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“Electron acceleration by an intense short-pulse laser in underdense plasma”. Yu MY, Yu W, Chen ZY, Zhang J, Yin Y, Cao LH, Lu PX, Xu ZZ, Physics of plasmas 10, 2468 (2003). http://doi.org/10.1063/1.1572158
Abstract: Electron acceleration from the interaction of an intense short-pulse laser with low density plasma is considered. The relation between direct electron acceleration within the laser pulse and that in the wake is investigated analytically. The magnitude and location of the ponderomotive-force-caused charge separation field with respect to that of the pulse determine the relative effectiveness of the two acceleration mechanisms. It is shown that there is an optimum condition for acceleration in the wake. Electron acceleration within the pulse dominates as the pulse becomes sufficiently short, and the latter directly drives and even traps the electrons. The latter can reach ultrahigh energies and can be extracted by impinging the pulse on a solid target. (C) 2003 American Institute of Physics.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.115
Times cited: 41
DOI: 10.1063/1.1572158
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“Numerical modelling of gas discharge plasmas for various applications”. Bogaerts A, Gijbels R, Vacuum: surface engineering, surface instrumentation &, vacuum technology 69, 37 (2003). http://doi.org/10.1016/S0042-207X(02)00306-8
Abstract: Gas discharge plasmas are used for a wide range of applications. To improve our understanding about gas discharges, which is necessary to obtain good results in the various application fields, we perform numerical modelling of gas discharge plasmas. Various kinds of modelling approaches, for various types of gas discharges, are being used in our group. In this paper, some examples of this modelling work are outlined. (C) 2002 Elsevier Science Ltd. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.53
Times cited: 16
DOI: 10.1016/S0042-207X(02)00306-8
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“Structural characterization of nanostructured Ni3Al processed by inert gas condensation”. Yandouzi M, Pauwels B, Schryvers D, Van Swygenhoven H, Van Tendeloo G, Diffusion and defect data : solid state data : part A : defect and diffusion forum 213, 19 (2003)
Abstract: High-resolution transmission electron microscopy was performed on compacted Ni(3)Al nanostructured material prepared by the inert gas condensation technique. From electron diffraction data an incomplete L1(2) ordering of the crystallites is observed in the free particles as well as in the room temperature compacted samples. However, a completely ordered L1(2) structure with much bigger and well-defined crystallites exhibiting several defects is observed in material compacted and annealed at 773 K. Sharp crystallite boundaries as well as amorphous material and voids are observed in between crystallites in all samples, the former being dominant in the annealed material, the latter in the as-prepared one.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
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“A novel approach to analyse FTIR spectra of precipitates in boron-doped silicon”. de Gryse O, Vanhellemont J, Clauws P, Lebedev O, van Landuyt J, Simoen E, Claeys C, Physica: B : condensed matter
T2 –, 22nd International Conference on Defects in Semiconductors (ICDS-22), JUL 28-AUG 01, 2003, UNIV AARHUS, AARHUS, DENMARK 340, 1013 (2003). http://doi.org/10.1016/j.physb.2003.09.194
Abstract: Infrared absorption spectra of composite precipitates are analysed with a modified Day-Thorpe algorithm, assuming a precipitated phase consisting of a mixture of two components with known optical properties. Additional constraints are introduced when solving the model equations by using a priori knowledge making the algorithm more reliable. It is shown that this novel approach allows determining both morphology and composition of precipitates. The method is applied to characterise oxide precipitates in boron-doped silicon. The results indicate that for the resistivity range above 60 mOmegacm, the precipitated phase is most probably SiO1.17+/-0.14, while for resistivities below 20 mOmega cm, precipitates consist of a SiO2/B2O3 composite with a large volume fraction of B(2)0(3) (up to 40% for 8 mOmegacm material). (C) 2003 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.386
Times cited: 4
DOI: 10.1016/j.physb.2003.09.194
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“The influence of crystal thickness on the image tone”. van Renterghem W, Schryvers D, van Landuyt J, van Roost C, de Keyzer R, Journal of imaging science 47, 133 (2003)
