Superior Transport Properties Research Articles

High directional water transport graphene oxide biphilic stack

ABSTRACT It is a widely held view that the hydrophilicity of graphene oxide (GO) enhances the water transport properties. In this study, it is shown that a combination of graphene and GO can yield superior transport properties including high mass flow rate and directionality. First, different membrane characteristics such as the smallest pore diameter for water molecules sieving and mass flow rate are evaluated. Furthermore, a combination of graphene and GO, a biphilic stack of hydrophobic and hydrophilic layers, is used to evaluate the mass flow rates and results are compared with that of normal GO laminates. This structure acts as a water diode i.e. conducts water molecules in the desired direction and increases the mass flow rate several times. The effects of interatomic potential, oxidation level and charge, and the spacing between layers on mass flow rate and directionality are examined. It is found that an optimized structure conducts water in the desired direction and increases mass flow rate up to 10 times for small interlayer distance of 7 Å compared with normal GO laminates. The given structures can be used in a wide range of filtration applications, where selective water sieving with a high mass flow rate is desired.

Super-structured defects modulation for synergistically optimizing thermoelectric property in SnTe-based materials

Among the intriguing p-type thermoelectric IV-VI compounds, SnTe is an important alternative to both PbTe and GeTe for free of toxicity of Pb and scarcity of Ge. However, pristine SnTe has poor thermoelectric performance because of its intrinsic high hole concentration, big energy difference between L and Σ bands and high lattice thermal conductivity. In this work, In and Cd co-doping SnTe material, which combines the effect of resonant level and band convergence together, was obtained by self-propagating high-temperature synthesis (SHS) and plasma activated sintering (PAS). The generated Te vacancies are regularly arranged to form super-structured defects in the subsequent constrained hot compressing process, which include regular array of atomic defects and nanoscale precipitates. As a result, the hole concentration of the compressed SnTe-based material is reduced due to the donor doping effect of Te vacancies, and the hole mobility is remarkably improved to 372.94 cm2V−1s−1 and 66.19 cm2V−1s−1 at room temperature for the SnTe and In0.01Cd0.02Sn0.97Te material with compressibility of 35%, respectively. These atomic and nanoscale super-structured defects not only ensure superior electrical transport properties, but also bring much stronger scattering effect on phonons, thus leading to extremely low lattice thermal conductivity of 1.2 Wm−1K−1 at 888 K for the 35% compressed In0.01Cd0.02Sn0.97Te material. With synergistically optimized carrier and phonon transport behavior through resonant level engineering, band convergence engineering and super-structured defects engineering, a peak ZT value of 0.8 is achieved in In0.01Cd0.02Sn0.97Te material with compressibility of 35%. This work provides an effective strategy to realize the decoupling of electron and phonon scattering through Te vacancy-based super-structured defects modulation, and makes up an important part of multiscale microstructure tailoring for thermoelectric materials.

Enhanced thermal transportation across an electrostatic self-assembly of black phosphorene and boron nitride nanosheets in flexible composite films.

For effective heat dissipation in portable electronics, there is a great demand for lightweight and flexible films with superior thermal transport properties. Despite extensive efforts, enhancing the intrinsic low thermal conductivity of polymers while simultaneously maintaining their flexibility is difficult to achieve due to the dilemma of quarrying appropriate filler loading. Herein, a cellulose nanofiber-based film with high in-plane thermal conductivity up to 72.53 W m-1 K-1 was obtained by harnessing the advantage of functionalized boron nitride nanosheets (f-BNNS) and black phosphorene (BP) via the vacuum filtration process. Besides, our unique design based on the electrostatic coupling of black phosphorene and functionalized boron nitride nanosheets significantly reduced the interfacial thermal resistance of the composite films. This work offers new insights into establishing a facile, yet efficient approach to preparing high thermal conductive heat spreaders.

