attoSNOM III
fiber based, low temperature scanning near-field optical microscope, tuning fork sensor
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This system is unique due to the collection of the reflected signal using an ellipsoidal aluminum mirror. Thus, the attoSNOM III impresses by its outstanding sensitivity combined with high spatial resolution. The applicable probes are optical fiber tips. The non-optical tip–sample distance control is achieved using a piezoelectric quartz force sensor for highly sensitive shear force detection.

Principle - The excellent spatial resolution of this instrument is achieved by bringing the aperture at the apex of an aluminum coated tapered optical fiber tip into close proximity to the sample surface. The non-optical tip–sample distance control is achieved by using a piezoelectric tuning fork force sensor which allows to measure the tip–sample friction and shear forces. In order to minimize the parasitic cable capacitance the tuning fork is directly mounted onto a low temperature preamplifier. In a typical friction force imaging mode, the tip vibration amplitude at the resonance frequency of the fork is adjusted with a mechanical dither excitation to be around 50 pm. The friction force is kept at a constant value using a feedback loop on the tip–sample distance. The optical fiber-based probe is used in illumination mode to excite the sample surface locally. The reflected signal containing the photoluminesence signal is either collected through the same fiber or using an ellipsoidal aluminum mirror (optional). Optical access to the sample / focus is enabled via a CCD camera.

Tip-Sample Distance Control - The tuning fork sensor as a tip-sample distance control mechanism is a non-optical method for measuring small vibrations of the SNOM probe by means of a quartz tuning fork. In general, the glass fiber tip is glued onto one leg of a small quartz tuning fork. The fiber based tip is vibrated in horizontal direction; as the tip approaches the sample in the nanometer range, the vibration amplitude of the tip decreases. This reduction of the amplitude by the sample due to lateral forces, the so-called shear forces, is monitored and kept constant, thus leading to a constant force or gap between the SNOM probe and the sample surface. The sensor allows to measure the tip–sample friction and shear forces ranging down to approximately 0.1 pN. In this configuration, the whole system behaves like a simple forced harmonic oscillator.

Probes - The attoSNOM III is compatible to any fiber-based SNOM probe.

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Detailed Specification Sheet

Complete System Solutions:
LTSYS	Complete system configurations for this product.