Pentacene single crystals were grown by physical vapor growth. It was found that large-sized pentacene single crystals can be grown under 1 atm argon either in a closed tube or in an opened tube. The morphology of surface and transect of pentacene crystals was characterized by optical microscope, atomic force microscope and scanning electron microscope. Pentacene monolayers and layer-like structures are observed on the surface and in the interior of single crystals, respectively. The array of large straight steps is also observed on the surface of pentacene single crystals. All results indicate that the growth mechanism of pentacene single crystals is a two-dimensional nucleation-elementary steps-large straight steps-layer-by-layer periods growth. (c) 2006 Elsevier B.V. All rights reserved.