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Near-field microscopy with synchrotron radiation successful

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Figure 1: Comparison of the nano FTIR spectra of silicon carbide (SiC) and gold (Au), recorded with broadband synchrotron radiation at the IR beamline of the MLS. The two measurement positions are identified with "X" in the near-field image of the sample surface (top right). The lateral resolution lies below 100 nm with this procedure.

At PTB’s electron storage ring Metrology Light Source (MLS), a scattering type near-field microscope for the infrared (IR) regime has been successfully put into operation in cooperation with the Freie Universität Berlin (group of Prof. E. Rühl). The near-field microscope is based on the principle of a scanning force microscope and enables the acquisition of the specimen’s infrared signature simultaneously with the topographic information. For this purpose, a sharp metallic tip – a so-called near-field probe – is placed within the focused beam while the sample is moved stepwise in order to scan the surface. The signal scattered by the irradiated tip provides optical information about the sample surface at the used excitation wavelength in the IR regime. With a typical diameter between 20 nm and 50 nm, the near-field probe provides a lateral resolution significantly below 100 nm, which is a significant improvement compared to other conventional methods. Commonly used tunable gas lasers for the IR regime, e.g. CO and CO2-lasers, only cover the wavelength ranges from 5.2 µm to 6.1 µm and from 9.2 µm to 10.8 µm, respectively.  In order to extend the accessible spectral range, the microscope has been combined with the IR beamline of the MLS. The use of this broadband synchrotron radiation source opens up the possibility to perform IR-spectroscopy for characterizing nanosystems in the spectral range from, initially, 1 µm to 20 µm.

P. Hermann, A. Hoehl, A. Patoka, F. Huth, E. Rühl, and G. Ulm, Optics Express 21, 2913 (2013)


P. Hermann, 7.24, e-mail: Peter.Hermann(at)ptb.de


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