eV Direct Band Gap Research Articles

Modulation of electronic and thermal properties of boron phosphide nanotubes under electric and magnetic fields

This work theoretically investigates the thermoelectric properties of boron phosphide nanotubes (BPNTs) using the tight-binding model, Green function method, and Kubo formalism, focusing on a zigzag BPNT with indices (20, 0). The tight binding parameters obtained by matching its band structure with calculated density functional theory band structure. The study examines the effects of transverse electric fields and axial magnetic fields on various physical properties, such as band structure, density of states (DOS), heat capacity, magnetic susceptibility, and other thermoelectric properties. BPNTs consistently show semiconducting properties with a nearly 1 eV direct band gap. The electronic properties of BPNTs are significantly affected by applied electric field, which at very strong strengths can induce a semiconducting to metallic phase transition. In contrast, the magnetic field leads to the splitting of energy bands, especially around the Fermi level. The DOS also changes with the electric field, including variations in the position, intensity, and number of DOS peaks. The thermal properties and thermoelectric performance of BPNTs are temperature-dependent. Increasing of excited electrons thermal energy cause more occupation of high energy levels in the conduction bands. The electric field further enhances the thermal properties of BPNTs by modifying their electronic properties and reducing the band gap. Stronger electric fields cause a noticeable enhancement in the BPNTs thermal properties because it is increasing the concentration of excited charge carriers. This aspect is crucial for improving the thermoelectric efficiency of BPNTs, making them more competitive for practical applications.

Low‐Temperature Synthesis of Stable CaZn2P2 Zintl Phosphide Thin Films as Candidate Top Absorbers

AbstractThe development of tandem photovoltaics and photoelectrochemical solar cells requires new absorber materials with bandgaps in the range of ≈1.5–2.3 eV, for use in the top cell paired with a narrower‐gap bottom cell. An outstanding challenge is finding materials with suitable optoelectronic and defect properties, good operational stability, and synthesis conditions that preserve underlying device layers. This study demonstrates the Zintl phosphide compound CaZn2P2 as a compelling candidate semiconductor for these applications. Phase‐pure, ≈500 nm‐thick CaZn2P2 thin films are prepared using a scalable reactive sputter deposition process at growth temperatures as low as 100 °C, which is desirable for device integration. Ultraviolet‐visible spectroscopy shows that CaZn2P2 films exhibit an optical absorptivity of ≈104 cm−1 at ≈1.95 eV direct bandgap. Room‐temperature photoluminescence (PL) measurements show near‐band‐edge optical emission, and time‐resolved microwave conductivity (TRMC) measurements indicate a photoexcited carrier lifetime of ≈30 ns. CaZn2P2 is highly stable in both ambient conditions and moisture, as evidenced by PL and TRMC measurements. Experimental data are supported by first‐principles calculations, which indicate the absence of low‐formation‐energy, deep intrinsic defects. Overall, this study shall motivate future work integrating this potential top cell absorber material into tandem solar cells.

Probing room temperature indirect and minimum direct band gaps of h-BN

Hexagonal boron nitride (h-BN) has attracted considerable interest as an ultrawide bandgap (UWBG) semiconductor. Experimental studies focused on the detailed near band-edge structure of h-BN at room temperature are still lacking. We report a direct experimental measurement of the near band-edge structure performed on h-BN quasi-bulk wafers via photocurrent excitation spectroscopy (PES). PES resolved the band-to-band transitions near M- and K-points in the Brillion zone (BZ), from which the room temperature indirect band gap of EgMK ∼6.02 eV, minimum direct bandgap at M-point of EgM=6.36eV and next lowest direct energy bandgap at K-point of EgK=6.56eV, have been simultaneously determined for the first time experimentally. The measured energy differences between K- and M-points in the conduction band minimum (CBM) and valence band maximum (VBM) are Δ ECMK=0.54eV and Δ EVMK = 0.34 eV, respectively, in good agreement with the calculation results. Significantly differing from its III-nitride wurtzite counterparts, in which only electrons and holes in the conduction and valence band extremes at the Γ-point are predominantly involved in the optical and transport processes, the results highlighted that charge carriers associated with both M- and K-valleys control to the optical excitation, recombination and charge transport processes in h-BN.

