Quantum-Confinement-Enhanced Thermoelectric Properties in Modulation-Doped GaAs–AlGaAs Core–Shell Nanowires

Nanowires (NWs) hold great potential in advanced thermoelectrics due to their reduced dimensions and low-dimensional electronic character. However, unfavorable links between electrical and thermal conductivity in state-of-the-art unpassivated NWs have, so far, prevented the full exploitation of their distinct advantages. A promising model system for a surface-passivated one-dimensional (1D)-quantum confined NW thermoelectric is developed that enables simultaneously the observation of enhanced thermopower via quantum oscillations in the thermoelectric transport and a strong reduction in thermal conductivity induced by the core–shell heterostructure. High-mobility modulation-doped GaAs/AlGaAs core–shell NWs with thin (sub-40 nm) GaAs NW core channel are employed, where the electrical and thermoelectric transport is characterized on the same exact 1D-channel. 1D-sub-band transport at low temperature is verified by a discrete stepwise increase in the conductance, which coincided with strong oscillations in the corresponding Seebeck voltage that decay with increasing sub-band number. Peak Seebeck coefficients as high as ≈65–85 µV K⁻¹ are observed for the lowest sub-bands, resulting in equivalent thermopower of S²σ ≈ 60 µW m⁻¹ K⁻² and S²G ≈ 0.06 pW K⁻² within a single sub-band. Remarkably, these core–shell NW heterostructures also exhibit thermal conductivities as low as ≈3 W m⁻¹ K⁻¹, about one order of magnitude lower than state-of-the-art unpassivated GaAs NWs.     

Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe₃O₄–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe₃O₄ (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe₃O₄ NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe₃O₄ NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe₃O₄ NPs with inverse spinel phase were formed. The results of VSM imply that the Fe₃O₄–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe₃O₄ NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.     

Preparation and Properties of a Group of Nanoporous Materials with Photo-semiconducting Host Structures

1. Introduction Preparation of nanostructured materials is a fundamental field for advances in nano-technology.Various chemical routes have been available that lead to well defined nanoparticles of metals or semiconductors, giving rise to different microelectronic applications.[1-4] Nanoporous crystals, on the other hand, having structures that contain pores of nanometer sizes, provide the possibility of ordering nanoparticles into strictly uniform arrays by occluding them in the pores. Nanoporous solids with insulating silicate host structures are well known.     

Core–Shell Structure and Luminescence of SrMoO_4:Eu~(3+)(10%) Phosphors

SrMoO_4:Eu~(3+)(10%) phosphors were produced via hydrothermal synthesis and co-precipitation.We systematically analyzed how the morphology and luminescence properties of the phosphors were affected by the synthesis conditions,including the p H of the precursor solution,stirring speed,and postsintering temperature.The samples synthesized at p H = 8 and 9 were spindle-like rods with a core–shell structure.When the stirring speed increased to Vs = 150 r/min,the core–shell structure disappeared.Photoluminescence measurements indicated that the Sr Mo O4:Eu3+samples under ultraviolet radiation produced strong red emission centered at 616 nm.The luminescence properties were greatly affected by the p H,stirring during hydrothermal reaction,and use of post-annealing.The related mechansim is discussed.     

Preparation and Properties of Nano-TiO_2 Powders

This paper reports the preparation of nano-TiO2 (about 10 nm) powder by the method of precipitation. In detail, some breparation conditions were investigated in order to find out how to control the grain size and reduce the agglomeration of powders. Also, the reflex spectra of nano-scale powders with different grain size were studied. It tvas found that the wave length and width of reflex spectra are connected with the grain size of nano-TiO2 powders     

Preparation and Magnetic Properties of InTe–Cr2Te3 Alloys

InTe–Cr₂Te₃ alloys were prepared and characterized by temperature-dependent magnetic measurements. The results lend support to earlier phase-diagram data indicating the formation of compounds with the compositions In₉Cr₂Te₁₂ and In₂Cr₆Te₁₁. In₉Cr₂Te₁₂ is shown to be a ferromagnet, while In₂Cr₆Te₁₁ has a more complex magnetic structure.     

Magneto-Plasmonic Effect in Cobalt Thin Film Incorporating Core–Shell Ag@Au Nanoparticles

We report enhanced magneto-optical Kerr rotation in the magneto-plasmonic structure of a cobalt thin film incorporating silver/gold core–shell nanoparticles. Metallic nanoparticles with core–shell structure of silver/gold were fabricated by laser ablation in liquid method and the magneto-optical medium was prepared by electron beam deposition technique. Excitation of localized surface plasmon resonance was demonstrated for various incidence angles. The experimental results show direct evidence for localized surface plasmon resonance enhancement effect on the polar magneto-optical Kerr effect of the cobalt thin film.     

Enriched Fe Doped on Amorphous Shell Enable Crystalline@Amorphous Core–Shell Nanorod Highly Efficient Electrochemical Water Oxidation

The rational design of efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) with sluggish kinetics, is imperative to diverse clean energy technologies. The performance of electrocatalyst is usually governed by the number of active sites on the surface. Crystalline/amorphous heterostructure has exhibited unique properties and opens new paradigms toward designing electrocatalysts with abundant active sites for improved performance. Hence, Fe doped Ni–Co phosphite (Fe-NiCoHPi) electrocatalyst with cauliflower-like structure, comprising crystalline@amorphous core–shell nanorod, is reported. The experiments uncover that Fe is enriched in the amorphous shell due to the flexibility of the amorphous component. Further density functional theory calculations indicate that the strong electronic interaction between the enriched Fe in the amorphous shell and crystalline core host at the core–shell interface, leads to balanced binding energies of OER intermediates, which is the origin of the catalyst-activity. Eventually, the Fe-NiCoHPi exhibits remarkable activity, with low overpotentials of only 206 and 257 mV at current density of 15 and 100 mA cm⁻². Unceasing durability over 90 h is achieved, which is superior to the effective phosphate electrocatalysts. Although the applications at high current remain challenges , this work provides an approach for designing advanced OER electrocatalysts for sustainable energy devices.     

