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

摘要

In metallic nanoparticles, shifts in the ionization energy of surface atomswith respect to bulk atoms can lead to surface bands. Within a simple TightBinding model we find that the projection of the electronic density of stateson these sites presents two overlapping structures. One of them ischaracterized by the level spacing coming from bulk states and the other arisesfrom the surface states. In very small particles, this contributes to anover-broadening of the NMR absorption spectra, determined by the Knight shiftdistribution of magnetic nuclei. We compare our calculated Knight shifts withexperiments on aluminum nanoparticles, and show that the deviation of thescaling law as a function of temperature and particle size can be explained interms of surface states.