Journal: ACS applied materials & interfaces

Article Title: High Trap Stiffness Microcylinders for Nanophotonic Trapping

doi: 10.1021/acsami.9b10041

Figure Lengend Snippet: Scanning electron microscope (SEM) images of (a) cleaved Si3N4 microcylinders and (b) lift-off Si3N4 microcylinders. The measured dimensions of these cylinders are shown below each image. The trapped orientations of the microcylinders on an nSWAT device were determined for both (c) cleaved Si3N4 microcylinders and (d) lift-off Si3N4 microcylinders based on their optical images. On an nSWAT device17, a 1064-nm laser is coupled into the TM mode of a Si3N4 waveguide (250 nm high and 750 nm wide) before passing through a 50/50 splitter that creates counter-propagating waves to form a standing wave within a fluidic pool region. The antinodes of the standing wave form trap centers for an array of traps. The entire trap array may also be translocated via a microheater, which changes the phase of one of the counter propagating waves. Bright field microscopy image scale bars in the inserts of (c) and (d) are 1 μm in length.

Article Snippet: To quantitatively assess trap stiffness enhancement with the use of Si 3 N 4 microcylinders, we first performed 3D full-field electromagnetic simulations of the microcylinders using the COMSOL Multiphysics finite element method software.

Techniques: Microscopy

Journal: ACS applied materials & interfaces

Article Title: High Trap Stiffness Microcylinders for Nanophotonic Trapping

doi: 10.1021/acsami.9b10041

Figure Lengend Snippet: (a) Trap stiffness may be measured by the power spectrum of the trapped particle motion. The example shown here is a measurement from a cleaved microcylinder at ~6 mW of laser power at the trapping region (540 Hz camera sampling rate, ~5–10 seconds per trace). A fit to the power spectrum using a Lorentzian function yields a trap stiffness of 4.16 pN/(nm-W). (b) Trap stiffness may also be measured by the variance of the trapped particle motion. The same trace as shown in (a) was analyzed based on the variance of the particle motion and equipartition theory. This yielded a trap stiffness of 3.94 pN/(nm-W). (c) A comparison of the measured trap stiffness enhancement for the cleaved (N = 11) and lift-off (N = 6) microcylinders relative to the measured values for more conventional 380-nm polystyrene microspheres (N = 18). The viscous drag coefficient was measured to be 22.2 ± 4.0 × 10−6 pN-sec/nm for lift-off microcylinders, and 19.2 ± 1.9 × 10−6 pN-sec/nm for cleaved microcylinders. Error bars are standard deviations. Results from simulations are also shown for comparison with error bars obtained from a distribution of simulated microcylinders that match the size distribution of fabricated microcylinders.

Article Snippet: To quantitatively assess trap stiffness enhancement with the use of Si 3 N 4 microcylinders, we first performed 3D full-field electromagnetic simulations of the microcylinders using the COMSOL Multiphysics finite element method software.

Techniques: Sampling, Comparison