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Single crystalline silicon nanowires (SiNWs) were grown using a gold (Au)-catalyzed vapor-liquid-solid (VLS) approach. In this study, we examine the influence of the size of Au catalyst droplets on the size of SiNWs and discuss the effect of Au diffusion and surface passivation on SiNW sidewall faceting and roughening in the VLS process. To simultaneously cover a variety of sizes of SiNWs on the same substrate, 2-nm-thick Au film was used on Si (111) substrate as a catalyst, since it is known that Au thin film–based seed offers relatively less control of the NW size, due to the randomness of the film breakup at reaction temperature. We then found that the grown SiNWs have two main types of surface morphologies on the sidewall of the nanowires (NWs). One type had a small and coarse surface morphology with no Au-Si droplets at the top of the NWs. The other type had a long and smooth surface and still had Au-Si droplets at the end. The fact that resulting SiNWs have two main different surface morphologies can be explained by three reasons: the size difference of Au-Si droplets, Au diffusion to the surface of the SiNWs, and surface passivation on the SiNW surface. Furthermore, we proposed a combined VLS and vapor-solid (VS) growth model to describe the creation of the facets and roughening of the sidewall of the NWs. Our results point toward the exciting possibility that the proposed well-controlled and coarse-surfaced SiNWs could be promising thermoelectric materials with low thermal conductivity, since the thermal conductivity is greatly reduced at the rough surface due to the enhancement of phonon scattering.

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The aim of this study was to profile the bioaccessibility and intestinal absorption of epicatechins and flavonols in different forms of green tea and its formulation: loose leaf tea, powdered tea, 35% catechins containing GTE, and GTE formulated with green tea-derived polysaccharide and flavonols (CATEPLUS™). The bioaccessibillity and intestinal absorption of epicatechins and flavonols was investigated by using an in vitro digestion model system with Caco-2 cells. The bioaccessibility of total epicatechins in loose leaf tea, powdered tea, GTE, and CATEPLUS™ was 1.27%, 2.30%, 22.05%, and 18.72%, respectively, showing that GTE and CATEPLUS™ had significantly higher bioaccessibility than powdered tea and loose leaf tea. None of the flavonols were detected in powdered tea and loose leaf tea, but the bioaccessibility of the total flavonols in GTE and CATEPLUS™ was 85.74% and 66.98%, respectively. The highest intestinal absorption of epicatechins was found in CATEPLUS™ (171.39 ± 5.39 ng/mg protein) followed by GTE (57.38 ± 9.31), powdered tea (3.60 ± 0.67), and loose leaf tea (2.94 ± 1.03). The results from the study suggest that formulating green tea extracts rich in catechins with second components obtained from green tea processing could enhance the bioavailability of epicatechins.

Single crystalline silicon nanowires (SiNWs) were grown on Si(100) substrate using a gold (Au)-catalyzed vapor-liquid-solid (VLS) approach. The dependence of the growth time (i.e., the time of exposure to the Si source) on the density and surface evolution of the grown SiNWs is considered. It was observed that the density of grown SiNWs on Si substrate increased with increasing growth time. The highest density (approximately 1.1 x 10(6) mm(-2)) was reached at 4 hr. Upon further exposure to the Si source, we observed that the density was maintained for up to 9 hr. We suggest that the increased Si chemical potential in Au-Si droplets with increased growth time enhanced the SiNW growth rate at the interfaces between Au-Si droplets and SiNWs, and enhanced the transition of the NWs from the existing Au-Si droplets onto Si substrate. This allows the SiNW density to increase with increased growth time of up to 4 hr. Moreover, we examined the influence of the growth time on surface evolution including Au diffusion, facet and taper formation, and vapor-solid (VS) growth of the SiNWs. To explain the behavior of the grown SiNWs in the VLS process, we propose a combined model using the VLS and VS growth mechanisms.