Highly Occupied Surface States at Deuterium-Grown Boron-Doped Diamond Interfaces for Efficient Photoelectrochemistry

Polycrystalline boron-doped diamond is a promising material for high-power aqueous electrochemical applications in bioanalytics, catalysis, and energy storage. The chemical vapor deposition (CVD) process of diamond formation and doping is totally diversified by using high kinetic energies of deuterium substituting habitually applied hydrogen. The high concentration of deuterium in plasma induces atomic arrangements and steric hindrance during synthesis reactions, which in consequence leads to a preferential (111) texture and more effective boron incorporation into the lattice, reaching a one order of magnitude higher density of charge carriers. This provides the surface reconstruction impacting surficial populations of C C dimers, C H, CO groups, and  COOH termination along with enhanced kinetics of their abstraction, as revealed by high-resolution core-level spectroscopies. A series of local densities of states were computed, showing a rich set of highly occupied and localized surface states for samples deposited in deuterium, negating the connotations of band bending. The introduction of enhanced incorporation of boron into (111) facet of diamond leads to the manifestation of surface electronic states below the Fermi level and above the bulk valence band edge. This unique electronic band structure affects the charge transfer kinetics, electron affinity, and diffusion field geometry critical for efficient electrolysis, electrocatalysis, and photoelectrochemistry.     

Electrochemical Oxidation of NADH at Highly Boron-Doped Diamond Electrodes

Conductive boron-doped chemical vapor-deposited diamond thin films, already known to have superior properties for general electroanalysis, including low background current and a wide potential window, are here shown to have additional advantages with respect to electrochemical oxidation of nicotinamide adenine dinucleotide (NADH), including high resistance to deactivation and insensitivity to dissolved oxygen. Cyclic voltammetry, amperometry, and the rotating disk electrode technique were used to study the reaction in neutral pH solution. Highly reproducible cyclic voltammograms for NADH oxidation were obtained at as-deposited diamond electrodes. The response was stable over several months of storage in ambient air, in contrast to glassy carbon electrodes, which deactivated within 1 h. The diamond electrode exhibited very high sensitivity for NADH, with an amperometric detection limit of 10 nM (S/N = 7). The response remained stable, even in the very low concentration range, for several months. In addition, interference effects due to ascorbic acid were minimal when the concentrations of NADH and ascorbic acid were comparable. An NADH-mediated dehydrogenese-based ethanol biosensor incorporating an unmodified diamond electrode is demonstrated. The present results indicate that diamond is a useful electrode material for the analytical detection of NADH, making it attractive for use in sensors based on enzyme-catalyzed reactions involving NADH as a cofactor.     

Superconducting Behavior of Interfaces in Graphite: Transport Measurements of Micro-constrictions

We have studied the magnetoresistance (MR) of thin highly oriented pyrolytic graphite mesoscopic samples without and with micro-constrictions of different widths between the voltage electrodes. The MR for fields parallel to the c-axis shows an anomalous hysteresis loop compatible with the behavior expected for granular superconductors. The smaller the constriction width, the larger is the anomalous hysteresis and the higher the temperature for its observation. Our results support the existence of granular superconductivity probably embedded at interfaces between crystalline graphite regions.     

Creating Highly Active Iron Sites in Electrochemical N2 Reduction by Fabricating Strongly-Coupled Interfaces

Electrochemical N_c reduction has been regarded as one of the most promising approaches to producing ammonia under mild conditions, but there are remaining pressing challenges in improving the reaction rate and efficiency. Herein, an unconventional galvanic replacement reaction is reported to fabricate a unique hierarchical structure composed of Fe₃O₄-CeO₂ bimetallic nanotubes covered by Fe₂O₃ ultrathin nanosheets. Control experiments reveal that CeO₂ species play the essential role of stabilizer for Fe²⁺ cations. Compared with bare CeO₂ and Fe₂O₃ nanotubes, the as-obtained Fe₂O₃/Fe₃O₄-CeO₂ possesses a remarkably enhanced NH₃ yield rate (30.9 µg h⁻¹ mg_cat⁻¹) and Faradaic efficiency (26.3%). The enhancement can be attributed to the hierarchical feature that makes electrodes more easily to contact with electrolytes. More importantly, as verified by density functional theory calculations, the generation of Fe₂O₃-Fe₃O₄ heterogeneous junctions can efficiently optimize the reaction pathways, and the energy barrier of the potential determining step (the *N₂ hydrogenates into *N*NH) is significantly decreased.     

