|
“Selective suppression of Dresselhaus or Rashba spin-orbit coupling effects by the Zeeman interaction in quantum dots”. Szafran B, Nowak MP, Bednarek S, Chwiej T, Peeters FM, Physical review : B : solid state 79, 235303 (2009). http://doi.org/10.1103/PhysRevB.79.235303
Abstract: We study single- and two-electron parabolic quantum dots in the presence of linear Dresselhaus and Rashba spin-orbit interactions. Contributions of both types of spin-orbit coupling are investigated in the context of the spin polarization of the system at high magnetic fields. We demonstrate that for negative Landé factors the effect of the Dresselhaus coupling is suppressed at high magnetic field, which for structures without inversion asymmetry leads to a completely spin-polarized system and a strict antisymmetry of the wave functions with respect to the interchange of spatial-electron coordinates. For negative Landé factor the Rashba coupling is preserved at high field and consequently the spin polarization of the systems as well as the spatial antisymmetry of the two-electron wave function remain approximate.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 13
DOI: 10.1103/PhysRevB.79.235303
|
|
|
“Shallow donor states near a semiconductor-insulator-metal interface”. Hao YL, Djotyan AP, Avetisyan AA, Peeters FM, Physical review : B : solid state 80, 035329 (2009). http://doi.org/10.1103/PhysRevB.80.035329
Abstract: The lowest energy electronic states of a donor located near a semiconductor-insulator-metal interface are investigated within the effective mass approach. The effect of the finite thickness of the insulator between the semiconductor and the metallic gate on the energy levels is studied. The lowest energy states are obtained through a variational approach, which takes into account the influence of all image charges that arise due to the presence of the metallic and the dielectric interfaces. We compare our results with a numerical exact calculation using the finite element technique.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 22
DOI: 10.1103/PhysRevB.80.035329
|
|
|
“Stability of spintronic devices based on quantum ring networks”. Földi P, Kálmán O, Peeters FM, Physical review : B : solid state 80, 125324 (2009). http://doi.org/10.1103/PhysRevB.80.125324
Abstract: Transport properties in mesoscopic networks are investigated, where the strength of the (Rashba-type) spin-orbit coupling is tuned with external gate voltages. We analyze in detail to what extent the ideal behavior and functionality of some promising network-based devices are modified by random (spin-dependent) scattering events and by thermal fluctuations. It is found that although the functionality of these devices is obviously based on the quantum coherence of the transmitted electrons, there is a certain stability: moderate level of errors can be tolerated. For mesoscopic networks made of typical semiconductor materials, we found that when the energy distribution of the input carriers is narrow enough, the devices can operate close to their ideal limits even at relatively high temperature. As an example, we present results for two different networks: one that realizes a Stern-Gerlach device and another that simulates a spin quantum walker. Finally we propose a simple network that can act as a narrow band energy filter even in the presence of random scatterers.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 41
DOI: 10.1103/PhysRevB.80.125324
|
|
|
“Structure of binary colloidal systems confined in a quasi-one-dimensional channel”. Yang W, Nelissen K, Kong M, Zeng Z, Peeters FM, Physical review : E : statistical physics, plasmas, fluids, and related interdisciplinary topics 79, 041406 (2009). http://doi.org/10.1103/PhysRevE.79.041406
Abstract: The structural properties of a binary colloidal quasi-one-dimensional system confined in a narrow channel are investigated through modified Monte Carlo simulations. Two species of particles with different magnetic moment interact through a repulsive dipole-dipole force are confined in a quasi-one-dimensional channel. The impact of three decisive parameters (the density of particles, the magnetic-moment ratio, and the fraction between the two species) on the transition from disordered phase to crystal-like phases and the transitions among the different mixed phases are summarized in a phase diagram.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.366
Times cited: 11
DOI: 10.1103/PhysRevE.79.041406
|
|
|
“Theoretical phonon dispersions in monolayers and multilayers of hexagonal boron-nitride”. Michel KH, Verberck B, Physica status solidi: B: basic research 246, 2802 (2009). http://doi.org/10.1002/pssb.200982307
Abstract: Starting from an empirical force constant model of valence interactions and calculating by Ewald's method the electrostatic force constants, we derive the dynamical matrix for a monolayer and for multilayer systems of hexagonal boron nitride (h-BN). Solution of the secular problem leads to the corresponding phonon dispersion relations. The interplay between valence forces and Coulomb forces is discussed. A comparison with previous results on graphene and graphene multilayers is made. Our spectra on the h-BN monolayer are rather similar to previous ab initio theory results. Comparison is also made with Raman and infrared experimental results.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.674
