Effect of peripheral substitution of copper phthalocyanine molecules on the electroconductivity in thin films during interaction with ammonia

A decrease in the ability for oxygen bonding of PcCu molecules in peripheral substitution has been studied by measurements of conductivity in the presence of ammonia.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1491–1493, August, 1995.The work was financially supported by the International Scientific and Technical Center (Project No. 015-94). The authors are grateful to Associate Professor G. P. Shaposhnikov (Ivanovo Institute of Chemical Technology) for the phthalocyanine samples he kindly supplied.     

Crystallization behavior of polylactide on highly oriented polyethylene thin films

The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃were investigated by means of optical microscopy,AFM and X-ray diffraction.The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably,which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition.The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals.It is further demonstrated that except for the different crystal orientation,the PE does not influence the crystalline modification and crystallinity of the PLA.     

Lattice expansion of highly oriented 2D phthalocyanine covalent organic framework films

Expanding into application: covalent organic framework (COF) films are ideally suited for vertical charge transport and serve as precursors of ordered heterojunctions. Their pores, however, were previously too small to accommodate continuous networks of complementary electron acceptors. Four phthalocyanine COFs with increased pore size well into the mesoporous regime are now described.     

Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces

The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77 K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333 K, at which point the size of individual crystallites typically exceeds 100 nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures.     

Dry etching of copper phthalocyanine thin films: effects on morphology and surface stoichiometry

We investigate the evolution of copper phthalocyanine thin films as they are etched with argon plasma. Significant morphological changes occur as a result of the ion bombardment; a planar surface quickly becomes an array of nanopillars which are less than 20 nm in diameter. The changes in morphology are independent of plasma power, which controls the etch rate only. Analysis by X-ray photoelectron spectroscopy shows that surface concentrations of copper and oxygen increase with etch time, while carbon and nitrogen are depleted. Despite these changes in surface stoichiometry, we observe no effect on the work function. The absorbance and X-ray diffraction spectra show no changes other than the peaks diminishing with etch time. These findings have important implications for organic photovoltaic devices which seek nanopillar thin films of metal phthalocyanine materials as an optimal structure.     

Structure of friction-transferred highly oriented poly(3-hexylthiophene) thin films

Oriented thin films of P3HT were obtained by a friction-transfer technique. The morphology and structure of the film were studied by means of optical microscopy, atomic force microscopy and transmission electron microscopy. Optical microscopy observation indicates that large size well-ordered P3HT thin films can be produced by a friction-transfer technique. Highly ordered lamellae were observed in P3HT friction-transferred films by electron microscopy. Electron diffraction results confirm the existence of high orientation with the a- and c-axes of P3HT crystals aligned in the film plane while the c-axis parallel to the friction-transfer direction. The atomic force microscopy observation of the as-prepared P3HT thin film shows, however, a featureless top surface morphology, indicating the structure inhomogeneity of the obtained film. To get highly oriented P3HT thin films with homogenous structure, high temperature annealing, solvent vapor annealing and self-seeding recrystallization of the friction-transferred film were performed. It is confirmed that solvent vapor annealing and self-seeding recrystallization methods are efficient in improving the surface morphology and structure of the frictiontransferred P3HT thin film. Highly oriented P3HT films with unique structure can be obtained through friction-transfer with subsequent solvent vapor annealing and self-seeding recrystallization.     

Post-synthetic modification of epitaxially grown, highly oriented functionalized MOF thin films

Thin films of MOFs grown on solid substrates offer a huge potential with regard to tailoring the properties of a surface, in particular if used in connection with post-synthesis modification (PSM). Here, we report on the PSM of surface-supported crystalline MOFs, with target molecules using an amine-based coupling strategy.     

Piezoresistive elements of polycrystalline semiconductor thin films

Polycrystalline Si and Ge films have been prepared by the CVD method and have been used as sensing elements of pressure sensors that have a semiconductor/insulator/stainless steel structure. Values of the gauge factor were 20 and 30 for polycrystalline Si and Ge films, respectively. Hysteresis and deviation from linearity were less than 0.6%.     