Effect of Power Line Interference on Microphone Calibration Measurements Made at or Near Harmonics of the Power Line Frequency

The electrical measurements required during the primary calibrations of laboratory standard microphones by the reciprocity method can be influenced by power line interference. Because of this influence, the protocols of international inter-laboratory key comparisons of microphone calibrations usually have not included measurements at power line frequencies. Such interference has been observed in microphone output voltage measurements made with a microphone pressure reciprocity calibration system under development at NIST. This system was configured for a particular type of standard microphone in such a way that measurements of relatively small signal levels, which are more susceptible to the effect of power line interference, were required. This effect was investigated by acquiring microphone output voltage measurement data with the power line frequency adjusted to move the frequency of the interference relative to the center frequency of the measurement system passband. These data showed that the effect of power line interference for this system configuration can be more than one percent at test frequencies harmonically related to the power line frequency. These data also showed that adjusting the power line frequency to separate the interference and test frequencies by as little as 1.0 Hz can reduce the effect of the interference by at least an order of magnitude. Adjustment of the power line frequency could enable accurate measurements at test frequencies that otherwise might be avoided.     

Ce Site in Amorphous Iron Oxyhydroxide Nanosheet toward Enhanced Electrochemical Water Oxidation

Iron oxyhydroxide has been considered an auspicious electrocatalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis due to its suitable electronic structure and abundant reserves. However, Fe-based materials seriously suffer from the tradeoff between activity and stability at a high current density above 100 mA cm⁻². In this work, the Ce atom is introduced into the amorphous iron oxyhydroxide (i.e., CeFeO_xH_y) nanosheet to simultaneously improve the intrinsic electrocatalytic activity and stability for OER through regulating the redox property of iron oxyhydroxide. In particular, the Ce substitution leads to the distorted octahedral crystal structure of CeFeO_xH_y, along with a regulated coordination site. The CeFeO_xH_y electrode exhibits a low overpotential of 250 mV at 100 mA cm⁻² with a small Tafel slope of 35.1 mVdec⁻¹. Moreover, the CeFeO_xH_y electrode can continuously work for 300 h at 100 mA cm⁻². When applying the CeFeO_xH_y nanosheet electrode as the anode and coupling it with the platinum mesh cathode, the cell voltage for overall water splitting can be lowered to 1.47 V at 10 mA cm⁻². This work offers a design strategy for highly active, low-cost, and durable material through interfacing high valent metals with earth-abundant oxides/hydroxides.     

Non‐intrusive Measurements of Headspace Gas Composition in Liquid Food Packages Made of Translucent Materials

The increase in chilled food consumption requires enhanced food safety and quality assurance. Food deteriorating processes are affected by the presence of oxygen, combined with factors such as time and temperature. To slow down deterioration processes and prolong shelf life, traditional packaging methods are being replaced by modified atmosphere packaging, for example. Oxygen, which is naturally present in the headspace of most food packages, is then reduced and controlled. Many sensing techniques for food quality assurance have been developed; however, almost all are intrusive, increasing the complication level and causing sample waste. The purpose of this paper is to introduce a non‐intrusive technique [gas in scattering media absorption spectroscopy (GASMAS)] for measuring gas composition in the headspace of liquid food packages. The GASMAS method uses diode laser absorption spectroscopy combined with diffuse light propagation to analyse gas located inside solids and liquids. By illuminating the package from the outside and analysing the scattered light that emerges, the absorption from the gas inside the headspace can be studied.The GASMAS technique was evaluated on a series of carton packages with a high‐quality orange juice and a nitrogen headspace. A clear variation in oxygen content was measured for samples with different storage times. The results demonstrate the possibility of using the GASMAS method for non‐intrusive quality measurements in food products and packaging. They also indicate the potential for the non‐intrusive quality assurance applications without waste of samples. A further development of the technique could include ‘in‐line’ quality control of packed food items throughout the food packaging supply chain. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhanced Acousto-Optic Diffraction Efficiency in a Symmetric SrTiO(3)/BaTiO(3)/SrTiO(3) Thin-Film Heterostructure

Guided-wave acousto-optic Bragg diffraction and surface acoustic-wave propagation in epitaxially matched SrTiO(3)/BaTiO(3)(001)/SrTiO(3) thin-film heterostructures have been theoretically studied. The optimum electromechanical coupling and Bragg diffraction efficiency have been determined at several acoustic frequencies by means of varying the thickness of the SrTiO(3) overlayer and the BaTiO(3) waveguiding layer. A strain-controlling nonpiezoelectric SrTiO(3) overlayer upon the BaTiO(3)/SrTiO(3) structure is found to enhance the coupling coefficient (k(2)) and the diffraction efficiency significantly. A comparison of asymmetric and symmetric structures shows an increase in the diffraction efficiency from 10.5% to 43.0% and a decrease in the untuned-transducer conversion efficiency from 36 to 23 dB at an operating frequency of 1 GHz with an interaction length of 1 mm and an acoustic power of 1 mW.     

