Epitaxial Growth of the Ionic Polymer Fluoroaluminum Phthalocyanine on the Basal Plane of Single Crystal Tin Disulfide

Abstract

The epitaxial growth of fluoroaluminum-phthalocyanine (FAlPc) thin films on the hep (0001) tin disulfide (SnS2) surface is reported. Growth conditions can be achieved that lead to FAlPc films of polymer-like aggregates (FAlPc)" with the long axis of the aggregate apparently standing perpendicular to the surface. When the substrate is held at a temperature of 260 °C during deposition, reflection high-energy electron diffraction of the resultant thin films showed that FAlPc grows epitaxially on SnS2 in a square lattice structure, starting with the first monolayer, with a unit cell dimension of 13.2 ± 0.8 A. One axis of the resulting FAlPc square lattice overlayer is oriented along the main axis of the basal plane SnS2. Scanning tunneling microscopy (STM) showed elongated crystallites growing along the main crystallographic axes of the substrate, and these same STM data indicate that phthalocyanine film growth may be initiated at step sites on the SnS2 surface. The development of H-aggregate (FAlPc)" in these thin films is confirmed by the position of the Q-band absorbance maximum observed for these thin films (642 nm), which is blue-shifted from the monomer absorbance maximum at ca. 675 nm. The Q-band spectrum of the epitaxial film is much narrower (fwhm 28 nm) than comparable spectra from less-ordered thin films of (FAlPc)" aggregates deposited on sapphire (fwhm 55 nm). The polarization dependence of these Q-band spectra was consistent with individual FAlPc molecules in these thin films, on average, lying parallel to the surface plane. Dye sensitization/photoelectrochemistry showed photocurrent action spectra that paralleled the absorbance spectra and made possible the characterization of even monolayer-level coverages. Quantum efficiencies for charge injection from the FAlPc aggregates into the SnS2 conduction band (<5%) was lower by at least a factor of 10, relative to previously explored phthalocyanine sensitizers which do not form linear cofacial aggregates.

Ultrathin Films of Perylenedianhydride and Perylenebis(dicarboximide) Dyes on (001) Alkali Halide Surfaces

“…All thin films were grown under high vacuum conditions in growth chambers similar to those previously described. 1c,7a, Evaporation occurred from Knudsen cell sublimation sources, and film thickness was estimated from a quartz crystal microbalance. Substrate temperatures were controlled by conventional resistive heating of the sample stage and monitoring with a thermocouple attached to a molybdenum plate to which the alkali halide crystals were attached via spring clips.…”

Self-Assembly of Zinc Oxide Thin Films Modified with Tetrasulfonated Metallophthalocyanines by One-Step Electrodeposition

“…However, the technology must also be developed in view of economy and ecology. Although gas-phase techniques such as vacuum evaporation, sputtering, chemical vapor deposition, or molecular beam epitaxy have successfully achieved ordered growth of inorganic compound thin films , or thin films of organic molecules, , these techniques inevitably need high temperature or vacuum, making them disadvantageous for large-scale productions. Film processing employing chemical and electrochemical reactions in solutions bears the highest advantages in this respect.…”

Molecular Interactions in Thin Films of Hexadecafluorophthalocyaninatozinc (F16PcZn) as Compared to Islands of N,N‘-Dimethylperylene-3,4,9,10-biscarboximide (MePTCDI)

“…Different molecular orientations leading to different crystal structures were observed for phthalocyanines, e.g., phthalocyaninatofluoroaluminum(III) on SnS 2 (1000), as concluded from electron diffraction (RHEED) as well as optical absorption data. 4 Also, after deposition annealing can lead to irreversible changes in the crystal structure of organic solids as long known from X-ray diffraction and optical absorption of phthalocyanine complexes of divalent metals. 5,6 Such changes have been interpreted widely in terms of exciton dipole interaction leading to band splitting and selection rules which could explain the obtained optical spectra as related to the structural analysis.…”