Structural Analysis of Aggregated n-alkanes by C K-Edge XANES Measurements and DFT/MD Calculations

Abstract

To clarify the σ* peak structures in C K-XANES of carbon materials and to analyze the structure of aggregated n-alkanes, C K-XANES spectra of various n-alkanes were measured in BL10/NewSUBARU, and the XANES profiles were theoretically analyzed by the first principles calculations. From the incident-angle-dependent C K-XANES, it can be found that n-C₃₆H₇₄ spin-coated on Au-substrate takes vertical-orientation but n-C₃₆H₇₄ pressed on In-substrate takes less orientation. It was also confirmed that the vertical-orientation of n-C₃₆H₇₄ on Au substrate reduced from solid state to melted state by heating. Considering the electric field vector directions on C K-XANES simulations by DFT calculations, the measured vertical-orientation of n-C₃₆H₇₄ can be well explained with the perpendicular conformations of alkane-chain-backbone to the substrate plane. MD calculations of n-C₃₆H₇₄ molecules on Au confirmed that aggregated n-C₃₆H₇₄ molecules partially take perpendicular conformations to the Au surface.