Defect Energy Research Articles

Simultaneous defect passivation and energy level modulation by multifunctional phthalocyanine for efficient and stable perovskite solar cells

Interface passivation is an effective means to decrease detrimental defects and realize highly efficient and stable perovskite solar cells (PSCs). Nevertheless, most of the interfacial passivators currently used are easily formed mismatched energy levels and impede the extraction of photogenerated charge carriers. Herein, a metal-free H2-phthalocyanine (H2Pc) is reported to passivate the interface defects and improve the crystallinity and energy level alignment. Contrasting metal Zn-phthalocyanine, the pyrrolic nitrogen and NH bond in the structure of the H2Pc molecule exhibit a higher capability to interact with unsaturated Pb and I site. It is found that the defects passivation and improved crystallinity in H2Pc molecule treatment are achieved by the formation of coordination bonding between N atoms and uncoordinated Pb2+ ions and hydrogen bonding between NH bond and I (iodine). Simultaneously, the H2Pc treatment can also improve energy level alignment and promote the charge extraction from perovskite to the hole transport material layer. As a result, a champion power conversion efficiency (PCE) of 20.59 % is achieved for the H2Pc PSCs, which is higher than that of 18.54 % for the ZnPc PSCs and 16.50 % for the pristine PSCs. Meanwhile, the H2Pc device shows significantly improved moisture, thermal, and illumination stability and with retaining over 90 % of its initial PCE after aging for 1000 h at about 20 % relative humidity in ambient conditions. The present work provides a practical and efficient method of simultaneous defect passivation and energy level modulation and toward the purpose of attaining superior performance PSCs and other perovskite-based electronics.

Passivation effect of theophylline on the surface defects of MAPbI3 perovskite

Employing molecular passivators to reduce defect density of perovskite surface is an effective way to improve the stability and photovoltaic performance of perovskite solar cells. Herein, the passivation effect and mechanism of theophylline molecule on the defects of MAPbI3 (001) surface were investigated by first-principles calculations based on density functional theory. Our results reveal that the theophylline can stably absorb on the MAPbI3 surface. Two passivation modes: defect-inhibiting mode and defect-healing mode, are proposed to describe the passivation mechanism. In the defect-inhibiting mode, the theophylline adsorbed on the MAPbI3 surface leads to the increase of formation energies of most defects, suppressing the generation of defects. In the defect-healing mode, the adsorption of theophylline on the defect site of MAPbI3 surface can effectively eliminate or weaken the defect impurity states in the bandgap, consequently healing the defects. Hence, incorporating theophylline molecule into MAPbI3 perovskite film is an effective strategy to passivate surface defects and improve the stability and performance of perovskite solar cells.

Near-Infrared Emission Material with Superlong Afterglow Performance and Its Multifunctional Applications.

A new near-infrared (NIR) emission material, BaSi1.5Ge2.5O9:Cr3+, with outstanding long afterglow properties is designed and synthesized successfully. Its structure, photoluminescence, and long afterglow emission features are studied in detail. Cr3+ occupies six-coordinated Ba2+ and Ge4+ sites in this system, which can emit characteristic broadband NIR light in the range of 700-1200 nm, and it has a long afterglow emission of more than 10 h. We calculated the band gap of the host at about 4.1 eV, the energy level distribution after Cr3+ doping, and the distribution of oxygen vacancies through density functional theory simulation, which theoretically proved the characteristic transition of Cr3+ and that the oxygen vacancies are crucial to form the defect energy levels. This is corroborated with the reflectance spectra, three-dimensional thermoluminescence spectra, and electron spin resonance (ESR) spectra. The oxygen-deficient environment favors the formation of oxygen vacancy defects and prevents the oxidation of Cr3+ to Cr6+, which are the key points for the luminescence and afterglow properties. A mechanistic model of defect formation and electron trapping and transport processes is successfully established. Finally, its multifunctional applications in information anticounterfeiting encryption, biological tissue penetration, and internal nondestructive testing and imaging are demonstrated.

