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Numrering	Referens	Omslagsbild	Hitta
1.	Magnuson, Martin, 1965-, et al. (författare) Electronic Structure and Chemical Bonding of AmorphousChromium Carbide Thin Films 2012 Ingår i: Journal of Physics. - IOP Publishing : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24, s. 225004- Tidskriftsartikel (refereegranskat)abstract The microstructure, electronic structure, and chemical bonding of chromium carbidethin films with different carbon contents have been investigated with high-resolutiontransmission electron microscopy, electron energy loss spectroscopy and soft x-rayabsorption-emission spectroscopies. Most of the films can be described as amorphousnanocomposites with non-crystalline CrCx in an amorphous carbon matrix. At highcarbon contents, graphene-like structures are formed in the amorphous carbon matrix.At 47 at% carbon content, randomly oriented nanocrystallites are formed creating acomplex microstructure of three components. The soft x-ray absorption-emissionstudy shows additional peak structures exhibiting non-octahedral coordination andbonding.
2.	Kahl, Gerhard, et al. (författare) Proceedings of the 7th Liquid Matter Conference (Lund, Sweden, 27 June-1 July 2008) PREFACE 2008 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:49 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
3.	Prinz, Christelle (författare) Interactions between semiconductor nanowires and living cells. 2015 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:23 Forskningsöversikt (refereegranskat)abstract Semiconductor nanowires are increasingly used for biological applications and their small dimensions make them a promising tool for sensing and manipulating cells with minimal perturbation. In order to interface cells with nanowires in a controlled fashion, it is essential to understand the interactions between nanowires and living cells. The present paper reviews current progress in the understanding of these interactions, with knowledge gathered from studies where living cells were interfaced with vertical nanowire arrays. The effect of nanowires on cells is reported in terms of viability, cell-nanowire interface morphology, cell behavior, changes in gene expression as well as cellular stress markers. Unexplored issues and unanswered questions are discussed.
4.	Feierabend, Maja, 1990, et al. (författare) Optical fingerprint of non-covalently functionalized transition metal dichalcogenides 2017 Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:38, s. Article no 384003 - Tidskriftsartikel (refereegranskat)abstract Atomically thin transition metal dichalcogenides (TMDs) hold promising potential forapplications in optoelectronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibit efficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combination with circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials, they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach, where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we apply the density matrix theory to investigate the potential of non-covalently functionalized monolayer TMDs. Considering exemplary molecules with a strong dipole moment, we predict spectral redshifts and the appearance of an additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular characteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs, leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipole moments open a channel for coherent intervalley coupling between the high-symmetry K and K' points which may create new possibilities for spin-valleytronics application.
5.	Gryglas-Borysiewicz, Marta, et al. (författare) Hydrostatic-pressure-induced changes of magnetic anisotropy in (Ga, Mn) As thin films 2017 Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:11 Tidskriftsartikel (refereegranskat)abstract The impact of hydrostatic pressure on magnetic anisotropy energies in (Ga, Mn) As thin films with in-plane and out-of-plane magnetic easy axes predefined by epitaxial strain was investigated. In both types of sample we observed a clear increase in both in-plane and out-of-plane anisotropy parameters with pressure. The out-of-plane anisotropy constant is well reproduced by the mean-field p-d Zener model; however, the changes in uniaxial anisotropy are much larger than expected in the Mn-Mn dimer scenario.
6.	John Mukkattukavil, Deepak, et al. (författare) Resonant inelastic soft x-ray scattering on LaPt2Si2 2022 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 34:32, s. 324003- Tidskriftsartikel (refereegranskat)abstract X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2 single crystal at the Si 2p and La 4d edges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Si s and d local partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4f excitations. Calculations show that Pt d-LPDOS dominates the occupied states, and a sharp localized La f state is found in the unoccupied states, in line with the observations.
7.	Lu, Hongduo, et al. (författare) Ionic liquid interface at an electrode: Simulations of electrochemical properties using an asymmetric restricted primitive model 2018 Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 30 Tidskriftsartikel (refereegranskat)abstract © 2018 IOP Publishing Ltd. We use Monte Carlo simulations of a coarse-grained model to investigate structure and electrochemical behaviours at an electrode immersed in room temperature ionic liquids (RTILs). The simple RTIL model, which we denote the asymmetric restricted primitive model (ARPM), is composed of monovalent hard-sphere ions, all of the same size, in which the charge is asymmetrically placed. Not only the hard-sphere size (d), but also the charge displacement (b), is identical for all species, i.e. the monovalent RTIL ions are fully described by only two parameters (d, b). In earlier work, it was demonstrated that the ARPM can capture typical static RTIL properties in bulk solutions with remarkable accuracy. Here, we investigate its behaviour at an electrode surface. The electrode is assumed to be a perfect conductor and image charge methods are utilized to handle polarization effects. We find that the ARPM of the ionic liquid reproduces typical (static) electrochemical properties of RTILs. Our model predicts a declining differential capacitance with increasing temperature, which is expected from simple physical arguments. We also compare our ARPM, with the corresponding RPM description, at an elevated temperature (1000 K). We conclude that, even though ion pairing occurs in the ARPM system, reducing the concentration of 'free' ions, it is still better able to screen charge than a corresponding RPM melt. Finally, we evaluate the option to coarse-grain the model even further, by treating the fraction of the ions that form ion pairs implicitly, only through the contribution to the dielectric constant of the corresponding dipolar (ion pair) fluid. We conclude that this primitive representation of ion pairing is not able to reproduce the structures and differential capacitances of the system with explicit ion pairs. The main problem seems to be due to a limited dielectric screening in a layer near the electrode surface, resulting from a combination of orientational restrictions and a depleted dipole density.
