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Reprints on Scanning Force Microscopy
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H.-U. Krotil, T. Stifter, H. Waschipky, K. Weishaupt, S. Hild, and O. Marti, "Pulsed Force Mode: a new method for the investigation of surface properties," Surf. Interface Anal. 27, 336-340 (1999).
Scanning force microscopy is extended by the pulsed force mode from simple imaging of topography to measuring elastic, electrostatic and adhesive sample properties. Lateral forces are virtually eliminated so that mapping of delicate samples with high resolution in air and fluids is easily possible. Scanning speed is comparable to that in contact mode. The new opportunities for scanning force microscopy given by the pulsed force mode is demonstrated in selected applications.
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.
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.
O. Marti, "AFM Signals and Imaging Modes: Conventional Imaging," in Handbook of Scanning Probe Microscopy, Ed. , edited by Colton, Engel et al. (John Wiley and Sons, Chichester, UK, 1998), pp. 105-109.
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.
T. Miyatani, S. Okamoto, A. Rosa, O. Marti, and M. Fujihira, "Surface charge mapping of solid surfaces in water by pulsed-force-mode atomic force microscopy.," Applied Physics A (Materials Science Processing) 66, 349-352 (1998).
We have studied the lateral distribution of charges on various surfaces in water by measuring the electrical double layer forces between a Si3N4 atomic force microscope (AFM) tip and the surfaces. By increasing the pH of the solution around the isoelectric point (IEP) of Si3N4 of approximately 6, the charge on the Si3N4 AFM tip was changed from positive to negative. The surface charges of the samples were also controlled by the pH of the solution in which the sample oxides were dipped. When the samples were electronically conductive, the surface charge was controlled by the electrode potentials. When the sample surface was heterogeneous in terms of the isoelectric point or point of zero charge (pzc), the surface charge was changed from one place to the other. As a heterogeneous oxide sample, a quartz plate patterned with alumina was used. The lateral charge distributions on such surfaces were mapped by pulsed-force-mode AFM. The lateral resolution of the present method was found to be approximately 20 nm.
T. Stifter, E. Weilandt, S. Hild, and O. Marti, "Influence of the topography on adhesion measured by SFM," Appl. Phys. A 66, S597-S605 (1998).
Surface properties such as adhesion are influenced by the surface topography. This dependency complicates any quantitative investigation of the material constants. A simple and efficient model is used to calculate the influence of the topography on the pull of force determined by a scanning force microscope (SFM). In the model the SFM tip is represented by a sphere. The sample surface is modeled by two geometries: a step on a plane and a blister (spherical cap) on a plane. The atomic interaction between the tip and the surface is of the Lennard-Jones type. The theoretical results are compared with SFM-measurements on highly oriented pyrolytic graphite (HOPG) in electrolytic environment. The calculations are in good agreement with the measured images.
O. Marti, "Instrumentation for Scanning Force Microscopy and Friction Force Microscopy," in Macro- and Microtribology, Ed. , edited by B. Bhushan (Kluwer Academic Publishers, Dordrecht, 1997).
Scanning force microscopes and friction force microscopes are built in a wide variety of designs. They have become welcome additions to industrial laboratories due to their ruggedness and because their measurement principle is, in many respects, a refinement of well established apparatus such as profilometers and tribometers. This article discusses the building blocks of scanning force microscopes.
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. Miyati, M. Horii, A. Rosa, M. Fujihira, and O. Marti, "Mapping of electrical double-layer force between tip and sample surfaces in water by pulsed-force-mode atomic force microscopy," Appl. Phys. Lett. 71 (18), 2632-2634 (1997).
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).
A. Rosa-Zeiser, E. Weilandt, S. Hild, and O. Marti, "The simultaneous measurement of viscoelastic, electrostatic and adhesive properties by SFM: pulsed force mode operation," Meas. Sci. Technol. 8, 1333-1338 (1997).
