Lab talk
Apr 20, 2012
Lissajous scan trajectories speed up scanning probe microscopy
Non-raster scan trajectories not only have the potential to significantly speed up the imaging process in scanning probe microscopy (SPM), but also offer advantages over conventional raster scanning. Scientists at IBM Research – Zurich, in collaboration with ETH Zurich have introduced a new non-raster scan trajectory for high-speed SPM in which the scanner traces a so-called Lissajous curve. Although Lissajous curves only require two single-tone actuation frequencies, the resulting trajectory covers a rectangular image area in a high-resolution grid-like pattern. Furthermore, owing to their unique multi-resolution property, Lissajous scan trajectories provide a preview of the entire image area in fractions of the overall scan time, with a spatial resolution that continuously increases until the complete image has been obtained.
Scan trajectories based on Lissajous curves have been studied previously in the field of medical imaging, such as in MRI devices. The key advantage of Lissajous scan trajectories is that they can be enabled using extremely narrow-band actuation signals, which do not excite any unwanted dynamics of the mechanical scanning device.
In a high-speed SPM, a pure single-tone frequency is used to actuate the SPM scanner in each of the two orthogonal in-plane axes. Owing to the interference between the two actuation frequencies, the scanner traces an elegant and smooth grid-like pattern. Also, with their narrow-band frequency spectrum, Lissajous trajectories can benefit from tailored scanner designs and control architectures with improved noise resiliency.
Multi-resolution effect
The curves possess a unique multi-resolution property (see image); they reveal the image area with a resolution that increases uniformly in time and space. This renders the Lissajous scan trajectories particularly attractive for modern high-speed interactive SPM applications.
Full details can be found in the journal Nanotechnology.
About the author
Tomas Tuma is with IBM Research – Zurich, where he works on novel concepts for high-speed positioning on the nanometer scale. He is also affiliated with the Automatic Control Laboratory, of the Swiss Federal Institute of Technology (ETH Zurich), where he works towards his PhD degree in control engineering.
