Information on our research can be found in the copies of some of our presentations and in the literature list.
H.-U. Krotil and O. Marti, "Dynamic Friction measurements with the AFM on polymer surfaces,"in Tribology 2000 - Plus, Ed. , edited by W. Bartz (Technische Akademie, Esslingen, 1999)Vol. 12, pp. 1633-1638.
The combination of scanning friction force microscopy (SFFM) with lock-in techniques leads to dynamic SFFM (DSFFM) and provides great advantages in friction force studies with sub-pm resolution. We present measurements on thin adsorbed organic films, on polymers (polymer blend of 75% poly(allylaminehydrochloride), PAA and 25% Poly(diallyl-dimethylammoniumchloride), PDDAC) and on mica (as a reference) The amplitude and phase response as a function of the excitation amplitude can be explained on hard surfaces by a simple static and dynamic friction model. This model aliows us to further distinguish static friction forces and kinetic friction forces in a quantitative way. Further more we demonstrate the use of these spectra to determinate the correct modulation amplitude of the excitation to achieve the optimal frictional contrasts directly. Polymer data suggest that the viscoelastic shear flow under the AFM tip is responsible for the shape of the phase and amplitude spectrum. Lastly we demonstrate that DSFFM is a useful technique for surface characterization in situations where SFFM may not be adequate.
H.-U. Krotil, E. Weilandt, T. Stifter, O. Marti, and S. Hild, "Dynamic friction force measurement with the scanning force microscope," Surf. Interface Anal. 27, 341-347 (1999).
The combination of scanning friction force microscopy (SFFM) with lock-in techniques leads to dynamic scanning friction force microscopy (DSFFM) and provides great advantages in friction force studies. In the present work theoretical considerations of DSFFM are proposed to obtain quantitative friction force values from quantitative friction force values from qualitative friction force contrasts. Amplitude versus amplitude spectra and amplitude versus phase spectra are presented, obtained by measuring the amplitude and the phase signal of the (bending) scanning force contrasts by a simple method and second to determine quantitative static and kinetic friction forces. Two different polymer systems (polymer blend of 75% poly(allylaminehydrochloride) (PAA) and 25% poly(diallyldimethylammoniumchloride) (PDDAC) and a silicon surface with polyolefine contamination) served as sample systems.
O. Marti and S. Hild, "Temperature dependent surface properties of thin polystyrene films,"in Symposium on Microstructure and Microtribilogy of Polymer Surfaces, ACS Symposium Series (Boston Meeting 1998), Ed. , edited by K. J. Wahl and V. V. Tsukruk (1999).
O. Marti, H. Waschipky, M. Quintus, and S. Hild, "Scanning Probe Microscopy of Heterogeneous Polymers," Colloids and Surfaces A: Physicochemical and Engineering Aspects 154 (1-2), 65-73 (1999).
S. Hild and O. Marti, "Temperature dependent properties of thin polymer films,"ACS Polymer Preprints (1998), submitted.
S. Hild, A. Rosa, and O. Marti, "Deformation induced changes in surface properties of polymers investigated by scanning force microscopy,"in Scanning Probe Microscopy of Polymers, Ed. , edited by B. D. Ratner and V. V. Tsukruk (Oxford University Press, 1998)Vol. 694, pp. 110-128.
H. G. Kilian, W. Oppermann, B. Zink, and O. Marti, "Relaxation of polymer molecules in networks - the extended aggregate molecules," Computational and Theoretical Polymer Science 8 (1/2), 99-111 (1998).
I. Luzinov, S. Miko, V. Senkovsky, A. Voronov, S. Hild, O. Marti, and W. Wilke, "Synthesis and Behavior of the Polymer Covering on a Solid Surface. 3. Morphology and Mechanism of Formation of Grafted Polystyrene Layers on the Glass Surface," Macromolecules 31, 3945-3952 (1998).
O. Marti, "AFM Instrumentation and Tips,"in Handbook of Micro/Nanotribology, Ed. 2, edited by B. Bhushan (CRC Press, Boca Raton, 1998), pp. 81-144.
M. Abraham, W. Ehrfeld, M. Lacher, O. Marti, K. Mayr, W. Noell, P. Güthner, and J. Barenz, "Micromachined aperture probe tip for multifunctional scanning probe microscopy," presented at the Micro-Optical Technologies for Measurement, Sensors and Microsystems II and Optical Fiber Sensor Technologies and Applications, Munich, Germany, 18-20 June, 1997 (unpublished).