We describe the pulsed-force mode, a new measuring mode for the scanning force microscope to image elastic, electrostatic and adhesive properties simultaneously with topography. The pulsed-force mode reduces lateral shear forces between the tip and the sample. Even very delicate samples can be mapped at high lateral resolution with full control over the force applied to the sample. The achieved scanning speed is comparable to that in contact-mode operation. The pulsed-force mode electronics can easily be added to many microscopes without much alteration of the original set-up. No change of the data acquisition software or of the feedback circuit is necessary.
J. P. Spatz, S. Sheiko, M. Möller, R. G. Winkler, P. Reineker, and O. Marti, "Tapping Scanning Force Microscopy in Air - Theory and Experiment," Langmuir 13, 4699-4703 (1997).
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.
J. Colchero, A. M. Baró, and O. Marti, "Energy dissipation in scanning force microscopy - friction on an atomic scale," Tribol. Lett. 2, 327-344 (1996).
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.
R. G. Winkler, J. P. Spatz, S. Sheiko, M. Moller, P. Reineker, and O. Marti, "Imaging material properties by resonant tapping-force microscopy: A model investigation," Physical Review B Condensed Matter 54 (12), 8908-8912 (1996).
The interaction of a cantilever performing a forced oscillation with a sample in a tapping-mode scanning force microscope is investigated within a simple model. The tip together with the cantilever is modeled as a periodically driven, damped harmonic oscillator. The viscoelastic sample is described by a friction force acting on the tip while it is in contact and a harmonic potential. The penetration of the probe and the phase shift of the oscillator due to contact with the sample are calculated for various sample parameters. In particular, an approximate solution of the model equations for the phase shift is presented. Moreover, a relation between the elastic constant of the model and the elastic modulus of a material is presented.
J. Colchero, O. Marti, and J. Mlynek, "Friction on an atomic scale," in Forces in Scanning Probe Methods, Ed. , edited by H. J. Güntherodt, D. Anselmetti, and E. Meyer (Kluwer, Dordrecht, 1995), NATO ASI Series E Vol. E:286, pp. 345-352.
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.
O. Marti and J. Colchero, "Scanning Probe Microscopy Instrumentation," in Forces in Scanning Probe Methods, Ed. , edited by H. J. Güntherodt, D. Anselmetti, and E. Meyer (Kluwer Academic Publishers, Dordrecht, 1995)Vol. E:286, pp. 15-34.
J. P. Spatz, S. Sheiko, M. Möller, R. G. Winkler, P. Reineker, and O. Marti, "Forces affecting the substrate in tapping mode," Nanotechnology 6, 40-44 (1995).
We propose a simple model to describe the interaction of a forced cantilever oscillation with a specimen in a tapping-mode scanning force microscope experiment in order to make a rough estimation of the forces affecting the surface with each touch down of the tip. Assuming weak damping of the cantilever (quality factor of the cantilever between 100 and 1000) and of the surface, we can estimate the forces to be in the range of those in the contact mode. These forces can vary by orders of magnitude, e.g. 10-6 to 10-11 N. To reduce the interaction force we suggest scanning on the low-frequency side of the resonance frequency of the non-contact cantilever oscillation. Increasing the difference of phase between the non-contact oscillation of the cantilever in air and the oscillation during contact introduces strong variations of the force. The improvement in resolution which can be achieved for soft samples by using the tapping-mode system results from the elimination of shear forces and the possibility of minimizing the force on the surface by varying the set-point of the scanning amplitude. Forces on the substrate will be enhanced by a large substrate stiffness.
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).
J. Burger, G. Dietler, M. Binggeli, R. Christoph, and O. Marti, "Aspects of the surface roughness of ceramic bonding tools on a nanometer scale investigated with atomic force microscopy," Thin.Solid.Films. 253, 308-310 (1994).