Unveiling the potential of CuAlxGa1−xSe2 (x = 0.25) chalcopyrite as absorbent for photovoltaic application: first-principles insights into the structural, elastic, mechanical, electronic, thermodynamic and optical properties

This study explores the structural, elastic, mechanical, electronic, and optical properties of CuAlxGa1−xSe2 (x = 0.25) chalcopyrite, a crucial material in photovoltaic cells. Utilizing type II-IV-V2 chalcopyrite, widely employed in high-efficiency solar cell production, we employ first-principles calculations with Tran–Blaha-modified Becke–Johnson exchange potential techniques. We aim to determine the band gap and optical properties to understand the compound’s morphology, crucial for solar cell development. Results show CuAlxGa1−xSe2 as a 1.36 eV direct band gap semiconductor. Optical characteristics, including dielectric tensor components and absorption coefficient, are calculated to assess its suitability for solar cell applications. Predictions of Young’s modulus E, Poisson’s ratio ν, bulk B, and shear G moduli provide insight into the crystal’s mechanical behavior. Additionally, phonon, dynamical stability, and thermodynamic properties are discussed, shedding light on the material’s potential in photovoltaic technology.

Optimizing phosphorene nanosheets for high performance all-solid asymmetric supercapacitors: A theoretical and experimental insight

This study probably for the first-time introduced a phase and morphology-tuned scalable, cost-effective method for large-scale production of Black Phosphorous/Phosphorene (BP), and investigated their in-depth electrochemical properties. Utilizing a one-pot mild wet chemical-assisted hydrothermal route in ethylenediamine, high-quality BP nanosheets were synthesized from amorphous red phosphorus (RP) with nearly 100 % conversion efficiency, yielding 7.1352 g for one batch at 130–170 °C. The resulting phosphorene nanosheets exhibited a small crystalline size (2.708 nm), hierarchically porous morphology, a 1.64 eV direct optical bandgap aligned with theoretically calculated bandgap using LDA approximation, and various structural defects, along with large specific surface area (50 m2g−1) and reduced number of layers (4–5) compared to prior literatures, suggesting electrochemical superiority. CV and GCD measurements in the potential window of −0.7 V to 0.1 V revealed its highest pseudo-capacitance response (84.91 %), reaching a maximum specific capacitance value of 759.748 Fg−1 at current density 2 Ag−1, surpassing all previous records. Moreover, BP displayed excellent cyclic stability of 89.8 % after 10,000 cycles, making it an excellent electrode material for supercapacitors. A solid-state asymmetric supercapacitor device (HASD), using BP, successfully lighted up 6 red LEDs for 10 s, achieving maximum specific energy density at 73.43 Wkg−1 at a power density of 1500 Wkg−1.

In vitro and in silico study of biosynthesized silver nanoparticles using Nigella sativa extract against SARS-CoV-2 and Candida albicans

