AFM-Raman-Nano-IR Systems
Modular AFM
Automated AFM
Practical AFM
 
 

SPM Principles

SNOM

 


Fig. 1 Schematic of a combined shear force and near-field scanning optical microscope [5].

The resolving power of classical optical microscopes is restricted by Abbe's diffraction limit to about to one-half of the optical wavelength. However, it is possible to overcome this limit.

If a subwavelength hole in a metal sheet is scanned close to an object, a super-resolved image can be built up from the detected light that passes through the hole. Scanning near-field microscopy based on this principle was first proposed by Synge [1] and demonstrated at microwave frequencies by Ash and Nicholls [2] with a resolution of l/60 [3]. At visible wavelengths this principle (optical stethoscopy, near-field optical-scanning microscopy, SNOM) was demonstrated by Pohl et al [3, 4]. In [5] Betzig et al they have demonstrated using fiber probes to image a variety of samples with a number of different contrast mechanisms.
To make the system easier to use and to extend its applicability to samples of arbitrary topography, it would be advantageous to have a distance regulation mechanism capable of automating the initial approach and maintaining the aperture at a fixed distance from the sample over the entire course of a scan. Several mechanisms have been proposed previously to SNOM and related evanescent field techniques, including electron tunneling, capacitance, photon tunneling and near-field reflection.
At present the most-used method of probe-sample distance regulation relies on the detection of shear forces between the end of  the near-field probe and the sample [5]. Shear Force based system allows Shear Force Microscopy alone, or simultaneous Shear Force and Near-Field imaging, including Transmission mode for transparent samples, Reflection mode for opaque samples and Luminescence mode for additional characterisation of samples.

References

  1. Philos. Mag. 6, 356 (1928).
  2. Nature (London) 237, 510 (1972). 
  3. Appl. Phys. Lett. 44, 651 (1984). 
  4. J. Appl. Phys. 59, 3318 (1986). 
  5. Appl. Phys. Lett. 60, 2484 (1992).
 
 
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