UVM Theses and Dissertations
Format:
Print
Author:
Stevenson, Kevin D.
Dept./Program:
Mechanical Engineering
Year:
2006
Degree:
MS
Abstract:
Micro-Electro-Mechanical Systems (MEMS) have enabled miniaturized, cutting-edge technologies in the aerospace, transportation, biomedical engineering, and communications industries. A critical issue lies in the reliability of MEMS materials in response to thermomechanical stresses and their ability to combine high tensile strength and ductility simultaneously. Those criteria are not met with typical semiconducting materials such as silicon, but can be overcome using novel nanostructured materials, such as nanocrystalline metal thin films. A key characteristic of nanocrystalline materials is the ability to tailor mechanical strength by varying the average grain size. Metals with nanoscale grain structure have been produced showing superior, unique properties such as high strength and flow stress and superplasticity at very low temperatures. However, the dense grain boundary network associated with nanocrystalline materials results in a breakdown of the classical deformation mechanisms. This size-dependent effect is not fully understood. Further advanced mechanical testing is required to gain a comprehensive understanding of the grain size evolution during deformation. This thesis will present (1) the development of an electrochemical technique for the synthesis of Ni nanostructures and (2) the surface characterization and mechanical properties of these materials at the nanoscale.
The surface structure of electrplated Ni films was investigated to determine the ideal electrochemical environment to produce grain sizes between 10-80 nm. Pulsed-current deposition and organic additives were critical for obtaining grain sizes less than 30 nm. Standard AFM cantilevers (tip radius ~10 nm) were found to be insufficient for imaging grains smaller than 30 nm. However, high-resolution AFM cantilevers (tip radius ~1 nm) enabled accurate surface and grain analysis over the range of produced sizes. This non-destructive appraoch provided additional insight into the structure-property relationship of thin films at the nanoscale. An X-ray diffraction study verified the accuracy of average grain sizes calculated via AFM. Initial microhardness testing also provided insight into the mechanical properties of the deposited nickel.
The surface structure of electrplated Ni films was investigated to determine the ideal electrochemical environment to produce grain sizes between 10-80 nm. Pulsed-current deposition and organic additives were critical for obtaining grain sizes less than 30 nm. Standard AFM cantilevers (tip radius ~10 nm) were found to be insufficient for imaging grains smaller than 30 nm. However, high-resolution AFM cantilevers (tip radius ~1 nm) enabled accurate surface and grain analysis over the range of produced sizes. This non-destructive appraoch provided additional insight into the structure-property relationship of thin films at the nanoscale. An X-ray diffraction study verified the accuracy of average grain sizes calculated via AFM. Initial microhardness testing also provided insight into the mechanical properties of the deposited nickel.