Showing papers by "Georg Schitter published in 2003"

Tuning the interaction forces in tapping mode atomic force microscopy

Abstract: Nanotechnology Group, Swiss Federal Institute of Technology, ETH Center/CLA, CH-8092 Zurich, Switzerland~Received 21 March 2003; published 7 August 2003!The driving frequency is a key parameter to determine the tip-sample interaction forces in tapping modeatomic force microscopy ~AFM!. By adjusting the driving frequency slightly above the resonance frequencystable imaging with net attractive forces can be achieved almost independently from the quality factor of thecantilever. A reduction of the driving frequency below the resonance leads to a repulsive imaging regime withminimized repulsive forces. Numerical simulations as well as experiments show the influence on the interac-tion forces between tip and sample. Appropriate adjustment of the excitation frequency in dynamic AFMallows one to adjust the interaction forces over the entire range from net attractive to net repulsive.DOI: 10.1103/PhysRevB.68.085401 PACS number~s!: 68.37.Ps, 07.79.Lh, 07.05.TpI. INTRODUCTION

Robust 2 DOF-control of a piezoelectric tube scanner for high speed atomic force microscopy

Abstract: Utilizing modern model-based control methods improves the performance of an atomic force microscope (AFM) substantially when compared to the state of the art commercial realizations. The design and implementation of a two-degree-of-freedom (2 DOF) controller on a commercial AFM system is presented enabling topography measurements on the nano-scale at higher scan rates with reduced measurement error. The closed-loop operation of the AFM system is performed by an H/sub /spl infin//-controller, while the scanner is simultaneously tracked to the last scan line by a model-based feedforward controller. Experimental results obtained at 15 Hz line-scan rate exhibit a maximum control error reduced by a factor of about 6 in comparison with the commercial system.

An integrated piezo-acoustic shear-force distance sensor with nanometer resolution for a micropipette tool

Abstract: We present an easy-to-use, piezo-acoustic shear-force detection system for tip-sample distance control of a micropipette. The setup provides free workspace around the pipette tip, requires only minor maintenance effort, proves to be robust and yields high reproducible performance. The micropipette is fixed in an aluminum block between two piezo-electric elements. One of the piezos excites the pipette at the mechanical resonance of its tapered tip while the other piezo is used for detection of the vibration. Upon approach of the pipette towards a sample surface the tip oscillation is damped due to shear-force interaction. The damping depends on the distance between tip and sample. Control of the tip-sample separation is accomplished by measuring the amplitude of the attenuated tip oscillation with the piezo detector. Tracking of a sample surface in closed-loop operation is demonstrated. A topographical resolution of about 1 nm is achieved with vibration amplitude of less than 40 nm. This micropipette setup may find application in automated handling of micrometer-sized particles and mirco- and nano-structuring of surfaces.

Tuning the Tip‐Sample Forces in Dynamic Atomic Force Microscopy

Abstract: The excitation frequency of the cantilever is a key parameter in tapping mode atomic force microscopy (AFM) that determines the tip‐sample forces. If the driving frequency is adjusted to values slightly above the resonance frequency stable imaging with net attractive forces can be achieved without manipulation of the quality factor of the cantilever resonance. A reduction of the driving frequency below the resonance leads to a repulsive imaging regime with minimized repulsive forces. These phenomena are studied by numerical simulations that show the variations of the interaction forces between tip and sample due to variations of the driving frequency. The interaction forces can be tuned over the entire range from net attractive to net repulsive by adjustment of the excitation frequency.