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1
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Field Dependence of Spin Lifetimes in Wurtzite Materials

100%
Majewski J.
Acta Physica Polonica A
|
2005
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vol. 108
|
issue 5
777-780
EN
We present first-principles calculations of the zero field spin splitting of energy bands in wurtzite materials. Our calculations reveal that the huge electric fields originating from strong piezo- and pyroelecric character of nitrides do not increase the spin splitting of bands in nitride heterostructures. This implicates long spin lifetimes in quantum structures based on these materials and weak possibility of tuning with external electric field.
2
Content available remote

Adsorption of Benzene on 4H-SiC (0001) Surface: First Principles Calculations

64%
Tokár K., Majewski J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1049-1051
EN
We study adsorption of the benzene molecule on the Si terminated (0001) surface of 4H-SiC by performing first principles calculations in the framework of density functional theory. We find out that chemical reaction leading to the chemisorption of benzene on the surface has endothermic character. The adsorbed benzene molecule is bounded to two surface Si atoms and it does not lose its integrity, however, it undergoes strong deformations and causes distortion of the substrate. We analyze also changes in the electronic structure caused by benzene adsorption.
3
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Density Functional Studies of Nonlinear Elastic Properties for Zinc-Blende Nitrides

64%
Łopuszyński M., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
443-447
EN
In this paper we present a method of calculating third-order elastic constants C_{ijk} and its application to zinc-blende nitrides AlN, GaN, and InN. Our approach is based on accurate ab initio calculations of both energy and stress as a function of applied strain. Ab initio computations are performed within density functional theory framework. To assess the reliability of the presented method, we compare our theoretical findings for GaAs with experimental results for C_{ijk} available for this material.
4
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Strain Induced k-Linear Spin Splitting in III-V Semiconductors

64%
Skierkowski A., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
455-460
EN
We present theoretical studies of the linear-k strain induced spin splitting of the conduction band in the zinc-blende semiconductors. The studies are based on ab initio calculations performed within the density functional theory with non-scalar relativistic effects fully taken into account. This permits one to construct effective Hamiltonian for the strain induced linear-k spin splitting of the zinc-blende semiconductors. This Hamiltonian reproduces fully the structure of the strain induced linear-k spin splitting and generalizes previously introduced and commonly used effective Hamiltonian.
5
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Pressure Dependence of Elastic Constants in Zinc-Blende III-N and Their Influence on the Light Emission in Nitride Heterostructures

64%
Łepkowski S., Majewski J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
559-566
EN
We studied the nonlinear elasticity effects for the case of III-N compounds. Particularly, we determined the pressure dependences of elastic constants, in zinc-blende InN, GaN, and AlN by performing ab initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We found significant and almost linear increase in C_{11}, C_{12} with pressure for considered nitrides compounds. Much weaker dependence on pressure was observed for C_{44}. We also discussed pressure dependences of two-dimensional Poisson's ratio and elastic anisotropy coefficient. Finally, we showed that the pressure dependence of elastic constants results in significant reduction of the pressure coefficient of the energy emission in cubic InGaN/GaN quantum wells and essentially improves the agreement between experimental and theoretical values.
6
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Theoretical Study of Spin Lifetimes in [110] Strained GaAs

64%
Skierkowski A., Majewski J.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
353-358
EN
We present first-principles studies of the zero field spin splitting of conduction band in [110] strained GaAs that determine spin lifetimes in semiconductors. Our calculations reveal strong anisotropy of the linear-k spin splitting in the (110) plane of the Brillouin zone and very minor in the (001) plane. This provides a qualitative understanding of the difference in the spin lifetimes in the GaAs/AlAs heterostructures grown along [100] and [110] crystallographic directions.
7
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Effects of Nonlinear Elasticity and Electromechanical Coupling on Optical Properties of InGaN/GaN and AlGaN/AlN Quantum Wells

64%
Łepkowski S., Majewski J.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
237-242
EN
We present theoretical studies of effects of the nonlinear elasticity and the electromechanical coupling on the optical properties of InGaN/GaN and AlGaN/AlN quantum wells. In these structures, due to the lattice misfit between constituents, the quantum wells are compressively strained and the intrinsic hydrostatic pressure is present. Therefore, the nonlinear elasticity is investigated by taking into account the pressure dependence of elastic stiffness tensor for the strained quantum wells. We show that this effect leads to (i) decrease in the volumetric strain and (ii) increase in the polarization-induced built-in electric field in the quantum wells. Consequently, the interband transition energies in the quantum wells decrease when the nonlinear elasticity of nitrides is considered. On the other hand, we show that the effect of electromechanical coupling, i.e., co-existence of ordinary and converse piezoelectric effects results in increase in the interband transition energies in the considered quantum wells. It turns out that the influence of the nonlinear elasticity on the optical properties is stronger than the influence of electromechanical coupling for InGaN/GaN quantum wells, while for AlGaN/GaN the opposite situation is observed.
8
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Resonant Spin Splitting in III-V Semiconductors

