Substrate In Air Research Articles

Oxidation-free silver porous sheet bonding onto a bare copper substrate in air

In this study, the sintering of Ag sheets on bare Cu substrate in an air atmosphere without oxidation was achieved by developing a uniform pressure and oxidation inhibition bonding process. Bare Cu substrates and Ag plated dies were bonded with a nano scaled porous Ag sheet at 250 °C and 280 °C in an air atmosphere using an oxygen-blocking pressure bonding system. Oxygen-free Ag nanoporous sheet bonding achieved over 39 MPa strength in air, with up to 30 % bonding ratio increase as temperature rose, depending on necking length and connection. The microstructure of the Ag sintered layer was further investigated by transmission electron microscopy (TEM) analysis.

Bonding Behavior and Quality of Pressureless Ag Sintering on (111)-Oriented Nanotwinned Cu Substrate in Ambient Air.

(111)-oriented nanotwinned Cu ((111)nt-Cu) has shown its high surface diffusion rate and better oxidation resistance over common polycrystalline Cu (C-Cu). The application of (111)nt-Cu as an interface metallization layer in Ag-sintered technology under the role of oxygen was investigated in this work, and its connecting behavior was further clarified by comparing it with C-Cu. As the sintering temperature decreasing from 300 to 200 °C, the shear strength on the (111)nt-Cu substrate was still greater than 55 MPa after sintering for 10 min. The fracture surface correspondingly changed from the interface of Ag/die to mixed fracture mode, involving the interface of the Ag/Cu substrate and Ag/die. The existence of copper oxide provided a tight connection between Ag and the (111)nt-Cu substrate at all of the studied temperatures. Although lots of small dispersed voids were seen at the interface between copper oxide and (111)nt-Cu at 300 °C, these impurity-induced voids would not necessarily be a failure position and could be improved by adjusting the sintering temperature and time; for example, 200 °C/10 min or heating to 300 °C, and then start cooling at the same time. The microstructure of Ag-Cu joint on (111)nt-Cu behaved better than that on C-Cu. The thinner copper oxide layer and the higher connection ratio of the interface between copper oxide and Ag were still found on the (111)nt-Cu connection's structure. The poor connection between copper oxide and Ag on C-Cu easily became the failure interface. By controlling the thickness of copper oxide and the content of impurity-induced voids, the use of (111)nt-Cu in advanced-packaging could be improved to a new level.

Detailed work function and structural investigations of layered MoO3 onto SiO2 and MoS2 in air

MoS2, its oxides and heterostructures are increasingly utilized in nanoscale opto-electronics and catalysis, where electrical properties such as work function (WF) affect their performance. Herein, a detailed study of the thickness-dependent work function in the case of thermally produced layered Mo oxides onto SiO2 and MoS2 substrates in air is presented. First, the effects of typical contaminants on the mechanically exfoliated MoS2 substrates are investigated. Then, high resolution structural characterization by atomic force microscopy supported by X-ray photoelectron spectroscopy shows that thermal MoS2 oxidation in humid air produces layered amorphous MoO3 with nano-crystallites. Kelvin-probe force microscopy analysis shows that the first MoO3 layer on both substrates is negatively charged and that the MoO3 work function depends on the oxide thickness. The thickness-dependent WF is explained by presence of screened electric field at the MoO3/substrate interface. The negative doping to MoO3 by the studied substrates is confirmed through density functional theory simulations. Moreover, an electrical device from amorphous MoO3 monolayer onto MoS2 is built and shows rectification behavior due to p-type doping of the MoS2 by the oxide layer. Overall, this study provides an insight to understand and manipulate electrical properties of MoO3 and MoO3/MoS2 heterostructures in various devices.

