Sectional Scanning Electron Microscope Images Research Articles

Structure-Mechanical Property Relations of Skin-Core Regions of Poly(p-phenylene terephthalamide) Single Fiber

This study aims to elucidate the relationship between the mechanical properties and microstructures of poly(p-phenylene terephthalamide) (PPTA) single fibers at the micro/nano scale. The skin-core structure of Kevlar® 29 fiber was revealed through a focused electron beam experiment inside a scanning electron microscope (SEM) chamber. Cross sectional SEM images of the broken fiber showed that the thickness of the skin ranged from 300 to 800 nm and that the core region consisted of highly packed layers of fibrils. The skin and the core regions showed different mechanical behaviour and structural changes during nanoindentation and micro-tensile tests, indicating that the core region possessed higher stiffness, whereas the skin region could undergo more plastic deformation. Furthermore, micro-tensile testing results showed that the ultimate tensile strength, the elongation at failure, and the tensile toughness of single fibers could be significantly enhanced by cyclic loading. Such findings are important to understand the contribution of different microstructures of Kevlar® fibers to their mechanical performance, which in turn can be utilized to design high-performance fibers that are not limited by the trade-off between toughness and stiffness.

Investigation of Li Source Influence on the Sinterability of Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12

Introduction The development and progress of portable electric devices require lithium-ion batteries with higher energy density. In addition, the safety of batteries also becomes more important, particularly for electric vehicles. As one of solutions to fulfill such requirements, all-solid-state lithium-ion batteries have attracted much attention. One of prospective solid electrolyte for all-solid-state lithium-ion batteries is Li7La3Zr2O12 (LLZ), which has a relatively high Li+ ion conductivity of ~10–4 S cm–1 and the chemical stability against Li metal. However, LLZ requires a very high sintering temperature at around 1100 °C, and basically the preparation of dense LLZ pellets is difficult. To realize the lower sintering temperature and densification of LLZ pellets, sintering additive such as Al and Nb have been investigated. However, there are few studies about the influence of starting materials for LLZ synthesis on the quality of resulting LLZ pellets. In this study, we synthesized Al-doped garnet-type Li6.25La3Zr2Al0.25O12by changing the Li sources to investigated the influence of Li sources on sintering process of Al-doped LLZ. Experimental Al-doped LLZ was synthesized from each Li sources, LiOH·H2O, Li2CO3 and CH3COOLi, by solid phase method. Stoichiometric amounts of Li sources (10% excess) La(OH)3 and ZrO2 were mixed by planetary ball-milling with zirconia balls and hexane, and then calcined at 900 °C for 5 h in alumina crucible. The calcined powders and stoichiometric amounts of γ-Al2O3were mixed by planetary ball-milling with zirconia balls and hexane. The mixed powders were pelletized, and then the pellets were sintered at 900 °C for 3 h and 1200 °C for 12 h with mother powder. Results and discussion X-ray diffraction (XRD) patterns of the samples prepared using LiOH·H2O, Li2CO3 and CH3COOLi as Li sources shows that all the samples are single phase of cubic garnet without impurity. Observation of cross sectional of each pellet was performed by scanning electron microscope (SEM). Al-doped LLZ pellet derived from LiOH·H2O was uniformly dense (Fig. 1(a)). However, many grain boundaries are found when Li2CO3 or CH3COOLi were used as Li sources (Fig. 1 (b) and (c)). These results indicated that Li sources have an influence on sintering behavior of Al-doped LLZ. To investigate difference in sintering behavior, XRD patterns of the calcined powders were measured. The calcined powders derived from Li2CO3 or CH3COOLi included La2Zr2O7 as main component and cubic LLZ, whereas XRD patterns of the calcined powder derived from LiOH·H2O were assigned to single phase of cubic LLZ. Difference between LiOH·H2O and other two Li sources is presence or absence of C element. The C element changed to CO2 and then this CO2 generated Li2CO3 by reacting with raw or calcined materials during calcination. It is known that Li2CO3 inhibits synthesis and sintering of LLZ. Therefore, sintering density of Al-doped LLZ derived from Li2CO3 and CH3COOLi was low. There results indicated that it is important to prepare calcined powders with single phase of cubic LLZ for densification of Al-doped LLZ pellets. Acknowledgement This work was partly supported by Advanced Low Carbon Technology Research and Development Program (ALCA-SPRING) of Japan Science and Technology Agency (JST). Figure captions Fig. 1 Cross sectional SEM images of LLZ pellets derived from (a) LiOH·H2O, (b) Li2CO3 and (c) CH3COOLi. Figure 1

The effect of Pb doping on the characteristic properties of spin coated ZnO thin films: Wrinkle structures

Un-doped and lead (Pb) doped ZnO thin films were deposited by sol–gel spin coating technique. Structural, morphological and optical properties of the films were investigated by means of Pb doping, in the range of 1–4% (with 1at% step). X-ray diffraction results indicated that all films have hexagonal wurtzite crystal structure. (002) Reflection peak has been seen as the most intense peak and the highest texture coefficient value. Grain size values of the films varied from 19.68nm to 13.37nm with the increasing Pb incorporation. The top-view and cross sectional scanning electron microscope images demonstrated that the films were made up of wrinkle network structures and the films' thicknesses changed in the range of 400–276nm. The direct optical band gap was calculated in 3 different functions and a significant harmony was observed among them. Additionally, all results indicated that the direct optical band gap and the Urbach values of the films increase with the increasing Pb doping content. Besides, the effects of Pb content on the photoluminescence properties of ZnO films were evaluated and it was observed that the decrease in the photoluminescence intensity was based on the Pb content. Moreover, the correlation between the optical and structural properties suggested that the optical band gap of Pb doped ZnO films were influenced by the lattice parameters a and c.

A quantitative assessment approach of feasible optical mechanisms contributing to structural color of golden-like Chrysina aurigans scarab beetles

Under normal incidence of non-polarized light, reflection spectra from the cuticle of golden-like C. aurigans scarabs shows a broad band displayed from 525 to 950nm, with a spectral ripple structure that consists of a uniform sequence of peaks superimposed on the main reflection band. Cross sectional Scanning Electron Microscope (SEM) images of the cuticle initially suggest the presence of a multilayered structure. A radiative transfer matrix formalism is first applied to describe as much as possible the main features of coherent reflection spectra, by assuming optically homogenous layers distributed through the exocuticle, with chitin as the major constituent material. Additional non-coherent multiple reflections due to layers in the endocuticle are also evaluated from this approach. The presence of a pigmented micron sized structure beneath the procuticle requires the evaluation of a diffuse light contribution to the reflection. This was carried out from a four-flux radiative transfer model. Optical anisotropy is introduced by interpreting the SEM images in terms of a twisted Bouligand-type structure, and reflection spectra are evaluated from an implementation of the so-called 4×4 Berreman׳s formalism. We have been able to approach the main features characterizing the reflection spectra of C. aurigans׳ elytra following this progressive way.