[1]R. Brunner, A. Simon, T. Stifter, and O. Marti, “Modulated shear-force distance control in near field optical microscopy (NSOM),” Rev. Sci. Instrum.71 (3), 1466-1471 (2000).
(Received 29 June 1999; accepted 29 November 1999)
The tip–sample distance in near-field scanning optical microscopy is typically controlled by the shear–force interaction between the laterally vibrating tip and sample. In this article, a mode of shear-force feedback is described in which an additional vertical modulation is introduced. Similar to the tapping mode applied in atomic force microscopy, the modulated shear–force technique deals with problem due to the snap to contact and therefore improves the mapping of soft and ductile materials, such as biological samples and soft polymers. The imaging properties of the modulated shear–force mode is demonstrated on structures of a soft polymer blend. Additionally, the modulated shear–force technique allows a simple comparison between effects in the optical far field and in the optical near field. ©2000 American Institute of Physics.
II: S0034-6748(00)02403-5
ACS: 07.79.Fc, 87.64.Xx

[2]T. Held, S. Emonin, O. Marti, and O. Hollricher, “A new method to produce high resolution scanning near field optical microscope probes by beveling optical fibers,” Review of Scientific Instruments (2000), submitted.

[3]P. Kröner, H. Baumeister, J. Rieger, E. Veuhoff, O. Marti, and H. Heinecke, “Comparison of structural and optical properties in strained GaInAsP MQW structures grown by MOVPE and MOMBE,” J. Cryst. Growth209, 424-430 (2000).
The growth parameter dependence of the transition from 2D to 3D growth of GaInAsP multiple quantum well (MQW) structures up to e B "0.5% tensile-strained barriers was examined. Identical MQW structures with e W "1% compressively strained wells were grown by metal organic vapor-phase epitaxy (MOVPE) and metal organic molecular beam epitaxy (MOMBE) and characterized by photoluminescence (PL), X-ray di!raction and transmission electron microscopy. Increasing the tensile barrier strain resulted in deteriorated optical and crystalline properties beyond a critical strain limit, which depends on growth temperature. The deterioration originates from lateral layer thickness and strain modulations. Their density, amplitude and thus their e!ect on the optical MQW properties are di!erent for both rowth methods. High-quality MOMBE-grown MQW structures up to e W "2% compressive well strain and
e B "0.5}1% tensile barrier strain could be achieved by inserting thin intermediate layers at each internal interface. The composition of these intermediate layers has a signi"cant e!ect on MQW material properties. ( 2000 Elsevier Science B.V. All rights reserved.

[4]O. Marti, “Measurement of adhesion and pull-off forces with the AFM,” in Handbook of Modern Tribology, Ed. , edited by B. Bhushan (CRC, 2000).

[5]C. Messerschmidt, A. Schulz, J. P. Rabe, A. Simon, O. Marti, and J.-H. Fuhrhop, “Formation of Stable Singularities in Mixed Monolayers of Porphyrins and Tetracosanoic Acid upon SFM Tapping,” Langmuir 16 (3), 1299-1305 (2000).
Langmuir films of tetracosanoic acid have been transferred at 10 mN/m from water to mica surfaces and were characterized by scanning force microscopy (SFM) in the tapping mode at first as a smooth monolayer. Then, upon repeated tapping cycles, many singularities appeared in form of 2.5 nm high pairs of peaks in a plane, which stretched only 1.8 nm above the mica subphase. These peaks are attributed to islands of upright-standing molecules in a layer of molecules tilted at an angle of 35. Transferring the films thus results first in a nonequilibrated film on mica, which undergoes relaxation upon tapping to a nonhomogeneous equilibrium phase. The same phenomenon was observed in films made of rigid porphyrin and tetracosanoic acid domains at 20 mN/m. The formation of fluid fatty acid structures at pressures where strong ordering prevails in pure fatty acid films was related to a reorientation in the rigid porphyrin domains after the transfer to mica. SFM phase shift images were applied to different hard and soft parts of the mixed monolayer, and scanning near-field optical microscopy was used to confirm the assignment of the porphyrin domains on the basis of their fluorescence.

[6]R. Brunner, M. E. Kosal, K. S. Suslick, R. Lamche, O. Marti, and J. O. White, “Near-field Scanning Optical Microscopy of Zinc-Porphyrin Crystals,” Ultramicroscopy (1999), in preparation.

[7]R. Brunner, O. Marti, and O. Hollricher, “Influence of environmental conditions on shear-force distance control in near field optical microscopy,” J. Appl. Phys.86 (12), 7100-7106 (1999).
~Received 20 January 1999; accepted for publication 7 September 1999!
In our experiments we show, that a contaminating water film is very important for the shear–force distance control in near-field optical microscopy. This is demonstrated at the transition between a hydrophilic glass surface and a hydrophobic Langmuir–Blodgett film of arachidic acid at different relative humidities. This contaminating water film is one, if not the important reason for the damping of an oscillating fiber during surface approach. It is further shown, that the bulk viscosity
of water alone cannot be responsible for the observed damping effect. A thickness dependent viscosity of this water film is proposed. These observations can also explain, why the shear–force distance control works on nearly all surfaces at ambient conditions, but fails to work at very low temperatures. © 1999 American Institute of Physics. @S0021-8979~99!00924-X#

[8]R. Brunner, T. Stifter, and O. Marti, Verfahren zur Bestimmung des Abstandes einer Nahfeldsonde von einer zu untersuchenden Probeoberfläche, Patent# H01Y 37/28, Germany (1999).

