Specific Transport Properties Research Articles

Preparation of grape branch-derived porous carbon by one-step blending and its multifunctional applications

In this study, an innovative methodology is presented for the rapid one-step synthesis of carbon materials with high specific surface area through doping and activation processes, utilizing ball milling techniques to reduce the particle size of the materials effectively and to achieve activation and doping. Nitrogen-doped grape branch carbon (NGBC) was characterized by abundant micro- and mesoporous structures with specific surface areas up to 1364 m2/g and high nitrogen content (atomic fraction of 4.89 %). At pH 8 and room temperature, NGBC showed excellent adsorption performance for malachite green (MG, a cationic dye) and reactive blue 19 (an anionic dye) with adsorption capacities of 409.91 mg/g and 213.36 mg/g, respectively, and the material can be reused several times. The analysis of adsorption kinetics revealed that multiple factors controlled the adsorption process of NGBC on MG, and the analysis of adsorption isotherms showed that the adsorption process was mainly monomolecular layer adsorption. Compared with the common carbon-based adsorbents for biomass currently available on the market, NGBC showed better adsorption efficacy, indicating its great potential for practical application. Further, when NGBC was applied to electrochemical performance tests as supercapacitor electrodes, the introduction of nitrogen significantly improved the specific capacitance and ion transport properties of the porous carbon material, effectively reducing the electrical resistance. At a current density of 0.5 A/g, the nitrogen-doped porous carbon showed a specific capacitance of 258.4 F/g, much higher than that of the undoped 136.8 F/g, as well as a high specific capacitance retention of 90.43 % after 5000 cycles. The sensitivity analysis points out that nitrogen source and labor expenditure are the key factors in the cost components. This research not only provides a simple method for industrialized recovery and reuse of grape branches, but also lays an experimental and theoretical foundation for promoting further applications of biomass waste in the fields of water purification and supercapacitor electrode materials.

Review of properties, synthesis, and energy applications of borophene, a novel boron-based 2D material

At least 16 bulk polymorphs of linked icosahedrons exist in boron that are not found in other materials, due to the low covalent radius and sp2 hybridization capacity of boron atoms. One of these is borophene, an exciting new nanomaterial with a wide range of possible energy uses. The existence of borophene, a two-dimensional (2D) material, has been proven by both theoretical and experimental studies. Borophene's high theoretical specific capacities, magnetic conductivity, and ion transport properties make it a promising candidate in energy applications. In this study, firstly, the structure, chemical, and physical properties of borophene were mentioned. Then, in terms of synthesis approaches, both top-down and bottom-up techniques (such as atomic layer deposition (ALD), chemical vapor deposition (CVD), exfoliation by sonochemistry, molecular beam epitaxy (MBE), and multi-step thermal decomposition (MTD) for ultrahigh-vacuum borophene deposition technologies) were discussed. Finally, its use as a catalyst in high-metal-ion batteries, hydrogen storage (HS), Nanoelectronics applications hydrogen evolution reaction (HER) was mentioned.

Investigating the impact of polarization on surface plasmon polariton characteristics in plasmonic waveguides under periodic driving fields

This study examines the impact of polarization in the driving field on the surface plasmon polariton (SPP) modes within plasmonic waveguides under the influence of a periodic driving field. Addressing a significant knowledge gap in the existing literature, we present a comprehensive investigation employing Floquet engineering techniques, with a specific emphasis on elliptically polarized fields as the dressing field. Our analysis reveals that the use of generalized Floquet states allows us to derive Floquet states for specific polarized dressing fields, such as linear, left-handed circular, and right-handed circular polarization. Remarkably, we demonstrate that Floquet states depend on the chirality of the dressing field’s polarization. Employing the Floquet-Fermi golden rule, we assess electron transport under various polarization types and find that the specific polarization type influence electron transport properties. However, we establish that the chirality of the polarization of the dressing field does not impact the transport properties. During our numerical analysis, we assess the alterations in SPP characteristics arising from two distinct types of polarization in dressing fields: linear polarization and circular polarization. Our results underscore the potential of employing a dressing field to effectively mitigate the propagation losses of SPPs in plasmonic metals, with the extent of improvement contingent on the specific polarization type. To quantify the performance enhancements of commonly used plasmonic metals under linearly and circularly polarized dressing fields, we employ a figure of merit (FoM). This study offers insights into the practical utilization of periodic driving fields as a powerful tool in advancing plasmonic communication within chip-scale environments.

