Highly Ordered Titanyl Phthalocyanine Films Grown by Directional Crystallization on Oriented Poly(Tetrafluoroethylene) Substrate

Abstract

Highly oriented films of titanyl phthalocyanine (TiOPc) were obtained by high-vacuum sublimation onto an oriented poly(tetrafluoroethylene) (PTFE) substrate. The dependence of the structure and morphology on deposition parameters (substrate temperature T s, deposition time t, and deposition rate τ) was followed by X-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy (AFM) to uncover the origin of the oriented growth process. At T s = 100 °C, an original growth mechanism was observed whereby α-TiOPc microcrystallites were formed by the static coalescence and reorganization of small amorphous aggregates in close contact. Nucleation of α-TiOPc is initiated at the PTFE macrosteps from which oriented crystallization propagates, leading to uniform α-TiOPc films with a twinned texture and a dense (0 1 0) contact plane. The molecules are in an edge-on orientation, with their molecular plane oriented parallel to the PTFE chains. At the mesoscale, the nucleation of crystalline α-TiOPc involves the alignment and oriented coalescence of amorphous prenucleation aggregates along the PTFE macrosteps, i.e., a graphoepitaxial process. At the molecular scale, it is proposed that the TiOPc orientation and the preferential nucleation of the α polymorph are enforced by the topography and structure of the PTFE macrosteps in conjunction with the requirement for a minimal nucleation free energy. The optical absorption of the films in the near infrared is found to be strongly correlated with the structural and morphological modifications in the films. The oriented character of the α-TiOPc films results in a strong polarization of the 850-nm band perpendicular to the PTFE chain axis direction.

An Ultra Closely π‐Stacked Organic Semiconductor for High Performance Field‐Effect Transistors

“…More complicated XRD peaks appeared at 150°C, in which the diffraction peaks at 7.5°, 12.5°, 25.3°, and 28.6°were assigned to a-phase and the diffraction peak at 26.2°was belonged to b-phase. [18][19][20] It was further confirmed from the XRD results that the vacuum deposited films of TiOPc on pure Si/SiO 2 surface were in amorphous or in mixed-phases states, which were consistent with the UV-NIR results. Yonehara and Brinkmann et al [18][19][20] found surface modifications of substrates with organic thin layers exerted remarkable effects on the molecular alignment of vacuum deposited TiOPc films.…”

“…[18][19][20] It was further confirmed from the XRD results that the vacuum deposited films of TiOPc on pure Si/SiO 2 surface were in amorphous or in mixed-phases states, which were consistent with the UV-NIR results. Yonehara and Brinkmann et al [18][19][20] found surface modifications of substrates with organic thin layers exerted remarkable effects on the molecular alignment of vacuum deposited TiOPc films. A highly ordered a-TiOPc film with an "edgeon" molecular orientation was selectively grown on the surfaces of the gold substrate modified with a self-assembled monolayer of octadecanethiol.…”

“…At 90°C, a weak peak at 6.8°(d = 12.9 Å) and an intense peak at 7.5°(d = 11.8 Å) emerged, in which the former was attributed to the XRD signal of a specific amorphous phase of TiOPc and the latter corresponded to a-TiOPc. [18][19][20] At 120°C, the peaks at 26.2°and…”

“…The XRD patterns of TiOPc films deposited on OTSmodified Si/SiO 2 substrates at 90, 120, 150°C were displayed in Figure 3b. An intense peak at 7.5°(d = 11.8 Å) due to the diffraction from (010) plane of a-phase [18][19][20] was observed, especially for 150°C, indicating highly ordered a-phase films with the (010) lattice plane parallel to the substrate, i.e., TiOPc molecules preferentially stood on substrates with an "edge-on" style orientation (Fig. 4b), in which the molecular plane made an angle of 62°with respect to the substrates.…”

Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning

“…[21][22][23] However, a more detailed analysis of the literature data shows that the LC films studied previously were not in the Col h phase. For example, the films of TiOPc [21] or HBC-C8,2 [23] were in the crystalline state whereas the films of HBC-PhC12 were in the LC state but in a mesophase different from Col h (Col r phase at room temperature [24] ). Similar studies have been conducted on Ada-PBT that was in the glassy state produced by quenching from hexagonal columnar plastic or hexagonal columnar ordered phases.…”