64%
Skierkowski A., Majewski J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
867-872
EN
We present first-principles studies of the zero field spin splitting of energy bands in typical III-V semiconductors. Our calculations reveal that the strain induces linear-k spin splitting of the conduction band in theΓ point, which is linear in strain, and determine the magnitude of the so-called acoustic phonon constant that characterizes the magnitude of the spin splitting. In addition, we show that optical phonons lead to spin-flip processes and we present quantitative results for the spin-phonon deformation potentials in GaAs. Most importantly, the calculations show that the linear-k spin splitting can be resonantly enhanced when bands cross in a particular point of the Brillouin zone. This resonant enhancement of the bulk inversion asymmetry coupling constant by more than one order of magnitude was observed in both valence and conduction bands and can be steered by the application of the external stress. This allows tailoring of the spin relaxation and spin precession of conduction electrons in nanostructures to a much larger extent than was hitherto assumed.
9
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Quantum Monte Carlo vs. Density Functional Methods for the Prediction of Relative Energies of Small Si-C Clusters

64%
Gonzalez Szwacki N., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
964-966
EN
In the present paper, we assess the accuracy of popular and widely used approaches based on density functional theory by relating them to the most accurate at present quantum Monte Carlo calculations. As the test case, we consider the relative stability of small Si_{n}C_{m} isomers. We find out that none of the studied DFT approaches employing local, semilocal, or even hybrid functionals are able to predict correctly the relative stability of the isomers.
10
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Structure and Charge Compensation of Heteropolar SiC/GaN Interfaces

64%
Sznajder M., Majewski J.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
772-774
EN
We present studies of the morphology and charge distribution at the 4H-SiC/wz-GaN heteropolar junctions. Our investigations are based on the first principles calculations in the framework of the density functional theory where the interfaces between the SiC substrate and GaN layers are represented by means of a slab. These studies reveal possible charge compensation patterns at the interfaces that lead to charge redistribution from monopole to dipole character and increase the stability of the junctions. It turns out that the interfaces with C-Ga and Si-Ga bonds across the junction and reconstructions involving substitution of group IV elements into Ga layer are the most favorable energetically.
11
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Ab Initio Study of CH₄, CH₃, and CO₂ Affinity to the (001) MgO Surface

64%
Siklitskaya A., Majewski J.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-145-A-147
EN
The dynamics of the methane, methyl, and carbon dioxide adsorption to the (001) surface of cubic magnesium oxide (periclase) has been studied within the ab initio molecular dynamics in the temperature range between 0 and 1000 K. For methane, neither chemisorption nor physisorption has been observed in the considered temperature range, whereas methyl group and carbon dioxide build chemical bond to the MgO surface at temperatures 350 K and 450 K, with adhesive energies of 0.218 and 0.935 eV, respectively.
12
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First Principles Study of Gas Adsorption Dynamics on Pristine and Defected Graphene

64%
Wlazło M., Majewski J.
Acta Physica Polonica A
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2016
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vol. 129
|
issue 1a
A-142-A-144
EN
We present the results of ab initio calculations of gas adsorption processes on graphene. Static density functional theory framework is used to obtain adsorption energies of several species on a Stone-Wales defected graphene monolayer. The Van der Waals interaction is taken into account by a semi-empirical correction. Sites closer to the defect are found to induce stronger adsorption compared to sites further away, where the graphene crystal structure is intact. The Car-Parrinello ab initio molecular dynamics simulations are performed at high temperatures. CH₃ is found to be stably physisorbed or chemisorbed at 300 K.
13
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Content available

Nonlinear Elasticity in Wurtzite GaN/AlN Planar Superlattices and Quantum Dots

52%
Łepkowski S., Majewski J., Jurczak G.
Acta Physica Polonica A
|
2005
|
vol. 108
|
issue 5
749-754
EN
The elastic stiffness tensors for wurtzite GaN and AlN show a significant hydrostatic pressure dependence, which is the evidence of nonlinear elasticity of these compounds. We have examined how pressure dependence of elastic constants for wurtzite nitrides influences elastic and piezoelectric properties of GaN/AlN planar superlattices and quantum dots. Particularly, we show that built-in hydrostatic pressure, present in both quantum wells of the GaN/AlN superlattices and GaN/AlN quantum dots, increases significantly by 0.3-0.7 GPa when nonlinear elasticity is used. Consequently, the compressive volumetric strain in quantum wells and quantum dots decreases in comparison to the case of the linear elastic theory. However, the z-component of the built-in electric field in the quantum wells and quantum dots increases considerably when nonlinear elasticity is taken into account. Both effects, i.e., a decrease in the compressive volumetric strain as well as an increase in the built-in electric field, decrease the band-to-band transition energies in the quantum wells and quantum dots.
14
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Morphology and Stability of the Diamond/BN (001) and (111) Interfaces Based on Ab Initio Studies

