Microcavity Surface Research Articles

Numerical study of flow boiling on microcavity surface under the action of an electric field using lattice Boltzmann method

The microcavity setting promotes bubble nucleation, and the presence of an electric field enables bubble detachment. In this study, the synergistic effect of electric field and microcavity in improved flow boiling heat transfer was analyzed based on the pseudopotential lattice Boltzmann method. The investigation was focused on the influence of wall superheat, Reynolds (Re) number, electric field intensity, liquid subcooling, and gravitational acceleration on the flow boiling performance under two forms of electric field distributions for uniform conducting microcavity surface (MC–UCS) and conducting–insulating microcavity surface (MC–CIS). Compared with the MC–UCS, the MC–CIS maintained a stable wetting state in the microcavity through inhibition of sliding and merging of bubbles. The increase in electric field intensity and Re number improved convective heat transfer in the microcavity but at the expense of a larger frictional pressure drop. The boiling phenomenon on the microcavity surface weakened with the increase in liquid subcooling, which caused difficulty for the electric field to improve the heat transfer performance by improving bubble behavior. Electrical force can replace buoyancy force to perturb the vapor–liquid interface under low gravitational acceleration. This condition allows the fluid shear force to drive bubbles away from the microcavity surface quickly. The results can provide theoretical and technical guidance for the realization of the enhanced synergistic heat transfer between electric fields and microstructures.

Emission Wavelength Control Based on Coupling of Surface Plasmon and Microcavity Mode in Organic Light-Emitting Diodes with Metal/Dielectric/Metal Anodes

Emission Wavelength Control Based on Coupling of Surface Plasmon and Microcavity Mode in Organic Light-Emitting Diodes with Metal/Dielectric/Metal Anodes

Control of the coupling degree between surface plasmon and microcavity mode in dual-cavity OLEDs

The metal/dielectric/metal (MDM) multilayer resonator is of increasing interest because of its functionality of surface plasmons generated at the interfaces. We aimed to control the EL spectra of OLED with an MDM electrode by actively utilizing the plasmon-microcavity coupling. The change in EL spectra of OLED with MDM electrode was simulated depending on the design of MDM structures by FDTD simulations. The strength of the plasmon-microcavity coupling can be controlled by the thickness of the Ag film in AZA, which can determine the tuning range of the EL peak position.

Harnessing sub-comb dynamics in a graphene-sensitized microresonator for gas detection

Since their inception, frequency combs generated in microresonators, known as microcombs, have sparked significant scientific interests. Among the various applications leveraging microcombs, soliton microcombs are often preferred due to their inherent mode-locking capability. However, this choice introduces additional system complexity because an initialization process is required. Meanwhile, despite the theoretical understanding of the dynamics of other comb states, their practical potential, particularly in applications like sensing where simplicity is valued, remains largely untapped. Here, we demonstrate controllable generation of sub-combs that bypasses the need for accessing bistable regime. And in a graphene-sensitized microresonator, the sub-comb heterodynes produce stable, accurate microwave signals for high-precision gas detection. By exploring the formation dynamics of sub-combs, we achieved 2 MHz harmonic comb-to-comb beat notes with a signal-to-noise ratio (SNR) greater than 50 dB and phase noise as low as − 82 dBc/Hz at 1 MHz offset. The graphene sensitization on the intracavity probes results in exceptional frequency responsiveness to the adsorption of gas molecules on the graphene of microcavity surface, enabling detect limits down to the parts per billion (ppb) level. This synergy between graphene and sub-comb formation dynamics in a microcavity structure showcases the feasibility of utilizing microcombs in an incoherent state prior to soliton locking. It may mark a significant step toward the development of easy-to-operate, systemically simple, compact, and high-performance photonic sensors.Graphical

Visual and quantitative lateral flow immunoassay based on Au@PS SERS tags for multiplex cardiac biomarkers