Times cited: 10
DOI: 10.1002/pssb.200982307
|
|
|
“Theory of elastic and piezoelectric effects in two-dimensional hexagonal boron nitride”. Michel KH, Verberck B, Physical review : B : solid state 80, 224301 (2009). http://doi.org/10.1103/PhysRevB.80.224301
Abstract: Starting from an empirical force constant model of valence interactions and calculating by Ewalds method the ion-ion force constants, we derive the dynamical matrix for a monolayer crystal of hexagonal boron nitride (h-BN). The phonon dispersion relations are calculated. The interplay between valence and Coulomb forces is discussed. It is shown by analytical methods that the longitudinal and the transverse optical (LO and TO) phonon branches for in-plane motion are degenerate at the Γ point of the Brillouin zone. Away from Γ, the LO branch exhibits pronounced overbending. It is found that the nonanalytic Coulomb contribution to the dynamical matrix causes a linear increase of the LO branch with increasing wave vector starting at Γ. This effect is general for two-dimensional (2D) ionic crystals. Performing a long-wavelength expansion of the dynamical matrix, we use Borns perturbation method to calculate the elastic constants (tension coefficients). Since the crystal is noncentrosymmetric, internal displacements due to relative shifts between the two sublattices (B and N) contribute to the elastic constants. These internal displacements are responsible for piezoelectric and dielectric phenomena. The piezoelectric stress constant and the dielectric susceptibility of 2D h-BN are calculated.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 96
DOI: 10.1103/PhysRevB.80.224301
|
|
|
“Transverse instabilities of multiple vortex chains in magnetically coupled NbSe2/permalloy superconductor/ferromagnet bilayers”. Karapetrov G, Milošević, MV, Iavarone M, Fedor J, Belkin A, Novosad V, Peeters FM, Physical review : B : solid state 80, 180506 (2009). http://doi.org/10.1103/PhysRevB.80.180506
Abstract: Using scanning tunneling microscopy and Ginzburg-Landau simulations, we explore vortex configurations in magnetically coupled NbSe2/permalloy superconductor/ferromagnet bilayer. The permalloy film with stripe domain structure induces periodic local magnetic induction in the superconductor, creating a series of pinning-antipinning channels for externally added magnetic flux quanta. Such laterally confined Abrikosov vortices form quasi-one-dimensional arrays (chains). The transitions between multichain states occur through propagation of kinks at the intermediate fields. At high fields we show that the system becomes nonlinear due to a change in both the number of vortices and the confining potential. The longitudinal instabilities of the resulting vortex structures lead to vortices levitating in the antipinning channels.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 38
DOI: 10.1103/PhysRevB.80.180506
|
|
|
“Tunable kinematics of phase-slip lines in a superconducting stripe with magnetic dots”. Berdiyorov GR, Milošević, MV, Peeters FM, Physical review : B : solid state 80, 214509 (2009). http://doi.org/10.1103/PhysRevB.80.214509
Abstract: Using numerical simulations, we study the dynamic properties of a superconducting stripe with a perpendicular magnetized ferromagnet on top in the presence of an applied dc current. In the resistive state conventional phase-slip lines are transformed into kinematic vortex-antivortex pairs with special dynamic behavior. In addition, the location of phase slippage in the sample is predetermined by the position of the magnetic dot. Both these effects directly influence the dynamics of the superconducting condensate and lead to periodic oscillations of the voltage across the sample with a frequency tunable both by the applied current and by the magnetization of the magnet. We found that the frequency of the voltage oscillations increases with increasing number of magnetic dots.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 33
DOI: 10.1103/PhysRevB.80.214509
|
|
|
“Tunneling, conductance, and wavevector filtering through magnetic barriers in bilayer graphene”. Masir MR, Vasilopoulos P, Peeters FM, Physical review : B : solid state 79, 035409 (2009). http://doi.org/10.1103/PhysRevB.79.035409
Abstract: We evaluate the transmission and conductance through magnetic barrier structures in bilayer graphene. In particular we consider a magnetic step, single and double barriers, -function barriers, as well as barrier structures that have average magnetic field equal to zero. The transmission depends strongly on the direction of the incident electron or hole wavevector and gives the possibility to construct a direction-dependent wavevector filter. The results contrast sharply with previous results on single-layer graphene. In general, the angular range of perfect transmission becomes drastically wider and the gaps narrower. This perfect transmission range decreases with the number of barriers, the barrier width, and the magnetic field. Depending on the structure, a variety of transmission resonances occur that are reflected in the conductance through the structure.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 80
DOI: 10.1103/PhysRevB.79.035409
|
|
|