52%
Sznajder M., Hrushka N., Majewski J.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1220-1223
EN
The morphology, charge distribution and energetic stability of interfaces in the diamond/c-BN heteropolar junctions grown along [001] and [111] crystallographic directions are obtained from first principles calculations in the framework of density functional theory. It turns out that there exist reconstructions of the abrupt interfaces of the C and N adjacent layers (C-N type) that induce charge compensation and lead to the stabilization of the interfaces. On the contrary, our studies strongly suggest that analogous reconstructions of the abrupt interfaces of C and B adjacent layers (C-B type) are not energetically favorable and do not stabilize abrupt interfaces.
15
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Ab Initio Study of Functionalized Carbon Nanotubes

52%
Milowska K., Birowska M., Majewski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
841-843
EN
In the present paper, we study the stability of (9, 0), (10, 0), (11, 0) carbon nanotubes functionalized with simple organic molecules -CH_{n} (for n = 2, 3, 4). Our studies are based on ab initio calculations within the framework of the density functional theory. We determine binding energies of the functionalized carbon nanotubes and the changes in the geometry and electronic structure caused by the functionalization. We observe the characteristic effects such as rehybridization of the bonds induced by fragments attached to carbon nanotubes and pentagon/heptagon (5/7) defects in -CH_{2} functionalized carbon nanotubes. We study also dependence of the binding energies of the functionalized carbon nanotubes on the density of the adsorbed molecules and diameter of the single-wall carbon nanotubes. Our calculations reveal that the -CH_{2} fragments exhibit the strongest cohesion and we determine the critical density of the -CH_{2} fragments which could be adsorbed.
16
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Van Der Waals Density Functionals for Graphene Layers and Graphite

52%
Birowska M., Milowska K., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
845-848
EN
In this communication, we present results of theoretical studies of various systems where Van der Waals interaction plays a considerable role. In the first-principle calculations performed in the density functional theory framework we implement novel functionals accounting for Van der Waals forces and employ to the test cases of graphite and graphene layers. It turns out that this approach provides a solution to the long standing problem of overbinding between graphene layers in bulk graphite, giving the distance between the carbon layers in excellent agreement with experiment. In graphene bilayers, Van der Waals functionals lead to energetic barriers for A-B to A-A ordering of graphene bilayers that are by a factor of two smaller than the barriers obtained with standard functionals. It may be of crucial importance, particularly, if one uses atomistic ab initio methods as a starting point for multi-scale modeling of materials and for determination of effective potentials.
17
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Structural and Electronic Properties of Functionalized Graphene

52%
Milowska K., Birowska M., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
|
issue 5
842-844
EN
In the present paper, we study the effects of functionalization of graphene with simple organic molecules OH, and NH_2, focusing on the stability and band gaps of the structures. We have performed DFT calculations for graphene supercells with various numbers of the attached molecules. We have determined adsorption energies of the functionalized graphene mono- and bilayers, the changes in the geometry, and the band structure. We observe the characteristic effects such as rehybridization of the bonds induced by fragments attached to graphene and opening of the graphene band gap by functionalization. We have also studied the dependence of the adsorption energies of the functionalized graphene on the density of the adsorbed molecules. Our calculations reveal that the -OH and -NH_2 groups exhibit the strong cohesion to graphene layers. Further, we determine the critical density of the OH fragments which lead to the opening of the band gap. We also show how to engineer the magnitude of the band gap by functionalizing graphene with NH_2 groups of various concentrations.
18
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Wide Range Wavelength Tuning of InGaAsP/InP Laser Diodes

52%
Bajda M., Trzeciakowski W., Majewski J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
852-855
EN
We present results of theoretical studies of external tuning for laser diodes based on InGaAsP/InP heterostructures at temperatures from 300 K down to 80 K and at hydrostatic pressures up to 2.27 GPa. The tuning range achieved by pressure and grating was 390 nm (from 1220 nm to 1610 nm). At lower temperatures the tuning range achieved with grating was significantly reduced. Our results indicate that pressure tuning is much more effective than temperature tuning when combined with tuning by external grating.
19
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Ab Initio Studies of Al and Ga Adsorption on 4H-SiC{0001} Surfaces

52%
Wachowicz E., Sznajder M., Majewski J.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 6
1045-1048
EN
Changes in the atomic and electronic structure of Si- and C-terminated 4H-SiC{0001} surfaces resulting from aluminium and gallium adsorption have been studied within density functional theory framework. Al and Ga coverages ranging from a submonolayer to one monolayer were considered. Our results show that Al binds more strongly to both surfaces than Ga. The binding is stronger to the C-terminated surface for both metals. The sites occupied by Al and Ga atoms at 1 monolayer are different and it is due to a different charge transfer from metal to the substrate.
20
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Theoretical Calculations of Cohesive and Electronic Properties of Quaternary AlGaInN Alloys

52%
Łopuszyński M., Bartoszek J., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
449-454
EN
We present theoretical studies of the AlGaInN nitride quaternary alloys. The studies are based on ab initio calculations performed within the density functional theory and virtual crystal approximation. The equilibrium lattice constants, bulk moduli, and elastic constants were calculated for the whole possible range of concentrations of the alloy constituents. The theoretical values were then fitted with second- and third-order polynomials. For all properties studied, the considerable bowing was observed.
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