J Burger, Ctr Suisse Electr & Microtech SA, Maladiere 71, CH-2007 Neuchatel, Switzerland Ceramic bonding capillaries were studied using a stand- alone atomic force microscope (AFM) demonstrating the importance of nanoscale characterization for industrial quality control. Bonding tools represent an example of a nanotribological system in industry as the friction at the bonding wire/capillary interface is responsible for the formation of the contact between the bonding wire and bonding pad. The detailed structure and homogeneity of micro- and nanometer scale structures on the surface are crucial for the performance of the capillary during the bonding process. The surface of bonding tools prepared under different conditions could be imaged at the very end, giving information on the formation of a nanoscale roughness. A special roughness analysis based on methods of fractal analysis was used in order to obtain a direct correlation between the roughness and lateral length scale of the AFM images
O. Marti, "Scanning force and friction microscopy applied to organic and biological samples," Proceedings of ICEM'13 (Paris 17-22 July 1994) , 569-570 (1994).
P. Niedermann, J. Burger, M. Binggeli, R. Christoph, H. E. Hintermann, and O. Marti, "A Scanning Force and friction Microscope," in NATO ARW on Ultimate Limits of Fabrication, Cambridge, April 5-8 (1994), Ed. , (1994).
E. Perrot, M. Dayez, A. Humbert, O. Marti, C. Chapon, and C. R. Henry, "Atomic-scale resolution on the MgO(100) surface by scanning force and friction microscopy," Europhys. Lett. 26, 659-663 (1994).
MgO(100) surfaces have been imaged at atomic-scale resolution by scanning force and friction microscopy (SFFM). The single crystals of MgO were cleaved and studied in dry air using a small loading force (4.10-10 N). Topographic and friction images reveal a square lattice of protrusions with a measured spacing of 0.274 nm. This value is close to the 2D surface lattice parameter of the MgO(100) surface (0.299 nm). The largest corrugation observed in the topographic images is 0.04 nm. Large-scale images reveal nearly parallel cleavage steps, separated by an average distance of 150 nm and 0.4 nm high.
M. Binggeli, R. Christoph, H.-E. Hintermann, J. Colchero, and O. Marti, "Friction Force Measurements on Potential Controlled Graphite in Electrolytic Environment," Nanotechnology 4, 59-63 (1993).
The authors show the simultaneous recording of normal and lateral forces arising in scanning force and friction microscopy on a potential controlled sample immersed in aqueous electrolyte. As a liquid film is present on virtually all solid surfaces under ambient conditions, it is important to control the properties of the solid/liquid interface. In order to obtain reliable information on the friction behaviour of such a surface, a set-up for potentiostatic control of the sample was established. Experiments have been carried out with a stand-alone scanning force and friction microscope (SFFM), combined with an electrochemical cell providing potential control of the sample. First results of simultaneous normal and friction force measurements, obtained on highly oriented pyrolytic graphite (HOPG) immersed in NaClO4, demonstrate the promising potential of the method.
A. Linder, H.-J. Apell, J. Colchero, and O. Marti, "Na,K-ATPase: Preparation and Scanning Force Microscopy," in STM and SFM in Biology, Ed. , edited by O. Marti and M. Amrein (Academic Press, San Diego, 1993), pp. 275-308.
O. Marti, "Nanotribology: Friction on a Nanometer Scale," Physica Scripta T49, 599-604 (1993).
The submicrometer length scale is mostly beyond the resolution of classical tribometers. The scanning force and friction microscope operated as a nanotribometer is a suitable tool for the investigation of nanotribological properties. The scanning force and friction microscope measures simultaneously forces normal and parallel to the sample surface with a resolution down to the atomic scale. The setup of a scanning force microscope based nanotribometer, its calibration and the methods for quantitative data analysis are discussed. It is shown that a two-dimensional histogram analysis yields quantitative data on the distribution of the indium on a nanometer scale. The concepts are applied to the analysis of a silicon oxide surface with indium clusters are discussed. The chemical sensitivity of the scanning force and friction microscope operated under ambient condition makes this instrument a promising candidate for a standardized tool in nanotribology.
