Generation Of Holes Research Articles

Ce-Doped Iron Oxide Anticorrosive Coatings: Effect of c(Ce4+):c(Fe3+) Ratio on Structure, Morphology, and Coating Anticorrosion Performance

Utilizing hydrothermal methods, Ce-doped iron oxide nanoparticles were synthesized from precursor solutions under different c(Ce4:c(Fe3+) precursor solutions. The effects of the c(Ce4+):c(Fe3+) ratio in the precursor solutions on the nanoparticle morphology and nanoparticle structure of the Ce-doped iron oxide were investigated using X-Ray diffraction, transmission electron microscopy, and scanning electron microscopy. Fourier transform infrared spectroscopy (FTIR) was used to examine the bond energy strength of the Ce-doped iron oxide nanoparticles. The electrochemical properties of the Ce-doped iron oxide nanoparticles were tested using an electrochemical workstation and a saltwater immersion resistance test. The corrosion resistance of Ce-doped iron oxide coatings at different c(Ce4+):c(Fe3+) ratios was systematically analyzed, uncovering corrosion resistance mechanisms and self-healing capabilities. The results show that as the c(Ce4+):c(Fe3+) ratio decreases, the lattice constants of the samples increase along with the average grain size. Both smaller and larger c(Ce4+):c(Fe3+) ratios are detrimental to lattice distortion in α-Fe2O3. The reduced number of valence electrons provided by cerium ions in Ce-doped iron oxide hinders the generation of holes and exerts a minor influence on the crystal band structure, leading to weaker electrochemical stability. The Ce-doped iron oxide coating prepared at a c(Ce4+):c(Fe3+) ratio of 1:60 readily generates a higher number of reactive hydroxyl radicals during corrosion, thus exhibiting enhanced self-healing capabilities and corrosion resistance.

Defect Structure and Luminescence of κ‐Ga2O3 Micro‐Monocrystals

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

Enhanced photocatalytic CO2 reduction to CH4 on oxygen vacancy-rich NiCo2O4 with surface pits: Synthesis, DFT calculations, and mechanistic insights

Unraveling the influence of surface microstructure in materials on their interaction with CO2 remains a critical challenge in achieving efficient and selective CO2 reduction. In this study, we report the engineering of pit structures on the NiCo2O4 surface for efficient photocatalytic reduction of CO2. Characterization results show that calcination temperature affects the distribution of surface pits and oxygen vacancy concentration. Oxygen vacancy sites accompanying surface pits facilitate the generation and movement of photogenerated electrons and holes, preventing their recombination and promoting the conversion of CO2. The CH4 yield from photocatalytic CO2 reduction reaches 52.4 μmol g−1 with the optimal pitted NiCo2O4 catalyst (PNCO2), significantly surpassing the 18.4 μmol g−1 yield of non-pitted NiCo2O4 (NPNCO). Additionally, PNCO2 improves selectivity from 81.8 % for NPNCO to 94.1 %. Density functional theory calculations show that CO2 adsorption on the PNCO2 surface is significantly enhanced as the d-band center shifts toward the Fermi level. The adsorbed CO2 combines with electrons enriched at the Ni sites at the edges of the surface pits, leading to further activation. The reduction of CO2 to intermediate products such as CHO* is analyzed based on in situ diffuse reflectance infrared Fourier transform spectroscopy, and a possible reaction pathway is proposed. This work offers fresh insights into engineering surface pit structures for the design and synthesis of catalysts for photocatalytic CO2 reduction.