Rapid and sensitive detection of multiple biomarkers by lateral flow immunoassay (LFIA) remains challenging for signal amplification for commonly used nanotags. Herein, we report a novel LFIA strip for visual and highly sensitive analysis of two cardiac biomarkers based on functionalized gold nanoparticles @ polystyrene microsphere (Au@PS）microcavity as surface-enhanced Raman scattering (SERS) tags. Antibody-modified Au@PS was designed as a SERS label. The evanescent waves propagating along the surface of the PS microcavity and the localized surface plasmons of the gold nanoparticles were coupled to enhance the light-matter interaction synergistically for Raman signal enhancement. In this strategy, the proposed Au@PS SERS tags-based LFIA was carried out to quantify the content of the heart failure and infarct biomarkers synchronously within 15 min and get the limits of detection of 1 pg/mL and 10 pg/mL for cardiac troponin I (cTnI) and N-terminal natriuretic peptide precursor (NT-proBNP), respectively. The results demonstrated 10–20 folds more sensitivity than that of the standard colloidal gold strip and fluorescent strip for the same biomarkers. This novel quantitative LFIA shows promise as a high-sensitive and visual sensing method for relevant clinical and forensic analysis.

A multi-modal microscope for integrated mapping of cellular forces and Brillouin scattering with high resolution

Mechanical forces and stiffness play key roles in the health and development of cells and tissue, but despite the physical connection between these quantities, they cannot be monitored in parallel in most cases. Here, we introduce a fully integrated microscope that combines a method for high-resolution cell force imaging (elastic resonator interference stress microscopy, ERISM) with non-contact mapping of the elastic properties of cells (via Brillouin microscopy). In order to integrate both techniques, we had to account for the strong back reflection on the surface of the microcavity used for ERISM measurements as well as the local destruction of the cavity under illumination for Brillouin microscopy measurements. Therefore, we developed an elastic optical microcavity with minimal absorption that can perform ERISM measurements without sustaining laser damage during Brillouin microscopy. Furthermore, an unequal-arm Michelson interferometer was designed to suppress the back reflection of the laser on the ERISM microcavity surface using division by amplitude interference to reduce the reflected light and enhance the Brillouin signal. We show the utility of our integrated microscope by simultaneously mapping cellular forces and Brillouin shifts in cultures of fibroblast cells.

Multifunctional Microcavity Surfaces for Robust Capture and Direct Rapid Sampling of Concentrated Analytes

Evaporation patterns of liquid droplets containing nanoparticles or colloids have extensive applications in diagnostics and printing. Controlling these patterns by studying the evaporation behavior of colloidal droplets on surfaces is important for enhancing sensing platforms. In this study, A liquid‐repellent microcavity surface is introduced to robustly capture deposited analytic particles. The proposed microcavity surface maintains stable air pockets for liquid repellency and strong pinning for the spatial stabilization of the evaporating droplet, thereby resulting in a coffee‐ring concentration. This microcavity surface also acts as a “microcontainer” for the deposited particles, thereby protecting them against external damage. To demonstrate the multifaceted capabilities of microcavity surfaces, further comparison is done of three different surface structures, planar, micropillared, and that with microcavities in a hexagonal arrangement, by analyzing their evaporation dynamics and dried deposit patterns. The microcavity surface exhibits superior particle capture, thereby revealing its applicability in on‐site testing. Using the direct rapid sampling of analytical materials, the potential of the fabricated microcavity surface for point‐of‐care testing is demonstrated. The proposed microcavity surfaces suggest new avenues for the development of more robust and sensitive sensing platforms.

Plasmon‐Coupled GaN Microcavity for WGM Lasing and Label‐Free SERS Sensing of Biofluids

AbstractA signal amplification strategy is always required to improve sensing performance, especially for mass‐prepared, miniature and highly sensitive testing equipment. Herein, an on‐chip integrated biosensor combining microcavity lasing and surface enhanced Raman scattering (SERS) for label‐free biochemical analysis is developed. The gallium nitride (GaN) microrings array is fabricated as a whispering gallery mode microlaser based on totally internal wall reflection, and gold nanoparticles (AuNPs) are further assembled on the cavity surface to confine the optical field synergistically. The improvement of lasing capability indicates the strong light‐matter interaction that is conducive to superior response of biomolecules. As a functional example, a GaN/AuNPs substrate is employed in a urine assay, which avoids the shortcomings of requiring specific reactive reagents on different display modules. Ultimately, the chip not only realizes a wide range of pH (3.6–7.8) identification depending on the ultra‐sensitivity feedback of lasing to the refractive index of liquids, but also significantly enhances SERS signals to enable real‐time determination of the biomolecules in human urine. Even the lowest levels of creatinine (0.02%) can be quantitatively detected in less than a minute; thus this work with dual‐mode spectral analyses realizes rapid diagnosis for urinary systems, as well as provides a more accurate reference for the screening of other diseases.

