Keeping semiconductors safe from harm Solar cells harvest the energy of sunlight to create electricity, but electricity is hard to store. Solar cells could also be used to make hydrogen from water, which can be stored as a fuel. Separating water into hydrogen and oxygen, however, presents challenges, especially if this is done directly by illuminating the anode that oxides water. Under the acidic or alkaline conditions needed for practical devices, semiconducting anode materials corrode during operation. Hu et al. now show that amorphous titanium dioxide coatings can protect semiconductors from alkaline corrosion while still allowing light through. Science , this issue p. 1005

Solid-state electrical, photoelectrochemical, and photoelectron spectroscopic techniques have been used to characterize the behavior and electronic structure of interfaces between n-Si, n + -Si, or p + -Si surfaces and amorphous coatings of TiO 2 formed using atomiclayer deposition. Photoelectrochemical measurements of n-Si/TiO 2 /Ni interfaces in contact with a series of one-electron, electrochemically reversible redox systems indicated that the n-Si/TiO 2 /Ni structure acted as a buried junction whose photovoltage was independent of the formal potential of the contacting electrolyte. Solid-state current−voltage analysis indicated that the built-in voltage of the n-Si/TiO 2 heterojunction was ∼0.7 V, with an effective Richardson constant ∼1/100th of the value of typical Si/metal Schottky barriers. X-ray photoelectron spectroscopic data allowed formulation of energy band-diagrams for the n-Si/ TiO 2 , n + -Si/TiO 2 , and p + -Si/TiO 2 interfaces. The XPS data were consistent with the rectifying behavior observed for amorphous TiO 2 interfaces with n-Si and n + -Si surfaces and with an ohmic contact at the interface between amorphous TiO 2 and p + -Si.

Figure 1S. J-V curves of ~18 nm hematite electrodes with (solid dark blue) and without (dashed red) Ga 2 O 3 underlayer, under water oxidation condition in dark.

Photoresponsive materials that adapt their morphologies, growth directions, and growth rates dynamically in response to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex 3D mesostructures via feedback between illumination and the structure that develops under optical excitation. We report the spontaneous development of ordered, nanoscale lamellar patterns in electrodeposited selenium-tellurium (Se-Te) alloy films grown under noncoherent, uniform illumination on unpatterned substrates in an isotropic electrolyte solution. These inorganic nanostructures exhibited phototropic growth in which lamellar stripes grew toward the incident light source, adopted an orientation parallel to the light polarization direction with a period controlled by the illumination wavelength, and showed an increased growth rate with increasing light intensity. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the template-free and pattern-free synthesis, on a variety of substrates, of woodpile, spiral, branched, or zigzag structures, along with dynamically directed growth toward a noncoherent, uniform intensity light source. Full-wave electromagnetic simulations in combination with Monte Carlo growth simulations were used to model light-matter interactions in the Se-Te films and produced a model for the morphological evolution of the lamellar structures under phototropic growth conditions. The experiments and simulations are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphological mode in the emergent nanoscale patterns.spontaneous pattern formation | dynamic response | nanostructured material | light-directed growth

Wire Growth Parameters. Silicon wires ranging from 40-100 µm in length were fabricated by the vapor-liquid-solid (VLS) growth technique through the use of an in-house reactor. 1 The growth substrate was a p+ Si (111) wafer (resistivity <0.005 Ω cm) that had been coated with a 300 nm thermal oxide layer. Photolithography was used to pattern a hexagonal

are deposited on Si, GaAs, and GaP electrodes by atomic layer deposition. The coatings prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of the protected semiconductors. Si photoanodes show continuous oxidation of aqueous KOH to O 2 for more than 100 h at photocurrent densities of >30 mA/cm 2 and about 100% Faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes show photovoltages of 0.81 and 0.59 V and light-limited photocurrent densities of 14.3 and 3.4 mA/cm 2 , respectively, for water oxidation. -(HU, S.; SHANER, M. R.; BEARDSLEE, J. A.; LICHTERMAN, M.; BRUNSCHWIG, B. S.; LEWIS*, N. S.; Science (Washington, DC, U. S.) 344 (2014) 6187, 1005-1009, http://dx.doi.org/10.1126/science.1251428 ; Div. Chem. Chem. Eng., Calif. Inst. Technol., Pasadena, CA 91125, USA; Eng.) -W. Pewestorf 34-009

Communication: Two single source precursors for vanadium oxide (vanadium oxytripropoxide, VO(OC 3 H 7 ) 3 and vanadium oxytrinitrate, VO(NO 3 ) 3 ) are used to prepare selective chemical sensors. Sensors demonstrate reduced sensitivity to compounds formed during their preparation. X-ray diffraction and electron microscopy studies suggest that this selectivity is likely due to preferred orientation resulting from differences in the molecular structures of the single source precursors used for preparing the vanadium oxide. Communication: Large-area (370mm  500mm) diamond-like carbon (DLC) films were deposited on the glass substrate by low-pressure dielectric barrier discharges. The deposited DLC films were hard, homogeneous and extremely smooth. The DLC film deposited on the large-area glass can be potentially used as a scratch resistant and corrosion barrier layer. Communication: SiCN films were produced by remote microwave hydrogen plasma CVD (RP-CVD) from tris(dimethylamino)silane precursor using different substrate temperature in the range T S = 30-400 8C. The effect of T S on the rate of RP-CVD, chemical structure, surface morphology, density, and photoluminescence (PL) of resulting films is reported. The increase in T S causes the formation of silicon carbonitride network, marked densification and smoothening of film surface, as well as shift of PL peak position.