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Abstract: The high temperature oxide thermoelectric materials of p-type Ca3Co4−x Ag x O9 (denoted as p-Co349/Ag x ) and n-type Ca1−y Sm y MnO3 (denoted as n-Mn113/Sm y ) were prepared by the self-ignition method combined with a sintering technique. The influence of doping Ag and Sm on the thermoelectric properties of the corresponding materials was evaluated. The figures of merit, ZT, for the p-Co349/Ag0.2 and n-Mn113/Sm0.02 materials reached maxima of 0.20 and 0.15 at 973K, respectively. The performances of thermoelectric devices constructed with the p- and n-type pairs were evaluated in terms of the maximum output power (P max) and manufacturing factor. The P max and volume power density for the four-leg devices reached 36.8mW and 81.9mWcm−3 at ΔT of 523K, respectively. [Copyright &y& Elsevier]

Abstract: Monodisperse Zn7.23Cd2.77S10 nanoparticles with uniform shape and a narrow size distribution were synthesized by a room temperature reaction, followed by a 200°C heat-treatment in an autoclave, using Na-oleate and oleic acid as surfactant and ligand, respectively. This method achieves a complete separation of the nucleation and growth. X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM characterizations showed that the monodisperse nanoparticles had a poly-crystalline hexagonal structure with a uniform crystallite size of 20nm with spike-like morphology and a very rough surface. The photoluminescence (PL) spectra of Zn7.23Cd2.77S10 had blue-shifted with a peak at 485nm. [Copyright &y& Elsevier]

Abstract: Ag-doped Na1.7Co2O4 thermoelectric oxides have been synthesized via a simple self-ignition route, which have different nominal compositions in the formula of Na1.7AgyCo2−yO4 (y =0, 0.1, 0.2, 0.3, 0.4, 0.5). The ceramic samples showed the property of high-crystallographic orientation. The electrical resistivity and Seebeck coefficient were measured using four silver probes method. Analysis showed that phase composition, thermoelectric performance and density of the Ag-doped Na1.7Co2O4 ceramics were influenced by Ag dopant. In the whole measurement temperature, Na1.7Ag0.2Co1.8O4 performed the best thermoelectric properties. The power factor of the doped oxide reached 687.431μWm−1 K−1 at 873K. [Copyright &y& Elsevier]

Abstract: Homogeneous non-integral stoichiometry semiconductor compound Zn x Cd1−x S nanorods have been successfully synthesized at 180°C by the reaction of a mixture ZnCl2 and CdCl2 with thiosemicarbazide (NH2SNHNH2) in the ethylenediamine. The compositions over the whole range according to JCPDS cards have been controlled only by changing the cation molar ratio of Zn:Cd in the reactants. The composition dependence of UV–vis spectra and the photoluminescence (PL) spectra of the series Zn x Cd1−x S nanocrystals has been revealed. The lattice parameters (a, c) calculated from XRD patterns increase linearly with the increasing of Cd content, which is consistent with Vegard''s law. Two well-defined relationships have been established among the lattice parameters, the band gap energy (E g), and the composition value (x) of the Zn x Cd1−x S. The mechanism of reaction and the selection of the reagents have also been investigated. [Copyright &y& Elsevier]

