A method to improve the detection ability of nanoscale chemical imaging using atomic force microscopy has been engineered at the University of Illinois. The noise and other measurement artifacts associated with microscope use are reduced, increasing the precision and range of nanostructured materials that can be studied.
To enable assessment of a material’s surface molecular composition, researchers previously combined atomic force microscopy and infrared (IR) spectroscopy. The microscope uses a cantilever, which is a beam connected to a support at one end and a sharp tip at the other, to measure subtle movements of the sample introduced by shining an IR laser. Light absorption causes the sample to expand and deflect the cantilever, generating an IR signal.
Cantilever deflection is susceptible to noise which in turn undermines measurement accuracy. A more precise means of generating data was afforded with a closed-loop piezo controller design for responsivity-corrected atomic force microscopy-IR imaging. The piezo device serves to maintain zero deflection, and instead of moving the cantilever the movement of the piezo crystal is used to record the IR signal. Deflection and noise are controlled by applying voltage to the piezo component, allowing researchers to more accurately document IR absorption by the target material.
The method was demonstrated to map IR absorption by nanoscale-thick acrylic films on glass and silicon without the need for sample preparation on gold or polymer-coated substrates. Compatible with existing instrumentation, the method described in Nature Communications is expected to improve the quality of nanoscale chemical measurements.