| 1. |
- Abou-Hamad, E., et al.
(författare)
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NMR strategies to study the local magnetic properties of carbon nanotubes
- 2012
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Ingår i: Physica. B, Condensed matter. - Amsterdam : Elsevier. - 0921-4526 .- 1873-2135. ; 407:4, s. 740-742
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Tidskriftsartikel (refereegranskat)abstract
- The local magnetic properties of the one dimensional inner space of the nanotubes are investigated using C-13 nuclear magnetic resonance spectroscopy of encapsulated fullerene molecules inside single walled carbon nanotubes. Isotope engineering and magnetically purified nanotubes have been advantageously used on our study to discriminate between the different diamagnetic and paramagnetic shifts of the resonances. Ring currents originating from the pi electrons circulating on the nanotube, are found to actively screen the applied magnetic field by -36.9 ppm. Defects and holes in the nanotube walls cancel this screening locally. What is interesting, that at high magnetic fields, the modifications of the NMR resonances of the molecules from free to encapsulated can be exploited to determine some structural characteristics of the surrounding nanotubes, never observed experimentally. (C) 2011 Elsevier B.V. All rights reserved.
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| 2. |
- Asghar, M., et al.
(författare)
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Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy
- 2012
-
Ingår i: Physica B: Condensed Matter. - : Elsevier. - 0921-4526.
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Konferensbidrag (refereegranskat)abstract
- In this study deep level transient spectroscopy has been performed on boron-nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N-A-N-D)similar to 3 x 10(17) cm(-3). We observed a hole H-1 majority carrier and an electron E-1 minority carrier traps in the device having activation energies E-nu + 0.24 eV, E-c -0.41 eV, respectively. The capture cross-section and trap concentration of H-1 and E-1 levels were found to be (5 x 10(-19) cm(2), 2 x 10(15) cm(-3)) and (1.6 x 10(-16) cm(2), 3 x 10(15) cm(-3)), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H-1 defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E-1 defect to a nitrogen donor.
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| 3. |
- Asghar, M., et al.
(författare)
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Study of deep level defects in doped and semi-insulating n-6H-SiC epilayers grown by sublimation method
- 2012
-
Ingår i: Physica B: Condensed Matter. - : Elsevier. - 0921-4526.
-
Konferensbidrag (refereegranskat)abstract
- Deep level transient spectroscopy (DLTS) is employed to study deep level defects in n-6H-SiC (silicon carbide) epilayers grown by the sublimation method. To study the deep level defects in n-6H-SiC, we used as-grown, nitrogen doped and nitrogen-boron co-doped samples represented as ELS-1, ELS-11 and ELS-131 having net (N-D-N-A) similar to 2.0 x 10(12) cm(-3), 2 x 10(16) cm(-3) and 9 x 10(15) cm(3), respectively. The DLTS measurements performed on ELS-1 and ELS-11 samples revealed three electron trap defects (A, B and C) having activation energies E-c - 0.39 eV, E-c - 0.67 eV and E-c - 0.91 eV, respectively. While DLTS spectra due to sample ELS-131 displayed only A level. This observation indicates that levels B and C in ELS-131 are compensated by boron and/or nitrogen-boron complex. A comparison with the published data revealed A, B and C to be E-1/E-2, Z(1)/Z(2) and R levels, respectively.
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| 4. |
- Banerjee, Mitali, et al.
(författare)
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Magnetism in NiFeMo disordered alloys : Experiment and theory
- 2010
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 405:20, s. 4287-4293
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Tidskriftsartikel (refereegranskat)abstract
- In this communication we carry out experimental investigation of the behavior of magnetization with temperature and magnetic field of six samples at different compositions of the disordered ternary alloy NiFeMo. We analyze the data using a fist-principles density functional based electronic structure method and a mean-field phase diagram study.
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| 5. |
- Bruhn, Benjamin, et al.
