Showing papers in "Journal of Materials Chemistry C in 2017"
TL;DR: In this paper, a review highlights the computational attempts that have been made to understand the physics and chemistry of this very promising family of advanced two-dimensional materials, and to exploit their novel and exceptional properties for electronic and energy harvesting applications.
Abstract: The recent chemical exfoliation of layered MAX phase compounds to novel two-dimensional transition metal carbides and nitrides, the so-called MXenes, has brought a new opportunity to materials science and technology. This review highlights the computational attempts that have been made to understand the physics and chemistry of this very promising family of advanced two-dimensional materials, and to exploit their novel and exceptional properties for electronic and energy harvesting applications.
654 citations
TL;DR: There are a wide variety of processing routes that have been developed for 2D-hBN, including also those for doping, substitution, functionalization and combination with other materials to form heterostructures or h-BNC hybrid nanosheets, which are systematically elaborated for novel functions.
Abstract: Two dimensional hexagonal boron nitride (2D-hBN), an isomorph of graphene with a very similar layered structure, is uniquely featured by its exotic opto-electrical properties together with mechanical robustness, thermal stability, and chemical inertness. It is thus extensively studied for application in field effect transistors (FETs), tunneling devices, deep UV emitters and detectors, photoelectric devices, and nanofillers. 2D-hBN is considered as one of the most promising materials that can be integrated with other 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), for the next generation microelectronic and other technologies. Although it is by itself an insulator, it can well be tuned by several strategies in terms of properties and functionalities, such as by doping, substitution, functionalization and hybridization, making 2D-hBN a truly versatile type of functional materials for a wide range of applications. In this review, the distinct structural characteristics of 2D-hBN, doping- and defect-induced variations in energy bands and structures, and resultant properties, are presented. There are a wide variety of processing routes that have been developed for 2D-hBN, including also those for doping, substitution, functionalization and combination with other materials to form heterostructures or h-BNC hybrid nanosheets, which are systematically elaborated for novel functions. The comprehensive overview provides the types of the state-of-the-art 2D-hBN made by new synthesis strategies, where the mainstream approaches include exfoliation, chemical vapor deposition, and gas phase epitaxy, together with several other new methods that have been successfully developed in the past few years. On the basis of the extraordinary electrical and functional properties and thermal–mechanical stability, the applications of hBN-based nanosheets as substrates and dielectrics, passivation layers, and nanofillers in nanodevices and nanocomposites are discussed, together with the peculiar optical and wetting characteristics.
643 citations
TL;DR: In this paper, a lightweight conductive porous graphene/thermoplastic polyurethane (TPU) foams with ultrahigh compressibility was successfully fabricated by using the thermal induced phase separation (TISP) technique.
Abstract: Lightweight conductive porous graphene/thermoplastic polyurethane (TPU) foams with ultrahigh compressibility were successfully fabricated by using the thermal induced phase separation (TISP) technique. The density and porosity of the foams were calculated to be about 0.11 g cm−3 and 90% owing to the porous structure. Compared with pure TPU foams, the addition of graphene could effectively increase the thickness of the cell wall and hinder the formation of small holes, leading to a robust porous structure with excellent compression property. Meanwhile, the cell walls with small holes and a dendritic structure were observed due to the flexibility of graphene, endowing the foam with special positive piezoresistive behaviors and peculiar response patterns with a deflection point during the cyclic compression. This could effectively enhance the identifiability of external compression strain when used as piezoresistive sensors. In addition, larger compression sensitivity was achieved at a higher compression rate. Due to high porosity and good elasticity of TPU, the conductive foams demonstrated good compressibility and stable piezoresistive sensing signals at a strain of up to 90%. During the cyclic piezoresistive sensing test under different compression strains, the conductive foam exhibited good recoverability and reproducibility after the stabilization of cyclic loading. All these suggest that the fabricated conductive foam possesses great potential to be used as lightweight, flexible, highly sensitive, and stable piezoresistive sensors.
546 citations
TL;DR: In this paper, the recent advances in inks, strategies, and the applications of inkjet-printed wearable electronics are summarized based on uniform and high-resolution patterns, well-compatible functional inks can be deposited to fabricate flexible/stretchable and durable wearable electronics.
Abstract: In recent years, wearable electronics have experienced tremendous development due to their promising applications in fields such as portable, flexible/stretchable human-interactive sensors, displays, and energy devices. To effectively fabricate wearable electronics, a high-efficient, cost-saving, and eco-friendly manufacture technology is required. Inkjet printing, which rapidly, precisely, and reproducibly deposits a broad variety of functional materials in a non-impact, addictive patterning, and maskless approach, serves as an effective tool for the fabrication of wearable electronics. In this review, the recent advances in inks, strategies, and the applications of inkjet-printed wearable electronics are summarized. Based on uniform and high-resolution patterns, well-compatible functional inks can be deposited to fabricate flexible/stretchable and durable wearable electronics. Perspectives on the remaining challenges and future developments are also proposed.
