Seiji Isoda

3,4:9,10-Perylenetetracarboxylic dianhydride (PTCDA) by electron crystallography

The crystal structures of the alpha and beta modifications of PTCDA were analyzed as projected structures along the a axes by electron crystallography using an imaging plate. The results for the alpha modification agree well with the sheet-and-stack structure obtained by X-ray diffraction by M. L. Kaplan et al. (private communication, full set of crystal structure data). Projected onto the (102) plane, which is parallel to the molecular sheets, the long molecular axis makes an angle of 42 degrees with the b axis and the hexagonal benzene rings appear slightly elongated, indicating a slight inclination of the molecular plane from the (102) lattice plane. For the beta modification, it was concluded that the molecules are aligned in a herringbone packing scheme on the (102) plane similar to that of the alpha modification, but with a slightly different angle of the long molecular axis with the b axis (38 degrees ).

Point-on-line coincidence in epitaxial growth of CuPcCl16 on graphite

Abstract Epitaxial growth of perchloro-copper-phthalocyanine (CuPcCl 16 ) on graphite was studied by STM and TEM. The crystals grew epitaxially with two slightly different orientations on the graphite surface. The corresponding orientations were also observed in a monolayer of CuPcCl 16 by STM. By detailed analysis of the moire-like pattern in the STM images, these orientations are interpreted as being consistent with a ‘point-on-line coincidence’ epitaxy. In order to realize the exact point-on-line coincidence for the respective orientation, the unit cell dimensions of the monolayer were slightly distorted at each orientation, although they are almost the same as the monoclinic structure of the thin film determined by TEM.

Structures of germanium and silicon phthalocyanine thin films: polymorphism and isomorphism

The polymorphism and isomorphism of Ge(OH)2Pc and Si(OH)2Pc (Pc: phthalocyanine ligand) are reported as well as those of the polymeric molecules of (GeOPc)n and (SiOPc)n. The polymeric Pcs were produced through dehydration polymerization by heating the respective monomer of Ge(OH)2Pc or Si(OH)2Pc. We also report the thin film structures of these phthalocyanine derivatives and discuss the similarities and differences in the structures formed by vacuum deposition, in relation to the coordinating metal species.

Molecular Orientation of Perfluoro-vanadyl-phthalocyanine Examined by Electron Energy Loss Spectroscopy

A polymorph of perfluoro-vanadyl-phthalocyanine was found to be formed epitaxially on a potassium iodide monocrystalline surface by vacuum deposition. The molecular orientation and molecular packing of the polymorph were analysed by a combination of several electron microscopic methods, namely electron diffraction, high-resolution imaging and electron energy loss spectroscopy. The polymorph is different from the tetragonal polymorph previously obtained on potassium chloride and potassium bromide single crystals. The molecular packing of the new polymorph on potassium iodide was found to be orthorhombic with a = 1.48 nm, b = 0.37 nm and c = 27 nm, the ab-plane being parallel to the substrate surface.

Monolayer epitaxy of a triangular molecule on graphite

Abstract 2,4,6-Tris(1,3-dithiol-2-ylidene)-1,3,5-cyclohexanetrione (C15xa0H6xa0O3xa0S6, abbreviated TDTCHTO) has a shape of triangular propeller-like structure, and is known to crystallize as an orthorhombic structure (orthorhombic-I) by solution-growth process. In this study, monolayer of TDTCHTO was grown on a graphite (0xa00xa01) surface by vacuum-deposition, and was studied on its structure and epitaxy by STM. The observed two-dimensional lattice of TDTCHTO monolayer is hexagonal with a=1.77xa0nm, in which the two molecules stack with their triangular molecular planes parallel onto the graphite surface. As a result, the monolayer of TDTCHTO forms a different layer structure from the known orthorhombic structure, and therefore the molecular packing with hexagonal symmetry may be promoted by the symmetry of graphite surface. From the STM observation, the epitaxy is concluded as commensurate, not point-on-line coincidence, which means that an interaction between TDTCHTO and graphite is stronger comparing with side-by-side intermolecular interaction in the monolayer. The a-axis of the monolayer TDTCHTO makes an angle of 14° with the a-axis of graphite, and every molecule is coordinated on equivalent lattice point of graphite. This monolayer structure is discussed in relation with the orthorhombic-II observed with TEM for a thicker film grown on graphite.

Structure analysis of C60 low-temperature phase by electron crystallography with cryo-TEM

The crystal structure of C60 at liquid helium temperature was examined by the electron diffraction method using an imaging plate and cryo-TEM (transmission electron microscopy). The crystal of C60 was so thin that the electron scattering from this sample was able to be treated kinematically. However, the least-squares fitting among observed and kinematically calculated diffraction intensities resulted in an R-factor of 0.23 for a structure model with only one major orientation. Similar large R-factors are usually reported in the electron crystallography of thin crystals, in which a single perfect structure was assumed as a model structure. By considering structural disorders in the C60 crystal, however, the R-factor could be reduced to 0.12, when a minor crystal in a different orientation and also the f.c.c. (face-centered cubic) component were introduced to the model in addition to the major orientation crystal. Disorder in the crystal might be as important a factor as the dynamical scattering effect to be considered in electron crystallography for analyzing structures of thin crystals.

Simulation of Long-Range Contrast Modulation in Scanning Tunneling Microscope Image of Perylene-3,4,9,10-Tetracarboxylic-Dianhydride Monolayer on Graphite

In order to simulate the scanning tunneling microscope (STM) image of perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) on graphite, we calculated the partial electron density, which is proportional to the tunneling current, by the extended Huckel tight binding method. The typical STM images of PTCDA have two characteristic features: (i) long-range contrast modulation caused by point-on-line coincidence and (ii) contrast difference due to molecular orientation with respect to the graphite substrate. Using the present simulation, these features can be reproduced from the expected geometrical relationship between PTCDA and graphite.

Selective on-top crystal nucleation in organic multilayer formation

Abstract Structure and epitaxy of double-layered heterostructure of organic materials formed on four kinds of alkali halides were investigated. These films were fabricated by vacuum deposition. Crystallographic orientation and mutual registration of organic double layers were examined by transmission electron microscopy(TEM) and atomic force microscopy(AFM). As concluded from these observations, we found three kinds of growth modes as for the second layers depending on the combination of materials. Selective on-top growth, one of the growth modes, is important phenomenon for fabrication of organicsuperlattice. Such selectivity originates not only in lattice matching between the two layers, but also in surface topography of the layers.

Structural aspects of reversible control of optical activities of bis(dimethylglyoximato)platinum(II) thin film

Abstract By iodine doping, the structure of Pt(dmg)2 is changed from the orthorhombic with one-dimensional metal chain to an amorphous-like state, which means that the doping induces fluctuation of metal-metal distance along the chain axis. This structural change is reversible; that is, the amorphous state turns back to the orthorhombic crystal by heating at 130°C, corresponding to the reversible change in optical properties.