Nano‐patterning photosensitive polymers using local field enhancement at the end of apertureless SNOM tips

Abstract

SummaryWe show experimentally that local optical field enhancement can occur at the end of an apertureless SNOM tip illuminated by an external light source. Our approach consists in the use of a photosensitive polymer, placed in the tip near-field, to record intensity distribution in the vicinity of the tip end. The excited nanometre-size light source permits us to produce nano-patterns on the polymer surface which are then characterized by atomic force microscopy. Experimental images show the influence, on the field enhancement, of three important experimental parameters: the polarization state of the incident light, the geometry of the external illumination and the radius of curvature of the tip apex. These results are shown to be in good agreement with two-dimensional numerical calculations based on the finite-difference time-domain method. We show preliminary nanometre-size patterns created by this nanosource excited at a metallic tip extremity and discuss the potential of this approach for near-field optical lithography.

Modification of single molecule fluorescence by a scanning probe

“…But as the tip moves beyond the molecule the field scattered by the tip counter-propagates against the incident laser beam, forming a standing wave pattern that modulates the excitation intensity at the position of the molecule. These features are well recovered in numerical calculations [13] and have been recently verified both by near-field lithography [14] and by single molecule fluorescence measurements [6]. However, in Fig.…”

“…These data clearly reveal an increase of molecular emission by about 60% when the glass tip is right above the molecule. In addition to this local enhancement of the fluorescence, we identify a modulation of emission caused by the interference between the incident beam (direction indicated by the vector k inc ) and the light scattered by the tip [6,13,14]. When the tip is before the molecule (to the left of the molecule) the incident beam and its scattered component co-propagate, resulting in a uniform intensity.…”

Modification of single molecule fluorescence close to a nanostructure: radiation pattern, spontaneous emission and quenching

“…Indeed, a number of groups have studied the effect of various dielectric tips on single emitters. While some researches [68,69] have reported quenching of fluorescence, others have observed enhancement [70,71]. In this section, we report on well-controlled experiments on aligned single molecules and a glass tip.…”

“…The different magnitudes of K can be partly attributed to a difference in shape and partly to the gap by which the plateau of the tip is separated from the molecule due to the presence of asperity. Sharp features generally give rise to stronger enhancements than dull ones [71] due to a stronger lightning-rod effect.…”

Optical near-field excitations on plasmonic nanoparticle-based structures

“…Despite the interesting nature of this phenomenon, there is a certain disadvantage to this design. Due to the location of the foci in the array, it is rather hard to use them subsequently to excite a plasmonic device [6,40,41,42] or as a source for subwavelength lithographic patterning [45]. Therefore, in the following we investigate for an alternative nanolens design, which would lead to a subwavelength focus in a more functional location for these type of applications.…”