Size-dependent Efficiency Research Articles

Enhanced size-dependent efficiency of InGaN/AlGaN near-ultraviolet micro-LEDs

This study presents an approach for enhancing the external quantum efficiency (EQE) of multiple-quantum-well InGaN/AlGaN near-ultraviolet (NUV) micro-light-emitting diodes (micro-LEDs) without changing the epitaxial layer. Unlike the size-dependent EQE reduction observed in blue, green, and red micro-LEDs, the EQE of NUV micro-LEDs at high current densities (≥10 A/cm2) improves as the device dimensions shrink from 500 × 500 μm2 to 20 × 20 μm2. A 20 × 20 μm2 micro-LED achieves a peak EQE of 12.3%, compared to 8.60% for a larger 500 × 500 μm2 micro-LED. Experimental results attribute this EQE enhancement to improved light-extraction efficiency, driven by better current spreading. In larger micro-LEDs, pronounced current crowding causes carrier overflow from the active region, leading to reduced EQE at high current densities. These findings highlight the promising potential of NUV micro-LEDs for diverse applications.

Lateral Carrier Diffusion in Ion-Implanted Ultra-Small Blue III-Nitride MicroLEDs.

Ultrasmall micro-light-emitting diodes (μLEDs), sized below 10 μm, are indispensable to create the next-generation augmented and virtual reality (AR/VR) devices. Their high brightness and low power consumption could not only enhance the user experience by providing vivid and lifelike visuals but also extend device longevity. However, a notable challenge emerges: a decrease in efficiency with a reduced size. This study casts light on this critical issue by investigating the lateral carrier diffusion in ion-implanted μLEDs. The implanted area restricts the carrier injection and defines the μLED size to diameters of 10, 5, and 2 μm without introduction of nonradiative recombination centers in the quantum well area. We observed a drop of efficiency for smaller devices, similar to the case of conventional μLEDs with etched sidewalls. Electroluminescence of μLEDs was studied using a Gaussian beam telescope to analyze light intensity profiles and hence the spatial carrier distribution within the active region of μLEDs. Lateral diffusion length was determined to be 11.2 μm at j = 1 A/cm2 and decreased down to 2.4 μm for j = 1000 A/cm2. We explain the underlying mechanism behind the size-dependent efficiency observed in μLEDs, attributed to lateral carrier diffusion.

A Critical Review on the Experimental Setups Used to Assess the Efficiency of Respirators Against Ambient Particulate Matter

Fine particulate matter (PM2.5) poses significant health risks, prompting public health organizations to recommend the use of respirators and facemasks (RFMs) to mitigate exposure. Consequently, interest in their usage has increased, leading to several studies assessing the efficiency of these personal-level interventions against various fractions of ambient particulate matter (PM). We conducted a comprehensive literature search across PubMed, Web of Science, and Scopus to identify relevant studies and address the following objectives: (1) explore the efficiency of RFMs in reducing ambient PM; (2) discuss discrepancies in efficiencies reported; (3) critique the experimental setups used to evaluate the efficiency of RFMs; and (4) propose recommendations for future research. Five relevant studies we reviewed reported significantly lower RFM effectiveness against ambient PM, with a size-dependent efficiency that decreases for smaller PM fractions. Variations in the reported efficiencies were primarily attributed to design-related factors, resulting in poor facial fit. Therefore, it is crucial to consider standardizing and properly designing these products. These studies overlooked essential factors, such as using dummy heads with flexible textures that mimic human skin. The use of rigid-textured dummy heads, as seen in previous studies, may fail to accurately represent real-world conditions. We recommend researchers take into account diverse facial profiles in their experiments. Moreover, it is essential to consider facial characteristics in the design of RFMs. We believe the evidence supports the increasing need for the adoption of appropriate guidelines and regulations to govern RFM suppliers at both national and international levels.

Advances in InGaN-based RGB micro-light-emitting diodes for AR applications: Status and perspective

Micro-light-emitting diodes (µLEDs) are gathering significant interest as a technology for emerging micro-displays. However, µLEDs encounter numerous obstacles, including size-dependent efficiency loss, poor efficiency of red µLEDs, and challenges associated with the mass transfer and integration of full-color µLEDs. These issues become more acute in ultra-small µLEDs (<5 µm), which were required by the augmented reality (AR) displays. Here, we discuss the principal challenges faced by µLEDs and explore the possible solutions. We highlight recent advances in InGaN-based RGB µLEDs tailored for AR displays. In particular, we discuss the advancements in ultra-small InGaN µLEDs scaled down to 1 µm, the developments in InGaN red µLEDs, and the implementation of tunnel junction-based cascaded InGaN µLEDs for monolithic integration.

