TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The etching solution comprises 5-20 vol.% hydrofluoric acid. The etching solution further comprises water.    TECHNOLOGY FOCUS - METALLURGY - Preferred Method: The substrate is doped with boron, polished in the (100) directions, and electrochemically etched in a single step. The method also includes applying a current density and providing an etching solution formulation according to one of the following alternatives: (a) 100-2000 mA/cm2 and 38% HF, (b) 1-50 mA/cm2 and 10% HF, or 15-30 mA/cm2 and 10% HF; electrochemically etching the substrate for 1 second to 24 hours, 1-60 minutes, or 1-10 minutes; removing the substrate from the etching solution and washing and/or drying the substrate; washing the substrate after removal from the etching solution with one or more of water, ethanol, hexane or pentane; drying the substrate by blowing an inert gas over a surface of the substrate; subjecting the substrate to a supercritical drying or freeze drying procedure; removing the silicon nanowires from the substrate surface; immersing the substrate in an ultrasonication solution and applying ultrasonic energy to the solution; at least partially oxidizing the etched substrate; and electrochemically etching the substrate to produce a porosity of greater than or equal to 80 or greater than or equal to 90%, on the etched surface of the substrate. The electrochemical etching is carried out in the dark or in the presence of a light source. The ultrasonic energy is applied for 5 minutes to 48 hours, or more. The current is direct current or alternating current. The substrate is partially polished, e.g. by electropolishing and/or evaporation induced polishing. Preferred Component: The substrate is of the p-type, p+ type, p++ type, or n-type. The substrate lacks a p-n junction. The structure also includes the silicon substrate; one or more thin films of silicon or silicon oxide interconnecting the silicon nanowires, thus forming an interconnected network; and a substrate comprising a boron-doped silicon wafer.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The etching solution comprises hydrofluoric acid (HF), water (H2O) and ethanol in the following proportions: 48% HF + 52% H2O solution:ethanol=1:4 by volume.