| 1. |
- Abbas, Ghazanfar, et al.
(författare)
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Electrochemical investigation of mixed metal oxide nanocomposite electrode for low temperature solid oxide fuel cell
- 2017
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Ingår i: International Journal of Modern Physics B. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 0217-9792. ; 31:27
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Tidskriftsartikel (refereegranskat)abstract
- Zinc-based nanostructured nickel (Ni) free metal oxide electrode material Zn-0.60/CU0.20Mn0.20 oxide (CMZO) was synthesized by solid state reaction and investigated for low temperature solid oxide fuel cell (LTSOFC) applications. The crystal structure and surface morphology of the synthesized electrode material were examined by XRD and SEM techniques respectively. The particle size of ZnO phase estimated by Scherer's equation was 31.50 nm. The maximum electrical conductivity was found to be 12.567 S/cm and 5.846 S/cm in hydrogen and air atmosphere, respectively at 600 degrees C. The activation energy of the CMZO material was also calculated from the DC conductivity data using Arrhenius plots and it was found to be 0.060 and 0.075 eV in hydrogen and air atmosphere, respectively. The CMZO electrode-based fuel cell was tested using carbonated samarium doped ceria composite (NSDC) electrolyte. The three layers 13 mm in diameter and 1 mm thickness of the symmetric fuel cell were fabricated by dry pressing. The maximum power density of 728.86 mW/cm(2) was measured at 550 degrees C.
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| 2. |
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| 3. |
- Almbladh, Carl-Olof, et al.
(författare)
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Variational total energies from Phi and Psi derivable theories
- 1999
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 13, s. 535-540
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Tidskriftsartikel (refereegranskat)abstract
- The old variational functional for the total energy of a many-electron system proposed by Luttinger and Ward (LW) in 1960 is here tested on the electron gas at the level of the GW approximation. Using a simple non-interacting Green function to evaluate the fuctional we obtain a correlation energy very close to that of a fully self-consistent $GW$ calculation which, in turn, is very close to that of an elaborate Monte-Carlo calculation. Encouraged by this success we have gone beyond the LW theory and constructed a new functional $Psi[G,W]$ having the Green's function $G$ and the screened interaction $W$ as two completely independent variables. The electronic self-energy $Sigma$ and the irreducible polarizability $P$ obtains from $Psi$ as functional derivatives with respect to $G$ and $W$. The new $Psi$ functional allows for an even simpler way of obtaining accurate correlation energies and, at the $GW$ level, alredy a non-interacting $G$ and a simple plasmon-pole approximation to $W$ gives almost the same correlation energy as before.
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| 4. |
- Bartkowiak, M., et al.
(författare)
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High-Density Expansion for the Spinless Fermion Model I : First Order in 1/z and Horwitz-Callen Renormalization
- 1988
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Ingår i: International Journal of Modern Physics B. - : World Scientific Publishing. - 0217-9792. ; 2:03-04, s. 483-520
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Tidskriftsartikel (refereegranskat)abstract
- A diagrammatic technique for Hubbard's operators is employed to perform systematically the high-density expansion for the three-dimensional spinless fermion model. The molecular field theory is obtained by the zero-order renormalization of blocks. Summation of the first order diagrams is carried out in both selfconsistent and correctional way. It turns out that the charge ordering parameter, calculated self-consistently, has a jump for a certain medial temperature. We have also shown, that the Horwitz-Callen renormalization leads to the first or second order phase transition, depending on t/W and fails when this ratio is large enough. The phase diagrams of the system for the half-filled band case, derived in both unrenormalized and renormalized first order of high-density expansion are presented.
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| 5. |
- Bartkowiak, M., et al.
