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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.

Electron irradiation experiments have investigated the diverse electron-induced optical and electrical signatures observed in ground-based tests of various space observatory materials at low temperature. Three types of light emission were observed: (i); long-duration cathodoluminescence which persisted as long as the electron beam was on (ii) short-duration (<1 s) arcing, resulting from electrostatic discharge; and (iii) intermediate-duration (~100 s) glow-termed "flares". We discuss how the electron currents and arcing-as well as light emission absolute intensity and frequency-depend on electron beam energy, power, and flux and the temperature and thickness of different bulk (polyimides, epoxy resins, and silica glasses) and composite dielectric materials (disordered SiO 2 thin films, carbon-and fiberglass-epoxy composites, and macroscopically-conductive carbon-loaded polyimides). We conclude that electron-induced optical emissions resulting from interactions between observatory materials and the space environment electron flux can, in specific circumstances, make significant contributions to the stray light background that could possibly adversely affect the performance of space-based observatories.

The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new twostage, closed-cycle helium cryostat which has an extended sample temperature range from <40 K to >450 K, with long-term controlled stability of <0.5 K. The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber (base pressure <10-7 Pa) that can simulate diverse space environments. These existing capabilities include controllable vacuum and ambient neutral gases conditions (<10-8 to 10-1 Pa), electron fluxes (5 eV to 30 keV monoenergetic, focused, pulsed sources over 10-4 to 10 10 nA-cm-2), ion fluxes (<0.1 to 5 keV monoenergetic sources for inert and reactive gases with pulsing capabilities), and photon irradiation (numerous continuous and pulsed monochromated and broad band IR/VIS/UV [0.5 to 7 eV] sources). The new sample mount accommodates 1 to 4 samples of 1 cm to 2.5 cm diameter in a low temperature carousel, which allows rapid sample exchange and controlled exposure of the individual samples. Custom hemispherical grid retarding field analyzer and Faraday cup detectors, custom high speed, high sensitivity electronics, and charge neutralization capabilities used with <50 pA, <5 μs, <3·10 3 electrons/pulse pulsed-beam sources permit high-accuracy electron emission measurements of extreme insulators with minimal charging effects. In situ monitoring of surface voltage, arcing, and luminescence (250 nm to 5000 nm) have recently been added.

Measurements of the charge distribution in electron-bombarded, thin-film, multilayered dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential's dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO 2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 s pulses at 1 nA/cm 2 to 500 nA/cm 2 . Results show that there are two basic charging scenarios which are consistent with simple charging models; these are analyzed using independent determinations of the material's electron range, yields, and conductivity. Large negative net surface potentials led to electrostatic breakdown and large visible arcs, which have been observed to lead to detrimental spacecraft charging effects. electron beam and grounded conductive layer. (a,b,c,d,g,h) were done at 298 K with (e,f) at 135 K. Exponential fits for the voltage was based on Eq. 3 with (a) τ=475 s (τ Q =6.6 μC), (c) τ=45 s (τ Q =0.63 μC), (g) τ=1137 s (τ Q =1.33 μC). Exponential fits for the currents were based on Eq. 5 with (b) τ=139 s (τ Q =1.93 μC), (d) conductive layer τ=99 s (τ Q =1.37 μC), rear electrode τ=206 s (τ Q =2.86 μC) (f) τ=2880 s (τ Q =3.37 μC), (h) τ=462 (τ Q =0.54 μC). Abstract USU Materials Physics Group Experimentation Fig. 7. Measurements of surface potentials vs time (a, c, e, g) and rear electrode and conductive layer currents vs time (b, d, f, h) for: (a, b) surface dielectric deposition with low energy electron beam and ungrounded conductive layer; (c, d) surface dielectric deposition with low energy electron beam and grounded conductive layer; (e, f) dielectric substrate deposition with high energy electron beam and ungrounded conductive layer; and (g, h) dielectric substrate deposition with high energy