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International audience; The photoluminescence (PL) of monolayer tungsten disulfide (WS2) is locally and electrically controlled using the nonplasmonic tip and tunneling current of a scanning tunneling microscope (STM). The spatial and spectral distribution of the emitted light is determined using an optical microscope. When the STM tip is engaged, short-range PL quenching due to near-field electromagnetic effects is present, independent of the sign and value of the bias voltage applied to the tip–sample tunneling junction. In addition, a bias-voltage-dependent long-range PL quenching is measured when the sample is positively biased. We explain these observations by considering the native n-doping of monolayer WS2 and the charge carrier density gradients induced by electron tunneling in micrometer-scale areas around the tip position. The combination of wide-field PL microscopy and charge carrier injection using an STM opens up new ways to explore the interplay between excitons and charge carriers in two-dimensional semiconductors.

In modern economic infrastructure, Al cables of overhead power transmission lines are used both without and with a steel core (respectively, all aluminum alloy conductor (AAAC) and aluminum conductor steel reinforced (ACSR) cables). In this article, the changes in structural, microstructural, and elastic-microplastic properties have been analyzed for the outer wires of the AAAC (A50) and ACSR cables (AC50/8 cables with a steel core of ~8 mm2 cross-section, hereinafter referred to as AC50) with the cross-section of the stranded conductor of ~50 mm2, which were in operation for 0–20 years in the Volgograd region of Russia. Using the techniques of X-ray diffraction, electron backscattered diffraction, densitometry, and the acoustic method, the structural and microstructural features of the wires have been compared and found to be correlated with their elastic-microplastic properties. It has been ascertained that the presence of a steel core in AC50 leads to a decrease in the defectiveness of the near-surface layer of their aluminum wires. Compared with A50 cables, the development of void defects in the near-surface layer of Al-wires of AC50 cables slows down (by ~1 year with a service life of ~10 years and by ~3 years with a service life of ~20 years).

There exist numerous experimental studies of the perpendicular and parallel upper critical magnetic fields in $$d$$ -wave layered superconductors. They are usually theoretically fitted by the so-called Werthamer, Helfand, and Hohenberg (WHH) results, obtained for an isotropic 3D s-wave superconductors. As theoretically shown by us and by Bulaevskii, layered compounds are characterized by different ratios of the parameter $${{H}_{{c2}}}(0){\text{/}}({\text{|}}d{{H}_{{c2}}}{\text{/}}dT{{{\text{|}}}_{{{{T}_{c}}}}}{{T}_{c}})$$ , where $${{H}_{{c2}}}(0)$$ is the upper critical magnetic field at $$T = 0$$ and $${\text{|}}d{{H}_{{c2}}}{\text{/}}dT{{{\text{|}}}_{{{{T}_{c}}}}}$$ is the so-called Ginzburg–Landau slope near $${{T}_{c}}$$ . In this paper, we show that for perpendicular upper critical magnetic field of a $$d$$ -wave layered superconductor, the above discussed parameter is equal to $${{H}_{{c2}}}(0){\text{/}}({\text{|}}d{{H}_{{c2}}}{\text{/}}dT{{{\text{|}}}_{{{{T}_{c}}}}}{{T}_{c}}) \approx $$ 0.629. To derive this result, we use exact method of the Green’s functions formulation of the BCS microscopic theory of superconductivity by Gor’kov. We compare our results with experimental ones, obtained on the d-wave superconductor YBa2Cu3O7 – δ.

Anisotropic periodic relief in form of ripples was formed on surface of amorphous hydrogenated silicon (a-Si:H) films by femtosecond laser pulses with the wavelength of 1.25 μm. The orientation of the surface structures relative to laser radiation polarization vector depended on the number of laser pulses N acting on the film surface. When N = 30, the structures with 0.88 μm period were formed orthogonal to the laser radiation polarization; at N = 750 the surface structures had period of 1.12 μm and direction parallel to the polarization. The conductivity of the laser-modified a-Si:H films increased by 3 to 4 orders of magnitude, up to 3.8·10–5 (Ω∙cm)–1, due to formation of nanocrystalline Si phase with a volume fraction from 17 to 30%. Anisotropy of the dark conductivity, as well as anisotropy of the photoconductivity spectral dependences was observed in the modified films due to depolarizing influence of periodic microscale relief and uneven distribution of nanocrystalline Si phase within such laser-induced structure.

It is well known that a four-fold symmetry of the parallel upper critical magnetic field disappears in the Ginzburg-Landau (GL) region in quasi-two-dimensional (Q2D) $d$-wave superconductors. Therefore, it has been accurately calculated so far as a correction to the GL results, which is valid close to superconducting transition temperature and is expected to be stronger at low temperatures. As to the case $T=0$, some approximated methods have been used, which are good only for closed electron orbits and unappropriate for the open orbits which exist in a parallel magnetic field in Q2D superconductors. For the first time, we accurately calculate the four-fold anisotropy of the parallel upper critical magnetic field in a pure Q2D $d$-wave superconductor at $T=0$, where it has the highest possible value. Our results are applicable to Q2D $d$-wave high-Tc and organic superconductors., Comment: 5 pages, 2 figeres

International audience; The exceptional electronic and optical properties of graphene are harmed by the unavoidable imperfections of the lattice resulting from mechanical or electronic interaction with the environment. Using a time dependent approach we theoretically address the sensitivity of the plasmon modes of graphene nanoakes to the presence of point vacancy defects and substitutional impurities. We nd that the fractions of the defects as low as 10 −3 from the total number of Carbon atoms in an ideal nanoake lead to strong broadening of the plasmon resonance in the optical absorption spectrum. In addition to this eect resulting from the elastic and inelastic processes associated with defect induced scattering and modication of the electronic structure of graphene, we also observe and explain a vacancy and impurity induced shifts of the plasmon energy. Our work extends the in depth theoretical studies of the optical properties of graphene nanomaterials towards practical situations of nonideal 2D lattices.

