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A novel method was developed for studying the ink-paper interface and the structural variations of a deposited layer of ink. Combining high-resolution x-ray tomography with laser ablation, the depth profile of ink (toner), i.e., its varying thickness, could be determined in a paper substrate. X-ray tomography was used to produce the 3D structure of paper with about 1 μm spatial resolution. Laser ablation combined with optical imaging was used to produce the 3D structure of the printed layer of ink on top of that paper with about 70 nm depth resolution. Ablation depth was calibrated with an optical profilometer. It can be concluded that a toner layer on a light-weight-coated paper substrate was strongly perturbed by protruding fibers of the base paper. Such fibers together with the surface topography of the base paper seem to be the major factors that control the leveling of toner and its penetration into a thinly coated paper substrate.

In this work, in-plane thermal conductivity measurement was carried out on graphene-based papers. Graphene-based papers were fabricated using various processing techniques such as chemical vapor deposition (CVD), hot pressing of graphene slurry, and evaporation induced self-assembly. The prepared materials were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. In-plane thermal conductivity measurement was performed via a steady state thin film thermal conductivity apparatus. The in-plane thermal conductivity measurements show that the CVD based sample has the highest thermal conductivity. COMSOL Multiphysics was used to simulate the in-plane thermal conductivity of graphene-based papers.

Graphene paper (GP) has been prepared by flow-directed assembly of graphene nanosheets. The mechanical properties of as-prepared GPs were investigated by tensile, indentation, and bending tests. Heat treated GPs demonstrate superior hardness, ten times that of synthetic graphite, and two times that of carbon steel; besides, their yielding strength is significantly higher than that of carbon steel. GPs show extremely high modulus of elasticity during bending test; in the range of a few terapascal. The high strength and stiffness of GP is ascribed to the interlocking-tile microstructure of individual graphene nanosheets in the paper. These outstanding mechanical properties of GPs could lead to a wide range of engineering applications. © 2011 American Institute of Physics.

Sustainable and microbiologically secure foodstuff production lines are of increasing scientific interest and are in the focus of recent research programs. Additionally, they are of great importance for the production industry due to the prevention of food-borne illnesses caused by pathogens such as Salmonella sp., Listeria monocytogenes, or Escherichia coli. These pathogens are responsible for production losses, loss of customer acceptance, and severe food-borne illnesses. A pathogenic threat is frequently combated with sanitizing steps of the production lines. For conveyor band cleaning, this study compares the cleaning abilities of nitric acid (HNO3) and plasma treated water (PTW), which have been sprayed via a commercially available nozzle on two different polymeric surfaces (polysiloxane and polyurethane). Additionally, the cleaning agents HNO3 and PTW have been characterized through their pH and their conductivity. These findings have been underpinned by experiments that focus on a possible influence of nozzle abrasion, such as brass and stainless-steel nanoparticles, on the antimicrobial potential of PTW and HNO3. Adversely acting effects like an enhanced abrasion of conveyer band materials due to PTW or HNO3 treatment have been checked by using light microscopic micrographs and topographic scans in high-resolution mode. Based on the presented results of the experiments, the suitability of an in-place sanitation step in foodstuff production lines has been demonstrated on a laboratory scale.

peer-reviewed Direct coating methods using metal particles from aqueous solutions or solvent-based inks become central in the roll-to-roll fabrication processes as these methods can lead to continuous or pre-defined conductive layers on a large variety of substrates. For good electrical conductivity, the metal particles have to be brought into contact, and traditionally, additional sintering treatments are required. Such treatments can degrade the sensitive substrates as paper or polymer films. In this study, the possibility of obtaining conductive layers at room temperature is investigated for direct coating methods with an emphasis on drop-casting and inkjet printing. Thus, it is shown that electrical conductive layers can be achieved if the metal particles can compact during the drop-substrate impact interaction. It is theoretically shown that the compaction process is directly related to the particle and ink drop size, the initial fractional particle loading of the ink, solvent viscosity, and drop velocity. The theoretical predictions on compaction are experimentally validated, and the particle compaction's influence on changes in the electrical conductivity of the resulting layers is demonstrated. (C) 2016 AIP Publishing LLC. PUBLISHED peer-reviewed

Intelligent engineering of graphene-based electronic devices on SiC(0001) requires a better understanding of processes used to deposit gate-dielectric materials on graphene. Recently, Al2O3 dielectrics have been shown to form conformal, pinhole-free thin films by functionalizing the top surface of the graphene with fluorine prior to atomic layer deposition (ALD) of the Al2O3 using a trimethylaluminum (TMA) precursor. In this work, the functionalization and ALD-precursor adsorption processes have been studied with angle-resolved photoelectron spectroscopy, low energy electron diffraction, and X-ray photoelectron spectroscopy. It has been found that the functionalization process has a negligible effect on the electronic structure of the graphene, and that it results in a twofold increase in the adsorption of the ALD-precursor. In situ TMA-dosing and XPS studies were also performed on three different Si(100) substrates that were terminated with H, OH, or dangling Si-bonds. This dosing experiment revealed that OH is required for TMA adsorption. Based on those data along with supportive in situ measurements that showed F-functionalization increases the amount of oxygen (in the form of adsorbed H2O) on the surface of the graphene, a model for TMA-adsorption on graphene is proposed that is based on a reaction of a TMA molecule with OH.