(författare)
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Temporal correlation of blinking events in CdSe/ZnS and Si/SiO2 nanocrystals
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 453, s. 63-67
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Tidskriftsartikel (refereegranskat)abstract
- Well passivated single Si/SiO2 nanoparticles obey mono exponential blinking statistics, whereas CdSe/ZnS quantum dots follow an apparent (truncated) power-law. Log-normal distributions are found to describe the interval length histograms at least as well as power-laws, while at the same time being more physically feasible and significantly easing the determination of the exponential cutoff in the ON-time distribution. The correlation of an ON- (OFF-)interval with its temporally displaced ON (OFF) neighbors, as well as that of intermixed intervals (ON with OFF and OFF with ON neighbors) has been studied. As expected from purely random processes, the correlation coefficients for events in silicon nanocrystals equal zero, whereas positive correlations between the pure and negative correlations between the mixed states in CdSe quantum dots hint at a switching process between two distinct blinking regimes that are slower than the blinking itself.
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| 6. |
- Chubarov, M., et al.
(författare)
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Boron nitride: A new photonic material
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 29-34
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Tidskriftsartikel (refereegranskat)abstract
- Rhombohedral boron nitride (r-BN) layers were grown on sapphire substrate in a hot-wall chemical vapor deposition reactor. Characterization of these layers is reported in details. X-ray diffraction (XRD) is used as a routine characterization tool to investigate the crystalline quality of the films and the identification of the phases is revealed using detailed pole figure measurements. Transmission electron microscopy reveals stacking of more than 40 atomic layers. Results from Fourier Transform InfraRed (FTIR) spectroscopy measurements are compared with XRD data showing that FTIR is not phase sensitive when various phases of sp(2)-BN are investigated. XRD measurements show a significant improvement of the crystalline quality when adding silicon to the gas mixture during the growth; this is further confirmed by cathodoluminescence which shows a decrease of the defects related luminescence intensity.
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| 7. |
- Durmus, Z., et al.
(författare)
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Synthesis and characterization of poly(1-vinyl-1,2,4-triazole) (PVTri)-barium hexaferrite nanocomposite
- 2011
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:11, s. 2298-2302
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for the fabrication of PVTri-BaFe12O19 nanocomposites by in-situ polymerization of PVTri in the presence of synthesized BaFe12O19 nanoparticles. Nanoparticles, polymer and nanocomposite were analyzed by XRD, FTIR, TGA, TEM, NMR, GPC and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 17 +/- 5 nm. Conjugation of PVTri to nanoparticle surface was assessed to be via carbonyl groups on the polymer. TG analysis revealed that 45 wt% of nanocomposite is inorganic phase (BaFe12O19). It was found out that the ac conductivity of nanocomposite under a certain frequency increases with temperature.
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| 8. |
- Engelbrecht, J.A. A., et al.
(författare)
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Impact of dielectric parameters on the reflectivity of 3C-SiC wafers with a rough surface morphology in the reststrahlen region
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 115-118
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Tidskriftsartikel (refereegranskat)abstract
- A layer-on-substrate model is used to obtain the infrared reflectance for 3C-SiC with a rough surface morphology. The effect of varying dielectric parameters of the "damaged layer" on the observed reflectivity of the 3C-SiC in the reststrahlen region is assessed. Different simulated reflectance spectra are obtained to those if the dielectric parameters of the "substrate" were varied. Most notable changes in the shape of the simulated reststrahlen peak are observed for changes in the high frequency dielectric constant, the phonon damping constant, the phonon frequencies and "thickness" of damaged surface layer.
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| 9. |
- Engelbrecht, J A A, et al.
(författare)
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The origin of a peak in the reststrahlen region of SiC
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1525-1528
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Tidskriftsartikel (refereegranskat)abstract
- A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.
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| 10. |
- Eriksson, Jens, et al.
(författare)
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Adjusting the electronic properties and gas reactivity of epitaxial graphene by thin surface metallization
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 105-108
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene-based chemical gas sensors normally show ultra-high sensitivity to certain gas molecules but at the same time suffer from poor selectivity and slow response and recovery Limes. Several approaches based on functionalization or modification of the graphene surface have been demonstrated as means to improve these issues, but most such measures result in poor reproducibility. In this study we investigate reproducible graphene surface modifications by sputter deposition of thin nanostructured Au or Pt layers. It is demonstrated that under the right metallization conditions the electronic properties of the surface remain those of graphene, while the surface chemistry is modified to improve sensitivity, selectivity and speed of response to nitrogen dioxide.