8.	Midtvedt, Daniel, 1988, et al. (författare) Multi-scale approach for strain-engineering of phosphorene 2017 Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:18, s. Article nr 185702 - Tidskriftsartikel (refereegranskat)abstract A multi-scale approach for the theoretical description of deformed phosphorene is presented. This approach combines a valence-force model to relate macroscopic strain to microscopic displacements of atoms and a tight-binding model with distance-dependent hopping parameters to obtain electronic properties. The resulting self-consistent electromechanical model is suitable for large-scale modeling of phosphorene devices. We demonstrate this for the case of inhomogeneously deformed phosphorene drum, which may be used as an exciton funnel.
9.	Roosen-Runge, Felix, et al. (författare) Self-diffusion of nonspherical particles fundamentally conflicts with effective sphere models 2021 Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 33:15 Tidskriftsartikel (refereegranskat)abstract Modeling diffusion of nonspherical particles presents an unsolved and considerable challenge, despite its importance for the understanding of crowding effects in biology, food technology and formulation science. A common approach in experiment and simulation is to map nonspherical objects on effective spheres to subsequently use the established predictions for spheres to approximate phenomena for nonspherical particles. Using numerical evaluation of the hydrodynamic mobility tensor, we show that this so-called effective sphere model fundamentally fails to represent the self-diffusion in solutions of ellipsoids as well as rod-like assemblies of spherical beads. The effective sphere model drastically overestimates the slowing down of self-diffusion down to volume fractions below 0.01. Furthermore, even the linear term relevant at lower volume fraction is inaccurate, linked to a fundamental misconception of effective sphere models. To overcome the severe problems related with the use of effective sphere models, we suggest a protocol to predict the short-time self-diffusion of rod-like systems, based on simulations with hydrodynamic interactions that become feasible even for more complex molecules as the essential observable shows a negligible system-size effect.
10.	Östman, Erik, et al. (författare) Ising-like behaviour of mesoscopic magnetic chains 2018 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:36 Tidskriftsartikel (refereegranskat)abstract We demonstrate an experimental realization of the short range magnetic order in a one-dimensional Ising chain using fabricated mesospins. We confirm an excellent agreement between the experimental findings and simulations obtained using the original Ising model. In particular, we are able to show that the thermal behaviour of the mesoscopic Ising chain dominates over the thermal behaviour of the individual mesospins themselves, confirming that fabricated mesospins can be viewed as artificial magnetic atoms.
11.	Jena, Suchit Kumar, et al. (författare) Slow spin dynamics of cluster spin-glass spinel Zn(Fe1-xRu (x))(2)O-4 : role of Jahn-Teller active spin-1/2 Cu2+ ions at B-sites 2022 Ingår i: Journal of Physics. - : IOP Publishing Ltd. - 0953-8984 .- 1361-648X. ; 34:40 Tidskriftsartikel (refereegranskat)abstract We report the slow spin dynamics of cluster spin-glass (SG) spinel Zn(Fe1-xRux)(2)O-4 by means of detailed dc-magnetization and ac-susceptibility studies combined with the heat capacity analysis. Two specific compositions (x= 0.5, 0.75) have been investigated in detail along with the substitution of Jahn-Teller (JT) active spin-1/2 Cu2+ ions at B-sites. Measurements based on the frequency and temperature dependence of ac-susceptibility (chi(ac)(f, T)) and the subsequent analysis using the empirical scaling laws such as: (a) Vogel-Fulcher law and (b) Power law reveal the presence of cluster SG state below the characteristic freezing temperature T-SG (17.77 K (x= 0.5) and 14 K (x= 0.75)). Relaxation dynamics of both the compositions follow the non-mean field de Almeida-Thouless (AT)-line approach (T-SG(H) = T-SG(0)(1 - AH(2/phi))), with an ideal value of phi = 3. Nevertheless, the analysis of temperature dependent high field dc-susceptibility, chi(hf) (2 kOe <= H-DC <= 20 kOe, T) provides evidence for Gabay-Toulouse type mixed-phase (coexistence of SG and ferrimagnetic (FiM)) behaviour. Further, in the case of Cu0.2Zn0.8FeRuO4 system, slowly fluctuating magnetic clusters persist even above the short-range FiM ordering temperature (T-FiM) and their volume fraction vanishes completely across similar to 6T(FiM). This particular feature of the dynamics has been very well supported by the time decay of the thermoremanent magnetization and heat-capacity studies. We employed the high temperature series expansion technique to determine the symmetric exchange coupling (J(S)) between the spins which yields J(S) = -3.02 x 10(-5) eV for Cu0.2Zn0.8FeRuO4 representing the dominant intra-sublattice ferromagnetic interactions due to the dilute incorporation of the JT active Cu2+ ions. However, the antiferromagnetic coupling is predominant in ZnFeRuO4 and Cu0.2Zn0.8Fe0.5Ru1.5O4 systems. Finally, we deduced the magnetic phase diagram in the H-DC - T plane using the characteristic parameters obtained from the field variations of both ac- and dc-magnetization measurements.
