One dimensional silicon nanostructures have attracted remarkable attentions due to their unique electronic, optoelectronic and thermal properties [1]. Recently, silicon nanowires (SiNWs) become the promising architecture in the present miniaturization of silicon-based devices, enabling many potential applications such as field-effect transistors (FET) [2], optoelectronics [3] and solar cells [3, 4]. In fact, the most crucial step to address the practical applications based on SiNWs is the control over dimensions, crystallographic orientation and doping level for the formation of SiNWs. These issues remain particularly challenging for constructing the complex SiNW- based devices [8] or integration of multifunctional elements [9], and one promising solution is the controlled synthesis of ultra-long SiNWs with uniform structure and properties which has been reported by W. Park et al [10]. So far, great efforts have been made to fabricate the ultra-long SiNWs, including thermal evaporation [11] and vapor- liquid- solid (VLS) growth [10]. Nevertheless, those aforementioned approaches involve serve vacuum condition, high process temperature and preparation of catalytic materials, leading the entire processes to be quite expensive and complex [10, 11] and incapable of fabricating a large area of well- aligned SiNW arrays.
As a consequence, we report the fabrication of single crystalline SiNW arrays with uniform length up to 450 μm via modified electroless metal deposition (EMD) method [12]. The utilization of conventional EMD method to fabricate ordered SiNW arrays is rather simple and inexpensive, in which the entire processes are carried out by mean of immersing silicon wafer into HF/ AgNO3 electrolyte solution at near room temperature. Nevertheless, we find that the succeeding formation of SiNWs via typical EMD approach is prohibited from the abundant Ag dendrites covering on the surface of SiNWs, impeding the controllability of SiNWs lengths over 250 μm [13-17]. To overcome it, the diluted HNO3 solution is introduced in EMD method to render the continuity of galvanic reaction, enabling the fabrication of wafer- scale well- aligned SiNW arrays with desired length ranging from several up to hundreds micrometers and even approaching to the thickness of used Si substrate
Indeed, the diameter of formed Si nanowire cannot be adjusted by using the conventional EMD method because multiple process factors are involved simultaneously in its galvanic reaction, so that their diameter has a wide distribution from 10 to 500 nm. Besides, SiNW-based structures are widely employed in diverse field and the high performance devices of SiNW are crucial to its diameter, especially the electrical and optical properties of SiNWs are strongly size dependent. Recently, researchers are effortfully searching for the appropriate diameter range of SiNWs to attain the corresponding optimal applications. Specifically, SiNWs smaller than 100 nm in diameter may be used in high-speed quantum-wire field effect transistors and light-emitting devices with extremely low power consumption [18], and SiNWs with width <150 nm are virtually sensitive to detect threshold shifts between buffer solutions of different pH [19]. On the contrary, the unique property such as, the independence of elastic modulus from their structure diameter [20] and a polarization-independent response in the building block for photovoltaic systems [21] are also exhibited if the diameter larger than 100 nm. In general, an average SiNW diameter of approximately 100 nm achieves satisfactorily their properties as mention above. Therefore, we apply Response Surface Methodology (RSM), a collection of statistical and mathematical techniques, for finding out the optimization of the response with the lowest standard deviation in order to fabricate 1D Silicon structures with 100 nm in diameter.

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