Whether contact time can evaluate the anti-icing properties of superhydrophobic surface - A research based on the MDPDE method

Impact freezing of droplets on a cold surface has attracted the attention of scholars. This process is vital for practical problems such as the anti-icing of aircraft wings and cables. Researchers have found that superhydrophobic surfaces can reduce the contact time of droplets and delay nucleation. However, whether contact time can evaluate the anti-icing properties of superhydrophobic surface needs further study. Considering the change in droplet temperature, we vary the dissipative force term of the conservative force in the many-body dissipative particle dynamics with the energy conservation (MDPDE) method. Then combined with the experimental results, a nucleation model of the recalescence rate related to the degree of undercooling is achieved. Finally, we obtain a droplet impact freezing model based on the MDPDE method for the first time, and the impact processes of supercooled droplets on the superhydrophobic surface with three different topological microstructures are explored. Effect of Weber number We on the critical adhesion temperature T* of micropillar surface is reversed when the solid fraction φ is different, and φ is the main factor affecting T*of the microcavity surface. When other conditions are the same, T* of the microridge surface is the lowest. And surprisingly, we observed that the contact time of droplets did not fully measure the anti-icing ability of the superhydrophobic surface.

Label-free, ultra-low detection limit DNA biosensor using high quality optical microcavity functionalized by DNA tetrahedral nanostructure probes

Abstract This study proposes and demonstrates a novel label-free DNA biosensor using high quality optical microcavity functionalized by 3D DNA nanostructure probes. To achieve ultra-low limit DNA biosensing, optical sensing interface of the hollow-core, thin wall-thickness microcavity was functionalized by self-assembled DNA tetrahedral nanostructure (DTN) probes with size of 17 bp and length of ∼5.8 nm. High efficiency binding of the DTN probes with the optical sensor interface and the target ssDNA are achieved. Whispering gallery mode (WGM) spectra with high-Q factor of >107 are excited and traced for DNA detection inside the microfluidic channel of the microcavity, with a small sample volume of nL. Incorporation of nanoscale DTN probes onto surface of the optical microcavity makes it an effective way for increasing efficient probe density and eliminating entanglement between DNA probes, thus ∼1000 times lower detection limit is achieved as compared to using 1D ssDNA probes. Due to its desirable merits of label-free, ultra-low LoD, real time and compact size, the proposed DNA biosensor has broad application prospects in bioengineering and medical diagnosis.

Effect of two-dimensional micro-cavity surface on hypersonic boundary layer

For hypersonic boundary layer, the porous coating comprising small blind holes is an effective passive method that can delay the laminar-turbulent transition by damping the second mode wave. In this paper, surface with two-dimensional rectangular cavities with larger size comparable to the thickness of boundary layer is numerically investigated. The micro-cavity surface affects not only the second mode wave, but also the base flow due to the roughness effects. The numerical results showed that the total drag of base flow can be reduced by the micro-cavity surface compared to the smooth surface, more significant with smaller cavity width and higher porosity, while the cavity depth has little influence on the drag performance. The total drag can be further reduced when the micro-cavity surface suffers moderate static deformation under the pressure difference in the base flow. The micro-cavity surface is able to damp the second mode wave like the porous coating, and thus also has the potential to delay the transition. The effect on the second mode wave is stronger with higher porosity and smaller cavity width, while not monotonic with the cavity depth. The static deformation of structure causes local change of cavity characteristics, resulting in the second mode more damped over the deformed micro-cavity surface. When the structure dynamically responses to the fluctuating pressure of the second mode wave, the intensity of wave is slightly further decreased.

Supreme-black levels enabled by touchproof microcavity surface texture on anti-backscatter matrix.

