AFM Based Manipulation And Mechanical Properties Measurement Of One-dimensional Nanomaterials

One-dimensional (1D) materials such as carbon nanotubes are considered as potential building blocks for various nanodevices due to their extraordinary physical and chemical properties. Before they can be used in engineering applications, these properties must be well understood. However, their extreme small size makes the task of directly measuring any individual nanotubes or nanowires extremely difficult. This dissertation aims at the measurement of the basic mechanical properties of 1D materials. And to this regard, a new technology dealing with manipulation assisted bending by using atomic force microscopy (AFM) was presented. As an important source of force measurement error, the spring constant of AFM cantilevers were calibrated with a novel calibration system. By a combined use of manipulation and force measurement technology, a simple method to separate the core and shell of 1D core-shell material was proposed. This research improves the efficiency of 1D materials manipulation, and increase the applicability and reliability of the conventional bending test. It may also benefit the works on nanodevice assembly. The achievement details include the following:1. A review of 1D material was presented. A new technology of manipulation assisted bending was proposed to measure the mechanical properties of any specified individual nanotubes or nanowires.2. The behaviors of different 1D materials under the manipulation of an AFM tip are modeled. Based on the behaviors modeling and the image processing technique, a computer program was developed to investigate the automatic transfer of 1D materials on a structured substrate. With this program, individual nanotubes and nanofibres were moved to bridge the target micro trenches, which could be used for the bending test. To solve the problem of tip contamination during the procedure of manipulation, two possible methods were proposed.3. The bending models of suspended 1D materials under vertical loading were studied. By the bending tests, the elastic moduli of five typical nanotube and nanofibre models, including the cantilever beam, the fixed-fixed beam, the fixed-supported beam, the supported-supported beam and the elastic string were measured. The errors of the measurement results were analyzed.4. A novel system based on an ultra-precision balance integrated with an optical measuring setup was developed to calibrate the spring constant of the AFM cantilevers. With this system, several types of commercial cantilevers were calibrated. The relative standard deviation of the measurement was less than 5%, and the results were traceable.5. A new method was presented to in situ separate 1D core-shell fibre into core and shell. By AFM manipulation, a double-walled carbon nanotube, which was the core of a nanofibre, was stretched out from its amorphous carbon shell. The elastic modulus of the same fibre was measured by bending after it was moved to bridge a trench. With the measured modulus, the friction between the shell and the substrate was obtained. By comparing this friction with the inner axial force between the core and the shell due to van der Waals potential, the in situ separation method could be understood through basic mechanics theory. With this method, ultra thin wires can be moved more freely on a relatively rough surface. This method may be useful to create nanocables for nanoelectronics.