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Cell Imaging Using Two-Photon Excited CdS Fluorescent Quantum Dots Working within the Biological Window
摘要： In recent years, two-photon excited semiconductor quantum dots (QDs) have been the subject of intense investigation due to their long excitation wavelength which helps to achieve deeper penetration and higher image resolution in optical bioimaging. In this paper, water-soluble CdS QDs were synthesized using a hydrothermal method and applied to human liver hepatocellular carcinoma (HepG2) cells. The first-principles calculation suggested that the S-rich defected structure contributes to a narrower band gap compared to the pristine structure. The resulting fluorescence wavelength was significantly red shifted, which was attributed to the deep defect states emission. The large Stokes shifts (> 200 nm) of the QDs can eliminate the possible cross-talk between the excitation light and the emission light. Two-photon induced red fluorescence emission can avoid overlapping with the autofluorescence emission of biological samples. The uptake and cell viability measurements of the HepG2 cells showed a good biocompatibility and a low toxicity of CdS QDs. Two-photon excited scanning microscopy images revealed that the HepG2 cells incubated with CdS QDs emitted bright red upconversion fluorescence and the fluorescence brightness was 38.2 times of that of the control group. These results support CdS QDs as a good candidate for application in cellular imaging.
关键词： two-photon absorption,CdS quantum dots,deep defect states,HePG2 cells,biological imaging
更新于2025-11-21 11:24:58
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Excellent corrosion resistance of graphene coating on copper due to the low defect overlapping structure
摘要： Nowadays, ultra-thin graphene coating can provide considerable resistance against corrosion for various metals, however, there is great variability and contradictory in corrosion resistance mechanism of graphene coating reported in different studies. In this work, the anti-corrosion behaviors of graphene coatings with different defect values on the copper surface were investigated systematically. The results indicated that all graphene coated Cu exhibited superior corrosion resistance than heat treated Cu, regardless of the layer number of graphene. Particularly, anti-corrosion performance of bi-layer graphene coating was the most effective, the corrosive medium transferred a long way to reach the interface between Cu and graphene. The corrosion resistance for mono-layer graphene was inferior to bi-layer graphene, and poor corrosion resistance for multi-layer graphene was due to the high value of defects increasing the corrosion pathways, which leads to easier transfer for the chloride ions among defects. Consequently, the corrosion resistance ability of graphene coatings was mainly determined by the defect density other than the layer number, multi-layer graphene coating may not behave better anti-corrosion performance if it contained a high value of defect.
关键词： graphene,galvanic corrosion,layer number,SVET,CVD,defect
更新于2025-11-21 11:08:12
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Surface Passivation of Perovskite Solar Cells Toward Improved Efficiency and Stability
摘要： The advancement of perovskite solar cells (PVSCs) technology toward commercialized promotion needs high efficiency and optimum stability. By introducing a small molecular material such as tetratetracontane (TTC, CH3(CH2)42CH3) at the fullerene (C60)/perovskite interface of planar p-i-n PVSCs, we significantly reduced the interfacial traps, thereby suppressing electron recombination and facilitating electron extraction. Consequently, an improved efficiency of 20.05% was achieved with a high fill factor of 79.4%, which is one of the best performances for small molecular-modified PVSCs. Moreover, the hydrophobic TTC successfully protects the perovskite film from water damage. As a result, we realized a better long-term stability that maintains 87% of the initial efficiency after continuous exposure for 200 h in air.
