General hypothesis for nanowire synthesis. I. Extended principles and evidential (experimental and theoretical) demonstration

Abstract

Nanowires, nanotubes, and nanodots (quantum dots) are nanomaterials (NMTs). While nanodots are miniaturized nanowires, nanotubes are hollow nanowires. A universal model for basic science of the synthesis and characteristics of NMTs must be established. To achieve this goal, a general hypothesis has been presented. This hypothesis makes use of the concept of droplets from seeds, the fundamentals of the adhesive properties of droplets, and a set of droplet characteristics. Fundamentals underlying the droplet formation from nanoparticle seeds under various physicochemical and thermodynamic conditions have been articulated. A model of thermodynamic imbalance of seeds at the growth temperature has been formulated. The dependence of thermodynamic imbalance on parameters such as surface energy, temperature, seed dimension, etc. has been described. The role of thermodynamic imbalance of seeds and of the foreign element catalytic agent (FECA) on NMT growth has been examined. Three different NMT growths, namely, FECA-free NMT growth; FECA-mediated non-eutectic NMT growth; and FECA-mediated eutectic NMT growth, have been considered. FECA-free NMT growth, and non-eutectic but FECA-mediated NMT growth, have been assumed to involve nanopores, grains, and grain boundaries in the seed. The basic science of all the NMT growths utilizes the concept of the creation of tiny component droplets (CODs). Extensive evidential (experimental and theoretical) demonstration of the hypothesis has been put forth. Both theoretical and experimental results lend support to the hypothesis. Calculated results address the roles of both the FECA-mediated and FECA-free droplets for NMT growths. The basics of multiple nucleation and biphasic structures have been spelled out. Possible relationship between the activation energy and the precursor decomposition on the droplet surface at the lowest possible temperature has been elucidated. The differences between the eutectic and no-eutectic seeds, the importance of thermodynamic imbalances in the creation of nanopores inside seeds, and the physicochemical reasons of nanowire growth at temperatures far below the seed’s eutectic temperature (and/or melting temperature) have been revealed. Experimental evidences, particularly for CODs, droplets, dipole moment of the seeds (droplets), immovability of droplets, multiple nucleation, biphasic structures, etc., quantify the validity of the hypothesis.