Sum-frequency generation and amplification processes in semiconductor superlattices

Semiconductor superlattices are very well-known structures due to their specific electron transport properties, making them extremely attractive to be employed in electronic or optoelectronic devices. The interest in such structures has been recently additionally stirred up due to the first successful experimental demonstration of parametric gain in GaAs/AlGaAs superlattices, resulting in the generation of harmonics, half-harmonics and fractional harmonics. This invention paves the way for a successful realization of superlattice-based generators and amplifiers up to the terahertz frequency range. Despite the emerging experimental results and decade-long theoretical research, unresolved aspects, related to the physical processes inside the superlattices, persist. Lately, the biasing effect was extensively analysed for the case of degenerate processes in the superlattice; however, the non-degenerate case was left out of frame until now. Within this research, we further expand the boundaries of previous investigation by exploring the differences of non-degenerate processes. The study uncovers the asymmetry appearance of the probe field vs. relative phase dependences as well as the possibility of parametric fractional frequency generation. Finally, the concept of energy reflow between two participating probes is predicted and discussed.

The transport properties of Kekulé-ordered graphene p–n junction

The transport properties of electrons in graphene p–n junction with uniform Kekulé lattice distortion have been studied using the tight-binding model and the Landauer–Büttiker formalism combined with the nonequilibrium Green’s function method. In the Kekulé-ordered graphene, the original K and Kʹ valleys of the pristine graphene are folded together due to the enlargement of the primitive cell. When the chiral symmetry breaking of a valley leads to a single-valley phase, there are special transport properties of Dirac electrons in the Kekulé lattice. In the O-shaped Kekulé graphene p–n junction, Klein tunneling is suppressed, and only resonance tunneling occurs. In the Y-shaped Kekulé graphene p–n junction, the transport of electrons is dominated by Klein tunneling. When the on-site energy modification is introduced into the Y-shaped Kekulé structure, both Klein tunneling and resonance tunneling occur, and the electron tunneling is enhanced. Under strong magnetic fields, the conductance of O-shaped and on-site energy-modified Y-shaped Kekulé graphene p–n junctions is non-zero due to the presence of resonance tunneling. It is also found that the disorder can enhance conductance, with conductance plateaus forming in the appropriate range of disorder strength.

Graphene Nanofoam Based Nanomaterials: Manufacturing and Technical Prospects

This article fundamentally reviews progress in the design and manufacturing of three-dimensional (3D) graphene-based nanocomposites for technical applications. The 3D graphene nanostructures have been manufactured using techniques like the template method, chemical vapor deposition, sol-gel, freeze-drying, hydrothermal technique, and other approaches. The nanofoam has been reinforced in polymers to achieve superior structural, morphological, and physical characteristics of the ensuing polymer/graphene nanofoam nanocomposites. The polymer/graphene nanofoam nanocomposites have been manufactured using the approaches like direct template method, in situ technique, infiltration process, and other methods. The 3D nanofoam- and polymer-based nanostructures have shown high specific surface area, suppleness, electron transport, thermal conduction, mechanical resilience, and other physical properties. The technical applications of hierarchical graphene nanofoams have been observed in the fields of radiation shielding, solar cells, supercapacitors, fuel cells, and other applications.

Tunable Ion Transport with Freestanding Vermiculite Membranes.

Membranes integrating two-dimensional (2D) materials have emerged as a category with unusual ion transport and potentially useful separation applications in both aqueous and nonaqueous systems. The interlayer galleries in these membranes drive separation and selectivity, with specific transport properties determined by the chemical and structural modifications within the inherently different interlayers. Here we report an approach to tuning interlayer spacing with a single source material─exfoliated and restacked vermiculite with alkanediamine cross-linkers─to both control the gallery height and enhance the membrane stability. The as-prepared cross-linked 2D vermiculite membranes exhibit ion diffusivities tuned by the length of the selected diamine molecule. The 2D nanochannels in these stabilized vermiculite membranes enable a systematic study of confined ionic transport.

