Thema der Dissertation:
Quantitative electron paramagnetic resonance spectroscopy in harsh aqueous environments
Quantitative electron paramagnetic resonance spectroscopy in harsh aqueous environments
Abstract: Quantitative electron paramagnetic resonance in harsh aqueous environments
Electron paramagnetic resonance (EPR) is the method of choice to investigate and quantify paramagnetic species in many applications in materials science, biology, and chemistry. In these fields, typical sample states include thin films and solutions. Of particular interest are dynamic processes in solution. Their investigation, however, is limited by the form factor of the utilized microwave (MW) resonators as the entire process needs to be confined to the resonator. The EPR-on-a-chip (EPRoC) dipstick device circumvents these limitations by integrating the entire EPR spectrometer into a single microchip, covered with a protective coating that enables the operation of the EPRoC submerged directly in the sample solution, thereby expanding the accessible sample environments for EPR measurements. In this approach, instead of a MW resonator, the coil of a voltage-controlled oscillator (VCO) with a size of a few hundred micrometers is simultaneously used as MW source and detector. In contrast to conventional EPR, the MW frequency may be swept while the magnetic field is held constant enabling the use of small permanent magnets, which could drastically reduce the experimental complexity of EPR.
As a test for the EPRoC dipstick and its protective coating, differently charged electrolyte solutions of a Vanadium redox flow battery with pH < 1 are investigated with the EPRoC and compared to conventional EPR results. The EPRoC shows the same spectral shape as conventional EPR as well as the same linear relationship of EPRoC and EPR signal intensities with respect to the state of charge (SOC) is found. Consequently, these experiments serve as proof of principle for an EPRoC dipstick device operating in a harsh sample environment.
For improved spin sensitivity, an array of VCOs may be phase-locked on a single microchip to form an EPRoC array. However, quantitative EPR measurements require a thorough understanding of the microwave field. The effect of the inherently inhomogeneous MW magnetic field on the recorded signal amplitude is investigated with a “point-like” sample of a stable organic radical and a thin film of amorphous silicon. The results of which are compared to finite-element simulations of the MW magnetic field and found to be in good agreement. The sensitive volume of the EPRoC array is determined from these experiments allowing for quantitative EPR.
In combination with a small permanent magnet, the EPRoC array dipstick may find its way beyond the laboratory as a quantification tool for paramagnetic species in solution.
Electron paramagnetic resonance (EPR) is the method of choice to investigate and quantify paramagnetic species in many applications in materials science, biology, and chemistry. In these fields, typical sample states include thin films and solutions. Of particular interest are dynamic processes in solution. Their investigation, however, is limited by the form factor of the utilized microwave (MW) resonators as the entire process needs to be confined to the resonator. The EPR-on-a-chip (EPRoC) dipstick device circumvents these limitations by integrating the entire EPR spectrometer into a single microchip, covered with a protective coating that enables the operation of the EPRoC submerged directly in the sample solution, thereby expanding the accessible sample environments for EPR measurements. In this approach, instead of a MW resonator, the coil of a voltage-controlled oscillator (VCO) with a size of a few hundred micrometers is simultaneously used as MW source and detector. In contrast to conventional EPR, the MW frequency may be swept while the magnetic field is held constant enabling the use of small permanent magnets, which could drastically reduce the experimental complexity of EPR.
As a test for the EPRoC dipstick and its protective coating, differently charged electrolyte solutions of a Vanadium redox flow battery with pH < 1 are investigated with the EPRoC and compared to conventional EPR results. The EPRoC shows the same spectral shape as conventional EPR as well as the same linear relationship of EPRoC and EPR signal intensities with respect to the state of charge (SOC) is found. Consequently, these experiments serve as proof of principle for an EPRoC dipstick device operating in a harsh sample environment.
For improved spin sensitivity, an array of VCOs may be phase-locked on a single microchip to form an EPRoC array. However, quantitative EPR measurements require a thorough understanding of the microwave field. The effect of the inherently inhomogeneous MW magnetic field on the recorded signal amplitude is investigated with a “point-like” sample of a stable organic radical and a thin film of amorphous silicon. The results of which are compared to finite-element simulations of the MW magnetic field and found to be in good agreement. The sensitive volume of the EPRoC array is determined from these experiments allowing for quantitative EPR.
In combination with a small permanent magnet, the EPRoC array dipstick may find its way beyond the laboratory as a quantification tool for paramagnetic species in solution.
Zeit & Ort
02.10.2024 | 11:15
Hörsaal A (1.3.14)
Fachbereich Physik, Arnimallee 14, 14195 Berlin