Bond-order bond-length bond-strength (bond-OLS) correlation mechanism for the shape-and-size dependence of a nanosolid

Abstract

A bond-order–bond-length–bond-strength (bond-OLS) correlation mechanism is presented for consistent insight into the origin of the shape-and-size dependence of a nanosolid, aiming to provide guidelines for designing nanomaterials with desired functions. It is proposed that the coordination number imperfection of an atom at a surface causes the remaining bonds of the lower-coordinated surface atom to relax spontaneously; as such, the bond energy rises (in absolute value). The bond energy rise contributes not only to the cohesive energy (ECoh) of the surface atom but also to the energy density in the relaxed region. ECoh relates to thermodynamic properties such as self-assembly, phase transition and thermal stability of a nanosolid. The binding energy density rise is responsible for the changes of the system Hamiltonian and related properties, such as the bandgap, core-level shift, phonon frequency and the dielectrics of a nanosolid of which the surface curvature and the portion of surface atoms vary with particle size. The bond-OLS premise, involving no assumptions or freely adjustable parameters, has led to consistency between predictions and experimental observations of a number of outstanding properties of nanosolids.

Elastic Theory of Nanomaterials Based on Surface-Energy Density

“…Furthermore, in recent years, the surface-energy density of nanomaterials was deeply studied and clarified [22,[62][63][64][65][66][67], which greatly facilitates investigating surface effects in nanomaterials from the point of view of energy.…”

Size-dependent Si nanowire mechanics are invariant to changes in the surface state

“…9,10 It must ultimately be related to properties of the electronic bonding, and some attempts have been made to explain this in connection with a charge redistribution on the surface, 11 and empirical bond order effects due to the reduced coordination of surface atoms. 11,12 Classical MD simulations of Si nanowires show striking size-dependent mechanical effects, but the specific mechanism and even the sign of the effect depend on which interatomic potential is used. Tersoff potentials, with strong bond-order effects, predict an increase in the Young's modulus (stiffening) of Si <001> nanowires with bare reconstructed surfaces as the size is decreased, 13 whereas the Stillinger-Weber potential results in softening.…”

“…This linear bond-order-bond-length relationship supports in part the conventional picture of the relationship between bond order, length and strength. 12 The longer bonds have lower BO. It is unexpected, however, that the BO never significantly exceeds the bulk value, instead of approaching a value of 2 for undercoordinated atoms.…”

Influence of mechanical stress on electron field emission of multiwalled carbon nanotube–polymer composites

“…Here we extend our discussion in lowering the work function of CNTs by introducing a lattice contraction argument when the material is mechanically stressed. We extend the current bond-order-length-strength ͑BOLS͒ correlation mechanism 14 to the core-level shift in a nanosized material by including the effect surface relaxation and bond contraction. The current BOLS correlation argument indicates that the bond contraction not only deepens the atomic "potential well," but also enhances the charge density in the relaxed surface region.…”