“Tunneling-lifetime model for metal-oxide-semiconductor structures”. Pourghaderi MA, Magnus W, Sorée B, Meuris M, de Meyer K, Heyns M, Physical review : B : solid state 80, 085315 (2009). http://doi.org/10.1103/PhysRevB.80.085315
Abstract: In this paper we investigate the basic physics of charge carriers (electrons) leaking out of the inversion layer of a metal-oxide-semiconductor capacitor with a biased gate. In particular, we treat the gate leakage current as resulting from two combined processes: (1) the time-dependent decay of electron wave packets representing the inversion-layer charge and (2) the local generation of new electrons replacing those that have leaked away. As a result, the gate current simply emerges as the ratio of the total charge in the inversion layer to the tunneling lifetime. The latter is extracted from the quantum dynamics of the decaying wave packets, while the generation rate is incorporated as a phenomenological source term in the continuity equation. Not only do the gate currents calculated with this model agree very well with experiment, the model also provides an onset to solve the paradox of the current-free bound states representing the resonances of the Schrödinger equation that governs the fully coupled metal-oxide-semiconductor system.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 2
DOI: 10.1103/PhysRevB.80.085315
|
|
|
“Unconventional vortex dynamics in mesoscopic superconducting corbino disks”. Lin NS, Misko VR, Peeters FM, Physical review letters 102, 197003 (2009). http://doi.org/10.1103/PhysRevLett.102.197003
Abstract: The discrete shell structure of vortex matter strongly influences the flux dynamics in mesoscopic superconducting Corbino disks. While the dynamical behavior is well understood in large and in very small disks, in the intermediate-size regime it occurs to be much more complex and unusual, due to (in)commensurability between the vortex shells. We demonstrate unconventional vortex dynamics (inversion of shell velocities with respect to the gradient driving force) and angular melting (propagating from the boundary where the shear stress is minimum, towards the center) in mesoscopic Corbino disks.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 8.462
Times cited: 18
DOI: 10.1103/PhysRevLett.102.197003
|
|
|
“Valley polarization due to trigonal warping on tunneling electrons in graphene”. Pereira JM, Peeters FM, Costa Filho RN, Farias GA, Journal of physics : condensed matter 21, 045301 (2009). http://doi.org/10.1088/0953-8984/21/4/045301
Abstract: The effect of trigonal warping on the transmission of electrons tunneling through potential barriers in graphene is investigated. We present calculations of the transmission coefficient for single and double barriers as a function of energy, incidence angle and barrier heights. The results show remarkable valley-dependent directional effects for barriers oriented parallel to the armchair or parallel to the zigzag direction. These results indicate that electrostatic gates can be used as valley filters in graphene-based devices.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.649
Times cited: 78
DOI: 10.1088/0953-8984/21/4/045301
|
|
|
“Violation of Onsager symmetry for a ballistic channel Coulomb coupled to a quantum ring”. Szafran B, Poniedziałek MR, Peeters FM, Europhysics letters 87, 47002 (2009). http://doi.org/10.1209/0295-5075/87/47002
Abstract: We investigate a scattering of electron which is injected individually into an empty ballistic channel containing a cavity that is Coulomb coupled to a quantum ring charged with a single electron. We solve the time-dependent Schrödinger equation for the electron pair with an exact account for the electron-electron correlation. Absorption of energy and angular momentum by the quantum ring is not an even function of the external magnetic field. As a consequence we find that the electron backscattering probability is asymmetric in the magnetic field and thus violates Onsager symmetry.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.957
Times cited: 4
DOI: 10.1209/0295-5075/87/47002
|
|
|
“Vortex-antivortex 'molecular crystals' in hybrid ferromagnet/superconductor structures”. Bending SJ, Neal JS, Milošević, MV, Potenza A, san Emeterio L, Marrows CH, Journal of physics : conference series 150, 052019 (2009). http://doi.org/10.1088/1742-6596/150/5/052019
Abstract: We have used high resolution Hall probe microscopy to image vortex-antivortex (V-AV) 'molecules' induced in superconducting Pb films by the stray fields from square arrays of ferromagnetic Co/Pt dots. We have directly observed spontaneous V-AV pairs and studied how they interact with added 'free' (anti)fluxons in an applied magnetic field. We observe a rich variety of subtle phenomena arising from competing symmetries in our system which can either drive added antivortices to join AV shells around nanomagnets or stabilise the translationally symmetric AV lattice between the dots. Added vortices annihilate AV shells, leading eventually to a stable 'nulling' state with no free fluxons, which should exhibit a strongly (field-)enhanced critical current. At higher densities we actually observe vortex shells around the magnets, stabilised by the asymmetric anti-pinning potential. Our experimental findings are in good agreement with Ginzburg-Landau calculations.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/150/5/052019
|
|
|
