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March 30th, 2009

NIST, University of Colorado discover way to stabilize AFM measurements

Published on March 30th, 2009 | By: pwray@ceramics.org
Credit: G.Kuebler/JILA/CU

Credit: G.Kuebler/JILA/CU

NIST and the University of Colorado, operating together as the JILA*, may have just made life a little simpler for those engaged in nano-oriented research by making it easier to use Atomic Force Microscopy.

AFM has become an essential tool in the past two decades because of its ability to build a nanoscale topographic image of a material using a laser and a tiny probe attached to a diving board-like device. Thus far, however, one of the significant downsides to AFM has been its sensitivity to outside “noise” including acoustic noise, vibration and temperature variations. The good news is that the JIAL team believes it has figured out a way to provide “a 100-fold improvement in the stability of the instrument’s measurements under ambient conditions.”

On a practical level, it isn’t surprising that a tool as sensitive as AFM – something that can measure atomic scale physical features and interactions (e.g., bonds) – is also sensitive to the macro conditions within a lab setting. One NIST scientist, Thomas Perkins, put the current situation this way: “At this scale, it’s like trying to hold a pen and draw on a sheet of paper while riding in a jeep.

Until now, this meant that researchers had to invest a lot of time and resources isolating the material and the AFM from outside interference via the use of ultralow temperatures, isolation tables, vacuums, etc. Even these isolation techniques are of no use if the material must be kept in a liquid, as is often the case with biomaterials.

According to a press release, the JILA solution uses a standard AFM probe, but adds two additional laser beams and a precisely marked substrate to sense and respond to the three-dimensional motion of both the test specimen and the probe. The extra beams create a reference system, and any non-material motion of the tip relative to the sample is corrected immediately by compensating for the shift in the substrate.

The method can control the probes position to 40 picometers over 100 seconds, and JILA says it has been able to keep long-term, room temperature drift at 5 picometers per minute, a level they say is a 100-fold improvement over previous ambient-condition AFM measurements.

“This is the same idea as active noise cancellation headphones, but applied to atomic force microscopy,” says Perkins.

An added benefit is that with this reduction in interference, AFM measurements can be performed slower, improving image resolutions by a factor of five.

(* The meaning of “JILA” gets a little confusing and is why I didn’t mention it earlier. It used to stand for Joint Institute for Laboratory Astrophysics, but the joint work between NIST and CU has grown way beyond astrophysics. The term JILA is still used in regard to the joint NIST/CU work, but doesn’t stand for anything anymore.)


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