Intrinsic Band Gap Research Articles

Boosting photocatalytic antibiotic degradation with simultaneous H2O2 production of g-C3N4 by building dual-dragging force for efficient charge separation

Graphitic carbon nitride (g-C3N4) is a promising candidate for photocatalytic antibiotic degradation with simultaneous H2O2 production. However, g-C3N4 suffers from a high charge recombination and insufficient visible-light absorption. Herein, the benzene-ring and cyano groups were successfully grafted onto the surface of g-C3N4 (BCN-ND) by a simple coupling route involving copolymerization and secondary calcination, which provided a dual-dragging force was generated for the directional separation of photogenerated electrons and holes. The benzene-ring establishes a mid-state slightly above the valence band, which results in a dragging force for holes and extends the response of g-C3N4 to visible light. Moreover, the cyano group exhibits a powerful electron-withdrawing capacity, acting as an electron-dragging force and narrowing the intrinsic bandgap. Therefore, BCN-ND exhibits remarkable photocatalytic activity with a sulfamethoxazole degradation percentage of 99.5 % and simultaneous H2O2 production of 62 μmol/L after 80 min of visible light irradiation. This work provides new perspectives for enhancing photocatalytic activity by constructing of a dual-dragging center for oppositely directional charge separation.

(26.55 %, or 23.69 %)-Limiting Highest Efficiencies, obtained respectively in

In the n+(p+)−p(n) crystalline (X≡ CdTe or CdSe)-junction solar cells at 300K, due to the effects of impurity size, temperature, heavy doping, and photovoltaic conversion, we show that, with an increasing donor (acceptor)-radius rd(a), both the relative dielectric constant and photovoltaic conversion factor decrease, and the intrinsic band gap (IBG) increases, according to the increase in photovoltaic efficiency, as observed in Tables 1-5, being in good accordance with an important result obtained by Shockley and Queisser (1961), stating that for an increasing IBG the photovoltaic efficiency increases. Further, for highest values of rd(a), the limiting highest efficiencies are found to be given in Tables 4, 6, as: 26.55 %, and 23.69 %, obtained in such n+(p+)−p(n) crystalline (CdTe, or CdSe)-junction solar cells at the open circuit voltage Voc=0.82 V, and 0.89 V, respectively, and at T=300 K. Furthermore, from the well-known Carnot-efficiency theorem, as given in Eq. (46), being obtained from the second principle of the thermodynamics, and from the above results of limiting highest efficiencies, the corresponding highest hot reservoir temperatures, TH=408.4 K, and 393.1 K, respectively. Thus, as noted above, ηmax. and TH both increase with an increasing IBG, for each (X≡ CdTe, or CdSe)- crystal at T=300 K≡TC.

Broad spectral response to photon energy unlimited by Schottky barrier from NiSi/Si junction

Recent advances in plasmonic absorption devices offer a novel approach for extending the range of silicon light detection. This is achieved by exploiting the Schottky interface energy barrier, which overcomes the limitation of the 1.12 eV photon energy conversion imposed by the silicon intrinsic bandgap. Internal photoemission has been widely accepted as the primary emission mechanism, which is mostly limited by the Schottky barrier height. However, we have discovered that carriers with energy lower than the Schottky barrier can generate electrical responses through the photothermal effect, breaking this restriction. In this study, we closely investigate two forms of photoresponses, namely photoelectric and photothermal, on a NiSi thin film Schottky photodetector, considering various factors such as temperature, applied bias, incident power, and wavelength regime. Without photothermal assistance, the device achieves a responsivity of 0.41 mA/W to a 1550 nm laser. Under bias-driven conditions, highly energized hot carriers generate a 2.18 μA photoelectric response, while a 0.861 μA photothermal response is simultaneously observed under 6 mW 1550 nm laser illumination. Through systematic investigation, we advance the mechanism of both responses by combining the hot carrier model and the Schottky barrier diagram. Finally, we experimentally obtain a 4.85 μA sheer photothermal response to a 0.475 mW 4-μm wavelength signal with 10.21 mA/W responsivity. It is expected that the device will also show responses to longer wavelengths.