378 citations
TL;DR: In this paper, the authors summarized recent research progress in non-fullerene small molecule acceptors and compared these molecules' performances in single junction organic solar cells (OSCs) employing the same donor materials.
Abstract: Power conversion efficiency (PCE) has surpassed 10% for single junction organic solar cells (OSCs) mainly through the design and synthesis of novel donor materials, the optimization of film morphology and the evolution of the devices. However, the development of novel acceptor materials is relatively sluggish compared with the donor compounds. Nowadays, fullerene derivatives, such as PC61BM and PC71BM, are still the dominant acceptors due to their superior charge transporting properties. Unfortunately, these two acceptors suffer from some intrinsic shortcomings such as limited absorption, difficult functionalization, and high production cost. Therefore, developing novel non-fullerene acceptors that can overcome the above-mentioned disadvantages is highly desirable. As a matter of fact, research on non-fullerene acceptors has made considerable progress in the last two years and a highest PCE of around 12% has been achieved. In this review, we will summarize recent research progress in non-fullerene small molecule acceptors and compare these molecules' performances in OSCs employing the same donor materials. Moreover, the acceptors with excellent photovoltaic performance are highlighted and the reasons are elaborated. Finally, the implications and the challenges are proposed.
363 citations
TL;DR: In this paper, the authors highlight recent major progress in the development of organic semiconductors as electron transport n-channel materials in organic field effect transistors (OFETs) and discuss three types of materials: small molecules, polymers, and n-doped small molecules and polymers.
Abstract: This review highlights recent major progress in the development of organic semiconductors as electron transport n-channel materials in organic field effect transistors (OFETs). Three types of materials are discussed: (1) small molecules, (2) polymers, and (3) n-doped small molecules and polymers. Much effort has been made in the modification of known building blocks, development of novel building blocks, and optimization of materials processing and device structures. These efforts have resulted in the achievement of record high electron mobilities for both small molecules (12.6 cm2 V−1 s−1) and polymers (14.9 cm2 V−1 s−1), which are approaching the highest hole mobilities achieved by p-type small molecules and polymers so far. In addition, n-doping of ambipolar and p-type organic semiconductors has proven to be an efficient approach to obtaining a greater number of n-type organic semiconductors. However, it is found that n-type organic semiconductors, in general, still lag behind p-type organic semiconductors in terms of carrier mobility and air stability. Further exploration of new building blocks for making novel materials and optimization of processing conditions and device structures are needed to improve the performance, particularly air stability.
324 citations
TL;DR: In this article, electrical conductivity and the electromagnetic interference (EMI) shielding effectiveness of poly(L-lactide)/multi-walled carbon nanotube (PLLA/MWCNT) nanocomposites without sacrificing their mechanical properties via simply choosing two different PLLA polymers with different viscosities and crystallinities.
Abstract: Electrically conductive segregated networks were built in poly(L-lactide)/multi-walled carbon nanotube (PLLA/MWCNT) nanocomposites without sacrificing their mechanical properties via simply choosing two different PLLA polymers with different viscosities and crystallinities. First, the MWCNTs were dispersed in PLLA with low viscosity and crystallinity (L-PLLA) to obtain the L-PLANT phase. Second, the PLLA particles with high viscosity and crystallinity (H-PLLA) were well coated with the L-PLANT phase at 140 °C which was below the melting temperature of H-PLLA. Finally, the coated H-PLLA particles were compressed above the melting temperature of H-PLLA to form the PLLA/MWCNT nanocomposites with segregated structures. The morphological observation showed the successful location of MWCNTs in the continuous L-PLLA phase, resulting in an ultralow percolation threshold of 0.019 vol% MWCNTs. The electrical conductivity and the electromagnetic interference (EMI) shielding effectiveness (SE) of the composites with the segregated structure are 25 S m−1 and ∼30 dB, showing three orders and 36% higher than that of the samples with a random distribution of MWCNTs with 0.8 vol% of MWCNT loading, respectively. High-performance electromagnetic interference (EMI) shielding was also observed mainly dependent on the highly efficient absorption shielding, which can be achieved by the densely continuous MWCNT networks and the abundant interfaces induced by the segregated structures. Furthermore, the composites with segregated structures not only showed higher Young's modulus and tensile strength than the corresponding conventional composites, but also maintained high elongation at break because of the continuous and dense MWCNT networks induced by the segregated structures and the high interfacial interaction between H-PLLA and L-PLLA.
317 citations
TL;DR: In this paper, a hierarchical sandwich microstructure of two-dimensional (2D) Ti3C2Tx MXene flakes is proposed for the design of a novel electromagnetic wave absorber, which not only provides an effective route for extending further the applications of 2D MXene materials in the field of electromagnetic wave absorption.