International audience; Contractile forces generated by cells and the stiffness of the surrounding extracellular matrix are two central mechanical factors that regulate cell function. To characterize the dynamic evolution of these two mechanical parameters during tissue morphogenesis, we developed a magnetically actuated micro-mechanical testing system in which fibroblast-populated collagen microtissues formed spontaneously in arrays of microwells that each contains a pair of elastomeric microcantilevers. We characterized the magnetic actuation performance of this system and evaluated its capacity to support long-term cell culture. We showed that cells in the microtissues remained viable during prolonged culture periods of up to 15 days, and that the mechanical properties of the microtissues reached and maintained at a stable state after a fast initial increase stage. Together, these findings demonstrate the utility of this microfabricated bio-magneto-mechanical system in extended mechanobiological studies in a physiologically relevant 3D environment.

The electric potential close to a boundary between two dielectric material layers reflects the geometry of such an interface. The local variations arise from the combination of material parameters and from the nature of the inhomogeneity. Here, the arising electric field is considered for both a sinusoidally varying boundary and for a “rough,” Gaussian test case. We discuss the applicability of a one-dimensional model with the varying layer thickness as a parameter and the generic scaling of the results. As an application we consider the effect of paper roughness on toner transfer in electrophotographic printing.

The use of graphene grown by chemical vapor deposition to fabricate solution-gated field-effect transistors (SGFET) on different substrates is reported. SGFETs were fabricated using graphene transferred on poly(ethylene 2,6-naphthalenedicarboxylate) substrate in order to study the influence of using a flexible substrate for pH sensing. Furthermore, in order to understand the influence of fabrication-related residues on top of the graphene surface, a fabrication method was developed for graphene-on-SiO2 SGFETs that enables to keep a graphene surface completely clean of any residues at the end of the fabrication. We were then able to demonstrate that the electrical response of the SGFET devices to pH does not depend either on the specific substrate on which graphene is transferred or on the existence of a moderate amount of fabrication-related residues on top of the graphene surface. These considerations simplify and ease the design and fabrication of graphene pH sensors, paving the way for developing low cost, flexible, and transparent graphene sensors on plastic. We also show that the surface transfer doping mechanism does not have significant influence on the pH sensing response. This highlights that the adsorption of hydroxyl and hydronium ions on the graphene surface due to the charging of the electrical double layer capacitance is responsible for the pH sensing mechanism.

Linear electro-optic properties of 0.24Pb(In1/2Nb1/2)O3-(0.76 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals, with compositions in the rhombohedral, morphotropic phase boundary (MPB) and tetragonal phases, have been investigated. Very large effective electro-optic coefficient γc (204 pm/V) was observed in a crystal with the MPB composition when it is poled along [001]. The rhombohedral phase (x = 0.27 and 0.30) single crystals poled along [111] direction and tetragonal phase (x = 0.39) single crystal poled along [001] direction are in single domain, and their electro-optic coefficients (γc = 76, 94, and 43 pm/V for the crystals with x = 0.27, 0.30, and 0.39, respectively) were found to be much higher than that of traditional electro-optic single crystal LiNbO3 (γc = 19.9 pm/V). The electro-optic coefficients of the single crystal in the rhombohedral phase have excellent temperature stability in the experimental temperature range of 10–40 °C. The half-wave voltage Vπ was calculated to be much lower (less than 1000 V) than that of LiNbO3 single crystal (2800 V). These superior properties make the ternary relaxor-PT single crystals very promising for electro-optic modulation applications.

We mechanically clean graphene devices using an atomic force microscope (AFM). By scanning an AFM tip in contact mode in a broom-like way over the sample, resist residues are pushed away from the desired area. We obtain atomically flat graphene with a root mean square (rms) roughness as low as 0.12 nm after this procedure. The cleaning also results in a shift of the charge-neutrality point toward zero gate voltage, as well as an increase in charge carrier mobility.

Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp 2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13 of electric-field effect. The Hall mobility is ∼40 cm 2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes.

Biological membranes are composed of a thermally disordered lipid matrix and therefore require non-crystallographic scattering approaches for structural characterization with x-rays or neutrons. Here we develop a continuous distribution (CD) model to refine neutron or x-ray reflectivity data from complex architectures of organic molecules. The new model is a flexible implementation of the composition-space refinement of interfacial structures to constrain the resulting scattering length density profiles. We show this model increases the precision with which molecular components may be localized within a sample, with a minimal use of free model parameters. We validate the new model by parameterizing all-atom molecular dynamics (MD) simulations of bilayers and by evaluating the neutron reflectivity of a phospholipid bilayer physisorbed to a solid support. The determination of the structural arrangement of a sparsely-tethered bilayer lipid membrane (stBLM) comprised of a multi-component phospholipid bilayer anchored to a gold substrate by a thiolated oligo(ethylene oxide) linker is also demonstrated. From the model we extract the bilayer composition and density of tether points, information which was previously inaccessible for stBLM systems. The new modeling strategy has been implemented into the ga_refl reflectivity data evaluation suite, available through the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR).

