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The surface crystallization behavior of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) spincoated thin films was compared by means of atomic force microscopy (AFM) with an in situ heating stage. As the films were heated up stepwise, characteristic surface crystals appeared at a crystallization temperature (T c ) in the near-surface region which is about 15 8C under the bulk T c , and were replaced by bulk crystals when the temperature was increased to the bulk T c . In the case of films whose thickness is less than 70 nm (PET) and 60 nm (PEN), significant increases in the bulk T c were observed. Scanning force microscopy (SFM) force-distance curve measurements showed that the glass transition temperature (T g ) of the near-surface region of PET and PEN were 22.0 and 26.6 8C below their bulk T g (obtained by DSC). After the onset of surface crystallization, edge-on and flat-on crystals appeared at the free surface of PET and PEN thin films, whose morphologies are very different to those of the bulk crystals. Although the same general behavior was observed for both polyesters, there are significant differences both the influence of the surface and substrate on the transition temperatures, and in morphology of the surface crystals. These phenomena are discussed in terms of the differences in the mobility of polymer chains near the surface.

Low-energy muons have been used to probe the local motion in a thin-film sample of polystyrene as a function of depth below the free surface. The muon spin relaxation in zero magnetic field is dominated by a muoniated radical state which is formed on the polystyrene ring. The muon spin-relaxation rate is found to be highly sensitive to the dynamical state of the polymer, and provides a local probe of changes in the dynamical correlation time around the glass transition. When high-energy muons are used to study the bulk properties, the glass-transition temperature T g is revealed as a change in the temperature dependence of. Reducing the muon implantation depth, while holding the sample a few degrees below the bulk T g , leads to a drop in , signifying a reduction in the local T g on approaching the surface. The width of the dynamical surface layer is found to be enhanced over previous estimates made at much lower temperatures, providing experimental evidence for critical divergence of the layer width on approaching the bulk T g .

Crystal growth in colloidal particle monolayers fabricated by Langmuir-Blodgett method on 4 in. sapphire wafers was investigated under the condition of two techniques, that is, ultrasonic annealing at 1.2 to 1.5 MHz and barrier-sway process at 0.2 to 0.5 Hz. Significant increases of the ordered area were obtained by the both techniques and more than 60 times growth was confirmed. The remaining crystal defects after the growth were categorized as grain boundary, vacancy, and line defect. Both techniques exhibited different features regarding the component ratio of the defects, and different mechanisms for the reorientation of particles are discussed. The driving force of these re-orientations is thought to be associated with the 2D Ostwald ripening of colloidal crystals.

Two-dimensional periodic corrugation was introduced into the surface of metallic cathodes of organic light-emitting diodes (OLEDs) to extract surface plasmon energy, which is trapped in that surface, as free-space photons. The dependence of the improvement factor of the emission efficiency on the modulation depth of the corrugation was systematically investigated. The corrugation was fabricated by using a colloidal lithography technique, which can be easily applied to a wide area. The obtained maximum improvement factor in current efficiency was 1.67 for an OLED with a 40 nm modulation depth, whereas the improvement in power efficiency was 2.35 for an OLED with a 60 nm modulation depth. We attributed the former improvement factor purely to optical effects and the latter to both optical and electrical effects, namely, a reduction of the electrical resistance of the organic layers due to the introduced corrugation.

A series of PET/PEN copolyesters were synthesized by molten transesterification. The degree of randomness and the sequence length of the copolymers were determined by 1H NMR spectroscopy, and the changes in the bulk glass transition temperature (TgB), bulk crystallization temperature (TcB), and bulk melting temperature (TmB) were observed by DSC. A clear relationship was obtained between the observed enthalpy of melting (ΔHm) and degree of randomness (B), and TmB was suppressed for the midcompositions. As with their homopolymer counterparts, there was significant depression in crystallization temperature at the surface (TcS) of the random/block copolymers compared with the bulk, and so surface‐localized crystallization could be induced in spin‐coated thick films (thickness ranging from ca. 400 to 700 nm) by annealing at a temperature in which the surface region is mobile, but the bulk is not. The formation of these clear surface crystals allows the morphology to be directly imaged by AFM, and we observed that the crystallizability and the lamellar morphology of the surface crystals deviated from those of the original homopolymers, depending on the mixing ratio of PET/PEN and degree of randomness. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46515.

Pencil-shaped silicon nanowires (SiNWs) were synthesized by colloidal lithography and inductively coupled plasma reactive ion etching for photovoltaic application. Light reflectance of below 10% could be obtained by the asymmetric pencil-shaped SiNW array. The pencil-shaped SiNW structure and properties were investigated and compared with metal catalyzed electroless etching (MCEE) and nanoimprinted SiNWs. Single-junction solar cells consisting of pencil-shaped n-SiNW substrates and p-Si shell layer grown by chemical vapor deposition were fabricated. A combination of two-step H2 annealing and back surface field formation was applied to improve the solar cell properties. Good crystal quality and surface of pencil-shaped SiNWs provided an excellent solar cell junction interface. The great light trapping of the pencil-shaped SiNW solar cell could enhance the conversion efficiency by more than 0.6% compared to the solar cells using MCEE and nanoimprinted SiNWs.

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