Multilayer Nanostructures Research Articles

Heterogeneous to Homogeneous Melting Transition Observed During a Single Process

The melting mechanism at medium heating rates is unclear, owing to the lack of accurate characterizations of structural changes in poly-directional melting conditions. Here, a particular multilayered nanostructure was selected to control the propagation of melting in a single direction. We predicted the heterogeneous to homogeneous melting (HeM to HoM) transition during a single melting process at medium heating rates of 10–400 K/ps by molecular dynamics (MD) simulations, without a change in heating rates. The information on structural changes for the HeM to HoM transition, including the loss of crystallinity and long- and short-range order, are clearly provided by both a single direction and the radial distribution functions. These results contribute to a more comprehensive understanding of the HeM to HoM transition induced by heating rates.

Atomic‐Level Structural Responses of Chang'e‐5 Ilmenite to Space Weathering

AbstractSpace weathering records provide insights to better understand the formation and evolution of the lunar regolith. Ilmenite has contrasting responses to different space weathering processes. However, the atomic‐scale structural modification of ilmenite induced using different space weathering processes remains poorly understood. Here, we investigate the effects of spacing weathering on lunar ilmenite grains returned from Chang'e‐5 (CE‐5) mission using a combination of transmission electron microscopy and thermodynamic modeling approaches. Experimental results show that melt shock induces the formation of twining structures and vein‐like Si‐Ca‐rich nanostructures in the outermost and sub‐outermost layers of ilmenite, respectively. In contrast, solar wind causes the formation of multilayered nanostructures surrounding the ilmenite grains. These structures are characterized by an outermost amorphous Si‐rich vapor deposited layer, a middle layer rich in titanium (Ti) oxides and zero‐valent iron (Fe0) nanoparticles, and an innermost layer hosting crystallographic orientation defect. The Ti oxides were identified as poorly crystallized anatase. Thermodynamic calculations indicate that the disruptive sputtering of solar wind and the reduction of hydrogen under lunar surface pressure conditions can promote ilmenite transformation into Fe0 and Ti oxides; nevertheless, the pressure increase associated with melt shock can lead to a rise in the decomposition temperature of ilmenite. In other words, solar wind irradiation plays a more significant role in promoting nanoparticle (such as anatase and Fe0) formation as compared to melt shock. Thus, unlike the chemical alteration of ilmenite induced by the solar wind irradiation, melt shock mainly causes physical changes in ilmenite grains.

Single activator doped fluoride nanoparticles for X-ray excited high-resolution and delayed flexible nonplanar imaging

Lanthanide doped fluoride nanoparticles (NPs) exhibit adjustable X-ray excited optical/persistent luminescence (XEOL/XEPL) and possessing extensive potential in XEPL-based delay imaging. However, the high-resolution and delayed XEPL-based delay imaging always requires strict introduction of sensitized or heterovalent ions and the construction of complex structures for excellent XEPL performance of lanthanide-doped fluoride NPs, which is attributed to a lack of effective and convenient strategies. Here we show that the intense XEPL strength was obtained by single Tb3+ activated ion doping and simple CsY2F7@NaYF4 core/shell structure for X-ray excited high-resolution and delayed flexible nonplanar imaging. The strict introduction and control of sensitized or heterovalent ions, and the construction of intricate multilayer nanostructure are avoided. In addition, we enable the NPs to achieve high and long-term XEPL performance by simply thermal processing strategy. We successfully mixed minimized amount of the NPs into flexible film to create a scintillation screen which consequently exhibit high surface smoothness, environmental stability, and transparency. Our results demonstrate high resolution delayed imaging of the NPs integrated flexible film for the interior of nonplanar objects. The spatial resolution of 14.3 lp mm−1 is substantially higher than the typical spatial resolutions required for medical CT scans (2 lp mm−1) and X-ray imaging (3.5 lp mm−1). These findings will promote the development of advanced delayed X-ray nonplanar imaging applications.

