Dimensional ZnO Nanostructures Research Articles

Growth Behavior and Characteristics of One Dimensional ZnO Nanostructures by Metalorganic Chemical Vapor Deposition

The ZnO nanorods have been grown on silicon substrates by a metalorganic chemical vapor deposition (MOCVD) process with/without Au catalytic layer. The growth behavior of ZnO nanorods changed with the catalytic layer. The presence of Au catalyst complicated the growth direction of ZnO nanorods in the MOCVD methods. The ZnO nanorods had single crystalline atomic structure and pure compositions without impurities and strong and narrow excitonic emission. We investigated the growth behavior of the ZnO nanostructures which are leading candidate for optical applications.

Tuning the aspect ratio of hydrothermally grown ZnO by choice of precursor

Variable aspect ratio (length/diameter), one dimensional ZnO nanostructures are synthesized by reacting Zn 2+ precursor derived from Zn·Ac 2, Zn·Cl 2 and Zn·(NO 3) 2 under hydrothermal treatment. The growth mechanism illustrating the formation of self-assembling from individual ZnO nanoparticles to rod-like form is explained briefly. XRD reveals that the ZnO obtained from various zinc salts are pure, wurtzite structure, with crystalline hexagonal phase. The qualitative analysis of ZnO formation and morphology of ZnO nanoparticles are estimated from FESEM and TEM micrographs. Strong UV absorption corresponding to the recombination of electron–hole pair is observed and the blue shift absorption obeys the size confinement effect. The extent of absorption relatively varies when the morphology is changed from nano-bundles to individual rod-like ZnO. When electrons are excited at wavelength of 240 nm, a strong near band edge (NBE) emission and surface defects emission are observed in the PL spectra. The broader emission situated in the blue-green region of the visible spectrum, originating from surface oxygen defects, is not observed in ZnO derived from Zn·Ac 2.

Synthesis of ZnO Nanoneedles on Flexible Polymer Substrates at Room Temperature by Activated Reactive Evaporation

Abstract: ZnO nanoneedles were successfully deposited on flexible polymer substrates at room temperature by activated reactive evapo-ration. Neither a catalyst nor a template was employed in this synthesis. These synthesized needles measured 500 - 600 nm in length and its diameter varied from 30 - 15 nm from the base to the tip. The single-crystalline nature of the nanoneedle was observed by high-resolution transmission electron microscopy studies. The Raman studies on these nanoneedles had shown that they are oxygen deficient in nature. A possible growth mechanism has been proposed here, in which the nanoneedles nucleate and grow in the gas phase by vapor-solid mechanism. Keywords: Nanoneedle, Activated reactive evaporation, ZnO, Gas phase, Nanostructures on flexible substrates. 1. INTRODUCTION Low dimensional nanostructured materials have attracted great interest because of their unique physical and chemical properties. ZnO, an important semiconductor of the II-VI group has many in-teresting properties such as wide band gap (3.37eV), large exciton binding energy, good piezoelectric characteristics, chemical stabil-ity and bio-compatibility [1, 2]. Nanostructures of ZnO have been widely investigated for potential application in UV laser, light emit-ting diode, sensors and solar cells [3-6]. Several techniques such as thermal evaporation, pulsed laser deposition (PLD), chemical vapor deposition (CVD) and molecular beam epitaxy (MBE) are widely employed to synthesis one dimensional (1D) ZnO nanostructures [7-11]. In general, all the above mentioned methods require high processing temperature and crystalline substrates for nanostructure growth. Hence they cannot be employed for synthesizing nanostruc-tures on flexible polymer substrates. Recently there has been increasing interest on the growth of 1D nanostructures over non-wafer based substrates such as flexible polymer and glass using inexpensive processing techniques. The assembly of semiconductor nanostructures on flexible polymer substrates is important and might provide merits in terms of per-formance, flexibility, shock resistance, reliability and cost over the analogous devices built on Si wafers. Combining the high flexibil-ity of the polymer substrates with the structural and electrical prop-erties of the semiconductor nanostructures may open up new areas of application such as flexible electronic devices and solar cells. Currently ZnO nanostructures on flexible polymer substrates for different applications are synthesized by wet-chemical techniques using different precursors and expensive top to bottom pattern transfer methods [4, 12-15]. To the best of our knowledge there is no report on the synthesis of 1D ZnO nanostructures on polymer substrates using an evaporation process. ZnO nanoneedles have been synthesized on highly flexible polymer and indium tin oxide (ITO) coated glass substrates at room temperature by activated reactive evaporation (ARE). The advan-tage of this process over the conventional process is that it does not require a catalyst or high substrate temperatures for the growth of the nanostructures [7, 8]. In this process nanostructures were syn-thesized at room temperature, independent of the substrate and relatively at high vacuum (~10

Dye-sensitized solar cells using ZnO tetrapods

One dimensional (1D) ZnO nanostructures are of interest for applications in dye-sensitized solar cells (DSSCs) since they exhibit significantly improved electron transport compared to that in porous films. However, 1D nanostructures also have a significantly lower surface area than the porous films. Thus, the achieved solar cell efficiencies are typically much lower in spite of the improved charge transport. In this work, we investigated DSSCs based on ZnO tetrapods to achieve an increased surface area compared to that of 1D nanostructures. The cell performance as a function of the tetrapod film thickness and the dye used was studied. To further increase the surface area, mixed morphologies (tetrapods with nanoparticles) were also investigated. Under optimal conditions, an AM 1.5 power conversion efficiency of ∼1.2% was achieved.

Simple fabrication of zinc oxide nanostructures

A simple and low cost methodology for fabricating one and two dimensional periodic ZnO nanostructures utilizing surface relief patterns on azopolymer films as templates is demonstrated.