Improved Tribological Performance of ta-C/MoSx Coatings Deposited on Laser Micro-Structured Steel Substrates in Both Vacuum and Air

Vacuum and air atmospheres impose very different requirements on tribological-loaded contacts, which usually require different surface materials. While hard tetrahedral amorphous carbon (ta-C) coatings provide good tribological properties in air, soft coatings such as molybdenum disulfide (MoS2) work well in a vacuum. Tribological performance in the respective other environment, however, is poor. In this work, the combination of laser microstructured (direct laser interference patterning) steel substrates and the deposition of ta-C and MoSx coatings with vacuum arc evaporation (LaserArc™) was studied, resulting in steel/DLIP, steel/DLIP/ta-C, steel/DLIP/MoSx, steel/DLIP/ta-C/MoSx, and steel/MoSx surface combinations. The tribological properties were studied using a ball-on-disk tribometer with a steel ball counter body in air and in a vacuum (p < 5 × 10−7 mbar). The type of the topmost coating governed their tribological properties in the respective atmosphere, and no general beneficial influence of the microstructure was found. However, steel/DLIP/ta-C/MoSx performed best in both conditions and endured the highest contact pressure, which is attributed to the mechanical support of the ta-C coating and MoSx reservoir in the remaining structure, as evidenced by Raman spectroscopy. The findings suggest that such combination allows for surfaces bearing a high load capacity that can be applied in both a vacuum and in air, for example, in multi-use space applications.

Low-cost O2 plasma activation assisted direct bonding of β-Ga2O3 and Si substrates in air

This study presents a novel technique for directly bonding β-Ga2O3 and Si substrates using O2 plasma activation at room temperature. The activation process resulted in excellent surface hydrophilicity and roughness. Annealing in an N2 atmosphere revealed a bonding strength of 6.23 MPa, with partial fracture of the Si substrate. The bonding interface was observed by TEM and EDS. A distorted amorphous intermediate layer with a thickness of 100 nm and amorphous bubbles were observed in the bonding interface. In addition, the Ga, O, and Si elements were diffused and enriched, forming approximately 30 nm nodules at the bonding interface. This method offers a promising approach for integrating wide bandgap semiconductor materials in devices, bypassing the need for vacuum treatment.

Mechanical Robust GO/PVA Hydrogel for Strong and Recyclable Adhesion in Air, Underwater, and Underoil Environments.

Adhesive hydrogels are considered to be promising interfacial adhesive materials for various applications; however, their adhesive strength is significantly reduced when immersed in liquid environments (water and oil) due to obstruction of the liquid layer or swelling in liquid, and they could not always be reused when the failure of the adhesive performance occurred. Herein, a graphite oxide/poly(vinyl alcohol) (GO/PVA) hydrogel with strong adhesion in air and under liquid environments was developed by rationally regulating the interactions of water and dimethyl sulfoxide (DMSO) in the binary liquid system. The strong interaction between water and DMSO allowed the water layer of the GO/PVA hydrogel on the hydrogel surface to act as a shield to repel oil in air, under water, and even when immersed in oil, and it also endowed the obtained hydrogel with antiswelling property when immersed in water and oil. Importantly, the GO/PVA hydrogel could serve as an advanced adhesive to firmly bond different substrates in air, under water, and under oil, and interestingly, its dry and wet adhesive performance was repeatable and recyclable. This work is expected to be an important addition to the field of adhesive soft materials.

Deposition of Ni-W-Mo ternary alloy coating on copper via pulsed current electrodeposition with enhanced corrosion resistance and mechanical properties