“Vortex matter in oblate mesoscopic superconductors with a hole: broken symmetry vortex states and multi-vortex entry”. Xu B, Milošević, MV, Peeters FM, New journal of physics 11, 013020 (2009). http://doi.org/10.1088/1367-2630/11/1/013020
Abstract: Using three-dimensional (3D) numerical discretization of the GinzburgLandau (GL) equations, we investigate the superconducting state of a sphere with a piercing hole in the presence of a magnetic field. In the case of samples with central perforation, in axially applied homogeneous magnetic field, we realized unconventional vortex states of broken symmetry due to complex, 3D competing interactions, which depend on the GL parameter ê. For certain sizes of the sample, non-hysteretic multi-vortex entry and exit is predicted with the non-existence of some vorticities as stable states. In a tilted magnetic field, we studied the gradual transformation of 3D flux patterns into 1D vortex chains, where vortices align along the perforation, and the evolvement of the multi-vortex entry as well. We analyze the flux-guiding ability of the hole in a tilted field, which leads to fractional flux response in magnetization M(H) curves.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.786
Times cited: 8
DOI: 10.1088/1367-2630/11/1/013020
|
|
|
“Vortex 'puddles' and magic vortex numbers in mesoscopic superconducting disks”. Connolly MR, Milošević, MV, Bending SJ, Clem JR, Tamegai T, Journal of physics : conference series 150, 052039 (2009). http://doi.org/10.1088/1742-6596/150/5/052039
Abstract: The magnetic properties of a superconducting disk change dramatically when its dimensions become mesoscopic. Unlike large disks, where the screening currents induced by an applied magnetic field are strong enough to force vortices to accumulate in a 'puddle' at the centre, in a mesoscopic disk the interaction between one of these vortices and the edge currents can be comparable to the intervortex repulsion, resulting in a destruction of the ordered triangular vortex lattice structure at the centre. Vortices instead form clusters which adopt polygonal and shell-like structures which exhibit magic number states similar to those of charged particles in a confining potential, and electrons in artificial atoms. We have fabricated mesoscopic high temperature superconducting Bi2Sr2CaCu2O8+δ disks and investigated their magnetic properties using magneto-optical imaging (MOI) and high resolution scanning Hall probe microscopy (SHPM). The temperature dependence of the vortex penetration field measured using MOI is in excellent agreement with models of the thermal excitation of pancake vortices over edge barriers. The growth of the central vortex puddle has been directly imaged using SHPM and magic vortex numbers showing higher stability have been correlated with abrupt jumps in the measured local magnetisation curves.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.1088/1742-6596/150/5/052039
|
|
|
“Water on graphene: hydrophobicity and dipole moment using density functional theory”. Leenaerts O, Partoens B, Peeters FM, Physical review : B : solid state 79, 235440 (2009). http://doi.org/10.1103/PhysRevB.79.235440
Abstract: We apply density-functional theory to study the adsorption of water clusters on the surface of a graphene sheet and find i) graphene is highly hydrophobic and ii) adsorbed water has very little effect on the electronic structure of graphene. A single water cluster on graphene has a very small average dipole moment which is in contrast with an ice layer that exhibits a strong dipole moment.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 292
DOI: 10.1103/PhysRevB.79.235440
|
|
|
“Wave packet dynamics in semiconductor quantum rings of finite width”. Chaves A, Farias GA, Peeters FM, Szafran B, Physical review : B : solid state 80, 125331 (2009). http://doi.org/10.1103/PhysRevB.80.125331
Abstract: The time evolution of a wave packet injected into a semiconductor quantum ring is investigated in order to obtain the transmission and reflection probabilities. Within the effective-mass approximation, the time-dependent Schrödinger equation is solved for a system with nonzero width of the ring and leads and finite potential-barrier heights, where we include smooth lead-ring connections. In the absence of a magnetic field, an analysis of the projection of the wave function over the different subband states shows that when the injected wave packet is within a single subband, the junction can scatter this wave packet into different subbands but remarkably at the second junction the wave packet is scattered back into the subband state of the incoming wave packet. If a magnetic field is applied perpendicularly to the ring plane, transmission and reflection probabilities exhibit Aharonov-Bohm (AB) oscillations and the outgoing electrons may end up in different subband states from those of the incoming electrons. Localized impurities, placed in the ring arms, influence the AB oscillation period and amplitude. For a single impurity or potential barrier of sufficiently strong strength, the period of the AB oscillations is halved while for two impurities localized in diametrically opposite points of the ring, the original AB period is recovered. A theoretical investigation of the confined states and time evolution of wave packets in T wires is also made, where a comparison between this system and the lead-ring junction is drawn.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 40
