SNOM/STM using a tetrahedral tip and a sensitive current‐to‐voltage converter

Abstract

SummaryScanning near-field optical microscopes (SNOM) using the tetrahedral-tip (T-tip) with scanning tunnelling microscopy (STM) distance control have been realized in transmission and reflection mode. Both set-ups used ordinary STM current-to-voltage converters allowing measurement of metallic samples. In the transmission mode, a resolution of 10 nm to 1 nm with regard to material contrast can be achieved on binary metal samples. Because of the great near-field optical potential of the T-tip with respect to the optical resolution, it is a challenging task to find out whether these results can be transferred to non-metallic sample systems as well. This paper reports on a newly designed SNOM/STM transmission mode set-up using the tetrahedral-tip. It implements a sensitive current-to-voltage converter to widen the field of measurable sample systems. Beyond this, mechanical and optical measuring conditions are substantially improved compared to previous set-ups. The new set-up provides a basis for the routine investigation of metal nanostructures and adsorbed organic monolayers at resolutions in the 10 nm range.

Surface plasmon mediated tip enhanced Raman scattering

“…1, with an auxiliary scanning tunneling microscope mode for distance control. 10,11 A tetrahedral glass fragment is used as a transparent body of our SNOM tip ͑T-tip͒. It is coated with a 50 nm thick gold film.…”

“…12 A slightly focused beam ͓numerical aperture ͑NA͒ 0.1, = 633 nm͔, which is directed into the glass body of the tip is expected according to the results of numerical investigations 13 to excite in an attenuated total reflection configuration, a highly confined edge plasmon mode of a gold coated glass edge of the T-tip, which leads then to a highly confined excitation of the tip apex acting as a SNOM probe. With such a SNOM configuration, images of metal silver grains embedded in a thin metal film could be imaged at a resolution below 10 nm 10,14 and SNOM images of SP excitations of metal nanostructures were reproducibly obtained at a resolution of 30 nm. 15 It was possible to interpret these latter SNOM images assuming as a SNOM probe a point dipole at a distance of 10 nm from the sample surface and which is tilted at an angle of 45°.…”

A tetrahedral tip as a probe for tip‐enhanced Raman scattering and as a near‐field Raman probe

“…[25] Images of metal silver grains embedded in a thin metal film registered at STM contact between the tip and the sample could be imaged at an even higher resolution below 10 nm. [22,23] As the resolution that is obtained in the SNOM images should roughly correspond to the field localization on a surface which is generated by the T-tip, we thought that a configuration of a metal tip and a metal substrate [9] should be especially favorable as a highly local and highly efficient TERS probe.…”

Correlated topographic and spectroscopic imaging by combined atomic force microscopy and optical microscopy

“…However, it has still been highly challenging to conduct routine NSOM imaging of biological samples because of certain technical difficulties [5][6][7][8]. To circumvent those difficulties, a new method of ''aperture-less NSOM'' has been demonstrated [9][10][11][12][13][14][15][16][17][18][19][20]. The key principle of the aperture-less NSOM technique is to use a sharp metallic tip as a near-field excitation enhancer.…”