Comparison of active and passive methods for the infrared scanning near-field microscopy

We systematically compare the active and the passive methods for infrared scattering-type scanning near-field optical microscopy (s-SNOM). The active SNOM makes use of IR lasers or incoherent thermal emitters to illuminate a sample, whereas the passive method directly measures extremely weak fluctua...

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Bibliographic Details
Published in:Applied physics letters 2019-04, Vol.114 (15)
Main Authors: Weng, Qianchun, Panchal, Vishal, Lin, Kuan-Ting, Sun, Liaoxin, Kajihara, Yusuke, Tzalenchuk, Alexander, Komiyama, Susumu
Format: Article
Language:English
Subjects:
Applied physics
Electron energy
Emitters
Emitters (electron)
Equilibrium methods
Mapping
Microscopy
Optical microscopy
Sampling methods
Variation
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Summary:We systematically compare the active and the passive methods for infrared scattering-type scanning near-field optical microscopy (s-SNOM). The active SNOM makes use of IR lasers or incoherent thermal emitters to illuminate a sample, whereas the passive method directly measures extremely weak fluctuating electromagnetic evanescent fields spontaneously generated at the sample surface without any external illumination. For this reason, our specific version of the passive SNOM is called a scanning noise microscope (SNoiM). In thermal equilibrium, the two methods are shown to be similar, both mapping the nanoscale variation of the complex dielectric constant of the sample. We demonstrate that a significant difference between the two methods emerges when the sample is driven out of thermal equilibrium, viz., the active SNOM is insensitive whereas the SNoiM is extremely sensitive to the electron temperature in locally heated nanoregions.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.5088056