Layered Crystalline Structure Research Articles

Electronic and thermoelectric properties of the layered Zintl phase CaIn2P2: first-principles calculations

ABSTRACT We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn2P2 layered Zintl phase at two fixed temperatures: T = 600 and 900 K through first-principles electronic band structure calculations combined with Boltzmann's transport theory within charge-carrier relaxation time and rigid band approximations. The band structure calculated using the Tran-Blaha modified Becke–Johnson potential shows a fundamental indirect energy band gap (E g) of 1.10 eV that comes from the polyanion (In2P2)−2. CaIn2P2 exhibit a mixture of flat and dispersive energy bands in the energy window from to eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn2P2 is equal to at 900 K and at 1250 K. This relatively low lattice thermal conductivity of CaIn2P2 can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn2P2, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of () at 900 K.

Surfactant-assisted β-NA supramolecular self-assembly in mini injection molding PP composite

The introduction of surfactant (polyoxyethylene sorbitan monoisostearic acid ester, Tween-60) conduces to the dispersion of β-NA (N,N′-dicyclohexylterephthalamide, TMB-5) and regulation of its self-assembly morphologies. In this work, surfactant-assisted β-NA was firstly utilized in a strong flow field when processing β-iPP by mini-jet injection molding. The polymorphism morphologies and crystalline structure in isotactic polypropylene (iPP)/surfactant-assisted β-NA self-assembly were explored. The SEM results indicated that hierarchical structures containing shish-kebab and cylindrites in the skin and mid layer, inter-locked β-transcrystals and spherulites structure in the core layer were obtained. The strong shear drove the surfactant-assisted β-NA self-assembly needles to align in a dense orientation along machine direction which induced the formation of inter-locked β-transcrystals. The crystalline structure and orientation of different layers were further investigated via small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) characterization. The variation of surfactant-assisted β-NA supramolecular self-assembly and crystalline structure in mini injection molding PP composites were systematically discussed. This paper would have referential significance for the β-NA self-assembly.

Structural and Electrical Investigation of Porous GaAs Layers on Different Crystallographically Oriented GaAs Substrates

In this paper, electrochemical anodization was used to fabricate porous layers on n-type GaAs substrates with different orientations, i.e., (511)A, (100) and (111)B, under the same experimental conditions. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD) were used to characterize the formed porous layers, with respect to the substrate orientation. Results obtained from SEM and AFM data are evidence of the formation of GaAs nanocrystallites and reveal that pores grow along definite crystallographic directions. XRD analysis confirm the single crystalline structure of porous layers and a relative peak shift as compared to GaAs, indicating a change in the lattice constant due to strain effects. The photoluminescence spectra of the porous layers showed red PL bands attributed to quantum confinement effects in GaAs nanocrystallites. The investigated current–voltage (I–V) in the forward bias region demonstrates that the transport mechanism in the Au/porous-GaAs/GaAs structures was governed by space-charge-limited current (SCLC). In fact, non-saturating behavior was observed in the reverse bias I–V characteristics due to both the effective barrier height dependence on the electric field and the thermionic field emission.

The growth and characteristics of In2Se3/(Bi1−xInx)2Se3 superlattices with asymmetric graded interfaces by molecular beam epitaxy

The growth of In2Se3/Bi2Se3 superlattices (SLs) by molecular beam epitaxy at an elevated temperature is explored. The crystalline phase structure of In2Se3 layers in the as-grown SLs is determined to be α-In2Se3. The diffusion of In from In2Se3 to Bi2Se3 is significantly promoted, while Bi diffusion into In2Se3 layers is insignificant as manifested by the in situ lattice evolution analysis, so that the achieved SL structure is of graded (Bi1−xInx)2Se3 solid-solution layers periodically separated by α-In2Se3 layers. The lattice vibration characteristics due to phonon confinement in the achieved SLs are also exhibited.

COFs Meet Graphene Nanoribbons

2D covalent organic frameworks (COFs) have received considerable attention because of their crystallinity, permanent porosity, and tunability, yet they exhibit low in-plane conductivity. In this issue of Chem, Fischer and co-workers report an approach for growing 2D COF thin films featuring high in-plane conductivity for potential use in organic electronics.