Magnetic field-induced reactions on the surface of chloroaluminum phthalocyanine thin films

The μ-(oxo)bis[phthalocyaninato] aluminum(III) (AlPc)(2)O films, with the crystallites oriented preferably in one direction, were obtained via chemical transformation of chloroaluminum(III) phthalocyanine AlClPc film upon its annealing in magnetic field. A comparative analysis of the influence of postdeposition annealing without and under applied magnetic field of 1 T on composition and morphology of AlClPc films has been carried out. The chemical transformation of AlClPc to (AlPc)(2)O on the substrate surface is studied by the methods of UV-vis and infrared spectroscopies, Raman, x-ray photoelectron spectroscopy as well as atomic force microscopy. Two interesting effects were observed upon heating the AlClPc films in magnetic field of 1 T. First, the temperature of the chemical transformation of AlClPc to (AlPc)(2)O decreased from 300 °C to 200 °C when magnetic field was applied during postdeposition annealing. Second, the formation of (AlPc)(2)O films with elongated crystallites with a preferential orientation was observed. The heating of (AlPc)(2)O films in a magnetic field at the same conditions did not demonstrate any effect on the structure and morphology of these films.     

Ultrathin layer chromatography on nanostructured thin films

Ultrathin layer chromatography (UTLC) is a relatively new variant of thin layer chromatography, with a 10mum thick monolithic silica sorbent layer that gives faster separations with lower limits of detection and reduced analyte and solvent volumes. We have produced UTLC plates with controllable nanostructure and thickness, and show that the layer separation characteristics depends on the film nanostructure. We also show that layers made with in-plane anisotropic nanostructures will exhibit a decoupling effect, where the analyte spots do not develop in the same direction as the solvent front movement. The added layer morphology and material selection adds a degree of freedom to UTLC, and may have applications in multi-dimensional TLC.     

High-resolution waveguide terahertz spectroscopy of partially oriented organic polycrystalline films

We have characterized the terahertz (THz) vibrational spectroscopy of organic polycrystalline thin films using the new experimental technique of waveguide terahertz time domain spectroscopy (waveguide THz-TDS). The organic materials used in this study are tetracyanoquinodimethane (TCNQ) and 1,3-dicyanobenzene (13DCB). For each material, a thin film is cast onto one of the inner surfaces of a metal parallel plate waveguide (PPWG), followed by measurement of the low-frequency vibrational spectrum using waveguide THz-TDS. The vibrational spectra of the waveguide films are compared to corresponding vibrational spectra of standard pellet samples made by dispersing the organic solid in transparent polyethylene. We show how the waveguide films produce significantly narrower THz vibrational line shapes and reveal additional spectral lines that are obscured by inhomogeneous broadening effects in the pellet samples. When TCNQ waveguide films are cooled to 77 K, vibrational line widths as sharp as 25-30 gigahertz (0.83-1.0 cm(-1)) at the full width at half-maximum are observed, which are among the narrowest far-infrared line widths measured for this material. The origin of the line-narrowing effect for the waveguide films is the suppression of inhomogeneous broadening due to the planar ordering of the film on the waveguide surface. The TCNQ waveguide films are further characterized using optical microscopic evaluation to understand how film morphology affects the THz vibrational spectrum. X-ray diffraction is used to determine the orientation of the polycrystalline TCNQ films on the PPWG surface and to qualitatively explain the different vibrational line strengths observed for the ordered waveguide film relative to the random pellet.     

Photoelectric properties of aluminium/copper phthalocyanine/gold photovoltaic cells

Solid-state photovoltaic cells based on the semiconductor copper phthalocyanine depend on the presence of dopants for their operation. Electronegative dopants such as oxygen, iodine and water form trap levels in the semiconductor, which aid the dissociation of photoproduced excited states into charge carriers. The cross section for this reaction has been estimated to be about the same as the molecular cross section of phthalocyanine.     

