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The transparent conductive CuCr1–xNixO2 (0 ≤ x ≤ 8%) films were prepared by sol–gel method with two-step annealing process. The structure, morphology, phonon modes, chemical composition, optical ba...

Many efforts are currently devoted to improving the stability and crystallinity of imine-based two-dimensional (2D) covalent organic frameworks (COFs) given their wide range of potential applications. The variation in the relative orientations of the imine bonds has been found to be a critical factor that impacts the stacking of the 2D COF layers, leads to the formation of isomer structures, and influences the crystallinity of the final product. Most investigations to date have focused only on the structural properties, while the role of the imine orientations on the electronic properties has not been studied systematically. Here, we explore this effect by examining how the electronic band structures, electronic couplings, and effective masses evolve when considering four isomeric structures of an imine-linked tetraphenyl-pyrene naphthalene-diimide COF. Our results provide an understanding of the impact of the imine orientations and how they need to be controlled to realize COF inter-layer stackings that can lead to efficient cross-plane electron transport. They can be used to guide the design and synthesis of imine-based COFs for applications where charge transport needs to be optimized.

ConspectusInteraction between nanomaterials (NMs) and biological systems can be beneficial for biological functions but also can present hazards to humans. Nanotoxicology and nanomedicine, as two s...

The first-principles calculation of pristine, B-, Al-, Ga-, Sb-, and Bi-doped blue phosphorene (BlueP) with adsorbed SO2, NO, and NO2 gas molecules including the transport and optical properties is reported. The electronic structures of pristine and doped BlueP are investigated, and the modifications in electronic band structures and density (DOS) of states are studied. The most considerable adsorption energies of BlueP after being exposed to paramagnetic gas molecules NO and NO2 show excellent sensitivity to the considered gas molecules, which is confirmed by the current–voltage characteristics. The pristine and doped BlueP can be encouraging alternatives for new-generation optical gas sensors due to notable alterations in the pristine and doped BlueP optical spectra.

Colloidal quantum dot (QD) light-emitting diodes (QLEDs) hold the promise of next-generation displays and illumination owing to their excellent color saturation, high efficiency, and solution processability. For achieving high-performance light-emitting diodes (LEDs), engineering the fine compositions and structures of QDs is of paramount importance and attracts tremendous research interest. The recently developed continuously graded QDs (cg-QDs) with gradually altered nanocompositions and electronic band structures present the most advanced example in this area. In this Perspective, we summarize the current progress in LEDs based on cg-QDs, mainly concentrating on their synthesis and advantages in addressing the great challenges in QLEDs, like efficiency roll-off at high current densities, short operation lifetimes at high brightness, and low brightness near the voltage around the bandgap. In addition, we propose accessible approaches exploiting the cutting-edge mechanisms and techniques to further optimize and improve the performance of QLEDs.

NdFe3(BO3)4 and NdGa3(BO3)4 crystals are of great interest due to their physical properties. For example, NdFe3(BO3)4 crystal demonstrates magnetodielectric and magnetopiezoelectric effects, and Nd...

p-type PbTe is the most sought-after material in thermoelectrics due to its ultrahigh thermoelectric figure of merit (zT), but the performance of n-type PbTe lags behind due to the simplicity of it...

A p-type semiconductor candidate of nickel oxide (NiO) desires longer carrier lifetimes with suitable conduction band edge, which holds a unique advantage to drive the hydrogen evolution toward eff...

By executing the Generalised Gradient Approximation (GGA) based on the Pethew Burke Emzerhof (PBE), the structural geometry, electronic band structures, total density of states (DOS), partial densi...