Abstract: It is known that the neutral image tone of a developed photographic film becomes brownish when the thickness of the original silver halide tabular crystals is reduced. We investigate by electron microscopy to what extent the silver filament structure has changed and how it induces the shift in image tone. Therefore, two samples of AgBr {111} tabular crystals with average thicknesses of 160 nm and 90 nm respectively, are compared. It is shown that the dimensions and defect structure of the filaments are comparable, but that the 90 nm crystals result in a more widely spaced structure, which explains the shift in image tone on a qualitative level. The influence of the addition of an image toner, i.e., phenylmercaptotetrazole, on the filament structure is also investigated. An even more open filament structure of longer, but smaller filaments was observed.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 0.348
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“Multiply connected mesoscopic superconductors”. Baelus BJ, Peeters FM, Modern physics letters B
T2 –, 3rd International Conference on Modern Problems in Superconductivity, SEP 09-14, 2002, YALTA, UKRAINE 17, 527 (2003). http://doi.org/10.1142/S021798490300555X
Abstract: Multiply connected mesoscopic: superconductors are considered within the framework of the nonlinear Ginzburg-Landau theory. The two coupled nonlinear equations are solved numerically and we investigated the properties of a superconducting ring, two concentric rings, and an asymmetric ring. We find that (i) for a mesoscopic superconducting ring the flux through the hole is not quantized, (ii) two concentric mesoscopic superconducting rings are magnetically coupled and the interaction energy increases with increasing sample thickness, and (iii) in asymmetric rings, a stationary phase slip state is predicted.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 0.617
DOI: 10.1142/S021798490300555X
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“On the nature of ferromagnetism in dilute magnetic semiconductors : GaAs:Mn and GaP:Mn”. Ivanov VA, Krstajic PM, Peeters FM, Fleurov V, Kikoin K, Journal of magnetism and magnetic materials
T2 –, 2nd Moscow International Symposium on Magnetism (MISM 2001), JUN 20-24, 2001, MOSCOW STATE UNIV, MOSCOW, RUSSIA 258, 237 (2003). http://doi.org/10.1016/S0304-8853(02)01023-5
Abstract: On the basis of a simplified Hamiltonian for transition metal impurities in diluted magnetic semiconductors (DMS), the nature of ferromagnetism in p-type III-V DMS are investigated. Ferromagnetism is governed by the Anderson-Hubbard parameter for 3d electrons of Mn2+ and their strong hybridization with the hole carriers in the semiconducting medium. The origin of ferromagnetism in these materials has similarity with the Zener mechanism. From the energetically preferable parallel orientation of Mn spins the Curie temperature is calculated for GaAs:Mn. (C) 2002 Published by Elsevier Science B.V.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.63
Times cited: 10
DOI: 10.1016/S0304-8853(02)01023-5
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“Present state of the composition evaluation of ternary semiconductor nanostructures by lattice fringe analysis”. Rosenauer A, Gerthsen D, Van Aert S, van Dyck D, den Dekker AJ, Institute of physics conference series , 19 (2003)
Abstract: Semiconductor heterostructures are used for the fabrication of optoelectronic devices. Performance of such devices is governed by their chemical morphology. The composition distribution of quantum wells and dots is influenced by kinetic growth processes which are not understood completely at present. To obtain more information about these effects, methods for composition determination with a spatial resolution at a near atomic scale are necessary. In this paper we focus on the present state of the composition evaluation by the lattice fringe analysis (CELFA) technique and explain the basic ideas, optimum imaging conditions, precision and accuracy.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
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“Ferroelectric and ionic-conductive properties of nonlinear-optical vanadate, Ca9Bi(VO4)7”. Lazoryak BI, Baryshnikova OV, Stefanovich SY, Malakho AP, Morozov VA, Belik AA, Leonidov IA, Leonidova ON, Van Tendeloo G, Chemistry of materials 15, 3003 (2003). http://doi.org/10.1021/cm031043s