To determine the phase relationships in the system (1 - 2x)BiSc03 • xPbTi03 • xPbMg1/3Nb2/303 near the morphotropic boundary, the ceramic samples for x = 0.34 and x = 0.46 were studied by the XRD method. The profiles of nine regions of the XRD patterns were analyzed using WinFit software. In both cases, a much better agreement with the experimental data was observed with the introduction of additional phases with cubic symmetry. The simulation of the full x-ray diffraction patterns of the samples using the Le Bail method was also carried out. The studied samples contain two phases: the main with a cubic (o = 4.0432 A) (x = 0.34) and tetragonal (o = 3,9963 А, с = 4.0580 A) (x = 0.46) unit cells and additional one. The additional phases with broad diffraction peaks can be considered cubic (with the unit cell parameters a - 4.045 A and a - 4.017 A, respectively).

Electrospray (ES) phase change cooling is investigated as a potential approach for heat dissipation from localized hot spots. Considering evaporation of electrospray-delivered liquid as a potentially effective and desirable heat removal scheme, experiments have been performed to characterize the behavior of liquid films formed on a heated surface by way of ES impingement under different conditions. A complementary heat transfer model has been developed to understand the heat and mass transfer mechanism underlying the process and to predict system thermal performance. With the help of the predictive model, the experimental observations have been interpreted to identify the key physical phenomena that determine evaporation from electrosprayed liquid films. It was discovered that the impinging jet is not only effective in delivering liquid to the surface, but also enables thinning of the films to only a few hundred nanometers, thus significantly reducing conduction resistance across the film. Additionally, mass transfer resistance for evaporation is also reduced by two orders of magnitude compared to natural convection as a result of the surrounding air entrainment by the spray jet, permitting significantly higher evaporation rates and heat removal than would occur in quiescent air. In summary, ES cooling is demonstrated to be uniquely capable of both liquid and gas phase heat/mass transfer enhancement supported by the electrohydrodynamics of high momentum ES spray-jets.

Vortical jet flows in the Reynolds number (Re) range from 1000 to 3425 and swirl number (S) below 0.5, alone and in combination with suction through a small aperture, are experimentally investigated using optical visualization. Schlieren photography is employed to assess the vortical flow structure and establish the fundamental understanding of the source-to-sink gas-dynamic coupling, including the role played by flow rate, jet diameter, and the separation distance between the gas jet source and the suction sink. Compared to vortex-free jets, vortical jets for Re>2700 with swirl number S>0.27 experience earlier laminar-to-turbulent transition, with resulting rapid growth of the jet boundary. The ability to control growth of the jet expansion and mass and momentum dissipation into the surrounding is demonstrated via use of a coaxially aligned flow suction placed in the path of a jet. When a swirling jet is completely coupled with a flow suction, jet expansion is significantly suppressed. The suction/sink flow rate imposes a limit on the maximum input/source flow rate of gas jet to achieve complete coupling. Furthermore, there is a maximum distance over which effective coupling can occur, and for all Reynolds numbers considered this distance is shorter than the distance at which the jet structure breaks up into turbulent eddies in the absence of a sink.

We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work., A.B., R.E., and J.A. acknowledge the National Project FIS2016-80174-P from the MICINN and Project PI2017-30 and Grant No. IT1164-19 for research groups of the Basque University system from the Department of Education of the Basque Government. A.B also thanks Dr. Garikoitz Aguirregabiria for valuable technical advice on the TDDFT simulations of metallic nanoparticles and the Department of Education of the Basque Government for a predoctoral fellowship (Grant No. PRE2017_1_0267).

It was theoretically predicted more than 20 years ago [A.G. Lebed and K. Yamaji, {\it Phys. Rev. Lett.} {\bf80}, 2697 (1998)] that a triplet quasi-two-dimensional (Q2D) superconductor could restore its superconducting state in parallel magnetic fields, which are higher than its upper critical magnetic field, $H > H_{c2}(0)$. It is very likely that recently such phenomenon has been experimentally discovered in the Q2D superconductor UTe$_2$ by Nicholas Butch, Sheng Ran and their colleagues and has been confirmed by Japanese-French team. We review our previous theoretical results, using such a general method that it describes the reentrant superconductivity in the above mentioned compound as well as will hopefully describe the similar phenomena, which can be discovered in other Q2D superconductors., Invited Brief Review for journal Modern Physics Letters B, accepted (2020)

