2.6 Field Emission Scanning Electron Microscopy (FESEM).
A Zeiss SUPRA™ 40 field emission scanning electron microscope was used for the morphological investigation of the AuNPs-SS. FESEM images were acquired using a high resolution in-lens secondary electron detector at the electron acceleration voltage (extra-high tension, EHT) of 20 kV, working distance of 4 mm and magnification in the range 100–1000k×. The size distribution of AuNPs as well as the thickness of the organic layer covering the AuNPs was estimated by FESEM images. For FESEM and XPS investigation, AuNPs-SS were dispersed in water, deposited by drop-casting onto small pieces of a Si(100) wafer, and analyzed after solvent evaporation at room temperature.