M. Zacharias, H.J. Fan, and D.S. Kim
We are evaluating different methods of nanolithography for the deposition of well ordered Au dot array which are then used for nanowire growth by either vapor-liquid-solid growth or vapor-solid growth. The growth conditions are studied which allow the growth of well separated periodically arranged ZnO nanowires for different applications. Optical and electronic properties of single nanowires are studied. Stimulated emission of the ZnO nanowires was already shown. The electronic properties of single nanowires is studied using nanomanipulators within a SEM. In addition, we are working on methods for nanowire doping during growth.
Nanowires have been fabricated either via self-organization or controlled assembly. Strategies for position-controlled and nanopatterned growth of semiconductor nanowire arrays are reviewed and discussed in terms of technical simplicity and the potential for larger-scale realization. Issues on nanowire-based devices are also addressed with a brief survey of recent advances.
By patterning the GaN substrate with ordered Au pad arrays and using suitable growth parameters, submicron ZnO pillars (diameter of 300 nm) are obtained. The optical and piezoelectric properties are investigated as well. These thick pillars show stimulated emission.
The traditional nanosphere lithography (NSL) technique are also used for nano-patterned growth of vertical ZnO nanowires arrays on GaN substrates.
Nano-patterned ZnO nanowire ordered in hexagonal arrays are fabricated using nanotube membrane as the Au deposition mask. The wire diameters are variable from 30 up to 250 nm by using different mask sizes and controlled reaction conditions.
This is the first demonstration of patterned growth of ZnO nanowires on GaN/Si substrates.
Using spatially and spectrally resolved cathodoluminescence microscopy, the emission from the nanowires can be distinguished from that from the wetting film (or laterally-grown ZnO).
2. Fan, H. J. , R. Scholz , M. Zacharias , U. Gösele , F. Bertram , D. Forster , and J. Christen
Local luminescence from ZnO nanowires-covered surface: a cathodoluminescence microscopy study, Appl. Phys. Lett. 86 (2005) 023113.
From a simple thermal evaporation and deposition process of metallic Zn powder, polyhedral or spherical-shaped Zn microcrystals can be harvested. When these Zn microcrystals are subjected to annealing under different conditions (open air, pure oxygen, Ar flow), different ZnO nanostructures are formed, including hollow cages, flowers, and dendrites.
2. Fan, H. J. , R. Scholz , F. M. Kolb , M. Zacharias , U. Gösele , F. Heyroth , C. Eisenschmidt , T. Hempel , and J. Christen
On the growth mechanism and optical properties of ZnO multi-layer nanosheets, Appl. Phys. A 79 (2004) 1895
Highly symmetrically arranged ZnO nanowire arrays (see image) are produced by laser-interference lithography and a chemical vapor transport process. The nanowires show a narrow diameter distribution and uniform spacing. A liquid-phase-assisted vapor-solid mechanism is proposed for one-to-one synthesized ZnO-nanowire growth.