Study of the contribution of long-wave bending vibrations to the destruction of ultrathin films by the method of molecular dynamics

Abstract

The molecular dynamics method is used to study the process of development of dynamic instability of a thin film, leading to its destruction. The calculations are performed for a thin (5 atomic layers) $fcc$ aluminum film using the interatomic interaction potential tested by comparing the numerical results with the analytical ones obtained in the framework of elasticity theory. For this purpose, an original approach is developed, which allows one to calculate the dispersion law of long-wave phonons in ultrathin films using the molecular dynamics method. The temperatures ($< 600 K$) at which the system remains stable over a time interval of $0.6 ns$ are found. This makes it possible to analyze the low-frequency part of the spectrum down to the minimum frequency $\nu_{min}=0.0166 THz$ (at $T = 50 K$), and to determine the vibration frequency of the longest, for this problem geometry, bending wave $\nu_{0}=0.033 THz$ which decreases with increasing temperature, hence, its period grows. Once the vibration period of this mode becomes comparable with the time of simulation, there occurs, during calculation, a continuous increase in the amplitude of this mode which will be referred to as "retarded mode". It is shown that the film destruction begins with the attainment of a certain critical value of the bending wave amplitude.