(författare)
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High-Density Expansion for the Spinless Fermion Model II : Second and Third Order in 1/z
- 1988
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Ingår i: International Journal of Modern Physics B. - : World Scientific Publishing. - 0217-9792. ; 2:03-04, s. 521-536
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Tidskriftsartikel (refereegranskat)abstract
- The selfconsistent high-density expansion for thermodynamic quantities of the quantum spin-polarized fermion lattice gas, derived in the preceding paper, is extended to higher orders. The (1/z)2terms in the free energy are evaluated by summing two-loop diagrams and the corresponding equation for critical temperature in the classical limit is discussed. Ground state phase diagram of the system for arbitrary electron density is derived in the first and second order of the expansion. Properties of the half-filled, one-dimensional spinless fermion model at T = 0, obtained here in the first three orders in 1/z, are compared with the results of exact calculations and of other approximate methods. This provides a test for the unrenormalized high-density expansion method.
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| 6. |
- Bartkowiak, M, et al.
(författare)
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High-Density Expansion for the Spinless Fermion Model III : Green-Functions
- 1990
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Ingår i: International Journal of Modern Physics B. - SINGAPORE : World Scientific Publishing. - 0217-9792. ; 4:13, s. 2025-2040
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Tidskriftsartikel (refereegranskat)abstract
- The single-particle electron Green's function and the charge-fluctuation Green's function for the spin-polarized fermion lattice gas are calculated within the framework of the high-density expansion up to the first order in 1/z. Violation of some conditions of consistency of diagrammatic perturbation expansion approximation schemes are discussed. Relations between the Green's functions and corresponding approximate free energy are established. Two kinds of approximations for Green's functions for the charge ordered phase are constructed and applied to determine the band structure of the spinless fermion model. The Green's functions for the nonordered phase are used to study the phase diagram of the model for finite temperatures and arbitrary band filling.
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| 7. |
- Bjurenstedt, Anton, 1979-, et al.
(författare)
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On the complexity of the relationship between microstructure and tensile properties in cast aluminum
- 2015
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 29:10-11
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between microstructure and mechanical properties in cast aluminium alloys is very complex. This relationship is also strongly affected by the casting process and melt handling. In the current study the mechanical properties were investigated and correlated with microstructural features such as porosity, Fe-rich particles, SDAS, Si-length. Process quality measures such as bifilm index, density index, and sludge factor were also investigated. The aim of the work was to understand the critical interactions between material microstructure and process quality in the development of high performance materials.
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| 8. |
- Borkar, Hemant, 1982-, et al.
(författare)
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Microstructure analysis of Al-Si-Cu alloys prepared by gradient solidification technique
- 2015
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 29:10-11
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Tidskriftsartikel (refereegranskat)abstract
- Al–Si–Cu alloys were cast with the unique gradient solidification technique to producealloys with two cooling rates corresponding to secondary dendrite arm spacing (SDAS) of ∼9 and ∼27 μm covering the microstructural fineness of common die cast components.The microstructure was studied with optical microscopy and scanning electronmicroscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electronbackscattered diffraction (EBSD). The alloy with higher cooling rate, lower SDAS, hasa more homogeneous microstructure with well distributed network of eutectic and intermetallicphases. The results indicate the presence of Al–Fe–Si phases, Al–Cu phases andeutectic Si particles but their type, distribution and amount varies in the two alloys withdifferent SDAS. EBSD analysis was also performed to study the crystallographic orientationrelationships in the microstructure. One of the major highlights of this study is theunderstanding of the eutectic formation mechanism achieved by studying the orientationrelationships of the aluminum in the eutectic to the surrounding primary aluminumdendrites.
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| 9. |
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| 10. |
- Dahlen, Nils-Erik
(författare)
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Effect of electron correlation on the two-particle dynamics of a helium atom in a strong laser pulse
- 2002
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 16:3, s. 415-452
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Forskningsöversikt (refereegranskat)abstract
- This review discusses the complicated two-electron dynamics of a helium atom in an intense, short laser pulse. A helium gas in femtosecond laser pulses at long wave lengths (lambda similar to 700 nm) and high intensities (I similar to 10(15) W/cm(2)) produces surprisingly high numbers of He2+ ions. These laser fields cause large and fast electron oscillations, which makes a solution of the time-dependent Schrodinger equation numerically demanding. The system can be studied using a one-dimensional model atom, which has many of the same properties as the He atom. Using the one-dimensional model, the importance of including electron correlation in a simplified description of the two-electron dynamics is demonstrated. It is shown that electron correlation becomes much less important if the laser field has a short wave length, in which case the electron oscillations are smaller and slower. The problem of including electron correlation in the calculations is discussed in terms of approaches such as time-dependent Hartree-Fock, time-dependent density functional theory and time-dependent extended Hartree-Fock. Some of the commonly used semi-classical models for describing the double-ionization process are presented.