Abstract: Structural, chemical, and physical properties of whitlockite-type Ca9Bi(VO4)(7) were studied by X-ray powder diffraction (XRD), electron diffraction (ED), second-harmonic generation (SHG), thermogravimetry, differential scanning calorimetry, dielectric, and electrical-conductivity measurements. A new phase-transition of the ferroelectric type was found in Ca9Bi(VO4)(7) with a transition temperature, T-c of 1053 +/- 3 K. The polar phase, beta-Ca9Bi(VO4)(7), is stable below T-c down to at least 160 K. The centrosymmetric beta'-phase is stable above T-c up to 1273 +/- 5 K. Above 1273 K, it decomposes to give BiVO4 and whitlockite-type solid solutions of Ca9+1.5xBi1-x(VO4)(7). The beta<---->beta' phase transition is reversible and of second order. Electrical conductivity of beta'-Ca9Bi(VO4)(7) is rather high (sigma = 0.6 x 10(-3) S/cm at 1200 K) and obeys the Arrhenius law with an activation energy of 1.0 eV. Structure parameters of Ca9Bi(VO4)(7) are refined by the Rietveld method from XRD data measured at room temperature (space group R3c; Z = 6; a = 10.8992(1) Angstrom, c = 38.1192(4) Angstrom, and V = 3921.6(1) Angstrom(3); R-wp = 3.06% and R-p = 2.36%). Bi3+ ions together with Ca2+ ions are statistically distributed among the M1, M2, M3, and M5 sites. Ca9Bi(VO4)(7) has a SHG efficiency of about 140 times that of quartz. Through the powder SHG measurements, we estimated the nonlinear optical susceptibility, Digital, at about 6.1-7.2 pm/V. This value for Ca9Bi(VO4)(7) is comparable with that for known nonlinear optical materials such as LiNbO3 and LiTaO3.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 51
DOI: 10.1021/cm031043s
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“Ordering of tetrahedral chains in the Sr2MnGaO5 brownmillerite”. Abakumov AM, Alekseeva AM, Rozova MG, Antipov EV, Lebedev OI, Van Tendeloo G, Journal of solid state chemistry 174, 319 (2003). http://doi.org/10.1016/S0022-4596(03)00226-3
Abstract: Tetrahedral chain ordering in the Sr2MnGaO5 structure is studied using electron diffraction (ED) and high-resolution electron microscopy. The ED patterns show the presence of satellite reflections, which indicate a commensurately modulated structure with a = 5.4056(8) Angstrom b 16.171(3) Angstrom, c = 5.5592(7) Angstrom, q – 1/2c*, superspace group Immma(00gamma,)s00. The Superstructure arises due to ordering of the two types of symmetry related tetrahedral chains (L and R) according to a ... LRLR ... sequence, where L and R chains alternate along the c-axis within the same (GaO) layer. Numerous defects at different structural levels were observed, comprising interleaving L and R chains, violation of the ... LRLR ... chain sequence within one layer, different stacking modes of the ... LRLR ... ordered layers with subsequent alternation of blocks of different width along the h-axis of the brownmillerite subcell and island fragmentation of the modulated superstructure. By in situ heating ED experiments it is found that the long-range ordering of the tetrahedral chains is stable tip to 665degreesC and is completely suppressed at 905degreesC. (C) 2003 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.299
Times cited: 34
DOI: 10.1016/S0022-4596(03)00226-3
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“Nano-structures at martensite macrotwin interfaces in Ni65Al35”. Boullay P, Schryvers D, Ball JM, Acta materialia 51, 1421 (2003). http://doi.org/10.1016/S1359-6454(02)00536-0
Abstract: The atomic configurations at macrotwin interfaces between microtwinned martensite plates in Ni65Al35 material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular {110} austenite planes, enclose a final angle larger or smaller than 90degrees. Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwinvariants are observed. The most reproducible deformations occur in a region of approximately 5-10 nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 31
DOI: 10.1016/S1359-6454(02)00536-0
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“Dislocations in diamond : dissociation into partials and their glide motion”. Blumenau AT, Jones R, Frauenheim T, Willems B, Lebedev OI, Van Tendeloo G, Fisher D, Martineau PM, Physical review : B : condensed matter and materials physics 68, 014115 (2003). http://doi.org/10.1103/PhysRevB.68.014115
Abstract: The dissociation of 60degrees and screw dislocations in diamond is modeled in an approach combining isotropic elasticity theory with ab initio-based tight-binding total-energy calculations. Both dislocations are found to dissociate with a substantial lowering of their line energies. For the 60degrees dislocation, however, an energy barrier to dissociation is found. We investigate the core structure of a screw dislocation distinguishing “shuffle,” “mixed,” and “glide” cores. The latter is found to be the most stable undissociated screw dislocation. Further, the glide motion of 90degrees and 30degrees partials is discussed in terms of a process involving the thermal formation and subsequent migration of kinks along the dislocation line. The calculated activation barriers to dislocation motion show that the 30degrees partial is less mobile than the 90degrees partial. Finally, high-resolution electron microscopy is performed on high-temperature, high-pressure annealed natural brown diamond, allowing the core regions of 60degrees dislocations to be imaged. The majority of dislocations are found to be dissociated. However, in some cases, undissociated 60degrees dislocations were also observed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 39
