Gardener, J.A.; (2008) Molecular thin films: fundamentals and potential routes for spintronic applications. Doctoral thesis , University of London.

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Abstract

Metal phthalocyanine (MPc) thin films are of interest for potential applications in spintronics and quantum computing. Two MPc-based routes towards spintronics devices are assessed here an organic-based approach and one in which MPc films serve as precursors for inorganic routes. For the all-organic approach, a selection of copper phthalocyanine (CuPc) thin films have been characterised these comprise molecular stacks (columns) that can be engineered to run parallel or orthogonal to the substrate plane. Electron paramagnetic resonance has been used to study interactions between unpaired electron spins of the CuPc molecules and shows that stronger intra- rather than inter-column interactions exist, implying that coherent spin transport would be most efficient along the column directions. Furthermore, this technique has been developed to assess the molecular structure of the CuPc films. Scanning tunnelling microscopy has been used to study the initial stages of CuPc growth on passivated Si(lOO) surfaces wherein an arrangement similar to the bulk a-phase is observed. Different growth modes are observed on surfaces passivated with hydrogen or ammonia this is attributed to differences in chemical interactions between the phthalocyanine ligand and passivating species. For the second route, a new method for introducing metal spins into silicon is presented wherein MPc films are irradiated with 172 nm UV light. The UV photons rupture the organic ligands forming volatile fragments, whilst the metals remain behind to form a metal oxide surface layer and are introduced into the substrate. X-ray absorption and secondary ion mass spectrometry measurements demonstrate that, for the specific example given of manganese phthalocyanine, Mn atoms do not cluster and instead occupy interstitial sites within the Si lattice. This method has the potential to create arrays of spins in silicon, which would be of interest as dilute magnetic semiconductors and for quantum computing applications.

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