Graphene nanoribbons hold great promise for future applications in nanoelectronic devices, as they may combine the excellent electronic properties of graphene with the opening of an electronic band gap – not present in graphene but required for transistor applications. With a two-step on-surface synthesis process, graphene nanoribbons can be fabricated with atomic precision, allowing precise control over width and edge structure. Meanwhile, a decade of research has resulted in a plethora of graphene nanoribbons having various structural and electronic properties. This article reviews not only the on-surface synthesis of atomically precise graphene nanoribbons but also how their electronic properties are ultimately linked to their structure. Current knowledge and considerations with respect to precursor design, which eventually determines the final (electronic) structure, are summarized. Special attention is dedicated to the electronic properties of graphene nanoribbons, also in dependence on their width and edge structure. It is exactly this possibility of precisely changing their properties by fine-tuning the precursor design – offering tunability over a wide range – which has generated this vast research interest, also in view of future applications. Thus, selected device prototypes are presented as well., On-surface synthesized atomically precise graphene nanoribbons are promising candidates for use in future devices. This article reviews atomically precise graphene nanoribbons, in particular focusing on their electronic properties.

We report a one-pot protocol to prepare ultrathin nanosheets of brookite-phase TiO2 through hydrolyzing TiCl3 in formamide. This 2D titania is defective and shows flexible electronic states and enhanced surface reactivity, which is probed by H2O2 adsorption, catalytic TMB oxidation, and X-ray absorption fine structure. The nanosheets provide a new 2D platform to exploit the applications of TiO2 in catalysis, energy conversion and storage.

As a class of metal-free two-dimensional (2D) semiconductor materials, polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures, availability in abundance and high stability. According to the different ratios of C and N atoms in the framework, a series of CxNy materials have been successfully synthesized by virtue of various precursors, which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing. In view of topological structures on their electronic structures and material properties, the as-reported CxNy could be generally classified into two main categories with three- or six-bond-extending frameworks. Owing to the effective n→π* transition in most CxNy materials, the relative energy level of the lone-pair electrons on N atoms is high, which thus endows the materials with the capability of visible light absorption. Meanwhile, the different repeating units, bridging groups and defect sites of these two kinds of CxNy allow them to effectively drive a diverse of promising applications that require specific electronic, interfacial and geometric properties. This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of CxNy materials. In the final part, we also discuss the existing challenges of CxNy and outlook the prospect possibilities.

CsSnI3 is a representative all-inorganic and less toxic perovskite material. However, extreme structural and chemical instability of perovskite CsSnI3 makes its optoelectronic applications highly c...

In recent times, an engrossing and newly discovered class of materials with unique electronic band properties, namely, zero-spin-gap half-metal, has gained acute attraction worldwide because of its...

The electronic and transport properties of borophene/phosphorene heterojunctions are systematically investigated by first-principles calculations. The geometrical structures and electronic band structures of monolayer borophene, monolayer phosphorene and heterojunctions with different distances between layers are analysed. The calculated results show that the band gap can be adjusted by tuning the distance between heterostructure layers. Then the transport properties of the heterojunction with different electrodes are also studied. It can be found that the selected different electrodes have significant effect on the transport property of the heterojunction. Interestingly, when the heterostructure is selected as the electrode, the heterostructure with an interlayer distance of 2.65 Å showed the best transport performance. It is hoped that this paper may provide useful insights for the design of nanoelectronic devices based on borophene/phosphorene heterojunctions.

The optical absorption properties of lithium transition-metal phosphates (LiTMPO4, TM = Mn, Fe, Co, Ni) with nanoscale particle sizes (300–500 nm in diameter) have been measured. The measured edges...

In this work we investigated the thermoelectric transport behaviors of p-type PbS and n-type PbS with an emphasis on its contrasting electronic band structures. We found that the Seebeck coefficients of p-type PbS increased faster with rising temperature than that of n-type PbS with the same carrier concentration. The Density functional theory (DFT) calculation of the energy band structure of PbS as a function of temperature illustrates a significant contribution from multiple valence bands in K-doped p-type PbS. This work revealed one important information that manipulating electronic bands is also suitable in developing high-performance PbS thermoelectric systems.

Perovskite solar cells (PSCs) have achieved power-conversion efficiency of 25.2%; however, their working principle remains under debate, and the stability issue has not been solved. Herein, we reve...

