Defects In Nanostructures Research Articles

Imaging the distribution of a surface plasmon induced electromagnetic field at the nanoscale with MFSM

Surface plasmons play a crucial role in the fields of microscopic imaging, spectroscopy, semiconductor devices, nonlinear optics, and so on. However, there is still no robust method for characterizing the surface plasmon at the nanoscale. Here, an approach for the characterization of the surface plasmon at the nanoscale was proposed by imaging the distribution of surface plasmon-induced electromagnetic field using magnetic force spectroscopy microscopy (MFSM), and the visualization of its induced electromagnetic field is demonstrated by combining magnetic force spectroscopy with a 3D reconstruction algorithm. Furthermore, an inhomogeneous electromagnetic field caused by nanostructure defects is identified by 3D imaging. The experimental method and results are of great significance for the study of surface plasmon and their effect at the nanoscale. This technique proves invaluable for investigating surface plasmon and has great prospects in the testing and application for plasmon excitation, quantum dots, and nanosensors.

Luminescence and dielectric investigations of crystalline niobate nanoceramics prepared through aqueous chemical process

The present study reflects the synthesis of MgNb2O6 using hydrofluoric acid via a wet chemical approach, followed by characterizations involving XRD, electron microscopy, Raman spectroscopy, optical analyses, and impedance spectroscopy. The crystallite size of the synthesized material was determined to be 44 nm through XRD analysis. The lattice parameters of MgNb2O6 a, b, and c, were found to be 14.1998 Å, 5.6844 Å, and 4.9813 Å, respectively. Raman spectroscopy identified molecular bonds ranging from 253 to 1011 cm−1, mainly indicating the presence of metal oxide bonds. EDX spectra confirmed the presence of Mg, Nb, and O atoms in the prepared ceramics, indicating phase purity. FESEM analysis revealed a grain size of approximately 48 nm, with the presence of agglomerated grains. Bright spots in the SAED pattern observed by HRTEM confirmed the crystallinity of the prepared niobate materials, with the HRTEM microstructure showing a particle size near 49 nm. The crystallite size by XRD, grain size by FESEM, and particle size by HRTEM are in accordance with each other. The direct band gap was determined to be approximately 2.76 eV using UV-Visible spectroscopy. Additionally, MgNb2O6 materials exhibited a broad and strong photoluminescence emission near 445 nm with excitation at 270 nm, possibly indicating the presence of radiative defects in the crystalline nanostructure. Furthermore, impedance studies conducted between 40 and 110 MHz demonstrated a decrease in the dielectric constant at higher frequencies, reaching 21.06 at 110 MHz. A low dielectric loss was also observed at 110 MHz. The moderate band gap and strong room-temperature photoluminescence in the visible range make magnesium niobates suitable for possible applications in optical devices. This investigation shows that a dielectric constant near 21 and low dielectric loss can be achieved in the high-frequency range around 110 MHz.

Achieving white electroluminescence and low current consumption in devices based on graphene oxide and silicon

This work reports the emission of white electroluminescence (EL) in devices based on silicon. These devices are formed by a heterostructure of porous silicon (PSi), graphene oxide (GO), silicon-rich-oxide (SRO) thin films, and zinc oxide (ZnO) as a transparent conductor oxide (contact). The current consumption in these devices has been reduced by approximately three orders of magnitude compared to the current currents commonly reported for electroluminescent devices. The white EL emission is corroborated by the EL spectra, which are very broad (from 400 to 750 nm) and are attributed to the different nanostructured defects present in the materials that make up the heterostructures. The devices exhibited EL only in negative bias. According to our analysis of the I–V curves, the space-charge limited current conduction mechanism is the dominant carrier conduction mechanism in the region where the EL takes place. The electroluminescence exhibited by these devices starts at a current of 1.1 μA and is the entire area electroluminescent at approximately 3 μA reaches its maximum value at 9 μA. We demonstrated that producing LEDs on a Si substrate can result in significant energy savings.

