Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

II.THEORY OF ELECTRON TRANSFER BETWEENLOCALIZED STATESHere, we introduce some of the theory relevant to determining the rate ofelectron transfer between two nanocrystals. In particular, we are interested inelectron transport in a solid film of nanocrystals, where the particles are fixedin position and separated typically by the organic ligand present on the nanocrystalsurface. We will examine how the charge transport is expected to varywith the size and spacing of the particles and will return to this question inSection V, where we present experimental results.The theory of electron transfer between localized states has beendeveloped to predict rates of electron transfer in molecular systems and hasbeen extended to treat electron transfer to and from molecules at a metallic orsemiconductor surface [10]. We will first give a brief review of this theory,which was initially developed by Marcus [11]. In this model the energy of theinitial and final states are considered as a function of nuclear coordinates, asshown in Fig. 3. The nuclear coordinates cannot change during the electrontunneling process from initial to final state, and electron transfer must thereforeoccur at nuclear coordinates which correspond to an intersection of theinitial and final potential energy surfaces. In Fig. 3, DGj represents the free-Figure 3 Energy as a function of configuration coordinate for the initial and finalstates in an electron transfer reaction. The reorganization energy, k, and the freeenergychange for the reaction, DGj, are shown.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.