Abstract
The design and characterization of a tip control unit for an apertureless scanning near field optical microscope (ASNOM) is reported. To make the instrument operation easier, the cantilever control parts (piezo excitation of the cantilever vibration for the dynamic mode feedback and the parts necessary for the optical lever scheme of the vibration control) were placed in a separate detachable assembly. To suppress the influence of vibrations of the setup, the assembly was made lightweight. Good optical access to the ASNOM tip from various directions is provided in the system. High long-term mechanical stability of the system (~50 nm lateral drift in 18 hours) as well as low sensitivity to seismic vibrations (~400 pm RMS) is demonstrated. It is shown that external sound is not a main source of noise in the topography image (~200 pm RMS). The light field distribution (with its amplitude and phase) around the ASNOM tip was acquired by scanning the focal spot around the tip, and a high optical quality of the system is demonstrated.
Highlights
A powerful tool for the local investigation of surface optical properties is apertureless scanning near field optical microscopy [1] apertureless scanning near field optical microscope (ASNOM)
The light field distribution around the ASNOM tip was acquired by scanning the focal spot around the tip, and a high optical quality of the system is demonstrated
Operation of the ASNOM is based on demodulation of the tip scattering variations caused by the tip tapping motion, which means that the conditions of the tip mechanical oscillation affect strongly the amplitude and phase of the recovered optical signal
Summary
A powerful tool for the local investigation of surface optical properties is apertureless scanning near field optical microscopy [1] ASNOM (scattering SNOM, s-SNOM). The optical signal recovered at the oscillation frequency of the tip [19] results mainly from scattered light caused by the interference between the tip and its image in the surface. These variations of the photocurrent are useless in the terms of near-field (nonradiative) electromagnetic interaction of the tip and the surface. Operation of the ASNOM is based on demodulation of the tip scattering variations caused by the tip tapping motion, which means that the conditions of the tip mechanical oscillation affect strongly the amplitude and phase of the recovered optical signal. It means that 1) sample loading, optical alignment and operation must be simple; 2) the fabrication of the hand-made tips (see e.g. [17,19]) should be excluded from the operation; the commercial tips should be used instead
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