Atomic Force Microscopy

Atomic force microscopy (AFM) is an example of the larger class of scanning probe microscopy (SPM) methods. Scanning probe techniques are powerful tools to characterize the local properties of a sample. For example, they can measure the topography, obtain electronic contrast, image magnetic features, or perform optical near-field spectroscopy with spatial resolutions from few nanometers to the atomic scale.

In AFM a sharp tip is used to probe the sample surface through the force interaction (primarily van der Waals forces, but also electrostatic and others) between the tip and sample. Beyond topography, by using specialized probes, and under electric or magnetic fields or optical illuminate AFM can readily be extended to measure more complex sample properties.

In contrast to scanning tunneling microscopy (STM), AFM is not limited to conductive samples but can be applied to any material, including molecular, oxide, or biomolecular surfaces.

Operating an AFM at cryogenic temperatures opens up access to otherwise inaccessible quantum phases and other states of matter. In addition, due to the reduced thermal motion, the cryogenic operation makes studying individual atoms, defects, or molecules easier for extended probing and manipulation under controlled conditions.

Below, performance characteristics recorded with an AFM operating in tapping mode while cooled by a CS204PF-DMX-20B closed-cycle cryocooler are shown.

The left shows the z-noise spectrum in the AFM tip-sample junction at different temperatures, demonstrating that the vibrations of the cryocooler have little effect on the AFM, contributing only negligible noise at very low temperatures.

The right shows the scanning noise performance at 20K, demonstrating RMS noise of 100-150pm, noise levels comparable with state of the art ambient condition tapping mode AFMs. The image shows raw data – with a Fourier filter the periodic ripples in the image can easily be removed in post-processing. However, due to their low amplitude, the ripples would not be observable against the sample topography in most samples, even samples only exhibiting monolayer step edges.

Customer References:

1. Sven Doenges and Markus Raschke, Department of Physics, University of Colorado, USA.

ARS Cryostats Ideal for AFM/SPM Applications