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A B S T R A C T S MONDAY, JUNE 28 N A N O S E A 2 0 1 0 18H30-18H50 Fabrication of Ordered Silicon Nanowires by Self-Assembling and Metal Assisted Etching. L. Boarino1, E. Enrico1, N. De Leo1, F. Celegato1, P. Tiberto1, E. Lepore2 and N. Pugno2 (1 NanoFacility Piemonte, Electromagnetism Division, Istituto Nazionale di Ricerca Metrologica, Stradadelle Cacce 91 - 10135 Turin, Italy; E-mail: l.boarino@inrim.it; Tel: +39 (11) 39196402 Dept. of Structural and Geotechnical Eng., Politecnico di Torino, C.so Duca degli Abruzzi 24 - 10148Turin, Italy) 1 – Introduction The field of silicon nanowires (SiNWs) saw, in the last years, a real boom in the number and quality of publications. A part the basic research, investigating the most fundamental properties like electron transport1 and mechanics2, several fields of application can take advantage from silicon nanowires, like energy, with photovoltaic devices of new generation3, energy harvesting by vibrations4 and new adhesives5. The recent development of the self-catalytic electroless etching in presence of metals6, give us a new degree of freedom in nanofabrication, because this kind of etching is only slightly dependent on silicon wafer doping and from solutions and etching conditions7 but mainly from metal distribution, thickness or patterning at the silicon surface. We used these different conditions, from continuous thin silver films deposited by different methods and with different thickness to nanopatterned thin films by means of self-assembled monolayers of polystyrene nanospheres to obtain forests of silicon nanowires with different spatial density, distribution and order. A preliminary analysis of contact angles is provided, since ordered arrays of SiNWs are interesting systems for the study and fabrication of self-cleaning surfaces and new types of adhesives. 2 – Abstract Silicon wafer by MEMC Corporation, 20-30 Ohm cm have been cleaned by RCA for one hour to remove organic contamination, and then silver thin films of different thicknesses (20, 30 and 40 nm) have been thermally evaporated and sputtered. On one serie of samples, after SEM inspection by a FEI Inspect F, to check thin film quality and adhesion, MAE etching has been performed with no patterning. On another serie, a large 2D crystal of Sigma Aldrich 500 nm polystyrene nanospheres has been selfassembled and applied. Sputter etching by Ar ions is then performed, with times ranging from 1 to 2 minutes (processing steps shown in Fig. 2), to obtain a silver film with regular indentation favouring the extrusion of silicon nanowires in the following etching step. At this point Metal Assisted Etching has been performed for both the series of samples for 60 seconds at 60° C in a solution of HF:H2O2:H2O, 22%:9%:69% in volume. After rinsing in water, the final SEM analysis reveals for the continuous silver thin films of different thickness, the expected disordered forest of silicon nanowires. What is interesting is the change in wire diameter and spatial distribution as a function of the silver thickness. Preliminary contact angle measurements confirmed contact angles close to 150°, in the regime of superhydrophobicity8. The serie patterned with nanospheres and then sputter-etched, shows large ordered areas, characterized by the memory of the spheres distributions, with nanopillars and nanowires depending on the time of etching and form the efficiency of the local reaction. Figure 2. Processing steps for SiNWs by MAE and PSNS self assembling 21
A B S T R A C T S MONDAY, JUNE 28 N A N O S E A 2 0 1 0 3 – Conclusion In this work ordered nanopillars and nanowires by MAE and PSNS self-assembling has been obtained with good uniformity on large area. A preliminary study of contact angles reveals superhydrophobicity of such a surface. Acknowledgements This work has been performed at NanoFacility Piemonte, INRiM, a laboratory supported by Compagnia di San Paolo. 1 Y. Li, F. Qian, J. Xiang et al., Materials Today 9 (10), 18-27 (2006). 2 M. Menon, D. Srivastava, I. Ponomareva et al., Physical Review B 70 (12) (2004). 3 T. Bozhi, X. Zheng, T. J. Kempa, Y. Fang, N. Yu, G. Yu, J. Huang, C. M. Lieber, Nature 449 (7164), 885 - 889 (2007). 4 L. Qu, Y. Li, H. Zhang, Y. Huang, X. Duan, Nano Letters 9 ( (12)), 4539-4543 (2009). 5 B. J. Alemn, K. E. Fischer, S. L. Tao, R. H. Daniels, E. M. Li, M. D. Bnger, G. Nagaraj, P. Singh, A. Zettl, T. A. Desai, Nano Letters 9 ( (2)), 716-720 (2009). 6. S. Chattopadhyay, Xiuling Li, and P. W. Bohn, Journal of Applied Physics 91 (9), 6134-6140 (2002). 7. S. Bastide, C. Chartier, and C. Levy-Clement, Electrochimica Acta 53, 5509–5516 (2008). 8. G. Piret, Y. Coffinier, C. Roux, O. Melnyk, R. Boukherroub; Langmuir 24, 1670 (2008) 18H50-19H10 Synthesis of cation-intercalated titanate nanobelts. Lei Miao 1, Sakae Tanemura2,1*, Rong Huang3, Chenyan Liu1, C.M.Huang1, Gang Xu1 (1. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No.2 Nengyuan Road, Wushan, Tianhe district, Guangzhou, 510640, P.R.China; 2. Japan Fine Ceramic Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan; 3. Key Laboratory of Polarized Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062, China). miaolei@ms.giec.ac.cn, *tanemura-sakae@jfcc.or.jp, rhuang@ee.ecnu.edu.cn 1 – Introduction Protonated-titanate nanostructured materials have attracted increasing attention owing to their potential applications on water photo-decomposition, photocatalysis, hydrogen storage, sensors, and batteries, electrochromism, photoluminescence, dye-sensitized solar cells, as well as active ion-exchange/ intercalation reaction. In order to explore more excellent performance, it is highly desirable to control the lectric and optical properties by different metal ion intercalation. Pure and cations (Li+, Sn2+, Al3+, Fe3+) intercalated titanate nanobelts with high aspect ratios, good crystal quality, large specific surface areas and uniform dispersion, were synthesized by alkaline hydrothermal treatment of ground TiO2 powdersfollowed by special washing-treatment process. The morphology, composition, crystal structure, and electrical conductivity of the obtained nanobelts are studied in this work. 2 – Abstract The ground TiO2 powders were hydrothermally treated using 10 M NaOH solution at 150 oC for 40 hrs in a stainless Teflon-lined autoclave. Details of the fabrication process were already reported elsewhere [1-2]. Cation-exchange reactions were carried out in aqueous ammonia solution with Li+, Sn2+, Al3+, and Fe3+ respectively for 4 kinds of intercalated samples, because of the stability of titanate nanobelts in basic solution and the stabilization of these substituting ions by complication with ammonia. In a typical process, 10 g of salts (SnCl2·2H2O, Al(NO3)·9H2O, LiCl and FeCl3·2H2O, (Alfa Aesar chemicals company), of the 22
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