DOI: 10.1103/PhysRevB.68.014115
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“Catalytic Nox reduction with simultaneous dioxin and furan oxidation”. Goemans M, Clarysse P, Joannès J, de Clercq P, Lenaerts S, Matthys K, Boels K, Chemosphere 50, 489 (2003). http://doi.org/10.1016/S0045-6535(02)00554-4
Abstract: The engineering, construction, performance and running costs of a catalytic flue gas cleaning component in the low dust area of a municipal waste incinerator is discussed. For this purpose, the case study of a Flemish incineration plant is presented, covering the history, the design procedure of the catalyst, relevant process data and the financial aspects. A reliable PCDD/F-destruction by means of oxidation by the catalyst to typical values of 0.001 ng TEQ/N m3 has been demonstrated. At the same time, NOx- and CO-emissions are reduced by 90% and 20% to about 50 mg/N m3 and below 10 mg/N m3, respectively.
Keywords: A1 Journal article
Impact Factor: 4.208
DOI: 10.1016/S0045-6535(02)00554-4
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“Effect of helium/argon gas ratio in a He-Ar-Cu+ IR hollow-cathode discharge laser : modeling study and comparison with experiments”. Bogaerts A, Grozeva M, Applied physics B : lasers and optics 76, 299 (2003). http://doi.org/10.1007/s00340-002-1093-3
Abstract: The He-Ar-Cu+ IR laser operates in a hollow-cathode discharge, typically in a mixture of helium with a few-% Ar. The population inversion of the Cu+ ion levels, responsible for laser action, is attributed to asymmetric charge transfer between He+ ions and sputtered Cu atoms. The Ar gas is added to promote sputtering of the Cu cathode. In this paper, a hybrid modeling network consisting of several different models for the various plasma species present in a He-Ar-Cu hollow-cathode discharge is applied to investigate the effect of Ar concentration in the gas mixture on the discharge behavior, and to find the optimum He/Ar gas ratio for laser operation. It is found that the densities of electrons, Ar+ ions, Ar-m* metastable atoms, sputtered Cu atoms and Cu+ ions increase upon the addition of more Ar gas, whereas the densities of He+ ions, He-2(+) ions and He-m* metastable atoms drop considerably. The product of the calculated Cu atom and He+ ion densities, which determines the production rate of the upper laser levels, and hence probably also the laser output power, is found to reach a maximum around 1-5% Ar addition. This calculation result is compared to experimental measurements, and reasonable agreement has been reached.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.696
Times cited: 6
DOI: 10.1007/s00340-002-1093-3
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“Optimization of the amount of catalyst and reaction time in single wall nanotube production”. Horvath ZE, Biro LP, Van Tendeloo G, Tondeur C, Bister G, Pierard N, Fonseca A, Nagy JB, Diffusion and defect data : solid state data : part B : solid state phenomena 94, 271 (2003)
Abstract: The influence of the amount of catalyst and the reaction time on the quantity and quality of catalytically grown single wall carbon nanotubes (SWNT) was investigated. The aim was to optimize some of the SWNT growth parameters using TEM and HRTEM. The thickness of catalyst layer influences the synthesis of the nanotube because the gas composition can differ between top and bottom. Microscopic investigation of the grown SWNT samples showed that the thicker the catalyst layer the lower relative nanotube content, so the deeper parts of the catalyst layer are less effective: The optimum time for the reaction was found to be 10 minutes. This may be understood assuming that nanotube growth needs an initial incubation time while the activity of the catalyst decreases steadily until the nariotube growth stops.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
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“Optical bistability and multistability in four-level systems”. Chen Z, Feng X, Xu Y, Yu MY, Physica scripta 68, 199 (2003). http://doi.org/10.1238/Physica.Regular.068a00199
