Size Confinement Research Articles

Brownian Diffusion of Hexagonal Boron Nitride Nanosheets and Graphene in Two Dimensions.

Two-dimensional (2D) nanomaterials have numerous interesting chemical and physical properties that make them desirable building blocks for the manufacture of macroscopic materials. Liquid-phase processing is a common method for forming macroscopic materials from these building blocks including wet-spinning and vacuum filtration. As such, assembling 2D nanomaterials into ordered functional materials requires an understanding of their solution dynamics. Yet, there are few experimental studies investigating the hydrodynamics of disk-like materials. Herein, we report the lateral diffusion of hexagonal boron nitride nanosheets (h-BN and graphene) in aqueous solution when confined in 2-dimensions. This was done by imaging fluorescent surfactant-tagged nanosheets and visualizing them by using fluorescence microscopy. Spectroscopic studies were conducted to characterize the interactions between h-BN and the fluorescent surfactant, and atomic force microscopy (AFM) was conducted to characterize the quality of the dispersion. The diffusion data under different gap sizes and viscosities displayed a good correlation with Kramers' theory. We propose that the yielded activation energies by Kramers' equation express the magnitude of the interaction between fluorescent surfactant tagged h-BN and glass because the energies remain constant with changing viscosity and decrease with increasing confinement size. The diffusion of graphene presented a similar trend with similar activation energy as the h-BN. This relationship suggests that Kramers' theory can also be applied to simulate the diffusion of other 2D nanomaterials.

Colloidal one-pot synthesis and characterization of Glycine capped Al(x) doped ZnS QDs for efficient UV light assisted photo-degradation of Stilbene 420 dye

In thisstudy, successful synthesis and characterization of undoped and Al-doped ZnS quantum dots (QDs) capped with bio-friendly glycine (ZnSAl/Gly) are described. The synthesis is accomplished through a one-pot colloidal co-precipitation process, followed by the characterization of QDs using various analytical techniques.X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) showed the formation of cubic-faced ZnS QDs, with the crystal size decreasing as the amount of Al doping increased. A ZnS phase layer on the QDs surface was also demonstrated by Fourier-transform infrared spectroscopy (FTIR) measurements. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS) analysis was employed to examine the stoichiometry and shape of the synthesized QDs. Thermogravimetric analysis (TGA) showed a remarkable stability of Al-doped ZnS QDs over an extended period, enhancing their potential for a variety of applications. Measurements of the absorption band edge in the UV–Visible range demonstrated that Al ions were successfully incorporated into the ZnS lattice, causing a substantial red shift. This change, which caused the energy band gap to rise from 3.2 eV (ZnS/Gly) to 4.42 eV (ZnSAl1%/Gly), was attributed to the size confinement effect. The degradation of the Stilbene-420 dye under UV irradiation served as a test for the photodegradation capability of the synthesized QDs. The photodegradation efficiency of Al doping ranged from 60 % to 92 %, showing the induction of a significant number of crystalline structures with rising Al concentration. The Al-doped ZnS/Gly QDs are highly catalytic and photoactive, and they show great promise in the field of photoluminescence, medical and biological areas. Their potential for use as effective catalysts in waste water treatment methods is also remarkable.

Effects of anisotropy on the electronic structure and nonlinear optical rectification in a quantum dot with hydrogen molecular ion

In this study, the effects of anisotropy and quantum dot size on energy levels and nonlinear optical rectification of a D_{2}^{ + } molecular complex confined to a two-dimensional quantum dot are investigated. The energy eigenvalues and corresponding eigenfunctions of the resulting eigenvalue equation are obtained using the adiabatic approach and the two-dimensional diagonalization method. We conclude that the evolution of the energy spectrum depends predominantly on the anisotropy-induced change of geometric confinement size. In addition, it has been determined that the peak position of the nonlinear optical rectification shifts to lower or higher energies as the asymmetry of the system increases, depending on whether the QD is in the oblate or prolate case. This feature can be considered an advantage in tuning the nonlinear optical properties of systems based on two-dimensional semiconductor heterostructures.

Topology of ferroelectric nematic droplets: the case driven by flexoelectricity or depolarization field.

The recent discovery of ferroelectric nematics provides new opportunities for exploring polar topology in liquid matter. Here, we report numerous potential polarization topological states (e.g., polar vortex-like and line disclination mediated structures) in confined ferroelectric nematics with similar free-energy levels. In the experiment, they appear according to the confinement size and surface anchoring conditions. Based on a minimal analytical approach, we reveal that the topological transformation is balanced among the nematic elasticity, the polarization gradient, the flexoelectric and the depolarization interactions.