Preparation of Sintered Titanium Anode and Its Electrochemical Properties

In this paper, the sintered Ti anodes (STA) with Ti suboxide intermediate layers and β-MnO_2 activelayers were investigated in detail. At usual industrial current densities, the oxygen evolutionoverpotential on STA is reduced by 350 mV compared with lead anodes. According to the equationobtained experimentally, the service life of STA may be expected to be more than 3 years. After los-ing activity, STA may be recoated with β-MnO_2 active layers and used again. The electrocatalyticactivity and the service life of the reused anodes remained almost unchanged. The possible reasonsfor losing activity of STA during the anodic evolution of oxygen were investigated by means of elec-tron probe microanalysis, electron scanning microscope and X-ray diffraction.     

Preparation and Properties of Some Chemical and Electrochemical γ-MnO_2

Chemically prepared electrolytic γ-MnO2 and an electrodeposited MnO2 doped with Ce(III)were subjected to physicochemical studies. X-ray diffractometry, density measurements, chemical analysis and thermal analysis were used to determine the structure and chemical disorder present.The samples prepared chemically(CMD) or electrochemically (EMD) showed a variable amount of de Wolff disorder(Pr) and microtwinning (Tw). Manganese dioxide prepared in the presence of Ce(III) showed appreciable decrease in de Wolff defect and a large amount of microtwinning. Thermal analysis showed a loss of weight due to the physically adsorbed and the structural(OH)water, from which the activation energy was calculated. Chemical composition and formulae calculated on the bases of cation vacancy model, cleared that Ce(III)-doped sample has a remarkable increase in the vacancies population associated with higher structural water content. This leads to lower activation energy of water release, and consequently it is supposed to acquire higher electrochemical activity.     

Gradient-Concentration Design of Stable Core–Shell Nanostructure for Acidic Oxygen Reduction Electrocatalysis

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual-criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the “defective-armored” structure of Pt shell and Pt–Ni core nanoparticle decorated on graphene (Pt–Ni@Pt_D/G) using a facile and controllable galvanic replacement reaction to generate gradient distribution of Pt–Ni composition from surface to interior, followed by a partial dealloying approach, leaching the minor nickel atoms on the surface to generate defective Pt skeleton shell, is reported. The Pt–Ni@Pt_D/G catalyst shows impressive performance for ORR in acidic (0.1 m HClO₄) electrolyte, with a high mass activity of threefold higher than that of Pt/C catalyst owing to the tuned electronic structure of locally concave Pt surface sites through synergetic contributions of Pt–Ni core and defective Pt shell. More importantly, the electrochemically active surface areas still retain 96% after 20 000 potential cycles, attributing to the Pt atomic shell acting as the protective “armor” to prevent interior Ni atoms from further dissolution during the long-term operation.     

Synthesis of Palladium-Based Crystalline@Amorphous Core–Shell Nanoplates for Highly Efficient Ethanol Oxidation

Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core–shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu_3−χP nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mg_Pd⁻¹, which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mg_Pd⁻¹).     

Core–Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na–S Batteries

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium–sulfur (RT Na–S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S₈→Na₂S_x→Na₂S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core–shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N₄), where isolated Ni–N₄ sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S₈ into Na₂S_x (4 < x ≤ 8), while Ni–N₄ sites realize the efficient conversion of Na₂S_x into Na₂S, bridged by the diffusion of Na₂S_x from the core to shell. Besides, Ni–N₄ sites on the shell can also induce an inorganic-rich cathode–electrolyte interface (CEI) on ZnS-NC@Ni-N₄ to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N₄/S cathode exhibits an excellent rate-performance (650 mAh g⁻¹ at 5 A g⁻¹) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na–S batteries.     

Mott–Schottky Effect in Core–Shell W@WxC Heterostructure: Boosting Both Electronic/Ionic Kinetics for Lithium Storage

The dynamics rate of traditional metal carbides (TMCs) is relatively slow, severely limiting its fast-charging capacity for lithium-ion batteries (LIBs). Herein, the core–shell W@W_xC heterostructure is developed to form Mott–Schottky heterostructure, thereby simultaneously accelerating the electronic and ionic transport kinetics during the charging/discharging process. The W nanoparticles are partially reduced into W_xC to form a particular core–shell structure with abundant heterogeneous interfaces. Benefiting from the Mott–Schottky effect, the electrons at the metal/semiconductor heterointerface can migrate spontaneously to realize an equal work function on both sides. In addition, the independent nanoparticle as well as the unique core–shell structure facilitate the ionic diffusion kinetics. As expected, the W@W_xC electrode exhibits excellent electrochemical stability for LIBs, whose capacity can be maintained at 173.8 mA h g⁻¹ after 1600 cycles at a high current density of 5 A g⁻¹. When assembled into a full cell, it can achieve an energy density of 360.2 Wh kg⁻¹. This work presents a new avenue to promote the electronic and ionic kinetics for LIBs anodes by constructing the unique Mott–Schottky heterostructure.