Keehan Rho

Ferromagnetic GaN:MnAlSi nanowires

The fabrication of crystalline Al-codoped GaN:Mn nanowires with a Mn doping rate of approximately 7at.% is reported. The magnetism measurements show that the Curie temperature is above 350K. X-ray and electron diffractions do not show the presence of any secondary magnetic phases. The electrical transport measurement indicates that the nanowires are of n-type semiconductor.The fabrication of crystalline Al-codoped GaN:Mn nanowires with a Mn doping rate of approximately 7at.% is reported. The magnetism measurements show that the Curie temperature is above 350K. X-ray and electron diffractions do not show the presence of any secondary magnetic phases. The electrical transport measurement indicates that the nanowires are of n-type semiconductor.

Low-temperature (∼250°C) route to lateral growth of ZnO nanowires

Zinc oxide nanowires were obtained through a vapor transport route at temperatures as low as around 250°C. The diameters of the nanowires are ∼40nm and their lengths reach up to a few microns. The high-resolution transmission electron microscopy showed that ZnO nanowires are of hexagonal wurtzite structures with the [112¯0] growth direction. Raman spectrum reveals that the ZnO nanowires are of high-quality crystal and have an oxygen deficiency. The energy dispersive x-ray spectroscopy result verifies that the nanowires contain a small amount of Bi besides Zn and O. The investigation of the growth mechanism suggests that BiI3 plays a key role on the fabrication of ZnO nanowires around 250°C.

Fabrication and photoluminescence of zinc silicate/silica modulated ZnO nanowires

Zinc silicate/silica modulated ZnO nanowires have been successfully prepared by a chemical vapour deposition route. The nanowires have a uniform diameter of ~30 nm and length of 1 µm. Photoluminescence spectra show four peaks at 382, 398, 478 and 520 nm. Two new additional peaks at 398 and 478 nm are assigned to modulation between ZnO and SiO2. The formation mechanism of the surface modified ZnO-based nanowires is also proposed.

Ferromagnetic ZnO bicrystal nanobelts fabricated in low temperature

Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI3, and MnCl2∙H2O at temperatures as low as 300°C. The bicrystal nanobelts, growing along the [011−3] direction, have the widths of 40–150nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18meV as compared to Bi–ZnO nanowires at 10K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature.

Temperature dependent phase transition of EuO on MgO(100)

We investigated the changes of magnetic properties and phase transition in EuO films grown on a MgO(100) substrate as a function of temperature. As the temperature was varied, we observed a clear phase transition and polarization change at 69K using spin resolved photoemission spectroscopy and low energy electron diffraction. We will elucidate the temperature driven changes in the electronic and magnetic properties of EuO films on a MgO(100) substrate.