Influence of the presence of RuO2 on the reactivity of Fe2O3 in the artificial photosynthesis reaction

Surface Plasmonic Resonance (SPR) is the oscillation of free electrons on the surface of a metal or metallic particle upon irradiation with light of a certain frequency. The incorporation of Fe2O3 (a H2O oxidising photocatalyst) with plasmonic RuO2 nanoparticles to form a composite is studied. XRD results show that RuO2 is formed in the rutile phase while Fe2O3 is rhombohedral and also suggests doping of the Fe2O3 lattice with Ru atoms in the composite. UV-Vis spectroscopy shows that RuO2 exhibits a plasmon peak at 511 nm, and CO2-TPD experiments show that RuO2 adsorbs and desorbs CO2. TEM also shows that the RuO2 particles are spherical, as are the Fe2O3 particles with some irregular polyhedra present, too. The composite is a mixture of these two morphologies. The effect of composite formation on the activity of the materials in the artificial photosynthesis reaction is dramatic. Neither RuO2 nor Fe2O3 alone produce significant quantities of gaseous CH4 or CO products. However, the composite material produces both (as well as generating levels of unidentified adsorbed hydrocarbonaceous species). This reactivity is ascribed to the generation of a heterojunction in the composite material. It is suggested that the generation of holes in Fe2O3 is used to provide protons (from H2O oxidation), and the decay of an SPR response on RuO2 provides hot electrons, which together with the protons reduce CO2 to produce CH4, CO and adsorbed hydrocarbonaceous species.

Efficient hole extraction to reactive oxidation sites over a Co3O4/Cs3Sb2Br9 p-n heterojunction for enhanced benzylic C(sp3)-H bond oxidation

Photocatalytic selective oxidation of aromatic hydrocarbons plays an important role in the production of value-added chemicals. A key step in this process is the activation of C(sp3)-H bond by photogenerated holes. However, the inadequate hole generation and lack of surface adsorption-activation sites severely hinders the improvement in photocatalytic C-H bond oxidation. In particular, the random charge migration to the surface impedes the effective capture of holes by surface active sites to dissociate the C(sp3)-H bond. Here, we design and fabricate a Co3O4/Cs3Sb2Br9 p-n heterojunction that effectively addresses these challenges. The p-n heterojunction forms strong built-in electric fields (BEF) facilitating spatial charge separation. Holes are accumulated on Co3O4, while electrons are accumulated on Cs3Sb2Br9, thereby offering abundant active holes and electrons. Moreover, Co3O4 shows stronger adsorption and activation capacity for the C(sp³)-H bond, enabling the C(sp3)-H bond dissociation with low reaction energy barrier. Consequently, the holes are directionally extracted from photoactive Cs3Sb2Br9 to catalytically active Co3O4 under visible light irradiation, thereby accelerating the toluene oxidation. The optimized 5 % Co3O4/Cs3Sb2Br9 exhibits a benzyl aldehyde (BAD) evolution rate of 5044 μmol g−1 h−1 and a benzyl alcohol (BA) production rate of 1820 μmol g−1 h−1, which are 12 and 17 times higher than that of blank Cs3Sb2Br9, respectively.

A comparative study for demonstrating the effect of the assist gas and E-field on hole generation characteristics induced by femtosecond laser layered ring hole-cutting of magnesium alloy AZ91D sheets

The widely-used magnesium alloy AZ91D is light-weight and energy-saving with good castability and mechanical performance. The traditional machining way for magnesium and its alloys is the high-speed mechanical contact cutting, which usually leads to uncontrollable intense ignition with some notable heat-induced machining defects. However, it has been rarely reported that the non-contact precision laser machining is used for cutting the magnesium and its alloys. The problems such as the local heat effect, the heat-induced defects and the local ignition as well as the vapor-plasma plume usually encountered during laser machining of magnesium and its alloys. Hence, in this study, a hybrid laser cutting way of femtosecond laser layered ring hole-cutting using the assist gas and E-field is reported to machine micro holes in the AZ91D material. The effect of the lateral E-field and assist gas on the hole formation characteristics was demonstrated for femtosecond laser cutting of the AZ91D sheets. It was indicated that the use of the lateral E-field and assist gas suppressed the ignition as well as the vapor-plasma plume. The hole depth was increased by the external assistance used especially the lateral nitrogen blowing. The hole wall formation quality was improved by using the lateral E-field and compressed air blowing, while it got poorer if using the lateral nitrogen blowing. The ignition-induced carbonization was effectively suppressed by the assist gas used. The hole depth, microstructure and micro hardness were improved by using the lateral E-field and assist gas.

