Aqueous Assembly of Oxide and Fluoride Nanoparticles into 3D Microassemblies.

We demonstrate rapid [∼mm3/(h·L)] organic ligand-free self-assembly of three-dimensional, >50 µm single-domain microassemblies containing up to 107 individual aligned nanoparticles through a scalable aqueous process. Organization and alignment of aqueous solution-dispersed nanoparticles are induced by decreasing their pH-dependent surface charge without organic ligands, which could be temperature-sensitive or infrared light absorbing. This process is exhibited by transforming both dispersed iron oxide hydroxide nanorods and lithium yttrium fluoride nanoparticles into high packing density microassemblies. The approach is generalizable to nanomaterials with pH-dependent surface charge (e.g., oxides, fluorides, and sulfides) for applications requiring long-range alignment of nanostructures as well as high packing density.

Reduced plasma-induced damage to near-surface nitrogen-vacancy centers in diamond.

Understanding plasma etch damage on near-surface nitrogen vacancy (NV) centers in diamond is essential for preserving NV emission in photonic structures and magnetometry systems. We have developed a methodology to compare the optical properties of ensemble NV centers initially 70 nm from the surface brought closer to the surface through etching with O2 plasmas in three different reactors. We employ a conventional reactive ion etcher, a barrel etcher, and a downstream etcher. We find that, irrespective of the etcher used, NV luminescence dims steadily as NVs are brought closer to the surface due to optical and surface effects. When NVs are less than 40 nm from the surface, differences in damage from the three different plasma processes affect the NV emission intensity in different ways. Diamond that is etched using the conventional etching method shows a greatly reduced NV luminescence, whereas NVs 15 nm from the surface still survive when the diamond is etched in the downstream reactor. As a result, downstream etching provides a possible alternative method for low damage etching of diamond for preservation of near surface NV properties.

Two-dimensional hybrid photonic/plasmonic crystal cavities.

We present a 2-D plasmonic crystal design with visible band-gap by combining a 2-D photonic crystal with TM band-gap and a silver surface. Simulations show that the presence of the silver surface gives rise to an expanded band-gap. A plasmonic crystal defect cavity with Q ~300 and mode volume ~1.9x10(-2) (λ/n) (3) can be formed using our design. The total Q of such a cavity is determined by both the radiative loss of the dielectric component, as well as absorption loss to the metal. We provide design criteria for the optimization of the total Q to allow high radiative or extraction efficiency.

Controlled mode tuning in 1-D 'RIM' plasmonic crystal trench cavities probed with coupled optical emitters.

We present a design of plasmonic cavities that consists of two sets of 1-D plasmonic crystal reflectors on a plasmonic trench waveguide. A 'reverse image mold' (RIM) technique was developed to pattern high-resolution silver trenches and to embed emitters at the cavity field maximum, and FDTD simulations were performed to analyze the frequency response of the fabricated devices. Distinct cavity modes were observed from the photoluminescence spectra of the organic dye embedded within these cavities. The cavity geometry facilitates tuning of the modes through a change in cavity dimensions. Both the design and the fabrication technique presented could be extended to making trench waveguide-based plasmonic devices and circuits.