Abstract: The optical behavior of a four-level system in a ring cavity driven by two coherent laser fields is studied. One laser field is treated as the incident field and the other the control field, respectively. It is found that there is optical transparency when the difference between the two frequency detunings of the incident and control fields from the corresponding atomic transition frequencies is zero. Optical bistability can be produced and controlled by increasing the magnitude of the frequency difference. The bistable hysteresis becomes larger when the frequency difference is increased. Further increase of the latter can lead to onset of multistability.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.28
Times cited: 8
DOI: 10.1238/Physica.Regular.068a00199
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“Structure and correlations in two-dimensional classical artificial atoms confined by a Coulomb potential”. Ferreira WP, Matulis A, Farias GA, Peeters FM, Physical review : E : statistical, nonlinear, and soft matter physics 67, 046601 (2003). http://doi.org/10.1103/PhysRevE.67.046601
Abstract: The ordering of N equally charged particles (-e) moving in two dimensions and confined by a Coulomb potential, resulting from a displaced positive charge Ze is discussed. This is a classical model system for atoms. We obtain the configurations of charged particles which, depending on the value of N and Z, may result in ring structures, hexagonal-type configurations, and for N/Z approximate to 1 in an inner structure of particles which is separated by an outer ring of particles. For N/Z << 1, the Hamiltonian of the parabolic confinement case is recovered. For N/Z approximate to 1, the configurations are very different from those found in the case of a parabolic confinement potential. A hydrodynamic analysis is presented in order to highlight the correlations effects.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.366
Times cited: 14
DOI: 10.1103/PhysRevE.67.046601
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“The superconducting bismuth-based mixed oxides”. Antipov EV, Khasanova NR, Pshirkov JS, Putilin SN, Bougerof C, Lebedev OI, Van Tendeloo G, Baranov A, Park YW, Journal of low temperature physics
T2 –, International Conference on Physics and Chemistry of Molecular and Oxide, Superconductors (MOS2002), AUG 13-18, 2002, HSINCHU, TAIWAN 131, 575 (2003). http://doi.org/10.1023/A:1022923924607
Abstract: The present paper describes the synthesis, characterization of mixed-valence bismuthates with 3- or 2-dimensional perovskite-like structures and structural criteria that influence superconductivity in these compounds. Single-phase samples of Sr1-xKxBiO3 were prepared for the broad range of K-content: 0.25 less than or equal to x less than or equal to 0.65. For these bismuthates the symmetry of the structure changes from monoclinic to orthorhombic and finally to tetragonal upon increasing the K-content thus resulting in the decrease of the Bi-O distances and reduction of the network distortions. Superconductivity with maximum T-c = 12K exists in the narrow range (x approximate to 0.5 – 0.6) within the stability field of the tetragonal phase (0.33 less than or equal to x less than or equal to 0.65), when the 3-dimensional octahedral framework has close to the ideal perovskite structure arrangement. At the same time compositions with close to optimal Bi-valence (x = 0.33 and 0.43) do not show any sign of superconductivity, probably, due to structural distortions. The layered type (BaK)(3)Bi2O7 and (Ba,K)(2)BiO4 bismuthates belonging to the A(n+1)B(n)O(3n+1) homologous series were investigated Buckling of the (BiO2) layers in the structure of the n = 2 member was revealed The formation of the n=1 bismuthate was found by Electron Microscopy and X-ray powder diffraction studies. Both types of compounds are considered to be possible candidates for new superconducting materials among bismuthates.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.3
Times cited: 3
DOI: 10.1023/A:1022923924607
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“Magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot”. Chang K, Xia JB, Peeters FM, Applied physics letters 82, 2661 (2003). http://doi.org/10.1063/1.1568825
Abstract: The spin interaction and the effective g factor of a magnetic exciton (ME) are investigated theoretically in a diluted magnetic semiconductor (DMS) quantum dot (QD), including the Coulomb interaction and the sp-d exchange interaction. At low magnetic field, the ME energy decreases rapidly with increasing magnetic field and saturates at high magnetic field for high Mn concentration. The ground state of the ME exhibits an interesting crossing behavior between sigma(+)-ME and sigma(-)-ME for low Mn concentration. The g(ex) factor of the ME in a DMS QD displays a monotonic decrease with increasing magnetic field and can be tuned to zero by an external magnetic field. (C) 2003 American Institute of Physics.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.411