Numerical simulation of size effect in concrete-encased high-strength steel columns under axial compression

Concrete-encased steel (CES) columns are extensively utilized in practical engineering due to their outstanding performance. However, there have been limited studies on the size effect of CES columns. To investigate the influences of stirrup ratio, steel ratio, and steel strength grade on the axial capacity and the mechanism of the size effect of members under axial compression, a finite element (FE) analysis model that considers the interaction between the size effect and the confinement effect is established and verified. The study results demonstrate that the nominal stress of CES columns can be remarkably increased by employing high-strength steel and enhancing the steel ratio. However, the nominal stress decreases as the cross-sectional size of specimen increases, indicating the presence of the size effect. Moreover, increasing the steel strength grade, stirrup ratio, and steel ratio can decrease the degree of reduction of the nominal stress. Furthermore, comparison of the FE analysis findings and the calculation results of EN1994–1–1:2010(Europe), AISC360–16 (U.S.), and JGJ138–2016(China) revealed that the three codes fail to accurately assess the axial capacity of CES columns. The accuracy and safety reserve of the codes calculation results are even more inadequate for the larger cross-sectional specimens. Finally, a theoretical formula that considers the size effect and confinement effect is developed to calculate the bearing capacity of CES columns, and its applicability and reliability are verified.

Tunable Fe+3 and W+6 Co-doped BiVO4 nanohybrids with efficient photocatalytic and electrochemical chemical sensing characteristics

Metal-doped inorganic nanohybrids are platitudinous to have enormous prospects for optical, catalytic, sensing, energy, and electronic applications, owing to their inimitable properties associated with their size confinement and anisotropic geometry. In this regard, the present study is focused on the fabrication of tunable Fe+3 and W+6 co-doped BiVO4 nanohybrids for photocatalytic and electrochemical sensing applications. We synthesized Bi1-xFexV1-yWyO4 (BFVWO) nanostructures with varying compositions (x = 0.0, 0.25; y = 0, 0.01, 0.02, 0.04, and 0.06) using a sonication-assisted hydrothermal method. The developed nanostructures were physiochemically characterized by XRD, SEM, EDX, FTIR, XPS, UV–Vis, BET, PL, TOC, EPR, EIS, and CV spectroscopy measurements to investigate the phase purity, morphology, chemical purity, and optical properties. The physicochemical characterization revealed reduced crystallite size (from 89 to 82 nm), a tunable optical bandgap (from 2.42 to 2.13 eV), and an increased surface area with co-doping content. Among the samples, the Bi0.75Fe0.25V0.96W0.04O4 (BFVWO-4) nanohybrid exhibited remarkable potential for photocatalytic decomposition/degradation of water contaminants (CR and MO azo dyes) and showed an outstanding response against the electrochemical detection of methanol in a K2SO4 background. This study emphasizes the significance of selecting an appropriate electrolyte solution for accurate methanol sensing applications. BFVWO-4 exhibited superior analytical parameters compared to previously reported methanol sensors, with exceptional sensor sensitivity and a low limit of detection (LOD) at (S/N = 3) of 0.1 μM with an extended dynamic range spanning from 0.01 to 1 mM. It also offers insights and emerges a novel commencement for the prospective potential of Fe+3 and W+6 co-doped BiVO4 with exceptional photocatalytic degradation of water contaminants and outstanding sensitivity for methanol detection. These attributes position it as a prospective candidate for future applications in environmental and clinical monitoring.

Synchrotron-based UV resonance Raman spectroscopy probes size confinement, termination effects, and anharmonicity of carbon atomic wires

Vibrational and electronic properties and anharmonicity of sp-carbon atomic wires (i.e., polyynes) have been studied using resonance Raman spectroscopy, focusing on the confinement effects connected to their structure (length and termination). We exploited the fine tunability of the synchrotron radiation to resonantly excite short H-, CH3-, and CN-capped carbon atomic wires at their vibronic transitions in the deep UV. We report for the first time the resonance Raman spectra of size-selected CH3-capped polyynic wires (HCnCH3, n = 8–12) and CN-capped wires (HC6CN and HC12CN). We observed that the degree of π-electron conjugation increases with the wire length and is related to the specific termination. The analysis of multiple quanta Raman overtone bands shows that the anharmonic correction of the vibrational potential energy becomes increasingly relevant as the wire length increases. Finally, studying the vibronic lines of the UV absorption spectra allows the determination of an effective displacement parameter between the minima of the ground and the low-lying excited state, proving that the strong electron-phonon coupling of these systems is sensitive to chain length and termination.