[9]H. U. Krotil, T. Stifter, and O. Marti, Verfahren und Vorrichtung zur gleichzeitigen Bestimmung der Adhäsion, der Reibung und weiterer Materialeigenschaften einer Probenoberfläche, Patent# 19900114.6, Germany (1999).

[10]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.

[11]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 (5-6), 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.

[12]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 (5-6), 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.

[13]O. Marti, “Raum und Zeit: eine physikalische Zeitreise,” ZAWIW (1999), in press.

[14]O. Marti and S. Hild, “Temperature dependent surface properties of thin polystyrene films,” in Symposium on Microstructure and Microtribology of Polymer Surfaces, ACS Symposium Series (Boston Meeting 1998), Ed. , edited by K. J. Wahl and V. V. Tsukruk (1999).

[15]O. Marti, T. Stifter, H. Waschipky, M. Quintus, and S. Hild, “Scanning Probe Microscopy of Heterogeneous Polymers,” Colloids and Surfaces A: Physicochemical and Engineering Aspects154 (1-2), 65-73 (1999)
Adhesion, elastic and viscoelastic properties are characteristic parameters of materials. These mechanical properties of polymers show a strong dependence on the manufacturing process, the molecular weight, the temperature and the environment. It would be desirable to have tools for characterization of small samples. The scanning force microscope seems to be an ideal instrument when working towards this goal. The nanometer sized probe in contact with the sample surface can be used to measure a variety of surface properties, ranging from friction to adhesion. The measurements could be truly quantitative if one knew exactly the shape of the tip and the strength and distance dependence of the interaction forces. It is shown in this paper how the measurement modes of a scanning force microscope can be tailored to obtain quantitative data. We discuss the advantages and disadvantages of the pulsed force mode investigations using homogeneous and heterogeneous polymer samples as test objects. (30 References).

[16]J. Barenz, P. Anger, O. Hollricher, O. Marti, M. Wachter, R. Butendeich, and H. Heinecke, “Spatially resolved Near Field Spectroscopy on Localized GaInAs/InP doubleheterostructures,” J. Appl. Phys.83 (2), 1-7 (1998).
We present investigations of band-gap variations on selective grown GaxIn1-xAsyP1-y multiple quantum wells (MQW, Q1.05) using near-field optical microscopy. The MQW is excited with the near-field probe and the luminescence is collected through the same tip. By this mode, we are able to detect variation of the band gap with a lateral resolution of about 550 nm at a luminescence wavelength of 1115 nm. We show a spatial band-gap modulation near the (0-11) facet of the selective grown structures, which we suggest, is a result of a variation of the material composition. Furthermore, together with the simultaneously recorded topography, we are able to allocate a recombination path at a center wavelength of lambda =1115 nm to the intersection of the (01-1) and (11-1) vertical side facets, which are formed by interfacet diffusion during surface selective growth of the GaxIn1-xAsyP1-y MQW.

[17]J. Barenz, A. Eska, O. Hollricher, O. Marti, M. Wachter, U. Schöffel, and H. Heinecke, “Near field luminescence measurements on GaInAsP/InP doubleheterostructures at room temperature,” Appl. Opt.37 (1), 106-112 (1998).
Spatially resolved near-field luminescence spectroscopy was carried out on locally grown InP ridges, overgrown by a GaInAsP layer in metal organic molecular beam epitaxy. For free access to the quaternary layer the cleaved surface was investigated. Two different reflection scanning near-field microscopy setups were used. In the illumination mode we were able to estimate the charge-carrier diffusion in the InP. For improving the spatial resolution, measurements were also carried out in the collection mode. Here a shift of the center wavelength toward lower energy occurs near the side facets. This can be a result of a material composition gradient or of strained growth near the side facets. A second recombination channel at 1115 nm occurs at the growth-nongrowth transition. With the simultaneous recorded topography this recombination channel can be localized in the quaternary layer grown on the side of the InP ridge.

[18]J. Colchero, E. Meyer, and O. Marti, “Friction on an atomic scale,” in Handbook of Micro/Nanotribology, Ed. 2, edited by B. Bhushan (CRC-Press, Boca Raton, 1998), pp. 273-333.

[19]D. Drews, W. Noell, W. Ehrfeld, M. Lacher, K. Mayr, O. Marti, C. Serwatzy, and M. Abraham, “Micromachined aperture probe for combined atomic force and near-field scanning optical microscopy (AFM/NSOM).,” presented at the Materials and Device Characterization in Micromachining, Santa Clara, CA, USA, 21-22 Sept, 1998 pp. 76-83, SPIE-Int. Soc. Opt. Eng, Vol. 3512 (unpublished).

