Differences in Charge Transfer between Surface and Bulk Species in Tetrathiafulvalene- Tetracyanoquinodimethane

The charge-transfer complex tetrathiafulvalene-tetracyanoquinodimethane has been studied by x-ray-photoelectron spectroscopy at both normal and grazing electron takeoff angles. Changes in the N₁ₛ and S₂ₚ spectra with angle show that a discrete layer exists at the surface of the a-b plane. Essentially zero electron transfer takes place in this layer versus {~} 0.8±{}0.2 in the bulk. The surface layer is ca. 1 to 5 layers of complex thick and appears to be intrinsic to "good" organic conductors.