The Evolution of Sol-Gel Films in the Environmental Scanning Electron Microscope
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for example, or of the processing conditions, on the quality of the films. Particular emphasis will be given to the advantages and disadvantages of the technique. EXPERIMENTAL Sol-gel films of lead titanate were prepared from 1 molar PbTi(OR) 6 solutions with4 R = CH 2 CH 2 OCH3 (methoxyethoxide). Details of the method are as given in Budd and Payne . The hydrolyzed solutions were aged overnight and spun coated onto cleaned silicon substrates at 2000 rpm for 60 seconds. The substrates were dried on a 200'C hotplate for 60 seconds between coatings. Most of the films examined were composed of 4 successive spin coatings. The films were aged at room temperature for several days prior to being examined in the environmental scanning electron microscope. The Electroscan E3 ESEM was used for the heating study of the sol-gel films. The heating stage has a range from room temperature to -1000 0 C. Cleaved fragments of the substrates (with air-dried sol-gel films) were placed in an alumina crucible in the hot stage. For temperatures of a few hundred degrees the heat shield was not installed to give the maximum field of view on the specimen. The actual temperature of the sol-gel film may have been slightly overestimated under these conditions. For higher temperature experiments the heat shield was installed to achieve the highest temperatures. The films were imaged at 20 kV, which was found to give an acceptable compromise between surface sensitivity and spatial resolution, in an atmosphere of - 4 torr water vapor. Drying experiments were attempted using a Peltier-cooled stage to minimize evaporation of the solvents from the sol. However the initial pump-down of the specimen chamber appears to be may be obtained from in situ too hostile a change for the sol to survive. More informative results deposition experiments, such as those described by Chiu et. al. 5 RESULTS The initial experiments were performed on relatively thick films prepared by depositing a drop o1 the sol on the substrate in the hot stage, and "vacuum-drying" it in the microscope. Undej these circumstances the films were heavily cracked, and macroscopic features such as cracl growth and the shrinkage of delaminated portions of the film were readily followed in the
Room Temperatu61reC
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Region of cracked and partly delaminated lead titanate film. The motion of tl. Figure 1. isolated island of film (A) and the width of the peninsula to the right was recorded as t1 temperature was raised from room temperature to 610TC.
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a ) Initial surface of aged PT sol-gel film, b) and c) same area as a) after Figure 2. increasing doses of electron beam bombardment. d) same area after heating to 1000°C. Note the mottled appearance of the film, and the presence of small dark pores. showing the gross change in morphology of the microscope. Figure 1 shows a pair of images film between room temperature and -600 0C. The gap between the bulk film and the separated fragment A has grown from 4.3 at room temperature to 5.7 gm at 80'C and 9.3 gm at
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