Non-destructive evaluation and fast conductivity calculation of various nanowire-based thin films with artificial neural network aided THz time-domain spectroscopy.

Terahertz time-domain spectroscopy (THz-TDS) has been utilized extensively to characterize materials in a non-destructive way. However, when materials are characterized with THz-TDS, there are many extensive steps for analyzing the acquired terahertz signals to extract the material information. In this work, we present a significantly effective, steady, and rapid solution to obtain the conductivity of nanowire-based conducting thin films by utilizing the power of artificial intelligence (AI) techniques with THz-TDS to minimize the analyzing steps by training neural networks with time domain waveform as an input data instead of a frequency domain spectrum.

Nanoscale Raman Characterization of a 2D Semiconductor Lateral Heterostructure Interface.

The nature of the interface in lateral heterostructures of 2D monolayer semiconductors including its composition, size, and heterogeneity critically impacts the functionalities it engenders on the 2D system for next-generation optoelectronics. Here, we use tip-enhanced Raman scattering (TERS) to characterize the interface in a single-layer MoS/WS lateral heterostructure with a spatial resolution of 50 nm. Resonant and nonresonant TERS spectroscopies reveal that the interface is alloyed with a size that varies over an order of magnitude─from 50 to 600 nm─within a single crystallite.

Breast cancer biomarker detection through the photoluminescence of epitaxial monolayer MoS flakes.

In this work we report on the characterization and biological functionalization of 2D MoS flakes, epitaxially grown on sapphire, to develop an optical biosensor for the breast cancer biomarker miRNA21. The MoS flakes were modified with a thiolated DNA probe complementary to the target biomarker. Based on the photoluminescence of MoS, the hybridization events were analyzed for the target (miRNA21c) and the control non-complementary sequence (miRNA21nc).

Investigating the Redox Properties of Two-Dimensional MoS Using Photoluminescence Spectroelectrochemistry and Scanning Electrochemical Cell Microscopy.

Control over photophysical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) is the key to advance their applications in next-generation optoelectronics. Although chemical doping and surface modification with plasmonic metals have been reported to tune the photophysical and catalytic properties of 2D TMDs, there have been few reports of tuning optical properties using dynamic electrochemical control of electrode potential. Herein, we report (1) the photoluminescence (PL) enhancement and red-shift in the PL spectrum of 2D MoS, synthesized by chemical vapor deposition and subsequent transfer onto an indium tin oxide electrode, upon electrochemical anodization and (2) spatial heterogeneities in its photoelectrochemical (PEC) activities.

Ultra-High Efficiency and Broad Band Operation of Infrared Metasurface Anomalous Reflector based on Graphene Plasmonics.

Infrared metasurface anomalous reflector with ultra-high efficiency and broad band operation is designed via multi-sheet graphene layer with triangular holes. The anomalous reflection angle covers the range of 10° to 90° with the efficiency higher than 80%, over a broad spectral range from 7 μm-40 μm of infrared spectrum. It reaches above 92% at the center wavelength in the spectral response.

Photoluminescence enhancement of monolayer MoS using plasmonic gallium nanoparticles.

2D monolayer molybdenum disulphide (MoS) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency. Herein, we use gallium hemispherical nanoparticles (Ga NPs) deposited by thermal evaporation on top of chemical vapour deposited MoS monolayers in order to enhance its luminescence. The influence of the NP radius and the laser wavelength is reported in PL and Raman experiments.

Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control.

We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low-mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force, which can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure.

A Facile Electrochemical Reduction Method for Improving Photocatalytic Performance of α-FeO Photoanode for Solar Water Splitting.

Electrochemical reduction method is used for the first time to significantly improve the photo-electrochemical performance of α-FeO photoanode prepared on fluorine-doped tin oxide substrates by spin-coating aqueous solution of Fe(NO) followed by thermal annealing in air. Photocurrent density of α-FeO thin film photoanode can be enhanced 25 times by partially reducing the oxide film to form more conductive FeO (magnetite). FeO helps facilitate efficient charge transport and collection from the top α-FeO layer upon light absorption and charge separation to yield enhanced photocurrent density.

