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Synthesis of TiO2/SiO2-B2O3 Ternary Nanocomposites: Influence of Interfacial Properties on their Photocatalytic Activities with High Resolution Mass Spectrometry Monitoring
摘要： An investigation on unusual interface properties of unprecedented ternary composites, formed by the inclusion of assorted proportions of B2O3 into TiO2/SiO2 structure, is conducted herein. The influences of B2O3 content and calcination temperature were evaluated. The precursor TiO2/SiO2 material was synthesized via a simple sol-gel procedure that was followed by B2O3 inclusion via maceration and calcination. The materials were fully characterized and their photocatalytic performance to degrade the Indigo Carmine dye investigated. The material prepared with a B/Ti molar ratio of 1 and at calcination temperature of 350 °C (B1-350) showed the best performance, with a superior photocatalytic activity than that of commercial TiO2. The presence of B2O3-TiO2-SiO2 interfaces in the structure of such material was of critical importance in producing a material with these attractive features. Finally, high resolution mass spectrometry monitoring allowed for the characterization of the main degradation products formed under these conditions.
关键词： high resolution mass spectrometry,degradation of Indigo Carmine,B2O3-TiO2-SiO2 ternary nanocomposites,photocatalytic activity,by-products characterization,structural defects
更新于2025-09-04 15:30:14
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Oxygen vacancy‐rich anatase TiO2 hollow spheres via liquid nitrogen quenching process for enhanced photocatalytic hydrogen evolution
摘要： Development of novel methods to obtain highly active catalysts for photocatalytic hydrogen evolution is desired. This work reports a facile preannealing-quenching strategy to synthesize oxygen vacancy-rich anatase TiO2 hollow spheres. TiO2 hollow spheres are first synthesized via a versatile kinetics-controlled coating method and then subjected to high temperature preannealing followed by rapid quenching in liquid-nitrogen (-196 oC). The as-quenched samples appear light grey suggesting the presence of abundant surface oxygen vacancies, which are subsequently confirmed by the comprehensive analyses of XRD, XPS and EPR spectra. The oxygen vacancies induced by quenching process are proved to have promoted the light adsorption and inhibited the recombination of photo-induced charges for TiO2 hollow spheres, which obviously improve the photocatalytic performance of those samples. The results showed that the TiO2 hollow spheres quenched at 500 oC exhibited a robust stability and the most excellent photocatalytic performance for hydrogen evolution (413.5 μmol·h-1) over other quenched samples and it displayed 1.51 times higher performance than that of samples normally cooled at 500 oC (273.7 μmol · h-1). Herein, this liquid-nitrogen quenching strategy presented here provides an effective route for the synthesis of high-performance TiO2 for water splitting and have a promising prospect in the other application.
关键词： quenching,hollow spheres,photocatalytic hydrogen evolution,oxygen defects,titanium dioxide
更新于2025-09-04 15:30:14
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One-step synthesis of petals-like graphitic carbon nitride nanosheets with triazole defects for highly improved photocatalytic hydrogen production
摘要： Reaction atmospheres during graphitic carbon nitride preparation can have a significant influence on the chemical composition and structure of the material, subsequently improving the photocatalytic activity. However, it is still a challenge to introduce an atmosphere by one-step heat-treated method to synthesis graphitic carbon nitride without additive gases. Herein, we developed a new one-step method to gather a variety of gases for preparing petals-like graphitic carbon nitride nanosheets (CNeC), such as CO(g), NH3(g) and H2O(g). NH3(g) and H2O(g) are respectively derived from melamine-cyanuric acid supermolecule during pyrolysis. The petals-like CNeC with more triazole defects (Nc) significantly increases the separation efficiency and the mobility of photogenerated photo-induced electron-hole pairs. Compared with the g-C3N4 calcined under nitrogen atmosphere (CNeN), CNeC has smaller grain, higher porosity with larger surface area, and remarkably longer lifetime of charge carriers. As expected, the product CNeC exhibited a hydrogen evolution rate of 1334 mmol g?1 h?1 under visible-light irradiation, which was 2.8 times higher activity than CNeN, as well as higher than most of the reported bulk g-C3N4.
