| 1. |
- Pinto, H., et al.
(författare)
-
First-principles studies of the effect of (001) surface terminations on the electronic properties of the negatively charged nitrogen-vacancy defect in diamond
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4
-
Tidskriftsartikel (refereegranskat)abstract
- Density functional calculations have been carried out on (001)-orientated slabs of diamond with different surface terminations. A negatively charged nitrogen-vacancy defect (NV-) is placed in the middle of the slab approximately 1 nm from each surface and the effect of the surface on the internal optical transition in NV- investigated. The calculations show that the chemical nature of the surface is important. We find that although the clean surface does not lead to charge transfer between the defect and the surface, there is a splitting of the empty excited state, the final state in optical absorption, arising from a strong hybridization of the surface and defect bands. This leads to a broadening of the 1.945-eV transition of the NV- defect. OH- and F-terminated surfaces have no surface states in the band gap and again charge transfer between the defect and surface does not occur. The splitting of the e levels responsible for the optical transitions for OH or F termination is similar to that found in periodic boundary condition simulations for bulk diamond where the defects are separated by 1 nm, and thus the calculations show that hydroxylated or fluorinated surfaces give favorable optical properties.
|
|
| 2. |
- Tiwari, Amit K., et al.
(författare)
-
Calculated electron affinity and stability of halogen-terminated diamond
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:24
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical termination of diamond has a dramatic impact on its electrical and chemical properties, where hydrogen and oxygen termination produce negative and positive electron affinities, respectively. However, the impact of halogen termination is not fully understood. We show that for low-index surfaces, 100% fluorinated surfaces exhibit chemically stable positive electron affinities in the 1.17 to 2.63 eV range, whereas 100% chlorination is energetically unfavorable. At lower coverage the positive electron affinity is smaller, being a combination of halogen-terminated and unterminated sites. For mixed halogen and hydrogen termination, a wide range of negative and positive electron affinities can be achieved by varying the relative concentrations of adsorbed species.
|
|
| 3. |
- Tiwari, Amit K., et al.
(författare)
-
Electronic and structural properties of diamond (001) surfaces terminated by selected transition metals
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:15
-
Tidskriftsartikel (refereegranskat)abstract
- The presence of adsorbate species on diamond surfaces, even in small concentrations, strongly influences electrical, chemical, and structural properties. Despite the technological significance, coverage of diamond by transition metals has received relatively little attention. In this paper, we present the results of density functional calculations examining up to a monolayer of selected metals (Cu, Ni, Ti, and V) on the (001) diamond surface. We find that addition of carbide forming species (Ti and V) results in significantly higher adsorption energies at all surface coverages relative to those of the non-carbide-forming species. For monolayer coverage by Cu or Ni, and submonolayer coverage by Ti and V, we find large, negative electron affinities. We propose that based upon the electron affinities and binding energies, metal-terminated (001) diamond surfaces are promising candidates for electron emission device applications
|
|
| 4. |
- Tiwari, Amit Kumar, et al.
(författare)
-
Transition metal oxide-diamond interfaces for electron emission applications
- 2013
-
Ingår i: Silicon carbide and related materials 2012. - Durnten-Zurich : Trans Tech Publications Inc.. - 9783037856246 ; , s. 761-764
-
Konferensbidrag (refereegranskat)abstract
- Diamond surfaces with suitable adsorbed chemical species can exhibit both negative and positive electron affinities, arising from the complex electrostatic interplay between adsorbates and surface carbon atoms of diamond lattice. We present the results of density functional calculations into the energetics and the electron affinity of diamond (100) surfaces terminated with the oxides of selected transition metals. We find that for a correct stoichiometry, oxides of transition metals, such as Ti and Zn, exhibit a large negative electronic affinity of around 3 eV. The desorption of transition metal oxides is found to be highly endothermic. We therefore propose that transition metal oxides are promising for the surface coating of diamond-based electron emitters, as these exhibit higher thermal stability in comparison to the commonly used Cs-O termination, while retaining the advantage of inducing a large negative electron affinity
|
|
| 5. |
- Tiwari, Amit K., et al.
(författare)
-
Ultra thin transition metal oxide coatings on diamond for thermionic applications
- 2013
-
Ingår i: Proceedings of the MRS Fall Meeting Symposim, MRS Fall Meeting, 24-29 November 2012, Boston, USA. - Warrendale : Materials Research Society. ; , s. 13-18
-
Konferensbidrag (refereegranskat)abstract
- We have investigated, using density functional simulations, the energetics and the electronic properties of oxides of selected transition metals, TMs, adsorbed onto a diamond (001) surface. We find that stoichiometric oxides of TMs, particularly Ti and Zn, influence the electron affinity of diamond strongly. The electron affinities of stoichiometric oxides of Ti and Zn are calculated to be around -3eV, significantly higher than 1.9eV of commonly used H-termination. The reactions of TMs with an oxygenated diamond are found to be highly exothermic. Based upon the energetics and the electronic properties, we propose that in the regime of ultra thin films, oxides of TMs are promising options for surface coating of diamond-based electron emitters, as these coatings are compatible with semiconductor device fabrication processes, while having the benefit of inducing a large negative electron affinity
|
|