Probing intrinsic magnon bandgap in a layered hybrid perovskite antiferromagnet by a superconducting resonator

Probing intrinsic magnon bandgap in a layered hybrid perovskite antiferromagnet by a superconducting resonator

K7In4As6 and K3InAs2 ‐ Two more Zintl phases showing the rich variety of In‐As polyanion structures

AbstractBinary phases of triel (Tr) and pentel (Pn) elements (III‐V semiconductors) represent a unique compound class due to their tunable intrinsic band gap in dependency of the element combination. We report here on two new compounds in the ternary system K−In−As. In K3InAs2 the edge‐sharing tetrahedral InAs4 units are connected via opposed edges of the tetrahedra forming linear [InAs2]3− chains and are thus iso(valence)‐ electronic with SiS2. In K7In4As6, the InAs4 tetrahedra are connected via neighboring edges of the tetrahedra forming zig‐zag chains. These chains are linked in two directions through dimeric [As3In−InAs3] units. Both reported Zintl phases extend the number of structures that possess the same In−As ratio. In K3InAs2 a one‐dimensional polyanion in contrast to known Na3InAs2 comprising a three‐dimensional polyanion structure is found. K7In4As6 forms together with the known phases K2In2As3 and K3In2As3 a series of Zintl phases with the ratio In : As=2 : 3. Even though the three phases differ only slightly in their valence electron concentration (VEC) of the polyanion, the VECs have a strong influence on the structures. Syntheses, crystal structures and the electronic band structures are reported. The compounds are discussed in the context of the Zintl concept.

Magnetoelastic and Magnetoelectric Coupling in Two-Dimensional Nitride MXenes: A Density Functional Theory Study.

Two-dimensional multiferroic (2D) materials have garnered significant attention due to their potential in high-density, low-power multistate storage and spintronics applications. MXenes, a class of 2D transition metal carbides and nitrides, were first discovered in 2011, and have become the focus of research in various disciplines. Our study, utilizing first-principles calculations, examines the lattice structures, and electronic and magnetic properties of nitride MXenes with intrinsic band gaps, including V2NF2, V2NO2, Cr2NF2, Mo2NO2, Mo2NF2, and Mn2NO2. These nitride MXenes exhibit orbital ordering, and in some cases the orbital ordering induces magnetoelastic coupling or magnetoelectric coupling. Most notably, Cr2NF2 is a ferroelastic material with a spiral magnetic ordered phase, and the spiral magnetization propagation vector is coupled with the direction of ferroelastic strain. The ferroelectric phase can exist as an excited state in V2NO2, Cr2NF2, and Mo2NF2, with their magnetic order being coupled with polar displacements through orbital ordering. Our results also suggest that similar magnetoelectric coupling effects persist in the Janus MXenes V8N4O7F, Cr8N4F7O, and Mo8N4F7O. Remarkably, different phases of Mo8N4F7O, characterized by orbital ordering rearrangements, can be switched by applying external strain or an external electric field. Overall, our theoretical findings suggest that nitride MXenes hold promise as 2D multiferroic materials.

Rational design of hybridized local and charge-transfer (HLCT) emitters towards blue OLEDs with high luminance and low efficiency roll-off

