ORNL researchers developed an innovative imaging method that possesses the
imaging capability of scanning near-field ultrasound holography and the chemical
specificity of reverse photoacoustic spectroscopy. This imaging method can achieve
chemical differentiation with nanometer resolution.
Atomic force microscopy is a well established technique for imaging surface features
of a nanometer or less. In conventional methods, a cantilever has a tip capable of
making a nanometer sized contact. However, any small variation in distance between
the probe and the sample surface can result in a large change in the contact force
between the probe’s tip and the sample.
To address this challenge, the invention includes two independent oscillators and is
able to distinguish the frequencies of the two acoustic waves applied to the probe. In
addition, electromagnetic energy is applied to the sample, causing a change in phase
of the second acoustic wave. The device can also be used for determining chemical
characteristics of a sample by applying different acoustic waves.
The invention allows for the physical/mechanical, and chemical, nanoscale features of various material samples to be measured. The invention provides nanoscale surface as well as subsurface information. With high resolution, the subsurface material such as embedded nanoparticles or other material inhomogeneities can be resolved with a resolution comparable to other existing atomic force microscopy-based approaches.
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