Surface effects on the statistics of the local density of states in metallic nanoparticles: manifestation on the NMR spectra

TL;DR

This paper investigates how surface effects influence the local density of states in metallic nanoparticles and how these effects manifest in NMR spectra, highlighting the role of surface states in spectral broadening.

Contribution

It introduces a simple Tight Binding model to analyze surface and bulk state contributions to the density of states and explains experimental NMR spectral deviations.

Findings

Surface states cause additional broadening of NMR spectra.

The model explains deviations in Knight shift scaling with temperature and particle size.

Surface effects are significant in small metallic nanoparticles.

Abstract

In metallic nanoparticles, shifts in the ionization energy of surface atoms with respect to bulk atoms can lead to surface bands. Within a simple Tight Binding model we find that the projection of the electronic density of states on these sites presents two overlapping structures. One of them is characterized by the level spacing coming from bulk states and the other arises from the surface states. In very small particles, this contributes to an over-broadening of the NMR absorption spectra, determined by the Knight shift distribution of magnetic nuclei. We compare our calculated Knight shifts with experiments on aluminum nanoparticles, and show that the deviation of the scaling law as a function of temperature and particle size can be explained in terms of surface states.