Emerging immersive high-dynamic range display technologies require not only high peak luminance but also true black levels with hemispherical reflectance below 0.001 (0.1%) to accommodate the wide dynamic range of the human eye (~105). Such low reflectance materials, denoted here as "supreme black," must exhibit near-perfect surface antireflection, extremely low in-matrix backscattering, and sufficient optical thickness, which, to date, have only been achieved by fragile sparse materials. We demonstrate a record-low hemispherical reflectance below 0.0002 (absorptance above 0.9998) in a touchproof material by satisfying the three requirements with a superwavelength surface microtexture with nanolevel details, low Mie backscattering composition, and optional additional underlayer. Our supreme black finishes are one to two orders of magnitude blacker than previously developed touchproof super-black materials. Thereby, unprecedented black levels enabling an ambient contrast ratio of ≳104 would be provided in display devices, contributing to immersive visual experiences that are critical for seamless remote collaboration and reliable virtual health care.

A lattice Boltzmann investigation of the saturated pool boiling heat transfer on micro-cavity/fin surfaces

Saturated pool boiling heat transfer on micro-cavity and micro-fin surfaces is examined by a mesoscopic phase change lattice Boltzmann method. The important interfacial processes and boiling heat transfer performance are explored concerning the effects of micro-structure configurations, specifically fin and cavity, and micro-structure parameters, including fin/cavity shape, height, length, and spacing between fins/cavities. It is discovered that both the micro-cavity and micro-fin surfaces are conducive to bubble nucleation and can enhance nucleate boiling heat transfer (NBHT) when compared with the smooth surface. By comparing fin and cavity surfaces, it is found that micro-cavity is more conducive to bubble nucleation, whereas micro-fin is more conducive to bubble departure. As a result, micro-cavity surface has a higher NBHT while a micro-fin surface has a higher critical heat flux (CHF). The saturated pool boiling heat transmission is significantly influenced by the micro-structure parameters as well, i.e., the boiling on the rectangular cavity/fin surfaces has an earlier nucleation time while that on the conical surfaces has a faster bubble escape speed. The mass of residual bubble left over after the bubble department increases with cavity/fin height, which leads to the advance of CHF. On the other hand, the CHF increases as the distance between micro-structures. Additionally, with the increase in micro-structure length, the CHF increases for the micro-cavity surface whereas decreases for the micro-fin surface. Finally, a series of fitting equations between CHF and the micro-structure parameters are presented and an improved hybrid surface is developed based on the theoretical predictions.

A high-throughput fully automatic biosensing platform for efficient COVID-19 detection

We propose a label-free biosensor based on a porous silicon resonant microcavity and localized surface plasmon resonance. The biosensor detects SARS-CoV-2 antigen based on engineered trimeric angiotensin converting enzyme-2 binding protein, which is conserved across different variants. Robotic arms run the detection process including sample loading, incubation, sensor surface rinsing, and optical measurements using a portable spectrometer. Both the biosensor and the optical measurement system are readily scalable to accommodate testing a wide range of sample numbers. The limit of detection is 100 TCID50/ml. The detection time is 5 min, and the throughput of one single robotic site is up to 384 specimens in 30 min. The measurement interface requires little training, has standard operation, and therefore is suitable for widespread use in rapid and onsite COVID-19 screening or surveillance.

Boiling heat transfer enhancement on titanium through nucleation-promoting morphology and tailored wettability

• Cavity- and spear-type TiO 2 nanostructures are prepared by hydrothermal treatment. • Nucleation-promoting cavity morphology is superior to spear-like microstructure. • Hydrophobic surface with microcavities (CTH) provides HTC enhancement of over 200%. • High nucleation site density on CHT surface narrows surface temperature distribution. • ONB at 2.5 K and D b of 0.55 mm are observed on hydrophobic microcavity surface. Surface engineering aimed at tuning the wettability and morphology of the boiling surface is a facile approach to moderate and enhance the nucleate boiling process. Key issues include control over the active nucleation site density, bubble departure frequency and liquid replenishment of active nucleation sites while simultaneously reducing the bubble nucleation temperature. In this study, we fabricated spear-type (ST) and cavity-type (CT) TiO 2 nanostructures on 25 μm titanium foils via hydrothermal etching in an alkaline solution. High-speed IR and video cameras were used to detect local phenomena in terms of temperature and heat flux fluctuations and observe the bubble dynamics during saturated pool boiling of water. Intrinsically hydrophilic ST and CT surfaces provided a moderate overall enhancement of the heat transfer coefficient compared to an untreated surface due to increased nucleation site density and bubble frequency. The CT surface also decreased the bubble nucleation temperature due to effective vapor-entrapping and nucleation-promoting cavities. In a further step, both surfaces were hydrophobized through chemical vapor deposition of a fluorinated silane to tailor the wettability of the surface into a superhydrophobic state. This further reduced the average surface superheat by at least 40%, while the nucleation frequencies exceeded 200 Hz on the hydrophobized CT surface. In comparison with the untreated reference surface, the heat transfer coefficient on hydrophobized ST and CT surfaces was enhanced by 89% and 237% at 100 kW m −2 , respectively. Moreover, the full width at half maximum (FWHM) value of the surface temperature distribution was reduced by 73% and 95% at the same heat flux, respectively. The study confirms that hydrophobic surface treatment can significantly enhance the nucleate boiling process when combined with an appropriate surface structure. Despite the affinity between the vapor and the hydrophobic layer, the cavity-type and spear-type TiO 2 structures are able to maintain active nucleation sites well-separated, which prevents the undesirable vapor spreading that possibly leads to an early onset of critical heat flux.

