Thickness-Driven Orthorhombic to Triclinic Phase Transformation in Pentacene Thin Films


  • The authors thank the National Science Foundation DMR-0084304, DMR-9707975 and the NSF sponsored IGERT program for Molecularly Designed Electronic, Photonic and Nanostructured Materials at the University of Michigan for funding.


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Pentacene films are thermally evaporated onto amorphous carbon-coated mica substrates held at room temperature. The crystal structure and morphology of the films are analyzed using electron microscopy and diffraction, and a new orthorhombic structure is characterized for films below a critical thickness (see Figure). Evidence that the orthorhombic structure is thermodynamically stable at low film thickness due to its low (001) surface energy is obtained.