A new, centered orthorhombic crystal, a = 20.7 Å, b = 19.3 Å, c = 3.4 Å, and β = 90 Å, of perylene, C20H12, has been grown epitaxially on a Cu(110) surface under UHV conditions. The crystal structure has been studied with HREELS, LEED, and STM. Vibrational spectra reveal that the molecular planes are parallel to the substrate. Electron diffraction indicates an almost square unit cell in the ab plane in which the a axis is commensurate along the 〈110〉 azimuth of the Cu substrate, while the b axis is incommensurate along the 〈001〉 azimuth. STM images show a large scale smooth morphology of the organic crystal indicative of layer-by-layer growth, while high-resolution images show the details of the centered orthorhombic structure of perylene and the nature of the 3D grain boundaries.

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