title: Co-operativity in a nanocrystalline solid-state transition.
abstract: Co-operativity is a remarkable phenomenon mostly seen in biology, where initial reaction events significantly alter the propensity of subsequent reaction events, giving rise to a nonlinear tightly regulated synergistic response. Here we have found unique evidence of atomic level co-operativity in an inorganic material. A thousand-atom nanocrystal (NC) of the inorganic solid cadmium selenide exhibits strong positive co-operativity in its reaction with copper ions. A NC doped with a few copper impurities becomes highly prone to be doped even further, driving an abrupt transition of the entire NC to the copper selenide phase, as manifested by a strongly sigmoidal response in optical spectroscopy and electron diffraction measurements. The examples presented here suggest that cooperative phenomena may have an important role in the solid state, especially in the nucleation of new chemical phases, crystal growth, and other materials' transformations.
authors: Department of Chemistry, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors: Sarah L
authors: SL
authors: White
authors: Department of Chemistry, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors: Jeremy G
authors: JG
authors: Smith
authors: Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
authors: Mayank
authors: M
authors: Behl
authors: 1] Department of Chemistry, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA [2] Materials Research Lab, University of Illinois at Urbana Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801, USA [3] Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, USA.
authors: Prashant K
authors: PK
authors: Jain