Effects and modulation mechanism of crystal structure on residual stress of Cu films used for metallization

Deformation cracking and delamination arising from residual stress are the main challenges for metallization in large-scale integrated circuits. Herein, an ultra-low residual stress Cu film is prepared on amorphous SiO2 by mixed power magnetron sputtering. Compared to conventional Cu films, the residual stress in the film decreases by 1434 times. The nano multi-layer structure produces lower stress and deformation as well as better reliability. The multi-layer Ti underlayer also reduces the residual stress and promotes the low-defect growth of Cu. The lower surface roughness, smaller dislocation density, predominant grain orientations of 〈111〉 and 〈001〉, and more substructures are beneficial to the reduction of residual stress. In addition, interlayer stress cancellation can be achieved by changing the number of 〈111〉 grains. The research on grain growth at the interface of nano multi-layer films reveals an effective means to fabricate films with low residual stress for metallization in integrated circuits.

Mechanics and Cutting Performance of Multilayer Nanostructured TiAlN/TiSiN/ZrN Coatings

The aerospace industry has made extensive use of titanium alloy material due to its exceptional qualities, which include high strength, low weight, and resistance to corrosion. However, these qualities also pose challenges for the material’s processing. This article examined the coated end mills for Ti6Al4V milling. First, an analysis was conducted on the solubility of Ti and Si elements. It was discovered that W and Co elements were far more soluble in Ti than Si and Zr elements, which could effectively stop element diffusion. Next, the base’s composition was planned. It was discovered that when the amount of Al increased, the base’s surface roughness increased, while its hardness and elastic modulus decreased. The binding force between the substrate and the base was greater at a 50:50 Ti:Al ratio. The H3/E2 was about 0.23 and the surface roughness was about 0.15 μm. TiSiN and TiSiN/ZrN functional layer properties were also examined. When Zr was added to TiSiN/ZrN coating, it improved the coating’s hardness and elastic modulus, increased density, and decreased surface roughness and friction coefficient when compared to TiSiN coating. There was an increase in hardness by 8.09% and an increase in elastic modulus by 9.65%. The average coefficient of friction decreased from 0.315 to 0.299. Lastly, an analysis of the initial and intermediate tool wear was done using the Ti6Al4V milling experiment. It was discovered that adding Zr element could successfully extend the tool’s cutting life by preventing adhesive wear.

DC vs AC Electrokinetics-Driven Nanoplasmonic Raman Monitoring of Charged Analyte Molecules in Ionic Solutions.

Electrokinetic surface-enhanced Raman spectroscopy (EK-SERS) is an emerging high-order analytical technique that combines the plasmonic sensitivity of SERS with the electrode interfacial molecular control of electrokinetics. However, previous EK-SERS works primarily focused on non-Faradaic direct current (DC) operation, limiting the understanding of the underlying mechanisms. Additionally, developing reliable EK-SERS devices with electrically connected plasmonic hotspots remains challenging for achieving high sensitivity and reproducibility in EK-SERS measurements. In this study, we investigated the use of two-tier nanolaminate nano-optoelectrode arrays (NL-NOEAs) for DC and alternating current (AC) EK-SERS measurements of charged analyte molecules in ionic solutions. The NL-NOEAs consist of Au/Ag/Au multilayered plasmonic nanostructures on conductive nanocomposite nanopillar arrays (NC-NPAs). We demonstrate that the NL-NOEAs exhibit high SERS enhancement factors (EFs) of ∼106 and can be used to modulate the concentration and orientation of Rhodamine 6G (R6G) molecules at the electrode surface by applying DC and AC voltages. We also performed numerical simulations to investigate the ion and R6G dynamics near the electrode surface under DC and AC voltage modulation. Our results show that AC EK-SERS can provide additional insights into the dynamics of molecular transport and adsorption processes compared to DC EK-SERS. This study demonstrates the potential of NL-NOEAs for developing high-performance EK-SERS sensors for a wide range of applications.

