This award supports integrated research and education in computational approaches aimed at understanding and quantifying the growth physics of nanocrystals, in particular semiconducting nanowires. The combination of quantum confinement, superior transport and diverse surface structures have led to the emergence of semiconducting nanowires as materials of choice for next generation nanoelectronic devices and nanoelectromechanical systems. The realization of almost all of the envisioned applications relies on high-yield nanowire synthesis with controlled morphology and composition. The research focuses on classical vapor-liquid-solid growth, wherein a low melting nanoparticle catalyses vapour phase reduction of the gas precursor and also serves as a conduit for essentially one-dimensional mass transfer to the growing nanowire. Fundamental questions remain on aspects related to nanowire growth rate, steady-state diameter and growth orientation selection, in particular for small nanowires with diameters less than a few tens of nanometers. The underlying size dependent effects related to structure, energetics and dynamics of constituent interfaces necessitate a detailed understanding of the growth process that bridges atomic and continuum scales.
The PIs will combine computational approaches on atomic and continuum scales to study both equilibrium and non-equilibrium aspects of nanocrystalline growth, focusing on the well-characterized Au-catalyzed silicon nanowire growth system. The atomistically informed multi-physics approach is centered around classical molecular dynamics and suitably tailored Monte-Carlo based techniques, integrated within appropriately designed kinetic Monte-Carlo and phase field simulations. The atomistic computations are aimed at quantifying the energetics and kinetics of the consitutent interfaces, and the equilibrium as well as near-equilibrium structure, composition and morphology of the nanowire/catalyst particle system. The atomistic understanding is transferred to i) a tailored kinetic Monte-Carlo approach, and ii) phase-field models that allow the PIs to address the growth aspects in their full complexity at the meso- and continuum scales. It is expected that the insights gained from this research will be applicable to a broad set of technologically relevant nanowire systems.
The research component will be integrated into educational and outreach activities that include i) the summer research discovery program and research internships made available through an NSF-funded interdisciplinary program to promote interest in Mathematics, Physics, Biology, and the sciences among college and high-school students, ii) participation and mentorship within the Materials Research Society chapter at Northeastern University, iii) the development of nanoscale-relevant curricula, iv) design of two capstone projects on nanowire growth and mechanics, v) participation in outreach at local schools and museums in the Boston area and through the Society for Women Engineers at Northeastern University, and vi) integration of related computational efforts within the region via the formation of a New England Network on Computational Sciences.
NONTECHNICAL SUMMARY
This award supports theoretical and computational research and educational activities centered on improving our fundamental understanding of the synthesis of technologically relevant materials that have some of their spatial dimensions confined to very small length scales. A primary focus will be semiconducting "nanowires", which are extended along one direction and have cross-sectional diameters of the order of up to several "nanometers", where a nanometer is one billionth the size of a meter. Such nanowires are of significant technological interest for next-generation electronic devices, energy systems, as well as systems that integrate electronic and mechanical functionality at the nanometer length scale. In spite of detailed experimental observations, the mechanisms that govern the formation of nanowires including size, shape, growth orientation and composition remain poorly understood. Since the realization of almost all of the envisioned applications of nanowires relies on high-yield nanowire synthesis with controlled structure and composition, a detailed theoretical understanding of the growth process at a fundamental level is urgently needed. In this research program, the PIs will combine various state-of-the-art computational approaches on the atomistic and continuum scales to elucidate basic mechanisms of nanowire formation. The insight gained from this multi-physics approach is expected to apply to a broad set of technologically relevant elemental and compound materials at the nanoscale.
The research component will be integrated into educational and outreach activities that include i) the summer research discovery program and research internships made available through an NSF-funded interdisciplinary program to promote interest in Mathematics, Physics, Biology, and the sciences among college and high-school students, ii) participation and mentorship within the Materials Research Society chapter at Northeastern University, iii) the development of nanoscale-relevant curricula, iv) design of two capstone projects on nanowire growth and mechanics, v) participation in outreach at local schools and museums in the Boston area and through the Society for Women Engineers at Northeastern University, and vi) integration of related computational efforts within the region via the formation of a New England Network on Computational Sciences.
