Realization of nanowires using break junctions at room temperature

The unceasing scaling-down of electronic devices and components in ICs has raised the prospect of nano-scale devices, which have electrical and mechanical properties different from those at larger dimensions. The property which has attracted much of interest is the increasing role of quantum effects on electron transport at nano-level. The aim of this study was to realize nanowires using break junctions and to probe their quantum properties. There are many techniques used to investigate these quantum properties but mechanically controllable break-junction (MCB) technique is considered to be one of the most promising tools. In this technique, quantized conductance traces are acquired during the process of mechanically breaking a metallic contact. In the breaking process, two metal (gold) electrodes in contact with each other are slowly retraced due to which the contact area undergoes abrupt changes in its structural arrangement until a state is reached where only few bridging atoms are left. At this stage, the electrical conductance through this metallic contact is always found to be close to value of (12.9kΩ)^-1 ≈ 7.75×10^-5 which is given by Landauer's formula 2e²/h N [1]. This value corresponds to one quantum unit of conductance and hence indicating single atom contact. According to A.I.Yanson et al., one such channel corresponds to a constriction having thickness≈^λF/2, where λ_F is Fermi wavelength (≈ 5 Å) [2]. Also, we know, diameter of a gold atom is≈^λF/2. Hence a single atom constriction is observed. Adopting an averaging statistical approach, using many conductance traces, a histogram was plotted for the breaking process of a gold contact. From the histogram analysis, we came to a conclusion that the narrowest thickness of constriction that can be achieved is in the order of Fermi wavelength. Also, the single atom contact observed was stretched over a distance of few Å before it finally broke. Hence, while pulling a singe atom contact between gold electrodes, a chain of atom was formed having thickness of 2.5 Å.