The SiNWs were grown in a CVD reactor by VLS method via gold catalysis on highly doped n-Si (111) substrate (doping level (i.e., the number of doping atoms per cubic centimeter of materials, N d = 5.1018 cm−3). Gold colloids with size of 50 nm are used as catalysts, H2 as carrier gas, silane (SiH4) as silicon precursor, phosphine (PH3) learn more as n-doping gas, and HCl as additive gas. As shown in our previous work

[19–21], the use of HCl in our process this website enables us to reduce the gold surface migration. Thus, the nanowires (NWs) morphology is improved and their length is not limited. Prior to the growth, the substrates surface has been prepared by successive dipping in (a) acetone, isopropanol and caro (H2SO4/H2O2, 3:1) to remove organic impurities followed by (b) 10% HF and NH4F solution to remove the native oxide layer. Then, 50-nm gold colloids are deposited on the surface with 10% HF from an aqueous gold colloid solution (British Bio

Cell EVP4593 chemical structure International Ltd., Llanishen, Cardiff, UK). The growth has been performed at 600°C, under 3 Torr total pressure, with 40 sccm (standard cubic centimeters) of SiH4, 100 sccm of PH3 gas (0.2% PH3 in H2), 100 sccm of HCl gas and 700 sccm of H2 as supporting gas [19]. Our VLS-CVD method enables an easier control of SiNWs parameters (length, density, diameter, doping type, and doping level) and growth on low cost substrates. The doping level of the SiNWs is managed by the pressure ratio: dopant gas/SiH4. In our almost setup the ratio can vary from 10−6 to 10−2 to obtain doping level from Nd ≈1016 to ≈1020 cm−3[20]. It was checked by resistivity measurements in four probes configuration [21, 22]. The SiNWs length is monitored by the gas injection time.

The growth rate is about 500 nm/min under these conditions. SiNWs morphologies are checked by scanning electron microscopy (SEM) before and after electrochemical cycling. SiNWs density is estimated by counting the number of gold colloids per square centimeters on several SEM images. SiNWs electrochemical characterization All experiments were performed in a glove box at room temperature. The electrolyte was 1 M NEt4BF4 (Fluka Chemika, Buchs, Switzerland) in propylene carbonate (Sigma Aldrich, St. Louis, MO, USA). Nanostructured silicon (n-SiNWs) and bulk silicon substrates (n-Si) were always directly used as electrodes. Micro-ultracapacitors with two identical n-SiNWs electrodes were built by clipping the aluminum current collector, silicon electrodes (Si = 1 cm2), and glass fiber paper as separator. The n-SiNWs with several lengths (5, 10, and 20 μm) were used. In the same way, a micro-EC with two bulk n-Si substrate was built. Electrochemical instruments consisted of Potentiostat/galvanostat equipped with low current channels (VMP3 from Biologic with Ec-Lab software, Slough Berkshire, UK). All SiNWs/SiNWs micro-ultracapacitors were first characterized by cyclic voltammetry with a 100 mV s−1 scan rate between 0.01 and 1 V (Figure 1).