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| 11. |
- Ghosh, Subhradip, et al.
(författare)
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Structural and elastic properties of Ni2+xMn1-xGa alloys
- 2011
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:11, s. 2240-2244
-
Tidskriftsartikel (refereegranskat)abstract
- The structural parameters and the energetics of the Ni2+xMn1-xGa alloys have been investigated by the first-principles Exact Muffin Tin Orbital-Coherent Potential Approximation (EMTO-CPA) for 0.10 < x < 0.30. The difference in total energies (delta E) between the low-temperature tetragonal phase and the high-temperature cubic phase has been considered as a qualitative indicator of the martensitic transformation temperature T-m. The qualitative behavior of delta E with variation of x has been found to be in agreement with the experimentally observed variation of T-m with x. The elastic constants for the entire range of x have also been calculated and the determination of a relationship between delta E and the elastic shear modulus has been attempted. It is seen that delta E varies linearly with elastic shear modulus C', qualitatively similar to the relation between T-m and C'. The energetics calculated with the EMTO method agrees quite well with the all-electron full-potential results ensuring the accuracy of the method. These results show that the EMTO-CPA method is one of the most reliable and accurate first-principles methods, in the context of off-stoichiometric alloys which undergo martensitic phase transformations.
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| 12. |
- Gällström, Andreas, et al.
(författare)
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Optical identification and electronic configuration of tungsten in 4H-and 6H-SiC
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1462-1466
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Tidskriftsartikel (refereegranskat)abstract
- Several optically observed deep level defects in SiC are still unidentified and little is published on their behavior. One of the commonly observed deep level defects in semi-insulating SiC is UD-1. less thanbrgreater than less thanbrgreater thanThis report suggests that UD-1 is Tungsten related, based on a doping study and previously reported deep level transient spectroscopy data, as well as photo-induced absorption measurements. The electronic levels involved in the optical transitions of UD-1 are also deduced. The transitions observed in the photoluminescence of UD-1 are from a Gamma(C3v)(4), to two different final states, which transform according to Gamma(C3v)(5)circle plus Gamma(C3v)(6) and Gamma(C3v)(4), respectively.
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| 13. |
- Hakim, M A, et al.
(författare)
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Spin-glass-like ordering in the spinel ZnFe2O4 ferrite
- 2011
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:1, s. 48-51
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, spin-glass-like ordering has been observed in the spinel ZnFe2O4 ferrite. Field cooled (FC) and zero-field cooled (ZFC) DC magnetizations display divergence at low temperature, which indicates a frozen state with the freezing temperature of T-f=21 K. Frequency dependence of AC susceptibility measurement was performed on the sample. It shows a peak at around T-f, with the peak position shifting as a function of driving frequency, indicating a spin-glass-like transition of the sample. The sample shows a typical spin-glass behavior with a manifestation of non-equilibrium dynamics of the spin glass, such as aging, rejuvenation and memory effects. These experimental findings indicate that Zn-ferrite exhibits a spin-glass-like phase at low temperature and it is not canted antiferromagnetic.
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| 14. |
- Henry, Anne, et al.
(författare)
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SiC epitaxy growth using chloride-based CVD
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1467-1471
-
Tidskriftsartikel (refereegranskat)abstract
- The growth of thick epitaxial SiC layers needed for high-voltage, high-power devices is investigated with the chloride-based chemical vapor deposition. High growth rates exceeding 100 mu m/h can be obtained, however to obtain device quality epilayers adjustments of the process parameters should be carried out appropriately for the chemistry used. Two different chemistry approaches are compared: addition of hydrogen chloride to the standard precursors or using methyltrichlorosilane, a molecule that contains silicon, carbon and chlorine. Optical and electrical techniques are used to characterize the layers.
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| 15. |
- Holtz, Per-Olof, et al.
(författare)
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Optical characterization of individual quantum dots
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1472-1475
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Tidskriftsartikel (refereegranskat)abstract
- Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.
