Michio Ashida

Molecular orientation of vacuum‐deposited thin films of zincnaphthalocyanine

Zinc 2,3‐naphthalocyanine (ZnNc) was vacuum evaporated onto glass, NaCl, and highly oriented pyrolytic graphite (HOPG) substrates, and the molecular orientation was investigated by x‐ray‐diffraction, Fourier‐transform‐infrared–reflection‐absorption spectroscopy, electronic spectroscopy, transmission electron microscopy, and scanning electron microscopy observations. Three types of molecular orientations were assigned for the deposited thin films depending on the different substrates kept at 250 °C. ZnNc molecules deposited on glass formed columnar crystals taking N orientation, in which molecular planes oriented perpendicularly to the substrate surface. Unidirectional epitaxic growth was observed in the film deposited on NaCl. ZnNc molecules seemed to be stacked in parallel having P orientation, where the molecular planes were parallel to the NaCl(001) surface. The ZnNc square lattice made an angle of 45° to the NaCl[100] direction (4×4‐type orientation). The film deposited on HOPG exhibited I orientation...

Epitaxial growth of naphthalocyanine thin films vacuum deposited on alkali halides

Epitaxial thin films of naphthalocyanines (Nc’s) were prepared on the (001) surface of alkali halide (AX) by a vacuum‐deposition technique. Two types of molecular stacking and orientation were found depending on the molecular structure. Metal‐free Nc(H2Nc) and divalent zinc Nc(ZnNc) took the face‐to‐face, eclipsed stacking, P orientation, in which their molecular planes came into a parallel contact to the substrate surface. Trivalent chloroaluminum Nc(AlNcCl) and fluorogallium Nc(GaNcF), and tetravalent vanadyl Nc(VONc) took the eclipsed, slipped stacking, I orientation, holding their molecular planes slightly inclined to the substrate surface. In the latter orientation an unexpected face‐to‐face stacking caused a stacking defect structure. The tetragonal lattice of the Nc crystals demonstrated five types of commensurate matchings to the ionic lattice of AX, depending on the lattice parameters of the Nc and AX crystals. On NaCl unidirectional AX(001)(4×4)R+45°‐Nc was a predominant orientation, and on KCl ...

Semiconducting Behavior of Substituted Tetra‐azaporphyrin Thin Films in Photoelectrochemical Cells

Phthalocyanines are well-known organic semiconductors and have attracted interest in application to electrophotography, chemical sensors, and solar energy conversion. Photoelectrochemical properties of zinc(II) and copper(II) complexes of (1) phthalocyanine, (2) tetrapyrido [2,3-b;2[prime],3[prime]-g;2[double prime],3[double prime]-1;2[prime][double prime],3[prime][double prime]-q]-5,10,15,20-tetra-azaporphyrin, and (3) tetrapyrazino[b;g;1;q]-5,10,15,20-tetra-azaporphyrin, were investigated in thin-film electrodes prepared by vacuum deposition (VD), drop-casting (DC) and in situ synthesis (IS). The opposing behavior, photoreduction at electrodes of 1 and photo-oxidation at electrodes of 2 and 3, are discussed in terms of a band-energy shift of tetra-azaporphyrin macrocycles caused by substitution with heterocyclic pyrido and pyrazino groups. The photoelectrochemical efficiency of the electrodes is strongly affected by the film morphology which is dependent on the preparation methods, and increased in order of DC

ELECTRICAL AND PHOTOCONDUCTIVE PROPERTIES OF ORIENTATION-CONTROLLED CHLOROALUMINUMPHTHALOCYANINE THIN FILMS

Structure dependence of electrical properties was investigated for amorphous and epitaxial thin films of chloroaluminumphthalocyanine vacuum deposited on both glass and KCl. The extrinsic conductivity in the dark was improved by elevating substrate temperatures, depending on the morphological change from granular, discontinuous films deposited at a substrate temperature of 25 °C to uniform, continuous ones at 250 °C. The photocurrents under monochromatic light illumination increased in proportion to the amount of adsorbed O2 in the amorphous films on glass. A regular doping form of O2 in the epitaxial film on KCl could enhance photocarrier generation. The granular, discontinuous morphology in the films caused a frequent charge‐carrier recombination at the grain boundaries and defect sites. In the intrinsic region the amorphous films exhibited a higher dark conductivity due to the π‐electron interaction between the randomly arranged molecules and gave a moderate activation energy for conduction. The epitax...

Crystal growth of tetraphenylporphyrin thin films

The crystal growth and the orientation of thin films of 5,10,15,20-tetraphenylporphyrin (H 2 TPP) vacuum-evaporated onto substrates of a KCl (001) surface and a semitransparent A1 electrode film have been investigated by electron microscopy and electron diffraction. The films deposited on a KCI (001) surface show epitaxial growth in which the crystals take a four-directional orientation, and the molecular plane of HzTPP stands perpendicular to the substrate surface. The H 2 TPP crystals with a morphology of rectangular islands grow on the KCI surface kept at 200 ° C, while a continuous thin film totally covers the KCI surface kept at 20 ° C with an identical epitaxial orientation. When H 2 TPP is deposited on a KCI (001) surface coated partially with a small number of Al particles, the crystals take the same orientation. This epitaxial orientation decreases with increasing the coverage of the A1 particles on the KCI surface, and the H 2 TPP film deposited on a semitransparent A1 film shows a random orientation of needle-like crystals. The growth of the thin film with oriented crystals depends on the electrostatic interaction of the H 2 TPP molecules with ionic charges on the KCI surface.

