Superstructures of Graphite Intercalation Compound Formed by Sodium-Hydroxide Solution Studied by Scanning Tunneling Microscopy

Highly oriented pyrolytic graphite (HOPG) treated with sodium hydroxide solution was found to show an X-ray diffraction pattern characteristic of a stage-8 intercalation compound. Superstructures such as 2 X 2, √3 X √3 and noble orthorhombic lattices were observed on the NaOH-treated graphite surfaces by scanning tunneling microscopy, as was previously observed on stage-1 alkali-metal graphite intercalation compound (GIC) surfaces formed by Li, K, Rb and Cs intercalates. The orthorhombic phase has a periodic structure formed by four bright and two dark rows, which were explained by the intercalant arrangement occupying two different sites, in the GIC

Exploring spin dynamics visualization and its application to new functional devices

科学研究費助成事業 研究成果報告書：基盤研究(S)2010-2014課題番号：2222600

Surface Charge-Density Wave on the One-Dimensional Organic Conductor β-(BEDT-TTF)2PF6

We performed STM and theoretical studies of the surface of β-(BEDT-TTF)2PF6 which is known to show a metal-insulator transition at 297 K with the nesting vector of Qbulk = a*+0.5c* as a bulk phase. Two typical charge-density wave (CDW) phases with QS1 = 0.13a*+0.26c* and QS2 = 0.19a*+0.20c* were observed at 285 K on the surface. The observed structures were correlated well with the analysis of the susceptibility χ(Q), given the incomplete surface-charge transfer in the polar surface of this material. This is the first observation of surface CDW phases that reflect the characteristics of the electronic structure. These results suggest the possible discovery of other surface properties, such as surface superconductivity, in organic materials with a polar surface

What Orchestrates the Self-Assembly of Glycine Molecules on Cu(100)?

The structures of two competing phases and their interrelationship in the self-organization of glycine molecules on a Cu(100) surface were clarified. Despite their similar structural energies predicted using first-principles calculation, completely different mechanisms were found to stabilize the two phases. The balance and coordination of the two mechanisms that induce a variety of self-assembled structures in this attractive system were revealed. Furthermore, the importance of the microscopic arrangement of the molecules in designing the macroscopic electronic structures was directly demonstrated

Next-Generation Time-Resolved Scanning Probe Microscopy

Understanding the nanoscale carrier dynamics induced by light excitation is the key to unlocking futuristic devices and innovative functionalities in advanced materials. Optical pump-probe scanning tunneling microscopy (OPP-STM) has opened a window to these phenomena. However, mastering the combination of ultrafast pulsed lasers with STM requires high expertise and effort. We have shattered this barrier and developed a compact OPP-STM system accessible to all. This system precisely controls laser pulse timing electrically and enables stable laser irradiation on sample surfaces. Furthermore, by applying this technique to atomic force microscopy (AFM), we have captured time-resolved force signals with an exceptionally high signal-to-noise ratio. Originating from the dipole-dipole interactions, these signals provide insights into the carrier dynamics on sample surfaces, which are activated by photo-illumination. These technologies are promising as powerful tools for exploring a wide range of photoinduced phenomena in conductive and insulating materials.Comment: 8 pages, 4 figure

p(2×2) Phase of Buckled Dimers of Si(100) Observed on n-Type Substrates below 40 K by Scanning Tunneling Microscopy

We have investigated the basic surface reconstruction of Si(100) on well defined surfaces fabricated on various substrates at low temperatures (-80  K) by scanning tunneling microscopy. Below 40 K, the single p(2×2) phase, a phase never observed before, was observed exclusively on n-type substrates doped in the range of 0.002 to 0.017  Ω cm. We also exclude the possibility of the (2×1) symmetric dimer commonly observed at low temperature (-10  K) being the basic surface reconstruction by showing that a buckled dimer can be flip-flopped by the tunneling tip

Phasons Formed on Si(100) Dimer Rows Observed by Scanning Tunneling Microscopy(STM-Si(100))

At～6K, dimers on Si(100) surface are buckled, and structural change occurs between c(4x2) and p(2x2) arrangements due to dimer flip-flop motion at phase boundaries on dimer rows. The phase defect appearing at boundaries has a structure similar to that of the type-C defect, two adjacent dimers are buckled in the same orientation. In consideration of the dimer arrangement around the phase boundary, there exist structures with two different conformations for the phase defect, however, according to the Ising spin model, both of which have the same energy higher compared to other buckled dimers with 2x anticorrelation along a dimer row. Therefore, dimer flip-flop motion at a phase boundary results in the migration of a solitary phase defect with higher energy, as a phason