利用APT研究RPV模拟钢中相界面原子偏聚特征

提高了Cu含量的核反应堆压力容器(RPV)模拟钢经调质处理(880℃保温0.5h,水淬;660℃保温10h)以及400℃时效1000h后,采用原子探针层析技术(APT)研究了碳化物/α-Fe基体,富Cu相/α-Fe基体以及富Cu相/碳化物界面处溶质或杂质原子的偏聚特征。结果表明:在碳化物/α-Fe基体界面处P原子偏聚最明显;在富Cu相/α-Fe基体界面处Ni原子偏聚最明显,Mn原子也有微弱的偏聚;在富Cu相/碳化物界面处未发现溶质或杂质原子的偏聚现象。不同相界处原子偏聚不仅与界面本身微观结构有关,也与相界附近化学特性有关。     

A Combined TD–FD Method for Enhanced Reflectometry Measurements in Liquid Quality Monitoring

Measurement and control of the dielectric parameters of liquids play a major role in industrial quality-control applications. Although several techniques are currently available to this aim, none of them is simultaneously accurate, cost-effective, and reasonably quick. On the other hand, reflectometry has become a very attractive method for monitoring applications, mostly thanks to its accuracy and flexibility. In this paper, a combined method based on time-domain reflectometry (TDR) and frequency-domain (FD) analysis is presented: the aim is to substantially improve the measurement accuracy of the dielectric parameters of liquids. Starting with typical TDR measurements, the associated FD evaluation of the dielectric parameters is considerably enhanced through the combined effect of the following: 1) specific data-processing techniques; 2) the implementation of a calibration procedure; and 3) the final modeling and minimization routine. Furthermore, to definitively assess the proposed combined procedure, results are compared with measurements directly performed in the FD through a vector network analyzer (VNA). The ultimate goal of the work is to pave the way for the adoption of inexpensive and portable TDR devices in practical industrial monitoring applications.     

Synergistically Designed Dual Interfaces to Enhance the Electrochemical Performance of MoO2/MoS2 in Na- and Li-Ion Batteries

It is indispensable to develop and design high capacity, high rate performance, long cycling life, and low-cost electrodes materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, MoO₂/MoS₂/C, with dual heterogeneous interfaces, is designed to induce a built-in electric field, which has been proved by experiments and theoretical calculation can accelerate electrochemical reaction kinetics and generate interfacial interactions to strengthen structural stability. The carbon foam serves as a conductive frame to assist the movement of electrons/ions, as well as forms heterogeneous interfaces with MoO₂/MoS₂ through C S and C O bonds, maintaining structural integrity and enhancing electronic transport. Thanks to these unique characteristics, the MoO₂/MoS₂/C renders a significantly enhanced electrochemical performance (324 mAh g⁻¹ at 1 A g⁻¹ after 1000 cycles for SIB and 500 mAh g⁻¹ at 1 A g⁻¹ after 500 cycles for LIBs). The current work presents a simple, useful and cost-effective route to design high-quality electrodes via interfacial engineering.     

Calorimetric Measurements at Low Temperatures in Toluene Glass and Crystal

The specific heat of toluene in glass and crystal states has been measured both at low temperatures down to 1.8 K (using the thermal relaxation method) and in a wide temperature range up to the liquid state (using a quasiadiabatic continuous method). Our measurements therefore extend earlier published data to much lower temperatures, thereby allowing to explore the low-temperature “glassy anomalies” in the case of toluene. Surprisingly, no indication of the existence of tunneling states is found, at least within the temperature range studied. At moderate temperatures, our data either for the glass or for the crystal show good agreement with those found in the literature. Also, we have been able to prepare bulk samples of toluene glass by only doping with 2% mol ethanol instead of with higher impurity doses used by other authors.     

International Intercomparison 75-A12 Voltage Standing Wave Ratios in Waveguide at 10 GHz

Five reduced-height, waveguide traveling standards, designed to give voltage standing wave ratios between 1.02 and 1.2, have been measured at 10 GHz by national standards laboratories in the UK, USA, Australia, Japan, Italy, and Canada. The mean values obtained by the six participants range from 1.0182 to 1.0212 on the lowest step and from 1.1976 to 1.2031 on the highest step.