Pathogens that are resistant to multiple drugs, commonly known as superbugs, including viruses and fungi, are posing a significant danger to human health. These superbugs are responsible for causing high rates of morbidity and mortality each year, and the numbers are continuing to rise. Therefore, the search for potent, safe, and viable alternative antimicrobial agents is imperative. In the current study, a rapid and eco-friendly method for synthesizing silver nanoparticles (AgNPs) using Nigella sativa seed extract was developed. Various characterization techniques, including ultraviolet–visible (UV–vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy associated with microanalysis by dispersive energy of X-rays (SEM-EDX), and Zeta-potential, were employed to confirm the formation of AgNPs. Agglomerated particles with a spherical shape and a size of approximately 50 nm were identified in the SEM images of AgNPs. The optical bandgap energy of the AgNPs was determined to be 2.43 eV for direct bandgap and 1.87 eV for allowable indirect band gap. The study also investigated the antiviral activity of AgNPs against the XBB.1.5 SARS-CoV-2 variant and assessed their Anti-Candida Assay against Candida albicans. Furthermore, we conducted molecular docking studies to explore the interactions between AgNPs and the Omicron receptor-binding motif (RBM). The spike protein RBD binds to the receptor angiotensin-converting enzyme 2 (ACE2) human cellular receptor (hACE2) that helps the virus enter the host cell. The results indicated that AgNPs can bind to the spike protein RBD, potentially elucidating their antiviral effects against SARS-CoV-2. The findings of this study suggest that silver nanoparticles (AgNPs) hold promise as potent agents for therapeutic applications, particularly in addressing multidrug-resistant strains of viruses and Candida. However, further research is essential to thoroughly elucidate the mode of action and assess the biosafety of AgNPs.

The physical attributes of rubidium-based Rb2TlRhF6 double perovskite halide: A first-principles investigation

Rubidium cations (Rb+) significantly improve the overall performance of organic-inorganic hybrid perovskite based devices and have gained exceptional attention due to their good thermal and structural stability. In this paper, we have evaluated the physical attributes of rubidium based Rb2TlRhF6 via DFT code using TB-mBJ potential. Structural stability has been confirmed through negative formation energy and calculated tolerance factor. Band structure and TDOS profile confirm semiconductor nature with 3.2 eV direct bandgap at (L-L) symmetry points. A ductile nature with metallic bonding is observed through the investigation of elastic attributes. Optical analysis of Rb2TlRhF6 indicates great absorption in the UV region. Low thermal conductivity and electrical resistivity, along with a high value for power factor, resulted in high ZT value of 0.8 and 800 K. The combined qualities provide a stunning and exciting picture of this compound for use in thermoelectric advanced technologies.

Comprehensive DFT investigation of X2MgSe4 (X = Dy, Tm) spinels for opto-spintronic and thermoelectric devices

Herein, a computational technique known as full potential linearized augmented plane wave (FP-LAPW) is applied for the analysis of magnetic, structural, optical, electronic, and thermoelectric features of X2MgSe4 (X= Dy, Tm) spinels within the density functional theory (DFT). Structural and thermodynamic stabilities are confirmed through the computation of tolerance factor (0.77) and formation enthalpies (-ve) for both spinels. Dy2MgSe4 behaves as a semiconductor with a 1.5 eV direct bandgap (Eg) in the majority spin state but as a metal in the minority spin state, resulting in its half-metallic ferromagnetic (HMF) nature. While Tm2MgSe4 demonstrated a semi-conducting nature in both spin up/down channels, with Eg of 1.41/1.34 eV, respectively. Absorption spectrum displays linear trend with peaks appearing at 6.10 eV for Dy2MgSe4 and 6.46 eV for Tm2MgSe4. Since peaks are appeared in the Ultraviolet (UV) region making them suitable materials for various optoelectronic application, including optical memory devices, sensors and optical filters. The calculated ZT values are 0.77 (at 800 K) and 0.766 (at 300 K), for Dy2MgSe4 and Tm2MgSe4, correspondingly. Overall, the study of X2MgSe4 (X = Dy, Tm) has shown a great potential for their potential usage in energy harvesting and spintronic applications.

Analysing the suitability of CaTiO3/Ca1–xSrxTiO3/SrTiO3 perovskite for fabrication of optoelectronic devices using QuantumATK tool: a study for electronic and optical properties