Cation substitution and size confinement effects on structure, magnetism and magnetic hyperthermia of BiFeO3-based multiferroic nanoparticles and hydrogels

Highly crystalline BiFeO3 (BFO), Bi0.97Sm0.03FeO3 and BiFe0.97Co0.03O3 nanoparticles are synthesized via the chemical co-precipitation method after calcination at 600 °C in air for 2 h. The effect of cation substitution, Sm for Bi and Co for Fe, on the structural and magnetic properties of BFO nanoparticles is investigated, whereas their magnetically induced heating efficiency in radio frequency alternating magnetic fields is examined. X-ray diffraction indicates the formation of the R3c phase in all compounds, while the corresponding Rietveld refinement reveals a variation of the lattice parameters upon doping, suggesting structural distortion within the BFO lattice due to the ionic radii mismatch between doped and host elements. Transmission electron microscopy unveils smaller particle sizes for the doped nanoparticles, owing to the frustrated particle growth induced by the dopants, whose presence is verified by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. The combined effect of cation substitution and size confinement results in the suppression of the spiral spin structure of BFO, leading to the significantly enhanced magnetic features of the doped nanoparticles at room temperature. For possible applications in the biomedical sector, we tested them as heating agents in magnetic hyperthermia. The dispersion of BiFe0.97Co0.03O3 nanoparticles in water at a concentration of 4 mg/mL could reach the therapeutic window of 41–45 °C for cancer treatment in 50 mT at 375 kHz, whereas the remarkable temperature increase of the BFO-based multiferroic hydrogels, under the same conditions, is auspicious for an effective local treatment at reduced toxicity.

Focus on perovskite emitters in blue light-emitting diodes.

Blue perovskite light-emitting diodes (PeLEDs) are essential in pixels of perovskite displays, while their progress lags far behind their red and green counterparts. Here, we focus on recent advances of blue PeLEDs and systematically review the noteworthy strategies, which are categorized into compositional engineering, dimensional control, and size confinement, on optimizing microstructures, energy landscapes, and charge behaviors of wide-bandgap perovskite emitters (bandgap >2.5 eV). Moreover, the stability of perovskite blue emitters and related devices is discussed. In the end, we propose a technical roadmap for the fabrication of state-of-the-art blue PeLEDs to chase and achieve comparable performance with the other two primary-color devices.

Realizing the Lowest Bandgap and Exciton Binding Energy in a Two-Dimensional Lead Halide System.

Finding stable analogues of three-dimensional (3D) lead halide perovskites has motivated the exploration of an ever-expanding repertoire of two-dimensional (2D) counterparts. However, the bandgap and exciton binding energy in these 2D systems are generally considerably higher than those in 3D analogues due to size and dielectric confinement. Such quantum confinements are most prominently manifested in the extreme 2D realization in (A)mPbI4 (m = 1 or 2) series of compounds with a single inorganic layer repeat unit. Here, we explore a new A-site cation, 4,4'-azopyridine (APD), whose size and hydrogen bonding properties endow the corresponding (APD)PbI4 2D compound with the lowest bandgap and exciton binding energy of all such compounds, 2.19 eV and 48 meV, respectively. (APD)PbI4 presents the first example of the ideal Pb-I-Pb bond angle of 180°, maximizing the valence and conduction bandwidths and minimizing the electron and hole effective masses. These effects coupled with a significant increase in the dielectric constant provide an explanation for the unique bandgap and exciton binding energies in this system. Our theoretical results further reveal that the requirement of optimizing the hydrogen bonding interactions between the organic and the inorganic units provides the driving force for achieving the structural uniqueness and the associated optoelectronic properties in this system. Our preliminary investigations in characterizing photovoltaic solar cells in the presence of APD show encouraging improvements in performances and stability.