Self-powered solar-blind ultrafast UV-C diamond detectors with asymmetric Schottky contacts

Single-crystal chemical vapour deposition (CVD) diamond samples with asymmetric Schottky contacts were used for the fabrication of vertical metal-semiconductor-metal detectors for deep ultraviolet (UV–C) radiation. Spectral photoconductivity measurements, performed in the 190 ÷ 1100 nm wavelength range, returned an ultraviolet-to-visible (UV/Vis) rejection ratio of 6.8 × 103 under photovoltaic operating conditions, ensuring solar blindness and zero power consumption at the same time. When applying bias, UV/Vis rejection ratio reached excellent values (>104) even at very low electric fields (0.01 V/μm), thanks to the excellent structural quality and the superior charge transport properties of the diamond bulk, as inferred from Raman analysis and spectral photoconductivity measurements. Mobility-lifetime (μτ) product of the photogenerated carriers was indeed measured to be about 5 × 10−3 cm2/V in the case of holes, which is the highest room-temperature μτ value ever reported for CVD diamond, enabling a response speed in the nanosecond range even at zero-bias operating conditions.

β-Alanine-Anchored SnO2 Inducing Facet Orientation for High-Efficiency Perovskite Solar Cells.

SnO2 films as a promising electron transport layer (ETL) have been widely used in planar-type perovskite solar cells to achieve an impressive improvement in the conversion efficiency. However, compared with a mesoporous ETL, the interfacial charge carrier transfer of the SnO2 ETL is severely limited due to the issues of oxygen vacancy defects and crystal lattice mismatch between SnO2 and the perovskite, which generally leads to the growth of randomly stacked and porous perovskite layers and subsequently impacts the charge transport and transfer properties. In this work, we developed a facile approach by inducing a bifunctional molecule, β-alanine, into the SnO2 ETL, which can serve as a bridge to modulate the interfacial charge transfer and the perovskite crystallization kinetics. Benefited by the interfacial β-alanine, we grew a highly orientational perovskite layer that exhibited superior charge transport properties. Meanwhile, the β-alanine caused an intimate connection between the perovskite and SnO2 to enhance the interfacial charge transfer. As a result, the power conversion efficiency (PCE) of the β-alanine-modified device achieved a much-improved value of 19.67% and showed high reproducibility. This work provides a way for developing a high-performance ETL toward the scalable fabrication of highly efficient PSCs.

Performance of thermal storage system with water based nanofluids

Thermal energy storage system is one type of the system used to store the energy in different industrial applications. Thermal performance of the system is important to analyze when it has been operated with nanofluids. There is lot of energy is wasted from many process which can be utilized for the another process such as to preheat the water. In the present paper, the effect of water based nanofluids is studied to store the energy and results have been compared with base fluid. It was observed the nanofluid have more capacity to store the energy as compared to the base fluid because of it superior thermal transport properties. The pressure drop is also slightly higher than of base fluid. The thermal storage capacity of the system is significantly increased when it has been used with nanofluids as compared to base fluid under the same operating condition.

Effects of Li ion-solvent interaction on ionic transport and electrochemical properties in highly concentrated cyclic carbonate electrolytes

In recent research, the importance of electrolytes with high Li + transference number ( t Li ) and ionic conductivity ( σ ion ) has been emphasized to realize rapid charge for Li secondary batteries. Simultaneously fulfilling high t Li and σ ion is still unsolved in liquid electrolytes; however, highly concentrated electrolytes (HCEs) of weakly coordinating solvents and Li salts will be promising for addressing this challenge. This idea is inspired by a recent study by Angell et al. on superprotonic ionic liquids comprising a weak Brønsted base and a superacid; highly labile and exchangeable H + can be formed between significantly weak proton accepting sites. Here, we studied weakly coordinating fluoroethylene carbonate (FEC)-based electrolytes with lithium bis(fluorosulfonyl)amide (Li[FSA]) and compared with ethylene carbonate (EC)-based electrolytes. Experimental and computational studies indicated that solvent and ion exchange is more pronounced in the FEC-based HCE, resulting in higher t Li PP (0.73) and ionic conductivity (1.02 mS cm −1 ) compared to those of the EC-based HCE ( t Li PP = 0.53 and σ ion = 0.84 mS cm −1 ). However, the FEC-based HCE exhibited lower electrochemical stability due to the intrinsically lower reductive stability of FEC and the oxidative decomposition of the liberated solvent in the HCE. Despite the superior transport properties, the Li/LiCoO 2 cell with the FEC-based electrolyte showed lower discharge capacities and lower Coulombic efficiencies at higher current densities due to side reactions of the electrolyte. This study demonstrates that weak Li-solvent interactions can simultaneously enhance t Li and σ ion of HCEs, but they have the potential to sacrifice the electrochemical stability. • An electrolyte design approach to high Li ion conductivity is proposed. • A weakly coordinating solvent/Li salt combination shows high Li ion conductivity. • Solvent/ion exchange is more pronounced in weakly coordinating system. • Weak solvent-Li interaction compromises electrochemical stability.