We conducted a large-scale density-functional theory study on the influence of the exchange-correlation functional in the calculation of electronic band gaps of solids. First, we use the large materials data set that we have recently proposed to benchmark 21 different functionals, with a particular focus on approximations of the meta-generalized-gradient family. Combining these data with the results for 12 functionals in our previous work, we can analyze in detail the characteristics of each approximation and identify its strong and/or weak points. Beside confirming that mBJ, HLE16 and HSE06 are the most accurate functionals for band gap calculations, we reveal several other interesting functionals, chief among which are the local Slater potential approximation, the GGA AK13LDA, and the meta-GGAs HLE17 and TASK. We also compare the computational efficiency of these different approximations. Relying on these data, we investigate the potential for improvement of a promising subset of functionals by varying their internal parameters. The identified optimal parameters yield a family of functionals fitted for the calculation of band gaps. Finally, we demonstrate how to train machine learning models for accurate band gap prediction, using as input structural and composition data, as well as approximate band gaps obtained from density-functional theory.

Differing from its bulk counterparts, atomically thin two-dimensional transition metal dichalcogenides that show strong interaction with light are considered as new candidates for optoelectronic devices. Either physical or chemical strategies can be utilized to effectively tune the intrinsic electronic structures for adopting optoelectronic applications. This review will focus on the different tuning strategies that include its physics principles, in situ experimental techniques, and its application of various optoelectronic devices.

In this paper, a reduced mutual coupling dual-band multiple-input-multiple-output (MIMO) antenna is reported. A thin rectangular slot is incorporated into an unlicensed 5.2 GHz band rectangular pat...

The discovery of compounds with novel topologies is likely to extend structural diversity and trigger intriguing physical properties. Herein, the interesting [Pb4Ba4O4]8+ species has been discovered in alkali-earth metal lead(II) oxyhalide Ba27Pb8O8Cl54. Besides, the crystal structures, infrared/Raman spectroscopy, UV-Vis-NIR diffuse reflectance spectroscopy and electronic band structures of Ba27Pb8O8Cl54 have been studied.

In the family of III–VI monochalcogenides M2X2 (M = gallium, indium; X = sulfur, selenide, etc.), the interlayer interaction and the electronic band edges share the contribution of the same chalcog...

Quaternary tantalum-based oxynitrides ATa(O,N)3, with electronic band gaps between 1.8 and 2.4 eV, are promising materials for photochemical water-splitting. The tailoring of their surface properties is a critical aspect to obtain efficient hole extraction. We report on the origin of improved photoelectrochemical (PEC) water oxidation by means of acidic treatment for this class of compounds on the example of cubic CaTaO2N particles. We address the effect of acidic treatment by using complementary physical characterization techniques, such as X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), 1H and 14N solid-state nuclear magnetic resonance (NMR) spectroscopy, electron microscopy and electronic band structure calculations at the density functional theory (DFT) level. In combination with photoelectrochemical measurements, solid-state NMR indicates that the restructured surface displays a meaningfully higher concentration of terminating OH groups. Subsequent deposition of a nickel borate (NiBi) catalyst on the acid-treated surface yields a higher percentual upsurge of photocurrent in comparison to pristine CaTaO2N. Our results highlight the application of solid-state NMR spectroscopy for understanding of the semiconductor-catalyst interface in photochemical devices.

Data-driven exploration for pressure-induced superconductors was performed based on the high-throughput first-principles screening of electronic band structures. In the screening conditions, we foc...

Unconventional fermions, such as threefold, fourfold, sixfold, and eightfold fermions have attracted intense attention in recent years. However, the concrete materials hosting unconventional fermions are still in urgent scarcity. In this work, based on first-principle calculations and symmetry analysis, we reveal rich unconventional fermions in existing compound ${R}_{2}{\mathrm{C}}_{3}$ ($R=\mathrm{Y}$, La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, Yb, Lu). We show that these compounds host quadratic dispersive threefold, linear dispersive fourfold, and sixfold points (SPs) near the Fermi level in their electronic band structures when spin-orbital coupling (SOC) is not included. We also find that a uniaxial strain can transform the unconventional fermions into other types of fermions, depending on the directions of strain. When SOC is considered, a SP transforms to an eightfold degenerate point and a fourfold degenerate point. Overall, our work provides a family of realistic materials to study the unconventional fermions.

