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

金属纳米触点，特别是仅由一个原子组成的单原子触点，在高偏置/大电流条件下会变得不稳定。本研究在2002-2003财政年度进行，实验研究了金属纳米接触中电流引起的不稳定性，阐明了其机制，并研究了合金是否抑制了不稳定性。在Au， Ag， Cu和Al触点中，单原子触点（SACs）的形成概率p随着偏置的增加而减小，并在临界偏置V^<bc>时消失。在较高的偏置/电流下，触点尺寸的缩小因此变得更加不稳定，从而减少了成为SAC的机会。p_<Au>的V^<bc>值为~ 2.3V, p_<Ag>、p_<Cu>、p_< Al>的V^<bc>值为0.6 ~ 0.8 V。尽管V^<bc>不同，但所有这些ps都表现出普遍的偏置依赖性，表明这四种金属具有共同的不稳定机制2。通过对贵金属纳米触点断裂电导的实验研究，揭示了触点断裂的临界电流密度。Au， Ag和Cu纳米触点的临界电流密度值相似，其数量级为10^<10>A/cm^2。当通过颈缩变形收缩触点时，一旦触点电流密度超过临界值，触点就会变得不稳定并断裂。然而，一些相对稳定的接触可能在不稳定中幸存下来并继续变形成为SAC。因此，SAC的形成概率基本上就是这种接触在不稳定条件下通过变形存活下来的概率。这种对p的新解释可以解释其观察到的偏倚依赖性。Ag和Cu纳米接触表现出另一种类型的不稳定性，这种不稳定性在低电导状态下占主导地位，而在Au中没有出现。这一新的不稳定性的存在提供了p_<Ag>和p_<Cu>的V_<bc>低于au5的原因。与AuAg和AuCu合金相比，AuPd和AuPt合金的SAC形成概率具有不同的偏置依赖性，随着偏置的增大SAC形成概率减小得更快。目前还不清楚是什么合金效应导致了四种合金ps的差异。少

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