| 1. |
- Prinz, Christelle
(författare)
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Interactions between semiconductor nanowires and living cells.
- 2015
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:23
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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.
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| 2. |
- Feierabend, Maja, 1990, et al.
(författare)
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Optical fingerprint of non-covalently functionalized transition metal dichalcogenides
- 2017
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:38, s. Article no 384003 -
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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.
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| 3. |
- Gryglas-Borysiewicz, Marta, et al.
(författare)
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Hydrostatic-pressure-induced changes of magnetic anisotropy in (Ga, Mn) As thin films
- 2017
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:11
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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.
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| 4. |
- Lu, Hongduo, et al.
(författare)
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Ionic liquid interface at an electrode: Simulations of electrochemical properties using an asymmetric restricted primitive model
- 2018
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 30
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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.
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| 5. |
- Midtvedt, Daniel, 1988, et al.
(författare)
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Multi-scale approach for strain-engineering of phosphorene
- 2017
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 29:18, s. Article nr 185702 -
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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.
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| 6. |
- Östman, Erik, et al.
(författare)
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Ising-like behaviour of mesoscopic magnetic chains
- 2018
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:36
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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.
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| 7. |
- Angelescu, Daniel G., et al.
(författare)
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Branched-linear polyion complexes at variable charge densities
- 2015
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:35
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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.
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| 8. |
- Blomberg, Sara, et al.
(författare)
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2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence
- 2016
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:45
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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.
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| 9. |
- Chen, Junsheng, et al.
(författare)
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Surface plasmon inhibited photo-luminescence activation in CdSe/ZnS core-shell quantum dots
- 2016
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:25
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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.
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| 10. |
- Guthrie, Malcolm
(författare)
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Future directions in high-pressure neutron diffraction.
- 2015
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 27:15
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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.
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