Phonons in Iron: From the Bulk to an Epitaxial Monolayer

Abstract

The confinement of materials in low-dimensional structures has significant impact on propagating excitations like phonons. Using the isotope-specific 57Fe nuclear resonant vibrational spectroscopy we were able to determine elastic and thermodynamic properties of ultrathin Fe films on W(110). With decreasing thickness one observes a significant increase of the mean atomic displacement that goes along with an enhancement of vibrational modes at low energies as compared to the bulk. The analysis reveals that these deviations result from atomic vibrations of the single atomic layers at the two boundaries of the film, while the atoms inside the films vibrate almost bulklike.

Lattice dynamics in Sn nanoislands and cluster-assembled films

“…(i) The decrease in intensity of high-energy modes (15 and 18 meV) was observed before in various nanoscale systems 12,13,16,19,[21][22][23][24][25] , an effect which was found to originate from phonon scattering. From the TEM study, it was concluded that a single Sn island is composed of many Sn crystallites.…”

“…The lower the Q value, the shorter the lifetime of the phonon state, and the broader the features in the phonon spectrum. For simplicity, Q is assumed to have the same average value for all phonon modes in our analysis, which has proven to be a successful method to describe phonon lifetime broadening in metallic nanostructures 13,19,60 . The aim of using the DHO model here is to provide a simple model to explain the overall changes observed in the experimental phonon spectra.…”

“…The phonon density of states (PDOS) of low dimensional systems is expected to be modified due to the restriction of phonon propagation [7][8][9][10][11] . Previously, clear differences between the phonon density of states of bulk and that of nanostructures have been observed, with as most commonly observed anomalies in the phonon spectra of nanostructures: an enhancement of low-energy modes, appearance of high-energy modes above the cut-off energy of the bulk material and a broadening of the PDOS features [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . For thin films, the broadening of features in the PDOS was attributed to phonon damping 13,19,27,28 and the enhancement of low-energy phonon modes due to the appearance of surface modes 14,19,27 .…”

Interplay between lattice dynamics and superconductivity in Nb3Sn thin films

“…Another source of reduction in the phonon lifetime originates from a smaller grain size. The DHO model has been used to describe size effects in metal nanostructures 29,30 . Indeed, the lifetime in nanostructures is expected to decrease due to the smaller mean-free-path induced by the smaller crystallite size.…”

Condensed Matter Physics Using Nuclear Resonant Scattering

“…The measurement of the PDOS under high pressures using a diamond anvil cell (DAC), where the sample size is typically less than 1 mm 2 , has been performed to study the core of the earth. [106][107][108] In addition, many important studies using the features of nuclear resonant inelastic scattering spectroscopy have been performed, e.g., on nanoparticles, [109][110][111][112][113][114] thin films, [115][116][117][118][119][120][121] quasi crystals, 122) clathrates, 123,124) superconductors, [125][126][127][128] filled skutterudites, [129][130][131][132] and glass. 133,134) The nuclear resonance scattering method can be applied to not only solids but also liquids.…”