Effect of ultrasonic field on grain refinement and stress relaxation of Be films by thermal evaporation

The beryllium (Be) films were prepared by vacuum evaporation with ultrasound on the glass slide substrates. The Be coating mainly consists of a-Be phase independent of ultrasonic vibration, while the texture and crystallinity are affected by ultrasonic vibration. With the increasing of ultrasonic power, the surface displays polygonal grains, but the grain size decreases from 130 nm to 60 nm. The cross section views show a transition from regular columnar structure to broken columnar structure owing to the ultrasonic mechanical agitation. When ultrasonic vibration is applied, the microstructure transforms from isolated islands to bicontinuous islands in the initial stage of film growth. In addition, the residual stress of Be films changes from a tensile stress to compressive stress under the effect of ultrasonic vibration, which is closely related to the transformation of microstructure.