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High-density and highly porous graphene-based pellets that exhibit an anomalous gas densification property have been fabricated by using zeolite-templated carbon (ZTC) as the major component and reduced graphene oxide (rGO) as a pure carbon binder. The unique structure of each ZTC particle consists of double-sided graphene fragments connected in a periodic, three-dimensional framework. The graphene-like sheets of rGO strongly connect the ZTC particles upon hot-pressing via the generation of a large amount of unpaired electron spins, yielding monolithic pellets with exceptional mechanical toughness. The uniaxial pressing applied to the isotropic ordered framework of ZTC during pelletization leads to unique anisotropic structures. The so-obtained pellets represent a high density packing of graphene nanofragments with high volumetric surface area that exhibits high volumetric H2 storage at room temperature.

Funding Information: This work was supported by the National Natural Science Foundation of China (Grant No. 21636007 ) and the Start-up Package of T10108 Professorship offered by Aalto University to Y. Li. J. Yuan, Q. Qiu, and L. Fan acknowledge the financial support from the China Scholarship Council (Grant No. 201906250030, 201906150314, and 201806250102). Z.-Z. Pan acknowledges the financial support of the Academy of Finland (Grant No. 324414). Publisher Copyright: © 2021 The Authors Non-aqueous redox flow batteries (NARFBs) are promising in the grid-scale energy storage for the harvesting of the intermittent renewable power sources. However, the lack of efficient separator is still impeding their further development. A flexible nanoporous separator is prepared through a “rolling dough” strategy, with zinc metal-organic framework (MOF-5) and polytetrafluoroethylene as the substrate. The prepared separator shows a remarkable ionic selectivity of Li+ over N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium ions (Fc1N112+) at a high ratio 26.6. A Li-based hybrid NARFB constructed with the separator exhibits substantially high Coulombic efficiency 99.7% and average discharge capacity 2.26 Ah L−1 with capacity retention 99.96% per cycle over 200 cycles at 4 mA cm−2. The excellent performance is attributed to the MOF nanoparticles and the designed composite structure, which achieves both high ionic selectivity and chemical stability simultaneously. This work provides a facile and efficient strategy to fabricate high-performance separator for NARFBs.

Ti3C2Tx MXene has drawn considerable attention as anode materials to store sodium ions because of the capability of accommodating the large sodium ions, enabling their intercalation without substantial structural change. However, the limited sodium-ion storage capacity of Ti3C2Tx hinders its real application in sodium-ion batteries (SIBs). To enhance its performance as anode materials in SIBs, here, we introduce nanopores into Ti3C2Tx sheets by sonication, and after which we assemble them with rGO and cellulose nanofibers into an elastic freestanding composite structure by mimicking the wasp nest. The wasp nest-like structure endows the resulting composite with more accessible surfaces of electrode materials to the electrolyte. Further, the nanopores on the Ti3C2Tx sheets and the TiO2 formed from the sonication provide more active sites for sodium storage. As a result, the resulting composite shows a high capacity of 280 mAh g−1 at 100 mA g−1 and remarkable cyclic life with a capacity retention of 84.8% after 1000 cycles at 1 A g−1.

The density and ion channel abundancy of an electrode material must be elaborately balanced to achieve a high volumetric energy density for any energy storage devices. As a typical example, graphene shows great potential in different energy storage devices but its low density and ion diffusion barrier effect limit its practical uses. In the present work, H2O2 etching was introduced into the hydrothermal assembly of graphene oxide (GO) to decrease the lateral size of GO and create in-plane holes, and after a capillary drying process, a high-density holey graphene monolith (HHGM) with numerous and interconnected ion transporting channels was obtained. The smaller sheet size leads to a more densified assembly while in-plane holes are beneficial to ion transportation in the HHGM, which well balance the high density and fast ion diffusion in the electrode. As a result, the HHGM shows an impressive rate performance, coupled with a high volumetric capacitance.

