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  Home > JCE Print > Journal of Chemical Education > Issues > 2007  > July  >
In the Laboratory
Modifying Optical Properties of ZnO Films by Forming Zn1-xCoxO Solid Solutions via Spray Pyrolysis
Anne K. Bentley, Gabriela C. Weaver, Cianán B. Russell, William L. Fornes, and Kyoung-Shin Choi
Department of Chemistry, Purdue University, West Lafayette, IN 47907

Susan M. Shih
Department of Chemistry, College of DuPage, Glen Ellyn, IL 60137

Cover
July 2007
Vol. 84 No. 7
p. 1183
Abstract
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.
Supplement
Handouts for the students, notes for the instructor, and additional information about supplies and tips about spray technique are available.
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Contents
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More Information
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Citation
Bentley, Anne K.; Weaver, Gabriela C.; Russell, Cianán B.; Fornes, William L.; Choi, Kyoung-Shin; Shih, Susan M. J. Chem. Educ. 2007, 84, 1183.
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Keywords
First-Year Undergraduate / General; Hands-On Learning / Manipulatives; Inorganic Chemistry; Laboratory Instruction; Materials Science; Semiconductors; Solid State Chemistry; UV-Vis Spectroscopy
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History
Created:
Last Updated:
5/29/2007
6/7/2007
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