Scatterometric defect measurements – uncertainty assessment by means of a virtual instrument and a statistical analysis

Defects in nanostructured surfaces have to be detected in or close to the manufacturing process in the production environment. For this purpose, scatterometry promises a non-contact approach with in-process capability. However, the achievable measurement uncertainty with a scatterometric measurement principle is difficult to assess by means of experiments. Especially for nano-surfaces with stochastic features, a large sample size is required. In addition, the influence of the natural uncertainty due to the inherent surface stochastics, which causes an ultimate uncertainty limit, remains hidden. Therefore, a virtual experimentation in combination with a statistical evaluation is proposed for the uncertainty assessment of scatterometric defect measurements of nanostructured surface. One virtual experiment calculates the scattered light distribution from a randomized modelled surface. For the uncertainty assessment, (a) multiple defective surfaces with the same defect grade are modelled, (b) the surfaces’ scattered light distributions are simulated, (c) the signal processing is applied for obtaining the virtual measurement results of the defect grade, and (d) the uncertainty is determined. The proposed virtual method is realized and demonstrated for defective ZnO nanograss surfaces, where the vacancy of nanograss is the studied defect as an example. As central results for the exemplarily studied defect grade measurement, the determined achievable mean uncertainty due to the nanostructure randomness is 3.2%, and the effect of the detector shot noise is negligibly small. Furthermore, the proposed method is universally applicable for any type of nanostructure/defect, and for any scatterometric principle, to clarify the respective potential for the reliable detection of nanostructure defects.

Insights into the Morphology and Structural Defects of Eu-Doped Ceria Nanostructures for Optoelectronic Applications in Red-Emitting Devices

Insights into the Morphology and Structural Defects of Eu-Doped Ceria Nanostructures for Optoelectronic Applications in Red-Emitting Devices

Greener approach for the synthesis of Ag decorated ZnO–CeO2 nanostructure using Moringa oleifera LE and its investigation as photocatalyst for degradation of ciprofloxacin and methylene orange

Green synthesis of silver decorated ZnO–CeO2 nanostructure (Ag@ZnO–CeO2 NS) mediated Moringa oleifera LE and its photocatalytic potential against ciprofloxacin antibiotic and Methylene orange dye under sunlight. The synthesized ZnO–CeO2 and Ag@ZnO–CeO2 NS were characterized using X-ray diffraction (XRD) analysis. The crystallite size and crystallinity were calculated to 74 nm and 89% respectively using XRD analysis. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of Ag, Zn, Ce and oxygen vacancies in green synthesized Ag@ZnO–CeO2 NS. Also, PL spectroscopy analysis showed the oxygen vacancies due to defects in nanostructure. The bandgap of prepared nanostructure was calculated to 2.0 eV by UV–visible spectroscopy analysis. Ag@ZnO–CeO2 NS average particles size was evaluated to 40 nm by scanning electron microscopy (SEM) analysis and energy-dispersive X-ray (EDX) analysis confirmed the presence of Ag, Zn and Ce in nanostructure. The Ag@ZnO–CeO2 NS showed an excellent Brunauer-Emmett-Teller (BET) surface area of 165 m2g-1 and 15 nm of pore diameter. Moreover, Fourier transform infrared (FTIR) spectroscopy was used to analyze chemical bonding and interaction and RAMAN spectroscopy confirmed the presence of oxygen vacancies. The thermal decomposition and heat flow was accessed by thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) The Ag@ZnO–CeO2 NS demonstrated great potential for environmental remediation which offered effective approach for the removal of Ciprofloxacin antibiotic and Methylene orange dye from wastewater with 74% and 85% photocatalytic activity respectively. The stability of catalyst after 5 cycles of reusability was evaluated by XRD analysis which showed the crystalline structure. This research contributes to the development of advanced nanomaterials with improved photocatalytic properties and the removal of emerging contaminants.

