| 1. |
- Arshadi, S., et al.
(författare)
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Pure and carbon-doped boron phosphide (6,0) zigzag nanotube: A computational NMR study
- 2015
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Ingår i: Physica B-Condensed Matter. - : Elsevier BV. - 0921-4526. ; 477, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Calculations were performed for investigation of the properties of the electronic structure of Carbon-Doped Boron Phosphide Nanotube (CDBPNT). Pristine and three models of C-doped structures of (6,0) zigzag BPNT were studied at density functional theory (DFT) in combination with 6-311G* basis set using Gaussian package of program. The calculated parameters reveal that various B-11 and P-31 nuclei are divided into some layers with equivalent electrostatic properties. The electronic structure properties are highly influence(' by replacement of B-11 and P-31 atoms by C-12 atoms in pristine model. Furthermore, the HOMO-LUMO gap energy for suggested doped models (l), (II) and (Ill) were lower than pure BPNT pristine systems. The dipole moment values of models (H) and (Ill) were decreased to 1.788 and 1.789, respectively while the dipole moments of model (l) were enhanced to 4.373, in compare to pure pristine one (2.586). The magnitude of changes in Chemical Shielding (CS) tensor parameters revealed that the electron density at the site of P-31 was higher than that at the sift of B-11 due to carbon doping. (C) 2015 Elsevier B.V. All rights reserved.
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| 2. |
- Beck, Christian, et al.
(författare)
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Neutron spectroscopy on protein solutions employing backscattering with an increased energy range
- 2019
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 562, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Novel cold neutron backscattering spectrometers contribute substantially to the understanding of the diffusive dynamics of proteins in dense aqueous suspensions. Such suspensions are fundamentally interesting for instance in terms of the so-called macromolecular crowding, protein cluster formation, gelation, and self-assembly. Notably, backscattering spectrometers with the highest flux can simultaneously access the center-of-mass diffusion of the proteins and the superimposed internal molecular diffusive motions. The nearly complete absence of protein-protein collisions on the accessible nanosecond observation time scale even in dense protein suspensions implies that neutron backscattering accesses the so-called short-time limit for the center-of-mass diffusion. This limit is particularly interesting in terms of a theoretical understanding by concepts from colloid physics. Here we briefly review recent progress in studying protein dynamics achieved with the latest generation of backscattering spectrometers. We illustrate this progress by the first data from a protein solution using the backscattering-and-time-of-flight option BATS on IN16B at the ILL and we outline future perspectives.
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| 3. |
- Belghit, R., et al.
(författare)
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Structural, elastic, electronic and optical properties of novel antiferroelectric KNaX (X = S, Se, and Te) compounds : First principles study
- 2018
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 545, s. 18-29
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Tidskriftsartikel (refereegranskat)abstract
- This work deals with the investigation of structural, elastic, electronic and optical properties of ternary compounds belonging to the inter-alkali metal chalcogenide family KNaS, KNaSe, and KNaTe by using density functional theory (DFT) based calculations. From the structural properties, it is found that the lattice parameters and the atomic coordinates of KNaX (X= S, Se, and Te) are in good agreement with the experimental results stated in the literature. The compounds are considered as soft materials since their bulk modulus values are small. In addition, the elastic properties indicate that KNaS possesses the largest parameters of elastic constant Cij compared with other compounds, thereby revealing that KNaX compounds exhibit an elastic anisotropy. Meanwhile, the bulk modulus, shear and Young moduli, and Poisson ratio are also calculated. It is observed that all compounds are brittle and that the ionic character is dominant. In order to confirm the anisotropic character of the mechanical properties, several parameters such as universal, bulk and shear anisotropic indexes are investigated. For instance, a novel fascinating approach has been proposed by using the 3D-surfaces. The electronic properties demonstrate their semiconductor nature with a direct wide band gap of 2.61, 2.25 and 2.00 eV for KNaS, KNaSe and KNaTe respectively, as well as confirm their ionic behavior by checking the charge density distributions. Furthermore, since the optical properties of our compounds have not been yet reported in previous works, the dielectric function, refraction index, extinction index, reflectivity, loss energy function, optical conductivity and absorption spectra have been studied in details.
