High-pressure Raman spectroscopy study of wurtzite ZnO

Abstract

The high pressure behavior of optical phonons in wurtzite zinc oxide (w-ZnO) has been studied using room temperature Raman spectroscopy and ab-initio calculations based on a plane wave pseudopotential method within the density functional theory. The pressure dependence of the zonecenter phonons (E2, A1 and E1) was measured for the wurtzite structure up to the hexagonal→cubic transition near 9 GPa. Above this pressure no active mode was observed. The only negative Grüneisen parameter is that of the E low 2 mode. E1(LO) and (TO) frequencies increase with increasing pressure. The corresponding perpendicular tensor component of the Born's transverse dynamic charge e * T is experimentally found to increase under compression like e * T (P) = 2.02 + 6.4 • 10 −3 .P whereas calculations give e * T (P) = 2.09−2.5•10 −3 .P (in units of the elementary charge e, P in GPa). In both cases, the pressure variation is small, indicating a weak dependence of the bond ionicity with pressure. The pressure dependence of the optical mode energies is also compared with the prediction of a model that treats the wurtzite-to-rocksalt transition as an homogeneous shear strain. There is no evidence of anomaly in the E2 and A1 modes behavior before the phase transition.

Photoluminescence and resonant Raman scattering from ZnO-opal structures

“…Note that this statement is supported by the position of very sensitive to strain E 2 high mode at 438 cm Ϫ1 in Raman scattering ͑RS͒ spectra, it coinciding with the position of respective mode in nonstressed ZnO single crystals. [15][16][17] Besides, the width of bound exciton lines in PL spectrum ͑2-3 meV͒, along with narrow lines observed in RS spectra ͑e.g., the width of the E 2 low mode is less than 1 cm Ϫ1 ) are indicative of high crystalline quality of ZnO layers grown on opals.…”

“…The peak in the resonant Raman spectrum is centered at 3.313 eV which implies that the phonon energy equals 72.5 meV. According to the first-order Raman scattering measurements, [15][16][17] this value is closer to the E 1 (LO) phonon energy. The peak at 584 cm Ϫ1 in the insert also corresponds to the E 1 (LO) phonon, although the asymmetrical low energy wing indicates to the contribution from the A 1 (LO) phonon.…”

A nondestructive tool for nanomaterials: Raman and photoluminescence spectroscopy

“…The pressure dependence of the optical mode energies can be related to homogeneous shear strain caused by a phase transition [29]. This shear strain in the crystal can be measured from the change in frequency of the Raman shift.…”

Effect of doping concentration on absorbance, structural, and magnetic properties of cobalt-doped ZnO nano-crystallites

“…Its fundamental structural properties were studied in 1935 for the first time by Bunn [1], and then detailed optical studies were carried out by Damen et al [2] and Decremps et al [3] using Raman spectroscopy.…”