Below a certain temperature T(c) (typically cryogenic), some materials lose their electric resistance R entering a superconducting state. Following the general trend toward a large scale integration of a greater number of electronic components, it is desirable to use superconducting elements in order to minimize heat dissipation. It is expected that the basic property of a superconductor, i.e., dissipationless electric current, will be preserved at reduced scales required by modern nanoelectronics. Unfortunately, there are indications that for a certain critical size limit of the order of approximately 10 nm, below which a "superconducting" nanowire is no longer a superconductor in a sense that it acquires a finite resistance even at temperatures close to absolute zero. In the present paper we report experimental evidence for a superconductivity breakdown in ultranarrow quasi-1D aluminum nanowires.

Progressive reduction of the effective diameter of a nanowire is applied to trace evolution of the shape of superconducting transition R(T ) in quasi-one-dimensional aluminum structures. In nanowires with effective diameter ≤ 15 nm the R(T ) dependences are much wider than predicted by the model of thermally activated phase slips. The effect can be explained by quantum fluctuations of the order parameter.

An ion beam based dry etching method has been developed for progressive reduction of dimensions of prefabricated nanostructures. The method has been successfully applied to aluminum nanowires and aluminum single electron transistors (SET). The method is based on removal of material from the structures when exposed to energetic argon ions and it was shown to be applicable multiple times to the same sample. The electrical measurements and samples imaging in between the sputtering sessions clearly indicated that the dimensions, i.e. cross-section of the nanowires and area of the tunnel junctions in SET, were progressively reduced without noticeable degradation of the sample structure. We were able to reduce the effective diameter of aluminum nanowires from ∼65 nm down to ∼30 nm, whereas the tunnel junction area has been reduced by 40 %.

Abstract. We report a new approach for progressive and well-controlled downsizing of nanostructures below the 10 nm scale. Low energetic ion beam (Ar + ) is used for gentle surface erosion, progressively shrinking the dimensions with ~ 1 nm accuracy. The method enables shaping of nanostructure geometry and polishing the surface. The process is clean room / high vacuum compatible being suitable for various applications. Apart from technological advantages, the method enables study of various size phenomena on the same sample between sessions of ion beam treatment.

Size-dependent quantization of energy spectrum of conducting electrons in solids leads to oscillating dependence of electronic properties on corresponding dimension(s). In conventional metals with typical energy Fermi E F~1 eV and the charge carrier's effective masses m* of the order of free electron mass m 0 , the quantum size phenomena provide noticeable impact only at nanometer scales. Here we experimentally demonstrate that in single-crystalline semimetal bismuth nanostructures the electronic conductivity non-monotonously decreases with reduction of the effective diameter. In samples grown along the particular crystallographic orientation the electronic conductivity abruptly increases at scales of about 50 nm due to metal-to-insulator transition mediated by the quantum confinement effect. The experimental findings are in reasonable agreement with theory predictions. The quantum-size phenomena should be taken into consideration to optimize operation of the next generation of ultra-small quantum nanoelectronic circuits.npj Quantum Materials (2017) 2:18 ; doi:10.1038/s41535-017-0017-8 INTRODUCTIONWith reduction of dimension(s) classic physics gradually degenerates into quantum. For example, energy separation between the n-th and the (n+1)-th energy levels of a particle with mass m confined to a space of characteristic dimension a is ΔE(n)~n/ma