*2.4. Characterization*

The phase structures of the PVDF filler and Au-TNR/PVDF nanocomposites were characterized by X-ray diffractometry (XRD, PANalytical, EMPYREAN). The surface morphologies of Au, TNRs, and the Au-TNR nanoparticles were revealed using transmission electron microscopy (TEM, FEI Tecnai G2 20). The chemical composition of each element in the Au-TNR hybrid nanoparticles was analyzed by X-ray photoelectron spectroscopy (XPS, PHI5000 VersaProbe II, ULVAC-PHI, Japan) at the SUT-NANOTEC-SLRI Joint Research Facility, Synchrotron Light Research Institute (SLRI), Thailand. The fracture microstructures, distributions, and percentages of each element in the Au-TNR/PVDF nanocomposites were investigated by focused ion beam–field emission scanning electron microscopy (FIB– FESEM, FEI Helios Nanolab G3 CX). The samples were fractured using liquid N2 and their surfaces were sputtered with Au before SEM characterization. The crystalline phases of the nanocomposites were determined using Fourier-transform infrared spectroscopy (FTIR, Bruker, TENSOR27) in the 700–1800 cm−<sup>1</sup> wavelength range. The dielectric properties of the samples were analyzed using an impedance analyzer (KEYSIGHT E4990A) in the 102–106 Hz and −60–150 ◦C frequency and temperature ranges, respectively, with an oscillation voltage of 0.5 V. Before any dielectric measurement, both sides of each circular sample were coated with Ag to form electrodes.
