Controlled Synthesis
Our objective is to develop general chemical approaches to synthesize
new nanowires and nanowire heterostructures, of which chemical, physical and
structural properties are well controlled.
A general
strategy for synthesizing nanowires involves exploiting a nanocluster ‘catalyst’ to
confine growth in 1 dimension. The nanocluster or nanodroplet serves as the site
that directs preferential addition of reactant to the end of a growing
nanowires. Several specific methods based on
this underlying strategy have been developed for the synthesis of nanowires,
including metal organic chemical vapor deposition, metal organic vapor-phase epitaxy,
laser ablation, chemical vapor deposition and physical evaporation.
Heterostructures in which the composition and/or
doping are varied on the nanometer scale represent equally important—if not
more significant—targets of synthesis since they could enable new and unique
functions or properties for integration in functional nanosystems. The elaboration of basic
homogenous structure to form
radial and axial heterostructures can be achieved as follows. Radial growth
of a shell of distinct material can be preferred by altering the synthetic
conditions to favor homogenous vapor-phase coating on the nanowire surface. On the
other hand, an axial heterostructure is prepared by varying the reactant
and/or dopant species while maintaining conditions for axial growth. Subsequent introduction of different reactants
and/or dopants produces structures of arbitrary composition and
doping, leading to great versatility of NWs structures.
Currently we are
exploring controlled synthesis of IV group and III-V nanowires (funded by
NSF CAREER) and heterostructures (funded by ARO) using
chemical vapor deposition and physical evaporation methods We are also
working on laser-guided growth through collaboration with Xu Group in ME
department at Purdue (funded by DARPA).
