Studies of growth behavior of tetracene on Ru(101¯0) at submonolayer coverage

The growth behavior and the adsorption geometries of tetracene on the Ru(101¯0) surface in the submonolayer regime were investigated by scanning tunneling microscopy (STM) and density-functional theory (DFT) calculations. Tetracene molecules are in the flat-lying geometry on Ru(101¯0), and orientated with their long axes mainly along the [12¯10] and [0 0 0 1] directions. Tetracene form neither islands, nor ordered structure at submonolayer coverages, and for the tetracene overlayer near to a monolayer, a parquet-like pattern evolves. The DFT calculations showed an adsorption energy of 4.23 eV for tetracene adsorbed between the top and the second Ru atoms rows with its long molecular axis along the [12¯10] direction, and a slightly smaller adsorption energy of 4.19 eV for tetracene adsorbed with its long axis perpendicular to [12¯10], consisting qualitatively with the orientational distributions observed by STM. The results indicate that growth of tetracene on Ru(101¯0) is mainly controlled by the adsorbate-substrate interactions, and the laterally intermolecular interaction has little influence on the growth.