Applications of variable angle spectroscopic ellipsometry to strained SiGe alloy heterostructures

Variable angle spectroscopic ellipsometry (VASE) has been used to characterize several Si_xGe_1−x/Ge heterostructures. First, Si_xGe_1−x/Ge superlattice (SL) structures were characterized in terms of the layer thicknesses, composition, x, of the Si_xGe_{1− x} layer, and oxide thickness. High-resolution X-ray diffraction results are also presented for the Si_xGe_1−x/Ge SL structures and are shown to be in close agreement with the VASE results once strain effects are taken into account. VASE has also been used to study thick, Ge-rich Si_xGe_1−x/Ge heterostructures that have been grown on Si substrates. A stepped buffer has been deposited first in order to minimize the strain in the Si_xGe_1−x/Ge layers. VASE can be used to give a qualitative determination of the residual strain along with the thickness of all layers within the optical penetration depth from the surface.     

Electronic band structure and electron transfer properties of two-dimensional metal oxide nanosheets and nanosheet films

The electronic properties of 2-dimensional metal oxide nanosheets are reviewed. Although the band structures of 2D nanosheets bear some resemblance with the band structures of the 3D parent compounds from they are derived, their 2D nature may have a profound influence on the location of the valence and conduction bands. The presence of structural defects, aliovalent dopants, and adsorbed molecules affects the mobility and concentration of charge carriers, and may even influence the band structure. The ability to transfer electrons to and from nanosheets is controlled by the charge density of the nanosheet, and/or the presence of electron donating or accepting species in the immediate vicinity. Charge transport and electron transfer in multilayer films and heterostructures are also discussed.     

Synthesis and tailored properties of covalent organic framework thin films and heterostructures

Porous polymeric covalent organic frameworks (COFs) have been under intense synthetic investigation with over 100 unique structural motifs known. In order to realize the true potential of these materials, converting the powders into thin films with strict control of thickness and morphology is necessary and accomplished through techniques including interfacial synthesis, chemical exfoliation and mechanical delamination. Recent progress in the construction and tailored properties of thin film COFs are highlighted in this review, addressing mechanical properties as well as application-focused properties in filtration, electronics, sensors, electrochemistry, magnetics, optoelectronics and beyond. Additionally, heterogeneous integration of these thin films with other inorganic and organic materials is discussed, revealing exciting opportunities to integrate COF thin films with other state of the art material and device systems.     

A cost-effective approach to synthesize NiFe2O4/MXene heterostructures for enhanced photodegradation performance and anti-bacterial activity

A cost-effective ultrasonication approach was employed to synthesize NiFe₂O₄/MXene heterostructures. The as-synthesized heterostructures demonstrated outstanding photodegradation performance and anti-bacterial activity as compared to individual NiFe₂O₄ (NiFe) or MXene. The NiFe nanoparticles (NPs) helped in effectively preventing the re-stacking of MXene flakes and in increasing the surface area of the heterostructure. The obtained sheet-sheet linkage provided an admirable opportunity for excellent wastewater treatment and antibacterial activity. The photocatalytic degradation of organic pollutants by the introduced photocatalyst NiFe/MXene heterostructures has been observed to be about 4 and 6.72 times boosted compared to MXene and NiFe, respectively. Furthermore, the heterostructure materials demonstrated outstanding anti-bacterial activity against gram negative E-coli bacteria, while the mechanism of methylene blue dye degradation by NiFe/MXene was clarified through kinetic studies of the degradation process. We hope this work will be considered a significant scientific contribution for young researchers dealing with water desalination.     

Fabrication,characterization and electrochemistry of organic–inorganic multilayer films containing polyoxometalate and polyviologen via layer-by-layer self-assembly

The novel organic–inorganic multilayer films containing poly(butanyl viologen) (abbreviated as PBV) and phosphomolybdic acid (H₃PMo₁₂O₄₀, abbreviated as PMo₁₂) have been fabricated on quartz slides, silicon wafers and glassy carbon electrode by the layer-by-layer self-assembly technique. The highly ordered multilayer films were characterized by the UV–visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), Atomic force microscopy (AFM) and cyclic voltammetry. UV–visible spectra revealed that the growth of the films for each deposition cycle was reproducible. FT-IR and XPS spectra confirmed the incorporation of PBV and PMo₁₂ into the multilayer films. XRR revealed the film thickness at nanoscale, and AFM showed film surface with uniform and smooth morphology. In addition, the electrochemical behavior of the multilayer films at room temperature was investigated. As a result, the films presented good electrocatalytic activity toward ₃BrO⁻${{\text{BrO}}_3}^{-}$, H₂O₂ and ₂NO⁻${{\text{NO}}_2}^{-}$, providing valuable information for exploring the potential applications in ₃BrO⁻${{\text{BrO}}_3}^{-}$ sensors.     

Partial conversion reaction of ZnO nanowires to ZnSe by a simple selenization method and their photocatalytic activities

A simple novel synthetic method for preparing ZnSe/ZnO heterostructured nanowire (NW) arrays via the selenization of ZnO NWs is reported. A hydrothermally grown ZnO NWs array on a glass substrate was reacted with selenium vapor to generate a 20–30 nm of zincblend ZnSe nanoparticles (NPs) on wurtzite ZnO NWs. A growth mechanism was proposed based on SEM, XRD, and TEM analysis to explain the partial chemical conversion of ZnO NW surfaces into ZnSe NPs. This mechanism is applicable to the synthesis of other chalcogenide compounds. The as-synthesized ZnSe/ZnO heterojunctions showed enhanced UV–visible light absorption properties. The materials exhibited excellent photocatalytic activity toward the decomposition of an organic dye compared to the bare ZnO due to enhanced light absorption and the type-II cascade band structure.     

MBE—Technology for nanoelectronics

Molecular beam epitaxy (MBE) is presented as a powerful and flexible technology for research and development (R&D) as well as for mass production of nanoelectronic structures, based on a huge variety of materials. Its historical background, basic properties, advantages—in particular the production potential—as well as some trends in the field are shown.     

C-V characterization of SF6 plasma treated AlGaN/GaN heterostructures

We studied influence of SF₆ plasma treatment on electrical parameters of AlGaN/GaN heterostructures by C-V, I-V and SIMS measurement. We found the C-V measurements as an effective tool that is able to help to analyze electrical manifestations of charge changes in heterostructures during the semiconductor processing. In contrary to previously published results we found out that for diminishing of the two-dimensional electron gas concentration in the channel layer positively charged ions implanted during the plasma treatment into the semiconductor and not F⁻ ions are responsible.