Poly(vinylidene fluoride) membrane design for efficient oil-in-water emulsion separation: Integrating superhydrophilicity, photocatalysis and self-cleaning

To solve the increasingly serious wastewater problems, developing membranes with excellent filtration performance and anti-fouling property has been a research focus. Herein, hydrophilic tannic acid/cysteine/tyrosine@titanium (TA/Cys/Tyr@Ti) double crosslinked coating was constructed on the poly (vinylidene fluoride) (PVDF) microfiltration membranes by two-step coating method, while the mineralized titanium dioxide (TiO2) nanoparticles were utilized to produce superhydrophilic membranes. The synergistic effect of the multilayered nanostructure and hydrophilic groups enables excellent underwater superoleophobicity and anti-fouling property of modified membranes. The addition of TiO2 provides photocatalytic degradation and self-cleaning properties. The optimized modified membrane (MF-4) showed outstanding oil–water separation potential (emulsion flux of 2760 ± 30 L·m−2·h−1, oil rejection rate of 99.5 ± 0.3 %) and stable recycling filter capacity. Moreover, MF-4 was able to efficiently degrade methylene blue under UV light, which was 99.1 % at 90 min. The flux recovery rate (FRR) was 97.4 % following simulated contamination and regeneration with bovine serum albumin. After UV irradiation, the FRR appeared to be significantly enhanced, proving its great anti-fouling and self-cleaning properties. This modified membranes with superhydrophilic and self-cleaning properties have great application potential in oily wastewater and achieving automatic operation of wastewater treatment.

Synthesis and characterization of natural rosin-modified silica nanocomposite and its green multifunctional applications for drilling fluid

The increasing energy demand and environmental pressure require the utilization of high-performance and eco-friendly drilling fluid materials for oil/gas exploration. Herein, a green nanocomposite involving the core structure of silica (SiO2), the resin shell structure of rosin dehydroabietic acid (DHAA) derivative [poly(DHAA-co-styrene) (PDS)], and the crown structure of hydrophilic layer [crosslinked poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-N, N-dimethylacrylamide) (CAD)] was prepared through semi-continuous emulsion polymerization and utilized as a high-performance and multifunctional additive for drilling fluid. The optimal composition of core, shell and crown was determined to be 0.3: 10: 2 in mass, and the DHAA component accounted for 50 wt% in the shell structure and the molar ratio of 2-acrylamido-2-methyl-1-propanesulfonic acid and N, N-dimethylacrylamide in the crown was 3:7. The core-shell-crown nanocomposite (SiO2-PDS-CAD) exhibited a well-organized multi-layered nanostructure with an effective encapsulation of PDS on nano-SiO2 and CAD on PDS, facilitating a uniform nano-dispersion of SiO2-PDS-CAD. The bulky copolymerized rosin-based segments coupled with nano-SiO2 resulted in high thermal stability of SiO2-PDS-CAD and broadened the softening point of raw rosin from 87°C to 141°C. Meanwhile, the environmental assessments of acute toxicity and biodegradability showed that SiO2-PDS-CAD was nontoxic and readily biodegradable, and the higher incorporation of rosin components enabled SiO2-PDS-CAD more biodegradable in contrast to the non-biodegradability of the analog without rosin. Moreover, SiO2-PDS-CAD showed versatile functions in bentonite-based drilling fluid by maintaining high yield points, lowering fluid loss and enhancing nano-porous plugging capacity (100–400 nm), especially at elevated temperatures (140–180°C). A maximum increment of 1200 % on yield point occurred after aging 170°C, and the highest improvement of approximately 72 %-75 % on fluid loss occurred at 150–180°C. It also could effectively inhibit clay swelling and decrease the lubrication coefficient. The enhancement mechanism was revealed to be the core-shell-crown synergistic effects, in which the hydrophilic crown contributed to the dispersion stability of SiO2-PDS-CAD and affinity with bentonite clay, and the rigid bridging of core and flexible deformation of rosin shell strengthened the interparticle interactions. The study highlighted a novel strategy for preparing high-value-added rosin-based biomass material for green multifunctional applications in water-based drilling fluids.

