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Web site updated 23.03.2000

Papers

We have published the following papers in the last year. You can search using keywords

1. R. Brunner, A. Simon, T. Stifter, and O. Marti, "Modulated shear-force distance control in near field optical microscopy (NSOM)," Review of Scientific Instruments (1999), submitted?
2. 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.
3. 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.
4. 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 (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.
5. O. Hollricher, R. Brunner, and O. Marti, "Piezoelectrical shear-force distance control in near-field optical microscopy for biological applications," Ultramicroscopy 71, 143-147 (1998).
6. 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.
7. M. Abraham, W. Ehrfeld, M. Lacher, O. Marti, K. Mayr, W. Noell, P. Güthner, and J. Barenz, "Micromachined aperture probe tip for multifunctional scanning probe microscopy," presented at the Micro-Optical Technologies for Measurement, Sensors and Microsystems II and Optical Fiber Sensor Technologies and Applications, Munich, Germany, 18-20 June, 1997 (unpublished).
   The paper presents a new concept of a micromachined integrated sensor for combined atomic force/near field optical microscopy. The sensor consists of a microfabricated cantilever with an integrated waveguide and a transparent near field aperture tip. The advantage compared to the fiber based near field tips is the high reproducibility of the aperture and the control of the tip-sample distance by the AFM-channel. The aperture tip is fabricated in a reliable batch process which has the potential for implementation in micromachining processes of scanning probe microscopy sensors and therefore leads to new types of multifunctional probes. For evaluation purposes, the tip was attached to an optical fiber by a microassembly setup and subsequently installed in a near-field scanning optical microscope. First measurements of topographical and optical near-field patterns demonstrate the proper performance of the hybrid probe.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. H. Bielefeldt, I. Horsch, G. Krausch, M. Luxsteiner, 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
14. O. Marti, "Near field optical microscopy and spectroscopy," Digest CLEO/Europe 1994 (Amsterdam, 28 August - 2 September 1994) , 85 (1994).
15. 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.
16. 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.
17. 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.
18. 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.

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Last modified: 23. März 2000