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| 16. |
- Högberg, Hans, et al.
(författare)
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beta-Ta and alpha-Cr thin films deposited by high power impulse magnetron sputtering and direct current magnetron sputtering in hydrogen containing plasmas
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 3-8
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of beta-Ta and alpha-Cr were deposited on Si(1 0 0) and 1000 angstrom SiO2/Si(1 0 0), by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dcMS) in hydrogen-containing plasmas. The films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy, elastic recoil detection analysis, and four-point probe measurements. The results showed that 001-oriented beta-Ta films containing up to similar to 8 at% hydrogen were obtained with HiPIMS, albeit with no chemical shift evident in XPS. The 110 oriented alpha-Cr films display a hydrogen content less than the detection limit of 1 at%, but H-2 favors the growth of high-purity films for both metals. The beta-Ta films deposited with dcMS are columnar, which seems independent of H-2 presence in the plasma, while the films grown by HIPIMS are more fine-grained. The latter type of microstructure was present for the alpha-Cr films and found to be independent on choice of technique or hydrogen in the plasma. The beta-Ta films show a resistivity of similar to 140-180 mu Omega cm, while alpha-Cr films exhibit values around 30 mu Omega cm; the lowest values obtained for films deposited by HiPIMS and with hydrogen in the plasma for both metals.
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| 17. |
- Jena, Ambika Prasad, et al.
(författare)
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Study of disorder-order transitions in Fe(x)Al(1-x) binary alloys using the augmented space recursion based orbital peeling technique
- 2011
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:20, s. 3810-3815
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Tidskriftsartikel (refereegranskat)abstract
- In this communication we propose a method for the study of disorder-order transitions in Fe(x)Al(1-x) binary alloys. We turn to our earlier development [1] of a combination of the recursion method introduced by Haydock et al. [2] and our augmented space approach [3] with the orbital peeling technique proposed by Burke [4] to determine the small energy differences required in obtaining the pair energies which go as input to the generalized perturbation technique [5] of studying disorder-order transitions.
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| 18. |
- Karlsson, K. Fredrik, et al.
(författare)
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Polarized emission and excitonic fine structure energies of InGaN quantum dots
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1553-1555
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Tidskriftsartikel (refereegranskat)abstract
- The linear polarization of the excitonic emission from quantum dot-like potential minima formed in a thin InGaN layer is investigated. The recorded emission lines exhibit significant intensity linearly polarized along the wurtize c-axis. For many of the studied spectra, the excitonic fine-structures were resolved, revealing energy splittings in the order of ∼200 μeV.
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| 19. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Comparative PL study of individual ZnO nanorods, grown by APMOCVD and CBD techniques
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1538-1542
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Tidskriftsartikel (refereegranskat)abstract
- The photoluminescence properties of individual ZnO nanorods, grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCV) and chemical bath deposition (CBD) are investigated by means of temperature dependent micro-PL. It was found that the low temperature PL spectra are driven by neutral donor bound exciton emission (DX)-X-0, peaked at 3.359 and 3.363 eV for APMOCVD and CBD ZnO nanorods, respectively. The temperature increase causes a red energy shift of the peaks and enhancement of the free excitonic emission (FX). The FX was found to dominate after 150 K for both samples. It was observed that while APMOCVD ZnO nanorods possess a constant low signal of visible deep level emission with temperature, the ZnO nanorods grown by CBD revealed the thermal activation of deep level emission (DLE) after 130 K. The resulting room temperature DLE was a wide band located at 420-550 nm. The PL properties of individual ZnO nanorods can be of importance for their forthcoming application in future optoelectronics and photonics.
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| 20. |
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| 21. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Morphology engineering of ZnO nanostructures
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1533-1537
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Tidskriftsartikel (refereegranskat)abstract
- Nanosized ZnO structures were grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD) in the temperature range 200-500 degrees C at variable precursor pressure. Temperature induced evolution of the ZnO microstructure was observed, resulting in regular transformation of the material from conventional polycrystalline layers to hierarchically arranged sheaves of ZnO nanowires. The structures obtained were uniformly planarly located over the substrate and possessed as low nanowires diameter as 30-45 nm at the tips. The observed growth evolution is explained in terms of ZnO crystal planes free energy difference and growth kinetics. For comparison, the convenient growth at constant precursor pressure on Si and SiC substrates has been performed, resulting in island-type grown ZnO nanostructures. The demonstrated nanosized ZnO structures may have unique possible areas of application, which are listed here.