Cerebral concentration and toxicity of endocrine disrupting chemicals: The implication of blood-brain interfaces

Endocrine disrupting chemicals (EDCs) act on peripheral endocrine organs or interfere with general endocrine pathways. Several EDCs alter the central regulation of neuroendocrine pathways, and affect neurological functions, and as such can be classified as neurotoxic molecules. Environmental pollutants classified as EDCs and affecting the central nervous system include perfluoroalcanes, parabens, phthalates, organotins, bisphenols, benzophenones, polychlorinated biphenyls, and dioxins. In this review we provide a brief description of these families of EDCs. We report and compare the EDC concentrations measured in the brain of humans and wild animals naturally exposed to these molecules, as well as in the brain of laboratory animals experimentally exposed to EDCs. The importance of using sophisticated analytical tools to detect EDCs in the brain is pointed out. The ability of blood-brain interfaces to reduce the brain exposition to EDCs in adult and during development is discussed in relation with the specific morphological, transport and metabolic properties of these cellular layers. Finally, we review the evidence that the neuroprotective functions of blood-brain interfaces can be altered by EDCs, a process that may participate to the central toxic action of these molecules. Overall this analysis points to the implication of blood-brain interfaces in setting the extent of central EDCs toxicity, although most evidence is indirect. Therefore, more specific blood-brain interface-oriented studies are called for in this field of EDC neurotoxicology.

The Pyrazinacenes.

Pyrazinacenes are a class of nitrogen-containing heteroacene molecules composed of linearly fused pyrazine units, which might also include dihydropyrazine groups leading to different reduced states of the compounds. While they are structurally similar to hydrocarbon acenes (e.g., pentacene) the presence of increasing numbers of N-heteroatoms introduces several different additional features of the compounds so that they can be considered for investigations beyond those suggested for acenes (i.e., organic field-effect transistors, solar cell components). Pyrazinacenes are in several ways complementary to C-H-only acenes based on the increasing stability of reduced states of the compounds with increasing numbers of fused pyrazine rings, although an acene-like electronic structure persists in the compounds so far studied. However, the introduction of multiple N atoms leads to properties that depart from C-H-only acenes. In particular, the compounds exhibit a delocalization of NH protons in extended reduced compounds and oxidation state switchability in solution and at interfaces. The presence of NH groups also allows an easy introduction of solubilizing groups at the pyrazinacene chromophore. In this Account, we will describe the preparation of extended pyrazinacenes from dipyrazino[2,3-b:2',3'-e]pyrazine (1,4,5,8,9,10-hexaazaanthracene; N6) derivatives up to 1,4,5,6,7,8,9,12,13,14,15,16,17,18-tetradecaazaheptacene (N14) and also assess structures of the relevant compounds based on X-ray crystallographic studies. Emergent properties of the molecules include highly unusual linear tautomeric processes based on a delocalization of protons (and the corresponding formation of orbitals based on multiple adjacent N lone electron pair interactions), which suggest special transport properties based on molecular protonics. Molecules such as decazapentacene (N10) exhibit multistability of oxidation state, and this is predicted to promote the redox catalytic properties of the compounds. The oxidation-state switching of on-surface processes is also described and has been investigated using scanning tunneling microscopy. The longest known pyrazinacene chromophore (N14) exhibits amphiprotism with its state of protonation being strongly coupled to its fluorescence emission properties in the near-infrared region indicating possible uses in pH-coupled bioimaging applications. The synthesis of the pyrazinacenes is flexible and allows the preparation of symmetrically or unsymmetrically substituted derivatives for the development of more complex molecules and for control of the electronic structure of the acene unit. Overall, the pyrazinacenes represent an emerging class of highly nitrogenous heteroacenes with unique properties and excellent potential for development in different applications based on their special supramolecular properties including guest binding or interactions in biological systems.

