Edge plasmon mediated tip enhanced spectroscopy
Final Report Abstract
A specific advantage of scanning near field optical microscopy (SNOM) with the tetrahedral metal coated glass tip (T-tip) is the internal illumination of the tip. A versatile SNOM configuration for internal illumination and detection (reflection mode) as well as for external detection (transmission mode) of the signal was developed. This configuration was adapted to 2 different SNOM instruments, one with a simultaneous STM (Scanning tunneling microscope) and one with a simultaneous SFM (scanning force microscope) mode at ambient conditions and the function of the instruments for edge mode enhanced tip enhanced spectroscopy (TES) was tested and the application for TES was verified. As the microscope promised to be suited especially well for the molecular characterization of monomolecular layers, we developed a method for the near-field photochemical and radiationinduced chemical fabrication of nanopatterns of a self-assembled silane monolayer (SAM). The method is of potential interest for the fabrication of functional nanostructured SAMs which have many interesting applications. At the same time chemical nanopatterns can be realized as test structures for the microscopic methods. The TES was not yet applied to the molecular characterization of the nanopatterned SAM’s. In the course of the project it was noticed that modified tetrahedral tips and partially metal coated 90°glass wedges can be used to detect the coupling of photon spin to electron orbital angular momentum due to the property of the T-Tip, that an internally incident beam is retroreflected. Since in the process of retroreflection the turning sense of a circularly polarized beam of light does not change and the direction of propagation is inverted, the photon spin is inverted. Due to conservation of angular momentum, a transfer of photon spin to electron orbital angular momentum of conduction electrons can occur. A circular movement of electrons is blocked in the specific structure because the closed conducting path for electrons is interrupted and the transferred spin can be detected as a photo-induced electromotive force. Depending on the polarization of the incident beam, a maximum photovoltage of about 0,2µV was measured. The same kind of experiments was performed for a different planar metal nanostructure, a semi-infinite slit of 50 nm width in a 20 nm thick gold film ending in a 25 nm narrow metal connection between both metal edges of the slit. Photovoltages of the same order of magnitude were observed as for the wedge samples with different characteristics for the different polarizations of the incident beam. The results are interpreted in terms of an electrodynamic model of the photon. A linearly polarized monochromatic photon is a solitary electromagnetic wave of finite energy hv which carries an angular momentum h/2π with the frequency v and Planck’s constant. The angular momentum and other electromagnetic properties of the photon are derived from the well known oscillatory solutions of the stationary electromagnetic radiation far fields of an oscillating dipole by extracting from these expressions the field distribution of a longitudinally propagating wave emitted from a dipole transition. The relative values of the measured photovoltages for different polarizations can well be explained by the electrodynamic model of the photon. The absolute values of the measured photovoltages are also consistent with the interpretation. This model is not only useful for an interpretation of the experimental results on the transfer of photon spin to electron orbital angular momentum but has far reaching consequences for the foundations of quantum electrodynamics. Apart from the spin angular momentum, one can derive a photon mass and an electric surface charge and one can thus derive the electrodynamic origin of the charge e of the electron, which paves the way to develop a unified quantum theory of electrodynamics and, since a mass of the photon is defined, of gravitation.
Publications
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“Near-field photochemical and radiation-induced chemical fabrication of nanopatterns of a selfassembled silane monolayer.“ Beilstein J. Nanotechnol. 2014, 5, 1441–1449
U.C. Fischer, C. Hentschel, F.Fontein, L. Stegemann, C. Hoeppener, H. Fuchs and S. Hoeppener
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On Photon Spin and the Electrodynamic Origin of the Charge of the Electron
U.C. Fischer