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| 22. |
- Khranovskyy, Volodymyr, et al.
(författare)
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Photoluminescence study of basal plane stacking faults in ZnO nanowires
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 50-53
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the photoluminescence (PL) of ZnO nanowires (NWs) containing a high density (similar to 1 x 10(6) cm(-1)) of basal plane stacking faults (BSFs). It was observed that the BSFs result in a specific PL peak at similar to 3.329 eV along with a donor bound excitonic emission (D degrees X) peak at 5 K. The observed BSF-related emission is of excitonic type and possesses longer PL lifetime than D degrees X (similar to 360 ps vs. similar to 70 ps). Via comparison of the microstructural and the PL properties of the ZnO NWs, it is shown that the observed BSF-related emission is due to the formation of crystal phase quantum wells (QWs). This is explained by the fact that BSF in wurtzite (WZ) ZnO is the thinnest segment of zinc blende (ZB) phase ZnO inserted in the WZ matrix, resulting in band alignment of type II due to the conduction and valence band offsets of ZB with respect to WZ ZnO. The mechanism of the BSF related PL is suggested to be an indirect exciton transitions clue to the recombination of electrons confined in the ZB QWs to holes in the WZ barriers localized near the BSFs.
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| 23. |
- Kumar, Mukesh, et al.
(författare)
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Structural, electronic and optical properties of silver delafossite oxides : A first-principles study with hybrid functional
- 2013
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 422, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Ternary delafossite compounds are potential materials for optoelectronic devices. Employing a first-principles method, we calculate the structural, electronic, and optical properties of the silver based compounds AgMO2 (M=Al, Ga or In), which crystallize in delafossite structure. Our calculations show that these AgMO2 oxides have indirect band gaps and the gap energies are in the region of 1.6-3.0 eV whereas, the lowest direct band gap energies are estimated in the range of 2.6-4.3 eV. Furthermore, we find that AgMO2 compounds exhibit a strong anisotropy for the dielectric function and absorption spectra. The absorption onset for these compounds occurs well above the band gap energies. Overall, we show that the hybrid functional improves the lattice parameters and band gap energies and the calculated values are in good agreement with the experimental values.
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| 24. |
- Markevich, V.P., et al.
(författare)
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Reconfigurations and diffusion of trivacancy in silicon
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 107:15, s. 2974-2977
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Tidskriftsartikel (refereegranskat)abstract
- Disappearance of the divacancy (V2) and trivacancy (V3) complexes upon isochronal and isothermal annealing of electron irradiated Si:O crystals has been studied by means of deep level transient spectroscopy. The annealing studies have shown that the V2 and V3 defects are mobile in Si at T>200 °C and in oxygen-rich material are trapped by interstitial oxygen atoms so resulting in the appearance of V2O and V3O defects. The activation energies for diffusion of the V2 and V3 centers have been determined. Density functional modeling calculations have been carried out to investigate the migration and reorientation mechanisms of V3 in large silicon supercells. It is proposed that these comprise a sequence of transformations between V3(D3) and V3(C2v) configurations.
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| 25. |
- Mohseni, Seyed Majid, et al.
(författare)
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Magnetic droplet solitons in orthogonal nano-contact spin torque oscillators
- 2014
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 435, s. 84-87
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Tidskriftsartikel (refereegranskat)abstract
- We study microwave signal generation as a function of drive current and applied perpendicular magnetic field in nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has strong easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The orthogonal NC-STOs exhibit a dramatic transition from the conventional ferromagnetic resonance-like spin wave mode to a magnetic droplet soliton mode. In particular, the field and current dependence of the droplet soliton near threshold are discussed. Near threshold the droplet soliton undergoes complex dynamics that include mode hopping, as evident in the experimental frequency domain and magnetoresistance response. © 2013 Elsevier B.V.