DOI: 10.1103/PhysRevB.80.125331
|
|
|
“Work and dissipation in 2D clusters”. Nelissen K, Partoens B, van den Broeck C, Europhysics letters 88, 30001 (2009). http://doi.org/10.1209/0295-5075/88/30001
Abstract: We show by extensive numerical simulations, that far-from-equilibrium experiments on dusty plasmas and on dipole particles in a circular cavity are good candidates for the verification of the Jarzynski equality, the Crooks relation and, to a lesser extent, of the recently obtained microscopic expression for the dissipated work.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.957
Times cited: 2
DOI: 10.1209/0295-5075/88/30001
|
|
|
“Magnetoexcitons in semiconductor quantum rings with complicated (Kane's) dispersion law”. Avetisyan AA, Ghazaryan AV, Djotyan AP, Kirakosyan AA, Moulopoulos K, Acta physica Polonica: A: general physics, solid state physics, applied physics
T2 –, 4th Workshop on Quantum Chaos and Localisation Phenomena, MAY 22-24, 2009, Polish Acad Sci, Ctr Theoret Phys, Inst Phys, Polish Acad Sci, Ctr Theoret Phys, Inst Phys, War 116, 826 (2009). http://doi.org/10.12693/APHYSPOLA.116.826
Abstract: The influence of the nonparabolicity of charge carriers dispersion law (Kane's dispersion) on a magnetoexciton energy spectrum in InSb quantum rings is theoretically investigated The analytical expression for the energy spectrum of exciton in a narrow-gap semiconductor nanoring in a magnetic field is obtained. The Aharonov – Bohm oscillations in the energy of excited states are studied.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.12693/APHYSPOLA.116.826
|
|
|
“Comparative assessment of air quality in two health resorts using carbon isotopes and palynological analyses”. Górka M, Jedrysek MO, Maj J, Worobiec A, Buczyńska A, Stefaniak E, Krata A, Van Grieken R, Zwozdziak A, Sówka I, Zwozdziak J, Lewicka-Szczebak D, Atmospheric environment 43, 682 (2009). http://doi.org/10.1016/J.ATMOSENV.2008.09.056
Abstract: This paper describes results of applying the palynological and carbon isotopic analysis of the organic fraction of Total Suspended Particles (TSP) to discriminate distinct pollution sources and assess the anthropogenic impact for the investigated areas. The samples of atmospheric particles were collected in Czerniawa and Cieplice (two health resorts in Lower Silesia, SW Poland) twice a year in summer and winter season (from July 2006 to February 2008). The palynological spectra represent in the vast majority local plant communities without a noticeable contribution of long-transported plant particles. Palynological analysis revealed also differences in the specificity of the two sampling areas, i.e. the higher contribution of identified organic material in Czerniawa stands for more natural character of this site, but is also responsible for the higher allergic pressure when compared to Cieplice. The carbon isotopic composition of TSP varied seasonally (ä13C value from −27.09 in summer to −25.47 in winter). The increased ä13C value in winter (heating period) is most probably caused by uncontrolled contribution of coal soot. On the basis of isotopic mass balance the calculated contribution of anthropogenic organic particles in the atmosphere reached in winter season 72% in Czerniawa and 79% in Cieplice.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Laboratory Experimental Medicine and Pediatrics (LEMP)
DOI: 10.1016/J.ATMOSENV.2008.09.056
|
|
|
“Composition of pigments on human bones found in excavations in Argentina studied with micro-Raman spectrometry and scanning electron microscopy”. Darchuk L, Stefaniak EA, Vázquez C, Palacios OM, Worobiec A, Van Grieken R, e-Preservation Science 6, 112 (2009)
Abstract: Results on analysis of prehistoric pigments from excavations and pigments on coloured child bones from North Patagonia, Argentina, are reported. To analyze their composition we used two micro-analytical techniques: micro- Raman spectrometry (MRS) and scanning electron microscopy coupled with X-ray micro-analysis (SEM/EDX). Most investigated excavated pigments show red or yellow ochres consistent with reddish or yellow minerals, such as á- and ã-goethite, haematite, erdite, haapalaite and jarosite. Raman spectra show also evidence of calcium oxalate monohydrate and calcite indicating lichen activity. Pigments covering human bones were identified as hematite and magnetite. This study allows us to infer that pigments found in excavation were employed for burial ceremonies, even though distances between excavated pigment archaeological site and buried remains are quite far, more than 50 km in a straight line.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Laboratory Experimental Medicine and Pediatrics (LEMP)
|
|
|
“Determination of fluorine in uranium oxyfluoride particles as an indicator of particle age”. Kips R, Pidduck AJ, Houlton MR, Leenaers A, Mace JD, Marie O, Pointurier F, Stefaniak EA, Taylor PDP, van den Berghe S, van Espen P, Van Grieken R, Wellum R, Spectrochimica acta: part B : atomic spectroscopy 64, 199 (2009). http://doi.org/10.1016/J.SAB.2008.12.001
