Surface transfer doping of hydrogen-terminated diamond by C60F48: Energy level scheme and doping efficiency

Surface sensitive C1s core level photoelectron spectroscopy was used to examine the electronic properties of C60F48 molecules on the C(100): H surface. An upward band bending of 0.74 eV in response to surface transfer doping by fluorofullerene molecules is measured. Two distinct molecular charge states of C60F48 are identified and their relative concentration determined as a function of coverage. One corresponds to ionized molecules that participate in surface charge transfer and the other to neutral molecules that do not. The position of the lowest unoccupied molecular orbital of neutral C60F48 which is the relevant acceptor level for transfer doping lies initially 0.6 eV below the valence band maximum and shifts upwards in the course of transfer doping by up to 0.43 eV due to a doping induced surface dipole. This upward shift in conjunction with the band bending determines the occupation of the acceptor level and limits the ultimately achievable hole concentration with C60F48 as a surface acceptor to values close to 1013 cm(-2) as reported in the literature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3695643]