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| 26. |
- Nur, Omer, et al.
(författare)
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Effect of elevated concentrations of strontium and iron on the structural and dielectric characteristics of Ba(1-x-y)Sr(x)Ti Fe(y)O3 prepared through sol-gel technique
- 2012
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:14, s. 2697-2704
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Tidskriftsartikel (refereegranskat)abstract
- Nano-composite Ba1-xSr(x)TiO3 (BST), where x=0.01-0.50 and doped with different concentrations of iron Ba(1-x-y)Sr(x)TiFe(y)O3 (BSTF), where x=0.01 and y=0.01-0.05 powders were prepared by sol-gel method. The effect of increasing the iron and strontium concentrations substituted in Barium strontium titanate system will be studied. The prepared samples have a tetragonal crystalline phase after sintering for 1 h at 750 degrees C in air. The structural and the morphological features of the systems have been studied using X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). The dielectric properties of the BST and BSTF systems have been investigated as a function of temperature and frequency. The dielectric measurements are carried out in the frequency range 42 Hz-1 MHz, at a temperature ranging between 25 and 250 degrees C. The results showed a decrease in T-c temperature giving the following values 90 and 85 degrees C for B10ST and B10ST5F prepared powder samples, respectively, implying tetragonal, feroelectric phase at lower temperature into cubic, para-electric phase at temperature higher than T-c.
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| 27. |
- Pal, P., et al.
(författare)
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Resonant photoemission spectroscopy studies of the magnetic phase transitions in Pr(0.5)Sr(0.5)MnO(3)
- 2011
-
Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:18, s. 3519-3523
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Tidskriftsartikel (refereegranskat)abstract
- The valence band electronic structure of Pr(0.5)Sr(0.5)MnO(3) has been investigated using resonant photoemission spectroscopies across its paramagnetic metallic (PMM)-ferromagnetic metallic (FMM)-antiferromagnetic insulator (AFMI) transition. Using bulk sensitive soft X-ray photoemission, we have confirmed the presence of a gap in the near Fermi level electronic spectrum in the charge ordering (CO) antiferromagnetic insulator (AFMI) phase. The Fermi level exhibits a rigid-band-like shift of about similar to 0.4 eV across the PMM to AFMI transition. Further, we have observed a similar shift of the Pr 4f states to higher binding energies when the sample goes to the CO-AFMI state. The spectral behavior indicates a strong charge carrier localization associated with a charge-density-wave gap related to the CO. On the other hand, the growth of spectral weight at the Fermi level in the PMM state could well be connected to the microscopic phase-separation model. (C) 2011 Elsevier B.V. All rights reserved.
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| 28. |
- Pal, Prabir, et al.
(författare)
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Resonant photoemission spectroscopy studies of the magnetic phase transitions in Pr0.5Sr0.5MnO3
- 2011
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 406:18, s. 3519-3523
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Tidskriftsartikel (refereegranskat)abstract
- The valence band electronic structure of Pr0.5Sr0.5MnO3 has been investigated using resonant photoemission spectroscopies across its paramagnetic metallic (PMM)-ferromagnetic metallic (FMM)-antiferromagnetic insulator (AFMI) transition. Using bulk sensitive soft X-ray photoemission, we have confirmed the presence of a gap in the near Fermi level electronic spectrum in the charge ordering (CO) antiferromagnetic insulator (AFMI) phase. The Fermi level exhibits a rigid-band-like shift of about similar to 0.4 eV across the PMM to AFMI transition. Further, we have observed a similar shift of the Pr 4f states to higher binding energies when the sample goes to the CO-AFMI state. The spectral behavior indicates a strong charge carrier localization associated with a charge-density-wave gap related to the CO. On the other hand, the growth of spectral weight at the Fermi level in the PMM state could well be connected to the microscopic phase-separation model. (C) 2011 Elsevier B.V. All rights reserved.
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| 29. |
- Pardo, Helena, et al.
