Formation of Unsaturated Hydrocarbons and Hydrogen: Surface Chemistry of Methyltrioxorhenium(VII) in ALD of Mixed-Metal Oxide Structures Comprising Re(III) Units

摘要

We present the full investigation of the atomic layer deposition (ALD) of a mixed rhenium-aluminum oxide, namely ReAl2O3CH3, a material with tunable resistance, comprising the building unit of conductive rhenium oxides, ReOx. The deposition, involving methyltrioxorhenium(VII) (MeReO3, MTO) and trimethylaluminum (TMA), was analyzed by employing complementary in situ diagnostic quartz-crystal microbalance (QCM), Fourier-transform infrared (FT-IR) spectroscopy, and quadrupole mass spectrometry (QMS) to explore and reveal the underlying growth mechanism of this material. A proposed mechanism includes reductive elimination steps, thereby creating a stable Re(III)-containing thin film, making this ALD process unique regarding its growth. In addition, as proven by QMS, the surface reactions include the formation of hydrogen and unsaturated hydrocarbons. From this straightforward process, an extraordinarily high growth rate of 4.5 angstrom cycle(-1) at temperatures as low as 150 degrees C was obtained. This material was found to exhibit highly promising electrical properties in terms of low thermal coefficient of resistance (TCR) in combination with high resistivity. By blending thin films of ReAl2O3CH3 with additional layers (1, 2, or 3) of Al2O3, we were able to fine-tune the electrical resistivity in the range of 3.9 x 10(6) -1.5 x 10(11) Omega.cm. Simultaneously, the TCR was lowered to about -0.014 degrees C--1,C- making this material highly resistive over a broad temperature range and a promising candidate for advanced detector applications, e.g., multichannel plates (MCPs).