Graphene is a highly promising material in the field of spin electronics. Recent experiments on electron spin resonance have observed a reduction in the g-factor of graphene. In our previous paper [J. Phys. Soc. Jpn. 88, 094707 (2019)], we demonstrated that one of sources for this reduction is the diamagnetic property of graphene. However, the diamagnetic property by itself does not fully account for the magnitude of the reduction observed in the experiments. In this paper, we focus on the Rashba effect, which is caused by the work function existing near the surface of graphene. The Rashba effect tilts the spin magnetic moment to the in-plane direction of the graphene sheet, potentially reducing the g-factor. We evaluate this reduction using a simple model system incorporating the Rashba and spin Zeeman effects. We then demonstrate that the resultant g-factor is in close agreement with that observed in the prior experiments, indicating that the Rashba effect is able to account for the remaining reduction in the g-factor of graphene., 24 pages, 2 figure, 2 tables

Hollow cathode plasma discharges are a fundamental part of a large variety of applications in industry, academia, and space. From surface processing and coatings deposition to plasma–surface interaction research and electric propulsion, advances in hollow cathode modeling and performance are critically important to the progress and evolution of these and other areas of technology. This paper describes perspectives on the progress that has been made in recent years in the capabilities and modeling of hollow cathodes used in plasma discharges. While many of the developments have been driven by the demanding requirements of electric propulsion applications, the information provided applies to all thermionic hollow cathodes and their applications. In the paper, we describe the status of 2D global simulations of hollow cathode plasmas, hollow cathode plume instabilities, and the development of higher current cathodes and low-current heaterless cathode technologies. Advances in our understanding and technology in these areas and some of the challenges that still need to be addressed and solved are discussed.

This Perspective reviews the fundamental physics of space–charge interactions that are important in various media: vacuum gap, air gap, liquids, and solids including quantum materials. It outlines the critical and recent developments since a previous review paper on diode physics [Zhang et al. Appl. Phys. Rev. 4, 011304 (2017)] with particular emphasis on various theoretical aspects of the space–charge limited current (SCLC) model: physics at the nano-scale, time-dependent, and transient behaviors; higher-dimensional models; and transitions between electron emission mechanisms and material properties. While many studies focus on steady-state SCLC, the increasing importance of fast-rise time electric pulses, high frequency microwave and terahertz sources, and ultrafast lasers has motivated theoretical investigations in time-dependent SCLC. We particularly focus on recent studies in discrete particle effects, temporal phenomena, time-dependent photoemission to SCLC, and AC beam loading. Due to the reduction in the physical size and complicated geometries, we report recent studies in multi-dimensional SCLC, including finite particle effects, protrusive SCLC, novel techniques for exotic geometries, and fractional models. Due to the importance of using SCLC models in determining the mobility of organic materials, this paper shows the transition of the SCLC model between classical bulk solids and recent two-dimensional (2D) Dirac materials. Next, we describe some selected applications of SCLC in nanodiodes, including nanoscale vacuum-channel transistors, microplasma transistors, thermionic energy converters, and multipactor. Finally, we conclude by highlighting future directions in theoretical modeling and applications of SCLC., Peer-reviewed (ritrýnd grein)

This paper evaluates the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash via molecular dynamics (MD) simulations. The short- and medium-range order of the constructed N-A-S-H structures shows good correlation with the experimental observations, signifying the viability of the N-A-S-H structures. The simulated fracture toughness values of N-A-S-H (0.4–0.45 MPa m0.5) appear to be of the same order as the available experimental values for fly ash-based geopolymer mortars and concretes. These results suggest the efficacy of the MD simulation toward obtaining a realistic fracture toughness of N-A-S-H, which is otherwise very challenging to obtain experimentally, and no direct experimental fracture toughness values are yet available. To further assess the fracture behavior of N-A-S-H, the number of chemical bonds formed/broken during elongation and their relative sensitivity to crack growth are evaluated. Overall, the fracture toughness of N-A-S-H presented in this paper paves the way for a multiscale simulation-based design of tougher geopolymers.

Internal electric fields can have a significant effect on the behavior of charged defects, dopants, and impurities in operating electronic devices that can adversely impact on their long-term performance and reliability. In this paper, we investigate the redistribution of charged centers in single crystal m-plane ZnO under the action of a DC electric field at 873 K using in-plane and in-depth spatially resolved cathodoluminescence (CL) spectroscopy. The CL intensities of the ultra-violet near band edge (NBE) emission at 3.28 eV and green luminescence (GL) at 2.39 eV were observed to both uniformly increase on the anode side of the electrode gap. Conversely, toward the cathode, the NBE and GL steadily decrease and increase, respectively. The GL quenched after hydrogen donor doping, confirming that the emission is related to acceptor-like centers. Based on the electro-migration and hydrogen doping results, the GL is attributed to radiative recombination involving Z n i and V Zn pairs. The intensity of an orange luminescence centered at 2.01 eV was unaffected by the electric field and is assigned to substitutional Li acceptors.Internal electric fields can have a significant effect on the behavior of charged defects, dopants, and impurities in operating electronic devices that can adversely impact on their long-term performance and reliability. In this paper, we investigate the redistribution of charged centers in single crystal m-plane ZnO under the action of a DC electric field at 873 K using in-plane and in-depth spatially resolved cathodoluminescence (CL) spectroscopy. The CL intensities of the ultra-violet near band edge (NBE) emission at 3.28 eV and green luminescence (GL) at 2.39 eV were observed to both uniformly increase on the anode side of the electrode gap. Conversely, toward the cathode, the NBE and GL steadily decrease and increase, respectively. The GL quenched after hydrogen donor doping, confirming that the emission is related to acceptor-like centers. Based on the electro-migration and hydrogen doping results, the GL is attributed to radiative recombination involving Z n i and V Zn pairs. The intens...

