During high-speed operation over a large area, all probe-based nanofabrication systems are confronted by the challenge of maintaining precision positioning of the probe with respect to the substrate. Large errors in probe-sample positioning will lead to defects in the fabricated pattern or device. There is also the risk of damage to the probe.

To tackle the problem, researchers based at Iowa State University, US, have developed a novel model-less inversion-based iterative control (MIIC) technique and applied the scheme to an atomic force microscope (AFM) set-up. The MIIC technique effectively eliminates adverse vibrational dynamics and nonlinear hysteresis of the piezoelectrical actuators and the cantilever probe, and the cross-axis dynamic coupling between the motions of the x, y and z axes.

To demonstrate the concept, the group programmed its nanofabrication system to mechanically scratch large patterns into a gold-coated silicon substrate at high speed.

As shown in the image above, without the use of the advanced control technique, large distortions appeared in (a) the large-size (~50 µm) pentagram pattern fabricated at high speed (~4.5 mm/s), which were substantially eliminated in (b) by using the MIIC technique. Large distortions also appeared in (c) when fabricating a dashed-line pentagram pattern (same size and same lateral speed), which requires a large up-down vertical motion of the probe. By applying the MIIC technique (d), the precision of the dashed-line pattern was dramatically improved, which highlights the efficacy of the control scheme for fabricating 3D nanostructures.

Probe-based processes have great potential as a low-cost, efficient approach for nanostructure and device fabrication. The control technique demonstrated by the researchers can be equally applied to other probe-based techniques, including "dip-pen" methods, laser-enhanced systems and thermal processes. The integration of advanced control techniques will bring these novel nanofabrication processes towards their practical implementation.

The researchers presented their work in Nanotechnology.