Enhanced size-dependent efficiency of removal of ultrafine particles: New solution of two-stage electrostatic precipitator with thermophoresis

Two-stage electrostatic precipitators (ESPs) are effective at removing ultrafine particles (UFPs) from gases; however, they fall short in capturing particles with diameters of less than 100 nm. In this study, an effective solution for removal of particles smaller than 300 nm was proposed. Our self-designed system combines a two-stage ESP with thermophoresis. We employed a combination of experimental and numerical simulation methods to examine the effects of temperature and thermophoresis on particle removal efficiency influenced by electrostatic forces. In our experiments, particle removal efficiency was positively correlated with gas temperature up to 75 °C, beyond which removal efficiency was no longer correlated with temperature. The findings also indicate that the introduction of thermophoresis improves particle removal efficiency, with the maximum increase approaching 8 %. However, this effect only occurs for particles smaller than 50 nm. The increase in the length of the thermophoresis segment and the decrease in inlet gas flow rate both enhance particle removal efficiency due to thermophoresis. Numerical simulations confirmed the experimental finding that nanoscale particles are more easily captured at higher temperatures. The simulations also revealed that the primary reasons for the enhanced removal efficiency are twofold: greater electric field strength and higher particle charge resulting from a higher temperature.

Nanomatryoshka as a nano-material for use in laser-induced hyperthermia in biological tissues: A multiphysics-based computational modeling approach

The growing demand for efficient and biocompatible materials in laser-induced medical hyperthermia applications has led us to investigate a novel material known as the gold nanomatryoshka. This unique structure, composed of three superimposed layers (Au–SiO2–Au), offers significant advantages over conventional plasmonic structures, such as gold nanorods, due to its spherical geometry and potential for achieving the highest available density. In this study, our primary motivation is to explore the tunable optical absorption properties of the gold nanomatryoshka by adjusting the core radius and the thickness of its two outer layers (shells). By applying the Mie theory to calculate the interaction of light with gold nanomatryoshka, the absorption and scattering cross sections of these structures were obtained. Additionally, by employing the Monte Carlo method (photon transport within biological tissue) and combining with the bioheat equation (thermal analysis in the tissue), the temperature distribution inside the tissue was obtained. The key aim of our research is to establish a robust computational modeling methodology for assessing the size-dependent efficiency of the gold nanomatryoshka in medical hyperthermia applications. The tunability of its optical properties, enabled by its unique structure, holds immense promise for optimizing its performance in laser-based cancer treatments and other biomedical applications.Present study concludes with the successful demonstration of the gold nanomatryoshka's potential for enhancing the effectiveness of laser-based cancer treatment. Furthermore, its biocompatibility, attributed to the outer gold layer, makes it a compelling candidate for treatment, particularly in nanoparticle-based treatments of cancer within organs like the prostate. The significance of this research lies in its contributions to the design and implementation of the gold nanomatryoshka in medical hyperthermia applications. By addressing concerns related to core-shell structures (Au–SiO2), our findings pave the way for developing more effective and targeted therapeutic strategies, thus advancing the field of laser-induced medical hyperthermia and its applications in cancer treatment.

Size-dependent photocatalytic inactivation of Microcystis aeruginosa and degradation of microcystin by a copper metal organic framework

Water eutrophication has led to increasingly serious algal blooms (HABs) that pose significant threats to aquatic environmental and human health. Differently sized copper metal organic frameworks (Cu-MOFs), including Cu-MOF-1 (30 nm), Cu-MOF-2, (40 nm), Cu-MOF-3 (50 nm), and Cu-MOF-4 (1 µm×100 nm), were synthesized. Their performance in inactivating Microcystis aeruginosa and degrading microcystin was assessed at the concentration of 0–60 mg/L under visible light irradiation for 6 h. The photocatalytic antialgal activity of Cu-MOF-4 was 10.5%, 14.2%, and 31.2% higher than that of Cu-MOF-3, Cu-MOF-2, and Cu-MOF-1; the efficacy in photocatalytic degradation of microcystin induced by Cu-MOFs also exhibited significant size-dependent efficiency, where Cu-MOF-4 was 2.6-, 1.8-, and 2.0-fold of Cu-MOF-3, Cu-MOF-2, and Cu-MOF-1, respectively. Cu-MOF-4 had greater performance than other Cu-MOFs could attributed to: 1) Cu-MOF-4 is easier to interact with algal cells due to its lower surface negative charge and higher hydrophobicity, resulting in more photocatalyst-algae heteroaggregates formation; 2) Cu-MOF-4 had greater electron-hole pairs separation ability, thus exhibiting higher reactive oxygen species (ROS) production; 3) Cu-MOF-4 had greater hydrostability than other Cu-MOFs, leading to more sustained ROS generation. Additionally, the reusability of Cu-MOF-4 was also greater than other Cu-MOFs.

