Showing papers in "Journal of Physics D in 2014"
TL;DR: In this paper, the basic physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first, then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed.
Abstract: The special mechanical properties of nanoparticles allow for novel applications in many fields, e.g., surface engineering, tribology and nanomanufacturing/nanofabrication. In this review, the basic physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first. Then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed. Afterwards, several of the main applications of nanoparticles as a result of their special mechanical properties, including lubricant additives, nanoparticles in nanomanufacturing and nanoparticle reinforced composite coating, are introduced. A brief summary and the future outlook are also given in the final part. (Some figures may appear in colour only in the online journal)
483 citations
TL;DR: Spintronics is one of the emerging research fields in nanotechnology and has been growing very rapidly as mentioned in this paper, which has led to the discovery of giant magnetoresistance in 1988, which utilized spin-polarized electron transport across a non-magnetic metallic layer.
Abstract: Spintronics is one of the emerging research fields in nanotechnology and has been growing very rapidly. Studies of spintronics were started after the discovery of giant magnetoresistance in 1988, which utilized spin-polarized electron transport across a non-magnetic metallic layer. Within 10 years, this discovery had been implemented into hard disk drives, the most common storage media, followed by recognition through the award of the Nobel Prize for Physics 19 years later. We have never experienced such fast development in any scientific field. Spintronics research is now moving into second-generation spin dynamics and beyond. In this review, we first examine the historical advances in spintronics together with the background physics, and then describe major device applications.
405 citations
TL;DR: In this paper, an overview of the range of available terahertz sources, emphasizing recent developments, is given, and the focus then narrows to the sources that rely on surface phenomena.
Abstract: Bibliometric data set the scene by illustrating the growth of terahertz work and the present interest in terahertz science and technology. After locating terahertz sources within the broader context of terahertz systems, an overview is given of the range of available sources, emphasizing recent developments. The focus then narrows to terahertz sources that rely on surface phenomena. Three are highlighted. Optical rectification, usually thought of as a bulk process, may in addition exhibit a surface contribution, which, in some cases, predominates. Transient surface currents, for convenience often separated into drift and diffusion currents, are well understood according to Monte Carlo modelling. Finally, terahertz surface emission by mechanical means—in the absence of photoexcitation—is described.
352 citations
University of Glasgow1, Technische Universität München2, Royal Institute of Technology3, University of Gothenburg4, Kaiserslautern University of Technology5, Global Alliance in Management Education6, University of Tokyo7, Delft University of Technology8, Tohoku University9, Seagate Technology10, Centre national de la recherche scientifique11, Carnegie Mellon University12, University of Mainz13, University of Grenoble14
TL;DR: This 2014 Magnetism Roadmap provides a view on several selected, currently very active innovative developments, each written by an expert in the field and addressing a specific subject, with strong emphasize on future potential.
Abstract: Magnetism is a very fascinating and dynamic field Especially in the last 30 years it has experienced many major advances in the full range from novel fundamental phenomena to new products Applications such as hard disk drives and magnetic sensors are part of our daily life, and new applications, such as in non-volatile computer random access memory, are expected to surface shortly Thus it is timely for describing the current status, and current and future challenges in the form of a Roadmap article This 2014 Magnetism Roadmap provides a view on several selected, currently very active innovative developments It consists of 12 sections, each written by an expert in the field and addressing a specific subject, with strong emphasize on future potential This Roadmap cannot cover the entire field We have selected several highly relevant areas without attempting to provide a full review - a future update will have room for more topics The scope covers mostly nano-magnetic phenomena and applications, where surfaces and interfaces provide additional functionality New developments in fundamental topics such as interacting nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and spin-caloric phenomena are addressed New materials, such as organic magnetic materials and permanent magnets are covered New applications are presented such as nano-magnetic logic, non-local and domain-wall based devices, heat-assisted magnetic recording, magnetic random access memory, and applications in biotechnology May the Roadmap serve as a guideline for future emerging research directions in modern magnetism
320 citations
TL;DR: In this article, a review of the results obtained in the period 2006-2014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries, is presented.