Calcium Titanate (CaTiO3) as a material has been researched for various applications like those in capacitors, piezoelectric devices and ceramic applications. Same has been possible owing to the exhibition of various characteristics of this material like high melting point (1,625 °C) and dielectric properties. However, only limited studies have been conducted to understand the impact of Strontium (Sr) doping and possibility of adopting this material into any kind of optoelectronic applications. This paper carries on an in-depth analysis on CaTiO3 and study effect of Sr as a dopant on its properties. Analysis has been carried out using Quantum ATK tool based on DFT approximations. CaTiO3 perovskite properties were studied by using the GGA (Generalized Gradient Approximation) and PBE (Perdew–Burke–Ernzerhof) functionals, which are used with the LCAO calculator. As a result of the inclusion of Sr at the Ca site, the electronic band structure of CaTiO3 was changed by the introduction of a gamma point. Bandgap of CaTiO3 was analysed to be dependent on the Sr site concentration and increased from 2.3 eV (Direct bandgap) to 2.3612 eV (Indirect bandgap), when Sr and Ca site concentration were equal, but it decreased with further increase in Sr site concentration to 1.7155 eV. Pure CaTiO3’s projected density of states changed after doping, providing evidence for the effects of the dopant on the system. As a result of an examination of the optical properties of both systems, it is found that CaTiO3 at 380 nm (close to infrared) exhibits an effective extinction coefficient (k) value of 0.78, whereas at 600 nm, the attenuation of light decreases to zero. This makes Sr doping in CaTiO3 another attractive candidate for optical devices in addition to its ability to change optical properties.

In situ tracking the phase change in metastable copper oxide thin film via thermal oxidation

Phase change (PC) materials, such as metal oxides, possess high fundamental and applied importance for modern memory, sensor, and photonic devices. However, revealing the kinetics and mechanisms of PC and achieving the reversible and irreversible PC regimes are still a challenge. Here, we report on 200 nm films of metastable Cu4O3 obtained by magnetron sputtering. In situ structural and optical analyses during air annealing revealed the thermal induced PC from Cu4O3 to CuO. Combination of x-ray diffraction and optical transmittance with heating up to 450 °C allowed us to explore the PC rate and then to correlate it with classical nucleation and crystal growth mechanism. We have also revealed two regimes of PC, possessing reversible 12% (1.42–1.25 eV) and irreversible 220% (1.25–2.75 eV) direct bandgap tuning by temperature. The results, thereby, pave the way for controllable transformation of copper oxide thin films to achieve the desired microstructure and its functionality.

(Invited) Atomic Layer Processing of MoS2

Molybdenum disulfide (MoS2) is one of several transition metal dichalcogenides consisting of a layer of transition atoms sandwiched between layers of chalcogens. Interest in MoS2 has been driven by its 1.8 eV direct electronic band gap in monolayer form and its moderate electron mobility (10-100 cm2/Vs) even when only three atoms (~6.5 Å) thick. These properties offer potential for retaining or improving speed and efficiency in scaled electronic devices.Advancing MoS2 and other 2D materials into high volume manufacturing of semiconductor devices requires scalable deposition and etching processes. The process of atomic layer deposition (ALD) has been used to deposit 2D materials and can deposit films at lower temperatures for back-end-of-line (BEOL) compatibility. However, ALD relies on covalent surface reactions. When these reactions occur at high density during film nucleation, the resulting film is typically amorphous or nanocrystalline and requires thermal annealing to form a more well-ordered layered crystal structure. A key challenge is to establish a low temperature ALD process that achieves a layered crystal structure with low defectivity. In terms of material removal, MoS2 films have been etched by plasma-based atomic layer etching (ALE). ALE is analogous to ALD except that cyclic surface reactions promote volatility and lead to film removal rather than deposition. Together, atomic layer deposition and atomic layer etching constitute complementary facets of atomic layer processing and enable new pathways for nanomanufacturing.Here, we describe our recent progress in thermal ALD and thermal ALE of MoS2 films. For ALD of MoS2, we use cycles of MoF6 and H2S between 150-350 °C. Nucleation on metal oxide surfaces shows a strong temperature dependence, which is attributed in part due to the temperature dependence of surface hydroxyl groups. Density functional theory (DFT) calculations support the role of hydroxyls in promoting nucleation and reveal that MoF6 dissociates on the surface rather than participating in a ligand exchange reaction. The dissociation reaction leads to the formation of a metal fluoride interface between the oxide surface and the MoS2 film. Surface species following MoF6 include MoOF4 and MoO3, both of which convert to MoS2 during the H2S pulse, which releases H2O and HF byproducts. Films deposited at 200 °C and below are amorphous but convert to a layered structure upon annealing in H2S. Deposition at 250 °C yields films with a layered crystal structure without post-deposition annealing.Thermal ALE of MoS2 films deposited by ALD can be achieved using alternating exposures of MoF6 and H2O. It was found that MoS2 films are fluorinated by the MoF6 and then oxygenated by H2O. Volatile byproducts are MoF2O2, H2S, and HF, which are primarily released during the H2O half-cycle. Thermal ALE of MoS2 is temperature dependent and follows Arrhenius behavior. At 200 °C, the mass loss per cycle is 6 ng/cm2 (~0.5 Å/cycle) and reaches 271 ng/cm2 at 300 °C. Etch stop behavior was observed once the etched film approached the metal fluoride interface of the growth surface. Layered MoS2 deposited by ALD with post-deposition annealing exhibited layer-by-layer etching at 0.2 Å/cycle at 250 °C.The ALD results provide key insights into the nucleation and growth of MoS2 films using low temperature ALD. Further work is required to control basal plane orientation but achieving crystalline films well within BEOL thermal budgets is promising. The results from the ALE study provide insights into the etching reactions for MoS2. Combining the two processes offers greater control over MoS2 films. Using ALD followed by ALE and post-deposition annealing, we achieved few-layer MoS2 films. These combined thermal processes represent a pathway for integration of MoS2 films into device manufacturing.

