Treatment of citrate-capped Au colloids with NaCl, NaBr and Na2SO4:: a TEM, EAS and EPR study of the accompanying changes

In the present study, effects of the treatment of citrate-reduced Au sols with NaCl, NaBr and Na2SO4 are described. The particles are characterized by transmission electron microscopy (TEM) and spectroscopic methods, suggesting an exchange of the citrate capping by the anions of the Na salts. Under electron beam exposure the capping of the NaCl- and NaBr-treated particles disappears. The specific electronic properties of the Na salt-treated particles are studied by electron absorption spectroscopy (EAS) and electron paramagnetic resonance (EPR). A discussion of the results in comparison with the spectroscopic responses from the original particles is given. A correlation between the data of EAS and EPR is found. The respective electron-withdrawing effect of the capping anions towards the Au core seems to be of considerable significance regarding the orbital situation around the Fermi level.