Benjamin Diroll
Argonne National Laboratories

Manipulating Changes Within Nanoparticles and Nanoparticles Superlattices

Location: EB1 Room 1011

Friday, February 17th 2017 - 11:00 am

Controlling the behavior of electrons and holes in materials is critical for engineering their chemical and optoelectronic behavior. This seminar will present two distinct approaches: (1) optical control of free carriers within individual nanoparticles and (2) compositional control of the conductivity in solid periodic arrays of nanoparticles over macroscopic distances. (1) Semiconductor nanoparticles can be synthesized with high free electron or hole populations through tunable incorporation of dopant atoms or vacancies, resulting in materials with metal-like plasmas that have strong absorption in the infrared. Optical excitation of these materials in the IR heats free carriers as hot as 5000 K, dramatically changing their transmission and index of refraction on a subpicosecond time-scale, marking these materials as promising candidates for all-optical switching. (2) Analogous to the emergence of properties from periodic arrays of atoms (i.e. crystals), nanoparticle superlattices offer the possibility of emergent optical and electrical behavior from the assembly of millions to billions of individual nanoparticle building blocks into periodic arrays. The judicious choice of two nanoparticle building blocks of nearly identical size allows the formation of a substitutionally-doped superlattice structure in which a hexagonal close packed superlattice of semiconductor nanoparticles randomly incorporates metallic nanoparticles at variable concentrations, engineering changes of conductivity up to 7 orders of magnitude.

After completing undergraduate studies at the University of Chicago, Benjamin Diroll obtained his Ph. D. in Chemistry from the University of Pennsylvania working under Dr. Christopher Murray in the synthesis and properties of inorganic nanomaterials. During this time, he also interned at IBM's Yorktown Heights research facility performing research on carbon nanotube electronics. Currently, he is a Director's Postdoctoral Fellow at Argonne National Laboratory focused on spectroscopy of nanomaterials.

North Carolina State University