Abstract: As swipe samples from enrichment activities typically contain uranium particles with a detectable amount of fluorine, the question was raised whether the analysis of fluorine in particles could complement the information on the uranium isotope ratios. For this, uranium oxyfluoride particles were prepared from the controlled hydrolysis of uranium hexafluoride (UF6). The relative amount of fluorine was characterized by scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDX), as well as ion-microprobe secondary ion mass spectrometry (IM-SIMS). Of particular interest was the assessment of the reduction of the amount of fluorine over time, and after exposure to UV-light and high temperatures. Micro-Raman spectrometry (MRS) was applied to look for differences in molecular structure between these various sample types. Both SEM-EDX and IM-SIMS showed a general reduction of the fluorine-to-uranium ratio after 12 years of storage. The exposure to UV-light and high temperatures was found to have accelerated the loss of fluorine. A distinct peak at 865 cm− 1 Raman shift was detected for the majority of particles analyzed by MRS. For the particles that were heat-treated, the Raman spectra were similar to the spectrum of U3O8. Although often large variations were observed between particles from the same sample, the three particle measurement techniques (IM-SIMS, SEM-EDX and MRS) showed some consistent trends. They therefore appear promising in terms of the ability to place bounds on particle age, as well as shedding light on the complex processes involved in UO2F2 particle ageing.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Chemometrics (Mitac 3)
DOI: 10.1016/J.SAB.2008.12.001
|
|
|
“Characterization of a degraded cadmium yellow (CdS) pigment in an oil painting by means of synchrotron radiation based X-ray techniques”. van der Snickt G, Dik J, Cotte M, Janssens K, Jaroszewicz J, de Nolf W, Groenewegen J, van der Loeff L, Analytical chemistry 81, 2600 (2009). http://doi.org/10.1021/AC802518Z
Abstract: On several paintings of James Ensor (1860−1949), a gradual fading of originally bright yellow areas, painted with the pigment cadmium yellow (CdS), is observed. Additionally, in some areas exposed to light, the formation of small white-colored globules on top of the original paint surface is observed. In this paper the chemical transformation leading to the color change and to the formation of the globules is elucidated. Microscopic X-ray absorption near-edge spectroscopy (ì-XANES) experiments show that sulfur, originally present in sulfidic form (S2−), is oxidized during the transformation to the sulfate form (S6+). Upon formation (at or immediately below the surface), the highly soluble cadmium sulfate is assumed to be transported to the surface in solution and reprecipitates there, forming the whitish globules. The presence of cadmium sulfate (CdSO4·2H2O) and ammonium cadmium sulfate [(NH4)2Cd(SO4)2] at the surface is confirmed by microscopic X-ray diffraction measurements, where the latter salt is suspected to result from a secondary reaction of cadmium sulfate with ammonia. Measurements performed on cross sections reveal that the oxidation front has penetrated into the yellow paint down to ca. 1−2 ìm. The morphology and elemental distribution of the paint and degradation product were examined by means of scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS) and synchrotron radiation based micro-X-ray fluorescence spectrometry (SR ì-XRF). In addition, ultraviolet-induced visible fluorescence photography (UIVFP) revealed itself to be a straightforward technique for documenting the occurrence of this specific kind of degradation on a macroscale by painting conservators.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 91
DOI: 10.1021/AC802518Z
|
|
|
“High resolution micro-XRF maps of iron oxides inside sensory dendrites of putative avian magnetoreceptors”. Falkenberg G, Fleissner GE, Fleissner GUE, Schuchardt K, Kühbacher M, Chalmin E, Janssens K, Journal of physics : conference series 186, 012084 (2009). http://doi.org/10.1088/1742-6596/186/1/012084
Abstract: Iron mineral containing sensory dendrites in the inner lining of the upper beak of homing pigeons [1] and various bird species [2] are the first candidate structures for an avian magnetic field receptor. A new concept of magnetoreception [3, 4] is based on detailed ultra-structural optical and electron microscopy analyses in combination with synchrotron radiation microscopic X-ray fluorescence analysis (micro-XRF) and microscopic X-ray absorption near edge structures (micro-XANES). Several behavioral experiments [5, 6] and first mathematical simulations [6] affirm our avian magnetoreceptor model. The iron minerals inside the dendrites are housed in three different subcellular compartments (bullets, platelets, vesicles), which could be clearly resolved and identified by electron microscopy on ultrathin sections [1, 3]. Micro-XRF and micro-XANES data obtained at HASYLAB beamline L added information about the elemental distribution and Fe speciation [3], but are averaged over the complete dendrite due to limited spatial resolution. Here we present recently performed micro-XRF maps with sub-micrometer resolution (ESRF ID21), which reveal for the first time subcellular structural information from almost bulk-like dendrite sample material. Due to the thickness of 30 μm the microarchitecture of the dendrites can be considered as undisturbed and artefacts introduced by sectioning might be widely reduced.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Times cited: 2