Bifunctional Polymeric Carbon Nitride via Tuning Fabrication Conditions for Photocatalysis

In this contribution, the hydrogen evolution reaction and photodegradation of Rhodamine B (RhB) dye were studied using urea-based polymeric carbon nitride (PCN) as photocatalyst. The effects of calcination temperature and heating rate of the PCN on structural, morphological, optical, photoelectrochemical, and photocatalytic properties were addressed. Different properties were found to be crucial in boosting photocatalytic performance dependending on the reaction type. The highest efficiency in hydrogen evolution was observed in the presence of PCN characterized by the superior charge transport and charge lifetime properties arising from higher degree of structural arrangement and lower defect content in comparison to that of other photocatalysts. However, photocatalytic degradation of RhB was the most powerful when the catalyst exhibited the highest specific surface area as a key parameter determining its efficiency, although it presented lower charge transport and charge carrier properties.

Superior Mechanical Properties of GaAs Driven by Lattice NanotwinningSupported by the National Key Research and Development Program of China (Grant No. 2018YFA0703400), the National Natural Science Foundation of China (Grant Nos. 11704044 and 11974134), the Jilin Province Outstanding Young Talents Project (Grant No. 20190103040JH), and the China Postdoctoral Science Foundation (Grant No. 2018M631870).

Gallium arsenide (GaAs), a typical covalent semiconductor, is widely used in the electronic industry, owing to its superior electron transport properties. However, its brittle nature is a drawback that has so far significantly limited its application. An exploration of the structural deformation modes of GaAs under large strain at the atomic level, and the formulation of strategies to enhance its mechanical properties is highly desirable. The stress-strain relations and deformation modes of single-crystal and nanotwinned GaAs under various loading conditions are systematically investigated, using first-principles calculations. Our results show that the ideal strengths of nanotwinned GaAs are 14% and 15% higher than that of single-crystal GaAs under pure and indentation shear strains, respectively, without producing a significantly negative effect in terms of its electronic performance. The enhancement in strength stems from the rearrangement of directional covalent bonds at the twin boundary. Our results offer a fundamental understanding of the mechanical properties of single crystal GaAs, and provide insights into the strengthening mechanism of nanotwinned GaAs, which could prove highly beneficial in terms of developing reliable electronic devices.

Improved Stability of Organic Photovotlaic Devices With FeCl3 Intercalated Graphene Electrodes

In this paper, we present the first organic photovoltaic (OPV) devices fabricated with FeCl3 intercalated few layer graphene (i-FLG) electrodes. i-FLG electrodes were first fabricated and characterized by electrical and spectroscopic means, showing enhanced conductive properties compared to pristine graphene. These electrodes were then used in the fabrication of OPV devices and tested against devices made with commercially available Indium Tin Oxide (ITO) electrodes. Both types of device achieved similar efficiencies, while the i-FLG based device exhibited superior charge transport properties due to the increase in work function characterizing i-FLG. Both types of device underwent a stability study using both periodic and continuous illumination measurements, which revealed i-FLG based OPVs to be significantly more stable than those based on ITO. These improvements are expected to translate to increased device lifetimes and a greater total energy payback from i-FLG based photovoltaic devices. These results highlight the potential benefits of using intercalated graphene materials as an alternative to ITO in photovoltaic devices.

