The electrical properties of excimer-laser-crystallized lightly phosphorus-doped polycrystalline silicon films were investigated. The electrical conductivity of the films increased from 6.0 × 10 −7 to 2.3 × 10 −1 S/cm as the laser energy density increased from 235 to 436 mJ/cm 2 because the carrier concentration varied from 1.0 × 10 11 to 1.8 × 10 17 cm −3. In contrast, the carrier mobility was 37.3 and 8.7 cm 2 /V•s at low-and high-laser-energy regimes, respectively, and showed a minimum value of 0.24 cm 2 /V•s at the intermediate laser energy density of 315 mJ/cm 2. These results can be well explained by a model featuring the localization of trap states at the grain boundary.
ABSTRACT:In immiscible blends of poly(2-ethylhexyl acrylate-ca-acrylic acid-ca-vinyl acetate) P(2EHA-AA-VAc) with poly(vinylidene fluoride-ca-hexafluoroacetone) P(VDF-HFA), depth profiling was carried out by PAS-FTIR and ATR-FTIR analyses. Integrated surface excesses of P(VDF-HFA) component (
ABSTRACT:The gradient structure was observed for the sectional layer of the poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate); P(2EHA-AA-V Ac)/poly(vinylidene fluoride-co-hexafluoro acetone); P(VDF-HFA) (30/70) blend thin film using SEM. The elipsoidal domain corresponded to P(2EHA-AA-VAc) particle was observed and its size increased from surface to bottom. In the bottom side, P(2EHA-AA-VAc) layer having -10 µm thickness was formed. The characteristic gradient domain morphology was reduced by adding the micrograin silica into P(2EHA-AA-VAc)/P(VDF-HFA) (30/70) blend. Finally, pressure sensitive adhesive; PSA properties (180° peel adhesion and probe tack) were evaluated in these blends on account of confirming the effect of the micrograin silica on the gradient structure.KEY WORDS Blends / Gradient Structure / Micrograin Silica / Pressure Sensitive Adhesive / Scanning Electron Microscopy/ Recently, the design of the gradient structure has been carried out for binary polymer blends. In the gradient structure, the concentration of one component changes from surface to bottom. The gradient structure made of metal and ceramics is already noted as an air-space material. 1 Agari et al. 2 prepared the gradient structure in the blends of poly(vinyl chloride): PVC with poly-(methyl methacrylate): PMMA by a dissolution and diffusion method. They classified gradient blend films prepared by various conditions, such as various kinds of solvent, casting temperature, molecular weights of PVC, and amounts of PMMA solution into five types. Finally, the physical properties (tensile strength, tan b) of the PVC/PMMA gradient blend were compared with those of a homogeneously miscible blends, PVC, PMMA, and a PVC-PMMA laminate film. Okazaki and coworkers 3 noted that the higher order structure of polyurethane elastomer could be changed by thermal hysteresis. They prepared the gradient structure by controlling temperature between surface and bottom of the mold.On the other hand, in the blends of P(2EHA-AA-VAc) and P(VDF-HFA) we 4 -10 prepared the gradient structure by coating from THF solution. Since P(VDF-HFA) component enriched on surface and P(2EHA-AA-VAc) segregated at bottom, the tack value of bottom side was remarkably larger than that of surface side. We presumed that the characteristic gradient structure was formed by miscibility, difference of surface tension between component, rate of solvent evaporation and convection in solution. Finally, we expected that these blends can be utilized as non-backing pressure sensitive adhesive. In the previous study, 7 • 10 the sectional layer of P(2EHA-AA-VAc)/P(VDF-HFA) blends was observed using SEM and TEM. In the P(2EHA-AA-1 To whom correspondence should be addressed.
158V Ac)/P(VDF-HFA) (50/50), (30/70) blends, the elipsoidal domain of P(2EHA-AA-VAc) was observed and its size increased from surface to bottom. Particularly, since P(2EHA-AA-VAc) layer of about 0.5-3µm thickness was observed in the bottom side, the difference of tackiness value between surface and bottom was very...
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