Carbon films and carbide formation on tungsten

The reaction of carbon films on tungsten substrates has been investigated u sing X-ray photoelectron spectroscopy (XPS). Thin C films were evaporated a t room temperature on polycrystalline tungsten. For comparison with a nonre active metal, gold substrates were used. After deposition, XPS analysis sho wed two different chemical states of unreacted carbon. A quantitative analy sis of the deposited carbon amount was performed using the XPS intensities. The gold surface did not react with C after all annealing steps up to 1170 K, and no changes in the integral C 1s intensity were observed. The two C 1s states initially observed in the spectra converged into one peak with in creased annealing temperatures. The tungsten samples were annealed up to te mperatures of 1270 K. XPS analysis showed the stepwise formation of two dif ferent carbide phases. At temperatures below 870 K, the XPS spectra did not reveal any significant changes. At 970 K, the C 1s photoelectron peak was shifted towards lower binding energies. After annealing at 1270 K, a second shift occurred, indicating WC and W2C formation. Above 870 K, the C concen tration of the surface decreased distinctly with increasing annealing tempe ratures. (C) 2000 Elsevier Science B.V. All rights reserved.