Enabling Multimodal Luminescence in a Single Nanoparticle for X-ray Imaging Encryption and Anticounterfeiting.

Multimodal luminescent materials hold great promise in a diversity of frontier applications. However, achieving the multimodal responsive luminescence at the single nanoparticle level, especially besides light stimuli, has remained a challenge. Here, we report a conceptual model to realize multimodal luminescence by constructing both mechanoluminescence and photoluminescence in a single nanoparticle. We show that the lanthanide-doped fluoride nanoparticles are able to produce excellent mechanoluminescence through X-ray irradiation, and color-tunable mechanoluminescence becomes available by selecting suitable lanthanide emitters in a core-shell-shell structure. Furthermore, the design of a multilayer core-shell nanostructure enables multimodal emissions including radioluminescence, persistent luminescence, mechanoluminescence, upconversion, downshifting, and thermal-stimulated luminescence simultaneously in a single nanoparticle under multichannel excitation and stimuli. These results provide new insights into the mechanism of X-ray induced mechanoluminescence in nanocrystals and contribute to the development of smart luminescent materials toward X-ray imaging encryption, stress sensing, and anticounterfeiting.

Tunnel transport problem for open multilayer nitride nanostructures with an applied constant magnetic field and time-dependent potential: An exact solution

A quantum mechanical theory for description of electronic quasistationary states in two-dimensional (2D) layered semiconductor nanostructure was developed. A constant external magnetic field B was directed along semiconductor layers. The presence of internal electric fields F originated from the potential barriers and wells in semiconductor layers was taken into account. The vector of F was directed perpendicularly to semiconductor layers. The interaction of tunneled electrons with a time-dependent electromagnetic fields was analyzed in detail. An approach to obtain an exact solution to the problem based on a combination of the Lewis-Riesenfeld method for complete Schrödinger equation and scattering theory was developed. Application of the scattering theory in combination with the -matrix and transfer-matrix methods allowed us to calculate the electron quasistationary spectra. Effects of magnetic field on the resonant energy and width of electronic quasistationary states as well as on the electronic conductivity were also discussed. Published by the American Physical Society 2024

Nano silicated-FeAl2O4 functionalized by DL-alaninium nitrate ionic liquid (FeAl2O4-SiO2@[DL-Ala][NO3]) as versatile promotor for aqua-mediated synthesis of spiro[chromenopyrazole-indene-triones and spiro[chromenopyrazole-indoline-diones

In this work, the spinel FeAl2O4 was prepared and functionalized step-by-step with silica and alaninium nitrate ionic liquid ([DL-Ala][NO3]) to produce a bio-based multi-layered nanostructure (nano FeAl2O4-SiO2@[DL-Ala][NO3]). The obtained magnetized inorganic-bioorganic nanohybrid characterized by Fourier transform infrared spectroscopy (FT-IR), vibrating-sample magnetometry (VSM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), X-ray fluorescence (XRF), and X-Ray diffraction (XRD) analysis. A facile synthesis of some tricyclic dihydro-spiro[chromeno[2,3-c]pyrazole-4,2′-indene]triones and dihydro-spiro[chromeno[2,3-c]pyrazole-4,3′-indoline]diones via domino four-component one-pot reaction of various hydrazine derivatives, ethyl acetoacetate, heterocyclic 1,2-ketones (ninhydrin, isatin, 5-bromoisatin) and cyclic 1,3-diketones (dimedone and 1,3-cyclohexanedine), examined in the presence of nano FeAl2O4-SiO2@[DL-Ala][NO3] nanohybrid in refluxing aqueous media, successfully. The multi-aspect characteristics of the nanohybrid which consist of magnetized inorganic and bioorganic parts, could be the reason of its special catalytic efficacy. The recovery and reusability of the FeAl2O4-SiO2@[DL-Ala][NO3] magnetized nanoparticles (MNPs) were performed in two runs without significant activity loss.