Defect physics in 2D monolayer I-VII semiconductor AgI

As a brand new two-dimensional (2D) material with promising electronic properties, monolayer I-VII silver iodide (AgI) has the potential for future 2D electronic devices. To advance the development of such devices, the exploration of n-type and p-type conductivities of AgI is indispensable. With first-principles calculations, we systematically investigate the properties of intrinsic defects and extrinsic dopants in monolayer AgI, including atomic structural pictures, formation energies, and ionization energies to offer carriers. Considering the divergence in energies of charged defects in 2D materials when the traditional jellium scheme is used, we adopt an extrapolation approach to overcome the problem. The Ag vacancy (VAg) and Be substitution on Ag site (BeAg) are found to be the most promising p-type and n-type doping candidates, respectively. They could provide bound carriers for transport through the defect-bound band edge states, although the ionization energies are still larger than thermal energy at room temperature. Furthermore, negative-U behaviors are demonstrated in I vacancy (VI), Zn substitution on Ag site (ZnAg), and Cd substitution on Ag site (CdAg). The present work, for the first time, offers a detailed study of the defect physics in 2D I-VII monolayer semiconductor, laying the foundation for subsequent physics and device explorations based on these brand new 2D materials.

Intrinsic defects on α, γ and δ-CsPbI3 (001) surfaces and implications for the α/γ to δ phase transition.

Compared with traditional organic-inorganic hybrid perovskites, CsPbI3 is considered to be a better solar photovoltaic absorption material. However, under environmental conditions, it will undergo the phase transition from the α phase to the γ phase and finally to the non-perovskite phase (δ), especially in a humid environment. Considering the important role of surface intrinsic defects in the phase transition process, we investigated the intrinsic defects on α, γ and δ-CsPbI3 (001) surfaces by first-principles calculations based on density functional theory (DFT). The formation energy of most defects on the surface is similar to that in the bulk in all three phases except for VPb and VI. The formation energy of VPb and VI on the α-CsPbI3 (001) surface is significantly increased, and the formation energy of VPb on the γ-CsPbI3 (001) surface is also increased, due to the relaxation and distortion of the surface Cs and the Pb-I octahedron. The formation energy of interstitial defects on the α-CsPbI3 (001) surface is the lowest due to the remaining large dodecahedral void, even though the Pb-I octahedron distortion has largely enhanced the stability of the α-CsPbI3 (001) surface. The formation energy of VCs is the lowest in all three phases, indicating that Cs ions in CsPbI3 are indeed flexible in CsPbI3. The results are expected to provide a theoretical basis and guidance for the stability improvement of all-inorganic halide perovskites especially in a humid environment.

COUPLED CRYSTAL PLASTICITY PHASE-FIELD MODEL FOR DUCTILE FRACTURE IN POLYCRYSTALLINE MICROSTRUCTURES

A wavelet-enriched adaptive hierarchical, coupled crystal plasticity, phase-field finite element model is developed in this work to simulate crack initiation and propagation in complex polycrystalline microstructures. The model accommodates initial material anisotropy and crack tension-compression asymmetry through orthogonal decomposition of stored elastic strain energy into tensile and compressive counterparts. The crack evolution is driven by stored elastic and defect energies, resulting from slip and hardening of crystallographic slips systems. A finite element model is used to simulate the fracture process in a statistically equivalent representative volume element reconstructed from electron back-scattered diffraction scans of experimental microstructures. Multiple numerical simulations with the model exhibits microstructurally sensitive crack propagation characteristics.

Imperfections are not 0 K: free energy of point defects in crystals.

Defects determine many important properties and applications of materials, ranging from doping in semiconductors, to conductivity in mixed ionic-electronic conductors used in batteries, to active sites in catalysts. The theoretical description of defect formation in crystals has evolved substantially over the past century. Advances in supercomputing hardware, and the integration of new computational techniques such as machine learning, provide an opportunity to model longer length and time-scales than previously possible. In this Tutorial Review, we cover the description of free energies for defect formation at finite temperatures, including configurational (structural, electronic, spin) and vibrational terms. We discuss challenges in accounting for metastable defect configurations, progress such as machine learning force fields and thermodynamic integration to directly access entropic contributions, and bottlenecks in going beyond the dilute limit of defect formation. Such developments are necessary to support a new era of accurate defect predictions in computational materials chemistry.

In situ dipole formation to achieve high open-circuit voltage in inverted perovskite solar cells via fluorinated pseudohalide engineering.