Thermal stimulated structural transformation of cubic Zn0.78Cd0.22S nanoparticles to ZnO nano-hexagons: Tailoring of optical band gap and emission spectra for optoelectronic implementations

Ternary alloys of Zn0.78Cd0.22S nanoparticles (NPs) are synthesized via the facile co-precipitation technique. The as-synthesized sample exhibits a zincblende-type cubic phase with an average crystalline size of 2 nm. Thermal annealing and UV irradiation are utilized as post-treatment processes for tailoring the optical properties of Zn0.78Cd0.22S NPs. The as-synthesized sample exhibits a stable cubic phase up to 400 °C, during which partial phase transformation to a hexagonal structure is observed at a higher temperature of 500 °C. The oxidation of Zn0.78Cd0.22S NPs to mixed oxide phases with the majority of ZnO begins at 600 °C which induces morphology transformation to a relatively large nano-hexagon with a single crystalline domain size. The increase of the annealing temperature is accompanied by a decrease of Zn0.78Cd0.22S NPs optical band gap (Eg) due to the weakness of size confinement as well as the formation of localized states below the mobility band edges. The brief UV irradiation results in the increase of Eg whereas a further increase in exposure time is accompanied by a reduction of Eg. The photoluminescence (PL) spectrum of the as-synthesized sample covers a wide spectral range from UV to visible. Thermal annealing has a slight effect on the PL emission at high excitation energy, whereas low excitation energy reveals higher sensitivity to deep-state emission. Thermal oxidation incorporates a high concentration of oxygen-related defects that induce strong enhancement in the green emission at the expense of UV emission. This indicates the thermal-induced bleaching of shallow trapping sites and the evolution of other deep trapping or recombination sites.

Sn-Induced Synthesis of Highly Crystalline and Size-Confined Si Nanorods at Moderately High Temperatures Using Hydrogen Silsesquioxane

Size-confined Si nanorods (NRs) have gained notable interest because of their tunable photophysical properties that make them attractive for optoelectronic, charge storage, and sensor technologies. However, established routes for fabrication of Si NRs use well-defined substrates and/or nanoscopic seeds as promoters that cannot be easily removed, hindering the investigation of their true potential and physical properties. Herein, we report a facile, one-step route for the fabrication of Si NRs via thermal disproportionation of hydrogen silsesquioxane (HSQ) in the presence of a molecular tin precursor (SnCl4) at a substantially lower temperature (450 °C) compared to those used in the synthesis of size-confined Si nanocrystals (>1000 °C). The use of these precursors allows the facile isolation of phase-pure Si NRs via HF etching and subsequent surface passivation with 1-dodecene via hydrosilylation. The diameters (7.7–16.5 nm) of the NRs can be controlled by varying the amount of SnCl4 (0.2–3.0%) introduced during the HSQ synthesis. Physical characterization of the NRs suggests that the diamond cubic structure is not affected by SnCl4, HF etching, and hydrosilylation. Surface analysis of NRs indicates the presence of Si0 and Sin+ species, which can be attributed to core Si and surface Si species bonded to dodecane ligands, respectively, and a systematic variation of the Si0:Si–C ratio with the NR diameter. The NRs show strong size confinement effects with solid-state absorption onsets (2.51–2.80 eV) and solution-state (Tauc) indirect energy gaps (2.54–2.70 eV) that can be tuned by varying the diameter (16.5–7.7 nm). Photoluminescence (PL) and time-resolved PL (TRPL) studies reveal size-dependent emission (1.95–2.20 eV) with short, nanosecond lifetimes across the visible spectrum, which trend closely with absorption trends seen in solid-state absorption data. The facile synthesis developed for size-confined Si NRs with high crystallinity and tunable optical properties will promote their application in optoelectronic, charge storage, and sensing studies.

Trace-level sensing of food toxins by flexible and cost-effective SERS sensors fabricated by pulsed-laser-deposition of gold nanoparticles on polycarbonate matrix

In viewpoint of rapid onsite screening of food contaminants, flexible surface enhanced Raman spectroscopy (SERS) sensors are developed by pulsed laser deposition process (PLD) with plasmonic gold nanoparticles (AuNPs) on the polycarbonate (PC) polymer matrix in the current study. PC/AuNPs with varying laser ablation pulses (200 NLP to 5000 NLP) tailored the morphological, structural and optical properties with their size and shape confinements. SERS properties of the prepared flexible PC/AuNPs sensors were optimized with Raman probe dye Rhodamine 6 G (R6G). Exorbitant SERS efficiency with highest enhancement factor of 1.1 × 108 was noted with sensor prepared at 3000 NLP (PA 3000 NLP). Sensor surface uniformity exhibited greater signal reproducibility with low values of % RSD (7.8). The fabricated flexible SERS sensor (PA 3000 NLP) achieved sensing of the food toxins effectively even in their trace levels of 10 − 10 M for methyl orange (MO) and 10 ppm for Butylated hydroxy anisole (BHA). Mechanism of SERS sensing dominated the electromagnetic enhancement was correlated well with their properties. Since SERS sensing need not require any intricate analyte pre-treatment, the fabricated PA 3000 NLP flexible SERS sensor can find the food toxins in rapid time (< 2 min), projecting a portable platform to conserve food safety.