Aerosol optical properties calculated from size distribution measurements: An uncertainty study

We use Monte Carlo uncertainty propagation to estimate the uncertainty of aerosol scattering coefficients, σs, that have been derived from measured particle size distributions. We consider the particular case where the size distributions are measured using a combination of a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). Uncertainties that are propagated include those intrinsic to the instruments and those that arise from variabilities in aerosol microphysical properties, including particle shape, density, and complex refractive index. Particular emphasis is put on the size dependent counting efficiency of both instruments which have weaknesses in a particle size range that dominates aerosol optical properties. The T-matrix method is utilized to simulate the effect of particle shapes on σs. To narrow the probability distribution of aerosol properties we discuss uncertainties for a single geographic location, which is the Southern Great Plains site (SGP) of the Department of Energy’s Atmospheric Radiation Measurement (ARM) User Facility. We estimate a 95% confidence interval for σs between −40% and +68%. A partial dependence analysis, for which we use generalized additive models, identifies uncertainties in counting efficiency and particle shapes as the dominant contributors to the size of the confidence interval.

Investigation of size and barrier dependent efficiency in InAs quantum dot solar cells

Semiconductor Quantum Dots have unique properties, such as the quantum size effect that provide the breakthrough in optoelectronic devices. The small effective mass of electron and hole open-up an avenue of wide bandgap tunability in InAs Quantum Dots (QDs), making them an attractive material for solar cell application. Therein, 4x4 Luttinger Kohn Hamiltonian method is used to calculate the absorption co-efficient of epitaxially grown InAs QDs. Further, we studied the size-dependent absorption co-efficient and the barrier material model of InAs QDs capping with InP and GaAs. Our theoretical simulation predicts the efficiency of InAs/GaAs and InAs/InP system in the intrinsic layer of p-i-n structure solar cells.

Investigating the potential of escape openings and reduced mesh size to optimize snow crab (Chionoecetes opilio) pot catches in the Barents Sea

In the Barents Sea Norwegian pot fishery for snow crab (Chionoecetes opilio), fishing effort regulations and bait expenses create incentives to improve the catch rates. The fishery also currently captures a large proportion of sub-legal sized crab which must be sorted out and released. In this study, we used comparative fishing trials to determine the size dependent capture efficiency of three modified pot types designed to address these issues. A pot constructed with 40 mm mesh caught ∼35% more (CPUE, number of individuals per soak time) large crab (≥ 100 mm carapace width [CW]) than the pot typically used in the commercial fishery (140 mm mesh). However, it also retained massive amounts of small individuals (< 100 mm CW). The addition of four stadium shaped escape openings into the 40 mm and 140 mm mesh designs resulted in large reductions in catches of small crab, but also a ∼30% reduction in large crab. Analysis of size dependent catch comparison rates and selectivity parameters supported the CPUE findings. Of the tested designs, catches were best optimized by the currently used commercial pot. However, we conclude that a small mesh pot with escape openings has the potential to increase catches of large crab and reduce catches of non-commercial small crab. Further development of this design, particularly in terms of the dimensions of the escape openings, is therefore required.

Influence of wafer quality on chip size-dependent efficiency variation in blue and green micro light-emitting diodes

We propose a key factor associated with both surface recombination velocity and radiative efficiency of an LED to estimate its chip size-dependent radiative efficiencies. The validity of the suggested factor is verified through experimental comparison between various LED wafers. Efficiencies of micro-LEDs from a blue and two green LED wafers are examined by temperature-dependent photoluminescence experiments. Surface recombination velocities are extracted from chip size dependent time-resolved PL results. Possible explanations on the reason why two green wafers show different properties are also given. With the suggested factor, we can provide more accurate prediction on the chip size-dependent efficiency of an LED wafer.

