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New NUANCE Staff Research: Thickness Resonance Acoustic Microscopy for Nanomechanical Sub-Surface Imaging

A research paper by Professor Vinayak Dravid and Dr. Gajendra Shekhawat, entitled "Thickness Resonance Acoustic Microscopy for Nanomechanical Sub-Surface Imaging," has been accepted for publication in ACS Nano. Co-authors of the paper are Dr. Oluwaseyi Balogun (Mechanical Engineering, Northwestern) and Arvind K. Srivastava of Systron Donner Inertial.

Abstract

A nondestructive scanning near field thickness resonance acoustic microscopy (SNTRAM), has been developed that provides high resolution mechanical depth sensitivity and sharp phase contrast of sub-surface features. In SNTRAM technology, we excited the sample at its thickness resonance at which sharp change in phase is observed and mapped with scanning probe microscopy stage in near field to provide nanometer scale nanomechanical contrast of sub-surface features/defects. We reported here the remarkable sub-subsurface phase contrast and sensitivity of SNTRAM by exciting the sample with a sinusoidal elastic wave at the frequency equal to the thickness resonance of the sample. This results in a large shift in phase component associated with the bulk longitudinal wave propagating through the sample thickness, thus suggesting the usefulness of this method for (a) generating better image contrast due to high S/N of the transmitted ultrasound wave to the other side of sample, and (b) sensitive detection of local variation in material properties at much better resolution due to sharp change in phase. We demonstrated that the sample excited at the thickness resonance has a more substantial phase contrast and depth sensitivity than that excited at off-resonance and related acoustic techniques. Sub-surface features down to 5-8 nm lateral resolution has been demonstrated using standard sample.

Image depicting the difference between AFM and Sample Resonance techniques

The full article can be found here.