Abstract: This review covers the results obtained in the period 2006–2014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries. Some benefits of pulsed high voltage discharges for kinetic study and for applications are demonstrated. The necessity of and the possibility of building a particular kinetic mechanism of plasma-assisted ignition and combustion are discussed. The most sensitive regions of parameters for plasma–combustion kinetic mechanisms are selected. A map of the pressure and temperature parameters (P–T diagram) is suggested, to unify the available data on ignition delay times, ignition lengths and densities of intermediate species reported by different authors.
274 citations
TL;DR: In this paper, the authors present a systematic review of measurement methods for both SAR and ILP, leading to recommendations for a standardised, simple and reliable method for measurements using non-adiabatic systems.
Abstract: In the clinical application of magnetic hyperthermia, the heat generated by magnetic nanoparticles in an alternating magnetic �耀eld is used as a cancer treatment. The heating ability of the particles is quanti�耀ed by the speci�耀c absorption rate (SAR), an extrinsic parameter based on the clinical response characteristic of power delivered per unit mass, and by the intrinsic loss parameter (ILP), an intrinsic parameter based on the heating capacity of the material. Even though both the SAR and ILP are widely used as comparative design parameters, they are almost always measured in non-adiabatic systems that make accurate measurements dif�耀cult. We present here the results of a systematic review of measurement methods for both SAR and ILP, leading to recommendations for a standardised, simple and reliable method for measurements using non-adiabatic systems. In a representative survey of 50 retrieved datasets taken from published papers, the derived SAR or ILP was found to be more than 5% overestimated in 24% of cases and more than 5% underestimated in 52% of cases.
269 citations
TL;DR: In this article, a computational investigation of the interaction of DBDs in humid air with a thin water layer covering tissue is presented. But the results are sensitive to the thickness of the water layer.
Abstract: The interaction of plasmas with liquids is of increasing importance in biomedical applications. Tissues treated by atmospheric pressure dielectric barrier discharges (DBDs) in plasma medicine are often covered by a thin layer of liquid, typically a blood serum like water with dissolved gases and proteins up to hundreds of micrometres thick. The liquid processes the plasma-produced radicals and ions prior to their reaching the tissue. In this paper, we report on a computational investigation of the interaction of DBDs in humid air with a thin water layer covering tissue. The water layer, 50–400 µm thick, contains dissolved O2aq (aq means an aqueous species) and alkane-like hydrocarbons (RHaq). In the model, the DBDs are operated with multiple pulses at 100 Hz followed by a 1 s afterglow. Gas phase reactive oxygen and nitrogen species (RONS) intersect the water-vapour saturated air above the liquid and then solvate when reaching the water. The photolysis of water by plasma-produced UV/VUV plays a significant role in the production of radicals. Without RHaq ,O − , ONOO − ,N O − and hydronium (H3O +) dominate the water ions with H3O + determining the pH. The dominant RONS in the liquid are O3aq ,H 2O2aq, and HNOxaq. Dissolved O2aq assists the production of HNO3aq and HOONOaq during the afterglow. With RHaq, reactive oxygen species are largely consumed, leaving an R·aq (alkyl radical) to reach the tissue. These results are sensitive to the thickness of the water layer.
254 citations
TL;DR: An overview of the modelling efforts that have been developed already, on both the atomistic and the macroscale, and the data that can be obtained with these models are identified to illustrate how modelling and simulation may contribute to this field.
Abstract: Plasma catalysis holds great promise for environmental applications, provided that the process viability can be maximized in terms of energy efficiency and product selectivity. This requires a fundamental understanding of the various processes taking place and especially the mutual interactions between plasma and catalyst. In this review, we therefore first examine the various effects of the plasma on the catalyst and of the catalyst on the plasma that have been described in the literature. Most of these studies are purely experimental. The urgently needed fundamental understanding of the mechanisms underpinning plasma catalysis, however, may also be obtained through modelling and simulation. Therefore, we also provide here an overview of the modelling efforts that have been developed already, on both the atomistic and the macroscale, and we identify the data that can be obtained with these models to illustrate how modelling and simulation may contribute to this field. Last but not least, we also identify future modelling opportunities to obtain a more complete understanding of the various underlying plasma catalytic effects, which is needed to provide a comprehensive picture of plasma catalysis.
245 citations
TL;DR: In this paper, the mechanical properties of single-layer black phosphorus under uniaxial deformation were investigated using first-principles calculations, and both the Young's modulus and ultimate strain were found to be highly anisotropic and nonlinear as a result of its quasi-two-dimensional puckered structure.