Influence of grain size on dynamic characterizations of laser-driven grain ejection

When intense laser pulse irradiates a target surface, the energetic processes of generation and expansion of laser-induced plasma will affect a localized pressure impulse around the irradiation zone. As a result, pulsed laser ablating granular target can drive a physical phenomenon of grain ejection. In this work, taking dry glass beads with different grain sizes as an example of granular targets and using high-speed video camera, we experimentally investigate the grain-size dependent dynamics of grain ejection driven by nanosecond laser pulses. The measured video sequences clearly exhibit that the laser-driven grain ejection process can be separated into two regimes: early-stage fast ejecting process and later-stage slow ejecting process. We find that there exists an obvious grain size effect on the kinetic energy of grains in the early-stage ejecting process. In addition, the temporal evolution of transient ejection of a curtain diameter &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ D\left(t\right) $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; corresponding to the later-stage ejecting process obeys the well-known “point source” law, &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$ {D\left(t\right)=\alpha t}^{\beta } $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, where both parameters &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$ \alpha $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$ \beta $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; depend on grain size. The observations mentioned above can be reasonably explained by considering the grain size dependent efficiency of impulse coupling between grain and plasma flow and plasma features generated by interaction of laser pulse with granular targets. These experimental results improve the understanding of the mechanism of laser-driven grain ejection.

Statistical capillary tube model for porous filter media: An application in modeling of gasoline particulate filter

A new statistical capillary tube model is presented to predict both filtration efficiency and permeability of particulate filters. The model considers the porous structure of the filter media as an assembly of curved capillary tubes with a statistical size distribution. The key model descriptors of pore microstructure are porosity, pore size, pore size distribution, and tortuosity. The model was validated by permeability and size dependent filtration efficiency measurements of bare and washcoated gasoline particulate filters (GPFs), using porosimetry data of the filter media as model inputs. Comparing with a more widely used spherical model for particulate filters with typical porosity range of 30–60%, the capillary tube model has similar input parameters but provides additional permeability prediction as well as better filtration predictions over a wider porosity range including the lower porosity of washcoated filters. Furthermore, it offers a more visually straightforward and intuitive correlation between filtration paths and filter performance. This allows convenient adoption of the capillary tube model in numerous applications that are currently based on spherical model assumption and provides improved guidance for filter optimization. Beyond ceramic automotive exhaust filters, this geometric model offers a new framework for examining porous filter media in general.

Synthesis of NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 nanorods and their size dependent uptake efficiency under flow condition

Lanthanide doped fluorescent nanoparticles have gained considerable attention in biomedical applications. However, the low uptake efficiency of nanoparticles by cells has limited their applications. In this work, we demonstrate how the uptake efficiency is affected by the size of nanoparticles under flow conditions. Using the same size NaYF4:20% Yb3+,2% Er3+,2% Ce3+ (the contents of rare earths elements are in molar fraction) nanoparticles as core, NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 core–shell structured nanorods (NRs) with different sizes of 60–224 nm were synthesized by thermal decomposition and hot injection method. Under excitation at 980 nm, a strong upconversion green emission (541 nm, 2H11/2 → 4I15/2 of Er3+) is observed for all samples. The emission intensity for each size nanorod was calibrated and is found to depend on the width of NRs. Under flow conditions, the nanorods with 96 nm show a maximum uptake efficiency by endothelial cells. This work demonstrates the importance of optimizing the size for improving the uptake efficiency of lanthanide-doped nanoparticles.

Uncertainty of laboratory and portable solid particle number systems for regulatory measurements of vehicle emissions

In the European Union’s emissions regulations, limits for solid particles >23 nm are applicable for the type-approval and in use compliance of vehicles. Consequently, particle number (PN) systems are used very often for both research and development of engines and vehicles, both in the laboratory and on the road. The technical specifications of the laboratory and portable on-board systems are not the same resulting in different measurement uncertainties. Furthermore, particles, in contrast to gases, can be lost in the transfer lines making comparisons at different sampling locations difficult. Moreover, the size dependent counting efficiency of the systems can result in high discrepancies when the measured particle sizes are close to the decreasing steep part of the curves. The different sampling locations (tailpipe or dilution tunnel) and thermal pretreatments of the aerosol further enhance the differences. The studies on the measurement uncertainty are scarce, especially for the PN systems measuring from 10 nm that will be introduced in the future regulations. This study quantified the uncertainty sources of the PN systems: (i) due to the technical requirements and the calibrations, (ii) due to the unknown particle sizes during measurement, (iii) due to particle losses from the vehicle to the PN systems at the tailpipe or the dilution tunnel, (iv) other parameters needed for the calculation of the emissions, non-related to the PN systems, e.g. flow and distance. The expanded uncertainty of the 23 nm laboratory systems sampling from the dilution tunnel was estimated to be 32%, with 18% originating from the calibration procedures, while of those sampling from the tailpipe 34%. For the 23 nm portable systems measuring on-road the uncertainty was 39%. The values were 2–8% higher for the 10 nm systems.

Size-dependent optical-electrical characteristics of blue GaN/InGaN micro-light-emitting diodes.