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| 4. |
- Booker, Ian D., et al.
(författare)
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Chloride-based SiC growth on a-axis 4H-€“SiC substrates
- 2016
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 480, s. 23-25
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Tidskriftsartikel (refereegranskat)abstract
- Abstract SiC has, during the last few years, become increasingly important as a power-device material for high voltage applications. The thick, low-doped voltage-supporting epitaxial layer is normally grown by CVD on 4° off-cut 4H–SiC substrates at a growth rate of 5 – 10 Ό m / h using silane (SiH4) and propane (C3H8) or ethylene (C2H4) as precursors. The concentrations of epitaxial defects and dislocations depend to a large extent on the underlying substrate but can also be influenced by the actual epitaxial growth process. Here we will present a study on the properties of the epitaxial layers grown by a Cl-based technique on an a-axis (90° off-cut from c-direction) 4H–SiC substrate.
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| 5. |
- Bouhou, S., et al.
(författare)
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Investigation of a core/shell Ising nanoparticle : Thermal and magnetic properties
- 2016
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 481, s. 124-132
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Tidskriftsartikel (refereegranskat)abstract
- The phase diagrams and magnetic hysteresis behavior of a spin-1/2 Ising core/shell nanoparticle are investigated by the use of the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. Nearest-neighbor pair interactions are incorporated between the Ising spins in the three parts of the nanoparticle that are core, core/shell and surface shell. The effects of the external magnetic field and core/shell exchange interaction on the thermal magnetization and susceptibility of the system are examined.
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| 6. |
- Bouhou, S., et al.
(författare)
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Magnetic properties of a single transverse Ising ferrimagnetic nanoparticle
- 2015
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 456, s. 142-150
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Tidskriftsartikel (refereegranskat)abstract
- Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation function, the thermal and the magnetic properties of a single Ising nanoparticle consisting of a ferromagnetic core, a ferromagnetic surface shell and a ferrimagnetic interface coupling are examined. The effect of the transverse held in the surface shell, the exchange interactions between core/shell and in surface shell on the free energy, thermal magnetization, specific heat and susceptibility are studied. A number of interesting phenomena have been found such as the existence of the compensation phenomenon and the magnetization profiles exhibit P-type, N-type and Q-type behaviors. (C) 2014 Elsevier B.V. All rights reserved.
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| 7. |
- Chafai, A., et al.
(författare)
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Binding energy of an exciton in a GaN/AlN nanodot : Role of size and external electric field
- 2019
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 559, s. 23-28
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Tidskriftsartikel (refereegranskat)abstract
- We report the impact of an external electric field on the energy spectrum of an exciton inside a spherical shaped GaN/AlN core/shell nanodot. The modulation of the confined exciton lowest state energy by the nanodot size is also treated. Our theoretical approach, based on a variational calculation, predicts a remarkable decrease in the exciton's energy when the electric field is switched on. Furthermore, our investigation shows that for a fixed nanodot size, the energy redshift is a unique function of the external electric field strength. On the other hand, it was observed that as the nanodot size increases the lowest exciton energy decreases and vice versa.
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| 8. |
- Colibaba, G. V, et al.
(författare)
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Effects of impurity band in heavily doped ZnO:HCl
- 2019
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 553, s. 174-181
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Tidskriftsartikel (refereegranskat)abstract
- A comparative study of properties of ZnO:HCl single crystals obtained by various methods is presented. Characterization by photoluminescence, optical and electrical measurements in the wide temperature range has allowed to analyze the energy spectra of Cl-containing stable defects in ZnO. Presence of shallow Cl donors, deeper donor complexes, incorporating several Cl atoms or stable H-Cl pairs and presence of compensating deep acceptors, attributed to VznClo centers, are demonstrated. The presence of shallow donor impurity band, as well as strong dependence of its activation energy on the doping level is shown. The controversy of various models for estimation of this dependence is discussed. It is demonstrated, that 90% of this dependence is caused by feature of temperature dependence of Hall coefficient related to conductive impurity band, and a more correct equation for activation energy is suggested. An abnormally low efficiency of neutral impurity scattering of charge carriers and strong optical absorption in the near-IR spectral range are demonstrated and attributed to upper conductive impurity band of negatively charged donors with an extra electron.