O. Marti, "Scanning Probe Microscopy: an Introduction," in STM and SFM in Biology, Ed. , edited by O. Marti and M. Amrein (Academic Press, San Diego, 1993), pp. 1-143.
O. Marti and M. Amrein, "STM and SFM in Biology," (Academic Press, San Diego, 1993).
O. Marti, J. Colchero, and J. Mlynek, "Friction and Forces on an Atomic Scale," in Nanosources and Manipulations of Atoms under High Fields and Temperatures: Applications, Ed. , edited by V. T. Binh, N. Garcìa, and K. Dransfeld (Kluwer Academic Publishers, Dordrecht, The Netherlands, 1993)Vol. E 235, pp. 253-269.
J. Mertz, O. Marti, and J. Mlynek, "Regulation of a Microcantilever Response by Active Control," Appl. Phys. Lett. 62, 2344-2346 (1993).
A feedback mechanism is used to control the forces incident on a mechanical microcantilever as a function of the monitored cantilever motion. The control is effected by modifying the intensity of an auxiliary laser beam that generates a thermally induced stress. The feedback is designed to reduce the effective resonance quality factor of the cantilever. The resultant regulation of the cantilever motion is shown to improve the measurement dynamics in atomic force microscopy, without significantly degrading the signal to noise ratio.
H.-J. Apell, J. Colchero, A. Linder, O. Marti, and J. Mlynek, "Na,K-ATPase in crystalline form investigated by Scanning Force Microscopy," Ultramicroscopy 42-44, 1133-1140 (1992).
Na,K-ATPase has been isolated in purified membrane fragments from kidney tissue and crystallized by phospholipase treatment to obtain two-dimensional, membrane-bound protein crystals. Scanning force microscopy has been used to identify and analyze the topography of the membrane fragments. Specific patterns in accordance with electron microscopic images have been found. In biological under physiological conditions the scanning force is a crucial parameter for the resulting image at high resolution.
J. Colchero, O. Marti, H. Bielefeldt, and J. Mlynek, "Scanning Force and Friction Microscopy," Phys. stat. sol. (a) 131, 73-75 (1992).
Using the optical lever technique the authors have developed a scanning force microscope (SFM) which simultaneously measures the topography as well as the lateral force on the tip in the scanning direction. This new microscope, the scanning force and friction microscope (SFFM), is sensitive to the chemical composition of the surface and should open new frontiers in tribology.
M. Hipp, H. Bielefeldt, J. Colchero, O. Marti, and J. Mlynek, "A Stand-Alone Scanning Force and Friction Microscope," Ultramicroscopy 42-44, 1498-1503 (1992).
The authors present a new design for a compact stand-alone force and friction microscope. Both the force sensor and the scanning unit are mounted on the microscope head, thus allowing the investigation of virtually all surfaces, independent of thickness and size, and minimizing the geometrical dimension. The beam deflection method in a collinear arrangement is used to detect the normal force and the friction force. The cantilever is fixed to the scanning piezo. The influences of the scanning motion on the force signal and the compensation schemes are discussed. The new design of the SFM allows a combination of optical surface manipulation and real-time detection of the stimulated processes with the scanning force microscope. The set-up also makes it possible to work under fluids.
A. Linder, J. Colchero, H.-J. Apell, O. Marti, and J. Mlynek, "Scanning Force Microscopy of Diatom Shells," Ultramicroscopy 42-44, 329-332 (1992).
The authors have imaged surfaces of several diatom species by scanning force microscopy with image areas of some squared micrometers. The algae cells were collected from a mud sample out of a small pond, rinsed briefly with ethanol to clean and immobilize them and deposited on a glass slide. The ease of obtaining images with a resolution of several ten nanometers makes the scanning force microscope competitive with scanning electron microscopy at medium magnification.
O. Marti, A. Ruf, M. Hipp, H. Bielefeldt, J. Colchero, and J. Mlynek, "Mechanical and thermal effects on force microscope cantilevers," Ultramicroscopy 42-44, 345 (1992).
