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Thin Film Characterization Using Resonant Ultrasound Spectroscopy

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With the development of mesoscopic and nanoscale electronic systems, there is currently great interest in the properties of the thin films which form the environment for the electrons. Diamond-like carbon films have also attracted attention for use as a protective coating against physical damage to delicate electronic components. As with bulk solids, important properties include elastic constants and acoustic attenuation, which may be related to the electron-lattice coupling and other effects. By using resonant ultrasound spectroscopy RUS and comparing the normal mode frequencies of a specimen before and after film deposition, the elements of the elastic tensor and attenuation coefficients of the thin film material may be determined. With the ability to perform RUS on samples as small as tens of micrograms, the possibility of examining the properties of thin films is feasible. In order to detect the properties of a thin film using RUS, it is necessary that the substrate supporting the film not dominate the measurement. Numerical estimates show that using substrates with sizes on the order of 500 x 400 x 100 microns enables the study of films as thin as 100 nm. Ideally, the study of a film should be made by measuring the resonance of the bare substrate, then depositing the film while the sample remains in the RUS apparatus, and then measuring the frequencies shifted by no change other than the film deposition Unfortunately, most film depositions require geometries or hostile conditions e.g., heated substrates which cannot be accommodated with the substrate still mounted in the RUS apparatus. Thus the substrate must be removed for the film deposition, and then replaced. In order to determine changes due to the film alone, it is necessary to demonstrate that simply removing and replacing the bare substrate produces no significant shifts in the measured frequencies.

Subject Categories:

  • Electrical and Electronic Equipment
  • Acoustics
  • Mechanics

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