Fabrication, Characterization And Measurement Of Electrostatic/Electric-Field-Induced Self-Assembled SWNT/Polymer Films And Their Devices Development

With silicon-based devices fabrication approaching their physical limits, the carbon nanotubes (CNTs) are emerging materials as high-performance building blocks for micro/nano electromechanical system (M/NEMS) devices. Moreover, the CNTs show significant promise in various frontier fields owing to their unique quasi-one-dimensional structure with central hollow core and nanometer size, and especially their exceptional mechanical, electrical and functional properties. Despite well-marked achievements and attractive potential of CNTs as next-generational novel material, the controllable self-assembly fabrication and devices characterization still constitute the major obstacles towards scalable device applications, and also construct currently one of most challenging subjects worldwide.To achieve possible solutions for CNT-based devices fabrication, two kinds of controllable approaches including electrostatic-induced layer-by-layer self-assembly and electric field-induced self-assembly to fabricate CNT-based films were presented. The tunable mechanical and dynamic properties of self-assembled CNT-based films were characterized through a combinative approach of piezoelectric excitation and laser vibrometer measurement. Furthermore, the application of self-assembled CNT/polymer to fabricate potential devices with special purposes was proposed. This exploration work not only offers a material candidate for M/NEMS devices, but also opens up a new approach toward next-generation self-assembled devices.The main contribution and conclusions of the present work are summarized as follows: The surface modification of CNTs through the oxidation with concentrated acid mixture facilitated the uniformly well-dispersion of CNTs into suspension, successfully allowing for electrostatic-induced layer-by-layer self-assembly with complementary polyelectrolyte to form a homogeneous hierarchical membrane with a molecular-level control over the architecture. The characterization of electrostatic self-assembling mechanism, membrane formation dynamics, micro-topography, Raman spectroscopy and electrical properties were experimental performed, and the fundamental issues involving new principle, new phenomenon and new material for micro/nano scale films preparation were further deeply analyzed.Layer-by-layer self-assembled carbon nanotube/polymer nanocomposite membranes for M/NEMS were successfully fabricated on the electro-active polymer (EAP) film under interaction of electrostatic-induced force. Their tunable mechanical properties in Young's modulus from hundreds to tens of GPa as a function of the SWNT volume fraction was observed. Such significant enhancement result from an effective loading of SWNTs to the polymeric matrix, SWNT-polymer reinforcement through dense bonding, and the polymer chains stiffening. The electrostatic-induced layer-by-layer self-assembly offers a way in which the embedded SWNTs can realize the true potential to strengthen SWNT/polymer nanocomposites.Controllable self-assembly of homogeneous and highly-compact pure CNT membranes were successfully deposited on the EAP film under electric field excitation. The experimental characterization of directed assembled high-density CNT films was performed with some equipments and techniques such as Electrochemical Analyzer, Scanning Electron Microscope, Raman Microscope and Profilometer. A tunable dynamic electromechanical performance for such CNT/EAP thin-film transducers in both resonant frequency and quality factor was demonstrated, compared with pure polymer. This observed enhancement can be exploited to tailor the thin-film transducers for desired electromechanical properties.The concept of using self-assembled CNT/polymer membranes to explore new generation of devices. A transparent film wind power generator was fabricated by exploiting self-assembled CNT/polymer films as transparent electrodes, allowing for power harvesting and sustainable energy development from reproducible and cost-effective natural energy. The micro/nano fabrication process for developing MEMS resonator and switch devices based on tunable self-assembled CNT/polymer films was performed in experiment, and their performances in theoretical prediction illustrated considerable resonance characteristics and low pull-in voltages for promising applications.The dedicative works presented create versatile and promising pathways for tailoring self-assembled CNT/polymer films as advanced M/NEMS engineering material, and also indicate theoretical and practical significances in developing next-generational macro/micro/nano devices and systems with high-performances and special purposes.