Impact of Bond Order Loss on Surface and Nanosolid Mechanics

Element Mapping in Single-Atom-Width Platinum-Iridium Wires

Single-atom-width wires (SAWWs) of platinum-iridium (PtIr) alloy were produced by mechanical breaking inside a transmission electron microscope. The formation dynamics, the atomic configuration, and the conductance were observed in situ. From the observed lattice images of the SAWWs and image simulation, the structure models, i.e., the configurations of atom position and element allocation, were constructed. Using the experiment-based structural models, the first-principle calculation of the conductance was performed. The atomic configuration and element allocation of the observed SAWWs were identified via the combination of the lattice imaging and calculation. The conductance of PtIr SAWWs changed in complexity for different element allocation in addition to the wire length and the configuration of the constituent atoms, which was difficult to presage from the conductance features of pure metal SAWWs. The present study revealed that the conductance of alloy SAWWs can be controlled by element allocation.

Integrating Biolayer Interferometry, Atomic Force Microscopy, and Density Functional Theory Calculation Studies on the Affinity between Humic Acid Fractions and Graphene Oxide

The interactions between nanoparticles and humic acid (HA) are critical to understanding the environmental risks and applications of nanoparticles. However, the interactions between HA fractions and graphene oxide (GO, a popular carbon nanosheet) at the molecular level remain largely unclear. Four HA fractions with molecular weights ranging from 4.6 to 23.8 kDa were separated, and the large HA fractions presented low oxygen contents and many aromatic structures. The binding constants of the large HA fractions on GO were 2.6- to 3551-fold higher than those of the small HA fractions, while the maximum adsorption capacities of the larger HA fractions onto GO were much higher. Atomic force microscopy (AFM) found that the small and large HA fractions were spread over the center and the edge of the GO nanosheets, respectively. Density functional theory (DFT) simulation and nuclear magnetic resonance spectroscopy confirmed the above phenomena (three adsorption patterns, "vs", "ps", and "pea") and revealed that HA bonded to the GO nanosheets mainly through van der Waals force and π-π interactions. The integrating analysis of binding affinity, AFM, and DFT provides new insights into the environmental behavior of GO and the applications of GO in pollutant removal under exposure from HA.

Interface effect on the cohesive energy of nanostructured materials and substrate-supported nanofilms

The cohesive energy is a key quantity to determine the mechanical, physical, chemical, and electronic properties of materials.

The Strongest Particle: Size-Dependent Elastic Strength and Debye Temperature of PbS Nanocrystals

We investigated the elastic compressibility of PbS nanocrystals (NCs) pressurized in a diamond anvil cell and simultaneously probed the structure using synchrotron-based X-ray diffraction. The compressibility of PbS NCs exhibits bimodal size dependence. The elastic modulus of small NCs increases with increasing diameter and peaks near a particle diameter of approximately 7 nm. For large NCs the elastic modulus decreases toward the bulk value with increasing NC diameter. We explain the bimodal size-dependence of the elastic modulus in terms of a core-shell model based on distinct elasticity of the crystal near the surface and in the core of the particle. We combined insights into the size-dependent elasticity and lattice spacing to determine the Debye temperature of PbS NCs as a function of particle diameter. Understanding the size-dependent elasticity of defect-free colloidal NCs provides new insights into their crystal structure and mechanical properties.

Electron beam irradiation stiffens zinc tin oxide nanowires

We report a remarkable phenomenon that electron beam irradiation (EBI) significantly enhances the Young's modulus of zinc tin oxide (ZTO) nanowires (NWs), up to a 40% increase compared with the pristine NWs. In situ uniaxial buckling tests on individual NWs were conducted using a nanomanipulator inside a scanning electron microscope. We propose that EBI results in substantial atomic bond contraction in ZTO NWs, accounting for the observed mechanically stiffening. This argument is supported by our experimental results that EBI also reduces the electrical conductivity of ZTO NWs.

Dominance of broken bonds and nonbonding electrons at the nanoscale

Although they exist ubiquitously in human bodies and our surroundings, the impact of nonbonding lone electrons and lone electron pairs has long been underestimated. Recent progress demonstrates that: (i) in addition to the shorter and stronger bonds between under-coordinated atoms that initiate the size trends of the otherwise constant bulk properties when a substance turns into the nanoscale, the presence of lone electrons near to broken bonds generates fascinating phenomena that bulk materials do not demonstrate; (ii) the lone electron pairs and the lone pair-induced dipoles associated with C, N, O, and F tetrahedral coordination bonding form functional groups in biological, organic, and inorganic specimens. By taking examples of surface vacancy, atomic chain end and terrace edge states, catalytic enhancement, conducting-insulating transitions of metal clusters, defect magnetism, Coulomb repulsion at nanoscale contacts, Cu(3)C(2)H(2) and Cu(3)O(2) surface dipole formation, lone pair neutralized interface stress, etc, this article will focus on the development and applications of theory regarding the energetics and dynamics of nonbonding electrons, aiming to raise the awareness of their revolutionary impact to the society. Discussion will also extend to the prospective impacts of nonbonding electrons on mysteries such as catalytic enhancement and catalysts design, the density anomalies of ice and negative thermal expansion, high critical temperature superconductivity induced by B, C, N, O, and F, the molecular structures and functionalities of CF(4) in anti-coagulation of synthetic blood, NO signaling, and enzyme telomeres, etc. Meanwhile, an emphasis is placed on the necessity and effectiveness of understanding the properties of substances from the perspective of bond and nonbond formation, dissociation, relaxation and vibration, and the associated energetics and dynamics of charge repopulation, polarization, densification, and localization. Finding and grasping the factors controlling the nonbonding states and making them of use in functional materials design and identifying their limitations will form, in the near future, a subject area of "nonbonding electronics and energetics", which could be even more challenging, fascinating, promising, and rewarding than dealing with core or valence electrons alone.

Behind the Quantum and Size Effects: Broken-Bond-Induced Local Strain and Skin-Depth Densified Quantum Trapping of Charge and Energy

Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young’s modulus, dielectric constant, melting point, etc. The variation of size also generates novel properties that can hardly be seen in the bulk such as the conductor-insulator and nonmagnetic-magnetic transition of noble metals at the nanoscale. Although the physics of materials at the nanoscale has been extensively investigated, the laws governing the energetic and dynamic behavior of electrons at such a scale and their consequences on the tunable physical properties of nanostructures have not been well understood [C. Q. Sun, Prog Solid State Chem 35, 1-159 (2007); Prog Mater Sci 54, 179-307 (2009)]. The objective of the contribution is to update the recent progress in dealing with the coordination-resolved energetic and dynamic behavior of bonds in the low-dimensional systems with consideration of the joint effect of temperature and pressure. It is shown that the broken-bond-induced local strain and the associated charge and energy quantum trapping at the defect sites perturbs the atomic cohesive energy, electroaffinity, the Hamiltonian and the associated properties of entities ranging from point defects, surfaces, nanocavities and nanostructures. Application of the theories to observations has led to consistent understanding of the behavior of nanometer-sized materials and the interdependence of these entities as well as the means of determining the bond energy through the temperature-dependent measurements.