Times cited: 56
DOI: 10.1063/1.1568825
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“Structural properties and melting of a quasi-one dimensional classical Wigner crystal”. Piacente G, Schweigert IV, Betouras JJ, Peeters FM, Solid state communications 128, 57 (2003). http://doi.org/10.1016/S0038-1098(03)00647-1
Abstract: The structural and melting properties of a quasi-one dimensional system of charged particles, interacting through a screened Coulomb potential are investigated. Depending on the density and the screening length, the system crystallizes in different lattice structures. The structural phase transitions between them are of first or second order. The melting of the system is studied through Monte Carlo simulations and reentrant behavior as a function of density is observed as well as evidence of anisotropic melting. (C) 2003 Published by Elsevier Ltd.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.554
Times cited: 9
DOI: 10.1016/S0038-1098(03)00647-1
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“Symmetry lowering at the structural phase transitions in NpO2 and UO2”. Nikolaev AV, Michel KH, Physical review : B : condensed matter and materials physics 68, 054112 (2003). http://doi.org/10.1103/PhysRevB.68.054112
Abstract: The structural phase transitions with electric-quadrupole long-range order in NpO2 (Fm (3) over barm-->Pn (3) over barm) and UO2 (Fm (3) over barm-->Pa (3) over bar) are analyzed from a group theoretical point of view. In both cases, the symmetry lowering involves three quadrupolar components belonging to the irreducible representation T-2g (Gamma(5)) of O-h and condensing in a triple-q structure at the X point of the Brillouin zone. The Pa (3) over bar structure is close to Pn (3) over barm, but allows for oxygen displacements. The Pa (3) over bar ordering leads to an effective electrostatic attraction between electronic quadrupoles while the Pn (3) over barm ordering results in a repulsion between them. It is concluded that the Pn (3) over barm structure can be stabilized only through some additional process such as strengthening of the chemical bonding between Np and O. We also derive the relevant structure-factor amplitudes for Pn (3) over barm and Pa (3) over bar, and the effect of domains on resonant x-ray scattering experiments.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 15
DOI: 10.1103/PhysRevB.68.054112
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“A microstructural study of the thermal stability of atomic layer deposited Al2O3 thin films”. Nistor LC, Richard O, Zhao O, Bender H, Stesmans A, Van Tendeloo G, Institute of physics conference series
T2 –, Microscopy of semiconducting materials , 397 (2003)
Abstract: The thermal stability of amorphous Al2O3 films (similar to8 and 80 nut thick) deposited by atomic layer deposition on HF-last and thin SiO2 covered (001) Si substrates is studied by transmission electron microscopy. The layers are in- and ex-situ annealed in the same temperature range.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
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“Secondary ion formation of low molecular weight organic dyes in time-of-flight static secondary ion mass spectrometry”. Lenaerts J, van Vaeck L, Gijbels R, Rapid communications in mass spectrometry 17, 2115 (2003). http://doi.org/10.1002/rcm.1160
Abstract: Time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) was used to characterize thin layers of oxy- and thiocarbocyanine dyes on Ag and Si. Apart from adduct ions a variety of structural fragment ions were detected for which a fragmentation pattern is proposed. Peak assignments were confirmed by comparing spectra of dyes with very similar structures. All secondary ions were assigned with a mass accuracy better than 50 ppm. The intensity of molecular ions as well as fragment ions has been studied as a function of the type of organic dye, the substrate, the layer thickness and the type of primary ion. A large yield difference of two orders of magnitude was observed between the precursor ions of cationic carbocyanine dyes and the protonated molecules of the anionic dyes. Fragment ions, on the other hand, yielded similar intensities for both types of dye. As the dye layers deposited on an Ag substrate yielded higher secondary ion intensities than those deposited on a Si substrate, the Ag metal clearly acts as a promoting agent for secondary ion formation. The effect was more pronounced for precursor signals than for fragment ions. The promoting effect decreased as the deposited layer thickness of the organic dye layer was increased. Copyright (C) 2003 John Wiley Sons, Ltd.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.998
