ABSTRACT
Recent interest in high-speed scanning probe microscopy for high-throughput applications including video-rate atomic force microscopy and probe-based nanofabrication has sparked attention on the development of high-bandwidth flexure-guided nanopositioning systems (nanopositioners). Such nanopositioners are designed to move samples with sub-nanometer resolution with positioning bandwidth in the kilohertz range. State-of-the-art designs incorporate uniquely designed flexure mechanisms driven by compact and stiff piezoelectric actuators. This paper surveys key advances in mechanical design and control of dynamic effects and nonlinearities, in the context of high-speed nanopositioning. Future challenges and research topics are also discussed.
ABSTRACT
A major disadvantage of scanning probe microscopy is the slow speed of image acquisition, typically less than one image per minute. This paper describes three techniques that can be used to increase the speed of a conventional scanning probe microscope by greater than one hundred times. This is achieved by the combination of high-speed vertical positioning, sinusoidal scanning, and high-speed image acquisition. These techniques are simple, low-cost, and can be applied to many conventional microscopes without significant modification. Experimental results demonstrate an increased scan rate from 1 to 200 Hz. This reduces the acquisition time for a 200 x 200 resolution image from 3 min to 1s.
ABSTRACT
Due to hysteresis exhibited by piezoelectric actuators, positioning stages in scanning probe microscopes require sensor-based closed-loop control. Although closed-loop control is effective at eliminating non-linearity at low scan speeds, the bandwidth compared to open loop is severely reduced. In addition, sensor noise significantly degrades achievable resolution in closed loop. In this work, charge drives are evaluated as a simple positioning alternative when feedback control cannot be applied or provides inadequate performance. These situations arise in high-speed imaging, where position sensor noise can be large or where no feedback sensors are present. Charge drives can reduce the error caused by hysteresis to less than 1% of the scan range. We review the design of charge drives and compare them to voltage amplifiers for driving lateral SPM scanners. The first experimental images using charge drive are presented.
