Electron beam exposure is a commonly used tool for fabricating and imaging graphene-based devices. Here we present a study of the effects of electron-beam irradiation on the electronic transport properties of graphene and the operation of graphene field-effect transistors (GFET). Exposure to a 30 keV electron-beam caused negative shifts in the charge-neutral point (CNP) of the GFET, interpreted as due to n-doping in the graphene from the interaction of the energetic electron beam with the substrate. The shift of the CNP is substantially reduced for suspended graphene devices. The electron beam is seen to also decrease the carrier mobilities and minimum conductivity, indicating defects created in the graphene. The findings are valuable for understanding the effects of radiation damage on graphene and for the development of radiation-hard graphene-based electronics.Comment: 8 pages, 3 figure

This Letter details a measurement of the ionization yield (Q y ) of 6.7 keV 40 Ar atoms stopping in a liquid argon detector. The Q y of 3.6-6.3 detected e − /keV, for applied electric fields in the range 240-2130 V/cm, is encouraging for the use of this detector medium to search for the signals from hypothetical dark matter particle interactions and from coherent elastic neutrino-nucleus scattering. A significant dependence of Q y on the applied electric field is observed and explained in the context of ion recombination. PACS numbers: 95.35.+d, 25.30.Pt, 34.50.Fa, 29.40.Mc Liquid-phase argon has long been used as a target medium for particle detection via scintillation and charge collection. Recently there has been considerable interest in direct detection of both hypothetical dark matter particles [1] and coherent elastic neutrino-nucleus scattering (CENNS) [2,3]. These as-yet unobserved neutral particle interactions are expected to result in a recoiling argon atom O(keV), generally referred to in the literature as a nuclear recoil. This prompts the question of the available signal produced by such recoils in a liquid argon detector. This quantity must be directly measured due to the difference in signals from nuclear recoils as opposed to electron recoils (e.g. Compton electrons and β-particles). In this Letter we report the first measurement of the ionization yield (Q y ) (detected electrons per unit energy) resulting from nuclear recoils in liquid argon, measured at 6.7 keV. This is also the lowest-energy measurement of nuclear recoils in liquid argon.These results are of interest not only for particle detection, but for theoretical studies of condensed media as well. Models of the production of ions and excited atoms from low-energy recoils in liquid argon exist, but are not fully understood in the few-keV energy range [4]. To study the influence of the electric field on recombination, and thus Q y , data were obtained at applied electric field values of 240, 640, 1600, 2130 V/cm.The scintillation efficiency of nuclear recoils in liquid argon has been measured from 10-250 keV at zero electric drift field using the kinematically constrained scatter of 2.8 MeV neutrons [5] and from 11-50 keV at electric drift fields from 0-1000 V/cm using the kinematically constrained scatter of 0.60 and 1.17 MeV neutrons [6]. No measurements of nuclear recoils in liquid argon exist below 10 keV.Liquid argon dual-phase detectors have been shown to be sensitive to single electrons generated in the bulk [7]. This enhances the detection capability of the ionization channel over the scintillation channel at very low energies. A lowenergy threshold and calibration are critical in both dark matter searches and CENNS discovery. Both interactions exhibit a recoil energy spectrum that rises rapidly with decreasing energy [4,8,9]. Our results suggest that dark matter searches using only the ionization channel in liquid argon (as has been done in liquid xenon [10]) could probe an interesting new parameter space. The observation and...

Although the existence of dark matter is supported by many evidences, based on astrophysical measurements, its nature is still completely unknown. One major candidate is represented by weakly interacting massive particles (WIMPs), which could in principle be detected through their collisions with ordinary nuclei in a sensitive target, producing observable low-energy (<100 keV) nuclear recoils. The DarkSide program aims at the WIPMs detection using a liquid argon time projection chamber (LAr-TPC). In this paper we quickly review the DarkSide program focusing in particular on the next generation experiment DarkSide-G2, a 3.6-ton LAr-TPC. The different detector components are described as well as the improvements needed to scale the detector from DarkSide-50 (50 kg LAr-TPC) up to DarkSide-G2. Finally, the preliminary results on background suppression and expected sensitivity are presented.

We describe the first demonstration of a sub-keV electron recoil energy threshold in a dual-phase liquid argon time projection chamber. This is an important step in an effort to develop a detector capable of identifying the ionization signal resulting from nuclear recoils with energies of order a few keV and below. We obtained this result by observing the peaks in the energy spectrum at 2.82 keV and 0.27 keV, following the K-and L-shell electron capture decay of 37 Ar, respectively. The 37 Ar source preparation is described in detail, since it enables calibration that may also prove useful in dark matter direct detection experiments. An internally placed 55 Fe x-ray source simultaneously provided another calibration point at 5.9 keV. We discuss the ionization yield and electron recombination in liquid argon at those three calibration energies.

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