Effect of Annealing and Microwave Hydrogen Plasma Treatment on Structural, Chemical, and Electronic Properties of Ion Ir
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Effect of Annealing and Microwave Hydrogen Plasma Treatment on Structural, Chemical, and Electronic Properties of Ion Irradiated Diamond Films
Alexander Laikhtman and Alon Hoffman Department of Chemistry, Technion - Israel Institute of Technology, Haifa 3200, Israel
ABSTRACT
In 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 asimplanted 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.
INTRODUCTION
It is very difficult to prepare synthetic diamond films free of defects and impurities in their crystal structure. The defects in microcrystalline diamond films mainly originate from grain boundaries, where the electronic properties of diamond may differ from those of the bulk crystal. Another source of defects in diamond, as well as in other semiconducting materials, is doping. The introduction of foreign atoms, such as boron, nitrogen, or phosphorus for preparation of either p- or n-type semiconducting diamond, always produces damage in the crystalline structure. In our previous works we correlated between the influence of defects of predetermined concentration on the photoelectron emission of hydrogenated polycrystalline diamond films and their near-surface structure and composition [1-3]. It was found that irradiation by low energy (30 keV) Xe+ ions to doses of as low as 2×1013 cm-2 resulted in a drastic decrease of absolute R3.31.1
quantum photoyield (Q
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