Bifunctional Pt-loaded steel slag matrix composites for the detection and degradation of tetracycline antibiotics

In this paper, a method for the simultaneous detection and degradation of tetracycline antibiotics (TCs) in water was investigated. Calcium silicate hydrate (CSH), FeO and calcium aluminate hydrate (CAH) were isolated from steel slag as carriers for Pt monomers. The produced Pt-modified modified steel slag (ALANH-Pt) possessed both peroxidase activity and photocatalytic properties. As a result, a sensitive and selective colorimetric sensor was exploited on the basis of ALANH-Pt for tetracycline (TC), oxytetracycline (OTC), and doxycycline (DOX), which exhibited a detection limit (LOD) of 1.696 μM, 0.999 μM and 3.607 μM, respectively. In addition, the degradation rate for TCs could be achieved 82 % within 60 min. The possible mechanisms of detection and degradation are discussed based on ESR spectroscopy, revealing the generation of hydroxyl radicals (OH), superoxide radicals (O2−) and holes (h+). The degradation pathway of TC was inferred by HPLC-MS. The selectivity of the colorimetric sensing platform and the application of the bifunctional ALANH-Pt to real water samples were investigated. This work provides a new idea that allows for the simultaneous detection and degradation of TCs, and offers a new approach to the utilization of steel slag.

Insight into photocatalytic chlortetracycline degradation by WO3/AgI S-scheme heterojunction: DFT calculation, degradation pathway and electron transfer mechanism

The construction of S-scheme heterojunction with excellent redox ability holds promising prospects for photocatalytic environment remediation. However, the rationally design of the heterojunction interface to achieve efficient charge transfer still faces challenges. In this study, we fabricated a tight-contacted S-scheme heterojunction by in situ anchoring AgI nanoparticles onto WO3 nanoplates. The significant difference in Fermi energy levels between WO3 and AgI results in the formation of a space charge region around the interface and bending of the energy band, facilitating directional migration and spatial separation of charge carriers. This contributes to enhanced generation of superoxide radicals (•O2−) and holes (h+) active species, leading to a significant increase in chlortetracycline (CTC) degradation rate. The apparent rate constant for CTC removal using the WO3/AgI (WA-2) is approximately 15 times higher than that observed for pure WO3. Furthermore, WA-2 exhibits universal degradation effects on tetracycline (TC) and oxytetracycline (OTC). Molecular dynamics (MD) simulation reveals the synergistic adsorption effect of WO3 and AgI on CTC and reactive oxygen species molecules. Based on Fukui function calculation of CTC molecules and degradation intermediates, liquid chromatography-mass spectrometry (LC-MS) analysis, photocatalytic degradation pathway over WO3/AgI was determined to be sequential demethylation followed by dechlorination and decarbonylation. These findings provide valuable insights into high-performance S-scheme heterojunctions interface design and elucidation of pollutant degradation mechanism.

Facile construction of a bifunctional Eu-MOF for selective fluorescence sensing and visible light photocatalysis of tetracycline

