Interface formation of pentacene on Al2O3

We examined the interface formed by pentacene deposition onto an Al2O3 substrate. We found that upon pentacene deposition onto Al2O3 the pentacene vacuum level aligns with that of Al2O3. We observe the immediate appearance of a measurable pentacene molecular orbital near the Fermi level upon deposition of as little as 2 Å of pentacene onto the Al2O3 surface. This suggests that there are no chemical bonds at this interface. The vacuum level change at the interface dipole is found to be less than 0.25 eV, and at least part of it can be attributed to the oxygen adsorbates at the in situ prepared aluminum oxide surface.