|A silver-gallium nanowire serves as an AFM probe; its mechanical oscillations can be reduced via laser cooling. Image: Quantum Optics Group, ANU
Researchers in the Quantum Optics Group of the Research School of Physics and Engineering, Australian National University (ANU; Canberra, Australia) are laser-cooling the probes of atomic-force microscopes (AFMs) to boost their sensitivity.1 The technique can cool a probe to 8K using feedback to allow the photo-induced force on the probe (which acts as a mechanical oscillator) to dampen the oscillator's motion and thus cool it.
One disadvantange is that the probe cannot be used while the laser is on, as the laser effect overwhelms the sensitive probe. So the laser has to be turned off and any measurements quickly made before the probe heats up within a few milliseconds. By making measurements over a number of cycles of heating and cooling, accurate AFM measurements can be made.
The technique boosts the sensitivity of the AFM by 20 times, resulting in a room-temperature force-measurement sensitivity of better than 2 x 10-16 N.
"The level of sensitivity achieved after cooling is accurate enough for us to sense the weight of a large virus," says Ping Koy Lam, leader of the Quantum Optics Group.
The force sensor used by the ANU team was a 200-nm-wide silver-gallium nanowire coated with gold.
OK, maybe laser not needed after all
"We now understand this cooling effect really well," says Ph.D. student Harry Slatyer. "With clever data processing we might be able to improve the sensitivity, and even eliminate the need for a cooling laser."
1. Mahdi Hosseini et al., Nature Communications (2014); doi: 10.1038/ncomms5663