A novel concept for the realization of a multifunctional scanning probe designed for simultaneous atomic force microscopy and near-field scanning optical microscopy measurements is described. It is based on micromachining and thin film technology and includes the fabrication of a cantilever, an integrated optical waveguide, an aperture probe tip, and the integration of all components into the complete sensor. Key processes are the fabrication of the probe providing a sharp tip together with a small optical aperture and the coupling of light from the integrated optical waveguide into the probe tip. The aperture probe consists of a transparent silicon nitride cone covered with aluminum except for the sharp cone tip thus forming a circular aperture around the protruding tip apex. In order to couple light from the waveguide into the tip a simple structure has been developed and optimized using numerical simulation procedures for the electromagnetic field distribution in the coupling structure. The complete sensor is fabricated in a reliable batch process and experimental evidence for the validity of the coupling concept is given.

[20]S. Hild, U. Krotil, and O. Marti, “Pulsed Force Mode: A new method for characterizing thin silane films by adhesive force measurements,” in Tribology Issues and Opportunities in MEMS, Ed. , edited by B. Bhushan (Kluwer Scientific Publishers, Dordrecht, 1998), pp. 247-260.

[21]S. Hild and O. Marti, “Temperature dependent properties of thin polymer films,” ACS Polymer Preprints, 1230-1231 (1998).

[22]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.

[23]O. Hollricher, R. Brunner, and O. Marti, “Piezoelectrical shear-force distance control in near-field optical microscopy for biological applications,” Ultramicroscopy71, 143-147 (1998).
We present a piezoelectrical shear-force distance control setup for scanning near field optical microscopy. The setup is compact and tip exchange is easy. The topographical sensitivity is comparable to optical feedback systems. With an acceptable vibration amplitude 5-10 nm we obtained a topographical resolution of 5 pm/ square root Hz. Because there is no laser necessary for tip position feedback, there is no extraneous light to interfere with spectroscopic and other low-light level experiments. Our technique permits measurements of soft biological samples in aqueous solution, which opens up many possible applications of near-field optical microscopy in biology and medicine.

[24]H. G. Kilian, W. Oppermann, B. Zink, and O. Marti, “Relaxation of polymer molecules in networks - the extended aggregate molecules,” Computational and Theoretical Polymer Science8 (1/2), 99-111 (1998).

[25]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,” Macromolecules31, 3945-3952 (1998).
ABSTRACT: Polystyrene films have been grafted by radical polymerization in situ on the surface of
glass slides. The morphology of these films resulting from different grafting temperatures has been
investigated by both the contact angle method and scanning probe microscopy with respect to the grafting
time. At a grafting density regime where the theory proposes the existence of a homogeneous layer, the
formation of island structures of grafted polymer with a size substantially higher than expected by the
theory has been observed. Overshot polymer structures of large sizes are created. The amount of grafted
polymer is substantially higher than that predicted from the conception of monolayer covering. The
grafting layer becomes impermeable for water only at a high amount of grafted polymer, which corresponds
to the multilayer structure of the coating. We suggested a mechanism for the grafting process that
included at least three stages: (a) first, a brushlike polymer layer is formed; (b) subsequently, a second
layer of ungrafted chains is created in the regime when excess chains are forced out from the first layer;
(c) big polymer clusters, with an average size of 100-200 nm due to gel polymerization in the clusters,
formed in the force out regime.

[26]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.

[27]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.

[28]O. Marti, J. Barenz, R. Brunner, M. Hipp, O. Hollricher, I. Hörsch, and J. Mlynek, “Photons and Local Probes,” in Nanoscale Science and Technology, Ed. , edited by N. Garcia, M. Nieto-Vesperinas, and H. Rohrer (Kluwer, Dordrecht, 1998)Vol. E:348, pp. 155-174.

[29]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.

[30]T. Stifter, E. Weilandt, S. Hild, and O. Marti, “Influence of the topography on adhesion measured by SFM,” Appl. Phys. A66, 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.

[31]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 pp. 248-256, SPIE-Int. Soc. Opt. Eng, Vol. 3099 (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.

[32]R. Brunner, A. Bietsch, O. Hollricher, and O. Marti, “Distance Control in Near-Field Optical Microscopy with electrical shear force detection suitable for imaging in liquids,” Rev. Sci. Instrum.68 (4), 1769-1772 (1997).
We introduce an improved piezoelectric shear-force feedback system for tip-sample distance control in a scanning near-field optical microscope. A tapered glass fiber is glued into a metal tube and both are integrated in a mounting, sandwiched between two piezosegments. One of the piezoelements excites the fiber tip at mechanical resonance while the other one is used for detection. During surface approach the fiber resonance is damped by shear forces, which is registered by the second piezoelement and used for distance control. The main attractions of this setup are its simplicity, its compactness, and the lack of disturbing light sources. The fiber is easy accessible and tip exchange is simple. With an acceptable fiber amplitude of 5-10 nm (peak to peak) we obtained a topographical resolution of 5 pm/ square root Hz. The geometry also allows the measurement of samples covered with a few millimeters of liquid, which is important for applications in biology and medicine.