Reduced phase space of heat-carrying acoustic phonons in single-crystalline InTe

Chalcogenide semiconductors and semimetals are a fertile class of efficient thermoelectric materials, which, in most cases, exhibit very low lattice thermal conductivity κph despite lacking a complex crystal structure such as the tetragonal binary compound InTe. Our measurements of κph(T) in single-crystalline InTe along the c axis show that κph exhibits a smooth temperature dependence upon cooling to about 50 K, the temperature below which a strong rise typical for dielectric compounds is observed. Using a combination of first-principles calculations, inelastic neutron scattering (INS), and low-temperature specific heat and transport properties measurements on single-crystalline InTe, we show that the phonon spectrum exhibits well-defined acoustic modes, the energy dispersions of which are constrained to low energies due to distributions of dispersionless, optical modes, which are responsible for a broad double peak structure in the low-temperature specific heat. The latter are assigned to the dynamics of In+ cations in tunnels formed by edge-sharing (In3+Te42−)− tetrahedra chains, the atomic thermal displacement parameters of which, probed as a function of temperature by means of single-crystal x-ray diffraction, suggest the existence of a complex energy potential. Indeed, the In+-weighted optical modes are not observed by INS, which is ascribed to the anharmonic broadening of their energy profiles. While the low κph value of 1.2Wm−1K−1 at 300 K originates from the limited energy range available for acoustic phonons, we show that the underlying mechanism is specific to InTe and argue that it is likely related to the presence of local disorder induced by the In+ site occupancy.

Formation of Multicontinuous 3D Network Nanostructures with Increased Complexity in ABC-Type Block Copolymers.

The multicontinuous network nature of polymer nanostructures provides them with many opportunities to fabricate multifunctional materials with specific mechanical, transport, optical, and other novel properties. In this paper, we generate an effective design principle to craft a series of multicontinuous network structures with controllable channels, including multicontinuous gyroid and O70 network morphologies via the self-assembly of ABC-type block copolymers. Importantly, we achieve a much wider (∼25%) compositional range than that of AB diblock copolymers (∼3%), which would increase the widespread application of these multicontinuous polymer networks. Even for the simplest ABC linear system, this method is valid for generating multicontinuous network structures, where gyroids and O70 are found to possess large phase regions. This finding can theoretically explain the experimental observation of gyroid and O70 phases. We believe that our proposed design principle along with the calculated phase diagram provides a compelling panacea for the fabrication of multicontinuous 3D network nanostructures.

Specific heat, thermal conductivity, electron transport and electronic band properties of CeNi9In2

We report the results of specific heat Cp(T), thermal conductivity κ(T), thermoelectric power S(T), magnetoresistance MR(H) and Hall coefficient RH(H,T) measurements on an intermediate valence (IV) CeNi9In2 compound in the temperature range 2–300 ​K and in magnetic fields up to 9 ​T. In addition, the data of DFT calculations using FP-LMTO ​+ ​LDA and FP-LAPW ​+ ​PBE-GGA methods are presented. The studied sample reveals an enhanced Sommerfeld coefficient, metallic behaviour in κ(T), S(T), MR(H) and RH(T) properties, but does not exhibit clear crossover phenomenon expected for IV compounds. The DFT studies enunciate a weak 4f-3d hybridization and a major input to density of states at the Fermi level coming from the Ni 3d-electrons. These findings indicate that the contribution of the Ni atoms on the physical properties prevails over that of CeNi9In2 and hence the characteristics of IV of the Ce atoms cannot be demonstrable in the measured physical quantities.

3D printing of rock analogues in sand: a tool for design and repeatable testing of geomechanical and transport properties

Natural rocks can be heterogeneous due to complex diagenetic processes that affect mineralogy and pore architecture. Correlation of geomechanical and transport properties of rocks in three dimensions can lead to large variances in data when tested experimentally. 3D-printing of rock analogues in sand is a promising alternative for experimental testing that can be used to calibrate variables during geotechnical testing. While 3D-printed sand is a homogeneous material, the parameters for creating grain packing and pore infill can be tuned to mimic specific geomechanical and transport properties. Initially, 3D-printed specimens have a low density due to a loose distribution of grains. Herein, we present our efforts at increasing the density through incorporating a roller in the printing process to compact individual layers. We also propose introduction of a more heterogeneous sand mixture that encompasses a wide range of grain-size distributions. Lastly, a discussion between binder saturation (that infills the pore space) of 3D-printed specimens and the axial strength, dimensional control, and porosity is described within. 3D printing of rock analogues is critical in pursuing rigorous destructive tests required for geotechnical and geological engineering because it can provide repeatable, controlled data on rock properties.