Cadmium sulfide (CdS) is a semiconducting absorber for photoelectrochemical (PEC) hydrogen production with suitable electronic band structures. However, it suffers from severe photocorrosion and ra...

Open in a separate window The tailored (computational) design of materials addressing future challenges requires a thorough understanding of their electronic structures. This becomes very apparent for a given material existing in a certain homogeneity range, as its particular composition influences its electronic structure and, eventually, its physical properties. This led us to explore the influence and, furthermore, the origin of vacancies in the crystal structures of rock salt-type superconductors by means of quantum-chemical techniques. In doing so, we examined the vibrational properties, electronic band structures, and nature of bonding for a series of superconducting transition-metal sulfides, i.e., MS (M = Sc, Y, Zr, Lu), which were identified to exist over certain homogeneity ranges. The outcome of our research indicates that the subtle competing interplay between two electronically unfavorable situations at the Fermi levels, i.e., the occupations of flat bands and the populations of antibonding states, appears to control the presence of vacancies in the crystal structures of the sulfides.

Two-dimensional (2D) carbon nitrides are drawing increasing interests due to the structural diversities and unique electronic properties, superiors to the pure 2D carbon materials. Motivated by the recent experimental progresses, we investigated from first-principles a new family of 2D carbon nitrides composed of sp- and sp2-hybridized carbon atoms and with kagome, rhombic and hexagonal lattices. The kagome and rhombic lattices exhibit moderate electronic band gaps (0.98–3.34 eV), high carrier mobility in the order of 3 × 105 cm2V−1s−1, high flexibility with critical strain up to 44%–47%, and type-II band alignment which are desired for applications in electronic devices and solar cells. Our findings are expected to offer theoretical bases for synthesis and applications of these novel 2D carbon nitrides and promote the following experimental exploration.

We have studied the structural, electronic and optical properties of chloro‑fluorinated graphene (CF1-xClx) as a function of Cl concentration (x) by employing DFT and beyond DFT approaches. The increase in Cl concentration brings about an increase in lattice parameters while binding energy and electronic band gap are reduced. For all the properties studied, a non-linear behavior is observed as x is increased from 0.25 to 0.375. In particular, electronic band gap exhibits a sharp decline (>1.5 eV) for x = 0.25–0.375; while the reduction is relatively smooth for x ≤ 0.25 and x ≥ 0.375. Optical gap presents similar trend albeit with much smaller magnitude due to the presence of strong excitonic effect. We show that the observed non-linear behavior is associated with sharp reduction in the minimum distance between Cl adsorbates as x is increased from 0.25 to 0.375. As a consequence, new states caused by Cl-Cl interaction appear at an energy level higher than those caused by C-F and F-F, thus considerably reducing the band gap. Our result provides helpful insight for tailoring the band gap through hetero-functionalization of graphene by halides.

By virtue of electron-rich structure, relatively low electronic band gap, and strong blue fluorescence emission, triphenylamine derivatives (TPAs) can serve as effective host units for the π-conjug...

We report a first-principles study of structural, mechanical and optoelectronic properties of the Sn3X4 (X = P, As, Sb, Bi) compounds. The calculations were performed using the full-potential linearized augmented plane wave approach (FP-LAPW). The structural and mechanical properties of Sn3X4 (X = P, As, Sb, Bi) compounds were obtained using GGA-PBE. In addition, The Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJGGA) technique was used to calculated the optoelectronic properties. The calculated electronic band structures and density of states reveal a direct band gap at Γ points varied from 0.11 eV to 1.23 eV for X = P, As, Sb, Bi. The optical absorption calculations show that all compounds have high absorption coefficients about twenty times greater than that of CuInSe2 and CdTe in the visible region. The high absorption of these materials could be attributed to the localized p-states of cation (X = P, As, Sb, Bi) in the lower region of the conduction band.

