Molecular ordering in a biaxial smectic-A phase studied by scanning transmission X-ray microscopy (STXM)

Abstract

Results of STXM investigations of a binary mixture (-TNF = 2 : 1; SmA(b) 140 M 180 Iso) known to form a SmA(b) phase [T. Hegmann, J. Kain, S. Diele, G. Pelzl and C. Tschierske, Angew. Chem. Int. Ed., 2001, 40, 887] are presented. Near edge X-ray absorption fine spectra (NEXAFS) of the -TNF board-like aggregates, in particular the intensity of the low energy peaks associated with aromatic ring pi* orbitals (284.5-286.5 eV), show that the molecular plane of these aggregates is very sensitive to the relative orientation of electric field vector E of linearly polarized light, which is used to determine the molecular orientation in the LC phase. The observed strong in-plane dichroic signal suggests the predominant orientation of the -TNF aggregates to be along the smectic layer normal as well as long-range ordering of the in-plane molecular orientation (biaxiality). Orientational maps derived from series of measurements at different sample rotation angles around the specimen normal clearly show a Schlieren-type texture, and permit a detailed examination of exclusive +/-(1/2) disclination theoretically predicted for the SmA(b) phase.

Imaging Nanoscale Morphology of Semiconducting Polymer Films with Photoemission Electron Microscopy

“…[3] Films of organic semiconducting polymers are, if at all, only semicrystalline and therefore exhibit an additional degree of complexity. Scanning transmission X-ray microscopy (STXM) [20,21,[32][33][34][35][36] has been proven useful for studying the morphology of organic semiconductors. Typical dimensions of these domains are on the nanometer scale.…”

“…[20,21,[32][33][34][35][36] Another feature of the PEEM technique presented here is its surface sensitivity. The data shown in this Communication demonstrate the technique's applicability to semiconducting polymer films on Si wafers with native SiO 2 surface layer.…”

“…www.advmat.de www.advancedsciencenews.com measurements of samples on substrates. Scanning transmission X-ray microscopy (STXM) [20,21,[32][33][34][35][36] has been proven useful for studying the morphology of organic semiconductors. The technique requires a synchrotron light source, but enables measurements of organic films on specially designed organic field-effect transistor (OFET) substrates.…”

“…In particular, STXM, which may deliver a degree of information comparable to the PEEM technique, is currently limited to TEM grids as substrates, X-ray-transparent membranes, or specially designed OFET substrates. [20,21,[32][33][34][35][36] Another feature of the PEEM technique presented here is its surface sensitivity. For the photon energy used in this experiment, we estimate the information depth to amount to roughly 5 nm based on the reported values for the electron mean free path in other polymers (PMMA, P2VP, Kapton).…”

Colloidal Crystals of Spheres and Cubes in Real and Reciprocal Space

“…The shorter wavelength of X-rays lift restrictions related to diffraction limitations that are problematic in optical microscopy and their higher penetration power is advantageous in comparison with electron microscopy, especially for in-situ studies in colloidal suspensions [109][110][111] . Moreover, X-rays can be used for practically all materials and hence index matching or fluorescent labelling of the colloids is not needed.…”