Contamination detection and removal are important steps in environmental monitoring and cleanup. In this study, europium metal-organic framework structures (Eu-MOF) were designed and prepared that can act as fluorescent probes and photocatalysts for the detection and removal of tetracycline (TC) antibiotics. Eu-MOF was generated by a one-step solvothermal method using europium ion as the metal ion and terephthalic acid as the organic ligand source. The red fluorescence of Eu-MOF is selectively enhanced by TC due to the antenna effect. Eu-MOF, which has a linear range of 0.5–60 μM, can be utilized as a fluorescent probe for tetracycline detection based on this phenomena. In particular, Eu-MOF was found to be able to effectively photocatalyze the degradation of TC, with tetracycline removal rates of about 70 % and 55 % after 180 min of irradiation under ultraviolet light (UV) light and simulated visible light, respectively. The photocatalytic ability of Eu-MOF originated from the generation of hydroxyl radicals (•OH), superoxide radicals (•O2−) and electron holes (h+) under light irradiation. This study innovatively proposed a bifunctional Eu-MOF for TC fluorescence detection and photocatalytic degradation, which provides a novel method for the quick and easy identification and elimination of pharmaceutical contaminants. It can also provide some reference value for the construction of ratiometric fluorescent probes and heterojunction photocatalysts and their application in the treatment of water pollution.

Improving the efficiency above 35 % of MoS2-based solar cells by through optimization of various wide-bandgap S-chalcogenides ETL

Molybdenum disulfide (MoS2)-based photovoltaic cells are increasingly attracting researchers’ due to their outstanding semiconducting properties. Single junction MoS2 based solar cell have been investigated with three distinct electron transport layer (ETL) layers made of SnS2, In2S3 and ZnSe in detail with and without back surface field (BSF). A thorough numerical analysis has been conducted of the effects of band alignment, defect density, absorber layer thickness, buffer layer thickness, interface defect density, electron and hole concentration, generation and recombination, open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), and power conversion efficiency (PCE) via SCAPS-1D simulation software. The MoS2 based solar cell produced the photo conversion efficiency (PCE) of 24.77 % with VOC of 0.913 V, JSC of 31.274 mA/cm2, and FF of 86.77 % without BSF. On the other hand, after in depth analysis, according to simulation results, SnS2 ETL produced the highest PCE of 35.60 % than ZnSe(33.56 %) and In2S3(34.94 %) ETL with VOC of 1.07 V, JSC of 37.55 mA/cm2, and FF of 88.80 % with inserting only 30 nm V2O5 BSF layer. The suggested research might provide information and a workable strategy for producing a MoS2-based thin-film solar cell that is affordable.

A theoretical investigation of MoS2-based solar cells with CdS electron transport layer and V2O5 hole transport layer for boosting performance

Researchers are becoming more interested in molybdenum disulfide (MoS2)-based photovoltaic cells because of their exceptional semiconducting qualities. The use of CdS ETL and V2O5 HTL in thin-film solar cells based on MoS2 has been studied. The effects of electron and hole concentration, generation and recombination, FF, VOC, JSC, band alignment, defect density, absorber layer thickness, buffer layer thickness, interface defect density, and PCE have all been thoroughly numerically analyzed. The SCAPS-1D simulation software was applied to conduct the aforementioned investigation. The study found that the V2O5 HTL design reached the maximum PCE at 35.13 % with a VOC of 1.0738 V, a JSC of 36.8308 mAcm−2, and a FF of 88.83 %. On the other hand, without HTL configuration, the PCE was 23.05 %, the VOC was 0.9049 V, the JSC was 29.4614 mAcm−2, and the FF was 86.45 %. These findings offer useful data and a practical plan for developing inexpensive, MoS2-based thin-film solar cells.

Band Gap Engineering and Lattice Distortion for Synergetic Tuning Optical Properties of NaNbO3 toward Enhanced Piezo-photocatalytic Activity.

Piezo-photocatalytic efficiency is severely constrained by the wide band gap and bad piezoelectric properties. Herein, La(Mn0.5Ni0.5)O3 was successfully introduced into NaNbO3 lattices (referred to as 0LMN, 0.05LMN, 0.10LMN, and 0.15LMN) through a water-based sol-gel method. The piezo-photocatalytic degradation ratio for Rhodamine B (RhB) is enhanced from 59.7% (0LMN) to 89.7% (0.10LMN) within 100 min, and the kinetic rate constant (k) is increased from 0.009 to 0.022 min-1. The enhanced performance is attributed to (i) the narrowed band gap (from 3.40 to 2.84 eV), which is conducive to the generation of photogenerated electrons and holes, and (ii) the enhanced piezoelectric properties, which can strengthen the piezoelectric polarization, thereby accelerating the separation of the photogenerated electrons and holes. And we also found that the synergetic effect of photocatalysis and piezocatalysis was superior to that of photocatalysis and piezocatalysis alone. This study could provide new perspectives for the reasonable construction of an efficient catalyst in the piezo-photocatalytic field.