12.	Johansson, Leif, 1945-, et al. (författare) Synchrotron radiation studies of the SiO2/SiC(0001) interface 2004 Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER ISSN (0953-8984). - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; , s. S3423-S3434 Konferensbidrag (refereegranskat)abstract Two questions thought to have a significant effect on SiC-MOS device characteristics are treated. The existence of carbon clusters or carbon containing by-products and the existence of sub-oxides at the SiO2/SiC interface. Results of photoemission studies using synchrotron radiation of the interface of the Si-terminated surface of n-type SiC(0001) crystals are presented. The results show that no carbon clusters or carbon containing by-product can. be detected at the interface of in situ or ex situ grown samples with an oxide layer thickness larger than similar to10 Angstrom. The presence of sub-oxides at the SiO2/SiC interface was predicted in a theoretical calculation and has been revealed in Si 2p core level data by several groups. These results were not unanimous; significant differences in the number of sub-oxide and shifts were reported. A study also including the Si 1s core level and Si KLL Auger transitions was therefore made. These data show the presence of only one sub-oxide at the interface, assigned to Si1+ oxidation states. The SiO2 chemical shift is shown to exhibit a dependence on oxide thickness, similar to but smaller in magnitude than the thickness dependence earlier revealed for SiO2/Si.
13.	Mulders, A. M., et al. (författare) On The Interface Magnetism Of Thin Oxidized Co Films : Orbital And Spin Moments 2009 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:12, s. 124211- Tidskriftsartikel (refereegranskat)abstract An x-ray magnetic circular dichroism study of a polycrystalline Co/CoO bilayer is presented. Using both the chemical specificity and surface sensitivity in the core level techniques, we find that uncompensated Co2+ spin moments participate in the remanent ferromagnetic response of the bilayer that has oxygen nearest neighbors. These are likely located at the Co/CoO interface. As intermixing of magnetic species is not present in Co/CoO, it is concluded that the observed interface moments are due to interface roughness. Given their direction, these moments appear to not directly correlate to the exchange bias in these bilayers.
14.	Karlsson, Krister (författare) Self-consistent GW combined with single-site dynamical mean field theory for a Hubbard model 2005 Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 17:48, s. 7573-7598 Tidskriftsartikel (refereegranskat)abstract We combine the single-site dynamical mean field theory (DMFT) with the non-local GW method. This is done fully self-consistently and we apply our formalism to a one-band Hubbard model. Eventually at self-consistency the full self-energy and polarization operator of the system are retrieved. Some numerical results, in the metallic as well as the insulator regime, are presented and briefly discussed. Depending on the involved interaction (GW) parameters, substantial changes are found when the GW self-energy is incorporated. However, the main point of this work is to demonstrate the applicability of the method, not to make any strict comparison with exact results and experiments.
15.	Magnuson, Martin, et al. (författare) Resonant soft x-ray Raman scattering of NiO 2002 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:13, s. 3669-3676 Tidskriftsartikel (refereegranskat)abstract Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p x-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9\underline L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.
16.	Mahani, Mohammad Reza, et al. (författare) Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface 2014 Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 26:39, s. Article ID: 394006- Tidskriftsartikel (refereegranskat)abstract Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.
17.	Manchon, A., et al. (författare) Currents and torques due to spin-dependent diffraction in ferromagnetic/spin spiral bilayers 2008 Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 20:50, s. 505213- Tidskriftsartikel (refereegranskat)abstract Spin-dependent transport through the interface between a ferromagnet and a spin spiral is investigated using both ballistic and diffusive models. We find that spin-dependent interferences lead to a new type of diffraction called 'spin diffraction'. It is shown that this spin diffraction leads to local spin and electrical current along the interface, as well as spin transfer torque acting on the spin spiral. This study also emphasizes that in highly inhomogeneous magnetic configurations, diffracted electrons must be taken into account to properly describe the spin transport.
18.	Björström, Cecilia M., et al. (författare) Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends 2005 Ingår i: Journal of Physics. - Philadelphia : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 17:50, s. L529-L534 Tidskriftsartikel (refereegranskat)abstract Blends of the low-bandgap polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole] (APFO-3) and the fullerene derivative [6,6]-phenyl–C61–butyric acid methyl ester (PCBM) were spin-coated from chloroform solution into thin films, which were examined with dynamic secondary ion mass spectrometry. For blends with high PCBM content, the depth profiles show composition waves that were caused by surface-directed phase separation during spin-coating. The formation of such multilayer structures by spontaneous self-stratification is likely to have implications for optimization strategies for the performance of organic solar cells
19.	Adell, Johan, 1980, et al. (författare) Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As 2011 Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 23:8 Tidskriftsartikel (refereegranskat)abstract Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.
20.	Ahlström, Bodil, 1968, et al. (författare) Prediction of structures and gel transitions in systems of colloids with moderate-range attractions 2007 Ingår i: Journal of Physics. Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19, s. 036102-036117 Tidskriftsartikel (refereegranskat)abstract Predictions of glass transitions from the idealized mode-coupling theory (MCT) are tested for systems with intermediate-range particle attractions. Liquid structure input to MCT is provided by the Asakura–Oosawa (AO) theory for the depletion interaction, used as an idealized model for structures in colloid–polymer mixtures. The effective one-component formulation of the AO theory is verified to capture the complete pair structure found from the binary version of the theory also for polymer–colloid size ratios somewhat larger than those for which an exact mapping of the two descriptions holds. The Percus–Yevick theory is shown to provide an accurate structural input to MCT, at least in the single-phase fluid region. With this combination of theories, very reasonable predictions for locations of glassy states in the experimental phase diagram are obtained for polymer–colloid size ratios somewhat larger than have been considered before. Simple approximations are also suggested for extracting the remaining pair structure from calculations of the one-component AO theory.
