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.

Review of near-field optics and superlenses for sub-diffraction-limited nano-imaging

“…However, care must be taken when simulating geometries with abrupt curvature and high field gradients. Detailed investigations of the field enhancement offered by different probe tips have been conducted using the multiple multipole, 112,113 finite element time domain, 114 finite difference time domain, 101,115 and finite element 108 techniques. The field enhancement at the apex of sharp probe tips has allowed for apertureless SNOM fluorescence imaging 116 down to single molecules.…”

Imaging Nanometre‐Sized Hot Spots on Smooth Au Films with High‐Resolution Tip‐Enhanced Luminescence and Raman Near‐Field Optical Microscopy

“…The extraordinary sensitivity of tip-enhanced Raman scattering spectroscopy has been demonstrated for resonant [1][2][3][4] as well as non-resonant molecules. [1,5] The method has the potential to reach single-molecule sensitivity, as recently shown for molecules that are resonant at the excitation frequency.…”

“…[1,5] The method has the potential to reach single-molecule sensitivity, as recently shown for molecules that are resonant at the excitation frequency. [3,6,7] However, tip-enhanced optical microscopy has so far been restricted to transparent [8,9] and semitransparent [1,2,10] samples with tip illumination from below. The first experimental demonstrations of tip-enhanced Raman spectroscopy (TERS) used rough silver films on transparent microscope slides supporting the molecules of interest.…”

Tuning of Plasmonic Nanoparticle and Surface Enhanced Wavelength Shifting of a Nanosystem Sensing Using 3-D-FDTD Method

“…asymmetric plasmonic nanoparticles have been studied by many world class researchers; Ryan et al, [15] have reported field enhancement induced between a metallic tip and metallic substrate [15]. The enhancement of the field has been investigated in multi-material trimmer nanostructures composed of Au nanoparticles surrounded by two Ag nanoparticles as a function of the gap between the two Ag nanoparticle and their size.…”

“…The diffraction and interference of the out coupled waves are investigated by using, in-house, the 3D-Finite Difference Time Domain (3D -FDTD) technique [17], [18]. The FDTD grid is excited using the total-field/scattered field formulation [15] with plane-wave polarized parallel to the x-axis. The source is placed at the cell grid number 4 after the PMLs.…”