Nickel-tungsten-molybdenum (Ni-W-Mo) alloy coatings have been used extensively in micro-electro-mechanical systems (MEMS) because of their thermal stability, superior toughness, and corrosion resistance in extreme environments. The aim of the present study is to characterize the corrosion resistance and mechanical performance of Ni-W-Mo ternary alloy coating on Cu substrate. Meanwhile, the Mo element was co-deposited in the Ni-based plating to enhance the toughness of the coating layer owing to its self-lubricant performance. The Ni-W-Mo coating was successfully fabricated on Cu substrate by pulse electro-deposition via pulse currents of 9.0 and 4.5 A/dm2. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) equipped with X-ray energy dispersive spectroscopy (EDS) were used to investigate the microstructure, morphology, rupture surface, and chemical composition of the Ni-W-Mo ternary alloy coating. A higher Mo content (27 wt%) and presence of nodules were obtained at a pulse current of 9.0 A/dm2. The nodules of the Ni-W-Mo ternary alloy coatings were observed using SEM, and a crack-free coating was confirmed to be completely bonded with the Cu substrate via scribe-grid testing. The corrosion resistance of the Cu substrate with and without the Ni-W-Mo ternary alloy coatings was evaluated in brine (3.5 wt% NaCl) via potentiodynamic polarisation testing in ambient temperature. The results showed that the alloy coating increased the corrosion resistance of the Cu substrate in brine. The quasi-crystal structure of the proposed alloy coating enhanced the micro-hardness and tensile resistance of the Cu substrate, which were evaluated in the ambient air and brine using the slow strain rate test (SSRT). The tensile strength of the specimen with the Ni-W-Mo ternary alloy coating (current density 9.0 A/dm2) increased by approximately 22 MPa compared with that of the Cu substrate in ambient air. These results confirm that the corrosion resistance and toughness of the Ni-W-Mo ternary alloy coatings deposited using the electrodeposition technique with pulsed-current power are superior to those of the Cu substrate.

All-printed wearable humidity sensor with hydrophilic polyvinylpyrrolidone film for mobile respiration monitoring

In this study, a capacitive-type wearable humidity sensor comprising a polyvinylpyrrolidone (PVP) film, as active sensing dielectric, and carbon nanotube (CNT) random networks, as electrodes, all-printed on flexible substrates in ambient air, is demonstrated for real-time respiration monitoring. The PVP-based humidity sensor achieved a high sensing response of 3.0 ± 0.15 nF/RH%∙cm2 (where RH stands for relative humidity) and a sensitivity of 6.4 ± 0.1 pF/%RH in the RH range of 40–90%. A significantly small hysteresis window, fast response/recovery (∼ 30 ms), and high reliability were noted. The sensing mechanism of the capacitive response toward humidity was investigated, and it is attributed to continuous proton hopping through water molecule layers. The operational stability of the proposed humidity sensor under temperature variations and mechanical deformation, was investigated to address existing issues related to wearable electronics. Finally, the feasibility of a mobile respiration monitoring device is demonstrated by developing an armband-type wireless-communication monitoring system equipped with the wearable humidity sensor. Real-time biophysical information can be analyzed by monitoring the changes in the respiration intensity and frequency, which were wirelessly transmitted to the user’s mobile interface. We note that very few studies have focused on all-printed wearable humidity sensors consisting of pristine PVP and immobilized CNT random networks for real-time mobile respiration monitoring of human breath regardless of bent and relaxed state.

A semitransparent and tough wood-based adhesive gels with excellent adhesion both in air and underwater for emergency pipeline repair

The instant biomass-based adhesive gels have demonstrated promising potentials in various applications, including wound dressing, sensors, and underwater repair engineering. However, existing biomass-based gels usually have relatively poor mechanical and adhesion properties, and even lose their adhesion in wet conditions or underwater due to their inherent hydrophilicity, which remains a considerable challenge for its further application. Herein, we developed a semitransparent wood-based gel patch that can achieve instant and robust adhesion to various substrates both in air and underwater. In briefly, natural wood with porous channels was employed as the skeleton to enhance the mechanical strength of gels. Polymerizable ionic liquid (PIL) and acrylic acid (AA) were selected as the polymeric monomer and filled into the wood channels to synthesize gels by in-situ polymerization in the absence of chemical cross-linker agents. Abundant noncovalent bonds gave gels with superior adhesion to various substrates such as plastic, metal, polytetrafluoroethylene (PTFE), glass and wood. Additionally, the presence of C-F bond endowed the gels with low surface energy which could repel water molecules from the interface between gels and substrates, resulting in the outstanding underwater adhesion. The resultant wood-based gels displayed high tensile stress (6.10–9.34 MPa), which was 3.56–5.46 times higher than that of pure gels without the incorporation of wood. The maximum adhesion strength of gels could reach approximately 350 kPa in air and 345 kPa underwater. This work showed a promising application in emergency repair engineering of broken pipeline both in air and underwater.