Epitaxial growth of 2,5-distyrylpyrazine from the vapor phase

Abstract 2,5-Distyrylpyrazine (DSP) was evaporated onto a cleavage face of KCl crystal in vacuo. The DSP film vacuum-evaporated on the KCl substrate without heat treatment was composed of randomly-oriented laminate and needle-like crystallites of α-form. When the substrate was heated at 150°C before vacuum evaporation and kept at 30°C during deposition, the DSP film was composed of slender needle-like crystallites of γ-form and flaky crystallites of α-form. The longitudinal direction of the γ-form crystals was aligned along the [100] and [010] directions of the KCl substrate. The faces of the α-form crystals made an angle of 10° with respect to the [100] and [010] directions of the KCl substrate. At the substrate temperature of 70°C, the DSP film grew epitaxially on the substrate to form thin plate-shaped crystals of γ-form. The DSP molecule took three kinds of orientations on the KCl substrate depending on the evaporation conditions: (100) α-form ∥(001) KCl , (010) α-form ∥ (001) KCl and [100] γ-form ⊥(001) KC l . These orientations are discussed in terms of the dehydroxylation of the KCl surface caused by the thermal treatment and of the adsorption energy of the DSP molecules.

Crystal growth of octacyanometalphthalocyanine-metal complexes in thin films

Abstract Octacyanometalphthalocyanine-metal complex (MPc(CN) 8 −M, M = Cu, Ni, Co, Fe, Zn and K 2 Pc(CN) 8 − K ) crystals were synthesized by vapor-solid reaction of tetracyanobenzene (TCNB) with metal films and a KCl crystal. Their crystal growth was investigated by electron microscopy. The crystal morphology depended on reaction temperature, pressure and kinds of substrate. Crystals of MPc(CN) 8 −M and K 2 Pc(CN) 8 −K grew long and thick, tentacle-like, on polycrystal metal films and on a KCl (001) surface at the reaction temperature of 350°C. Growth of the crystals was inactive at reaction temperatures below 300°C. Crystal defects such as bends and folds increased with rising reaction pressure. The growth mechanism was assumed as follows: MPc(CN) 8 molecules are formed on a substrate metal by tetramerization of TCNB vapor, and peripheral nitrile groups of MPc(CN) 8 molecules coordinate to metal atoms of the substrate to form a MPc(CN) 8 − M complex. MPc(CN) 8 molecules are piled up in parallel to form a column structure and the complex crystal grows by diffusion of metal atoms from the substrate. The crystal growth is well-defined when metal atoms are supplied sufficiently from the substrate.

Polymerization to graphite‐like nitride clusters from tetracyanoethylene vapor

Various types of graphite‐like nitride clusters were synthesized by chemical vapor deposition of tetracyanoethylene (TCE) onto a substrate of cleaved KCl crystals at 230–300 °C. At a low reaction temperature of 230 °C, TCE was polymerized to ribbon‐like clusters, which resembled curved graphitic sheets. Upon increasing the reaction temperature to 250–300 °C, polymerized TCE condensed on KCl to form spheric clusters. The most regular structure of the clusters was obtained at 300 °C in a nanoscale needle‐like morphology. High‐resolution electron microscopy suggested that these clusters were composed of polymerized TCE layers with a interlayer distance of 0.34–0.35 nm.

Direct observation of the secondary structure of unfolded pseudomonas-cytochrome c551 by scanning tunneling microscopy

Abstract The denaturation of pseudomonas-cytochrome c 551 at the air-water interface was studied using scanning tunneling microscopy (STM). The STM images indicate that the native secondary and tertiary structures of this protein has been virtually lost at such interface. The polypeptide chains of the unfolded protein are nearly fully extended, and highly aggregated in a localized region, forming a crystalline or a twisted rope-like structure. Our observation demonstrates the capability of STM in studying the unfolding of proteins, and also suggests the possibility of using STM to directly sequence the amino acid residues of a protein.

An Investigation of the Electrochromism of (Octacyanophthalocyaninato)metal‐Metal Complex Thin Films by Means of In Situ Visible and Raman Spectroscopies

The electrochromism of (octacyanophthalocyaninato)metal-metal complex (MPc(CN) 8 -M, M=Cu,Co) films was investigated by in situ visible and Raman spectroscopies in 1M HCl and 0.1M KOH/1M KCl. A new absorption band was observed in the near-infrared region during electrochemical reduction in these electrolytes. In the CuPc(CN) 8 -Cu film, charges stored in the cathodic waves were 1.1 and 1.3 F/mol in the acid and alkaline electrolytes, respectively