Times cited: 10
DOI: 10.1002/rcm.1160
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“Transmission electron microscopy on interface engineered superconducting thin films”. Bals S, Van Tendeloo G, Rijnders G, Huijben M, Leca V, Blank DHA, IEEE transactions on applied superconductivity 13, 2834 (2003). http://doi.org/10.1109/TASC.2003.812023
Abstract: Transmission electron microscopy is used to evaluate different deposition techniques, which optimize the microstructure and physical properties of superconducting thin films. High-resolution electron microscopy proves that the use of an YBa2Cu2Ox buffer layer can avoid a variable interface configuration in YBa2Cu3O7-delta thin films grown on SrTiO3. The growth can also be controlled at an atomic level by, using sub-unit cell layer epitaxy, which results in films with high quality and few structural defects. Epitaxial strain in Sr0.85La0.15CuO2 infinite layer thin films influences the critical temperature of these films, as well as the microstructure. Compressive stress is released by a modulated or a twinned microstructure, which eliminates superconductivity. On the other hand, also tensile strain seems to lower the critical temperature of the infinite layer.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 13
DOI: 10.1109/TASC.2003.812023
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“Characterization of the main causes of deterioration of grisaille paint layers in 19th C. stained-glass windows by J.-B. Capronnier”. Schalm O, Janssens K, Caen J, Spectrochimica acta: part B : atomic spectroscopy 58, 589 (2003). http://doi.org/10.1016/S0584-8547(02)00282-3
Abstract: Twenty-seven glass fragments containing dark coloured grisaille paint layers of different qualities were collected from ten windows of the cathedral St. Michael & St. Gudule in Brussels (Belgium). The windows were made by J.-B. Capronnier (18141891) and cover the period between 1843 and 1878. The samples were cross-sectioned and examined in an electron microscope. Grisaille paint layers are not homogeneous and therefore, it is not meaningful to characterize them in terms of their average composition. Instead, parameters such as granularity, the number of residual gas bubbles per running millimetre of paint, the type of pigments, and the thickness of the paint layer were used to characterize them. The microscopic morphology allows a classification of the grisaille paint layers in four groups, every group associated with a quality level. Moreover, the main causes of the accelerated degradation of some of these paint layers could be explained. The classification made it possible to distinguish two periods in the work of Capronnier: (1) the early period (18431848) is characterized by the presence of either single granular paint layers or of double-layered systems consisting of a granular paint layer on top of a well-melted paint layer. The granular grisaille paint layers tend to pulverize; (2) the later period (18481878) is characterized by the presence of only well-vitrified paint layers. No sign of deterioration was found on the well-vitrified paint layers.
Keywords: A1 Journal article; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.241
DOI: 10.1016/S0584-8547(02)00282-3
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“Ion-bombardment artifact in TOF-SIMS analysis of ZrO2/SiO2/Si stacks”. de Witte H, Conard T, Vandervorst W, Gijbels R, Applied surface science 203, 523 (2003). http://doi.org/10.1016/S0169-4332(02)00728-6
Abstract: We analyzed ultra-thin ZrO2/SiO2/Si gate dielectrics under post-deposition anneals in dry O-2 at temperatures from 500 to 700 degreesC. TOF-SIMS profiling of ZrO2/SiO2/Si stacks is hampered by many sputter induced artifacts. The depletion of oxygen leads to a decrease in SIMS intensities. However, preferential sputtering is accompanied by transport of the depleted species towards the surface. Due to recoil implantation oxygen gets piled-up near the ZrO2/SiO2 interface. Either normal or radiation-enhanced diffusion transports oxygen back to the surface. Simultaneously also segregation of zirconium towards and through the interface is observed, resulting in a large zirconium tail in the underlying silicon substrate. (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.387
Times cited: 15
DOI: 10.1016/S0169-4332(02)00728-6
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“Few-particle states in coupled electron-hole quantum dots”. Anisimovas E, Peeters FM, Functions II , 330 (2003). http://doi.org/10.1142/9789812705129_0029
