Transcript A Mechanistic Study of Monomer Formation in the Synthesis of II

A Mechanistic Study of Monomer Formation in the Synthesis of
II-VI Semiconductor Nanoparticles
Jonathan S. Owen, Haitao Liu, and A. Paul Alivisatos
Univ. of California- Berkeley and Lawerence Livermore National Lab
kTHERM
Cd(CH3)2
kPROT
Cd0 + TOPSe
CdSe + TOP
Thermal
Pathway
+ 2 H2-ODPA
- 2 CH4
Se
+ Cd(ODPA-H)2
P
R
R
R
Cd(ODPA-H)2
O
Se
CdSe +
+
P
P
R
R
R
R
R
R
O
O
C18H37 P O P C18H37
OH OH
Protolytic
Pathway
Multiple chemical pathways convert cadmium and selenium precursors into monomeric units of
semiconductor that then nucleate and crystallize into nanometer scale particles. In order to
better control particle growth kinetics we have uncovered the dominant chemical mechanisms
that govern monomer formation. Shown above are the thermal and protolytic mechanisms that
operate when alkylcadmium and phosphine selenides are used as particle precursors. The
relative rates of the thermal and protolytic pathways impact the extant of nucleation at early
reaction times and can be used to control the final particle concentration and size.