Surface plasmon resonance in surfactant coated copper sulfide nanoparticles: Role of the structure of the capping agent

Hypothesis: The optical properties of as-synthesized CuS nanoparticles are affected by shape, size and morphology and exhibit increased optical absorbance in the infrared range due to localized surface plasmon resonance (LSPR), which is also affected by these parameters. An additional parameter which affects the LSPR-related absorbance is crystallinity of the surfactant coating. Experiments: CuS nanoparticles with varying morphologies were synthesized using a single source, single surfactant/solvent route. Thereafter, the particles were heat treated at temperatures varying from 130. °C to 230. °C with and without protective environment. Prior to and following the treatments, the particles were characterized using various techniques. Additionally, temperature resolved structural study and thermal analysis of the surfactant coating were performed. Findings: We confirm that the previously reported effects of particle dimensions and chemical composition on LSPR apply for the synthesized particles. Moreover, we report an additional, previously unreported effect, connecting the crystal structure of the nanoparticle surfactant coating to LSPR. This in turn allows control over LSPR peak position by varying the degree of crystallinity of the capping surfactant layer. Thermal study of the surfactant coating showed gradual structural transition and high dependence of phase transformation on atmospheric environment during treatment.