Non-aqueous redox flow batteries (NARFBs) are promising for large-scale energy storage. However, the lack of high performance membrane is still impeding their further development. Two-dimensional (2D) metal-organic framework (MOF) nanosheets-modified porous separators are prepared by the filtration method. The NARFBs constructed with the 2D MOF nanosheets-modified separator exhibit substantially higher Coulombic efficiency (91.0% vs 82.9%) without obvious compromise on voltage efficiency (93.7% vs 94.2%), and larger average discharge capacity (1.30 vs 0.86 Ah L−1) compared with the pristine Celgard separator at 4 mA cm−2. Such performance is originated from the unique microstructure of 2D-MOF nanosheets. The interlayer spaces assembled by the nanosheet layers enable the fast transport of supporting electrolyte but impede the crossover of active materials and impose limited effect on the separator resistance. This work provides a facile and efficient strategy to mitigating the crossover effect in NARFB.

Redox flow battery (RFB) is promising in grid-scale energy storage, and potentially applicable for facilitating the harvest of the intermittent renewable power sources, like wind and solar, and stabilizing the power grid. Early RFBs are based on aqueous electrolytes and the all-vanadium as well as Zn/Br systems have been demonstrated in close commercial scale. Non-aqueous RFBs (NARFBs) are the second-generation flow batteries based on organic solvent which have potentially much wider electrochemical window, and thus possible much higher energy density, and temperature window than those of the aqueous systems. As a crucial component of NARFBs, the membrane serves to prevent the crossover of the positive and negative active species whilst facilitating the transfer of the supporting electrolyte ions. However, the membranes utilized in the state-of-the-art publications still need great improvements in performance. In this article, the fundamentals, classifications, and performances of the membranes in NARFB are introduced. The recent progresses and challenges on the innovation of NARFB membranes are summarized. A perspective on the near future developments of NARFB membranes are presented. The composite membranes are likely the promising direction to forward the development of the NARFB technologies.

A multi hierarchical construction is designed for flexible supercapacitor electrodes. Specifically, we chose activated carbon fiber cloth (ACFC) as flexible substrates, deposited polyaniline (PANI) on fiber surface first, then constructed continuous carbon nanotube (CNT) networks between fibers and finally deposited PANI on the CNT networks to obtain ACFC/PANI/CNT/PANI textile electrodes. Repeated deposition of PANI and application of ACFC substrate lead to high content of electrochemically active materials ( i.e. , PANI and activated carbon fiber); meanwhile, these active materials are located in different locations in the electrodes (fiber itself, fiber surface and the space between fibers), thus avoiding serious aggregation. The fabricated electrodes exhibit superior capacitive performances: areal capacitance, energy density and power density are 4039 mF cm −2 , 131 μW h cm −2 and 11424 μW cm −2 , respectively, remarkably higher than those of previously reported flexible supercapacitor electrodes; our electrodes also have good cycling stability and flexibility. Furthermore, high-performance thick electrodes (capacitance: 7804 mF cm −2 ; energy output: 214 μW h cm −2 ) and flexible fiber-like electrodes (capacitance: 805 mF cm −2 ; energy density: 23 μW h cm −2 ) are easily produced from our textile electrodes. This study offers a new direction for optimizing micro-structures and electrochemical properties of flexible electrodes in wearable energy storage devices.

A three-dimensional (3D) hierarchical porous graphene macrostructure coupled with uniformly distributed α-Fe2O3 nano-particles (denoted Fe-PGM) was designed as a sulfur host in a lithium-sulfur battery, and was prepared by a hydrothermal method. In this hybrid structure, the α-Fe2O3 nano-particles are proved to not only strongly interact with the polysulfides, but more importantly, chemically promote their transformation to insoluble species during the charge/discharge process, working as chemical barriers for the shuttling of the lithium polysulfides (LiPSs). Therefore, together with 3D hierarchical porous structure facilitating fast electron/ion transfer, Fe-PGM as a sulfur host in a cathode contributes to a high rate performance (565 mAh g−1 at a high rate of 5 C relative to 1571 mAh g−1 at 0.3 C) as well as long cyclic stability (an ultralow capacity fading rate of 0.049% per cycle over 1000 cycles at the high current rate of 5 C).

