VIBRATION ANALYSIS OF SINGLE WALLED BORON NITRIDE NANOTUBE BASEDMASS SENSOR

Abstract

After Iijima's uncovering of carbon nanotubes (CNTs) in 1991, during the last decade the experimental and theoretical works have been initiated by researchers on exploitation of other hollow tubular nanostructures, particularly inorganic nanotubes. The various fascinating properties are associated with their nano-scale dimensions, high anisotropy and atomic structures. Among such inorganic tubular nanostructures, boron nitride nanotube (BNNT) has received the most attention. The mass based sensing application, using such nanostructures is highly correlated with their dynamic characteristics. Therefore, it is essential to analyse the dynamic behaviour of nanostructures for their use as sensor systems. The nano-scale added/attached masses can be considered in the form of chemical molecules or biological objects. The main objective of the work presented in the thesis is to perform the vibrational analysis of the single walled BNNT as a mass sensor system. This objective integrates the vibrational characterization of all the possible atomic structures (achiral, chiral, pristine and defective) of the single walled BNNT. First, the extensive reviews of the literatures related to the background of BNNTs, modeling and simulation methodologies for vibrating nanotubes, modeling to back out the static and dynamic properties of BNNTs and the use of vibration measurements to characterize the mechanical properties of nanotube have been performed inline with the main objective of the presented work. Considering single walled BNNT as a transversely anisotropic material, the anisotropic constitutive relationship (stress-strain relationship) has been developed and used as an input data for continuum solid modeling based finite element method (FEM), simulation approach. The continuum mechanics based analytical analysis has been used to validate the continuum solid modeling based FEM simulation approach. Using both the approaches (analytical approach and continuum solid modeling based simulation approach), the parametric variation analysis has been performed by considering the resonant frequency variation analysis, for cantilevered and bridged configurations of the nanotube. The feasibility of the single walled BNNT as a mass sensor system has been ensured for the possible detection of the mass of nano-scale level. Further, the molecular structural mechanics based finite element (FE) modeling approach has been developed and used to perform the vibrational analysis of single walled BNNT as a mass sensor system. The capabilities of molecular structural mechanics based FE modeling approach (i) efficient simulation of all forms of atomic structures of nanotube (zigzag, armchair and chiral) and (ii) possible simulation of atomic level, have been fully utilized to ii analyse the different forms of pristine and defective atomic structures of single walled BNNT. The molecular structural mechanics based FE modeling approach has been used to identify the intermediate landing positions of the added mass along the length of the nanotube by considering the frequency variation analysis of higher order modes of vibration. Also, using molecular structural mechanics based FE modeling approach, the sensitivity analysis based on resonant frequency variation has been reported for the different forms of atomic structures of the single walled BNNT. The capability of atomic level simulation of the molecular structural mechanics based FE modeling approach has been efficiently utilized to explore the defective atomic structures of single walled BNNT as mass sensor systems. The possible defective atomic structures of single walled BNNT have been analysed by considering the point defects (single atom vacancies: VB and VN; BN divacancy: VBN) and extended-defect (dislocation line). Also, the vibrational characterization of defective single walled BNNT has been performed by considering the combined effect of chirality and the presence of different types of defect to assure the feasibility of mass sensor system using defective single walled BNNTs. The nano-scale mass detection capability of single walled BNNT as a nanomechanical resonator has been utilized to demonstrate the possible applications of biosensing and gas sensing by considering the possible adsorption/absorption of biological objects and chemical molecules. The possible minimum mass sensitivity limit of 10-23 g can be achieved using single walled BNNT as a mass sensor system. The performed parametric variation analysis indicates that the effect of variation in diameter of the nanotube is not so significant as compared to the variation in length of the nanotube. The different forms of atomic structure of single walled BNNTs and different boundary conditions can be efficiently simulated using molecular structural mechanics based FE modeling approach. The main features of this approach are time saving and simplicity. The proposed simulation approaches (continuum solid modeling based FEM approach and molecular structural mechanics based FE modeling approach) can be used as toolkits to develop systematic analysis for novel design of single walled BNNT based mass sensor system for a wide range of applications. The presented resonant frequency based analysis may be useful to practically realize the future single walled BNNT based sensor systems for the real time detection of biological objects and chemical molecules.