Magnetic properties and magnetoresistance of hybrid multilayer nanostructures {[(Co40Fe40B20)34(SiO2)66]/[ZnO]}n

The structural, electrical, magnetic, magneto-optical properties and magnetoresistance of {[(Co40Fe40B20)34(SiO2)66]/[ZnO]}n multilayer structures, where n = 50 is the number of bilayers (Co40Fe40B20)34(SiO2)66 nanocomposite and ZnO have been studied. The thicknesses of (Co40Fe40B20)34(SiO2)66 nanocomposite layers as well as ZnO spacers were varied in a wide range. The samples were synthesized by ion-beam sputtering onto glass ceramic substrates. The (Co40Fe40B20)34(SiO2)66 composite have an amorphous structure and the semiconductor ZnO interlayers have a hexagonal crystalline structure with the p63mc symmetry group. The nanocomposite layers containing a ferromagnetic component far from the percolation threshold are in a superparamagnetic state. The presented in the paper data of magnetization, magneto-optical transverse Kerr effect and magnetoresistance indicates that long-range ferromagnetic order does not form down to 77 K both for references ZnO films and studied multilayers with thin and thick ZnO interlayers. An increase in the magneto-optical signal in multilayers compared to references (Co40Fe40B20)34(SiO2)66 composite films has been detected at 1.2 eV. The magnetoresistance of {[(Co40Fe40B20)34(SiO2)66]/[ZnO]}n multilayers with thick (>32 nm) ZnO interlayers is lower than in reference (Co40Fe40B20)34(SiO2)66 nanocomposite, while at thin ZnO interlayers magnetoresistance is significantly higher and reaches 12 % at temperatures of 77 К. Possible mechanisms of ferromagnetic and antiferromagnetic ordering, enhancement of the magneto-optical response and magnetoresistance in {[(Co40Fe40B20)34(SiO2)66]/[ZnO]}n multilayer nanostructures are discussed.

Bioinspired nanostructured hydroxyapatite-polyelectrolyte multilayers for stone conservation

Stone-built cultural heritage faces threats from natural forces and anthropogenic pollutants, including local climate, acid rain, and outdoor conditions like temperature fluctuations and wind exposure, all of which impact their structural integrity and lead to their degradation. The development of a water-based, environmentally-friendly protective coatings that meet a combination of requirements posed by the diversity of the substrates, different environmental conditions, and structures with complex geometries remains a formidable challenge, given the numerous obstacles faced by current conservation strategies. Here we report the structural, electrical, and mechanical characterization, along with performance testing, of a nanostructured hydrophilic and self-healing hybrid coating based on hydroxyapatite (HAp) nanocrystals and polyelectrolyte multilayers (PEM), formed in-situ on Greek marble through a simple spray layer-by-layer surface functionalization technique. The polyelectrolyte-hydroxyapatite multilayer (PHM) structure resembled the design of naturally forming trabecular bone, attained at a short procedural time. It exhibited chemical affinity, aesthetical compatibility and resistance to weathering while offering reversibility. The proposed method is able to generate micron-sized coatings with controlled properties, such as adhesion and self-healing, leading to less weathered surfaces. Our results show that the PHM is a highly effective protective material that can be applied for stone protection and other similar applications.

