Modulated Binary–Ternary Dual Semiconductor Heterostructures

A generic modular synthetic strategy for the fabrication of a series of binary‐ternary group II‐VI and group I‐III‐VI coupled semiconductor nano‐heterostructures is reported. Using Ag₂Se nanocrystals first as a catalyst and then as sacrificial seeds, four dual semiconductor heterostructures were designed with similar shapes: CdSe‐AgInSe₂, CdSe‐AgGaSe₂, ZnSe‐AgInSe₂, and ZnSe‐AgGaSe₂. Among these, dispersive type‐II heterostructures are further explored for photocatalytic hydrogen evolution from water and these are observed to be superior catalysts than the binary or ternary semi‐conductors. Details of the chemistry of this modular synthesis have been studied and the photophysical processes involved in catalysis are investigated.     

Design of Enhanced Catalysts by Coupling of Noble Metals (Au,Ag) with Semiconductor SnO2 for Catalytic Reduction of 4‐Nitrophenol

The reduction of 4‐nitrophenol (Nip) into 4‐aminophenol (Amp) by NaBH₄, which is catalyzed by both binary and ternary yolk–shell noble‐metal/SnO₂ heterostructures, is reported. The binary heterostructures contain individual Au or Ag nanoparticles (NPs) and the ternary heterostructures contain both Au and Ag NPs. The Au@SnO₂ yolk–shell NPs are synthesized via a silica seeds‐mediated hydrothermal method. Subsequently, the Au@SnO₂@Ag and Au@SnO₂@Au yolk–shell–shell (YSS) NPs are synthesized, whereby SnO₂ is located between the Au and Ag NPs. The morphology, composition, and optical properties of the as‐prepared samples are analyzed. For the binary heterostructures, the rate of the reduction reaction increases with decreasing particle size. The catalytic results demonstrate the synergistic effect of Au and Ag in the ternary metal–semiconductor heterostructures, which is beneficial to the catalytic reduction of Nip into Amp. Both the binary and ternary heterostructures exhibit significantly better catalytic performances than the corresponding bare Au and Ag NPs. It is envisaged that the current synthesized strategy will promote further interest in the field of bimetal NP‐based catalysis.     

Magnetically‐Confined Fe‐Mn Bimetallic Oxide Encapsulation as an Efficient and Recoverable Adsorbent for Arsenic(III) Removal

Synthesis of bimetallic‐oxide‐encapsulated magnetic nanoparticles is still significantly challenging and has rarely been attempted previously, due to the effects of lattice mismatch, weak chemical interactions and variances in growth rates between different components, as well as the difficulty in process control for uniform co‐deposition. In the present work, Fe‐Mn bimetallic oxide (FMBO) nanoplatelet encapsulated magnetic nanoparticles (Mag‐FeMn) are prepared by controlled engineering of the interparticle coupling of Fe₃O₄ and FMBO, with its multifunctional capabilities highlighted in terms of the potentially superior As(III) sequestration and convenient recoverability. Multiple characterization techniques are employed to examine the derived morphologies and to accurately resolve both compositionally and magnetically the hierarchical structure in detail. The synthesized magnetic composites retain highly porous structure with the main components of Fe₂O₃, FeOOH, Fe₃O₄, and Mn₃O₄. Mag‐FeMn exhibits a quite competitive high capacity for As(III) capture (56.1 mg g^–1), whereby As(III) oxidation coupled with synchronous sorption contributes to the improved performance. The unique heterostructure of FMBO encapsulation with an embedded magnetic core would be applicable to help with rational synthesis of other bimetallic oxide encapsulated magnetic nanoparticles, and definitely shows promise for the development of new nanotechnology enabled approaches for adsorption‐based water purification.     

Magnetic properties of (Co Pd ) superstructures on Pd(100) and Pd(111)

The magnetic properties of (Co_nPd_m)_r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic anisotropy energy. Received 3 November 1999 and Received in final form 18 January 2000     

A physical explanation for the origin of self-similar magnetoconductance fluctuations in semiconductor billiards

We report quantum-mechanical calculations which replicate the self-similar magnetoconductance fluctuations observed in recent experiments on semiconductor Sinai billiards. We interpret these fluctuations by considering the mixed stable-chaotic classical dynamics of electrons in the billiard. In particular, we show that the fluctuation patterns are dominated by individual stable orbits. The scaling characteristics of the self-similar fluctuations depend on the geometry of the associated stable orbit. We find that our analysis is insensitive to the details of the potential landscape, and is applicable to real devices with a wide range of soft-wall profiles. We show that our analysis also provides a possible explanation for the distinct series of magnetoconductance fluctuations observed in recent experiments on carbon nanotubes.     