Organic blue emitters have been get more and more attention by scientists and industries in the field of organic light-emitting diodes (OLEDs). The design of efficient blue emitters, especially deep-blue ones, is still a challenge because of their intrinsic wide band-gaps and unbalanced carrier mobilities. Herein, two donor‒π‒acceptor (D‒π‒A) type molecules with phenanthro[9,10-d]imidazole (PI) as A and pyridinyl as π-bridge were designed and synthesized by fine-turning the D moieties, namely mPTPA and mP3PCZ, respectively. Theoretical calculation and single-crystal analysis showed that there exist intramolecular hydrogen bond (IHB) interactions inducing small torsion angles between pyridinyl and adjacent phenyls. The rigid 9-phenyl-9H-carbazole (PCZ) and IHB interactions makes mP3PCZ exhibiting planar configuration along the long-axis of the molecule, which could increase the orbital overlap and oscillator strength (fos). The solvatochromic effect manifested that both two emitters have hybridized local and charge-transfer (HLCT) characteristics, and the excited state of mP3PCZ exhibited LE-dominated HLCT state which is beneficial for high photoluminescence efficiency. Ultimately, the non-doped devices based on mPTPA and mP3PCZ achieved maximum luminance larger than 12000 cd m−2. Furthermore, the doped device based on mP3PCZ exhibited maximum external quantum efficiency of 5.14% with low efficiency roll-off, and with the corresponding deep-blue Commission international de l’éclairage (CIE) coordinate of (0.166, 0.085).

Mixed phase ZnSnN2 thin films for solar energy applications: Insight into optical and electrical properties

Zinc tin nitride (ZnSnN2, ZTN) films synthesized by magnetron co-sputtering at a temperature close to the ZTN decomposition point and with the cation ratio close to stoichiometric have been studied to gain insight into their structural, optical and electrical properties. According to X-ray diffraction and Raman spectroscopy, the samples are polycrystalline with some disorder in the cation sublattice. Hall effect measurements reveal n-type conductivity and very high carrier density above 1019 cm−3. At the lowest carrier density, the mobility achieves the best value ∼19 cm2/(V*s), which is acceptable for device applications. The optical band gap shows a blue shift with increasing electron density, which is related to the increase in tin content and the Burstein-Moss effect. Analysis of the blue shift in terms of the Burstein-Moss effect theory gives a value of 1.43 eV for the intrinsic band gap of ZTN in the mixed-phase state.

Nitrogen vacancies-engineered graphitic carbon nitride nanosheets for boosting photocatalytic H2 production

Defect engineering can be considered a powerful strategy for enhancing photocatalytic performance. Here, we successfully synthesized tri-coordinated nitrogen vacancies-modified graphitic carbon nitride (Nv-GCN) by employing a simple sintering process. The optimized Nv-GCN shows boosted photocatalytic H2 production (5.45 mmol g−1 h−1) in comparison with that of the pristine GCN (0.69 mmol g−1 h−1) under visible light irradiation. It is found that the nitrogen vacancies provide more active sites in photocatalytic reactions. Meanwhile, the electronic structure of Nv-GCN can be modulated by nitrogen vacancies, and defect levels are formed in the intrinsic bandgap. The introduced nitrogen vacancies not only broaden the range of visible-light absorption and narrow the band gap of GCN but also accelerate the separation and transfer of the photogenerated charges. This study provides an effective route for designing high-performance photocatalysts for highly efficient conversion of solar energy.

13.05% (14.82 %) – Limiting Highest Efficiencies Obtained Respectively in n+(p+)-p(n) Crystalline Ge-Junction Solar Cells at T=300 K, Due to the Effects of Impurity Size, Temperature, Heavy Doping, and Photovoltaic Conversion

In the n+(p+)−p(n) crystalline Ge-junction solar cells at 300K, due to the effects of impurity size, temperature, heavy doping, and photovoltaic conversion, we show that, with an increasing donor (acceptor)-radius rd(a), both the relative dielectric constant and photovoltaic conversion factor decrease, and the intrinsic band gap (IBG) increases, according to the increase in photovoltaic efficiency, as observed in Tables 1, 2 and 3, being in good accordance with an important result obtained by Shockley and Queisser (1961), with the use of the second law of thermodynamics, stating that for an increasing IBG the photovoltaic efficiency increases. Further, for highest values of rd(a), the limiting highest efficiencies are found to be given in Tables 2 and 3, as: 13.05 % (14.82 %), obtained in such n+(p+)−p(n) crystalline Ge-junction solar cells at 300 K, respectively. Then, from the well-known Carnot-efficiency theorem, as given in Eq. (47), being obtained by the second principle of thermodynamics, and from those limiting highest efficiencies, the corresponding highest hot reservoir temperatures, TH, are found to be given by: 345.04 K (352.20 K), respectively. In other words, TH also increases with an increasing IBG, being a new result.

