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Atomic microscopes need atomic standards

If you want to be able to claim you can see things at atomic resolution, you better make sure your microscope is properly tuned up. That’s the message coming out of a special session at the Material Research Society in Boston on the future challenges for Scanning Probe Microscopy.

This technique involves moving a tiny tip over the surface of the object you want to study. But as researchers increasingly use the technology to make quantitative claims, the need for proper calibration standards has arrived, the meeting heard.

“Now is the time for the scanning probe community to develop standards,” said Robert Cook, from Nanomechanical Properties Group at the US National Institute of Standards and Technology (NIST).

Cook notes that scanning probe instruments are increasingly being used for absolute measurements, but for these to be valid such instruments need to be calibrated. Proper calibration could also facilitate easy comparison between experiments.

NIST manufacturers some ‘standard reference materials’ for calibration purposes, such as tiny cantilevers for force calibration.

“We’re really on the verge of being able to do really great things because we can measure things absolutely,” says Cook. He adds, “My belief is many in the community are on the verge of needing them now.”

The session chair, Dawn Bonnell of the University of Pennsylvania, says that the issue of quantification has come up at a number of recent meetings. It is especially important for those involved in manufacturing areas such as nano-materials, where it is vital to be able to prove what you have made and are selling.

“In some ways it’s holding the scientific community back,” she told Nature, “but certainly it’s holding the manufacturing side back.”

At a certain point though objects such as NIST’s cantilevers won’t be of much help, as the smaller the measurement being made the smaller the object used for calibration needs to be. When researchers are measuring things at less than one nanometre, Cook suggests they might have to start considering using real basic properties of standard objects, for example, the force used in stretching DNA strands or the pulling apart of single atoms on a chain of silver to calibrate machines.

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