Tailored silicon nanopost arrays for resonant nanophotonic ion production

Nanostructures that have dimensions commensurate with the wavelength of the electromagnetic radiation exhibit near-field effects and, as optical antennas, can couple laser radiation to the local environment. Laserinduced silicon microcolumn arrays behave as nanophotonic ion sources that can be modulated by rotating the plane of light polarization. However, the limited range of surface morphologies available for these substrates makes it difficult to study the underlying mechanism that governs ion production. Here we demonstrate that nanopost arrays (NAPAs) can be tailored to exhibit resonant ion production. Ion yields from posts with subwavelength diameter show sharp resonances at high aspect ratios. The resonant enhancement in ion intensities can be modulated by adjusting the periodicity. In addition to strong molecular ion formation, the presence of high-energy fragmentation channels is observed. Ion yields from NAPAs exhibit dramatic differences for p-and s-polarized laser beams, indicating that energy coupling is similar to antenna arrays. These nanophotonic ion sources can control the degree of ion fragmentation and could eventually be integrated with micromachined mass spectrometers and microfluidic devices.