Journal
APPLIED PHYSICS LETTERS
Volume 94, Issue 23, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3152244
Keywords
catalysts; elemental semiconductors; etching; nanoparticles; optical constants; porosity; reflectivity; silicon
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Funding
- U. S. Department of Energy [DE-AC36-08GO28308]
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We fabricate and measure graded-index black silicon surfaces and find the underlying scaling law governing reflectance. Wet etching (100) silicon in HAuCl(4), HF, and H(2)O(2) produces Au nanoparticles that catalyze formation of a network of [100]-oriented nanopores. This network grades the near-surface optical constants and reduces reflectance to below 2% at wavelengths from 300 to 1000 nm. As the density-grade depth increases, reflectance decreases exponentially with a characteristic grade depth of about 1/8 the vacuum wavelength or half the wavelength in Si. Observation of Au nanoparticles at the ends of cylindrical nanopores confirms local catalytic action of moving Au nanoparticles.
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