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| 11. |
- De Woul, Jonas, et al.
(författare)
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Fermions in Two Dimensions, Bosonization, and Exactly Solvable Models
- 2012
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 26:22, s. 1244005-
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Forskningsöversikt (refereegranskat)abstract
- We discuss interacting fermion models in two dimensions, and, in particular, such that can be solved exactly by bosonization. One solvable model of this kind was proposed by Mattis as an effective description of fermions on a square lattice. We review recent work on a specific relation between a variant of Mattis' model and such a lattice fermion system, as well as the exact solution of this model. The background for this work includes well-established results for one-dimensional systems and the high-T c problem. We also mention exactly solvable extensions of Mattis' model.
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| 12. |
- Garg, K B, et al.
(författare)
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A comparative study of oxygen loss on in situ heating in PrMnO3 and BaMnO3
- 2011
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 25:9, s. 1235-1250
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Tidskriftsartikel (refereegranskat)abstract
- We have thoroughly investigated the Oxygen loss in PrMnO3 and BaMnO3 the end members of the AMnO(3) system, on in situ heating in a reducing at This was done to drive some oxygen out from them and thus possibly alter the valence of the Mn cation. Sample characterization was done through X-ray diffraction and SEM measurements. The core-level photoemission point to oxygen loss from only BaMnO3 changing some of Mn4+ to Mn3+ in it, transfer of some spectral weight to the highly localized Fehrenbacher-Rice states and an increased Mn 3d-O 2p hybridization. Magnetization measurements show that at low temperatures, the samples depict a canted antiferromagnetic ordering.
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| 13. |
- Garg, K. B., et al.
(författare)
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Mechanism of quenching of superconductivity in the YBa2Cu3O7-delta system on substitution of Zn for Cu
- 2010
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 24:14, s. 2135-2148
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Tidskriftsartikel (refereegranskat)abstract
- Substituting Zn for Cu is known to rapidly quench superconductivity in the doped perovskites but the mechanism behind it is still not clearly understood. Single phase YBa2(Cu1-xZnx)(3)O7-delta (x=0.0 to 0.06) samples were synthesized and characterized using XRD, wet titration, resistivity, and ac susceptibility. Angle-integrated Valence Band Photo emission and Zn K-edge XAFS results clearly show that their oxygen stoichiometry (delta) changes on Zn substitution, there by adversely affecting the density of free charge carriers and hence the normal state resistivity and the T-c. However, the observed changes in the two happen to be too large to be accounted for solely on the basis of changes in the oxygen stoichiometry delta. We find that the Zn cation acts as a strong "impurity" scattering centre in the YBCO lattice and causes local lattice distortion (LLD). It consequently induces local magnetic moment, seen in our dc susceptibility measurements. It is thus a composite of (Delta delta), LLD and possibly also magnetic pair-breaking that is responsible for the rapid quenching of the super conductivity observed with Zn doping in this system.
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| 14. |
- Haindl, S., et al.