Size-Dependent Behaviour of Hard Rock Under Triaxial Loading

Understanding size effects is important to rigorously analyse the behaviour of rocks and rock masses at different scales and for different applications. A number of empirical and numerical studies have included size effects on the uniaxial compressive strength of different rocks, but only few have focussed on the triaxial compressive strength. In this study, several triaxial tests were conducted on granite samples at different confinements (from 0.2 to 15 MPa) and sizes (from 30 to 84 mm in diameter). The most relevant strength parameters were recovered including peak and residual strengths, orientation and frictional response of shear bands. Size effects were observed to be less dominant at high confining pressures for both peak and residual strengths. The resulting data were analysed in the context of size-dependent rock strength theories. For peak strength analyses, the unified size effect law (USEL) and the improved unified size law (IUSEL) were used, in which the double trends, ascending descending behaviours were observed. Size-dependent Hoek–Brown modified failure criteria based on USEL and IUSEL were fit to peak strengths exhibiting a good agreement between the models and the laboratory data. The brittle-ductile transition and the frictional behaviour of shear band under triaxial loading were also analysed. A clear brittle behaviour was particularly observed in samples with large-diameters tested at low confinements. Finally, in regards to frictional behaviour, the shear band angle found to be affected by both confinement and sample size.

Collective migration of cells in geometric spaces: Intrinsic correlation length racing against extrinsic confinement size

Many experiments showed that cell groups can exhibit various impressive motion modes (e.g., global rotation and local swirling) in different-sized geometrical spaces, with the underlying mechanisms still unclear. However, recent experiments showed that different types of cells perform distinct motion modes (i.e., global rotation and coherent oscillation) in the same constraint conditions, which brings further puzzles on the movements of collective cells. Here, by comprehensively considering the social interactions between adjacent cells and internal mechanical processes of the cell itself, we propose an active vertex model to bring physical insights into collective cell migration in geometrical constraints. Using this model, we can reproduce all reported motion modes of cells in circular constraints observed in existing experiments. Specifically, as the confinement size decreases, local swirling and global rotation modes successively appear in cell groups with finite correlation length, while eccentric rotation and coherent oscillation modes successively emerge in cell groups with scale-free correlations. We demonstrate that these distinct modes are subtly coded by the intrinsic correlation length of cell groups and the extrinsic confinement size. Unexpectedly, we discover that, in small-size confinements, cell groups with scale-free correlations can spontaneously transition from eccentric rotation into coherent oscillation modes, because the strong social interactions reconcile the movements of all cells. In addition, we propose a velocity indicator that can directly distinguish migration modes emerging in small-scale confinements. These findings are in broad agreement with many experiments, and shed light on the spatiotemporal dynamics of active matter.

The Nature of the Low-Temperature Crossover of Water in Hard Confinement.

The dynamics of water confined in mesoporous MIP (2-3 nm pores in size) with silica gel (secondary silica; further, the abbreviation SG will be used) and MAP (10-35 nm pores in size) without SG borosilicate glasses have been studied by broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). MIP samples contain secondary silica inside the pores and provide a confinement size of about 2-3 nm, whereas MAP samples are free of secondary silica and provide a confinement size of about 10-35 nm. It is shown by BDS and NMR techniques that water exhibits a dynamic crossover of around 180 K when it is confined in MIP samples. By contrast, water confined in larger pores (MAP) does not exhibit any changes in its relaxation behavior. It is also shown that the crossover temperature depends on the hydration level (the higher the hydration level, the lower the crossover temperature). Below the crossover temperature, we find that water reorientation is isotropic (NMR) and that the temperature-dependent dielectric relaxation strength (BDS) follows the tendency expected for a solid-like material. In contrast, water reorientation is related to long-range diffusion above the crossover temperature, and the dielectric relaxation strength follows the tendency expected for a liquid-like material. Furthermore, the calorimetric results are compatible with crossing a glass transition near 180 K. Finally, the results are discussed within the Gibbs-Thomson model. In this framework, the crossover could be related to ice crystals melting.

