Michael Foxe

Effect of electron-beam irradiation on graphene field effect devices

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 (GFETs). 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 in 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.

Graphene Field-Effect Transistors on Undoped Semiconductor Substrates for Radiation Detection

The use of a graphene field-effect transistors (GFETs) to detect radiation is proposed and analyzed. The detection mechanism used in the proposed detector architecture is based on the high sensitivity of graphene to the local change of electric field that can result from the interaction of radiation with a gated undoped semiconductor absorber (substrate) in a GFET. We have modeled a GFET-based radiation detector, and discussed its anticipated performance and potential advantages compared to conventional detector architectures.

First measurement of the ionization yield of nuclear recoils in liquid argon

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.

Detection of ionizing radiation using graphene field effect transistors

We propose schemes of using graphene field effect transistors (GFET) to detect ionizing radiation. The detection is based on the high sensitivity of graphene to local change of electrical field that can result from the interaction of radiation with a semiconductor substrate in a GFET. We present preliminary modeling and experimental work to develop a prototype sensor, and discuss potential advantages compared to conventional detectors.

Directional Neutron Detection Using a Time Projection Chamber

Measurement of the three dimensional trajectory and specific ionization of recoil protons using a hydrogen gas time projection chamber provides directional information about incident fast neutrons. Here we demonstrate directional fast neutron detection using such a device. The wide field of view and excellent gamma rejection that are obtained suggest that this device is well suited to searches for special nuclear materials, among other applications.

Graphene field effect transistor as radiation sensor

A novel radiation sensor based on a graphene field effect transistor (GFET) is experimentally demonstrated. The detection relies on the high sensitivity of the resistivity of graphene to the local change of electric field that can result from ionized charges produced in the underlying semiconductor substrate. We present the experimental results of our study on the response of graphene-based radiation detectors to X-rays, gamma-rays, and light photons. We observed increasing resistance change of graphene with increasing X-ray flux in an electrically biased GFET based on Si, SiC, and GaAs substrates. We have measured the temporal characteristics of our detector, along with the sensitivity of the device at high (40 keV, 80 µA) and low (15 keV, 15 µA) X-ray fluxes. Furthermore, we demonstrate room-temperature operation of a GFET based on a SiC absorber and explore new architecture for a faster response.

Effect of energetic electron irradiation on graphene and graphene field-effect transistors

We present a study of the effects of electron-beam irradiation on the Raman spectra and electronic transport properties of graphene and the operation of graphene field-effect transistors (GFET). Exposure to a 30 keV electronbeam causes 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 electron beam is seen to also decrease the carrier mobilities and minimum conductivity of the graphene, as well as increase the intensity of the Raman D peak, all of which indicate defects generated in the graphene. We also study the relaxation of electronic properties after irradiation. The findings are valuable for understanding the effects of radiation damage on graphene and for the development of radiation-hard graphene-based electronics.

Graphene field effect transistors for detection of ionizing radiation

A novel radiation detector based on a graphene field effect transistor (GFET) is experimentally demonstrated. The detection in GFET relies on the high sensitivity of the resistivity of graphene to the local change of electric field that can result from ionized charges produced in the underlying semiconductor substrate. We present the experimental results of our study on the graphene-based radiation detector response to X-rays. We observed increasing resistance change of graphene with increasing X-ray flux in an electrically biased GFET based on a Si substrate. We have measured the temporal characteristics of our detector, along with the sensitivity of the device at high (40 kV-80 μA) and low (15 kV-15 μA) X-ray fluxes. Furthermore, we demonstrate room-temperature operation of a graphene radiation sensor based on a SiC absorber.

Effect of Energetic Electron Irradiation on Graphene

Electron beam exposure is a commonly used tool for fabrication and imaging of graphene‐based devices. Using Raman spectroscopy and electronic transport measurements, we have studied the effect of prolonged exposure of electron beams on exfoliated graphene on SiO2/Si substrates and the performance of electronic devices based on exfoliated graphene. Raman spectra indicate emergence of characteristic defects. Electronic transport measurements show an overall decrease in graphene’s conductivity and a shift of the Dirac point. Our results are valuable for understanding the possible defects generated in graphene by electron beam exposure and in high‐radiation environment in general.

Low-energy (<10keV) electron ionization and recombination model for a liquid argon detector

Abstract Detailed understanding of the ionization process in noble liquid detectors is important for their use in applications such as the search for dark matter and coherent elastic neutrino-nucleus scattering. The response of noble liquid detectors to low-energy ionization events is poorly understood at this time. We describe a new simulation tool which predicts the ionization yield from electronic energy deposits ( E 10 keV ) in liquid Ar, including the dependence of the yield on the applied electric drift field. The ionization signal produced in a liquid argon detector from 37Ar beta decay and 55Fe X-rays has been calculated using the new model.