Developing high-performance flexible film-like electrodes is still a primary task for the practical applications of wearable/portable planar supercapacitors. In this work, a facile and effective approach, i.e., stacking up layers of polyaniline (PANI)/carbon nanotube (CNT) composite networks inside air-laid papers, is proposed to fabricate highly flexible paper electrodes with large areal capacitance and superior rate capability. The layer-by-layer deposition of PANI/CNT networks endows the fabricated paper electrodes with high loading and uniform distribution of PANI; meanwhile, the good electrical conductivity and porous structure of these introduced PANI/CNT networks guarantee sufficient paths for electron movement and ion transportation in the electrodes. Consequently, when 4 layers of PANI/CNT networks (with optimal PANI content) are stacked inside papers, the areal capacitance of the prepared electrode is as high as 1506 mF cm−2 at a charge/discharge current of 10 mA cm−2 and 1298 mF cm−2 at 100 mA cm−2; the electrode also exhibits high flexibility and good cycling stability (with 82% capacitance retention after 11 500 charge/discharge cycles). These merits make our PANI/CNT/papers promising candidates for flexible planar supercapacitor electrodes. Besides, this work is believed to provide a new thought for producing high-loading and high-energy wearable/portable energy storage devices.

Metal–organic frameworks (MOFs) have gained significant attention as precursors for the fabrication of porous hybrid materials due to their highly controllable composition, structure and pore size. However, at present, MOF-derived materials have rarely been investigated as anode materials for sodium-ion batteries. In this work, we report the fabrication of a Ni-doped Co/CoO/N-doped carbon (NC) hybrid using bimetallic Ni–Co-ZIF as the starting precursor. The resulting Ni-doped Co/CoO/NC hybrid is highly microporous with a high specific surface area of 552 m2 g−1. When employed as an anode material for sodium-ion batteries, the Ni-doped Co/CoO/NC hybrid exhibited both good rate performance with a high discharge capacity of 218 mA h g−1 at a high current density of 500 mA g−1 and good cycling stability, as a high discharge capacity of 218.7 mA h g−1 can be retained after 100 cycles at 500 mA g−1, corresponding to a high capacity retention of 87.5%. The excellent electrochemical performance of the Ni-doped Co/CoO/NC hybrid for SIBs may be attributed to the synergistic effects of various factors, including: (i) the presence of a carbon matrix which provides protection against aggregation and pulverization during sodiation/desodiation; (ii) the highly microporous nature along with the presence of a few mesopores which facilitates better insertion/de-insertion of Na+ ions; (iii) the Ni-doping which introduces defect sites into the atomic structure of CoO via partial substitution, thus enhancing the conductivity of the cobalt oxide (CoO) component and hence, the overall hybrid material, and (iv) the N-doping which promotes a faster migration speed of sodium ions (Na+) across the carbon layer by creating defect sites, thereby improving the conductivity of the carbon frameworks in the hybrid material.

The precise control of the ice crystal growth during a freezing process is of essential importance for achieving porous cryogels with desired architectures. The present work reports a systematic study on the achievement of multi-structural cryogels from a binary dispersion containing 50 wt% 2,2,6,6-tetramethylpiperidin-1-oxyl, radical-mediated oxidized cellulose nanofibers (TOCNs), and 50 wt% graphene oxide (GO) via the unidirectional freeze-drying (UDF) approach. It is found that the increase in the sol's pH imparts better dispersion of the two components through increased electrostatic repulsion, while also causing progressively weaker gel networks leading to micro-lamella cryogels from the UDF process. At the pH of 5.2, an optimum between TOCN and GO self-aggregation and dispersion is achieved, leading to the strongest TOCN-GO interactions and their templating into the regular micro-honeycomb structures. A two-faceted mechanism for explaining the cryogel formation is proposed and it is shown that the interplay of the maximized TOCN-GO interactions and the high affinity of the dispersoid complexes for the ice crystals are necessary for obtaining a micro-honeycomb morphology along the freezing direction. Further, by linking the microstructure and rheology of the corresponding precursor sols, a diagram for predicting the microstructure of TOCN-GO cryogels obtained through the UDF process is proposed.