Rapid Hole Generation via D–A Structure‐Dependent Built‐In Electric Field of Deacetylated Chitin‐PDI for Efficient Photocatalytic Oxidation

AbstractBreaking the trade‐off between broad spectrum response and efficient charge separation is a major challenge in the photocatalysis. Unlike the conventional practice of suppressing charge separation when shrinking the bandgap, a series of deacetylated chitin‐perylene diimide (DC‐PDI) donor–acceptor (D–A) photocatalysts is proposed with tunable charge distribution by modulating the C─N covalent bond content, expanding the spectral absorption range as the expanded D–A. The enlarged D–A structure achieves efficient photogenerated electron–hole separation by increasing the charge of the positive and negative charge centers, inducing larger dipole moments, generating 4.7 times higher built‐in electric field, and reducing the charge transfer barrier. Among them, the optimum DC/PDI (2:1) with enlarged D–A enables to capture the largest number of electrons for persulfate activation, and concurrently affords the highest hole generation efficiency with the deepest valence band (1.67 V). Such merits contribute to 1.2–2.8 times higher degradation rate and 1.1–1.6 times higher mineralization rate of organic pollutants in comparison with other counterparts. The mineralization rate can reach 100% in the engineered microreactor setup. This study elucidates the structure‐mechanism‐performance relationship of D–A modulation and charge separation/transport, guiding the rational molecular structure design for efficient photocatalytic oxidation.

Heavy ions and alpha particles irradiation impact on III-V broken-gap gate-all-around TFET

This report deals with the impact of radiation on III-V and Si gate-all-around tunnel field effect transistors (GAA TFET). The highly energetic particles (HEPs) such as heavy ions and alpha particles are allowed to strike the device at several locations along the channel to determine the sensitive location of the device. Once the sensitive location is determined, then the device is irradiated to different energies of heavy ions and alpha particles. Further, to get a proximate match as a practically exposed device, the device has been irradiated to several incident angles. Before analyzing the device's behaviour, the models used for the analysis are calibrated with the transfer characteristics of an experimentally published report on III-V GAA TFET. Thereafter, analysis of charge collection, transient current, hole generation in the channel, and different incident angles are analyzed. Finally, it is concluded that III-V GAA TFET shows better immunity towards different incident angles under a radiation environment when compared to Si GAA TFET.

Ti-MOG derived TiO2 facet heterojunction rich in C/Ti3+/Ov for adsorption-photocatalytic removal of pharmaceutical pollutants from water