Different molar ratios Bi 7 WO 13.5 (BWO) as sintering aids are used to modify Nd 2 Ce 2 O 7 (NCO) material by mechanical method. The influence of Bi 7 WO 13.5 additions on the phase structure, linear shrinkage, micromorphology and electrical conduction behaviors of Nd 2 Ce 2 O 7 are characterized by X-Ray diffraction(XRD), dilatometry technique, Raman spectroscopy, Scanning electron microscopy(SEM) and Electrochemical impedance spectroscopy(EIS). All modified samples still retain the fluorite-type structure. BWO additives in all molar ratios greatly improve the sintering ability. It is found that 5mol% BWO doped NCO(NCO-5) promote the linear shrinkage from 6.60% to 21.23% at 1300 °C. Electrochemical characterizations reveal that high total conductivities of all modified ceramics are obtained through this modified method. The conductivity of modified NCO sample sintered at 1300 °C is higher than that of unmodified NCO pellet sintered at 1500 °C. Especially the NCO-5 pellet offers 1.38 × 10−2 and 2.26 × 10−2 Scm−1 at 750 °C in dry air and 5% H 2 -Ar conditions, respectively. Furthermore, an anode-supported single cell with NCO-5 electrolyte is manufactured and test, the cell displays a peak power density of 613 mWcm−2 at 750 °C. All these results indicate the BWO can be used as sintering aids for NCO electrolyte to improve the sintering ability and electrochemical performance. • Bi 7 WO 13.5 was used as the sintering aids for Nd 2 Ce 2 O 7 proton-conducting oxide. • High sinterability and improved electrical conductivity were achieved at lower sintered temperatures. • A single cell with NCO-5 electrolyte is successfully fabricated with higher performance. [ABSTRACT FROM AUTHOR]

In this study, a new robust ohmic contact preparation process for GaN p-FETs application is developed on p-GaN/AlGaN/GaN, which excluded the commonly used descum step. A specific contact resistivity of approximately 2.0 × 10–3 Ω·cm2 is obtained based on Ni/Au metal stack. X-ray photoelectron spectroscopy (XPS) analysis revealed that the p-GaN surface underwent oxidation by O 2 plasma in the descum step, forming Ga 2 O 3 as a barrier layer between the metal and p-GaN. The resulting Ga 2 O 3 could not be completely removed using a hydrochloric acid solution, resulting in a Schottky contact. Moreover, the Ni/Au ohmic contact mechanism was revealed for the first time by varying the O 2 content in the annealing atmosphere. The X-ray transmission electron microscopy–energy-dispersive X-ray spectroscopy and XPS results proved that the Ni (III) oxide or Ni 2 O 3 present at the metal/p-GaN interface and the Ga vacancies formed on the p-GaN surface played a crucial role in facilitating the formation of ohmic contacts. • Novel robust ohmic contact preparation process for GaN p-FETs application with low contact resistivity. • XPS analysis reveals descum step impact on formation of ohmic contact. • Insights into Ni/Au ohmic contact mechanism by manipulating oxygen content during annealing. [ABSTRACT FROM AUTHOR]

Colloidal hybrid perovskite quantum dots (QDs) of formamidinium lead halides (FAPbX 3 , X = Cl, Br, I and their mixture), which possess a full visible waveband tunable photoluminescence ranging from 429 nm to 782 nm verified by the calculated bandgap of FAPbX 3 (2.720eV–2.115eV–1.401eV; from Cl to Br to I) , have been prepared by regulating the halogen in FAPbBr 3. Herein, the as-obtained FAPbX 3 QDs feature a high quantum yield up to 85% and narrow emission line-widths low to 20 nm, benefiting from the highly uniform cubic morphology. In addition, the mechanism of anion-exchange in FAPbX 3 QDs is expounded from two aspects of defects and temperature by theoretical calculation and experiment method. Trichromatic LEDs are fabricated to demonstrate the photoelectric properties by employing the FAPbX 3 QDs, which have a pure color and narrow full width at half maximum (FWHM, 20.6 nm for Blue, 22 nm for Green, 36.6 nm for Red, respectively). More interestingly, the green one reaches the Rec.2020 standard and the corresponding QD white LED presents a high luminous efficiency of 48.8 lm/w and color rendering index (CRI) 90.2 together with the CIE color coordinate at (0.32,0.31). • The FAPbX 3 QDs tuned from 429 nm to 782 nm are synthesized by anion-exchange. • The mechanisms of exchange process and the band structure are expounded. • The obtained QDs feature a high PLQY up to 85% and narrow FWHM low to 20 nm. • WLEDs are fabricated with high luminous efficiency (48.8 lm/w) and CRI (90.2). [ABSTRACT FROM AUTHOR]

