Nanodielectric properties of high conductivity carbon-loaded polyimide under electron-beam irradiation

Abstract

Electron irradiation experiments were conducted to investigate the electron transport, charging, discharging, cathodoluminescence and emission properties of high-conductivity carbon-loaded polyimide (Black Kapton™). We discuss how these results are related to the nanoscale structure of the composite material. Measurements were conducted in an ultrahigh vacuum electron emission test chamber from <;40 K to 290 K, using a monoenergetic beam with energies ranging from 3 keV to 25 keV and flux densities from 0.1 nA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 100 nA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to deposit electrons in the material surface layer. Various experiments measured transport and displacement currents to a rear grounded electrode, absolute electron emission yields, electron-induced absolute photon emission yields and photon emission spectra (~250 nm to 1700 nm), and arcing rates and location. Numerous arcing events from the material edge to an electrically isolated grounded sample holder (particularly at lower temperatures) were observed, which are indicative of charge accumulation within the insulating regions of the material. Three types of light emission were also observed: (i) short duration (<;1 s) arcing resulting from electrostatic discharge, (ii) long duration cathodoluminescence that turned on and off with the electron beam and (iii) intermediate duration (~100 s) glow that dissipated exponentially with time after infrequent and rapid onset. We discuss how the electron currents and arcing, as well as light emission absolute intensity and frequency, depend on electron beam energy, power, flux and temperature.