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Kakanakova-Georgieva, Anelia
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Publications (10 of 91) Show all publications
Sangiovanni, D. G., Kostov Gueorguiev, G. & Kakanakova-Georgieva, A. (2018). Ab initio molecular dynamics of atomic-scale surface reactions: insights into metal organic chemical vapor deposition of AlN on graphene. Physical Chemistry, Chemical Physics - PCCP, 20(26), 17751-17761
Open this publication in new window or tab >>Ab initio molecular dynamics of atomic-scale surface reactions: insights into metal organic chemical vapor deposition of AlN on graphene
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 26, p. 17751-17761Article in journal (Refereed) Published
Abstract [en]

Metal organic chemical vapor deposition (MOCVD) of group III nitrides on graphene heterostructures offers new opportunities for the development of flexible optoelectronic devices and for the stabilization of conceptually-new two-dimensional materials. However, the MOCVD of group III nitrides is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques. We use density-functional ab initio molecular dynamics (AIMD) with van der Waals corrections to identify atomistic pathways and associated electronic mechanisms driving precursor/surface reactions during metal organic vapor phase epitaxy at elevated temperatures of aluminum nitride on graphene, considered here as model case study. The results presented provide plausible interpretations of atomistic and electronic processes responsible for delivery of Al, C adatoms, and C-Al, CHx, AlNH2 admolecules on pristine graphene via precursor/surface reactions. In addition, the simulations reveal C adatom permeation across defect-free graphene, as well as exchange of C monomers with graphene carbon atoms, for which we obtain rates of approximate to 0.3 THz at typical experimental temperatures (1500 K), and extract activation energies Eexca = 0.28 +/- 0.13 eV and attempt frequencies A(exc) = 2.1 (x1.7(+/- 1)) THz via Arrhenius linear regression. The results demonstrate that AIMD simulations enable understanding complex precursor/surface reaction mechanisms, and thus propose AIMD to become an indispensable routine prediction-tool toward more effective exploitation of chemical precursors and better control of MOCVD processes during synthesis of functional materials.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-149847 (URN)10.1039/c8cp02786b (DOI)000437473300021 ()29915819 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR) through FLAG-ERA JTC project GRIFONE [VR 2015-06816, VR 2017-04071]; Olle Engkvist Foundation

Available from: 2018-08-02 Created: 2018-08-02 Last updated: 2019-06-28
Nilsson, D., Janzén, E. & Kakanakova-Georgieva, A. (2016). Lattice parameters, structural and optical properties of AlN true bulk, homoepitaxial and heteroepitaxial material grown at high temperatures of up to 1400 °C. Journal of Physics D: Applied Physics, 49(17)
Open this publication in new window or tab >>Lattice parameters, structural and optical properties of AlN true bulk, homoepitaxial and heteroepitaxial material grown at high temperatures of up to 1400 °C
2016 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 17Article in journal (Refereed) Published
Abstract [en]

The lattice parameters and residual strain of homo- and heteroepitaxial AlN layers grown at elevated process temperatures (1200-1400 °C) by hot-wall MOCVD are studied. The average lattice parameters for the homoepitaxial AlN layers grown on true bulk AlN substrates are determined to be a = 3.1113 ± 0.0001 Å and c = 4.9808 ± 0.0001 Å are discussed in relation to previously published data. The lattice parameters measured from biaxially strained AlN layers grown on SiC are used to determine the biaxial strain relaxation coefficient to be RB = -0.556 ± 0.021. The structural and optical quality of the heteroepitaxial layers improved with increasing layer thickness and at a thickness of 1.3 μm, crack-free AlN of high crystalline quality with full widths at half maximum of the (0002) and (1012) rocking curves of 25 arc sec and 372 arc sec, respectively, were obtained. Tensile strain developed with increasing layer thickness despite the higher crystalline quality of these layers. This can be explained by the thermal mismatch between the AlN and SiC in combination with island coalescence at the initial stage and/or during the growth.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
National Category
Natural Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-106726 (URN)10.1088/0022-3727/49/17/175108 (DOI)000374146600013 ()
Note

Funding agencies: Swedish Research Council (VR); Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM, VR); Swedish Governmental Agency for Innovation Systems (VINNOVA)

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Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2017-12-05Bibliographically approved
Freitas, R. R., de Brito Mota, F., Rivelino, R., de Castilho, C. M., Kakanakova-Gueorguie, A. & Gueorguiev, G. K. (2016). Tuning band inversion symmetry of buckled III-Bi sheets by halogenation. Nanotechnology, 27(5), 1-11, Article ID 055704.
Open this publication in new window or tab >>Tuning band inversion symmetry of buckled III-Bi sheets by halogenation
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2016 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 5, p. 1-11, article id 055704Article in journal (Refereed) Published
Abstract [en]

