Jun Nogami

Nanopatterns at near atomic dimensions with controllable quantum dot states (QDSs) are promising candidates for the continued downscaling of electronic devices. Herein, we report a phase transition-induced QD system achieved on the root 3 x root 3-Bi/Si(111) surface reconstruction, which points the way to a novel strategy on QDS implementation. Combining scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory (DFT) calculations, the structure, energy dispersion, and size effect on band gap of the QDs are measured and verified. As-created QDs can be manipulated with a dot size down to 2 nm via Bi phase transformation, which, in turn, is triggered by thermal annealing at 700 K. The transition mechanism is also supported by our DFT calculations, and an empirical analytical model is developed to predict the transformation kinetics.

Discovery of a -Pb/Bi/Si(111) surface reconstruction with sizable Rashba spin splitting and achievable quantum well states.

Ultra-thin CsBr overlayers on the Ag (111) surface have been grown using physical vapor deposition and studied by scanning tunneling microscopy. Atomically resolved images of CsBr show the formation of the NaCl crystal structure rather than the bulk structure of CsBr, i.e., CsCl, in the first two atomic layers. The structure remains the same up to five monolayers, the maximum layer thickness being studied. Mobility of CsBr islands up to 1.1 nm thickness has been observed at room temperature. CsBr is one of the binary constituents for the growth of CsPbBr3 perovskites. Exploring the growth of CsBr on Ag (111) will provide reference information for the better understanding of the growth of CsPbBr3 perovskite thin films under similar growth conditions.

We examined the dynamics of adsorption and the subsequent growth of submonolayered silver on Si(001) from 100 K to 230 K, using scanning tunneling microscopy and density functional theory. The dynamics is demonstrated to depend on substrate temperature, as described in the following three stages: (I) at 100–140 K, silver is adsorbed as isolated aggregates (regular-Ag₄, variant-Ag₄ and Ag₂), in the absence of single silver adatoms. The spontaneous formation of silver aggregates arises from the hot-atom motion upon the initial impingement of individual silver atoms onto the Si(001) substrate. (II) At 140–190 K, the migration of isolated Ag-aggregates is sufficiently activated, leading to the formation of Ag-chains by surface polymerization. (III) At 190–230 K, there is implication that the Ag-chains become mobile on Si(001), en route to forming patches of 2×2 Ag-films by agglomeration.

The design of low dimensional materials through surface assisted self-assembly requires a better understanding of the factors that limit and control surface diffusion. We reveal how substrate surface defects hinder the mobility of sub-monolayer organic adsorbates on a metal surface with the model CuPc/Cu(111) system. Post-deposition annealing bonds CuPc molecules into dendritelike clusters that are often mobile at room temperature. Surface defects on Cu(111) create energetic barriers that prevent CuPc cluster motion on the metal surface. This phenomenon was unveiled by the motion of small clusters that show rigid-body diffusion solely in the available space in between defects. When clusters are sufficiently surrounded by defects, they become completely pinned in place and become immobilized.

The design of low dimensional materials through surface assisted self-assembly requires a better understanding of the factors that limit and control surface diffusion. We reveal how substrate surface defects hinder the mobility of submonolayer organic adsorbates on a metal surface with the model CuPc/Cu(111) system. Postdeposition annealing bonds CuPc molecules into dendritelike clusters that are often mobile at room temperature. Surface defects on Cu(111) create energetic barriers that prevent CuPc cluster motion on the metal surface. This phenomenon was unveiled by the motion of small clusters that show rigid-body diffusion solely in the available space in between defects. When clusters are sufficiently surrounded by defects, they become completely pinned in place and become immobilized.

We describe the atomic structure of the silver film grown on Si(001) at room temperature, as studied by low-temperature scanning tunneling microscopy and density functional theory. Experiment and theory agree on a film structure in which Ag-tetramers are identified for the first time. Ag-tetramers are found to be adsorbed exclusively at the trough between two Si-rows, interacting with four adjacent Si-dimers via covalent bonding. Consequently, the π-bonds of the Si-dimers underneath the silver film are eliminated.