January 20, 2017 at 2.30 pm in AG-69
Strategy to Tune Equilibrium Dopant Composition in Semiconductor Nanocrystals
Intentional incorporation of dopants into the semiconductor nanocrystals can dramatically alter the electronic, optical, magnetic, and electrical properties. Understanding the fundamental chemical boundaries of nanocrystal composition control for new and challenging dopant/host combinations could yield unprecedented doped semiconductor nanomaterials for applications from spectral conversion in lighting and luminescent solar concentrators (LSCs), to optical nano-thermometry, bioimaging, plasmonics, or spinbased electronic/photonic information processing. Enormous efforts and many attempts have been made to dope semiconductor nanocrystals with transition metal ions by means of colloidal chemical synthesis. Despite these efforts, successful dopant incorporation into host nanocrystals remains a long-standing challenge. The primary challenges are associated with unfavorable impurity/host competition kinetics during nanocrystal growth. To overcome these challenges, a qualitatively new method of nanocrystal diffusion doping under thermodynamic control has recently been developed where dopants are introduced into preformed nanocrystals via stoichiometric addition of cations and anions, followed by diffusion of these impurities into the nanocrystal's internal volume while maintaining the nanocrystal size, shape, and structural uniformity. This talk focuses on broadening the scope of this powerful chemistry, in conjunction with cation exchange chemistries, to allow dopants to be incorporated into the host nanocrystal lattice, thereby providing a general methodology for controlling dopant composition under thermodynamic equilibrium. In addition, mechanistic understanding of the dopant ion diffusion in these nanocrystals will be discussed, which contributes to our fundamental understanding of this rich area of nanoscience and improves our ability to tailor the compositions of nanostructures for future advanced technological applications.