Nanoscale physics

Short-wave breakup modes in nanowires with a BCC lattice structure
V.V. Tereshchuk1, V. N. Gorshkov2
1,2 Department of Physics, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Building 7, 37 Peremogy Avenue, Kiev-56, 03056, Ukraine. 
E-mail: volodymyr379@gmail.com
The classical theoretical model of the break-up of metal nanowires [1] draws an analogy of this process with the break-up into droplets of liquid filaments (Plateau Rayleigh instability). The appearance of periodic modulations of the cross-section of a nanowire at the temperatures below the melting point occurs as a result of surface diffusion of atoms. If the surface energy density is isotropic, then the modification of the nanowire shape is resulting from decreasing in its surface energy (surface area) for the perturbation wavelengths  (-initial radius of the nanowire). On the other hand, when the nanowire breaks up into fragments of equal length, the total surface area of the formed spherical nanodroplets is less than the lateral surface area of the initial cylinder if . Nevertheless, the thermodynamically allowed “energetic instability” formally cannot be realized in the range  according to the dynamical rules established in known theoretical models [2]. However, such short-wave breakup modes are observed in numerous experimental studies (see Fig. 1(a)). In our work, we show that the noted short-wave perturbations occur due to the effect of the roughening transition when the initially flat surface becomes periodically modulated in height if the temperature exceeds a certain critical value (see Fig. 1(b),(c) that is an example of our Monte-Carlo simulations). This effect is accompanied by a decrease in the free energy of the system at a given temperature and is clearly manifested due to the structural features of the BCC lattice, as it is shown by the obtained results.

1.	Nichols F. A., Mullins W. W.. Surface- (interface-) and volume-diffusion contributions to morphological changes driven by capillarity. Trans. Metal. Soc. AIME. -1965.  233, 1840–1848.
2.	Wong H., Energetic instability of polygonal micro- and nanowires. J APPL PHYS. - 2012. 111, 103509.