Honeycomb structures have been attracting attention from researchers mainly for their high strength-to-weight ratio. As one type of structure, honeycomb monoliths having microscopically dimensioned channels have recently gained many achievements since their emergence. Inspired by the microhoneycomb structure that occurs in natural tree xylems, we have been focusing on the assembly of such a structure by using the major component in tree xylem, cellulose, as the starting material. Through the path that finally led us to the successful reconstruction of tree xylems by the unidirectional freeze-drying (UDF) approach, we verified the function of cellulose nanofibers, toward forming xylem-like monoliths (XMs). The strong tendency of cellulose nanofibers to form XMs through the UDF approach was extensively confirmed with surface grafting or a combination of a variety of second components (or even a third component). The resulting composite XMs were thus imparted with extra properties, which extends the versatility of this kind of material. Particularly, we demonstrated in this paper that XMs containing reduced graphene oxide (denoted as XM/rGO) could be used as strain sensors, taking advantage of their penetrating microchannels and the bulk elasticity property. Our methodology is flexible in its processing and could be utilized to prepare various functional composite XMs.

A commercial carbon molecular sieve (CMS) demonstrates excellent Na ion storage performance and is the best among current commercially available materials and much better than most hard carbons reported with complex microstructures. With a very low specific surface area measured by N 2 adsorption, the CMS shows a high reversible capacity of 297 mA h/g at a relatively high current density of 100 mA/g, and, more promising, a very high initial Coulombic efficiency of up to 73.2%, which is the highest among unmodified commercial carbons. Such good performance is mainly the result of its abundant ultra-small (0.3–0.5 nm) pores that only allow the insertion of Na ions while rejecting the electrolyte, thus preventing its contact with the carbon surface, which is a basic principle for the design of a high performance anode material for a sodium-ion battery (SIB). The CMS also exhibits high rate and cyclic performance. Such performance basically meets the demand for commercial anode materials for a SIB, and hopefully, this finding will promote the commercialization of SIBs for practical use as graphite does for lithium-ion batteries.

Understanding the chemistry in the gelation (interfacial assembly) of graphene oxide (GO) is very essential for the practical uses of graphene-based materials. Herein, with the designed artificial interfaces due to the introduction of water-miscible isopropanol, the gelation of GO is achieved in water at an ultralow concentration (0.1 mg mL-1 , the lowest ever-reported) with a solvothermal treatment. Intrinsically, with a lower intercalation energy, water shows much stronger attraction with GO than isopropanol, inducing a microphase separation in the miscible mixture of isopropanol and water. In the solvothermal process, the partially reduced GO sheets interact with each other along the water-isopropanol interface and assemble into interconnected frameworks. In general, the formation of the artificial interface results in locally concentrated GO in the water phase, which is the final driving force for the gelation at ultralow concentration. Thus, the threshold for the GO gelation concentration is dependent upon the water fraction in the mixture and water acts as the spacer to facilitate the gelation and final control of the resulting materials microstructure. This study enriches interface/gelation chemistry of GO and indicates a practical way for precise structural control and scale-up preparation of graphene-based materials.

© 2018 Journal of Visualized Experiments. Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb monoliths (MHMs) with micrometer-scale channels are expected as efficient platforms for reactions and separations because of their large surface areas. Up to now, MHMs have been prepared by a unidirectional freeze-drying (UDF) method only from very limited precursors. Herein, we report a protocol from which a series of MHMs consisting of different components can be obtained. Recently, we found that cellulose nanofibers function as a distinct structure-directing agent towards the formation of MHMs through the UDF process. By mixing the cellulose nanofibers with water soluble substances which do not yield MHMs, a variety of composite MHMs can be prepared. This significantly enriches the chemical constitution of MHMs towards versatile applications.

