Pyrolysis of Alucone Molecular Layer Deposition Films Studied Using In Situ Transmission Fourier Transform Infrared Spectroscopy

Abstract

The pyrolysis of alucone molecular layer deposition (MLD) films was studied in vacuum using in situ transmission Fourier transform infrared spectroscopy. The initial alucone MLD films were grown using trimethylaluminum (TMA) and either ethylene glycol (EG) (HO−(CH 2 ) 2 − OH) or hydroquinone (HQ) (HO−C 6 H 4 −OH) at 150°C. The alucone MLD films were then pyrolyzed in vacuum at temperatures ranging from 400 to 750°C. The absorbance features for the C−H, C−C, and C−O stretching vibrations were observed to be lost at pyrolysis temperatures from 350 to 500°C. For the alucone films grown using TMA and EG, the loss of these absorbance features was coupled to an increase in carboxylate (R-COO − ) absorbance features. The carboxylate absorbance features reached their peak at a pyrolysis temperature of 450°C and then decreased slowly with higher pyrolysis temperatures. The carboxylate absorbance features are consistent with an Al 2 O 3 /carbon composite material with Al 3+ /COO − species at the interface. In addition, the presence of carbon in the Al 2 O 3 /carbon composite led to an increase in the background infrared absorbance for the pyrolyzed alucone films grown using HQ containing six carbons. This background infrared absorbance is linked to electrical conductance in a network of carbon domains in the pyrolyzed alucone films, as described by Drude−Zener theory. In contrast, the alucone films grown using EG containing two carbons did not display an increase in the background infrared absorbance. This absence of background infrared absorbance is consistent with less carbon in the Al 2 O 3 /carbon composite grown using EG. The pyrolysis of the alucone films on ZrO 2 particles led to very conformal Al 2 O 3 /carbon composite films, as observed by transmission electron microscopy images. I. INTRODUCTIONAtomic layer deposition (ALD) and molecular layer deposition (MLD) are ideal techniques to deposit ultrathin inorganic and organic films. 1−4 Both ALD and MLD are based on sequential, self-limiting surface reactions that allow conformal film growth on high aspect ratio structures with precise thickness control. The precursors for ALD and MLD can be combined to grow hybrid organic−inorganic metal alkoxide polymers known as "metalcones". 5,6 These hybrid MLD films can possess interesting mechanical and electrical properties. 7,8 ALD and MLD can also be combined to form ALD/MLD alloys and nanolaminates that can be fine-tuned by varying the composition of the alloy. 6,9,10 Metalcone MLD films can also serve as a precursor to a new set of ceramic materials. Hybrid organic−inorganic MLD films can be annealed in air to burn out the carbon and yield porous metal oxide films. 11−14 These porous metal oxide films have been shown to contain micropores and mesopores. 11 Hybrid organic−inorganic MLD films can also be pyrolyzed under vacuum or inert atmosphere to yield electrically conducting metal oxide/carbon composite films. 15 This strategy is similar to the fabrication of ceramics from polymers in polymerderived ceramic processing....

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