161. Helical structure of single-crystalline ZnGa2O4 nanowires

Fig. 1 (a) SEM micrograph shows the vertically aligned ZnGa2O4 nanowires on a large area of the Si substrate. (b) A magnified image shows the sharp tip of ZnGa2O4 nanowires. (c) TEM image showing the general morphology of the nanowires. The average diameter is 80 nm. (d) HRTEM image for a nanowire having a sharp tip. The SAED pattern reveals the [111] growth direction (inset). (e) Atom-resolved image for the marked area in (d) reveals the (111) planes separated by 4.8 Å. (f) PL spectrum of ZnGa2O4 nanowires measured at 298 K (room temperature) and 8 K. The excitation wavelength is a 325 nm line from a He-Cd laser. (b) CL spectrum at room temperature.

Fig. 2 (a) TEM image shows the general morphology of the nanovines. (b) The growth direction of the helical nanowire changes zigzagged with a constant oblique angle of 45°. Atomic-resolved image and corresponding FFT ED pattern (inset) for (c) the straight ZnSe nanowire and (d) the helical ZnGa2O4 nanowire. (e) General morphology of the nanospring having a constant angle and pitch. (f) The single-crystalline ZnGa2O4 crystal has a [0-11] growth direction, as confirmed by the FFT ED pattern (inset). Schematic models for (g) the nanovines and (h) the nanosprings. (i) Top-view diagram showing the four growth directions of the helical nanowires. (k) PL spectrum of the ZnGa 2 O 4 /ZnSe nanovines and pure ZnSe nanowires measured at room temperature (298 K). The excitation wavelength is the 325 nm line (3.815 eV) from a He-Cd laser.

Seung Yong Bae, et al, J. Am. Chem. Soc. 127, 10802 (2005)
https://doi.org/10.1021/ja0534102

(1) Helical ZnGa2O4 nanostructures were synthesized by a two-step thermal evaporation method.
(2) The helical ZnGa2O4 nanowires described in the present study have four equivalent 〈011〉 growth directions.
(3) Lattice matching occurs when the ZnGa2O4 nanowire winds around the ZnSe nanowire. The interlayer distances of the (022) and (400) planes of ZnGa2O4 are 2.946 and 2.083 Å, respectively. The (002) and (220) planes of the ZnSe nanowires, which are lying along the growth direction and zone axis of the ZnGa2O4 nanowires, respectively, are separated by distances of 2.835 and 2.004 Å.
(4) The surface of the ZnSe nanowires may melt into the Au nanoparticles, so as to act as the Zn source. The Au nanoparticle acts as a catalyst to melt the Zn and moves along the surface of the ZnSe nanowire during the growth of the ZnGa2O4 nanowire.
(5) The ZnGa2O4 nanowires have a blue emission at 3.1 eV, originating from the self-activation center of the octahedral Ga-O.
(6) The ZnGa2O4 nanosprings could be used as more efficient sensing materials or mechanical resonators.
(7) Room-temperature resistivity has been reported at an order of 30 mW cm for polycrystalline ZnGa2O4 with a band gap of 4.4-4.7 eV.
(8) It can also act as an excellent host material for multicolor emitting phosphor layers; manganese-activated ZnGa2O4 (ZnGa2O4: Mn) for green emission and ZnGa2O4: Cr for red emission.
(9) The Si substrates were coated with HAuCl4•3H2O (98+%, Sigma) ethanol solution, forming the Au catalytic nanoparticles. Argon flowed at a rate of 500 sccm. ZnO (99.99%, Aldrich) powders and Ga metal (99.9999%, Aldrich) were placed in a quartz boat located inside a quartz tube reactor for synthesis of ZnGa2O4 nanowires over the temperature range 800-1000 °C.