Focussing Nanoacoustic Waves Through AFM Tips
I.S. Sabee (TU Delft - Mechanical Engineering)
G.J. Verbiest – Mentor (TU Delft - Mechanical Engineering)
R.H. Guis – Mentor (TU Delft - Mechanical Engineering)
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Abstract
Imaging below sample-surfaces non-destructively at the nanometre scale is challenging. Overcoming this challenge will enable applications such as 3D imaging of computer chips or characterising adhesion between materials. A promising candidate is to combine Atomic Force Microscopy (AFM) with GHz photoacoustics (PASSAFM). AFM is capable of lateral resolutions in the nanometre range due to its tip-size, but cannot image three-dimensionally. Ultrasound propagates non-destructively through any material with a depth resolution proportional to the acoustic wavelength, but the lateral resolution is in the micrometre range for high-tech applications.
The AFM probe guides the acoustic waves, focussing the sound into the tip. The amount of focussing and acoustic transmission depends on the shape of the AFM probe, especially at the tip. This thesis investigates the influence of tip-diameter and geometry of nine different AFM probes. We observe nine discernable acoustic signals, following similar trends for frequencies between 40 GHz and 85 GHz. We show that the relation between tip-diameter and acoustic focussing follows a linear scaling trend.
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