Boosting cobalt ditelluride quantum-rods anode materials for excellent potassium-ion storage via hierarchical physicochemical encapsulation

The exploration of anode materials that can store large-sized K-ion to solve the poor kinetics and large volume expansion issues has become the key scientific bottlenecks hindering the development of potassium-ion batteries (PIBs). Herein, ultrafine CoTe2 quantum rods physiochemically encapsulated by graphene and nitrogen-doped carbon (CoTe2@rGO@NC) are regarded as anode electrodes for PIBs. Dual physicochemical confinement and quantum size effect not only enhance electrochemical kinetics but also restrain large lattice stress during repeated K-ion insertion/extraction process. Superior electronic conductivity, K-ion adsorption, and diffusion ability can be acquired for CoTe2@rGO@NC, confirmed through first-principles calculations and kinetics study. K-ion insertion/extraction proceeds via a typical conversion mechanism relying on Co as the redox site, where the robust chemical bond of COCo plays an important role in maintaining the electrode stability. Accordingly, CoTe2@rGO@NC contributes a high initial capacity of 237.6 mAh·g−1 at 200 mA·g−1, a long lifetime over 500 cycles with low-capacity decay of 0.10% per cycle. This research will lay the materials science foundation for the construction of quantum-rod electrodes.

Enzymatic Catalysis in Size and Volume Dual-Confined Space of Integrated Nanochannel-Electrodes Chip for Enhanced Impedance Detection of Salmonella.

Nanochannel-based confinement effect is a fascinating signal transduction strategy for high-performance sensing, but only size confinement is focused on while other confinement effects are unexplored. Here, a highly integrated nanochannel-electrodes chip (INEC) is created and a size/volume-dual-confinement enzyme catalysis model for rapid and sensitive bacteria detection is developed. The INEC, by directly sandwiching a nanochannel chip (60µm in thickness) in nanoporous gold layers, creates a micro-droplet-based confinement electrochemical cell (CEC). The size confinement of nanochannel promotes the urease catalysis efficiency to generate more ions, while the volume confinement of CEC significantly enriches ions by restricting diffusion. As a result, the INEC-based dual-confinement effects benefit a synergetic enhancement of the catalytic signal. A 11-times ion-strength-based impedance response is obtained within just 1min when compared to the relevant open system. Combining this novel nanoconfinement effects with nanofiltration of INEC, a separation/signal amplification-integrated sensing strategy is further developed for Salmonella typhimurium detection. The biosensor realizes facile, rapid (<20min), and specific signal readout with a detection limit of 9 CFU mL-1 in culturing solution, superior to most reports. This work may create a new paradigm for studying nanoconfined processes and contribute a new signal transduction technique for trace analysis application.

Influence of Losses, Device Size, and Mode Confinement on Integrated Micro-Ring Resonator Performance for Absorption Spectroscopy Using Evanescent Field Sensing

This work presents a detailed modeling-based analysis of integrated micro-ring resonators used for absorption spectroscopy. Generally, sensors based on micro-ring resonators detect changes in the real part of the sensing medium refractive index, at critical coupling. In absorption spectroscopy, however, micro-ring resonators are used to measure changes in the imaginary part of the index and are most sensitive away from critical coupling, with separate maxima in the under- and over-coupled regimes. In this work, we present a detailed analysis of the under-coupled regime, explaining the relationships between sensitivity, mode confinement, and losses. The analysis is based on reverse-symmetry waveguides to increase the proportion of mode power in the sensing medium and incorporates a realistic model of propagation losses based on experimental measurements of sidewall roughness. The analysis demonstrates that the resonant nature of the sensor is most effective at small radii compared to a non-resonant structure of equal size and shows a behavior of diminishing returns at larger device sizes regarding sensitivity and elevated proportions of mode power in the evanescent field.

Flame Retardant Polymer Nanocomposites: An Overview

AbstractThe overwhelming use of polymer as substitutes for metal, glass, wood, and ceramic has posed the challenge to develop polymer with flame retardant behavior after chemical modification and making composites for effective use of polymer in a wide range of applications. In this context, the present review article describes the advances in the preparation of flame retardant polymer nanocomposite (FPNC) along with the mechanism and properties. The evolved properties of FPNCs are discussed along with illustration and applications such as coating, sheet, and films for different applications in the light chemical composition, size confinement, and dimension alignments.