Abstract: The mechanical properties of single-layer black phosphorus under uniaxial deformation are investigated using first-principles calculations. Both the Young's modulus and ultimate strain are found to be highly anisotropic and nonlinear as a result of its quasi-two-dimensional puckered structure. Specifically, the in-plane Young's modulus is 41.3?GPa in the direction perpendicular to the pucker and 106.4?GPa in the parallel direction. The ideal strain is 0.48 and 0.11 in the perpendicular and parallel directions, respectively.
232 citations
TL;DR: In this article, the evolution of silicon cryoetching is reported from its very first introduction by a Japanese team to today's advanced technologies, and the main defects encountered in the process are presented and discussed.
Abstract: The evolution of silicon cryoetching is reported in this topical review, from its very first introduction by a Japanese team to today's advanced technologies. The main advances in terms of the performance and comprehension of the mechanisms are chronologically presented. After presenting the principle of silicon cryoetching, the main defects encountered in cryoetching (such as undercut, bowing and crystal orientation dependent etching) are presented and discussed. Mechanisms involved in SiOxFy passivation layer growth in standard cryoetching are investigated through several in situ characterization experiments. The STiGer process and alternative cryoetching processes for high-aspect-ratio structures are also proposed to enhance the process robustness. The over-passivation regime, which can provide self-organized columnar microstructures, is presented and discussed. Finally, advanced technologies, such as the cryoetching of sub-20 nm features and porous OSG low-k cryoetching, are described.
217 citations
TL;DR: High-resolution mass spectrometry revealed that sulfur-containing and aromatic amino acids were preferentially decreased by the plasma treatment, providing fundamental information for elucidating the mechanism of protein inactivation for biomedical plasma applications.
Abstract: Plasma medicine is an attractive new research area, but the principles of plasma modification of biomolecules in aqueous solution remain elusive. In this study, we investigated the chemical effects of atmospheric-pressure cold plasma on 20 naturally occurring amino acids in aqueous solution. High-resolution mass spectrometry revealed that chemical modifications of 14 amino acids were observed after plasma treatment: (i) hydroxylation and nitration of aromatic rings in tyrosine, phenylalanine and tryptophan; (ii) sulfonation and disulfide linkage formation of thiol groups in cysteine; (iii) sulfoxidation of methionine and (iv) amidation and ring-opening of five-membered rings in histidine and proline. A competitive reaction experiment using 20 amino acids demonstrated that sulfur-containing and aromatic amino acids were preferentially decreased by the plasma treatment. These data provide fundamental information for elucidating the mechanism of protein inactivation for biomedical plasma applications.
TL;DR: In this article, first-principles studies based on density functional theory, and their applications to elucidate the microscopic origins of the linear and NLO properties in NLO crystals, are reviewed.
Abstract: With the development of laser technology and related scientific fields, understanding of the structure–property relationships in nonlinear optical (NLO) crystals is becoming more and more important. In this article, first-principles studies based on density functional theory, and their applications to elucidate the microscopic origins of the linear and NLO properties in NLO crystals, are reviewed. The ab initio approaches have the ability to accurately predict the optical properties in NLO crystals, and the developed analysis tools are vital to investigating their intrinsic mechanism. This microscopic understanding has further guided molecular engineering design for NLO crystals with novel structures and properties. It is anticipated that first-principle material approaches will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new NLO crystals with good performance.
TL;DR: A review of the state-of-the-art of microfabrication techniques and of the structures of dielectrophoretic microdevices aimed towards different applications is provided in this paper.
Abstract: The development of lab-on-a-chip (LOC) devices over the past decade has attracted growing interest. LOC devices aim to achieve the miniaturization, integration, automation and parallelization of biological and chemical assays. One of the applications, the ability to effectively and accurately manipulate and separate micro- and nano-scale particles in an aqueous solution, is particularly appealing in biological, chemical and medical fields. Among the technologies that have been developed and implemented in microfluidic microsystems for particle manipulation and separation (such as mechanical, inertial, hydrodynamic, acoustic, optical, magnetic and electrical methodologies), dielectrophoresis (DEP) may prove to be the most popular because of its label-free nature, ability to manipulate neutral bioparticles, analyse with high selectivity and sensitivity, compatibility with LOC devices, and easy and direct interface with electronics. The required spatial electric non-uniformities for the DEP effect can be generated by patterning microelectrode arrays within microchannels, or placing insulating obstacles within a microchannel and curving the microchannels. A wide variety of electrode- and insulator-based DEP microdevices have been developed, fabricated, and successfully employed to manipulate and separate bioparticles (i.e. DNA, proteins, bacteria, viruses, mammalian and yeast cells). This review provides an overview of the state-of-the-art of microfabrication techniques and of the structures of dielectrophoretic microdevices aimed towards different applications. The techniques used for particle manipulation and separation based on microfluidics are provided in this paper. In addition, we also present the theoretical background of DEP.
