Self-assembly of LiMo3Se3 nanowire networks from nanoscale building-blocks in solution.

LiMo(3)Se(3) is a highly anisotropic solid comprised of a regular pattern of quasi-1-D wire-like structures. Solutions of LiMo(3)Se(3) deposited on substrates and TEM grids reveal the presence of two-dimensional network morphologies. High resolution STEM imaging reveals that the junctions within these networks are not formed by discrete overlying LiMo(3)Se(3) fibers or wires. Rather the junctions are continuous in that the wires are seamlessly interwoven from one bundle to the next. We investigated network formation by dynamic light scattering and AFM and demonstrate that the networks are not pre-existent in solution but rather form via self-assembly of nanoscale building blocks that is driven by solvent evaporation.

Microstructure-hardened silver nanowires.

To exploit the novel size-dependent mechanical properties of nanowires, it is necessary for one to develop strategies to control the strength and toughness of these materials. Here, we report on the mechanical properties of silver nanowires with a unique fivefold twin structure using a lateral force atomic force microscopy (AFM) method in which wires are held in a double-clamped beam configuration. Force-displacement curves exhibit super elastic behavior followed by unexpected brittle failure without significant plastic deformation. Thermal annealing resulted in a gradual transition to weaker, more ductile materials associated with the elimination of the twinned boundary structure. These results point to the critical roles of microstructure and confinement in engineering the mechanical properties of nanoscale materials.

A generalized description of the elastic properties of nanowires.

We report a model of nanowire (NW) mechanics that describes force vs displacement curves over the entire elastic range for diverse wire systems. Due to the clamped-wire measurement configuration, the force response in the linear elastic regime can be linear or nonlinear, depending on the system and the wire displacement. For Au NWs the response is essentially linear since yielding occurs prior to the onset of the inherent nonlinearity, while for Si NWs the force response is highly nonlinear, followed by brittle fracture. Since the method describes the entire range of elastic deformation, it unequivocally identifies the yield points in both of these materials.

Mechanical properties of ultrahigh-strength gold nanowires.

Nanowires have attracted considerable interest as nanoscale interconnects and as the active components of both electronic and electromechanical devices. Nanomechanical measurements are a challenge, but remain key to the development and processing of novel nanowire-based devices. Here, we report a general method to measure the spectrum of nanowire mechanical properties based on nanowire bending under the lateral load from an atomic force microscope tip. We find that for Au nanowires, Young's modulus is essentially independent of diameter, whereas the yield strength is largest for the smallest diameter wires, with strengths up to 100 times that of bulk materials, and substantially larger than that reported for bulk nanocrystalline metals (BNMs). In contrast to BNMs, nanowire plasticity is characterized by strain-hardening, demonstrating that dislocation motion and pile-up is still operative down to diameters of 40 nm. Possible origins for the different mechanical properties of nanowires and BNMs are discussed.