Heterogeneous nucleation on defects in MoS2 nanostructures as a proxy for assessing active sites for hydrogen production

In the present work, we applied heterogeneous nucleation of gold nanoparticles to assess the density of defects on MoS2 nanostructures presenting different morphologies and surface areas. The use of L-cysteine resulted in the formation of flower-shaped MoS2 nanostructures with a diameter of about 300 nm and petals measuring around 30 nm. In contrast, when 3-mercaptopropionic acid was employed, it led to the formation of large agglomerates, here referred to as nanoclouds, with a diameter of approximately 500 nm. The nucleation of gold nanoparticles on defect sites of MoS2 suggested that MoS2 obtained from 3-mercaptopropionic acid has a higher content of active sites for hydrogen production compared to MoS2 obtained from L-cysteine.

Antimicrobial cetylpyridinium chloride causes functional inhibition of mitochondria as potently as canonical mitotoxicants, nanostructural disruption of mitochondria, and mitochondrial Ca2+ efflux in living rodent and primary human cells

People are exposed to high concentrations of antibacterial agent cetylpyridinium chloride (CPC) via food and personal care products, despite little published information regarding CPC effects on eukaryotes. Here, we show that low-micromolar CPC exposure, which does not cause cell death, inhibits mitochondrial ATP production in primary human keratinocytes, mouse NIH-3T3 fibroblasts, and rat RBL-2H3 immune mast cells. ATP inhibition via CPC (EC50 1.7 μM) is nearly as potent as that caused by canonical mitotoxicant CCCP (EC50 1.2 μM). CPC inhibition of oxygen consumption rate (OCR) tracks with that of ATP: OCR is halved due to 1.75 μM CPC in RBL-2H3 cells and 1.25 μM in primary human keratinocytes. Mitochondrial [Ca2+] changes can cause mitochondrial dysfunction. Here we show that CPC causes mitochondrial Ca2+ efflux from mast cells via an ATP-inhibition mechanism. Using super-resolution microscopy (fluorescence photoactivation localization) in live cells, we have discovered that CPC causes mitochondrial nanostructural defects in live cells within 60 min, including the formation of spherical structures with donut-like cross section. This work reveals CPC as a mitotoxicant despite widespread use, highlighting the importance of further research into its toxicological safety.

Planar Defects as a Way to Account for Explicit Anharmonicity in High Temperature Thermodynamic Properties of Silicon

Silicon is indispensable in semiconductor industry. Understanding its high-temperature thermodynamic properties is essential both for theory and applications. However, first-principle description of high-temperature thermodynamic properties of silicon (thermal expansion coefficient and specific heat) is still incomplete. Strong deviation of its specific heat at high temperatures from the Dulong–Petit law suggests substantial contribution of anharmonicity effects. We demonstrate, that anharmonicity is mostly due to two transverse phonon modes, propagating in (111) and (100) directions, and can be quantitatively described with formation of the certain type of nanostructured planar defects of the crystal structure. Calculation of these defects' formation energy enabled us to determine their input into the specific heat and thermal expansion coefficient. This contribution turns out to be significantly greater than the one calculated in quasi-harmonic approximation.

Passivation-free high performance self-powered photodetector based on Si nanostructure-PEDOT:PSS hybrid heterojunction

Hybrid heterojunction between organic PEDOT:PSS and inorganic Silicon (Si) nanostructures is promising for high-performance self-powered photodetectors due to their favourable band energetics and ease of processing. Traditionally, Si nanostructures require additional passivation layers to reduce surface defect states, which adds complexity and involves the use of harmful organic solvents. Here in, we demonstrate a simple chemical polishing process to reduce defects and fabricate a conformable heterojunction between Si nanostructures and PEDOT:PSS. Si nanostructures fabricated by metal-assisted chemical etching (MACE) technique and subsequently treated by the chemical polishing process are spin-coated with PEDOT:PSS to form heterojunction and employed as self-powered broadband photodetector. The optimized device shows superior performance, such as high responsivity of 555.34 mA/W, quick rise/fall times of 79 ms/81 ms, high External Quantum Efficiency (EQE) of 0.8 at zero bias (0 V) and high photostability up to 500 illumination cycles. Dark I-V characteristics and carrier lifetime measurements reveal that the enhanced performance of chemically polished devices is attributed to the formation of a conformable heterojunction and reduction in defects in the Si nanostructures. Given the scalability and simplicity of the demonstrated passivation-free approach, this work may aid the fabrication of high-performance hybrid Si nanostructured photodetectors.