The paper presents a new concept of a micromachined integrated sensor for combined atomic force/near field optical microscopy. The sensor consists of a microfabricated cantilever with an integrated waveguide and a transparent near field aperture tip. The advantage compared to the fiber based near field tips is the high reproducibility of the aperture and the control of the tip-sample distance by the AFM-channel. The aperture tip is fabricated in a reliable batch process which has the potential for implementation in micromachining processes of scanning probe microscopy sensors and therefore leads to new types of multifunctional probes. For evaluation purposes, the tip was attached to an optical fiber by a microassembly setup and subsequently installed in a near-field scanning optical microscope. First measurements of topographical and optical near-field patterns demonstrate the proper performance of the hybrid probe.
O. Marti, S. Hild, J. Staud, A. Rosa, and B. Zink, "Nanomechanical interactions of scanning force microscope tips with polymer surfaces,"in Micro/Nanotribology and its applications, Ed. , edited by B. Bhushan (Kluwer Scientific Publishers, Dordrecht, 1997), Nato ASI Series Vol. E:330, pp. 455-465.
PMMA-surfaces have been investigated by scanning force microscopy as a function of temperature and imaging conditions. A stand-alone type scanning force microscope was employed together with a heating stage to investigate a model polymer substance, PMMA, as a function of temperature. Contact mode imaging induced wavy structures at higher temperatures, whereas intermittent imaging in the pulsed force mode showed negligible interactions.
T. Müller, M. Lohrmann, T. Kässer, O. Marti, J. Mlynek, and G. Krausch, "Frictional force between a sharp asperity and a surface step," Phys. Rev. Lett. 79, 5666-5669 (1997).
We report a detailed study of the frictional force between the tip of a scanning force microscope and a step on a crystalline surface. Experiments on surfaces of freshly cleaved graphite reveal different contributions to the lateral force at steps with distinctly different dependencies on normal load and scan direction. The different contributions can be attributed to topography-induced tip twisting and an increased dissipative force due to the Schwoebel barrier at the steps. The latter contribution is strongly reduced when near-surface step dislocations are imaged.
A. Rosa, H. G. Kilian, S. Hild, and O. Marti, "Pulsed Scanning Force Microscopy on the Surface of Linear Deformed, Filler Loaded Rubber - a New Method of Investigation," presented at the Intern. Rubber Conference 1997, 1997 (unpublished).
E. Weilandt, B. Zink, T. Stifter, and O. Marti, "Nanotribology in electrolytic environments,"in Micro/Nanotribology and its Applications, Ed. , edited by B. Bhushan (Kluwer Academic Publishers, Dordrecht, 1997), NATO ASI Series , pp. 283-297.
To get a fundamental knowledge about forces acting at surfaces it is necessary to perform measurements under conditions that are as defined as possible. Measurements in an electrochemical cell provide such a condition with the additional benefit that external parameters like the surface potential or the electrolyte composition can be varied. In this paper selected theoretical and practical aspects of measuring in an electrochemical cell are shown. The experimental setup for nanotribological experiments with an SFM is introduced. Some examples for adhesion and friction measurements are shown. Friction measurements on surface steps on a potential controlled HOPG surface show a potential dependence of friction at the steps as well as on the flat terraces. Force vs. distance curves performed on a conductive, potential controlled HOPG sample show characteristic changes with potential. From the potential dependent adhesion changes the actual surface charge can be calculated. The behavior of the adhesion force at surface steps is observed.
S. Hild and O. Marti, "Structural changes during stretching uniaxially oriented polypropylene film investigated by AFM," Polymer Preprints 37.2 (1996).
T. Müller, T. Kässer, M. Labardi, M. Lux-Steiner, O. Marti, J. Mlynek, and G. Krausch, "Scanning force and friction microscopy at highly oriented polycrystalline graphite and CuP2(100) surfaces in ultrahigh vacuum," J. Vac. Sci. Technol B 14 (2), 1296-1301 (1996).
N1 - We present a novel scanning force and friction microscope for applications in ultrahigh vacuum (UHV) using the optical beam deflection method for detection. All optical components are positioned on the air side enabling a simple way of adjustment, the possibility of good decoupling of topography and lateral signal, and the absolute estimation of lateral force values, We demonstrate lateral atomic resolution on mica surfaces freshly cleaved in UHV. As model systems, we investigate the complex CuP2(100) surface on the unit cell level which exhibits a wide range of atomic stick-slip phenomena. In addition, first results on the friction behavior at step edges on highly oriented polycrystalline graphite surfaces are presented.
A. Rosa, S. Hild, and O. Marti, "Deformation induced changes in surface properties of natural rubber," ACS Polymer Preprints , 616-617 (1996).
