Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 286) Show all publications
Bathen, M. E., Coutinho, J., Ayedh, H. M., Hassan, J. U., Farkas, I., Öberg, S., . . . Vines, L. (2019). Anisotropic and plane-selective migration of the carbon vacancy in SiC: Theory and experiment. Physical Review B, 100(1), Article ID 014103.
Open this publication in new window or tab >>Anisotropic and plane-selective migration of the carbon vacancy in SiC: Theory and experiment
Show others...
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 1, article id 014103Article in journal (Refereed) Published
Abstract [en]

We investigate the migration mechanism of the carbon vacancy (VC) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The VC, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for VC removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that VC migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, VC(h), and pseudocubic, VC(k)] and their consequences for VC migration have not been considered so far. The first part of the paper presents a theoretical study of VC migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for VC migration. In 3C-SiC, VC is found to migrate with an activation energy of EA=4.0 eV. In 4H-SiC, on the other hand, we anticipate that VC migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of EA=4.2 eV, and a striking preference for basal migration within the h plane with a barrier of EA=3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of VC in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of EA=(4.4±0.3) eV and EA=(3.6±0.3) eV were found for VC migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D0=0.54cm2/s and 0.017cm2/s are in line with a simple jump process, as expected for a primary vacancy point defect.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-75557 (URN)10.1103/PhysRevB.100.014103 (DOI)000474364500002 ()2-s2.0-85070111566 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-16 (johcin)

Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Löfgren, R., Pawar, R., Öberg, S. & Larsson, A. (2019). The bulk conversion depth of the NV-center in diamond: computing a charged defect in a neutral slab. New Journal of Physics, 21, Article ID 053037.
Open this publication in new window or tab >>The bulk conversion depth of the NV-center in diamond: computing a charged defect in a neutral slab
2019 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, article id 053037Article in journal (Refereed) Published
Abstract [en]

The negatively charged nitrogen vacancy (NV-) center in diamond has properties that make it a promising candidate for applications such as a qubit in room temperature quantum computing, single-molecule photoluminescence and NMR sensor, and as a single photon source for quantum cryptography. For many of its uses it is desirable to have the NV-center close to the diamond surface. In this work, we use density functional theory simulations to investigate how the distance of the NV- center to a surface, and its orientation, affect its properties, including the zero-phonon-line. We study the three technologically important surfaces terminated with fluorine, oxygen/hydroxyl and nitrogen. Since the NV-center is charged it requires special measures to simulate within a slab-model. We use the recently proposed charging with a substitutional donor in the diamond lattice resulting in a neutral super-cell, which provides very satisfactory results. We have found that the NV-centers properties converge to bulk values already at 5 angstrom depth.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2019
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-74898 (URN)10.1088/1367-2630/ab1ec5 (DOI)000469973900007 ()2-s2.0-85069479116 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-24 (johcin)

Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-08-21Bibliographically approved
Allali, N., Urbanova, V., Etienne, M., Devaux, X., Mallet, M., Vigolo, B., . . . Mamane, V. (2018). Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules. Beilstein Journal of Nanotechnology, 9, 2750-2762
Open this publication in new window or tab >>Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules
Show others...
2018 (English)In: Beilstein Journal of Nanotechnology, ISSN 2190-4286, Vol. 9, p. 2750-2762Article in journal (Refereed) Published
Abstract [en]

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

Place, publisher, year, edition, pages
Beilstein-Institut, 2018
Keywords
biosensing, carbon nanotubes, covalent functionalization, electrocatalysis, ferrocene
National Category
Other Physics Topics
Research subject
Experimental Physics; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-71587 (URN)10.3762/bjnano.9.257 (DOI)000448782500001 ()30416926 (PubMedID)2-s2.0-85056284634 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-15 (johcin)

Available from: 2018-11-15 Created: 2018-11-15 Last updated: 2019-04-11Bibliographically approved
Berezovsky, V. & Öberg, S. (2018). Computational study of the CO adsorption and diffusion in zeolites: validating the Reed–Ehrlich model. Adsorption, 24(4), 403-413
Open this publication in new window or tab >>Computational study of the CO adsorption and diffusion in zeolites: validating the Reed–Ehrlich model
2018 (English)In: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 24, no 4, p. 403-413Article in journal (Refereed) Published
Abstract [en]

Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in zeolites (MFI, CHA and DDR). On the basis of classical force fields, grand canonical Monte Carlo simulations are performed to predict the adsorption properties (isotherms) of these types of zeolites up to high pressure. Subsequent careful analysis yields details the microscopic mechanism in play, along the whole adsorption process, together with a considering of the arrangements of CO in MFI at high pressure. This work also summarizes an approach which uses single component diffusion data in prediction of multicomponent diffusion.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Condensed Matter Physics Physical Chemistry Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-68541 (URN)10.1007/s10450-018-9948-z (DOI)000432610800006 ()2-s2.0-85046018279 (Scopus ID)
Funder
Swedish National Infrastructure for Computing (SNIC)Swedish Foundation for Strategic Research
Note

Validerad;2018;Nivå 2;2018-08-07 (rokbeg)

Available from: 2018-04-28 Created: 2018-04-28 Last updated: 2019-01-18Bibliographically approved
Santos, P., Coutinho, J. & Öberg, S. (2018). First-principles calculations of iron-hydrogen reactions in silicon. Journal of Applied Physics, 123(24), Article ID 245703.
Open this publication in new window or tab >>First-principles calculations of iron-hydrogen reactions in silicon
2018 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 24, article id 245703Article in journal (Refereed) Published
Abstract [en]

Controlling the contamination of silicon materials by iron, especially dissolved interstitial iron (Fe-i), is a longstanding problem with recent developments and several open issues. Among these, we have the question whether hydrogen can assist iron diffusion or if significant amounts of substitutional iron (Fe-s) can be created. Using density functional calculations, we explore the structure, formation energies, binding energies, migration, and electronic levels of several FeH complexes in Si. We find that a weakly bound FeiH pair has a migration barrier close to that of isolated Fe-i and a donor level at E-v + 0.5 eV. Conversely, FeiH2 (0/+) is estimated at E-v + 0.33 eV. These findings suggest that the hole trap at E-v + 0.32 eV obtained by capacitance measurements should be assigned to FeiH2 . FesH-related complexes show only deep acceptor activity and are expected to have little effect on minority carrier life-time in p-type Si. The opposite conclusion can be drawn for n-type Si. We find that while in H-free material Fe i defects have lower formation energy than Fe-s , in hydrogenated samples Fe-s -related defects become considerably more stable. This would explain the observation of an electron paramagnetic resonance signal attributed to a FesH-related complex in hydrogenated Si, which was quenched from above 1000 degrees C to iced-water temperature.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-70160 (URN)10.1063/1.5039647 (DOI)000437034500044 ()2-s2.0-85049239103 (Scopus ID)
Note

Validerad;2018;Nivå 2; 2018-07-25 (inah)

Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-08-08Bibliographically approved
Wright, E., Coutinho, J., Öberg, S. & Torres, V. (2017). A first-principles model of copper-boron interactions in Si: for the light-induced degradation of solar Si. Journal of Physics: Condensed Matter, 29(6), Article ID 065701.
Open this publication in new window or tab >>A first-principles model of copper-boron interactions in Si: for the light-induced degradation of solar Si
2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 6, article id 065701Article in journal (Refereed) Published
Abstract [en]

The recent discovery that Cu contamination of Si combined with light exposure has a significant detrimental impact on carrier life-time has drawn much concern within the solar-Si community. The effect, known as the copper-related light-induced degradation (Cu-LID) of Si solar cells, has been connected to the release of Cu interstitials within the bulk (2016 Sol. Energy Mater. Sol. Cells 147 115-26). In this paper, we describe a comprehensive analysis of the formation/dissociation process of the CuB pair in Si by means of first-principles modelling, as well as the interaction of CuB defects with photo-excited minority carriers. We confirm that the long-range interaction between the Cu-i(+) cation and the B-s(-) anion has a Coulomb-like behaviour, in line with the trapping-limited diffusivity of Cu observed by transient ion drift measurements. On the other hand, the short-range interaction between the d-electrons of Cu and the excess of negative charge on B-s(-) produces a repulsive effect, thereby decreasing the binding energy of the pair when compared to the ideal point-charge Coulomb model. We also find that metastable CuB pairs produce acceptor states just below the conduction band minimum, which arise from the Cu level emptied by the B acceptor. Based on these results, we argue that photo-generated minority carriers trapped by the metastable pairs can switch off the Coulomb interaction that holds the pairs together, enhancing the release of Cu interstitials, and acting as a catalyst for Cu-LID.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-61817 (URN)10.1088/1361-648X/aa4d78 (DOI)000391564700001 ()2-s2.0-85011968739 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-02-03 (andbra)

Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2018-11-16Bibliographically approved
Pinto, H., Haapasilta, V., Lokhandwala, M., Öberg, S. & Foster, A. S. (2017). Adsorption and migration of single metal atoms on the calcite (10.4) surface. Journal of Physics: Condensed Matter, 29(13), Article ID 135001.
Open this publication in new window or tab >>Adsorption and migration of single metal atoms on the calcite (10.4) surface
Show others...
2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 13, article id 135001Article in journal (Refereed) Published
Abstract [en]

Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-62127 (URN)10.1088/1361-648X/aa5bd9 (DOI)000425246600001 ()2-s2.0-85015159437 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-02-22 (andbra)

Available from: 2017-02-22 Created: 2017-02-22 Last updated: 2018-11-16Bibliographically approved
Vaqueiro-Contreras, M., Markevich, V. P., Halsall, M. P., Peaker, A. R., Santos, P., Coutinho, J., . . . Svensson, B. (2017). Powerful recombination centers resulting from reactions of hydrogen with carbon–oxygen defects in n-type Czochralski-grown silicon. Physica Status Solidi. Rapid Research Letters, 11(8), Article ID 1700133.
Open this publication in new window or tab >>Powerful recombination centers resulting from reactions of hydrogen with carbon–oxygen defects in n-type Czochralski-grown silicon
Show others...
2017 (English)In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 11, no 8, article id 1700133Article in journal (Refereed) Published
Abstract [en]

It has been acknowledged for over 50 years that treatments with hydrogen can improve silicon semiconductor devices. In recent years, these have been used to an advantage in silicon solar cells reducing the loss of photo-generated carriers at the silicon surface or at the silicon interface with dielectrics. However, we have found that in some types of silicon the in-diffusion of hydrogen can result in the formation of powerful recombination centers composed of carbon, oxygen, and hydrogen which reduce the carrier lifetime and ultimately the efficiency of solar cells made from such material

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-65354 (URN)10.1002/pssr.201700133 (DOI)000407919400003 ()2-s2.0-85021346191 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-08-28 (andbra)

Available from: 2017-08-28 Created: 2017-08-28 Last updated: 2018-07-10Bibliographically approved
Talwelkarshimpi, M., Öberg, S., Giri, L. & Pedireddi, V. R. (2017). Some hydrated molecular complexes of 4-cyanophenylboronic acid: Significance of water in the structure stabilization by theoretical investigation. Crystal Growth & Design, 17(12), 6247-6254
Open this publication in new window or tab >>Some hydrated molecular complexes of 4-cyanophenylboronic acid: Significance of water in the structure stabilization by theoretical investigation
2017 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 17, no 12, p. 6247-6254Article in journal (Refereed) Published
Abstract [en]

Molecular complexes 1a – 1c, of 4-cyanophenylboronic acid, 1, with N-donor compounds, 4,4'-bipyridine (a), 1,2-bis(4-pyridyl)ethene (b) and melamine (c), respectively, have been prepared, in the form of single crystals, by slow solvent evaporation method. Three-dimensional structures of all the complexes have been determined by X-ray diffraction technique. All the complexes 1a – 1c were noted to be crystallized as hydrates. Variations in the patterns of intermolecular interactions amongst the complexes and also the geometrical features of 1 have been analysed comparing with the features found in the native structure of 1 by determining its crystal structure also. -B(OH)2 moiety in the native form of 1 and also in the molecular complexes, 1a – 1c, adopts syn - anti conformation. Further, calculations were performed, using DFT-D3 method, to rationalize the propensity of formation of hydrate structures and to deliberate the observed structural features with respect to the strength of the intermolecular interactions, for instance, hydrogen bonds.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-66157 (URN)10.1021/acs.cgd.7b00798 (DOI)000417669900013 ()
Note

Validerad;2017;Nivå 2;2017-12-06 (rokbeg)

Available from: 2017-10-17 Created: 2017-10-17 Last updated: 2018-01-11Bibliographically approved
TalwelkarShimpi, M., Öberg, S., Giri, L. & Pedireddi, V. R. (2017). Some Hydrated Molecular Complexes of 4-Cyanophenylboronic acid: Significanceof Water in the Structure Stabilization by Theoretical Investigations. In: : . Paper presented at 17th International Conference on Density-Functional Theory and its Applications, Tällberg, Sweden, 21-25 August 2017.
Open this publication in new window or tab >>Some Hydrated Molecular Complexes of 4-Cyanophenylboronic acid: Significanceof Water in the Structure Stabilization by Theoretical Investigations
2017 (English)Conference paper, Poster (with or without abstract) (Other academic)
National Category
Other Physics Topics
Research subject
Applied Physics
Identifiers
urn:nbn:se:ltu:diva-66273 (URN)
Conference
17th International Conference on Density-Functional Theory and its Applications, Tällberg, Sweden, 21-25 August 2017
Projects
223110
Available from: 2017-10-26 Created: 2017-10-26 Last updated: 2017-11-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0292-1159

Search in DiVA

Show all publications