Real-time atomic force microscopy observation was carried out during crystallization in
thin films of chiral poly(R-3-hydroxybutyrate-co-R-3-hydroxyhexanoate) copolymer, and the development
details of single lamellae in the banded spherulites are revealed for the first time. The lamellae exhibit
complicated growth behaviors: twisting, bending, backward growth, and branching. The lamellae
continuously twist to show alternating edge-on and flat-on views along the radii of the spherulites. Giant
screw dislocations bring forth to the birth of new lamellae. Interaction between the leading and trailing
lamellae contributes to cooperative stacking of the twisting crystals. The lamellae twist before screw
dislocations appear, demonstrating that screw dislocations are not causal of twisting. All the observed
twisting occurs in the right-handed sense, likely resulting from the chirality of the crystal structure.
Increased crystallization temperature results in decreased magnitude of lamellar twisting and bending.
Models for morphological development are discussed in the context of these observations.
CuIn x Ga 1−x Se 2 thin films, with various Ga/(Ga+In) ratios, suitable for solar cells were processed by selenizing stacked Cu, Ga, and In precursor layers in a H2Se reactor in the temperature range of 400–500 °C. Cu/Ga/In and Cu/In/Ga precursors were obtained by sequential sputtering of the elemental layers. The Cu/Ga/In and Cu/In/Ga precursors, and the selenized films were characterized by scanning electron microscopy, x-ray diffraction, energy dispersive spectroscopy, and Auger electron spectroscopy. The precursors contained only binary and elemental phases in the as-deposited condition and after annealing. The selenized films had a nonuniform distribution of Ga and In. The surface of the selenized films were In rich, while the Mo/film interface in these films was Ga rich. The selenized films with Ga/(Ga+In) ratios greater than 0.25 contain graded Ga and In compositions, and the selenized films with Ga/(Ga+In) ratios less than 0.6 contain a phase-separated mixture of CuInSe2 and CuGaSe2 with the CuInSe2 near the surface and the CuGaSe2 near the Mo/film interface. Single phase, homogeneous CuInxGa1−xSe2 films were obtained by annealing the as-selenized films in argon in the temperature range of 500–600 °C for 60 min. Interdiffusion of In and Ga between the CuGaSe2 and the CuInSe2 phases was found to be responsible for the homogenization process. This homogenization process does not occur in the presence of a selenium atmosphere. Diffusion measurements yielded similar interdiffusion coefficients for Ga and In. The annealing temperature and time to effect homogenization depends on the Ga/(Ga+In) ratio of the absorber films. Films with lower Ga/(Ga+In) ratios require a homogenization temperature of 600 °C or more and films with higher Ga/(Ga+In) ratios homogenize at a lower temperature of 400–500 °C, for an annealing time of 60 min.
An x‐ray diffraction method for the simultaneous determination of crystallinity (including intracrystalline defects), effective Debye‐Waller factors, and atomic positions has been developed and applied to semicrystalline polyethylene. It was found that this material unambiguously constitutes a two‐phase system. Measurements of intracrystalline lattice disorder in the chain direction and perpendicular to the chain direction show these to be in the ratio 1:2.5. Lattice disorder was principally of the first kind. Paracrystalline disorder in the [110] direction was less than 2.4% at all experimental conditions. Results include measurements of degree of crystallinity, particle size, space group, and unit cell parameters and variation of these quantities with crystallization temperature, ambient temperature, and time.
Poly(vinylidene fluoride) (PVDF) fibers spun at different take-up speeds (10.6−61.0 m/min)
were subjected to stretch−hold deformation at room temperature and in-situ simultaneous synchrotron
small- and wide-angle X-ray scattering measurements. Crystal transformation from α to β form and
morphological changes in lamellar and fibrillar structures were analyzed in detail. All fibers were found
to yield at an early stage of deformation, resulting in alternating necked and unnecked regions along the
fiber. From the two-dimensional (2-D) wide-angle X-ray diffraction (WAXD) patterns, mixed α and β
(minor fraction) forms were found to coexist in the undrawn fibers. Deformation assisted in the conversion
from the α-form into the β-form. In necked regions, more α to β transformation took place than in unnecked
regions. The overall crystallinity index and unit cell parameters of the α form did not change significantly
prior to necking. From the 2-D small-angle X-ray scattering (SAXS) patterns, two kinds of equatorial
streaks were observed. The first kind originated from fiber of high take-up speed (61.0 m/min) under
zero or small strain, and the second kind came from highly deformed fibers (all take-up speeds) in both
necked and unnecked regions. These two kinds of equatorial streaks were attributed to the formation of
microfibrils and microvoids, respectively. The dimensions of the lengths of microfibrils and microvoids
were estimated by Ruland's method. Meridianal scattering maxima from a lamellar morphology were
observed in the SAXS patterns in fibers under zero or low strain. The long period of the lamellar structure,
estimated using correlation function analysis, increased with strain. Results from SAXS and WAXD
analysis suggest that the formation of defects during yielding and plastic flow facilitates the α to β crystal
phase transformation, and a phase, similar to conformationally disordered phase, whose density is close
to that of crystal, is induced out of the amorphous phase in lamellar structure with application of strain.
In the present study, the structural and morphological development during melt spinning of polyethylene and poly(vinylidene fluoride) fibers was studied using simultaneous in-situ synchrotron small-and wide-angle X-ray scattering (SWAXS) techniques. The spinning apparatus consisted of a single screw extruder, which was mounted on a horizontal platform that could be translated in the vertical direction allowing different spinneret distances to be sampled with the X-ray beam. Effects of take-up speed (10.6-61.0 mpm) and spinneret distance (30-87.5 cm) on crystallinity and morphological parameters were investigated. A suggested model of structural development during crystallization details the formation of defective shish crystals, followed by the formation of kebob crystals. The defective shish-kebob structure eventually transforms into a well-defined lamellar structure. This model is consistent with the qualitative appearance of the two-dimensional SAXS and WAXS patterns, as well as the quantitative analysis of the SAXS/WAXS data using position-sensitive wire detectors.
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