TECHNOLOGY

Growth of ZnO Nanowires

Growth of ZnO Nanowires

Introduction

The Nano-structured ZnO materials are currently receieving great attention mainly due to their unique performance in the electronics, photonics and optics fields. The fusion of ZnO thin ?lms is considered as an appropriate material since 1960's because they serve as sensors, catalysts and transducers. In the past few decades, the nano-technology initiative that was led by the United States related to the study of one dimensional (1D) materials has become a leading edge in nano-technology and nano-science. Due to the reduction in size, mechanical, novel electrical, optical and chemical properties were introduced that were considered as the results of quantum con?nement and surface effects. The structures just like Nano-wire are the most effective system that can be used in studying the process of transportation that is found in one dimentional confined objects that can benefit not only for getting the idea about the basic phenomena in the lower dimensional systems (Archer, 2001, pp.844 ).

ZnO is an essential technological material that is used in vaious fields. Due to lack of centre of symmetry in wurtzite, which is joined to huge electro-mechanical combinations mostly results in strong pyroelectric and piezo-electric properties. Moreover, ZnO is a broad band-gap compounded semi-conductor, which is suitable for relatively short wave length opto-electronic applications. The high exciton binding energy (60 meV) in ZnO crystal can guarantee ef?cient excitonic emission at room temperature. The room temperature ultra-violet (UV) luminescence has been reported in thin ?lms and disordered nanoparticles. ZnO is clear in visible light and through doping it can be made highly conductive (Thorp, 1997, pp. 295-301). ZnO is an effective functional material that is holding an assorted group of growth morphologies such as nanowires, nanocombs, nanohelixes, nanobelts, and nanorings, nanocages.

The Surface and Crystal Structure of ZnO

ZnO is having hexagonal structure with lattice parameters a = 0.3296 and c = 0.520 65 nm. The number of alternative planes that are composed of tetra-hedrally coordinated Zn2+ and O2- ions along the c-axis is the simple description of ZnO's structure (Yablonovich, 1982, pp. 300-304). The tetrahedral harmonization in Zno results in non-central symmetric strucutres that are commonly known as pyroelectricity and piezoelectricity. Another most essential characteristic of ZnO is its polar surfaces, which is a basal plane that are composed of both positive and negatively charged ions. The negatively charged ions results in O-(0001) and the positively charged ions results in Zn-(0001) surfaces. These ions results in a spontaneous polarization and dipole moment that is placed along with the c-axis. Some promising materials have been suggested, such as films and coatings formulated with polysaccharides, proteins and lipids. Among them, starch films, as decent oxygen and carbon dioxide barriers, have been proven to possess some potential. Being biodegradable, the use of starch films can also help reduce the amount of plastic waste. In addition to starch films, antibacterial agents can be added to enhance the antibacterial effect.

Typical growth structures of ZnO

Due to attomic termination in the polar surfaces of ZnO a ...