Label-Free LSPR-Vertical Microcavity Biosensor for On-Site SARS-CoV-2 Detection.

Cost-effective, rapid, and sensitive detection of SARS-CoV-2, in high-throughput, is crucial in controlling the COVID-19 epidemic. In this study, we proposed a vertical microcavity and localized surface plasmon resonance hybrid biosensor for SARS-CoV-2 detection in artificial saliva and assessed its efficacy. The proposed biosensor monitors the valley shifts in the reflectance spectrum, as induced by changes in the refractive index within the proximity of the sensor surface. A low-cost and fast method was developed to form nanoporous gold (NPG) with different surface morphologies on the vertical microcavity wafer, followed by immobilization with the SARS-CoV-2 antibody for capturing the virus. Modeling and simulation were conducted to optimize the microcavity structure and the NPG parameters. Simulation results revealed that NPG-deposited sensors performed better in resonance quality and in sensitivity compared to gold-deposited and pure microcavity sensors. The experiment confirmed the effect of NPG surface morphology on the biosensor sensitivity as demonstrated by simulation. Pre-clinical validation revealed that 40% porosity led to the highest sensitivity for SARS-CoV-2 pseudovirus at 319 copies/mL in artificial saliva. The proposed automatic biosensing system delivered the results of 100 samples within 30 min, demonstrating its potential for on-site coronavirus detection with sufficient sensitivity.

Optical coupling enhancement of multi-color terahertz quantum well detector

Multi-color terahertz (THz) detector has attracted much attention in various applications because of the ability to obtain more comprehensive information simultaneously. THz quantum well photodetectors (QWPs) have great advantages in realizing multi-color detection because of high speed, sensitivity, and mature technology. In this work, QWPs based on antenna coupled microcavity (AM-QWP) and etched antenna coupled microcavity (EAM-QWP) structures are proposed to realize multi-color THz detection. Thanks to the combination of the microcavity resonance and surface plasmon polariton mode, AM-QWP achieves a coupling efficiency of one order of magnitude higher than that of the conventional 45° edge facet coupler (45°-QWP) in multiple bands. The EAM-QWP only retains the active region where the effective photocurrent is generated so that the coupling light is highly localized in a small area, improving the optical coupling efficiency by two orders higher compared with 45°-QWP. It is theoretically estimated that the responsivity of AM-QWP and EAM-QWP at the temperature of 4 K is 9.6–24.0 A/W and 78.4–196.0 A/W while their noise equivalent power (NEP) is 5.4 × 10−4–1.1 × 10−3 pW/Hz1/2 and 1.7 × 10−5–3.5 × 10−5 pW/Hz1/2, and the specific detectivity is 4.4 × 1012–8.9 × 1012 and 6.9 × 1013–1.4 × 1014 cm Hz1/2/W, respectively. This work provides a guideline for the experimental realization of high-performance multi-color THz QWPs.