We present a simple design for a broadband tunable terahertz (THz) metamaterial absorber (MMA) consisting of a complementary cross-oval-shaped graphene (CCOSG) structure and dielectric substrate placed on a continuous metal film. Both numerical simulation and theoretical calculation results indicate that the absorbance is greater than 80% from 1.2 to 1.8 THz, and the corresponding relative bandwidth is up to 40%. Simulated electric field and power loss density distributions reveal that the broadband absorption mainly originates from the excitation of continuous surface plasmon resonance (SPR) on the CCOSG. In addition, the MMA is polarization-insensitive for both transverse-electric (TE) and transverse-magnetic (TM) modes due to the geometry rotational symmetry of the unit-cell structure. Furthermore, the broadband absorption properties of the designed MMA can be effectively tunable by varying the geometric parameters of the unit-cell and chemical potential of graphene. Our results may find promising applications in sensing, detecting, and optoelectronic-related devices.

Lithium-sulfur (Li-S) batteries are considered as one of the most promising energy storage systems for next-generation electric vehicles because of their high-energy density. However, the poor cyclic stability, especially at a high sulfur loading, is the major obstacles retarding their practical use. Inspired by the nacre structure of an abalone, a similar configuration consisting of layered carbon nanotube (CNT) matrix and compactly embedded sulfur is designed as the cathode for Li-S batteries, which are realized by a well-designed unidirectional freeze-drying approach. The compact and lamellar configuration with closely contacted neighboring CNT layers and the strong interaction between the highly conductive network and polysulfides have realized a high sulfur loading with significantly restrained polysulfide shuttling, resulting in a superior cyclic stability and an excellent rate performance for the produced Li-S batteries. Typically, with a sulfur loading of 5 mg cm-2, the assembled batteries demonstrate discharge capacities of 1236 mAh g-1 at 0.1 C, 498 mAh g-1 at 2 C and moreover, when the sulfur loading is further increased to 10 mg cm-2 coupling with a carbon-coated separator, a superhigh areal capacity of 11.0 mAh cm-2 is achieved.

We design an ultra-thin multi-band polarization-insensitive metamaterial absorber (MMA) using a single circular sector resonator (CSR) structure in the microwave region. Simulated results show that the proposed MMA has three distinctive absorption peaks at 3.35 GHz, 8.65 GHz, and 12.44 GHz, with absorbance of 98.8%, 99.7%, and 98.3%, respectively, which agree well with an experiment. Simulated surface current distributions of the unit-cell structure reveal that the triple-band absorption mainly originates from multiple-harmonic magnetic resonance. The proposed triple-band MMA can remain at a high absorption level for all polarization of both transverse-electric (TE) and transverse-magnetic (TM) modes under normal incidence. Moreover, by further optimizing the geometric parameters of the CSRs, four-band and five-band MMAs can also be obtained. Thus, our design will have potential application in detection, sensing, and stealth technology.

In this paper, the optical properties of the chiral metamaterial (CMM) with complementary U-shaped structure assembly have been investigated numerically in infrared frequencies. Here, we systematically study the dependence of CMM's optical properties to the structural parameters. The giant optical activity, circular dichroism (CD), and high negative refraction can be obtained by properly selecting the parameters, respectively. CMMs will also lead to many applications in photonic devices due to their strong polarization effect and CD effect.

Aerogels are one of the most popular composite reinforcement materials because of their high porosity and their continuous and homogeneous network. Most aerogels are isotropic, thus leading to isotropic composites when they are used as fillers. This fundamentally limits their applications in areas where anisotropy is needed. Here, an anisotropic microhoneycomb cellulose nanofiber- (CellF)-carbon nanotube (CNT) aerogel (denoted MCCA) is reported that contains unidirectionally aligned penetrating microchannels, which is prepared by a unidirectional freeze-drying method, using the structure-directing function of the CellFs. Due to its anisotropic nature, MCCA-reinforced polydimethylsilexane (denoted MCCA/PDMS) shows distinct anisotropic behavior, with the electrical conductivity and Young's modulus along the direction of penetrating microchannels being approximately twice those in the orthogonal direction. MCCA/PDMS is used to make "directional" strain sensors with electrical resistance as the output signal. They demonstrate a 92% sensitivity difference between the microchannel direction and its orthogonal direction. This approach can be used to prepare anisotropic MCCA-based composites with other polymers for different applications.

