The reflectivity of the ultradense silicon nanowire arrays was also characterized to verify the effectiveness of light trapping in the structure as predicted by simulations [28, 29]. Reflectivity measurement on a 5-μm-long silicon nanowire array is presented in Figure 5 and shows a strong difference compared to bulk silicon. Reflectivity is indeed reduced from 45 to around 5%, revealing a strong absorption of light by the nanostructured surface of the sample. It is interesting to notice that even if the nanowires are not as perfectly ordered as in simulations or with lithographically patterned top-down arrays, light absorption is still greatly
improved close to 1. This enhanced optical property combined with the very high density of nanowires on the samples is very promising towards the future use of this kind of nanowire arrays Small molecule library as detectors or photovoltaic devices. Figure 5 Reflectivity. Measured reflection coefficient for bulk silicon (blue) and a 5-μm-long silicon nanowire array (red). Conclusions Silicon nanowire arrays were produced presenting top-down features but using a bottom-up CVD process. A very high density was reached with a planarized overall surface and long-range periodicity leading to interesting optical behavior such as an increased
light this website absorption. Silicon nanowires are monocrystalline and grew on a nonpreferential (100) silicon substrate, opening the way to the use of this technique on noncrystalline universal substrates such as glass or metals. Acknowledgments The authors would like to thank Marc Zelsmann for his help in the deposition of thick aluminum. Special thanks go to the BM2-D2AM beamline staff of ESRF for their technical support. This work was financially supported by the French Ministère de la Défense-Direction Générale de l’Armement and by the Region Rhône-Alpes Scientific Research Department via Clusters de Micro et Nanotechnologies. References 1. Tian B, Zheng X, Kempa TJ, Fang Y, Yu N, Yu G, Huang J, Lieber CM: Coaxial PtdIns(3,4)P2 silicon nanowires as solar cells and nanoelectronic power sources. Nature 2007, 449:885–889.CrossRef 2. Hochbaum AI, Chen R, Delgado
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