Dual-mode excitable Vis/NIR-II luminescence of lanthanide-doped core@multishell nanostructures for anti-counterfeiting and imaging of latent fingerprints

The development of luminescent materials that can simultaneously realize multiple emissions can help improve the reliability of anti-counterfeiting and the security of encrypted information. Lanthanide-doped nanomaterials are very suitable for advanced anti-counterfeiting applications because of their abundant 4 f energy levels and near-infrared (NIR) laser excitability. Herein, we design lanthanide-doped core@multishell nanoparticles NaYF4:Yb,Er/Ho/Tm@NaYF4@NaYF4:Nd@NaYF4, which can realize upconversion luminescence of Er/Ho/Tm under 980 nm excitation, as well as non-overlapping NIR-II luminescence under 980 nm or 808 nm excitation. By precisely controlling the distribution of lanthanide ions in the core-shell layer, the luminescence interference of nanomaterials under different wavelength excitation can be avoided. Experiments show that multi-color security and information encryption under NIR laser excitation can be achieved using aqueous inks containing the designed multilayered core-shell nanostructures, which are covert and difficult to forge. And the multilayer core-shell nanopowder can be used for efficient identification of latent fingerprints on complex surfaces.

Selective adsorption of coalbed methane on multilayer defective graphene nanostructures and their Mn-modified nanostructures: A DFT study

Coalbed methane (CBM) is an unconventional natural gas with CH4 as the main component. It is found in coal seams and surrounding rocks. The development and exploitation of CBM is a promising approach to ensure the safety of coal mine production, reduce greenhouse effects, and increase clean energy resources. Based on the first-principles calculations in conjunction with a grand canonical Monte Carlo (GCMC) simulation, this paper aims to examine the effects of interlayer spacing and Mn modification on CBM and CO2 adsorption. We assess the CH4 storage performance in multilayered defective graphene nanostructures (MDGNs). Using density functional theory in conjunction with the Grimm correction method (DFT-D approach), both the adsorption energy and charge distribution between CBM components and extended line defects (ELD) are appropriately evaluated in the presence or lack of Mn modification (Mn-ELD). The GCMC simulation is implemented to investigate CH4 adsorption isotherms of MDGN and Mn-MDGN configurations at 298.15 K. The selective adsorption capabilities of MDGNs and Mn-MDGNs for CO2, N2, and CH4 are also systematically analyzed. The obtained results reveal that an Mn-MDGN configuration with an interlayer spacing of dGL=1.02 nm is effective in sequestering CO2 from CBM. In contrast, MDGN configurations with interlayer spacings of dGL=0.68 and 1.02 nm are more effective for the storage of purified CBM. In continuing, the CH4 purification mechanism in Mn-MDGNs and the CH4 storage mechanism in MDGNs are also methodically explored at the molecular level. The research work reported here can serve as a crucial guide for the future development and utilization of CBM.

Giant Optical Nonlinear Response up to 60th‐Order Induced by the Ytterbium Energy Relay Mediated Photon Avalanches

AbstractThe exploration of photon avalanching (PA) luminescence in different lanthanide emitters has profound implications in plentiful frontier applications. However, studies for universal mechanisms at the nanoscale to exhibit giant nonlinear responses in various avalanching emitters are limited. Here, record‐breaking nonlinear responses up to 60th‐order in high‐lying emitting levels of various emitters at room temperature are generated by proposing a universal mechanism named energy relay‐mediated photon avalanche (enrePA). By harnessing energy from the avalanching nano‐engine through the energy relay of Yb3+ ions, the brightness of blue emissions from Tm3+ and Ho3+ can be enhanced with giant optical nonlinearity up to 60th and 38th order, respectively. Further incorporating gadolinium‐based systems, more emitters (Tb3+, Eu3+, Dy3+, Nd3+) can be activated with extreme optical nonlinearities up to 48th‐order. By expanding PA into the full‐spectrum range, the enrePA mechanism opens exciting avenues for flexible and high‐efficiency PA modulation in multilayer nanostructures, enabling the applicability of PA in more technologies such as super‐resolution imaging, lithography, and optical detection.

