Showing papers by "Georg Schitter published in 2007"

Design and Modeling of a High-Speed AFM-Scanner

Abstract: A new mechanical scanner design for a high-speed atomic force microscope (AFM) is presented and discussed in terms of modeling and control. The positioning range of this scanner is 13 mum in the X- and Y-directions and 4.3 mum in the vertical direction. The lowest resonance frequency of this scanner is above 22 kHz. This paper is focused on the vertical direction of the scanner, being the crucial axis of motion with the highest precision and bandwidth requirements for gentle imaging with the AFM. A second- and a fourth-order mathematical model of the scanner are derived that allow new insights into important design parameters. Proportional-integral (Pl)-feedback control of the high-speed scanner is discussed and the performance of the new AFM is demonstrated by imaging a calibration grating and a biological sample at 8 frames/s.

A Tutorial on the Mechanisms, Dynamics, and Control of Atomic Force Microscopes

Abstract: The atomic force microscope (AFM) is one of the most versatile tools in nanotechnology. For control engineers this instrument is particularly interesting, since its ability to image the surface of a sample is entirely dependent upon the use of a feedback loop. This paper will present a tutorial on the control of AFMs. We take the reader on a walk around the control loop and discuss each of the individual technology components. The major imaging modes are described from a controls perspective and recent advances geared at increasing the performance of these microscopes are highlighted.

In situ observation of fluoride-ion-induced hydroxyapatite-collagen detachment on bone fracture surfaces by atomic force microscopy

Abstract: The topography of freshly fractured bovine and human bone surfaces was determined by the use of atomic force microscopy (AFM). Fracture surfaces from both kinds of samples exhibited complex landscapes formed by hydroxyapatite mineral platelets with lateral dimensions ranging from ~90 nm × 60 nm to ~20 nm × 20 nm. Novel AFM techniques were used to study these fracture surfaces during various chemical treatments. Significant topographical changes were observed following exposure to aqueous solutions of ethylenediaminetetraacetic acid (EDTA) or highly concentrated sodium fluoride (NaF). Both treatments resulted in the apparent loss of the hydroxyapatite mineral platelets on a timescale of a few seconds. Collagen fibrils situated beneath the overlying mineral platelets were clearly exposed and could be resolved with high spatial resolution in the acquired AFM images. Time-dependent mass loss experiments revealed that the applied agents (NaF or EDTA) had very different resulting effects. Despite the fact that the two treatments exhibited nearly identical results following examination by AFM, bulk bone samples treated with EDTA exhibited a ~70% mass loss after 72 h, whereas for the NaF-treated samples, the mass loss was only of the order of ~10%. These results support those obtained from previous mechanical testing experiments, suggesting that enhanced formation of superficial fluoroapatite dramatically weakens the protein–hydroxyapatite interfaces. Additionally, we discovered that treatment with aqueous solutions of NaF resulted in the effective extraction of noncollagenous proteins from bone powder.

Advanced Mechanical Design and Control Methods for Atomic Force Microscopy in Real-Time

Abstract: This article reviews mechanical design and control of atomic force microscopes (AFM) with a special emphasis on high-speed imaging. The mechanical design and the control system determine the achievable imaging speed of the AFM. To enable AFM imaging at video-rates, imaging speed - and thus system performance - has to be increased by at least two orders of magnitude relative to today's commercial AFMs. Methods and results presented in this paper demonstrate how this can be achieved.

Imaging of bone ultrastructure using atomic force microscopy

Abstract: Neuroscience Research Institute, Santa Barbara, CA 93106, USA Atomic force microscopy (AFM) is a superb tool for imaging of bone ultrastructure in a close to physiological state. AFM provides similar spatial resolution as transmission electron microscopy without the need of excessive sample dehydration and preparation. Due to this fact AFM imaging of bone ultrastructure can be performed in a functional manner, i.e. imaging can be combined with

Real-time microdamage and strain detection during micromechanical testing of single trabeculae

Abstract: For the assessment of local deformations, we recently combined mechanical testing of trabecular bone with high-speed photography. In a previous study on cuboids of human vertebral trabecular bone we found strained trabeculae to whiten, and scanning electron microscopy showed excessive microdamage in whitened zones. In the presented study we tested single trabeculae from bovine femur and tibia in a three-point-bending geometry. Whitening was detected in the form of an ellipsoid zone on the tension side on tested trabeculae. Upon crack formation the whitening fades and a whitened zone following the propagating crack tip can be seen In addition to whitening/microdamage assessment we use ink marks applied to the samples and a modified digital image correlation to obtain the local strains involved in whitening and formation. In the presented loading case the tensile strain along the long axis of the trabecula qualitatively correlates best with the whitening zones seen. Whitening and thus microdamage initiates around a local tensile strain of 3%, whereas crack initiation occurs at strains around 13%. Our results allow for the first time to correlate microdamage and local strains directly, which is direly needed for the development of realistic damage models used in finite element analyses.