TL;DR: The pathway of the biologically active molecule hydrogen peroxide (H2O2) from the plasma generation in the gas phase by an atmospheric pressure argon plasma jet, to its transition into the liquid phase and finally to its inhibiting effect on human skin cells is investigated for different feed gas humidity settings as discussed by the authors.
Abstract: The pathway of the biologically active molecule hydrogen peroxide (H2O2) from the plasma generation in the gas phase by an atmospheric pressure argon plasma jet, to its transition into the liquid phase and finally to its inhibiting effect on human skin cells is investigated for different feed gas humidity settings Gas phase diagnostics like Fourier transformed infrared spectroscopy and laser induced fluorescence spectroscopy on hydroxyl radicals (OH) are combined with liquid analytics such as chemical assays and electron paramagnetic resonance spectroscopy Furthermore, the viability of human skin cells is measured by Alamar Blue® assay By comparing the gas phase results with chemical simulations in the far field, H2O2 generation and destruction processes are clearly identified The net production rate of H2O2 in the gas phase is almost identical to the H2O2 net production rate in the liquid phase Moreover, by mimicking the H2O2 generation of the plasma jet with the help of an H2O2 bubbler it is concluded that the solubility of gas phase H2O2 plays a major role in generating hydrogen peroxide in the liquid Furthermore, it is shown that H2O2 concentration correlates remarkably well with the cell viability Other species in the liquid like OH or superoxide anion radical do not vary significantly with feed gas humidity
TL;DR: In this article, the problem of air pollution and related air-cleaning technologies is summarized and different ways to couple non-thermal plasmas with catalytic or adsorbing materials are listed.
Abstract: The first part of the review summarizes the problem of air pollution and related air-cleaning technologies. Volatile organic compounds in particular have various effects on health and their abatement is a key issue. Different ways to couple non-thermal plasmas with catalytic or adsorbing materials are listed. In particular, a comparison between in-plasma and post-plasma coupling is made. Studies dealing with plasma-induced heterogeneous reactivity are analysed, as well as the possible modifications of the catalyst surface under plasma exposure. As an alternative to the conventional and widely studied plasma–catalyst coupling, a sequential approach has been recently proposed whereby pollutants are first adsorbed onto the material, then oxidized by switching on the plasma. Such a sequential approach is reviewed in detail.
TL;DR: In this article, a single discharge pulse at three different voltages was directed onto a 200 µm water layer covering tissue followed by a 10 µm afterglow, and the magnitude of the voltage and its pulse length determined if the ionization wave producing the plasma plume reached the surface of the liquid.
Abstract: In the use of atmospheric pressure plasma jets in biological applications, the plasma-produced charged and neutral species in the plume of the jet often interact with a thin layer of liquid covering the tissue being treated. The plasma-produced reactivity must then penetrate through the liquid layer to reach the tissue. In this computational investigation, a plasma jet created by a single discharge pulse at three different voltages was directed onto a 200 µm water layer covering tissue followed by a 10 s afterglow. The magnitude of the voltage and its pulse length determined if the ionization wave producing the plasma plume reached the surface of the liquid. When the ionization wave touches the surface, significantly more charged species were created in the water layer with H3O+aq, O3−aq, and O2−aq being the dominant terminal species. More aqueous OHaq, H2O2aq, and O3aq were also formed when the plasma plume touches the surface. The single pulse examined here corresponds to a low repetition rate plasma jet where reactive species would be blown out of the volume between pulses and there is not recirculation of flow or turbulence. For these conditions, NxOy species do not accumulate in the volume. As a result, aqueous nitrites, nitrates, and peroxynitrite, and the HNO3aq and HOONOaq, which trace their origin to solvated NxOy, have low densities.
TL;DR: In this paper, an embedded active region structure in which the wavelength-scale active region is buried with an InP PhC slab was proposed to improve the thermal resistance of the device.
Abstract: Lasers with ultra-low operating energy are desired for use in chip-to-chip and on-chip optical interconnects. If we are to reduce the operating energy, we must reduce the active volume. Therefore, a photonic crystal (PhC) laser with a wavelength-scale cavity has attracted a lot of attention because a PhC provides a large Q-factor with a small volume. To improve this device's performance, we employ an embedded active region structure in which the wavelength-scale active region is buried with an InP PhC slab. This structure enables us to achieve effective confinement of both carriers and photons, and to improve the thermal resistance of the device. Thus, we have obtained a large external differential quantum efficiency of 55% and an output power of ?10?dBm by optical pumping. For electrical pumping, we use a lateral p?i?n structure that employs Zn diffusion and Si ion implantation for p-type and n-type doping, respectively. We have achieved room-temperature continuous-wave operation with a threshold current of 7.8??A and a maximum 3?dB bandwidth of 16.2?GHz. The results of an experimental bit error rate measurement with a 10?Gbit?s?1 NRZ signal reveal the minimum operating energy for transferring a single bit of 5.5?fJ. These results show the potential of this laser to be used for very short reach interconnects. We also describe the optimal design of cavity quality (Q) factor in terms of achieving a large output power with a low operating energy using a calculation based on rate equations. When we assume an internal absorption loss of 20?cm?1, the optimized coupling Q-factor is 2000.
TL;DR: In this paper, a flexible GaN-based micro-LED array was used as an optical cochlear implant for application in a mouse model, where the fabrication of 15 µm thin and highly flexible devices is enabled by a laser-based layer transfer process of the GaNLEDs from sapphire to a polyimide-on-silicon carrier wafer.
Abstract: Currently available cochlear implants are based on electrical stimulation of the spiral ganglion neurons. Optical stimulation with arrays of micro-sized light-emitting diodes (µLEDs) promises to increase the number of distinguishable frequencies. Here, the development of a flexible GaN-based micro-LED array as an optical cochlear implant is reported for application in a mouse model. The fabrication of 15 µm thin and highly flexible devices is enabled by a laser-based layer transfer process of the GaN-LEDs from sapphire to a polyimide-on-silicon carrier wafer. The fabricated 50 × 50 µm2 LEDs are contacted via conducting paths on both p- and n-sides of the LEDs. Up to three separate channels could be addressed. The probes, composed of a linear array of the said µLEDs bonded to the flexible polyimide substrate, are peeled off the carrier wafer and attached to flexible printed circuit boards. Probes with four µLEDs and a width of 230 µm are successfully implanted in the mouse cochlea both in vitro and in vivo. The LEDs emit 60 µW at 1 mA after peel-off, corresponding to a radiant emittance of 6 mW mm−2.
TL;DR: In this article, a review of the fundamental and applied research done on encapsulated molecules in carbon nanotubes is presented, particularly focusing on the weak and van der Waals interactions which rule the molecule-tube coupling.
Abstract: Carbon nanotubes are fascinating nano-objects not only from a fundamental point of view but also with respect to their remarkable properties, holding great potential in new materials design. When combined with organic molecules, these properties can be enhanced or modulated in order to fulfil the demand in domains as diverse as molecular electronics, biomaterials or even construction engineering, to name a few. To adequately conceive these hybrid materials it is essential to fully appreciate the nature of molecule–carbon nanotube interactions. In this review, we will discuss some relevant fundamental and applied research done on encapsulated molecules in carbon nanotubes. We will particularly focus on the weak and van der Waals interactions which rule the molecule–tube coupling. Therefore a small state of the art on the theoretical methods used to describe these interactions is presented here. Then, we will discuss various applications of molecular encapsulation, where we will consider structural, magnetic, charge transfer and transport, and optical properties.
TL;DR: The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of THz radiation offering high power, high spectral purity and moderate tunability as discussed by the authors.
Abstract: The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of THz radiation offering high power, high spectral purity and moderate tunability. As such, these sources are particularly suited to the application of THz frequency imaging across a range of disciplines, and have motivated significant research interest in this area over the past decade. In this paper we review the technological approaches to THz QCL-based imaging and the key advancements within this field. We discuss in detail a number of imaging approaches targeted to application areas including multiple-frequency transmission and diffuse reflection imaging for the spectral mapping of targets; as well as coherent approaches based on the self-mixing phenomenon in THz QCLs for long-range imaging, three-dimensional imaging, materials analysis, and high-resolution inverse synthetic aperture radar imaging.
TL;DR: In this paper, the conditions for laser sintering of copper nanoparticle (NP) inks in ambient conditions while avoiding oxidation were studied and determined the regime for stable, low resistivity copper (< × 3 bulk resistivity value) generation in terms of laser irradiance and exposure duration.
Abstract: Copper nanoparticle (NP) inks serve as an attractive potential replacement to silver NP inks in functional printing applications However their tendency to rapidly oxidize has so far limited their wider use In this work we have studied the conditions for laser sintering of Cu-NP inks in ambient conditions while avoiding oxidation We have determined the regime for stable, low-resistivity copper (< × 3 bulk resistivity value) generation in terms of laser irradiance and exposure duration and have indicated the limits on fast processing The role of pre-drying conditions on sintering outcome has also been studied A method, based on spectral reflectivity measurements, was used for non-contact monitoring of the sintering process evolution It also indicates preferred spectral regions for sintering Finally, we illustrated how selective laser sintering can generate high-quality, fine line (<5 µm wide) and dense copper circuits
TL;DR: In this paper, the authors proposed a broadband and high-efficiency transition from a microstrip line to a conformal surface plasmon (CSP) waveguide that is made of an ultrathin corrugated metallic strip.
Abstract: We propose a broadband and high-efficiency transition from a microstrip line to a conformal surface plasmon (CSP) waveguide that is made of an ultrathin corrugated metallic strip, to transform the guide wave into a spoof surface plasmon polariton (SPP) in the microwave region. The transition consists of three parts: a convertor which converts the direction of the electric field from perpendicular to parallel to the strip, a matching area with gradient corrugations and a flaring metallic line to match both the momentum and impedance, and a CSP waveguide to support the SPP waves. A back-to-back transition sample is fabricated using the proposed method. Experimental results of S parameters and near-field distributions verify the excellent performance of the sample to transform guided waves to SPPs and transmit SPP waves in a wide band. The sample exhibits low energy loss when the CSP waveguide is bent or even twisted. The proposed transition may have potential applications in integrating conventional microwave devices with the SPP devices.
TL;DR: In this paper, the authors summarized and analyzed the numerous experimental, computational and analytical works on breakdown at microscale dimensions, discusses implications and new areas emerging in microscale devices that take advantage of field emission and presents perspectives looking ahead at new opportunities for field emission-driven microplasmas.
Abstract: Gas breakdown at microscale dimensions has been of great interest to the microelectromechanical systems (MEMS) and plasma communities for nearly 15 years as the first reports of deviations from traditional theory began to emerge. Since those first reports, a significant amount of work has investigated why gas breakdown deviates from the classic Paschen’s Law when the dimensions are in the range of 1–10 µm. Nearly universally, these deviations that form the so-called modified Paschen’s curve have been attributed to electron field emission, where electrons directly tunnel from the cathode into the gas due to the very high electric fields at microscale dimensions. Furthermore, because of ionization in the gas gap, field emission is enhanced by positive ions and thus is inherently coupled to the gas and discharge dynamics. Progress in understanding the mechanisms and physics of this process has in turn led to new ideas and devices that capitalize on the high surface-to-volume ratio in microscale dimensions and take advantage of cathode emission processes. This topical review summarizes and analyzes the numerous experimental, computational and analytical works on breakdown at microscale dimensions, discusses implications and new areas emerging in microscale devices that take advantage of field emission and presents perspectives looking ahead at new opportunities for field emission-driven microplasmas.
TL;DR: This review article outlines the technological bottlenecks that have been overcome which have made biomedical terahertz research possible and the limitations that remain.
Abstract: Interest in biomedical terahertz research is growing rapidly and there are now several terahertz groups in Asia, Europe and the US investigating potential applications such as pharmaceutical quality control, protein characterization and cancer detection. This review article outlines the technological bottlenecks that have been overcome which have made biomedical terahertz research possible. Key research findings will be presented, and the limitations that remain and the research initiatives that strive to address them will also be discussed.
TL;DR: In this paper, the authors proposed a solid-phase epitaxy method for SiC growth on Si. The new method is based on the substitution of some atoms in the silicon matrix by the carbon atoms to form the molecules of silicon carbide.
Abstract: The recent advances in epitaxial SiC films' growth on Si are overviewed. The basic classical methods currently used for SiC films' growth are discussed and their advantages and disadvantages are explored. The basic idea and the theoretical background for a new method of the synthesis of epitaxial SiC films on Si are given. It will be shown that the new method is significantly different from the classical techniques of thin-film growth where the evaporation of the atoms onto the substrate surface is exploited. The new method is based on the substitution of some atoms in the silicon matrix by the carbon atoms to form the molecules of silicon carbide. It will be shown that the following process of SiC nucleation happens gradually without destroying the crystalline structure of the silicon matrix, and the orientation of a grown film is imposed by the original crystalline structure of the silicon matrix (not only by the substrate surface as in conventional methods of film growth). A comparison of the new method with other epitaxy techniques will be given.The new method of solid-phase epitaxy based on the substitution of atoms and on the creation of dilatation dipoles solves one of the major problems in heteroepitaxy. It provides the synthesis of low-defective unstrained epitaxial films with a large difference between the lattice parameters of the film and the substrate without using any additional buffer layers. This method has another unique feature distinguishing it from the classical techniques of SiC films' growth—it allows the growing of SiC films of hexagonal polytypes. A new kind of phase transformation in solids owing to the chemical transformation of one substance into another will be described theoretically and revealed experimentally. This type of phase transformation, and the mechanism of a broad class of heterogeneous chemical reactions between gas and solid phases, will be illustrated by an example of the growth of SiC epitaxial layers due to the chemical interaction of CO gas with the monocrystalline silicon matrix. The discovery of this mechanism yields a new kind of template: namely, substrates with buffer transition layers for wide-gap semiconductor growth on silicon. The properties of a variety of heteroepitaxial films of wide-gap semiconductors (SiC, AlN, GaN and AlGaN) grown on a SiC/Si substrate by solid-phase epitaxy will be reported. Grown films contain no cracks and have a quality sufficient to manufacture micro- and opto-electronic devices. Also, the new abilities in the synthesis of large (150 mm diameter) low-defective SiC films on Si substrates will be demonstrated.
TL;DR: In this article, a helium plasma jet is generated by applying pulsed high voltage of 8kV with 10kV using a quartz tube with an inner diameter of 4mm.
Abstract: The atmospheric-pressure helium plasma jet is of emerging interest as a cutting-edge biomedical device for cancer treatment, wound healing and sterilization Reactive oxygen species such as OH and O radicals are considered to be major factors in the application of biological plasma In this study, density distribution, temporal behaviour and flux of OH and O radicals on a surface are measured using laser-induced fluorescence A helium plasma jet is generated by applying pulsed high voltage of 8 kV with 10 kHz using a quartz tube with an inner diameter of 4 mm To evaluate the relation between the surface condition and active species production, three surfaces are used: dry, wet and rat skin When the helium flow rate is 15 l min−1, radial distribution of OH density on the rat skin surface shows a maximum density of 12 × 1013 cm−3 at the centre of the plasma-mediated area, while O atom density shows a maximum of 10 × 1015 cm−3 at 20 mm radius from the centre of the plasma-mediated area Their densities in the effluent of the plasma jet are almost constant during the intervals of the discharge pulses because their lifetimes are longer than the pulse interval Their density distribution depends on the helium flow rate and the surface humidity With these results, OH and O production mechanisms in the plasma jet and their flux onto the surface are discussed
TL;DR: In this article, the effect of pulsing the plasma source power (source pulsing), the electrode bias power (bias pulsing) or both source and bias power(synchronous) on the time evolution of species densities, electron energy distribution function and ion energy and angular distributions on the substrate is discussed.