Many studies have shown that the severe photoluminescence quantum yield (PLQY) loss at the interface between the perovskite and electron transport layer (ETL) is the main cause of voltage loss in inverted perovskite solar cells (p-i-n PSCs). However, currently there are no effective in situ passivation techniques to minimize this nonradiative recombination. Here, the fluorinated pseudohalide ionic liquid (FPH-IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) is introduced into the perovskite precursor formulation. EMIMTFSI can change the dielectric environment and energy-level arrangement of the perovskite by accumulating on the top surface and spontaneously forming dipoles. As a result, the excitonic binding energy (Eb) and nonradiative recombination loss are significantly reduced. At the same time, TFSI- reduces the formation energy of vacancy defects and stabilizes the perovskite phase by forming N-H⋯F hydrogen bonds between FA+ and the C-F bond in EMIMTFSI. Finally, the EMIMTFSI-modified p-i-n PSCs achieve an excellent efficiency of 24.81% with an impressive open-circuit voltage of 1.191 V for a 1.57 eV low-bandgap perovskite. In addition, the modified devices can maintain more than 95% PCE after continuous thermal aging at 85 °C for 500 h or illumination at the maximum power point for 800 h. This work provides a new idea for minimizing the non-radiative recombination losses in p-i-n PSCs.

The Mystery and Clarity of Leonardo da Vinci's Coefficient of Friction

The science of friction has been using the coefficient of friction as the main quantitative characteristic of the friction process for more than five centuries. The concept of the coefficient of friction as a characteristic of the resistance to the movement of rubbing surfaces in a hidden form was formulated by Leonardo da Vinci: "Each rubbing body exerts a friction resistance equal to one quarter of its weight, provided that the flat plane is in contact with the polished surface". Two centuries later, the coefficient of friction appeared explicitly, in the form of a formula, in the works of G. Amontons. It is clear that the coefficient of friction is a convenient friction parameter, easily determined in the experiment. However, what is the physical meaning of resistance to the movement of rubbing surfaces? Modern engineering believes that the coefficient of friction has no physical meaning. Thermodynamic analysis of the friction process is performed. The evolutionary patterns of the behavior of the friction contact are shown. A structural-energy interpretation of the logic of the coefficient of friction (resistance) is proposed: accumulation of potential energy of defects in the crystal structure of the deformable volume by friction contact. The static potential energy of the formed defects in the crystal structure of the contact is a measure of the decrease in the kinetic energy of the relative motion of the rubbing surfaces. Such a formulation of resistance to movement under friction has a deep physical and clear meaning for a scientist and engineer. The substantiation of Leonardo da Vinci's formulation of friction that the friction resistance should be equal to 0.25 is given. The interpretation of this rule is given for the case of friction in mechanisms (machines).

Multicolor and multimode luminescence regulation and anti-counterfeiting application of lanthanide ions doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors

Multicolor and multimode luminescence materials have important applications in the field of information security encryption. However, the design and synthesis of multicolor multimode luminescent materials is still a challenge, and only several materials have been reported. In this paper, a series of single doped and double doped Li<sub>1–<i>x</i></sub>K<sub><i>x</i></sub>NbO<sub>3</sub>:Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup> phosphors are prepared by high temperature solid state method. The structure, morphology, optical properties and thermoluminescence (TL) spectra are characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), luminescence spectrometer and self-made heating device. Firstly, the effects of different values of K<sup>+</sup> content on the luminescence and trap distribution of LiNbO<sub>3</sub> materials are studied. The results show that the ionic lattice is distorted when a small quantity of K<sup>+</sup> ions replace Li<sup>+</sup>. With the addition of K<sup>+</sup>, the photoluminescence excitation (PLE) spectra monitored emission of 620 nm shows that the ratios of the absorption peaks from matrix (200–310 nm) to absorption peaks from the intrinsic transition of Pr<sup>3+</sup> ions 4f→5d (310–430 nm) change significantly, showing a double-peak characteristic. When the concentration of K<sup>+</sup> ions is 0.5, the absorption peak from the matrix disappears, which may be due to the phase transition of the matrix lattice caused by excessive K<sup>+</sup> ions or the introduction of a large number of defect energy levels into the matrix lattice. Moreover, K<sup>+</sup> ion doping can regulate the density and distribution of traps. TL curves show that a small quantity of K<sup>+</sup> doping increases the trap density of shallow traps. When a large quantity of K<sup>+</sup> is doped, the phase changes of matrix lattice and the defect density decrease. Secondly, the doping of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> matrix by different luminescent centers (Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup>) is studied. The results show that the multicolor luminescence emission in red, blue and green bands and the tunable multimode luminescence (up/down conversion luminescence, afterglow luminescence and photo-stimulated luminescence) are realized by the selective excitation. According to the multicolor and multimode characteristics of the phosphors, a butterfly-shaped anti-counterfeiting pattern is designed. Owing to the different energy level positions of the luminescence centers, dynamic multicolor photoluminescence is realized by selective excitation at different wavelengths. Based on the upconversion luminescence characteristics of Er<sup>3+</sup> and the excellent afterglow characteristics of Pr<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> material, the designed anti-counterfeiting pattern shows the dynamic color change and multicolor, multimode high-order anti-counterfeiting application.

