Conductance in Nanocontacts of Soft Metals and Liquid Metals

点击翻译按钮获取中文摘要

It is well known that the conductance quantization in quantum point contacts of metals can be best observed in soft metals such as Au. However, no systematic studies have been performed so far on how mechanical strength of metals influences the conductance quantization in their contacts. This study was conducted through 1999-2000 fiscal years to clarify the interrelation between hardness of metals and the appearance of conductance quantization in their atom-sized contacts. Main results obtained in this work are listed below.1. We investigated the conductance of five transition metals of different hardness, Pd, Pt, Rh, Ru, and Ir, and found that none of them exhibit the conductance quantization as clearly as that of Au. However, the conductance characteristics depends on metals, and a weak correlation can be found between the degree of conductance quantization and the mechanical strength of metals.2. Although liquid Hg represents the softest metals, it also exhibits hardly any evidences … More of the conductance quantization. We found that the conductance characteristics of Hg depend on the speed of contact breaking. In fast-breaking relay contacts, Hg shows no conductance plateaus in transient conductance traces. With the use of a slow-breaking mechanical contact, we can observe, not often but occasionally, well-defined quantized conductance plateaus.3. Alloying is a typical method of strengthening metals. We, therefore, carried out experiments on AuPd alloys to clarify the influence of alloying on the conductance quantization. In AuPd, it is found that the conductance characteristics transform gradually from that of pure Au to that of pure Pd with increasing the Pd concentration. Quantized conductance peaks in the histogram of Au are reduced by alloying with Pd, and gradually replaced by a broad structure characteristic of the Pd histogram. An important finding is that the first conductance peak shows no peak shift upon Pd alloying. This observation suggests that the electron scattering by solute atoms is much stronger than to generate the peak shift. Less