DOI: 10.1088/1742-6596/186/1/012084
|
|
|
“Possibilities and limitations of synchrotron X-ray powder diffraction with double crystal and double multilayer monochromators for microscopic speciation studies”. de Nolf W, Jaroszewicz J, Terzano R, Lind OC, Salbu B, Vekemans B, Janssens K, Falkenberg G, Spectrochimica acta: part B : atomic spectroscopy 64, 775 (2009). http://doi.org/10.1016/J.SAB.2009.06.003
Abstract: The performance of a combined microbeam X-ray fluorescence/X-ray powder diffraction (XRF/XRPD) measurement station at Hamburger Synchrotronstrahlungslabor (HASYLAB) Beamline L is discussed in comparison to that at European Synchrotron Radiation Facility (ESRF) ID18F/ID22. The angular resolution in the X-ray diffractograms is documented when different combinations of X-ray source, optics and X-ray diffraction detectors are employed. Typical angular resolution values in the range 0.30.5° are obtained at the bending magnet source when a pink beam form of excitation is employed. A similar setup at European Synchrotron Radiation Facility beamlines ID18F and ID22 allows to reach angular resolution values of 0.10.15°. In order to document the possibilities and limitations for speciation of metals in environmental materials by means of Hamburger Synchrotronstrahlungslabor Beamline L X-ray fluorescence/X-ray powder diffraction setup, two case studies are discussed, one involved in the identification of the crystal phases in which heavy metals such as chromium, iron, barium and lead are present in polluted soils of an industrial site (Val Basento, Italy) and another involved in the speciation of uranium in depleted uranium particles (Ceja Mountains, Kosovo). In the former case, the angular resolution is sufficient to allow identification of most crystalline phases present while in the latter case, it is necessary to dispose of an angular resolution of ca. 0.2° to distinguish between different forms of oxidized uranium.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.241
Times cited: 7
DOI: 10.1016/J.SAB.2009.06.003
|
|
|
“Solid state speciation and potential bioavailability of depleted uranium particles from Kosovo and Kuwait”. Lind OC, Salbu B, Skipperud L, Janssens K, Jaroszewicz J, de Nolf W, Journal of environmental radioactivity 100, 301 (2009). http://doi.org/10.1016/J.JENVRAD.2008.12.018
Abstract: A combination of synchrotron radiation based X-ray microscopic techniques (ì-XRF, ì-XANES, ì-XRD) applied on single depleted uranium (DU) particles and semi-bulk leaching experiments has been employed to link the potential bioavailability of DU particles to site-specific particle characteristics. The oxidation states and crystallographic forms of U in DU particles have been determined for individual particles isolated from selected samples collected at different sites in Kosovo and Kuwait that were contaminated by DU ammunition during the 1999 Balkan conflict and the 1991 Gulf war. Furthermore, small soil or sand samples heavily contaminated with DU particles were subjected to simulated gastrointestinal fluid (0.16 M HCl) extractions. Characteristics of DU particles in Kosovo soils collected in 2000 and in Kuwait soils collected in 2002 varied significantly depending on the release scenario and to some extent on weathering conditions. Oxidized U (+6) was determined in large, fragile and bright yellow DU particles released during fire at a DU ammunition storage facility and crystalline phases such as schoepite (UO3·2.25H2O), dehydrated schoepite (UO3·0.75H2O) and metaschoepite (UO3·2.0H2O) were identified. As expected, these DU particles were rapidly dissolved in 0.16 M HCl (84 ± 3% extracted after 2 h) indicating a high degree of potential mobility and bioavailability. In contrast, the 2 h extraction of samples contaminated with DU particles originating either from corrosion of unspent DU penetrators or from impacted DU ammunition appeared to be much slower (2030%) as uranium was less oxidized (+4 to +6). Crystalline phases such as UO2, UC and metallic U or UTi alloy were determined in impacted DU particles from Kosovo and Kuwait, while the UO2,34 phase, only determined in particles from Kosovo, could reflect a more corrosive environment. Although the results are based on a limited number of DU particles, they indicate that the structure and extractability of DU particles released from similar sources (metallic U penetrators) will depend on the release scenarios (fire, impact) and to some extent environmental conditions. However, most of the DU particles (7396%) in all investigated samples were dissolved in 0.16 M HCl after one week indicating that a majority of the DU material is bioaccessible.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 2.31
Times cited: 49
DOI: 10.1016/J.JENVRAD.2008.12.018
|
|
|
“Spatially resolved micro-X-ray fluorescence and micro-X-ray absorption fine structure study of a fractured granite bore core following a radiotracer experiment”. Denecke MA, Brendebach B, de Nolf W, Falkenberg G, Janssens K, Simon R, Spectrochimica acta: part B : atomic spectroscopy 64, 791 (2009). http://doi.org/10.1016/J.SAB.2009.05.025
