Link to publication in University of Groningen/UMCG research database Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We investigate the formation of nanogaps in gold wires due to electromigration. We show that the breaking process will not start until a local temperature of typically 400 K is reached by Joule heating. This value is rather independent of the temperature of the sample environment ͑4.2-295 K͒. Furthermore, we demonstrate that the breaking dynamics can be controlled by minimizing the total series resistance of the system. In this way, the local temperature rise just before breakdown is limited and melting effects are prevented. Hence, electrodes with gaps Ͻ2 nm are easily made, without the need of active feedback. For optimized samples, we observe quantized conductance steps prior to the gap formation.

Transition voltage spectroscopy (TVS) has been proposed as a tool to analyze charge transport through molecular junctions. We extend TVS to Au-vacuum-Au junctions and study the distance dependence of the transition voltage V(t)(d) for clean electrodes in cryogenic vacuum. On the one hand, this allows us to provide an important reference for V(t)(d) measurements on molecular junctions. On the other hand, we show that TVS forms a simple and powerful test for vacuum tunneling models.

We study the interaction between single apex atoms in a metallic contact, using the break junction geometry. By carefully training our samples, we create stable junctions in which no further atomic reorganization takes place. This allows us to study the relation between the so-called jump out of contact (from contact to tunneling regime) and jump to contact (from tunneling to contact regime) in detail. Our data can be fully understood within a relatively simple elastic model, where the elasticity k of the electrodes is the only free parameter. We find 5

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Current-voltage characteristics of H 2 -Au molecular junctions exhibit intriguing steps around a characteristic voltage of V s Ϸ 40 mV. Surprisingly, we find that a hysteresis is connected to these steps with a typical time scale Ͼ10 ms. This time constant scales linearly with the power dissipated in the junction beyond an off-set power P s = IV s . We propose that the hysteresis is related to vibrational heating of both the molecule in the junction and a set of surrounding hydrogen molecules. Remarkably, by stretching the junction the hysteresis' characteristic time becomes Ͼdays. We demonstrate that reliable switchable devices can be built from such junctions.