Nanostructuring Low Dimensions into Devices: Thermoelectric Materials and Form Factors

Title of Technical Proposal

Electrochemical Atomic Layer Epitaxy (EC-ALE) for the production of thermoelectric materials with directed low-dimensionality on flexible films and ribbons.

Technical Abstract
Electrochemical Atomic Layer Epitaxy (EC-ALE) will be applied for directed growth of thermoelectric semiconductor nanowires and superlattices segmented between doped layers of Bi2Te3/Sb2Te3. EC-ALE is a robust, ambient pressure semiconductor production process where elements are deposited individually from different baths (instead of electrochemical codeposition) where monolayer (ML) formation is directed by underpotential deposition (upd), rather than by substrate temperature and partial pressure as in MBE. The material will be deposited onto metalized, patterned and flexible substrate form-factors of films and ribbons, and their thermoelectric properties will be measured on substrate and in form factor. The program will include determination of desired form factors (for bottom-up design considerations), identification of appropriate semiconductor segments and dopants according to band structure and process ability, construction of an EC-ALE reactor capable of multiple element baths and geometric substrates, optimization of deposition potentials per element per cycle, and thermoelectric measurement of the grown materials. Physical and thermoelectric characteristics of the materials will be quantified. Product purity (liquid solute and solvent) will be addressed relative to the near vacuum process in quality, cost and capital. If time permits, the continuous substrates will be folded into the application's final form-factor and measured for figure of merit.

Anticipated Benefits/Potential Commercial Applications of the Research or Development.
Development of growth processes of nanostructured materials that do not require vacuum processing will be commercially beneficial in two ways. The first is the energy savings in not having to pump down to near-vacuum pressures and apply high temperatures, and the second is the observed benefit in efficiency from quantum, or low-dimensional, confinement of atomically architectured materials. Additionally, since process temperatures are much lower, a variety of flexible form factors may be grown upon and production capital is significantly lower due to ambient processing (although atmosphere composition is controlled). Finally, EC-ALE provides direction of molecular assembly from dopants to monolayers to multiple layers on an elemental basis, thus providing a benefit of process control not available to electro-co-deposition techniques. Molecular direction of assembly has been correlated to an increase in thermoelectric conversion efficiency though quantum considerations. This is an economic and commercial benefit in an electronics age of smaller and faster.

Keywords
Thermoelectrics, EC-ALE, Epitaxy, Electrochemical, Semiconductor, Superlattice, Underpotential deposition