| Nanostructures exhibit physical properties that are dramatically different from their bulk forms due to their extremely high surface-to-volume ratio, which we call nano-size effect. Therefore, understanding the physical properties of nanostructure would be essential for developing nanodevice when it is used as functional components. Among various experimental methods for exploring physical properties of nanostructure, mechanical loading would be the most important one since it varies the internal structure directly. However, applying mechanical load to nanostructure would be experimentally challenging due to the nanoscale of the specimen. There have been several experimental researches on applying mechanical load on nanostructure in TEM/SEM using AFM/probe technology or MEMS technology. AFM/probe loading technology has the disadvantages of low controllability and high complexity of testing system. Compared with AFM/probe, MEMS actuator has the advantage of smaller volume, lower power consumption, higher precision and easy to fabricate. However, most of the in-situ TEM/SEM MEMS devices for performing mechanical test on nanostructure is very complicated due to the integrated microforce/displacement sensing structure. Furthermore, there has been few experimental researches which are capable of performing mechanical and electrical test on nanostructure simultaneously, or their testing system is too complicated.To solve the problems mentioned above, this doctoral dissertation, based on former experimental achievements, designs and fabricates a simple and easier-to-fabricate MEMS actuator for performing in-situ TEM/SEM mechanical test on nanostructures. Using this device, in-situ TEM/SEM tensile test is performed on different nanostructures, and mechanical/electrical properties are characterized in process of the tensile test. Furthermore, a modified design is given for the MEMS actuator to improve the tensile experiment. Detailed work includes:(1) Based on previous work, an experimental platform for measuring lattice parameters of single crystal silicon (SCS) nanobeam is developed. And selected-area electron diffraction working mode of TEM is used to measure the lattice parameters of SCS nanobeam in process of tensile test, from which the lattice behavior of SCS nanobeam is studied.[110]-stretched lattice model and dislocation model are used to explain the experimental results.(2) In order to achieve simultaneous characterization of mechanical and electrical properties of nanostructure using simple testing device, a simple and easy-to-fabricate electrostatic actuator is developed for performing in-situ SEM mechanical and electrical test on nanowire simultaneously. A Cu nanowire and a SiC nanowire are integrated to the actuator using nanomanipulation and tested by the actuator. Stress-strain relations and I-V characteristic of both nanowires are obtained.(3) In order to explain the results of tensile experiments on Cu nanowire and SiC nanowire, high resolution TEM images are taken and possible theories are investigated. As a result, the oxide layer surrounding Cu nanowire acting as a tunneling barrier is responsible for the obvious nonlinearity of I-V curves, and the significant nano-piezoresistive effect of SiC nanowire is attributed to the stress-induced modulation of the surface potential barrier.(4) Finally, in order to overcome the disadvantage of electrostatic actuator being only compliant for single-tilt TEM specimen holder due to the its comparably big size and, more importantly, the disadvantage of movable combs’vibration which would break nanowire easily, a thermally actuated tensile device which is much smaller and has the advantages of being compliant for double-tilt TEM holder and generates less vibration is described. Dimensional parameters are designed for the thermal actuator using elastic mechanics and thermal expansion theory. Finite element method simulation is adopted to optimize the thermal tensile device, and possible fabrication process is designed. |
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