Exploration of the Interaction of Electromagnetic Fields with Nanoscale Materials.

Abstract

Nanoscale materials usually present strikingly different properties in comparison with their bulk counterparts, such as quantum size effects, surface plasmon resonance (SPR). To explore new properties as well as for novel applications, nanomaterials are being extensively investigated. This project investigates the interactions of electromagnetic fields with nanoscale materials, particularly gold nanoparticles (GNPs), over a wide range of frequency bands, including static field, 261 kHz, 13.56 MHz, 2.45 GHz, millimetre wave, THz, and the visible light. Especially, the efforts have been devoted to the study of heating effect of GNPs in association with potential biomedical applications. To explain the electromagnetic heating of GNPs, dielectric properties of GNP dispersions has been studied from 100 MHz to 20 GHz, as well as in the millimetre wave and THz ranges. The static field induced effects on the size distribution of GNPs has also been examined using ultra-violet spectroscopy and correlated to SPR. It has been revealed that purified GNPs cannot increase the specific absorption rate substantially at whichever frequency points of 261 kHz, 13.56 MHz, or 2.45 GHz. However, a greater temperature rise has been observed in the impurified GNP dispersions compared to deionisedwater, after 10 min RF treatment at 13.56 MHz. The measurements on dielectric properties show that impurified samples have much higher effective conductivity than that of deionised-water, while the conductivity change of purified ones is very small and not detectable within the measurement accuracy. This observation supports that the heating effect of GNP dispersions is mostly contributed by the impurities and disproves that GNPs can increase the specific absorption rate significantly. The magnetic field heating at 261 kHz suggests that GNPs have very weak magnetic properties. It has been found that a static field can change the size distribution of GNPs. Up to 2 THz, it is measured that the dielectric properties of GNP dispersions have no convincing change compared to deionised-water, implying that the electromagnetic heating of GNP below 2 THz may be insignificant. In addition, it is confirmed that GNPs have strong absorption in the visible light range due to SPR.