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CeO2 nanoparticles (NPs) with average particle size of ∼17 nm were grown on graphene sheets by simply mixing cerium chloride as the Ce precursor with graphene oxide (GO) in distilled water and the simultaneous reduction of GO to reduced graphene oxide (rGO), followed by a one-step hydrothermal treatment at 150 °C. A unique blue to green tuneable luminescence was observed as a function of the excitation wavelength. With this method, significant applications of rGO-CeO2 nanocomposites in many optical devices could be realized. The photocatalytic activity of the as-synthesized CeO2 and rGO-CeO2 nanocomposite was investigated by monitoring the degradation of methylene blue (MB) dye under direct sunlight irradiation. The rGO-CeO2 nanocomposite exhibited excellent photocatalytic activity compared to CeO2 NPs by degrading 90% of the MB dye in 10 min irradiation under sunlight. This property of rGO-CeO2 nanocomposites was ascribed to the significant suppression of the recombination rate of photo-generated electron-hole pairs due to charge transfer between rGO sheets and CeO2 NPs and the smaller optical band-gap in the rGO-CeO2 nanocomposite.

GaN films have been deposited by radio frequency sputtering of a GaAs target with pure nitrogen. The growth, composition, and structure of the films deposited on quartz substrates have been studied by x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Films deposited below 300°C are amorphous and As rich. Above 300°C, polycrystalline, hexagonal GaN is formed, along with As rich amorphous phase, which reduces with increasing substrate temperature. At a substrate temperature of 700°C, GaN films, practically free of amorphous phase, and As (<0.5at.%) are formed. The preferred orientation depends strongly on the substrate temperature and is controlled by surface diffusion of adatoms during growth stage. Below 500°C, the surface diffusion between planes dominates and results in the (101¯1) preferred orientation. Above 500°C, the surface diffusion between grains takes over and results in (0002) preferred orientation.

aWe have grown homoepitaxial GaN nanowall networks on GaN template using an ultra-high vacuum laser assisted molecular beam epitaxy system by ablating solid GaN target under a constant r.f. nitrogen plasma ambient. The effect of laser repetition rate in the range of 10 to 30 Hz on the structural properties of the GaN nanostructures has been studied using high resolution X-ray diffraction, field emission scanning electron microscopy and Raman spectroscopy. The variation of the laser repetition rate affected the tip width and pore size of the nanowall networks. The z-profile Raman spectroscopy measurements revealed the GaN nanowall network retained the same strain present in the GaN template. The optical properties of these GaN nanowall networks have been studied using photoluminescence and ultrafast spectroscopy and an enhancement of optical band gap has been observed for the nanowalls having a tip width of 10-15 nm due to the quantum carrier confinement effect at the wall edges. The electronic structure of the GaN nanowall networks has been studied using X-ray photoemission spectroscopy and it has been compared to the GaN template. The calculated Ga/N ratio is largest ($2) for the GaN nanowall network grown at 30 Hz. Surface band bending decreases for the nanowall network with the lowest tip width. The homoepitaxial growth of porous GaN nanowall networks holds promise for the design of nitride based sensor devices.

Chemical vapor deposited diamond films grown on strained gallium nitride-coated quartz substrate are found to display a dominantly hexagonal diamond phase. The phase identification is done using Raman spectroscopy and orientation imaging microscopy (OIM). The presence of a 1324.4cm−1 band in the Raman spectra is attributed to a hexagonal diamond symmetry, but the unambiguous signature of the hexagonal phase is confirmed by OIM. A phase map of the sample clearly shows that 88% of the scanned sample area is hexagonal diamond.

Properties of InxGa1−xN films in terahertz range Appl. Phys. Lett. 100, 071913 (2012) Thermal carrier emission and nonradiative recombinations in nonpolar (Al,Ga)N/GaN quantum wells grown on bulk GaN J. Appl. Phys. 111, 033517 (2012) Surface depletion mediated control of inter-sub-band absorption in GaAs/AlAs semiconductor quantum well systems Appl. Phys. Lett. 100, 051110 (2012) High-Q optomechanical GaAs nanomembranes Appl. Phys. Lett. 99, 243102 (2011) Mg-induced terahertz transparency of indium nitride films Appl. Phys. Lett. 99, 232117 (2011) Additional information on J. Appl. Phys. GaN films have been deposited by reactive rf sputtering of GaAs target in 100% nitrogen ambient on quartz substrates at different substrate temperatures ranging from room temperature to 700°C. A series of films, from arsenic-rich amorphous to nearly arsenic-free polycrystalline hexagonal GaN, has been obtained. The films have been characterized by phase modulated spectroscopic ellipsometry to obtain the optical parameters, viz., fundamental band gap, refractive index, and extinction coefficient, and to understand their dependence on composition and microstructure. A generalized optical dispersion model has been used to carry out the ellipsometric analysis for amorphous and polycrystalline GaN films and the variation of the optical parameters of the films has been studied as a function of substrate temperature. The refractive index values of polycrystalline films with preferred orientation of crystallites are slightly higher ͑2.2͒ compared to those for amorphous and randomly oriented films. The dominantly amorphous GaN film shows a band gap of 3.47 eV, which decreases to 3.37 eV for the strongly c-axis oriented polycrystalline film due to the reduction in amorphous phase content with increase in substrate temperature.

Magnetic skyrmions are topological spin-textures having immense potential for energy efficient spintronic devices. Here, we report the observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film heterostructures at room temperature in remnant state employing magnetic force microscopy. It is shown that these skyrmions consisting of ultrathin ferromagnetic CFA Heusler alloy result from strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as evidenced by Brillouin light scattering measurements, in agreement with the results of micromagnetic simulations. We also emphasize on room temperature observation of multiple skyrmions which can be stabilized for suitable combinations of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These results provide a significant step towards designing of room temperature spintronic devices based on skyrmions in full Heusler alloy based thin films.

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