We theoretically study the upper critical magnetic fields at zero temperature in a quasi-two-dimensional (Q2D) superconductor in the parallel and perpendicular fields, $H_{c2}^{\parallel}(0)$ and $H_{c2}^{\perp}$(0), respectively. We find that $H_{c2}^{\parallel}(0) \approx 0.75 \ | d H_{c2}^{\parallel}/ dT|_{T_c} T_c $ and that $H_{c2}^{\perp}(0) \approx 0.59 \ | dH_{c2}^{\perp}/ d T|_{T_c} T_c$, where $| d H_{c2}^{\parallel}/ dT|_{T_c}$ and $| d H_{c2}^{\perp}/ d T|_{T_c}$ are the corresponding Ginzburg-Landau slopes of the upper critical magnetic fields. Our results demonstrate the breakdown of the so-called effective mass model in Q2D case and may be partially responsible for the experimentally observed deviations from the effective mass model in a number of layered superconductors, including $MgB_2$., Comment: 5 pages, 1 figure

Overhead power-transmission lines are one of the most important components of modern infrastructure. Their service life is determined by the state of the near-surface defect layers (NSDLs) of wires constituting these lines. Both the structure and microstructure of the NSDLs of wires of the AAAC type (All Aluminum Alloy Conductor), which were in operation during 0 (new) to 62 years, were investigated by methods of the X-ray (XRD) and electron back-scattering diffraction, optical microscopy, and resistivity measurements, as well as by means of densitometric and acoustic measurements with layer-by-layer removal of the near-surface material by etching. Two characteristic thicknesses of the NSDLs were obtained, different methods providing close results, namely, ~30–50 μm and ~56–140 μm. According to the mass-density distribution (XRD), these characteristic thicknesses correspond to the depths from the surface where they occur, respectively, ~70% and ~99% of the density drop in comparison with the bulk density value. The rate of increase in NSDL thickness is ~4 μm/year in the interval from 0 to 18 years. Results of investigation of elastic and microplastic properties of wires after removal of ~35 μm of the upper layer are also presented.

This paper presents the full research and development cycle of a high-precision absolute linear encoder based on a standard calibrated scale. Already available and used in industry standard scales of invar alloy were employed in the study. The scales have incremental indexes with 1 mm spacing intervals without an absolute code. However, the existing technical task is to measure the absolute position in the range of 2 m with accuracy less than 5 μ m. For that, the developed encoder rationally combines magnetic measuring channel for the index numbering and an optical channel for the precise estimation of the encoder position. First, for the development, a simulation was performed to synthesize and analyze an image of an index. This image was used to develop a real-time double-threshold image processing algorithm to estimate the index position. Later the developed image processing algorithm was verified by preliminary testing and supported by a presented three-stage calibration procedure. The final measurements proved that the designed and developed encoder has the accuracy of 1.65 μ m (3 standard deviations) at the speed up to 3 m/s. The possibility of use of standard calibrated scales with the presented encoder to solve existing and new industrial tasks forms the value of this paper. A possible use of the existing scales also provides unification and compatibility with conventional metrology equipment.

The phase structure, dielectric, ferroelectric, and piezoelectric properties of (1-2x)BiScO3 - xPbTiO3 - xPbMg1/3Nb2/3O3 ceramics (x=0.30-0.46) were studied. It was found that an increase in x leads to a structural phase transition between the rhombohedral and tetragonal phase via an intermediate monoclinic phase and to a crossover from the nonergodic relaxor state to the ferroelectric one. It was proposed that at x>0.42 the phase transition changes from second to first order. The assumption about the existence of a tricritical point on the phase diagram at x≈0.42 with the enhanced dielectric response has been made. The observed structure-property relationships of the studied solid solutions are discussed. It is shown that the solid solutions with x=0.42 are characterized by the high piezoelectric parameters (d33 = 509 pC/N, d31 = -178 pC/N, dh = 153 pC/N), which makes possible their applications in sonar equipment. This article is protected by copyright. All rights reserved.

Understanding two-phase convective heat transfer under extreme conditions of high heat and mass fluxes and confined geometry is of fundamental interest and practical significance. In particular, next generation electronics are becoming thermally limited in performance, as integration levels increase due to the emergence of ‘hotspots’ featuring up to ten-fold increase in local heat fluxes, resulting from non-uniform power distribution. An ultra-small clearance, 10 μm microgap, was investigated to gain insight into physics of high mass flux refrigerant R134a flow boiling, and to assess its utility as a practical solution for hotspot thermal management. Two configurations – a bare microgap, and inline micro-pin fin populated microgap – were tested in terms of their ability to dissipate heat fluxes approaching 1.5 kW/cm 2 . Extreme flow conditions were investigated, including mass fluxes up to 3000 kg/m 2 s at inlet pressures up to 1.5 MPa and exit vapor qualities approaching unity. Dominant flow regimes were identified and correlated to two phase heat transfer coefficients which were obtained using model-based data reduction for both device configurations. The results obtained were compared to predictions using correlations from literature, with the maximum heat transfer coefficient reaching 1.5 MW/m 2 K in the vapor plume regime in the case of the finned microgap.