Bismuth nanoparticles and oxygen vacancies synergistically modified HNb3O8 nanosheets for enhanced photocatalytic N2 reduction towards NH3.

Due to the high stability of the N2 molecule and the low charge separation efficiency, the photocatalytic reduction of N2 to high-value chemicals (NH3) under mild conditions remains a great challenge. Herein, a composite photocatalyst (Bi/HNb3O8-Vo nanosheets) with Bi nanoparticles modified the HNb3O8-Vo nanosheets are designed for the conversion of N2 into NH3. In this design, the introduction of oxygen vacancies on the catalyst surface facilitates the formation of defective energy levels within the band gap of HNb3O8-Vo NS, which promotes the absorption of visible light, and enhances the charge carrier transport and separation. Bi nanoparticles co-catalyst not only facilitates the separation and migration of photogenerated charges, but also acts as reaction sites to adsorb and activate N2 molecule. Consequently, the optimized 5% Bi/HNb3O8-Vo photocatalysts show a NH3 yield of 372.7μmol/L g-1h-1 under full spectral irradiation without sacrificial agent, which is much higher than that of HNb3O8 NS (92.2μmol/L g-1h-1). This work provides a new way for the design of efficient N2 reduction photocatalysts through the synergistic effect of surface vacancies and metal co-catalysts.

Highly efficient and robust multi-color afterglow of ZnO nanoparticles.

Room temperature phosphorescence (RTP) materials are widely used in various fields. However, the realization of multicolor RTP via facile approaches still remains a great challenge. In this study, we propose an in situ hydrolysis method using different solvents to synthesize blue, green, and yellow phosphorescence ZnO/SiO2 composites. By investigating the photoluminescence (PL) and phosphorescence mechanisms of ZnO/SiO2 composites, it is discovered that the solvents not only introduce impurities to ZnO but also affect the position of defect energy levels, leading to the variation in luminescent performance. Meanwhile, the as-synthesized ZnO/SiO2 composites exhibit stable PL and phosphorescence under extreme conditions. Specifically, the PL and phosphorescence properties of the composites are well maintained at high temperature (523 K) or underwater. Owing to the multicolor phosphorescence properties of these ZnO/SiO2 products, herein, we demonstrate that ZnO/SiO2 composites can act as new smart materials for information encryption, fingerprint identification, and white light-emitting diodes (WLEDs).

Bluish-green afterglow and blue photoluminescence of undoped BaAl2O4.

Undoped BaAl2O4 was derived via sol-gel combustion technique. The afterglow and photoluminescence (PL) properties of undoped BaAl2O4 were explored with the combination of experiments and density functional theory (DFT) calculations. Undoped BaAl2O4 is found to display bluish-green afterglow that is discernible to naked eye in dark for about 20 s. The broad afterglow spectrum of undoped BaAl2O4 is peaked at around 495 nm. As a contrast, the broad PL spectrum of undoped BaAl2O4 can be decomposed into a bluish-green PL band peaking at about 2.53 eV (490 nm) and a blue PL band centered at about 3.08 eV (402.6 nm). DFT calculations indicate that the defect energy levels generated by oxygen and barium vacancies are critical to the afterglow and PL of undoped BaAl2O4. This work demonstrates that the oxygen and barium vacancies in undoped BaAl2O4 are liable for the bluish-green afterglow and blue PL of undoped BaAl2O4. The recorded bluish-green afterglow of BaAl2O4 is particularly important to understand the afterglow mechanisms of rare-earth doped BaAl2O4.

Unveiling sub-bandgap energy-level structures on machined optical surfaces based on weak photo-luminescence.