International audience; An Acoustic Black Hole (ABH) is a passive and efficient way to control the flexural vibrations of beams or plates. In its classical form, an ABH consists in a local reduction of the thickness of a structure according to a power law profile, associated to a thin visco-elastic coating placed in the thinnest region. A focalisation and a wave trap effect occur, leading to a localised energy dissipation which induces a local temperature increase. The objective of this paper is twofold. Firstly, the goal is to develop an adequate experimental methodology enabling to map accurately the small temperature variations induced by the local dissipation mechanism. Secondly, from the thermal standpoint, the goal is to provide experimental evidence of a local temperature increase associated to a damping effect in the case of an ABH beam. This paper thus describes a new kind of experimental methodology able to provide original data, bringing some new insight in the ABH physical understanding and the analysis of structural damping.

Field electron emission (FE) has relevance in many different technological contexts. However, many related technological papers use a physically defective elementary FE equation for local emission current density (LECD). This equation takes the tunneling barrier as exactly triangular, as in the original FE theory of 90 years ago. More than 60 years ago, it was shown that the so-called Schottky-Nordheim (SN) barrier, which includes an image-potential-energy term (that models exchange-and-correlation effects) is better physics. For a metal-like emitter with work-function 4.5 eV, the SN-barrier-related Murphy-Good FE equation predicts LECD values that are higher than the elementary equation values by a large factor, often between around 250 and around 500. By failing to mention/apply this 60-year-old established science, or to inform readers of the large errors associated with the elementary equation, many papers (aided by defective reviewing) spread a new kind of "pathological science", and create a modern research-integrity problem. The present paper aims to enhance author and reviewer awareness by summarizing relevant aspects of FE theory, by explicitly identifying the misjudgment in the original 1928 Fowler-Nordheim paper, by explicitly calculating the size of the resulting error, and by showing in detail why most FE theoreticians regard the 1950s modifications as better physics. Suggestions are made, about nomenclature and about citation practice, that may help to diminish misunderstandings., Comment: Submitted for publication; in v2 a correction to historical information (with no numerical consequences) has been made in Appendix A

Monte Carlo (MC) simulations are a powerful tool for the analysis of ion-solid interactions. The MC code McChasy (Monte Carlo CHAnneling SYmulation) allows the evaluation of Rutherford Backscattering Spectrometry spectra in the Channeling mode to quantify implantation damage. The code works on common personal computers and takes into account randomly displaced atoms as well as certain types of extended defects. In this paper, we report recent improvements of the McChasy code, including a unique approach to the calculation of impact parameters between ions and target atoms in three dimensions (along with computing thermal vibrations also in three dimensions). Furthermore, the use of a rotation matrix to provide different orientations of dislocation lines and an updated model of edge dislocations were also implemented in the code. Dislocation parameters are obtained directly from high-resolution Transmission Electron Microscopy micrographs. Two case studies are presented to highlight the importance of these improvements: Ni-implanted Al was analyzed as an example of a crystal mainly containing dislocations; Er-implanted ZnO was studied, revealing the strength of MC analysis for materials containing a mixture of different defect types, namely, randomly displaced atoms and dislocations.Monte Carlo (MC) simulations are a powerful tool for the analysis of ion-solid interactions. The MC code McChasy (Monte Carlo CHAnneling SYmulation) allows the evaluation of Rutherford Backscattering Spectrometry spectra in the Channeling mode to quantify implantation damage. The code works on common personal computers and takes into account randomly displaced atoms as well as certain types of extended defects. In this paper, we report recent improvements of the McChasy code, including a unique approach to the calculation of impact parameters between ions and target atoms in three dimensions (along with computing thermal vibrations also in three dimensions). Furthermore, the use of a rotation matrix to provide different orientations of dislocation lines and an updated model of edge dislocations were also implemented in the code. Dislocation parameters are obtained directly from high-resolution Transmission Electron Microscopy micrographs. Two case studies are presented to highlight the importance of these...

