Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

Abstract

Surface scattering of neutral helium beams created by supersonic expansion is an established technique for measuring structural and dynamical properties of surfaces on the atomic scale. Helium beams have also been used in Fraunhofer and Fresnel diffraction experiments. Due to the short wavelength of the atom beams of typically 0.1 nm or less, Fraunhofer diffraction experiments in transmission have so far been limited to grating structures with a period (pitch) of up to 200 nm. However, larger periods are of interest for several applications, for example for the characterization of photonic crystal membrane structures, where the period is typically in the micron/high sub-micron range. Here we present helium atom diffraction measurements of a photonic crystal membrane structure with a two dimensional square lattice of 100 × 100 circular holes. The nominal period and hole radius were 490 nm and 100 nm respectively. To our knowledge this is the largest period that has ever been measured with helium diffraction. The helium diffraction measurements are interpreted using a model based on the helium beam characteristics. It is demonstrated how to successfully extract values from the experimental data for the average period of the grating, the hole diameter and the width of the virtual source used to model the helium beam.

Velocity distributions in microskimmer supersonic expansion helium beams: High precision measurements and modeling

“…This corresponds well to the theoretically expected and experimentally verified behavior of a spatial increase in the free jet expansion with pressure. 17,18,21,22 A higher source pressure leads to an increase in the detected source intensity likewise agreeing well with theoretical considerations. The most probable beam velocity and the beam velocity distribution were obtained by time of flight measurements (TOF).…”

Nanometer-Resolution Mask Lithography with Matter Waves: Near-Field Binary Holography

“…In the simulations we model the supersonic helium source by using an adapted version of the virtual source model introduced by Beijerinck and Verster [34]. Recently, the same source model was used successfully to describe experimental measurements of the scattering of a beam of helium atoms from a photonic crystal structure [35]. The virtual source model is based on the idea that after an initial region behind the nozzle where the atoms collide, they will eventually reach a free-flow regime at a distance from the nozzle referred to as the "quitting surface."…”

Optimal Design of Grid-Based Binary Holograms for Matter-Wave Lithography

“…More recently a diffraction grating for molecular interferometry was created out of a graphene membrane [11] (see also [12]). This year helium diffraction from a micron scale structure was achieved for the first time [13].…”