Variation in defects and properties in composite of ZnO and α-Fe2O3 for sustainable wastewater treatment

Defects in nanostructures play a pivotal role in determining their properties and performance in the desired applications. Herein, the defect states and structural properties of the bi-metal oxide composite of ZnO and α-Fe2O3 (ZF-W) are varied by annealing the composite at different temperatures. The changes in defects, structures, and phase are evaluated thoroughly using transmission electron microscopy, x-ray diffraction, photoluminescence, and Mössbauer spectroscopy techniques. The defect-rich ZF-W composite is found to be composed of defect-deficient ZnFe2O4 attaining the equilibrium state when as-synthesized ZF-W is annealed at 500 °C [ZF-W(500)]. Further annealing at 1000 °C, ZF-W(1000), a non-stoichiometric and highly defected ZnFe2O4 is evidenced in the composite. The changes in the composite with the annealing temperature are correlated with the cationic migration and evolution of defect states. Moreover, the transition associated with the vacancy defects, which trapped the excited electron and dispel the free electrons, thereby inhibiting fast electron–hole pair recombination, is corroborated from the photoluminescence spectra. When implemented for methyl blue adsorption/degradation without the assistance of any external sources, the degradation efficiency of ZF-W, ZF-W(300), ZF-W(500), and ZF-W(1000) is found to be 86%, 84%, 68%, and 82%, respectively. The prepared samples are highly stable and can be used repeatedly without losing effectiveness. The simultaneous evolution of defects and structural properties of the composite are attributed for the variation in methyl blue adsorption/degradation. The present study reveals the importance of defects present in the mixed metal oxide composite in obtaining high-performance dye degradation/adsorption properties for sustainable wastewater treatment.

Hybrid Coating of Polystyrene–ZrO2 for Corrosion Protection of AM Magnesium Alloys

A hybrid material of polystyrene (PS)–ZrO2 was developed by the sol–gel technique and deposited by spin-coating on AM60 and AM60–AlN nanocomposite surfaces to enhance corrosion resistance in marine environments. PS–ZrO2 with an average thickness of ≈305 ± 20 nm was dispersed homogeneously, presenting isolated micro–nano-structure defects with air trapped inside, which led to an increase in roughness (≈4 times). The wettability of the coated substrates was close to the hydrophobic border (θCA=90°–94°). The coated samples were exposed for 30 days to SME solution, simulating the marine–coastal ambience. The initial pH = 7.94 of the SME shifted to more alkaline pH ≈ 8.54, suggesting the corrosion of the Mg matrix through the coating defects. In the meantime, the release of Mg2+ from the PS–ZrO2-coated alloy surfaces was reduced by ≈90% compared to that of non-coated. Localized pitting attacks occurred in the vicinity of Al–Mn and β–Mg17Al12 cathodic particles characteristic of the Mg matrix. The depth of penetration (≈23 µm) was reduced by ≈85% compared to that of non-coated substrates. The protective effect against Cl ions, attributed to the hybrid PS–ZrO2-coated AM60 and AM60–AlN surfaces, was confirmed by the increase in their polarization resistance (Rp) in 37% and 22%, respectively, calculated from EIS data.

Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures.

In this study, three different morphologies, nanoflower (NF), nano sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures were synthesized successfully via a mild hydrothermal method. After synthesis, the samples were annealed in the atmosphere at 300, 600, and 800 °C. Although annealing provides different degradation kinetics for different morphologies, ZnO NS performed significantly better than other morphologies for all annealing temperatures we used in the study. When the photoluminescence, electron paramagnetic resonance spectroscopy, BET surface, and X-ray diffraction analysis results are examined, it is revealed that the defect structure, pore diameter, and crystallinity cumulatively affect the photocatalytic activity of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity in rhodamine B (RhB) degradation, it is necessary to develop a ZnO catalyst with fewer core defects, more oxygen vacancies, near band emission, large crystallite size, and large pore diameter. The ZnO NS-800 °C nanocatalyst studied here had a 35.6 × 10-3 min-1 rate constant and excellent stability after a 5-cycle photocatalytic degradation of RhB.