Melting behavior and heat transfer performance of gallium for spacecraft thermal energy storage application

A typical low melting point metal (LMPM), gallium, is proposed for spacecraft thermal energy storage due to its superior thermal transport properties, and its dynamic melting behavior and heat transfer performance under microgravity are investigated. The role of thermocapillary convection in melting is analyzed, and the dimensionless equations for predicting liquid fraction as well as Nusselt number are developed. The results show that compared with conventional phase change materials including ice and n-octadecane, the utilization of gallium under microgravity can reduce the melting time by 88.3% and 96.4% respectively, while increase the total energy storage capacity by 20.7% and 123.3% respectively. The thermocapillary convection promotes the melting under microgravity, and the promotion effect for gallium is much weaker than that for ice or n-octadecane due to its smaller Marangoni number. The melting time of gallium, ice and n-octadecane under normal gravity are 65.8%, 39.4% and 69.2% less than those under microgravity respectively. The deviations of liquid fraction and Nusselt number predicted by dimensionless equations from numerical results are within ±10%. The results indicate that the thermal energy storage using gallium is effective for temperature control of spacecraft electronic devices under high and periodic heat flux.

Correlation between Structural and Transport Properties of Ca-Doped La Nickelates and Their Electrochemical Performance

This work presents the results from a study of the structure and transport properties of Ca-doped La2NiO4+δ. La2−xCaxNiO4+δ (x = 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by X-ray diffraction (XRD), in situ XRD using synchrotron radiation, thermogravimetric analysis (TGA) and isotope exchange of oxygen with C18O2. The structure was defined as orthorhombic (Fmmm) for x = 0 and tetragonal (I4/mmm) for x = 0.1–0.4. Changes that occurred in the unit cell parameters and volume as the temperature changed during heating were shown to be caused by the excess oxygen loss. Typical for Ruddlesden–Popper phases, oxygen mobility and surface reactivity decreased as the Ca content was increased due to a reduction in the over-stoichiometric oxygen content with the exception of x = 0.1. This composition demonstrated its superior oxygen transport properties compared to La2NiO4+δ due to the enhanced oxygen mobility caused by structural features. Electrochemical data obtained showed relatively low polarization resistance for the electrodes with a low Ca content, which correlates well with oxygen transport properties.

Crystallization of CsPbBr3 single crystals in water for X-ray detection

Metal halide perovskites have fascinated the research community over the past decade, and demonstrated unprecedented success in optoelectronics. In particular, perovskite single crystals have emerged as promising candidates for ionization radiation detection, due to the excellent opto-electronic properties. However, most of the reported crystals are grown in organic solvents and require high temperature. In this work, we develop a low-temperature crystallization strategy to grow CsPbBr3 perovskite single crystals in water. Then, we carefully investigate the structure and optoelectronic properties of the crystals obtained, and compare them with CsPbBr3 crystals grown in dimethyl sulfoxide. Interestingly, the water grown crystals exhibit a distinct crystal habit, superior charge transport properties and better stability in air. We also fabricate X-ray detectors based on the CsPbBr3 crystals, and systematically characterize their device performance. The crystals grown in water demonstrate great potential for X-ray imaging with enhanced performance metrics.

Bidimensional H‐Bond Network Promotes Structural Order and Electron Transport in BPyMPMs Molecular Semiconductor

AbstractThe presence of a hydrogen bond (H‐Bond) network has been proved to impact significantly the efficiency of organic light‐emitting diode (OLED) devices by promoting molecular orientation and structural anisotropy in thin films. The design of specific compounds to control H‐Bond network formation in an amorphous material, and hence to improve OLED performances, is needed. A successful example is given by the bi‐pyridyl‐based family n‐type of organic semiconductors named BPyMPM. The experimental evidences demonstrate a surprisingly higher electron mobility in thin film composed of 4,6‐bis(3,5‐di(pyridine‐4‐yl)phenyl)‐2‐methylpyrimidine (B4PyMPM (B4)), which is almost two order of magnitude higher than mobility measured for very similar member of the family, 4,6‐bis(3,5‐di(pyridine‐2‐yl)phenyl)‐2‐methylpyrimidine (B2PyMPM (B2)). Herein, a comprehensive computational study is presented, wherein classical and ab initio methods are combined, to investigate the 2D H‐Bond network in B4 and B2 thin films. The results indicate that B4 forms a larger number of intermolecular C‐H···N H‐Bonds that promote a higher orientational and positional order in B4 films, and superior electron transport properties.

