Thermodynamics of GaO Heteroepitaxy and Material Growth Via Metal Organic Chemical Vapor Deposition.

Heteroepitaxy of gallium oxide (GaO) is gaining popularity to address the absence of p-type doping, limited thermal conductivity of GaO epilayers, and toward realizing high-quality p-n heterojunction. During the growth of β-GaO on 4H-SiC (0001) substrates using metal-organic chemical vapor deposition, we observed formation of incomplete, misoriented particles when the layer was grown at a temperature between 650 °C and 750 °C. We propose a thermodynamic model for GaO heteroepitaxy on foreign substrates which shows that the energy cost of growing β-GaO on 4H-SiC is slightly lower as compared to sapphire substrates, suggesting similar high-temperature growth as sapphire, typically in the range of 850 °C-950 °C, that can be used for the growth of β-GaO on SiC.

Epitaxial Growth of (-201) β-GaO on (001) Diamond Substrates.

Heteroepitaxial growth of β-GaO on (001) diamond by metal-organic chemical vapor deposition (MOCVD) is reported. A detailed study was performed with Transmission Electron Microscopy (TEM) elucidating the epitaxial relation of (-201) β-GaO||(001) diamond and [010]/[-13-2] β-GaO ||[110]/[1-10] diamond, with the presence of different crystallographically related epitaxial variants apparent from selected area diffraction patterns. A model explaining the arrangement of atoms along ⟨110⟩ diamond is demonstrated with a lattice mismatch of 1.

Managing dose-, damage- and data-rates in multi-frame spectrum-imaging.

As an instrument, the scanning transmission electron microscope is unique in being able to simultaneously explore both local structural and chemical variations in materials at the atomic scale. This is made possible as both types of data are acquired serially, originating simultaneously from sample interactions with a sharply focused electron probe. Unfortunately, such scanned data can be distorted by environmental factors, though recently fast-scanned multi-frame imaging approaches have been shown to mitigate these effects.

Tungsten oxide nanorod growth by pulsed laser deposition: influence of substrate and process conditions.

Tungsten oxide nanorods (NRs) have been grown on W, Ta and Cu substrates following 193 nm pulsed laser ablation of a WO3 target in a low background pressure of oxygen. The deposited materials were analysed by scanning and (high resolution) transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray diffraction, Raman and X-ray photoemission spectroscopy, and tested for field emission. In each case, HRTEM analysis shows NR growth along the [100] direction, and clear stacking faults running along this direction (which are also revealed by streaking in the SAED pattern perpendicular to the growth axis).

Electro-induced orientational ordering of anisotropic pigment nanoparticles.

The response of anisotropic pigment particle suspensions to externally applied electric fields has been explored for possible application in reflective display technologies. Three different types of pigment particle were suspended in dodecane, using a polymeric stabilizer, and showed Schlieren textures between crossed polarizers at high concentrations (greater than 25-30 wt%), indicating the formation of colloidal nematic phases. Orientational order parameters were determined by X-ray scattering, and the influence of polydispersity on the values is discussed.

Investigating the role of microbes in mineral weathering: nanometre-scale characterisation of the cell-mineral interface using FIB and TEM.

Focused ion beam (FIB) sample preparation in combination with subsequent transmission electron microscopy (TEM) analysis are powerful tools for nanometre-scale examination of the cell-mineral interface in bio-geological samples. In this study, we used FIB-TEM to investigate the interaction between a cyanobacterium (Hassallia byssoidea) and a common sheet silicate mineral (biotite) following a laboratory-based bioweathering, incubation experiment. We discuss the FIB preparation of cross-sections of the cell mineral interface for TEM investigation.

Raman scattering in Me-doped ZnO nanorods (Me = Mn, Co, Cu and Ni) prepared by thermal diffusion.

We have investigated normal and resonant Raman scattering in Me-doped ZnO nanorods (Me = Mn, Co, Cu and Ni) prepared by thermal diffusion. Experimental results show that the normal Raman spectra consist of the conventional modes associated with wurtzite ZnO and impurity-related additional modes. Under resonant conditions, only longitudinal optical (LO) phonon scattering and its overtones are observed.

Investigation of the charge on threading edge dislocations in GaN by electron holography.

We present direct evidence for the charging around end-on threading edge dislocations in n-type GaN doped with silicon by off-axis electron holography in a transmission electron microscope. It is shown that the inner potential is reduced by up to 2.5 V within 10 nm of the dislocation, consistent with a negatively charged core.