Ambipolar Superconductivity with Strong Pairing Interaction in Monolayer 1T'-MoTe2.

Gate tunable two-dimensional (2D) superconductors offer significant advantages in studying superconducting phase transitions. Here, we address superconductivity in exfoliated 1T'-MoTe2 monolayers with an intrinsic band gap of ∼7.3 meV using field effect doping. Despite large differences in the dispersion of the conduction and valence bands, superconductivity can be achieved easily for both electrons and holes. The onset of superconductivity occurs near 7-8 K for both charge carrier types. This temperature is much higher than that in bulk samples. Also the in-plane upper critical field is strongly enhanced and exceeds the BCS Pauli limit in both cases. Gap information is extracted using point-contact spectroscopy. The gap ratio exceeds multiple times the value expected for BCS weak-coupling. All of these observations suggest a strong enhancement of the pairing interaction.

Fabrication of visible-light-driven bulk carbon doped carbon nitride with enhanced photocatalytic activity for tetracycline degradation and mechanism insight

Carbon nitride (CN) has garnered considerable attention in the realm of pollutant treatment. However, the photocatalytic activity of pristine CN is severely restricted due to its limited light absorption and rapid recombination of photoinduced carriers. Herein, a rational configuration of dopant and precursor with similar chemical structure was employed to synthesize C doped CN (CCN) through the copolymerization of 2,4,6-triamine-pyrimidine (TAP) and melamine. The characterization results demonstrate that the incorporation of pyrimidine block from TAP monomer not only realizes nearly homogeneous C doping in bulk, but also controls the doping site accurately. Consequently, it enables the CN to process significant absorption in the visible light region, narrow the intrinsic band gap from 2.73 to 2.53 eV, and enhance separation efficiency of photoinduced carriers. As a result, the CCN as a visible-light-driven photocatalyst shows markedly enhanced photocatalytic activity compared with pristine CN in the degradation of tetracycline. The degradation rate constant of the optimal CCN is almost 6.30 times that of pristine CN under visible light. Moreover, the cyclic experiments reveal the favorable stability of CCN. In addition, •O2− and h+ responsible for the degradation of tetracycline are demonstrated by trapping experiments and electron spin resonance analysis. The work provides a straightforward and impactful copolymerization strategy to achieve bulk doping and control doping position within the CN framework for ameliorating the photoelectrical properties and photocatalytic activity.

Green Synthesis and Characterization of Magnesium Oxide Nanoparticles from Leaf Extracts of Amaranthus retroflexus and Azadirachta indica

Among plant extracts, neem leaf extract was found effective for successful synthesis of MgO nanoparticles. The main phytochemicals present in neem leaf extract acts as reducing and capping agents for synthesis of MgO nanoparticles. The bio reduced MgO nanoparticles were characterized by using surface plasmon resonance analysis (UV–Vis spectroscopy), particle size and distribution analysis (PSA), surface morphology analysis (SEM) and elemental distribution analysis (EDX). The UV–Vis spectral analysis confirmed that the maximum absorption at 279 nm range corresponds to the intrinsic band gap of MgO nanoparticles. Particle size analyzer confirmed synthesized particles are of nanoscale i.e., 48.1 nm. SEM images confirmed synthesized nanoparticles were found to be relatively oval shaped and EDX confirmed peak is of MgO nanoparticles. This is a simple and effective method which could be an alternative for chemical and physical methods for the large-scale production of MgO nanoparticles.