Plasmon-Induced Transparency by Hybridizing Concentric-Twisted Double Split Ring Resonators.

As a classical analogue of electromagnetically induced transparency, plasmon induced transparency (PIT) has attracted great attention by mitigating otherwise cumbersome experimental implementation constraints. Here, through theoretical design, simulation and experimental validation, we present a novel approach to achieve and control PIT by hybridizing two double split ring resonators (DSRRs) on flexible polyimide substrates. In the design, the large rings in the DSRRs are stationary and mirror images of each other, while the small SRRs rotate about their center axes.

Spectroscopic Characteristics of Three Dimensional Split-Ring Resonator Arrays at Terahertz Frequencies.

In this work, three-dimensional, stacked arrays of subwavelength, square, dual, concentric split ring resonators exhibiting characteristics at the Terahertz frequencies have been designed, simulated, and fabricated through a photolithographic lift-off process and electron beam evaporation metal deposition. Characterization of the split-ring resonator arrays was performed by transmission mode Terahertz time domain spectroscopy. The effects of the split-ring resonator unit cell spatial dimensions on resonant absorption frequencies and relative absorption strength are investigated as well as effects from the addition of a dielectric spacing layer and additional split-ring resonator layer.

Impact of Substrate and Bright Resonances on Group Velocity in Metamaterial without Dark Resonator.

Manipulating the speed of light has never been more exciting since electromagnetic induced transparency and its classical analogs led to slow light. Here, we report the manipulation of light group velocity in a terahertz metamaterial without needing a dark resonator, but utilizing instead two concentric split-ring bright resonators (meta-atoms) exhibiting a bright Fano resonance in close vicinity of a bright Lorentzian resonance to create a narrowband transmittance. Unlike earlier reports, the bright Fano resonance does not stem from an asymmetry of meta-atoms or an interaction between them.

Observation of hydrofluoric acid burns on osseous tissues by means of terahertz spectroscopic imaging.

Terahertz technologies have gained great amount of attention for biomedical imaging and tissue analysis. In this study, we utilize terahertz imaging to study the effects of hydrofluoric acid on both compact bone tissue and cartilage. We compare the differences observed in the exposure for formalin fixed and raw, dried, tissue as well as those resulting from a change in hydrofluoric (HF) concentration.

Design and analysis of perfect terahertz metamaterial absorber by a novel dynamic circuit model.

Metamaterial terahertz absorbers composed of a frequency selective layer followed by a spacer and a metallic backplane have recently attracted great attention as a device to detect terahertz radiation. In this work, we present a quasistatic dynamic circuit model that can decently describe operational principle of metamaterial terahertz absorbers based on interference theory of reflected waves. The model comprises two series LC resonance components, one for resonance in frequency selective surface (FSS) and another for resonance inside the spacer.

Direct measurement of band edge discontinuity in individual core-shell nanowires by photocurrent spectroscopy.

Group III-V coaxial core-shell semiconducting nanowire heterostructures possess unique advantages over their planar counterparts in logic, photovoltaic, and light-emitting devices. Dimensional confinement of electronic carriers and interface complexity in nanowires are known to produce local electronic potential landscapes along the radial direction that deviate from those along the normal to planar heterojunction interfaces. However, understanding of selected electronic and optoelectronic carrier transport properties and device characteristics remains lacking without a direct measurement of band alignment in individual nanowires.

High resolution, two-dimensional image mapping of ZnO nanowires by confocal microphotoluminescence and microraman spectroscopy.

High-quality ZnO nanowires were synthesized using both Au catalysts and ZnO seeds by chemical vapor depositionon basal plane sapphire substrates. The nanowires were hexagonal and aligned with their c-axis closely perpendicular to the sapphire substrate surface. The structural characteristics of the nanowiresgrown using the different catalysts/seeds were compared using scanning electron microscopyand X-ray diffraction.