In an optical lever set-up one or two modulated laser beams of 0.1 to 6 mW modulation amplitude at a wavelength of 670 nm were focused at uncoated and gold-coated microfabricated cantilevers. The motion of the levers was analyzed by an optical lever set-up. The mechanical resonance (30 to 60 kHz) of the cantilevers was excited by the modulated light both in air and under vacuum conditions (10-6 mbar). The measured resonance frequencies and the width of the resonances were identical to the values found by exciting the cantilevers by piezo ceramics. At low frequencies under vacuum conditions, the authors found an increase of the oscillation amplitude with decreasing frequency. The time constant of this increase is of the order of 5 ms. At the resonance frequency of uncoated cantilevers light pressure effects dominate thermal effects; the resonance is thus excited by light pressure. Gold-coated cantilevers, however, are driven by the bimetal effect, even above 10 kHz. A possible application of the light pressure effects is the use of a modulated light beam in the attractive mode operation of a scanning force microscope to excite the cantilever oscillation.
J. Colchero, O. Marti, J. Mlynek, A. Humbert, C. R. Henry, and C. Chapon, "Palladium Clusters on Mica: A Study by Atomic Force Microscopy," J. Vac. Sci. Technol. B9, 794-797 (1991).
A compact scanning force microscope with a force sensor based on the light beam deflection method was used to study palladium clusters on mica. The force microscope was equipped to measure topography of the sample surface and the friction force between the sample and the tip. The evaporation of palladium on mica was done under UHV conditions, which were closely monitored to control both the morphology and the size of the clusters. The resulting clusters were characterized by transmission electron microscopy. The samples were then transferred in air and imaged with the scanning force microscope under ambient conditions. The diameter to height ratio near 10 and the truncated triagonal shapes of the palladium clusters agree well with the results obtained by transmission electron microscopy and with the results of a scanning tunneling microscopy study of palladium clusters on graphite. Friction images show, that the interaction between the tip and the clusters does charge them.
O. Marti, J. Colchero, and J. Mlynek, "Combined Scanning Force and Friction Microscopy of Mica," Nanotechnology 1, 141-144 (1990).
A scanning force microscope using the optical lever detection method was modified to measure simultaneously the force normal to the sample surface and the friction force arising from scanning. The bending of sheet-like cantilevers is used to detect the normal force whereas the twisting of the same cantilever measures the friction force. The two effects cause, to first order, orthogonal deflections of the light beam and can therefore be measured simultaneously and independently. The relationship between normal and frictional forces and the resulting deflection angles is discussed. The authors present constant-force topographs and friction images of the surface unit-cell structure of mica and of single-layer steps on mica.
S. Alexander, L. Hellemans, O. Marti, J. Schneir, V. Elings, P. K. Hansma, M. Longmire, and J. Gurley, "An atomic-resolution atomic-force microscope implemented using an optical lever," J. Appl. Phys. 65, 164 (1989).
The authors present the first atomic-resolution image of a surface obtained with an optical implementation of the atomic-force microscope (AFM). The native oxide on silicon was imaged with atomic resolution, and approximately=5-nm resolution images of aluminium, mechanically ground iron, and corroded stainless steel were obtained. The relative merits of an optical implementation of the AFM as opposed to a tunneling implementation are discussed.
S. Gould, O. Marti, B. Drake, L. Hellemans, C. E. Bracker, P. K. Hansma, N. L. Keder, M. M. Eddy, and G. D. Stucky, "Molecular resolution images of amino acid crystals with the atomic force microscope," Nature 332, 332-334 (1988).
The atomic force microscope has been used to image arrays of molecules at the surface of DL-leucine crystals. Lattice spacings are consistent with X-ray diffraction data. In contrast to metals and semiconductors, the surface of these amino acid crystals seems to be a simple termination of the bulk; there is no evidence of a surface reconstruction for this molecular crystal. This initial success in imaging amino acid molecules points to the potential usefulness of atomic force microscopy for imaging molecules of biological importance.