(författare)
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Lessons from oxypnictide thin films
- 2013
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 27:4, s. 1330001-
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Forskningsöversikt (refereegranskat)abstract
- First experiments on the growth of oxypnictide F-doped LaFeAsO thin films indicated an incomplete normal-to-superconducting transition and offered a work programme challenging to overcome possible difficulties in their fabrication. In this regard the possibility of an all in-situ epitaxial growth appeared to be a matter of time and growth parameters. The following review clarifies that F-doped oxypnictide thin films are extremely difficult to grow by in-situ PLD due to the formation of very stable impurity phases such as oxyfluorides (LaOF) and oxides (La2O3) and the loss of stoichiometry possibly due to incongruent evaporation of the target or re-evaporation of volatile elements at the substrate surface. However, the review also demonstrates that the employed two-step fabrication process for oxypnictide thin films has been successfully applied in the preparation of clean polycrystalline as well as of epitaxial thin films. Fundamental investigations on the upper critical field, its temperature dependence and its anisotropy contributed to an understanding of multiband superconductivity in oxypnictides.
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| 15. |
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| 16. |
- Hussain, Fida, et al.
(författare)
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A modeling approach for low-temperature SOFC-based micro-combined heat and power systems
- 2019
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Ingår i: International Journal of Modern Physics B. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 0217-9792. ; 33:4
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Tidskriftsartikel (refereegranskat)abstract
- The world's challenge is to determine a more efficient, economical and environmental-friendly energy source to compete and replace the ongoing conventional energy resources. Solid oxide fuel cells (SOFCs) provide a highly efficient system to use divergent energy resources and have proved to provide the cleanest energy, least energy use, and lowest emissions. A techno-economic study is required to investigate the model design for SOFC-based micro-combined heat and power (m-CHP) systems for applications in terms of educational and commercial buildings. This work models and explores the optimized application of hydrogen gas-fueled SOFC-based m-CHP systems in educational buildings. Two educational departments' loads are presented and model of SOFC-based m-CHP system against the different electric power demands is performed, in order to provide a techno-economic assessment of the technology. For successful development of the technology, results are related to system rightsizing, operating strategies, thermal to electric ratios, and match between end-use, with an aim towards classifying the overall feasibility and essential application requirements.
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| 17. |
- Karlsson, Krister, 1961-, et al.
(författare)
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Core level chemical shifts and line shapes for systems with different valencies and Cu-O networks
- 2000
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Ingår i: International Journal of Modern Physics B. - : World Scientific. - 0217-9792 .- 1793-6578. ; 14:32, s. 3791-3830
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the Cu-2p core level photoemission spectrum of a variety of cuprates, mainly focusing on the chemical shift and the shape of the leading peak. The spectra are calculated using the Anderson impurity model and we obtain a very good agreement with the experimental data. We find that the shape of the leading peak depends crucially on the structure of the Cu-O network. The main peak turns out to be quite narrow if the network consists of Cu-O-Cu bond angels of the order of 90°. On the other hand, if the Cu-O atoms are arranged with bond angles of approximately 180°, the main peak becomes substantially broader and contains a rather complicated structure. However, in some cases it is not sufficient only to consider the Cu-O network because interactions with other atoms are also important. In the model compounds Cu2O, CuO and NaCuO2, where Cu is formally monovalent, divalent and trivalent, respectively, we find that the number of 3d electrons is rather similar. Nevertheless, the binding energy increases with the valence as expected from chemical intuition. The spectra exhibit a large variation in the strength of the d9-like satellite and in the width of the main line. We, furthermore, study the chemical shift of three inequivalent Cu atoms in YBa2Cu3O6.5, and compare the results with the model compounds, which suggests that the different Cu atoms in YBa2Cu3O6.5 have formal valences of approximately one, two and three. These findings are analyzed and related to the formal valence.
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| 18. |
- Karlsson, Krister, et al.
(författare)
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Exchange-correlation kernel in time-dependent density functional theory derived from many-body theory
- 2004
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Ingår i: International Journal of Modern Physics B. - : World Scientific. - 0217-9792. ; 18:7, s. 1055-1067
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Tidskriftsartikel (refereegranskat)abstract
- We derive a simplified Bethe–Salpeter equation for calculating optical absorption based on the assumption of a local electron–hole interaction. The original four-point equation for the kernel is reduced to a two-point one. A connection to the exchange–correlation kernel in time-dependent density functional theory can be established. The resulting fxc is found to be -W/2 where W contains only the short-range (local) part of the Coulomb screened interaction. This simple approximation was successfully applied to optical absorption spectra of some excitonic crystals, reproducing not only the continuum excitons but also the bound ones.