The application of high-capacity silicon anodes in lithium batteries is restricted by the significant volume changes that occur during electrochemical alloying and long-term galvanic segregation cycles. In this work, we proposed a gas-phase magnesiothermic reduction strategy to fabricate highly porous SiOx/nanoSi@C (0 < x < 2) composites. This approach diffused the evaporated magnesium atoms into the interior of the SiO 2 , preventing the fast self-propagating magnesium thermal reduction reaction only on the surface of the silicon oxide particles and regulating the distribution and relative content of SiOx and nanoSi in the active material network. Thus, the proposed approach formed a porous structure of silicon nanocrystals that were diffusely distributed in the silicon oxide matrix. For the as-prepared SiOx/nanoSi@C composites, the nano-Si component increased the reversible capacity of the composite, the porous SiOx matrix suppressed the volume expansion of crystalline silicon by generating Li 2 O and lithium silicate protective layers, and the carbon coatings further accommodated volume expansion and increased surface contact between the active material and the electrolyte. As a result, the 0.75SiOx/0.25nanoSi@C anode exhibited excellent electrochemical performance with a reversible capacity of 1067.92 mAh/g after 400 cycles at a current density of 1 A/g. [Display omitted] • Fabrication of SiOx/nanoSi@C via a gas-phase magnesium thermal reduction. • This strategy avoids the fast self-propagation only on the surface of silicon oxide. • Highly porous SiOx/nanoSi@C composites suppress the volume expansion of silicon. • SiOx/nanoSi@C anode exhibits excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

A facile synthesis of aqueous CdZnTe quantum dots (QDs) incorporated in CaCO 3 matrix is demonstrated, providing a new type of solid-state light conversion material. Highly luminescent CdZnTe QDs were firstly synthesized using CdCl 2 , ZnCl 2 and Te as precursors and 3-Mercaptopropionic acid (MPA) as ligand. Then CdZnTe QDs were incorporated into CaCO 3 matrix through a co-precipitation method. Due to the protection of the tight matrix, the resulting CdZnTe QDs/CaCO 3 composites exhibit good photostability and processability as well as high photoluminescence properties. A white light-emitting diode (WLED) applying the composites as a red color conversion layer was also fabricated, which showed excellent performance including a Commission Internationale de I'eclairage (CIE) color coordinate of (0.3662, 0.3396), a high color rendering index (Ra) of 92.7 and a low correlated color temperature (Tc) of 4146 K under 20 mA forward-bias current, suggesting the promising application of the composites in solid-state lighting systems. [ABSTRACT FROM AUTHOR]

Here we present the observation of a unique phenomenon of converting electrical conductivity types in surface atomic-ligand exchanged of PbS quantum dots (QDs), while tuning the gate voltage of PbS QD-based thin film field-effect transistors (TFTs). The synthesized PbS-QD thin films showed different conductivity (n- or p-) types depending on the direction of gate voltage sweeping. When increasing gate voltage from negative to positive voltage, the TFT devices produced n-channel characteristics with a typical mobility on the order of μ n = 10 −1 cm 2 V −1 s −1 . By contrast, the devices showed p-channel characteristics with similar mobility when sweeping the gate voltage from positive to negative. The studies based on density functional theory (DFT) theoretical calculations and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the band gap of ligand exchanged PbS-QDs changes upon gate voltage sweeping, affecting the surface states of the QDs due to the adhered Br − and therefore altering the conductivity type of the materials. These findings signify the carrier type switching behavior via gate voltage tuning in atomic-ligand exchange QD thin films, suggesting great application potential of QD for advanced new-generation nano-electronic devices. [ABSTRACT FROM AUTHOR]

Two-terminal nonvolatile resistive switching (RS) memory devices based on n -CdSe nanoribbon (NR)/ p -Si heterojunction were fabricated. These memory devices exhibited excellent memory characteristics with high current ON/OFF ratio exceeding six orders of magnitude, long retention time over 10 4 s, and good endurance over 6 months. The capacitance-voltage ( C - V ) measurement was carried out to confirm the electrons traping and detrapping processes in interface oxide layer. The high-performance of memory devices and simple processing techniques will offer new opportunities for memory applications of one-dimensional nanomaterials. [ABSTRACT FROM AUTHOR]

