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22 results on '"Lewis, Nathan S."'

6. High Broadband Light Transmission for Solar Fuels Production Using Dielectric Optical Waveguides in TiO2Nanocone Arrays

Author

Yalamanchili, Sisir, Verlage, Erik, Cheng, Wen-Hui, Fountaine, Katherine T., Jahelka, Philip R., Kempler, Paul A., Saive, Rebecca, Lewis, Nathan S., and Atwater, Harry A.

Abstract

We describe the fabrication and use of arrays of TiO2nanocones to yield high optical transmission into semiconductor photoelectrodes covered with high surface loadings of light-absorbing electrocatalysts. Covering over 50% of the surface of a light absorber with an array of high-refractive-index TiO2nanocones imparted antireflective behavior (<5% reflectance) to the surface and allowed >85% transmission of broadband light to the underlying Si, even when thick metal contacts or opaque catalyst coatings were deposited on areas of the light-facing surface that were not directly beneath a nanocone. Three-dimensional full-field electromagnetic simulations for the 400–1100 nm spectral range showed that incident broadband illumination couples to multiple waveguide modes in the TiO2nanocones, reducing interactions of the light with the metal layer. A proof-of-concept experimental demonstration of light-driven water oxidation was performed using a p+n-Si photoanode decorated with an array of TiO2nanocones additionally having a Ni catalyst layer electrodeposited onto the areas of the p+n-Si surface left uncovered by the TiO2nanocones. This photoanode produced a light-limited photocurrent density of ∼28 mA cm–2under 100 mW cm–2of simulated air mass 1.5 illumination, equivalent to the photocurrent density expected for a bare planar Si surface even though 54% of the front surface of the Si was covered by an ∼70 nm thick Ni metal layer.

Published
2020
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11. Microwave Near-Field Imaging of Two-Dimensional Semiconductors

Author

Berweger, Samuel, primary, Weber, Joel C., additional, John, Jimmy, additional, Velazquez, Jesus M., additional, Pieterick, Adam, additional, Sanford, Norman A., additional, Davydov, Albert V., additional, Brunschwig, Bruce, additional, Lewis, Nathan S., additional, Wallis, Thomas M., additional, and Kabos, Pavel, additional

Published
2015
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21. High Broadband Light Transmission for Solar Fuels Production Using Dielectric Optical Waveguides in TiO 2 Nanocone Arrays.

Author

Yalamanchili S, Verlage E, Cheng WH, Fountaine KT, Jahelka PR, Kempler PA, Saive R, Lewis NS, and Atwater HA

Abstract

We describe the fabrication and use of arrays of TiO 2 nanocones to yield high optical transmission into semiconductor photoelectrodes covered with high surface loadings of light-absorbing electrocatalysts. Covering over 50% of the surface of a light absorber with an array of high-refractive-index TiO 2 nanocones imparted antireflective behavior (<5% reflectance) to the surface and allowed >85% transmission of broadband light to the underlying Si, even when thick metal contacts or opaque catalyst coatings were deposited on areas of the light-facing surface that were not directly beneath a nanocone. Three-dimensional full-field electromagnetic simulations for the 400-1100 nm spectral range showed that incident broadband illumination couples to multiple waveguide modes in the TiO 2 nanocones, reducing interactions of the light with the metal layer. A proof-of-concept experimental demonstration of light-driven water oxidation was performed using a p + n-Si photoanode decorated with an array of TiO 2 nanocones additionally having a Ni catalyst layer electrodeposited onto the areas of the p + n-Si surface left uncovered by the TiO 2 nanocones. This photoanode produced a light-limited photocurrent density of ∼28 mA cm -2 under 100 mW cm -2 of simulated air mass 1.5 illumination, equivalent to the photocurrent density expected for a bare planar Si surface even though 54% of the front surface of the Si was covered by an ∼70 nm thick Ni metal layer.

Published
2020
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22. Secondary ion mass spectrometry of vapor-liquid-solid grown, Au-catalyzed, Si wires.

Author

Putnam MC, Filler MA, Kayes BM, Kelzenberg MD, Guan Y, Lewis NS, Eiler JM, and Atwater HA

Subjects
Catalysis, Gases, Microscopy, Electron, Scanning, Nanotubes, Temperature, Thermodynamics, Gold chemistry, Mass Spectrometry methods, Nanotechnology methods, Silicon chemistry
Abstract

Knowledge of the catalyst concentration within vapor-liquid-solid (VLS) grown semiconductor wires is needed in order to assess potential limits to electrical and optical device performance imposed by the VLS growth mechanism. We report herein the use of secondary ion mass spectrometry to characterize the Au catalyst concentration within individual, VLS-grown, Si wires. For Si wires grown by chemical vapor deposition from SiCl 4 at 1000 degrees C, an upper limit on the bulk Au concentration was observed to be 1.7 x 10(16) atoms/cm(3), similar to the thermodynamic equilibrium concentration at the growth temperature. However, a higher concentration of Au was observed on the sidewalls of the wires.

Published
2008
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