Vibrational Characteristics of Au-Doped Si Nanowires: A Molecular Dynamics Study with a Modified Embedded Atom Method Potential Developed for Si-H-Au Systems

Abstract

Silicon nanowires (SiNWs) are promising structures as resonators for applications in ultrasensitive force and mass transducers. In the present work, large-scale molecular dynamics simulations were conducted to explore the effect of gold (Au), a commonly used catalyst, on the vibrational properties of [1 0 0] and [1 1 0] SiNWs. The force field was established using the modified embedded atom method (MEAM) formalism. The parameterization focused on the properties of the hydrogen-covered SiNWs doped with Au, involving the formation energy as well as the structural and vibrational characteristics. The vibrational characteristics of a clamped-clamped SiNW were examined through excitation using a sinusoidal velocity field after energy minimization and thermal equilibration. Different doping concentrations and distributions can significantly change the frequency response, quality factor $Q$ , and beat phenomenon. The natural frequency $f_0$ decreased with increasing Au concentration, whereas the effect of the impurity distribution on $f_0$ was negligible. Furthermore, $Q$ was sensitive to the Au concentration and distribution, and the increased concentration led to an overall increment in $Q$ , accompanied by considerably increased scattering. Besides, the beat period of [1 1 0] SiNWs showed a strong positive correlation with the concentration. The vibration along the elementary axes cannot produce the beat phenomenon. Deflection of the elementary axes in a very small range would lead to a higher energy dissipation rate. In addition, owing to the considerable difference between the atomic masses of Au and Si, randomly distributed Au atoms significantly disturb the symmetry of the SiNWs. However, the elementary axes of the [1 1 0] SiNWs remained stable, even in the models with extremely radial or longitudinal impurity segregation. In contrast, we failed to capture the distinguishable elementary axes for most of the doped [1 0 0] samples. The features described above indicate that the impurity Au can effectively tune the resonant frequency of the [1 1 0] SiNWs, meanwhile, causes no large frequency shift that could be potentially caused by the deflection of the elementary coordinate system.