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JUNE 28 WEDNESDAY AFTERNOON RIVA-SS-WeA-P.3 ELECTRON STIMULATED DESORPTION STUDY OF DEFCT SITES ON THE MgO(100) SURFACE USING QUADRUPOLE MASS SPECTROMETRY AND TIME OF FLIGHT. I. Colera * , J. L. de Segovia ** , D. Cáceres * , E. Román ** and R. González * . * Departamento de Física. Universidad Carlos III de Madrid. Leganés. 28911 Madrid. Spain. ** Laboratorio de Física e Ingeniería de Superficies. Instituto de Ciencia de Materiales. CSIC.Cantoblanco. 28049 Madrid. Spain While the quadrupole mass spectrometer (QMS) is an excellent tool to identify desorbed ions and energy thresholds in electron stimulated desorption (ESD) experiments, its analysis of the ion kinetic energy distribution is questionable. However, time of flight (TOF) is an excellent technique to analyse the ion energies by using the QMS as the driving tube for the time of flight. The simultaneous use of the ESDQMS and ESDTOF techniques yields excellent results in the determination of the ion nature, ion threshold, and ion energy distribution in the study of site defects of on the MgO(100) surface. Defect sites are identified by exposing the MgO(100) surface to D 2 O and H 2 18 O. Thus, the D and 18 O can be differentiated from the 16 O and H surface atoms. The energy of the exploring electrons varied from 200 to 600 eV, and an intensity of 100 nA was used to avoid surface damage. The sample charge was also studied as a function of the incident electron en energy. 114
JUNE 28 WEDNESDAY AFTERNOON RIVA-SS-WeA-P.2 SECONDARY ELECTRON EMISSION YIELDS OF EXTER- NAL DIELECTRIC COATINGS USED IN SPACE . Isabel Montero, Ainhoa Pardo, Pablo Rios and José Luis de Segovia. Instituto de Ciencia de Materiales de Madrid. CSIC. Cantoblanco. 28049-Madrid. Spain. Luis Galán. Universidad Autónoma de Madrid. Cantoblanco. 28049-Madrid. Spain. Léon Lévy. Office National d'Etudes et de Recherche Aerospatiales, 2 Avenue Edouard Belin, 31055 Toulouse, Cedex 4, France. Marc Van Eesbeek. European Space Research and Technology Centre (ESTEC), European Space Agency (ESA), Keplerlaan 1, PO Box 299, NL-2200 AG Noordwijk, The Netherland Within ESA Program, AO4136 “Material Characterisation for Plasma Interaction Analysis”, headed as prime contractor by ONERA, our group from ICMM (CSIC) and UAM has been developing a research on secondary electron emission and photoemission properties of reliable insulator materials to study their charging behaviour in space. The spacecraft surface potential is a function of the net current flow to or from the spacecraft surface. Electrons impinging on the spacecraft can produce secondary electron emission. Photoemission from the extreme ultraviolet photon range is the most important since in that region many materials have rather large photoelectric yields and the solar spectrum also has significant energy there. This work presents results on secondary electron emission and photoemission yields of space used external dielectric coatings. The dielectric materials studied was polymers: kapton, betacloth and upilex, and doped silicon glasses: CMX and CMO. The total secondary electron emission coefficient, σ, per primary electron, versus primary energy, Ep, curve was characterized by the following parameters: σm the maximum value and the corresponding primary energy Em, and the two crossover energies: E1, the lowest Ep for σ =1, and E2 the highest Ep for σ =1. The beam pulsing measuring technique was used in order to reduce or avoid the charge incorporation into the samples. SEY was measured for normal incidence and as a function of primary electron energy. Current pulses of 0.1 -1 μs of low intensity (1nA-50 nA) were used to reduce the electron dose received by the sample (≤106electrons/pulse). For each primary energy, the sample was bombarded with only one current pulse. Surface charge decay occurs immediately when the e-irradiation is stopped, but it depends on the discharging time constants. After each measurement, the charge of the sample was removed: the trapped charge was liberated with the mercury lamp (negative surface charging) and the flood-gun (positive surface charging). Analysis of the coatings was performed, apart from SEY and PES measurements, by XPS (X-ray Photoemission Spectroscopy), SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-ray Spectroscopy) and UVS (Ultraviolet spectroscopy). 113
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Sigilum Universitatis Studii Salama
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