Abstract: We apply the exact diagonalization technique to calculate the ground and excited states of a bipolar artificial molecule composed of two vertically coupled quantum dots containing different types of carriers electrons and holes in equilibrium. In this system, the magnetic field tunes the relative role of intra-dot Coulomb interaction while the inter-dot separation sets the strength of inter-dot correlations. We find an intricate pattern of the switching of the ground-state angular momentum with increasing magnetic field and a rearrangement of approximate single-particle levels as a function of the inter-dot coupling strength.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
DOI: 10.1142/9789812705129_0029
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“Ferromagnetism in Mn-doped GaAs : the kinematic exchange”. Krstajic PM, Ivanov VA, Peeters FM, Fleurov V, Kikoin K, Journal of superconductivity
T2 –, PASPS Conference 2002, JUL, 2002, WURZBURG, GERMANY 16, 111 (2003). http://doi.org/10.1023/A:1023253205699
Abstract: We developed a microscopic model in order to describe the onset of ferromagnetism (FM) in GaAs:Mn. The proposed kinematic mechanism bears resemblances with the Zener exchange. The calculated Curie temperature for GaAs: Mn is in good agreement with available experimental data of the Curie temperature as a function of the manganese concentration.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 2
DOI: 10.1023/A:1023253205699
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“Precursor phenomena in a quenched and aged Ni52Ti48 shape memory alloy”. Somsen C, Wassermann EF, Kästner J, Schryvers D, Journal de physique: 4
T2 –, 10th International Conference on Martensitic Transformations, JUN 10-14, 2002, ESPOO, FINLAND 112, 777 (2003). http://doi.org/10.1051/jp4:2003997
Abstract: We measured the electrical resistivity R(T) and specific heat C-p(T) between room temperature (RT) and 4.2 K as well as the microstructure by transmission electron microscopy (TEM) of a Ni-52 Ti-48 SMA quenched from 1000degreesC (B2-Phase range) to RT and then annealed for 1h at T=380degreesC, 550degreesC and 650degreesC. In the “as quenched” and the “650degreesC annealed” state no martensitic transformations (MT's) occur. The diffraction patterns show faint reflections originating from coherent Ni4Ti3 precipitates in an early state of formation. Additional reflections of the type 1/2 <110>, 1/2 <111> and 1/3 <110> result from various lattice displacement waves, which are precursors of the MT's to the B19' and R-phase, respectively. Indeed, high resolution TEM micrographs of the [001] zone of the “as quenched” sample reveal transverse 1/2 <110> <110> lattice displacement waves, precursors of the B19' martensite. The coherent Ni4Ti3 precipitates, homogeneously distributed on a small length scale, binder the MT's in the “as quenched” and the “650degreesC annealed” state, and thus only the precursors appear. When annealed at T=380degreesC, however, coherent Ni4Ti3 precipitates with a length of 10nm are clearly visible in TEM. These precipitates trigger the NIT from the B2 to the R-phase on cooling, as evidenced also by anomalies in R(T) and C-p(T). Annealing at T-550degreesC leads to the well known two step MT's from the B2 to the R-phase and then into the B19'-phase. These martensitic transitions are clearly seen as additional peaks in the specific heat and anomalies in the resistance, while the “as quenched” and 650degreesC annealed samples show weak features in R(T) and C-p(T).
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 2
DOI: 10.1051/jp4:2003997
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“MgB2 : superconductivity and pressure effects”. Ivanov VA, Betouras JJ, Peeters FM, , 35 (2003)
Abstract: We present a Ginzburg-Landau theory for a two-band superconductor with emphasis on MgB2. We propose experiments which lead to identification of the possible scenarios: whether both sigma- and pi-bands superconduct or sigma-alone. According to the second scenario a microscopic theory of superconducting MgB2 is proposed based on the strongly interacting or-electrons and non-correlated pi-electrons of boron ions. The kinematic and Coulomb interactions of sigma-electrons provide the superconducting state with an anisotropic gap of s(*)-wave symmetry. The critical temperature T-c has a non-monotonic dependence on the distance r between the centers of gravity of sigma- and pi-bands. The position of MgB2 on a bell-shaped curve T-c (r) is identified in the overdoped region. The derived superconducting density of electronic states is in agreement with available experimental and theoretical data. It is argued that the effects of pressure are crucial to identify the microscopic origin of superconductivity in MgB2. Possibilities for increase of T, are discussed.
Keywords: P1 Proceeding; Condensed Matter Theory (CMT)
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