Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data
Adsorption of ammonia at NH3/NH2/H-covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH3/NH2/H-covered GaN(0001) surface was divided into zones of differently pinned Fermi level: at the Ga broken bond state for dominantly bare...
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| Format: | Article |
| Language: | English |
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AIP Publishing LLC
2014-11-01
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| Series: | AIP Advances |
| Online Access: | http://dx.doi.org/10.1063/1.4901922 |
| _version_ | 1818359859249152000 |
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| author | Paweł Kempisty Stanisław Krukowski |
| author_facet | Paweł Kempisty Stanisław Krukowski |
| author_sort | Paweł Kempisty |
| collection | DOAJ |
| description | Adsorption of ammonia at NH3/NH2/H-covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH3/NH2/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 NH2 and H-covered surface (region II), and at the conduction band minimum (CBM) for NH3-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-NH2-NH3 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 HN2 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 NH2 radical at the surface and escape of H2 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. |
| first_indexed | 2024-12-13T20:51:35Z |
| format | Article |
| id | doaj.art-a888bac3206947efb3bf8989c27f9d17 |
| institution | Directory Open Access Journal |
| issn | 2158-3226 |
| language | English |
| last_indexed | 2024-12-13T20:51:35Z |
| publishDate | 2014-11-01 |
| publisher | AIP Publishing LLC |
| record_format | Article |
| series | AIP Advances |
| spelling | doaj.art-a888bac3206947efb3bf8989c27f9d172022-12-21T23:31:51ZengAIP Publishing LLCAIP Advances2158-32262014-11-01411117109117109-2410.1063/1.4901922017411ADVAdsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio dataPaweł Kempisty0Stanisław Krukowski1Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, PolandInstitute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, PolandAdsorption of ammonia at NH3/NH2/H-covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH3/NH2/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 NH2 and H-covered surface (region II), and at the conduction band minimum (CBM) for NH3-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-NH2-NH3 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 HN2 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 NH2 radical at the surface and escape of H2 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.http://dx.doi.org/10.1063/1.4901922 |
| spellingShingle | Paweł Kempisty Stanisław Krukowski Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data AIP Advances |
| title | Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data |
| title_full | Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data |
| title_fullStr | Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data |
| title_full_unstemmed | Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data |
| title_short | Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data |
| title_sort | adsorption of ammonia at gan 0001 surface in the mixed ammonia hydrogen ambient a summary of ab initio data |
| url | http://dx.doi.org/10.1063/1.4901922 |
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