Defects influence the electronic and optical properties of crystals, so their identification is crucial to develop device technology for materials of micro-/optoelectronics and photovoltaics. The identification requires the accurate calculation of the electronic transitions and the paramagnetic properties of defects. The achievable accuracy is strongly limited in the case of the (semi)local approximations to density functional theory, because of the underestimation of the gap and of the degree of localization. In the past two decades, hybrid functionals, mixing semilocal and nonlocal exchange semiempirically, have emerged as an alternative. Very often, however, the parameters of such hybrids have to be tuned from material to material. In this paper, we describe the theoretical foundations for the proper tuning and show that if the relative positions of the band edge states are well reproduced, and the generalized Koopmans's theorem is fulfilled by the given parameterization, the calculated defect levels and localizations can be very accurate. As demonstrated here, this can be achieved with the two-parameter Heydt-Scuseria-Ernzerhof hybrid, HSE(α,μ) for diamond, Si, Ge, TiO2, GaAs, CuGaS(Se)2, GaSe, GaN, and Ga2O3. The paper describes details of the parameterization process and discusses the limitations of optimizing HSE functionals. Based on the gained experience, future directions for improving exchange functionals are also provided.

International audience; This paper presents significant new developments concerning the full band, quantum simulation of nanostructured systems and nanoscale electron devices based on an empirical pseudopotential Hamiltonian. We demonstrate that the method is of general applicability, in fact we show results for planar, ultra-thin body FETs and also for three-dimensional, nanowire FETs, we deal with different crystal orientations and account for possible stress/strain conditions in the simulated systems. Some of the simulations reported in this paper have been made computationally viable by the substantial improvements of the numerical efficiency compared to our previous pseudopotentials based methodology. Most of the methods and algorithms discussed in this paper are not specific to an empirical pseudopotential Hamiltonian, on the contrary they can be applied also to different Hamiltonians described with a plane waves basis, which are frequently employed for ab-initio, Density Functional Theory based calculations. The application of the methodologies described in this work may thus be more far reaching than it is illustrated by the case studies explicitly addressed in the present paper.

The possibility to control supersonic acoustic wave propagation is intriguing, but when modeling phononic crystal devices, supersonic surface acoustic waves are mired by radiative attenuation and, hence, eschewed in many device designs. In this paper, we study supersonic surface acoustic wave modes in shallow hole phononic crystals computationally with respect to the three bulk wave sound barriers of cubic (001) GaAs. From a first principles modeling approach of linear elasticity, the finite element method, and with the aid of characterization parameters for systematic modal categorization, detailed nuances are observed for supersonic surface waves propagating along the [110]-direction of GaAs with a periodically patterned surface. Modes of interest are distinguished by possessing both strain energy and squared polarization ratios above defined thresholds. The square array of shallow inclusions imparts a metamaterial surface layer effect that results in marked changes in the dispersion, the bulk wave hybridization, and the modal interactions of the surface modes in the Γ-X direction of the phononic crystal, which are characterized by their modal profiles and attenuation via bulk wave radiation. From these findings, we propose an extended sound cone concept to accommodate supersonic surface acoustic waves with low attenuation. Furthermore, at frequencies above the shear vertical bulk dispersion line, well-bounded surface acoustic wave modes are revealed, and the phenomenon of these supersonic modes with limited bulk wave coupling is explored. From these detailed band structures, the systematic method of mode characterization reveals deeper insights into modes that exist in shallow phononic crystals on cubic GaAs.The possibility to control supersonic acoustic wave propagation is intriguing, but when modeling phononic crystal devices, supersonic surface acoustic waves are mired by radiative attenuation and, hence, eschewed in many device designs. In this paper, we study supersonic surface acoustic wave modes in shallow hole phononic crystals computationally with respect to the three bulk wave sound barriers of cubic (001) GaAs. From a first principles modeling approach of linear elasticity, the finite element method, and with the aid of characterization parameters for systematic modal categorization, detailed nuances are observed for supersonic surface waves propagating along the [110]-direction of GaAs with a periodically patterned surface. Modes of interest are distinguished by possessing both strain energy and squared polarization ratios above defined thresholds. The square array of shallow inclusions imparts a metamaterial surface layer effect that results in marked changes in the dispersion, the bulk wave hybr...

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon.III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-ba...

In this paper, we propose a new multi-resonator metamaterial (MRM) for attenuating impact stress waves. Theoretical analyses show that the MRM has wider bandgaps than those of a single-resonator metamaterial (SRM) and a dual-resonator metamaterial (DRM), and numerical studies are conducted to compare the performances of the MRM, SRM, and DRM in mitigating impact forces. The influences of the number of unit cells, the spring stiffnesses, and the resonator masses on the mitigation of impact force are analyzed by studying a one-dimensional impact wave model. In addition, the calculation results of a three-dimensional crash model clearly confirm the outstanding features of the MRM, which can provide a thin and light structure with a wider attenuation region of the frequency spectrum and a better mitigation effect of the impact force.In this paper, we propose a new multi-resonator metamaterial (MRM) for attenuating impact stress waves. Theoretical analyses show that the MRM has wider bandgaps than those of a single-resonator metamaterial (SRM) and a dual-resonator metamaterial (DRM), and numerical studies are conducted to compare the performances of the MRM, SRM, and DRM in mitigating impact forces. The influences of the number of unit cells, the spring stiffnesses, and the resonator masses on the mitigation of impact force are analyzed by studying a one-dimensional impact wave model. In addition, the calculation results of a three-dimensional crash model clearly confirm the outstanding features of the MRM, which can provide a thin and light structure with a wider attenuation region of the frequency spectrum and a better mitigation effect of the impact force.

