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Photoconductive antennas (PCAs) are among the most conventional devices used for emission as well as detection of terahertz (THz) radiation. However, due to their low optical-to-THz conversion efficiencies, applications of these devices in out-of-laboratory conditions are limited. In this paper, we report several factors of enhancement in THz emission efficiency from conventional PCAs by coating a nano-layer of dielectric (TiO2) on the active area between the electrodes of a semi-insulating GaAs-based device. Extensive experiments were done to show the effect of thicknesses of the TiO2 layer on the THz power enhancement with different applied optical power and bias voltages. Multiphysics simulations were performed to elucidate the underlying physics behind the enhancement of efficiency of the PCA. Additionally, this layer increases the robustness of the electrode gaps of the PCAs with high electrical insulation as well as protect it from external dust particles.

Abstract A numerical simulation program, based upon a finite difference nodal network, was used to simulate two Los Alamos test cells (one single and one multi-room cell) and a typical residence — all of which were exposed to intense insolation and large changes in ambient weather conditions. For the test cells, the predicted surface and globe temperatures are in good agreement with the measured values and indicate the acceptability of thermal modeling. The program was used to predict the behavior of a residential structure. The process of refining these predictions, guided by observations, led to the development of a stepwise simulation methodology. The insights gained as a result of this interdisciplinary involvement have been stimulating and instructive. The importance of recognizing the differences in the thought processes and the work styles of the several professions has been demonstrated. The most effective simulation methodology was that based upon human comfort, which appeared to be a common perception amongst all the program users.

Abstract Theoretical analysis of the interaction between concentrated solar radiation and a honeycomb matrix or a bed of particles cooled by a gas is presented. The computation and the experimental results show evidence of overheating of the solid near the irradiated surface. To prevent the upper surface from this phenomenon and to reduce the radiative heat losses, we propose to use selective semi-transparent porous absorbers. The first results about coatings on silica are presented.

It is critical and challenging to develop high performance transition metal phosphides (TMPs) electrocatalysts for oxygen evolution reaction (OER) to address fossil energy shortages. Herein, we report the synthesis of Co2P embedded in N-doped porous carbon (Co2P@N-C) via a facile one-step strategy. The obtained catalyst exhibits a lower overpotential of 352 mV for OER at a current density of 10 mA cm−2 and a small Tafel slope of 84.6 mV dec−1, with long-time reliable stability. The excellent electrocatalytic performance of Co2P@N-C can be mainly owed to the synergistic effect between the Co2P and highly conductive N-C substrate, which not only affords rich exposed active sites but also promotes faster charge transfer, thus significantly promoting OER process. This work presents a promising and industrially applicable synthetic strategy for the rational design of high performance nonnoble metal electrocatalysts with enhanced OER performance.

Owing to its amorphous structure, a chalcogenide glass exhibits a thermal conductivity k approaching the theoretical minimum of its composition, called the Einstein’s limit. In this work, this limit is beaten in an amorphous solid consisting of glassy particles joined by nanosized contacts. When amorphous particles are sintered below the glass transition temperature under a high pressure, these particles can be mechanically bonded with a minimized interfacial thermal conductance. This reduces the effective k below the Einstein’s limit while providing superior mechanical strength under a high pressure for thermal insulation applications under harsh environments. The lowest room temperature k for the solid counterpart can be as low as 0.10 W/m·K, which is significantly lower than k≈0.2 W/m·K for the bulk glass.

AbstractErbium doped silicon-rich silica offers broad band and very efficient excitation of erbium photoluminescence (PL) due to a sensitization effect attributed to silicon nanocrystals (Si-nc), which grow during thermal treatment. PL decay lifetime measurements of sensitised Er3+ ions are usually reported to be stretched or multi exponential, very different to those that are directly excited, which usually show a single exponential decay component.In this paper, we report on SiO2 thin films doped with Si-nc's and erbium. Time resolved PL measurements reveal two distinct 1.54μm Er decay components; a fast microsecond component, and a relatively long lifetime component (10ms). We also study the structural properties of these samples through TEM measurements, and reveal the formation of Er clusters. We propose that these Er clusters are responsible for the fast μs decay component, and we develop rate equation models that reproduce the experimental transient observations, and can explain some of the reported transient behaviour in previously published literature.

AbstractThe VO2‐based smart windows can dynamically and reversibly adjust the indoor solar irradiation to reduce the energy consumption for building glasses. This paper reports the first successful preparation of Mg‐doped VO2@ZrO2 core−shell nanocrystals with promoted thermochromic performance as well as tunable appearance and wettability. The achieved combination of Tlum of 52.4% and ∆Tsol of 7.1% is comparable to the best‐reported results of VO2‐based core−shell rod structures. The thickness of ZrO2 shell is tunable between 3 and 14 nm, resulting in a slightly hydrophobic surface and a slight color change toward blue‐green and brighter produced films. The preparation method based on hydrothermal and UV‐curing methods is facile. This work may inspire future development of VO2 synthesis, their structure−property, and the application the thermochromic films for energy‐saving purposes in buildings or automobiles.

We report the synthesis of novel diphenylalanine/cobalt(II,III) oxide (Co(3)O(4)) composite nanowires by peptide self-assembly. Peptide nanowires were prepared by treating amorphous diphenylalanine film with aniline vapor at an elevated temperature. They were hybridized with Co(3)O(4) nanocrystals through the reduction of cobalt ions in an aqueous solution using sodium borohydride (NaBH(4)) without any complex processes such as heat treatment. The formation of peptide/Co(3)O(4) composite nanowires was characterized using multiple tools, such as electron microscopies and elemental analysis, and their potential application as a negative electrode for Li-ion batteries was explored by constructing Swagelok-type cells with hybrid nanowires as a working electrode and examining their charge/discharge behavior. The present study provides a useful approach for the synthesis of functional metal oxide nanomaterials by demonstrating the feasibility of peptide/Co(3)O(4) hybrid nanowires as an energy storage material.