Optically Coherent Nitrogen-Vacancy Defect Centers in Diamond Nanostructures

An analysis and improvement of the spectral properties of nitrogen-vacancy defects in diamond nanostructures paves the way for efficient entanglement generation necessary for many quantum information applications.

The influence of sample mass (scaling effect) on the synthesis and structure of non-graphitizing carbon (biochar) during the analytical pyrolysis of biomass.

The porous non-graphitizing carbon (NGC) known as biochar is derived from the pyrolytic conversion of organic precursors and is widely investigated due to its multifunctional applications. At present, biochar is predominantly synthesized in custom lab-scale reactors (LSRs) to determine the properties of carbon, while a thermogravimetric reactor (TG) is utilized for pyrolysis characterization. This results in inconsistencies in the correlation between the structure of biochar carbon and the pyrolysis process. If a TG reactor can also be used as an LSR for biochar synthesis, then the process characteristics and the properties of the synthesized NGC can be simultaneously investigated. It also eliminates the need for expensive LSRs in the laboratory, improves the reproducibility, and correlatability of pyrolysis characteristics with the properties of the resulting biochar carbon. Furthermore, despite numerous TG studies on the kinetics and characterization of biomass pyrolysis, none have questioned how the properties of biochar carbon vary due to the influence of the starting sample mass (scaling) in the reactor. Herein, with a lignin-rich model substrate (walnut shells), TG is utilized as an LSR, for the first time, to investigate the scaling effect starting from the pure kinetic regime (KR). The changes in the pyrolysis characteristics and the structural properties of the resultant NGC with scaling are concurrently traced and comprehensively studied. It is conclusively proven that scaling influences the pyrolysis process and the NGC structure. There is a gradual shift in pyrolysis characteristics and NGC properties from the KR until an inflection mass of ∼200 mg is reached. After this, the carbon properties (aryl-C%, pore characteristics, defects in nanostructure, and biochar yield) are similar. At small scales (≲100 mg), and especially near the KR (≤10 mg) carbonization is higher despite the reduced char formation reaction. The pyrolysis is more endothermic near KR with increased emissions of CO2 and H2O. For a lignin-rich precursor, at masses above inflection point, TG can be employed for concurrent pyrolysis characterization and biochar synthesis for application-specific NGC investigations.

Unraveling the Supramolecular Structure and Nanoscale Dislocations of Bacterial Cellulose Ribbons Using Correlative Super-Resolution Light and Electron Microscopy.

Cellulose is a structural linear polysaccharide that is naturally produced by plants and bacteria, making it the most abundant biopolymer on Earth. The hierarchical structure of cellulose from the nano- to microscale is intimately linked to its biosynthesis and the ability to process this sustainable resource for materials applications. Despite this, the morphology of bacterial cellulose microfibrils and their assembly into higher order structures, as well as the structural origins of the alternating crystalline and disordered supramolecular structure of cellulose, have remained elusive. In this work, we employed high-resolution transmission electron and atomic force microscopies to study the morphology of bacterial cellulose ribbons at different levels of its structural hierarchy and provide direct visualization of nanometer-wide microfibrils. The non-persistent twisting of cellulose ribbons was characterized in detail, and we found that twists are associated with nanostructural defects at the bundle and microfibril levels. To investigate the structural origins of the persistent disordered regions that are present along cellulose ribbons, we employed a correlative super-resolution light and electron microscopy workflow and observed that the disordered regions that can be seen in super-resolution fluorescence microscopy largely correlated with the ribbon twisting observed in electron microscopy. Unraveling the hierarchical assembly of bacterial cellulose and the ultrastructural basis of its disordered regions provides insights into its biosynthesis and susceptibility to hydrolysis. These findings are important to understand the cell-directed assembly of cellulose, develop new cellulose-based nanomaterials, and develop more efficient biomass conversion strategies.

