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The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.

Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga 0.96 Mn 0.04 As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm -1 ) observed in Mn ion-implanted NWs, which we attribute to E g (TO) and A 1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell.

Orthorhombic α-BaTeMo2O9 nonlinear optical single crystals were investigated at ambient pressure by micro-Raman and infrared spectroscopy with a focus on the polarization properties of the vibrational modes. These results were analyzed based on classical lattice dynamics calculations, allowing us to propose the normal-mode symmetries and assignments. In addition to the ambient-pressure studies, high-pressure Raman scattering studies were performed. These studies showed the onset of a reversible first-order phase transition near 3.5 GPa. The pressure dependence of Raman bands provides strong evidence that the phase transition involves significant distortion of the TeOx (x = 3,4) polyhedra, whereas the MoO6 octahedra are less affected. A large increase in the number of observed bands points to lower symmetry of the high-pressure phase.

RbNd(WO(4))(2) was investigated by high pressure Raman spectroscopy in the 0.1-12.3 GPa pressure interval. The assignment of modes was made based on lattice dynamics calculations and the results of these calculations helped us to also discuss the high pressure behavior of phonon spectra in this material. Our results show that a double oxygen bridge plays a fundamental role in the vibrational properties of this system. A density functional theory (DFT) calculation of hydrostatic pressure effects on RbNd(WO(4))(2) was performed in order to understand the effect of internal bond changes on the vibrational properties of RbNd(WO(4))(2). No pressure induced structural phase transition was observed in the Raman study at room temperature, and the DFT calculation (T = 0 K) is consistent with this result. The anomalous softening of the bridge stretching mode at 770 cm(-1) was attributed to the decrease of W-O1-W bond angle with increasing pressure.

Lattice dynamics calculations and a high-pressure Raman scattering study of nanocrystalline Bi(2)MoO(6), a member of the bismuth-layered Aurivillius family of ferroelectrics, are presented. These studies showed the onset of two reversible second-order or weakly first-order phase transitions near 2.5 and 4.5 GPa as well as some subtle structural changes at 8.2 GPa. Symmetry increases upon application of pressure and the first phase transition involves, most likely, the loss of the MoO(6) tilt mode around a pseudo-tetragonal axis. The second phase transition is associated with the instability of a low wavenumber mode, which behaves as a soft mode. This soft mode most likely corresponds to the polar E(u) mode of the tetragonal I4/mmm aristotype and Bi(2)MoO(6) transforms at 4.5 GPa into the centrosymmetric orthorhombic phase. The sequence of the pressure-induced phase transitions in nanocrystalline Bi(2)MoO(6) is similar to that observed for bulk Bi(2)WO(6) but the critical pressures are significantly lower for the molybdenum compound. Our results also show that the critical pressure of the first phase transition is slightly lower for the nanocrystalline Bi(2)MoO(6) (2.5 GPa) than for the microcrystalline (bulk) Bi(2)MoO(6) (2.8 GPa).

A high pressure Raman scattering study of Bi(2)MoO(6), a member of the bismuth layered Aurivillius family of ferroelectrics, is presented. This study showed the onset of two reversible second-order phase transitions near 2.8 and 7.0 GPa. The pressure dependence of the Raman bands provides strong evidence that the structural changes in Bi(2)MoO(6) are mainly related to the rigid rotations of MoO(6) octahedra. Symmetry increases upon application of pressure and the first phase transition involves, most probably, the loss of the MoO(6) tilt mode. This structural change may be the same as that observed at ambient pressure at elevated temperature (from P 2(1)ab to a polar orthorhombic structure of unknown symmetry). The second phase transition is associated with some subtle structural changes and the structure above 7.0 GPa is most probably still orthorhombic.

The new compound K(3)Fe(MoO(4))(2)(Mo(2)O(7)) was synthesized and characterized by a single-crystal x-ray structure determination, and IR and Raman spectroscopic studies. The crystal structure at room temperature and ambient pressure is monoclinic, space group C 2/c, with the unit cell dimensions a = 32.885(7), b = 5.7220(11), c = 15.852(3) Å, β = 91.11°, Z = 8. The FeO(6) octahedra are joined by corners with MoO(4)(2-) tetrahedra and Mo(2)O(7)(2-) units. Some of the K(+) ions form layers in the b × c-plane. The origin of various Raman and IR vibrational modes is discussed. These results indicate that a clear energy gap exists between the stretching and remaining modes. High-pressure Raman scattering studies were also performed. These studies showed the onset of two reversible first-order phase transitions near 1.2 and 7.4 GPa, which are associated with strong distortion of the MoO(4)(2-) and Mo(2)O(7)(2-) units.