Temperature dependence of exchange bias in NiFe2O4/BiFeO3 bilayers

In BiFeO3-based ferromagnet/anitferromagnet (FM/AFM) bilayers, field cooling is required through the Néel temperature to achieve significant exchange bias (EB) at room temperature (RT). In this work, NiFe2O4/BiFeO3 (NFO/BFO) all-oxide bilayer films were selected and deposited on SrTiO3 substrates by pulsed laser deposition to avoid the possible interfacial oxidization during the field cooling process. In combination with X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM) characterizations, the NFO/BFO bilayers are shown to have good crystalline layered structure. After field cooling at various temperatures, the samples show sizable EB effect at low temperature region, which is attributed to spin-glass-pinned effect. More importantly, significant EB can be obtained at RT after the sample was field cooled from temperatures higher than 400 K. The maximal values of the exchange bias field (HE) and the ratio between HE and coercivity (i.e. HE/HC) are 48 Oe and 0.6 at RT, respectively. The EB effect at RT is considered to result from the pinned and uncompensated spins near the NFO-BFO interface.

Three dimensional nanosuperstructures made of two-dimensional materials by design: Synthesis, properties, and applications

The recent search for advanced materials with desired properties for next-generation flexible energy and electronic devices has focused on the unique class of two-dimensional (2D) materials made of layered crystalline structures. In particular, intensive interest has been devoted to configuring 2D materials into three-dimensional (3D) nanoporous superstructures (3DSs), which can effectively prevent aggregative restacking and maximize the exposure of active nanoscale planar surfaces. Here, we survey the recent progress of 3DSs made of several important 2D materials, including graphene, boron nitride (BN), transition metal dichalcogenide (TMD), and transition metal carbide/carbonitride (MXene). The characteristics of the formed 3DSs, including density, porosity, electrochemical activity, electronic and surface properties, depend on respective synthesis approaches and conditions. The obtained 3DSs, exhibiting distinctive properties, have been exploited in an array of applications, including shielding electromagnetic, thermal, and acoustic energies; sensing chemical, optical, and mechanical signals; serving as 3D scaffolds of energy and environment devices; and supporting 3D growth of live cells and tissues. At the end, this comprehensive review is summarized with future outlooks, including the great potentials, challenges, and bottleneck issues in fabrication and large-scale implementation of 3DSs.

Investigations of Different Ion Intercalations on the Performance of FBG Hydrogen Sensors Based on Pt/MoO3.

α-MoO3 has been used as a hydrogen sensing material due to its excellent properties and unique crystalline layer structure. However, the low repeatability of α-MoO3 based hydrogen sensor restricts its practical application. In this paper, the effect of intercalated ion species and the amount in α-MoO3 is experimentally investigated and discussed. It is concluded that the repeatability of the sensor depends on the radius of intercalated ions and amount of ionic bonds. The optimal ion species is Na+ and the optimal amount of precursor is 1 mmol.

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

SummaryEven though the energy density of O3-type layer-structured metal oxide cathode can fully reach the requirement for large-scale energy storage systems, the cycling lifespan still cannot meet the demand for practical application once it is coupled with a non-sodium-metal anode in full-cell system. Transition metal dissolution into the electrolyte occurs along with continuous phase transformation and accelerates deterioration of the crystal structure, followed by migration and finally deposition on the anode to form a vicious circle. Surface engineering techniques are employed to modify the interface between active materials and the electrolyte by coating them with a thin layer of AlPO4 ion conductor. This stable thin layer can stabilize the surface crystal structure of the cathode material by avoiding element dissolution. Meanwhile, it can protect the anode from increased resistance by suppressing the dissolution-migration-deposition process. This technique is a promising method to improve the lifetime for the future commercialization.

Structure and Optical Properties of CdTe and CdS Thin Films after Hard Ultraviolet Irradiation

The influence of hard ultraviolet radiation on the crystalline structure, surface morphology and optical characteristics of CdS and CdTe semiconductor layers obtained by direct current magnetron sputtering are investigated. It was established that the optical characteristics of the studied films CdS and CdTe are insensitive to hard ultraviolet irradiation. The crystalline structure of the CdS and CdTe layers is changed after irradiation. The period of the lattice for cadmium sulfide films increases from c = 6.77(01) Å to c = 6.78(88) Å, which may be due to the formation of point defects and defective complexes. Decrease the integral FWHM of the peaks on the X-ray diffraction patterns of the layers of CdS and CdTe was observed, due to the increase of the coherent scattering regions as a result in the process of near-surface layers partial recrystallization of the investigated films.