Abstract: Ti3C2Tx MXenes modified with in situ grown carbon nanotubes (CNTs) are fabricated via a simple catalytic chemical vapor deposition (CVD) process. The as-prepared Ti3C2Tx/CNT nanocomposites show that one-dimensional (1D) carbon nanotubes are uniformly distributed in the interlayers of two-dimensional (2D) Ti3C2Tx MXene flakes. Compared with the pristine Ti3C2Tx MXenes, the hierarchical sandwich microstructure makes a contribution to the excellent electromagnetic wave absorption performance in the frequency range of 2–18 GHz, including higher absorption intensity (the minimum reflection coefficient reaches −52.9 dB, ∼99.999% absorption), broader effective absorption bandwidth (4.46 GHz), lower filler loading (35 wt%) and thinner thickness (only 1.55 mm). In addition, with the adjustment of thickness from 1.55 to 5 mm, the effective absorption bandwidth can reach up to 14.54 GHz (3.46–18 GHz). Different absorption mechanisms mainly based on polarization behaviors and conductivity loss are discussed. This work not only proposes the design of a novel electromagnetic wave absorber, but also provides an effective route for extending further the applications of 2D MXene materials in the field of electromagnetic wave absorption.
309 citations
TL;DR: In this paper, a brief introduction to graphene-based composites and their electromagnetic absorption properties is given, and two key factors, impedance matching behavior and attenuation ability, are given particular attention.
Abstract: Owing to the fast development of wireless information technologies at the high-frequency range, the electromagnetic interference problem has been of increasing significance and attracting global attention. One key solution for this problem is to develop materials that are able to attenuate the unwanted electromagnetic waves. The desired properties of these materials include low reflection loss value, wide attenuation band, light weight, and low cost. This review gives a brief introduction to graphene-based composites and their electromagnetic absorption properties. The ultimate goal of these graphene absorbers is to achieve a broader effective absorption frequency bandwidth (fE) at a thin coating thickness (d). Representative and popular composite designs, synthesis methods, and electromagnetic energy attenuation mechanisms are summarized in detail. The two key factors, impedance matching behavior and attenuation ability, that determine the electromagnetic behavior of graphene-based materials are given particular attention in this article.
292 citations
TL;DR: In this paper, the authors systematically summarized and analyzed the information and digital convolution aspects of metamaterials and metasurfaces with particular emphasis on the information-and-digital convolution aspect.
Abstract: Traditionally, “metamaterials” have been described by effective medium parameters due to the subwavelength nature of unit particles. The continuous nature of medium parameters makes traditional metamaterials behave as analog metamaterials. Recently, the concept of coding metamaterials or “metasurfaces” has been proposed, in which metamaterials are characterized by digital coding particles of “0” and “1” with opposite phase responses. It has been demonstrated that electromagnetic waves can be manipulated by changing the coding sequences of “0” and “1”. The coding particles provide a link between the physical world and digital world, leading to digital metamaterials and even field programmable metamaterials, which can be used to control electromagnetic waves in real time. The digital coding representation of metamaterials or metasurfaces can also allow the concepts and signal processing methods in information science to be introduced to physical metamaterials, thereby realizing extreme control of electromagnetic waves. Such studies have set the foundation of information metamaterials and metasurfaces. In this review article, the coding, digital, and field programmable metamaterials and metasurfaces are systematically summarized and analyzed with particular emphases on the information and digital convolution aspects. The future trend of information metamaterial/metasurface is predicted, including software-defined metamaterials/metasurfaces and cognitive metamaterials/metasurfaces.
287 citations
TL;DR: In this paper, an ultrathin and highly aligned reduced graphene oxide (RGO)/cellulose nanofiber (CNF) composite films with excellent EMI shielding performance and strong anisotropy of thermal conductivity were fabricated by vacuum-assisted filtration followed by hydroiodic acid reduction.
Abstract: With the extensive use of portable and wearable electronic devices, ultrathin electromagnetic interference (EMI) shielding materials with excellent thermal management are increasingly desirable. In this study, ultrathin and highly aligned reduced graphene oxide (RGO)/cellulose nanofiber (CNF) composite films with excellent EMI shielding performance and strong anisotropy of thermal conductivity were fabricated by vacuum-assisted filtration followed by hydroiodic acid (HI) reduction. The obtained 50 wt% RGO/CNF composite films, which are only ≈23 μm in thickness, possess the remarkable electrical conductivity of ≈4057.3 S m−1 and outstanding EMI shielding effectiveness (SE) of ≈26.2 dB owning to the uniform dispersion and self-alignment into the layered structure of RGO. In addition, the RGO/CNF composite films with 50 wt% RGO loadings possess high in-plane thermal conductivity (K ≈ 7.3 W m−1 K−1) and, unexpectedly, very low cross-plane thermal conductivity (K⊥ ≈ 0.13 W m−1 K−1), resulting in strong anisotropy of the thermal conductivity (K/K⊥ ≈ 56). Thus, these ultrathin RGO/CNF composite films have great application potential as effective lightweight shielding materials against electromagnetic microwaves and heat, especially in flexible portable electronic devices and wearable devices.
TL;DR: In this article, a single Bi2(Li0.5Ta1.5)O7 + xBi2O3 (x = 0, 0.01 and 0.02) ceramics were prepared using a solid state reaction method.
