Local in situ Raman analysis of the gas and solid phase for understanding the catalytic growth process of carbon nanotubes by chemical vapor deposition (CVD)

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In the first project period a strategy was developed and successfully applied to in situ monitor the gas phase composition and the gas phase temperature during the chemical vapor deposition (CVD) of carbon nanotubes (CNTs) on a Si/SiO2-wafer, which was carrying iron nanoparticles to catalyze the CNT formation. This was possible by applying gas phase linear Raman spectroscopy. The resulting CNTs were characterized ex situ via scanning electron microscopy (SEM) and solid phase Raman spectroscopy. The goal of the second project period is to continue the investigations in exploring the influence of different parameters on the decomposition kinetics of the carbon source. In accordance with the results so far achieved, the parameters to be changed comprise the substrate material (Si/SiO2 should be replaced by Al2O3 and MgO), the hydrogen concentration and the carbon source (acetylene and alcohol). The final goal is to combine the measurement technique based on linear Raman spectroscopy for the simultaneous analysis of the gas and the solid phase in situ during the CVD of CNTs. This makes possible the simultaneous in situ measurement of the gas phase composition, the gas phase temperature and the microstructure of the deposited CNTs with high temporal and spatial resolution, such that finally the decomposition of the carbon source and its effect on the gas temperature and on the CNTs growth can be followed as a function of time. Additionally, the characterization of the resulting CNTs via SEM and Raman spectroscopy will be carried out ex situ for validation. These comprehensive investigations into the CNT formation will provide a sustained understanding of the CNTs nucleation and growth mechanism, which for the first time will experimentally consider the intermediate reactions steps taking place inside the CNT reactor.