Ultrafast Dynamics of Strong Near‐Field Coupled Localized and Delocalized Surface Plasmons

AbstractThis paper reports transient dynamics of strong near‐field coupling behavior of plasmons in a multilayer metal nanostructure that enables ultrahigh‐efficient optical switching. Particle plasmon on the top array units couples with localized/delocalized plasmons on the bottom Au film to produce dipolar and high‐order hybrid modes with nearly suppressed reflection. The mode coupling can be tuned from near‐field to far‐field regime readily mediated by the spacer thickness. The dipolar mode inherits the high dispersive property of the delocalized plasmon, but the higher‐order one shows limited dispersion. Transient spectroscopy illustrates both hybrid modes have a picosecond timescale redshift under on‐ and off‐resonance excitation. However, the higher‐order mode exhibits a longer decay lifetime than the dipolar one because of resonance characteristics and cavity properties. An ultrafast optical switching effect with a response time of τ = 3.2 ps and an ultrahigh efficiency of 5100 mOD mJ−1 cm2 is achieved under an extremely low pump fluence.

Carbon nanostructures synthesis by catalyst-free atmospheric pressure plasma jet

In this study, carbon nanostructures were synthesized utilizing a warm plasma jet at atmospheric pressure in a continuous and catalyst-free process. The procedure and apparatus were designed and constructed in our laboratory. Plasma was generated with 600 W of electrical energy, using a high-voltage, high-frequency alternating current power source. The working gas utilized was a propane/butane mixture, with a concentration ratio of 60:40, respectively. A production rate of 300 mg min−1 of powdered material was achieved, with a particle size between 20 and 100 nm. The product was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Results show the formation of multilayer carbon nanostructures with a low content of functional groups; the obtained material presented structural defects and amorphous carbon. This work demonstrates that, with adequate control, warm plasma jet discharges can be employed for the synthesis of carbon nanostructures. The process is scalable and can be utilized for hydrocarbon reforming and hydrogen production. However, further studies are needed to improve the quality of the nanostructures and process efficiency. The synthesized material can potentially be used in gas adsorption or in the manufacture of polymeric nanocomposites with enhanced thermal, electrical, and mechanical properties.

Effect of vacuum atomic oxygen irradiation on tribological properties of MoS2/WC multilayer films

The adaptability of molybdenum disulfide (MoS2) films in space environments is crucial for aerospace applications. However, atomic oxygen (AO) in low Earth orbit can damage the friction and wear performance of MoS2 films, leading to a reduction in the service life of the film. To enhance the resistance of the film to atomic oxygen irradiation, we constructed a nano-multilayer structure composed of MoS2-WC-MoS2. Studies have shown that MoS2/WC multilayer films exhibit an ultra-low friction coefficient of 0.010 due to their (002) preferred orientation. Even after high-dose AO irradiatione at 1.84 × 1020 atoms·cm−2, the film still maintains a friction coefficient of 0.009. This is attributed to the presence of MeOX nanoparticles in the MoS2 transfer film at the friction interface after AO irradiation, and the existence of MeOX nanoparticles plays a key role in maintaining ultra-low friction of the film. These findings are of great significance for extending the service life of molybdenum disulfide films in space environments and enhancing their resistance to atomic oxygen irradiation.

Asymmetric thermal optofluidics based on plasmonic multilayered nanostructures

Manipulating thermo-convective fluid flow induced by plasmonic nanostructures under light illumination has garnered significant attention in various fields, such as biomedical sensing, particle trapping, and drug delivery. However, achieving symmetric optical manipulation of fluid flow encounters challenges in certain applications due to the inherent temporal and spatial symmetry in the energy transfer process. Here, a design of plasmonic nanostructures is proposed to achieve a platform for the asymmetric manipulation of thermally induced fluid flow in an optofluidic environment. The difference in fluid flow rate between forward and backward directions is due to the combined effect of the local asymmetry of the heat transfer in multilayer plasmonic nanostructure and nonreciprocity. The nonreciprocity originates from the violation of time-symmetry due to the temperature gradient-induced convection. We show that the asymmetric convective flow can also be achieved when the size of the plasmonic structure enlarges from nanometer to micrometer, and it can be used for efficient particle separation or transportation in microfluidic systems. Our findings expand the scope of optofluidic applications and stimulate the exploration of design approaches for optical devices.