Plasmonics provides great promise for nanophotonic applications. However, the high optical losses inherent in metal-based plasmonic systems have limited progress. Thus, it is critical to identify alternative low-loss materials. One alternative is polar dielectrics that support surface phonon polariton (SPhP) modes, where the confinement of infrared light is aided by optical phonons. Using fabricated 6H-silicon carbide nanopillar antenna arrays, we report on the observation of subdiffraction, localized SPhP resonances. They exhibit a dipolar resonance transverse to the nanopillar axis and a monopolar resonance associated with the longitudinal axis dependent upon the SiC substrate. Both exhibit exceptionally narrow linewidths (7-24 cm(-1)), with quality factors of 40-135, which exceed the theoretical limit of plasmonic systems, with extreme subwavelength confinement of (λ(res)3/V(eff))1/3 = 50-200. Under certain conditions, the modes are Raman-active, enabling their study in the visible spectral range. These observations promise to reinvigorate research in SPhP phenomena and their use for nanophotonic applications.

Low-loss surface phonon polariton (SPhP) modes supported within polar dielectric crystals are a promising alternative to conventional, metal-based plasmonic systems for the realization of nanophotonic components. Here we show that monopolar excitations in 4H-silicon carbide nanopillar arrays exhibit an unprecedented stable efficiency even when the resonator filling fraction is varied by an order of magnitude. This provides a powerful mid-IR platform with excellent spectral tunability and strong field confinement. Combining IR spectroscopy measurements with full electrodynamic calculations, we elucidate the nature of the optical modes in these elongated subwavelength nanostructures by investigating their spectral behavior and local field dependence on the size and periodicity. The present study also gives a clear understanding and practical guidelines for the spectral tuning of localized SPhP and the coupling mechanisms at play. This work is integral with the development of phonon-polariton based applications for surface-enhanced infrared absorption spectroscopy (SEIRA), polychromatic detectors, and thermal imaging.

Efforts to create reproducible surface-enhanced Raman scattering (SERS)-based chemical and biological sensors has been hindered by difficulties in fabricating large-area SERS-active substrates with a uniform, reproducible SERS response that still provides sufficient enhancement for easy detection. Here we report on periodic arrays of Au-capped, vertically aligned silicon nanopillars that are embedded in a Au plane upon a Si substrate. We illustrate that these arrays are ideal for use as SERS sensor templates, in that they provide large, uniform and reproducible average enhancement factors up to ∼1.2 × 10(8) over the structure surface area. We discuss the impact of the overall geometry of the structures upon the SERS response at 532, 633, and 785 nm incident laser wavelengths. Calculations of the electromagnetic field distributions and intensities within such structures were performed and both the wavelength dependence of the predicted SERS response and the field distribution within the nanopillar structure are discussed and support the experimental results we report.

A conventional thermal emitter exhibits a broad emission spectrum with a peak wavelength depending upon the operation temperature. Recently, narrowband thermal emission was realized with periodic gratings or single microstructures of polar crystals supporting distinct optical modes. Here, we exploit the coupling of adjacent phononpolaritonic nanostructures, demonstrating experimentally that the nanometer-scale gaps can control the thermal emission frequency while retaining emission line widths as narrow as 10 cm −1 . This was achieved by using deeply subdiffractional bowtie-shaped silicon carbide nanoantennas. Infrared far-field reflectance spectroscopy, near-field optical nanoimaging, and full-wave electromagnetic simulations were employed to prove that the thermal emission originates from strongly localized surface phonon-polariton resonances of nanoantenna structures. The observed narrow emission line widths and exceptionally small modal volumes provide new opportunities for the user-design of near-and far-field radiation patterns for advancements in infrared spectroscopy, sensing, signaling, communications, coherent thermal emission, and infrared photodetection.

Radiation patterns and the resonance wavelength of a plasmonic antenna are significantly influenced by its local environment, particularly its substrate. Here, we experimentally explore the role of dispersive substrates, such as aluminum-or gallium-doped zinc oxide in the near infrared and 4H-silicon carbide in the mid-infrared, upon Au plasmonic antennas, extending from dielectric to metal-like regimes, crossing through epsilon-near-zero (ENZ) conditions. We demonstrate that the vanishing index of refraction within this transition induces a "slowing down" of the rate of spectral shift for the antenna resonance frequency, resulting in an eventual "pinning" of the resonance near the ENZ frequency. This condition corresponds to a strong backward emission with near-constant phase. By comparing heavily doped semiconductors and undoped, polar dielectric substrates with ENZ conditions in the nearand mid-infrared, respectively, we also demonstrate the generality of the phenomenon using both surface plasmon and phonon polaritons, respectively. Furthermore, we also show that the redirected antenna radiation induces a Fano-like interference and an apparent stimulation of optic phonons within SiC.

