| 1. |
- Alijan Farzad Lahiji, Faezeh, et al.
(författare)
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Unusual tilted growth and epitaxial relationship of NaCl B1-structured NiO and CrN on r-plane Al2O3
- 2024
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Ingår i: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 135:6
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial NiO and CrN thin films were deposited on a single-crystal Al2O3(11¯02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110)NaCl(B1)∥(44¯03)Al2O3 and [11¯2]NaCl(B1)∥[1¯1¯20]Al2O3. This relationship differs from the previously observed orientation of (100)NaCl(B1)∥(11¯02)Al2O3 and [100]NaCl(B1)∥[101¯0]Al2O3. These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected.
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| 2. |
- Aperis, Alex, et al.
(författare)
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Charge density waves beyond the Pauli paramagnetic limit in 2D systems
- 2020
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 128:8
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional materials are ideal candidates to host Charge Density Waves (CDWs) that exhibit paramagnetic limiting behavior, similar to the well-known case of superconductors. Here, we study how CDWs in two-dimensional systems can survive beyond the Pauli limit when they are subjected to a strong magnetic field by developing a generalized mean-field theory of CDWs under Zeeman fields that includes incommensurability, imperfect nesting, and temperature effects and the possibility of a competing or coexisting Spin Density Wave (SDW) order. Our numerical calculations yield rich phase diagrams with distinct high-field phases above the Pauli limiting field. For perfectly nested commensurate CDWs, a q-modulated CDW phase that is completely analogous to the superconducting Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase appears at high fields. In the more common case of imperfect nesting, the commensurate CDW ground state undergoes a series of magnetic-field-induced phase transitions first into a phase where commensurate CDW and SDW coexist and subsequently into another phase where CDW and SDW acquire a q-modulation that is, however, distinct from the pure FFLO CDW phase. The commensurate CDW+SDW phase occurs for fields comparable to but less than the Pauli limit and survives above it. Thus, this phase provides a plausible mechanism for the CDW to survive at high fields without the need for forming the more fragile FFLO phase. We suggest that the recently discovered 2D materials like the transition metal dichalcogenides offer a promising platform for observing such exotic field-induced CDW phenomena.
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| 3. |
- Arslanov, T. R., et al.
(författare)
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Large pressure-induced magnetoresistance in a hybrid ferromagnet-semiconductor system : Effect of matrix modification on the spin-dependent scattering
- 2020
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 128:21
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanocomposites based on MnAs clusters embedded in a chalcopyrite host usually do not exhibit large magnetoresistance (MR) at room temperature, while pronounced effects are localized at very low temperatures. In the present work, we observed an appearance of large pressure-induced negative and positive MR at room temperature in the Zn0.1Cd0.9GeAs2 hybrid system containing 10% MnAs inclusions. With the applied pressure, a substantial modification of the electron transport from semimetallic to semiconducting type occurs, followed by a subsequent structural transition at P approximate to 3.5GPa into almost metallic high-pressure phase. This picture is simultaneously supported by temperature-dependent and room temperature high-pressure transport measurements. Using a semiempirical expression, taking into account a spin-dependent scattering of charge carriers due to MnAs nanoclusters, as well as a two-band conductivity model, we have been able to partially describe the observed MR effects. The predominantly weak positive contribution at P=1GPa, which is well described in the framework of the proposed approach indicates the presence of spin-polarized charge carriers. Based on the two-band model calculations, a negative spin polarization was found at P >= 3GPa that ascribed to a structural change of the matrix. As our results indicate, an emerging MR in the structural transition region is characterized by a complex behavior. In particular, the negative part of MR demonstrates a magnetic field dependence different than Delta rho/rho (0)similar to H-2, suggesting the presence of unusual scattering mechanisms in magnetotransport.
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| 4. |
- Artemchuk, P. Y., et al.
(författare)
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Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 127:6
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Tidskriftsartikel (refereegranskat)abstract
- A method to perform spectrum analysis on low power signals between 0.1 and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of an evanescent spin current. It is first shown that the ATJ oscillation frequency can be tuned linearly with time. Then, it is shown that the ATJ output is highly dependent on matching conditions that are highly dependent on the dimensions of the dielectric tunneling barrier. Spectrum analysis can be performed by using an appropriately designed ATJ, whose frequency is driven to increase linearly with time, a low pass filter, and a matched filter. This method of THz spectrum analysis, if realized in the experiment, will allow miniaturized electronics to rapidly analyze low power signals with a simple algorithm. It is also found by simulation and analytical theories that for an ATJ with a 0.09 mu m(2) footprint, spectrum analysis can be performed over a 0:25 THz bandwidth in just 25 ns on signals that are at the Johnson-Nyquist thermal noise floor. Published under license by AIP Publishing.
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| 5. |
- Azarov, A., et al.
(författare)
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Effects of annealing on photoluminescence and defect interplay in ZnO bombarded by heavy ions : Crucial role of the ion dose
- 2020
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 127:2
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Tidskriftsartikel (refereegranskat)abstract
- Bombardment of ZnO with heavy ions generating dense collision cascades is of particular interest because of the formation of nontrivial damage distribution involving a defected layer located between the surface and the bulk damage regions, as seen by Rutherford backscattering spectroscopy in the channeling mode. By correlating photoluminescence and channeling data, we demonstrate that the thermal evolution of defects in wurtzite ZnO single crystals implanted with Cd ions strongly depends on the implanted dose. Specifically, the ion dose has a profound effect on the optical response in the spectral range between the near-band-edge emission and deep-level emission bands. The interplay between interstitial and vacancy type defects during annealing is discussed in relation to the evolution of the multipeak damage distribution.
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| 6. |
- Bafekry, A., et al.
