# Incommensurate Smectic Order at the Free Surface in the Nematic Phase of $$4-N-Heptylphenyl-4'-(4"-Nitrobenzoyloxy)Benzoate (DB7NO_2)$$

 Title: Incommensurate Smectic Order at the Free Surface in the Nematic Phase of $$4-N-Heptylphenyl-4'-(4"-Nitrobenzoyloxy)Benzoate (DB7NO_2)$$ Author: Ocko, B. M.; Pershan, Peter S.; Safinya, C. R.; Chiang, L. Y. Note: Order does not necessarily reflect citation order of authors. Citation: Ocko, B. M., Peter S. Pershan, C. R. Safinya, and L. Y. Chiang. 1987. Incommensurate smectic order at the free surface in the nematic phase of $$4-n-heptylphenyl-4'-(4"-nitrobenzoyloxy)benzoate (DB7NO_2)$$. Physical Review A 35(4): 1868-1872. Full Text & Related Files: Ocko_Incommensurate.pdf (865.3Kb; PDF) Abstract: We report x-ray reflectivity measurements on the free surface of $$4-n-heptylphenyl-4'-(4"-nitrobenzoyloxy)benzoate (DB7NO_2)$$ at the nematic to smectic-A phase transition, $$T_{NA}=99.9^{\circ}C$$. The free surface in the nematic phase exhibits smecticlike ordering at two q vectors, one which is commensurate with the smectic-A monolayer q vector $$q_2$$. The other q vector is incommensurate corresponding to ordering at $$\sim 0.59q_2$$. The commensurate peak constructively interferes with the air-liquid interface while the incommensurate peak destructively interferes. These results are compared with bulk-phase x-ray scattering measurements. Published Version: doi:10.1103/PhysRevA.35.1868 Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10357480 Downloads of this work: