Showing papers in "Journal of Physics D in 2017"

The 2017 terahertz science and technology roadmap

Abstract: Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2017 Plasma Roadmap: Low temperature plasma science and technology

Abstract: Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.

Magnonic crystals for data processing

Abstract: Magnons—the quanta of spin waves—propagating in magnetic materials with wavelengths at the nanometer-scale and carrying information in the form of an angular momentum, can be used as data carriers in next-generation, nano-sized low-loss information processing systems. In this respect, artificial magnetic materials with properties periodically varied in space, known as magnonic crystals, are especially promising for controlling and manipulating the magnon currents. In this article, different approaches for the realization of static, reconfigurable, and dynamic magnonic crystals are presented along with a variety of novel wave phenomena discovered in these crystals. Special attention is devoted to the utilization of magnonic crystals for processing of analog and digital information. Magnonic crystals for data processing 2

Modelling ultrafast laser ablation

Abstract: This review is devoted to the study of ultrafast laser ablation of solids and liquids. The ablation of condensed matter under exposure to subpicosecond laser pulses has a number of peculiar properties which distinguish this process from ablation induced by nanosecond and longer laser pulses. The process of ultrafast ablation includes light absorption by electrons in the skin layer, energy transfer from the skin layer to target interior by nonlinear electronic heat conduction, relaxation of the electron and ion temperatures, ultrafast melting, hydrodynamic expansion of heated matter accompanied by the formation of metastable states and subsequent formation of breaks in condensed matter. In case of ultrashort laser excitation, these processes are temporally separated and can thus be studied separately. As for energy absorption, we consider peculiarities of the case of metal irradiation in contrast to dielectrics and semiconductors. We discuss the energy dissipation processes of electronic thermal wave and lattice heating. Different types of phase transitions after ultrashort laser pulse irradiation as melting, vaporization or transitions to warm dense matter are discussed. Also nonthermal phase transitions, directly caused by the electronic excitation before considerable lattice heating, are considered. The final material removal occurs from the physical point of view as expansion of heated matter; here we discuss approaches of hydrodynamics, as well as molecular dynamic simulations directly following the atomic movements. Hybrid approaches tracing the dynamics of excited electrons, energy dissipation and structural dynamics in a combined simulation are reviewed as well.

The 2017 Magnetism Roadmap

Abstract: Building upon the success and relevance of the 2014 Magnetism Roadmap, this 2017 Magnetism Roadmap edition follows a similar general layout, even if its focus is naturally shifted, and a different group of experts and, thus, viewpoints are being collected and presented. More importantly, key developments have changed the research landscape in very relevant ways, so that a novel view onto some of the most crucial developments is warranted, and thus, this 2017 Magnetism Roadmap article is a timely endeavour. The change in landscape is hereby not exclusively scientific, but also reflects the magnetism related industrial application portfolio. Specifically, Hard Disk Drive technology, which still dominates digital storage and will continue to do so for many years, if not decades, has now limited its footprint in the scientific and research community, whereas significantly growing interest in magnetism and magnetic materials in relation to energy applications is noticeable, and other technological fields are emerging as well. Also, more and more work is occurring in which complex topologies of magnetically ordered states are being explored, hereby aiming at a technological utilization of the very theoretical concepts that were recognised by the 2016 Nobel Prize in Physics. Given this somewhat shifted scenario, it seemed appropriate to select topics for this Roadmap article that represent the three core pillars of magnetism, namely magnetic materials, magnetic phenomena and associated characterization techniques, as well as applications of magnetism. While many of the contributions in this Roadmap have clearly overlapping relevance in all three fields, their relative focus is mostly associated to one of the three pillars. In this way, the interconnecting roles of having suitable magnetic materials, understanding (and being able to characterize) the underlying physics of their behaviour and utilizing them for applications and devices is well illustrated, thus giving an accurate snapshot of the world of magnetism in 2017. The article consists of 14 sections, each written by an expert in the field and addressing a specific subject on two pages. Evidently, the depth at which each contribution can describe the subject matter is limited and a full review of their statuses, advances, challenges and perspectives cannot be fully accomplished. Also, magnetism, as a vibrant research field, is too diverse, so that a number of areas will not be adequately represented here, leaving space for further Roadmap editions in the future. However, this 2017 Magnetism Roadmap article can provide a frame that will enable the reader to judge where each subject and magnetism research field stands overall today and which directions it might take in the foreseeable future. The first material focused pillar of the 2017 Magnetism Roadmap contains five articles, which address the questions of atomic scale confinement, 2D, curved and topological magnetic materials, as well as materials exhibiting unconventional magnetic phase transitions. The second pillar also has five contributions, which are devoted to advances in magnetic characterization, magneto-optics and magneto-plasmonics, ultrafast magnetization dynamics and magnonic transport. The final and application focused pillar has four contributions, which present non-volatile memory technology, antiferromagnetic spintronics, as well as magnet technology for energy and bio-related applications. As a whole, the 2017 Magnetism Roadmap article, just as with its 2014 predecessor, is intended to act as a reference point and guideline for emerging research directions in modern magnetism.

