Decoupling absorption and radiative cooling in mid-wave infrared bolometric elements.

We present a spectrally selective, passively cooled mid-wave infrared bolometric absorber engineered to spatially and spectrally decouple infrared absorption and thermal emission. The structure leverages an antenna-coupled metal-insulator-metal resonance for mid-wave infrared normal incidence photon absorption and a long-wave infrared optical phonon absorption feature, aligned closer to peak room temperature thermal emission. The phonon-mediated resonant absorption enables a strong long-wave infrared thermal emission feature limited to grazing angles, leaving the mid-wave infrared absorption feature undisturbed. The two independently controlled absorption/emission phenomena demonstrate decoupling of the photon detection mechanism from radiative cooling and offer a new design approach enabling ultra-thin, passively cooled mid-wave infrared bolometers.

Coherent light filter.

We demonstrate efficient filtering of coherent light from a broad spectral background. A Michelson interferometer is used to effectively filter out the coherent emission of mid-infrared lasers from the co-propagating incoherent emission of a broadband thermal source. We show coherent light suppression as high as 16.9 dB without any modification of the broadband incoherent background spectrum. In addition, we demonstrate the ability to measure the spatially dependent (incoherent) thermal emission from a patterned surface, using our filter to remove a coherent signal which would otherwise overload our detection system. The demonstrated filter is rapidly tunable and wavelength-flexible, and has potential for imaging and spectroscopy applications in the presence of an otherwise overpowering coherent signal.

Extending plasmonic response to the mid-wave infrared with all-epitaxial composites.

Highly doped semiconductor "designer metals" have been shown to serve as high-quality plasmonic materials across much of the long-wavelength portion of the mid-infrared. These plasmonic materials benefit from a technologically mature semiconductor fabrication infrastructure and the potential for monolithic integration with electronic and photonic devices. However, accessing the short-wavelength side of the mid-infrared is a challenge for these designer metals. In this work we study the perspectives for extending the plasmonic response of doped semiconductors to shorter wavelengths by leveraging charge confinement, in addition to doping. We demonstrate, theoretically and experimentally, negative permittivity across the technologically vital mid-wave infrared (3-5 µm) frequency range. The semiconductor composites presented in our work offer an ideal material platform for monolithic integration with a variety of semiconductor optoelectronic devices operating in the mid-wave infrared.

Engineering the Berreman mode in mid-infrared polar materials.

We demonstrate coupling to and control over the broadening and dispersion of a mid-infrared leaky mode, known as the Berreman mode, in samples with different dielectric environments. We fabricate subwavelength films of AlN, a mid-infrared epsilon-near-zero material that supports the Berreman mode, on materials with a weakly negative permittivity, strongly negative permittivity, and positive permittivity. Additionally, we incorporate ultra-thin AlN layers into a GaN/AlN heterostructure, engineering the dielectric environment above and below the AlN. In each of the samples, coupling to the Berreman mode is observed in angle-dependent reflection measurements at wavelengths near the longitudinal optical phonon energy. The measured dispersion of the Berreman mode agrees well with numerical modes. Differences in the dispersion and broadening for the different materials is quantified, including a 13 cm-1 red-shift in the energy of the Berreman mode for the heterostructure sample.

Platinum germanides for mid- and long-wave infrared plasmonics.

Platinum germanides (PtGe) were investigated for infrared plasmonic applications. Layers of Pt and Ge were deposited and annealed. X-ray diffraction identified PtGe(2) and Pt(2)Ge(3) phases, and x-ray photo-electron spectroscopy determined vertical atomic composition profiles for the films. Complex permittivity spectra were measured by ellipsometry over the 2 to 15 µm wavelength range. Surface plasmon polariton (SPP) characteristics such as propagation length and field penetration depth were calculated. Photon-to-SPP couplers in the form of 1D lamellar gratings were fabricated and characterized in the range 9 - 10.5 µm via wavelength-dependent specular reflection spectra for multiple angles of incidence. The observed resonances compare well with calculated spectra for SPP excitation on PtGe(2). Platinum germanides are CMOS compatible and may serve as SPP hosts for on-chip mid-IR plasmonic components with tighter field confinement than noble-metal hosts.

All-semiconductor plasmonic nanoantennas for infrared sensing.