Self-powered photodetectors based on Er-doped MoS2 film for NIR photo-communication and laser calibration

Molybdenum disulfide (MoS2) is a promising two-dimensional material for optoelectronic applications owing to its strong light–matter interactions, high carrier mobility, and ability to combine with other materials. However, the intrinsic bandgap (1.3–1.8 eV) of MoS2 limits its applications in the near-infrared (NIR) region. Herein, a heterojunction NIR photodetector based on the Er-doped MoS2 film is developed. The photodetector presents self-powered NIR response with a fast rise/fall time of ∼9.2 μs/∼168 μs and a high detectivity of ∼3.25 × 1010 Jones at 980 nm. The high performance of the device is attributed to the improved separation of the photogenerated electron–hole pairs and the characteristic trapping capacity induced by Er dopants. Density functional theory calculations reveal that Er-doping introduces an additional energy level in the forbidden band of the MoS2:Er, and the Er-f electron orbital locates near its Fermi energy level, both of which contribute to the formation of photogenerated carriers. The MoS2:Er-based device with a 3-dB bandwidth of 5.4 kHz exhibits promising application potential in the NIR photo-communication field. Moreover, the laser calibration application of the high-performance photodetector is demonstrated. This work not only develops an effective strategy to enhance the NIR photoresponse of MoS2 films but also extends the application of MoS2-based devices.

Introduction of localized spin-state transitions in the optical absorption spectrum of Cr-doped GaN

Using a hybrid density functional, we study the electronic, magnetic, and neutral excitations of the paradigmatic Cr-doped GaN solid. Our results indicate that the $\ensuremath{\approx}1$% doped wurtzite GaN crystal retains the semiconducting nature of the host, associated with a magnetic moment of 3 ${\ensuremath{\mu}}_{B}$. As a consequence of Cr doping, additional hybridized bands are formed within the intrinsic band gap of GaN, leading to a considerable band gap narrowing by 1.4 eV and low-energy optical transitions. Our results indicate dark Cr $d\text{\ensuremath{-}}d$ transitions at very low energy (0.5--0.7 eV), followed by bright transitions in the visible energy range (1.8--2.2 eV). Characterization of the electron-hole pairs suggests that the latter originates from the internal transitions among hybridized ${\mathrm{Cr}}_{d}\text{--}{\mathrm{N}}_{p}$ states. With the existence of these additional optical features within the visible energy window, one can expect an enhancement to the photoelectric conversion efficiency of GaN upon Cr doping, in addition to applications in spintronics.

Effect of impurity distribution on optical properties of Cr-doped ZnSe nanowires: A first-principles study

In this study, we used first-principles calculation methods to investigate the effects of Cr doping at different positions on the electronic and optical properties of ZnSe nanowires. We found that the bandgap of the nanowires is larger than that of the bulk. After doping, it was found that the easiest doping position is on the surface, while all positions require heating for doping. After doping, the change in the intrinsic bandgap was very small, and a large number of defect bands appeared in the middle of the intrinsic bandgap, which are mainly composed of Cr(d) orbital electrons, Se(p) orbital electrons, and d-p hybridized bands. The doping of Cr atoms also affects the distribution of LUMO and HOMO. In the parallel direction of the nanowires, the absorption spectrum exhibits a prominent absorption peak near 0.8 eV, which is caused by transitions between defect bands. Therefore, Cr-doped ZnSe (111) nanowires doped at radius ½ positions are more suitable as mid-infrared laser gain materials.

Comparing supercapacitors with graphene/graphyne electrodes and [Bmim][PF6], [Emim][BF4], [Ch][Gly] and [Pyr][Tfsi] ionic liquids using molecular dynamics

Two-dimensional carbon materials, such as graphene and graphyne, have been very relevant in the context of energy storage applications. Such materials have unique physical, chemical and electronic properties. Graphyne, in particular, exhibits even more remarkable properties related to its larger specific area, greater electronic mobility, and its intrinsic band-gap. In this work, we present a series of results from an extensive set of atomistic molecular dynamics simulations that compare the efficiency of these two materials as electrodes in electric double layer capacitors. Although there is already a considerable volume of work on graphene and graphyne, an extensive comparison of their performances in energy storage applications under thermodynamic conditions has not yet been presented. Here our simulations investigate the electrostatic properties of eight different supercapacitors, four of which are graphene and the other graphyne, in different electrolytes. A detailed analysis of the energetic and electrostatic of these is reported for all systems. The performance of the supercapacitors is described in terms of their electrode capacitance, providing a set of results that indicate the superiority of the graphyne electrode over the graphene electrodes.