Abstract: Power-modulated (pulsed) plasmas have demonstrated several advantages compared to continuous wave (CW) plasmas. Specifically, pulsed plasmas can result in a higher etching rate, better uniformity, and less structural, electrical or radiation (e.g. vacuum ultraviolet) damage. Pulsed plasmas can also ameliorate unwanted artefacts in etched micro-features such as notching, bowing, micro-trenching and aspect ratio dependent etching. As such, pulsed plasmas may be indispensable in etching of the next generation of micro-devices with a characteristic feature size in the sub-10nm regime. This work provides an overview of principles and applications of pulsed plasmas in both electropositive (e.g. argon) and electronegative (e.g. chlorine) gases. The effect of pulsing the plasma source power (source pulsing), the electrode bias power (bias pulsing), or both source and bias power (synchronous pulsing), on the time evolution of species densities, electron energy distribution function and ion energy and angular distributions on the substrate is discussed. The resulting pulsed plasma process output (etching rate, uniformity, damage, etc) is compared, whenever possible, to that of CW plasma, under otherwise the same or similar conditions.
TL;DR: A comprehensive review of advances in multilayer Laue lens (MLL) is provided in this paper, which includes extensive theoretical modelling on focusing performance, discussion on fabrication challenges, their current capabilities and notable results from x-ray focusing experiments.
Abstract: Multilayer Laue lens (MLL) is a new class of x-ray optics that offer great promise for achieving nanometre-level spatial resolution by focusing hard x-rays. Fabricating an MLL via thin-film deposition provides the means to achieve a linear Fresnel-zone plate structure with zone widths below 1?nm, while retaining a virtually limitless aspect ratio. Despite its similarity to the Fresnel-zone plate, MLL exhibits categorically distinctive focusing properties and their fabrication comes with a wide array of challenges. This article provides a comprehensive review of advances in MLLs, and includes extensive theoretical modelling on focusing performance, discussion on fabrication challenges, their current capabilities and notable results from x-ray focusing experiments.
TL;DR: In this article, a laser-induced fluorescence (LIF) model is used to estimate air and water penetration inside the jet and proves to be well adapted to characterize the plasma jet under biomedical application conditions, showing that the plasma produced by the plasma gun counter-propagates after impinging the surface which, for the same operating parameters, leads to an increase of almost one order of magnitude in the maximum OH density (from 2 × 1013 cm−3 for open-air propagation to ~ 1 × 1014 cm −3 for a grounded metal target).
Abstract: In the field of biomedical application, many publications report on non-thermal plasma jet potentialities for cell behaviour modifications in cancer treatment, wound healing or sterilization. However most previous plasma jet characterizations were performed when jets expend freely in air. Only recently has the influence of the targeted surface been properly considered. In this work, modifications induced by various types of targets, mimicking the biological samples, in the plasma propagation and production of hydroxyl radicals are evidenced through time-resolved intensified charge-coupled device imaging and laser-induced fluorescence (LIF) measurements. A LIF model, also specifically dedicated to estimate air and water penetration inside the jet, is used and proves to be well adapted to characterize the plasma jet under biomedical application conditions. It is shown that the plasma produced by the plasma gun counter-propagates after impinging the surface which, for the same operating parameters, leads to an increase of almost one order of magnitude in the maximum OH density (from ~2 × 1013 cm−3 for open-air propagation to ~1 × 1014 cm−3 for a grounded metal target). The nature of the target, especially its electrical conductivity, as well as gas flow rate and voltage amplitude are playing a key role in the production of hydroxyl radicals. The strong interplay between gas flow dynamics and plasma propagation is here confirmed by air and water distribution measurements. The need for a multi-diagnostic approach, as well as great care in setting up the in situ characterization of plasma jets, is here emphasized. Special attention must not only be paid to voltage amplitude and gas flow rate but also to the nature, humidity and conductivity of the target.
TL;DR: The physical and chemical aspects of plasma surface interaction in high-power impulse magnetron sputtering (HiPIMS) discharges are overviewed in this article, where the data obtained by various plasma diagnostic methods representing the important sputtering discharge regions, namely the cathode vicinity, plasma bulk, and substrate vicinity, are reported.
Abstract: The physical and chemical aspects of plasma–surface interaction in high-power impulse magnetron sputtering (HiPIMS) discharges are overviewed. The data obtained by various plasma diagnostic methods representing the important sputtering discharge regions, namely the cathode vicinity, plasma bulk, and substrate vicinity, are reported. After a detailed introduction to the problem and description of the plasma characterization methods suitable for pulsed magnetron discharge analysis, an overview of the recent plasma diagnostics achievements in both non-reactive and reactive HiPIMS discharges is presented. Finally, the conclusions and perspectives suggesting possible directions and research strategies for increasing our knowledge in this domain are given.