Abstract: Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolution on actinide-containing samples provide information necessary for safety assessment of nuclear waste disposal. In this paper one example of such an experiment is presented. This example entails neptunium speciation in a fractured granite bore core from the Swedish Äspö Hard Rock Laboratory following a radiotracer experiment using µ-XAFS and µ-XRF. In order to probe micro-volumes below the surface in the granite samples and thereby avoid potential changes in the Np speciation during cutting of the bore core, a confocal irradiationdetection geometry is employed. µ-XAFS results for a selected granite bore core cross section with ~ 3 nmol Np/g reveal that Np, originally introduced as Np(V) in the tracer cocktail, is present in the granite in its reduced Np(IV) form. The Np(IV) is often present as particles, tens of µm in size. Elemental distribution maps show the tracer Np to be located in fissures and permeable channels not larger than 100 µm. The Np distribution appears often correlated with Zn also present in some fissures. We observe small granite fissures containing Fe (presumably Fe(II)), where we do not detect any Np. It is feasible that inflowing Np(V) has a shorter residence time in large fractures, while in the smaller fissures migration is slower, leading to longer residence times, i.e., reaction times, where it is reduced to less soluble Np(IV) and becomes thereby immobilized.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.241
Times cited: 21
DOI: 10.1016/J.SAB.2009.05.025
|
|
|
“Study on the impregnation of archaeological waterlogged wood with consolidation treatments using synchrotron radiation microtomography”. Bugani S, Modugno F, Lucejko JJ, Giachi G, Cagno S, Cloetens P, Janssens K, Morselli L, Analytical and bioanalytical chemistry 395, 1977 (2009). http://doi.org/10.1007/S00216-009-3101-5
Abstract: In favourable conditions of low temperature and low oxygen concentration, archaeological waterlogged wooden artefacts, such as shipwrecks, can survive with a good state of preservation. Nevertheless, anaerobic bacteria can considerably degrade waterlogged wooden objects with a significant loss in polysaccharidic components. Due to these decay processes, wood porosity and water content increase under ageing. In such conditions, the conservation treatments of archaeological wooden artefacts often involve the replacement of water with substances which fill the cavities and help to prevent collapse and stress during drying. The treatments are very often expensive and technically difficult, and their effectiveness very much depends on the chemical and physical characteristics of the substances used for impregnation. Also important are the degree of cavity-filling, penetration depth and distribution in the structure of the wood. In this study, the distribution in wood cavities of some mixtures based on polyethylene glycols and colophony, used for the conservation of waterlogged archaeological wood, was investigated using synchrotron radiation X-ray computed microtomography (SR-A mu CT). This non-destructive imaging technique was useful for the study of the degraded waterlogged wood and enabled us to visualise the morphology of the wood and the distribution of the materials used in the wood treatments. The study has shown how deposition is strictly related to the dimension of the wooden cavities. The work is currently proceeding with the comparison of synchrotron observations with the data of the solutions viscosity and with those of the properties imparted to the wood by the treatments.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.431
Times cited: 30
DOI: 10.1007/S00216-009-3101-5
|
|
|
“Analysis of indoor gaseous formic and acetic acid, using radial diffusive samplers”. Stranger M, Potgieter-Vermaak S, Sacco P, Quaglio F, Pagani D, Cocheo C, Godoi AFL, Van Grieken R, Environmental monitoring and assessment 149, 411 (2009). http://doi.org/10.1007/S10661-008-0217-6
Abstract: A diffusive sampling method for the determination of gaseous acetic and formic acids, using a radial symmetry diffusive sampler, has been optimised for a 7-day exposure time in this study. Sampling rate determinations were performed on data obtained from a dynamic exposure chamber, simulating the indoor conditions of an empty, closed, room, at room temperature and minimal wind speed. Analysis has been performed by means of ion chromatography. The sampling rates for formic acid concentrations of 128 ìg m−3 and 1248 ìg m−3 were determined to be 91.2 ± 3.9 ml min−1 and 111.6 ± 2.8 ml min−1, respectively. The acetic acid sampling rate was independent of the concentration in the range 160 ìg m−31564 ìg m−3, and amounted to 97.3 ± 3.1 ml min−1. Experimentally determined sampling rates showed deviations of 3% for acetic acid, and 321% for formic acid, in relation to theoretically derived values. The blank values were as low as 1.69 ± 0.07 ìg for formic acid and 1.21 ± 0.14 ìg for acetic acid, and detection limits lower than 0.5 ìg m−3 could be achieved, which is an improvement of 9899% compared to previously validated diffusive sampling methods. This study describes the first step of an extended validation program in which the applicability of these types of samplers for the measurement of organic acids will be validated and optimised for the environmental conditions typical for museum showcases.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1007/S10661-008-0217-6
|
|