Abstract: Bi2(Li0.5Ta1.5)O7 + xBi2O3 (x = 0, 0.01 and 0.02) ceramics were prepared using a solid state reaction method. All compositions were crystallized in a single Bi2(Li0.5Ta1.5)O7 phase without secondary peaks in X-ray diffraction patterns. Bi2(Li0.5Ta1.5)O7 ceramics were densified at 1025 °C with a permittivity (er) of ∼ 65.1, Qf ∼ 15 500 GHz (Q ∼ microwave quality factor; f ∼ resonant frequency; 16 780 GHz when annealed in O2) and the temperature coefficient of resonant frequency (TCF) was ∼ −17.5 ppm °C−1. The sintering temperature was lowered to ∼920 °C by the addition of 2 mol% excess Bi2O3 (er ∼ 64.1, a Qf ∼ 11 200 GHz/11 650 GHz when annealed in O2 and at a TCF of ∼ −19 ppm °C−1) with compositions chemically compatible with Ag electrodes. Bi2(Li0.5Ta1.5)O7 + xBi2O3 are ideal for application as dielectric resonators in 5G mobile base station technology for which ceramics with 60 < er < 70, high Qf and close to zero TCF are commercially unavailable. They may additionally prove to be useful as high er and high Qf materials in low temperature co-fired ceramic (LTCC) technology.
TL;DR: In this paper, a flexible bidentate polyaromatic acid ligand 4,4′-oxybis(benzoic acid) (H2oba) was used for the construction of a novel luminescent Tb(III)-based metal-organic framework (MOF), namely {(Me2NH2]Tb(OBA)2]·(Hatz)·( H2O)1.5}n, with 3-amino-1,2,4-triazole (Hatz), as the template reagent.
Abstract: A flexible bidentate polyaromatic acid ligand 4,4′-oxybis(benzoic acid) (H2oba) was used for the construction of a novel luminescent Tb(III)-based metal–organic framework (MOF), namely {(Me2NH2)[Tb(OBA)2]·(Hatz)·(H2O)1.5}n, with 3-amino-1,2,4-triazole (Hatz) as the template reagent. In the structure of the Tb-MOF, there co-exist single-stranded and double-stranded helical chains along the c axis, and the overall network shows a three-fold interpenetrated qtz net. This MOF is capable of selectively sensing Fe3+ and Al3+ ions in water via quenching the luminescence and tuning the emission ratio between the ligand-based and metal-based luminescence, respectively. More importantly, this MOF can realize fast detection for p-xylene (PX) vapor with a response time of less than 10 s and 40% fluorescence enhancement, while nitrobenzene (NB) vapor could lead to a quenching effect in 10 min with a 75% quenching efficiency. Remarkably, this is the first example of a multi-responsive luminescent Tb-MOF sensor for Fe3+ and Al3+ ions and VOC vapor detection. In connection to these, the probable sensing mechanisms were also discussed in this paper.
TL;DR: In this article, a polypyrrole functionalized nano-magnetite (Fe3O4-PPy) was used to enhance the electromagnetic wave absorption performance and flame retardancy.
Abstract: Epoxy nanocomposites reinforced with polypyrrole functionalized nano-magnetite (Fe3O4–PPy) showed significantly enhanced electromagnetic wave absorption performance and flame retardancy. The Fe3O4–PPy nanocomposites were prepared by the surface initiated polymerization method. The epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites possess a minimum reflection loss (RL) value of −35.7 dB, which is much lower than that of either epoxy/(7.5 wt%)PPy nanocomposites with a minimum RL value of −11.0 dB or epoxy/(30.0 wt%)Fe3O4 with a minimum RL value of −17.8 dB at the same thickness (1.7 mm). Meanwhile, the bandwidth of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites for RL < −10 dB and RL < −20 dB is 4.0 GHz and 0.8 GHz, respectively. The increased interface area, eddy current loss and anisotropic energy are essentially important to achieve higher reflection loss and broader absorption bandwidth for epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites. Moreover, the significantly reduced flammability was observed in the epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites compared with pure epoxy. The total heat release of epoxy/(30.0 wt%)Fe3O4–PPy nanocomposites decreased from 25.5 kJ g−1 of pure epoxy to just 12.3 kJ g−1. The tensile strength of the epoxy nanocomposites was reported as well. These new nanocomposites with an enhanced electromagnetic wave absorption property and flame retardancy possess great potential for safer electromagnetic wave absorbers in the electronic industry to satisfy stringent industrial standards.
TL;DR: In this article, the changes in the grazing incidence X-ray diffraction (GIXRD) patterns of HfO2 films doped with Si, Al, and Gd are systematically examined.