Infrared absorption spectroscopy of vibro-rotational molecular resonances provides a powerful method for investigation of a wide range of molecules and molecular compounds. However, the wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross sections of the molecules under investigation. This mismatch makes infrared detection and identification of nanoscale volumes of material challenging. Here we demonstrate a new type of infrared plasmonic antenna for long-wavelength nanoscale enhanced sensing. The plasmonic materials utilized are epitaxially grown semiconductor engineered metals, which results in high-quality, low-loss infrared plasmonic metals with tunable optical properties. Nanoantennas are fabricated using nanosphere lithography, allowing for cost-effective and large-area fabrication of nanoscale structures. Antenna arrays are optically characterized as a function of both the antenna geometry and the optical properties of the plasmonic semiconductor metals. Thin, weakly absorbing polymer layers are deposited upon the antenna arrays, and we are able to observe very weak molecular absorption signatures when these signatures are in spectral proximity to the antenna resonance. Experimental results are supported with finite element modeling with strong agreement.

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers.

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability. Here we propose, demonstrate, and analyze a mid-infrared absorber architecture leveraging monolayer films of nanoplasmonic colloidal tin-doped indium oxide nanocrystals (ITO NCs). We fabricate a series of ITO NC monolayer films using the liquid-air interface method; by synthetically varying the Sn dopant concentration in the NCs, we achieve spectrally selective perfect absorption tunable between wavelengths of two and five micrometers. We achieve monolayer thickness-controlled coupling strength tuning by varying NC size, allowing access to different coupling regimes. Furthermore, we synthesize a bilayer film that enables broadband absorption covering the entire midwave IR region (λ = 3-5 µm). We demonstrate a scalable platform, with perfect absorption in monolayer films only hundredths of a wavelength in thickness, enabling strong light-matter interaction, with potential applications for molecular detection and ultrafast nonlinear optical applications.

Measuring Molecular Diffusion Through Thin Polymer Films with Dual-Band Plasmonic Antennas.

A general and quantitative method to characterize molecular transport in polymers with good temporal and high spatial resolution, in complex environments, is an important need of the pharmaceutical, textile, and food and beverage packaging industries, and of general interest to the polymer science community. Here we show how the amplified infrared (IR) absorbance sensitivity provided by plasmonic nanoantenna-based surface enhanced infrared absorption (SEIRA) provides such a method. SEIRA enhances infrared (IR) absorbances primarily within 50 nm of the nanoantennas, enabling localized quantitative detection of even trace quantities of analytes and diffusion measurements in even thin polymer films. Relative to a commercial attenuated total internal reflection (ATR) system, the limit of detection is enhanced at least 13-fold, and as is important for measuring diffusion, the detection volume is about 15 times thinner. Via this approach, the diffusion coefficient and solubility of specific molecules, including l-ascorbic acid (vitamin C), ethanol, various sugars, and water, in both simple and complex mixtures (e.g., beer and a cola soda), were determined in poly(methyl methacrylate), high density polyethylene (HDPE)-based, and polypropylene-based polyolefin films as thin as 250 nm.

Nanosecond modulation of thermal emission.

Femtosecond laser pulses are used to modulate the thermal emission from semiconductor materials at the nanosecond timescale. A visible-frequency laser photoexcites energetic free carriers in intrinsic Si and GaAs wafers. As these free carriers return to equilibrium, they not only emit thermal radiation on a picosecond time scale but also modulate the semiconductor thermal emission on a nanosecond to microsecond time scale, offering a novel route towards ultrafast infrared optical pulses.

The influence of ketamine on drug discovery in depression.

Recent research demonstrating that the glutamatergic modulator ketamine has rapid, robust, and sustained antidepressant effects has been a turning point in drug discovery for depression. The recent FDA approval of esketamine for adults with treatment-resistant major depressive disorder (MDD) has further underscored the relevance of this agent in spurring investigation into novel and mechanistically distinct agents for use in depression. Over the past two decades, ketamine research has ushered in a new wave of studies seeking to not only identify its mechanism of action but also to examine the antidepressant potential of novel or repurposed agents. This article reviews the approaches that have proven particularly fruitful for the field of neuropsychiatry.

Measurement of carrier lifetime in micron-scaled materials using resonant microwave circuits.

The measurement of minority carrier lifetimes is vital to determining the material quality and operational bandwidth of a broad range of optoelectronic devices. Typically, these measurements are made by recording the temporal decay of a carrier-concentration-dependent material property following pulsed optical excitation. Such approaches require some combination of efficient emission from the material under test, specialized collection optics, large sample areas, spatially uniform excitation, and/or the fabrication of ohmic contacts, depending on the technique used. In contrast, here we introduce a technique that provides electrical readout of minority carrier lifetimes using a passive microwave resonator circuit. We demonstrate >105 improvement in sensitivity, compared with traditional photoemission decay experiments and the ability to measure carrier dynamics in micron-scale volumes, much smaller than is possible with other techniques. The approach presented is applicable to a wide range of 2D, micro-, or nano-scaled materials, as well as weak emitters or non-radiative materials.

