Electrochemical Deposition Mechanism for ZnO Nanorods: Diffusion Coefficient and Growth Models

Abstract

Fabrication of nanostructured ZnO thin films is a critical process for many applications based on semiconductor devices. So on understanding of the electrochemical deposition mechanism is also fundamental for knowing the optimal conditions on growth of ZnO nanorods by electrodeposition. In this paper the electrochemical mechanism for ZnO nanorods formation is studied. Results are based on the evolution of the diffusion coefficient using the Cotrell equation, and different growth models proposed by Scharifcker and Hills for nucleation and growth. A broad range of high-technology applications, ranging from surface acoustic wave filters, photonic crystals, light emitting diodes, photodetectors, photodiodes, optical modulator waveguides, varistors, and gas sensor to solar cells, are based on ZnO nanostructures, due to its wide bandgap, excellent chemical and thermal stability, and its specific electrical and optoelectronic property of being a II-VI semiconductor with a large exciton binding energy. In particular, the electrodeposition technique has advantages over other processes due to its simplicity, low equipment cost and the possibility of obtaining large area thin films. 5 Also electrodeposition is an efficient and reliable technique for preparing ZnO nanocrystallites, nanowires and nanofibers.There have been many reports on the electrodeposition of ZnO using aqueous 6-8 and non aqueous routes. 9 Most of the reported work on electrodeposition was done using solutions based on ZnCl 2 and Zn(NO) 3 , in aqueous solution. Though the temperature required for the synthesis is important, the same as ion concentration, the morphology of the ZnO grown depends really on nucleation leading from unoriented polycrystalline films, 10, 11 to nanorods 6 and sheets. 9 A key issue is the relation of electrochemical variables on nucleation for controlling the morphology of these films. 12The aim of this study is to determine the electrochemical growth mechanism for ZnO nanorods in a ZnCl 2 5 · 10 −3 M, KCl 0.1M solution, at different temperatures. As shown by Pauporté and Lincot 12 the electrochemical reactions that compete in the nucleation stage are:This paper analyzes the kinetic control for both reactions at different temperatures and proposes a nucleation model mechanism for ZnO nanostructures. Through the presented models a better control of electrodeposited ZnO morphology can be attained. ExperimentalSamples were prepared from ITO sputtered glass (resistivity at room temperature 10 ( /cm 2 ). The substrates were cleaned using ultrasonic agitation in a mixture of distilled water with liquid neutral soap during 10 minutes, rinsing in distilled water for 10 minutes, and finally immersion in isopropanol for 10 minutes prior to drying in nitrogen current. * Electrochemical Society Student Member. z E-mail: mareto@upvnet.upv.esFor the experiment a solution containing the following electrolytes was used: 0,1 M KCl Rectapur purity > 99%), ZnCl2 5 · 10 −3 M (Panreac purity > 98%), and continuous oxygenation by a bubbling flow of 0...

Nucleant layer effect on nanocolumnar ZnO films grown by electrodeposition

“…ZnO thin films have been prepared by a wide variety of techniques such as pulsed laser deposition [1,2], sputtering [3,4], and electrodeposition with or without templates [5-8]. In particular, the electrodeposition technique has advantages over other processes due to its simplicity, low equipment cost, and the possibility of obtaining large-area thin films.…”

Modelo de nucleación y crecimiento de capas nanoestructuradas de óxido de zinc sobre sustratos cerámicos con aplicación a materiales fotovoltaicos híbridos

“…A special emphasis on the electrochemical processes involved is the core for the thesis as controlling means for the optimal properties. Relevant scientific results have been published [91,92,110]. 4.…”

“…Del estudio de nucleación y crecimiento puede extraerse que la reacción de formación de hidróxidos sigue un comportamiento de nucleación progresivo, es decir, los núcleos se generan y crecen a lo largo del tiempo en el que se está aplicando la diferencia de potencial que garantiza la formación de hidróxidos. Sin embargo , la reacción de formación de ZnO sigue un comportamiento de nucleación instantánea, esto es, los núcleos se generan una vez se alcanza el máximo de corriente en el transitorio de la misma, una vez comienza el descenso en la densidad de corriente tiene lugar el proceso de crecimiento del material sobre los núcleos generados [91].…”

“…Concluyendo que en el mecanismo electroquímico del ZnO, se da en primer lugar la formación de núcleos Zn(OH) 2 y a partir de estos tiene lugar el crecimiento del material ZnO, haciéndolo este de forma nanoestructurada. Dicha conclusión, la hemos extraído de las investigaciones realizadas durante la ejecución del presente trabajo y que ha sido publicada en una revista internacional [91], donde se muestra el estudio realizado de los modelos de nucleación y crecimiento, , y que en el presente trabajo se ha expuesto de manera más extensa, a partir del cálculo del coeficiente de difusión a partir de las correlaciones de Cottrell.…”

“…El estudio realizado de esta capa ha sido el más exhaustivo, obteniendo los modelos de nucleación y crecimiento del mismo, así como el desarrollo de una novedosa técnica de electrodeposición que permite la obtención de nanoestruturas de ZnO con las propiedades óptimas para su funcionalidad. Los avances científicos obtenidos en esta capa han sido publicados en revistas internacionales [91,92,110]. 4.…”