Sub-bandgap defect energy levels (SDELs) introduced by the point defects located in surface defect areas are considered the main factors in decreasing laser-induced damage thresholds (LIDTs). The suppression of SDELs could greatly increase LIDTs. However, no available method could detect SDELs, limiting the characterization and suppression of SDELs. Herein, a self-designed photo-luminescence detection system is developed to explore the weak transient-steady photo-luminescence properties of machined surfaces. Based on the excitation laser wavelength dependence of photo-luminescence properties, a sub-bandgap energy-level structure (SELS) containing SDELs is unveiled for the first time. Based on the developed mathematical model for predicting LIDTs, the feasibility of the detection method was verified. In summary, this work provides a novel approach to characterize SDELs on machined surfaces. This work could construct electronic structures and explore the transition behaviors of electrons, which is vital to laser-induced damage. Besides, this work could predict the LIDTs of the machined surfaces based on their PL properties, which provides convenience for evaluating the LIDTs of various optical elements in industrial production. Moreover, this work provides a convenient method for raising the LIDTs of various optical elements through monitoring and suppressing the SDELs on machined surfaces.

Ni-doped hybrids of TiO2 and two-dimensional Ti3C2 MXene for enhanced photocatalytic performance

Transition metal ion doping is an effective strategy by which to enhance the photocatalytic activity of semiconductor materials. Herein, Ni-doped TiO 2 /Ti 3 C 2 photocatalysts were designed and fabricated using a simple dipping method and their catalytic performance was verified via the degradation of rhodamine B (RhB). Ni doping induces the formation of a defect energy level in TiO 2 , which shortens the transition distance of photogenerated electrons. Ti 3 C 2 acts as a hole acceptor, which is conducive to the transfer of photogenerated charge. The results show that the Ni-doped TiO 2 /Ti 3 C 2 heterojunction structure exhibits the lowest photoluminescence peak intensity, the highest instantaneous current, and excellent photocatalytic performance compared to TiO 2 /Ti 3 C 2 and TiO 2 . At optimal Ni content, the removal efficiency of RhB is 90%, around 3.7 times higher than that of pure TiO 2 . This work details the preparation of an excellent Ni-doped heterojunction structure for enhanced photocatalytic performance, demonstrating an effective strategy by which to improve the charge separation ability. • Ni-doped hybrids of TiO 2 and Ti 3 C 2 MXene structure was prepared for enhanced photocatalytic performance. • The charge separation ability of TiO 2 was enhanced due to the doping of Ni and the coupling of co-catalyst Ti 3 C 2 . • The removal efficiency of RhB by Ni–TiO 2 /Ti 3 C 2 was 3.7 times higher than that of pure TiO 2 .

Probing into the conduction band and type of carriers/traps on red/orange persistent phosphors in vacancy & solid-solution induced (Sr/Ba)1-xCaxGe4-yO9:Mn2.

Long-wavelength afterglow has been a key issue in the investigation of afterglow materials. Herein, the orange/red (Sr/Ba)1-xCaxGe4-yO9:0.01Mn2+ is prepared by the introduction of vacancy induction and solid solution. The (Sr/Ba)Ge4O9:Mn2+ hardly possesses an afterglow phenomenon and exhibits only red/orange photo-luminescence (PL) attributed to the d-d transition of Mn2+, while samples with reduction of the Ge4+ content and with replacement by Ca2+ show bright afterglow emission with the peak located at about 612 nm/620 nm. The emerging broadband peak comes from charge transfer involving Mn2+ and nearby defect clusters and the bottom of the conduction band (CB). The introduction of V''''Ge creates a defective energy level above the valence band, but the ground state energy difference with Mn2+ is too large (>1 eV) to allow hole transfer, which was confirmed by ultraviolet photoelectron spectroscopy (UPS), spherical aberration-corrected transmission electron microscopy (AC-STEM), charge differential density (CDD) analysis, electron paramagnetic resonance (EPR) analysis, etc. With this achievement, we propose an original design strategy for long-wavelength afterglow and a more reasonable afterglow mechanism, which is of great importance for the investigation of long-wavelength afterglow materials.

Host-Guest Chemistry in Boron Nitride Nanotubes: Interactions with Polyoxometalates and Mechanism of Encapsulation.

