2:00 PM - SF01.13.06
A Synchrotron-Assisted Investigation of the Thermal Decomposition of Zirconium Acetylacetonate—Pathways to the Formation of Metal-Containing Intermediates in the Gas Phase
Sebastian Grimm1,Seung-Jin Baik1,Patrick Hemberger2,Andreas Kempf1,3,Tina Kasper1,3,Burak Atakan1,3
University of Duisburg-Essen1,Paul Scherrer Institute2,Center for Nanointegration Duisburg-Essen (CENIDE)3
Show Abstract
Solid layers1,2 of ZrO2 are often deposited by chemical vapor deposition (CVD), where a metal-containing precursor is evaporated and forms a film in a surface reaction. To design such a process, the gas phase reactions, especially their temperature-dependent kinetics, should be known, which is seldom the case. Intermediates, formed in the gas phase can lead to film formation or to a depletion of the precursor and therefore a reduction in growth rate. The analysis of these early stages of growth requires fast and sensitive analytical techniques with sufficiently low detection limits for elusive gas phase species. Experimental limitations precluded the detection of most of the postulated intermediate species, and reaction mechanisms are predominantly hypothetical so far.3,4 An experimental approach to enlighten the gas phase chemistry of an often used precursor, zirconium acetylacetonate, is presented here, using a microreactor coupled to a mass spectrometer with mild ionization from a synchrotron source. This was demonstrated previously, to be an effective way to detect and characterize gas phase intermediates with short lifetime.5,6
A combined numerical and experimental study of the vacuum pyrolysis of zirconium acetylacetonate, Zr(C5H7O2)4, in a microreactor at short residence times of < 60 μs was carried out. The precursor is sublimed, subsequently transported by argon or helium carrier gas, and expanded through a pinhole into a resistively heated 1 mm inner diameter SiC-microreactor. Products leaving the reactor are expanded and ionized by tuneable vacuum ultraviolet (VUV) synchrotron radiation and characterized by imaging photoelectron photoion coincidence spectroscopy (i2PEPICO) and mass spectrometry at the Swiss Light Source in Switzerland. From the temperature-dependent photoionization mass spectra between 130 and 650 °C, two initial decomposition steps were identified and temperature regimes for the following pathways of thermal decomposition at higher reactor temperatures were determined. In addition, we recorded photoionization efficiency curves and threshold photoelectron spectra (TPES) at photon energies of 6.5-11.5 eV, which gave us direct evidence about the intermediates and products formed. Six important Zr-intermediates were identified for the first time, as for example Zr(C5H7O2)2(C5H6O2), and ZrO(C5H7O2)2, together with several organic products, which aided us to describe the predominant thermolysis pathways in the temperature range of 130-650 °C. In conjunction with the simultaneous numerical simulation of the flow field in the microreactor, the application of synchrotron radiation coupled to the i2PEPICO experimental apparatus is a promising way to enlighten pyrolysis pathways and kinetics of metal-organic precursors.
References
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