Effect of Annealing and Microwave Hydrogen Plasma Treatment on Structural, Chemical, and Electronic Properties of Ion Irradiated Diamond Films

Abstract

ABSTRACTIn the present study we correlate between the secondary electron emission (SEE) of variously treated Xe+ ion-damaged diamond films and their bonding structure in the near-surface region as identified by near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy. The 50 keV Xe+ ion bombardment of hydrogenated polycrystalline diamond films to a dose of 2×1015 cm−2 results in the transformation of near-surface diamond to sp2-bonded amorphous carbon, increased oxygen adsorption, shift of the electron affinity from negative to positive, and strong degradation of its electron emission properties, although it does not induce a pronounced depletion of hydrogen. Exposure of the ion-bombarded films to microwave (MW) hydrogen plasma treatment for 30 min produces negative electron affinity diamond surfaces, but only partially regenerates SEE properties, retains some imperfection in the near-surface atomic layers, as determined by NEXAFS, and the concentration of oxygen remains relatively high. Subsequent annealing to 610 °C produces oxygen-free diamond films and somewhat increases their SEE. Annealing to 1000 °C results in desorption of the surface hydrogen, formation of a positive electron affinity surfaces and drastically degrades their electron emission properties. Prolonged, up to three hours MW hydrogen plasma treatment of as-implanted diamond films gradually improves the crystal quality and results in further increase of SEE intensity. This treatment does not, however, substantially reduce the concentration of oxygen in the previously damaged diamond, indicating its bulk diffusion during or after ion bombardment. To fully recover electron emission properties it is necessary to both remove the defects and hydrogenate the diamond surfaces.