Tunable characteristics of porous silicon optical microcavities by energetic N ion beam interactions

The present study demonstrates the tuning of optical characteristics of porous silicon (PSi)-based microcavities by N ion beam interactions. These optical microcavities are prepared by using electrochemical etching of heavily doped p+-type Si. The PSi microcavities were exposed to N ions of 200 keV and 1 MeV at an optimized ion fluence of 1 × 1015 ions cm−2. A significant red-shifting of 32 ∼ 60 nm in the resonance cavity mode was observed due to ion interaction. The experimental results are in good agreement with the transfer matrix simulations. A substantial modification of the PSi microcavity surface states is visualized through Raman and x-ray photoelectron spectroscopy (XPS) techniques. The Raman spectral results show modifications from crystalline Si to nanostructured Si and subsequently to amorphous Si. The XPS indicates the modification of Si–Si and Si–O bonds and the formation of new Si–N bonds, implying the presence of Si3N4. These experimental observations, along with analytical simulations and transfer-matrix method microcavity modeling, conclusively support the realization of cavity tunability and substantial modification in the optical field intensity and photon confinement within the spacer layer of the microcavity. These results suggest that ion beams are the effective tool to produce wider tunable optical properties in microcavities with highly stable designer optical structures suitable for photonic applications.

Microstructured Surfaces for Reducing Chances of Fomite Transmission via Virus-Containing Respiratory Droplets.

Evaporation-induced particle aggregation in drying droplets is of significant importance in the prevention of pathogen transfer due to the possibility of indirect fomite transmission of the infectious virus particles. In this study, particle aggregation was directionally controlled using contact line dynamics (pinned or slipping) and geometrical gradients on microstructured surfaces by the systematic investigation of the evaporation process on sessile droplets and sprayed microdroplets laden with virus-simulant nanoparticles. Using this mechanism, we designed robust particle capture surfaces by significantly inhibiting the contact transfer of particles from fomite surfaces. For the proof-of-concept, interconnected hexagonal and inverted pyramidal microwall were fabricated using ultraviolet-based nanoimprint lithography, which is considered to be a promising scalable manufacturing process. We demonstrated the potentials of an engineered microcavity surface to limit the contact transfer of particle aggregates deposited with the evaporation of microdroplets by 93% for hexagonal microwall and by 96% for inverted pyramidal microwall. The particle capture potential of the interconnected microstructures was also investigated using biological particles, including adenoviruses and lung-derived extracellular vesicles. The findings indicate that the proposed microstructured surfaces can reduce the indirect fomite transmission of highly infectious agents, including norovirus, rotavirus, or SARS-CoV-2, via respiratory droplets.

Enhancement of flow boiling heat transfer in microchannel using micro-fin and micro-cavity surfaces

• A numerical investigation into the flow boiling process in a microchannel with a micro-structured surface was performed. • Micro-fin, micro-cavity, and smooth surfaces with varying wettabilities were investigated. • The enhancing effects and detailed mechanisms of micro-structured surfaces were revealed. Micro-structured surfaces have a significant impact on the flow boiling process in microchannels, but few numerical studies have been carried out due to their complex nature. In this study, the numerical investigation of flow boiling on micro-fin, micro-cavity, and smooth surfaces in a microchannel was conducted, with water serving as the working fluid. The volume-of-fluid (VOF) method, the phase change model, and solid-fluid thermal coupling were adopted in an OpenFOAM solver to perform the computation. The enhancing effects and detailed mechanisms of the micro-fin and micro-cavity surfaces on the heat transfer process are discussed, and the influences of wettability on these surfaces are investigated. With a contact angle of 60°, the heat transfer coefficient of the micro-fin surface was 61.92% larger, and the overall thermal resistance was 36.64% lower than that of a smooth surface, respectively. The confined bubbles on the micro-fin surface had a much smaller dryout area on the heated wall due to the capillary wetting effect. Moreover, the micro-fin surface with the rising nucleate bubbles can induce vortexes, which strengthens the convective heat transfer. As for the micro-cavity surface, it had a moderate heat transfer enhancement with a 17.16% larger heat transfer coefficient and a 13.55% lower thermal resistance when compared with a smooth surface. When the wettability of a heating surface is enhanced, the dryout area is minimized. Thus, the heat transfer performance of the smooth and micro-cavity surfaces is enhanced. The enhancement resulting from modified surface wettability has less of an effect on the micro-fin surface because the micro-fin array serves a similar function to minimize the dryout area.