Effect of Pd/Pt decoration on MoSSe monolayer for CH4 signature through surface adsorption mechanism

Considering the current breakthrough in gas sensor technology, we have examined impact of CH4 in the vicinity of pristine MoSSe and Pd/Pt decorated MoSSe monolayers using first principles approach. The negative formation energies confirm structural stability of considered monolayers. The pristine MoSSe monolayer is semiconductor having 1.52 eV direct band gap. This value decreases in the presence of Pd/Pt adatom. Further, adsorption strength of CH4 to monolayers is validated by sensing parameters such as adsorption energy, recovery time, charge transfer and work function. Though we found maximum adsorption energies of − 0.674 and − 0.636 eV for adsorption on Se site of Pd/Pt decorated MoSSe monolayers, the overall sensing response also reveals high sensitivity for Se surface. However, both sites S and Se are favorable for CH4 adsorption. When CH4 is activated on Pd/Pt decorated monolayers, band gaps vary with marginal alterations and transform to direct type. Moreover, optical dielectric response alters strongly in the visible region after activation of CH4 on to Pd/Pt decorated MoSSe monolayers. This result identifies sensitivity response in the presence of methane which may detect CH4 gas easily in visible region. Generally, these interesting results of methane sensing study provoke Pd/Pt decorated MoSSe monolayers to be good sensing nano-device.

High-efficiency photocatalytic degradation of antibiotics and molecular docking study to treat the omicron variant of COVID-19 infection using biosynthesized ZnO@Fe3O4 nanocomposites

