Comparison of ion beam and electron beam induced transport of hot charge carriers in metal-insulator-metal junctions
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Comparison of ion beam and electron beam induced transport of hot charge carriers in metal-insulator-metal junctions Johannes Hopster1, Detlef Diesing2, Andreas Wucher1 and Marika Schleberger1 1 Universität Duisburg-Essen, Fakultät für Physik, 47048 Duisburg, Germany 2 Universität Duisburg-Essen, Fakultät für Physikalische Chemie, 45117 Essen, Germany ABSTRACT The generation of hot charge carriers within a solid bombarded by charged particles is investigated using biased thin film metal-insulator-metal (MIM) devices. For slow, highly charged ions approaching a metal surface the main dissipation process is electronic excitation of the substrate, leading to electron emission into the vacuum and internal electron emission across the MIM junction. In order to gain a deeper understanding of the distribution and transport of the excited charge carriers leading to the measured device current, we compare ion induced and electron induced excitation processes in terms of absolute internal emission yields as well as their dependence on the applied bias voltage. INTRODUCTION The interaction of charged particles with surfaces has been intensively investigated in the last years. Therefore the main stages of the interaction process are well understood [1-6]. The ions carry energy, which may be both kinetic energy due to their velocity and potential energy due to their charge state. During the impact, ions introduce energy into the surface either via nuclear or electronic stopping. We are interested in the interaction of slow highly charged ions (HCI) with metal surfaces, where the main dissipation process is electronic excitation due to elementary Auger processes [7,8]. This excitation, localized in the near-surface region, produces electron emission into the vacuum and internal electron emission in the metal film. The external electron emission into the vacuum is well understood and has been discussed and reviewed in many works before [6,9]. The internal electron emission is based on the transport of excited charge carriers into the bulk of the substrate across an internal energy barrier located below the surface. Since the internal barrier is lower than the work function of the irradiated metal, it is possible to gain new insights into the lower energy part of the excited electron distribution. In this work, we use thin film metal-insulator-metal (MIM) tunnel junctions as sensitive detectors to investigate the electronic excitation created in the top metal film [10]. In order to gain a deeper understanding of the distribution and transport of the excited charge carriers leading to the measured internal emission yields, we compare the device current measured under impact of highly charged ions with that produced during monoenergetic electron bombardment of the surface. By varying the bias voltage between the top and bottom metal electrodes of the MIM device, it is possible to modify the barrier characteristics of the MIM junction. From the resulting bias voltage dependence of the measured device current, we will draw conclusions
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