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| 19. |
- Karlsson, Krister
(författare)
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Vertex corrections and time-dependent GW approximation
- 2004
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Ingår i: International Journal of Modern Physics B. - : World Scientific. - 0217-9792. ; 18:26, s. 3381-3397
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Tidskriftsartikel (refereegranskat)abstract
- In a many-body perturbation treatment of electronic excitations, one has to solve the so-called Bethe–Salpeter equation (BSE) for the kernel (vertex) describing the interaction between electrons. In general, the BSE exhibits a non-local and frequency-dependent screened interaction and consequently it is extremely difficult to solve. We have developed a scheme that solves the BSE equation iteratively, including dynamically screening, by considering the change in the electron self-energy upon applying a time-dependent field. The BSE is obtained from the self-energy in the GW approximation (GWA) using the Schwinger functional technique. We apply our formalism to a simple model system and discuss briefly changes in the charge response, when dynamical screening is taken into account.
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| 20. |
- Kawabata, Shiro, et al.
(författare)
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TWO-DIMENSIONAL MACROSCOPIC QUANTUM DYNAMICS IN YBCO JOSEPHSON JUNCTIONS
- 2009
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 23:20-21, s. 4329-
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically study classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a YBa2Cu3O7-δ(YBCO) Josephson junction coupled with an LC circuit. The TA and MQT escape rate are calculated by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling leads to the slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson junctions.
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| 21. |
- Luo, Wei, et al.
(författare)
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NANOLAYERED MAX PHASES FROM ab initio CALCULATIONS
- 2008
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 22:25-26, s. 4495-4499
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Tidskriftsartikel (refereegranskat)abstract
- The advancement in new materials processing and fabrication techniques has made it possible to better control the atomistic level of structures in a way, which was not feasible only a decade ago. If one can couple this atomic control with a good understanding of the relationship between structure and properties, this will in the future lead to a significant contribution to the synthesizing of tailor-made materials. In this paper we have focused on, the structurally related nanolayered ternary compounds M(N+1)AX(N), (MAX) where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N, which has attracted increasing interest owing to their unique properties. The general relations between the electronic structure and materials properties of MAX phases have been elaborated based on ab initio calculations.
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| 22. |
- Malyarenko, Anatoliy, 1957-, et al.
(författare)
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Fractal planetary rings: energy inequalities and random field model
- 2017
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 31:30
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Tidskriftsartikel (refereegranskat)abstract
- This study is motivated by a recent observation, based on photographs from the Cassini mission, that Saturn’s rings have a fractal structure in radial direction. Accordingly, two questions are considered: (1) What Newtonian mechanics argument in support of such a fractal structure of planetary rings is possible? (2) What kinematics model of such fractal rings can be formulated? Both challenges are based on taking planetary rings’ spatial structure as being statistically stationary in time and statistically isotropic in space, but statistically nonstationary in space. An answer to the first challenge is given through an energy analysis of circular rings having a self-generated, noninteger-dimensional mass distribution [V. E. Tarasov, Int. J. Mod Phys. B 19, 4103 (2005)]. The second issue is approached by taking the random field of angular velocity vector of a rotating particle of the ring as a random section of a special vector bundle. Using the theory of group representations, we prove that such a field is completely determined by a sequence of continuous positive-definite matrix-valued functions defined on the Cartesian square F^2 of the radial cross-section F, where F is a fat fractal.
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| 23. |
- Mikhailov, Sergey
(författare)
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Edge magnetoplasmons for a new type of quantum-well microwave detector
- 2007
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 21:8-9, s. 1491-1496
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically study the wavelength and the propagation length of the edge magnetoplasmons (EMP's), running along the edge of a two-dimensional (2D) electron layer in a semiconductor quantum-well structure with and without metallic gates. We show that the metallic gate suppresses the propagation of the EMP's, but the quality factor of the wave (q'/q '', where q' and q '' are the real and imaginary parts of the complex EMP wavevector) can be larger in the gated structures as compared to the structures without the gate. The results may be useful for analysis of operation of the recently discovered microwave detectors and spectrometers operating at liquid nitrogen temperatures (Kukushkin et al., Appl. Phys. Lett. 86, 044101 (2005)).