Two aspects of the contribution of grazing incidence fast atom diffraction (GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD to provide \emph{in-situ} a precise description of the atomic-scale surface topology, and its ability to follow larger-scale changes in surface roughness during layer-by-layer growth. Recent experimental and theoretical results obtained for the He atom beam incident along the highly corrugated $[ 1\bar{1}0 ]$ direction of the $\beta_{2}$(2$\times$4) reconstructed GaAs(001) surface are summarized and complemented by the measurements and calculations for the beam incidence along the weakly corrugated [010] direction where a periodicity twice smaller as expected is observed. The combination of the experiment, quantum scattering matrix calculations, and semiclassical analysis allows in this case to reveal structural characteristics of the surface. For the in situ measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we analyse the change in elastic and inelastic contributions in the scattered beam, and the variation of the diffraction pattern in polar angle scattering. This analysis outlines the robustness, the simplicity and the richness of the GIFAD as a technique to monitor the layer-by-layer epitaxial growth.

The presence of variable heat fluxes, such as localized hotspots in integrated circuit (IC) architectures poses a key challenge for thermal management of existing (2D) and emerging three-dimensionally (3D) stacked chips. The use of conventional microchannel or uniform pin fin arrays for microfluidic cooling do not provide adequate surface area for heat transfer in the vicinity of regions of concentrated high power (hotspots), and therefore significant temperature gradients might arise in such zones. In the present investigation, the concept of using a single microfluidic loop for the combined and efficient cooling of hotspot and moderate power (background) areas is proposed, experimentally demonstrated, and supported by a comprehensive numerical model. Two different thermal device vehicles (TDVs) are considered for a range of operating conditions, in which the surface area is locally increased by clustering a dense array of pin fins in the hotspot region for one configuration, while for the other the clustering is uniform in the spanwise direction. De-ionized (DI) water is used as the coolant through a silicon (Si) microgap with 200 μm spacing; the hotspot heat flux is varied from 250 to 750 W/cm 2 , while the background heat flux is fixed at 250 W/cm 2 . Results indicate the capability of the proposed designs to keep the maximum temperature of the combined device below 65 °C for an inlet water temperature of 21.3 °C, with moderate temperature gradients and pressure drop. In addition, a robust computational fluid dynamics/heat transfer (CFD–HT) model capable of predicting spatially resolved temperature fields arising from heterogeneous heating is validated with relevant experimental data. Detailed benchmark simulations are provided, so they can be reproduced and used for reference in numerical studies with variable pin fin densities. The described methodology represents a cost-effective thermal modeling technique that may be applicable to virtually any type of heat flux distribution or power map, and IC architecture.

It is known that the field-induced spin-density-wave (FISDW) phases are experimentally observed in the quasi-one-dimensional (Q1D) organic conductors with chemical formula ${(\mathrm{TMTSF})}_{2}\mathrm{X}$ ($\mathrm{X}={\mathrm{PF}}_{6}$, ${\mathrm{ClO}}_{4}$, etc.) and some others in moderate magnetic fields. From a theoretical point of view, they appear as a result of ``one dimensionalization'' of the Q1D electron spectra due to the orbital electron effect in a magnetic field. We predict that the novel FISDW phases with different physical meaning have to appear in inclined high magnetic fields in Q1D conductors as a result of combination of the spin-splitting and orbital electron effects. We suggest performing the corresponding experiments in the ${(\mathrm{TMTSF})}_{2}\mathrm{X}$ materials.

An approach for the determination of the distribution of density of electronic states in organic photoconductors is proposed. It is based on the analysis of absorption coefficient spectral dependence and the photoconductivity temperature dependence of photosensitive thin solid films. Feasibility of the approach is demonstrated by a study of the dependences using co-polymer of phenylquinoline derivative and 2,1,3-benzothiadiazole as an organic photoconductor. The distributions of density of electronic states are described well by the Gaussian function, and the corresponding full-width at-half-maxima are determined.

We use classical electrodynamics, time-dependent density functional theory, and random-phase approximation to study the gap plasmons propagating in the nm-wide gap between metal surfaces. Particular emphasis is given to the quantum effects emerging when the junction is functionalized with a nanostructure supporting unoccupied gap localized electronic states. With the example of a quantum well (QW) introduced in the junction we show that the optically assisted electron transport across the junction via the gateway QW localized electronic states might strongly affect the lifetime and the propagation length of the gap plasmon. The coupling to the single-particle electron-hole excitations from occupied electronic states at metal surfaces into the QW-localized electronic states provides an efficient decay channel of the gap plasmon mode. Different from the through-gap electron tunneling discussed in the plasmonics literature, the electron transport involving the gateway electronic state is characterized by the threshold behavior with plasmon frequency. As a consequence, the dynamics of the gap plasmon can be controlled by varying the binding energy of the QW-localized electronic state. In more general terms, our results demonstrate strong sensitivity of the gap plasmons to the optically assisted electron transport properties of the junction which opens further perspectives in design of nanosensors and integrated active optical devices.

It is known that, in a pure one-dimensional case, the charge-density-wave phase is destroyed by a magnetic field, whereas the spin-density-wave (SDW) phase does not ``feel'' the field. In reality, the SDW phase is often observed in quasi-one-dimensional (Q1D) conductors due to the so-called ``nesting'' property of their electron spectra. We show that, in the latter case, a high magnetic field generates some ``antinesting'' term in a Q1D electron spectrum, which destroys the SDW phase. We suggest performing the corresponding experiments in SDW phases of the real Q1D organic conductors with chemical formula ${(\mathrm{TMTSF})}_{2}X$ ($X={\mathrm{PF}}_{6}$, ${\mathrm{ClO}}_{4}$, etc.).

