Quantum reflection pole method for determination of quasibound states in semiconductor heterostructures

The quantum reflection pole method (QRPM) is introduced for determining quasibound state eigenenergies and their lifetimes in symmetric, asymmetric, biased, and unbiased quantum heterostructures. In the QRPM the single-band effective-mass Schrödinger equation is solved without using complex arithmetic. Calculations are much simpler to perform than with previous methods. Further, results are found to be in excellent agreement with other rigorous techniques.     

Current distribution in the integer quantum Hall effect: The role of bulk states

The role of bulk and edge currents in a two-dimensional electron gas under the conditions of the integer quantum Hall effect (IQHE) was studied by means of an inductive coupling to Hall bar geometry. From this study we conclude that the extended states at the bulk of the sample below the Fermi energy are capable of carrying a substantial amount of Hall current. For Hall bar geometry sample with a back gate we demonstrated that injected current can be pushed from one edge to another by reversing the direction of the external magnetic field.     

Fourier-inversion and wavelet-transform methods applied to X-ray reflectometry and HRXRD profiles from complex thin-layered heterostructures

We show that X-ray scattering techniques can be used for the assessment of individual layer thicknesses inside complicated semi-conductor heterostructures dedicated to the opto-electronic domain. To this end, we propose methods to overcome two main drawbacks coming from: (1) the complexity of the X-ray profiles and, hence the difficulty to use model-dependent tools such as fitting procedures and (2) large dynamics in intensity due to numerous high diffraction superlattice peaks from superlattices which limit the use of the model-independent Fourier-inversion method.We demonstrate first the reliability of the Fourier-inversion method applied to high-resolution X-ray diffraction profiles curve from quantum well infrared photodetectors heterostructures, complementary to the model-dependent fitting tools. Then, a wavelet-transform-based procedure has been successfully used on X-ray reflectometry profiles containing intense SL Bragg peaks.     

Low frequency and weakly nonlinear spin transport in ferromagnet/insulator single and double junctions

In this paper, we apply Büttiker's gauge invariant, charge conservation, nonlinear transport theory to explore the spin-polarized tunneling of ferromagnet/insulator (semiconductor) single and double junctions. The Green function of spin-polarized tunneling is calculated by the tight-binding approximation method. The energy and the angle (between the molecular field and the vertical axis) dependences of the weakly nonlinear dc transport coefficient and the linear low frequency ac transport coefficient are investigated. The ac tunneling magnetoresistance is also discussed. Received 1st September 2000 and Received in final form 5 December 2000     

InGaAsP/InP Heterostructure Doped by Cobalt

The preparation of a new type of InGaAsP/InP heterostructures for light emitting diodes is presented. The active region of the heterostructure contains thin layers of nondoped InGaAsP (λ=1.3μ) alternating with barrier layers of InGaAsP (λ=1.1μ) doped by cobalt. Properties of prepared heterostructures were tested on edge emitting diodes with the stripe geometry. Curves of the minority carrier lifetime and the optical power versus current are compared with those obtained on classical bulk InGaAsP/InP double heterostructure. It is shown that the new structure is very eligible for construction of high‐ speed noncoherent 1.3μ diodes operating at low pumping current.     

Formation of Hierarchical FeCoS2–CoS2 Double‐Shelled Nanotubes with Enhanced Performance for Photocatalytic Reduction of CO2

Hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes have been rationally designed and constructed for efficient photocatalytic CO₂ reduction under visible light. The synthetic strategy, engaging the two‐step cation‐exchange reactions, precisely integrates two metal sulfides into a double‐shelled tubular heterostructure with both of the shells assembled from ultrathin two‐dimensional (2D) nanosheets. Benefiting from the distinctive structure and composition, the FeCoS₂–CoS₂ hybrid can reduce bulk‐to‐surface diffusion length of photoexcited charge carriers to facilitate their separation. Furthermore, this hybrid structure can expose abundant active sites for enhancing CO₂ adsorption and surface‐dependent redox reactions, and harvest incident solar irradiation more efficiently by light scattering in the complex interior. As a result, these hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO₂ reduction, affording a high CO‐generating rate of 28.1 μmol h^?1 (per 0.5 mg of catalyst).     

Two Step Chemical Vapor Deposition of In2Se3/MoSe2 van der Waals Heterostructures

Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide interest not only for the fundamental research,but also for the application of next generation electronic and optoelectronic devices.Herein,we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In₂Se₃/MoSe₂ heterostructures.Transmission electron microscopy characterization reveals clearly that the In₂Se₃ has well-aligned lattice orientation with the substrate of monolayer MoSe₂.Due to the interaction between the In₂Se₃ and MoSe₂ layers,the heterostructure shows the quenching and red-shift of photoluminescence.Moreover,the current rectification behavior and photovoltaic effect can be observed from the heterostructure,which is attributed to the unique band structure alignment of the heterostructure,and is further confirmed by Kevin probe force microscopy measurement.The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.     

The transverse ferromagnet spin-1 Ising model of alternating magnetic superlattice

Within the framework of the effective field theory with a probability distribution technique that accounts for the single-site spin correlations, we examine the critical behavior of the transverse ferromagnetic spin-1 Ising model of an alternating magnetic superlattice. The critical temperature of the alternating magnetic superlattice has been studied as a function of the interlayer and intralayer exchange interactions and the strength of the transverse field and the thickness of the finite superlattice. Received 12 January 2000 and Received in final form 14 September 2000     

Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane

A Nb-containing siliceous porous clay heterostructure (PCH) with Nb contents from 0 to 30 wt %) was prepared from a bentonite and used as support in the preparation of supported NiO catalysts with NiO loading from 15 to 80 wt %. Supports and NiO-containing catalysts were characterised by several physicochemical techniques and tested in the oxidative dehydrogenation (ODH) of ethane. The characterisation studies on Nb-containing supports showed the presence of well-anchored Nb⁵⁺ species without the formation of Nb₂O₅ crystals. High dispersion of nickel oxide with low crystallinity was observed for the Nb-containing PCH supports. In addition, when NiO is supported on these Nb-containing porous clays, it is more effective in the ODH of ethane (ethylene selectivity of ca. 90 %) than NiO supported on the corresponding Nb-free siliceous PCH or on Nb₂O₅ (ethylene selectivities of ca. 30 and 60 %, respectively). Factors such as the NiO–Nb⁵⁺ interaction, the NiO particle size and the properties of surface Niⁿ⁺ species were shown to determine the catalytic performance.