Direct tip-position control using magnetic actuation for achieving fast scanning in tapping mode atomic force microscopy

Abstract

This article presents the development of a faster control loop for oscillation amplitude regulation in tapping mode operation of atomic force microscopy. Two techniques in relation to actuation and measurement are developed, that together significantly increase the bandwidth of the control loop. Firstly, magnetic actuation is employed to directly control the tip position of the cantilever to improve both the speed and the dynamics of the positioning system. Secondly, the signal path for oscillation amplitude regulation is separated from that for topography estimation in order to eliminate measurement delay that degrades the performance of the feedback loop. As a result, the phase-crossover frequency and gain margin of the control system are both increased, leading to a faster and more stable system. Two experiments are performed, one in air and the other in aqueous solution, to compare the developed control system with a commercial one and demonstrate the improvement. The results verify that the combination of the two techniques along with other existing methods eliminates all limitations associated with the instrument for the purpose of oscillation amplitude regulation, which is therewith dictated by the bandwidth of the cantilever.

High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes

“…At present, small self-actuation cantilevers cannot be manufactured. There have been several reports describing the direct actuation of cantilevers coated with or attached to ferromagnetic materials using a magnetic field [102,103]. Unfortunately, the magnetic coating stiffens the cantilevers and the attachment of magnetic materials lowers the cantilever resonant frequency.…”

Single molecule transcription profiling with AFM

“…Multipurpose AFMs are not constructed for high-speed scanning, since they have to fulfill conflicting requirements, such as large vertical motion range and various modes of operation. AFMs designed for highspeed scanning can image with molecular resolution at speeds up to ∼60-75 µm s −1 ; some emerging designs may be able to image at a cm s −1 rate [198][199][200][201][202][203][204][205][206][207][208][209][210][211][212][213][214][215][216]. High-speed AFMs have emerged over the past 5-7 years, and incorporate more compact scanner designs, smaller and piezo-actuated cantilevers, and improved feedback electronics.…”

Tip-sample distance control using photothermal actuation of a small cantilever for high-speed atomic force microscopy

“…One possible technique is the magnetic actuation of a cantilever. 13 However, when the cantilever is coated with a magnetic material, its resonant frequency reduces and it also becomes stiff, which is inappropriate for high-speed imaging on biological samples. Another possible technique is to actuate the cantilever by laser illumination onto the cantilever.…”