Layered ternary M(n+1)AX(n) phases and their 2D derivative MXene: an overview from a thin-film perspective

Abstract: Inherently and artificially layered materials are commonly investigated both for fundamental scientific purposes and for technological application. When a layered material is thinned or delaminated ...

Collective spin excitations of helices and magnetic skyrmions: review and perspectives of magnonics in non-centrosymmetric magnets

Abstract: Magnetic materials hosting correlated electrons play an important role for information technology and signal processing. The currently used ferro-, ferri- and antiferromagnetic materials provide microscopic moments (spins) that are mainly collinear. Recently more complex spin structures such as spin helices and cycloids have regained a lot of interest.The interest has been initiated by the discovery of the skyrmion lattice phase in noncentrosymmetric helical magnets. In this review we address how spin helices and skyrmion lattices enrich the microwave characteristics of magnetic materials and give rise to bottom-up magnonic crystals. When discussing perspectives for microwave electronics and magnonics we focus particularly on insulating materials as they avoid eddy current losses, offer low spin-wave damping, and allow for electric field control. Thereby, they further fuel the vision of magnonics operated at low energy consumption.

Granular and particle-laden flows: from laboratory experiments to field observations

Abstract: This review article provides an overview of dry granular flows and particle fluid mixtures, including experimental and numerical modeling at the laboratory scale, large scale hydrodynamics approaches and field observations. Over the past ten years, the theoretical and numerical approaches have made such significant progress that they are capable of providing qualitative and quantitative estimates of particle concentration and particle velocity profiles in steady and fully developed particulate flows. The next step which is currently developed is the extension of these approaches to unsteady and inhomogeneous flow configurations relevant to most of geophysical flows. We also emphasize that the up-scaling from laboratory experiments to large scale geophysical flows still poses some theoretical physical challenges. For example, the reduction of the dissipation that is responsible for the unexpected long run-out of large scale granular avalanches is not observed at the laboratory scale and its physical origin is still a matter of debate. However, we believe that the theoretical approaches have reached a mature state and that it is now reasonable to tackle complex particulate flows that incorporate more and more degrees of complexity of natural flows.

Physical models of collective cell motility: from cell to tissue.

Abstract: In this article, we review physics-based models of collective cell motility. We discuss a range of techniques at different scales, ranging from models that represent cells as simple self-propelled particles to phase field models that can represent a cell's shape and dynamics in great detail. We also extensively review the ways in which cells within a tissue choose their direction, the statistics of cell motion, and some simple examples of how cell-cell signaling can interact with collective cell motility. This review also covers in more detail selected recent works on collective cell motion of small numbers of cells on micropatterns, in wound healing, and the chemotaxis of clusters of cells.

Surface charge migration and dc surface flashover of surface-modified epoxy-based insulators

Abstract: Epoxy-based model insulators were manufactured and fluorinated under a F2/N2 mixture (12.5% F2) at 50 °C and 0.1 MPa for 15 min and 60 min. Surface charge accumulation and decay behavior were studied with and without dc voltage application. The effect of direct fluorination on surface charge migration as well as on flashover voltage was verified. The obtained results show that the charge decay of epoxy-based insulators is a slow process, but the decay rate increases when an outer dc electric field is applied. The surface charge distribution is changed when a streamer is triggered on the insulator surface. The existence of heteropolarity surface charges can decrease the dc surface flashover voltage to some extent, while the surface flashover voltage is almost unchanged when charges of the same polarity accumulate on the insulator surface. The short time fluorinated insulator can modify the surface resistivity, and the rate of surface charge dissipation is greatly increased under a dc electric field.

Optically pumped VECSELs: review of technology and progress

Abstract: Vertical-external-cavity surface-emitting lasers (VECSELs) are the most versatile laser sources, combining unique features such as wide spectral coverage, ultrashort pulse operation, low noise properties, high output power, high brightness and compact form-factor. This paper reviews the recent technological developments of VECSELs in connection with the new milestones that continue to pave the way towards their use in numerous applications. Significant attention is devoted to the fabrication of VECSEL gain mirrors in challenging wavelength regions, especially at the yellow and red wavelengths. The reviewed fabrication approaches address wafer-bonded VECSEL structures as well as the use of hybrid mirror structures. Moreover, a comprehensive summary of VECSEL characterization methods is presented; the discussion covers different stages of VECSEL development and different operation regimes, pointing out specific characterization techniques for each of them. Finally, several emerging applications are discussed, with emphasis on the unique application objectives that VECSELs render possible, for example in atom and molecular physics, dermatology and spectroscopy.

Jamming transitions in cancer.

Abstract: The traditional picture of tissues, where they are treated as liquids defined by properties such as surface tension or viscosity has been redefined during the last few decades by the more fundamental question: under which conditions do tissues display liquid-like or solid-like behaviour? As a result, basic concepts arising from the treatment of tissues as solid matter, such as cellular jamming and glassy tissues, have shifted into the current focus of biophysical research. Here, we review recent works examining the phase states of tissue with an emphasis on jamming transitions in cancer. When metastasis occurs, cells gain the ability to leave the primary tumour and infiltrate other parts of the body. Recent studies have shown that a linkage between an unjamming transition and tumour progression indeed exists, which could be of importance when designing surgery and treatment approaches for cancer patients.

Theory of metasurface based perfect absorbers

Abstract: Based on an analytic approach, we present a theoretical review on the absorption, scattering, and extinction of both dipole scatterers and regular arrays composed of such scatterers i.e. metasurfaces. Besides offering a tutorial by outlining the maximum absorption limit for electrically/magnetically resonant dipole particles/metasurfaces, we give an educative analytical approach to their analysis. Moreover, we put forward the analysis of two known alternatives in providing perfect absorbers out of electrically and or magnetically resonant metasurfaces; one is based on the simultaneous presence of both electric and magnetic responses in so called Huygens metasurfaces while the other is established upon the presence of a back reflector in so called Salisbury absorbers. Our work is supported by several numerical examples to clarify the discussions in each stage.

Recent Advances in Interfacial Engineering of Perovskite Solar Cells

Abstract: Due to recent developments, organometallic halide perovskite solar cells (PSCs) have attracted even greater interest owing to their impressive photovoltaic properties and simple device manufacturing processes with the potential for commercial applications. The power conversion efficiencies (PCEs) of PSCs have surged from 3.8% for methyl ammonium lead halide-sensitized liquid solar cells, CH3NH3PbX3 (X = Cl, Br, I), in 2009, to more than 22% for all-solid-state solar cells in 2016. Over the past few years, significant effort has been dedicated to realizing PSCs with even higher performance. In this review, recent advances in the interfacial engineering of PSCs are addressed. The specific strategies for the interfacial engineering of PSCs fall into two categories: (1) solvent treatment and additives to improve the light-harvesting capabilities of perovskite films, and (2) the incorporation of various functional materials at the interfaces between the active layers (e.g. electron transporting layer, perovskite layer, and hole transporting layer). This review aims to provide a comprehensive overview of strategies for the interfacial engineering of PSCs with potential benefits including enhanced light harvesting, improved charge separation and transport, improved device stability, and elimination of photocurrent hysteresis.

