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 highconductivity carbon-loaded polyimide (Black Kapton TM ). 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 2 to 100 nA/cm 2 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.

Variations in Cathodoluminescent Intensity of Spacecraft Materials Exposed to Energetic Electron Bombardment

“…At higher current densities (̇≫̇), saturation occurs when trap states fill, limiting the number of states electrons can decay into; approaches a constant material-specific saturation intensity. Such saturation effects, at increasing current densities and fixed incident energies, have been reported for disordered SiO 2 [3], nanodielectric carbon-loaded polyimide [9], cynate ester/graphite fiber composites [12], and bisphenol/amine epoxy [1,13].…”

“…5 Absolute cathodoluminescent spectral radiance versus incident electron energy of four materials, scaled to 10 nA/cm 2 electron current density. The plot shows data for SiO2-coated mirror (green square) [3,4], carbon-loaded polyimide (black diamonds) [1,9], cynate ester/graphite fiber composite (red circle) [12], and bisphenol/amine epoxy (blue triangles) [1,13]. Data were taken with the CCD video camera at USU (solid symbols) and MSFC (open symbols).…”

“…Previous studies have focused on how the relative spectral radiance of cathodoluminescent materials varies with changes in environmental conditions, including electron energy, current density, absorbed power density, and temperature. This has led to the development of a quantitative, physicsbased model to predict the intensity of glow as a function of incident electron current density and energy, temperature, and intrinsic material properties [1,3,7,9]. However, from a practical point of view, it is also important to develop an understanding of the variations of the cathodoluminescent intensity of diverse spacecraft materials exposed to energetic electron bombardment in both the space environment and space simulation studies.…”

Temporal and Spatial Correlations in Electron-Induced Arcs of Adjacent Dielectric Islands

“…These were located around the edges of a large, conductive, polymeric/carbon nanocomposite (Black Kapton TM ) substrate (see Fig. 1) [11]. The substrate was mounted inside a high-vacuum chamber, attached to a cooled, grounded, metal plate.…”

“…However, the physical processes involved have farreaching applications with similar electric fields related to electrostatic breakdown field strength and arcing. Theses include-in order of decreasing length scales-high voltage devices and switching circuits, insulators in plasma applications, breakdown field measurements [2,10], microelectronics capacitors and dielectric layers, and nanodielectric composites [11].…”