A method for the preparation of uniaxially oriented thin films of terthiophene (20–50 μm thick) is introduced. It relies on the crystal growth with a Bridgman-type process that decouples nucleation and growth phenomena. An effective thermal gradient of 6–11.6 °C/mm has been used in which the sample (terthiophene powder deposited on either glass or fluorinated glass substrates) is displaced from a hot zone to a cold zone at a constant rate of 2.5–5 μm/s. The size and orientation of crystals have been investigated by polarized optical microscopy and X-ray diffraction measurements. A coexistence of two polymorphs of terthiophene has been observed, but optimal gradient conditions enabling the selective crystallization of only the room temperature stable polymorph have been found. Terthiophene films deposited on fluorinated glass substrates and crystallized using the thermal gradient technique show a stronger tendency to polymorphism and random orientation of crystallites for all gradient conditions tested. The monoclinic unit cell (a = 15.410 Å, b = 5.709 Å, c = 26.052 Å, β = 97.77°) of the room temperature phase orients its ab plane parallel to the substrate. Pole figures demonstrate the growth of uniaxially aligned crystals with the [100] and [−100] directions along the gradient axis. Finally, a tentative explanation for this peculiar in-plane orientation is given based on crystal morphology calculations.

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The layer growth, thermal stability, and desorption kinetics of ultrahigh vacuum (UHV)-grown organic discoid molecules (hexaaza-triphenylene-hexacarbonitrile (HATCN)) on Ag(111) have been studied by atomic force microscopy (AFM), thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In the initial growth stage (e0.24 nm mean film thickness) a strongly bonded monolayer of face-on oriented molecules is formed which does not desorb upon heating to 900 K, probably due to the formation of paracyanogen. With increasing film thickness the monolayer of face-on oriented molecules transforms at room temperature into a monolayer built up of edgeon oriented molecules, which saturates at a mean film thickness of around 0.8 nm. This layer partially decomposes during heating, and C 2 N 2 fragments desorb between 650 and 900 K. On the monolayer of standing molecules a second, metastable, layer forms, which saturates at 1.36 nm. With further increase of the coverage, this metastable layer dewets abruptly upon heating at about 350 K, and all molecules, besides those in the first monolayer, get incorporated into the island-like bulk phase. The formed three-dimensional (3D) islands, which are thermally stable up to 400 K, possess bulk crystal structure, as verified by XRD measurements, but the crystallites are randomly oriented.

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