Micro-reflectance and transmittance spectroscopy: a versatile and powerful tool to characterize 2D materials

Abstract: Optical spectroscopy techniques such as differential reflectance and transmittance have proven to be very powerful techniques for studying 2D materials. However, a thorough description of the experimental setups needed to carry out these measurements is lacking in the literature. We describe a versatile optical microscope setup for carrying out differential reflectance and transmittance spectroscopy in 2D materials with a lateral resolution of ~1 µm in the visible and near-infrared part of the spectrum. We demonstrate the potential of the presented setup to determine the number of layers of 2D materials and characterize their fundamental optical properties, such as excitonic resonances. We illustrate its performance by studying mechanically exfoliated and chemical vapor-deposited transition metal dichalcogenide samples.

Review of Cellular Mechanotransduction.

Abstract: Living cells and tissues experience physical forces and chemical stimuli in a human body The process of converting mechanical forces into biochemical activities and gene expression is mechanochemical transduction or mechanotransduction Significant advances have been made in understanding mechanotransduction at cellular and molecular levels over the last two decades However, major challenges remain in elucidating how a living cell integrates signals from mechanotransduction with chemical signals to regulate gene expression and to generate coherent biological responses in living tissues in physiological conditions and diseases

Insights into the use of polyethylene oxide in energy storage/conversion devices: a critical review

Abstract: In this review, latest updates in the poly (ethylene oxide) based electrolytes are summarized. The ultimate goal of researchers globally is towards the development of free standing solid polymeric separator for energy storage devices. This single free standing solid polymeric separator may replace the liquid and separator (organic/Inorganic) used in existing efficient/smart energy technology. As an example polyethylene oxide (PEO) consist of an electron donor rich group which provides coordinating sites to the cation for migration. Owing to this exclusive structure PEO exhibits some remarkable properties such as; low glass transition temperature, excellent flexibility and ability to make complexation with various metal salts which are unattainable by another polymer host. Hence, the PEO is the most emerging candidate that have been examined or is currently under audition for application in energy storage devices. So, this review article first provides the detailed study of the PEO properties, characteristic of constituents of the polymer electrolyte and suitable approaches for the modification of polymer electrolytes. Then, the synthesization and characterizations techniques are outlined. The structures, characteristics, and performance during charge-discharge of four types of electrolyte/separators which are Liquid, Plasticized, and dispersed/intercalated electrolyte are highlighted. The suitable ion transport mechanism proposed by researchers in the different renowned group have been discussed for better understanding of the ion dynamics in such systems.

Strong interaction between graphene layer and Fano resonance in terahertz metamaterials

Abstract: Graphene has emerged as a promising building block in modern optics and optoelectronics due to its novel optical and electrical properties. In the mid-infrared and terahertz (THz) regime, graphene behaves like metals and supports surface plasmon resonances (SPRs). Moreover, the continuously tunable conductivity of graphene enables active SPRs and gives rise to a range of active applications. However, the interaction between graphene and metal-based resonant metamaterials has not been fully understood. In this work, a simulation investigation on the interaction between the graphene layer and THz resonances supported by the two-gap split ring metamaterials is systematically conducted. The simulation results show that the graphene layer can substantially reduce the Fano resonance and even switch it off, while leaving the dipole resonance nearly unaffected, which is well explained with the high conductivity of graphene. With the manipulation of graphene conductivity via altering its Fermi energy or layer number, the amplitude of the Fano resonance can be modulated. The tunable Fano resonance here together with the underlying physical mechanism can be strategically important in designing active metal-graphene hybrid metamaterials. In addition, the 'sensitivity' to the graphene layer of the Fano resonance is also highly appreciated in the field of ultrasensitive sensing, where the novel physical mechanism can be employed in sensing other graphene-like two-dimensional materials or biomolecules with the high conductivity.

