Surface-Enhanced Raman Spectroscopy of 2D Organic Semiconductor Crystals

Recently developed ultrathin two-dimensional (2D) organic semiconductor crystals are a promising platform for advanced organic electronic devices. Remarkable quality of such crystals results in charge-carrier mobilities comparable to those of bulk crystals, but their structure and orientation are hard to study because of their extremely small thickness. Here, we applied surface-enhanced Raman spectroscopy (SERS) to investigate the structure of the thinnest 2D single crystals—monolayers, which are based on thiophene-phenylene co-oligomers: 1,4-bis(5′-decyl-2,2′-bithiene-5-yl)benzene and 1,4-bis(5′-hexyl-2,2′-bithiene-5-yl)benzene. Their Raman spectra were calculated as a function of the molecule orientation and SERS microscopy maps were acquired. High sensitivity of SERS allowed us to study monolayer single-crystal domains with the optical spatial resolution. Raman anisotropy was used to probe the orientations of single-crystal domains and the molecule orientation within them. Notably, the SERS microscopy ...