On the preparation of clean tungsten single crystals

Abstract The cleaning procedure consists of two-step-flashing: (i) cycles of low power flashes ( T ∼ 1200 K ) at an oxygen partial pressure of P O 2 = 6 × 10 - 8 mbar , to remove the carbon from the surface, and (ii) a single high power flash ( T ∼ 2200 K ) , to remove the oxide layer. The removal of carbon from the surface through the chemical reaction with oxygen during low power flash cycles is monitored by thermal desorption spectroscopy. The exposure to O 2 leads to the oxidation of the W surface. Using a high power flash, the volatile W-oxides and the atomic oxygen are desorbed, leaving a clean crystal surface at the end of procedure. The method may also be used for cleaning other refractory metals like Mo, Re and Ir.