关键词： Photocatalysis,g-C3N4,Triazole defects,Multiple gases,Hydrogen evolution
更新于2025-09-04 15:30:14
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Abnormal Curie-temperature shift in Ho-doped BaTiO3 ceramics with the self-compensation mode
摘要： Nominal (Ba1?xHox)(Ti1?xHox)O3 ceramics (BHTH) were prepared at 1400 °C using a mixed-oxides method. The structure, microstructure, dielectric properties, and point defects of BHTH were investigated using X-ray di?raction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, electron paramagnetic resonance (EPR), and dielectric measurements. Ho3+ in BaTiO3 prefers a self-compensation mode with a slight Ba-site preference, and the solubility limit of Ho3+ in the ?ne-grained BHTH (0.5 μm) was determined by XRD to be x = 0.03. An abnormal phenomenon was observed: the Curie temperature of BHTH shifted towards high temperatures from 128 °C at x = 0.01 to 131 °C at x = 0.03. Ho3+ is inferred to be a potential codopant to achieve X8R speci?cation when BaTiO3 is doped with Ho3+ and other types of ions.
关键词： Self-compensation mode,Point defects,Ho-doped BaTiO3,The Curie temperature,Dielectrics
更新于2025-09-04 15:30:14
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-related Materials
摘要： Dominant recombination paths in AlN and AlxGa1?xN-related structures are investigated using cathodoluminescence (CL) mapping measurements and photoluminescence (PL) spectroscopy. The dark spot contrasts originating from nonradiative recombination at threading dislocations (TDs), which are observed in CL intensity maps, drastically decrease upon elevating the temperature. This is because carriers can reach TDs at low temperatures (9–60 K), but are captured by point defects (PDs) even in the vicinity of TDs near RT. Calculations based on the experimental results indicate that in the current AlN and Al-rich AlxGa1?xN crystals, TDs scarcely affect the internal quantum efficiency (IQE) at RT as long as the TD density is less than 2.6 × 1010 cm?2. Because a TD density less than 2.6 × 1010 cm?2 has already been achieved even for heteroepitaxially grown AlN films on sapphire substrates, it is evident that the most effective method to further improve the IQE of AlxGa1?xN-related materials is to reduce PDs not TDs. Moreover, we clarify the existence of two types of PD states, which mainly degrade the emission efficiency, using temperature-dependent PL measurements. Combining the CL and PL results allows the activation energies of these PDs and TDs to be evaluated. Furthermore, we highlight the probability that PDs, which predominantly act as nonradiative recombination centers at room temperature, are complexes formed by Al vacancies and oxygen impurities that enhance the deep-level emissions at 3.2 and 3.5–3.7 eV near room temperature. Such a large impact of PDs on the efficiency degradation may be attributed to the high density of Al-vacancy–related PDs in AlN and Al-rich AlxGa1?xN compared with that of Ga-vacancy–related PDs in GaN due to the small formation energy.
关键词： AlxGa1?xN,cathodoluminescence,internal quantum efficiency,point defects,photoluminescence,nonradiative recombination,AlN,threading dislocations
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS) - San Diego, CA, USA (2018.10.15-2018.10.17)] 2018 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS) - 450 GHz <tex>$f_{\text{T}}$</tex> SiGe:C HBT Featuring an Implanted Collector in a 55-nm CMOS Node
摘要： This paper deals with the optimization of a Si/SiGe HBT featuring an implanted collector and a DPSA-SEG emitter-base architecture. Arsenic and phosphorous doping species are studied. On the one hand, both silicon defects and dopants profiles control are evaluated and on the other hand, hf performances are presented. Carbon-phosphorous co-implantation is also investigated and a state-of-the-art 450 GHz fT HBT compatible with 55-nm MOSFETs is demonstrated through a device layout study.