关键词： Surface defect,Charge transport,Surface passivation,Perovskite solar cells
更新于2025-11-21 11:01:37
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Defect-assisted symmetric cleavage of naphthalene sulphonic acid group in azo dyes using β-In2S3 quantum dots as visible light photocatalyst
摘要： Naphthalene sulfonic acid, which is used in the synthesis of azo dye pigments, rubber processing chemicals and pharmaceuticals, is a carcinogenic substance that pollutes water bodies. In this work, we report on the visible light-driven symmetric cleavage of naphthalene sulfonic acid group, present in methyl orange dye and its conversion into the intermediate compounds. These compounds further degrade to inorganic ions such as carbon-di-oxide, nitrates, sulfates, water, and chlorine. Complete degradation of the dye, under visible light irradiation, is attained using β-In2S3 quantum dots as photocatalyst. During homogenous precipitation process, the β-In2S3 quantum dots (~ 9 nm) self-assemble to form microflowers (~ 50 nm) with high surface-to-volume ratio. These quantum dots exhibit size-dependent, active F2g, Eg and Ag1 Raman modes with peaks at ~ 150 cm?1 (In–In stretching mode), 219 cm?1 (In–S bending mode) and 300 cm?1, corresponding to the vibrational modes of cubic phase β-In2S3. The cubic phase β-In2S3 quantum dots are photoactive under visible light exposure and releases highly oxidizing OH· radicals. They have strong band-to-band emission in ultraviolet region (~ 380 nm) and exhibit broad band defect emission with maxima at blue (~ 484 nm), green (~ 580 nm) and red (~ 600 nm) region of electromagnetic spectrum. The emission intensity from these defect energy bands, which are due to sulfur vacancy, indium interstitials and oxygen incorporation, are tuned by varying the In-to-S ratio in the sample. These defects enhance their visible light absorption coefficient and assist in improving the photocatalytic efficiency of the cubic phase β-In2S3 quantum dots. Thus, defect-assisted complete (100%) photodegradation of the azo dye is achieved using cubic β-In2S3 quantum dots with low In-to-S ratio (1:1), low mass of 20 mg and minimum irradiation time (30 min). These photocatalysts can be reused 4 times under 30-min visible light irradiation. Cubic β-In2S3 quantum dots-microflowers is a highly efficient, ecofriendly photocatalyst, which even in very low concentration can remove toxicity from the dye-contaminated water, by exposure to direct sunlight for 30 min.
关键词： Indium sulphide,Defect emission,photocatalysis,Water treatment
更新于2025-11-19 16:56:42
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Synthesis, Morphology, Optical and Electrical Properties of Cu <sub/> 1? <i>x</i> </sub> Fe <sub/><i>x</i> </sub> O Nanopowder
摘要： The pure and Fe-doped CuO nanoparticles of the series Cu1?xFexO (x = 0, 0.027, 0.055, 0.097 and 0.125) were synthesized by a simple low temperature sol–gel method. Synthesized samples were characterized by a series of techniques including Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray electron spectroscopy (EDX), Diffuse Reflectance Spectroscopy (DRS), Fourier Transform Infrared Spectroscopy (FTIR), Hall Effect Set-up and Current–Voltage (I–V) characteristics. FESEM analysis shows formation of disc type structure increasing in grain size with Fe concentration in CuO. EDX confirmed the incorporation of iron in CuO. FTIR results of pure and Fe doped CuO samples have confirmed the formation of monoclinic CuO. The optical band gap estimated using Diffuse Reflectance Spectroscopy (DRS) shows the increment in the band gap values with Fe substitution. The Hall measurements show predominantly p-type conduction in all the samples and carrier densities decrease with increased Fe substitution. I–V characteristics of pure and Fe doped CuO nanoparticles show rectification behaviour of Schottky diodes.
关键词： Defect States,Hall Effect,Schottky Diode,Cation Vacancies,Fe-Substituted CuO
更新于2025-11-19 16:56:35
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Device simulation of Cu(In,Ga)Se2 solar cells by means of voltage dependent admittance spectroscopy
摘要： The simulation of solar cell devices is important for the understanding of defect physics and loss mechanisms in real solar cells. On the other hand, voltage dependent admittance spectroscopy delivers essential information for establishing a baseline simulation model of Cu(In,Ga)Se2 (CIGSe) solar cells. Here we give an explanation for the weak temperature dependence of the N1-signal, the latter being not compatible with a bulk defect or with a simple hole barrier at the Mo back contact. Furthermore, we find a Ed,IF – EV ≈ 0.3 eV deep recombination-active acceptor state at the absorber/buffer interface made of air-light exposed CIGSe absorbers. This gives us the ability to explain the reduction of power conversion efficiency of solar cells made from air-light exposed absorbers. From the voltage dependent capacitance step of this interface defect we can deduce the formerly unknown position of the Fermi level at the hetero junction in equilibrium which is close to mid-gap. Simulation of dark J-V curves allows a refinement of the parameter of this absorber/buffer interface defect, resulting in a defect density of Nd,IF ≈ 3.5·1011 cm-2 as well as capture cross sections of σn ≈ 4·10-16 cm2 for electrons and σp ≈ 3·10-11 cm2 for holes.
