Conductance quantization

Kraus JM, Ruitenbeek JM, Fisun VV et al (1995) The signature of conductance quantization in metaUic point contacts. Nature 375 767-769... 

In the Center "Probe Microscopy and Nanotechnology" of Moscow Institute of Electronic Technology (Technical University) we started nanotechnology researches in 1985. A number of unique results, including the conductance quantization in quasi-one-dimensional molecular wires at room temperature was demonstrated. Wide area research in a creation of nanoelectronic device principles has been initiated. 

Fig. 1 presents a picture of a path (nanowire) - the constriction in an electrical conductor with dimension W (width), H (thickness) and L (length). The quantization of electric conductance depends neither on the kind of element nor on temperature. For conductors and semiconductors the conductance quantization in units of Go = 2e /h = (12.9 kQ)" was measured in many experiments. In our experiments the quantization of conductance was evident [3]. 

Figure 1. A system for measurements of conductance quantization an electrical circuit (left) and a piezoelectric actuators (PI and P II) for precise moving of electrodes (right).

Figure 2. Conductance quantization in metallic nanowires golden nanowires (left) and copper nanowires (right). The characteristics presented are chosen from 20000 consecutive measurements for both metals.

The conductance quantization has proved to be observable in an experimental setup, giving opportunity to investigate quantum effects in electrical conductivity. The curves of histograms from nanowires with an electrode of cobalt, nickel or tungsten do not contain peaks. In our opinion, a curve of histograms without peaks for some nanowires can be caused by the hardness of magnetie metals [3]. 

Nano wires in soft metals are formatted more frequently. The quantization in good electrical conductor (Au, C ) occurs more frequently and its histograms have peaks because of easier formation of nanowires from soft metals than from hard metals (Ni, Co, W). For a nanowire formed by a pair of metals, a soft metal and a hard one, the histogram is like the histogram of the softer metal. Probably the nanowire formed from such pair of metals contains mostly atoms of the soft metal. The study of the nanowires forming effect enables to allow for conductance quantization in electronic circuits containing mechanical contacts, e.g. relay contacts. 

Figure 2. Conductance quantization in Co-Ge contacts a) traces from 1 to 500 with a step 40 b) histogram from conductance measurements (at room temperature).

Peres, N., Castro, A., 8c Guinea, F. (2006). Conductance quantization in mesoscopic graphene. Physical Review B, 73,195411. 

Li, J., Nakato, Y, and Murakoshi, K. 2005. Electrochemical fabrication of Pd-Au heterogeneous nanocontact showing stable conductance quantization under applying high bias voltage. Chem. Lett. 34 374-375. 

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