AFM-IR IDs Chemicals at Nanometer Scale

Atomic force microscopy (AFM) has been used to measure and characterize materials at the nanometer scale for more than two decades, but a new AFM technique now can measure a material’s chemistry and chemical composition.

Researchers at the University of Illinois at Urbana-Champaign have measured the chemical properties of polymer structures as small as 15 nm — not generally possible using AFM — with a technique called atomic force microscope infrared spectroscopy (AFM-IR).

A graphic illustrating the atomic force microscope infrared spectroscopy of polymer nanostructures. The technique was developed by researchers at the University of Illinois at Urbana-Champaign. Images courtesy of the University of Illinois at Urbana-Champaign.

“AFM-IR is a new technique for measuring infrared absorption at the nanometer scale,” said William P. King, an Abel Bliss Professor in the Department of Mechanical Science and Engineering at the university. “The first AFM-based measurements could measure the size and shape of nanometer-scale structures. Over the years, researchers improved AFM to measure mechanical properties and electrical properties on the nanometer scale. However chemical measurements have lagged far behind, and closing this gap is a key motivation for our research.

“These infrared absorption properties provide information about chemical bonding in a material sample, and these infrared absorption properties can be used to identify the material. The polymer nanostructures are about an order of magnitude smaller than those measured previously.”

The chemical properties of these polymer nanostructures were measured using AFM-IR.

The investigators analyzed the AFM-IR dynamics using a wavelet transform, which organizes the AFM-IR signals that vary in both time and in frequency. By separating the time and frequency components, they improved the signal-to-noise within AFM-IR, measuring significantly smaller samples than previously possible.

The method is suitable for a variety of applications, including semiconductors, composite materials and medical diagnostics.

The study appeared in the Review of Scientific Instruments (doi: 10.1063/1.4793229).

For more information, visit: www.illinois.edu