Experimental study of Rayleigh instability in metallic nanowires using resistance fluctuations measurements from 77K to 375K

Nanowires with high aspect ratio can become unstable due to Rayleigh-Plateau instability. The instability sets in below a certain minimum diameter when the force due to surface tension exceeds the limit that can lead to plastic flow as determined by the yield stress of the material of the wire. This minimum diameter is given $d_m \approx 2\sigma_S/\sigma_Y$ , where $\sigma_S$ is the surface tension and $\sigma_Y$ is the Yield force. For Ag and Cu we estimate that $d_m \approx$ 15nm. The Rayleigh instability (a classical mechanism) is severely modified by electronic shell effect contributions. It has been predicted recently that quantum-size effects arising from the electron confinement within the cross section of the wire can become an important factor as the wire is scaled down to atomic dimensions, in fact the Rayleigh instability could be completely suppressed for certain values of $k_F r_O$. Even for the stable wires, there are pockets of temperature where the wires are unstable. Low-frequency resistance fluctuation (noise) measurement is a very sensitive probe of such instabilities, which often may not be seen through other measurements. We have studied the low-frequency resistance fluctuations in the temperature range 77K to 400K in Ag and Cu nanowires of average diamete $\approx$ 15nm to 200nm. We identify a threshold temperature T* for the nanowires, below which the power spectral density $S_V(f) \sim 1/f$. As the temperature is raised beyond T* there is onset of a new contribution to the power spectra. We link this observation to onset of Rayleigh instability expected in such long nanowires. T* \sim 220K for the 15nm Ag wire and \sim 260K for the 15nm Cu wire. We compare the results with a simple estimation of the fluctuation based on Rayleigh instability and find good agreement