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, B. Drake, S. Gould, and P. K. Hansma, "Atomic resolution atomic force microscopy of graphite and the 'native oxide' on silicon," J. Vac. Sci. Technol. A 6, 287-290 (1988).
An atomic force microscope (AFM) can image surfaces of conductors, insulators, and even organic materials. Images of highly oriented pyrolytic graphite show atomic structure with a corrugation height of 0.03 nm. Images of the 'native oxide' layer grown in ambient pressure on a (111) facet on a (100) silicon wafer show steps. Images of the native oxide layer on a (111) silicon wafer show features 0.6 nm apart and aligned with the silicon substrate. The images shown here were obtained with an instrument that can also operate as a scanning tunneling microscope (STM); it is an AFM/STM.
O. Marti, B. Drake, S. Gould, and P. K. Hansma, "Atomic force microscopy and scanning tunneling microscopy with a combination atomic force microscope/scanning tunneling microscope," J. Vac. Sci. Technol. A 6, 2089-2092 (1988).
Since almost all the electronic and mechanical requirements for an atomic force microscope (AFM) are the same as for a scanning tunneling microscope (STM), it is convenient and practical to build a combination AFM/STM with interchangeable heads. The conversion from one to another can be made in a few minutes. Representative images demonstrate that atomic resolution can be obtained in both modes of operations. With the two modes of operation, it can image conductors, semiconductors and insulators.
O. Marti, B. Drake, S. Gould, and P. K. Hansma, "Probing Surfaces with the Atomic Force Microscope," SPIE Proceedings 897, 22 (1988).
The atomic force microscope can resolve features on conducting or nonconducting surfaces down to the atomic level. The heights of features are recorded as a sharp tip scans over the surface in parallel scans. The interaction between the tip and the surface is the interaction potential between atoms. Individual carbon atoms separated by 0.146 nm have been resolved on graphite. Ordered structure on the 'native' oxide of silicon has been observed. Rows of molecules that are separated by 0.5 nm have been resolved in an organic monolayer. The key to the operation of an AFM is the development of a system for sensing tracking forces that are small enough to avoid damaging the surface. The images in this report were obtained by sensing with electron tunneling the deflection ( approximately=1-10 nm) of springs (k approximately=0.1-100 N/m) fabricated from silicon oxide or fine wires.
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.
J. Schneir, O. Marti, G. Remmers, D. Gläser, R. Sonnenfeld, B. Drake, P. K. Hansma, and V. Elings, "Scanning tunneling microscopy and atomic force microscopy of the liquid-solid interface," J. Vac. Sci. Technol. A 6, 283-286 (1988).
The liquid-solid interface is important not only for science, but also for technology. Scanning tunnel microscopes (STMs) and atomic force microscopes (AFMs) can image and even manipulate solids covered with liquids. An image of a line 75 nm long and 5 nm wide drawn with at STM on a liquid-covered Au (111) surface demonstrates the potential for manipulating surfaces. Images of a Pt film demonstrate the ability of STMs to find new features by zooming from large-area scans down to the atomic scale. Finally, an AFM image of a liquid-covered graphite surface demonstrates atomic resolution.
O. Marti, B. Drake, and P. K. Hansma, "Atomic force microscopy of liquid- covered surfaces: Atomic resolution images," Appl. Phys. Lett. 51 ( 7), 484-486 (1987).
Images of graphite surfaces that are covered with oil reveal the hexagonal rings of carbon atoms. Images of a sodium chloride surface, protected from moisture by oil, exhibit a monoatomic step. Together, these images demonstrate the potential of atomic force microscopy (AFM) for studying both conducting and nonconducting surfaces, even surfaces covered with liquids. The authors' AFM uses a cross of double wires with an attached diamond stylus as a force sensor. The force constant is approximately=40 N/m. The resonant frequency is approximately=3 kHz. The lateral and vertical resolutions are 0.15 nm and 5 pm.
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Othmar Marti Last modified: Montag, 11. November 2002