Mark D. Huntington

Plasmonic Bowtie Nanolaser Arrays

Plasmonic lasers exploit strong electromagnetic field confinement at dimensions well below the diffraction limit. However, lasing from an electromagnetic hot spot supported by discrete, coupled metal nanoparticles (NPs) has not been explicitly demonstrated to date. We present a new design for a room-temperature nanolaser based on three-dimensional (3D) Au bowtie NPs supported by an organic gain material. The extreme field compression, and thus ultrasmall mode volume, within the bowtie gaps produced laser oscillations at the localized plasmon resonance gap mode of the 3D bowties. Transient absorption measurements confirmed ultrafast resonant energy transfer between photoexcited dye molecules and gap plasmons on the picosecond time scale. These plasmonic nanolasers are anticipated to be readily integrated into Si-based photonic devices, all-optical circuits, and nanoscale biosensors.

Programmable soft lithography: solvent-assisted nanoscale embossing.

This paper reports an all-moldable nanofabrication platform that can generate, from a single master, large-area nanoscale patterns with programmable densities, fill factors, and lattice symmetries. Solvent-assisted nanoscale embossing (SANE) could increase the spacing of patterns up to 100% as well as decrease them down to 50% in a single step by stretching or heating a polymer substrate. Also, SANE could reduce critical feature sizes as small as 45% compared to the master by controlled swelling of patterned molds with different solvents. These capabilities were applied to generate plasmonic nanoparticle arrays with continuously variable separations and hence different optical properties on the same substrate.

Extraordinary Nonlinear Absorption in 3D Bowtie Nanoantennas

This paper reports that arrays of three-dimensional (3D), bowtie-shaped Au nanoparticle dimers can exhibit extremely high nonlinear absorption. Near-field interactions across the gap of the 3D bowties at the localized surface plasmon resonance wavelengths resulted in an increase of more than 4 orders of magnitude in local field intensity. The imaginary part of the third-order nonlinear susceptibility (Im χ((3))) for the 3D bowtie arrays embedded in a dielectric material was measured to be 10(-4) esu, more than 2 orders of magnitude higher than reported for other metal nanoparticle-dielectric composites. Moreover, 3D dimers with increased nanoscale structure (such as folding) exhibited increased optical nonlinearity. These 3D nanoantennas can be used as critical elements for nanoscale nonlinear optical devices.

Polymer nanowrinkles with continuously tunable wavelengths

This paper describes a parallel method to generate polymer nanowrinkles over large areas with wavelengths that were continuously tuned down to 30 nm. Reactive ion etching using fluorinated gases was used to chemically treat thermoplastic polystyrene films, which resulted in a stiff skin layer. Upon heating, the treated thermoplastic, microscale, and nanoscale wrinkles were formed. We used variable-angle spectroscopic ellipsometry to characterize the thickness of the skin layer; this thickness could then be used to predict and control the nanowrinkle wavelength. Because the properties of these nanotextured polymer surfaces can be tuned over a large range of wrinkle wavelengths, they are promising for a broad range of applications, especially those that require large-area and uniform surface patterning.

Controlled three-dimensional hierarchical structuring by memory-based, sequential wrinkling

This paper describes how a memory-based, sequential wrinkling process can transform flat polystyrene sheets into multiscale, three-dimensional hierarchical textures. Multiple cycles of plasma-mediated skin growth followed by directional strain relief of the substrate resulted in hierarchical architectures with characteristic generational (G) features. Independent control over wrinkle wavelength and wrinkle orientation for each G was achieved by tuning plasma treatment time and strain-relief direction for each cycle. Lotus-type superhydrophobicity was demonstrated on three-dimensional G1-G2-G3 hierarchical wrinkles as well as tunable superhydrophilicity on these same substrates after oxygen plasma. This materials system provides a general approach for nanomanufacturing based on bottom-up sequential wrinkling that will benefit a diverse range of applications and especially those that require large area (>cm(2)), multiscale, three-dimensional patterns.

High-rotational symmetry lattices fabricated by Moiré nanolithography

This paper describes a new nanofabrication method, moiré nanolithography, that can fabricate subwavelength lattices with high-rotational symmetries. By exposing elastomeric photomasks sequentially at multiple offset angles, we created arrays with rotational symmetries as high as 36-fold, which is three times higher than quasiperiodic lattices (≤12-fold) and six times higher than two-dimensional periodic lattices (≤6-fold). Because these moiré nanopatterns can be generated over wafer-scale areas, they are promising for a range of photonic applications, especially those that require broadband, omnidirectional absorption of visible light.

A Portable, Benchtop Photolithography System Based on a Solid‐State Light Source

Advances in photolithography have enabled the development of microelectromechanical systems (MEMS) [ 1 ] as well as facilitated studies of physical systems at spatial dimensions that mimic natural environments. [ 2–6 ] The primary challenge to producing such structures is the high cost of the infrastructure and processing tools necessary for fabrication, such as dedicated cleanroom facilities and mask aligners. Although soft lithography methods have enabled low-cost solutions for the rapid prototyping of microand nanometer patterns, mask aligners are still often required to fabricate the masters. [ 3 , 4 ]

Polarization-dependent multipolar plasmon resonances in anisotropic multiscale au particles

This paper reports the fabrication and characterization of three-dimensional (3D) multiscale Au particles with different aspect ratios. Increasing the length of the particles resulted in excitation of a longitudinal mode and two different transverse modes having different multipolar orders. The multipolar orders increased for both longitudinal and transverse modes as the aspect ratio increased. Finite-difference time-domain calculations revealed that the structural asymmetry of the 3D anisotropic particles were the reason for the two distinct transverse plasmon resonances. When the 3D structural change occurred at the ends of the multiscale particle, however, the optical response showed two resonances in the longitudinal direction and only a single resonance in the transverse direction.

Controlling the Orientation of Nanowrinkles and Nanofolds by Patterning Strain in a Thin Skin Layer on a Polymer Substrate

We describe herein how to control the orientation of polymer nanowrinkles and nanofolds with large amplitudes. Nanowrinkles were created by chemically treating thermoplastic polystyrene sheets to form a thin skin layer and then heating the substrate to relieve strain. By manipulating the strain globally and locally in the skin layer, we could tune whether wrinkles or folds formed, as well as the distances over which these structures could be produced. This unique materials system provided access to high strain regimes, which enabled mechanisms behind the spontaneous formation of complex structures to be explored.

Delocalized Lattice Plasmon Resonances Show Dispersive Quality Factors.

This Letter describes how out-of-plane lattice plasmon (OLP) resonances in 2D Au nanoparticle (NP) arrays show dispersive quality factors. These quality factors can be tailored simply by controlling NP height. Numerical calculations of near-field optical properties and band diagrams were performed to understand the measured dispersion effects of the OLPs. The results revealed that delocalized OLPs are a type of surface Bloch mode composed of many Bloch harmonics. As the OLP dispersion evolves from a stationary state to a propagating state, the nonradiative loss decreases because of weak local field confinement, whereas the radiative loss increases because of strong coupling to the leaky zero-order harmonic.