Limited solid solution Li(Ni0,33Mn0,33Co0,33)1-xFexO2 with structure α-NAFEO2

In the framework of this work, the compositions Li (Ni0.33Mn0.33Co0.33)1-xFexO2 (0 ≤ x ≤ 1) of the tetrahedron LiNiO2-LiMnO2-LiCoO2-LiFeO2 were investigated. The samples were synthesized by the gel combustion method with starch. For the first time it was obtained without admixtures LiNi0.2Mn0.2Co0.2Fe0.4O2 solid solution with a layered crystalline structure a-NaFeO2, which can be used as a cathode material of lithium-ion batteries. An electrochemical testing of the homogeneous sample LiNi0.2Mn0.2Co0.2Fe0.4O2 and the sample with a minimum iron content LiNi0.3Mn0.3Co0.3Fe0.1O2 was conducted. The results show feasibility of further studying the homogeneity region and the properties of the solid solution Li (Ni, Mn, Co, Fe)O2.

V2O5 nanopaper as a cathode material with high capacity and long cycle life for rechargeable aqueous zinc-ion battery

Aqueous batteries are suitable for large scale energy storage due to cost and safety concerns. Among all aqueous batteries, rechargeable aqueous zinc-ion battery is a promising choice because zinc electrode has low equilibrium potential, high exchange current density, and high hydrogen evolution overpotential. However, since zinc ion is a divalent cation, it is difficult to find a cathode material in which zinc ion can reversibly insert and extract. In this work, we introduce a novel V2O5 nanopaper consisting of V2O5 nanofibers and carbon nanotubes as reversible Zn-ion cathode. V2O5 has a layered crystalline structure. The spaces between the oxide layers may serve as 2-dimensional diffusion pathways for Zn ions. Meanwhile, the nanofiber morphology endows the material with short ionic diffusion distance and may tolerate high volume change. As a result, the V2O5 nanopaper cathode delivers a high capacity of 375 mAh g−1 and long cycle life up to 500 cycles.

Approaching the Lithiation Limit of MoS2 While Maintaining Its Layered Crystalline Structure to Improve Lithium Storage.

MoS2 holds great promise as high-rate electrode for lithium-ion batteries since its large interlayer can allow fast lithium diffusion in 3.0-1.0 V. However, the low theoretical capacity (167 mAh g-1 ) limits its wide application. Here, by fine tuning the lithiation depth of MoS2 , we demonstrate that its parent layered structure can be preserved with expanded interlayers while cycling in 3.0-0.6 V. The deeper lithiation and maintained crystalline structure endows commercially micrometer-sized MoS2 with a capacity of 232 mAh g-1 at 0.05 A g-1 and circa 92 % capacity retention after 1000 cycles at 1.0 A g-1 . Moreover, the enlarged interlayers enable MoS2 to release a capacity of 165 mAh g-1 at 5.0 A g-1 , which is double the capacity obtained under 3.0-1.0 V at the same rate. Our strategy of controlling the lithiation depth of MoS2 to avoid fracture ushers in new possibilities to enhance the lithium storage of layered transition-metal dichalcogenides.

Approaching the Lithiation Limit of MoS2 While Maintaining Its Layered Crystalline Structure to Improve Lithium Storage

AbstractMoS2 holds great promise as high‐rate electrode for lithium‐ion batteries since its large interlayer can allow fast lithium diffusion in 3.0–1.0 V. However, the low theoretical capacity (167 mAh g−1) limits its wide application. Here, by fine tuning the lithiation depth of MoS2, we demonstrate that its parent layered structure can be preserved with expanded interlayers while cycling in 3.0–0.6 V. The deeper lithiation and maintained crystalline structure endows commercially micrometer‐sized MoS2 with a capacity of 232 mAh g−1 at 0.05 A g−1 and circa 92 % capacity retention after 1000 cycles at 1.0 A g−1. Moreover, the enlarged interlayers enable MoS2 to release a capacity of 165 mAh g−1 at 5.0 A g−1, which is double the capacity obtained under 3.0–1.0 V at the same rate. Our strategy of controlling the lithiation depth of MoS2 to avoid fracture ushers in new possibilities to enhance the lithium storage of layered transition‐metal dichalcogenides.

Осаждение пленок кремния, легированных бором и фосфором газоструйным плазмохимическим методом

AbstractDoped silicon films are fabricated using diborane and phosphine as doping gases by gas-jet plasma-chemical deposition with the application of an electron beam. The influence of the dopant-gas concentration, the addition of a fluorine-containing gas, and the background pressure on the conductivity and crystalline structure of silicon layers is investigated. Boron-doped amorphous films ( a -Si:H) with a conductivity up to 5.2 × 10^–3 (Ω cm)^–1 are fabricated; when doping with phosphorus, microcrystalline silicon films ( mc -Si:H) with a crystallinity up to 70% and conductivity at a level of 1 (Ω cm)^–1 are fabricated.