This work demonstrates the production of a well-controlled, chemical gradient on the surface of graphene. By inducing a gradient of oxygen functional groups, drops of water and dimethyl-methylphosphonate (a nerve agent simulant) are "pulled" in the direction of increasing oxygen content, while fluorine gradients "push" the droplet motion in the direction of decreasing fluorine content. The direction of motion is broadly attributed to increasing/decreasing hydrophilicity, which is correlated to high/low adhesion and binding energy. Such tunability in surface chemistry provides additional capabilities in device design for applications ranging from microfluidics to chemical sensing.

Mie-resonances in vertical, small aspect-ratio and subwavelength silicon nanopillars are investigated using visible bright-field µ-reflection measurements and Raman scattering. Pillar-to-pillar interactions were examined by comparing randomly to periodically arranged arrays with systematic variations in nanopillar diameter and array pitch. First- and second-order Mie resonances are observed in reflectance spectra as pronounced dips with minimum reflectances of several percent, suggesting an alternative approach to fabricating a perfect absorber. The resonant wavelengths shift approximately linearly with nanopillar diameter, which enables a simple empirical description of the resonance condition. In addition, resonances are also significantly affected by array density, with an overall oscillating blue shift as the pitch is reduced. Finite-element method and finite-difference time-domain simulations agree closely with experimental results and provide valuable insight into the nature of the dielectric resonance modes, including a surprisingly small influence of the substrate on resonance wavelength. To probe local fields within the Si nanopillars, µ-Raman scattering measurements were also conducted that confirm enhanced optical fields in the pillars when excited on-resonance.

As an emerging optical material, graphene's ultrafast dynamics are often probed using pulsed lasers yet the región in which optical damage takes place is largely uncharted. Here, femtosecond láser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged área has a linear correlation with the optical fluence. These results demónstrate local modification of sp 2 -carbon bonding structures with optical pulse fluences as low as 14 mJ/cm 2 , an order-of-magnitude lower than measured and theoretical ablation thresholds. [doi:10.1063/1.3663875] Graphene's combination of nearly uniform, broad spectral absorption with -2.3% absorption per monolayer is desirable for broadband optical devices. These intrinsic properties make it useful for mode-locking ' and Q-switching and also as neutral density filters for cw light and low fluence optical pulses. Practical graphene optical devices require large, uniform, high-quality films measuring at least 5x5 mm and deposition on optically compatible substrates. The most promising synthesis methods to meet these criteria are either through Si sublimation from SiC (epitaxial graphene) or chemical vapor deposition (CVD) growth on Cu substrates, where it is possible to transfer these graphene films onto different surfaces. ' 7 In particular, CVD graphene from Cu is attractive because large-area films are inexpensive, simple to fabrícate, and transferable for applications in optics and photonics. In addition, graphene's strong optical absorption enables processing and patterning with lasers. Current optical patterning approaches depend upon the linear absorption of highly focused cw láser light causing localized heating, exceeding 1000K. These results are similar to other localized thermal methods for altering graphene compounds, for example, heating with scanning probes.In general, laser-induced damage of materials arises from either thermal or non-thermal effects. The cw láser produces thermal damage by absorption of photons and subsequent energy dissipation through phonons, which at sufficient incident optical energy can be violent enough to break bonds. Alternatively, the energy from femtosecond láser pulses is transferred at rates significantly faster than the phonon relaxation time. Thus, hot electrons are created and then cool by giving their energy to phonons on a time scale shorter than thermal diffusion. This ultrafast absorption creates unique energy transfer mechanisms within the solid that depend on the amount of energy absorbed. As such, the absorption of femtosecond optical pulses can produce both thermal and non-thermal effects. Low pulse fluence creates localized heating and causes melting, vaporization, and/or sublimation, while higher fluence produces a large, non-'Electronic mail: marc.cuirie@nrl.navy.mil. 'Previously with GSG, NA, Crofton, MD 21114 resident at Naval Research Laboratory, Washington DC, 20375.