Pentacene Thin Film Growth

Pentacene is a common organic semiconductor with a relatively high conductivity that increases when crystallized. In this experiment pentacene was studied by depositing it on highly ordered pyrolytic graphite (HOPG) using a thermal evaporator and characterizing it with scanning tunneling microscopy (STM). The daily pressure inside the evaporation chamber had small day-to-day variations, between 1 and 7x10-5 torr, which caused significant variations in growth rates. We subsequently developed a method to measure the growth rate immediately before the deposition by opening the shutter of the thermal evaporator to a specific angle so that the growth rate could be measured with a quartz crystal monitor without depositing any material on the HOPG substrate. Examining the resulting depositions with STM, we find several images showing the deposited pentacene either forming into clumps, or into seemingly more ordered track-like patterns. These images were analyzed to find the dimensions of these structures and compared to previously gathered pentacene data from other groups.