First-principles calculations are employed to investigate structural, electronic and topological insulating properties of XBi (X = B, Al, Ga, and In) monolayers upon halogenation. It is known that Y-XBi (X = Ga, In, Tl; Y = F, Cl, Br, I) can originate inversion-asymmetric topological insulators with large bulk band gaps. Our results suggest that Y-XBi (X = B, Al; Y = F, Cl, Br, I) may also result in nontrivial topological insulating phases. Despite the lower atomic number of B and Al, the spin-orbit coupling opens a band gap of about 400 meV in Y-XBi (X = B, Al), exhibiting an unusual electronic behavior for practical applications in spintronics. The nature of the bulk band gap and Dirac-cone edge states in their nanoribbons depends on the group-III elements and Y chemical species. They lead to a chemical tunability, giving rise to distinct band inversion symmetries and exhibiting Rashba-type spin splitting in the valence band of these systems. These findings indicate that a large family of Y-XBi sheets can exhibit nontrivial topological characteristics, by a proper tuning, and open a new possibility for viable applications at room temperature.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
Keywords
bismuth-based 2D materials; topological insulators; halogenation; spin-orbit coupling
National Category
Condensed Matter Physics Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-125293 (URN)10.1088/0957-4484/27/5/055704 (DOI)000368894300018 ()26752271 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR) through the Swedish Research links project [348-2014-4249]; Linkoping Linnaeus Initiative for Novel Functionalized Materials (LiLi-NFM, VR); Swedish Foundation for Strategic Research (SSF) Synergy Grant on Functional Carbides and Advanced Surface Engineering (FUNCASE) [RMA11-0029]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Fundacao de Amparo a Pesquisa do Estado da Bahia (FAPESB); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Available from: 2016-02-24 Created: 2016-02-19 Last updated: 2017-11-30
dos Santos, R. B., de Brito Mota, F., Rivelino, R., Kakanakova-Gueorguie, A. & Gueorguiev, G. K. (2016). Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties. Nanotechnology, 27(14), 145601
Open this publication in new window or tab >>Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties
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2016 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 14, p. 145601-Article in journal (Refereed) Published
Abstract [en]

Graphite-like hexagonal AlN (h-AlN) multilayers have been experimentally manifested and theoretically modeled. The development of any functional electronics applications of h-AlN would most certainly require its integration with other layered materials, particularly graphene. Here, by employing vdW-corrected density functional theory calculations, we investigate structure, interaction energy, and electronic properties of van der Waals stacking sequences of few-layer h-AlN with graphene. We find that the presence of a template such as graphene induces enough interlayer charge separation in h-AlN, favoring a graphite-like stacking formation. We also find that the interface dipole, calculated per unit cell of the stacks, tends to increase with the number of stacked layers of h-AlN and graphene.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
Keywords
2D materials beyond graphene; layered group-III nitrides; hexagonal AlN; van der Waals stacks; density functional theory
National Category
Condensed Matter Physics Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-126239 (URN)10.1088/0957-4484/27/14/145601 (DOI)000371020700011 ()26902955 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR) through Swedish Research Links project [348-2014-4249, VR 621-2013-5818]; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Fundacao de Amparo a Pesquisa do Estado da Bahia (FAPESB)

Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2018-03-21
dos Santos, R. B., Rivelino, R., de Brito Mota, F., Kostov Gueorguiev, G. & Kakanakova-Gueorguie, A. (2015). Dopant species with Al-Si and N-Si bonding in the MOCVD of AlN implementing trimethylaluminum, ammonia and silane. Journal of Physics D: Applied Physics, 48(29), Article ID 295104.
Open this publication in new window or tab >>Dopant species with Al-Si and N-Si bonding in the MOCVD of AlN implementing trimethylaluminum, ammonia and silane
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2015 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 29, article id 295104Article in journal (Refereed) Published
Abstract [en]

We have investigated gas-phase reactions driven by silane (SiH4), which is the dopant precursor in the metalorganic chemical vapor deposition (MOCVD) of aluminum nitride (AlN) doped by silicon, with prime focus on determination of the associated energy barriers. Our theoretical strategy is based on combining density-functional methods with minimum energy path calculations. The outcome of these calculations is suggestive for kinetically plausible and chemically stable reaction species with Al-Si bonding such as (CH3)(2)AlSiH3 and N-Si bonding such as H2NSiH3. Within this theoretical perspective, we propose a view of these reaction species as relevant for the actual MOCVD of Si-doped AlN, which is otherwise known to be contributed by the reaction species (CH3)(2)AlNH2 with Al-N bonding. By reflecting on experimental evidence in the MOCVD of various doped semiconductor materials, it is anticipated that the availability of dopant species with Al-Si, and alternatively N-Si bonding near the hot deposition surface, can govern the incorporation of Si atoms, as well as other point defects, at the AlN surface.