The effect of the synthesis conditions on the crystal structure of palladium(II) oxide nanofilms

Nanocrystalline films of palladium(II) oxide obtained by oxidation of the initial metallic Pd layers with a thickness of 35 nm on Si (100) substrates in atmospheric air were studied using XRD analysis, TEM, and RHEED. PdO/SiO2/Si (100) heterostructures were synthesised in two stages. First, we obtained finely dispersed layers of metallic Pd on SiO2/Si (100) substrates with an ~ 300 nm SiO2 buffer layer using thermal sublimation in a high vacuum. The Pd layers were then oxidised in the temperature range Tox = 620 – 1100 K in atmospheric air (with the partial pressure of oxygen of about 21 kPa). The study determined that the deformation of the tetragonal crystal structure of homogeneous nanocrystalline PdO films is explained by an increase in the values of lattice parameters with the oxidation temperature. The deformation reaches its maximum values at Tox ~ 970 K. Comparison of the obtained results with the earlier data regarding PdO/SiO2/Si (100) heterostructures synthesised in a dry oxygen atmosphere (with the partial pressure of oxygen of about 101.3 kPa) demonstrated that PdO films synthesized in an oxygen atmosphere are characterized by a higher degree of deformation of the crystal structure. The effect of the oxidation temperature and O2 partial pressure on the increase in the tetragonal lattice parameters of the PdO films can be explained by the formation of interstitial oxygen atoms in the octahedral void in the centre of the palladium(II) oxide unit cell.

Numerical study of feature-distribution effects foranti-reflection structured surfaces on binary gratings.

Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating. Various distribution designs were investigated at 633nm wavelength for TE and TM polarization states at normal incidence, comparable to EMT fill fractions for a fused silica substrate in air. The results show differences in performance between ARSS transverse feature distributions, exhibiting better overall performance for subwavelength and near-wavelength scaled unit cell periodicities with short auto-correlation lengths, in comparison to equivalent effective permittivity designs that have less complicated profiles. We conclude that structured layers of quarter-wavelength depth and specific feature distributions can outperform conventional periodic subwavelength gratings as antireflection treatments on diffractive optical components.

Nanotopography of Polystyrene/Poly(methyl methacrylate) for the Promotion of Patient Specific Von Willebrand Factor Entrapment and Platelet Adhesion in a Whole Blood Microfluidic Assay.

Platelet function testing is essential for the diagnosis of patients with bleeding disorders. Specifically, there is a need for a whole blood assay that is capable of analysing platelet behaviour in contact with a patient-specific autologous von Willebrand factor (vWF), under physiologically relevant conditions. The creation of surface topography capable of entrapping and uncoiling vWF for the support of subsequent platelet adhesion within the same blood sample offers a potential basis for such an assay. In this study, spin coating of polystyrene/poly (methyl methacrylate) (PS/PMMA) demixed solutions onto glass substrates in air has been used to attain surfaces with well-defined topographical features. The effect of augmenting the PS/PMMA solution with uniform 50 µm PS microspheres that can moderate the demixing process on the resultant surface features has also been investigated. The topographical features created here by spin coating under ambient air pressure conditions, rather than in nitrogen, which previous work reports, produces substrate surfaces with the ability to entrap vWF from flowing blood and facilitate platelet adhesion. The direct optical visualisation of fluorescently-labelled platelets indicates that topography resulting from inclusion of PS microspheres in the PS/PMMA spin coating solution increases the total number of platelets that adhere to the substrate surface over the period of the microfluidic assay. However, a detailed analysis of the adhesion rate, mean translocating velocity, mean translocation distance, and fraction of the stably adhered platelets measured during blood flow under arterial equivalent mechanical shear conditions indicates no significant difference for topographies created with or without inclusion of the PS microspheres.

