pentacene was deposited on a muscovite mica surface by physical vapor deposition from a knudsen cell in an ultrahigh vacuum chamber . the cell temperature was about 500 k to realize a deposition rate of 1 monolayer / min . the mica samples ( 10  10  0.01 mm ) were attached to a steel plate via tantalum wires . the steel plate was heated resistively , and its temperature was controlled by a ni , the temperature of the mica sample could be varied between 100 and 1000 k. for a quantitative determination of the deposited material , a quartz microbalance was used , which was located next to the mica substrate . the mica substrate was cleaved with adhesive tape prior to installation into the vacuum chamber and subsequently gently sputtered by argon ions . ten minutes of sputtering with 500 ev ar ions at an argon pressure of 5  10 mbar was sufficient to change the 5a film morphology from needle - like islands , composed of lying molecules , to compact islands composed of standing molecules . the surface chemical composition was analyzed by auger electron spectroscopy and x - ray photoelectron spectroscopy . thermal desorption spectroscopy was applied to determine the thermal stability of the pentacene film and the sticking coefficient . ex situ atomic force microscopy ( nanosurf , easyscan2 ) was used to analyze the film morphology .