AFM 개선하기

Atomic force microscopy is used to scan the surfaces of materials to generate an image of their height but the technique cannot easily identify the molecular composition. Researchers have previously developed a combination of AFM and infrared spectroscopy called AFM-IR. The AFM-IR microscope uses a cantilever, which is a beam that is 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. The absorption of light by the sample causes it to expand and deflect the cantilever, generating an IR signal.

"Although the technique is widely used, there is a limit to its performance," said Rohit Bhargava, a Founder Professor of Engineering and the director of the Cancer Center at the University of Illinois at Urbana-Champaign. "The problem is that there were unknown sources of noise that limited the quality of the data."

"The cantilever deflection is susceptible to noise which becomes worse as the deflection increases,"

"The cantilever deflection is susceptible to noise which becomes worse as the deflection increases," said Seth Kenkel, a graduate student in the Chemical Imaging and Structures Laboratory, which is led by Bhargava. "Instead of detecting cantilever deflection, we used a piezo component as a stage to maintain zero deflection. By applying a voltage to the piezo material, we can maintain small deflection with low noise while recording the same chemical information which is now encoded in the piezo voltage."

Instead of moving the cantilever, the researchers use the movement of the piezo crystal to record the IR signal. "This is the first time anyone has controlled a piezo actuator to detect the signal. Other researchers work around challenges such as noise by using more complex detection systems that don't address the underlying problems associated with AFM-IR," Kenkel said.

"People have only been able to use this technique to measure samples that have a strong signal because of the noise problem,"

 

reference

"Closed-Loop Atomic Force Microscopy-Infrared Spectroscopic Imaging for Nanoscale Molecular Characterization" Nature Communications (2020). DOI: 10.1038/s41467-020-17043-5