In this study, ZnO@Fe3O4 nanocomposite (NC) was synthesized using a green synthesis method with Mentha pulegium leaf extract. Characterization techniques such as UV–vis, FTIR, SEM, TGA, and XRD were employed to confirm the formation of ZnO@Fe3O4 NC and thermogravimetric analysis to evaluate the breakdown of NC in the presence of heat. XRD analysis showed a crystallite size of about 25.59 nm and SEM images of ZnO@Fe3O4 NC revealed spherical-shaped agglomerated particles. The optical bandgap energy of the ZnO@Fe3O4 NC was estimated to be 2.51 eV for direct bandgap and 1.57 eV for allowable indirect bandgap. Photocatalytic activity of the ZnO@Fe3O4 NC was evaluated for the degradation of Amoxicillin, Cephalexin, and Metronidazole antibiotics under sunlight irradiation, showing degradation efficiencies of 71%, 69%, and 99%, respectively, suggesting the potential of ZnO@Fe3O4 NC for removal of antibiotics from waterways. First-principles theory was employed to establish the adsorption energy (Ead) of the antibiotic species, including Amoxicillin, Cephalexin, and Metronidazole, on the surface of ZnO@Fe3O4 nanocomposite, which was found to be −8.064, −8.791, and −21.385 eV, respectively, indicating strong adsorption. Furthermore, molecular docking studies were conducted to upgrade Fe3O4 nanoparticles to ZnO@Fe3O4 NC to enhance composite efficiency. Leveraging the FDA-approved use of Fe3O4 nanoparticles and their known antiviral activity, our docking experiment demonstrated promising results in the interaction between ZnO@Fe3O4 nanocomposite and the spike protein receptor-binding domain of SARS-CoV-2 S Omicron. These findings suggest that ZnO@Fe3O4 nanocomposite could potentially inhibit virus attachment to host cell receptors more stably, providing a promising avenue for further exploration in developing effective medications against SARS-CoV-2.

The synergistic regulation effect on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain

The synergistic regulation effects on the structure and electronic properties of graphene by methane plasma, Stone-Wales defect and equibiaxial strain has been investigated. It is found that the graphene containing Stone-Wales defect (SWG77) has metallicity, when surface adsorbing a CH3+ion, CH3+@SWG77 is a semiconductor with 0.339 eV indirect band gap. The stress-strain curve results indicate that adsorbing different plasma fragments in methane may influence to varying degrees on the ultimate strain of the SWG77 system. The hole mobility has an enhanced tendency as the tensile strain increases for the CH3+@SWG77 system. In addition, the hole mobilities seem to reach saturation when applied equibiaxial strain increase to 2 % or larger. Applying equibiaxial strain on the system substrate, the band gaps of CH3+@ SWG77 and 2CH3+@ SWG77 systems are almost unaffected. In addition, the concentration of CH3+ ion has a certain effect on the light absorption coefficient, reflectivity, and energy loss of the SWG77 system in the visible light region (1.62 eV–3.11 eV) and ultraviolet regions (3.11 eV–5.50 eV). Therefore, defect graphene with appropriate carrier mobility and band gap may be designed by adjusting the equiaxial strain and methyl concentration, which provides useful theoretical support for the development of optical electrical multifunctional electronic devices based on graphene, and is conducive to promoting the application of graphene materials in the field of band gap engineering.

Sunlight-driven photocatalytic degradation of Norfloxacin antibiotic in wastewater by ZnSe microsphere functionalized RGO composite

The release of hazardous pollutants into the water, such as dyes, phenolic compounds, pesticides, different heavy metals, and antibiotics is the primary cause of environmental pollution. The solar energy-based photocatalysis technique has the potential to eliminate pollutants from the aquatic environment. ZnSe is a significant and commendable II-VI group photocatalyst having 2.82 eV direct band gap energy. Its performance towards degrading antibiotics in the presence of light was improved by anchoring it on the Reduced graphene oxide (RGO) matrix. Solution-processable RGO-ZnSe composites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Several spectroscopic studies like Raman spectroscopy, ultraviolet-visible spectroscopy, and photoluminescence spectroscopy were employed to illustrate the optical properties of the composites. The findings demonstrate that the ZnSe microsphere was supported effectively onto the two-dimensional RGO matrix. The performance of as-synthesized RGO-ZnSe composites was assessed based on the photocatalytic degradation of the antibiotic Norfloxacin in the presence of simulated solar light. An optimized RGO-ZnSe composite degrades approximately 83.5% of Norfloxacin in 40 min, while controlled-ZnSe photocatalysis only yields 33% in an identical experimental condition. The optimized RGO-ZnSe achieves the highest degradation reaction rate constant (k) of Norfloxacin (k = 0.057 min−1), and the k value is 4.38 times greater compared to the controlled-ZnSe microsphere. The light-dependent catalytic degradation mechanism was examined by employing scavenger experiments which gave away the responsible reactive radicals. Our results establish that the photo-generated hole has the leading role in the degradation of Norfloxacin in our system. In addition to that, the oxide radical and hydroxyl radical has also an important role in the degradation of Norfloxacin under our experimental condition. The finding suggests that the addition of RGO has enhanced photocatalytic performance and cyclic stability by preventing photo-generated electron-hole pair recombination. The photocatalytic oxidative deactivation mechanism of the Norfloxacin antibiotic was proposed. Our study offers new perceptiveness for the design of efficient solution-processable solar light-responsible photocatalysts for environmental pollution remediation.