(författare)
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Raman characterization of bulk ferromagnetic nanostructured graphite
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 407:16, s. 3206-3209
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectroscopy was used to characterize bulk ferromagnetic graphite samples prepared by controlled oxidation of commercial pristine graphite powder. The G:D band intensity ratio, the shape and position of the 2D band and the presence of a band around 2950 cm(-1) showed a high degree of disorder in the modified graphite sample, with a significant presence of exposed edges of graphitic planes as well as a high degree of attached hydrogen atoms.
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| 30. |
- Rahaman, Moshiour, et al.
(författare)
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Study of optical response in disordered alloys using the generalized recursion in augmented space : Application to ferromagnetic FeCo alloy
- 2011
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 406:11, s. 2121-2125
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Tidskriftsartikel (refereegranskat)abstract
- We propose and briefly describe the generalized recursion in augmented space using a minimal TB-LMTO basis set for the calculation of configuration averaged current response functions in disordered binary alloys. Since disorder in the current terms is off-diagonal and non-separable, single-site mean-field approaches are unable to deal with it without further approximations. The augmented space approach is ideally suited for such situations and the generalized recursion proposed by Viswanath and Muller provides a fast and accurate O(N) technique for the actual calculations of the configuration averaged susceptibilities. We have applied the method to the disordered FeCo alloy. The results agree reasonably well with available experimental data on ordered versions of both the alloy systems, with extra broadening due to disorder induced lifetime effects.
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| 31. |
- Serenkov, I.T., et al.
(författare)
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Structural distortions induced during stress relaxation affecting electrical transport of nanometer-thick La0.67(Ba,Ca)0.33MnO3 films
- 2010
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 404:23-24, s. 5234-5236
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction (XRD) and medium-energy ion scattering (MEIS) were used to clarify distortions induced during mechanical stress relaxation in nanometer-thick epitaxial La0.67Ba0.33MnO3 (LBMO) and La0.67Ca0.33MnO3 (LCMO) films fabricated by pulsed laser deposition. It follows from measured XRD and MEIS spectra that LBMO films grown on mismatched LaAlO3 were partly relaxed in the main part of the film, leaving about 4 nm heavily strained portion close to the interface. The critical thickness of LCMO films grown on LaAlO3 substrates was several times larger than that of LBMO due to a better match in lattice parameters. Electro- and magneto-transport parameters of nanometer-thick manganite films grown on mismatched substrates differed markedly from those of LBMO and LCMO layers nucleated and grown on well-matched ones because of non-stoichiometry, biaxial mechanical stresses, and phase separation. The resistivity ρ of manganite films grown coherently at a substrate with small mismatch obeyed the relation ρ=ρ1+ρ2(H)T4.5 at temperatures well below the Curie point. Parameter ρ1 was temperature T and magnetic field H independent while ρ2 was temperature independent but decreased linearly with increasing H.
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| 32. |
- Sinha, T. P., et al.
(författare)
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Electronic structure and optical properties of ordered compounds potassium tantalate and potassium niobate and their disordered alloys
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 407:24, s. 4615-4621
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Tidskriftsartikel (refereegranskat)abstract
- The electronic energy band structure, site and angular momentum decomposed density of states (DOS) of cubic perovskite oxides KNbO 3 and KTaO 3 have been obtained from a first principles density functional based full potential linearized augmented plane wave (FLAPW) method within a generalized gradient approximation (GGA). The total DOS in valence region is compared with the experimental photo-emission spectra (PES). The calculated DOS is in good agreement with the experimental energy spectra and the features in the spectra are interpreted by comparison with the projected density of states (PDOS). The valence band PES is mainly composed of Nb-4d/Ta-5d and O 2p states in KNbO 3 and KTaO 3, respectively. Using the PDOS and the band structure we have analyzed the inter-band contribution to the optical properties of these materials. The real and imaginary parts of the dielectric function have been calculated and compared with experimental data. They are found to be in a reasonable agreement. The role of band structure on the optical properties have been discussed.
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| 33. |
- Smolentsev, Nikolay, et al.
