Epitaxial 2D MoSe₂ (HfSe₂) Semiconductor/2D TaSe₂ Metal van der Waals Heterostructures

Molecular beam epitaxy of 2D metal TaSe₂/2D MoSe₂ (HfSe₂) semiconductor heterostructures on epi-AlN(0001)/Si(111) substrates is reported. Electron diffraction reveals an in-plane orientation indicative of van der Waals epitaxy, whereas electronic band imaging supported by first-principles calculations and X-ray photoelectron spectroscopy indicate the presence of a dominant trigonal prismatic 2H-TaSe₂ phase and a minor contribution from octahedrally coordinated TaSe₂, which is present in TaSe₂/AlN and TaSe₂/HfSe₂/AlN but notably absent in the TaSe₂/MoSe₂/AlN, indicating superior structural quality of TaSe₂ grown on MoSe₂. Apart from its structural and chemical compatibility with the selenide semiconductors, TaSe₂ has a workfunction of 5.5 eV as measured by ultraviolet photoelectron spectroscopy, which matches very well with the semiconductor workfunctions, implying that epi-TaSe₂ can be used for low-resistivity contacts to MoSe₂ and HfSe₂

Compositional effect of Cr contamination susceptibility of La9.83Si6−x−yAlxFeyO26±δ apatite-type SOFC electrolytes in contact with CROFER 22 APU

Apatite-type lanthanum silicates (ATLS) are attracting great interest as a new class of solid electrolytes possessing high oxide-ion conductivity at relatively low temperatures for solid oxide fuel cells (SOFC). In this study, doped ATLS of the composition La9.83Si6−x−yAlxFeyO26±δ (x: 0, 0.25, 0.75, 1.5 and/or y: 0, 0.25, 0.75, 1.5) were successfully prepared by solid state chemistry. They were brought into direct contact with CROFER-22 interconnector alloy in order to study Cr migration into the electrolyte. Due to inconclusive SEM-EDX results, a depth profile was acquired by Laser Induced Breakdown Spectroscopy (LIBS) and the results showed that the increase of Fe concentration in the apatite oxide's composition enhanced Cr uptake. At the same time, lower conductivity values were measured for the materials after Cr contamination i.e. in Fe containing ATLS. No significant change in conductivity was found for Fe-free ATLS sample

Aqueous dispersions of C-60 fullerene by use of amphiphilic block copolymers: Preparation and nonlinear optical properties

Journal URL: http://pubs.acs.org/journals/jpcbfk/index.htm

Type-III Dirac fermions in HfxZr1-xTe2topological semimetal candidate

Topological semimetals host interesting new types of low-energy quasiparticles such as type-I and type-II Dirac and Weyl fermions. Type-III topological semimetals can emerge exactly at the border between type-I and II, characterized by a line-like Fermi surface and a flat energy dispersion near the topological band crossing. Here, we theoretically predict that 1T-HfTe2 and 1T-ZrTe2 transition metal dichalcogenides are type-I and type-II DSMs, respectively. By alloying the two materials, a new HfxZr1-xTe2 alloy with type-III Dirac cone emerges at x = 0.2, in combination with 1% in-plane compressive strain. By imaging the electronic energy bands with in situ angle-resolved photoemission spectroscopy of this random alloy with the desired composition, grown by molecular beam epitaxy on InAs(111) substrates, we provide experimental evidence that the tοp of type-III Dirac cone lies at - or very close to - the Fermi level. © 2021 Author(s)

Heterostructured coox–tio2 mesoporous/photonic crystal bilayer films for enhanced visible-light harvesting and photocatalysis

Heterostructured bilayer films, consisting of co-assembled TiO2 photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoOx nanoclusters, are demonstrated as highly efficient visible-light photocatalysts. Broadband visible-light activation of the bilayer films was implemented by the surface modification of both titania layers with nanoscale clusters of Co oxides relying on the chemisorption of Co acetylacetonate complexes on TiO2, followed by post-calcination. Tuning the slow photon regions of the inverse opal supporting layer to the visible-light absorption of surface CoOx oxides resulted in significant amplification of salicylic-acid photodegradation under visible and ultraviolet (UV)–visible light (Vis), outperforming benchmark P25 films of higher titania loading. This enhancement was related to the spatially separated contributions of slow photon propagation in the inverse opal support layer assisted by Bragg reflection toward the CoOx-modified mesoporous P25 top layer. This effect indicates that photonic crystals may be highly effective as both photocatalytically active and backscattering layers in multilayer photocatalytic films. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Epitaxial ZrSe2/MoSe2 semiconductor v.d. Waals heterostructures on wide band gap AlN substrates

Using molecular beam epitaxy (MBE) of ZrSe2 and ZrSe2/MoSe2 heterostructures are grown on crystalline AlN(0 0 0 1)/Si(1 1 1) substrates. Electron diffraction (RHEED) and valence band imaging by angle resolved photoelectron spectroscopy (ARPES) indicate high quality heteroepitaxial growth with very good in-plane crystallographic alignment with the substrate. The workfunction and band offsets are estimated by photoelectron spectroscopy and compared with first principles calculations. The constructed band alignments show that the heterostructure could form the basis for atomically thin p-n junction and 2D vertical tunneling devices. (C) 2015 Elsevier B.V. All rights reserved

Graphene quantum Dot-TiO2 photonic crystal films for photocatalytic applications

Photonic crystal structuring has emerged as an advanced method to enhance solar light harvesting by metal oxide photocatalysts along with rational compositional modifications of the materials’ properties. In this work, surface functionalization of TiO2 photonic crystals by blue luminescent graphene quantum dots (GQDs), n–π* band at ca. 350 nm, is demonstrated as a facile, environmental benign method to promote photocatalytic activity by the combination of slow photon-assisted light trapping with GQD-TiO2 interfacial electron transfer. TiO2 inverse opal films fabricated by the co-assembly of polymer colloidal spheres with a hydrolyzed titania precursor were post-modified by impregnation in aqueous GQDs suspension without any structural distortion. Photonic band gap engineering by varying the inverse opal macropore size resulted in selective performance enhancement for both salicylic acid photocatalytic degradation and photocurrent generation under UV–VIS and visible light, when red-edge slow photons overlapped with the composite’s absorption edge, whereas stop band reflection was attenuated by the strong UVA absorbance of the GQD-TiO2 photonic films. Photoelectrochemical and photoluminescence measurements indicated that the observed improvement, which surpassed similarly modified benchmark mesoporous P25 TiO2 films, was further assisted by GQDs electron acceptor action and visible light activation to a lesser extent, leading to highly efficient photocatalytic films. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Epitaxial 2D MoSe2 (HfSe2) Semiconductor/2D TaSe2 Metal van der Waals Heterostructures

Molecular beam epitaxy of 2D metal TaSe2/2D MoSe2 (HfSe2) semiconductor heterostructures on epi-AlN(0001)/Si(111) substrates is reported. Electron diffraction reveals an in-plane orientation indicative of van der Waals epitaxy, whereas electronic band imaging supported by first-principles calculations and X-ray photoelectron spectroscopy indicate the presence of a dominant trigonal prismatic 2H-TaSe2 phase and a minor contribution from octahedrally coordinated TaSe2, which is present in TaSe2/AlN and TaSe2/HfSe2/AlN but notably absent in the TaSe2/MoSe2/AlN, indicating superior structural quality of TaSe2 grown on MoSe2. Apart from its structural and chemical compatibility with the selenide semiconductors, TaSe2 has a workfunction of 5.5 eV as measured by ultraviolet photoelectron spectroscopy, which matches very well with the semiconductor workfunctions, implying that epi-TaSe2 can be used for low-resistivity contacts to MoSe2 and HfSe2. © 2016 American Chemical Society

Nonlinear optical properties of ferrocene- and porphyrin-[60]fullerene dyads

A series of novel [60]fullerene-ferrocene and [60]fullerene-porphyrin dyads, in which a fullerene and an electron donating moiety are attached through a flexible triethylene glycol linker are synthesized and their nonlinear optical (NLO) response studied. Specifically the third-order susceptibility chi((3)) of all fullerene derivatives are measured in toluene solutions by the optical Kerr effect (OKE) technique using 532 nm, 35 ps laser pulses and their second hyperpolarizability gamma are determined. All fullerene dyads studied exhibit enhancement of their NLO response compared to pristine fullerenes which has been attributed to the formation of a charge separated state. All experimentally measured hyperpolarizability gamma values are also calculated by the semiempirical methods AM1 and PM3. A good correlation is found between the theoretical and experimental values, suggesting that simple semi-empirical methods can be employed for the designing and optimization of the fullerene-containing dyads displaying improved nonlinear responses