As the feature size of Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) continues to decrease, large numbers of new problems appear. Techniques such as strain project, new channel materials and new device structures are considered by academics and industry to be effective ways to continue to improve device performance. In this paper, the scattering mechanism of carriers in the device channel is studied from three aspects: strain technique, new channel material and new structure device: (1) strain technique: Biaxial tensile strain can change carrier distribution among different energy levels, which affects Coulomb scattering and Coulomb mobility. Furthermore, from the TEM image, it is found that biaxial tensile reduces the channel surface roughness for Si nMOSFET, leading an enhancement of electron mobility. However, no such similar phenomena were observed in pMOSFET. Based on this, a new method for calculating the mobility of MOSFET surface roughness scattering using TEM image has been proposed. (2) New channel material: In the germanium (Ge) transistors with different crystal faces, the scattering mechanisms of electron under high field conditions are different. The phonon scattering dominates the Ge(100) transistor, while the surface roughness scattering dominates the Ge(110), (111) transistors. This result is quite different from Si MOSFET. Therefore, a unified model for the scattering mechanism of electron in Ge nMOSFET has been proposed. In SiGe transistors, alloy scattering mainly play a role in the region with relatively small effective electric field (Eeff). The strength of alloy scattering would be weakened in high field and could be decreased by reducing the thickness of SiGe layer. (3) New structure devices: In ultra-thin body germanium (GeOI) transistors, carrier transport is influenced by high- k /channel interfaces, as well as Ge channel/buried oxide (BOX) interface. As the Ge layer thickness decreases, carrier distribution is closer to the interfaces, which intensifies Coulomb scattering and surface roughness scattering. As a result, the mobility in GeOI transistor decreases as the thickness scaling. In addition, the distribution of electron in different energy valleys changes with the thickness decrease in Ge layer, which affects the scattering of electrons. When the Ge film is lower than 10 nm, a part of electron in the L valley will move to the Γ valley, causing the decrease of electron effective mass and increasing the electron mobility.

In this paper, a multi-band chiral metamaterials (CMMs) based on complementary cross-wire structure is proposed and studied numerically. The finite element method (FEM) method was used to simulate the EM properties of the designed structure. Numerical results indicate that the giant optical activity and multiband negative refractive index can be realized in terahertz region. The proposed CMMs may have some potential applications in novel terahertz device.Particle size of bayerite (d50) was about 24 μm. Al2O3was obtained after calcination at 1050 °C for 1.5 h.

Breathable and wearable energy storage is achieved based on an innovative design solution. Carbon nanotube/MnO2 -decorated air-laid paper electrodes, with outstanding flexibility and good electrochemical performances, are prepared. They are then assembled into solid-state supercapacitors. By making through-holes on the supercapacitors, breathable and flexible supercapacitors are successfully fabricated.

A low losses broadband planar negative refractive index metamaterial based on split-ring resonator (SRR) pairs is proposed and investigated experimentally and numerically at microwave frequency range. The transmission spectra of the single-layer SRR pairs were measured, and exhibited left-handed (LH) transmission passband clearly. The metal-dielectric-metal structure exhibits strong magnetic and electric responses simultaneously, and leads to negative permeability and negative permittivity. To further verify the LH properties of planer structure metamaterials, effect media parameters were retrieved, a refraction phenomenon based on a wedge-shaped model and negative phase advance between consecutive numbers of layers were also demonstrated.

The magnetic properties, electronic structure, and optical properties of the filled skutterudite BaFe 4 Sb 12 are calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) plus local orbital method. It is found that the local spin density approximation (LSDA) method appears more accurate than the generalized gradient approximation (GGA) method in calculating the electronic structures and optical properties of this compound. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method are in overall better agreement with experiment. In contrast with recent experiment, our calculations are in good agreement with experimental reflectivity spectra and optical conductivity spectrum.