21.	Angelescu, Daniel G., et al. (författare) Branched-linear polyion complexes at variable charge densities 2015 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:35 Tidskriftsartikel (refereegranskat)abstract Structural behavior of complexes formed by a charged and branched copolymer and an oppositely charged and linear polyion was examined by Monte Carlo simulations employing a coarse-grained bead-spring model. The fractional bead charge and the branching density were systematically varied; the former between 0e and 1e and the latter such that both the comb-polymer and the bottle-brush limits were included. The number of beads of the main chain of the branched copolymer and of the linear polyion was always kept constant and equal, and a single side-chain length was used. Our analysis involved characterization of the complex as well as investigation of size, shape, and flexibility of the charged moieties. An interplay between Coulomb interaction and side-chain repulsion governed the structure of the polyion complex. At strong Coulomb interaction, the complexes underwent a gradual transition from a globular structure at low branching density to an extended one at high branching density. As the electrostatic coupling was decreased, the transition was smoothened and shifted to lower branching density, and, eventually, a behavior similar to that found for neutral branched polymer was observed. Structural analogies and dissimilarities with uncharged branched polymers in poor solutions are discussed.
22.	Benediktsson, Magnús, et al. (författare) Stability and mobility of vacancy-H complexes in Al 2013 Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:37, s. 375401- Tidskriftsartikel (refereegranskat)abstract The effect of hydrogen loading on the stability and mobility of vacancy-H complexes in aluminum is determined by applying DFT and the minimum-mode-following method. The binding energy per H-atom within a complex is found to range from -0.36 eV/atom to -0.34 eV/atom for an occupancy of, respectively, a single and eight H-atoms. When eight H-atoms are neighboring the vacancy the total binding energy becomes -2.72 eV. However, already at a load level of two H-atoms the total binding energy reaches -0.70 eV, which fully compensates the vacancy creation energy. It is observed that for complexes with four or more H-atoms the vacancy gets pinned, as the diffusion barrier increases by a factor of two, reaching a value of 1.03 eV or more. The explanation for the increased energy barrier is that at the higher hydrogen load levels the system must traverse an energetically unfavorable configuration where two or more H-atoms are separated from the vacancy. As a possible consequence of the decreased mobility and increased stability, highly loaded vacancy-H complexes are likely to act as nucleation sites for extended defects.
23.	Beutler, A., et al. (författare) Identification of a laterally mobile state during CO adsorption 2000 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:6, s. 765-772 Tidskriftsartikel (refereegranskat)abstract We have investigated CO adsorption at 300 K on ∼ 1.5 atomic layer thick Pd films on a Mo(110) surface by high-resolution core level photoemission. We describe how high-resolution core level spectroscopy may be utilized to study the influence of laterally mobile states on the sticking probability of molecules on such a laterally heterogeneous surface. The present Pd films are laterally heterogeneous in the sense that the additional ∼ 0.5 atomic Pd layer forms mesoscopic one-layer thick islands on top of the first Pd layer. At 300 K, CO chemisorbs on these two-layer thick islands but not on the one-layer parts of the film. The rate at which these two-layer islands are filled by CO molecules as the surface is exposed to CO is found to be consistent with a picture where CO molecules that initially impinge on the one-layer parts of the surface enter a laterally mobile state and diffuse to the two-layer islands and adsorb there. This mobile state is in many respects similar to a classical precursor state.
24.	Blomberg, Sara, et al. (författare) 2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence 2016 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:45 Forskningsöversikt (refereegranskat)abstract In recent years, efforts have been made in catalysis related surface science studies to explore the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. Techniques such as high pressure scanning tunneling/atomic force microscopy (HPSTM/AFM), near ambient pressure x-ray photoemission spectroscopy (NAPXPS), surface x-ray diffraction (SXRD) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at semi-realistic conditions have been used to study the surface structure of model catalysts under reaction conditions, combined with simultaneous mass spectrometry (MS). These studies have provided an increased understanding of the surface dynamics and the structure of the active phase of surfaces and nano particles as a reaction occurs, providing novel information on the structure/activity relationship. However, the surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface. Therefore, the catalytic activity of the sample itself will act as a gas-source or gas-sink, and will affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, we have applied planar laser induced fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts. Our measurements demonstrate that the gas composition differs significantly close to the catalyst and at the position of the MS, which indeed should have a profound effect on the surface structure. However, PLIF applied to catalytic reactions presents several beneficial properties in addition to investigate the effect of the catalyst on the effective gas composition close to the model catalyst. The high spatial and temporal resolution of PLIF provides a unique tool to visualize the on-set of catalytic reactions and to compare different model catalysts in the same reactive environment. The technique can be applied to a large number of molecules thanks to the technical development of lasers and detectors over the last decades, and is a complementary and visual alternative to traditional MS to be used in environments difficult to asses with MS. In this article we will review general considerations when performing PLIF experiments, our experimental set-up for PLIF and discuss relevant examples of PLIF applied to catalysis.
25.	Bolinsson, J, et al. (författare) Direct observation of atomic scale surface relaxation in ortho twin structures in GaAs by XSTM 2009 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 21:5 Tidskriftsartikel (refereegranskat)abstract We have studied the (110) GaAs surface of a structure containing ortho twins by cross-sectional scanning tunnelling microscopy and we have compared the experimental results with ab initio density functional theory calculations and STM simulations. Both experimentally and theoretically we find that the surface of different twin crystallites are significantly displaced with respect to each other, parallel to the twin boundary. This result is explained by a surface relaxation of the atoms in the (110) GaAs surface and the difference between the atomic configuration of the ortho twins.
