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  • 1
    Electronic Resource
    Electronic Resource
    Influence of environmental conditions on shear–force distance control in near-field optical microscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7100-7106 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371798
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  • 2
    Electronic Resource
    Electronic Resource
    Multicolor images acquisition by scanning near-field optical microscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4820-4824 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A multicolor scanning near-field optical microscope (color-SNOM) has been developed to provide real color images of nanoscopic samples for biological and spectroscopical purposes. The sample illumination consists either of a single or a combined beam of different laser wavelengths. A common SNOM setup has been modified in a way that three photomultipliers for blue, green, and red light detection and color separating dichroic filters have been implemented. With this beam splitter device, it is possible to acquire simultaneously with the topography three color optical images on three different channels. In order to improve the signal-to-noise ratio, etched fiber tips with a high transmission intensity were used. Fluorescence experiments on latex beads labeled with two different dyes and transmission measurements on gold nanoparticles show a wavelength dependent optical contrast. The color-SNOM appears as a powerful tool for high resolution color spectroscopy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408265
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  • 3
    Electronic Resource
    Electronic Resource
    An easy-to-use non-optical shear-force distance control for near-field optical microscopes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1912-1916 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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 or 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. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146995
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  • 4
    Electronic Resource
    Electronic Resource
    Distance control in near-field optical microscopy with piezoelectrical shear-force detection suitable for imaging in liquids (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1769-1772 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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/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. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147990
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  • 5
    Electronic Resource
    Electronic Resource
    Generation of guided polaritons in electro-optic LiTaO3 probes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1093-1096 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: LiTaO3 is a widely used material for electro-optic sampling of electrical pulses. Many groups now use thin sensor crystals of 20 μm thickness, which is an optimum thickness for best measurement accuracy and minimum invasiveness of the probe. We demonstrate that by using these crystals of 20 μm thickness, a severe distortion of the measured signal can occur, if the bandwidth of the probed electrical signal exceeds about 700 GHz. In this case, polaritons are generated during reflection of the electrical signal at the LiTaO3-to-air interface in the rear of the crystal. Because the thin LiTaO3 crystal acts as a planar waveguide for the polaritons, not only can the electrical signal be seen during the measurement, but also these guided polaritons. We propose the use of longer crystals of at least 1 mm length to overcome this problem. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358970
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  • 6
    Electronic Resource
    Electronic Resource
    Ultrahigh frequency measurements of magnetic penetration length and surface impedance of YBa2Cu3O7−x microstriplines on Si and GaAs substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5282-5286 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting microstriplines of YBa2Cu3O7−x have been deposited and patterned on substrates of silicon on sapphire and GaAs. In both substrates fast semiconducting photoswitches were fabricated and integrated into the microstriplines. Short lightpulses of 100 fs length generated electrical pulses in the semiconducting photoswitches. The electrical pulses were launched into the superconducting striplines, where they were detected by electro-optical sampling. This method permits the analysis of the frequency dependence of the YBa2Cu3O7−x surface impedance Zs(T,ν) and the magnetic penetration depth λ(T,ν) in the temperature regime 10≤T≤90 K and the frequency range 10 GHz≤ν≤600 GHz. The Zs and λ measurements showed that the electrical data of the YBa2Cu3O7−x were comparable to those of YBa2Cu3O7−x deposited on LaAlO3. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359281
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  • 7
    Electronic Resource
    Electronic Resource
    Spatially resolved near-field spectroscopy on localized GaInAsP/InP double heterostructures (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 870-876 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 λ=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. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366770
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  • 8
    Electronic Resource
    Electronic Resource
    Method to produce high-resolution scanning near-field optical microscope probes by beveling optical fibers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3118-3122 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new two-step method to fabricate scanning near-field optical microscope (SNOM) probes with an aperture size clearly below 100 nm has been developed. For the first step, a chemical etching process is used in which an optical fiber is dipped with its acrylate jacket into hydrofluoric acid to get a suitable tapered shape of the fiber. The second step consists of beveling the etched fiber using a modified micropipette beveler to obtain a tip diameter in the nanometer range as well as a smooth surface to allow a good aluminum metallization by evaporation. By varying the beveling angle tapered shapes with different cone angles can be obtained. First transmission experiments with our probes show an optical resolution below 80 nm. In comparison to fiber tips obtained by a standard heating and pulling method, the transmission efficiency of these tips is up to three orders of magnitude higher due to the optimized tapered shape. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304866
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  • 9
    Electronic Resource
    Electronic Resource
    High quality epitaxy of YBa2Cu3O7−x on silicon-on-sapphire with the multiple buffer layer YSZ/CeO2 (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1429-1431 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality YBa2Cu3O7−x films on silicon-on-sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109647
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  • 10
    Electronic Resource
    Electronic Resource
    Vertical silicon metal–semiconductor–metal photodetectors with buried CoSi2 contact (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 866-868 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on design, fabrication, and characterization of an ultrafast vertical metal–semiconductor–metal photodetector. A CoSi2 layer in silicon acts both as a bottom Schottky contact and a buried light reflector. A semi-transparent metallization on top of a photosensitive silicon mesa serves as top Schottky contact. Time-domain studies of the pulse response are performed by electro-optic sampling measurements on photodetectors integrated monolithically into microstrip transmission lines. At room temperature, carrier sweep-out is dominated by hopping transport involving shallow traps. At low temperatures, hopping transport is strongly suppressed. As a consequence, the speed of the diode is considerably enhanced, reaching a pulse response with a full width at half maximum of 6.5 ps. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113413
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