Understanding the Size Dependence of Indium Tin Oxide Nanocrystals

This report aims to understand the role of reaction time, temperature, and precursor concentration on the size distribution of indium tin oxide (ITO) nanoparticles. These materials are increasingly recognized as promising candidates for near- and mid-infrared plasmonics. Their ability to strongly absorb specific wavelengths offers opportunities to improve photosensing, spectrometry, and photovoltaics. Furthermore, its wide variety of synthetic pathways allows for the formation of many different particle morphologies. Here, we synthesized colloidal ITO nanoparticles by heating a solution of In(acac)₃ and Sn(acac)₂Cl₂ in oleylamine to the point of decomposition of the precursors, leading to the creation of a supersaturated solution. Ten trials were performed and the resulting particles were compared to particles heated at 250°C for five hours. The ten trials were reaction for 3, 4, 6, and 7 hours, heating at 200°C, 225°C, 275°C, and 300°C, and reducing the amount of oleylamine used by 25% and by 50%. The morphology and size distribution of the resulting particles was determined using scanning electron microscopy (SEM) . Infrared spectroscopy provided access to plasmonic response. The results show that reaction time most strongly influences nanoparticle size. At a low enough temperature, the nanoparticles were no longer usable and a temperature high enough to cause a significant increase in size nears the boiling point of oleylamine. Increasing the precursor concentration increased the nanoparticle size, but also led to an increase in particle agglomeration.