Hydrogen-induced atomic structure evolution of the oxygen-chemisorbed Cu(110) surface

Revealing an Intermediate Cu-O/OH Superstructure on Cu(110)

Identifying the atomic structure and formation mechanism of intermediates during chemical transformations is challenging because of their short-lived nature. With a combination of microscopic and spectroscopic measurements and first-principles calculations, herein we report the formation of a metastable intermediate Cu-O/OH superstructure during the reaction of hydrogen with oxygen-covered Cu(110). This superstructure resembles the parent c(6 × 2)-O phase and can be termed as c(6 × 2)-(4O+2OH) with OH groups occupying the missing Cu sites between isolated Cu atoms. Using atomistic calculations, we elucidate the reaction pathways leading to the c(6 × 2)-(4O+2OH) formation via both molecular and dissociative H₂ adsorption. These results demonstrate the complex surface dynamics resulting from the parallel reaction pathways and may open up the possibility of directing the reaction dynamics by deliberately manipulating transient surface structure and composition.

Tuning the surface composition of Cu3Au binary alloy

Using ambient-pressure X-ray photoelectron spectroscopy, here we report the real-time monitoring of dynamic surface composition evolution of Cu₃Au(100) in response to the imposed environmental stimuli. Segregation of Au to the pristine surface under ultrahigh vacuum annealing leads to the phase separation with pure Au at the surface and alloyed Au in the subsurface. Upon switching to an oxidizing atmosphere, oxygen adsorption drives the surface segregation of Cu along with inward migration of pure Au to the subsurface. Switching to a H₂ atmosphere results in oxygen loss from the oxygenated surface, thereby promoting Au surface segregation and reverting the surface to the pristine state with the Au termination. These measurements demonstrated the tunability of the surface composition of the binary alloy by utilizing the interplay between the tendency of segregating a more noble constituent to the surface and the tendency to segregate the more reactive one with the chemical stimuli.

In situ atomic-scale observation of inhomogeneous oxide reduction

We report in situ atomic-scale transmission electron microscopy observations of the surface dynamics during Cu2O reduction. We show inhomogeneous oxide reduction caused by the preferential adsorption of hydrogen at step edges that induces oxygen loss and destabilizes Cu atoms within the step edge, thereby resulting in the retraction motion of atomic steps at the oxide surface.

Unexpected refacetting of palladium nanoparticles under atmospheric N2 conditions

In situ TEM observations and DFT calculations reveal that the “inert” gas N₂ has the ability to modify the structure of metal nanoparticles.