Chemical Bonding and Physical Properties in Quasicrystals and Their Related Approximant Phases: Known Facts and Current Perspectives

Quasicrystals are a class of ordered solids made of typical metallic atoms but they do not exhibit the physical properties that usually signal the presence of metallic bonding, and their electrical and thermal transport properties resemble a more semiconductor-like than metallic character. In this paper I first review a number of experimental results and numerical simulations suggesting that the origin of the unusual properties of these compounds can be traced back to two main features. For one thing, we have the formation of covalent bonds among certain atoms grouped into clusters at a local scale. Thus, the nature of chemical bonding among certain constituent atoms should play a significant role in the onset of non-metallic physical properties of quasicrystals bearing transition-metal elements. On the other hand, the self-similar symmetry of the underlying structure gives rise to the presence of an extended chemical bonding network due to a hierarchical nesting of clusters. This novel structural design leads to the existence of quite diverse wave functions, whose transmission characteristics range from extended to almost localized ones. Finally, the potential of quasicrystals as thermoelectric materials is discussed on the basis of their specific transport properties.

Surface State Dynamics of Topological Insulators Investigated by Femtosecond Time- and Angle-Resolved Photoemission Spectroscopy

Topological insulators (TI) are known for striking quantum phenomena associated with their spin-polarized topological surface state (TSS). The latter in particular forms a Dirac cone that bridges the energy gap between valence and conduction bands, providing a unique opportunity for prospective device applications. In TI of the BixSb2−xTeySe3−y (BSTS) family, stoichiometry determines the morphology and position of the Dirac cone with respect to the Fermi level. In order to engineer specific transport properties, a careful tuning of the TSS is highly desired. Therefore, we have systematically explored BSTS samples with different stoichiometries by time- and angle-resolved photoemission spectroscopy (TARPES). This technique provides snapshots of the electronic structure and discloses the carrier dynamics in surface and bulk states, providing crucial information for the design of electro-spin current devices. Our results reveal the central role of doping level on the Dirac cone structure and its femtosecond dynamics. In particular, an extraordinarily long TSS lifetime is observed when the the vertex of the Dirac cone lies at the Fermi level.

Human health risk assessment for nanoparticle-contaminated aquifer systems

Nanosized particles (NPs), such as TiO2, Silver, graphene NPs, nanoscale zero-valent iron, carbon nanotubes, etc., are increasingly used in industrial processes, and releases at production plants and from landfills are likely scenarios for the next years. As a consequence, appropriate procedures and tools to quantify the risks for human health associated to these releases are needed.The tiered approach of the standard ASTM procedure (ASTM-E2081-00) is today the most applied for human health risk assessment at sites contaminated by chemical substances, but it cannot be directly applied to nanoparticles: NP transport along migration pathways follows mechanisms significantly different from those of chemicals; moreover, also toxicity indicators (namely, reference dose and slope factor) are NP-specific. In this work a risk assessment approach modified for NPs is proposed, with a specific application at Tier 2 to migration in groundwater. The standard ASTM equations are modified to include NP-specific transport mechanisms. NPs in natural environments are typically characterized by a heterogeneous set of NPs having different size, shape, coating, etc. (all properties having a significant impact on both mobility and toxicity). To take into account this heterogeneity, the proposed approach divides the NP population into classes, each having specific transport and toxicity properties, and simulates them as independent species. The approach is finally applied to a test case simulating the release of heterogeneous Silver NPs from a landfill. The results show that taking into account the size-dependent mobility of the particles provides a more accurate result compared to the direct application of the standard ASTM procedure. In particular, the latter tends to underestimate the overall toxic risk associated to the nP release.

Probing DNA Translocations with Inplane Current Signals in a Graphene Nanoribbon with a Nanopore.

