We have studied the hydrogenation of germanene synthesized on Ge2Pt crystals using scanning tunneling microscopy and spectroscopy. The germanene honeycomb lattice is buckled and consists of two hexagonal sub-lattices that are slightly displaced with respect to each other. The hydrogen atoms adsorb exclusively on the Ge atoms of the upward buckled hexagonal sub-lattice. At a hydrogen exposure of about 100 L, the (1 × 1) buckled honeycomb structure of germanene converts to a (2 × 2) structure. Scanning tunneling spectra recorded on this (2 × 2) structure reveal the opening of a bandgap of about 0.2 eV. A fully (half) hydrogenated germanene surface is obtained after an exposure of about 9000 L hydrogen. The hydrogenated germanene, also referred to as germanane, has a sizeable bandgap of about 0.5 eV and is slightly n-type.
We have studied the
dynamic behavior of decanethiol and air-oxidized
decanethiol self-assembled monolayers (SAMs) on Au(111) using time-resolved
scanning tunneling microscopy at room temperature. The air-oxidized
decanethiols arrange in a lamellae-like structure leaving the herringbone
reconstruction of the Au(111) surface intact, indicating a rather
weak interaction between the molecules and the surface. Successive
STM images show that the air-oxidized molecules are structurally more
stable as compared to the nonoxidized decanethiol molecules. This
is further confirmed by performing current–time traces with
the feedback loop disabled at different locations and at different
molecular phases. Density function theory calculations reveal that
the diffusion barrier of the physisorbed oxidized decanethiol molecule
on Au(111) is about 100 meV higher than the diffusion barrier of a
chemisorbed Au-decanethiol complex on Au(111). A two-dimensional activity
map of individual current–time traces performed on the air-oxidized
decanethiol phase reveals that all the dynamic events take place within
the vacancy lines between the air-oxidized decanethiols. These results
reveal that the oxidation of thiols provides a pathway to produce
more robust and stable self-assembled monolayers at ambient conditions.
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