Amyopathic dermatomyositis resembling stasis dermatitis.

This case describes an unusual presentation of dermatomyositis in a patient with ovarian carcinoma. The eruption appeared as a venous stasislike dermatitis. The temporal sequence of onset after chemotherapy administration suggested a possible drug-induced process. However, in the context of underlying ovarian carcinoma, a paraneoplastic process offered an alternative explanation for the dermatomyositis.

A report of GJB2 (N14K) Connexin 26 mutation in two patients--a new subtype of KID syndrome?

Keratitis-ichthyosis-deafness syndrome is a rare congenital ectodermal disorder, characterized by presence of skin lesions, neurosensory hearing loss, and vascularizing keratitis. Several autosomal dominant mutations in the Connexin 26 gene (GJB2) have been discovered as a cause of this syndrome. We report two patients who presented with a combination of clinical features of keratitis-ichthyosis-deafness syndrome (e.g., congenital bilateral neurosensory hearing loss and erythrokeratoderma), however, lacking other characteristics typical of this condition. In addition, they both demonstrated striking mucocutaneous findings (e.g., chronic lip fissuring, gingival hyperemia), resulting in diagnostic difficulties. In both patients, a GJB2 mutation (N14K) was identified, which shares the same gene with classic Keratitis-ichthyosis-deafness syndrome but has never been described in patients with this condition. We propose that the findings observed in our patients are a distinct subtype of Keratitis-ichthyosis-deafness syndrome, thus expanding the spectrum of connexin-associated keratodermias.

Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching.

Producing densely packed high aspect ratio In0.53Ga0.47As nanostructures without surface damage is critical for beyond Si-CMOS nanoelectronic and optoelectronic devices. However, conventional dry etching methods are known to produce irreversible damage to III-V compound semiconductors because of the inherent high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform, array-based In0.53Ga0.47As pillars with diameters as small as 200 nm using the damage-free metal-assisted chemical etching (MacEtch) technology combined with the post-MacEtch digital etching smoothing. The etching mechanism of InxGa1-xAs is explored through the characterization of pillar morphology and porosity as a function of etching condition and indium composition. The etching behavior of In0.53Ga0.47As, in contrast to higher bandgap semiconductors (e.g., Si or GaAs), can be interpreted by a Schottky barrier height model that dictates the etching mechanism constantly in the mass transport limited regime because of the low barrier height. A broader impact of this work relates to the complete elimination of surface roughness or porosity related defects, which can be prevalent byproducts of MacEtch, by post-MacEtch digital etching. Side-by-side comparison of the midgap interface state density and flat-band capacitance hysteresis of both the unprocessed planar and MacEtched pillar In0.53Ga0.47As metal-oxide-semiconductor capacitors further confirms that the surface of the resultant pillars is as smooth and defect-free as before etching. MacEtch combined with digital etching offers a simple, room-temperature, and low-cost method for the formation of high-quality In0.53Ga0.47As nanostructures that will potentially enable large-volume production of In0.53Ga0.47As-based devices including three-dimensional transistors and high-efficiency infrared photodetectors.

Cochleosaccular dysplasia associated with a connexin 26 mutation in keratitis-ichthyosis-deafness syndrome.

OBJECTIVE: The objective of this study was to characterize the temporal bone phenotype associated with a mutation of GJB2 (encoding connexin 26). STUDY DESIGN: The authors conducted correlative clinical, molecular genetic, and postmortem histopathologic analysis. METHODS: The study subject was a male infant with keratitis-ichthyosis-deafness (KID) syndrome. We performed a nucleotide sequence analysis of GJB2 and a histopathologic analysis of the temporal bones. RESULTS: The subject was heterozygous for G45E, a previously reported KID syndrome mutation of GJB2. The primary inner ear abnormality was dysplasia of the cochlear and saccular neuroepithelium. CONCLUSIONS: GJB2 mutations can cause deafness in KID syndrome, and possibly in other GJB2 mutant phenotypes, by disrupting cochlear differentiation.

Enhanced Optical Transmission through MacEtch-Fabricated Buried Metal Gratings.

Metallic films with subwavelength apertures, integrated into a semiconductor by metal-assisted chemical etch (MacEtch), demonstrate enhanced transmission when compared to bare semiconductor surfaces. The resulting "buried" metallic structures are characterized spectroscopically and modeled using rigorous coupled wave analysis. These composite materials offer potential integration with optoelectronic devices, for simultaneous near-uniform electrical contact and strong optical coupling to free space.