Young-Geun Roh

GaAs-based near-infrared omnidirectional reflector

We introduce a compound-semiconductor-based omnidirectional reflector. A four-layer-pair stack of GaAs/AlAs was grown epitaxially using molecular-beam epitaxy, and was then converted to a GaAs/Al2O3 multilayer stack by selective oxidation of the AlAs layers. The resultant one-dimensional photonic crystal exhibited omnidirectional reflection properties in near-IR wavelength range below 1 μm. Reflectance spectra measured at various incidence angles and polarizations were observed to be in good agreement with theoretically simulated results.

Effectiveness, safety, and pharmacokinetic and pharmacodynamic characteristics of microemulsion propofol in patients undergoing elective surgery under total intravenous anaesthesia

BACKGROUND The aims of this study were to investigate the effectiveness, safety, pharmacokinetics, and pharmacodynamics of microemulsion propofol, Aquafol (Daewon Pharmaceutical Co., Ltd, Seoul, Republic of Korea). METHODS In total, 288 patients were randomized to receive 1% Aquafol or 1% Diprivan (AstraZeneca, London, UK) (n=144, respectively). A 30 mg test dose of propofol was administered i.v. over 2 s for assessing injection pain. Subsequently, a bolus of propofol 2 mg kg(-1) (-30 mg) was administered. Anaesthesia was maintained with a variable rate infusion of propofol and a target-controlled infusion of remifentanil. Mean infusion rates of both formulations and times to loss of consciousness (LOC) and recovery of consciousness (ROC) were recorded. Adverse events and pharmacokinetic and pharmacodynamic characteristics were evaluated. RESULTS Mean infusion rate of Aquafol was not statistically different from that of Diprivan (median: 6.2 vs 6.3 mg kg(-1) h(-1)). Times to LOC and ROC were slightly prolonged in Aquafol (median: 21 vs 18 s, 12.3 vs 10.8 min). Aquafol showed similar incidence of adverse events to Diprivan. Aquafol (vs Diprivan caused more severe (median VAS: 72.0 vs 11.5 mm) and frequent (81.9 vs 29.2%) injection pain. The dose-normalized AUC(last) of Aquafol and Diprivan was 0.71 (0.19) and 0.74 (0.20) min litre(-1). The V(1) of both formulations were proportional to lean body mass. Sex was a significant covariate for k(12) and Ce(50) of Aquafol, and for k(e0) of Diprivan. CONCLUSIONS Aquafol was as effective and safe as Diprivan, but caused more severe and frequent injection pain. Aquafol demonstrated similar pharmacokinetics to Diprivan.

Photonic Crystal Slab Waveguides Fabricated by the Combination of Holography and Photolithography

We have fabricated air-bridge type two-dimensional photonic crystal waveguides (2D-PCWs) using two high-throughput processes only: holography and photolithography. Despite the existence of misalignments of a defect line with respect to the air-hole arrays, waveguiding in both straight and 90°-bent PCWs was clearly observed at the wavelength of 1.55 µm. We also estimated the upper bound in propagation loss of our straight PCWs, which was measured to be about 40 cm-1.

Large Work Function Modulation of Monolayer MoS2 by Ambient Gases

Although two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS2 via ambient gases. The work function was measured by an in situ Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O2 exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much narrower than bulk semiconductors.

Optical Gain in MoS2 via Coupling with Nanostructured Substrate: Fabry-Perot Interference and Plasmonic Excitation

Despite the direct band gap of monolayer transition metal dichalcogenides (TMDs), their optical gain remains limited because of the poor light absorption in atomically thin, layered materials. Most approaches to improve the optical gain of TMDs mainly involve modulation of the active materials or multilayer stacking. Here, we report a method to enhance the optical absorption and emission in MoS2 simply through the design of a nanostructured substrate. The substrate consisted of a dielectric nanofilm spacer (TiO2) and metal film. The overall photoluminescence intensity from monolayer MoS2 on the nanostructured substrate was engineered based on the TiO2 thickness and amplified by Fabry-Perot interference. In addition, the neutral exciton emission was selectively amplified by plasmonic excitations from the local field originating from the surface roughness of the metal film with spacer thicknesses of less than 10 nm. We further demonstrate that the quality factor of the device can also be engineered by selecting a spacer material with a different refractive index.

Experimental verification of cross talk reduction in photonic crystal waveguide crossings

We have experimentally demonstrated a very low cross talk in photonic crystal waveguide crossings of any kind. For cross talk reduction, we added a resonant cavity to the waveguide intersection designed to operate in microwave frequencies. The two-dimensional waveguide crossing structure was sandwiched between two parallel metal plates to eliminate radiation loss in the vertical direction. Transmission measurements revealed that when designed properly the cross talk reduction was as large as −30dB at resonance, which is qualitatively consistent with simulation results. From the experimental results, the detailed resonant mode shape at the waveguide intersection was found to play a key role in relaying the input signal in the forward direction and therefore reducing cross talk.

Pharmacokinetics and pharmacodynamics of a new reformulated microemulsion and the long-chain triglyceride emulsion of propofol in beagle dogs

Background and purpose:  Microemulsion propofol was developed to eliminate lipid solvent‐related adverse events of long‐chain triglyceride emulsion (LCT) propofol. We compared dose proportionality, pharmacokinetic and pharmacodynamic characteristics of both formulations.

Photonic crystal waveguides with multiple 90° bends

In order to emphasize and demonstrate the importance of light confinement in the vertical direction, an otherwise ordinary two-dimensional photonic crystal waveguide structure operating at microwave frequencies was sandwiched between two metal plates. Such waveguides exhibited excellent guiding properties despite the existence of multiple 90° bends. From the experimental data, we have estimated that the propagation velocity of the waveguide is about 0.47 c, regardless of the number of bends, and that the bending loss is only 0.1 dB per bend.

Nanoscale patterning of colloidal quantum dots on transparent and metallic planar surfaces.

The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing and microcontact printing of quantum dots have been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10 nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum.

Directional radiation of Babinet-inverted optical nanoantenna integrated with plasmonic waveguide

We present a Babinet-inverted optical nanoantenna integrated with a plasmonic waveguide. Using an integrated nanoantenna, we can couple the plasmon guide mode in a metal-insulator-metal (MIM) structure into the resonant antenna feed directly. The resonantly excited feed slot then radiates to free space and generates a magnetic dipole-like far-field pattern. The coupling efficiency of the integrated nanoantenna is calculated as being approximately 19% using a three-dimensional finite-difference time-domain (3D FDTD) simulation. By adding an auxiliary groove structure along with the feed, the radiation direction can be controlled similar to an optical Yagi-Uda antenna. We also determine, both theoretically and experimentally, that groove depth plays a significant role to function groove structure as a reflector or a director. The demonstrated Babinet-inverted optical nanoantenna integrated with a plasmonic waveguide can be used as a “plasmonic via” in plasmonic nanocircuits.