We theoretically study the orbital destructive effect against superconductivity in a parallel magnetic field in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF) phase at zero temperature in a quasi-two-dimensional (Q2D) conductor. We demonstrate that at zero temperature a special parameter, $\lambda = l_{\perp}(H)/d$, is responsible for strength of the orbital effect, where $l_{\perp}(H)$ is a typical "size" of the quasi-classical electron orbit in a magnetic field and $d$ is the inter-plane distance. We discuss applications of our results to the existing experiments on the FFLO phase in the organic Q2D conductors $\kappa$-(ET)$_2$Cu(NCS)$_2$ and $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Cl., Comment: 5 pages, 0 figures

Recently, we have suggested Fermi-liquid - non-Fermi-liquid angular crossovers which may exist in quasi-one-dimensional (Q1D)conductors in high tilted magnetic fields [see A.G. Lebed, Phys. Rev. Lett. $\textbf{115}$, 157001 (2015).] All calculations in the Letter, were done by using the quasi-classical Peierls substitution method, whose applicability in high magnetic fields was questionable. Here, we solve a fully quantum mechanical problem and show that the main qualitative conclusions of the above mentioned Letter are correct. In particular, we show that in high magnetic fields, applied along one of the two main crystallographic axis, we have 2D electron spectrum, whereas, for directions of high magnetic fields far from the axes, we have 1D electron spectrum. The later is known to promote non-Fermi-liquid properties. As a result, we expect the existence of Fermi-liquid - non-Fermi-liquid angular crossovers or phase transitions. Electronic parameters of Q1D conductor (Per)$_2$Pt(mnt)$_2$ show that such transitions can appear in feasible high magnetic fields of the order of $H \simeq 20-25 \ T$., 4 pages, 0 figures

We report on the theoretical study of the second and third harmonic generation in plasmonic dimer nanoantennas with narrow gaps. Our study is based on the time dependent density functional theory. This allows us to address the nonlinear response of a tunneling junction in a subnanometric plasmonic gaps with a quantum calculation, which goes beyond conventional classical local and nonlocal treatments. We demonstrate that the nonlinear electron transport in a plasmonic junction, associated to the corresponding strong field enhancement in the narrow gap, allows to reach orders of magnitude enhancement in the efficiency of the second and third harmonic generation. Depending on the size of the junction and the frequency of the fundamental incident wave, we show that the frequency conversion in plasmonic dimer gaps can be determined by (i) the intrinsic nonlinearity of each individual nanoparticle, (ii) the nonlinear ac tunneling current across the gap, and (iii) the resonant excitations of the plasmon modes of the dimer. The study of the nonlinear response of plasmonic gaps within a full quantum treatment allows us to understand the fundamental mechanisms of nonlinearity in nanoplasmonics., G.A., R.E., and J.A. acknowledge the projects FIS2016-80174-P from Spanish MINECO, project 70NANB15H32 from U.S. Department of Commerce, National Institute of Standards and Technology. G.A., R.E., and A.K.K. acknowledge project PI2017-30 of the Department of Education of the Basque Government.

Advancement of focused electron beam-induced deposition (FEBID) as a versatile direct-write additive nanoscale fabrication technique has been inhibited by poor throughput, limited choice of precursors, and restrictions on possible 3D topologies. Here, we demonstrate FEBID using nanoelectrospray liquid precursor injection to grow carbon and pure metal nanostructures via direct decomposition and electrochemical reduction of the relevant precursors, achieving growth rates 10(5) times greater than those observed in standard gas-phase FEBID. Initiating growth at the free surface of a liquid pool enables fabrication of complex 3D carbon nanostructures with strong adhesion to the substrate. Deposition of silver microstructures at similar growth rates is also demonstrated as a promising avenue for future development of the technique.

A direct liquid fuel injection/variable volume reactor integrated with a hydrogen selective membrane (CHAMP-DDIR) has been recently shown to be a promising new concept for hydrogen production in portable and distributed applications. The CHAMP-DDIR reactor performance has been analyzed using a simplified transport model with which conditions for maximum performance, e.g. highest volumetric power density, were identified. A prototype reactor demonstrated the ability to realize performance improvement, while also indicating a need for more a rigorous model for accurate exploration of the design and operation space. In this paper, we present a comprehensive reactor model which carefully considers the effects of heat and mass transfer, including rigorous treatment of multi-component species transport. The model is validated against experimental results through comparison of predicted and measured hydrogen production rate, reactor pressure, and temperature. The experimentally validated model is used to identify the relationship between CHAMP-DDIR design and operating parameters and the rate-limiting processes that govern reactor output. In addition, effects of heat and mass transfer limitations on CHAMP-DDIR performance are investigated by comparing the predictions among multiple cases with increasing level of complexity used for modeling the transport phenomena within the reactor.

