It can be hard to appreciate just how small some things really are in the world of nanotechnology, where scientists routinely study structures that are only a few nanometers in size.

A nanometer is one billionth of a meter, or one millionth of a millimeter. On that scale, the thickness of a single human hair, typically about 50,000 nanometers, is enormous. Seeing things at this nanometer scale requires some very powerful microscopes.  
University of Richmond physics professor Matt Trawick has just invented a new way to make some of these microscopes even better.

Trawick’s work is described in an article accepted for publication in the leading international microscopy journal, Ultramicroscopy. He co-authored the article with two former research students, 2006 graduate Dan Katz and 2008 graduate Brian Salmons. The article details a new technique for studying structures using an atomic force microscope, or AFM.

The AFM works by physically scanning a very sharp tip (usually a single crystal of silicon) back and forth over a surface, much like mowing a lawn. The tip follows the contours of the surface, tracing out a map of its topography with nanometer scale precision.  

“It turns out that actually positioning a tip on a surface with that kind of precision is a really tough engineering problem,” Trawick said. “One of the biggest challenges is coping with the fact that all materials expand and contract slightly with small changes in temperature.”  

When the temperature inside a microscope drifts up or down by a hundredth of a degree, that expansion can cause the position of the microscope’s tip to shift tens of nanometers—a small change to most of us, but a big deal for scientists trying to image things only a few nanometers in size.  

“Imagine you’re painting a picture of the Mona Lisa, starting from the top of the canvas and working methodically down to the bottom,” Trawick said. “But suppose Mona Lisa herself doesn’t quite stay still, and is slowly inching to the left in her chair as the room gets a little warmer.  By the time you paint her waist, it’s no longer directly below where her head was.  As a result, your painting appears skewed, or distorted—as if somebody grabbed your canvas with both hands and stretched it like a rubber sheet.”

Trawick invented a way to correct these distorted images. His new technique involves rescanning, (or “repainting”) a small vertical sliver of the surface after each full image pass—only this time scanning from left to right, rather than from top to bottom. The full image and the rescanned partial image are then compared mathematically by a computer.  
Both images appear distorted, but because of their different scan directions, they are each distorted slightly differently. By analyzing this difference, Trawick is able to quantify the distortion and digitally reconstruct a single, undistorted image.

Mike Leopold, a professor of chemistry at Richmond, also uses atomic force microscopy for his research with nanoparticles. AFM is a widespread tool used in not only chemistry, but physics engineering, materials science and biology as well.  

“The problem of thermal drift in AFM imaging has been a pervasive issue for AFM users for nearly two decades and caused many researchers to spend enormous time and resources, usually complex and costly hardware or environmental controls, to combat thermal drift and legitimize the accuracy of their AFM images,” he said. “The work that Matt and his students have accomplished is significant in that it approaches the problem of thermal drift from a different perspective, using software manipulation to successfully minimize thermal drift distortion.”

Leopold believes that Trawick’s technique will be widely adopted, both by other researchers and by companies who make atomic force microscopes.  

Trawick is currently working to improve his technique, to correct for other related imaging artifacts. Nathan Follin, ’13, worked with him on the project this past summer.