W. Gebicki

Raman scattering study of Ga1−xMnxN crystals

Raman spectra of Ga1−xMnxN crystals grown by the resublimation method have been investigated. New bands around 300 and 667 cm−1, as well as a broad structure near 600 cm−1, not observed in undoped GaN have been found. The temperature dependence of major Raman bands has been measured. The simple model of GaN lattice dynamics has been presented, and the observed bands have been assigned to disorder-activated phonon modes, in good agreement with the calculated phonon density of states.

Charging and discharging processes of carbon nanotubes probed by electrostatic force microscopy

Electrostatic properties of individually separated single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multiwalled carbon nanotubes (MWCNTs) deposited on insulating layers have been investigated by charge injection and electric force microscopy (EFM) experiments. Delocalized charge patterns are observed along the CNTs upon local injection from the EFM tip, corresponding to (i) charge storage in the nanotubes and to (ii) charge trapping in the oxide layer along the nanotubes. The two effects are dissociated easily for CNTs showing abrupt discharge processes in which the charge stored in the CNT are field emitted back to the EFM tip, while trapped oxide charge can subsequently be imaged by EFM, clearly revealing field-enhancement patterns at the CNT caps. The case of continuous discharge processes of SWCNTs, DWCNTs, and MWCNTs is discussed, as well as the evolution of the discharge time constants with respect to the nanotube diameter.

Charging and emission effects of multiwalled carbon nanotubes probed by electric force microscopy

Electrostatic properties of single-separated multiwalled carbon nanotubes (MWCNTs) deposited on a dielectric layer have been investigated by charge injection and electric force microscopy (EFM) experiments. We found that upon local injection from the biased EFM tip, charges delocalize over the whole nanotube length (i.e., 1–10μm), consistent with a capacitive charging of the MWCNT-substrate capacitance. In addition, the insulating layer supporting the nanotubes is shown to act as a charge-sensitive plate for electrons emitted from the MWCNTs at low electric fields, thus allowing the spatial mapping of MWCNT field-emission patterns.

Raman scattering study of gallium nitride heavily doped with manganese

Abstract Small MnxGa1−xN crystals grown by the resublimation method have been characterised by Raman scattering technique. It has been shown, that for small concentration of manganese the concentration of free electrons in the material is high as in typical free standing GaN crystals, but for higher contents of manganese the concentration of free carriers in the alloy has been substantially reduced. The measured Raman spectra have been compared with the calculated phonon density of states, and it has been shown that the Raman peaks correspond to the peaks of the phonon density of states. In consequence the new Raman peaks found in the material are ascribed to disorder activated phonon modes.

The influence of erbium on the physical properties of GaN crystals grown from N solution in Ga at high nitrogen pressure

Abstract Oxygen contamination is the main source of free electrons in bulk GaN grown at high-pressure. We used erbium as a promising getter/compensation center to reduce the electron content in GaN. Both optical and electrical measurements indicate the reduction of electron concentration from the initial 6 × 1019cm−3 down to 1 × 1019cm−3. A photoluminescence study proves that erbium is incorporated into the GaN host lattice, and emits light at ∼ 1.5μm.