Ab Initio Dynamics of Graphene and Graphyne Electrodes in Vacuum and in the Presence of Electrolytes

Graphene and graphyne electrodes are both relevant for electrochemical energy storage applications due to their unique physical, chemical, and electronic properties. Graphyne has been considered even more attractive than graphene due to its larger specific surface area, greater electronic mobility, and intrinsic band gap. The analyses presented here reveal relevant features of graphyne in an interaction with an electrolyte that can be useful for practical applications. Although there is already a considerable volume of work on graphyne, the analysis of its properties taking into account the dynamics of its network and the interaction with the condensed medium has not yet been presented. In this work, ab initio molecular dynamics simulations were performed to study the energetic, structural, spectroscopic, and electronic properties of graphene and graphyne electrodes in vacuum and in the presence of an electrolyte (EMIM-BF4). A detailed analysis of the electrode–electrolyte interaction is reported for both systems. Structural features are presented in terms of both radial and spatial distribution functions and angular orientation distributions. Power spectral analyses and molecular orbital maps provided important insights into the intermolecular interactions in graphene and graphyne systems, describing the main differences as well as revealing similarities between them.

Theoretical insight into optical properties of ZnGa2O4 transparent ceramic

The spinel-type ZnGa 2 O 4 transparent ceramic with extremely wide infrared transmission range exhibited great potential applications in numerous fields. Based on the comparative study with MgAl 2 O 4 and ZnAl 2 O 4 , the optical properties of ZnGa 2 O 4 transparent ceramic in the entire wavelength range from ultraviolet to infrared were theoretically investigated by first-principles calculations. With the in-depth understanding of crystal, electronic, phonon structures and chemical bonding, the origin of the variations in the optical properties was clarified. Due to the inherent 3d 10 electronic configuration in both Zn and Ga, the significant p-d hybridization between Zn/Ga 3d states and O 2p states resulted in a smaller band gap and a higher refractive index of ZnGa 2 O 4 . The weaker tetrahedral Zn-O bond led to ZnGa 2 O 4 considerably broaden its infrared transmission range. The easily formed oxygen vacancy defect coupled with the intrinsic narrow band gap may provide opportunities for new functionalization of ZnGa 2 O 4 transparent ceramic. The comprehensive insight also offers guidance for designing novel transparent ceramics with desired optical properties. • Significant O 2p-Zn/Ga 3d hybridization resulted in a smaller band gap and a higher refractive index of ZnGa 2 O 4 . • Effective charge calculated from phonon frequency was used to evaluate the covalency of chemical bonds. • Weaker Zn-O bond and heavier cationic masses broaden infrared transmission range of ZnGa 2 O 4 . • Oxygen vacancy was easily formed in ZnGa 2 O 4 and defect level was generated in band structure.

Understanding the hydrogen evolution reaction activity of doped single-atom catalysts on two-dimensional GaPS4 by DFT and machine learning

As a zero-carbon fuel, hydrogen can be produced via electrochemical water splitting using clean electric energy by the hydrogen evolution reaction (HER) process. The ultimate goal of HER catalyst is to replace the expensive Pt metal benchmark with a cheap one with equivalent activities. In this work, we investigated the possibility of HER process on single-atom catalysts (SACs) doped on two-dimensional (2D) GaPS4 materials, which have a large intrinsic band gap that can be regulated by doping and tensile strain. Based on the machine learning regression analysis, we can expand the prediction of HER performance to more catalysts without expensive DFT calculation. The electron affinity and first ionization energy are the two most important descriptors related to the HER behavior. Furthermore, constrain molecular dynamics with solvation models and constant potentials were applied to understand the dynamics barrier of HER process of Pt SAC on GaPS4 materials. These findings not only provide important insights into the catalytic properties of single-atom catalysts on GaPS4 2D materials, but also provides theoretical guidance paradigm for exploration of new catalysts.