In starch granule, although the molecular structures of amylose and amylopectin are almost becoming clear, their hierarchic structures in molecular level is stillunknown. Recently, a blocklet model that the starch granule consists of two kinds of blocklets with different size (∼500 nm and ∼50 nm) and crystallinity (hard and soft) was proposed, and the both sizes of blocklets have been observed by scanning electron microscopy (SEM). However, by atomic force microscopy (AFM), only the smaller size (∼50 nm) of blocklet has been detected. Thus, we developed a resin-embedded section method specific to starch granule observation. As a result, we successfully observed both the big blocklet and small blocklet were clearly observed in corn starch granules by AFM. Furthermore, we found a new structure with fibrous form (10∼12 nm in height) at a center of a granule, which might be a cluster structure of amylopectin molecule with a diameter of 10∼15 nm.
STM light emission (STML) has been shown to be a promising technique for nanometer scale analyses of electronic states of molecules on metals as the light emission due to the electronic transition between molecular levels is comparably intense with the plasmon induced light emission for noble metals. The energy forbidden light emission in the spectra observed for porphyrin molecules on Au has been discussed on the basis of strong coupling between molecules and plasmon field in STM nano-cavity. The substrate material dependence of plasmon enhancement is well reproduced by an electromagnetic calculation using the effective dielectric constant for the molecular film/substrate material.
Electrocatalytic properties of electrochemically deposited Pt ultra-thin films on Au single crystal electrode surfaces for oxygen reduction reaction (ORR) were investigated. Although it was reported that the order of activity of low index faces of the Pt single crystal electrodes increased in the sequence Pt(100) < Pt(111) < Pt(110), the order of activity of Pt ultra-thin films electrodeposited on the low index faces of the Au single crystal electrodes increased in the sequence Pt/Au(111) < Pt/Au(110) < Pt/Au(100), which was same trend of the Au single crystal substrates.
Self-assembly is a key process to assemble micro- and nanoscale objects into ordered macroscopic structures. Many studies have been conducted about formation process of self-assembled films and their electric properties using various materials. In recent, carbon nanotubes have been paid much attention because they exhibit attractive electronic, chemical and mechanical properties due to their quasi-one-dimensional structures. Remarkable feature of carbon nanotubes is that the physical properties are tuneable by controlling their fine structures. For this reason their assembled films are considered to be applicable to building biological sensors, chemical sensors, field-effect transistors and transparent conductive films in near future. Here we report self-assembly of pre-formed multiwalled carbon nanotubes (MWCNTs) into two-dimensional patterns without using pre-printing substrates. We found that the thickness of the self-assembled MWCNTs films is controllable by changing MWNCT density of suspension and base pressure during solvent evaporation. This result would help us to understand the assembly mechanism of asymmetric nanoscale materials.
The bonding and electronic configuration of double-decker single molecule magnets (SMM) LnPc2 (Ln = Tb(III) and Dy(III); Pc = phthalocyanine) and non-SMM YPc2 were measured using the cryogenic, UHV scanning tunneling microscope (STM) and scanning tunneling spectroscopy (STS). Two types of molecules were observed as isolated molecules on the Au(111) surface at 4.7 K; one has a shape of eight-lobe with a height of ∼400 pm and the other is four-lobe with a height of ∼140 pm. The former was assigned as a double decker molecule, while the latter was assigned as dissociated species of the molecule; i. e., MPc and Pc. The dI/dV mapping successfully distinguished MPc and Pc by detecting HOMO-1 and LUMO state, which are originated from the ligand Pc but enhanced only in the molecule of MPc.
In order to exactly analyze a crystal structure it is necessary to consider from two viewpoints of long range order (LRO) and short range order (SRO). The information on the reciprocal lattice which is obtained by electron diffraction or X-ray diffraction concerns mainly on the long range order. On the other hand, the images observed by STM (tunnel scanning microscopy) concern mainly with the short range order. For the analysis of the STM images, we must construct the structure which does not contradict to the diffraction patterns. We observe sometimes the streak reflections in LEED (low energy electron diffraction) and RHEED (reflection high energy electron diffraction) patterns taken from the surface structures. When such streak patterns appear, we are apt to deal with it as the case that the crystallinity is not good. There are actually such cases, but some cases suggest a deep meaning on the structure. In this paper, from the standpoint of diffraction theory, we consider the streak reflection patterns which were observed often in 5×2 (s)-Au surface structure formed on the Si(111) surface when Au atoms are deposited on the Si(111) surface. Since by coexisting with the streak reflections and the sharp diffraction points of 5 times structure in the pattern of this surface structure, it is the case of that we cannot simply neglect it by saying that the crystallinity is not good. When this diffraction pattern is examined in detail, an important hint of the structure is obtained which shows an intermediate state of one dimensional and two dimensional lattices. A suggested structure is that for one dimensional lattice of Au atoms (Au chain), the position of the neighboring chain is decided with a connection probability α. The calculation method of diffracted intensity of the streaks in the 5×2 (s)-Au structure is a typical example of diffraction theory and worthwhile to consider in details and instructive also to understand many other diffraction phenomena.
The electronic states of cobalt nano-islands on a nitrogen-saturated Cu(001) surface have been studied by soft X-ray emission spectroscopy and soft X-ray absorption spectroscopy. The L3 resonant X-ray emission spectrum was decomposed into two components; emission from nitrogen-adsorbed single-layer Co islands and that from more than double-layer islands. A narrower width and a lower binding energy of the former agrees with the 3d density of states calculated by a first-principles method for a nitrogen-adsorbed single-layer Co film on Cu(001). When the surface is covered with small nitrogen-adsorbed Co islands, a shoulder structure in L-edge absorption spectrum was observed at an energy ∼3 eV higher than the absorption edge. By considering the calculated unoccupied 3d states and X-ray photoelectron spectra, the shoulder was attributed to the correlation among 3d electrons. The perimeter Co atoms of the islands are assigned as the origins of the correlation satellite considering the surface morphology observed by scanning tunneling microscopy. The 3d band narrowing and enhanced correlation in the Co nano-islands are clearly demonstrated.
We have investigated magnetic properties of atomic wires of Ga-substituted Mn on the GaAs(110) surface using first-principles calculations based on the spin-density functional theory. Mn atomic wires are assumed to align along the <110>-, <001>-, and <211>-directions. The <110>-oriented wire is most stable energitically, and has the ferromagnetic ground state with the magnetic moment of 4.0 μB per Mn atom. The band structure has a large dispersion along the wire and exhibits a half-metallic state. The ferromagnetic character of the Mn wire results from the double exchange interaction through the p-d hybridization between the Mn-3d and the GaAs surface states.