ZnO nanoparticles obtained by hydrothermal method at low temperature

Abstract

ABSTRACT The structural properties and morphology of ZnO nanoparticles obtained by hydrothermal method were studied. ZnO samples were obtained by hydrothermal method, in soft synthesis conditions, temperature of solution about 70 o C, in presence of a bidentate ligand or a tensioactive agent. The resulted oxides morphologies were compared with the morphologies of ZnO samples obtained in absence of ligands or tensioactive agents. Samples present a hexagonal phase of ZnO with lattice parameters about a=0.32nm and c=0.5nm, values confirmed by XRD measurements. Morphological properties are studied using bright field images, measuring the nanopartic les diameter and nanopellets size. Keywords: ZnO, hydrothermal, TEM, XRD 1. INTRODUCTION In last years, there has been an explosive growth of nanoscience and nanotechnology, primarily because of the availability of new methods of synthesizi ng nanomaterials, as well as tools fo r characterization and manipulation. ZnO has attracted much recent attention motivated by potential application as an oxide electronic material and in optoelectronic and lighting applications. These applications are direct related on size and shape of obtained ZnO nanocrystals. There is a better understanding of size-dependent electrical, optical and magnetic properties of individual nanostructures of semiconductors, metals and other materials. An important field of research is the development of new synthetic processes to produce ultrafine pa rticles with nanocrystalline structure. Nanostructured materials are characterized by at least one dimension in the nanometer range. Nanostructured objects constitute a bridge between single molecules and bulk systems. The chemical and physical properties of nanomaterials can significantly differ from those of the atomic molecular and bulk materials of the same composition.[1] In recent years, more attentions have been paid to the nanoscaled semiconductors and quantum dots materials. Zinc oxide is a semiconductor with a wide band gap of 3.37eV, which has found many applications in various fields (photonics, optoelectronics, gas sensing, field emission, piezoe lectrics), including solar cells (in special in dye-sensitized solar cells - DSSC) and LED’s.[2] As for other semiconductors, the zinc oxide optical and electrical properties are dependent of particles size. Exceptional properties like UV lasing at room temperature result in great interest in the synthesis of ZnO nanostructures.[3] Up to now, a variety of ZnO nanostructures, such as nanowires [4, 5], nanorods [6], tetrapod nanorods [7], nanoribbons/belts [8], nanoneedle [9], nanosheet [10], porous plates [11] etc. have been reported. ZnO nanostructures have been synthesized by a number of methods, including thermal evaporation [12], thermal decomposition [13], metal organic vapor phase epitaxy (MOVPE) [14], laser ablation [15], hydrothermal synthesis [9], template-based synthesis [8], microwave irradiation [16, 17], electro-hydrodynamic technique [18], arc discharge [19] etc. The materials used in syntheses were zinc salts, metallic zinc and complex compounds. Zinc oxide can be produced in various phase such as: wurtzite, zincblende, rocksalt or cesium chloride. Also, ZnO e xhibit a large number of nanost ructures, some of these are nanopellets, nanorods, nanobelts, nanorings, nanocombs, nanostar, etc. These nanostructures formation was investigated relative to synthesis methods.