Near-field optical microscopy Principles and applications
Near-field optical microscopy (English name: SNOM) is based on the principle of non-radiation field detection and imaging, can break through the diffraction limit of the ordinary optical microscope, the use of sub-wavelength scale probe in the near-field range of a few nanometers away from the surface of the sample for scanning and imaging technology, in the near-field observation range, scanning in the sample and at the same time to obtain a resolution higher than the diffraction limit of the topographic image and optical images of the Microscope.
Near-field optical microscopy is suitable for nanoscale optical imaging and nanoscale spectroscopic studies at ultra-high optical resolution. The resolution of conventional optical microscopes is affected by the optical diffraction limit, and the resolution does not exceed that wavelength scale. Unlike conventional optical microscopes, near-field optical microscopes utilize sub-wavelength scale probes to obtain smaller resolutions.
Principle of near-field optical microscopy:
The use of fused or corroded fiber optic waveguide made of probes, coated with a metal film on the outside has formed the end of the 15nm to 100nm diameter size of the optical aperture (optical aperture) of the near-field optical probe, and then can be used as a precision displacement and scanning detection of piezoelectric ceramic materials (piezoelectric ceramics) with the atomic force Atomic force microscopy (atomic force microscopy, AFM) to provide accurate height feedback control, the near-field optical probe will be very accurate (vertical and horizontal in the direction of the sample surface of the spatial resolution can be about 0.1nm and 1nm) control in the sample surface on the height of 1nm to 100nm, three-dimensional spatial feedback control of near-field Scanning (scanning), and has a nano optical aperture of the fiber optic probe can be used to receive or transmit optical information, thus obtaining a real space of the three-dimensional near-field optical image, because the distance between it and the sample surface is much smaller than the general wavelength of light, the measured information are all near-field optical information, without the usual common far-field optical optical limit of the limit of optical resolution of the surrounded shot.
Application of near-field optical microscope:
Near-field optical microscope breaks through the traditional optical bypass limit, can directly use light to observe nanomaterials, analyze the microstructure and defects of nanoelements, and in recent years has been applied to analyze semiconductor laser components. Because of its high resolution, it can be used for high-density data access. Currently, over 100 GB of super-resolution near-field optical disks have been successfully produced using this technology. It can also be used for near-field microscopic analysis of biomolecules and protein fluorescence.
Principle and structure of near-field optical microscope:
In general, the resolution of an optical microscope is only a few hundred nanometers when observing in the far-field due to the limitation of light wave circumference. However, when observed in the near field, the winding and interference can be avoided, and the limitation of the winding can be overcome to increase the resolution to about tens of nanometers. In the structure of a near-field optical microscope, a tapered optical fiber with an aperture of tens of nanometers at the end is used as a probe. The distance between the probe and the object to be measured is precisely controlled within the near-field observation range, and the piezoelectric ceramics that can be precisely positioned and scanned are used to carry out three-dimensional spatial near-field scanning in conjunction with the high-feedback control system provided by the atomic force microscope. The fiber optic probe receives or transmits optical signals to obtain a 3D near-field optical image.
