The controllable fabrication of functional molecular thin films on noble metal substrates is impressive for the potential application in electronic and optoelectronic devices. The ability to control the structure of molecular thin films provides a method of tuning the functional properties in a discrete manner. However, the interaction between the molecules or between the molecules and substrate is not completely understood yet, which cause the difficulty of thin film controllable fabrication. In this presentation, the role of the additional alkyl chain in the adjustment of the QAnC molecular structure on Ag(110) substrates will be discussed. In situ organic molecular-beam-epitaxy and low energy electron diffraction (OMBE-LEED) technines are used to examine the adsorption of QAnC molecules with alkyl chains of 4 and 16 carbon atoms respectively. First-principles density-functional-theory and molecular mechanics calculations are employed to evaluate the preferred adsorption sites of QAnC molecules on Ag(110) and their behavior due to different alkyl chains. It is found that the alkyl chains determine the orientation of the molecular overlayers. While the interaction of QA and the Ag substrate is primarily due to chemical bonding of oxygen to the silver substrate, determining the molecular orientation and preferred adsorption site, the intermolecular arrangement can be adjusted via the length of alkyl chains. Further STM experiments confirm our calculation results. It is verified that uniform QA films with very well controlled physical properties can be fabricated by the adjustment of additional non functional chains.
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