Possible evidence of quantum size effects in x-ray photoemission spectra of ultrathin Si layers

Abstract

This letter reports the experimental evidence of a 2.3 eV blue shift of the plasmon loss lines observed in the x-ray photoelectron spectra of an ultrathin Si layer equivalent to 1.5×1015 at./cm2 deposited onto a randomly oriented Al2O3 single crystal. The plasmon line shifts, which is roughly proportional to the deposited Si(mass)−2/3, are attributed to quantum confinement effects in agreement with electron energy loss measurements performed on nanosized Si particles.

Electronic Structure of Germanium Nanocrystal Films Probed with Synchrotron Radiation

“…A similar study has been performed by Dibiasi et al on ultrathin silicon layers with photoemission spectroscopy. [88] Dibiasi et al find bulk-plasmon shifts in their systems up to 2.3 eV, which they also attribute to quantum size effects in the particle. They deduce, based on the ideas of Mitome et al, a cluster size of 2.0 nm.…”

“…The plasmon excitation allows one to draw qualitative conclusions about the crystal structure, since the energy and position of the plasmon excitation are sensitive to changes in the valence band and thus crystal structure. [38] The plasmon excitation has been used previously to investigate quantum size effects [87,88] as well as phase transitions [89] in semiconductor nanocrystals. As quantum size effect, a shift in the plasmon energy is expected.…”

Quantum size effect of valence band plasmon energies in Si and SnOx nanoparticles

“…4 Within the nearly free electron model, the excitation energies are expected to be proportional to the square root of the charge carrier density. An increase of the plasmon energy with decreasing size or thickness has been reported for Si clusters, 8 Si ultrathin films, 11 and porous Si 9 as well as CdS quantum dots. Quantum size effects of plasmon energies have been widely studied for metal clusters and particles.…”

“…[1][2][3] Volume plasmons are long-wavelength, collective excitations of charge carriers. 3 Only a few studies exist on confinement effects of valence band plasmons in dielectrics [8][9][10][11][12][13][14][15] although changes of the plasmon energy are of practical relevance for adjustable optical edge filters in the ultraviolet range. While this relationship is usually well fulfilled for dielectrics, it is violated in transition metals due to mixing of d-and s-electron states.…”

Synchrotron radiation x-ray photoelectron spectroscopy of Si nanocrystals grown onto Al2O3∕Si surfaces

“…24,25 It has been shown, 24 for example, that the plasmon energy for Si NCs is higher than that of bulk Si. For this reason, we cannot discount a contribution from phonon broadening in the measured width.…”