PHOTOELECTRON SPECTROSCOPIC INVESTIGATIONS AND EXOELECTRON EMISSION OF CVD DIAMOND SURFACES MODIFIED WITH OXYGEN AND POTASSIUM

The surface chemistry of oxygen and alkali (K) treated CVD diamond sur faces was studied with X-ray induced photelectron spectroscopy (XPS) a nd UV-light induced photoelectron spectroscopy (UPS). The oxygen modif ication was achieved ex-situ using oxidizing acids (hydrochloric and n itric acid) or in-situ by evaporation of K from a SAES getter source. XPS analysis of the C 1s and O 1s spectra demonstrated that the acid t reatment leads to a considerably uptake of oxygen (or OH groups). Owin g to the presence of surface oxygen the C 1s peaks splits into two com ponents with binding energies of 284.2 (diamond) and 287.3 eV (carbon bonded to oxygen). The adsorption of K was followed with XPS and UPS ( HeI) spectroscopy. With XPS the evaluation of the K 2p states demonstr ates that the amount of K which can be accommodated at 300 K depends o n the oxygen precoverage; the maximum obtainable K coverage increases with the surface oxygen concentration. In the presence of K the C 1s s tate from the C-O bonding shifts to lower binding energy, 286.4 eV. Wi th UPS a broad unstructured emission probably from carbon 2p+2s states is detected between 3.5-10 eV below E(F) from the untreated diamond s urface. The emission between 0.0-2.5 eV was fairly low (band gap of di amond), it could be considerably reduced by the acid treatment of the sample. This is suggested to be owing to the removal of graphitic or a morphous carbon impurities. Owing to the presence of oxygen the broad emission peak shifted to higher binding energy (from 6.8 to about 8.0 eV). Low doses of K lead to a reduction of the 2p+2s emission from car bon and oxygen, with a center of the reduction at 5.0 eV. For higher K coverages new K-induced states evolves. One state is located in the b and gap of diamond near E(F); further peaks were found at 3.5, 7.0 and about 14 eV below E(F). K covered diamond surfaces showed a strong ex oelectron emission after oxygen exposure in vacuum.