Orientation–free and differentially pumped addition of a low-flux reactive gas beam to a surface analysis system

Abstract

We describe an example of a piecewise gas chamber that can be customized to incorporate a low flux of gas-phase radicals with an existing surface analysis chamber for in situ and stepwise gas-surface interaction experiments without any constraint in orientation. The piecewise nature of this gas chamber provides complete angular freedom and easy alignment and does not require any modification of the existing surface analysis chamber. In addition, the entire gas-surface system is readily differentially pumped with the surface chamber kept under ultra-high-vacuum during the gas-surface measurements. This new design also allows not only straightforward reconstruction to accommodate the orientation of different surface chambers but also for the addition of other desired features, such as an additional pump to the current configuration. Stepwise interaction between atomic oxygen and a highly ordered pyrolytic graphite surface was chosen to test the effectiveness of this design, and the site-dependent O-atom chemisorption and clustering on the graphite surface were resolved by a scanning tunneling microscope in the nm-scale. X-ray photoelectron spectroscopy was used to further confirm the identity of the chemisorbed species on the graphite surface as oxygen.

Spatially Resolved Modification of Graphene’s Band Structure by Surface Oxygen Atoms

“…Gas–surface interaction experiments were performed on chemically vapor deposited (CVD) monolayer graphene supported on copper foil (Graphenea Inc.., with >95% coverage) samples that had been annealed under UHV condition at a mild temperature of ∼600 K for about 6 h. Pt 0.8 /Ir 0.2 tips (Nanoscience Instruments) were used after being either mechanically cut or electrochemically etched. A beam of low-flux oxygen atoms was produced using a gas cracker with an Ir capillary tube and an Ir filament (Mantis Deposition) and was directly aligned to the STM tip–sample junction . We typically avoided graphene on top of noncrystalline copper surfaces that were difficult for high-resolution characterizations, and all STM and STS measurements were conducted on top of crystalline Cu substrate areas at room temperature.…”

“…Using a UHV STM and a low-flux gas beam of atomic oxygen, we report that the graphene band structure can be immediately altered with an extremely low surface O-atom coverage. Our STM images indicate that, at this low coverage (with a O/C ratio of ∼1/150), O-atoms distribute themselves randomly, instead of evenly, on graphene.…”