26.	Borck, O., et al. (författare) Adsorption of methylamine on Ni3Al(111) and NiAl(110)-a high resolution photoelectron spectroscopy and density functional theory study 2010 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 22:39 Tidskriftsartikel (refereegranskat)abstract Methylamine adsorption on the ordered Ni3Al(111) and NiAl(110) surfaces has been investigated by high resolution photoelectron spectroscopy and density functional theory calculations. Methylamine adsorbs molecularly at both surfaces at low temperature (90 K). The experiments show that methylamine interacts with the surface aluminium atoms on both surfaces, resulting in a positive binding energy shift relative to the Al 2p bulk contributions. A shift towards lower binding energy is also observed on NiAl(110) attributed to first and second layer surface Al atoms not bonded to methylamine. According to total energy calculations methylamine binds through its N atom to Al on-top sites on NiAl(110) while the Ni on-top site is found to be slightly preferred over the Al on-top site on Ni3Al(111). Calculated adsorbate induced shifts are, however, in good agreement with the experimental values only when methylamine is situated in the Al on-top site on both surfaces. In both cases, a lone pair bonding mechanism is found.
27.	Calder, S., et al. (författare) Neutron scattering and mu SR investigations of the low temperature state of LuCuGaO4 2013 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 25:35 Tidskriftsartikel (refereegranskat)abstract LuCuGaO4 has magnetic Cu2+ and diamagnetic Ga3+ ions distributed on a triangular bilayer and is suggested to undergo a spin glass transition at T-g similar to 0.4 K. Using mu SR (muon spin rotation) and neutron scattering measurements, we show that at low temperature the spins form a short range correlated state with spin fluctuations detectable over a wide range of timescales: at 0.05 K magnetic fluctuations can be detected in both the mu SR time window and also extending beyond 7 meV in the inelastic neutron scattering response, indicating magnetic fluctuations spanning timescales between similar to 10(-5) and similar to 10(-10) s. The dynamical susceptibility scales according to the form chi '' (omega)T-alpha, with alpha = 1, throughout the measured temperature range (0.05-50 K). These effects are associated with quantum fluctuations and some degree of structural disorder in ostensibly quite different materials, including certain heavy fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond glasses. We therefore suggest that LuCuGaO4 is an interesting model compound for the further examination of disorder and quantum magnetism.
28.	Castaneda-Priego, R., et al. (författare) On the calculation of the structure of charge-stabilized colloidal dispersions using density-dependent potentials 2012 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:6 Tidskriftsartikel (refereegranskat)abstract The structure of charge-stabilized colloidal dispersions has been studied through a one-component model using a Yukawa potential with density-dependent parameters examined with integral equation theory and Monte Carlo simulations. Partial thermodynamic consistency was guaranteed by considering the osmotic pressure of the dispersion from the approximate mean-field renormalized jellium and Poisson-Boltzmann cell models. The colloidal structures could be accurately described by the Ornstein-Zernike equation with the Rogers-Young closure by using the osmotic pressure from the renormalized jellium model. Although we explicitly show that the correct effective pair-potential obtained from the inverse Monte Carlo method deviates from the Yukawa shape, the osmotic pressure constraint allows us to have a good description of the colloidal structure without losing information on the system thermodynamics. Our findings are corroborated by primitive model simulations of salt-free colloidal dispersions.
29.	Chen, Junsheng, et al. (författare) Surface plasmon inhibited photo-luminescence activation in CdSe/ZnS core-shell quantum dots 2016 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:25 Tidskriftsartikel (refereegranskat)abstract In a composite film of Cdx Sey Zn1-x S1-y gradient core-shell quantum dots (QDs) and gold nanorods (NRs), the optical properties of the QDs are drastically affected by the plasmonic nanoparticles. We provide a careful study of the two-step formation of the film and its morphology. Subsequently we focus on QD luminescence photoactivation - a process induced by photochemical changes on the QD surface. We observe that even a sparse coverage of AuNRs can completely inhibit the photoactivation of the QDs' emission in the film. We demonstrate that the inhibition can be accounted for by a rapid energy transfer between QDs and AuNRs. Finally, we propose that the behavior of emission photoactivation can be used as a signature to distinguish between energy and electron transfer in the QD-based materials.
30.	Csontos, Dan, et al. (författare) Scattering-matrix formalism of electron transport through three-terminal quantum structures: formulation and application to Y-junction devices 2002 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 14:47, s. 12513-12528 Tidskriftsartikel (refereegranskat)abstract In this paper we present a formalism for the calculation of electron transport through three-terminal junction devices, which have received attention due to their recently demonstrated non-linear electrical properties. The formalism, which is based on the scattering-matrix method, takes quantum interference effects fully into account. Furthermore, the formalism provides numerical stability in the calculations as well as large flexibility in the modelling of arbitrary potential profiles due to the common basis approach used in the formulation. The method is used to calculate the transport properties for Y-shaped three-terminal ballistic junction (TBJ) structures with configurations typical of recently performed experiments. Quantum interference effects are shown to strongly influence the transport characteristics of TBJ structures due to complex scattering of the electrons in the cavity-like coupling window between the three arms of the device. The theoretical approach presented in this paper provides a flexible tool for the study of such quantum interference effects, which may play an important role in the design and functionality of future nanoscale devices based on three-terminal junctions.