Transition metal sulfides (TMSs) are widely used in energy storage and energy conversion systems because of their excellent electrochemical properties. However, their application is restricted by a low electron transfer efficiency, few active sites and poor stability. In this paper, CoNi bimetallic sulfides supported by carbon skeleton (CoNi-SP/NPC) were prepared using bimetallic organic frameworks (MOFs) as templates and modified with phosphorus doping. Compared with single metal sulfides, the bimetallic sulfides are more favorable for electron transfer in the catalytic process. Meanwhile, the carbon skeleton support gives the catalyst higher mechanical stability, and the P-doping brings more active sites into to contact with the aqueous solution. The overpotential of CoNi-SP/NPC catalyst is only 105 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) and 313 mV at 100 mA cm−2 for oxygen evolution reaction (OER). In addition, CoNi-SP/NPC also displays remarkable performance in the course of overall water splitting, which can achieve 50 mA cm−2 at only 1.8 V and remains good stability for 12 h. This work proposes a feasible strategy to synthesize highly efficient water splitting electrocatalysts. • CoNi-SP/NPC exhibits synergy between bimetallic sulfides. • P-doping increases the active sites of bimetallic sulfides. • Metal-organic frameworks enhance electrical conductivity of materials. • Composite exhibits high-efficient OER and HER catalytic capacities and good stability. [ABSTRACT FROM AUTHOR]

• A AlN thickness of 150 nm gives a smooth surface N-polar GaN with reduced defects. • A thicker AlN changes the polarity of GaN to Ga-polar while a thinner one roughens the GaN surface. • The undulated interface between GaN and AlN plays an important role in the polarity inversion and surface roughening. • A polarity controllable method for GaN could be realized by simply changing the thickness of AlN. The influence of the thickness of aluminum nitride (AlN) on the surface morphology, crystalline quality, and polarity of N-polar gallium nitride (GaN) grown by metal organic chemical vapor deposition (MOCVD) is investigated in this study. With a medium temperature (1000 ℃) AlN buffer layer of 150 nm, a hexagonal-defect-free N-polar GaN thin film with low dislocation densities (4.2 × 108 cm-2 for screw dislocation density and 3.7 × 109 cm-2 for edge dislocation density) is obtained on a 2-in. vicinal sapphire substrate (c off m plane 2°). With the reduction of the AlN thickness to 80 nm, the N-polar GaN surface becomes rough and the crystalline quality is exacerbated. While the thickness of AlN is increased to 200 nm, the polarity of GaN is changed to Ga-polar. The transmission electron microscopy (TEM) results reveal an undulated interface between GaN and AlN with a large density of pyramidal defects which may contribute to the polarity inversion of GaN. The controllable polarity inversion through changing the thickness of AlN provides a promising method for the polarity engineering of nitride-based devices. [ABSTRACT FROM AUTHOR]

Abstract: A novel homogeneous precipitation process was employed to prepare nanosized W–Cu powders. Precipitates of CuWO4·2H2O and Cu2(OH)2WO4 were first obtained by adding sodium tungstate and copper chloride into aqueous ammonia solution, and then heating the solution to remove ammonia. The precipitates were subsequently washed, dried and dehydrated, followed by reducing in H2 atmosphere to convert into W–Cu composite powders. Properties of the precipitates, as well as the W–Cu composite powders and their sintered parts were characterized. It was shown that W–Cu powders produced by the homogeneous precipitation process have a nearly spherical shape, with particle size ranging from 50 to 100nm and a well-mixed state of W and Cu ingredients. Relative density of more than 94% and 98% was obtained for W–Cu samples sintered at 1050 and 1150°C, respectively. Homogeneous microstructure, good physical and mechanical properties were also achieved for the sintered W–Cu parts. [Copyright &y& Elsevier]