To derive the impact of chip size reduction on optical efficiency in micro-LED array panels, blue InGaN/GaN LEDs, which consist of 21×7 arrays (60 ppi display) with different mesa sizes on sapphire substrates, are designed and fabricated in this study. Changing the mesa area of the chip is first proposed to investigate the luminous efficiency (cd/A) of the screen. The current efficiency with a peak wavelength of 450 nm reaches up to 14.29 cd/A for the biggest pixel 50µm×60µm and to 12.25 cd/A for the 15µm×25µm chip, delivering high-level efficiencies to the current LED research field. The mechanisms of size-dependent efficiency variation trends and efficiency droops of blue LEDs are investigated experimentally, confirming that the current efficiency is more efficient at high injection current density while exhibiting poorer performance at the low current density region for smaller chips. The peak efficiency corresponds to higher current density with a decrease in chip size according to the carrier recombination ABC model. Moreover, the characteristic curve of the spectrum and the changes in the yellow light band under different incident light conditions (i.e., 355 nm and 375 nm) are analyzed by photoluminescence.

Size dependence of quantum efficiency of red emission from GaN:Eu structures for application in micro-LEDs.

GaN-based micro-LEDs typically suffer from a size-dependent efficiency due to the relatively long carrier lifetime and sidewall-related recombination effects. We demonstrate that for red-emitting Eu-doped GaN, sidewall-related recombination is hardly an issue for emission efficiency. We determine the photoluminescence quantum efficiency (PL QE) of Eu-related emission as a function of the size of square structures ranging from 3 to 192 µm. With the support of finite-difference time-domain simulations, we show that the light extraction efficiency and material losses are responsible for the decrease in PL QE for large sizes. For sizes smaller than 24 µm, there is an influence of the sidewall-related non-radiative recombination of carriers on the PL QE; however, it is only minor as a result of the limited carrier diffusion lengths in the Eu-doped material. These properties combined with the high efficiency of luminescence indicate the potential of this material for micro-LED applications.

Size-independent peak efficiency of III-nitride micro-light-emitting-diodes using chemical treatment and sidewall passivation

Micro-light-emitting-diodes (μLEDs) with size-independent peak external quantum efficiency behavior was demonstrated from 10 × 10 μm2 to 100 × 100 μm2 by employing a combination of chemical treatment and atomic-layer deposition (ALD) sidewall passivation. The chemical treatment and sidewall passivation improved the ideality factors of μLEDs from 3.4 to 2.5. The results from the combination of chemical treatment and ALD sidewall passivation suggest the issue of size dependent efficiency can be resolved with proper sidewall treatments after dry etching.

Size-dependent efficiencies of ultrafine particle removal of various filter media

Ultrafine particles (UFPs) are hazardous air pollutants produced by human activities in outdoor and indoor environments. Filtration in mechanical ventilation systems or air purifiers is an effective technology for removal of outdoor- or indoor-originated particles, to reduce human exposure to UFPs in indoor environments, where people spend most of their time. The filtration efficiency of filter media is critical to performance, and the efficiency significantly depends on particle diameter. Thus, the size-dependent efficiencies of 47 commercial filter media with 17 filter classes were measured at typical air flow velocities. The pressure drops at different velocities were also measured to obtain the ratios of pressure drops to media velocities. Total efficiencies of UFP removal were estimated based on the size-dependent efficiencies and size distributions of UFPs in three typical cases. The average efficiency of the UFP removal of coarse filters, fine filters, high-efficiency particulate air filters, and ultra-low particulate air filters in typical cases were 10.85%, 76.87%, 99.37%, and 99.92%, respectively. The maximum range of the total efficiency was 18.17%, which was significantly smaller than that of size-dependent efficiency (45.15%). The efficiencies for particles with the mean diameter and mean value of the total efficiency of the UFPs were similar, with absolute differences of less than 5%. These results can provide guidance for selection of filter media under the comprehensive consideration of air quality and energy consumption and offer reference values for the evaluation of new filter media as well as basic data for the assessment of human exposure to UFPs.

The influence of ZnS buffer layer on the size dependent efficiency of CdTe quantum dot sensitized solar cell

Abstract We report the investigations on the quantum dot size dependence of efficiency of a CdTe sensitized solar cell. With an additional layer of ZnS over the QD layer, the efficiency of solar cell was found to vary according to the size of the synthesized CdTe QDs. The presence of trap states due to the surface imperfections of the QDs as a result of the colloidal growth mechanism was also found to affect the overall efficiency of the solar cell. By coating a buffer layer of ZnS over the CdTe QD layer with the help of SILAR method, the efficiency enhanced up to 2.16% by decreasing the charge recombination rate between QDs and metal oxide layer.