work describes the properties of gold nanoparticles (AuNPs) thin film on silicon (Si) substrates. The AuNPs can be divided into two major shapes: gold nanospheres (AuNSs) and gold nanorods (AuNRs). Two sizes of AuNSs (15 nm and 30 nm) and three aspect ratios of AuNRs (3.12, 3.39 and 3.60) were synthesised using the seeding-growth method. The AuNPs produced were deposited on Si substrates by using a spin-coating method followed by heat treatment at 200 °C. The number of AuNPs coatings varied as one, three and five coating depositions, respectively. From the field emission scanning electron microscopy, the AuNPs were uniformly distributed on the Si substrate surface. The AuNPs distribution increased with increasing number of AuNPs coating. Various deposited AuNPs with different shapes and sizes were analysed using current–voltage (I–V) measurement in light–dark conditions. The results showed that the resistance of samples became lower under light condition as the number of AuNPs coatings increased on the Si substrate due to the large amount of AuNPs particles, which had better properties in absorbing and scattering the light intensity. Among these samples, five-coating depositions of 15 nm AuNSs and 3.12 aspect ratio of AuNRs thin films gave the best sensitivity in light–dark condition. The higher sensitivity implied the better sensing and recovery properties since it can amplify a small signal from the same light source power/intensity.