Search

This article provides a careful comparison between the electric and mechanical excitation of a tuning fork for shear force feedback in scanning probe microscopy, an analysis not found in present literature. A setup is designed and demonstrated for robust signal and noise measurements at comparable levels of physical movement of the probe. Two different signal amplification methods, combined with two excitation ways provide three possible configurations. For each method a quantitative analysis, supported by analytical elaboration and numerical simulations, is provided. Finally, it is shown that in practical circumstances electric excitation followed by detection with a transimpedance amplifier provides the best result. • Shear force feedback provides height feedback in scanning probe microscopy. • Quartz tuning forks outfitted with sharp probe suit purpose of shear force detection. • Sub-micrometer movement of a tuning fork induces interaction between tip and sample. • Possible tuning fork excitation and signal detection methods impact measurement. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a simple and accurate method for calibrating the amplitude of vibration of quartz tuning fork sensors commonly used in atomic force- and near field optical-microscopy. Unlike interferometric methods, which require a complex optical setup, the method we present requires only a simple measurement of the electro-mechanical properties of the tuning-fork oscillator and can be performed in a matter of minutes without disturbing the experimental setup. Comparison with interferometric methods shows that an accuracy of better than few percent can be routinely achieved. [Copyright &y& Elsevier]

Abstract: In this article results of a comparison of two NSOM probe characterization methods are presented. Scanning electron microscopy analysis combined with electromagnetic field modeling using the finite difference in time domain method are compared with measured far-field radiation diagrams of NSOM probes. It is shown that measurement of far-field radiation diagrams can be an efficient tool for daily checking of the NSOM probes quality. Moreover, it is shown that the inner probe geometry has large influence on the directional radiation of an NSOM probe and the far-field radiation diagram can be used as a simple method to distinguish between different probe geometries. [Copyright &y& Elsevier]

Abstract: The shape and size variations of the nanopatterns produced on a positive photoresist using a near-field scanning optical microscope (NSOM) are investigated with respect to the process variables. A cantilever-type nanoprobe having a 100nm aperture at the apex of the pyramidal tip is used with the NSOM and a He–Cd laser at a wavelength of 442nm as the illumination source. Patterning characteristics are examined for different laser beam power at the entrance side of the aperture (P in), scan speed of the piezo stage (V), repeated scanning over the same pattern, and operation modes of the NSOM (DC and AC modes). The pattern size remained almost the same for equal linear energy density. Pattern size decreased for lower laser beam power and greater scan speed, leading to a minimum pattern width of around 50nm at P in=1.2μW and V=12μm/s. Direct writing of an arbitrary pattern with a line width of about 150nm was demonstrated to verify the feasibility of this technique for nanomask fabrication. [Copyright &y& Elsevier]

The submicron domain structure of coexisting liquid condensed (LC) and liquid expanded (LE) phases in monolayers composed of palmitic acid and 20 wt% of a lung surfactant protein B fragment has been investigated. Near-field microscopy was used to simultaneously measure topography and fluorescence images of monolayers that were prepared at a surface pressure of 15 mN/m and a temperature of 22°C. The use of a fluorescently tagged peptide allowed for unambiguous determination of the peptide location in the two-component system. The LC and LE phases in the monolayers are measured on the submicron length scale. A 6–11 A˚ height difference between the LC and LE phases was evident in the height images. Gradual transitions between the LC and LE domains were observed across a 1.3 μm length scale in the near-field fluorescence images, but were significantly sharper in the simultaneously collected topography images and in the separately measured AFM images. These results may reflect the occurrence of peptide encroachment into the LC domains. [Copyright &y& Elsevier]

An effective method of DNA stretching on mica surfaces is proposed for an extremely low concentration of DNA. The method is based on an electric field and well applied on the concentration range from 57×10−3 to 57×10−6 ng/ml. The stretching exists in a gap between positive and negative electrodes. The difference in the stretching efficiency among the different surfaces of bare mica, Mg2+ soaked mica and AP-mica is discussed. The best performance of the stretching is found from the surface of AP-mica for the same experimental condition of sample concentration and applied voltage. Finally, from a Scanning near-field optical microscope image, it is found that well-stretched DNA molecules have shown more similar optical resolution, which is inferred from an optical fiber probe, itself. [Copyright &y& Elsevier]