Carbon films and carbide formation on tungsten

The reaction of carbon films on tungsten substrates has been investigated using X-ray photoelectron spectroscopy (XPS). Thin C films were evaporated at room temperature on polycrystalline tungsten. For comparison with a non-reactive metal, gold substrates were used. After deposition, XPS analysis showed two different chemical states of unreacted carbon. A quantitative analysis 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 increased annealing temperatures. The tungsten samples were annealed up to temperatures of 1270 K. XPS analysis showed the stepwise formation of two different 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 concentration of the surface decreased distinctly with increasing annealing temperatures.