Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

Kempisty, Paweł; Krukowski, Stanisław

doi:10.1063/1.4901922

Title: Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

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Abstract

Adsorption of ammonia at NH{sub 3}/NH{sub 2}/H-covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH{sub 3}/NH{sub 2}/H-covered GaN(0001) surface was divided into zones of differently pinned Fermi level: at the Ga broken bond state for dominantly bare surface (region I), at the valence band maximum (VBM) for NH{sub 2} and H-covered surface (region II), and at the conduction band minimum (CBM) for NH{sub 3}-covered surface (region III). The electron counting rule (ECR) extension was formulated for the case of adsorbed molecules. The extensive ab intio calculations show the validity of the ECR in case of all mixed H-NH{sub 2}-NH{sub 3} coverages for the determination of the borders between the three regions. The adsorption was analyzed using the recently identified dependence of the adsorption energy on the charge transfer at the surface. For region I ammonia adsorbs dissociatively, disintegrating into a H adatom and a HN{sub 2} radical for a large fraction of vacant sites, while for region II adsorption of ammonia is molecular. The dissociative adsorption energy strongly depends on the Fermi level at the surface (pinned) and in the bulk (unpinned) while the molecular adsorption energy is determined by bondingmore »« less

Authors:

Kempisty, Paweł ^[1]; Krukowski, Stanisław ^[1]

Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland)

Publication Date:: Sat Nov 15 00:00:00 EST 2014

OSTI Identifier:: 22420154

Resource Type:: Journal Article

Journal Name:: AIP Advances

Additional Journal Information:: Journal Volume: 4; Journal Issue: 11; Other Information: (c) 2014 Author(s); Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 2158-3226

Country of Publication:: United States

Language:: English

Subject:: 36 MATERIALS SCIENCE; ADSORPTION; AMMONIA; ELECTRON CYCLOTRON-RESONANCE; ELECTRONS; FERMI LEVEL; GALLIUM NITRIDES; HYDROGEN; MOLECULES; SURFACES

Citation Formats


                    Kempisty, Paweł, Krukowski, Stanisław, and Interdisciplinary Centre for Materials Modelling, Warsaw University, Pawińskiego 5a, 02-106 Warsaw. Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data.  United States: N. p., 2014. 
        Web.  doi:10.1063/1.4901922.

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                    Kempisty, Paweł, Krukowski, Stanisław, & Interdisciplinary Centre for Materials Modelling, Warsaw University, Pawińskiego 5a, 02-106 Warsaw. Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data.  United States.  https://doi.org/10.1063/1.4901922

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                    Kempisty, Paweł, Krukowski, Stanisław, and Interdisciplinary Centre for Materials Modelling, Warsaw University, Pawińskiego 5a, 02-106 Warsaw. 2014.  
        "Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data".  United States.  https://doi.org/10.1063/1.4901922.

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@article{osti_22420154,

  title        = {Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data},

  author       = {Kempisty, Paweł and Krukowski, Stanisław and Interdisciplinary Centre for Materials Modelling, Warsaw University, Pawińskiego 5a, 02-106 Warsaw},

  abstractNote = {Adsorption of ammonia at NH{sub 3}/NH{sub 2}/H-covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH{sub 3}/NH{sub 2}/H-covered GaN(0001) surface was divided into zones of differently pinned Fermi level: at the Ga broken bond state for dominantly bare surface (region I), at the valence band maximum (VBM) for NH{sub 2} and H-covered surface (region II), and at the conduction band minimum (CBM) for NH{sub 3}-covered surface (region III). The electron counting rule (ECR) extension was formulated for the case of adsorbed molecules. The extensive ab intio calculations show the validity of the ECR in case of all mixed H-NH{sub 2}-NH{sub 3} coverages for the determination of the borders between the three regions. The adsorption was analyzed using the recently identified dependence of the adsorption energy on the charge transfer at the surface. For region I ammonia adsorbs dissociatively, disintegrating into a H adatom and a HN{sub 2} radical for a large fraction of vacant sites, while for region II adsorption of ammonia is molecular. The dissociative adsorption energy strongly depends on the Fermi level at the surface (pinned) and in the bulk (unpinned) while the molecular adsorption energy is determined by bonding to surface only, in accordance to the recently published theory. Adsorption of Ammonia in region III (Fermi level pinned at CBM) leads to an unstable configuration both molecular and dissociative, which is explained by the fact that broken Ga-bonds are doubly occupied by electrons. The adsorbing ammonia brings 8 electrons to the surface, necessitating the transfer of these two electrons from the Ga broken bond state to the Fermi level. This is an energetically costly process. Adsorption of ammonia at H-covered site leads to the creation of a NH{sub 2} radical at the surface and escape of H{sub 2} molecule. The process energy is close to 0.12 eV, thus not large, but the direct inverse process is not possible due to the escape of the hydrogen molecule.},

  doi          = {10.1063/1.4901922},

  url          = {https://www.osti.gov/biblio/22420154},
  journal      = {AIP Advances},

  issn         = {2158-3226},

  number       = 11,

  volume       = 4,

  place        = {United States},

  year         = {Sat Nov 15 00:00:00 EST 2014},

  month        = {Sat Nov 15 00:00:00 EST 2014}

}

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