In this paper, the 2D band structure of a mixed-mode metamaterial resonator array for in-plane waves is investigated. The band structure in the interior and on the boundary of the irreducible Brillouin zone as well as 1D dispersion diagrams for different propagation angles are calculated numerically and presented. Additionally, a reduced order analytical method is established to compare and approximate the band structure. The studied metamaterial, with a T-shaped cantilever beam as resonator in its square array repeating unit cells, exhibits branches with mixed P and SV waves except at exactly one angle of propagation. This paper also reports on the occurrence of avoided level crossings, which are related to the existence of exceptional points in the complex domain. A reduced order analytical approach is used that can generate partial (low branches) band structure with relatively little computational effort. The reduced order model agrees well with the numerical results for these low branches and can provide support in mode identification and band sorting. With proper adjustments in parameters, this analytical method will be applicable for other metamaterials that have similar unit cell structure.

This paper presents the calculation of new elastic scattering cross sections for the simulation of electron interactions in liquid water. The calculations are based on the “ELastic Scattering of Electrons and Positrons by neutral Atoms” code, which adopts a Dirac partial wave analysis. A Muffin-tin potential was used in order to account for the liquid-phase of water, and the optical parameters of the correlation-polarization and the inelastic absorption potentials were optimized against vapour-phase water data. The differential and total elastic scattering cross sections calculated in the present work show a global agreement with the experimental data. The impact of these elastic scattering cross sections on the transport of electrons in liquid water was evaluated by track-structure simulations of range, dose-point-kernel, microdosimetric spectra, and ionization clustering using the Geant4-DNA simulation toolkit. The results are compared against those obtained with the elastic scattering models already available in Geant4-DNA and are discussed.This paper presents the calculation of new elastic scattering cross sections for the simulation of electron interactions in liquid water. The calculations are based on the “ELastic Scattering of Electrons and Positrons by neutral Atoms” code, which adopts a Dirac partial wave analysis. A Muffin-tin potential was used in order to account for the liquid-phase of water, and the optical parameters of the correlation-polarization and the inelastic absorption potentials were optimized against vapour-phase water data. The differential and total elastic scattering cross sections calculated in the present work show a global agreement with the experimental data. The impact of these elastic scattering cross sections on the transport of electrons in liquid water was evaluated by track-structure simulations of range, dose-point-kernel, microdosimetric spectra, and ionization clustering using the Geant4-DNA simulation toolkit. The results are compared against those obtained with the elastic scattering models already av...

Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. In this paper, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. The purpose of using the architecture of nand flash memories is to reuse a mature technology to create large arrays of silicon qubits. Current high-density nand flash memories use sufficiently small FG cells to make the number of electrons stored in each cell small and countable. The high packing density of these cells creates mutual capacitive couplings that can be used to generate cell-to-cell interactions. We explore these characteristics to derive an Ising Hamiltonian for the FG system in the single-electron regime. Considering the size of a cell (10 nm), the ideal operation temperature of a quantum annealer based on FG cells is estimated to be approximately that of liquid nitrogen. Assuming the parameters of a commercial 64 Gbit nand, we estimate that it is possible to create 2-megabyte (MB) qubit systems solely using conventional fabrication processes. Our proposal demonstrates that a large qubit system can be obtained as a natural extension of the miniaturization of commercial-grade electronics, although more effort will likely be required to achieve high-quality qubits.Quantum annealing machines based on superconducting qubits, which have the potential to solve optimization problems faster than digital computers, are of great interest not only to researchers but also to the general public. In this paper, we propose a quantum annealing machine based on a semiconductor floating gate (FG) array. The purpose of using the architecture of nand flash memories is to reuse a mature technology to create large arrays of silicon qubits. Current high-density nand flash memories use sufficiently small FG cells to make the number of electrons stored in each cell small and countable. The high packing density of these cells creates mutual capacitive couplings that can be used to generate cell-to-cell interactions. We explore these characteristics to derive an Ising Hamiltonian for the FG system in the single-electron regime. Considering the size of a cell (10 nm), the ideal operation temperature of a quantum annealer based on FG cells is estimated to be approximately that of liquid nitr...

In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied with commercial simulations marking the first PHE system, promise an proper candidate for new photonic applications, especially new tunable magneto-based lenses and photonic magneto-thermal sensors.In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied...

