Domains Beyond the Grain Boundary

Thin films of inorganic materials are used in diverse applications, typically in polycrystalline form due to their relatively simple production. We have used enhanced piezoresponse force microscopy to investigate the domain distribution within neighbouring grains in thin polycrystalline films of the ferroelectric–ferroelastic system lead zirconate titanate (PZT). We demonstrate that domains are organized into areas with a correlated alignment of the ferroelastic and ferroelectric domains, spanning multiple grain boundaries. We present five typical arrangements of such structures: azimuthal, radial, gradient, and short‐ and long‐ range linear domain organizations. Moreover, we discuss the mechanical and electrical constraints that dictate these structures.     

Scale effects on the in-situ tensile strength and fracture of ice Part I: Large grained freshwater ice at Spray Lakes Reservoir, Alberta

At lab-scale, issues such as inhomogeneity and polycrystallinity are especially important to the fracture of S1 freshwater ice. S1 freshwater ice is typically composed of large grains with predominantly vertical c-axes. Because of the very large grain sizes that one can encounter in S1 macrocrystalline ice sheets, it is essential that the effects of sample size on the fracture behavior be determined. In other words, are small scale (lab-scale) results applicable at larger scales (at the scale of ice-structure interactions, for instance)? To answer this question, a set of lab- to structural-scale (0.34>L>28.64m) fracture tests were conducted on S1 freshwater lake ice at Spray Lakes, Alberta, using the base-edge-notched reverse-tapered plate geometry and covering a size range of 1:81. A Ba?ant-type size effect analysis of the measured fracture strengths (which do reveal a significant dependence on scale) is unexpectedly clouded by the fact that the data collected violates the associated scatter requirements, even though the size range tested is large. Moreover, via Hillerborg's fictitious crack model, large fracture energies were back-calculated (of order 20 J/m2), but for miniscule process zone sizes; in addition, not all of the measured deformations for each test could be matched simultaneously. Apparently, these very warm S1 macrocrystalline lake ice experiments were dominated by nonlocal deformation and energy release rate mechanisms, in all likelihood brought about by grain boundary sliding. The reduced effectiveness of both the Ba?ant-type size effect analysis and Hillerborg's fictitious crack model is due mainly to the lack of crack growth stability achieved in the experiments. These unstable fractures truncated the fracture process. Given the irregular and large grain structure, the very warm ice temperatures, and the diffuse grain boundary surface energy, there is a marked dependence on specimen size to grain size ratio and distinctly non-unique pre-failure process zones occurred. Micromechanical simulations are required to resolve these coupled issues.     

Mapping of Domain Orientation and Molecular Order in Polycrystalline Semiconducting Polymer Films with Soft X‐Ray Microscopy

We utilize scanning transmission X‐ray microscopy (STXM) to study the domain structure of polycrystalline films of the semiconducting polymer poly(9,9’‐dioctylfluorene‐co‐benzothiadiazole) (F8BT). By taking several images at different orientations of the film with respect to the polarization of the X‐ray beam, we are able to compute quantitative maps of molecular alignment/order and molecular orientation, including both the backbone direction and phenyl ring plane orientation, as well as the in‐plane and out‐of‐plane components. We show that polycrystalline F8BT films consist of well‐ordered micron‐sized domains with the transition from one domain orientation to another characterized either by a smooth transition of orientation or by ～ 200 nm wide disordered domain boundaries. The morphology of the disordered domain boundaries resemble the electroluminescence patterns observed previously in F8BT light‐emitting field‐effect transistors suggesting that charge trapping at these disordered domain boundaries facilitates charge recombination in ambipolar operation. A relatively narrow distribution of local average tilt angles is observed that correlates with film structure, with the ordered domains in general showing a higher tilt angle than the disordered domain boundaries. We also use secondary electron detection to image the surface domain structure of polycrystalline F8BT films and demonstrate that the polycrystalline structure extends to the film/air interface. Finally, we calculate ideal NEXAFS spectra corresponding to a perfect F8BT crystal oriented with the 1s – π^* transition dipole moment parallel and perpendicular to the electric field vector of a perfectly linearly polarized X‐ray beam.