טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPine Polina
SubjectAtomistic Simulation of Nano-Electro Mechanical Systems
Based on Carbon Nanotubes
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors Dr. Joan Adler
Dr. Yuval Yaish
Full Thesis textFull thesis text - English Version


Abstract

Carbon nanotubes (CNTs) posses unique electrical and mechanical properties and are of great interest for both basic and applied research. One active research field is that of nano-electro-mechanical systems (NEMS) based on CNTs. With respect to conventional NEMS, CNTs are extremely light, have very high Young's Moduli (~ 5TPa), contain a small amount of structural defects, and it is anticipated that they will oscillate at high frequencies. Hence, assuming all other properties being equal, carbon nanotube resonators are expected to reach the ultimate mass, stress and pressure sensitivities.

Since, the natural frequency is sensitive to the applied external load, one of the principles of sensing is based on the natural frequency shift of a carbon nanotube resonator under an external perturbation. Hence, in order to design and optimize CNT NEMS one has to understand vibrational behavior of these systems.

 This thesis presents numerical studies of vibrational behavior of single walled carbon nanotubes (SWCNTs). Molecular dynamics simulations of doubly clamped armchair SWCNTs including a precise analysis of the four lowest modes of vibrations are presented. We provide clear evidence for the failure of simple analytic models such as Euler-Bernoulli to accurately extract resonance frequencies as the ratio, (R/L), between the tube radius (R) and the length (L) varies. Our results are in excellent agreement with the Timoshenko beam model. Yakobson's paradox, relates to a scatter of between 1 and 5 TPa in the Young's modulus from atomistic simulations. In this thesis we shed light on this by giving an upper cutoff estimate for the effective SWCNT thickness, and show that in the Timoshenko model, there are two different sources for the nanotube thickness.

In an attempt to determine whether the nanotube type affects vibration we report on the vibrational behavior of four different types of SWCNTs: armchair, zigzag and two different chiral ones, which were fully clamped at both ends. Comparison between the vibrational behavior of these four types of nanotubes gave the result that the SWCNT structure does not affect the vibrational frequencies under these conditions.

We also studied SWCNTs with boundary conditions which imitate the partly clamped experimental conditions. Our results demonstrate that three nanotubes indeed vibrate differently. The symmetry between the two perpendicular directions is broken, and SWCNT type does influence the vibrational modes. A final study of proof of concept for varying atomic mass shows that the vibrating doubly clamped nanotube can sense zeptogram masses.