Nassiopoulou et al. Nanoscale Research Letters 2011, 6:597 http://www.nanoscalereslett.com/content/6/1/597 N A N O E X P R E S S Open Access Si nanowires by a single-step metal-assisted chemical etching process on lithographically defined areas: formation kinetics Androula Galiouna Nassiopoulou*, Violetta Gianneta and Charalambos Katsogridakis Abstract In this paper, we investigate the formation kinetics of Si nanowires [SiNWs] on lithographically defined areas using a single-step metal-assisted chemical etching process in an aqueous HF/AgNO3 solution. We show that the etch rate of Si, and consequently, the SiNW length, is much higher on the lithographically defined areas compared with that on the non-patterned areas. A comparative study of the etch rate in the two cases under the same experimental conditions showed that this effect is much more pronounced at the beginning of the etching process. Moreover, it was found that in both cases, the nanowire formation rate is linear with temperature in the range from 20°C to 50°C, with almost the same activation energy, as obtained from an Arrhenius plot (0.37 eV in the case of non-patterned areas, while 0.38 eV in the case of lithographically patterned areas). The higher etch rate on lithographically defined areas is mainly attributed to Si surface modification during the photolithographic process. PACS: 68; 68.65-k. Keywords: Si nanowires, metal-assisted chemical etching, lithographically defined areas, formation kinetics Introduction Si nanostructures such as quantum dots, nanocrystals, porous Si, and Si nanowires [SiNWs] exhibit interesting properties [1-4] that are very different from their bulk counterparts and make them interesting for several applications. These properties include a diameter-depen- dent bandgap, very-high-density electronic states, an increased surface-to-volume ratio, an enhanced exciton binding energy, enhanced thermoelectric properties, and increased surface scattering for electrons and phonons. These properties make SiNWs interesting for applica- tion in electronic and photonic devices [4-16], sensors [17], energy harvesting devices, and solar cells [18-20]. Different methods have been developed for the fabri- cation of SiNWs either by Si etching [12,21,22] or by Si nanowire synthesis [1,23]. Among them, the technique of metal-assisted chemical etching [MACE] [24-29] has gained an increasing interest in the last years due to its * Correspondence: A.Nassiopoulou@imel.demokritos.gr Institute of Microelectronics (IMEL), National Center for Scientific Research (NCSR) Demokritos, Terma Patriarhou Gregoriou, Aghia Paraskevi, Athens, 15310, Greece simplicity and the high crystalline quality of the obtained SiNWs, resulting from etching of the single crystalline Si material. SiNWs with lengths ranging from a few micrometers to several tens of micrometers can be obtained using either a two-step process involving metal (Ag, Pt) nanoparticle deposition on Si followed by etching or a single-step chemical dissolution process in an aqueous HF solution containing the metal salt. The SiNWs can be fabricated on large areas, which can cover the whole Si wafer. However, for the different applications (Si devices), it is interesting to form the SiNWs on specific confined areas of the Si wafer. It is thus important to develop a technology for their local formation on Si on preselected areas. In this work, we report on the formation kinetics of SiNWs on lithographically defined areas on the Si wafer using a single-step MACE process based on an aqueous HF/AgNO3 solution. We investigated the etch rate of Si, and the corresponding SiNW length, on lithographically defined Si areas compared to that on large non-pat- terned areas. Field emission scanning electron micro- scopy [FE-SEM] was used to characterize the samples. © 2011 Nassiopoulou et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.