Developing efficient, stable, and broad-spectrum responsive photocatalysts is an effective way to degrade pharmaceutical pollutants in water. In this work, using concentrated hydrochloric acid (HCl) as a modulator, titanium metal–organic gel (Ti-MOG) was prepared and used as a template for calcination in air to obtain anatase TiO2 facet heterojunction rich in C/Ti3+/oxygen vacancy (Ov) (MOG-TiO2), which has a hierarchical porous structure, large specific surface area, and highly dispersed active site. Compared to P25, P25 + C and MIL-125(Ti) derived TiO2 (MOF-TiO2), MOG-TiO2 exhibited obviously enhanced adsorption-photocatalytic performance for tetracycline (TC) and low concentrations ethenzamide (ETH) under broad-spectrum light irradiation. The photocatalytic degradation efficiency of ETH by MOG-TiO2 reached 92.8, 100 and 98.7 % within 240, 60 and 6 min under Vis, UV and VUV light illumination, respectively, which were much higher than those of P25 (62.7, 33.2 and 73.0 %), P25 + C (61.7, 31.2 and 72.5 %) and MOF-TiO2 (79.2, 86.8 and 88.7 %). Furthermore, concentrated HCl promoted the formation of Ti3+/Ov in MOG-TiO2, which was conducive to the improvement of its photocatalytic performance. MOG-TiO2 also displayed great adsorption-photocatalytic stability and reusability. Moreover, the biotoxicity of TC toward E. coli DH5a obviously decreased after photocatalytic degradation. Based on the TiO2 facet heterojunction rich in C/Ti3+/Ov and the generation of hole, hydroxyl radicals, and superoxide radicals, the possible photocatalytic degradation mechanism of MOG-TiO2 was proposed. Overall, this work provides insights into constructing a novel hierarchical porous carbon-doped facet heterojunction photocatalyst for efficient pharmaceutical contaminants removal.

Adsorption induced bipolar excitation at semiconductor surface

Adsorption on metal surfaces has been shown to lead to chemisorption induced electronic excitation but direct experimental evidence of chemisorption induced excitation on semiconductor surfaces is still missing. Here, we design and use high-quality Silicon (Si) p-n diodes to in-situ probe the charge transfer process taking place during vapor and liquid phase chemisorption of iodine molecules on H-Si (100) surface. We find that the diodes can generate electricity and feed an external circuit during the chemisorption process, demonstrating chemisorption-induced electron and hole generation and the means to electrically monitor the process. A bipolar semiconductor electrochemical model where a single semiconductor surface hosts the spontaneous oxidation (electron injection) and reduction (hole injection) reactions simultaneously on its conduction and valence bands without any electrolytes is proposed to explain the observations. Our work provides new insight on the energy relaxation processes of chemisorption and also calls for further studies on the observed chemovoltaic effect. Overall, the results indicate a possibility for developing electrolyte-free vapor phase chemical energy-to-electricity converters and detectors.

Insight into bay-/end-substituted perylene diimide and its S-scheme heterojunction for enhanced photocatalytic H2O2 production under visible-light irradiation

Here, 1D bis(N-carboxymethyl) peryleneimide (H2PDI), 0D 1,6,7,12-tetrachloro-bis(N-carboxymethyl) peryleneimide (4Cl-H2PDI), and 2D 4Cl-H2PDI/graphene quantum dot (4Cl-H2PDI/GQD) nanostructures are synthesized and carefully analyzed. The effect of bay-/end-substitution and S-scheme heterojunction of PDI-based materials as main catalysts on the photocatalytic H2O2 evolution is first studied through the oxygen reduction reaction (ORR). Under the visible-light irradiation (> 420 nm), 4Cl-H2PDI and 4Cl-H2PDI/GQD as photocatalysts exhibit the ∼7 and ∼16 times H2O2 evolution rate than H2PDI (1059.6 vs. 2484.0 vs. 160.0 µM g−1 h−1), respectively. The systematical experiments reveal that 4Cl-H2PDI and 4Cl-H2PDI/GQD should prefer a two-step single-electron ORR process, while H2PDI may involve a 4e‒ water oxidation and one-step 2e‒ ORR process. Further experiments confirm that the bay-substitution and GQD doping of H2PDI can promote the generation, transportation, and separation of photogenerated electrons and holes, and prolong the carrier lifetime. This work provides insight into PDI-based photocatalytic H2O2 production.

