Eric Jaquay

Light-Assisted, Templated Self-Assembly Using a Photonic-Crystal Slab

We experimentally demonstrate the technique of light-assisted, templated self-assembly (LATS). We excite a guided-resonance mode of a photonic-crystal slab with 1.55 μm laser light to create an array of optical traps. We demonstrate assembly of a square lattice of 520 nm diameter polystyrene particles spaced by 860 nm. Our results demonstrate how LATS can be used to fabricate reconfigurable structures with symmetries different from traditional colloidal self-assembly, which is limited by free energetic constraints.

Light-Assisted, Templated Self-Assembly of Gold Nanoparticle Chains

We experimentally demonstrate the technique of light-assisted, templated self-assembly (LATS) to trap and assemble 200 nm diameter gold nanoparticles. We excite a guided-resonance mode of a photonic-crystal slab with 1.55 μm laser light to create an array of optical traps. Unlike our previous demonstration of LATS with polystyrene particles, we find that the interparticle interactions play a significant role in the resulting particle patterns. Despite a two-dimensionally periodic intensity profile in the slab, the particles form one-dimensional chains whose orientations can be controlled by the incident polarization of the light. The formation of chains can be understood in terms of a competition between the gradient force due to the excitation of the mode in the slab and optical binding between particles.

Near-Field, On-Chip Optical Brownian Ratchets

Nanoparticles in aqueous solution are subject to collisions with solvent molecules, resulting in random, Brownian motion. By breaking the spatiotemporal symmetry of the system, the motion can be rectified. In nature, Brownian ratchets leverage thermal fluctuations to provide directional motion of proteins and enzymes. In man-made systems, Brownian ratchets have been used for nanoparticle sorting and manipulation. Implementations based on optical traps provide a high degree of tunability along with precise spatiotemporal control. Here, we demonstrate an optical Brownian ratchet based on the near-field traps of an asymmetrically patterned photonic crystal. The system yields over 25 times greater trap stiffness than conventional optical tweezers. Our technique opens up new possibilities for particle manipulation in a microfluidic, lab-on-chip environment.

Optical Epitaxial Growth of Gold Nanoparticle Arrays

We use an optical analogue of epitaxial growth to assemble gold nanoparticles into 2D arrays. Particles are attracted to a growth template via optical forces and interact through optical binding. Competition between effects determines the final particle arrangements. We use a Monte Carlo model to design a template that favors growth of hexagonal particle arrays. We experimentally demonstrate growth of a highly stable array of 50 gold particles with 200 nm diameter, spaced by 1.1 μm.

Design and optical characterization of high-Q guided-resonance modes in the slot-graphite photonic crystal lattice.

A new photonic crystal structure is generated by using a regular graphite lattice as the base and adding a slot in the center of each unit cell to enhance field confinement. The theoretical Q factor in an ideal structure is over 4 × 10(5). The structure was fabricated on a silicon-on-insulator wafer and optically characterized by transmission spectroscopy. The resonance wavelength and quality factor were measured as a function of slot height. The measured trends show good agreement with simulation.

Near-field optically driven Brownian motors(Conference Presentation)

Brownian ratchets are of fundamental interest in fields from statistical physics to molecular motors. The realization of Brownian ratchets in engineered systems opens up the potential to harness thermal energy for directed motion, with applications in transport and sorting of nanoparticles. Implementations based on optical traps provide a high degree of tunability along with precise spatiotemporal control. Near-field optical methods provide particular flexibility and ease of on-chip integration with other microfluidic components. Here, we demonstrate the first all-optical, near-field Brownian ratchet. Our approach uses an asymmetrically patterned photonic crystal and yields an ultra-stable trap stiffness of 253.6 pN/nm-W, 100x greater than conventional optical tweezers. By modulating the laser power, optical ratcheting with transport speed of ~1 micron/s can be achieved, allowing a variety of dynamical lab-on-a-chip applications. The resulting transport speed matches well with the theoretical prediction.

Correction to Light-Assisted, Templated Self-Assembly Using a Photonic-Crystal Slab

W this erratum, we provide the corrected optical force map and optical potential for Figure 5. The grid resolution used in the original calculation was not sufficient to guarantee convergence. The grid spacing has been reserved to 5 nm, and the forces are now calculated with the bottom edge of the particle 5 nm above the surface of the slab. The forces are obtained from a volumetric integral of the Lorentz force, using the electromagnetic fields obtained from a finite-difference time domain simulation (Lumerical). This method allows smaller particle-slab separations than the Maxwell Stress Tensor method used previously. The corrected forces are shown in Figure 5a. The corrected in-plane potential is shown in Figure 5b,c. The minimum is at the center of the unit cell. The total potential, which includes the effect of sinking, also has a minimum at the center of the unit cell. The total potential is deeper than the in-plane potential. Shao-Hua Wu and Ningfeng Huang contributed to this correction. They were not authors on the original manuscript. N. H. identified the convergence issues in the original calculation. S.-H. W. carried out calculations and verified convergence.

Optical epitaxial growth of gold nanoparticle arrays (Presentation Recording)

We demonstrate optical trapping of a periodic array of closely spaced gold nanoparticles. To achieve the experimental result, we considered competition between optical gradient forces and strong interparticle interactions. We achieve control of the gradient forces using a photonic-crystal template designed to create a periodic optical trapping potential. We modeled the interparticle interactions using a kinetic Monte Carlo approach. The results predict the formation of different particle superstructures (such as chains or filled-in arrays) depending on lattice constant and symmetry. Using the model prediction, we designed and demonstrated a template that allows trapping of a regular periodic array.

Experimental demonstration of light-assisted, templated self assembly using photonic-crystal slabs

We demonstrate experimentally that the near field of a photonic-crystal slab can be used to trap square arrays of nanoparticles. This process of light-assisted, templated, self assembly exploits the guided-resonance mode of the photonic crystal for force enhancement.

Light-Assisted Assembly of Nanoparticle Arrays Using Resonant Modes of Photonic-Crystal Slabs

We demonstrate for the first time the trapping of arrays of particles using guided resonance modes in photonic-crystal slabs. The resonantly-enhanced evanescent field attracts particles toward the slab, resulting in the formation of periodic nanoparticle arrays.