9 Microsensor Vapor Detectors Based on Coating Films of Phthalocyanine and Several of Its Metal Complexes 1
2
3
W. R. Barger, Hank Wohltjen, Arthur W. Snow, John Lint , and Neldon L. Jarvis
Downloaded by YORK UNIV on November 21, 2012 | http://pubs.acs.org Publication Date: May 29, 1986 | doi: 10.1021/bk-1986-0309.ch009
Chemistry Division, U.S. Naval Research Laboratory, Washington, DC 20375-5000
Experiments were conducted to assess relative sensitivities of phthalocyanine and its Fe, Co, Ni, Cu, and Pb complexes to vapors that cause changes in the resistance of thin films of these materials. When sulfur dioxide, benzene, air, ethanol, water, dimethyl methylphosphonate, and ammonia vapors were introduced into a stream of helium flowing over thin layers of phthalocyanines that were sublimed onto the surface of interdigital electrodes, the conductivities of the coatings increased or decreased depending on the type of phthalocyanine and on the type and concentration of vapor. Behavior of the sublimed coatings is briefly contrasted to the behavior of coatings of an organic derivative of copper phthalocyanine deposited by the Langmuir-Blodgett technique. A program of research directed at the eventual development of small, low-cost gas sensors that take advantage of modern microfabrication technology and advances in microcomputing capabilities is presently under way at our laboratory. Specifically, thin, chemically selective coating films are being placed on the surfaces of micro interdigital electrodes, and the usefulness of these devices as vapor detectors is being investigated. Figure 1 illustrates the size and typical design of such devices. A significant part of the effort is directed at fundamental studies of the materials to be used as coating films for the microsensors and at techniques to deposit these films on sensor surfaces. There are numerous coating techniques that might be used, such as casting from a volatile solvent, polymerization after contact with the surface, spin coating, sublimation, dipping, or deposition of one monomolecular layer at a time by the Langmuir-Blodgett technique. This paper describes studies in which phthalocyanine and metal complexes of phthalocyanine were sublimed onto the surfaces of 1
Current address: Microsensor Systems, Inc., P.O. Box 90, Fairfax, VA 22030 Current address: 5536 Fillmore Ave., Alexandria, VA 22311 Current address: Chemical Research and Development Center, U.S. Army, Aberdeen Proving Grounds, MD 21010 This chapter not subject to U.S. copyright. Published 1986, American Chemical Society
2 3
In Fundamentals and Applications of Chemical Sensors; Schuetzle, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by YORK UNIV on November 21, 2012 | http://pubs.acs.org Publication Date: May 29, 1986 | doi: 10.1021/bk-1986-0309.ch009
156
FUNDAMENTALS AND APPLICATIONS OF CHEMICAL SENSORS
i n t e r d i g i t a l electrodes i n order to measure the change i n the conductivity when the coating films were exposed to a series of test gases. We are currently developing vapor detectors based on organic derivatives of phthalocyanine and i t s metal complexes which can be deposited on electrode surfaces by the Langmuir-Blodgett (L-B) technique {1) . The L-B work w i l l be the subject of a future report, but some preliminary data i s included here for comparison of the general c h a r a c t e r i s t i c s of sublimed films and those of the L-B films. Phthalocyanines were chosen for these experiments because they are electronic semiconductors and because they are quite stable materials — an important consideration i n fabricating any p r a c t i c a l gas-detecting device. A considerable body of l i t e r a t u r e exists describing the physical and chemical properties of the phthalocyanines. A review of the work p r i o r to 1965 i s contained i n the chapter by A. B. P. Lever i n Volume 7 of Advances i n Inorganic Chemistry and Radiochemistry (2_) . E l e c t r i c a l properties of phthalocyanines have been receiving increased attention i n recent years. The photoconductivity of metal-free phthalocyanine has been studied i n d e t a i l (3 4) . E l e c t r i c a l properties of lead phthalocyanine have been studied extensively, especially by Japanese workers (5,6,7,8). They have also studied the a l t e r a t i o n of the conductivity of this material upon exposure to oxygen (9,10). The e f f e c t s of a series of adsorbed gases (O , CO, and NO) on the conductivity of iron phthalocyanine have been recently reported (11). A study of general e l e c t r i c a l properties of metal phthalocyanines of the f i r s t t r a n s i tion period with some assessments of the e f f e c t s of oxygen has been prepared by Beales et a l . (12). The use of thin Cu, Ni, and metalfree phthalocyanine films as the sensing material i n a gas sensor has been described by Sadaoka et a l . (JL3) . These workers studied the effect of N0 , NO, SO , O , N , and CO on the e l e c t r i c a l conductivity of the phthalocyanine films. A quantitative study of the e f f e c t s of a series of gases adsorbed on the surface of single crystals of Mn, Co, Ni, Cu, Zn, Pb, and metal-free phthalocyanines and of other semiconducting materials has been done by van Ewyk et a l . (14). Gases studied included N0 + NO, 0 , BF^, NH^, ethylene, CO, and other organic vapors. Recently, Jones and Bott studied gas sensors made by sublimation of several phthalocyanines onto i n t e r d i g i t a l platinum electrodes and reported on the influence of temperature on performance (15) . They also used a multisensor array that included PbPc as a sensor for N0 and NO^ i n hazardous atmospheres (16). The preparation of L-B films from metal-free phthalocyanine and from t e t r a t e r t - b u t y l phthalocyanine was reported by Baker et a l . i n 1983 (17). Since then the preparation of a series of tetracumylphenoxy derivatives suitable for preparing L-B coating films has been reported by Snow and Jarvis (1J3) , and the results of tests of gas sensors made with these coatings have been reported by Barger et a l . (19) . f