We solve the theoretical problem of restoration of superconductivity in a triplet quasi-one-dimensional, layered superconductor in an ultra-high magnetic field. With the field perpendicular to the conducting chains as well as having a component normal to the layers, we suggest a new quantum limit superconducting phase and derive an analytical expression for the transition temperature as a function of magnetic field, T ⁎ ( H ) . Using our theoretical results along with the known band and superconducting parameters of the presumably triplet superconductor Li0.9Mo6O17, we determine the orientation of H that maximizes T ⁎ ( H ) for a given value of the field. Subsequently, we show that reentrant superconductivity in this compound is attainable with currently available non-destructive pulsed magnetic fields of order H ≃ 100 T , when such fields are perpendicular to conducting chains and parallel to the layers. For its possible experimental discovery, we give a detailed specification on how small angular inclinations of the magnetic field from its best experimental geometry decrease the superconducting transition temperature of the reentrant phase.

A novel dynamically-controlled membrane batch reactor, which combines the variable volume operation of CHAMP (CO2/H2 Active Membrane Piston) with the direct injection of liquid fuel of DDIR (Direct Droplet Impingement Reactor) for enhanced power density, is demonstrated and experimentally characterized in this study. A laboratory-scale CHAMP-DDIR, consisting of a variable volume piston-cylinder reactor chamber and an actively-controlled micro injector for liquid fuel atomization, is used with a Pd–Ag foil membrane and Cu/ZnO/Al2O3 catalyst to steam reform methanol for hydrogen generation. Two modes of CHAMP-DDIR operation, pulse-modulated fuel injection and batch reaction with dynamically-adjusted reactor volume, were investigated, and their performance was quantified using metrics such as hydrogen yield and volumetric power density, and compared with those for a baseline operation (single fuel injection with fixed reactor volume). The experimental results showed that the residence time for the same hydrogen yield can be reduced by compressing the reactor volume during the conversion cycle. The residence time reduction was primarily as a result of higher hydrogen partial pressure in the reactor chamber and thus higher rates of hydrogen permeation. In addition, pulse-modulated fuel injection experiments revealed that a significant reduction in required reactor volume can be achieved with multi-shot split fuel introduction. Both the reduction in required cycle time and the reduction in required reactor volume increase the volumetric power density of CHAMP-DDIR. The demonstrated power density enhancement achieved through the dynamic compression of reactor volume was 17%, and the enhancement achieved through time-modulated fuel introduction was 38% (for 85% hydrogen yield efficiency and under the constraints of the same maximum operating pressure and total amount of fuel).

We have observed intriguing stick-slip behavior during capillary pressure driven filling of borosilicate microtubes coated with hydrogel on their inner wall. Swelling of hydrogel upon exposure to a translating waterfront is accompanied by "stick-and-slip" motion. This results in the macroscopic filling velocity for water penetration into glass capillaries coated with poly(N-isopropylacrylamide) (PNIPAM) being constant throughout the filling process, and reduced by three orders of magnitude when compared to filling of uncoated capillaries. A simple scaling analysis is used to introduce a possible explanation by considering the mechanisms responsible for pinning and unpinning of the contact line. The explanation assumes that the time scale for water diffusion into a hydrogel film and the resulting swelling/change of the local meniscus contact angle define the duration of each "stick" event. The "slip" length scale is in turn established by the elastocapillary deformation of dry hydrogel at the pinning point of the contact line. The sequential dynamics of these processes then determine the rate of water filling into a swelling capillary. Collectively, these experimental and theoretical results provide a new conceptual framework for liquid motion confined by soft, dynamically evolving polymer interfaces, in which the system creates an energy barrier to further motion through elasto-capillary deformation, and then lowers the barrier through diffusive softening. This insight has implications for optimal design of microfluidic and lab-on-a-chip devices based on stimuli-responsive smart polymers.

The self-consistent electron-ion potential V(r) is calculated for H ions in an electron gas system as a function of the projectile energy to model the electronic stopping power for conduction-band electrons. The results show different self-consistent potentials at low projectile-energies, related to different degrees of excitation of the electron cloud surrounding the intruder ion. This behavior can explain the abrupt change of velocity dependent screening-length of the potential found by the use of the extended Friedel sum rule and the possible breakdown of the standard free electron gas model for the electronic stopping at low projectile energies. A dynamical interpolation of V(r) is proposed and used to calculate the stopping power for H interacting with the valence electrons of Al. The results are in good agreement with the TDDFT benchmark calculations as well as with experimental data., We are indebted to the Brazilian agencies CAPES, CNPq and FAPERGS for the partial support of this research project. One of the authors (PLG) acknowledges funding by the Alexander-von-Humboldt foundation. NEK and RDM acknowledge financial support by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-756-13) and the Spanish Ministerio de Economía y Competitividad (Grants FIS2013-48286-C02-02-P and FIS2016-76471-P).

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO2 adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.

Evaporation from thin films is a key feature of many processes, including energy conversion, microelectronics cooling, boiling, perspiration, and self-assembly operations. The phase change occurring in these systems is governed by transport processes at the contact line where liquid, vapor, and solid meet. Evidence suggests that altering the surface chemistry and surface topography on the micro- and the nanoscales can be used to dramatically enhance vaporization. The 2013 International Workshop on Micro- and Nanostructures for Phase-Change Heat Transfer brought together a group of experts to review the current state-of-the-art and discuss future research needs. This article is focused on the thin-film evaporation panel discussion and outlines some of the key principles and conclusions reached by that panel and the workshop attendees.

Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes short-lived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surface-enhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others. © 2013 American Chemical Society., J.A. acknowledges financial support from the Department of Industry of the Basque Government through the ETORTEK project nanoiker, the Department of Education of the Basque Government through project IT756/13 for consolidated groups, and the Spanish Ministerio de Ciencia e Innovación through Project No. FIS2010-19609-C02-01.

Thin liquid films can provide efficient means for heat and mass transfer by supporting a large rate of evaporation, while maintaining temperatures under saturation conditions. The use of nanoporous membranes establishes thin liquid films minimizing the possibility of dryout by exploiting capillary confinement of the fluid. In combination with gas jet impingement, this yields record high heat and mass fluxes. Consequently, for applications relying on efficient heat and mass transfer, such as, phase change cooling of electronics and membrane distillation of water, it is essential to identify and characterize all the underlying transport mechanisms affecting overall performance. A detailed computational analysis of heat and mass transfer is therefore carried out to predict the performance of thin film evaporation. Heat conduction and convection are both found crucial in determining the temperature distribution within the thin film region, which ultimately controls the rate of evaporation from the liquid–vapor interface. Furthermore, the effect of vapor transport from the liquid–vapor interface on overall performance is also assessed. The relative effects of these performance-governing parameters are discussed and quantitatively compared at different operating conditions. The results of the computational analysis are supported by comparison with experiments.

We investigate a theoretical problem of electron-electron interactions in an inclined magnetic field in a quasi-one-dimensional (Q1D) conductor. We show that they result in strong non-Fermi-liquid corrections to a specific heat, provided that the direction of the magnetic field is far from the so-called Lebed's magic angles (LMAs). If magnetic field is directed close to one of the LMAs, the specific heat corrections become small and the Fermi-liquid picture restores. As a result, we predict Fermi-liquid--non-Fermi-liquid angular crossovers in the vicinities of the LMA directions of the field. We suggest to perform the corresponding experiment in the Q1D conductor ${(\mathrm{Per})}_{2}\mathrm{Au}{(\mathrm{mnt})}_{2}$ under pressure in magnetic fields of the order of $H\ensuremath{\simeq}25\phantom{\rule{0.28em}{0ex}}\text{T}$.

We derive a so-called gap equation for superconductivity in a quasi-one-dimensional (Q1D) layered conductor in a magnetic field, which is parallel to both its conducting plane and its conducting axis. This equation demonstrates that the orbital destructive effects against superconductivity cannot destroy it, if the perpendicular to the plane coherence length is less than the inter-plane distance. On the basis of our results, we suggest arguments that some triplet superconducting phase was indeed discovered in ultrahigh magnetic fields in the Q1D superconductor Li$_{0.9}$Mo$_6$O$_{17}$ [see Xiaofeng Xu et al., Phys. Rev. Lett., $\bf{102}$, 206602 (2009).] We also discuss a possibility that the above-mentioned superconducting phase can be stable at arbitrary high magnetic fields.

Using the time-dependent density functional theory, we perform quantum calculations of the electron dynamics in small charged metallic nanoparticles (clusters) of spherical geometry. We show that the excess charge is accumulated at the surface of the nanoparticle within a narrow layer given by the typical screening distance of the electronic system. As a consequence, for nanoparticles in vacuum, the dipolar plasmon mode displays only a small frequency shift upon charging. We obtain a blue shift for positively charged clusters and a red shift for negatively charged clusters, consistent with the change of the electron spill-out from the nanoparticle boundaries. For negatively charged clusters, the Fermi level is eventually promoted above the vacuum level leading to the decay of the excess charge via resonant electron transfer into the continuum. We show that, depending on the charge, the process of electron loss can be very fast, on the femtosecond time scale. Our results are of great relevance to correctly interpret the optical response of the nanoparticles obtained in electrochemistry, and demonstrate that the measured shift of the plasmon resonances upon charging of nanoparticles cannot be explained without account for the surface chemistry and the dielectric environment., M.Z. acknowledges financial support from the Departamento Administrativo de Ciencia, Tecnologia e Innovacion-COLCIENCIAS and Facultad de Ciencias from Universidad de los Andes. M.Z. also gratefully acknowledges the hospitality of the Donostia International Physics Center and the Materials Physics Center in San Sebastian. J.A. acknowledges support from the Spanish Ministry of Economy and Competitiveness through project FIS2013-41184-P and project 2015CD0010 of the CSIC scientific cooperation program for development “ICOOP LIGHT” 2015.

We have derived the so-called gap equation, which determines the upper critical magnetic field, perpendicular to conducting chains of a quasi-one-dimensional superconductor. By analyzing this equation at low temperatures, we have found that the calculated angular dependence of the upper critical magnetic field is qualitatively different than that in the so-called effective mass model. In particular, our theory predicts a non-analytical angular dependence of the upper critical magnetic field, $H_{c2}(0) - H_{c2}(\alpha) \sim \alpha^{3/2}$, when magnetic field is close to some special crystallographic axis and makes an angle $\alpha$ with it. We discuss possible experiments on the superconductor (DMET)$_2$I$_3$ to discover this non-analytical dependence., Comment: 5 pages

