Ultra stable tuning fork sensor for low-temperature near-field spectroscopy

Physics Department, Swiss Federal Institute of Technology Lausanne.
Ultramicroscopy (Impact Factor: 2.44). 03/2001; 90(2-3):97-101. DOI: 10.1016/S0304-3991(01)00144-9
Source: PubMed


We report on a distance control system for low-temperature scanning near-field optical microscopy, based on quartz tuning fork as shear force sensor. By means of a particular tuning fork-optical fiber configuration, the sensor is electrically dithered by an applied alternate voltage, without any supplementary driving piezo, as done so far. The sensitivity in the approach direction is 0.2nm, and quality factors up to 2850 have been reached. No electronic components are needed close to the sensor, allowing to employ it in a liquid He environment. The system is extremely compact and allows for several hours of stability at 5 K.

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    • "By bringing the tapered fibre probe into close proximity with the sample surface, the inevitable diffraction limit encountered in conventional far-field optical methods can be overcome. Since initial demonstrations that crystal quartz tuning forks can be used as sensors for acoustic (Güthner et al ., 1989) and force (Karrai & Grober, 1995) microscopy, applications of this technique have been extended to near-field optical microscopy (Davydov et al ., 1999; Crottini et al ., 2002), atomic force microscopy (Giessibl, 2000; Callaghan et al. , 2002), and electrostatic force microscopy (Seo et al ., 2002; Wang et al ., 2002). Recently, we demonstrated the working principles of the tapping-mode tuning fork near-field scanning optical microscopy (TMTF-NSOM; Tsai & Lu, 1998) and successfully applied this new method to study the physical properties of a single mode optical fibre waveguide (Tsai et al ., 1999), superresolution near-field structures (Tsai & Lin, 2000), and semiconductor lasers (Lu et al ., 2001). "
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    ABSTRACT: We present the implementation of a short-tip tapping-mode tuning fork near-field scanning optical microscope. Tapping frequency dependences of the piezoelectric signal amplitudes for a bare tuning fork fixed on the ceramic plate, a short-tip tapping-mode tuning fork scheme and an ordinary tapping-mode tuning fork configuration with an 80-cm optical fibre attached are demonstrated and compared. Our experimental results show that this new short-tip tapping-mode tuning fork scheme provides a stable and high Q factor at the tapping frequency of the tuning fork and will be very helpful when long optical fibre probes have to be used in an experiment. Both collection and excitation modes of short-tip tapping-mode tuning fork near-field scanning optical microscope are applied to study the near-field optical properties of a single-mode telecommunication optical fibre and a green InGaN/GaN multiquantum well light-emitting diode.
    Journal of Microscopy 04/2003; 209(Pt 3):205-8. DOI:10.1046/j.1365-2818.2003.01135.x · 2.33 Impact Factor
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    ABSTRACT: V groove GaAs/AlGaAs quantum wires are investigated by spatially resolved photoluminescence spectroscopy using a low-temperature scanning near-field optical microscope. The spectra along the wires feature several sharp emission lines, which are understood as the emission from exciton states localized in inhomogeneities of the confining potential. It is expected that these exciton states spatially overlap and that their energies are correlated, which leads to level repulsion. The statistical analysis of the spectra in terms of autocorrelation functions clearly reveals this effect. In order to model photoluminescence rather than absorption spectra, we perform detailed simulations of exciton relaxation and luminescence kinetics in a disordered one-dimensional system, taking into account the realistic structure of the facets at the bottom of the V groove in our disorder model. Combining near-field measurements and numerical simulations we show that disorder prevents the full relaxation of excitons towards the local ground states in the dips of the disordered potential. As a consequence, luminescence from excited states is observed. We identify in the spatial and energy correlation between localized states the origin of the observed level repulsion and discuss the role played by the two facets at the bottom of the V groove in this mechanism. This analysis also highlights the relevance of the broad photoluminescence background observed in this and in analogous experiments. We propose as explanation for the origin of this broad background the strong exciton-acoustic phonon coupling that results in phonon sidebands in the spectrum of each localized state.
    Physical Review B 05/2004; 69(20). DOI:10.1103/PhysRevB.69.205321 · 3.74 Impact Factor
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    ABSTRACT: We present the results of an experimental and theoretical study on the optimum design of shear-force sensors, used in scanning probe microscopes. We have optimized a configuration consisting of a tuning-fork/fiber-tip assembly, achieving quality factors (Q) exceeding 8000, and have presented a theoretical analysis of the design wherein the force holding the fiber and fork in contact is provided solely by elastic mechanical deformation, which allows full control of the performance of the system. On this basis, we constructed a high-quality-factor configuration with the fiber glued onto the tuning fork.
    Applied Physics Letters 03/2005; 86(6-86):064103 - 064103-3. DOI:10.1063/1.1861983 · 3.30 Impact Factor
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