Boron nitride nanotubes (BNNTs) are an emerging class of molecular container offering new functionalities and possibilities for studying molecules at the nanoscale. Herein, BNNTs are demonstrated as highly effective nanocontainers for polyoxometalate (POM) molecules. The encapsulation of POMs within BNNTs occurs spontaneously at room temperature from an aqueous solution, leading to the self-assembly of a POM@BNNT host-guest system. Analysis of the interactions between the host-nanotube and guest-molecule indicate that Lewis acid-base interactions between W═O groups of the POM (base) and B-atoms of the BNNT lattice (acid) likely play a major role in driving POM encapsulation, with photoactivated electron transfer from BNNTs to POMs in solution also contributing to the process. The transparent nature of the BNNT nanocontainer allows extensive investigation of the guest-molecules by photoluminescence, Raman, UV-vis absorption, and EPR spectroscopies. These studies revealed considerable energy and electron transfer processes between BNNTs and POMs, likely mediated via defect energy states of the BNNTs and resulting in the quenching of BNNT photoluminescence at room temperature, the emergence of new photoluminescence emissions at cryogenic temperatures (<100 K), a photochromic response, and paramagnetic signals from guest-POMs. These phenomena offer a fresh perspective on host-guest interactions at the nanoscale and open pathways for harvesting the functional properties of these hybrid systems.

Plasma surface treatment facilitated visible light-driven H2 production over TiO2

TiO2 precursors were treated by plasma technology in three atmospheres (N2, Ar, H2). Interstitial N-doping can be facilely realized in N2 atmosphere, the light absorption range of N2-TiO2 is enlarged, and the surface oxygen vacancies (OVs) are significantly increased. Surface OVs enhance the efficient separation of photogenerated e−/h+ pairs in TiO2. The microscopic oxide layer on the surface of TiO2 is destroyed, bringing about Ti3+ defects and formation of more surface OVs in H2 and Ar atmosphere. Ti3+ defects, high concentration of surface OVs and the Ti3+-OVs defect energy level significantly reduce the photogenerated electron excitation energy. The photocatalytic H2 production activity of TiO2 treated via plasma technique in the different atmospheres was evaluated under visible light irradiation. Consequently, the H2 production efficiency on N2-TiO2 is 103.6 umolh−1 g−1, which is 2.1 times, 1.6 times, and 1.3 times of that on the pristine TiO2, H2-TiO2, and Ar-TiO2, respectively. The apparent quantum efficiency (AQE) of H2 generation on N2-TiO2 is 0.08%, which is 1.6 times of that over the reference TiO2 under 420 nm monochromatic light irradiation. The photocatalytic mechanisms for H2 production over all the photocatalysts were discussed according to a series of characterizations.

Construction of an S-scheme g-C3N4/TiOF2 Heterostructures with abundant O vacancies: Enhanced photocatalytic activity and mechanism insight

Photocatalysis has been proved to be a promising technology to alleviate the antibiotic problem in the aqueous environment. In this work, an S-scheme g-C3N4/TiOF2 heterostructure was synthesized and then applied to degrade tetracycline hydrochloride (TCH) under simulated solar light irradiation. Compared with pure g-C3N4 and TiOF2, all the g-C3N4/TiOF2 composites showed enhanced photocatalytic activity for TCH degradation. Among them, the 20% g-C3N4/TiOF2 composite exhibited the best activity, which could degrade 85.5% TCH (10 mg/L) in 2.5 h with a rate constant of 1.0520 min−1. Essentially, the metal cycle of the variable state of Ti4+/Ti3+ in the CNTOF20 compensated for the charge balance and reduced the recombination rate of photogenerated electron-hole pairs on the heterojunction interface. The abundant oxygen vacancies in CNTOF20 could produce a defect energy level, narrow the band gap and modulate the electronic structure to speed up the charge transfer. The photocatalytic systemʼs predominant species was determined to be •O2-. Additionally, the AQE based on COD removal efficiency was calculated to be 0.13%. Based on the above results, the charge carriers followed the S-scheme transfer pathway, which endowed the strong redox ability and the efficient separation of charge carriers. This study provided some in-depth insights into the design of S-scheme heterojunctions for the practical treatment of wastewater.

A machine-learned spin-lattice potential for dynamic simulations of defective magnetic iron

A machine-learned spin-lattice interatomic potential (MSLP) for magnetic iron is developed and applied to mesoscopic scale defects. It is achieved by augmenting a spin-lattice Hamiltonian with a neural network term trained to descriptors representing a mix of local atomic configuration and magnetic environments. It reproduces the cohesive energy of BCC and FCC phases with various magnetic states. It predicts the formation energy and complex magnetic structure of point defects in quantitative agreement with density functional theory (DFT) including the reversal and quenching of magnetic moments near the core of defects. The Curie temperature is calculated through spin-lattice dynamics showing good computational stability at high temperature. The potential is applied to study magnetic fluctuations near sizable dislocation loops. The MSLP transcends current treatments using DFT and molecular dynamics, and surpasses other spin-lattice potentials that only treat near-perfect crystal cases.