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| 9. |
- El Hamri, M., et al.
(författare)
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Hysteresis loop behaviors of a decorated double-walled cubic nanotube
- 2017
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 524, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- The effect of surface shell parameters on the hysteresis loop behaviors of a decorated Ising cubic nanotube, consisting of a ferromagnetic spin-12 core which is interacting ferrimagnetically with a ferromagnetic spin-1 surface shell, is investigated, in the present work, within the effective-field theory with correlations based on the probability distribution technique. We have found that these parameters have a strong effect on the shape and the number of hysteresis loops and also on the coercive field and remanent magnetization behaviors. Indeed, triple, quintuple, septuple and nonuple hysteresis loop patterns have also been observed.
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| 10. |
- El Hamri, M., et al.
(författare)
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Magnetic behaviors of a transverse spin-1/2 Ising cubic nanowire with core/shell structure
- 2017
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 507, s. 51-60
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Tidskriftsartikel (refereegranskat)abstract
- The surface shell exchange coupling effect on the magnetic properties (surface shell, core, total longitudinal and total transverse magnetizations, susceptibility, phase diagram and hysteresis loops) of a transverse spin-1/2 Ising cubic nanowire is investigated, in the present work, by employing the effective-field theory based on the probability distribution technique with correlations, for both ferro-and antiferromagnetic cases. We have found that this parameter has a strong effect on the magnetic properties in both cases. In the ferromagnetic case, the total longitudinal magnetization curves display Q-and S-type behaviors and the hysteresis loop has just one loop, whereas in the antiferromagnetic case, the N-type behavior, in which one compensation temperature appears below the critical temperature, exists in the total longitudinal magnetization curve versus reduced temperature, and triple hysteresis loops are found. The effect of applied field is also investigated on the total longitudinal magnetization for the both cases, and we have found that a large applied field value can overcome the antiferromagnetic coupling leading to a ferromagnetic-like behavior.
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| 11. |
- Jaffari, G. Hassnain, et al.
(författare)
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Extrinsic contributions to the dielectric response in sintered BaTiO3 nanostructures in paraelectric and ferroelectric regimes
- 2017
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 525, s. 70-77
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Tidskriftsartikel (refereegranskat)abstract
- Post sintering studies of BaTiO3 (BTO) nanoparticles are presented in detail. Bulk nanostructures were prepared via three different compaction processes, namely, uniaxial cold pressing (UCP), Cold Isostatic Pressing (CIP) and Spark Plasma Sintering (SPS). Effect of compaction technique on microstructures have been investigated and correlated with electrical response for each sample. In addition to the transport properties, temperature and frequency dependent dielectric response of variously sintered samples and bulk counterpart was recorded. Several aspects have been identified that are essential to be taken into account in order to completely understand physical processes. Drastically distinct features were observed in paraelectric (PE) regime well above ferroelectric (FE)-PE transition temperature. These features include intra grain conduction with a reduction in the magnitude of PE to FE peak dielectric constant magnitude. Role of strain, grain boundary conduction associated with observation of Maxwell Wagner relaxation and hopping conduction in dielectric and ferroelectric response have been observed and discussed. Densification with presence of oxygen vacancies, significantly enhances conductivity associated with the hopping of the carriers, in turn deteriorated ferroelectric response.
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| 12. |
- Kanaki, Kalliopi, et al.