31.	Darnton, N., et al. (författare) Hydrodynamics in 2 1/2 dimensions : Making jets in a plane 2001 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:21, s. 4891-4902 Tidskriftsartikel (refereegranskat)abstract We show that a careful analysis of the Navier-Stokes equation in the low Reynolds number limit has two distinct solutions, one valid for a deep, thin curtain of flow and the other for a thin wide flow. We derive a solution to the latter situation and use the results to develop a new way to control fluid flows in thin, wide sheet flow.
32.	De Padova, Paola, et al. (författare) Mn-silicide nanostructures aligned on massively parallel silicon nano-ribbons 2013 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 25:1 Tidskriftsartikel (refereegranskat)abstract The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation.
33.	Ellström, Carl, et al. (författare) Exciton fine structure splitting in InP quantum dots in GaInP 2007 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 19:29 Tidskriftsartikel (refereegranskat)abstract We have investigated the electronic structure of excitons in InP quantum dots in GaInP. The exciton is theoretically expected to have four states. Two of the states are allowed to optically decay to the ground ( vacuum) state in the dipole approximation. We see these two lines in photoluminescence (PL) experiments and find that the splitting between the lines ( the fine structure splitting) is 150(+/- 30) mu eV. The lines were perpendicularly polarized. We verified that the lines arise from neutral excitons by using correlation spectroscopy. The theoretical calculations show that the polarization of the emission lines are along and perpendicular to the major axis of elongated dots. The fine structure splitting depends on the degree of elongation of the dots and is close to zero for dots of cylindrical symmetry, despite the influence of the piezoelectric polarization, which is included in the calculation.
34.	Engström, Christian (författare) Structural information of nanocomposites from measured optical properties 2007 Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 19:10 Tidskriftsartikel (refereegranskat)abstract This paper is concerned with the estimation of the volume fraction and the anisotropy of a two-component composite from measured bulk properties. An algorithm that takes into account that measurements have errors is developed. This algorithm is used to study data from experimental measurements for a nanocomposite with an unknown nanostructure. The dependence on the nanostructure is quantified in terms of a measure in the representation formula introduced by D Bergman. We use composites with known nanostructures to illustrate the dependence on the underlying measure and show how errors in the measurements affect the estimates of the structural parameters.
35.	Gebresenbut, Girma, 1982-, et al. (författare) Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system 2014 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:32, s. 322202- Tidskriftsartikel (refereegranskat)abstract The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9Â K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.
36.	Goss, J.P., et al. (författare) Small aggregates of interstitials and models for platelets in diamond 2000 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10257-10261 Tidskriftsartikel (refereegranskat)abstract By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties
37.	Gustafson, Johan, et al. (författare) A high pressure x-ray photoelectron spectroscopy study of CO oxidation over Rh(100). 2013 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 26:5 Tidskriftsartikel (refereegranskat)abstract We have studied the oxidation of CO over Rh(100) using high pressure x-ray photoelectron spectroscopy under CO and O2 pressures ranging from 0.01 to 1 mbar. The results show a very low or no conversion for the CO covered surface found at low temperatures, while the activity rises slightly when the temperature is high enough for some CO to desorb, exposing surface sites for dissociative O2 adsorption. As the temperature is increased further, more CO desorbs and oxygen replaces CO as the dominating species at the surface. At the same time we find a sudden increase in the reactivity, such that all CO that reaches the surface is instantly transformed into CO2. We find that the O coverage in the active state is highly dependent on the total pressure and, although we do not detect any presence of a surface oxide as in previous surface x-ray diffraction studies, the highest O coverage indicates that the surface is close to being oxidized.
38.	Gustafson, Johan, et al. (författare) The Rh(100)-(3 × 1)-2O structure. 2012 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:22 Tidskriftsartikel (refereegranskat)abstract The O adsorption on Rh(100) has been studied using high resolution core level spectroscopy, low energy electron diffraction and scanning tunnelling microscopy. In addition to the well known (2 × 2), (2 × 2)-pg and c(8 × 2) structures at coverages of 0.25, 0.5 and 1.75 ML respectively, an intermediate (3 × 1) structure with a coverage of 2/3 ML is identified.
39.	Guthrie, Malcolm (författare) Future directions in high-pressure neutron diffraction. 2015 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:15 Forskningsöversikt (refereegranskat)abstract The ability to manipulate structure and properties using pressure has been well known for many centuries. Diffraction provides the unique ability to observe these structural changes in fine detail on lengthscales spanning atomic to nanometre dimensions. Amongst the broad suite of diffraction tools available today, neutrons provide unique capabilities of fundamental importance. However, to date, the growth of neutron diffraction under extremes of pressure has been limited by the weakness of available sources. In recent years, substantial government investments have led to the construction of a new generation of neutron sources while existing facilities have been revitalized by upgrades. The timely convergence of these bright facilities with new pressure-cell technologies suggests that the field of high-pressure (HP) neutron science is on the cusp of substantial growth. Here, the history of HP neutron research is examined with the hope of gleaning an accurate prediction of where some of these revolutionary capabilities will lead in the near future. In particular, a dramatic expansion of current pressure-temperature range is likely, with corresponding increased scope for extreme-conditions science with neutron diffraction. This increase in coverage will be matched with improvements in data quality. Furthermore, we can also expect broad new capabilities beyond diffraction, including in neutron imaging, small angle scattering and inelastic spectroscopy.