Place, publisher, year, edition, pages
IOP Publishing: Hybrid Open Access, 2015
Keywords
AlN; doping; MOCVD; ab initio calculations
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-120337 (URN)10.1088/0022-3727/48/29/295104 (DOI)000357604800009 ()
Note

Funding Agencies|Swedish Research Council (VR) (Swedish Research Links Project) [348-2014-4249]; Linkoping Linnaeus Initiative on Novel Functional Materials (VR); Swedish Governmental Agency for Innovation Systems (VINNOVA); Swedish Research Council (VR); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Available from: 2015-07-31 Created: 2015-07-31 Last updated: 2017-12-04
Feneberg, M., Nguyen, S. T. & Kakanakova-Gueorguie, A. (2015). Exciton luminescence in AIN triggered by hydrogen and thermal annealing. Applied Physics Letters, 106(24), 242101
Open this publication in new window or tab >>Exciton luminescence in AIN triggered by hydrogen and thermal annealing
2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 24, p. 242101-Article in journal (Refereed) Published
Abstract [en]

Exciton recombination bands in homoepitaxial AIN layers are strongly dependent on the presence of hydrogen. By thermal treatment under hydrogen-free and hydrogen-rich ambient, respectively, several sharp bound exciton lines are modulated in intensity reversibly. In contrast, the exciton bound at the neutral donor silicon remains unaffected. The mechanism causing these effects is most probably hydrogen in-and out-diffusion into the AIN sample. The main factor determining hydrogenation of AIN layers is found to be molecular H-2 in contrast to NH3. We find hints that carbon incorporation into AIN may be closely related with that of hydrogen. Besides photoluminescence spectra of exciton bands, our model is supported by theoretical reports and comparison to the case of hydrogen in GaN.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-120167 (URN)10.1063/1.4922723 (DOI)000356618700019 ()
Note

Funding Agencies|Swedish Research Council (VR); Swedish Governmental Agency for Innovation Systems (VINNOVA); Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM, VR)

Available from: 2015-07-13 Created: 2015-07-13 Last updated: 2017-12-04
dos Santos, R. B., Rivelino, R., de Brito Mota, F., Kakanakova-Gueorguie, A. & Gueorguiev, G. K. (2015). Feasibility of novel (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations. Dalton Transactions, 44(7), 3356-3366
Open this publication in new window or tab >>Feasibility of novel (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations
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2015 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 7, p. 3356-3366Article in journal (Refereed) Published
Abstract [en]

We employ ab initio calculations to predict the equilibrium structure, stability, reactivity, and Raman scattering properties of sixteen different (H3C)(n)X(SiH3)(3-n) compounds (X = B, Al, Ga, In) with n = 0-3. Among this methylsilylmetal family, only the (H3C)(3)X members, i.e., trimethylboron (TMB), trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI), are currently well-studied. The remaining twelve compounds proposed here open up a two-dimensional array of new possibilities for precursors in various deposition processes, and evoke potential applications in the chemical synthesis of other compounds. We infer that within the (H3C)(n)X(SiH3)(3-n) family, the compounds with fewer silyl groups (and consequently with more methyl groups) are less reactive and more stable. This trend is verified from the calculated cohesive energy, Gibbs free energy of formation, bond strength, and global chemical indices. Furthermore, we propose sequential reaction routes for the synthesis of (H3C)(n)X(SiH3)(3-n) by substitution of methyl by silyl groups, where the silicon source is the silane gas. The corresponding reaction barriers for these chemical transformations lie in the usual energy range typical for MOCVD processes. We also report the Raman spectra and light scattering properties of the newly proposed (H3C)(n)X(SiH3)(3-n) compounds, in comparison with available data of known members of this family. Thus, our computational experiment provides useful information for a systematic understanding of the stability/reactivity and for the identification of these compounds.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2015
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-115338 (URN)10.1039/c4dt03406f (DOI)000349403100048 ()25599815 (PubMedID)
Note

Funding Agencies|Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [YR2009-7017]; Swedish Research Council (VR) [348-2014-4249]; Linkoping Linnaeus Initiative on Novel Functionalized Materials (VR); Swedish Foundation for Strategic Research (SSF) Synergy on Functional Carbides and Advanced Surface Engineering (FUNCASE) [RMA-110029]; Swedish Governmental Agency for Innovation Systems (VINNOVA); Swedish Research Council (VR); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Fundacao de Ampar a Pesquisa do Estado da Bahia (FAPESB); Coordenacao de Aperfeicoamento de Pessoal de Novel Superior (CAPES)

Available from: 2015-03-13 Created: 2015-03-13 Last updated: 2017-12-04
Nilsson, D., Trinh, X. T., Janzén, E., Son, T. N. & Kakanakova-Georgieva, A. (2015). On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers. Physica status solidi. B, Basic research, 252(6), 1306-1310
Open this publication in new window or tab >>On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers
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2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1306-1310Article in journal (Refereed) Published
Abstract [en]

We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX state..