Morphology-Controlled Reststrahlen Band and Infrared Plasmon Polariton in GaN Nanostructures.

Due to ultrabright and stable blue light emission, GaN has emerged as one of the most famous semiconductors of the modern era, useful for light-emitting diodes, power electronics, and optoelectronic applications. Extending GaN's optical resonance from visible to mid- and-far-infrared spectral ranges will enable novel applications in many emerging technologies. Here we show hexagonal honeycomb-shaped GaN nanowall networks and vertically standing nanorods exhibiting morphology-dependent Reststrahlen band and plasmon polaritons that could be harnessed for infrared nanophotonics. Surface-induced dipoles at the edges and asperities in molecular beam epitaxy-deposited nanostructures lead to phonon absorption inside the Reststrahlen band, altering its shape from rectangular to right-trapezoidal. Excitation of such surface polariton modes provides a novel pathway to achieve far-infrared optical resonance in GaN. Additionally, surface defects in nanostructures lead to high carrier concentrations, resulting in tunable mid-infrared plasmon polaritons with high-quality factors. Demonstration of morphology-controlled Reststrahlen band and plasmon polaritons make GaN nanostructures attractive for infrared nanophotonics.

Diagnosis of a periodic nanostructure with a defect using circularly polarized light

The paper considers the reflection of a circularly polarized light wave from a periodic nanostructure. The method of characteristic matrices was used to calculate the ellipsometric parameters ρ 0 and Δ of reflected light. It is shown that a wave initially polarized in the left circle changes polarization upon reflection, turning into an elliptically polarized wave. The results obtained for an ideal periodic medium are compared with the results of reflection from a periodic medium with a single defect - the upper layer of the original periodic medium is replaced by an absorbing dielectric layer. The analysis showed that the spectral dependences of the ellipsometric parameters for two structures, periodic and defective, differ significantly. In the range of wavelengths λ from 0.4 μm to 0.6 μm, the ellipsometric parameter ρ 0 for the considered periodic medium and the medium with a defect differ significantly from each other - where the maximum is for one medium, there is approximately the minimum for the other. In turn, the parameter Δ demonstrates a significant difference for the two structures in the wavelength range λ from 0.46 μm to 0.55 μm. The use of circularly polarized light demonstrates wide possibilities for studying defects in periodic nanostructures.

A novel GSH-capping MXene QD-based ECL biosensor for the detection of miRNA221 in triple-negative breast cancer tumor

In this work, we have constructed a novel electrochemiluminescence (ECL) biosensor for the detection of miRNA221 based on glutathione-capped MXene-derived quantum dots (GSH-MQDs) and magnetic biomimic vesicles. Glutathione is used as precursor in the synthesis of MXene-derived QDs, which effectively improves the oxidation resistance of MXene. In the sensing system, GSH-MQDs still possess the advantages of MXene, including the excellent electrical conductivity and good electrochemical activity. The combination of the metal atoms on the MXene and the sulfhydryl group of GSH further reduce the defects in nanostructures of MXene-derived QDs. As a result, the stability and the luminescent properties of GSH-MQDs as ECL emitter have been significantly improved. Furthermore, magnetic biomimic vesicles are prepared as sensing platform to improve the feasibility and sensitivity for the miRNA221 detection. Moreover, a sensing strategy for miRNA221 detection is designed based on the cyclic amplification with T7 exonuclease. The biosensor is used to detect miRNA221 in the triple-negative breast cancer tumor tissues. The satisfactory results have indicated that this sensing strategy on the basis of GSH-MQD and magnetic biomimic vesicles possesses great potential for clinical analysis.

Tailoring the Mn–O Covalency and Surface Oxygen Defects of Ferrite Nanostructures for Peroxymonosulfate Activation and Norfloxacin Degradation

Tailoring the Mn–O Covalency and Surface Oxygen Defects of Ferrite Nanostructures for Peroxymonosulfate Activation and Norfloxacin Degradation