title: Resonant-plasmon field enhancement from asymmetrically illuminated conical metallic-probe tips.
abstract: Optical-field enhancement and confinement for an asymmetrically illuminated nanoscopic Au tip suspended over a planar Au substrate is investigated both numerically and experimentally. The spatial field distribution of the tip-sample system was calculated using the full 3D finite-difference time-domain method. The calculation enables investigation of the effects of the substrate-tip placement, angle of incidence, and spectral response. The tip plasmon response leads to a significant (up to ~70 times) local field enhancement between the tip and substrate. The enhancement is found to be extremely sensitive to the tip-sample separation distance. Tip-enhanced Raman scattering experiments were performed and the numerical results provide a consistent description of the observed field localization and enhancement.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Roth
authors.forename: Nicolae C
authors.initials: NC
authors.lastname: Panoiu
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Adams
authors.forename: Richard M
authors.initials: RM
authors.lastname: Osgood
authors.forename: Catalin C
authors.initials: CC
authors.lastname: Neacsu
authors.forename: Markus B
authors.initials: MB
authors.lastname: Raschke