Junghwan Chun

Growth of Ga-doped ZnO nanowires by two-step vapor phase method

A two-step route is presented to dope Ga into ZnO nanowires and also fabricate heterostructures of Ga-doped ZnO nanowires on ZnO. The content of Ga in ZnO nanowires is about 7 at. % from energy-dispersive x-ray analysis. The single crystal Ga doped ZnO nanowires with the diameter of 40 nm and the length of 300–500 nm are well aligned on the ZnO bulk. The growth direction is along [001]. Raman scattering analysis shows that the doping of Ga into ZnO nanowires depresses Raman E1L mode of ZnO, manifesting that Ga sites in ZnO are Zn sites (GaZn). The formation mechanism of Zn1−xGaxO nanowires/ZnO heterostructures is proposed.

Electrical properties and near band edge emission of Bi-doped ZnO nanowires

Electrical transport of Bi–ZnO nanowires shows n-type semiconducting behavior with a carrier concentration of ∼3.5×108cm−1 (2.7×1019cm−3) and an electron mobility of 1.5cm2∕Vs. The carrier concentration is one order of magnitude larger than that of undoped ZnO nanowires, indicating that Bi acts as donor rather than the usual acceptor in ZnO films. The low mobility may be in association with electron scatterings at the boundaries from small size effect of nanowires. Near band edge emission in photoluminescence spectrum of Bi–ZnO nanowires is redshifted relative to undoped ZnO nanorods as a result of enhanced carrier concentration. The donor-acceptor pair transition associated with Bi was also observed at 3.241eV.

Structural characterization and low temperature growth of ferromagnetic Bi–Cu codoped ZnO bicrystal nanowires

Ferromagnetic Bi–Cu codoped ZnO nanowires were fabricated at temperatures as low as 300°C via a vapor phase transport using the mixture of Zn, BiI3 and CuI powders. They are grown as a bicrystal, along the [011¯2] direction, have a width of 40–150nm, and a length of a few microns. The investigation of the growth mechanism proposes that the synergy of BiCu and iodine/iodide induces the formation of bicrystallinity. The photoluminescence measurement shows the cooperative effect of Bi and Cu ions. The ferromagnetism observed in this study is the result of the combined effect of structural defects, the substitution of Cu into Zn site along the c axis, and codoping of Bi.

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.

The selectively manipulated growth of crystalline ZnO nanostructures

Aligned ZnO nanorods on film, tetrapod nanowires and nanotubes have been selectively fabricated by a simple one-step route and characterized by x-ray diffractometry (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and photoluminescence (PL). PL spectra exhibit different intensity of the green emission relative to the UV emission for different nanostructures. The effects of the process parameters on different nanostructures have been discussed. The wettability of well aligned nanorods on film was investigated, which reveals a super-hydrophobicity.