Organization of nanostructures on the surface of Fe/Si

• Main Author: Jiang, Zongye
• Other Authors: School of Materials Science and Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52112
• Institution: Nanyang Technological University

The use of Focused Ion Beam (FIB) in micromanufacturing has been prevalent since its invention in the 1970s. Nanoneedle structures were observed after ion sputtering using the FIB system on Fe deposited thin films. The surface modification of Fe deposited silicon resulted in a recent discovery of nanonipple structures by the bombardment of Ga+ ions. This fabrication process involved the FIB ion irradiation of Ga+ ions directed perpendicular to the substrate surface at implant energy of 30KeV. The resultant nanonipple structure consists of a crystalline silicon stub encapsulated beneath an amorphous outer layer and a nipple tip. This amorphous phase was discovered to contain a high wt% of Fe and Ga elements. Recrystallization of this amorphous layer while maintaining the geometry integrity exudes the possibility of improved magnetoelectronic properties for future applications. Recrystallization of this nanonipple structure was carried out via tube furnace annealing treatment under argon gas environment to prevent sublimation of substrate at high temperatures. Maximum annealing temperatures and dwell times were experimented to achieve suitable recrystallization parameters. Maximum annealing temperatures were narrowed down to 250°C, with the nanonipple tip kept visible under SEM observations. Electron diffraction pattern analysis using TEM ascertains the success of recrystallization in the nanonipple sidewall and recrystallization of Ga component that is attached to the nanonipple tip. Under Fast Fourier Transformation (FFT), reciprocal lattice patterns in the silicon sidewall and nanonipple tip were analysed. It was found that silicon sidewall recrystallization displayed crystalline silicon in the direction [111] while the nanonipple tip achieved a partial recrystallization. Overall, recrystallization was successfully achieved in this study at temperatures within the range 200°C - 250°C. In conclusion, nanonipple structures can be replicated under ion irradiation of Ga+ and recrystallization of these structures can provide an opportunity to improve its properties to be used in future applications.