Fig. 5.

XRD from CB7CB and 8CB. An electron density modulation (EDM) associated with the periodic structure observed in FFTEM images of CB7CB would generate sharp XRD peaks at wavevector q ∼ 2π/8 nm⁻¹ and its harmonics (yellow bands). Here, in a search for this scattering, synchrotron-based powder XRD from CB7CB is compared with that from the smectic A layering in 8CB, which computer simulation shows to have a fractional EDM of 0.25. Subtraction of the background (cyan line) leaves only the shot noise from the background to limit detectability of a peak. No peaks above this limit are observed, indicating that the fractional EDM in any TB scattering structure in CB7CB must be less than 0.005. (A) Linear intensity scale. (B) Log intensity scale.