关键词： device simulation,Cu(In,Ga)Se2,admittance spectroscopy,defect physics,solar cells
更新于2025-11-14 17:28:48
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The characteristics of Cu(In, Ga)Se2 thin-film solar cells by bandgap grading
摘要： The performance of CIGSe-1 and CIGSe-2 absorber layers are compared with Eg grading such that a higher Ga content is incorporated into the back region. A wider depth range of the high-Ga region near the back of a CIGSe absorber layer can reduce its performance due to the increased formation of Ga-related defects and defect clusters. Therefore, for an Eg-graded CIGSe layer with a wider Eg on the back surface, appropriate Eg grading can improve its performance.
关键词： CIGSe,bandgap grading,defect,surface potential,solar cell
更新于2025-11-14 17:28:48
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Defect dipole evolution and its impact on the ferroelectric properties of Fe-doped KTN single crystals
摘要： The ferroelectric and piezoelectric properties of doped potassium tantalum niobate crystals with different Fe doping amounts and the adjustability of the properties are investigated. The hysteresis loops and current density curves show that the defect dipoles have an obvious effect on domain reorientation, and the effect decreases with increasing doping amount. The ferroelectric and piezoelectric properties can be adjusted via the defect dipoles, and the adjustability is reduced with increasing doping amount. A change of the doping amount leads to defect dipole structure evolution in the crystals, in which the defect dipoles transform from a polar structure to a nonpolar structure, which is the reason for the transition of the domain reorientation determined by the defect dipoles. This result has proved that introducing defects is an effective way to improve and regulate perovskite properties, and the doping amount is one of the important factors controlling the defect dipoles.
关键词： Ferroelectric,domain orientation mechanism,defect dipoles,doping behavior
更新于2025-11-14 17:28:48
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Influence of aging on electrocaloric effect in Li+ doped BaTiO3 ceramics
摘要： Aging creates significant changes in the properties of the ferroelectric materials such as dielectric and piezoelectric properties. However, the influence of aging on the electrocaloric effect (ECE) has not yet been investigated. In this work, we investigate the effect of the aging on the ECE in acceptor (Li+) doped BaTiO3 ceramics. We observe that aging induced defect polarization (PD) reduces the saturation polarization of the doped samples until Tc=115 oC. Above that temperature PD loses its effectiveness and material behaves like a fresh sample. Suppression of polarization below TC due to aging effect results in a sharper slope change in the temperature dependence of electrical polarization in aged samples which causes an increase in the electrocaloric temperature change of Li+ doped BaTiO3 ceramics up to 23 % at TC. Above a critical Li doping amount, both negative and positive electrocaloric effect are observed in the same sample.
关键词： Aging,BaTiO3,Li-doping,Electrocaloric effect,Defect dipoles
更新于2025-11-14 17:28:48
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Construction of dual defect mediated Z-scheme photocatalysts for enhanced photocatalytic hydrogen evolution
摘要： The construction of Z-scheme system is a promising approach for photocatalytic hydrogen evolution (PHE). In this study, we fabricated a direct Z-scheme system consisting of defect-rich g-C3N4 nanosheets (DR-CNNS) crumpled nanosheets with defect-rich TiO2 (DR-TiO2) nanoparticles via a dual defective strategy. The optimized dual-defective rich TiO2/CNNS composite showed a superior PHE rate of ?651.79 μmol/h with a turnover frequency of ?419.3 h?1 as well as high stability and recyclability, which presented the highest value in single defective TiO2 or g-C3N4-based photocatalysts families reported previously. Furthermore, this protocol could also be extended to synthesize other dual defective g-C3N4/oxides (ZnO, SnO2, etc.) heterostructures. The improved photocatalytic performances could be ascribed to the following aspects: (1) rich dual defect, narrowing the band gap and providing more reactive sites for PHE; (2) intimate interface, facilitating interfacial migration and utilization of photogenerated charges; (3) Z-scheme structure, accelerating photogenerated electron-hole pair separation and thus leading to more e?cient PHE. Our work highlights the critical role of defects in construction of Z-scheme system and provides the possibility of utilizing dual defective g-C3N4-based systems for other photocatalytic applications including CO2 reduction and water puri?cation.
关键词： Photocatalytic hydrogen evolution,Dual defect,Oxides/g-C3N4,Heterojunction,Direct Z-scheme
更新于2025-11-14 15:27:09