Cleaning procedure for single-crystal tungsten substrates

Single-crystal tungsten substrates produced by electron-beam melting were c leaned by annealing in an oxygen atmosphere (similar to 10(-3) Pa, similar or equal to 2500 degreesC) for a few hours to remove adsorbed carbon and by high-temperature ultrahigh-vacuum annealing (similar or equal to2 x 10(-8) Pa, greater than or equal to 2500 degreesC) for a few minutes to remove re sidual oxygen. The process was followed by low-energy ion scattering, Auger electron spectroscopy, and low-energy electron diffraction. The carbon and oxygen adsorbed on the surface of single-crystal tungsten were found to fo rm ordered, oriented structures. The resultant high-purity, structurally pe rfect W substrates were used to study electron emission in the Ba/W and Re/ W systems.