Many theoretical studies predict that DNA sequencing should be feasible by monitoring the transverse current through a graphene nanoribbon while a DNA molecule translocates through a nanopore in that ribbon. Such a readout would benefit from the special transport properties of graphene, provide ultimate spatial resolution because of the single-atom layer thickness of graphene, and facilitate high-bandwidth measurements. Previous experimental attempts to measure such transverse inplane signals were however dominated by a trivial capacitive response. Here, we explore the feasibility of the approach using a custom-made differential current amplifier that discriminates between the capacitive current signal and the resistive response in the graphene. We fabricate well-defined short and narrow (30 nm × 30 nm) nanoribbons with a 5 nm nanopore in graphene with a high-temperature scanning transmission electron microscope to retain the crystallinity and sensitivity of the graphene. We show that, indeed, resistive modulations can be observed in the graphene current due to DNA translocation through the nanopore, thus demonstrating that DNA sensing with inplane currents in graphene nanostructures is possible. The approach is however exceedingly challenging due to low yields in device fabrication connected to the complex multistep device layout.

ZIP13: A Study of Drosophila Offers an Alternative Explanation for the Corresponding Human Disease.

The fruit fly Drosophila melanogaster has become an important model organism to investigate metal homeostasis and human diseases. Previously we identified dZIP13 (CG7816), a member of the ZIP transporter family (SLC39A) and presumably a zinc importer, is in fact physiologically primarily responsible to move iron from the cytosol into the secretory compartments in the fly. This review will discuss the implication of this finding for the etiology of Spondylocheirodysplasia-Ehlers-Danlos Syndrome (SCD–EDS), a human disease defective in ZIP13. We propose an entirely different model in that lack of iron in the secretory compartment may underlie SCD-EDS. Altogether three different working models are discussed, supported by relevant findings made in different studies, with uncertainties, and questions remained to be solved. We speculate that the distinct ZIP13 sequence features, different from those of all other ZIP family members, may confer it special transport properties.

Features of Charging–Discharging of Supercapacitors

We present the results of experimental investigations of supercapacitors produced by Panasonic using several methods, namely, measurements of temporal dependences of charging–discharging currents, cyclic dc charging, and cyclic voltammetry. The values of the internal resistance, static and dynamic capacitance, as well as their dependences on the bias voltage of the capacitors, have been determined. Measurements have shown that the initial stage of relaxation of current is well approximated by the exponential time dependence, and then transition to a powerlike dependence occurs. This well-known effect is explained on the basis of the allowance for specific transport properties of a porous fractal-type medium. These processes are adequately described by the fractional-differential model of anomalous diffusion. A weak dependence of relaxation curves on the voltage at low values of the latter ( 3 V) is explained by the appearance of new percolation paths blocked at low charging voltages due to the presence of high-potential barriers. The internal resistance and the static capacitance have been determined by measuring the voltage across the supercapacitor in the mode of dc charging. These parameters have been shown to depend on the voltage applied to the capacitor. The dependence of the dynamic capacitance on the voltage has been determined using cyclic voltammetry. It has been shown that the capacitance depends not only on the voltage, but also on the prehistory of charging and discharging of the capacitor. Comparison of the experimental results and the published data on the models and equivalent circuits with passive R, L, and C elements allows one to conclude that such models and equivalent circuits can be applied only when explaining a limited number of phenomena, in particular, behavior at small relaxation times.

Tailor-made temperature-dependent thermal conductivity via interparticle constriction.

Managing heat is a major challenge to meet future demands for a sustainable use of our energy resources. This requires materials, which can be custom-designed to exhibit specific temperature-dependent thermal transport properties to become integrated into thermal switches, transistors, or diodes. Common crystalline and amorphous materials are not suitable, owing to their gradual changes of the temperature-dependent thermal conductivity. We show how a second-order phase transition fully controls the temperature-dependent thermal transport properties of polymer materials. We demonstrate four major concepts based on a colloidal superstructure: (i) control of transition temperature, (ii) width of phase transition regime, (iii) multistep transitions, and (iv) step height of the transition. Most importantly, this unique control over thermal conductivity is only governed by the interparticle constriction, the particle composition, and its mesostructure. Our concept is therefore also applicable to a wide variety of other particulate materials.