(författare)
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Local atomic structure around Mn ions in GaN:Mn thin films: Quantitative XANES analysis
- 2011
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 406:14, s. 2843-2846
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Tidskriftsartikel (refereegranskat)abstract
- GaN:Mn dilute magnetic semiconductors with zinc-blende type of lattice and room temperature ferromagnetism were investigated by the X-ray absorption near edge structure (XANES) with a high accuracy approach of the multidimensional interpolation, which makes it possible to determine the nanoscale local atomic structure around Mn impurities. It is found that Mn atoms are substantially incorporated into the GaN lattice and Jahn-Teller distortion around Mn atom is observed. Our results show that symmetry changes around Mn atom influence on XANES spectrum significantly. Furthermore, the possible impact of local distortions on the magnetic properties is discussed. (C) 2011 Elsevier B.V. All rights reserved.
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| 34. |
- Strobl, Markus, et al.
(författare)
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Using a grating analyser for SEMSANS investigations in the very small angle range
- 2012
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 407:21, s. 4132-4135
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Tidskriftsartikel (refereegranskat)abstract
- Spin-echo modulation small-angle neutron scattering (SEMSANS) is based on the detection of spatial beam modulation, which is induced by triangular spin echo precession regions and subsequent spin analyses. In order to detect such signal and exploit it for small angle scattering investigations neutron detection with sub-millimeter spatial resolution is required. Here an approach is reported where instead of a position sensitive detector an absorption grating is used to analyze the beam modulation stepwise. The spin-echo length scan in this case is performed by varying the sample-to-detector distance. The real space correlation functions of reference sample structures in the range 10(2) nm, i.e. giving rise to small-angle scattering in the very small-angle range, are recorded and analyzed successfully. (C) 2012 Elsevier B.V. All rights reserved.
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| 35. |
- Tassin, Philippe, 1982, et al.
(författare)
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Effective material parameter retrieval for thin sheets: Theory and application to graphene, thin silver films, and single-layer metamaterials
- 2012
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 407:20, s. 4062-4065
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Konferensbidrag (refereegranskat)abstract
- An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media.
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| 36. |
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| 37. |
- Yakimova, Rositsa, et al.
(författare)
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Morphological and electronic properties of epitaxial graphene on SiC
- 2014
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Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 439, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H-SiC (0 0 0 1), 6H-SiC (0 0 0 1), and 3C-SiC (1 1 1) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C-SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces, It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C-SiC (1 1 1) is also reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at similar to 4.5 eV and the free-charge carrier scattering time, on the other are established It is shown that the interface structure on the Si- and C-polarity of the 3C-SiC (1 1 1) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene. (C) 2014 Elsevier B.V. All rights reserved
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| 38. |
- Zhang, Renyun, et al.
(författare)
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Single layer porous gold films grown at different temperatures
- 2010
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 405:21, s. 4517-4522
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Tidskriftsartikel (refereegranskat)abstract
- Large area porous gold films can be used in several areas including electrochemical electrodes, as an essential component in sensors, or as a conducting material in electronics. Here, we report on evaporation induced crystal growth of large area porous gold films at 20, 40 and 60 °C. The gold films were grown on liquid surface at 20 °C, while the films were grown on the wall of beakers when temperature increased to 40 and 60 °C. The porous gold films consisted of a dense network of gold nanowires as characterized by TEM and SEM. TEM diffraction results indicated that higher temperature formed larger crystallites of gold wires. An in situ TEM imaging of the coalescence of gold nanoparticles mimicked the process of the growth of these porous films, and a plotting of the coalescence time and the neck radius showed a diffusion process. The densities of these gold films were also characterized by transmittance, and the results showed film grown at 20 °C had the highest density, while the film grown at 60 °C had the lowest consistent with SEM and TEM characterization. Electrical measurements of these gold films showed that the most conductive films were the ones grown at 40 °C. The conductivities of the gold films were related to the amount of contamination, density and the diameter of the gold nanowires in the films. In addition, a gold film/gold nanoparticle hybrid was made, which showed a 10% decrease in transmittance during hybridization, pointing to applications as chemical and biological sensors. © 2010 Elsevier B.V. All rights reserved.
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