Carbon nanostructures for directional light dark matter detection

Carbon nanostructures offer exciting new possibilities in the detection of light dark matter. A darkmatter particle with mass between 1 MeV and 1 GeV scattering off an electron in the carbon wouldtransfer sufficient energy to extract the electron from the lattice. In 2D materials, such as grapheneor carbon nanotubes, these electrons would be released directly into the vacuum, avoiding theirre-absorption in the medium. We present two novel detector concepts: a ’Graphene-FET’ design,based on graphene sheets, developed at Princeton University; and a ’Dark-PMT’ based on alignedcarbon nanotubes, developed in University of Rome Sapienza. We discuss their light dark matterdiscovery potential, the status of the RD, and the recent commissioning of a state-of-the-art carbonnanotube growing facility in Rome

Searching for Light Dark Matter with Aligned Carbon Nanotubes: The ANDROMeDa Project

The ANDROMeDa (Aligned Nanotube Detector for Research On MeV Dark matter) project aims to develop a novel Dark Matter detector based on carbon nanotubes: the “Dark-PMT”. The detector is designed to be sensitive to dark matter particles with mass between 1 MeV and 1 GeV. The detection scheme is based on dark matter-electron scattering inside a target made of vertically-aligned carbon nanotubes. Vertically-aligned carbon nanotubes have reduced density in the direction of the tube axis, therefore the scattered electrons are expected to leave the target without being re-absorbed only if their momentum has a small enough angle with that direction, which is what happens when the tubes are parallel to the dark matter wind. This grants directional sensitivity to the detector, a unique feature in this dark matter mass range

Transmission through graphene of electrons in the 30 – 900 eV range

Here, we report on accurate transmission measurements of electrons below 1 keV through suspended monolayer graphene. Monolayer graphene was grown via chemical vapor deposition and transferred onto transmission electron microscopy (TEM) grids. A monochromatic electron gun has been employed to perform the measurements in the 30 – 900 eV range in ultra-high vacuum. The graphene transparency is obtained from the absolute measurement of the direct beam current and the transmitted one, by means of a Faraday cup. We observed a transmission going from 20 to 80% for monolayer graphene within the experimental electron energy range. The high quality and the grid coverage of the suspended graphene has been proved via micro-Raman, X-ray photoemission, electron energy loss spectroscopies and field-emission scanning electron microscopy. After a 550 °C in-vacuum annealing of the samples, the main contribution to the C 1s spectrum is due to the component and the evidence of suspended monolayer graphene has been observed through the -plasmon excitation

The dark-PMT: A novel directional light dark matter detector based on vertically-aligned carbon nanotubes

The ANDROMeDa project, recently funded by the italian ministry of research with a 1M€ grant, has the objective of developing, over the course of the next three years, a novel dark matter (DM) detector based on carbon nanotubes: the ‘dark-PMT’. Such a detector would be sensitive to DM-electron recoils in the eV energy range, and could have world-leading sensitivity for DM masses below 30 MeV with an exposure of only . Significant R&D is needed to produce carbon nanotubes with ideal properties for a DM target. In particular two by-products of synthesis (non-aligned crust layer and the sub-m ‘waviness’) are expected to reduce electron transmission probability, and therefore need to be minimized. This will be done via a precise tuning of the evaporation and growth parameters, and of post-growth plasma etching

Searching for Light Dark Matter with Aligned Carbon Nanotubes: The ANDROMeDa Project

The ANDROMeDa (Aligned Nanotube Detector for Research On MeV Dark matter) project aims to develop a novel Dark Matter detector based on carbon nanotubes: the “Dark-PMT”. The detector is designed to be sensitive to dark matter particles with mass between 1 MeV and 1 GeV. The detection scheme is based on dark matter-electron scattering inside a target made of vertically-aligned carbon nanotubes. Vertically-aligned carbon nanotubes have reduced density in the direction of the tube axis, therefore the scattered electrons are expected to leave the target without being re-absorbed only if their momentum has a small enough angle with that direction, which is what happens when the tubes are parallel to the dark matter wind. This grants directional sensitivity to the detector, a unique feature in this dark matter mass range

Plasma-Etched Vertically Aligned CNTs with Enhanced Antibacterial Power

The emergence of multidrug-resistant bacteria represents a growing threat to public health, and it calls for the development of alternative antibacterial approaches not based on antibiotics. Here, we propose vertically aligned carbon nanotubes (VA-CNTs), with a properly designed nanomorphology, as effective platforms to kill bacteria. We show, via a combination of microscopic and spectroscopic techniques, the ability to tailor the topography of VA-CNTs, in a controlled and time-efficient manner, by means of plasma etching processes. Three different varieties of VA-CNTs were investigated, in terms of antibacterial and antibiofilm activity, against Pseudomonas aeruginosa and Staphylococcus aureus: one as-grown variety and two varieties receiving different etching treatments. The highest reduction in cell viability (100% and 97% for P. aeruginosa and S. aureus, respectively) was observed for the VA-CNTs modified using Ar and O-2 as an etching gas, thus identifying the best configuration for a VA-CNT-based surface to inactivate both planktonic and biofilm infections. Additionally, we demonstrate that the powerful antibacterial activity of VA-CNTs is determined by a synergistic effect of both mechanical injuries and ROS production. The possibility of achieving a bacterial inactivation close to 100%, by modulating the physico-chemical features of VA-CNTs, opens up new opportunities for the design of self-cleaning surfaces, preventing the formation of microbial colonies

Response of Windowless Silicon Avalanche Photo-Diodes to Electrons in the 90-900 eV Range

We report on the characterization of the response of windowless silicon avalanche photo-diodes to electrons in the 90-900 eV energy range. The electrons were provided by a monoenergetic electron gun present in the LASEC laboratories of University of Roma Tre. We find that the avalanche photo-diode generates a current proportional to the current of electrons hitting its active surface. The gain is found to depend on the electron energy $E_e$, and varies from $2.147 \pm 0.027$ (for $E_e = 90$ eV) to $385.8 \pm 3.3$ (for $E_e = 900$ eV), when operating the diode at a bias of $V_{apd} = 350$ V.} This is the first time silicon avalanche photo-diodes are employed to measure electrons with $E_e < 1$ keV