[33]R. Brunner, A. Bietsch, O. Hollricher, O. Marti, and A. Lambacher, “Application of a near-field optical microscope to investigate the fluorescence energy transfer between chromophores embedded in Langmuir-Blodgett films,” Surf. Interface Anal.25 (7-8), 492 (1997).
Scanning near-field optical microscopy (SNOM) was used to investigate the fluorescence energy transfer between a monomolecular film of monomethin oxacyanine and a layer of monomethin thiacyanine in arachidic acid, The donor and acceptor chromophores are fixed in Langmuir-Blodgett (LB) films, spaced by the identical chains of the arachidic acid and dye, respectively. The length of these hydrophobic chains guarantees a fixed distance between the different kinds of chromophores. The dye molecules are oriented parallel to the plane of the LB film, In the LB layer assembly, a step was prepared to separate two different regions. One area contains both kinds of chromphores, whereas in the other area only the donor dyes are present, We used the SNOM technique because of the possibility to measure simultaneously the fluorescence behaviour and topographical structure. (C) 1997 by John Wiley & Sons, Ltd.

[34]R. Brunner, O. Hering, O. Marti, and O. Hollricher, “Piezoelectrical shear-force control on soft biological samples in aqeuous solution,” Appl. Phys. Lett.71, 3628-3639 (1997).
In order to apply scanning near-field optical microscopy to life science, it is essential to have an accurate distance feedback that also works on soft biological samples in liquids. In this letter, the authors report measurements of neuron cells in aqueous solution using an advanced piezoelectrical shear-force detection setup. Simultaneously obtained topographical and fluorescence images are presented, demonstrating a resolution below 100 nm in the optical image. The influence of the water level on the shear-force signal and the interaction between near-field probe and soft organic samples are discussed. Stable feedback in fluids is obtained with tip-sample interaction forces below 100 pN.

[35]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), Nato ASI Series E Vol. 330, pp. 455-465.

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.

[36]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.

[37]O. Marti, E. Weilandt, A. Rosa, J. Staud, B. Zink, I. Hörsch, R. Kusche, O. Kirschenhofer, and O. Hollricher, “SFFM and SNOM of Heterogeneous Materials,” in Chemical, Structural and Electronic Analysis of Heterogeneous Surfaces on Nanometer Scale, Ed. , edited by R. Rosei (Kluwer Academic Publishers, Dordrecht, 1997), Nato ASI Series E Vol. 333, pp. 25-41.

[38]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).

[39]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.

[40]W. Noell, M. Abraham, K. Mayr, A. Ruf, J. Barenz, O. Hollricher, O. Marti, and P. Güthner, “Micromachined aperture probe tip for multifunctional scanning probe microscopy,” Appl. Phys. Lett.70 (10), 1236-1238 (1997).
A novel micromachined aperture tip has been developed for near-field scanning optical microscopy. The advantages of the new probe over commonly used fiber probes are illustrated. 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-held scanning optical microscope. First measurements of topographical and optical near-held patterns demonstrate the proper performance of the hybrid probe. (C) 1997 American Institute of Physics.

[41]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 pp. , (unpublished).

[42]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,” Measurement Science and Technology8, 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.

[43]J. P. Spatz, S. Sheiko, M. Möller, R. G. Winkler, P. Reineker, and O. Marti, “Tapping Scanning Force Microscopy in Air - Theory and Experiment,” Langmuir13, 4699-4703 (1997).

[44]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.

[45]J. Barenz, O. Hollricher, and O. Marti, “An easy-to-use non-optical shear-force distance control for near-field optical microscopes,” Rev. Sci. Instrum.67 (5), 1912-1916 (1996).
We present an easy-to-use non-optical shear-force detection system for tip-sample distance control in scanning near-field optical microscopes. The fibre tip is fixed in a four-segmented piezo-tube by a polymer, Polyisobutylene, which couples the tip stiffly to the piezo at frequencies of 10 kHz or more at room temperature. One segment of the piezo-tube excites the fibre tip in resonance, while the other three segments detect the tip vibration in the manner of a piezo-microphone. When the tip is damped by shear forces the induced voltage at the three segments changes and can easily be detected with a lock-in amplifier. Further our method allows a fast and reproducible tip exchange with minor adjustments of mechanical ol electrical components. We demonstrate the performance of our distance control on a holographically fabricated line pattern with 417 nm lattice spacing and 10 nm height. A height resolution of better than 1 nm is demonstrated. (C) 1996 American Institute of Physics Article

[46]J. Colchero, A. M. Baró, and O. Marti, “Energy dissipation in scanning force microscopy - friction on an atomic scale,” Tribol. Lett.2, 327-343 (1996).
Stick-slip behaviour for a typical scanning force microscope setup operated in the wearless friction regime is modelled. Not only the deflection of the cantilever but also the local elastic deformation of tip and sample are taken into account. The combined effect of macroscopic spring and microscopic elastic deformation is a key feature to the scanning motion of the tip. Within this model, energy dissipation arises naturally due to mechanical instabilities either of the macroscopic cantilever or of the microscopic tip sample contact. Our model reproduces all features of atomically resolved friction loops, which can be calculated from interatomic potentials. Moreover, a general scheme is introduced which allows the exact response of the tip-sample system to be calculated from the different interacting potentials. (20 References).

