Fig. 1. Scanning electron micrographs of (a) The fiber taper on a quartz tuning fork and (b) a fiber taper attached with a 100 nm gold nanosphere.

Fig. 2. (a) The silicon thin film sample. The shaded color results from a thickness variance caused by chemical-mechanical polishing (CMP). (b) Schematic Illustration of the optical setup. Black arrows indicate the preferential polarization directions of light beams (with polarizers implemented) and the LSPR mode. The excitation (red) and collection (blue) light paths are spatially defined using orthogonally placed irises. The polarizers and irises were combined for preferential excitation and collection of the longitudinal LSPR mode scattering, and for suppression of background scattering and reflection. The inset graph illustrates that a TIR evanescent field of the illumination light was intentionally used to couple to the nanosphere in order to reduce fiber taper scattering.

Fig. 3. A schematic illustration of the longitudinal and transverse plasmon resonance modes for a metallic nanosphere near a mirror plane. Arrows indicate the equivalent dipole moments of the nanosphere and its mirror image.

Fig. 4. (a) A set of scattering spectra recorded as a gold nanosphere on a fiber taper end approached a silicon film. The tuning fork resonance frequency shift setpoint, Δf, ranges from 0.5 Hz to 3.5 Hz with a 0.2 Hz step, corresponding to the spectral curves from bottom to top. These data have been smoothed using a Gaussian filter with a full-width at half-maximum of 11.4 nm. The dashed line is an eye guide for LSPR peak wavelength tuning. (b) Longitudinal LSPR mode shift versus gap distance, with a ${\pm} $0.1 nm per step system noise which has been converted to the gap distance error bars.

Fig. 5. Scattering spectra for three 100 nm gold nanospheres which were attached to a fiber taper suspended in air (a), adhered to a glass coverslip (b), and adhered to a silicon film (c).

Fig. 6. FDTD simulation of a 100 nm gold nanosphere on top of a 200 nm thick silicon film. (a) The simulation configuration, including water meniscus, fiber taper and a 3 nm native oxide layer. The black arrow indicates the incident light’s polarization. (b) Scattering spectra for gap distances of 2-8 nm. The dashed line is an eye guide for LSPR peak wavelength tuning.