Light concentration and electron transfer in plasmonic-photonic Ag,Au modified Mo-BiVO inverse opal photoelectrocatalysts.

Plasmonic photocatalysis based on metal-semiconductor heterojunctions is considered a key strategy to evade the inherent limitations of poor light harvesting and charge separation of semiconductor photocatalysts. It can be profitably combined with three-dimensional photonic crystals (PCs) that offer an ideal scaffold for loading plasmonic nanoparticles and a unique architecture to intensify photon capture. In this work, Mo-doped BiVO inverse opals were applied as visible light-responsive photonic hosts of Ag and/or Au plasmonic nanoparticles in order to exploit the synergy of plasmonic and photonic amplification effects with interfacial charge transfer for the photoelectrocatalytic degradation of recalcitrant pharmaceutical contaminants under visible light.

Exploiting the Close-to-Dirac Point Shift of the Fermi Level in the SbTe/BiTe Topological Insulator Heterostructure for Spin-Charge Conversion.

Properly tuning the Fermi level position in topological insulators is of vital importance to tailor their spin-polarized electronic transport and to improve the efficiency of any functional device based on them. Here, we report the full in situ metal organic chemical vapor deposition (MOCVD) and study of a highly crystalline BiTe/SbTe topological insulator heterostructure on top of large area (4″) Si(111) substrates. The bottom SbTe layer serves as an ideal seed layer for the growth of highly crystalline BiTe on top, also inducing a remarkable shift of the Fermi level to place it very close to the Dirac point, as visualized by angle-resolved photoemission spectroscopy.

Co-assembled MoS-TiO Inverse Opal Photocatalysts for Visible Light-Activated Pharmaceutical Photodegradation.

Heterostructured photocatalytic materials in the form of photonic crystals have been attracting attention for their unique light harvesting ability that can be ideally combined with judicious compositional modifications toward the development of visible light-activated (VLA) photonic catalysts, though practical environmental applications, such as the degradation of pharmaceutical emerging contaminants, have been rarely reported. Herein, heterostructured MoS-TiO inverse opal films are introduced as highly active immobilized photocatalysts for the VLA degradation of tetracycline and ciprofloxacin broad-spectrum antibiotics as well as salicylic acid. A single-step co-assembly method was implemented for the challenging incorporation of MoS nanosheets into the nanocrystalline inverse opal walls.

Engineering Heat Transport Across Epitaxial Lattice-Mismatched van der Waals Heterointerfaces.

Artificially engineered 2D materials offer unique physical properties for thermal management, surpassing naturally occurring materials. Here, using van der Waals epitaxy, we demonstrate the ability to engineer extremely insulating thermal metamaterials based on atomically thin lattice-mismatched BiSe/MoSe superlattices and graphene/PdSe heterostructures with exceptional thermal resistances (70-202 m K/GW) and ultralow cross-plane thermal conductivities (0.012-0.

Visible Light Trapping against Charge Recombination in FeO-TiO Photonic Crystal Photocatalysts.

Tailoring metal oxide photocatalysts in the form of heterostructured photonic crystals has spurred particular interest as an advanced route to simultaneously improve harnessing of solar light and charge separation relying on the combined effect of light trapping by macroporous periodic structures and compositional materials' modifications. In this work, surface deposition of FeO nanoclusters on TiO photonic crystals is investigated to explore the interplay of slow-photon amplification, visible light absorption, and charge separation in FeO-TiO photocatalytic films. Photonic bandgap engineered TiO inverse opals deposited by the convective evaporation-induced co-assembly method were surface modified by successive chemisorption-calcination cycles using Fe(III) acetylacetonate, which allowed the controlled variation of FeO loading on the photonic films.

Anisotropic Thermal Conductivity of Crystalline Layered SnSe.

The degree of thermal anisotropy affects critically key device-relevant properties of layered two-dimensional materials. Here, we systematically study the in-plane and cross-plane thermal conductivity of crystalline SnSe films of varying thickness (16-190 nm) and uncover a thickness-independent thermal conductivity anisotropy ratio of about ∼8.4.

Ultrathin epitaxial Bi film growth on 2D HfTetemplate.

