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No abstract

triqiie appliqu6, en sorte que la courbure des bandes est.faible, infbrieure 8 environ 0,3 eV.

Total energy distribution measurements of electrons field‐emitted from clean iridium (111) plane, prepared by low temperature field evaporation, reveal two types of spectra which differ essentially by a structure at 0.45 eV below the emitter Fermi level. Work function results for clean and hydrogen covered surfaces are presented and used in order to determine whether the probed region of the surface is flat or stepped. It is shown that the spectra exhibit a free electron behaviour without any structure when the surface is flat, while current contribution from edge atoms on the stepped surface gives rise to a structure at 0.45 eV.

BYInjection of electrons into glass by tunneling from metallic tipsspecially platinum tipsis investigated in a field-emission microscope. KO current is detected a t applied voltages up to 30 kV when the thickness of glass layers is larger than a few microns. On the contrary, in the case of very thin glass coatings ( s 0.1 pm), current-voltage characteristics can be measured; a t lowest currents, the emission obeys the Fowler-Nordheim equation, while periodic current oscillations are observed a t higher currents ( i = A). Field-electron and field-ion micrographs from platinum tips whose glass coating is removed by various treatments (heating in vacuum, dissolution of glass in hydrofluoric acid) are also presented and discussed.On a examink, A l'aide de la microscopie h emission de champ, l'injection d'6lectrons dans le verre par effet tunnel & I'interface mktal-verre. Dans le cas de pointes enrob6es par des couches de verre dont 1'6paisseur est de quelques microns, aucun courant n'est d6tect6, m@me A des voltages aussi &lev&s que 30 kV. Par contre, des caractkristiques courant-tension ont ktk mesurkes dans le cas d'enrobages de verre minces ( s 0,l pm); aux faibles courants, l'kmission obkit h 1'6quation de Fowler-Nordheim, tandis que des oscillations pkriodiques de courant ont ktk observkes dans le domaine des courants plus 61ev6s (i = 10-8 A). On prksente 6galement des micrographies 6lectroniques e t ioniques de champ obtenues avec des pointes de platine dont l'enrobage de verre a k t k enlev6 par divers traitements (chauffage sous vide, dissolution du verre dans l'acide fluorhydrique).