Moiré pattern in LEED obtained by van der Waals epitaxy of lattice mismatched WS2/MoTe2(0001) heterointerfaces

Thin films of WS₂ have been grown by van der Waals epitaxy (vdWE) on the basal planes of 2H-MoTe₂(0001). Despite a lateral mismatch of 10.3%, epitaxial growth is achieved by metal organic vdWE (MOvdWE). In low energy electron diffraction (LEED) measurements a Moiré-like superstructure is observed originating from and correlated to the lateral mismatch between film and substrate. I–V LEED investigations in the course of sequential film growth reveal an undulation of the lattice at the interfaces as the origin of the Moiré-like structure rather than simple multiple scattering between overlayer and substrate.     

Two-Dimensional Conjugated Metal-Organic Framework/Graphene π–π Stacked Heterostructures for Ultrafast Photonics

2D conjugated metal-organic frameworks (MOFs) with high in-plane-π-conjugation are attracting significant attention in various fields owing to their outstanding electrical transport property, substantial specific surface areas, and tunable structures. However, their potential in ultrafast photonics has not been extensively explored. Herein, 2D conjugated Ni₃(HITP)₂ metal-organic framework (MOF) and graphene (GR) π–π stacked vertical heterostructures (NG-VHS) are synthesized using an ultrasound-assisted method. Based on theoretical simulations and characterization analyses, the results suggest that the fast interface charge transfer and the extension of the π-conjugated electron cloud will significantly enhance the electrical conductivity and the nonlinear optical properties, which is attributed to the π–π stacking interactions between Ni₃(HITP)₂ and GR. The charge transfer rate of NG-VHS is given by 6.9 × 10¹¹ s⁻¹. Noticeably, NG-VHS can serve as an excellent saturable absorber (SA) that can achieve fundamental mode-locking with a pulse width of 451 fs, harmonic mode-locking with repetition frequencies up to 1.205 GHz, and tunable dual-wavelength mode-locking. These results indicate the potential of NG-VHS as a promising nonlinear optical material for ultrafast optical applications and a new platform for the design of advanced optoelectronic devices based on 2D conjugated MOFs.     

Ultrathin,Porous and Oxygen Vacancies‐Enriched Ag/WO3−x Heterostructures for Electrocatalytic Hydrogen Evolution

Exploring advanced electrocatalysts for electrocatalytic hydrogen evolution is highly desired but remains a challenge due to the lack of an efficient preparation method and reasonable structural design. Herein, we deliberately designed novel Ag/WO_3?x heterostructures through a supercritical CO₂‐assisted exfoliation‐oxidation route and the subsequent loading of Ag nanoparticles. The ultrathin and oxygen vacancies‐enriched WO_3?x nanosheets are ideal substrates for loading Ag nanoparticles, which can largely increase the active site density and improve electron transport. Besides, the resultant WO_3?x nanosheets with porous structure can form during the electrochemical cycling process induced by an electric field. As a result, the exquisite Ag/WO_3?x heterostructures show an enhanced hydrogen evolution reaction (HER) activity with a low onset overpotential of ≈30 mV, a small Tafel slope of ≈40 mV dec^?1 at 10 mA cm^?2, and as well as long‐term durability. This work sheds light on material design and preparation, and even opens up an avenue for the development of high‐efficiency electrocatalysts.     

Magnetospectroscopy of double HgTe/CdHgTe QWs with inverted band structure in high magnetic fields up to 30 T

Magnetoabsorption in far and mid IR ranges in double HgTe/CdHgTe quantum wells with inverted band structure has been studied in high magnetic fields up to 30 T. Numerous intraband and interband transitions have been revealed in the spectra and interpreted within axial 8 × 8 k·p model. Splitting of dominant magnetoabsorption lines resulting from optical transitions from hole-like zero-mode Landau level has been discovered and discussed in terms of a built-in electric field and collective phenomena.