Vibrational dynamics of Fe in amorphous Fe–Sc and Fe–Al alloy thin films

Abstract

The atomic vibrational dynamics of 5 7Fe in 800-A thick amorphous (a-) 57Feo.25ScO.75, a-57Feo.67ScO.33 and a-57Feo.14Alo.86 alloy thin films has been investigated at room temperature by nuclear resonant inelastic X-ray scattering (NRIXS) of synchrotron radiation. The amorphous phase has been successfully stabilized by codeposition of Fe and Sc or Al in ultrahigh vacuum onto substrates held at -140°C during deposition. The amorphous structure of the samples was confirmed by X-ray diffraction and conversion electron Mossbauer spectroscopy. The 57Fe-projected partial vibrational density of states, geE), has been obtained from the measured NRIXS vibrational excitation probability, together with thermodynamic quantities such as the probability of recoilless absorption (f-factor), the average kinetic energy per Fe atom, the average force constant, and the vibrational entropy per Fe atom. A plot of the reduced density of states, g(E)/E 2, versus excitation energy E proves the existence of non-Debye-like vibrational modes (boson peak) with a peak energy, Ebp, in the range of 3-7 meV. Both, the boson peak height H bp and Ebp were found to depend on the composition. Above the boson peak, g(E)/E 2 exhibits an exponential decrease. Our results demonstrates that the features of the boson peak depend on the amount and type of element M (M = AI, Si, Mg, Sc).Key words amorphous alloys · Fe-Sc · Fe-AI· thin films · conversion electron Mossbauer spectroscopy (CEMS) · nuclear resonant inelastic X-ray scattering. atomic vibrational density of states · boson peak B. Sahoo (181) .

Phonon confinement and interface lattice dynamics of ultrathin high-k rare earth sesquioxide films: the case of Eu2O3 on YSZ(001)

“…The presented results demonstrate that in addition to spatial confinement, 35 structural disorder, 41 surface- 30 and interface- 33 specific vibrational modes, sub-nanometer-thick layers exhibiting exotic crystal phases that might form at the interface between two materials constitute a source of novel vibrational dynamics of thin films and multilayers. Moreover, the targeted embedment of such ultrathin layers might be a successful approach towards ultimately engineered heterostructures for phononic applications.…”

“…50,51 In amorphous thin lms, the broad low-energy peak originates from the reduced mean force constants with a large width of distribution associated with the structural disorder. [39][40][41] In addition to these well studied effects, below we unveil another potential source of anomalies in the lattice dynamics of thin lms and multilayers.…”

“…[28][29][30][31][32][33][34][35][36][37][38] In amorphous thin lms, the structural disorder induces a reduction and a broad distribution of the mean force constants, leading to a signicant enhancement of the number of lowenergy states. [39][40][41] Fundamentally, the origin of the high-k property is directly related to the vibrational spectrum of a solid, since the static dielectric constant is a sum of the electronic and lattice contributions. While the former equals to the square of the refractive index and thus is intrinsically limited to low values, the high-k values originate from the lattice component, which is inversely proportional to the square of the frequency of transverse optical phonons.…”