Laurdan and Di-4-ANEPPDHQ probe different properties of the membrane.

Abstract: Lipid packing is a crucial feature of cellular membranes. Quantitative analysis of membrane lipid packing can be achieved using polarity sensitive probes whose emission spectrum depends on the lipid packing. However, detailed insights into the exact mechanisms that cause the changes in the spectra are necessary to interpret experimental fluorescence emission data correctly. Here, we analysed frequently used polarity sensitive probes, Laurdan and di-4-ANEPPDHQ, to test whether the underlying physical mechanisms of their spectral changes are the same and, thus, whether they report on the same physico-chemical properties of the cell membrane. Steady-state spectra as well as time-resolved emission spectra of the probes in solvents and model membranes revealed that they probe different properties of the lipid membrane. Our findings are important for the application of these dyes in cell biology.

Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses

Abstract: Using a liquid phase epitaxy (LPE) technique (1 1 1) yttrium iron garnet (YIG) films with thicknesses of ≈100 nm and surface roughnesses as low as 0.3 nm have been grown on (1 1 1) gadolinium gallium garnet (GGG) substrates as a basic material for spin-wave propagation experiments in microstructured waveguides. The continuously strained films exhibit nearly perfect crystallinity without significant mosaicity and with effective lattice misfits of and below. The film/substrate interface is extremely sharp without broad interdiffusion layer formation. All LPE films exhibit a nearly bulk-like saturation magnetization of () Gs and an 'easy cone' anisotropy type with extremely small in-plane coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy with a pronounced six-fold symmetry observed for the saturation field <1.5 Oe. No significant out-of-plane anisotropy is observed, but a weak dependence of the effective magnetization on the lattice misfit is detected. The narrowest ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is the lowest value reported so far for YIG films of 100 nm thicknesses and below. The Gilbert damping coefficient for investigated LPE films is estimated to be close to .

Raw material ‘criticality’—sense or nonsense?

Abstract: The past decade has seen a resurgence of interest in the supply security of mineral raw materials. A key to the current debate is the concept of ‘criticality’. The present article reviews the criticality concept, as well as the methodologies used in its assessment, including a critical evaluation of their validity in view of classical risk theory. Furthermore, it discusses a number of risks present in global raw materials markets that are not captured by most criticality assessments. Proposed measures for the alleviation of these risks are also presented. We find that current assessments of raw material criticality are fundamentally flawed in several ways. This is mostly due to a lack of adherence to risk theory, and highly limits their applicability. Many of the raw materials generally identified as critical are probably not critical. Still, the flaws of current assessments do not mean that the general issue of supply security can simply be ignored. Rather, it implies that new assessments are required. While the basic theoretical framework for such assessments is outlined in this review, detailed method development will require a major collaborative effort between different disciplines along the raw materials value chain. In the opinion of the authors, the greatest longer-term challenge in the raw materials sector is to stop, or counteract the effects of, the escalation of unit energy costs of production. This issue is particularly pressing due to its close link with the renewable energy transition, requiring more metal and mineral raw materials per unit energy produced. The solution to this problem will require coordinated policy action, as well as the collaboration of scientists from many different fields—with physics, as well as the materials and earth sciences in the lead.

Fundamentals and applications of the Landau–Lifshitz–Bloch equation

Abstract: The influence of thermal excitations on magnetic materials is a topic of increasing relevance in the theory of magnetism. The Landau–Lifshitz–Bloch equation describes magnetisation dynamics at finite temperatures. It can be considered as an extension of already established micromagnetic methods with a comparable numerical effort. This review is a brief summary of this new field of research, with a focus on the fundamentals of the Landau–Lifshitz–Bloch equation, its connection with the stochastic Landau–Lifshitz equation, and its applications in modern magnetism.