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Register a new userResonance shift effects in apertureless scanning near-field optical microscopy
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Authors
J.A. Porto
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We develop a theory to study apertureless scanning near-field optical microscopy which takes into account retardation, higher multipoles of the tip, and the multiple scattering between the tip and the surface. We focus on metallic systems and discuss the implication of the formation of tip-induced surface plasmon modes in the tip-surface system. We discuss the effects associated with the shift in energy of those modes as a function of the tip-surface distance. Both the local field and the scattering cross section are enhanced when the tip approaches the surface, but there is no general correspondence between the two enhancements.
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A theory is presented to describe the heat-flux radiated in near-field regime by a set of interacting nanoemitters held at different temperatures in vacuum or above a solid surface. We show that this thermal energy can be focused and even amplified in spots that are much smaller than those obtained with a single thermal source. We also demonstrate the possibility to locally pump heat using specific geometrical configurations. These many body effects pave the way to a multi-tip near-field scanning thermal microscopy which could find broad applications in the fields of nanoscale thermal management, heat-assisted data recording, nanoscale thermal imaging, heat capacity measurements and infrared spectroscopy of nano-objects.
The finite-difference time-domain (FDTD) method is employed to solve the three dimensional Maxwell equation for the situation of near-field microscopy using a sub-wavelength aperture. Experimental result on unexpected high spatial resolution is reproduced by our computer simulation.
Imaging dynamical processes at interfaces and on the nanoscale is of great importance throughout science and technology. While light-optical imaging techniques often cannot provide the necessary spatial resolution, electron-optical techniques damage the specimen and cause dose-induced artefacts. Here, Optical Near-field Electron Microscopy (ONEM) is proposed, an imaging technique that combines non-invasive probing with light, with a high spatial resolution read-out via electron optics. Close to the specimen, the optical near-fields are converted into a spatially varying electron flux using a planar photocathode. The electron flux is imaged using low energy electron microscopy, enabling label-free nanometric resolution without the need to scan a probe across the sample. The specimen is never exposed to damaging electrons.
We present numerical simulations of scattering-type Scanning Near-Field Optical Microscopy (s-SNOM) of 1D plasmonic graphene junctions. A comprehensive analysis of simulated s-SNOM spectra is performed for three types of junctions. We find conditions when the conventional interpretation of the plasmon reflection coefficients from s-SNOM measurements does not apply. Our results are applicable to other conducting 2D materials and provide a comprehensive understanding of the s-SNOM techniques for probing local transport properties of 2D materials.
Aperture based scanning near field optical microscopes are important instruments to study light at the nanoscale and to understand the optical functionality of photonic nanostructures. In general, a detected image is affected by both, the transverse electric and magnetic field components of light. The discrimination of the individual field components is challenging, as these four field components are contained within two signals in the case of a polarization-resolved measurement. Here, we develop a methodology to solve the inverse imaging problem and to retrieve the vectorial field components from polarization- and phase-resolved measurements. Our methodology relies on the discussion of the image formation process in aperture based scanning near field optical microscopes. On this basis, we are also able to explain how the relative contributions of the electric and magnetic field components within detected images depend on the probe geometry, its material composition, and the illumination wavelength. This allows to design probes that are dominantly sensitive either to the electric or magnetic field components of light.
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