Jiaou Wang

Epitaxial Growth and Air-Stability of Monolayer Antimonene on PdTe2

Monolayer antimonene is fabricated on PdTe2 by an epitaxial method. Monolayer antimonene is theoretically predicted to have a large bandgap for nanoelectronic devices. Air-exposure experiments indicate amazing chemical stability, which is great for device fabrication. A method to fabricate high-quality monolayer antimonene with several great properties for novel electronic and optoelectronic applications is provided.

Thin-Layer Fe2TiO5 on Hematite for Efficient Solar Water Oxidation

A thin Fe2TiO5 layer was produced on hematite either by evaporating a TiCl4 solution on FeOOH or by a simple HF-assisted Ti treatment of FeOOH, both followed by annealing. The prepared Fe2TiO5-hematite heterostructure showed a significant enhancement in photocurrent density compared to that of the pristine hematite. For example, the sample after HF-assisted Ti treatment exhibited a significantly enhanced photocurrent of 2.0 mA/cm(2) at 1.23 V vs RHE. Moreover, the performance of the Fe2TiO5-hematite heterostructure can be further improved by coupling with Co-Pi catalysts, achieving a higher photocurrent of 2.6 mA/cm(2) at 1.23 V vs RHE. Synchrotron-based soft X-ray absorption spectroscopy analyses clearly revealed the existence of an Fe2TiO5 structure on hematite forming a heterojunction, which reduced the photogenerated hole accumulation and then improved the performance.

A dye-sensitized visible light photocatalyst-Bi24O31Cl10

The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%.

Quasi-freestanding epitaxial silicene on Ag(111) by oxygen intercalation

Quasi-freestanding silicene with massless Dirac fermion characteristics has been successfully obtained by oxygen intercalation. Silicene is a monolayer allotrope of silicon atoms arranged in a honeycomb structure with massless Dirac fermion characteristics similar to graphene. It merits development of silicon-based multifunctional nanoelectronic and spintronic devices operated at room temperature because of strong spin-orbit coupling. Nevertheless, until now, silicene could only be epitaxially grown on conductive substrates. The strong silicene-substrate interaction may depress its superior electronic properties. We report a quasi-freestanding silicene layer that has been successfully obtained through oxidization of bilayer silicene on the Ag(111) surface. The oxygen atoms intercalate into the underlayer of silicene, resulting in isolation of the top layer of silicene from the substrate. In consequence, the top layer of silicene exhibits the signature of a 1 × 1 honeycomb lattice and hosts massless Dirac fermions because of much less interaction with the substrate. Furthermore, the oxidized silicon buffer layer is expected to serve as an ideal dielectric layer for electric gating in electronic devices. These findings are relevant for the future design and application of silicene-based nanoelectronic and spintronic devices.

Electronic structure of antimonene grown on Sb2Te3 (111) and Bi2Te3 substrates

We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi2Te3 and Sb2Te3 substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi2Te3 are flatter than on Sb2Te3, which attributes to Bi2Te3 substrate lattice constants lager than Sb2Te3. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

Effects of Oxygen Adsorption on the Surface State of Epitaxial Silicene on Ag(111)

Epitaxial silicene, which is one single layer of silicon atoms packed in a honeycomb structure, demonstrates a strong interaction with the substrate that dramatically affects its electronic structure. The role of electronic coupling in the chemical reactivity between the silicene and the substrate is still unclear so far, which is of great importance for functionalization of silicene layers. Here, we report the reconstructions and hybridized electronic structures of epitaxial 4 × 4 silicene on Ag(111), which are revealed by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. The hybridization between Si and Ag results in a metallic surface state, which can gradually decay due to oxygen adsorption. X-ray photoemission spectroscopy confirms the decoupling of Si-Ag bonds after oxygen treatment as well as the relatively oxygen resistance of Ag(111) surface, in contrast to 4 × 4 silicene [with respect to Ag(111)]. First-principles calculations have confirmed the evolution of the electronic structure of silicene during oxidation. It has been verified experimentally and theoretically that the high chemical activity of 4 × 4 silicene is attributable to the Si pz state, while the Ag(111) substrate exhibits relatively inert chemical behavior.

Electronic structure of BiFe 1-x Mn x O 3 thin films investigated by X-ray absorption spectroscopy

Multiferroic polycrystalline BiFe1-xMnxO3 (0 ≤ x ≤ 0.3) thin films have been prepared on the Pt(111)/Ti/SiO2/Si(100) substrates by pulsed laser deposition method. The influence of Mn substitution on the electronic structure and magnetic properties has been studied. X-ray diffraction spectroscopy shows that Mn substitution slightly modulates crystal structure of the BiFe1-xMnxO3 system within the same structural phase. According to Fe L edge X ray absorption spectroscopy, Fe ions are found to be formally trivalent for doping amount x in BiFe1-xMnxO3. The enhanced magnetization by increasing Mn content is attributed to an alternation degree of hybridization between Fe 3d-O 2p and Mn 3d-O 2p orbitals, basing on the carefully examined Fe L and O K edge X-ray absorption spectroscopy. The crystal structural and the electronic structural results show a causal relation between them by demonstrating intrinsic mutual dependence between respective variations.

In vitro model on glass surfaces for complex interactions between different types of cells.

This report establishes an in vitro model on glass surfaces for patterning multiple types of cells to simulate cell-cell interactions in vivo. The model employs a microfluidic system and poly(ethylene glycol)-terminated oxysilane (PEG-oxysilane) to modify glass surfaces in order to resist cell adhesion. The system allows the selective confinement of different types of cells to realize complete confinement, partial confinement, and no confinement of three types of cells on glass surfaces. The model was applied to study intercellular interactions among human umbilical vein endothelial cells (HUVEC), PLA 801 C and PLA801 D cells.

Hydrogen Impurity Defects in Rutile TiO2

Hydrogen-related defects play crucial roles in determining physical properties of their host oxides. In this work, we report our systematic experimental and theoretical (based on density functional theory) studies of the defect states formed in hydrogenated-rutile TiO2 in gaseous H2 and atomic H. In gas-hydrogenated TiO2, the incorporated hydrogen tends to occupy the oxygen vacancy site and negatively charged. The incorporated hydrogen takes the interstitial position in atom-hydrogenated TiO2, forming a weak O-H bond with the closest oxygen ion, and becomes positive. Both states of hydrogen affect the electronic structure of TiO2 mainly through changes of Ti 3d and O 2p states instead of the direct contributions of hydrogen. The resulted electronic structures of the hydrogenated TiO2 are manifested in modifications of the electrical and optical properties that will be useful for the design of new materials capable for green energy economy.

Band gap engineering of TiO2 through hydrogenation

The band gap of rutile TiO2 is reduced remarkably through high-temperature annealing in hydrogen atmosphere, and the absorption of visible light of the hydrogenated-TiO2 can be enhanced. These modifications of hydrogenated-TiO2 become more evident with the increase in annealing hydrogen pressure. A defect band arises near the valence band upon hydrogenation while the conduction band remains almost unchanged, which helps for meeting the requirements for hydrogen production through water splitting. This method could be also indicative for the band gap adjustment of other oxide semiconductors.