Distribution of single molecules in polymer thin films

Distribution of fluorescent dye molecules in polymer thin (100 nm) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide distribution, varying in the number of fluorescent spots composed of one, two, three or group of molecules. The number of the molecules present in the fluorescent spots was also ascertained by fluorescence photobleaching experiments. Photocounts associated with maxima of the histograms were found to be independent of the concentrations; however, the number of occurrences associated with more than one molecule decreased with decreasing concentration. By reducing concentration as well as by mixing dye molecules into a polymer solution, fluorescent spots grouping more than one molecule were separated considerably into fluorescent spots including a single-molecule.     

Gas sensing mechanism in chemiresistive cobalt and metal-free phthalocyanine thin films

The gas sensing behaviors of cobalt phthalocyanine (CoPc) and metal-free phthalocyanine (H2Pc) thin films were investigated with respect to analyte basicity. Chemiresistive sensors were fabricated by deposition of 50 nm thick films on interdigitated gold electrodes via organic molecular beam epitaxy (OMBE). Time-dependent current responses of the films were measured at constant voltage during exposure to analyte vapor doses. The analytes spanned a range of electron donor and hydrogen-bonding strengths. It was found that, when the analyte exceeded a critical base strength, the device responses for CoPc correlated with Lewis basicity, and device responses for H2Pc correlated with hydrogen-bond basicity. This suggests that the analyte-phthalocyanine interaction is dominated by binding to the central cavity of the phthalocyanine with analyte coordination strength governing CoPc sensor responses and analyte hydrogen-bonding ability governing H2Pc sensor responses. The interactions between the phthalocyanine films and analytes were found to follow first-order kinetics. The influence of O2 on the film response was found to significantly affect sensor response and recovery. The increase of resistance generally observed for analyte binding can be attributed to hole destruction in the semiconductor film by oxygen displacement, as well as hole trapping by electron donor ligands.     

Undulatory delamination of thin polymer films on gold surfaces

Using two-dimensional surface plasmon resonance measurements, we have observed the formation of traveling waves in the delamination of thin films of polydimethylsilane (PDMS) exposed to methanol. Films were spin-coated on a gold surface and the methanol was added to the top surface. The stress-induced instability caused by the swelling of the PDMS thin film when its edge is pinned to the gold surface leads to wrinkle formation and propagation at the interface. The periodic pattern is thought to be the result of an Asaro-Tiller-Grinfeld (ATG) instability.     

Comments on angle-resolved photoemission from oriented films of lead phthalocyanine on a Cu100 surface

The use of single plane-wave final states in the interpretation of angle-resolved photoemission data is critized. The application of a model-based on the dipole character of photoemission is shown to be more appropriate to give reasonable agreement with experiment.     

Evolution of ordered films of copper phthalocyanine according to EPR data

The procedure for calculating the orientation distribution of molecules using the angular dependence of EPR spectra was employed to study copper(II) phthalocyanine (CuPc) films varying in thickness and obtained by depositing the molecular complex on flat quartz plates. At the first stage of deposition, a layer of the α-CuPc phase with preferable orientation of molecular stacks along the plate surface is formed. At the second stage, a layer with an orthogonal arrangement of molecular stacks is condensed over the first layer. The interaction with NO₂ forms CuPc binuclear associates. Analysis of the EPR spectra made it possible to determine the symmetry of the structure and the distance between the paramagnetic Cu²⁺ ions; the structure of the associates has been proposed. The orientation distribution of CuPc dimers in the film depends both on the initial ordering in the film and on processing conditions. Strong disordering of molecular stacks in ordered films during the α-CuPc to α-CuPc phase transition has been found.     

Growth of highly oriented crystalline polyaniline films by self-organization

Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH(2)) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate-polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.