In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites

Author(s)

Bernhard C. Bayer, David A. Bosworth, F. Benjamin Michaelis, Raoul Blume, Gerlinde Habler, Rainer Abart, Robert S. Weatherup, Piran R. Kidambi, Jeremy J. Baumberg, Axel Knop-Gericke, Robert Schloegl, Carsten Baehtz, Zoe H. Barber, Jannik C. Meyer, Stephan Hofmann

Abstract

Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni

₃C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni

₃C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400-800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal-carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni

₃C as a catalyst phase in graphene and carbon nanotube growth.

Organisation(s)

Physics of Nanostructured Materials, Department of Lithospheric Research

External organisation(s)

University of Cambridge, Helmholtz-Zentrum Berlin für Materialien und Energie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Helmholtz-Zentrum Dresden-Rossendorf

Journal

The Journal of Physical Chemistry Part C (Nanomaterials and Interfaces)

Volume

120

Pages

22571-22584

No. of pages

14

ISSN

1932-7447

DOI

https://doi.org/10.1021/acs.jpcc.6b01555

Publication date

10-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

104017 Physical chemistry, 103018 Materials physics, 210004 Nanomaterials

Keywords

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Energy(all), Surfaces, Coatings and Films, Physical and Theoretical Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/in-situ-observations-of-phase-transitions-in-metastable-nickel-carbidecarbon-nanocomposites(9c9633aa-9bff-4cc7-b847-1ff91af8ce20).html