G. Krausch, M. Hipp, M. Boeltau, O. Marti, and J. Mlynek, "High-Resolution Imaging of Polymer Surfaces with Chemical Sensitivity," Macromolecules 28 (1), 260-263 (1995).
We have studied the potential of friction and stiffness measurements with high spatial resoln. for the surface characterization of glassy polymers. We present exptl. evidence for quasi-chem. sensitivity on a heterogeneous surface consisting of polystyrene islands on a poly(Me methacrylate) base layer. Although similar in their bulk mech. properties, the two polymers are easily distinguished by their different nanomech. behavior. As an example, we characterize the domain pattern formed after spinodal decompn. of a sym. blend of the two polymers.
W. Straub, F. Bruder, R. Brenn, G. Krausch, H. Bielefeldt, A. Kirsch, O. Marti, J. Mlynek, and J. F. Marko, "Transient wetting and 2D spinodal decomposition in a binary polymer blend," Europhys. Lett. 29, 353-358 (1995).
We have used ion beam analysis and scanning near-field optical microscopy to characterize the three-dimensional domain structure of a thin film of a phase-separating polymer mixture. In the initially mixed film, there first occurs coverage of one of its surfaces by an unbroken layer of one phase; between this <> surface and the substrate, layers of domains form. Eventually, the layered domain structure becomes unstable, and a transformation occurs to the equilibrium wetting state where both phases are in contact with both surfaces, causing a phase separation to be purely two-dimensional at later times. During this "transient wetting" process, lateral and vertical domain sizes grow with time as t1/3 independent of the dimensionality of the domains.
E. Weilandt, A. Menck, M. Binggeli, and O. Marti, "Friction Force Measurements on Graphite Steps under Potential Control,"in Electrochemistry, Ed. , edited by A. A. Gewirth and H. Siegenthaler (Kluwer, Doordrecht, 1995), NATO ASI Series Vol. E:288, pp. 307-315.
E. Weilandt, A. Menck, and O. Marti, "Friction studies at steps with friction force microscopy," Surf.Interface Anal. 23, 428-430 (1995).
P. K. Hansma, V. Elings, O. Marti, and C. E. Bracker, "Scanning tunneling microscopy and atomic force microscopy: application to biology and technology," Science 242, 209 (1988).
The scanning tunneling microscope (STM) and the atomic force microscope (AFM) are scanning probe microscopes capable of resolving surface detail down to the atomic level. The potential of these microscopes for revealing subtle details of structure is illustrated by atomic resolution images including graphite, an organic conductor, an insulating layered compound, and individual adsorbed oxygen atoms on a semiconductor. Application of the STM for imaging biological materials directly has been hampered by the poor electron conductivity of most biological samples. The use of thin conductive metal coatings and replicas has made it possible to image some biological samples, as indicated by recently obtained images of a recA-DNA complex, phospholipid bilayer, and an enzyme crystal. The potential of the AFM, which does not require a conductive sample, is shown with molecular resolution images of a nonconducting organic monolayer and an amino acid crystal that reveals individual methyl groups on the ends of the amino acids. Applications of these new microscopes to technology are demonstrated with images of an optical disk stamper, a diffraction grating a thin-film magnetic recording head, and a diamond cutting tool. The STM has even been used to improve the quality of diffraction gratings and magnetic recording heads.
O. Marti, S. Gould, and P. K. Hansma, "Control electronics for atomic force microscopy," Review of Scientic Instruments 59 (6), 836-839 (1988).
The control electronics for the atomic force microscope (AFM) are described. The set of electronic devices described allow convenient operation of an atomic force microscope. The key device is the force controller, which automates the otherwise tedious and time-consuming readjustment of the force to a preset value by controlling two gated feedback loops. The preset value of the force can be easily changed by simply turning a potentiometer. This automated system allows one to obtain reliable data, with known forces, despite piezoelectric creep and thermal drift in the force determining mechanical setup. The electronic devices and concepts presented work for AFMs that use tunneling, capacitance measurements, or optical interference to sense small deflections of the spring.
O. Marti, H. O. Ribi, B. Drake, T. R. Albrecht, C. F. Quate, and P. K. Hansma, "Atomic Force Microscopy of an Organic Monolayer," Science 239, 50-52 (1988).
Atomic force microscope images of polymerized monolayers of n-(2-aminoethyl)-10,12-tricosadiynamide revealed parallel rows of molecules with a side-by-side spacing of approximately=0.5 nanometer. Forces used for imaging (10-8 newton) had no observable effect on the polymer strands. These results demonstrate that atomic force microscope images can be obtained for an organic system.
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