Surface molecular doping of all-inorganic perovskite using zethrenes molecules

Nano Research - We present an optical and photoelectron spectroscopic study to elucidate the interfacial electronic properties of organic-inorganic semiconductor heterojunctions formed in a...     

Reversible hydrogenation and bandgap opening of graphene and graphite surfaces probed by scanning tunneling spectroscopy

The effects of hydrogenation on the topography and electronic properties of graphene and graphite surfaces are studied by scanning tunneling microscopy and spectroscopy. The surfaces are chemically modified using an Ar/H(2) plasma. By analyzing thousands of scanning tunneling spectroscopy measurements it is determined that the hydrogen chemisorption on the surface of graphite/graphene opens on average an energy bandgap of 0.4 eV around the Fermi level. Although the plasma treatment modifies the surface topography in an irreversible way, the change in the electronic properties can be reversed by moderate thermal annealing and the samples can be hydrogenated again to yield a similar, but slightly reduced, semiconducting behavior after the second hydrogenation.     

Unveiling the strong coulomb interaction effect on electronic structures and mechanical properties of C4AF

There are works have reported the crystal structures and mechanical properties of ferrite cement (C₄AF) at the atomic scale with deviation owing to the omission of the Coulomb interaction effect (U_eff) between 3d electrons of Fe in C₄AF. In this work, the DFT+U method was used to evaluate its effect on their electronic structures and mechanical properties of C₄AF with two different phases I2mb (C₄AF-I) and Pnma (C₄AF-P). The Fe O bonds of the two phases are all weaker and display U_eff due to the presence of Fe ions. The mechanical properties of C₄AF calculated using DFT+U method significantly differ from those obtained without considering U_eff, in which the former shows lower inferior mechanical properties than the latter. This work presents a comparative study the effect of Coulomb interaction to the internal electronic structures and mechanical properties, which will pave the way for designing high hydration reaction cement and high toughness materials.     

Unveiling the amorphization of sodalite topology zeolitic imidazolate frameworks and zeolites by pressure and stress

As a flexible porous material, the amorphous behavior of zeolitic imidazolate framework-8 (ZIF-8) has garnered considerable interest. However, the association between its strain behavior and topology has not yet been exhaustively studied computationally. We perform molecular dynamic simulations on both ZIF-8 and its topological silicate isomer sodalite (SOD) to investigate the pressure-induced development of the mid- and short-range structures. We find that both ZIF-8 and SOD undergo two successive transformations. The first is the amorphization process, which is characterized by the breakdown of the mid-range structure without a significant change in the elastic modulus. The other type of densification involves a change in the short-range structure, during which the mechanical properties are improved as the short-range disorder increases.     

Temperature-dependent elastic and thermodynamic properties of ZrC,HfC, and their solid solutions (Zr0.5Hf0.5)C

Zirconium carbide (ZrC) and hafnium carbide (HfC) have been identified as ultrahigh temperature ceramics with excellent thermal conductivity performance. The temperature profiles of ZrC and HfC have been studied; however, the temperature-dependent of solid solution of (Zr_0.5Hf_0.5)C is still lacking. Herein, we report the temperature-dependent elastic and thermodynamic properties of (Zr_0.5Hf_0.5)C using first-principles calculations. The covalent characters of ZrC, HfC, and (Zr_0.5Hf_0.5)C are weakened at high temperatures by analyzing their respective electronic structures. In addition, the equilibrium volumes at different temperatures can be determined from the energy–volume (E–V) curves under the quasi-harmonic approximation. Throughout the temperature ranges studied, the HfC material shows the highest bulk modulus and lowest thermal expansion. When T > 1000 K, (Zr_0.5Hf_0.5)C exhibits better shear and Young's modulus performance close to HfC and shows the highest anisotropy. The lattice thermal conductivity decreased as temperature increased for ZrC, HfC, and (Zr_0.5Hf_0.5)C, and (Zr_0.5Hf_0.5)C has the smallest lattice thermal conductivity. These results provide fundamental and useful information for the practical application of ZrC, HfC, and (Zr_0.5Hf_0.5)C.