Among ultrathin monoelemental two-dimensional (2D) materials, bismuthene, the single layer of heavier group-VΑ element bismuth (Bi), has been predicted to have large non trivial gap. Here, we demonstrate the growth of Bi films by molecular beam epitaxy on 2D-HfTetemplate. At the initial stage of Bi deposition (1-2 bilayers, BL), both the pseudocubic Bi(110) and the hexagonal Bi(111) phases are formed.

Graphene Quantum Dot-TiO 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 TiO 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-TiO interfacial electron transfer.

Heterostructured CoO-TiO Mesoporous/Photonic Crystal Bilayer Films for Enhanced Visible-Light Harvesting and Photocatalysis.

Heterostructured bilayer films, consisting of co-assembled TiO photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoO 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 TiO, followed by post-calcination. Tuning the slow photon regions of the inverse opal supporting layer to the visible-light absorption of surface CoO 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.

Advanced Photocatalysts Based on Reduced Nanographene Oxide-TiO Photonic Crystal Films.

Surface functionalization of TiO inverse opals by graphene oxide nanocolloids (nanoGO) presents a promising modification for the development of advanced photocatalysts that combine slow photon-assisted light harvesting, surface area, and mass transport of macroporous photonic structures with the enhanced adsorption capability, surface reactivity, and charge separation of GO nanosheets. In this work, post-thermal reduction of nanoGO-TiO inverse opals was investigated in order to explore the role of interfacial electron transfer vs. pollutant adsorption and improve their photocatalytic activity.

Direct versus reverse vertical two-dimensional MoC/graphene heterostructures for enhanced hydrogen evolution reaction electrocatalysis.

MoC/graphene heterostructures prepared by chemical vapor deposition have demonstrated excellent electrocatalytic activity in a hydrogen evolution reaction (HER). This is attributed to the high catalytic activity of MoC while the high electrical conductivity of graphene facilitates charge transfer. In the as-grown direct vertical order, graphene is placed above the MoC film.

MoC/graphene heterostructures: low temperature chemical vapor deposition on liquid bimetallic Sn-Cu and hydrogen evolution reaction electrocatalytic properties.

Thin 2D MoC/graphene vertical heterostructures have attracted significant attention due to their potential application as electrodes in the hydrogen evolution reaction (HER) and energy storage. A common drawback in the chemical vapor deposition synthesis of these structures is the demand for high temperature growth, which should be higher than the melting temperature of the metal catalyst. The most common metallic catalyst is Cu, which has a melting temperature of 1084 °C.

Massless Dirac Fermions in ZrTe Semimetal Grown on InAs(111) by van der Waals Epitaxy.

Single and few layers of the two-dimensional (2D) semimetal ZrTe are grown by molecular beam epitaxy on InAs(111)/Si(111) substrates. Excellent rotational commensurability, van der Waals gap at the interface and moiré pattern are observed indicating good registry between the ZrTe epilayer and the substrate through weak van der Waals forces. The electronic band structure imaged by angle resolved photoelectron spectroscopy shows that valence and conduction bands cross at the Fermi level exhibiting abrupt linear dispersions.

Epitaxial 2D SnSe2/ 2D WSe2 van der Waals Heterostructures.

van der Waals heterostructures of 2D semiconductor materials can be used to realize a number of (opto)electronic devices including tunneling field effect devices (TFETs). It is shown in this work that high quality SnSe2/WSe2 vdW heterostructure can be grown by molecular beam epitaxy on AlN(0001)/Si(111) substrates using a Bi2Se3 buffer layer. A valence band offset of 0.

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.

Observation of surface Dirac cone in high-quality ultrathin epitaxial Bi2Se3 topological insulator on AlN(0001) dielectric.

Bi2Se3 topological insulators (TIs) are grown on AlN(0001)/Si(111) substrates by molecular beam epitaxy. In a one-step growth at optimum temperature of 300 °C, Bi2Se3 bonds strongly with AlN without forming interfacial reaction layers. This produces high epitaxial quality Bi2Se3 single crystals with a perfect registry with the substrate and abrupt interfaces, allowing thickness scaling down to three quintuple layers (QL) without jeopardizing film quality.