Interface-charged impurity scattering in semiconductor MOSFETs and MODFETs: temperature-dependent resistivity and 2D ‘metallic‘ behavior

We present the results on the anomalous 2D transport behavior by employing Drude–Boltzmann transport theory and taking into account the realistic charge impurity scattering effects. Our results show quantitative agreement with the existing experimental data in several different systems and address the origin of the strong and nonmonotonic temperature-dependent resistivity.     

High Adsorption Pearl‐Necklace‐Like Composite Membrane Based on Metal–Organic Framework for Heavy Metal Ion Removal

The zeolitic imidazolate framework‐67 (ZIF‐67)‐based “pearl‐necklace‐like” composite membranes are prepared by in situ intergrown on the surface of 2‐methylimidazole/cellulose acetate (MIM/CA) electrospun nanofibers for the first time. With the aid of MIM, the ZIF‐67 nanocrystals successfully grow throughout the composites and attach to the fibers just like the pearls in necklace. The incubation time of ZIF‐67 has a significant influence on the structures and properties of the composites. And with an approximate saturation of ZIF‐67 nanocrystals, the integrated composites achieve a much higher surface area of 463.1 m2 g⁻¹, which is as dozens of times as that of pure MIM/CA electrospun nanofibers (6.9 m2 g⁻¹). In addition, the composites performed a high Cu(II) and Cr(VI) adsorption of 18.9 mg g⁻¹ and 14.5 mg g⁻¹, respectively. The adsorption data are well fitted with the pseudo‐second‐order kinetics. Moreover, adsorption mechanism is also discussed, and the electrostatic adsorption and ions exchange contribute to the high adsorption of Cu(II) and Cr(VI), and the existence of Cr(III) indicates that the Cr(VI) ions are partially reduced to Cr(III) during the adsorption. Therefore, the fabricated metal organic framework‐composite membrane with special “pearl‐necklace‐like” is a promising environmental material for removing heavy metal ions from water.     

Ultrathin‐Carbon‐Layer‐Protected PtCu Nanoparticles Encapsulated in Carbon Capsules: A Structure Engineering of the Anode Electrocatalyst for Direct Formic Acid Fuel Cells

Structure engineering is an effective strategy to enhance the performance of electrocatalysts for the formic acid oxidation reaction. However, it remains a challenge to prepare a highly active electrocatalyst based on a distinct understanding of its structure‐dependent performance. The design and synthesis of ultrathin‐carbon‐layer‐protected PtCu nanoparticles (NPs) encapsulated in a N‐doped carbon capsule (PtCu@NCC) is reported. This system is fabricated by using Zn‐based metal–organic frameworks as the carbon support source and metal‐containing tannic acid as the protecting shell template. It displays 9.8‐ and 9.6‐fold enhancements in mass activity and specific activity compared to commercial Pt/C. Moreover, a constructed direct formic acid fuel cell using PtCu@NCC as the anodic electrocatalyst delivers a maximum power density of 121 mW cm^?2. Significantly, PtCu@NCC exhibits superior structural stability and catalytic durability in both half‐cell and full‐cell tests. A mechanism study reveals that the enhanced activity is partially attributed to facilitated electro‐oxidation kinetics of formic acid in the unique structure of PtCu@NCC, while the excellent durability stems from the “protecting effect” of the in‐situ‐formed ultrathin carbon layer on the surface of the PtCu NPs. This work opens a new avenue for the development of high‐performance electrocatalysts for fuel‐cell applications by offering essential insights into the structure–performance relationship of the materials.     

Metal–insulator transition in quantum dot arrays

We present evidence for a re-entrant metal–insulator transition that arises in quantum dot arrays as the gate voltage is used to sweep their density of states past the Fermi level. The form of the temperature variation of the conductance observed in these arrays can be accounted for using a functional form derived from studies of the metal–insulator transition in two dimensions, although the values obtained for the fit parameters suggest that the behavior we observe here may be quite distinct to that found in two dimensions.     

Review of the Theoretical Description of Time‐Resolved Angle‐Resolved Photoemission Spectroscopy in Electron‐Phonon Mediated Superconductors

We review recent work on the theory for pump/probe photoemission spectroscopy of electron‐phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal‐Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson‐Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity.     

Adamantyl‐endcapped polyynes

Polyynes spanning from a diyne to a dodecayne with adamantyl endgroups have been synthesized using the Fritsch–Buttenberg–Wiechell rearrangement as a key step to construct the acetylenic framework. Molecular properties as a function of polyyne length have been analyzed by UV–Vis spectroscopy, cyclic voltammetry, differential scanning calorimetry, and X‐ray crystallography. Copyright © 2011 John Wiley & Sons, Ltd.     

