Q-factor and wavelength adjustable ultra-perfect absorption under critical coupling through epsilon-near-zero-based absorbers.

Perfect absorption with adjustable Q factor and wavelength is essential in both theory and application. To address this issue, a structure composed of an epsilon-near-zero (ENZ)- SiO2 grating and a multilayer dielectric structure was designed. In the structure, the intrinsic loss is related to the ENZ thickness, while the external leakage depends on the grating parameters. By adjusting the ENZ film thickness, the intrinsic loss rate was tuned to match the external leakage rate corresponding to different grating parameters, realizing the critical couplings with different Q factors and wavelengths. Under critical coupling, the absorption rate reached a maximum of 99.999%, demonstrating ultra-perfect absorption. The Q factor was adjusted from 4350 to 35800, and the absorption wavelength was modified from 1050 to 1282 nm. The design work may provide new ideas for developing wavelength- and Q-selective absorbers, optical modulators, dielectric sensors, and photodetectors.

Enantioselective Ni-Catalyzed Electrochemical Synthesis of Biaryl Atropisomers.

A scalable enantioselective nickel-catalyzed electrochemical reductive homocoupling of aryl bromides has been developed, affording enantioenriched axially chiral biaryls in good yield under mild conditions using electricity as a reductant in an undivided cell. Common metal reductants such as Mn or Zn powder resulted in significantly lower yields in the absence of electric current under otherwise identical conditions, underscoring the enhanced reactivity provided by the combination of transition metal catalysis and electrochemistry.

Water as a Hydrogenating Agent: Stereodivergent Pd-Catalyzed Semihydrogenation of Alkynes.

Palladium-catalyzed transfer semihydrogenation of alkynes using H2O as the hydrogen source and Mn as the reducing reagent is developed, affording cis- and trans-alkenes selectively under mild conditions. In addition, this method provides an efficient way to access various cis-1,2-dideuterioalkenes and trans-1,2-dideuterioalkenes by using D2O instead of H2O.

Nickel-catalyzed Enantioselective Hydroarylation and Hydroalkenylation of Styrenes.

We have developed a Ni-catalyzed enantioselective hydroarylation of styrenes with arylboronic acids using MeOH as the hydrogen source, providing an efficient method to access 1,1-diarylalkanes, which are essential structural units in many biologically active compounds. In addition, Ni-catalyzed enantioselective hydrovinylation of styrenes with vinylboronic acids is also realized with good yields and enantioselectivities. The synthetic utility was demonstrated by the efficient synthesis of ( R)-(-)-ibuprofen.

Regioselective Ni-Catalyzed Carboxylation of Allylic and Propargylic Alcohols with Carbon Dioxide.

An efficient Ni-catalyzed reductive carboxylation of allylic alcohols with CO2 has been successfully developed, providing linear ß,γ-unsaturated carboxylic acids as the sole regioisomer with generally high E/Z stereoselectivity. In addition, the carboxylic acids can be generated from propargylic alcohols via hydrogenation to give allylic alcohol intermediates, followed by carboxylation. A preliminary mechanistic investigation suggests that the hydrogenation step is made possible by a Ni hydride intermediate produced by a hydrogen atom transfer from water.

Realization of Plasmonic Microcavity with Full Transverse and Longitudinal Mode Selection.

Surface plasmon polaritons (SPPs) manipulation is of vital importance to construct ultracompact integrated micro/nano-optical devices and systems. Here we report the design, fabrication, and characterization of a SPP microcavity with full transverse and longitudinal mode selection and control on the surface of gold film. The designed microcavity supports the fundamental and first-order transverse modes of Gaussian mode beam with controllable longitudinal modes, respectively. The transverse mode is determined by two holographic mirrors made from deliberately designed groove patterns via the surface electromagnetic wave holography methodology, while the longitudinal mode is determined by the length of cavity. Both numerical simulations and leaky-wave SPP mode observations confirm the realization of full mode selection in the fabricated cavity. Our work opens up a powerful way to fully explore longitudinal and transverse mode control in SPP microcavities, which will be beneficial for light-matter interaction enhancement, construction of novel SPP nanolaser and microlaser, optical sensing, and optical information processing.

Broadband focusing and demultiplexing of surface plasmon polaritons on metal surface by holographic groove patterns.

Manipulation of surface plasmon polaritons (SPPs) on metal surfaces is important for constructing ultracompact integrated micro/nano optical devices and systems. We employ the method of surface electromagnetic wave holography (SWH) to design holographic groove patterns for managing the transport of broadband SPPs on metal surface. Several sets of groove patterns corresponding to different wavelengths are etched on the same region on metal surface to form a broadband SPP hologram. The incident SPPs are scattered by the composite hologram and interfere with each other to focus at different or the same positions for SPPs of different wavelengths. Finite-difference time-domain simulations show that broadband demultiplexing of SPPs is realized by the designed plasmonic holographic structures. In addition, the broadband SPPs can be focused to a pre-designated spot by a designed plasmonic hologram and as a result focusing of an ultrashort plasmonic pulse can be achieved. The results show that the SWH can successfully handle design of plasmonic holographic structures for SPPs wavelength management on metal surface.

Direct method to control surface plasmon polaritons on metal surfaces.

The manipulation of surface plasmon polaritons (SPPs) on metal surfaces is an important aspect in the design of ultra-compact integrated micro/nano optical systems. We present a direct method for the easy, yet accurate design of complicated groove patterns to control SPPs traveling on metal surfaces, using a surface electromagnetic wave holography method, based on the Huygens-Fresnel principle. SPPs are scattered by these deliberately and appropriately determined groove patterns and interfere with each other to form new paths with desire. Two devices are demonstrated, with predesignated functionalities fully implemented by the designed plasmonic holographic structures, according to the finite-difference time-domain simulations. The results strongly indicate that this direct method is effective, efficient, and user friendly in its application to control SPPs on metal surfaces.