Growth of Be2C(100) films on Be(0001) substrate using C60 as precursor

Abstract

Highly oriented crystalline beryllium carbide films were grown on Be͑0001͒ substrate using C 60 as a carbon source. The films were characterized by low energy electron diffraction, photoemission spectroscopy, and near-edge x-ray absorption fine structure. C 60 begins to decompose on Be͑0001͒ at about 250°C, forming beryllium carbide completely after further annealing to 450°C. The beryllium carbide film is observed as sets of ͑100͒ surfaces, arranged in three domains rotated by 120°from each other. Extra C 60 deposited on Be 2 C(100)/Be(0001) at temperature below 200°C and heated to 450°C leads to an increase of the film thickness, indicating the decomposition of C 60 on Be 2 C(100)/Be(0001) at an elevated temperature and formation of new carbide layers on the sample surface. It further implies that the Be 2 C/Be surface has the ability to supply Be atoms to interact with the new carbon atoms on top, and that Be atoms can diffuse through the beryllium carbide layer at the temperature of 450°C, possibly involving a vacancy mechanism.

Covalent bonding and hole–electron Coulomb interactionUin C60on Be(0001) surfaces

“…Hence the covalent bonding in C 60 /Be is stronger than that in C 60 /Al in which the first few satellite features remain [21], but nearer C 60 /Pt(111) [48,53]. We emphasize that the decomposition temperature of C 60 on Be surfaces between 200 and 250 • C is the least among the systems studied so far [44], consistent with strong covalent bonding [21].…”

“…The crystal was cleaned with cycles of sputtering with 1.5 keV Ar ions and annealing until a sharp LEED pattern was observed. A cleaning procedure was established to ensure that no measurable C and O contamination was observed from core-level photoemission [44]. The C 60 was evaporated from a resistively heated Ta evaporator.…”

“…A small rate of growth (5-20 min per layer) served to favour growth layer by layer. As the desorption temperature of multilayer C 60 (∼180 • C) [17] is near the decomposition temperature of C 60 on Be (between 200 and 250 • C) [44], the commonly used method to produce an ordered monolayer by annealing was inapplicable. No overlayer LEED pattern was observed, indicating a lack of long-range order.…”