Semiconducting and Piezoelectric Oxide Nanostructures Induced by Polar Surfaces

Abstract

Zinc oxide, an important semiconducting and piezoelectric material, has three key characteristics. First, it is a semiconductor, with a direct bandgap of 3.37 eV and a large excitation binding energy (60 meV), and exhibits near‐UV emission and transparent conductivity. Secondly, due to its non‐centrosymmetric symmetry, it is piezoelectric, which is a key phenomenon in building electro‐mechanical coupled sensors and transducers. Finally, ZnO is bio‐safe and bio‐compatible, and can be used for biomedical applications without coating. With these unique advantages, ZnO is one of the most important nanomaterials for integration with microsystems and biotechnology. Structurally, due to the three types of fastest growth directions—<0001>, <01$ \bar 1 $0>, and <2$ \bar 1 $$ \bar 1 $0>—as well as the ±(0001) polar surfaces, a diverse group of ZnO nanostructures have been grown in our laboratory. These include nanocombs, nanosaws, nanosprings, nanorings, nanobows, and nanopropellers. This article reviews our recent progress in the synthesis and characterization of polar‐surface‐induced ZnO nanostructures, their growth mechanisms, and possible applications as sensors, transducers, and resonators. It is suggested that ZnO could be the next most important nanomaterial after carbon nanotubes.

Optical Properties of ZnO/ZnS and ZnO/ZnTe Heterostructures for Photovoltaic Applications

“…In addition, more complicated structures such as nanobelts 7,8 , nanohelices 9 , and others [10][11][12] have been synthesized. Unfortunately, the ZnO band gap (3.4 eV) is too large for use in efficient photovoltaic devices.…”

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

“…The development and investigation of ZnO nanostructures for optoelectronic applications is extensive and well-documented, showcasing a variety of morphologies achievable across a wide range of deposition techniques [1][2][3][4][5][6][7][8][9] . Of particular interest for device applications is the growth of ZnO nanorod arrays (NRAs) from low temperature, aqueous deposition techniques [10] which, over the past decade, has seen morphological improvements in alignment and uniformity through the introduction of precursor ZnO seed layers [11] , pH control of the growth environment [12,13] , additive incorporation [14] , as well as manipulation of growth variables including duration and temperature [15][16][17][18] .…”

Synthesis, Characterization and Electrochemical Property of Polypyrrole Nanoparticles

“…The spectrum of polypyrrole nanoparticles shows two distinct bands at 381 and 572 nm. These two transitions corresponded to the transitions from valence bond to polarons and bipolarons of the oxidized form of polypyrrole nanoparticles 9 .…”