The influence of the ion exchange on the atomic-scale structure of clay mineral surface has not been revealed. We conducted the observation of the montmorillonite surface by frequency modulation atomic force microscopy (FM-AFM) in order to compare the atomic-scale change of the montmorillonite surfaces before and after the cation exchange. The sodium ions of natural montmorillonite were exchanged by ammonium and alminium ions before experiment. The montmorillonite surfaces after the cation exchange showed the hexagonal pattern corresponding with the natural montmorillonite. No lattice vacancy was observed, whereas the vacancies should be formed after the cation exchange. It suggests that the lattice vacancies were filled with the water molecules. Our method will lead to in situ observation of the replacement of the ions. We believe that the atomic-scale observation will provide the deeper understanding of the ion exchange property of clay minerals.
We performed spin-polarized scanning tunneling microscopy and spectroscopy measurements on a double layer (DL) Mn film formed on a W(110) substrate, which has a complicated spin arrangement called a conical spin spiral structure. As a spin-polarized tip for this study, we use a bulk Cr tip that can be made relatively easily and maintains the spin polarization longer than conventional magnetic thin film coated W tips do. We successfully observed images with a striped pattern on the Mn DL, which is attributed to the previously reported spin structure. The tunneling conductance measurements with non-spin polarized and spin polarized tips clarify the electronic structure and the strong spin polarization around the Fermi level of the Mn DL, respectively.
We studied low-energy (∼1.5keV) spin-polarized 4He+ ion scattering on Bi(111) ultrathin films epitaxially grown on a Si(111) substrate. Even though Bi is a non-magnetic element, we observed that the scattered ion intensity differed between the incident He+ ions with up and down spins, i.e., a spin asymmetric scattering. The spin asymmetry was not affected by the surface structure but depended on the scattering angle and the incident energy. These data indicate that the spin asymmetry originates from the spin-orbit coupling that acts transiently on the He+ 1s electron spin in the binary collision and the resonant electron transfer between 4He+ ions and Bi electronic orbitals possibly alters the behavior of the spin asymmetry compared to established models.
We have performed spin- and angle-resolved photoemission spectroscopy of Bi islands on a silicon substrate and found the metallic one-dimensional (1D) edge states with unexpectedly large Rashba-type spin-orbit coupling. This result is the first experimental demonstration that directly determines the purely 1D band structure. We have also found a sizable in-plane and out-of-plane spin polarization of the 1D edge state, consistent with our first-principles band-calculations. Our result provides a new platform to understand novel quantum phenomena at the edge of the strong spin-orbit-coupling systems.
Hot carrier dynamics in the Dirac band of n-type epitaxial graphene on a SiC substrate were traced in real time using femtosecond-time-resolved photoemission spectroscopy. The spectral evolution directly reflects the energetically linear density of states superimposed with a Fermi-Dirac distribution. The transient variation of electronic temperature, reflecting that of carrier distribution, was successfully defined by spectral fitting, and the observed electronic temperature may indicate the occurrence of cascade carrier multiplication.
We investigated the substrate-dependence of bioinertness of self-assembled monolayers of methoxy-tri (ethylene glycol)-terminated alkanethiol (EG3-OMe SAMs). Our surface force measurements revealed that strong water-induced repulsion operated between bioinert Au-supported EG3-OMe SAM. In contrast, there was no such repulsion observed for a bio-adhering Ag-supported EG3-OMe SAM. Surface-enhanced infrared absorption spectra showed that state of hydrogen bondings between interfacial water molecules near the EG3-OMe SAMs are different depending on the substrates. These results clearly indicate that interfacial water plays a key role in the bioinertness of the SAMs.