High pressure H2 treatment for deep cleaning of Fe single crystals

• Fast high-pressure H 2 reduction of a iron single crystals contaminated with S, C and O • Autoclave treatment at 600°C and 50 bar for 3 hours • LEED images and XPS/UPS to confirm cleanliness of surfaces • Work functions and valence band spectra of clean Fe(100), Fe(111) and Fe(110) Iron single crystals Fe(100), Fe(111) and Fe(110) were reduced with a high-pressure autoclave H 2 -treatment to obtain clean surfaces. By increasing the pressure, the reduction was finished after 3 hours with temperature T = 600°C and pressure P = 50 bar. Typical contaminations present in Fe single crystals are C, O and S. Especially S contamination is hard to purge and usually requires week-long atmospheric pressure hydrogen treatments at high temperatures. In this work we show a fast method that achieves a deep removal of non-metal trace impurities of the Fe surface and bulk in under a day. The cleanliness of the single crystals was studied by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The cleaning procedure consisted of a high-pressure H 2 -treatment and subsequent sputtering and annealing in vacuum at ∼650°C to obtain clean LEED images. Clean (1 × 1) patterns were recorded for Fe(100), Fe(111) and Fe(110). Before undergoing high-pressure H 2 -treatment, impurities in Fe(100) and Fe(111) present faceted surfaces, whereas Fe(110) shows complex overstructures. Further confirmation for successful reduction is given by XPS results. Fe2p 3/2 is shown to be at 706.7 eV. Moreover, ultraviolet photoelectron spectroscopy (UPS) was employed for valence band and work function measurements.