Abstract: The origin of the unexpected ferroelectricity in doped HfO2 thin films is now considered to be the formation of a non-centrosymmetric Pca21 orthorhombic phase. Due to the polycrystalline nature of the films as well as their extremely small thickness (∼10 nm) and mixed orientation and phase composition, structural analysis of doped HfO2 thin films remains a challenging task. As a further complication, the structural similarities of the orthorhombic and tetragonal phase are difficult to distinguish by typical structural analysis techniques such as X-ray diffraction. To resolve this issue, the changes in the grazing incidence X-ray diffraction (GIXRD) patterns of HfO2 films doped with Si, Al, and Gd are systematically examined. For all dopants, the shift of o111/t101 diffraction peak is observed with increasing atomic layer deposition (ALD) cycle ratio, and this shift is thought to originate from the orthorhombic to P42/nmc tetragonal phase transition with decreasing aspect ratio (2a/(b + c) for orthorhombic and c/a for the tetragonal phase). For quantitative phase analysis, Rietveld refinement is applied to the GIXRD patterns. A progressive phase transition from P21/c monoclinic to orthorhombic to tetragonal is confirmed for all dopants, and a strong relationship between orthorhombic phase fraction and remanent polarization value is uniquely demonstrated. The concentration range for the ferroelectric properties was the narrowest for the Si-doped HfO2 films. The dopant size is believed to strongly affect the concentration range for the ferroelectric phase stabilization, since small dopants can strongly decrease the free energy of the tetragonal phase due to their shorter metal–oxygen bonds.
TL;DR: In this article, the authors compared the performance of reduced graphene oxide (RGO)/polylactic acid (PLA) and carbon nanotubes (CNTs)/PLA nanocomposites by ultrasound assisted dispersion and a hot-pressing method for comparative studies.
Abstract: Reduced graphene oxide (RGO)/polylactic acid (PLA) and carbon nanotubes (CNTs)/PLA nanocomposites were prepared by ultrasound-assisted dispersion and a hot-pressing method for comparative studies. The RGO and CNT nanofillers, which had a hydrogen-bonding interaction with the PLA matrix, were uniformly dispersed in the PLA matrix, and low percolation thresholds (0.11 wt% for RGO/PLA and 0.80 wt% for the CNTs/PLA nanocomposites) were achieved in the PLA nanocomposites. The addition of RGO resulted in weak crystallization ability and significant enhancement in thermal stability of the PLA matrix owing to the two-dimensional characteristic of RGO, while opposite results were obtained for the CNTs nanocomposites (the degree of crystallinity Xc is 49.82% for 0.8 wt% CNTs and 9.21% for 0.8 wt% RGO, respectively). During ten extension–retraction cycles, the values of the max and min ΔR/R0 for the RGO/PLA nanocomposites shift upwards gradually with the increase of the cycle number, resulting from the breakdown of conductive networks caused by the slippage of overlapped RGO layers; while the values of the max and min ΔR/R0 for CNTs/PLA nanocomposites decrease gradually owing to the formation of a better conductive network caused by the rearrangement of CNTs. This study is meaningful for the application of conductive polymer composite based strain sensors in many fields, such as structural health monitoring, wearable electronic devices, soft robotics, etc.
TL;DR: In this paper, a review of DFT calculations to optimize geometries for the visualization of frontier molecular orbital separation was surveyed to find that the B3LYP/6-31G(d) level of theory is the overwhelmingly used approach.
Abstract: The field of organic light-emitting devices (OLEDs) has undergone a remarkable journey since its discovery by Tang and VanSlyke with an alternation of utilizing fluorescence and phosphorescence as the emitting vehicle. The latest generation of thermally activated delayed fluorescence (TADF) materials harvest triplet excited states back into the singlet manifold. This booming field has yielded a large array of new compounds as both emitters and hosts. This review is limited to TADF emitters utilizing at least one carbazole unit as a donor and organized according to the various acceptor building blocks such as cyanophenyl, pyridine, biphenyls, anthraquinone, phenyl(pyridine-2-yl)methanone, benzophenone, xanthon, sulfones, triazines, benzils, dicyanopyrazines, diazatriphenylene, and others. A survey of carbazole-containing host materials follows. Density functional theory (DFT) has carved out a significant role in allowing the theoretical prediction of ground state properties for materials applied in OLED technology. Time-dependent DFT extends the reach to model excited state properties important to rationalize the light-output in OLED technology. For TADF, two fundamental factors are of interest: significant separation of frontier molecular orbitals and minimal singlet–triplet energy gap (ΔEST). In this review, the utilization of DFT calculations to optimize geometries for the visualization of frontier molecular orbital separation was surveyed to find that the B3LYP/6-31G(d) level of theory is the overwhelmingly used approach. In addition, we review the more in-depth approaches to utilizing DFT and time-dependent DFT (TD-DFT) with optimized percentage Hartree–Fock (OHF) and long-range corrected hybrid functionals, tuning procedures and others in an attempt to best quantify the size of ΔEST as well as the nature of the triplet state as locally excited state (LE) and charge-transfer state (CT).
TL;DR: A relaxor ferroelectric ceramic for high energy storage applications based on 0.9BaTiO3-0.1BZZ was successfully fabricated via a conventional solid-state method.