[47]S. Hild and O. Marti, “Structural changes during stretching uniaxially oriented polypropylene film investigated by AFM,” Polymer Preprints37.2 (1996).

[48]I. Hörsch, R. Kusche, O. Marti, B. Weigl, and K. J. Ebeling, “Spectrally resolved near-field mode imaging of vertical cavity semiconductor lasers,” J. Appl. Phys.79 (8 Part 1), 3831-3834 (1996).

[49]M. Kamp, M. Mayer, A. Pelzmann, S. Menzel, H. Y. A. Chung, H. Sternschulte, O. Marti, and K. J. Ebeling, “NH3 as nitrogen source in MBE growth of GaN,” Mat. Res. Soc. Symp. Proc.395, 135-140 (1996).
We report on the growth of GaN in GSMBE using NH3 as nitrogen source. Special focus will be on the NH3 cracking, where we applied an On Surface Cracking technique (OSC). Using OSC we achieve photoluminescence linewidths as narrow as 5.5 meV (5 K) and mobilities of 220 cm2/Vs at room temperature. (5 References).

[50]O. Marti, “Transversale Moden in Laserdioden,” Phys. Blätter52, 1132-1133 (1996).

[51]O. Marti and J. Mlynek, “Reibungsmikroskopie als neuer Weg: Vorstoss in die Nanowelt,” DFG-Nachrichten1/96, 11-12 (1996).

[52]O. Marti and J. Mlynek, “Friction Microscopy as a New Way - Novel Methods involve Incursion into the Nano Range,” German Research3/96, 28-29 (1996).

[53]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 B14 (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.

[54]A. Rosa, S. Hild, and O. Marti, “Deformation induced changes in surface properties of natural rubber,” ACS Polymer Preprints, 616-617 (1996).

[55]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 Matter54 (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.

[56]J. Burger, M. Binggeli, R. Christoph, H. E. Hintermann, and O. Marti, “Nanotribology and chemical sensitivity on a nanometer scale,” , Ed. , edited by H. J. Güntherodt, D. Anselmetti, and E. Meyer (Kluwer, Dordrecht, 1995), NATO ASI Series E Vol. 286, pp. 325-330.

[57]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.

[58]M. Hipp, J. Mertz, J. Mlynek, and O. Marti, “Optical Near-Field Imaging by Force Microscopy,” in Photons and Local Probes, Ed. , edited by O. Marti and R. Möller (Kluwer Academic Publishers, Dordrecht, Netherlands, 1995), Nato ASI Series E Vol. E 300, pp. 109-122.

A scanning force microscope (SFM) is used to detect near field light by a mechanism based on optical modulation of the image force between a semiconducting probe tip and a glass surface. The modulation stems from a phenomenon called surface photo-voltage (SPV). The performance of the mechanism for near-field microscopy is demonstrated by imaging a standing evanescent light wave and profiling structured samples. The lateral resolution is found to be better 110 nm (sub-wavelength) and a representative minimum detectable power is 0.1 pW/ square root Hz in air. A simple theoretical model is described which yields a good agreement with experimental results. As a first application of this technique imaging results on light induced space charge gratings in photorefractive materials are presented.

[59]I. Hörsch, R. Kusche, O. Hollricher, O. Kirschenhofer, O. Marti, R. Sieber, G. Krausch, and J. Mlynek, “A Stand-Alone Scanning near-Field Optical Microscope,” in Photons and Local Probes, Ed. , edited by O. Marti and R. Möller (Kluwer Academic Publishers, Dordrecht Boston London, 1995), Nato ASI Series Vol. E 300, pp. 139-144.

A scanning near-field optical microscope (SNOM), where the tip is scanned rather than the sample, is presented. The advantage of this 'stand-alone' type SNOM besides its compact setup is its ability to scan on arbitrarily extended samples. Furthermore, the sample can be manipulated during scanning (e.g. heated or extended), which may be of special interest in material sciences applications. An optical shear-force detection unit is implemented to control the tip-sample distance. Design problems specific to the stand-alone setup are discussed. Using uncoated fiber tips in reflection and transmission mode, lateral resolutions of better than 120 nm and 300 nm, respectively, are shown.

[60]G. Krausch, M. Hipp, M. Boeltau, O. Marti, and J. Mlynek, “High-Resolution Imaging of Polymer Surfaces with Chemical Sensitivity,” Macromolecules28 (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.

[61]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.

[62]O. Marti and G. Krausch, “Nahfeldoptik mit fast-atomarer Auflösung,” Phys. Blätter51, 493-496 (1995).

[63]O. Marti and R. Möller, “Photons and Local Probes,” in NATO ASI Series (Kluwer Scientific Publishers, Dordrecht, 1995), Vol. E:300.

The following topics were dealt with: near field optics theory; near field optics instrumentation and applications; near field optical spectroscopy; scanning tunneling microscopy and photons; and related techniques.