Heteroepitaxial growth of wide bandgap cuprous iodide films exhibiting clear free-exciton emission

Cuprous iodide (CuI) is an emerging wide-bandgap semiconductor of superior optical and transport properties. In particular, CuI shows high stability and large oscillator strength of free excitons that are of great advantage for optoelectronic applications. However, thin films of CuI reported so far have not been genuine single crystals, containing a sizable density of impurity and defect. Here, we demonstrate a dramatic improvement in the quality of CuI films grown by molecular beam epitaxy on a lattice-matched InAs substrate. The film is revealed to be in a single-crystal structure with high lattice coherence and an atomically flat surface. The low-temperature photoluminescence spectra exhibit extremely sharp emission from free excitons and much-suppressed emission from trapped states. The high-quality CuI films realized in the present study will not only facilitate the device application of CuI films but also provide unprecedented functionalities in halide semiconductors at the atomically sharp heterointerfaces.

Substantial and stable magnetoresistance and spin conductance in phosphorene-based spintronic devices with Co electrodes.

Designing devices with excellent spin-polarized properties has been a challenge in physics and materials science. In this work, we report a theoretical investigation of the spin injection and spin-polarized transport properties of monolayer and bilayer phosphorene devices with Co electrodes. Based on the analysis of transmission coefficients, spin-polarized current, magnetoresistance (MR) (or tunnel MR) ratio and spin injection efficiency (SIE), both devices show superior spin-polarized transport properties. As phosphorene in the device is changed from monolayer to bilayer, the charge carrier type can be tuned from n-type to p-type. For the monolayer phosphorene device, the tunnel MR ratio reaches about 210% and the SIE is about 80.7% at zero bias. Notably, the SIE and tunnel MR ratio maintain almost constant values against bias voltage and gate voltage, which makes it suitable for magnetic sensors. As for the bilayer phosphorene device, it not only exhibits a considerable tunnel MR ratio, but also shows significantly enhanced conductance, beneficial to the sensitivity of spintronic devices. Further analysis shows that the improvement of conductance is attributed to the low barrier height between the bilayer phosphorene channel and Co electrodes. According to our results, the studied phosphorene devices with Co electrodes demonstrate superior spin injection and transport properties. We believe that these theoretical findings will be a strong asset for future experimental works in spintronics.

Nanoelectromagnetic of a highly conductive 2D transition metal carbide (MXene)/Graphene nanoplatelets composite in the EHF M-band frequency

Highly conductive materials, with minimal thickness and capable to afford electromagnetic interference (EMI) shielding, are highly advantageous, particularly if they are able to be easily processed into thin films. Here, we demonstrate the potential of a sandwich-like structure of a two-dimensional Ti3C2Tx MXene/Graphene nanoplatelets (GNPs) composites for EMI shielding in the extreme high frequency (EHF) M-band, ranging from 60 to 80 GHz. First, we investigated systematically the microstructural and electrical transport properties of these composites with respect to the GNP contents. After graphene integration, the composite-surface roughness has been found to decrease, while both electrical conductivity and Hall carrier mobility demonstrated a clear trend to increase, reaching the values of ∼105 S/cm and 55 cm2/V, respectively, for only 2.5 wt % of graphene content, reporting thereby one of the most electrically conductive MXene based composite to date. Furthermore, a 1.75 μm-thick Ti3C2Tx MXene/GNP film was found to exhibit an EM absorbance of about 64 dB, which is one of the highest values, normalized to the thickness, among tested materials so far. This remarkable performance could be associated to three key factors, namely the superior transport properties of the composite films, the dominant absorption mechanism, and the multiple internal reflections from Ti3C2Tx and graphene multilayers configuration. These reported results would lead to unprecedented applications in the fields of space, aeronautics, radars, air travels and mobile phones.

