Fig. 2: Morphological characterizations and optical anisotropy of C8-BTBT crystals.
a Angle-resolved CPOM images of the C8-BTBT crystal array. b SEM image of the C8-BTBT crystal array. The darker ribbons indicate the C8-BTBT crystals while the brighter regions represent SiO2 surface. The right inset shows the structure of a C8-BTBT molecule, and the left inset is an AFM image of a C8-BTBT crystal inside the SiO2 channel. c Colored cross-sectional SEM image of a C8-BTBT crystal inside the SiO2 channel in a 5° oblique view. d TEM image of a C8-BTBT crystal. The inset SAED pattern clearly reveals the diffraction spots of (l00) and (0l0) crystal planes. e High-resolution AFM scan of a C8-BTBT crystal. The inset shows the corresponding FFT pattern. f Schematic illustrations of the in-plane projections of μ (red arrows) in a C8-BTBT crystal lattice and the vector component of μ (black dashed arrows) along different crystal axes. g Polarized absorption spectra of a C8-BTBT crystal grown on quartz substrate. The inset is the calculated molecular orbitals of C8-BTBT, indicating the overlap of electron clouds at the molecular π cores. Electronic transitions from HOMO to LUMO (red arrow) can happen upon UV light absorption.
