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The interaction between K atoms and oxygen molecules on solid surfaces is of topical interest to oxidation–reduction processes in K–O2 batteries. Alkali metals have one ns electron in their valence shell, making them highly chemically reactive toward oxidizing reactants. Mechanistic information on the oxygen reduction by K at the atomic level is scarce despite its key role in defining the alkali metal–O2 battery performance. Here, we use scanning tunneling microscopy and density functional theory to investigate the reduction of a single oxygen molecule by K atoms codeposited on the Ag(111) surface. Our study provides fundamental chemical information on the binary and collective interactions between the O2 and K atoms on metal surfaces. 

Surface Plasmon Polariton (SPP), as a novel information carrier, offers unprecedented opportunity for confining electromagnetic fields that carry orbital angular momentum (OAM) to subwavelength dimensions. In this thesis, I focus experimentally on the generation, manipulation, and spatio-temporal evolution—and theoretically on the analytical modeling—of plasmonic phase singularities, known as plasmonic vortices, at the silver (Ag)/vacuum interface. I image and study the dynamics of plasmonic vortices by interferometric time-resolved multi-photon photoemission electron microscopy (ITR-mP-PEEM). Firstly, I report on the generation, evolution, and topological properties of plasmonic vortices carrying pure geometrically induced orbital angular momentum (OAM), generated by illuminating Archimedean spiral coupling structures with normally incident, linearly polarized light. Next, I present an analytical model describing the generation and evolution of these plasmonic vortices, and based on this model, I further analyze their spatial structure and dynamics. I also derived the spin angular momentum (SAM) of plasmonic vortices, whose textures reveal transient plasmonic spin-Skyrmion topological quasiparticles. In parallel, I also record images of plasmonic vectoral vortex field evolution on the nanometer spatial and femtosecond temporal scale, from which I derive the plasmonic spin Skyrmion boundary and topological charge. The excellent agreement between analytical model and experimental results confirms the topological spin texture at surface plasmon polariton vortex core. To extend the understanding of ITR-PEEM imaging, I perform a simple experiment withv double line coupling structure at the silver/vacuum interface, which reveals an asymmetric cross term between the different components of the SPP field that also appear in the ITR-PEEM imaging. Finally, I approach a novel method to manipulate momentum transport between two plasmonic vortices analytically and experimentally. By tuning the relative distance between two vortex generator structures with same sign and sign of the geometric charge, a conveyor belt-like field could be observed at the center of the device, which can be applied to transport the field, momentum, and energy between two plasmonic vortices. 

We apply ultrafast nanoscale microscopic imaging and analytical modeling to investigate the coherent field and spin textures of dual plasmonic vortices as a means to design the momentum flow, and spin topology by interaction of their gyrating fields. The ultrafast laser normal incidence illumination by circularly polarized light of two vortex generator structures with variable separations in silver films launches structured surface plasmon polariton fields. Two distinct primary vortices and a third emergent vortex, generated by interaction of the primary vortices and tunable by design of their separation, form through the spin–orbit interaction of light. The gyration of plasmon fields and the consequent vectorial Poynting momentum flow is imaged with sub-optical cycle phase and spatial resolution by interferometric time-resolved two-photon photoemission electron microscopy (ITR-2P-PEEM). The ultrafast imaging and analytical modeling of the interaction of the dual plasmonic vortices examines the nanoscale control of plasmon spin topology and momentum driven transport. 

Molecular constructs define the elementary units in porous materials for efficient CO2 capture. The design of appropriate interpore and intermolecular space is crucial to stabilize CO2 molecules and maximize the capacity. While the molecular construct usually has a fixed dimension, whether its intermolecular space could be self-adjustable during CO2 capture and release, behaving as a balloon, has captured imagination. Here we report a flexible intermolecular space of the double chain structure of self-assembled 1,4-phenylene diisocyanide (PDI) molecules on Ag(110) surface, which dynamically broadens and recovers during the CO2 capture and release. The incipient PDI double chains organize along the [001] direction of Ag(110), in which individual PDI molecules stand up in a zigzag order with the interchain width defined by twice the Ag lattice distance along [11¯0] direction (2α[11¯0]). When CO2 molecules are introduced, they assemble to occupy the interchain spaces, expanding the interchain width to 3α[11¯0], 4α[11¯0] and 5α[11¯0]. Warming up the sample leads to the thermally-driven CO2 desorption that recovers the original interchain space. High-resolution scanning tunneling microscopy (STM) jointly with density functional theory (DFT) calculations determine the structural and electronic interactions of CO2 molecules with the dynamical PDI structures, providing a molecular-level perspective for the design of a self-adjustable metal-organic construct for reversible gas capture and release. 

By frequency-time spectroscopy, microscopy, and electronic structure theory, we investigate the low coverage adsorption and electronic structure of Ca on an Ag(111) surface. The chemisorption of alkaline-earth Ca atoms starting from their closed 4s2 shell electronic configuration differs from that of the open ns1 shell alkali-metal atoms because they retain some 4s electron charge and can involve hybridization with low-lying unoccupied 3d orbitals. Spectroscopic investigation of the unoccupied electronic structure of Ca on Ag(111) by three-photon photoemission (3PP) reveals the electronic states with dominant 3d-orbital character, as confirmed by electronic structure theory. Coverage-specific spectral features enable attribution to two distinct chemisorption phases at submonolayer coverages, which are confirmed at the atomic scale by scanning tunneling microscopy and spectroscopy measurements. Furthermore, time-resolved 3PP spectroscopy reveals a resonant two-photon transition between occupied (∼−0.3 eV) and unoccupied (∼2.7 eV) states with dominant s- and d-orbital character. Interferometric time-resolved measurements probing this resonance reveal a dephasing time of ∼21 fs and population lifetime of ∼52 fs for the transiently populated d-like state at ∼2.7 eV above EF . Contrary to alkali-metal atom chemisorption, the characteristic development of the chemisorption and electronic structure of Ca reveals the importance of Ca adsorbate and Ag substrate interactions that cause a low-coverage atomic condensation into compact islands. Discovery of the long-lived d-character state informs on the catalytic and optoelectronic applications of the alkaline-earth element Ca.