(författare)
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A novel two-dimensional boron-carbon-nitride (BCN) monolayer: A first-principles insight
- 2021
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 130:11
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Tidskriftsartikel (refereegranskat)abstract
- The optical, electronic, and structural properties of a theoretically predicted new boron-carbon-nitride (BCN) two-dimensional monolayer have been explored using density functional theory calculations. The phonon dispersion, molecular dynamics simulation, the cohesive energy, and the Born criteria of elastic constant calculations of the BCN monolayer confirm its stability. The phonon spectrum illustrates an out-of-plane flexure mode with quadratic dispersion in the long-wavelength limit. The BCN monolayer is a semiconductor with a direct bandgap of 0.9 (1.63) eV determined via the Perdew-Burke-Ernzerhof (Heyd-Scuseria-Ernzerhof) functional. The same electron and hole effective masses and mobility values indicate the high recombination rate of electrons and holes. Meanwhile, the BCN monolayer can absorb ultraviolet radiation more effectively than visible light. Due to its interesting physical properties, the novel BCN monolayer could be a rather good candidate material for electro-optical applications.& nbsp;Published under an exclusive license by AIP Publishing
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| 7. |
- Bahaloohoreh, Hassan, 1983-, et al.
(författare)
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Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size
- 2022
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 131:2
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Tidskriftsartikel (refereegranskat)abstract
- We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.
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| 8. |
- Bathellier, Didier, et al.
(författare)
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Effect of cationic chemical disorder on defect formation energies in uranium-plutonium mixed oxides
- 2022
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 132:17, s. 175103-
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Tidskriftsartikel (refereegranskat)abstract
- At the atomic scale, uranium-plutonium mixed oxides (U,Pu)O-2 are characterized by cationic chemical disorder, which entails that U and Pu cations are randomly distributed on the cation sublattice. In the present work, we study the impact of disorder on point defect formation energies in (U,Pu)O-2 using interatomic-potential and density functional theory (DFT + U) calculations. We focus on bound Schottky defects (BSD) that are among the most stable defects in these oxides. As a first step, we estimate the distance R-D around the BSD up to which the local chemical environment significantly affects their formation energy. To this end, we propose an original procedure in which the formation energy is computed for several supercells at varying levels of disorder. We conclude that the first three cation shells around the BSD have a non-negligible influence on their formation energy (R-D similar or equal to 7.0 angstrom). We apply then a systematic approach to compute the BSD formation energies for all the possible cation configurations on the first and second nearest neighbor shells around the BSD. We show that the formation energy can range in an interval of 0.97eV, depending on the relative amount of U and Pu neighboring cations. Based on these results, we propose an interaction model that describes the effect of nominal and local composition on the BSD formation energy. Finally, the DFT + U benchmark calculations show a satisfactory agreement for configurations characterized by a U-rich local environment and a larger mismatch in the case of a Pu-rich one. In summary, this work provides valuable insights on the properties of BSD defects in (U,Pu)O-2 and can represent a valid strategy to study point defect properties in disordered compounds.
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| 9. |
- Bosma, Tom, et al.
(författare)
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Broadband single-mode planar waveguides in monolithic 4H-SiC
- 2022
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 131:2
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Tidskriftsartikel (refereegranskat)abstract
- Color-center defects in silicon carbide promise opto-electronic quantum applications in several fields, such as computing, sensing, and communication. In order to scale down and combine these functionalities with the existing silicon device platforms, it is crucial to consider SiC integrated optics. In recent years, many examples of SiC photonic platforms have been shown, like photonic crystal cavities, film-on-insulator waveguides, and micro-ring resonators. However, all these examples rely on separating thin films of SiC from substrate wafers. This introduces significant surface roughness, strain, and defects in the material, which greatly affects the homogeneity of the optical properties of color centers. Here, we present and test a method for fabricating monolithic single-crystal integrated-photonic devices in SiC: tuning optical properties via charge carrier concentration. We fabricated monolithic SiC n-i-n and p-i-n junctions where the intrinsic layer acts as waveguide core, and demonstrate the waveguide functionality for these samples. The propagation losses are below 14 dB/cm. These waveguide types allow for addressing color centers over a broad wavelength range with low strain-induced inhomogeneity of the optical-transition frequencies. Furthermore, we expect that our findings open the road to fabricating waveguides and devices based on p-i-n junctions, which will allow for integrated electrostatic and radio frequency control together with high-intensity optical control of defects in silicon carbide.
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| 10. |
- Burcea, Razvan, et al.
(författare)
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Effect of induced defects on conduction mechanisms of noble-gas-implanted ScN thin films
- 2023
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 134:5
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Tidskriftsartikel (refereegranskat)abstract
- Noble-gas implantation was used to introduce defects in n-type degenerate ScN thin films to tailor their transport properties. The electrical resistivity increased significantly with the damage levels created, while the electron mobility decreased regardless of the nature of the ion implanted and their doses. However, the transport property characterizations showed that two types of defects were formed during implantation, named point-like and complex-like defects depending on their temperature stability. The point-like defects changed the electrical conduction mode from metallic-like to semiconducting behavior. In the low temperature range, where both groups of defects were present, the dominant operative conduction mechanism was the variable range hopping conduction mode. Beyond a temperature of about 400 K, the point-like defects started to recover with an activation energy of 90 meV resulting in a decrease in resistivity, independent of the incident ion. The complex-like defects were, therefore, the only remaining group of defects after annealing above 700 K. These latter, thermally stable at least up to 750 K, introduced deep acceptor levels in the bandgap resulting in an increase in the electrical resistivity with higher carrier scattering while keeping the metallic-like behavior of the sample. The generation of both types of defects, as determined by resistivity measurements, appeared to occur through a similar mechanism within a single collision cascade.
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