An atom passing through a hole in a dielectric membrane: Impact of dispersion forces on mask-based matter-wave lithography

Fast, large area patterning of arbitrary structures down to the nanometre scale is of great interest for a range of applications including the semiconductor industry, quantum electronics, nanophotonics and others. It was recently proposed that nanometre-resolution mask lithography can be realised by sending metastable helium atoms through a binary holography mask consisting of a pattern of holes. However, these first calculations were done using a simple scalar wave approach, which did not consider the dispersion force interaction between the atoms and the mask material. To access the true potential of the idea, it is necessary to access how this interaction affects the atoms. Here we present a theoretical study of the dispersion force interaction between an atom and a dielectric membrane with a hole. We look at metastable and ground state helium, using experimentally realistic wavelengths (0.05-1 nm) and membrane thicknesses (5-50 nm). We find that the effective hole radius is reduced by around 1-7 nm for metastable helium and 0.5-3.5 nm for ground-state helium. As expected, the reduction is largest for thick membranes and slow atoms.

Formation and destruction of striation plasmas in helium glow discharge at medium pressures

The striation plasmas are usually generated in positive column of glow discharge, in which abundant and complex physics are involved, especially, in medium or high pressures. This paper was aimed at investigating the formation and deformation of helium striation plasmas at kPa level pressures. The characteristics of helium striation plasmas, especially, the optical emission characteristics were investigated. The emission lines of 706.52 nm and 391.44 nm related to energetic electrons and high energy metastable helium atoms were focused on during the discharge process. Formation of striation plasmas in helium glow discharge, is mainly associated with the instability resulting from stepwise ionization vis high energy metastable state atoms, Maxwellization of electron distribution functions and gas heating. The deformation effect of helium striation plasmas is very significant when a small amount of nitrogen or oxygen is mixed into the discharge plasmas. The reduction of mean electron energy and the consumption of high energy metastable helium atoms are the potential reasons for deformation of striation plasmas.

The Posttransit Tail of WASP-107b Observed at 10830 Å

Understanding the effects of high-energy radiation and stellar winds on planetary atmospheres is vital for explaining the observed properties of close-in exoplanets. Observations of transiting exoplanets in the triplet of metastable helium lines at 10830 Å allow extended atmospheres and escape processes to be studied for individual planets. We observed one transit of WASP-107b with NIRSPEC on Keck at 10830 Å. Our observations, for the first time, had significant posttransit phase coverage, and we detected excess absorption for over an hour after fourth contact. The data can be explained by a comet-like tail extending out to ∼7 planet radii, which corresponds to roughly twice the Roche lobe radius of the planet. Planetary tails are expected based on three-dimensional simulations of escaping exoplanet atmospheres, particularly those including the interaction between the escaped material and strong stellar winds, and have been previously observed at 10830 Å in at least one other exoplanet. With both the largest midtransit absorption signal and the most extended tail observed at 10830 Å, WASP-107b remains a keystone exoplanet for atmospheric escape studies.

Fano interference in quantum resonances from angle-resolved elastic scattering

Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states. Such line shapes are well known for multichannel systems, for example, in photoionization or Feshbach resonances in molecular scattering. On the other hand, in resonant single channel scattering, the signature of such interference may disappear due to the orthogonality of partial waves. Here, we show that probing the angular dependence of the cross section allows us to unveil asymmetric Fano profiles also in a single channel shape resonance. We observe a shift in the peak of the resonance profile in the elastic collisions between metastable helium and deuterium molecules with detection angle, in excellent agreement with theoretical predictions from full quantum scattering calculations. Using a model description for the partial wave interference, we can disentangle the resonant and background contributions and extract the relative phase responsible for the characteristic Fano-like profiles from our experimental measurements.

Electron Ionization of Size-Selected Positively and Negatively Charged Helium Droplets

A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role.