The paper presents a systematic characterization of pure hydrogen capacitively coupled discharges, produced in a parallel plate cylindrical setup. A two-dimensional, time-dependent fluid model is used to describe the production, transport, and destruction of electrons and positive ions H+,H2+, and H3+, at different frequencies(13.56 - 60 MHz), pressures (0.2 - 8 Torr), rf applied voltages (50 - 450 V) and geometric dimensions (1.6 - 12.8 cm radii and 1.6 - 6.4 cm interelectrode distances). A good agreement is found between calculation results and experimental measurements for the coupled electrical power, the plasma potential, and the self-bias potential, at various frequencies and rf applied voltages. However, the model generally underestimates the electron density with respect to its measured values. The paper discusses different space-time events, such as the development of double-ionization structures or the occurrence of field inversion and field reversal phenomena. The dependencies on pressure and frequency of the time-average electric field distribution are analyzed and related to the electron displacement within space-charge sheaths.This study is later used to understand the variations of the hydrogen dissociation rate, with changes in discharge operating conditions. The influence of reactor dimensions on the spatial profiles of the plasma potential, the rf electric field, the electron density, and the electron mean energy are analyzed in terms of discharge symmetry. An investigation of the space-time averaged rf electric field variations, with changes in the applied voltage, pressure, and geometric dimensions is carried out.These variations are shown to follow a universal similarity curve, if an adequate normalization is used when plotting the rf electric field as a function of pressure.This innovative representation of rf discharges allows a univocal definition of a reactor working point, for given operating conditions., Portugal. Ministério da Ciência Tecnologia e Ensino Superior (MTCES). Instituto Superior Técnico (IST). Centro de Física dos Plasmas – PRAXIS XXI (BD/15716/98), SFRH/BD/5012/2001., French Embassy, Gabinete de Relações Internacionais da Ciência e do Ensino Superior (GRICES) - ScientificTechnical Luso-French Cooperation Program - Project 539-B4 - Université Paris-Sud. Laboratoire de Physique des Gaz et des Plasmes.

In this paper, we study terahertz generation through optical rectification in reflection at normal incidence in a dielectric nonlinear crystal. We first analyze, with a nonlinear optical model, the sample parameters (thickness, absorption at both laser and terahertz wavelengths, etc.) for which a terahertz optical rectification reflection scheme is preferable to the common transmission scheme. Then, we report our experimental observations of a reflected terahertz signal generated at the surface of a ZnTe crystal. The reflected terahertz signal shares all the characteristics of a signal generated in transmission but is not limited by absorption losses in the crystal, thereby providing a broader bandwidth. At high pump laser power, the signal exhibits saturation, which is caused by the decrease of the nonlinear susceptibility due to photocarriers generated by two-photon absorption. This reflection scheme could be of great importance for terahertz microscopy of opaque materials like, e.g., humid samples or samples exhibiting strong absorption bands or to study samples for which the transmitted signal cannot be recorded.

International audience; In this paper, the development of a 1D physical conductivity model that describes charge transport in dielectric materials under space radiations with application to Kapton-HN is discussed. This model allows a good description of the charging behavior in dielectric materials. Former experiment run at ONERA on Kapton-HN showed that conductivity is temperature and electric field dependent. These results confirmed the need of implementing these dependences to our 1D model. This paper focuses on the electric field dependence. After a thorough analysis in the literature, several physical theories have been found that can explain this electric field dependence on the conductivity. They are the Onsager theory and the electric field assisted de-trapping mechanisms: direct tunneling, hopping transport, and the Poole-Frenkel theory. This paper is divided as follows: first the experiments that brought into evidence the electric field dependence of the conductivity in Kapton-HN are pointed out. Then the theories that could explain this dependence are described and implemented into the model. Finally, numerical and experimental conductivity results are compared and presented in the last sections.

This paper is to study ramping turn-to-turn loss and magnetization loss of a no-insulation (NI) hightemperature superconductor (HTS) pancake coil wound with (RE)Ba2Cu3Ox (REBCO) conduc-tors. For insulated (INS) HTS coils, a magnetization loss occurs on superconducting layers during aramping operation. For the NI HTS coil, additional loss is generated by the “bypassing” current onthe turn-to-turn metallic contacts, which is called “turn-to-turn loss” in this study. Therefore, theNI coil’s ramping loss is much different from that of the INS coil, but few studies have beenreported on this aspect. To analyze the ramping losses of NI coils, a numerical method is developedby coupling an equivalent circuit network model and a H-formulation finite element method model.The former model is to calculate NI coil’s current distribution and turn-to-turn loss, and the lattermodel is to calculate the magnetization loss. A test NI pancake coil is wound with REBCO tapesand the reliability of this model is validated by experiments. Then the characteristics of the NIcoil’s ramping losses are studied using this coupling model. Results show that the turn-to-turn lossis much higher than the magnetization loss. The NI coil’s total ramping loss is much higher thanthat of its insulated counterpart, which has to be considered carefully in the design and operation ofNI applications. This paper also discusses the possibility to reduce NI coil’s ramping loss bydecreasing the ramping rate of power supply or increasing the coil’s turn-to-turn resistivity.

This paper considers the technique of investigating diffusion processes via monitoring spectroscopically the ground state energy of an exciton confined in a quantum well. It is shown that the change in the exciton energy E−E0 during linear diffusion, can be described by an empirical relationship E−E0=(Ebg−E0)(1−exp{−γ√Dt/lw}), where Ebg is the band gap of the initial barrier material, D the diffusion constant and t the time. Detailed calculations accounting for the changes in the exciton binding energy have shown that the parameter γ∼1.5 for all wells of width lw≳40 A regardless of the material system. It is proposed that this relationship could be used to determine the linear diffusion coefficient D. Once D has been determined the relationship could then be utilized as a predictive tool, e.g., to determine the annealing time necessary to produce a given energy shift for a particular quantum well width. The paper goes on to discuss the effects non‐linear diffusion processes could have on exciton energies ...

