This thesis concerns the discovery of superconductivity in the intercalated graphite compounds C6Yb and C6Ca. A novel technique for synthesis of these intercalates has been developed, and is presented in detail. These two materials are shown to superconduct at 6.5K and 11.5K respectively. The superconductivity is demonstrated by measurements of the magnetisation and resistivity. Initial measurements of the superconducting transition of these materials as a function of pressure shows an increase in the transition with increasing pressure.

Superconductivity in the intercalated graphite compounds C6Yb and C6Ca

Outstanding strength, optical characteristics and thermal conductivity of graphene-like BC3 and BC6N semiconductors

Hybrid porous magnetic bentonite-chitosan beads for selective removal of radioactive cesium in water.

Graphene has exhibited a wealth of fascinating properties, but is also known not to be a superconductor. Remarkably, we show that graphene can be made a conventional Bardeen-Cooper-Schrieffer superconductor by the combined effect of charge doping and tensile strain. While the effect of doping obviously enlarges the Fermi surface, the effect of strain profoundly increases the electron-phonon coupling. At the experimental accessible doping (~4×10(14) cm(-2)) and strain (~16%) levels, the superconducting critical temperature T(c) is estimated to be as high as ~30 K, the highest for a single-element material above the liquid hydrogen temperature.

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First-Principles Calculations on the Effect of Doping and Biaxial Tensile Strain on Electron-Phonon Coupling in Graphene

Porous silicon has found wide applications in many different fields including catalysis and lithium-ion batteries. Three-dimensional hierarchical macro-/mesoporous silicon is synthesized from zero-dimensional Stober silica particles through a facile and scalable magnesiothermic reduction process. By systematic structure characterization of the macro-/mesoporous silicon, a self-templating mechanism governing the formation of the porous silicon is proposed. Applications as lithium-ion battery anode and photocatalytic hydrogen evolution catalyst are demonstrated. It is found that the macro-/mesoporous silicon shows significantly improved cyclic and rate performance over the commercial nanosized and micrometer-sized silicon particles. After 300 cycles at 0.2 A g–1, the reversible specific capacity is still retained as much as 959 mAh g–1 with a high mass loading density of 1.4 mg cm–2. With the large current density of 2 A g–1, a reversible capacity of 632 mAh g–1 is exhibited. The coexistence of both macro- ...

Self-Templating Construction of 3D Hierarchical Macro-/Mesoporous Silicon from 0D Silica Nanoparticles

By using first-principles calculations, we investigate the electron-phonon interaction and phonon-mediated superconductivity of charge doped and Li-deposited monolayer C3N. No superconductivity is found for 0.2 e/cell doped C3N due to a small electron-phonon coupling (EPC) strength which is less that 0.1. Surprisingly, when Li atom is deposited the monolayer, much more low lying optical phonon modes especially the out-of-plane vibration mode participate the EPC process. This results in a pronounced boost of EPC constant to 0.86 and the transition temperature Tc obtained according to isotropical McMillan–Allen–Dynes formula reaches 13.03 K, which is higher than 8.1 K of Li-deposited graphene and 1.4 K of Ca-deposited graphene. Our findings not only widening the potential application of the intriguing two-dimensional material C3N, but also enrich the world of two dimensional superconductors with a relatively high Tc.

Phonon-mediated superconductivity in charge doped and Li-deposited two dimensional C3N

Superconductivity origin of PdTe and pressure effect: Insights from first-principles investigation

A new hole-bridge structure based on a SiO2 nanoarray and its ferromagnetism

Very recently, a new Ni-based antiperovskite nitride superconductor CuNNi3 has been successfully synthesized. We investigate the electronic structures, phonon dispersions, and electron–phonon interactions of CuNNi3 and the isostructual ZnNNi3 by first-principles approach. By analyzing the Eliashberg function we obtain the superconducting transition temperature Tc 3.16 K (3.53 K), which is in good agreement with corresponding experimental Tc 3.2 K (3 K) for CuNNi3 (ZnNNi3). They can be verified as conventional phonon-mediated superconductors.

First-principles verification of CuNNi 3 and ZnNNi 3 as phonon mediated superconductors

A detailed study of a new method for preparing ordered porous silicon (PS) is reported. An Ag@SiO2 two-dimensional template was caused to self-assemble on a silicon surface using the vertical deposition method. Ordered PS was obtained by electrodeless etching of the Si wafer plus template in a mixed solution of HF and H2O2. The ordered PS was characterized using Field Emission Scanning Electron Microscopy, Spectrofluorimetry and Fourier Transform Infrared Absorption Spectroscopy. The diameter of the nanopores is about 500 nm. And the thermal conductivities of the ordered PS were found to be reduced compared to bulk silicon and disordered PS, due to enhanced phonon scattering. Compared with disordered PS, the ordered PS has a lower specific surface area. Straight holes and columnar structure in the ordered PS result in high absorption when the wavelength is longer than 890 nm and a high transmittance in the test range of 400–4000 wavenumbers.

Xing Wang

Papers

Phonon-mediated superconductivity in charge doped and Li-deposited two dimensional C3N

Superconductivity origin of PdTe and pressure effect: Insights from first-principles investigation

A new hole-bridge structure based on a SiO2 nanoarray and its ferromagnetism

First-principles verification of CuNNi 3 and ZnNNi 3 as phonon mediated superconductors

A template-based method for preparing ordered porous silicon