(författare)
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Simulation tools for detector and instrument design
- 2018
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 551, s. 386-389
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Tidskriftsartikel (refereegranskat)abstract
- The high performance requirements at the European Spallation Source have been driving the technological advances on the neutron detector front. Now more than ever is it important to optimize the design of detectors and instruments, to fully exploit the ESS source brilliance. Most of the simulation tools the neutron scattering community has at their disposal target the instrument optimization until the sample position, with little focus on detectors. The ESS Detector Group has extended the capabilities of existing detector simulation tools to bridge this gap. An extensive software framework has been developed, enabling efficient and collaborative developments of required simulations and analyses – based on the use of the Geant4 Monte Carlo toolkit, but with extended physics capabilities where relevant (like for Bragg diffraction of thermal neutrons in crystals). Furthermore, the MCPL (Monte Carlo Particle Lists) particle data exchange file format, currently supported for the primary Monte Carlo tools of the community (McStas, Geant4 and MCNP), facilitates the integration of detector simulations with existing simulations of instruments using these software packages. These means offer a powerful set of tools to tailor the detector and instrument design to the instrument application.
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| 13. |
- Nozaki, Hiroshi, et al.
(författare)
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Magnetic structure for NaCr2O4 analyzed by neutron diffraction and muon spin-rotation
- 2018
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 551, s. 137-141
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the magnetic ground state of a novel one-dimensional compound, NaCr2O4, in which Cr2O4 double chains, i.e. zig-zag chains are aligned parallel to the b-axis, by means of both muon-spin rotation and relaxation (mu+SR) and neutron diffraction (ND) measurements. The mu+SR results reveal the formation of static antiferromagnetic order below Neel temperature (T-N = 124 K). The ND measurements also demonstrate the appearance of magnetic Bragg peaks with the propagation vector (k) over right arrow = (1, 0, 1) below T-N. Combined analyses of the mu+SR and ND data clarify that the Cr moments in each zig-zag chain are aligned ferromagnetically along the c-axis, whereas antiferromagnetically along the alpha-axis between the adjacent zig-zag chains.
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| 14. |
- Oubelkacem, A., et al.
(författare)
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The magnetic properties and hysteresis behaviors of the mixed spin-(1/2,1) Ferrimagnetic nanowire
- 2018
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 549, s. 82-86
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the mixed spin Ising nanowire model consisting of a spin-1 ferromagnetic core, which is surrounded by a spin-1/2 ferromagnetic surface shell is studied in the presence of magnetic and crystal fields using of the Monte Carlo (MC) Simulations based on the heat bath algorithm. We assume that the exchange interaction between two nearest-neighbor spins at the surface shell and the core is antiferromagnetic. We have examined the effects of the surface and the crystal field on the critical and compensation temperatures. The thermodynamic properties, the hysteresis behaviors are also studied. For appropriate values of the system parameters, the compensation point and multi-loops are found.
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| 15. |
- Shu, J., et al.
(författare)
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Monte-Carlo simulations of optical efficiency in luminescent solar concentrators based on all-inorganic perovskite quantum dots
- 2018
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Ingår i: Physica. B, Condensed matter. - : Elsevier B.V.. - 0921-4526 .- 1873-2135. ; 548, s. 53-57
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Tidskriftsartikel (refereegranskat)abstract
- Luminescent solar concentrator (LSC) devices emerge as a promising technology to reduce the cost of electricity generated by photovoltaic solar cells. Here, we demonstrate the detailed fabrication process of non-crystalline LSC prototype devices based on all-inorganic perovskite quantum dots (QDs) for the first time. The as-prepared all-inorganic perovskite QDs show many advantages, such as tunable absorption spectrum over the entire visible spectral region, high photoluminescence (PL) quantum yield (QY) up to 50%, and narrow emission line widths with FWHM (full width at half maximum) of 17–26 nm, which may greatly improve the optical efficiency of LSC prototype devices. On the optimal doping concentrations, Monte Carlo ray-tracing simulations indicate the LSC prototype devices have an extremely high average optical efficiency, which is 1.22% for CsPbCl3 QDs, 5.43% for CsPbBr3 QDs, and 7.39% for CsPbI3 QDs, respectively. We anticipate these potential high-efficiency LSC prototype devices based on perovskite QDs will shed light on future research of large-scale and high-performance LSCs applications.