Abstract: A relaxor ferroelectric ceramic for high energy storage applications based on 0.9BaTiO3–0.1Bi(Zn0.5Zr0.5)O3 (0.9BT–0.1BZZ) was successfully fabricated via a conventional solid-state method. The sintered samples have a perovskite structure with a pseudocubic phase, showing a moderate dielectric constant (500–2000), low dielectric loss (tan δ < 0.15) and highly diffusive and dispersive relaxor-like behavior. The weak dielectric nonlinearity exhibits a dielectric constant change of ∼10% as the bias electric field increases from 0 kV cm−1 to 40 kV cm−1. Extra slim polarization–electric field loops accompanying the slow decrease of breakdown strength from 266.5 kV cm−1 to 217.7 kV cm−1 are observed in a measured temperature range of 30–150 °C. A maximum energy density of 2.46 J cm−3 was obtained at the electric field of 264 kV cm−1 close to the breakdown strength at ambient temperature. Temperature stability of both energy density and energy efficiency exists in a wide temperature range, which makes BT–BZZ ceramics promising candidates for high power electric applications.
TL;DR: In this article, the magnetic properties of 2D metal dihalides are investigated based on first-principles calculations, and it is shown that single-layer dihalide is energetically and dynamically stable and can be exfoliated from their bulk layered forms.
Abstract: Based on first-principles calculations, we investigate a novel class of 2D materials – MX2 metal dihalides (X = Cl, Br, I). Our results show that single-layer dihalides are energetically and dynamically stable and can be potentially exfoliated from their bulk layered forms. We found that 2D FeX2, NiX2, CoCl2 and CoBr2 monolayers are ferromagnetic (FM), while VX2, CrX2, MnX2 and CoI2 are antiferromagnetic (AFM). The magnetic properties of 2D dihalides originate from the competition between AFM direct nearest-neighbor d–d exchange and FM superexchange via halogen p states, which leads to a variety of magnetic states. The thermal dependence of magnetic properties and the Curie temperature of magnetic transition are evaluated using statistical Monte Carlo simulations based on the Ising model with classical Heisenberg Hamiltonian. The magnetic properties of single-layer dihalides can be further tuned by strain and carrier doping. Our study broadens the family of existing 2D materials with promising applications in nanospintronics.
TL;DR: In this paper, the most commonly adopted preparation strategies for conductive polymer nanocomposites are summarized, which mainly include direct mixing/blending (ex situ) and in situ methods (in situ polymerization or nanostructure synthesis).
Abstract: As a unique group of advanced polymer-based materials, conductive polymer nanocomposites combining the flexibility and/or conductivity of the polymer with the distinct properties of nanofillers have found many intriguing applications in various modern devices. This review provides a concise yet inclusive introduction to the concept of conductive polymer nanocomposites backed by some modern technologically advanced devices resulting from the advances made in this area. The most commonly adopted preparation strategies are first summarized, which mainly include direct mixing/blending (ex situ) and in situ methods (in situ polymerization or nanostructure synthesis). Selective examples of device applications are then detailed including organic light emission diodes (OLEDs), photovoltaics (PV), electrochromic devices (ECDs) and others. Lastly, concluding remarks and future perspectives are given for conductive polymer nanocomposites as viable electronic integration tools.
TL;DR: In this article, a self-powered ultraviolet photodetector was constructed with GaN/Ga2O3 p-n junction by depositing n-type Ga 2O3 thin film on Al2O 3 single crystals substrate covered by p-type GAN thin film, which exhibits a typical rectification behavior in dark and excellent photovoltaic characteristics under 365 nm and 254 nm light illumination.
Abstract: A self-powered ultraviolet photodetector was constructed with GaN/Ga2O3 p–n junction by depositing n-type Ga2O3 thin film on Al2O3 single crystals substrate covered by p-type GaN thin film. The fabricated device exhibits a typical rectification behavior in dark and excellent photovoltaic characteristics under 365 nm and 254 nm light illumination. The device shows an extremely high responsivity of 54.43 mA W−1, a fast decay time of 0.08 s, a high Ilight/Idark ratio of 152 and a high detectivity of 1.23 × 1011 cm Hz1/2 W−1 under 365 nm light with a light intensity of 1.7 mW cm−2 under zero bias. Such excellent performances under zero bias are attributed to the rapid separation of photogenerated electron–hole pairs driven by built-in electric field in the interface depletion region of GaN/Ga2O3 p–n junction. The results strongly suggest that the GaN/Ga2O3 p–n junction based photodetectors are suitable for applications in secure ultraviolet communication and space detection which require high responsivity and self-sufficient functionality.
TL;DR: In this article, a novel porous flower-like NiO@graphene composites were prepared using a method involving a facile hydrothermal reaction and an annealing process.
Abstract: Novel porous flower-like NiO@graphene composites were prepared using a method involving a facile hydrothermal reaction and an annealing process. The precursor Ni(OH)2 was grown to a flower-like microsphere under weak basic conditions and was partly coated with graphene oxide flakes. The final porous composites were obtained after the annealing process. The structure of the flower-like NiO@graphene composites was characterized by XRD, Raman spectroscopy, XPS, SEM, TEM, and N2 adsorption–desorption. The influence of base strength on the morphology of the three-dimensional structure of NiO@graphene was investigated. The flower-like NiO@graphene is highly porous and has a large surface area of 107 m2 g−1. As an absorber, the composite with a filler loading of 25 wt% exhibited superior microwave absorption capacities owing to its special porous flower-like structure, polarization effect, good impedance matching, and synergistic action. The maximum reflection loss can reach −59.6 dB at 14.16 GHz, and the absorption bandwidths (RL below −10 dB) ranged from 12.48 GHz to 16.72 GHz with a thickness of only 1.7 mm. The results indicate that the lightweight NiO@graphene composites with high-performance microwave absorption properties are promising materials for Ku-band electromagnetic wave absorption.
