Multicolored Vertical Silicon Nanowires

Abstract

We demonstrate that vertical silicon nanowires take on a surprising\nvariety of colors covering the entire visible spectrum, in marked\ncontrast to the gray color of bulk silicon. This effect is readily\nobservable by bright-field microscopy, or even to the naked eye. The\nreflection spectra of the nanowires each show a dip whose position\ndepends on the nanowire radii. We compare the experimental data to\nthe results of finite difference time domain simulations to elucidate\nthe physical mechanisms behind the phenomena we observe. The nanowires\nare fabricated as arrays, but the vivid colors arise not from scattering\nor diffractive effects of the array, but from the guided mode properties\nof the individual nanowires. Each nanowire can thus define its own\ncolor, allowing for complex spatial patterning. We anticipate that\nthe color filter effect we demonstrate could be employed in nanoscale\nimage sensor devices.