Study on shallow configuration preparation and macroscopic and microscopic properties of cemented carbide surface

This study aimed to reduce surface configuration defects and improve the service performance of the configuration surface. The configuration was prepared using the principle of preset powder feeding laser cladding. Macroscopic and microscopic properties of the shallow configuration were tested to understand the mechanism behind the preset cladding material's ability to repair defects and improve surface hardness, and the preparation process of the shallow configuration was obtained. Finally, the method's potential for improving the wear resistance of the configuration surface was evaluated through friction and wear tests. The results indicate that the flow of molten preset powder can fill in pores, leading to the formation of a dense cladding layer on the configuration surface. This process also minimizes the generation of defects and holes. The incorporation of hard phases, such as TiN, Ti2N, and the solid solution (Ti, W)C1-X, positively influences the improvement of surface hardness and wear resistance of shallow configuration. When the average laser energy density ranges from 70 to 120 W·cm−2, the average microhardness of the shallow configuration surface is elevated by 13.4% compared to that of the conventional configuration surface. The friction force on the shallow configuration surface is 13.1% lower than that on the conventional configuration surface when the laser power is set to 80%, the scanning speed is maintained at 1500 mm/s, the scanning passes are 9, the spacing between configurations is 130 μm, and the configuration diameter is 50 μm. This technique presents a novel approach to producing configuration surfaces with enhanced quality.

Origin and Recovery of Negative VTH Shift on 4H–SiC MOS Capacitors: An Analysis Based on Inverse Laplace Transform and Temperature-Dependent Measurements

SiC power MOSFETs are reported to suffer from both positive and negative threshold voltage shifts. Positive shift is well understood in the literature and attributed to electron trapping in near interface oxide traps (NIOTs). Negative shift is explained by hole generation and trapping in the oxide via impact ionization favored by the strong oxide field. However, studies on negative shift are still ongoing, and the origin and nature of the process are not fully understood. This study advances the comprehension of negative threshold voltage shift by investigating MOS capacitors subject to positive bias stress.We demonstrate that: a) a significant negative threshold shift is observed when the electric field is greater than 7.5 MV/cm; b) the detected shift is not recoverable at zero bias. Recovery can be obtained only by applying a positive gate voltage indicating a field-driven detrapping process. c) Trap-state mapping measurements were carried out to extract the activation energy of the detrapping processes, and a weak thermal activation was observed.Results collected within this paper indicate that holes are trapped at deep centers, and thermal detrapping is not possible. Hole release is only possible when a high field is applied to the insulator, possibly due to the recombination between leaking electrons and trapped holes.

A Z-scheme heterojunction ZIF67/N, P-WO3 nanocomposite for photocatalytic degradation of levofloxacin

In this work, a ZIF67/N, P-WO3 (ZNPW) Z-scheme heterojunction was constructed by N, P-codoped WO3 (NPW), and ZIF67 and developed as a highly efficient photocatalyst for Levofloxacin (LFX) removal. A series of characterization measurements including FTIR, XRD, SEM, DRS, PL, and XPS are conducted to confirm the formation of the ZNPW. After optimization on the composition of WO3, NPW and ZIF67, the optimal ZNPW shows superior photocatalytic activity, yielding a higher removal efficiency of LFX ∼91.2% in 100 min than those of pure WO3 (9.4%), NPW (47.8%) and ZIF67 (14.3 %). Additionally, ZNPW exhibits remarkable stability and reusability for up to five consecutive runs. Reactive species scavenging experiments and ESR have revealed that the degradation of LFX is primarily facilitated by the generation of holes (h+) and hydroxyl radicals (·OH). Moreover, the degradation process of LFX was identified through an integrated LC-MS analysis and density functional theory computation of the Fukui indices. This process consists of three pathways: the opening of the piperazinyl ring, separation of piperazinyl and quinoline moieties, and cleavage of the pyridine ring on the quinoline moieties. The superior photocatalytic properties can be attributed to the N, P co-doping in the WO3 structure and the simultaneous coupling with ZIF67, leading to the formation of a heterojunction with a reduced band gap, efficient charge separation and transport, and a new N 2p and P 2p energy level. In conclusion, this study provides novel insights into designing high-efficiency antibiotics degradation using WO3-based Z-scheme heterojunction photocatalysts.