TL;DR: In this paper, a review of the recent advances in organic polymer thermoelectric composites is presented, where their preparation strategies have been discussed and an outlook on future investigations is provided.
Abstract: Thermoelectric materials can realize the direct energy conversion between heat and electricity, having diverse applications in energy harvesting (especially for waste heat and low-grade heat) and local cooling and sensing. In recent years, organic polymer thermoelectric composites have received extensive attention and have experienced a rapid development because of their low densities, low thermal conductivities, high flexibilities, and the synergistic combination of the advantages of both constituents. This review covers the recent advances in organic polymer thermoelectric composites. Herein, their preparation strategies have been discussed. In addition, the non-conducting polymer-based composites, ternary composites, and the devices have also been discussed. Finally, an outlook on future investigations is provided.
TL;DR: In the field of solid-state lighting (SSL) technologies, light-emitting electrochemical cells (LECs) are the leading example of easy-to-fabricate and simple-architecture devices as mentioned in this paper.
Abstract: In the field of solid-state lighting (SSL) technologies, light-emitting electrochemical cells (LECs) are the leading example of easy-to-fabricate and simple-architecture devices. The key-aspect of this technology is the use of a single active layer that consists of a mixture of an emitter and an ionic polyelectrolyte. The presence of mobile anions efficiently assists both charge injection and charge transport processes using air-stable electrodes. This concept reported in the mid-90s was considered as a game-changer approach, leading to a new field in SSL. Since then, the evolution of the LEC technology has involved different stages, namely (i) the search for the best combination of emitters (luminescent conjugated polymers and ionic transition complexes) and additives (ionic polyelectrolytes, ionic liquids, and neutral polymers), (ii) the understanding of the device mechanism using several techniques like electrostatic force microscopy (EFM), microcavity effects, scanning Kelvin probe microscopy (SKPM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), electrochemical impedance spectroscopy (EIS), etc., (iii) the development of simple and up-scalable device fabrication processes and, recently, (iv) the quest for new emitters like copper(I) complexes, small-molecules, quantum dots, and perovskites. This review provides a general overview of the first three points and, in particular, an in-depth revision of the recent advances in designing new architectures and emitters for LECs.
TL;DR: In this paper, a cyan-emitting phosphor BLS:Ce3+ is reported that has a broad emission band covering both the blue and green regions of the visible spectrum.
Abstract: In this paper, a cyan-emitting phosphor BLS:Ce3+ is reported that has a broad emission band covering both the blue and green regions of the visible spectrum, which can be used instead of two separate blue and green phosphors. The excitation peak of BLS:Ce3+ is located at 400 nm, which matches well with the emission light of efficient near-ultraviolet (NUV) chips. The BLS:Ce3+ phosphor has an internal quantum efficiency (IQE) higher than 90% at room temperature (RT) and an excellent thermal stability (a small reduction of 3% at 150 °C relative to the IQE at RT) and is environmentally robust (a small degradation of 6% occurs after aging for 1600 h at 85 °C/85% RH relative to the room-temperature IQE value). Using the BLS:Ce3+ phosphor, coupled only with a CaAlSiN3:Eu2+ red phosphor and a 395 nm NUV chip, a NUV-based WLED with a high color rendering index of 90.6 has been achieved. Moreover, the luminous efficiency reaches as high as 32.2 lm W−1, which is much better than that of the NUV-WLEDs employing three phosphors (blue, green and red).
TL;DR: In this paper, an organic nanoparticle-based surface pre-treatment was applied to textiles to enable all inkjet-printed graphene e-textiles for the first time.
Abstract: Inkjet printing of graphene inks is considered to be very promising for wearable e-textile applications as benefits of both inkjet printing and extra-ordinary electronic, optical and mechanical properties of graphene can be exploited. However, the common problem associated with inkjet printing of conductive inks on textiles is the difficulty to print a continuous conductive path on a rough and porous textile surface. Here we report inkjet printing of an organic nanoparticle based surface pre-treatment onto textiles to enable all inkjet-printed graphene e-textiles for the first time. The functionalized organic nanoparticles present a hydrophobic breathable coating on textiles. Subsequent inkjet printing of a continuous conductive electrical path onto the pre-treated coating reduced the sheet resistance of graphene-based printed e-textiles by three orders of magnitude from 1.09 × 106 Ω sq−1 to 2.14 × 103 Ω sq−1 compared with untreated textiles. We present several examples of how this finding opens up opportunities for real world applications of printed, low cost and environmentally friendly graphene wearable e-textiles.
