The PI plans to investigate the possibilities and limitations of spray pyrolysis methods for producing semiconductor and multicomponent nanocrystals of sufficiently small size to exhibit size- and shape-dependent optical and electronic properties. A vast array of potential applications based on these size and shape-tunable properties may be possible, ranging from biological imaging to solar cells and light-emitting diodes. Development of reproducible, controllable, and scalable continuous processes for producing these materials is essential to the realization of these applications. In spray pyrolysis, variants of which will be developed and explored here, a liquid precursor solution is sprayed as a mist of fine droplets (an aerosol) that is heated to induce formation of solid particles. He will study two spray pyrolysis approaches: (1) complete evaporation/vapor phase nucleation mode in which the aerosol serves as a means of delivering high concentrations of moderate volatility precursors into the gas phase, and (2) incomplete evaporation mode with formation of multiple product particles per precursor droplet, in which each aerosol droplet serves as a femtoliter-scale liquid phase reactor that, by virtue of its small size, can be heated or cooled very rapidly and remains uniform in concentration and temperature. The first approach expands on the capabilities of other vapor-phase synthesis approaches by allowing use of lower-volatility and lower-stability precursors than would otherwise be possible. The second approach allows one to extend powerful solution-phase methods to higher temperatures and shorter reaction times than are practical in conventional batch processes in solution.
Intellectual Merit:
The PI's recent advances in solution phase synthesis of anisotropic and hybrid semiconductor nanocrystals and in spray pyrolysis synthesis of other materials, suggest natural research directions for combining and extending these approaches. This will advance both nanoparticle synthesis capabilities and our understanding of the kinetics of nanocrystal nucleation, growth, and shape evolution. The project goals are to: (1) Establish the extent to which solution-phase methods of producing semiconductor nanocrystals and hybrid nanocrystals can be applied in the vapor-phase via complete evaporation and gas phase reaction of precursors delivered as an aerosol. (2) Demonstrate continuous production of high quality spherical, anisotropic, and hybrid semiconductor nanocrystals within aerosol droplets at higher temperature and shorter reaction times than are feasible in batch solution phase syntheses. (3) Apply principles and tools of chemical reaction engineering to the spray pyrolysis process to investigate the kinetics of nanocrystal nucleation and growth, and to design improved spray pyrolysis processes that produce higher quality nanocrystals.
Broader Impact:
The proposed work will lead to development of new, continuous, relatively high-throughput processes for the production of semiconductor nanocrystals, particularly anisotropic and hybrid nanocrystals. This will have technological impact by expanding the range of applications for which such semiconductor nanocrystals can be considered. Through this work, two Ph.D. students will be trained in the aerosol synthesis of nanoscale materials and develop cross-disciplinary skills in chemistry, materials science, and chemical engineering. Undergraduates will participate in this project through the NSF REU program, and through additional targeted programs such as the McNair Scholars program and the Louis Stokes Alliance for Minority Participation (LS-AMP) program. The PI's group has had increasing success in recruiting minority participants, and this project will build on this success and expand it with outreach to middle and high-school students and teachers.
