ABSTRACT
We successfully fabricated two-dimensional metallic CoBi nanoislands on SrTiO3(001) substrate by molecular beam epitaxy, and systematically investigated their electronic structures by scanning tunneling microscopy and spectroscopyin situat 4.2 K. Coulomb blockade and Coulomb staircases with discrete and well-separated levels are observed for the individual nanoisland, which is attributed to single-electron tunneling via two tunnel junction barriers. They are in excellent agreement with the simulations based on orthodox theory. Furthermore, we demonstrated that the Coulomb blockade becomes weaker with increasing temperature and almost disappears at â¼22 K in our variable temperature experiment, and its full-width at half-maximum of dI/dVpeaks with temperature is â¼6 mV. Our results provide a new platform for designing single-electron transistors that have potential applications in future microelectronics.
ABSTRACT
As a universal physical scheme, effective light couplings to waveguides favor numerous applications. However, the low coupling efficiency at wide angles prohibits this fundamental functionality and thus lowers the performance levels of photonic systems. As previously found, the transmission gratings patterned on waveguide facets could significantly improve the large-angle-inputted efficiency to the order of 10-1. Here, we continue this study with a focus on a common scenario, i.e., a grating-modified waveguide excited by the Gaussian beam. A simplified 2D theoretical model is firstly introduced, proving that the efficiency lineshape could be well flattened by elaborately arranged diffractive gratings. For demonstration, subsequent explorations for proper grating geometries were conducted, and four structural configurations were selected for later full-wave numerical simulations. The last comparison studies showcase that the analytical method approximates the finite element method-based modelings. Both methods highlight grating-empowered coupling efficiencies, being 2.5 bigger than the counterparts of the previously reported seven-ring structure. All in all, our research provides instructions to simulate grating effects on the waveguide's light-gathering abilities. Together with algorithm-designed coupling structures, it would be of great interest to further benefit real applications, such as bioanalytical instrumentation and quantum photon probes.
ABSTRACT
High-performance triiodide reduction reaction (IRR) catalysts in dye-sensitized solar cells (DSSCs) and hydrogen evolution reaction (HER) catalysts in electrochemical water splitting are extremely compelling for renewable energy conversion and storage. The best IRR and HER catalysts generally rely on the use of noble metal platinum (Pt), which suffers obstacles in real-world implementation. The rational design of efficient bifunctional IRR and HER catalysts based on inexpensive and earth-abundant elements to replace scarce Pt could enable low-cost photoelectric conversion and hydrogen production but is challenging and rarely reported. Herein, we present a bifunctional NiFeCoW@NC hybrid with the unique architecture of WC loaded on the in situ formed carbon nanotubes embedded with Co-doped FeNi3 nanoparticles based on the anisotropic integration design principle, which operates efficiently for DSSCs and hydrogen evolution. The assembled DSSCs using the designed multimetal-based NiFeCoW@NC counter electrode delivered a high power conversion efficiency of 6.92% and long-term stability superior to bimetal-based NiFe@NC, CoW@NC, and Pt counterparts. It also exhibited eminent hydrogen evolution performance with a low overpotential of 127.8 mV to drive a 10 mA cm-2 current density, a Tafel slope of 60.4 mV dec-1, and satisfactory durable stability in 0.5 M H2SO4. This work provides a design principle for low-cost and highly active bifunctional catalysts to replace Pt for DSSCs and hydrogen evolution.
ABSTRACT
A novel 4,4'-bipyridine linked dinuclear copper(II) complex, [Cu2L2(bipy)](NO3)2·bipy (L = 2-[2-(2-hydroxyethylamino) ethylimino]methyl-6-methylphenol; bipy = 4,4'-bipyridine), was prepared and characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. The Cu···Cu distance is 11.129(2) Å. The CuII atom is coordinated by one phenolate O, one imine N, and one amine N atoms of a Schiff base ligand, and one N atom of the bridging 4,4'-bipyridine ligand, forming a square planar geometry. In the crystal structure of the complex, the dinuclear copper complex cations are linked by 4,4'-bipyridine molecules through intermolecular O-H···N hydrogen bonds, to form 1D chains running in the [2 0 -1] direction.