Hydrogen transport and loading into single-walled carbon nanotubes (SWCNT) encapsulated by thin Pd layers onto a massive Pd substrate were studied using a complex of vacuum thermal desorption, cyclic voltammetry and ESR methods. By adding SWCNT the hydrogen capacity of the Pd–SWCNT composite under electrochemical loading increases as much as 25% relative to Palladium metal alone. This provides moderate growth in the gravimetric capacity of the total composite based on a massive Pd substrate. The hydrogen binding energy in the SWCNT (eH = 0.075 eV/H-atom), estimated by studies of hydrogen transport in the Pd–SWCNT composite was lower than predicted for the Pd–SWCNT complex, but higher than the physisorption on the bare SWCNT. Using ESR we established that the Pd–Cx e-complexes formed at the wall of nanotube could be considered as hydrogen adsorption site, providing both high net gravimetric capacity and low hydrogen binding energy in the Pd encapsulated SWCNT. The results obtained provide an opportunity to probe a condensed hydrogen phase of nanometer scale confined in SWCNT, encapsulated by transition metals.

Highly localized light-induced phase transformation of electron beam induced deposited carbon nanostructures (dots and squares) on noble metal surfaces is reported. The phase transformation from the amorphous phase to the disordered graphitic phase is analyzed using the characteristic Raman signatures for amorphous and graphitized carbon and conductive force microscopy. The extent of the transformation is found to be largely dependent on the plasmon absorption properties of the underlying metal fi lm. It is observed that the amorphous carbon deposits on the silver fi lms consisting of 12 nm particles with the plasmon absorption near the laser excitation wavelength (514 nm), undergo fast graphitization to a nanocrystalline or a disordered graphitic phase. This transformation results in the formation of a highly conductive carbon/metal interface with at least seven orders of magnitude lower electrical resistivity than the initial insulating interface. It is suggested that the fast graphitization of nanoscale carbon deposits might serve as an effi cient path for the formation of complex patterned nanoscale metal-carbon interconnects with high electrical conductivity.

We theoretically determine the Ginzburg-Landau slopes of the anisotropic upper critical magnetic field in a quasi-one-dimensional superconductor and correct the previous works on this issue. By using the experimentally measured values of the Ginzburg-Landau slopes in the superconductor (TMTSF)ClO4, we determine band parameters of its electron spectrum. Our main result is that the so-called quantum dimensional crossover has to happen in this material in magnetic fields, H = 3–8 T, which are much lower than the previously assumed. We discuss how this fact influences metallic and superconducting properties of the (TMTSF)2ClO4.

We suggest explanation of the high upper critical magnetic field, perpendicular to conducting chains and parallel to conducting layers Hc2b′ ≃ 6 T, experimentally observed in the organic superconductor (TMTSF)2ClO4. In particular, we show that Hc2b′ can be higher than both the quasiclassical upper critical field and Clogston-Chandrasekhar paramagnetic limit in a singlet quasi-one-dimensional superconductor. We predict the coexistence of the hidden Reentrant and Larkin-Ovchinnikov-Fulde-Ferrell phases in a magnetic field. Our results are compared to the recent experimental data and shown to be in a good agreement with the experiments.

In this article we describe a novel cooling scheme utilizing a combination of fluidic (single-phase convection and phase change) and solid-state (superlattice cooler) techniques to simultaneously remove high background heat fluxes (∼100 W/cm2) over the entire chip and dissipate ultra high heat fluxes (∼0.5–1 kW/cm2) from multiple localized hot spots. This article focuses on the conceptual design to assess the feasibility of the proposed cooling scheme.

We report on a theoretical study of the escape of confined surface states electrons from quantum corrals made of Cu adatoms on a Cu(1 1 1) surface. This study maps electron transmission through the corral wall and provides an extension of our earlier work focused on confinement in Cu corrals [S. Diaz-Tendero, F.E. Olsson, A.G. Borisov, J.P. Gauyacq, Phys. Rev. B 77 (2008) 205403]. The existence of two decay modes for the confined surface state is stressed: (i) non-resonant tunnelling through the corral wall concentrated on the Cu adatoms and (ii) a resonant-induced decay involving the transient formation of a resonant state localized on top of the corral wall. The present mapping of the electron transmission reveals how the interference between the two decay modes works: there exist regions where the electron leaves the corral, balanced by regions where it enters the corral, though the global behaviour of the quasi-stationary states is electron escape from the corral.

A new cooling scheme utilizing evaporation from an ultrathin, spatially confined liquid film is described and analyzed for thermal management of hot spots with local heat fluxes in excess of 600 W/cm2. This is achieved by a stable monolayer of liquid maintained on the surface and using fully dry sweeping gas (e.g., air) blown at high velocity (50–100 m/s) above this liquid monolayer. We also demonstrate how dielectric coolants like FC72 can outperform water as an evaporative coolant for this scheme. This work presents the conceptual system design, the results of performance analysis supporting the feasibility of the proposed cooling scheme, and experimental results that demonstrate the idea as well as validate the computational results. The analysis allows one to elucidate the salient physical features of evaporative cooling from spatially confined thin films subjected to a sweeping gas and to identify the key parameters resulting enhanced performance. The simplified model provides results in a form suita...

In this paper we review the recent contributions of polyelectrolyte microcapsules in the biomedical field, comprising in vitro and in vivodrug delivery as well as their applications as biosensors.