Physical and Analytical Chemistry Seminar
Lecturer: Ekaterina Dikarov
Location: Faculty Seminar Room
Advanced methods in magnetic resonance for studying physical properties and processes of paramagnetic centers in the solid state
This research was performed under the supervision of Prof. Aharon Blank
Electron spin resonance (ESR) spectroscopy and imaging has been a leading analytical tool for studying paramagnetic centers for years. It has found applications in various scientific fields such as chemistry, biology and physics. In the solid state, ESR can be used to probe paramagnetic centers such as, electrons in unfilled conduction bands, electrons trapped in radiation damaged sites, broken bonds, dopants and impurities in semiconductors and oxides. Although conventional ESR is a powerful tool its implementation is limited by the low spin sensitivity (~109 spins in 1 second acquisition time) and imaging resolution (~20-30µm) available in commercial systems. This is especially critical in the case of small samples with low spin concentration and heterogeneous samples with several types or varying concentrations of paramagnetic species. In this work we made use of recent developments in the field of ESR that enable high spatial resolution (down to 400nm) and high sensitivity (~104 spins in second acquisition time) measurements as a basis for novel techniques for studying unique physical properties and process of the paramagnetic centers in the solid state. First, we present a high selectivity and sensitivity method for characterizing paramagnetic defects inside thin (~1µm) layers of poly-silicon on top of a glass substrate. This is achieved by a new surface loop gap resonator we developed for the purpose of selective measurement of the relevant layer and elimination of background signals generated from the substrate. Our spectroscopic results show high measurement selectivity and efficient background removal. Our next project involves the observation and characterization of diffusion and migration properties of paramagnetic species inside bulk amorphous SiO2 following heat treatments making use of the high imaging resolution and sensitivity capabilities of our ESR system. In the last work we experimentally demonstrate for the first time how the rate of the flip flop mechanism (one of the major mechanisms which contribute to the decoherence time in an electron spin system) of electron spins in the solid state can be measured directly by the means of pulsed ESR combined with powerful pulsed magnetic field gradients.