Covalent electron density analysis and surface energy calculation of gold with the empirical electron surface model

Based on the empirical electron surface model （EESM）,the covalent electron density of dangling bonds （CEDDB） was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed （111） surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.

Extraction Difficulty of Lithium Ions from Various Crystal Planes of Lithium Titanate

To study the extraction difficulty of lithium ions from various crystal planes of Li2 TiO3, according to the first principle, four representative crystal surfaces of Li2TiO3（precursor）,（-133）,（-206）,（002） and（-131）, were selected to establish a model and to calculate the surface energy, bond length and population using Materials Studio 5.5（MS 5.5）. The results demonstrate that there is no direct relationship between the surface energy and the order of disappearance of the four diffraction peaks when lithium titanate is treated with hydrochloric acid, instead, the difficulty of Li~＋ extraction from various crystal faces corresponds to the Li-O bond strength. Lithium ion is easy to remove from（-133） and（-206） due to the relatively weak Li-O bond strength. In contrast, Li＋ extraction requires a longer time for（002） and（-131）.

Electronic states and shapes of silicon quantum dots

A curviform surface breaks the symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in the bandgap. The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides localized levels in bandgap and its bonding energy is shallower than that on the facet. The red-shifting ofthe photoluminescence spectrum on smaller silicon quantum dots can be explained by the curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided by the curved surface effect.

PL Emission and Shape of Silicon Quantum Dots

The calculation results show that the bonding energy and electronic states of silicon quantum dots are different on various curved surfaces, for example, a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. The red-shifting of PL spectra on smaller silicon quantum dots can be explained by curved surface effect. Experiments demonstrate that silicon quantum dots are activated for emission due to the localized levels provided in curved surface effect.

Exploring electronic-level principles how size reduction enhances nanomaterial surface reactivity through experimental probing and mathematical modeling

Size reduction can generally enhance the surface reactivity of inorganic nanomaterials.The origin of this nano-effect has been ascribed to ultrasmall size,large specific surface area,or abundant defects,but the most intrinsic electronic-level principles are still not fully understood yet.By combining experimental explorations and mathematical modeling,herein we propose an electronic-level model to reveal the physicochemical nature of size-dependent nanomaterial surface reactivity.Experimentally,we reveal that competitive redistribution of surface atomic orbitals from extended energy band states into localized surface chemical bonds is the critical electronic process of surface chemical interactions,using H_(2)O_(2)-TiO_(2)chemisorption as a model reaction.Theoretically,we define a concept,orbital potential(G),to describe the electronic feature determining the tendency of orbital redistribution,and deduce a mathematical model to reveal how size modulates surface reactivity.We expose the dual roles of size reduction in enhancing nanomaterial surface reactivity-inversely correlating to orbital potential and amplifying the effects of other structural factors on surface reactivity.

Electron beam surface heating-diffusion bonding:An effective joining method for aluminum alloy metal-matrix composite with high SiC volume

As a novel method to reduce the temperature during electron beam welding,and to subsequently inhibit interfacial reaction between SiC and Al matrix,the electron beam surface heating-diffusion bonding is proposed for joining SiC particle reinforced aluminum alloy metal-matrix composite of 45 vol.%SiC/2024 Al.The defocused electron beam was used to heat the base metal surface,and the simultaneous pressure was applied to the butt surface to achieve bonding.The base metals were successfully joined by diffusion.The maximum temperature of the whole joint was effectively decreased to less than 650°C.The Gibbs free energy change of interfacial reaction was calculated,meaning a positive value reaching 218 kJ/mol and a consequently prominent inhibitory effect on the formation of brittle Al_(4)C_(3)that was proved by microstructural observation.The tensile strength for the bonded joint was increased by 35%compared to that for ordinary welded joint.When the TC4 layer was added,TiC strengthening particles were formed with the deficiency of Al_(4)C_(3),corresponding to the significantly increased tensile strength of 63%of base metal(154 MPa).

Metals Supported Water Monomers:the Bonding Nature Revisited

A single water monomer is known as a hard-to-observe molecule even in the presence of metal surfaces as supporting matrix. This review highlights effort in experimental characterizations and theoretical modeling of transition metals supported water monomers with attention given to its structure and bonding, together with the insights that we have provided into the bonding nature of the water-interactions by the newly employed projected PDOS （partial density of states） difference analysis, which is proved to be an effective tool to be elucidate such bonding nature. The general s-d hybridization and d-shell effect are summarized, and how these effects can be tuned by tailoring local surface configurations is discussed.