Orientation and symmetry control of inverse sphere magnetic nanoarrays by guided self-assembly

Inverse sphere shaped Ni arrays were fabricated by electrodeposition on Si through the guided self-assembly of polystyrene latex spheres in Si/SiO2 patterns. It is shown that the size commensurability of the etched tracks is critical for the long range ordering of the spheres. Moreover, noncommensurate guiding results in the reproducible periodic triangular distortion of the close packed self-assembly. Magnetoresistance measurements on the Ni arrays were performed showing room temperature anisotropic magnetoresistance of 0.85%. These results are promising for self-assembled patterned storage media and magnetoresistance devices

Integration of spintronics into silicon microelectronics

Practical application of spin-electronics and nanotechnology depends largely on compatibility with conventional technology.  The work presented in this thesis is on the integration of spintronic devices and nano-fabrication with silicon.  A review of spintronics is presented and the importance of semiconductors to this field is highlighted.  A metallisation technique for silicon of different resistivities is developed using electrodeposition.  No seed layer is required and a back-contact is not essential.  Selective electrodeposition on patterned Si/SiO2 is achieved demonstrating compatibility with microelectronics processes.  The film growth modes are studied and a correlation among the electrochemical conditions, the roughness and the magnetic properties of the film is established. Latex sphere self-assembly is used for the fabrication of inverse sphere magnetic arrays electrodeposited directly on Si.  Lithographic patterns on Si guide the self-assembly along particular directions and improve the long-range order.  Size commensurability between the pattern and the spheres is critical for the long range ordering of the spheres.  Non-commensurate guiding results in reproducible periodic triangular distortion of the close packed self-assembly.  The alignment of self-assembly arrays on both sides of a guiding line is achieved.  This technique is promising for applications such as patterned recording media and Si-integrated magnetoresistance devices but also for photonic applications such as waveguides and photonic crystals. The Schottky Barrier (SB) at magnetic metal - semiconductor interfaces are of particular importance for spin injection and detection and for suppressing substrate leakage currents at magnetoresistance devices grown directly on semiconductors.  Physical and electrical characterisation of the SB at electrodeposited Ni - lowly doped Si contacts is performed.  A high quality rectifying behaviour is observed.  The results are explained using modern SB models.  The Ni-Si SB is used to suppress leakage currents and allow anisotropic magnetoresistance measurements in self-assembled magnetic anti-sphere arrays directly on Si.</p