Resumen de Modifying Optical Properties of ZnO Films by Forming Zn1-xCoxO Solid Solutions via Spray Pyrolysis.
Anne K. Bentley, Gabriela C. Weaver, Cianan B. Russell, William L. Fornes, Kyoung-Shin Choi, Susan M. Shih
A simple experiment is designed for the general chemistry laboratory that can demonstrate the presence of an energy band gap in a semiconductor and its relationship to the material's composition. In this experiment, students prepare thin films of ZnO, a wide band-gap semiconductor (Eg = 3.2 eV), by spraying a zinc nitrate solution onto glass microscope slides heated by a hot plate. Addition of varying quantities of cobalt nitrate to the spray solution results in the formation of a series of Zn1-xCoxO solid solutions. Incorporation of Co2+ ions into the ZnO structure decreases its band-gap energy to the visible region. As a result Zn1-xCoxO solid solutions bear colors, and their compositions directly affect their colors. Owing to the thin-film morphology resulting from spray pyrolysis, the optical properties of ZnO and Zn1-xCoxO solid solutions can be easily characterized using UV�vis absorption spectroscopy. This experiment can provide an integrated understanding of solid-state materials by connecting the concepts of material composition, semiconductor band gap, observed color, and UV�vis absorption.
