Structure of CdS Evaporated Films in Relation to Their Use as Ultrasonic Transducers

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Abstract
The crystallographic orientation of obliquely evaporated CdS films has been investigated by x‐ray and electron diffraction to provide the information required to control the fabrication of shear mode thin film ultrasonic transducers. Some degree of preferred orientation, with the c axis normal to the film plane, was observed in the initial layers of all of the films examined. The degree of preference was primarily dependent upon the structure of the substrate. As the films increased in thickness, on all except highly (111)‐oriented gold substrate, an oblique orientation developed with the c axis of the crystallites strongly inclined towards the incident vapor beam. On the highly (111)‐oriented gold‐film substrates, the CdS films remained c‐axis preferred. The effects of substrate structure and of the rate and angle of the deposition have been examined. Ultrasonic transducer data are presented and compared with the crystallographic structure of the transducer films showing the expected correlation between the c‐axis orientation and the ultrasonic mode generated.