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In
a vacuum deposition chamber, nanometer-thick insulating and metal layers are
deposited on a metal substrate. The resulting Metal-Insulator-Metal (M-I-M)
heterostructure can deliver ballistic hot electrons to the surface from the
solid side of the vacuum/solid interface. These electrons can induce nonthermal
surface chemistry and/or escape into the vacuum.
An applied voltage bias between the upper and lower metal layers will cause substrate electrons to tunnel into the conduction band of the insulator, where they ballistically travel across the upper metal layer to the vacuum interface. The applied bias tunes the energy distribution of the hot electrons to median values ranging from the Fermi level to well above the vacuum level.
A proposal, for increasing the current of ballistic electrons reaching the surface, involves depositing metal nanodots across the metal underlayer of the M-I-M device, where the dots can serve as emitter sites for inducing electron tunneling across the insulating layer. Nanosphere lithography shows great promise for inexpensively depositing a periodic array of monodispersed metal nanodots across the metal underlayer. The performance of the prototype M-I-M devices will be evaluated by measuring the current density and energy distribution of emitted electrons as a function of the applied bias and the surface temperature. Design optimization of the M-I-M structures will entail understanding how device performance is affected by the thickness, roughness, and composition of the metal and insulating layers.