Wet‐Etching Induced Abnormal Phase Transition in Highly Strained VO2/TiO2 (001) Epitaxial Film

The metal–insulator transition (MIT) behavior in vanadium dioxide (VO₂) epitaxial film is known to be dramatically affected by interfacial stress due to lattice mismatching. For the VO₂/TiO₂ (001) system, there exists a considerable strain in ultra‐thin VO₂ thin film, which shows a lower T_c value close to room temperature. As the VO₂ epitaxial film grows thicker layer‐by‐layer along the “bottom‐up” route, the strain will be gradually relaxed and T_c will increase as well, until the MIT behavior becomes the same as that of bulk material with a T_c of about 68 °C. Whereas, in this study, we find that the VO₂/TiO₂ (001) film thinned by “top‐down” wet‐etching shows an abnormal variation in MIT, which accompanies the potential relaxation of film strain with thinning. It is observed that even when the strained VO₂ film is etched up to several nanometers, the MIT persists, and T_c will increase up to that of bulk material, showing the trend to a stress‐free ultra‐thin VO₂ film. The current findings demonstrate a facial chemical‐etching way to change interfacial strain and modulate the phase transition behavior of ultrathinVO₂ films, which can also be applied to other strained oxide films.     

Metal–Organic Framework Supported Palladium Nanoparticles: Applications and Mechanisms

Heterogeneous palladium (Pd)‐based catalysts are extensively applied to improve the catalytic performance and/or expand the reaction scope in many catalytic processes, involving the cross‐coupling, hydrogenation, reduction, and oxidation reactions. Among them, metal–organic framework (MOF)‐supported Pd nanoparticles (Pd NPs) are becoming the most popular one for their excellent catalytic performance and reusable property. To motivate the development of this technology, the applications of MOF‐supported Pd NPs (Pd NPs/MOFs) in heterogeneous catalysis are critically summarized herein, including the hydrogenation reduction of nitro‐ and polyunsaturated compounds, synthesis of carbon–carbon (C? C) bonds compounds, chromium (Cr(VI)) reduction, dehalogenation, alcohol oxidation, CO₂ conversion, and CO oxidation. The influences of base, solvents, electron character of substitutes, and type of halogen on the catalytic performance are comprehensively discussed. Finally, the application prospects of Pd NPs/MOFs and existing shortcomings in the catalytic field are proposed.     

Optical–optical double resonance spectroscopy of the transition of CaOH

The state of CaOH was investigated using optical–optical double resonance spectroscopy. A combined least-squares fit of the double resonance transition data along with optical transition data and the millimeter-wave pure rotational data of the state was performed using an effective Hamiltonian. The spin–rotation constant was determined for the state for the first time. An analysis of these constants showed that the Ca–O bond length and spin–rotation parameter of the state have the smallest values of all the observed ²Σ⁺ states of CaOH. This evidence suggests the assignment of the state as arising from a Ca⁺ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.     

Co3O4@Co Nanoparticles Embedded Porous N‐Rich Carbon Matrix for Efficient Oxygen Reduction

Oxygen reduction reaction (ORR) is an important reaction in many energy conversion systems, but it is severely restricted by its slow kinetics. Developing efficient non‐noble‐metal catalysts for ORR has attracted extended interests, but still remains a great challenge. Herein, an efficient catalysts consisting of Co₃O₄@Co nanoparticles embedded in N‐rich mesoporous carbon matrix is developed by the carbonization of Co‐containing zeolitic imidazolate framework precursor. The derived matrix exhibits outstanding catalytic activity with onset potential of 0.97 V vs. RHE, half‐wave potential of 0.88 V vs. RHE, and good catalytic durability when tested with the rotation speed of 1600 rpm. Carbinization under NH₃ introduces extra elemental N, which subsequently enhances the limiting current densities. This study provides insight into the rational design of highly active ORR catalysts.     

Gate‐controlled metal–insulator transition in the LaAlO3/SrTiO3 system with sub‐critical LaAlO3 thickness

We studied the electrical conduction in the LaAlO₃/SrTiO₃ (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ～3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling the formation of local highly aluminum‐doped silicon regions by rapid thermal annealing of screen‐printed aluminum

The formation of local highly aluminum‐doped (Al‐p⁺) regions by rapid thermal annealing (firing) of screen‐printed aluminum strongly depends on the temperature profile and the contact geometry. We measure the local Al‐p⁺ layer thickness W_Al‐p+ as a function of the point and line contact size. Using quantitative yet simple analytical modeling, the time‐dependent silicon concentration in the Al melt is described by elementary differential equations. From this we calculate W_Al‐p+ and find agreement with the measurements. In contrast to the formation of full area Al‐p⁺ layers we find a smaller silicon concentration at the end of the firing process compared to the equilibrium concentration. This is a result of the process dynamics such as the dissolution rate of solid silicon and the transport of silicon in the Al melt. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

From metal/semiconductor separation to single‐chirality separation of single‐wall carbon nanotubes using gel

In the present work, a review of the metallic (M) and semiconducting (S) separation of single‐wall carbon nanotubes (SWCNTs) using polysaccharide gels is presented. First, the progress of the M/S separation is described, including the following: the discovery of high‐yield separation using agarose gel electrophoresis, the separation of SWCNTs without an electric field, such as through the use of the freeze and squeeze method, the development of continuous separation using column chromatography, and the single‐chirality separation of SWCNTs using a multicolumn with dextran‐based gel. Next, the separation mechanism using gel is discussed, in which separation is achieved by selective adsorption of S‐SWCNTs by gel with a specific combination of surfactant and gel. Lastly, future directions for the separation of SWCNTs and for the use of the separated SWCNTs are discussed.