A novel and simple approach of rare earth ions (Y3+ and La3+) decorated nano calcium carbonate/ polyethylene glycol for photocatalytic degradation of organic pollutants in wastewater

Pristine and rare earth ions (Y3+ and La3+) decorated rhombohedral nano CaCO3/PEG were extracted from natural dolomite rock using a novel green route biomimetic synthesis. XRD analysis confirmed the crystal phase and doping of Y3+ and La3+ in the CaCO3/PEG. The FTIR analysis confirmed the presence of various functional groups in the synthesized nanoparticles. The obtained products exhibited good thermal stability at the temperatures up to 844 °C. The absorption and emission peaks were blue-shifted due to the impact of the doping ion concentration. The surface chemical compositions were analyzed using XPS. The direct and indirect bandgap energies of nCY1 (0.02 M Y3+: CaCO3/PEG) and nCL1 (0.02 M La3+: CaCO3/PEG) were 3.95, 3.27 eV (direct bandgap) and 2.52, 2.09 eV (indirect bandgap) respectively. The measured fluorescence quantum yields of nCY1 and nCL1 were 22% and 26%, respectively. FESEM with EDX mapping and HR-TEM with SAED analysis was used to determine the morphology, elemental mapping, and crystalline behavior. The photocatalytic activity of prepared samples were performed against methylene blue under UV irradiation. Based on photocatalytic results, nCL1 showed extremely high photocatalytic activity (92%). The effects of the scavenging agents were investigated using superoxide radicals, photogenerated holes, electrons, and OH radicals. Hence, the prepared samples could be an effective catalysts for significant environmental issues. This is the first study for preparing Y3+ and La3+ doped CaCO3/PEG nanoparticles from natural dolomite rock using a low-cost and nontoxic biomimetic method to get enhanced photodegradation efficiency.

Novel Functional Materials of Hydrogen Storage B20N24: A First-Principles Calculation

In this paper, a N-rich B–N polymorph named as B20N24 is proposed through first-principles calculations. The stability of the B20N24 polymorph at ambient conditions is confirmed using the phonon dispersion spectra and the Born stability criteria. Electronic properties calculations show that B20N24 exhibits a semiconducting feature, with a 0.87 eV direct band gap derived from HSE06 functions, which is much lower than many other B–N polymorphs. Specifically, owing to its cage-like framework, B20N24 may be used in hydrogen storage at a capacity of ~6.8 wt.%. The B20N24 polymorph enriches the B–N system theoretically, and this polymorph is promising for use in electronic devices and hydrogen storage.