TL;DR: In this paper, the authors reviewed recent advances in the study of the thermoelectric properties of 2D transition metal dichalcogenides (2D TMDs).
Abstract: 2D transition metal dichalcogenides (2D TMDs) (MoS2, WS2, etc.) have attracted considerable attention recently due to their unique structures, strong chemical stability and attractive semiconducting characteristics. In particular, these 2D materials have shown great potential for thermal management and thermoelectric energy generation due to their favourable combination of electrical and thermal transport properties, which can lead to a significantly large figure-of-merit. Importantly, recent studies have shown that various approaches, such as chemical functionalization, chemical doping, defect engineering, strain engineering and also forming heterostructures, can further enhance their figure-of-merit (ZT). In this article, we review recent advances in the study of the thermoelectric properties of 2D TMDs. We first briefly discuss thermoelectric effects, such as the Peltier and Seebeck effects, the coefficient of performance and figure-of-merit (ZT), and point out why TMD materials are ideal candidates for thermal management and thermoelectric applications. Next, we review the progress made in the understanding of the thermoelectric properties of 2D TMDs. Then, we discuss how chemical functionalization, chemical doping, defect engineering, strain engineering, forming heterostructures affect the thermoelectric properties of 2D TMDs. Finally, we present our conclusions and future perspectives.
TL;DR: In this article, the authors provided an in-depth description of the charge localization sites underlying the generation of radiative centres and their corresponding decay dynamics, highlighting the formation of small polarons trapped within their lattice distortion field.
Abstract: Two-dimensional (2D) perovskites with the general formula APbX4 are attracting increasing interest as solution processable, white-light emissive materials. Recent studies have shown that their broadband emission is related to the formation of intra-gap colour centres. Here, we provide an in-depth description of the charge localization sites underlying the generation of such radiative centres and their corresponding decay dynamics, highlighting the formation of small polarons trapped within their lattice distortion field. Using a combination of spectroscopic techniques and first-principles calculations to study the white-light emitting 2D perovskites (EDBE)PbCl4 and (EDBE)PbBr4, we infer the formation of Pb23+, Pb3+, and X2− (where X = Cl or Br) species confined within the inorganic perovskite framework. Due to strong Coulombic interactions, these species retain their original excitonic character and form self-trapped polaron–excitons acting as radiative colour centres. These findings are expected to be relevant for a broad class of white-light emitting perovskites with large polaron relaxation energy.
TL;DR: In this paper, the intermolecular arrangements in the ITIC film via atomistic molecular dynamics simulations were studied and it was shown that three-dimensional molecular packing is formed in the ItIC film through local intermolescular π-π stacking between the terminal acceptor units.
Abstract: In recent years, great progress has been achieved in the field of non-fullerene organic solar cells. In particular, the power conversion efficiencies for the photovoltaic devices based on A–π–A fused-ring electron acceptors, e.g. ITIC, can catch up with or even surpass the fullerene-based ones. However, the detailed molecular packing structures and charge transport properties of these acceptors are rarely studied and still unclear, which has become the major obstacle for rational molecular design to further improve the photovoltaic performance. Here, we have unravelled the intermolecular arrangements in the ITIC film via atomistic molecular dynamics simulations. The simulated results point to that three-dimensional molecular packing is formed in the ITIC film through local intermolecular π–π stacking between the terminal acceptor units. In sharp contrast, the ITIC crystal grown by the slow solvent vapor diffusion approach exhibits a one-dimensional edge-to-face stacking structure. Consequently, excellent isotropic electron mobilities along three dimensions are found for the film and unprecedentedly, the overall mobility is even higher than that of the crystal. Our work suggests that judicious modulation of the terminal acceptor unit to increase local intermolecular π–π interaction would be an effective way to improve the electron mobilities and photovoltaic performance of the A–π–A electron acceptors.
TL;DR: A terbium(III) lanthanide-organic framework (534-MOF-Tb) with a green-emission signal was successfully obtained by the solvothermal reaction of Tb3+ ions with the organic ligand H3TBOT (2,4,6-tris[1-(3-carboxylphenoxy)ylmethyl]mesitylene).
Abstract: A terbium(III) lanthanide–organic framework (534-MOF-Tb) with a green-emission signal was successfully obtained by the solvothermal reaction of Tb3+ ions with the organic ligand H3TBOT (2,4,6-tris[1-(3-carboxylphenoxy)ylmethyl]mesitylene). 534-MOF-Tb contains microporous quadrangle channels with accessible Lewis-base sites and coordinated water molecules, which are feasible to anchor and recognise multifarious analytes. It can serve as a recyclable multi-responsive sensing material for detecting Fe3+, MnO4−, Cr2O72−, and p-nitrotoluene (4-NT). Significantly, this is the first reported MOF-based sensor for detecting explosive 4-NT. Moreover, the mechanism of the selective luminescence quenching response for Fe3+, MnO4−, Cr2O72− or 4-NT can be mainly explained in terms of the competition between the absorption of the light source energy and the electronic interaction between the analyte and the TBOT ligand.