[64]P. Niedermann, J. Burger, M. Binggeli, R. Christoph, H. E. Hintermann, and O. Marti, “A Scanning Force and friction Microscope,” in Ultimate Limits of Fabrication & Measurement, Proceedings of the NATO Advanced Research Workshop on "Ultimate Limits of Fabrication & Measurement", Cambridge, April 1-3 (1994), Ed. , edited by M. E. Welland and J. K. Gimzewski (Kluwer Academic Publishers, 1995), NATO ASI Series E: Applied Sciences Vol. 292.

[65]J. P. Spatz, S. Sheiko, M. Möller, R. G. Winkler, P. Reineker, and O. Marti, “Forces affecting the substrate in tapping mode,” Nanotechnology6, 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.

[66]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.

[67]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.

[68]E. Weilandt, A. Menck, and O. Marti, “Friction studies at steps with friction force microscopy,” Surf.Interface Anal.23, 428-430 (1995).

[69]H. Bielefeldt, I. Hörsch, G. Krausch, M. Lux-Steiner, J. Mlynek, and O. Marti, “Reflection-Scanning Near-Field Optical Microscopy and Spectroscopy of Opaque Samples,” Appl.Phys.A-Solid.Surf.59, 103-108 (1994).
Opaque samples are imaged by Scanning Near-field Optical Microscopy (SNOM) in reflection mode: A quartz glass fiber tip is used both to illuminate the sample and to collect light locally reflected from or emitted by the surface. The collected light is coupled out by a 2 x 2 fiber coupler and fed into a grating spectrometer for spectral analysis at each sampled point. The tip-sample distance is controlled by a shear-force feedback system. The simultaneous measurement of topography and optical signals allows an assessment of imaging artifacts, notably topography-induced intensity changes. It is demonstrated that an optical reflectance contrast not induced by topographic interference can be found on suitable samples. Local spectral analysis is shown in images of a photoluminescent layer

[70]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

[71]M. Hipp, J. Mertz, J. Mlynek, and O. Marti, “Near-field microscopy with a semiconductor probe tip,” presented at the IQEC '94, Anaheim, CA, USA, 8-13 May, 1994 pp. 205-206, Opt. Soc. America, Vol. 9 (unpublished).

Summary form only given. We present quantitative measurements of mechanical forces induced by evanescent light on a semiconductor probe tip by the surface-photovoltage effect (SPV). The semiconducting tip is used as a sensitive subwavelength-sized light detector. Scanning techniques allow the profiling of laterally inhomogeneous light distributions, such as standing wave patterns. In our experimental setup an evanescent wave is generated by using the standard technique of total internal reflection (TIR) of a laser beam inside a glass prism. The probe tip (n-doped silicon) of a scanning force microscope is placed inside the region of the evanescent field.

[72]O. Marti, “Near field optical microscopy and spectroscopy,” presented at the Digest CLEO/Europe 1994 (Amsterdam, 28 August - 2 September 1994), 1994 pp. 85, (unpublished).

[73]O. Marti, “Scanning force and friction microscopy applied to organic and biological samples,” presented at the Proceedings of ICEM'13 (Paris 17-22 July 1994), 1994 pp. 569-570, (unpublished).

[74]J. Mertz, M. Hipp, J. Mlynek, and O. Marti, “Optical Near Field Imaging with a Semiconductor Probe Tip,” Appl. Phys. Lett.64, 2338-2340 (1994).
We present an optical near-field detection mechanism based on optical modulation of the image force between a semiconducting probe tip and a glass surface. The modulation stems from a phenomenon called surface photovoltage. The performance of the mechanism for near-field imaging is demonstrated by using a scanning force microscope over a standing evanescent light wave. The lateral resolution is found to be 170 nm (subwavelength) and a representative minimum detectable power is 0.1 pW/ square root Hz in air. We develop a simple theoretical model and discuss some possible applications.

[75]T. Müller, U. Jäkle, G. Krausch, O. Marti, and J. Mlynek, Rasterkraft- und Reibungsmikroskop für Anwendungen im Ultrahochvakuum, Patent# Gebrauchsmuster #69414994.1, Germany (1994).

[76]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.

[77]H. Bielefeldt, B. Hecht, S. Herminghaus, O. Marti, and J. Mlynek, “Direct Measurement by Scanning Tunneling Optical Microscopy of the Field Enhancement caused by Surface Plasmons,” in Near Field Optics, Ed. , edited by D. Courjon and D. Pohl (Kluwer, Dordrecht, 1993), Nato ASI Series: E Vol. 242, pp. 281-286.

[78]M. Binggeli, R. Christoph, H. E. Hintermann, and O. Marti, “Atomic Scale Tribometer for Friction Studies in Controlled Atmosphere,” Surface and Coatings Technology62, 523-528 (1993).

[79]M. Binggeli, R. Christoph, H.-E. Hintermann, J. Colchero, and O. Marti, “Friction Force Measurements on Potential Controlled Graphite in Electrolytic Environment,” Nanotechnology4, 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.

[80]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.

[81]O. Marti, “Nanotribology: Friction on a Nanometer Scale,” Physica ScriptaT49, 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.