Visible-light overall water splitting on g-C3N4 decorated by subnanometer oxide clusters

Two-dimensional (2D) nitrogenated holey carbon materials are promising non-precious photocatalysts for clean energy production. However, their efficiency is limited by the fast electron-hole recombination and lack of active sites. To overcome these drawbacks, here for the first time, we show that loading subnanometer p-block metal oxide clusters on 2D porous carbon-based semiconductors can trigger peculiar synergistic effect and offer an effective route for manipulating the photocatalytic behavior at atomic precision. As a prototype system, g-C3N4 monolayer decorated by MgO tubular clusters for overall water splitting is explored by time-dependent ab initio nonadiabatic molecular dynamic simulations. Such novel (MgO)n/g-C3N4 heterostructures possess excellent stability in aqueous solution, high activity for water splitting, and superior photocarrier transport properties. The basic rules for optimally steering the relaxation pathway and lifetime of excited carriers and creating bifunctional reaction centers by controlling the concentration and size of oxide clusters are thoroughly unveiled. Our work provides a new strategy to modify 2D porous carbon materials for practical solar energy conversion and shines light on utilizing subnanometer p-block oxide clusters with earth-abundant and low-cost elements for precisely dictating the performance of hybrid photocatalysts.

Pore penetration of porous catalyst supports by in-situ-adsorbed, agglomeration-quenched nanoparticles from pulsed laser ablation in supercritical CO2

To synthesize nanoparticles for catalytic applications, pulsed laser ablation (PLA) in liquids has been established as a cost-effective method complementary to wet-chemical synthesis routes. Due to mass transport limitations in water, recent studies conducted PLA in supercritical CO2 (scCO2) to use the superior transport properties. Unfortunately, PLA in scCO2 so far led to the formation of bigger particles and agglomerates, which are unfavorable for the application as catalytically active material. As will be shown in this paper, the former are being avoided by means of an in-situ deposition approach of gold and platinum in scCO2 in presence of mesoporous γ-Al2O3 support. Transmission electron microscopy reveals that the resulting nanoparticle size is quenched while careful adjustment of the mixing conditions during PLA is shown to significantly reduce the agglomeration tendency. Cross-sections of the heterogeneous catalyst prove, that the nanoparticles penetrate the mesoporous support up to 109 nm deep.

Improved performance of ternary blend polymer solar cells via work function tuning and suppressed interface recombination using hybrid PEDOT:PSS-graphene oxide hole transport layer

In this work, we present a solution-processed poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)-graphene oxide (PEDOT:PSS-GO) composite as a novel hole transporting material with excellent hole extraction properties which boost the performance of ternary blend polymer solar cells (TPSCs). TPSCs employing ternary blend active layer composed of two conjugated polymer donors i.e., poly(3-hexyl)thiophene):poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2–6-diyl)] (P3HT:PTB7-th) blended with organic acceptor [6,6]-phenyl C71-butyric-acid-methyl-ester (PC71BM) have shown high performance when PEDOT:PSS-GO is used as hole transport layer (HTL). The best TPSC, ITO/PEDOT:PSS-GO(1:1)/P3HT:PTB7-th:PC71BM(0.3:0.7:1)/LiF/Al, has showed improved performance with power conversion efficiency (PCE) as high as 7.1% and external quantum efficiency of 70–80% in a broad wavelength range of 350–800 nm. There is an increment of 55% in PCE compared to TPSCs with PEDOT:PSS-only HTL. The improvement in performance of TPSCs with PEDOT:PSS-GO HTLs is predominantly attributed to the better charge extraction and carrier collection owing to significantly reduced photo-generated exciton lifetime, tuned work function, reduced potential barrier at HTL/active layer interface, remarkably improved film morphology, and increased conductivity of PEDOT:PSS-GO films. PEDOT:PSS-GO HTLs significantly boost the performance and lifetime stability of (P3HT:PTB7-th:PC71BM) ternary blend-based TPSCs. Our work demonstrate the superior hole transport properties of PEDOT:PSS-GO over conventional PEDOT:PSS HTLs for the accelerating development of TPSCs.