Growth and structural characterization of multifunctional Oxide-Based Nanostructures

Abstract

Semiconducting oxide-based materials are fundamental to the development of smart and functional materials, devices, and systems. In general, the oxide-based materials have two unique structural features: mixed cation valences and an adjustable oxygen deficiency, which are the bases for creating and tuning many novel materials’ properties, from electric, chemical, and optical to magnetic. The synthesis of functional oxide-based materials with a controlled structure and morphology are critical for scientific and technological applications. Among the various oxide-based materials, ZnO has been studied extensively owing to its wide direct bandgap of 3.37 eV, large exciton binding energy of 60 meV at room temperature, and high transparency in the visible region. In particular, low-dimensional ZnO nanostructures such as nanowires, nanobelts, nanorings, nanowalls, etc, have attracted a great deal of interest for development of advanced nano-scale photonic and electronic devices due to their unique optical and electrical properties compared to those of ZnO bulk and thin film materials. The nanowall structures are especially advantageous in chemical and photonic sensing devices because of its superior surface-to-volume ratio and easy device fabrication. Since the initial report on ZnO nanowalls by Ng et al., vertically arrayed nanowall structures have been employed for the development of gas sensor and light-emitting diode applications. Additionally, integration process for device fabrication is relatively simple for nanowall arrays compared to nanowire structures, due to their two-dimensional morphology. However, synthesis of nanowall structures has narrow growth window and low reproducibility, which have limited their use in realization of assembled devices for mass production. Therefore, it is vital to understand and control the growth evolution of nanowall structures and find a convenient and suitable method of fabricating them with high reproducibility. A detailed...