[82]O. Marti, “Friction and measurement of friction on a nanometer scale,” Surface and Coatings Technology62, 510-516 (1993).

[83]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.

[84]O. Marti and M. Amrein, “STM and SFM in Biology,” (Academic Press, San Diego, 1993).

[85]O. Marti and V. Balykin, “Light Forces,” in Near Field Optics, Ed. , edited by D. Courjon and D. Pohl (Kluwer, Dordrecht, 1993), Nato ASI Series: E Vol. 242, pp. 121-130.

[86]O. Marti, H. Bielefeldt, S. Herminghaus, P. Leiderer, and J. Mlynek, “Near Field Optical Measurement of the Surface Plasmon Field,” Opt. Comm.96, 225-228 (1993).
The intensity of the evanescent electromagnetic wave of optically excited surface plasmons was measured directly using a scanning tunneling optical microscope (STOM) setup. When resonant coupling of the driving field to the surface plasmons was achieved, the measured intensity was increased by a factor of 30 larger than the corresponding evanescent wave intensity on a bare glass surface, in agreement with the theoretical prediction. Experimental results are presented for three laser wavelengths (514 nm, 633 nm, 670 nm). Possible applications of the technique to study surface plasmon field are discussed.

[87]O. Marti, J. Colchero, H. Bielefeldt, M. Hipp, and A. Linder, “Scanning Probe Microscopy: Applications in Biology and Physics,” Microsc.Microanal.Microstruct.4 (5), 429-440 (1993).
Scanning probe microscopes can probe a variety of quantities characterizing surfaces. This overview paper describes techniques applicable in an ambient environment and having the power to distinguish different materials: the scanning force and friction microscope and the scanning near-field optical microscope combined with a spectrometer. The basic operating principles of these two microscopes are described. Selected experiments point to possible future applications: we discuss scanning force and friction microscopy of ZnSe on GaAs and of Na, K- ATPase and near-field optical microscopy of a grating and of micropores

[88]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.

[89]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.

[90]H.-J. Apell, J. Colchero, A. Linder, O. Marti, and J. Mlynek, “Na,K-ATPase in crystalline form investigated by Scanning Force Microscopy,” Ultramicroscopy42-44, 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.

[91]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.

[92]M. Hipp, H. Bielefeldt, J. Colchero, O. Marti, and J. Mlynek, “A Stand-Alone Scanning Force and Friction Microscope,” Ultramicroscopy42-44, 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.

[93]A. Linder, J. Colchero, H.-J. Apell, O. Marti, and J. Mlynek, “Scanning Force Microscopy of Diatom Shells,” Ultramicroscopy42-44, 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.

[94]O. Marti and J. Colchero, “Reibungsmikroskopie,” Physikalischen Blätter12, 1007-1009 (1992).

[95]O. Marti, A. Ruf, M. Hipp, H. Bielefeldt, J. Colchero, and J. Mlynek, “Mechanical and thermal effects on force microscope cantilevers,” Ultramicroscopy42-44, 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.

[96]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.

[97]J. Colchero, O. Marti, and J. Mlynek, “Ein kompaktes Kraftmikroskop aufgebaut mit Laserdiode und positionsempfindlicher Photodiode mit atomarer Auflösung,” Helv. Phys. Acta63, 491-492 (1990).
[98]P. K. Hansma, R. Sonnenfeld, J. Schneir, O. Marti, S. A. C. Gould, C. B. Prater, A. L. Weisenhorn, B. Drake, H. Hansma, G. Slough, W. W. McNairy, and R. V. Coleman, “Scanning Probe Microscopy of Liquid- Solid Interfaces,” in Scanning Tunneling Microscopy and Related Methods, Ed. , edited by R. J. Behm, N. Garcìa, and H. Rohrer (1990), NATO ASI Series E: Applied Sciences Vol. E 184, pp. 299-313.

[99]O. Marti, J. Colchero, and J. Mlynek, “Combined Scanning Force and Friction Microscopy of Mica,” Nanotechnology1, 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.

[100]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.

[101]M. S. d. Capua and O. Marti, “Nato Advanced Study Institute on Scanning Tunneling Microscopy (STM) - Physical Concepts, Related Techniques, and Major Applications,” ESNIB89 (09), 49-62 (1989).

[102]P. K. Hansma, B. Drake, O. Marti, S. A. C. Gould, and C. B. Prater, “The Scanning Ion-Conductance Microscope,” Science243, 641-643 (1989).
A scanning ion-conductance microscope (SICM) has been developed that can image the topography of nonconducting surfaces that are covered with electrolytes. The probe of the SICM is an electrolyte-filled micropipette. The flow of ions through the opening of the pipette is blocked at short distances between the probe and the surface, thus limiting the iron conductance. A feedback mechanism can be used to maintain a given conductance and in turn determine the distance to the surface. The SICM can also sample and image the local ion currents above the surfaces. To illustrate its potential for imagining ion currents through channels in membranes, a topographic image of a membrane filter with 0.80-micrometer pores and an image of the ion currents flowing through such pores are presented.

