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Reference (phdthesis)

D. J. Bell, "NEMS Based On Nanocoil Structures", ETH Zurich, 2007.

BibTeX entry

@PHDTHESIS{Bell_Thesis_07,
Author = {Dominik J. Bell},
Title = {NEMS Based On Nanocoil Structures},
School = {ETH Zurich},
Year = {2007},
Abstract = {With the fabrication method for the self-formation of three-dimensional nanostructures based on work by Prinz et al. better control over the material properties, geometry, and location of the resulting structures can be achieved than with other types of bottom-up fabrication processes. The goal of the research presented in this thesis was to extend this fabrication method in several ways in order to create functional elements for NEMS and MEMS. For this purpose several processes have been developed to further increase the control over the fabrication, to increase the flexibility in terms of the achievable geometries, to allow for the batch integration of these structures, and to functionalize them. This has been done for two material systems - InGaAs/GaAs and SiGe/Si. Nanorobotic manipulation in an SEM was used for the experimental characterization of the mechanical, electrical, and electromechanical properties of the structures. The structures exhibit low axial stiffness on the order of mN/m and a high elastic deformation capability. They are therefore suitable as sensing elements in high-resolution, large-range mechanical sensors. With their piezoresistive response they exhibit self-sensing capability. Simulation has been used to verify the experimental results. A program was developed that allows for the fast creation of simulation models for helical multilayer structures, and can serve as a design tool. Two types of devices that are based on nanocoils are presented. In conductometric sensors the highly responsive nanocoils act as the sensing element. They have been used to measure temperature and to detect optical signals. The high surface-to-volume ratio results in high resolution and fast response time for this type of device. Parasitic effects from the substrate are minimized with the coils suspended some distance from the surface. Moreover, the structures are single-crystalline, and the faces of the structures that are exposed to the environment are always the same. All of these attributes are beneficial for conductometric sensors. In another application magnetic nanocoils are demonstrated to act as a flagella-like propeller. In this micropropulsion system the energy is generated with a setup of external Helmholtz coils. The nanocoils rotate with the rotating, homogeneous field. Due to the domination of friction forces in the low Reynold’s number regime the rotation of the nanocoil causes a net propulsive force in the axial direction. Numerical modeling was used to estimate the friction coefficients of these structures. Analytical results that have been presented previously are not applicable due to the high-aspect-ratio, rectangular cross-section of the nanobelts.}
}

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