Current-Induced Instability in the Quantized Conductance States of MetaNanowires and Their Reinforcement by Alloying

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Metal nanocontacts, single-atom contacts consisting of only one atom in particular are found to become unstable when they are subject to high bias/high-current conditions. This research, conducted through 2002-2003 fiscal years, was to study experimentally this current induced instability in metal nanocontacts, clarify its mechanism(s), and investigate whether alloying suppresses the instability or not Main results obtained in this work are listed below.1. In Au, Ag, Cu, and Al contacts, the formation probability p of single-atom contacts (SACs) decreases with increasing bias and vanishes at a critical bias V^<bc>. Under higher biases/currents, a contact shrinking in size thus becomes more unstable, leaving less chance to be a SAC. The value of V^<bc> is 〜2.3V for p_<Au> and 0.6-0.8 V for p_<Ag>, p_<Cu>, and P_<Al>, respectively. Despite the difference in V^<bc>, all these ps show a universal bias dependence, indicating an instability mechanism common to these four metals2. Experiments … More on the fracture conductance of noble metal nanocontacts have ervealed the existence of a critical current density for contact rupture. Au, Ag, and Cu nanocontacts have similar values for their critical current density, which is the order of 10^<10>A/cm^2. When one shrinks a contact by necking deformation, the contact becomes unstable and fractures once the contact current density exceeds the critical value.3. However, some relatively stable contacts may survive the instability and continue the deformation to become a SAC. Therefore, the SAC formation probability is basically a survival rate of such a contact through its deformation under unstable condition. This new interpretation of p can account for its observed bias dependence.4. Ag and Cu nanocontacts show another type of instability which dominates in a low conductance regime and does not appear in Au. The existence of this new instability provides the reason why p_<Ag> and p_<Cu> have lower V_<bc> than that of Au.5. SAC formation probabilities of AuPd and AuPt alloys have different bias dependence from those of AuAg and AuCu alloys and diminish more rapidly with increasing the bias. It is not clear at this time what alloying effects bring about this difference in ps of four alloys. Less