Quantum oscillations in the surface excitations of ultrathin Mg(0001) films

Abstract

Using reflection electron energy-loss spectroscopy (EELS), we unveil a direct correlation between the thickness-dependent oscillatory charge spilling of quantum-well states in epitaxial Mg(0001) films, and the linear dispersion coefficient of the monopole surface plasmon mode. In addition, the spectral intensities of the photoemission threshold excitation and multipole surface plasmon mode follow a similar but mutually anticorrelated quantum oscillatory pattern. These oscillatory features of the collective response are attributed to quantum oscillations in the ground-state charge-density profile, specifically its decay into the vacuum. Because the decay lengths can be controlled through the quantum-size effects and appropriate choice of the quantum-size boundary conditions, these insights are expected to be significant in the design of quantum-sized plasmonic devices.

Plasmonic excitations in ultrathin metal films on dielectric substrates

“…Using the semi-classical local optics model, we further elucidate the underlying physics of the TDLDA spectra for the Mg-Si systems. In addition, we establish the consistency between our theoretical results and the recent experimental measurement for the Mg-Si systems [47].…”

“…In the second approach, we use a semi-classical local optics model to reveal an intrinsic connection between the broad absorption feature and the multipole surface plasmon modes. Our theoretical predictions on the plasmon dispersions and absorption spectra are also shown to be qualitatively consistent with the latest experimental observations using electron energy loss spectroscopy (EELS) for Mg thin films grown on Si substrates [47].…”

“…We now compare our theoretical results with our recent EELS measurements performed on Mg thin films grown on Si(111) [47]. First, we stress that the spectra measured by EELS are typically obtained at some fixed incident and scattering angles of the probing electrons, while the theoretical absorption is calculated for a certain parallel momentum q transferred to the plasmons.…”

“…Experimental measurements of the absorption spectra from a 4.5 ML Mg film on a Si substrate for different off-specular angles (a) −°4 , (b) −°2 , (c)°4 , (d)°6 , (e)°1 2 , and (f)°14 , after background subtraction[47]. The lines highlighted with different symbols are the fitting results for the absorption resonances labeled as surface plasmon (solid line, square), multipole surface plasmon (dotted line, diamond), bulk plasmon (dot-dashed line, triangle), and threshold resonance (dashed line, disk).…”

Dimensionality and Valency Dependent Quantum Growth of Metallic Nanostructures: A Unified Perspective

“…By contrast, Ag(110) ultrathin films on NiAl(110) were observed to display QSEs with strong bilayer oscillations . Especially, the most intensively studied 2D nanostructure is Pb(111) ultrathin films, where the Fermi wavelength is nearly commensurate with the interlayer spacing, resulting in the bilayer-by-bilayer growth mode up to more than 40 ML. , Other metal films such as Al(111), Mg(0001), and Bi(111) ultrathin films were also found to dramatically exhibit QSEs − of many other physical properties including work function, superconducting transition temperature, , and electron-photon coupling, which are strongly dependent on the film thickness.…”