In this paper, we study the effect of the tunnel barrier thickness non-uniformity in Nb/Al-AlOx/Nb tunnel junctions using the measurement results of the junctioncapacitance (C) and the normal resistance (Rn). The local thickness distribution of the AlOx tunnel barrier in Nb/Al-AlOx/Nb trilayer (RnA ∼ 30 Ω μm2) was studied by high resolution transmission electron microscopy. The specific resistance (RnA) values of the measured junctions range from 8.8 to 68 Ω μm2. We observed scatter in both the junction specific resistance and capacitance data, which is considerably higher than the measurement uncertainty. We also observed noticeable scatter in the RnC product, which does not stem from junction area estimation uncertainties. We discuss the possible reasons that contribute to this scatter. We suggest that the local thickness non-uniformity of the tunnel barrier significantly contributes to the scatter in the RnC product. We confirm this conclusion through an illustrative model based on the barrier imaging data, which results in the variation of the RnC data consistent with the measurements in this paper.

Lithium-ion batteries are highly complex electrochemical systems whose performance and safety are governed by coupled nonlinear electrochemical-electrical-thermal-mechanical processes over a range of spatiotemporal scales. Gaining an understanding of the role of these processes as well as development of predictive capabilities for design of better performing batteries requires synergy between theory, modeling, and simulation, and fundamental experimental work to support the models. This paper presents the overview of the work performed by the authors aligned with both experimental and computational efforts. In this paper, we describe a new, open source computational environment for battery simulations with an initial focus on lithium-ion systems but designed to support a variety of model types and formulations. This system has been used to create a three-dimensional cell and battery pack models that explicitly simulate all the battery components (current collectors, electrodes, and separator). The models are used to predict battery performance under normal operations and to study thermal and mechanical safety aspects under adverse conditions. This paper also provides an overview of the experimental techniques to obtain crucial validation data to benchmark the simulations at various scales for performance as well as abuse. We detail some initial validation using characterization experiments such as infrared and neutron imaging and micro-Raman mapping. In addition, we identify opportunities for future integration of theory, modeling, and experiments.

In this paper, we show that multiaxial fields can induce time-averaged, noncentrosymmetric interactions between particles having polarization anisotropy, yet the multiaxial field itself does not exert either a force or a torque on an isolated particle. These induced interactions lead to particle assemblies whose energy is strongly dependent on both the translational and orientational degrees of freedom of the system. The situation is similar to a collection of permanent dipoles, but the symmetry of the time-averaged interaction is quite distinct, and the scale of the system energy can be dynamically controlled by the magnitude of the applied multiaxial field. In this paper, the case of polarizable rods is considered in detail, and it is suggested that collections of rods embedded in spheres can be used to create a material with a dynamically tunable magnetic permeability or dielectric permittivity. We report on Monte Carlo simulations performed to investigate the behavior of assemblies of both multiaxial-field induced dipoles and permanent dipoles arranged onto two-dimensional lattices. The ground state of the induced dipoles is an orientational soft mode of aligned dipoles, whereas that of the permanent dipoles is a vortex state.

Here, we show that the peak temperature on a non-uniformly heated domain can be decreased by embedding a high-conductivity insert in it. The trunk of the high-conductivity insert is in contact with a heat sink. The heat is generated non-uniformly throughout the domain or concentrated in a square spot of length scale 0.1 L0, where L0 is the length scale of the non-uniformly heated domain. Peak and average temperatures are affected by the volume fraction of the high-conductivity material and by the shape of the high-conductivity pathways. This paper uncovers how varying the shape of the symmetric and asymmetric high-conductivity trees affects the overall thermal conductance of the heat generating domain. The tree-shaped high-conductivity inserts tend to grow toward where the heat generation is concentrated in order to minimize the peak temperature, i.e., in order to minimize the resistances to the heat flow. This behaviour of high-conductivity trees is alike with the root growth of the plants and trees. They also tend to grow towards sunlight, and their roots tend to grow towards water and nutrients. This paper uncovers the similarity between biological trees and high-conductivity trees, which is that trees should grow asymmetrically when the boundary conditions are non-uniform. We show here even though all the trees have the same objectives (minimum flow resistance), their shape should not be the same because of the variation in boundary conditions. To sum up, this paper shows that there is a high-conductivity tree design corresponding to minimum peak temperature with fixed constraints and conditions. This result is in accord with the constructal law which states that there should be an optimal design for a given set of conditions and constraints, and this design should be morphed in order to ensure minimum flow resistances as conditions and constraints change., Scientific and Technological Research Council of Turkey (114M592)

Thin film transistors (TFTs) on elastomers promise flexible electronics with stretching and bending. Recently, there have been several experimental studies reporting the behavior of TFTs under bending and buckling. In the presence of stress, the insulator capacitance is influenced due to two reasons. The first is the variation in insulator thickness depending on the Poisson ratio and strain. The second is the geometric influence of the curvature of the insulator-semiconductor interface during bending or buckling. This paper models the role of curvature on TFT performance and brings to light an elegant result wherein the TFT characteristics is dependent on the area under the capacitance-distance curve. The paper compares models with simulations and explains several experimental findings reported in literature. (C) 2014 AIP Publishing LLC.