The set of known single-atomic-layer (SAL) superconductors has been limited so far by a few examples, including Si(111)-hex- 7 × 3 -In reconstruction, Si(111)-SIC-Pb and -HIC-Pb phases, and Si(111) 3 × 3 -(Tl, Pb) compound phase. In the present study where transport properties of SAL compounds of Tl-Pb with different composition ratios on Ge(111) and Si(111) substrates have been studied in situ in ultrahigh vacuum, the list of SAL superconductors has been enlarged by three new members, Ge(111) 3 × 3 (Tl, Pb), Ge(111)3×3-(Tl, Pb), and Si(111)4×4-(Tl, Pb) systems which show superconducting transition at the critical temperatures of 2.03 K, 0.83 K and 0.79 K, respectively. Bearing in mind that the atomic arrangements and electronic band structures of these SAL compounds of Tl-Pb have already been established, the obtained data set is believed to constitute a solid basis for the prospective theoretical investigations on the nature of SAL superconductivity. In addition, all the new systems demonstrate a noticeable Rashba-type spin splitting in the metallic surface-state bands and, therefore, they might be promising materials for future superconducting spintronics as well as for basics research of exotic superconductivity.

Based on density functional theory, we systematically study the mechanical and electronic properties of monolayer and bilayer SnS2 and SnSe2. The electronic properties of these layers can be significantly tuned by applying in-plane strains and electric fields perpendicular to the sheets. The band gaps of monolayer SnS2 and SnSe2 slightly increase with the in-plane tensile strains, and they start to decrease after critical strains (5% for monolayer SnS2 and 7% for monolayer SnSe2). The band gaps of bilayer SnS2 and SnSe2 have a similar tendency to the monolayers with smaller critical strains (1% for bilayer SnS2 and 2% for bilayer SnSe2), which enables a semiconductor-to-metal transition at 10% strain for bilayer SnSe2. We also find that an external electric field perpendicular to bilayer SnS2 and SnSe2 modulates their electronic band gaps. Semiconductor-to-metal transitions are achieved at the electric fields of 0.27 V/A for bilayer SnS2 and 0.13 V/A for bilayer SnSe2.

Ferroelectric tunnel junction (FTJ) is a promising low power nonvolatile memory for beyond-CMOS applications. In this paper, Co/BaTiO3/SrRuO3 FTJs are fabricated, simulated, and their electrical characteristics are measured by capacitance–voltage ( ${C}$ – ${V}$ ), current–voltage ( ${I}$ – ${V}$ ), and high-frequency S-parameter measurements. Ferroelectricity of the ultrathin BaTiO3 (~3.2 nm) film is first verified by a butterfly shaped hysteresis ${C}$ – ${V}$ profile, from which saturation polarizations are calculated in the ON state and OFF state as ${P}_{ \mathrm{ON}}=+ {20}\,\,\mu {C} / {\text{cm}}^{ {2}}$ and ${P}_{ \mathrm{OFF}}=- {25}\,\,\mu {C}/{\text{cm}}^{ {2}}$ , respectively. The numerical simulation of the FTJ device is performed using experimental electronic band parameters of the heterostructure. The device structure was optimized for ON/OFF ratio, ${I}_{ \mathrm{ON}} / {I}_{ \mathrm{OFF}}= {75}$ for a depolarization field, ${E}_{{dpol}} . The calculated tunnel currents of $ {250}\,\,{nm}\times {250}\,\,{nm}$ FTJ in ON state ( ${I}_{ \mathrm{ON}}= {250}\times {250}^{- {250}}\,\,{A}$ ) and OFF state ( ${I}_{{OFF}}={{1.75}\times {250}}^{{-9}}\,\,{A}$ ) match with experimental values. From the S-parameters of RF measurements, the high-frequency small-signal device model of the FTJ in ON state ( ${C}_{ \mathrm{ON}}= {250}\,\,{fF},{R}_{ \mathrm{ON}}={0.8}\,\,{M}\Omega$ ) and OFF state ( ${C}_{ \mathrm{OFF}}={ {250}}\,\,{fF},{R}_{ \mathrm{OFF}}= {250}\,\,{M}\Omega$ ) is developed for a frequency range from 50 MHz to 5 GHz. The extracted capacitor model of Co/BaTiO3/SrRuO3 FTJ is useful for high-frequency simulation of benchmark FTJ circuits.