Supporting Information: Fabrication of ultra-dense sub-10 nm in-plane Si nanowire arrays from a novel block copolymer method: optical properties

Materials: Ethylene oxide (all materials Sigma Aldrich unless stated) was dried over CaH 2 , purified through n-BuLi twice for 30 min at-10 0 C and was then distilled into an appropriately calibrated Pyrex ampule for use. Phosphazene base (P 4-t-Bu) (1M solution in hexane), sec-BuLi (1.4 M solution in cyclohexane) and acetic acid (Panreac) were used without further purification. Benzene (Chem Lab, 99.7%) was freshly distilled from CaH 2 and polystyryl lithium (PS (+) Li (and and kept for further use. Styrene and dibutylmagnesium were purified through CaH 2 distillation and added to calibrated Pyrex ampules. Various other solvents/salts were used as detailed toluene, Tetrahydrofuran (THF), anhydrous alcohol (ETH), Dimethylformamide (DMF) and Lithium chloride. Single crystal (100) boron doped (P type) silicon wafers with a native silica layer were used as general substrates. Different hard mask substrates such as Si-ARC (anti-reflective coating), alumina and carbon hard mask (CHM) etc. are selected to check the applicability of the pattern formation. For filtration, Fluoropore ™ PTFE filter membranes with a pore size 0.2 μm, diameter of 25 mm thickness was used. Polymerization: Styrene (2.5 g, 0.024 mol) was introduced from the Pyrex ampoule into a flask under high vacuum containing 200 mL of freshly distilled benzene. Approximately, 1 mmol of sec-BuLi (initiator) was added and the mixture was left to react for 24 hours at room temperature. Then, 2.5 g (0.057 mol) ethylene oxide was introduced in the mixture from a Pyrex ampule. The red solution due to active PS (-) Li (+) became transparent after the addition Electronic Supplementary Material (ESI) for Nanoscale.