We report galvanic deposition of Si onto 6061 Al alloy from dilute aqueous hydrofluoric acid ͑HF͒ at pH 2.5. The overall reaction involves reduction of SiF 6 2− to Si with simultaneous oxidation and dissolution of Al. The Si film is about 12 m thick after 6 h of deposition. High resolution scanning electron microscopy shows that these Si films are nanoporous, with pore sizes ranging from 3 to 8 nm. The nanoporous Si films oxidize rapidly upon sample emersion. Elemental analysis by energy dispersive X-ray spectroscopy demonstrates that the as-deposited film contains 1-3 atom % Al, 3-6 atom % Cu, and 90-95 atom % Si. We believe that this is the first report of electrochemical deposition of Si thin films that does not involve organic solvents or molten salt electrolytes.

We report room temperature deposition of compact Si films onto 6061 Al alloy from aqueous solutions containing 10 mM HF and 20 mM Na 2 SiF 6 in 80 wt % formic acid (HCO 2 H) by a combination of galvanic and electroless deposition. Deposition for 30 h. yields a 7-10 m thick, dark grey Si thin film that does not change color upon exposure to air. Elemental analysis demonstrates that the as-deposited film contains 2-3 atom % Al, 4-5 atom % Cu, and 92-94 atom % Si. We believe that this is the first report of aqueous, room temperature deposition of thick, compact Si films.

We report galvanic deposition of Mo films onto 6061 Al alloy from aqueous solutions containing 1 mM HNO 3 and 10 mM MoCl 5 . Deposition for 40 min. yields an 9 μm thick Mo film, which also contains 18 atom% Al. The corrosion resistance of the Mo film is studied by voltammetry and electrochemical impedance spectroscopy in 0.5 M H 2 SO 4 and in 3.5 wt% NaCl electrolyte at pH 2, 7 and 12. These demonstrate that the galvanic Mo film significantly improves the corrosion resistance of the underlying Al 6061 substrate. Galvanic deposition appears to yield elemental, amorphous Mo films.Mo thin films have many technological applications, including back contacts for photovoltaic devices and corrosion-resistant coatings. 1,2 However, Mo thin film deposition currently requires expensive vacuum methods such as magnetron sputtering. 3 Electrochemical methods for thin film growth are often less expensive, easier to scale-up, and more amenable to high-volume manufacturing than vacuum methods. 4 Electrochemical deposition of refractory metals from aqueous electrolytes is difficult due to the relatively cathodic standard reduction potentials, multiple valence states, and complex oxy-anion solution phase chemistry. 5 Mo electrodeposition has been reported mainly from non-aqueous electrolytes such as high temperature molten salts. 6-8 More recently, Mo electrodeposition from aqueous electrolytes has also been reported, 9,10 but either without evidence for complete reduction to Mo(0), 9 or with extremely low current efficiency due to copious hydrogen evolution. 10 Mo alloys with a Mo content less than 50% can also be obtained from aqueous electrolytes. [11][12][13] We report galvanic deposition of compact Mo thin films onto Al 6061 alloy from a simple aqueous electrolyte. Energy dispersive X-ray spectroscopy (EDX) measurements indicate that these films contain primarily Mo and Al. These galvanic Mo films are also characterized by voltammetry and electrochemical impedance spectroscopy (EIS) in 0.5 M H 2 SO 4 and in 3.5 wt% NaCl electrolyte at pH 2, 7 and 12. ExperimentalConcentrated HNO 3 was obtained from J.T. Baker, MoCl 5 was obtained from Alfa Aesar, and 99.999% pure Al rod and 6061 Al foil (76 μm thick) were obtained from ESPI Metals. Al 6061 alloy typically contains 0.8-1.2 wt% Mg, 0.4-0.8 wt% Si, ≤ 0.70 wt% Mg, 0.15-0.40 wt% Cu, 0.04-0.35 wt% Cr, and smaller amounts of Mn, Ti, and Zn. Prior to Mo deposition, 6061 Al alloy was roughened with 150 grit Al 2 O 3 sandpaper and rinsed with water according to ASTM standard B253-11. MoCl 5 is corrosive and water-reactive, so it was stored under vacuum, and all experiments were performed in a chemical fume hood. All experiments were performed at room temperature (20 • C).Voltammetry and open circuit potential measurements were performed with an EG&G PAR model 273A potentiostat/galvanostat with an Al 6061 foil working electrode, Pt counter electrode, and SCE reference electrode. Electrochemical impedance spectroscopy (EIS) measurements were performed with a Solartron 1250 frequency respo...