关键词： MOSFET,Implanted Collector,Heterojunction Bipolar Transistor (HBT),Silicon-Defects
更新于2025-09-04 15:30:14
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Reversible and selective ion intercalation through the top surface of few-layer MoS2
摘要： Electrochemical intercalation of ions into the van der Waals gap of two-dimensional (2D) layered materials is a promising low-temperature synthesis strategy to tune their physical and chemical properties. It is widely believed that ions prefer intercalation into the van der Waals gap through the edges of the 2D flake, which generally causes wrinkling and distortion. Here we demonstrate that the ions can also intercalate through the top surface of few-layer MoS2 and this type of intercalation is more reversible and stable compared to the intercalation through the edges. Density functional theory calculations show that this intercalation is enabled by the existence of natural defects in exfoliated MoS2 flakes. Furthermore, we reveal that sealed-edge MoS2 allows intercalation of small alkali metal ions (e.g., Li+ and Na+) and rejects large ions (e.g., K+). These findings imply potential applications in developing functional 2D-material-based devices with high tunability and ion selectivity.
关键词： defects,MoS2,electrochemical control,two-dimensional materials,ion intercalation
更新于2025-09-04 15:30:14
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Geometric stabilisation of topological defects on micro-helices and grooved rods in nematic liquid crystals
摘要： We demonstrate how the geometric shape of a rod in a nematic liquid crystal can stabilise a large number of oppositely charged topological defects. A rod is of the same shape as a sphere, both having genus g = 0, which means that the sum of all topological charges of defects on a rod has to be (cid:2)1 it usually shows only one hyperbolic hedgehog or a Saturn ring defect with negative unit charge. Multiple unit charges can be stabilised either by friction or large length, which screens the pair-interaction of unit charges. Here we show that the curved shape of helical colloids or the grooved surface of a straight rod create energy barriers between neighbouring defects and prevent their annihilation. The experiments also clearly support the Gauss–Bonnet theorem and show that topological defects on helices or grooved rods always appear in an odd number of unit topological charges with a total topological charge of (cid:2)1.
关键词： topological defects,geometric stabilisation,micro-helices,nematic liquid crystals,grooved rods
更新于2025-09-04 15:30:14
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Lack of correlation between C-V hysteresis and capacitance frequency dispersion in accumulation of metal gate/high- <i>k</i> /n-InGaAs metal-oxide-semiconductor stacks
摘要： The correlation between capacitance-voltage hysteresis and accumulation capacitance frequency dispersion of metal gate/high-k/n-InGaAs metal-oxide-semiconductor stacks is experimentally assessed. Samples fabricated employing forming gas annealing (FGA) or substrate air exposure to obtain different densities of defects were thoroughly characterized and the results were compared with previous literature on the topic. Results indicate a lack of correlation between capacitance-voltage hysteresis and accumulation capacitance dispersion with frequency, suggesting that defects with remarkably different kinetics are involved in each phenomenon. This is assessed through the dependence of the capacitance-voltage hysteresis with DC bias and stress time, observing that permanent interface defect depassivation under bias has no effect on the hysteresis width after stress. Overall, capacitance-voltage hysteresis probes slow trapping mechanisms throughout the oxide and the bandgap, which are consistent with the negative charge trapping characteristic of the current-time curves for FGA samples at constant voltage stress. Instead, accumulation capacitance frequency dispersion probes defects with short trapping/detrapping characteristic times that can be linked to the stress induced leakage current of air exposed samples under constant DC stress. Experimental results indicate that each effect must be assessed separately due to the large difference in the kinetics of the probed defects.
关键词： metal-oxide-semiconductor stacks,forming gas annealing,defects,metal gate/high-k/n-InGaAs,trapping mechanisms,capacitance-voltage hysteresis,accumulation capacitance frequency dispersion
更新于2025-09-04 15:30:14