Surface lattice dynamics of NiO (001) by inelastic He atom scattering

Abstract

High-resolution inelastic He atom scattering experiments, employing a time-of-flight (TOF) technique, have been carried out on NiO (001) in the (l00) and (Ito) high symmetry directions. The targets were prepared by cleaving single-crystal NiO in air and then baking in vacuum. Nearly all of the experiments reported here were carried out at a target temperature of 575 K, which is above the Neel point ( TN = 523 K), and with He atom wave vectors in the range of 7-9 A -I (25-45 meV). Because of these high temperatures, the peaks in the TOF spectra were found to be somewhat broader and the multiphonon background somewhat higher than in reported spectra from this instrument for alklai halide surfaces. Nonetheless, sufficient data were obtained to allow the determination of the Rayleigh wave almost to the Brillouin zone boundary. The results for this mode are found to be in good agreement with recently published, roomtemperature electron energy loss spectroscopy experiments. In contrast, there is a substantial difference between these data and the dispersion data reported for Ni (001) with chemisorbed o atoms [the O-e(2 X 2) structure]. Experiments that were tried at low temperatures were unsuccessful due to the rapid accumulation of surface contaminants.

Helium-atom-scattering study of the structure and phonons of the NiO(100) and CoO(100) surfaces

“…Helium atom scattering ͑HAS͒ has the advantages that the neutral helium atoms are not affected by surface charging and because of the low kinetic energies (Ͻ50 meV) they do not disturb the surface. Only one previous inelastic HAS measurement was reported by Brug et al 17 for a NiO͑100͒ sample cleaved in air. However, due to the low quality of that surface, no diffraction and only the initial part of the Rayleigh phonon dispersion curves could be observed.…”

Surface-phonon dispersion of a NiO(100) thin film

“…[4][5][6][7][8][9] The surface-phonon dispersion has been studied for the low-index (100) cleavage plane by high-resolution electron energy loss spectroscopy (HREELS) and inelastic Helium atom scattering (HAS) previously. [10][11][12] However, charging of the NiO single crystal restricted previous electron scattering investigations in the accessible energy range and prevented full dispersion analysis. 10 The high-resolution HAS studies, on the other hand, have been limited to the investigation of the very low-lying excitations.…”

Surface phonons of NiO(001) ultrathin films grown pseudomorphically on Ag(001)

“…However, the details of the phonon dispersion of NiO attracted also recently new attention due to a significant spin-phonon coupling [4][5][6]. The vibrational properties of the surface of NiO(001) and the specific surface phonon dispersion have been addressed only by a few studies by means of Helium atom scattering (HAS) [7,8] and high-resolution electron energy loss spectroscopy (HREELS) [9,10]. Whereas the former has an excellent energy resolution, it is restricted to low-energy phonon modes due the limited kinetic energy of the scattering Helium atoms.…”