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| 24. |
- Mikhailov, Sergey, et al.
(författare)
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Microwave response of a two-dimensional electron stripe: Electrodynamic effects and the influence of contacts
- 2007
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 21:8-9, s. 1497-1501
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Tidskriftsartikel (refereegranskat)abstract
- Microwave response of a two-dimensional (2D) electron stripe, supplied by two semi-infinite side contacts, is theoretically studied taking into account retardation and radiative effects. Absorption spectra of the stripe are calculated as a function of the microwave frequency omega, magnetic field B, parameters of the 2D electron gas and of the contacts. It is shown that the contacts substantially modify the position, the linewidth and the strength of the absorption resonances, leading for instance to the inversion of the absorption maxima of the right and left circularly polarized radiation in magnetic fields.
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| 25. |
- Mikhailov, Sergey
(författare)
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On the distribution of interacting fermions over single-particle quantum states
- 2007
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 21:10, s. 1729-1736
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Tidskriftsartikel (refereegranskat)abstract
- Using an exact diagonalization technique, we calculate the distribution of electrons n(nu) over single-particle quantum states in few-electron parabolic quantum dots. We show that n(nu) is a function of quantum numbers nu, but not of the energy of the states E-nu, n(nu) not equal n(E-nu). The common property n(nu) = n(E-nu) remains valid only if electron-electron interaction is neglected. For certain cases in the strong interaction regime, the occupation numbers of higher-energy levels may be larger than those of the lower-energy states: n(nu) > n(nu ') at E-nu > E-nu '.
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| 26. |
- Minnhagen, Petter, 1946-, et al.
(författare)
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The groundstates and phases of the two-dimensional fully frustrated XY model
- 2009
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Ingår i: International Journal of Modern Physics B. - Singapore : World Scientific. - 0217-9792. ; 23:20-21, s. 3939-3950
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Tidskriftsartikel (refereegranskat)abstract
- The 2D Fully Frustrated XY(FFXY) class of models is shown to contain a new groundstate in addition to the checkerboard groundstate of the standard 2D XY model. The spin configuration of this additional groundstate is obtained and its connection to a broken Z2-symmetry explained. This means that the class of 2D FFXY models belongs within a U(1) ⊗ Z2 ⊗ Z2-symmetry phase-transition representation. The phase diagram is reviewed and the central charges of the four multicritical points described. The implications for the standard 2D FFXY-model are discussed and elucidated, in particular with respect to the long standing controversy concerning the phase transitions of the standard 2D FFXY-model.
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| 27. |
- Peterson, Carsten
(författare)
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Determining Dependency structures and estimating nonlinear regression errors without doing regression
- 1995
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 6:4, s. 611-616
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Tidskriftsartikel (refereegranskat)abstract
- A general method is discussed, the δ-test, which establishes functional dependencies given a table of measurements. The approach is based on calculating conditional probabilities from data densities. Imposing the requirement of continuity of the underlying function the obtained values of the conditional probabilities carry information on the variable dependencies. The power of the method is illustrated on synthetic time-series with different time-lag dependencies and noise levels. For N data points the computational demand is N2. Also, the same method is used for estimating nonlinear regression errors and their distributions without performing regression. Comparing the predicted residual errors with those from linear models provides a signal for nonlinearity. The virtue of the method in the context of feedforward neural networks is stressed with respect to preprocessing data and tracking residual errors.
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| 28. |
- Sanyal, Biplab, et al.