[103]O. Marti, V. Elings, M. Haugan, C. E. Bracker, J. Schneir, B. Drake, S. A. C. Gould, J. Gurley, L. Hellemans, K. Shaw, A. L. Weisenhorn, J. Zasadzinski, and P. K. Hansma, “Scanning probe microscopy of biological samples and other surfaces,” J. Microscopy152, 803-809 (1989).

[104]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,” Nature332, 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.

[105]P. K. Hansma, V. Elings, O. Marti, and C. E. Bracker, “Scanning tunneling microscopy and atomic force microscopy: application to biology and technology,” Science242, 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.

[106]O. Marti, B. Drake, S. Gould, and P. K. Hansma, “Probing Surfaces with the Atomic Force Microscope,” SPIE Proceedings897, 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.

[107]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. A6, 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.

[108]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. A6, 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.

[109]O. Marti, S. Gould, and P. K. Hansma, “Control electronics for atomic force microscopy,” Review of Scientic Instruments59 (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.

[110]O. Marti, H. O. Ribi, B. Drake, T. R. Albrecht, C. F. Quate, and P. K. Hansma, “Atomic Force Microscopy of an Organic Monolayer,” Science239, 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.

[111]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. A6, 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.

[112]J. Schneir, R. Sonnenfeld, O. Marti, P. K. Hansma, J. E. Demuth, and R. J. Hamers, “Tunneling microscopy, lithography, and surface diffusion on an easily prepared, atomically flat gold surface,” J. Appl. Phys.63, 717-721 (1988).
The authors show that a gold surface with atomically flat terraces as large as (150 nm)2 can be easily prepared in air by melting a gold wire with an oxyacetylene torch. Features with characteristic dimensions as low as 10 nm can be written and observed on these terraces with a scanning tunneling microscope. The features are appreciably distorted by diffusion within an hour.

[113]O. Marti, “Scanning tunneling microscope at low temperatures,” Ph.D Thesis, Physics, ETH (Federal Institute of Technology), 1987.

[114]O. Marti, G. Binnig, H. Rohrer, and H. Salemink, “Low-temperature scanning tunneling microscope,” Surf. Sci.181, 230-234 (1987).
A scanning tunneling microscope operating at cryogenic temperatures is described. Results from topographic and spectroscopic measurements are presented for surfaces of NbN and graphite at a temperature of 6.5 K. A unique feature of this system is the very low spatial drift and the resulting high positional stability. The topographical data on NbN display a grainy structure. No indications for a superconductive energy gap are found from the tunnel spectroscopy. In the ordered graphite structure, domains are found separated by dislocations.

[115]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.

[116]E. P. Stoll and O. Marti, “Restoration of Scanning-Tunneling Microscope Data Blurred by Limited Resolution, and Hapered by 1/f like noise,” Surf. Sci.181, 222 (1987).
Least-squares or Wiener filters are powerful tools to restore blurred and noisy pictures. For an optimal implementation, a knowledge of the noise and of the point-spread function (PSF) is needed; whereas the resolution PSF is relatively well known from recent theories of STM, the noise spectrum can be investigated by recording and analyzing the signal of the feedback which should keep the tunneling current constant. A 1/fbeta noise spectrum is found with beta =1.4+or-0.2. This noise can give rise to pretended hills and valleys or to spurious stripes parallel to the scanning direction in STM images. With a Wiener filter, in which the model noise-to-signal ratio is 1/fbeta -like these artificial features are eliminated. However, since the noise spectrum may partly overlap the desired spectrum of the surface corrugation, care has to be taken not to generate new artifacts.

[117]C. Gerber, G. Binnig, H. Fuchs, O. Marti, and H. Rohrer, “Scanning tunneling microscope combined with a scanning electron microscope,” Review of Scientic Instruments57, 221-224 (1986).
We have developed a small scanning tunneling microscope (STM) to be incorporated into a scanning electron microscope (SEM). Vibration isolation and damping is achieved solely with Viton dampers. As a stand-alone unit, a tunnel-gap stability of about 1 Å is reached at atmospheric air pressure without additional sound protection. Stability improves by at least an order of magnitude when incorporated into a SEM. Review of Scientific Instruments is copyrighted by The American Institute of Physics

[118]C. Gerber and O. Marti, “Magnetostrictive positionner,” IBM Techn. Discl. Bul.27, 6373 (1985).

[119]G. Binnig, C. Gerber, and O. Marti, “Sound and vibration insulation for sensitive apparatus,” IBM Techn. Discl. Bul.27, 3137 (1984).
The present damping system comprises a stack of copper plates separated by elastic pads, the cross section of which decreases from bottom to top of the stack, forming individual filter stages with differing resonant frequencies acting as an acoustical mismatch

[120]H. R. Ott, O. Marti, and F. Hulliger, “Low temperature thermal conductivity of CeAl3,” Solid State Comm.49, 1129-1131 (1984).
Measurements of the thermal and electrical conductivity of CeAl3 reveal the validity of the Wiedemann-Franz law in this substance at temperatures below 1K, hence confirming the Fermi-liquid behaviour as implied by previous data of the specific heat and the magnetic susceptibility in this temperature range.