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Highly controlled fabrication of carbon nanotube based probes for atomic force microscopy

Abstract

This thesis describes a fabrication process to grow a single carbon nanotube (CNT) based probe on an atomic force microscopy (AFM) cantilever by direct current plasma enhanced chemical vapor deposition (DC-PECVD). Electron beam induced deposition (EBID) of carbon dots is utilized for catalyst patterning without using any e-beam resist. Its resist-free characteristic makes EBID a good choice for fabrication of patterns on the edge of the cantilever. CNT probes with < 10 nm tip radius and desired growth direction were produced by electric-field-guided DC-PECVD growth. This process is also capable of being integrated in batch fabrication. A tunable CNT growth technique was also developed to control the plasma-induced surface stresses on cantilever beams during PECVD process. By introducing hydrogen gas to the (acetylene + ammonia) feed gas during CNT growth and adjusting the ammonia to hydrogen flow ratio, the cantilever surface stress can be altered from compressive to tensile stress, and in doing so controlling the degree of cantilever bending. This technique enables us to solve the serious bending of low stiffness cantilevers after PECVD growth, which makes the CNT probe unsuitable for AFM measurements. High resolution imaging of thin film specimens and deep trenches were demonstrated using these CNT based probes in tapping-mode, as well as in contact-mode. The mechanical durability of CNT probes was examined by continuous scanning on silicon nitride surface. No degradation in imaging performance was observed after 8 hours of operation. Additionally, high coercivity iron-platinum coated CNT probes have been fabricated for magnetic force microscopy (MFM) applications. The FePt-coated CNT probe has much localized magnetic stray field due to the high-aspect-ratio geometry and small radius of the tip. The MFM imaging on magnetic recording media was performed, and images with 20 nm lateral resolution have been demonstrated

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