The effect of metal concentration and annealing temperature on the growth of ultrasmall metallic nanoparticles inside a silica matrix

Abstract text (incl. figure legends and references)

The nanocomposites (NCs) comprising ultra-small metallic Nanoparticles (NPs) embedded in silica matrix are more stable over time than chemically grown NPs and have shown improved practical efficiency, leading to a wide range of applications in plasmonics, nano-photonics, bio-medical and catalysis due to Localized Surface Plasmon Resonance (LSPR) [1-2]. The stability of these ultra-small NPs (diameter < 10 nm) is essential for high-temperature applications [3].The LSPR frequencies associated with NPs are strongly dependent on particle morphology and metal concentration, thus knowledge about the effect of metal concentration and the growth mechanisms of NPs at different annealing temperatures (ATs) are crucial to controlling the morphology of NPs for application purposes.

We have prepared Ag-SiO2 NC thin films using the atom beam co-sputtering technique at two different metal concentrations [4]. The evolution of silver NPs inside the silica matrix was discussed in Ref [4] utilising UV-Visible spectroscopy and High-Resolution Transmission Electron Microscopy (HRTEM) up to the annealing temperature of 400 °C. This work is now extended to the high annealing temperature of 900 °C. At each AT, HRTEM pictures, diffraction patterns, and STEM images are acquired to closely monitor the growth process of Ag NPs. A similar temperature-dependent growth investigation is also performed on Au and Au-Ag alloy NPs embedded in silica surrounds.

For Ag-SiO₂ NC, UV-Visible absorption spectra show a red shifting in the LSPR peak position, indicating the increase in the size of NPs with ATs. A quantum model simulation is combined with absorption results to estimate the size of the NPs at different ATs, suggesting the size of NPs is increasing. The morphological changes in NPs with ATs are monitored by HRTEM. We observed that the majority of the NPs are spherical in shape and remain in quantum size or ultra-small size regime (diameter < 10 nm). The diameter of the NPs varies from ~5 nm to 6.5 nm when the temperature rises from RT to 800 °C. However, exponential growth is observed at 900 °C. We observed that these ultra-small NPs have shown excellent stability up to the temperature of 800 °C, hence suitable for high-temperature applications. Similar primary results are observed for Au and Au-Ag alloy NCs, however, their detailed analysis is still ongoing. Based on the results, a three-stage mechanism is proposed to understand the process of nucleation and growth of the silica-embedded Ag NPs.

References:

[1] Campos, A., Troc, N., Cottancin, E., Pellarin, M., Weissker, H. C., Lermé, J.,& Hillenkamp, M. Nature Physics 2019, 15, 275-280.

[2] Amendola, V., Pilot, R., Frasconi, M., Marago, OM. Iati, MA. Jour. of Phy.: Cond. Mat. 2017, 29, 203002.

[3] Goodman, E.D., Carlson, E.Z., Dietze, E.M., Tahsini, N., Johnson, A., Aitbekova, A., Taylor, T.N., Plessow, P.N. and Cargnello, M., Nanoscale 13(2), 930-938 (2021)

[4] Jatav, Hemant, Ambuj Mishra, and D. Kabiraj. Materials Today: Proceedings 57 (2022): 234-238.