(författare)
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Study of the electronic and structural properties of ZnO clusters
- 2010
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 24:17, s. 3297-3309
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic first-principle study of the structures, energetics and electronic structure of (ZnO)(n) clusters in the size range 1 <= n <= 12. We show that the planar ring structures are stable for n < 8, while spheroidal structures made out of rings of (ZnO)(3) and (ZnO)(2) are stable for n >= 8. We examine the binding energies and HOMO-LUMO gaps of the clusters and try to understand our results from simple physical ideas.
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| 29. |
- Vettchinkina, Valeria, et al.
(författare)
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The Monte Carlo method applied to carrier transport in Si/SiGe quantum wells
- 2005
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 19:21, s. 3353-3377
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Tidskriftsartikel (refereegranskat)abstract
- We present a complete Monte Carlo simulation of the transport properties of a Si/SiGe quantum well. The scattering mechanisms, viz. intervalley phonons, acoustic phonons, interface roughness and impurity scattering (including resonant scattering), are considered in detail, and we derive analytic expressions for the scattering rates, in each case properly taking the quantized electron wave functions into account. The numerically obtained distribution function is used to discuss the influence of each scattering mechanism for different electric fields applied parallel to the interfaces and also different temperatures.
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| 30. |
- Yuan, F., et al.
(författare)
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Effect of Pr doping on ferroelectric behaviors of Pb(Zr0.65Ti0.35)O-3
- 2008
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Ingår i: International Journal of Modern Physics B. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 0217-9792. ; 22:13, s. 2070-2081
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Tidskriftsartikel (refereegranskat)abstract
- Pr-doped Pb(Zr0.65Ti0.35)O-3 (Pb1-xPr (Zr0.65Ti0.35)(1-x)/O-4(3), PPZT) ceramic samples are prepared using conventional solid-state sintering method, and their structural, dielectric, ferroelectric, and piezoelectric properties are investigated, focusing on the effects of Pr-doping. Upon increasing Pr doping level x, a transition of the crystallographic structure from rhombohedral symmetry to tetrahedral and finally to pseudocubic symmetry is observed at x similar to 0.08. The detailed dielectric measurements present a clear indication of relaxor-like behaviors at x = 0.08, while the samples at x less than 0.08 offer slightly improved ferroelectric properties compared with pure Pb(Zr0.65Ti0.35)O-3. In spite of the dielectric relaxor behaviors induced by Pr-doping, both the ferroelectric and piezoelectric properties of PPZT are degraded at x = 0.08. The physics underlying the Pr-doping induced relaxor behaviors is then discussed.
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| 31. |
- Zhang, Zhibin, et al.
(författare)
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Formation of C54TiSi(2) on Si(100) using Ti/Mo and Mo/Ti bilayers
- 2002
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Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 16:1-2, s. 205-212
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Mo on the formation of C54 TiSi2 on Si (100) substrates is studied using crosssectional transmission electron microscopy. For a Ti/Mo bilayer on Si, the interfacial Mo film reacts with Ti and Si to form C40 (Mo,Ti)Si-2 at 550 degreesC. Crystal grains of metastable C40 TiSi2 and equilibrium C54 TiSi2 are found in the region near the interfacial (Mo,Ti)Si-2 layer due to the template phenomenon. Increasing the temperature to 600 degreesC leads to the growth of C54 TiSi2 throughout the film. No C49 grains can be detected. The findings confirm that the usual sequence for the formation of C54 TiSi2, i.e. the C49 TiSi2 forms first followed by a phase transition to the C54 TiSi2, is altered by the interposed Mo layer. For a Mo/Ti bilayer on Si, the surface Mo layer is found to be present sequentially in (Mo,Ti)(5)Si-3 at 550 degreesC, C49 (Mo,Ti)Si-2 at 600 degreesC and C54 (Mo,Ti)Si-2 at 650 degreesC. The bulk Ti beneath forms the C54 TiSi2 following the usual route through the C49-C54 phase transition. However, this transition is now enhanced, in comparison with the C54 TiSi2 formation with pure Ti, by the C54 (Mo,Ti)Si-2 atop that plays the role as a template precisely as the interfacial C40 (Mo,Ti)Si-2.
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