Cleaning procedure for single-crystal tungsten substrates

Single-crystal tungsten substrates produced by electron-beam melting were cleaned by annealing in an oxygen atmosphere (10–3Pa, 1500°C) for a few hours to remove adsorbed carbon and by high-temperature ultrahigh-vacuum annealing (2 × 10–8Pa, 2500°C) for a few minutes to remove residual 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 form ordered, oriented structures. The resultant high-purity, structurally perfect W substrates were used to study electron emission in the Ba/W and Re/W systems