Fig. 1. (a) SEM image of a fabricated nanohole array. The nanoslot is designed to connect the nanoholes of diameter d, along the x direction, and w is the width of the nanoslot, i.e., the separation between the nanotips. Λ is the period for both the x and y directions; (b) higher magnification image of double nanoholes, fabricated using the same conditions as for (a) and located 3 μm from the edge of the array. The z direction is pointing into the plane of the paper.

Fig. 2. (a) Simulated and (b) experimental extinction curves extracted from the transmission spectra; (c) energy density from the highest near-field confined area and (d) trapping force along the z direction as a function of wavelength.

Fig. 3. (a) Electric field distribution for the y=0 plane; (b) trapping force and (c) the corresponding potential curve as a function of particle position along the z direction for x=0  nm and y=0  nm.

Fig. 4. Electric field distribution on the (a) z=18  nm and (b) x=0  nm planes. Potential plots for a 30 nm particle as a function of the position of the particle along (c) the x direction and (d) the y direction. The sweep directions are shown in (a) and (b) using white arrows for illustration purposes.

Fig. 5. Raw data trace of transmission signal against time. A zoomed in step increase around the time point of 147.7 s is shown in the inset, which represents a time interval of 0.003 s.

Fig. 6. (a) Trap stiffness for a single 30 nm PS sphere in a near-field trap as a function of wavelength. The experiment was done for an incident laser intensity of 0.57  mW/μm2. The presented theoretical calculation and experimental observations were normalized to 1  mW/μm2 laser intensity. Stars, theory; solid circles, experiment; (b) trap stiffness as a function of laser intensity for an incident trapping wavelength of 980 nm. Squares, theory; polygons, experiment.