Size and oxidation effects on the vibrational properties of nanocrystallineα−Fe

Lattice dynamics in Sn nanoislands and cluster-assembled films

“…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 .…”

“…In general it was found that for thin films the phonon behaviour is strongly influenced by the monolayer in contact with the substrate and the monolayer at the surface. Nanocrystalline structures with a high density of grain boundaries have been studied theoretically 7,9,26,29 and experimentally 8,12,15,16,18,21,23,24 for different materials. In these nanocrystalline structures, an enhancement of low-energy modes and broadening of different features of the PDOS was observed.…”

“…Phonon softening in these structures was attributed to grain boundary atoms and the decrease of the phonon lifetime was attributed to phonon scattering at the grain boundaries 7,8,11,12,15,18,21,23,24 . In some nanocrystalline structures an enhancement of high-energy modes above the cut-off energy was observed which was attributed to surface oxides 12,16 , grain boundary atoms 9,21 or to changes in the inter-atomic force constants 11,18,26 . Another type of nanostructure that was studied is isolated nanoparticles 7,8,10,17,20,22,25 for which also an enhancement of low-and high-energy phonon modes as well as a broadening of the PDOS features was observed.…”

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.…”

Vibrations of Micro-eV Energies in Nanocrystalline Microstructures

“…More recently, neutron and x-ray inelastic scattering measurements revealed that nanocrystalline materials have an increased number of vibrational modes at the highest and lowest energies of their measured spectra, compared to materials with crystals of conventional sizes [5][6][7][8][9][10][11][12]. Enhanced intensity above the high-energy cutoff of the bulk material has been attributed to phonon lifetime broadening caused by phonon interactions with grain boundaries [9][10][11] and recent measurements on iron have isolated a contribution from surface oxides [12]. The increased number of phonon modes at low energies [5][6][7][8][9][10][11] is less well understood.…”