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| 16. |
- Stenberg, Pontus, et al.
(författare)
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Defects in silicon carbide grown by fluorinated chemical vapor deposition chemistry
- 2018
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER SCIENCE BV. - 0921-4526 .- 1873-2135. ; 535, s. 44-49
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Tidskriftsartikel (refereegranskat)abstract
- Point defects in n- and p-type 4H-SiC grown by fluorinated chemical vapor deposition (CVD) have been characterized optically by photoluminescence (PL) and electrically by deep-level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS). The results are considered in comparison with defects observed in non-fluorinated CVD growth (e.g., using SiH4 instead of SiF4 as silicon precursor), in order to investigate whether specific fluorine-related defects form during the fluorinated CVD growth, which might prohibit the use of fluorinated chemistry for device-manufacturing purposes. Several new peaks identifying new defects appear in the PL of fluorinated-grown samples, which are not commonly observed neither in other halogenated chemistries, nor in the standard CVD chemistry using silane (SiH4). However, further investigation is needed in order to determine their origin and whether they are related to incorporation of F in the SiC lattice, or not. The electric characterization does not find any new electrically-active defects that can be related to F incorporation. Thus, we find no point defects prohibiting the use of fluorinated chemistry for device-making purposes.
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| 17. |
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Tunable magnetic anisotropy in obliquely sputtered Co60Fe40 thin films on Si(100)
- 2019
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Ingår i: Physica. B, Condensed matter. - : ELSEVIER. - 0921-4526 .- 1873-2135. ; 570, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Effect of substrate rotation on the structural, magneto-optic and magneto-transport properties of DC magnetron sputtered Co60Fe40 thin films is investigated. Two thin film samples (each of 20 nm thickness) were prepared by rotating (S-WR) and without rotating (S-WOR) the substrate during deposition. X-ray diffraction (XRD) patterns reveal that the films exhibit textured crystallographic orientation. Surface morphological analysis of these films indicate that the surface of S-WR is smooth in comparison to the sample S-WOR. The magneto-optic Kerr effect analysis reveals that the sample S-WR is isotropic in nature whereas a large uniaxial anisotropy is present in the sample S-WOR due to textured orientation as supported by XRD study. The effect of rotation on the anisotropy is further demonstrated by measuring magneto-resistance (MR) in two configurations, i. e., longitudinal (LMR) and transverse magnetoresistance (TMR) configurations. In the sample S-WOR, the values of MR are quite different, i. e., 0.29% (TMR) and -0.10% (LMR) whereas identical MR values, i. e., 0.19% (for both LMR and TMR), were observed in the sample S-WR. This indicates that the anisotropy in CoFe can be suppressed by rotating the substrates during growth. Thus the tunability of anisotropy is possible by rotating the substrate which is potentially useful for manipulating the properties of ferromagnetic materials for spintronic applications.
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| 18. |
- Uzdin, V M, et al.
(författare)
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The effect of confinement and defects on the thermal stability of skyrmions
- 2018
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 549, s. 6-9
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Tidskriftsartikel (refereegranskat)abstract
- The stability of magnetic skyrmions against thermal fluctuations and external perturbations is investigated within the framework of harmonic transition state theory for magnetic degrees of freedom. The influence of confined geometry and atomic scale non-magnetic defects on the skyrmion lifetime is estimated. It is shown that a skyrmion on a track has lower activation energy for annihilation and higher energy for nucleation if the size of the skyrmion is comparable with the width of the track. Two mechanisms of skyrmion annihilation are considered: inside the track and escape through the boundary. For both mechanisms, the dependence of activation energy on the track width is calculated. Non-magnetic defects are found to localize skyrmions in their neighborhood and strongly decrease the activation energy for creation and annihilation. This is in agreement with experimental measurements that have found nucleation of skyrmions in presence of spin-polarized current preferably occurring near structural defects.
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