Local strain engineering in Janus MoSSe nanoribbons induces tunable electronic structures and remarkable magnetic moments

Local strain, as a small degree and single direction strain method, can effectively regulate the structures and electronic properties of armchair Janus MoSSe nanoribbon, so that the system can be transformed from the original 0.467 eV indirect band gap into 0.259 eV (3-zig), 0.117 eV (3-arm), 0.080 eV (6-arm) and 0.139 eV (9-zig) direct band-gap semiconductor according to the different strain degrees and directions. Compared with traditional MoS2 and MoSe2 nanoribbons, Janus MoSSe nanoribbon shows relatively stable band structure under local strain. The structure and electronic properties of Janus MoSSe nanoribbon are anisotropic when the local strain is along different directions. Due to the broken mirror symmetry of the Janus system and the appearance of in-plane local polarization, the spin polarization effect of Janus nanoribbon under local strain is more remarkable. When the local strain degree C = 0.167 is along the zigzag direction and the local strain C ⩾ 0.056 is along the armchair direction, the Janus nanoribbon exhibits half-metallic properties and surprisingly induces a magnetic moment. For the local strain along the armchair direction, the total magnetic moment of the system can be up to 2.05 μB when C = 0.111. A local strain method is applied to the nanoribbon system, which can effectively regulate the geometric configuration and electronic structure without external doping, and introduce magnetism, providing the possibility for expanding nanoribbons as potential nanoelectronic and spintronic materials.

Tunability of silicon clathrate film properties by controlled guest-occupation of their cages.

Type I and type II silicon clathrates are guest-host structures made of silicon polyhedral cages large enough to contain atoms that can be either inserted or evacuated with only a slight volume change of the structure. This feature is of interest not only for batteries or storage applications but also for tuning the properties of the silicon clathrate films. The thermal decomposition process can be tuned to obtain Na8Si46 and Na2<x<10Si136 silicon clathrate films on intrinsic and p-type c-Si (001) wafer. Here, from a unique synthesized NaxSi136 film, a range of resistivity of minimum four order of magnitude is possible by using post-synthesis treatments, switching from metallic to semiconductor behavior as the Na content is lowered. Extended exposition to sodium vapor allows us to obtain fully occupied Na24Si136 metallic films, and annealing under iodine vapor is a way to reach the guest-free Si136, a semiconducting metastable form of silicon with a 1.9eV direct bandgap. Electrical measurements and resistance vs temperature measurements of the silicon clathrate films further discriminate the behavior of the various materials as the Na concentration is changing, additionally shouldered by density functional theory calculations for various guest occupations, further motivating the urge of an innovative pathway toward true guest-free type I and type II silicon clathrates.

Properties of GdSF and phase diagram of the GdF3 - Gd2S3 system

The objectives of this study were to refine the phase diagram of the GdF3-Gd2S3 system and to calculate their liquidus, and to synthesize GdSF and to study their properties. The GdSF compound (ST PbFCl, P4/nmm, a (Å) 3.83006(17), c (Å) 6.8529(3), has an optical band gap for a direct interband transition of 2.56 ​eV and is characterized by a pronounced increase in the Kubelka-Munk function in the region of this transition. Direct optical bandgap of GdSF is measured to be equal to 2.77 ​eV. Two indirect bandgaps are detected to be 1.54 and 2.4 ​eV. Meta-GGA simulations of band structure predicting 1.481 ​eV direct bandgap of GdSF are in good agreement with these features of the experimental absorption spectrum. To explain this complicated case, we argue that formally direct optical transitions to highly dispersive subbands contribute not to direct but to indirect bandgaps measured by Tauc analysis. The GdSF compound melts incongruently with the formation of a melt and γ-Gd2S3 compound at t ​= ​1280 ​± ​2°С, ΔН ​= ​40.6 ​± ​2.8 ​kJ/mol, ΔS ​= ​26.1 ​± ​1.8 ​J/mol∗K. The eutectic has a composition of 13 ​mol.% Gd2S3 (0.74 GdF3 ​+ ​0.26 GdSF), the melting characteristics of the eutectic are 1182 ​± ​2°С, ΔН ​= ​36.2 ​± ​2.5 ​kJ/mol, ΔS ​= ​24.9 ​± ​1.7 ​J/mol∗K. In the system GdF3 - Gd2S3 the balance equations for five phase transformations recorded by the DSC method were compiled. Convergence was achieved in the liquidus of the system constructed according to DSC data and calculated with the use of the Redlich-Kister equation.