Gavagnin, Marco (2011) Sintesi plasma-assistita di nanosistemi a base di Co3O4 per applicazioni funzionali in sensoristica di gas e fotocatalisi. [Laurea specialistica biennale]
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Plasma-assisted synthesis of Co3O4 nanosystems for gas-sensing and photocatalytic applications The present work reports the synthesis and the characterization of supported Co3O4 thin films obtained by plasma assisted-chemical vapor deposition (PA-CVD) on different substrates [Si(100), Al2O3 polycrystalline, MgO(100) and MgAl2O4(100)], using two different CVD precursors [Co(dpm)2 and Co(hfa)2•TMEDA]. The attention was devoted to develop multifunctional materials with controlled characteristics for gas-sensing and photocatalytic application by a fine-tuning of PA-CVD process parameters, precursor and substrate type. In this regard, a multi-technique characterization of Co3O4 thin films (LRI, IR, XPS, SIMS, XRD, SEM, AFM, TEM) was of fundamental importance for a broad investigation of their properties as a function of the synthesis conditions. The materials grown from the two different precursors show diverse proprieties in terms of composition, crystalline structure and morphology. In particular, Co(hfa)2•TMEDA enabled to obtain a controlled anionic doping with fluorine due to the fluorinated b-dichetonate ligand contained in the metal complex. The samples deposited on Al2O3 showed good performances in the detection of both reducing (hydrogen, acetone, ethanol) and oxidizing (ozone) gases. The best properties were obtained for the films synthesized from Co(hfa)2•TMEDA, in particular the one with the highest fluorine content. Photo-assisted hydrogen production was tested on the samples deposited on Si(100). These experiments were carried out on water:ethanol mixtures using both the UV and visible irradiation. In both cases the samples deposited from Co(hfa)2•TMEDA led to higher hydrogen production rates than those from Co(dpm)2. Finally, Co3O4 depositions were performed on single crystals of MgO(100) and MgAl2O4(100) from Co(dpm)2. In this regard, to obtain more specific structural information, 2D-XRD analysis were performed. The obtained films show particular morphologies, ascribable to the highly orientated growth on these particular substrates. The present results evidenced that Co3O4 thin films supported on different substrates are good candidates for multi-functional applications, and that their nucleation and growth phenomena can be suitably tailored by controlling the processing conditions
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