• Angastiniotis, Nicos

Abstract

The metastability process has the fundamental capability to convert an inhomogeneous particle into a building block with tailor-made nanoscale features, i.e., grain size, structure and deliberate nonstoichiometric compositional constituency. The key aspect of the process is its enabling and generic capability to size the grain within a range where a variety of confinement effects dramatically change the properties of the material (a property is altered when the entity or mechanism responsible for that property is confined within a space smaller than the critical length associated with that entity or mechanism). The additional capability of the metastability process to regulate the non-stoichiometric constituency within the frame of the aforementioned building blocks provides flexibility in regulating even further the material properties, thus multiplying enormously the number of novel substance alternatives available for producing devices and products. The metastability process is designed to either isolate metastable metallic phases or induce deliberately the formation of low temperature amorphous metallic metastable templates. Once such structures are established, they are intrinsically susceptible to controlled nitridation, carburization, and oxidation at even lower temperatures, thus enabling the formation of amorphous carbides, nitrides, and oxides. These amorphous states when subjected to appropriate low temperature thermal treatment give way to sequential, gradually augmented, controlled nanocrystallization. Each nanocrystallite comprises a domain within the building block and its composition can be regulated to be non-stoichiometric or stoichiometric. To date nanosynthetic development tends to be irreproducible, producing ceramic particles with limited stability and uncontrolled crystallinity, i.e., non-uniform grain size, irregular structure, and variable composition with erratic or undesired stoichiometric or non-stoichiometric constituency. The metastability process has the enabling capability to convert each and every one of such particles into an integrated assembly of domains, each domain being as small as 1 nm, comprising therefore a near amorphous template or a collection of atomic or molecular clusters. Regulated low temperature, progressive, albeit quick and efficient, metastable thermochemical treatment of such extraordinary nanoscale structure is shown to create stable and uniform building blocks with predefined grain size, structure, and tailor-made non-stoichiometric composition. The metastability process constitutes a unique thermodynamic and kinetic tool that has the intrinsic advantage to operate with nanoscale precision, providing therefore, extraordinary nanosynthetic ability. The premise of this approach is to arrest across predefined length scales that range from 1 to 100 nm, dramatic changes in properties, due to confinement and compositional effects. Even though the process has been exemplified through the use of tungsten based prototype compositions, it can be applied on all refractory based systems. The enabling capability of the metastability process to regulate the physicochemical characteristics of particles should provide enhanced understanding of material properties across length scales which should sequentially lead to the ability to develop nanomaterials via a priori prediction of structure-property relationships. By using therefore the metastability process, a future database that details structure-property relationships at all length scales (1-100 nm) could be prepared. Conversely, such databases could be utilized as a reference for producing nanomaterial building blocks with predicted properties. Synthesis of these nanomaterials based on the predictive design rules should simply validate the understanding of fundamentals. These two approaches are inextricably intertwined and together will be needed in the future to provide the foundation for new nanosynthetic material production. By adopting this methodical, predictive approach we will be in position to identify and validate a priori structure-property-processing parameters. Such capability will enable the "bottom up" synthesis of nanomaterial building blocks with predictable properties. Predictive design comprises only the beginning in the progression from nanomaterials to dispersions and finally, to spatially resolved nanostructures. To realize the promise of predictive design, building blocks must be incorporated into larger-scale devices and systems while retaining their novel attributes. Incorporating nanomaterial building blocks into thin films, coatings, and netshaped components will require the design and development of processes that retain the properties and functionality of the nanoscale building blocks.

Topics

• impedance spectroscopy
• dispersion
• cluster
• amorphous
• grain
• grain size
• phase
• thin film
• nitride
• carbide
• tungsten
• crystallinity