1,478 research outputs found

    Two-dimensional Dirac plasmon-polaritons in graphene, 3D topological insulator and hybrid systems

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    Collective oscillations of massless particles in two-dimensional (2D) Dirac materials offer an innovative route toward implementing atomically thin devices based on low-energy quasiparticle interactions. Strong confinement of near-field distribution on the 2D surface is essential to demonstrate extraordinary optoelectronic functions, providing means to shape the spectral response at the mid-infrared (IR) wavelength. Although the dynamic polarization from the linear response theory has successfully accounted for a range of experimental observations, a unified perspective was still elusive, connecting the state-of-the-art developments based on the 2D Dirac plasmon-polaritons. Here, we review recent works on graphene and three-dimensional (3D) topological insulator (TI) plasmon-polariton, where the mid-IR and terahertz (THz) radiation experiences prominent confinement into a deep-subwavelength scale in a novel optoelectronic structure. After presenting general light-matter interactions between 2D Dirac plasmon and subwavelength quasiparticle excitations, we introduce various experimental techniques to couple the plasmon-polaritons with electromagnetic radiations. Electrical and optical controls over the plasmonic excitations reveal the hybridized plasmon modes in graphene and 3D TI, demonstrating an intense near-field interaction of 2D Dirac plasmon within the highly-compressed volume. These findings can further be applied to invent optoelectronic bio-molecular sensors, atomically thin photodetectors, and laser-driven light sources

    RKKY Interaction in Disordered Graphene

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    We investigate the effects of nonmagnetic disorder on the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction in graphene by studying numerically the Anderson model with on-site and hopping disorder on a honeycomb lattice at half filling. We evaluate the strength of the interaction as a function of the distance R between two magnetic ions, as well as their lattice positions and orientations. In the clean limit, we find that the strength of the interaction decays as 1/R^3, with its sign and oscillation amplitude showing strong anisotropy. With increasing on-site disorder, the mean amplitude decreases exponentially at distances exceeding the elastic mean free path. At smaller distances, however, the oscillation amplitude increases strongly and its sign changes on the same sublattice for all directions but the armchair direction. For random hopping disorder, no sign change is observed. No significant changes to the geometrical average values of the RKKY interaction are found at small distances, while exponential suppression is observed at distances exceeding the localization length.Comment: 4+\epsilon\ pages, 5 figure

    Evaluation of automated calibration and quality control processes using the Aptio total laboratory automation system

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    Background The objective of this study was to determine whether manually performed calibration and quality control (QC) processes could be replaced with an automated laboratory system when installed analyzers fail to provide automated calibration and QC functions. Methods Alanine aminotransferase (ALT), total cholesterol (TC), creatinine (Cr), direct bilirubin (DB), and lipase (Lip) items were used as analytes. We prepared pooled serum samples at 10 levels for each test item and divided them into two groups; five for the analytical measurement range (AMR) group and five for the medical decision point (MDP) group. Calibration and QC processes were performed for five consecutive days, and ALT, TC, Cr, DB, and Lip levels were measured in the two groups using automated and manual methods. Precision and the mean difference between the calibration and QC methods were evaluated using the reported values of the test items in each group. Results Repeatability and within-laboratory coefficients of variation (CVs) between the automated system and the conventional manual system in the AMR group were similar. However, the mean reported values for test items were significantly different between the two systems. In the MDP group, repeatability and within-laboratory CVs were better with the automation system. All calibration and QC processes were successfully implemented with the Aptio total laboratory automation system. Conclusion The Aptio total laboratory automation system could be applied to routine practice to improve precision and efficiency

    Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer

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    The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> alloy using sulfurization of super-cycle atomic layer deposition Mo<inf>1-x</inf>W<inf>x</inf>O<inf>y</inf>. Various spectroscopic and microscopic results indicate that the synthesized Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> alloys have complete mixing of Mo and Watoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet-visible spectrophotometer results reveal that a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer. Further, we demonstrate that a VCC Mo<inf>1-x</inf>W<inf>x</inf>S<inf>2</inf> multilayer photodetector generates three to four times greater photocurrent than MoS<inf>2</inf>-and WS<inf>2</inf>-based devices, owing to the broadband light absorption. © 2015 Macmillan Publishers Limitedopen1