External-Strain-Induced Raman Scattering Modification in g-C3N4 Structures

Regulation of optical properties and electronic structure of graphitic carbon nitride （g-C3N4 ） via external strain has attracted much attention due to its potential in photocatalyst and electronic devices. However, the identifi- cation of g-C3N4 structure transformation induced by strain is greatly lacking. In this work, the Raman spectra of g-C3N4 with external strain are determined theoretically based on the density function theory. Deformation induced by external strain not only regulates the Raman mode positions but also leads to a I^aman mode split- ting, which can be ascribed to crystal symmetry destruction by strain engineering. Our results suggest the use of Raman scattering in structural identification in deformed 9-C3N4 structure.

Thermal conductivity of carbon-based nanomaterials:Deep understanding of the structural effects

The thermal conductivity of carbon-based nanomaterials(e.g.carbon nanotubes,graphene,graphene aerogels,and carbon fibers)is a physical property of great scientific and engineering importance.Thermal conductivity tailoring via structure engineering is widely conducted to meet the requirement of different applications.Traditionally,the thermal conductivity-temperature relation is used to analyze the structural effect but this relation is extremely affected by effect of temperature-dependence of specific heat.In this paper,detailed review and discussions are provided on the thermal reffusivity theory to analyze the structural effects on thermal conductivity.For the first time,the thermal reffusivity-temperature trend in fact uncovers very strong structural degrading with reduced temperature for various carbon-based nanomaterials.The residual thermal reffusivity at the 0 K limit can be used to directly calculate the structure thermal domain(STD)size,a size like that determined by x-ray diffraction,but reflects phonon scattering.For amorphous carbon materials or nanomaterials that could not induce sufficient x-ray scattering,the STD size probably provides the only available physical domain size for structure analysis.Different from many isotropic and anisotropic materials,carbon-based materials(e.g.graphite,graphene,and graphene paper)have Van der Waals bonds in the c-axis direction and covalent bonds in the a-axis direction.This results in two different kinds of phonons whose specific heat,phonon velocity,and mean free path are completely different.A physical model is proposed to introduce the anisotropic specific heat and temperature concept,and to interpret the extremely long phonon mean free path despite the very low thermal conductivity in the c-axis direction.This model also can be applied to other similar anisotropic materials that feature Van der Waals and covalent bonds in different directions.

Strategies for baryon resonance analysis

The analytic properties theoretical investigations of baryon of scattering amplitudes provide a meeting point for experimental and resonances. Pole positions and residues allow for a parameterization of resonances in a well-defined way which relates different reactions. The recent progress made within the Jiilich model is summarized.

Resonance properties from a coupled channel meson exchange model

In this talk, I present the results on the pole structure of pion-nucleon scattering in an analytic model based on meson exchange. The analytic properties of scattering amplitudes provide important information. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions.