AVS 59th Annual International Symposium and Exhibition
    Thin Film Wednesday Sessions
       Session TF+AS-WeA

Paper TF+AS-WeA2
Seed-Mediated Growth of 1D Pyrite (FeS2) Structures

Wednesday, October 31, 2012, 2:20 pm, Room 11

Session: Thin Films: Growth and Characterization-I
Presenter: Y.J. Kwon, University of California Irvine
Authors: Y.J. Kwon, University of California Irvine
N. Berry, University of California Irvine
M. Law, University of California Irvine
J.C. Hemminger, University of California Irvine
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Iron pyrite is a promising semiconductor for use in solar cells due to its earth-abundance, suitable bandgap, and high absorption coefficient. Pyrite device efficiency is only about 3% due to a low open-circuit photovoltage and high dark current, possibly as a result of sulfur deficiency at the surface resulting in thermionic field emission. Although fabrication of pyrite thin films has been studied by various methods, specific details of the pyrite growth process in the presence of homogeneous nucleation sites has not been studied. In this project, the role of pyrite nucleation sites is investigated in the growth of pyrite thin films by atmospheric-pressure chemical vapor deposition (AP-CVD). The pyrite nanoparticle nucleation sites are fabricated by sulfurization of pre-deposited Fe2O3 grains on the step edges of highly oriented pyrolytic graphite (HOPG) using H2S, elemental sulfur or a combination of the two annealing treatments and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy. H2S-sulfurized Fe2O3 nuclei coalesce to form FeS2 nanowires containing both pyrite and marcasite phases. A subsequent elemental sulfur treatment on either H2S-sulfurized samples or pre-deposited Fe2O3 samples yield pure pyrite; however, the nanowires convert to a less desirable morphology of randomly sized spherical grains as a result of this annealing treatment. Atmospheric Pressure-CVD of FeS2 from iron-(III) acetylacetonate and tert-butyl disulfide was performed to grow pyrite on these seeded substrates. Initial deposition on the H2S-annealed samples leads to only seed-mediated growth and the formation of linear arrays of polycrystalline FeS2 nanowires. However, due to marcasite phase presence on pre-covered FeS2 nanoparticle seeds, both marcasite and pyrite phases could be observed. Initial deposition on elemental sulfur treated samples with pure pyrite phase showed deposition occurring throughout the substrate. No preferential growth on seeded pyrite nucleation sites was observed. It is proposed that during elemental sulfur treatment, new nucleation sites form, leading to deposition covering the substrate. Further work is in process to clearly determine or identify the growth mechanism of pyrite. In this work, we will gain a greater understanding of early stages of pyrite growth process in the presence of homogeneous nucleation sites.