40.	Irbäck, Anders (författare) A minimalistic all-atom approach to protein folding 2003 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 15:18, s. 1797-1807 Tidskriftsartikel (refereegranskat)abstract Using simple sequence-based potentials, the folding properties of a designed three-helix-bundle protein, an alpha-helix and a beta-hairpin are studied. The three-helix-bundle protein is modelled using 5-6 atoms per amino acid and is found to undergo a first-order-like folding transition in which chain collapse and helix formation cannot be separated, which is in-accord with experimental data. The other two sequences are studied using a model that contains all atoms and are indeed found to make an alpha-helix and a beta-hairpin, respectively, for exactly the same choice of parameters. The calculated melting curves are, moreover, in reasonable quantitative agreement with experimental data, for both peptides. The melting curves are found to be quite well described by a simple two-state model, although the energy distributions lack a clear bimodal shape.
41.	Irbäck, Anders (författare) Peptide folding and aggregation studied using a simplified atomic model 2005 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 17:18, s. 1553-1564 Tidskriftsartikel (refereegranskat)abstract Using an atomic model with a simplified-sequence-based potential, the folding properties of several different peptides are studied. Both alpha-helical (Trp cage, F-s) and beta-sheet(GB1p, GB1m2, GB1m3, Betanova, LLM) peptides are considered. The model is able to fold these different peptides for one and the same choice of;parameters, and the melting behaviour of the peptides (folded population against temperature) is in very good agreement with experimental data. Furthermore, using the same model with unchanged parameters, the aggregation behaviour of a fibril-forming fragment of the Alzheimer's A beta peptide is studied, with very promising results.
42.	Isvoranu, Cristina, et al. (författare) Tuning the spin state of iron phthalocyanine by ligand adsorption 2010 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 22:47 Tidskriftsartikel (refereegranskat)abstract The future use of single-molecule magnets in applications will require the ability to control and manipulate the spin state and magnetization of the magnets by external means. There are different approaches to this control, one being the modification of the magnets by adsorption of small ligand molecules. In this paper we use iron phthalocyanine supported by an Au(111) surface as a model compound and demonstrate, using x-ray photoelectron spectroscopy and density functional theory, that the spin state of the molecule can be tuned to different values (S similar to 0, 1/2, 1) by adsorption of ammonia, pyridine, carbon monoxide or nitric oxide on the iron ion. The interaction also leads to electronic decoupling of the iron phthalocyanine from the Au(111) support.
43.	Johansson, Emil, et al. (författare) Hydrogen uptake and optical properties of sputtered Mg-Ni thin films 2004 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16, s. 7649- Tidskriftsartikel (refereegranskat)abstract The hydrogen uptake and distribution in wedged Mg–Ni films, with composition ranging from Mg0.85Ni0.15 to Mg0.55Ni0.45, were investigated. Upon hydrogen loading at 298 K these films undergo a transition from a mirror-like metallic to a semiconducting transparent state. After exposure to a hydrogen pressure of 1 bar, the samples exhibit large variation in optical appearance, ranging from a pale yellowish (Mg rich side) to a brownish shade (Ni rich side). The change in the effective optical band gap Egeff as a function of sample composition and hydrogen concentration was determined; it showed changes from 3.6 eV in the Ni poor domain to 2.4 eV in the Ni rich domain. Composition analysis using the 15N nuclear resonance method showed close to homogeneous hydrogen distribution throughout the film and close to linear increase in the hydrogen uptake with increasing Mg content. The thermal stability of the films is limited; annealing above 393 K results in significant redistribution of the constituents. Mg is enriched at the surface, reacting with Pd and thereby degrading the capping layer through the formation of Mg6Pd and MgO, as determined by x-ray diffraction, x-ray photoelectron spectroscopy and Rutherford backscattering studies. This redistribution results in a severe decrease of the hydrogen uptake rate, as monitored by in situ resistivity measurements.
44.	Kanski, Janusz, 1946, et al. (författare) Mn-induced modifications of Ga 3d photoemission from (Ga, Mn)As: evidence for long range effects 2012 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:43, s. 1-435802 Tidskriftsartikel (refereegranskat)abstract Using synchrotron based photoemission, we have investigated the Mn-induced changes in Ga 3d core level spectra from as-grown Ga(1-x)Mn(x)As. Although Mn is located in Ga substitutional sites, and therefore does not have any Ga nearest neighbors, the impact of Mn on the Ga core level spectra is pronounced even at Mn concentrations in the region of 0.5%. The analysis shows that each Mn atom affects a volume corresponding to a sphere with around 1.4 nm diameter.
45.	Karlstrom, Gunnar, et al. (författare) Effects of different boundary conditions on the long-range structure of polar liquids 2008 Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:49 Konferensbidrag (refereegranskat)abstract The long-range order in strongly coupled dipolar systems has been studied using large-scale simulations for systems containing up to 100 000 particles. It is found that the boundary conditions used strongly influence the result. It is found that a periodic system modeled with the minimum image approximation yields an artificial order, whereas the same system described using the Ewald summation technique is slightly less long-range ordered, as compared to the results obtained from studies on a non-periodical spherical droplet. Analytical expressions together with scaling considerations suggest that dipolar systems are structured on all length scales. However, more extensive studies are needed to fully assess the impact of using different boundary conditions on the long-range structure of polar liquids.
