The Dimensional Effect in the Adsorption Properties of Ultrasmall Gold Particles

In the framework of the theory of tunneling resonance electron-vibrational spectroscopy, taking into account the interelectron (Coulomb) interaction, which is essential for ultrasmall metal nanoparticles (≤5 nm), a model is constructed that quantitatively explains the results of published spectroscopic experiments carried out using scanning tunneling microscopy, in which for nanoparticles of gold (Au NPs) deposited on pyrolytic graphite, previously there were observed equidistant series of negative differential resistances with periods of 0.1–0.5 V. It was found that series with sufficiently large periods (~0.3–0.5 V), having growing (by the measure of increasing voltage on the nanocontact) envelopes correlate with the sizes of Au NPs and are formed by the Coulomb blockade mechanism. Series with small periods (~0.1 V) correspond to vibrational transitions of atomic particles adsorbed on the surface of Au NPs. A new size effect was discovered for the first time, consisting in the increased adsorption ability of ultrasmall gold nanoparticles having the same sizes (≈3.2 nm) as particles with increased catalytic activity. The new adsorption effect gives a direct and affirmative answer to the frequently discussed question of the “intrinsic” Au NP superactivity, which is not related to the properties of carriers.