D2 on Pd(110): Surface and subsurface phases, absolute coverages, and interconversion

Abstract

The adsorption of deuterium on Pd(110) has been studied by means of low‐energy electron diffraction, work function measurements (Δφ), thermal desorption spectroscopy, nuclear reaction analysis (NRA), and Rutherford backscattering (RBS). These measurements show that, upon D2 adsorption at low temperature, (2×1) and (1×2) phases are formed in sequence. The RBS data show that the (2×1) structure is unreconstructed, while the (1×2) is reconstructed, with an entire monolayer (ML) of Pd atoms displaced laterally from their bulklike locations by ≳0.01 nm. The NRA data demonstrate that depending on the method of preparation, the (2×1) phase can be associated with a total coverage of 1 or 1.5 ML, while the (1×2) phase can be produced with total coverages of 1.5 or 2 ML. The additional 0.5 ML, associated with the high coverage form of each phase, is due to subsurface adsorbed species.