Georg Schitter

Publications of Georg Schitter

• Applied physics. High-speed atomic force microscopy.

  Authors: Paul K Hansma, Georg Schitter, Georg E Fantner, Craig Prater

  Science (New York, N.Y.). 11/2006; 314(5799):601-2.

• Sacrificial bonds and hidden length: unraveling molecular mesostructures in tough materials.

  Authors: Georg E Fantner, Emin Oroudjev, Georg Schitter, Laura S Golde, Philipp Thurner, Marquesa M Finch, Patricia Turner, Thomas Gutsmann, Daniel E Morse, Helen Hansma, Paul K Hansma

  Biophysical journal. 03/2006; 90(4):1411-8.

  Sacrificial bonds and hidden length in structural molecules and composites have been found to greatly increase the fracture toughness of biomaterials by providing a reversible, molecular-scaleSacrificial bonds and hidden length in structural molecules and composites have been found to greatly increase the fracture toughness of biomaterials by providing a reversible, molecular-scale energy-dissipation mechanism. This mechanism relies on the energy, of order 100 eV, needed to reduce entropy and increase enthalpy as molecular segments are stretched after being released by the breaking of weak bonds, called sacrificial bonds. This energy is relatively large compared to the energy needed to break the polymer backbone, of order a few eV. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby additionally providing a "self-healing" property to the material. Due to the nanoscopic nature of this mechanism, single molecule force spectroscopy using an atomic force microscope has been a useful tool to investigate this mechanism. Especially when investigating natural molecular constructs, force versus distance curves quickly become very complicated. In this work we propose various types of sacrificial bonds, their combination, and how they appear in single molecule force spectroscopy measurements. We find that by close analysis of the force spectroscopy curves, additional information can be obtained about the molecules and their bonds to the native constructs.

• Velocity dependent friction laws in contact mode atomic force microscopy.

  Authors: Robert W. Stark, Georg Schitter, Andreas Stemmer

  Ultramicroscopy. 09/2004; 100(3-4):309-17.

  Friction forces in the tip-sample contact govern the dynamics of contact mode atomic force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a fewFriction forces in the tip-sample contact govern the dynamics of contact mode atomic force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a few nanometers. In order to account for the large interaction area the dynamics of contact mode atomic force microscope (AFM) is investigated under the assumption of a multi-asperity contact interface between tip and sample. Thus, the kinetic friction force between tip and sample is the product of the real contact area between both solids and the interfacial shear strength. The velocity strengthening of the lateral force is modeled assuming a logarithmic relationship between shear-strength and velocity. Numerical simulations of the system dynamics with this empirical model show the existence of two different regimes in contact mode AFM: steady sliding and stick-slip where the tip undergoes periodically stiction and kinetic friction. The state of the system depends on the scan velocity as well as on the velocity dependence of the interfacial friction force between tip and sample. Already small viscous damping contributions in the tip-sample contact are sufficient to suppress stick-slip oscillations.

• Veloctity Dependent Friction Laws in Contact

  Authors: Robert W. Stark, Georg Schitter, Andreas Stemmer

  02/2004;

  Friction forces in the tip-sample contact govern the dynamics of contact mode atomic-force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a fewFriction forces in the tip-sample contact govern the dynamics of contact mode atomic-force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a few nanometers. In order to account for the large interaction area the dynamics of contact mode AFM is investigated under the assumption of a multi-asperity contact interface between tip and sample. Thus, the kinetic friction force between tip and sample is the product of the real contact area between both solids and the interfacial shear strength. The velocity strengthening of the lateral force is modeled assuming a logarithmic relationship between shear-strength and velocity. Numerical simulations of the system dynamics with this empirical model show the existence of two di#erent regimes in contact mode AFM: steady sliding and stick-slip where the tip undergoes periodically stiction and kinetic friction. The state of the system depends on the scan velocity as well as on the velocity dependence of the interfacial friction force between tip and sample. Already small viscous damping contributions in the tip sample contact are su#cient to suppress stick-slip oscillations.

• Components for high speed atomic force microscopy.

  Authors: Georg E Fantner, Georg Schitter, Johannes H Kindt, Tzvetan Ivanov, Katarina Ivanova, Rohan Patel, Niels Holten-Andersen, Jonathan Adams, Philipp J. Thurner, Ivo W Rangelow, Paul K Hansma

  Ultramicroscopy. 106(8-9):881-7.