Deposition of Silicon Films Doped with Boron and Phosphorus by the Gas-Jet Plasma-Chemical Method

Doped silicon films are fabricated using diborane and phosphine as doping gases by gas-jet plasma-chemical deposition with the application of an electron beam. The influence of the dopant-gas concentration, the addition of a fluorine-containing gas, and the background pressure on the conductivity and crystalline structure of silicon layers is investigated. Boron-doped amorphous films (a-Si:H) with a conductivity up to 5.2 × 10–3 (Ω cm)–1 are fabricated; when doping with phosphorus, microcrystalline silicon films (mc-Si:H) with a crystallinity up to 70% and conductivity at a level of 1 (Ω cm)–1 are fabricated.

Influence of Annealing in Freon on the Crystalline Structure of Cadmium-Telluride Layers and the Efficiency of Thin-Film Solar Cells on Their Basis

Solar cells (SCs) based on cadmium-telluride base layers, obtained by thermal evaporation and closed-space sublimation (CSS), are investigated. The base layers are activated via annealing in Freon. Structural and morphological studies are carried out to compare the recrystallization processes occurring during annealing in CdTе layers fabricated by different methods. The output parameters and light diode characteristics of the SCs are investigated, and the possibility of applying Freon annealing in the commercial production technology of thin-film CdS/CdTе SCs with base layers formed by thermal vacuum evaporation is analyzed.

Impact of crystalline structures on the thermal stability and Schottky barrier height of NiGe/Ge contact

We have investigated the effect of crystalline structures on the thermal stability and electrical properties of nickel monogermanide (NiGe)/Ge contacts. The crystalline structure of the NiGe layer was found to be a determining factor for the thermal stability. Compared with the polycrystalline NiGe layer, the epitaxial NiGe layer with the orientation NiGe(100) ǁ Ge(110) exhibited a promising thermal stability due to its uniform interface and small residual stress. We have also demonstrated the alleviation of Fermi level pinning (FLP) by controlling the crystalline structures of NiGe layers on Ge(110) substrates. These works give us a hint that controlling the crystalline structure of metal layers enables one to control the Schottky barrier height of metal/Ge contacts, and the origin of FLP is not due to the intrinsic factor, e.g., metal induced gap states, but due to the extrinsic factors such as strong anisotropy of the work function and disorders at the metal/Ge interfaces.

The formation and characterization of titanium dioxide layers deposited on copper middle nano-layer

In this research, two thin layers of Cu with thicknesses of 20 ± 2 nm and 30 ± 2 nm are coated on substrates of quartz. A layer of titanium dioxide with a thickness of 300 ± 25 nm is coated on each nano layer. Also, in order to compare, a layer of titanium dioxide with a thickness of 300 ± 25 nm is coated on a substrate of quartz. All coatings are conducted using physical vapor deposition and electron beam deposition methods. The major goal is to study the impact of Cu nano layer on the surface morphology, grain size, grain boundaries, crystalline structure and phases, and some optical properties such as absorption and transmission of titanium dioxide layers. The field emission scanning electron microscope is used to analyze the surface morphology. Moreover, the crystalline structure of layers is determined using X-ray diffraction. The transmission and absorption of titanium dioxide layers are also determined using ultraviolet–visible spectroscopy. These analyses indicate that the existence of a middle nano layer of copper makes the layers’ surfaces denser and more uniform; however, it has no effect on the structure of layers’ crystalline phase and the way of transferring the layers’ crystalline phase caused by annealing. A slight increase in layers’ absorption and a small shift in absorption edge occur due to the presence of middle nano layer of copper and its thickening. Another remarkable effect that happens due to the presence of copper’s middle nano layer is the amplification and shift of absorption bands in the visible spectrum.

Electronic structure of ferromagnetic semiconductor CrGeTe3 by angle-resolved photoemission spectroscopy

As one of the rare ferromagnetic semiconductors, ${\mathrm{CrGeTe}}_{3}$ has recently attracted a great deal of attention as a potential candidate for next-generation high-performance nano-spintronic devices. In this study, by combining density functional theory calculations and angle-resolved photoemission spectroscopy measurements, we explore the electronic structure of ${\mathrm{CrGeTe}}_{3}$ directly. The low-lying valence bands are centered around the $\mathrm{\ensuremath{\Gamma}}$ point and mainly consist of Te $5p$ orbitals. The majority of the bands show almost no ${k}_{z}$ dispersion, consistent with its layered crystalline structure. Due to the higher hopping integral along the out-of-plane direction, however, bands comprised of ${p}_{z}$ orbitals exhibit significant ${k}_{z}$ dispersion. Furthermore, an indirect band gap of 0.38 eV is directly measured by surface electron doping with potassium deposition.