With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for XCd2(SO4)3 (X =Tl, Rb). The results show that Tl2Cd2(SO4)3 (TlCdS) has a larger band gap than Rb2Cd2(SO4)3 (RbCdS) and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states (PDOS), we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation (Tl and Rb) and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds (Cd-O, Rb-O, and Tl-O). The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.

Full potential linearized augmented plane wave (FPLAPW) method calculations are carried out for semiconducting orthorhombic BaSi2. The optical properties and the origin of the different optical transitions are investigated. Our calculated band gap of 1.0918 eV is indirect, which is in good agreement with the experimental result. The bonds between Ba and Si are considered to be electrovalent bond. The anisotropy in the imaginary part e2(ω) and real part e1(ω) of the optical dielectric tensor are analysed. The contributions of various transition peaks are explained from the imaginary part of the dielectric function.

The electronic devices are becoming smaller, more flexible, and wearable, thus requiring the energy storage unit to have not only high volumetric energy density but also small thickness and high flexibility. Supercapacitors (SCs), as a typical energy storage device, have the advantage of fast energy charging and releasing. The present progress on SCs implies a tremendous need to transform traditional configuration into flexible and thin enough membrane-like supercapacitors. This work shows a high volumetric energy density membrane-like flexible supercapacitor with an rGO-TiO2/GO/rGO-TiO2 sandwich structure, in which the rGO-TiO2 layer is used as the active material and the middle GO layer acts as the separator. The supercapacitor in one compact graphene-based membrane has shown great flexibility and at the same time guarantees a high volumetric capacity of 237 F cm−3 and a high volumetric energy density of 16 mWh cm−3.

Full-Potential Linearized Augmented Plane Wave plus local orbital method (FPLAPW +lo) calculations are performed for ThFe4P12 in the filled skutterudite in order to investigate the optical properties and to show the origin of the different optical transitions. It is found that the band gap is indirect for ThFe4P12. Then the contributions of the different transition peaks are analyzed from the imaginary part of the dielectric function. In contrast to recent experimental expectations, our calculations are in good agreement with experimental reflection spectra and 1(ω) spectrum.

Full-Potential Linearized Augmented Plane Wave plus local orbital method (FPLAPW +lo) calculations were performed for CeFe 4 P 12 in the filled skutterudite in order to investigate the optical properties and to show the origin of the different optical transitions. It is found that the CeFe 4 P 12 compound has a indirect band gap: 413.41meV. Then the contributions of the different transition peaks are analyzed from the imaginary part of the dielectric function. In contrast to recent experimental expectations, our calculations are in good agreement with experimental reflectivity spectra. Furthermore, the different optical properties have been investigated. We have studied the absorption coefficient, the electron energy loss function, the refractive index, and the extinction coefficient.

Pt/Au Schottky contacts were fabricated on modulation-doped Al0.22GaN0.78/GaN heterostructures. Some different pre-deposition surface treatments were used to prevent the formation of the native oxide layer on the Al0.22GaN0.78 surface. X-ray photoelectron spectroscopy measurements indicate that the pre-deposition surface treatment with boiling (NH4)2S solution can remove the native oxide layer on the Al0.22Ga0.78N surface effectively. The highest Schottky barrier height of 1.13 eV was obtained on the (NH4)2S-treated Al0.22GaN0.78/GaN heterostructure.

The subbands occupation and subband transport properties in modulation-doped Al0.22Ga0.78N/GaN heterostructures are studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The occupation of two subbands is observed from the Shubnikov-de Haas oscillations. It is found that the total density of the two-dimensional electron gas (2DEG) as a function of the electron sheet density in the second subband is linear. The threshold of the 2DEG density that the second subband begins to be occupied is 7.3×1012cm-2. The transport mobility of the 2DEG in the two subbands is obtained by using the mobility spectrum technique. It is found that the transport mobility in the first subband decreases significantly when the relaxation of the Al0.22Ga0.78N barrier occurs. The electron mobility in the second subband is much larger than that in the first one. The results indicate that the interface roughness scattering and the alloy disorder are the main mechanisms in determining the 2DEG mobility in AlxGa1-x N/GaN heterostructures.