Bi-Axial Growth Mode of Au–TTF Nanowires Induced by Tilted Molecular Column Stacking

In this study, to understand the molecular self-organization in metal–organic charge-transfer nanowires, single gold-tetrathiafulvalene (Au–TTF) nanowires were analyzed using polarized Raman spectroscopy, combined with density functional theory (DFT) calculations. To verify the methodology, an investigation was done for neutral tetrathiafulvalene (TTF) bulk crystals with well-known structure. On the basis of the DFT calculation of the molecular Raman tensor and simulation of the angular-dependent depolarization ratio, the molecular orientation in single TTF crystals was verified. Thereon, the combined experimental and ab initio-simulation method was applied to study single Au–TTF nanowires. Our results clearly demonstrate, in contrast to the commonly accepted parallel molecular stacking model, that at least two molecules with different orientations are located in the unit cell of the nanowire’s crystal structure. The new tilted molecular column stacking wire model explains also the axial and radial growth mechanism of Au–TTF wires.