Optical, electrical, and solar energy-conversion properties of gallium arsenide nanowire-array photoanodes

Periodic arrays of n-GaAs nanowires have been grown by selective-area metal–organic chemical-vapor deposition on Si and GaAs substrates. The optical absorption characteristics of the nanowire-arrays were investigated experimentally and theoretically, and the photoelectrochemical energy-conversion properties of GaAs nanowire arrays were evaluated in contact with one-electron, reversible, redox species in non-aqueous solvents. The radial semiconductor/liquid junction in the nanowires produced near-unity external carrier-collection efficiencies for nanowire-array photoanodes in contact with non-aqueous electrolytes. These anodes exhibited overall inherent photoelectrode energy-conversion efficiencies of [similar]8.1% under 100 mW cm^−2 simulated Air Mass 1.5 illumination, with open-circuit photovoltages of 590 ± 15 mV and short-circuit current densities of 24.6 ± 2.0 mA cm^−2. The high optical absorption, and minimal reflection, at both normal and off-normal incidence of the GaAs nanowire arrays that occupy <5% of the fractional area of the electrode can be attributed to efficient incoupling into radial nanowire guided and leaky waveguide modes

Room-Temperature Pressure Synthesis of Layered Black Phosphorus–Graphene Composite for Sodium-Ion Battery Anodes

Sodium-ion batteries offer an attractive option for grid-level energy storage due to the high natural abundance of sodium and low material cost of sodium compounds. Phosphorus (P) is a promising anode material for sodium-ion batteries, with a theoretical capacity of 2596 mAh/g. The red phosphorus (RP) form has worse electronic conductivity and lower initial Coulombic efficiency than black phosphorus (BP), but high material cost and limited production capacity have slowed the development of BP anodes. To address these challenges, we have developed a simple and scalable method to synthesize layered BP/graphene composite (BP/rGO) by pressurization at room temperature. A carbon-black-free and binder-free BP/rGO anode prepared with this method achieved specific charge capacities of 1460.1, 1401.2, 1377.6, 1339.7, 1277.8, 1123.78, and 720.8 mAh/g in a rate capability test at charge and discharge current densities of 0.1, 0.5, 1, 5, 10, 20, and 40 A/g, respectively. In a cycling performance test, after 500 deep cycles, the capacity of BP/rGO anodes stabilized at 1250 and 640 mAh/g at 1 and 40 A/g, respectively, which marks a significant performance improvement for sodium-ion battery anodes

Mapping behavioral specifications to model parameters in synthetic biology

With recent improvements of protocols for the assembly of transcriptional parts, synthetic biological devices can now more reliably be assembled according to a given design. The standardization of parts open up the way for in silico design tools that improve the construct and optimize devices with respect to given formal design specifications. The simplest such optimization is the selection of kinetic parameters and protein abundances such that the specified design constraints are robustly satisfied. In this work we address the problem of determining parameter values that fulfill specifications expressed in terms of a functional on the trajectories of a dynamical model. We solve this inverse problem by linearizing the forward operator that maps parameter sets to specifications, and then inverting it locally. This approach has two advantages over brute-force random sampling. First, the linearization approach allows us to map back intervals instead of points and second, every obtained value in the parameter region is satisfying the specifications by construction. The method is general and can hence be incorporated in a pipeline for the rational forward design of arbitrary devices in synthetic biology