Abstract
Copper deposition onto Cu2O thin films grown on Au(111) results in the formation of monolayer islands with hexagonal and rhombic shapes, as observed with scanning tunnelling microscopy. The differential conductance through the Cu islands is governed by distinct quantum well states (QWS), accompanied by pronounced electron standing wave patterns. Below the onset of the QWS, an extended region of negative differential conductance opens up, in which also the tunnelling current declines markedly with increasing bias voltage. The effect is assigned to the quantised electronic structure of the Cu islands in combination with the p-type conductance behaviour of the oxide film underneath. The latter promotes electron transport across the islands around the Fermi level, but leads to a closure of this transport channel at negative bias.
Highlights
A fundamental goal in the development of novel electronic devices is the fabrication of elements with strongly nonlinear current–voltage characteristics [1]
We note that the phenomenon is neither observed for Cu islands grown directly on Au(111) (figure 2(a), lowest curve) nor for islands bound to ML-thick oxide films
ML Cu islands grown on Cu2O thin films are subject to lateral quantisation effects that come along with pronounced electron standing wave patterns, as detected with scanning tunnelling microscopy and spectroscopy
Summary
A fundamental goal in the development of novel electronic devices is the fabrication of elements with strongly nonlinear current–voltage characteristics [1]. Such a conductance behaviour beyond Ohms law forms the basis for various electronic applications, e.g. switches, amplifiers and smart control systems. Of particular interest are elements with negative differential resistance (NDR), exhibiting a decreasing current at increasing voltage or synonymously a differential conductance (dI/dV ) with negative sign. The NDR effect typically arises from electron tunnelling through systems with a strongly non-monotonic density of states (DOS) [2]. Electron tunnelling across the gap gives rise to the NDR effect with ratios between forward and valley current of about ten
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