Dependency of Sliding Friction for Two Dimensional Systems on Electronegativity

We study the role of electronegativity in sliding friction for five different two-dimensional (2D) monolayer systems using ab-initio calculations within density functional theory (DFT) with van der Waals (vdW) corrections. We show that the friction depends strongly on the involved atoms’ electronegativity difference. All the studied systems exhibit almost the same magnitude of the friction force when sliding along the nonpolar path, independent of the material and the surface structures. In contrast, for sliding friction along a polar path, the friction force obeys a universal linear scaling law where the friction force is proportional to atoms electronegativity difference of its constituent atoms. We show that atomic dipoles in the 2D monolayers, induced by the electronegativity difference, enhance the corrugation of the charge distribution and increase the sliding barriers accordingly. Our studies reveal that electronegativity plays an important role in friction of low dimensional systems, and provides a strategy for designing nanoscale devices.

Electrically controlled valley polarization in 2D buckled honeycomb structures

Generating and manipulating valley polarization in a controlled method is significant. The inherently broken centrosymmetry of the buckled honeycomb structures gives it both ferroelectricity and valley degree of freedom, which provides an opportunity to realize electrically controlled valley polarization. In the first step, we explored the origin of buckling. The hexagonal structure is polar due to buckling of the surface, but the degree of buckling and the energy barrier to switching electric polarization are determined not solely by the chemical composition. We combined the electronegativity difference, bond length and the distribution of charge density to describe quantificationally the polarity of chemical bonds. It shows the characteristics of relatively long bond-length but relatively small electronegativity-difference. For exploring the ferroelectricity of buckling structures and the behavior of ferroelectric (FE) control of the valley degree of freedom, the [Formula: see text]-GaP is used as a model system to elucidate the strain effect on FE behavior and the magnetic proximity effect on the polarization and switching of valley. We found that the spontaneous polarization is positively correlated with the electronegativity difference within a certain range, and the compression strain can effectively manipulate spontaneous polarization and switch barrier. A combination of the magnetic proximity effect and the inversion of electric polarization can generate and switch valley polarization effectively.

The role of dysprosium ions as a dopant on linear and nonlinear optical dispersion parameters in a-Se thin film

Thin films of un-doped and doped a-Se with Dysprosium rare-earth ions have been prepared by the thermal evaporation technique. The optical transmission spectra of the investigated films have been measured in a wide spectral range and used to calculate the linear optical constants together with the optical energy gap of studied films. The observed decrease in the values of the energy gap against the increase of the Dysprosium (Dy) content in a-Se films has been explained using Mott and Davis Model and in terms of electronegativity difference of the constituent atoms. Furthermore, the dispersion of nonlinear parameters such as second-order refractive index and nonlinear absorption coefficient (two-photon absorption coefficient) of investigated films are presented and discussed.

Inductive Effect as a Universal Concept to Design Efficient Catalysts for CO2 Electrochemical Reduction: Electronegativity Difference Makes Difference

CO2 electrochemical reduction (CO2ER) into valuable chemical feedstocks holds great promise for energy supply and environmental remediation but remains a challenge due to the lack of high-performance electrocatalysts. Inductive effect,...

Collaboration between a Pt-dimer and neighboring Co–Pd atoms triggers efficient pathways for oxygen reduction reaction

Charge localization via compression strain and electronegativity difference extracts electrons from Pd and Co, thereby opening efficient oxygen reduction pathways around the Pt dimer.

Anion Charge and Lattice Volume Maps for Searching Lithium Superionic Conductors

<p><a>The effects of anion charge and lattice volume (lithium-anion bond length) on lithium ion migration have been investigated by utilizing the density functional theory calculations combined with the anion sublattice models, e.g. <i>fcc</i>, <i>hcp</i> and <i>bcc</i>. It is found that the anion charge and lattice volume have great impacts on the activation energy barrier (E_a) of lithium ion migration, which is validated by some reported sulfides. For the tetrahedrally occupied lithium, the less negative anion charge is, the lower the lithium ion migration barrier is likely to be. While for the octahedrally occupied lithium, the more negative anion charge is, the lower the lithium ion migration barrier is. There are opposite effects of anion charge on E_a and optimum lattice volumes for minimum E_a of lithium ion migration along the <i>Tet-Oct-Tet</i> and <i>Oct-Tet-Oct </i>pathways in the <i>hcp</i>-type sublattices. Based on the full understandings of anion sublattice model, general design strategies for developing lithium superionic conductors were proposed. Adjusting the electronegativity difference between the anion element and non-mobile cation element by selecting the most suitable non-mobile cation element without changing the crystal structure sublattice can achieve low E_a for lithium ion migration. For the desired lithium superionic conductors with tetrahedrally occupied lithium ions, the fine non-mobile cation element should give preferences to those elements located at the right top of the periodic table of elements with large electronegativities. For the lithium superionic conductors with octahedrally occupied lithium ions, the fine non-mobile cation element should give preferences to the elements located at the left bottom of the periodic table with small electronegativities.</a><br></p>