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106725 (URN)10.1002/pssb.201451559 (DOI)000355756200016 ()
Note

Swedish Research Council (VR); VR Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); Swedish Energy Agency; Knut and Alice Wallenberg Foundation (KAW); Swedish Governmental Agency for Innovation Systems (VINNOVA)

Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2017-12-05Bibliographically approved
Freitas, R. R. Q., de Brito Mota, F., Rivelino, R., de Castilho, C. M., Kakanakova-Georgieva, A. & Kostov Gueorguiev, G. (2015). Spin-orbit-induced gap modification in buckled honeycomb XBi and XBi3 (X = B, Al, Ga, and In) sheets. Journal of Physics: Condensed Matter, 27(48), 485306
Open this publication in new window or tab >>Spin-orbit-induced gap modification in buckled honeycomb XBi and XBi3 (X = B, Al, Ga, and In) sheets
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2015 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 48, p. 485306-Article in journal (Refereed) Published
Abstract [en]

The band structure and stability of XBi and XBi3 (X = B, Al, Ga, and In) single sheets are predicted using first-principles calculations. It is demonstrated that the band gap values of these new classes of two-dimensional (2D) materials depend on both the spin-orbit coupling (SOC) and type of group-III elements in these hetero-sheets. Thus, topological properties can be achieved, allowing for viable applications based on coherent spin transport at room temperature. The spin-orbit effects are proved to be essential to explain the tunability by group-III atoms. A clear effect of including SOC in the calculations is lifting the spin degeneracy of the bands at the Gamma point of the Brillouin zone. The nature of the band gaps, direct or indirect, is also tuned by SOC, and by the appropriate X element involved. It is observed that, in the case of XBi single sheets, band inversions naturally occur for GaBi and InBi, which exhibit band gap values around 172 meV. This indicates that these 2D materials are potential candidates for topological insulators. On the contrary, a similar type of band inversion, as obtained for the XBi, was not observed in the XBi3 band structure. In general, the calculations, taking into account SOC, reveal that some of these buckled sheets exhibit sizable gaps, making them suitable for applications in room-temperature spintronic devices.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2015
Keywords
bismuth; 2D materials; topological insulators; DFT; spin-orbit coupling
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123752 (URN)10.1088/0953-8984/27/48/485306 (DOI)000365346900008 ()26569356 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR) [348-2014-4249]; Linkoping Linnaeus Initiative for Novel Functionalized Materials (LiLi-NFM, VR); Swedish Foundation for Strategic Research (SSF) Synergy on Functional Carbides and Advanced Surface Engineering (FUNCASE) [RMA11-0029]; ConselhoNacional de DesenvolvimentoCientifico e Tecnologico (CNPq); Fundacao de Amparo a Pesquisa do Estado da Bahia (FAPESB); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-11-30Bibliographically approved
Freitas, R. R. Q., Rivelino, R., Mota, F. d., Castilho, C. M., Kakanakova-Georgieva, A. & Gueorguiev, G. K. (2015). Topological Insulating Phases in Two-Dimensional Bismuth-Containing Single Layers Preserved by Hydrogenation. The Journal of Physical Chemistry C, 119(41), 23599-23606
Open this publication in new window or tab >>Topological Insulating Phases in Two-Dimensional Bismuth-Containing Single Layers Preserved by Hydrogenation
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 41, p. 23599-23606Article in journal (Refereed) Published
Abstract [en]

Two-dimensional (2D) binary XBi compounds, where X belongs to group III elements (B, Al, Ga, and In), in a buckled honeycomb structure may originate sizable gap Z2 topological insulators (TIs). These are characterized by exhibiting single band inversion at the Γ point as well as nontrivial edge states in their corresponding nanoribbons. By using first-principles calculations, we demonstrate that hydrogenation of XBi single layers leads to distinct and stable crystal structures, which can preserve their topological insulating properties. Moreover, hydrogenation opens a band gap in this new class of 2D Z2 TIs, with distinct intensities, exhibiting an interesting electronic behavior for viable room-temperature applications of these 2D materials. The nature of the global band gap (direct or indirect) and topological insulating properties depend on the X element type and spatial configuration of the sheet, as well as the applied strain. Our results indicate that the geometric configuration can be crucial for preserving totally the topological characteristics of the hydrogenated sheets. We identify sizable band inversions in the band structure for the relaxed hydrogenated GaBi and InBi in their chairlike configurations and for hydrogenated BBi and AlBi under strain. Based on these findings, hydrogenation gives rise to a flexible chemical tunability and can preserve the band topology of the pristine XBi phases.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123945 (URN)10.1021/acs.jpcc.5b07961 (DOI)000363068400036 ()
Available from: 2016-01-14 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved
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