The effect of hydrogen dilution on the optical, transport, and structural properties of amorphous and microcrystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (rf) plasma-enhanced chemical vapor deposition using substrate temperatures ${\mathrm{(T}}_{\mathrm{sub}})$ of 100 and 25 °C is reported. Microcrystalline silicon $\mathrm{(\mu c-}\mathrm{Si:H})$ is obtained using HW with a large crystalline fraction and a crystallite size of ∼30 nm for hydrogen dilutions above 85% independently of $T_{\mathrm{sub}}.$ The deposition of $\mathrm{\mu c-}\mathrm{Si:H}$ by rf, with a crystallite size of ∼8 nm, requires increasing the hydrogen dilution and shows decreasing crystalline fraction as $T_{\mathrm{sub}}$ is decreased. The photoconductivity, defect density, and structure factor of the amorphous silicon films $\mathrm{(a-}\mathrm{Si:H})$ are strongly improved by the use of hydrogen dilution in the $T_{\mathrm{sub}}$ range studied. $\mathrm{a-}\mathrm{Si:H}$ films with a photoconductivity-to-dark conductivity ratio above ${10}^5,$ a deep defect density below ${10}^{17} {\mathrm{cm}}^{\text{−3}},$ an Urbach energy below 60 meV and a structure factor below 0.1 were obtained for rf films down to 25 °C (at growth rates ∼0.1–0.4 Å/s) and for HW films down to 100 °C (at growth rates ∼10 Å/s), using the appropriate hydrogen dilution. In the low $T_{\mathrm{sub}}$ range studied, the growth mechanism, film properties, and the amorphous to microcrystalline silicon transition depend on the flux of atomic hydrogen available. The properties of the films are compared to those of samples produced at 175 and 250 °C in the same reactors.

Ultrafine molybdenum sulfide (MoS2) nanocrystals are grown on a porous cobalt (Co) foam current collector by atomic layer deposition (ALD) using molybdenum hexacarbonyl and hydrogen sulfide as precursors. When used to catalyze the oxygen evolution reaction (OER), the optimal Co@MoS2 electrode, even with a MoS2 loading as small as 0.06 mg cm−2, exhibits a large cathodic shift of ca. 200 mV in the onset potential (the potential at which the current density is 5 mA cm−2), a low overpotential of only 270 mV to attain an anodic current density of 10 mA cm−2, much smaller charge transfer resistance and substantially improved long-term stability at both low and high current densities, with respect to the bare Co foam electrode, showing substantial promise for use as an efficient, low-cost and durable anode in water electrolyzers.