46.	Kikas, A., et al. (författare) Resonant inelastic x-ray scattering and UV-VUV luminescence at the Be 1s edge in BeO 2010 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 22:37 Tidskriftsartikel (refereegranskat)abstract We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO single crystals with incident photon energies in the vicinity of the Be 1s absorption edge. The x-ray emission spectra show that at the Be 1s photoabsorption edge the lattice relaxation processes in the excitation site take place already on the timescale of the radiative decay of the core excitation. Comparison of the x-ray emission and the luminescence spectra indicates that the maximum energy loss of the process of lattice relaxation during the decay of inner-shell holes is similar to the loss that occurs in the self-trapping process of valence excitons. The possible decay channels of core excitations have been discussed and the mechanism for the creation of 5.2 eV luminescence at the photoabsorption resonances has been suggested.
47.	Koskinen, M., et al. (författare) Spectral properties of rotating electrons in quantum dots and their relation to quantum Hall liquids 2007 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 19:7 Tidskriftsartikel (refereegranskat)abstract The exact diagonalization technique is used to study many-particle properties of interacting electrons with spin, confined in a two-dimensional harmonic potential. The single-particle basis is limited to the lowest Landau level. The results are analysed as a function of the total angular momentum of the system. Only at angular momenta corresponding to the filling factors 1, 1/3, 1/5, etc is the system fully polarized. The lowest energy states exhibit spin waves, domains, and localization, depending on the angular momentum. Vortices exist only at excited polarized states. The high angular momentum limit shows localization of electrons and separation of the charge and spin excitations.
48.	Krasnikov, S. A., et al. (författare) An X-ray absorption and photoemission study of the electronic structure of Ni porphyrins and Ni N-confused porphyrin 2008 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:23, s. 1-235207 Tidskriftsartikel (refereegranskat)abstract Investigations of chemical bonding and electronic structure features for polycrystalline (porphyrinato)nickel (II) (NiP, the simplest Ni porphyrin), (5,10,15,20-tetraphenylporphyrinato)nickel (II) (NiTPP) and (2-aza-21-carba-5,10,15,20-tetraphenylporphyrinato)nickel (II) (N-confused NiTPP, NiNCTPP) have been performed by means of high-resolution soft x-ray absorption and x-ray photoemission spectroscopy. The Ni 2p3/2 x-ray absorption spectra show strong pi-back-bonding in these compounds leading to a high-energy shift (1.2 eV for the NiP and NiTPP) of the entire absorption structure compared to Ni metal. It has been found that the main absorption line of the Ni 2p3/2 spectrum of the NiNCTPP is shifted by an additional 0.5 eV to higher energies in comparison with those for other nickel porphyrins. This shift is evidence of stronger back-donation (metal-to-ligand charge transfer) and a smaller effective number of 3d electrons on the central Ni atom in the NiNCTPP as compared to other Ni porphyrins. The confused N atom in the NiNCTPP is of pyrrolic type (protonated nitrogen), which was confirmed by the N 1s absorption and core-level photoemission spectra.
49.	Langreth, D. C., et al. (författare) A density functional for sparse matter 2009 Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:8, s. 084203- Tidskriftsartikel (refereegranskat)abstract Sparse matter is abundant and has both strong local bonds and weak nonbonding forces, in particular nonlocal van der Waals (vdW) forces between atoms separated by empty space. It encompasses a broad spectrum of systems, like soft matter, adsorption systems and biostructures. Density-functional theory (DFT), long since proven successful for dense matter, seems now to have come to a point, where useful extensions to sparse matter are available. In particular, a functional form, vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401; Thonhauser et al 2007 Phys. Rev. B 76 125112), has been proposed for the nonlocal correlations between electrons and applied to various relevant molecules and materials, including to those layered systems like graphite, boron nitride and molybdenum sulfide, to dimers of benzene, polycyclic aromatic hydrocarbons (PAHs), doped benzene, cytosine and DNA base pairs, to nonbonding forces in molecules, to adsorbed molecules, like benzene, naphthalene, phenol and adenine on graphite, alumina and metals, to polymer and carbon nanotube (CNT) crystals, and hydrogen storage in graphite and metal–organic frameworks (MOFs), and to the structure of DNA and of DNA with intercalators. Comparison with results from wavefunction calculations for the smaller systems and with experimental data for the extended ones show the vdW-DF path to be promising. This could have great ramifications.
50.	Lapushkin, I, et al. (författare) A self-consistent investigation of the semimetal-semiconductor transition in InAs/GaSb quantum wells under external electric fields 2004 Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 16:26, s. 4677-4684 Tidskriftsartikel (refereegranskat)abstract We investigate the phase transitions in InAs/GaSb quantum wells sandwiched between two wide-gap AlSb barrier layers under an external electric field perpendicular to interfaces. The Schrodinger and the Poisson equations are solved self-consistently to derive the subband dispersions, the potential profile, the electron charge distribution in the InAs layer, and the hole charge distribution in the GaSb layer. The Burt-Foreman envelope function theory and the scattering matrix method are used to solve the Schrodinger equation in the framework of the eight-band k (.) p model, including the spin-splitting of subbands in our calculation. We have found that in a thick InAs/GaSb quantum well, which has been investigated experimentally by Cooper et al (1998 Phys. Rev. B 57 11915), under low external electric fields, two electron levels stay below the highest hole level at zero in-plane wavevector k(parallel to) = 0. Then, the anticrossings of electron and hole levels produce several minigaps in the inplane dispersions, inside which the states of other subbands exist. As a result, the system is in a sernimetal phase. With increasing external electric field, the semimetal phase changes to semiconductor phase with only one hybridization gap. When all electron levels become higher than the hole levels at higher electric fields, the system has a semiconducting gap.

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