Shenghao Han

Graphene/g-C3N4 bilayer: considerable band gap opening and effective band structure engineering

The layered graphene/g-C3N4 composites show high conductivity, electrocatalytic performance and visible light response and have potential applications in microelectronic devices and photocatalytic technology. In the present work, the stacking patterns and the correlations between electronic structures and related properties of graphene/g-C3N4 bilayers are investigated systematically by means of first-principles calculations. Our results indicate that the band gap of graphene/g-C3N4 bilayers can be up to 108.5 meV, which is large enough for the gap opening at room temperature. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to g-C3N4. Interestingly, the investigation also shows that external electric field can tune the band gap of graphene/g-C3N4 bilayers effectively. Our research demonstrates that graphene on g-C3N4 with a tunable band gap and high carrier mobility may provide a novel way for fabricating high-performance graphene-based nanodevices.

Bias voltage dependence of properties for depositing transparent conducting ITO films on flexible substrate

Abstract Good transparent conducting indium tin oxide films with good adherence were deposited on water-cooled polypropylene adipate substrate using bias r.f. magnetron sputtering. The films with resistivity as low as 6.3×10 −4 Ω cm and transmittance over 80% have been obtained by adjusting the bias voltage. It was observed that the structural, electrical and optical properties of the films depend on the bias voltage applied to substrate table.

Structure and Electronic Properties and Phase Stabilities of the Cd1−xZnxS Solid Solution in the Range of 0≤x≤1

As an excellent bandgap-engineering material, the Cd(1-x)Zn(x)S solid solution, is found to be an efficient visible light response photocatalyst for water splitting, but few theoretical studies have been performed on it. A better characterization of the composition dependence of the physical and optical properties of this material and a thorough understanding of the bandgap-variation mechanism are necessary to optimize the design of high-efficience photocatalysts. In order to get an insight into these problems, we systematically investigated the crystal structure, the phase stability, and the electronic structures of the Cd(1-x)Zn(x)S solid solution by means of density functional theory calculations. The most energetically favorable arrangement of the Cd, Zn, S atoms and the structural disorder of the solid solution are revealed. The phase diagram of the Cd(1-x)Zn(x)S solid solution is calculated based on regular-solution model and compared with the experimental data. This is the first report on the calculated phase diagram of this solid solution, and can give guidance for the experimental synthesis of this material. Furthermore, the variation of the electronic structures versus x and its mechanism are elaborated in detail, and the experimental bandgap as a function of x is well predicted. Our findings provide important insights into the experimentally observed structural and electronic properties, and can give theoretical guidelines for the further design of the Cd(1-x)Zn(x)S solid solution.

Phase-sensitive Bloch surface wave sensor based on variable angle spectroscopic ellipsometry

In this paper, we propose a phase-sensitive Bloch surface wave sensor based on the variable angle spectroscopic ellipsometry and numerically simulate the phase behavior of the sensor. The simulation results show that the dependence of resonant phase is step-like when BSWs are excited. In contrast to the reflectance behavior, even though losses of the dielectric layers are very small, the resonance dip in the reflectivity will be shallow while the step-like change of the reflection phase of the BSW still be remarkable. This means that phase detection is an alternative to reflectivity intensity detection for the sensing applications of the BSWs in this case. Our experimental results indicate that phase detection for the BSW sensors has the potential to achieve the higher sensitivity and the lower limit of detection.

Phase properties of Bloch surface waves and their sensing applications

We study the phase properties of Bloch surface waves (BSWs) on truncated one-dimensional photonic crystals and find an abrupt change of the phase induced by BSWs. The phase of the BSW device shows a prominent response to the refractive index changes of the environment under resonance conditions. Furthermore, we demonstrate that the phase sensitivity of the BSW device is higher by nearly 1 order of magnitude than its amplitude sensitivity in terms of the figure of merit. This means that phase detection can be utilized to enhance the sensitivity of the BSW devices.

Magnetism in Co-doped tris-8-hydroxyquinoline aluminum studied by first-principles calculations

The electronic and magnetic properties of Co-doped tris-8-hydroxyquinoline aluminum (Alq3) are studied by first-principles calculations. Our results indicate that the local magnetic moments in doped Alq3 originate from the localized d states of Co atom. Electron transfer takes place from Co atom to Alq3 molecule, which is mainly localized on the quinolate ligand, resulting in formation of bound magnetic polarons. The indirect ferromagnetic exchange interaction between two bound magnetic polarons antialigning with the same magnetic ion promotes the collective magnetism found in recent experiments.

Structure of Co-Doped Alq3 Thin Films Investigated by Grazing Incidence X-ray Absorption Fine Structure and Fourier Transform Infrared Spectroscopy

The structural properties of Co-doped tris(8-hydroxyquinoline)aluminum (Alq(3)) have been studied by grazing incidence X-ray absorption fine structure (GIXAFS) and Fourier transform infrared spectroscopy (FTIR). GIXAFS analysis suggests that there are multivalent Co-Alq(3) complexes and the doped Co atoms tend to locate at the attraction center with respect to N and O atoms and bond with them. The FTIR spectra indicate that the Co atoms interact with the meridional (mer) isomer of Alq(3) rather than forming inorganic compounds.

Electronic structure of polyacetylene and poly(p-phenylene) diblock copolymers

The electronic structure of diblock copolymers consisting of poly(p-phenylene) and polyacetylene were studied in the framework of an inter-component coupling model. It was found that the band gaps could be tuned by the proportion of the homopolymers. The interfacial coupling between the components also affected the band gaps obviously. Localized states and hybridized states appeared in copolymers due to the interactions between the homopolymers. The doped charges accumulated in its one segment of a copolymer. The accumulation condition is discussed.

Structures and photoluminescence properties of Alq3 1D materials prepared by an extremely facile solution method

Ultra-long crystalline Alq3 1 dimensional (1D) materials were prepared by using an extremely facile solution approach without any surfactant, SDS, anti-solvent, or other reagents. The Alq3 1D materials have smooth surfaces and pentagonal or hexagonal cross-sections. The length of the microrods have α-phase crystalline structures. The prepared Alq3 samples exhibit excellent green-light photoluminescence (PL) performance. The growth mechanism of the Alq3 1D structures were discussed. The limitation conditions of the Alq3 microrods were also studied. In addition, the influence of the volume of CHCl3 on the microrods was discussed. This controllable growth method can potentially be extended to other functional organic nanomaterials.

Realization of tunable Dirac cone and insulating bulk states in topological insulators (Bi1-xSbx)2Te3

The bulk-insulating topological insulators with tunable surface states are necessary for applications in spintronics and quantum computation. Here we present theoretical evidence for modulating the topological surface states and achieving the insulating bulk states in solid-solution (Bi1−xSbx)2Te3. Our results reveal that the band inversion occurs in (Bi1−xSbx)2Te3, indicating the non-triviality across the entire composition range, and the Dirac point moves upwards till it lies within the bulk energy gap accompanying the increase of Sb concentration x. In addition, with increasing x, the formation of prominent native defects becomes much more difficult, resulting in the truly insulating bulk. The solid-solution system is a promising way of tuning the properties of topological insulators and designing novel topologically insulating devices.