  Many applications in materials science, life science and process control would benefit from atomic force microscopes (AFM) with higher scan speeds. To achieve this, the performance of many of the AFMMany applications in materials science, life science and process control would benefit from atomic force microscopes (AFM) with higher scan speeds. To achieve this, the performance of many of the AFM components has to be increased. In this work, we focus on the cantilever sensor, the scanning unit and the data acquisition. We manufactured 10 microm wide cantilevers which combine high resonance frequencies with low spring constants (160-360 kHz with spring constants of 1-5 pN/nm). For the scanning unit, we developed a new scanner principle, based on stack piezos, which allows the construction of a scanner with 15 microm scan range while retaining high resonance frequencies (>10 kHz). To drive the AFM at high scan speeds and record the height and error signal, we implemented a fast Data Acquisition (DAQ) system based on a commercial DAQ card and a LabView user interface capable of recording 30 frames per second at 150 x 150 pixels.

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

  Authors: Daniel Haefliger, Marc Muenchinger, Georg Schitter, Andreas Stemmer

  Sensors and Actuators A: Physical.

  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 minorWe 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.

• Design and input-shaping control of a novel scanner for high-speed atomic force microscopy

  Authors: Georg Schitter, Philipp J. Thurner, Paul K. Hansma

  Mechatronics.

  A novel design of a scanning unit for atomic force microscopy (AFM) is presented that enables scanning speeds three orders of magnitude faster than compared to conventional AFMs. The new scanner isA novel design of a scanning unit for atomic force microscopy (AFM) is presented that enables scanning speeds three orders of magnitude faster than compared to conventional AFMs. The new scanner is designed for high mechanical resonance frequencies, based on a new scanner design, which is optimized using finite element analysis. For high-speed scanning a new controller, based on input-shaping techniques, has been developed that reduces imaging artifacts due to the scanner’s dynamics. The implementation of the new AFM system offers imaging capabilities of several thousand lines per second with a scanning range of 13 μm in both scanning directions, and the freedom to choose the fast scan-axis in any arbitrary direction in the X–Y-plane.

• Hierarchical interconnections in the nano-composite material bone: Fibrillar cross-links resist fracture on several length scales

  Authors: Georg E. Fantner, Olexandr Rabinovych, Georg Schitter, Philipp Thurner, Johannes H. Kindt, Marquesa M. Finch, James C. Weaver, Laura S. Golde, Daniel E. Morse, Everett A. Lipman, Ivo W. Rangelow, Paul K. Hansma

  Composites Science and Technology.

  Bone is a complex and very important multi-constituent bio-composite. In this work, we focus on the arrangement of bone constituents from the nanoscopic to the microscopic scale, and investigate theBone is a complex and very important multi-constituent bio-composite. In this work, we focus on the arrangement of bone constituents from the nanoscopic to the microscopic scale, and investigate the influence of their arrangements on the fracture mechanisms of the whole composite. We find that bone, on the nanoscopic scale, consists of mineralized collagen fibrils held together by a non-fibrillar organic matrix, which results in a primary failure mode of delamination between mineralized fibrils. In turn, these mineralized fibrils form one of three types of filaments that span microcracks in fractured bone samples, possibly resisting the propagation of these cracks.

• The effect of NaF in vitro on the mechanical and material properties of trabecular and cortical bone

  Authors: Philipp J. Thurner, Blake Erickson, Patricia Turner, Ralf Jungmann, Jason Lelujian, Alexander Proctor, James C Weaver, Georg Schitter, Daniel E Morse, Paul K Hansma

  High doses of sodium fluoride in bones lead to severe softening, by weakening interfacial properties between the inorg. minerals and the org. components, while leaving mineralization unchanged. ThisHigh doses of sodium fluoride in bones lead to severe softening, by weakening interfacial properties between the inorg. minerals and the org. components, while leaving mineralization unchanged. This leads to redn. of microdamage and assocd. stress-whitening pointing to a change in failure mode. Accordingly, elastic modulus, failure stress, and indentation-distance increase are decreased, whereas failure strain is increased. [on SciFinder (R)]