Single phase ZnV2O6 nanorods with excellent visible light photodetection capability

We report a facile synthetic route for the growth of single phase ZnV2O6 nanorods via a simple acid–base reaction of the Lewis acid forms of ZnCl2 and VCl3 with NaOH in an aqueous solution followed by the thermal treatment of the resulting metal hydroxides on a SiO2 substrate in air. The as-grown ZnV2O6 nanorods exhibited a well-defined rectangular cross-section with a width of approximately 300–350 nm and thickness of 100–150 nm, and they extended in random directions up to a length of 3 µm. The as-grown ZnV2O6 nanorods possessed a single-phase monoclinic brannerite-type structure, as determined via X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopic investigations. The synthesized ZnV2O6 sample exhibited a band gap of ∼2.06 eV and excellent photodetection properties in the visible light region of 635 nm, which is the band-edge wavelength. The new ZnV2O6 synthetic method proposed in this report could be used to develop various photocatalysts and energy conversion materials in the future.

Determining the laser-induced release probability of a nanoparticle from a soft substrate.

This Letter presents a study of laser-induced nanoparticle release from a soft substrate in air under different conditions. A continuous wave (CW) laser heats a nanoparticle and causes a rapid thermal expansion of the substrate, which gives an upward momentum that releases the nanoparticle from the substrate. The release probability of different nanoparticles from different substrates under different laser intensities is studied. The effects of surface properties of substrates and surface charges of the nanoparticles on the release are also investigated. The mechanism of nanoparticle release demonstrated in this work is different from that of laser-induced forward transfer (LIFT). Owing to the simplicity of this technology and the wide availability of commercial nanoparticles, this nanoparticle release technology may find applications in nanoparticle characterization and nanomanufacturing.

Impact of Excitation Intensity-Dependent Fluorescence Intensity Ratio of Upconversion Nanoparticles on Wide-Field Thermal Imaging

Erbium ion (Er3+)-doped upconversion nanoparticles (UCNPs) are frequently used for nanothermometry because their fluorescence intensity ratio (FIR) between two green emission bands at ∼525 and ∼545 nm is sensitive to temperature variation. One of the prerequisites for nanothermometry is that the FIR be independent of excitation intensity at constant temperature. In this work, the effect of excitation intensity on the FIR of core–double-shell NaYF4:Yb3+,Er3+@NaYF4:Yb3+,Nd3+@NaYF4 UCNPs was investigated in two environments. The first environment is in aqueous solution, and the second is a monolayer of UCNPs on top of a silica–silicon substrate in air. The experimental results showed that the FIR decreases with the excitation intensity at constant temperature in each case. We further found that the excitation intensity-dependent FIR indeed deteriorated the thermal images acquired by wide-field upconversion fluorescence microscopy, in which a Gaussian laser beam was used to excite UCNPs uniformly coated on a silica–silicon substrate. The nonuniform excitation intensity of the incident laser beam resulted in thermal images that showed nonuniform temperature distributions in a 100 μm range field of view, even though the whole sample was maintained at constant temperature in air. To tackle this problem, we first measured the excitation intensity and temperature dependence of the FIR and the excitation laser intensity distribution on the sample. We then developed a correction scheme to correct the thermal images. With our correction process, the temperature distribution on the sample can be accurately mapped even with nonuniform illumination.

Formation of silicone thin films by ArF excimer laser induced photo‐desorption

AbstractLow molecular weight silicones were ejected from silicone rubber target irradiated by a 193 nm ArF excimer laser through the photo‐desorption. The ejected silicones were successfully deposited on a fused silica glass substrate in air. An approximately 0.3 mm of the target‐substrate distance was required for the deposition. The deposited silicones became a thin film, showing an interference color when the ArF excimer laser was irradiated for a long time. Chemical bonding state of the formed thin films was analyzed by the Fourier transform infrared spectroscopy. The thin films were slightly different from the original silicone rubber structure, still it was composed of Si‐O‐Si bonds and Si‐CH3 bonds. Also, OH bonds were clearly produced in the silicone thin films. As a result, contact angle of water on the silicone thin films was measured to be approximately 20 degrees, indicating a hydrophilic property.

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules.

A zeroth-order, non-diffracting Bessel beam, generated by picosecond laser pulses (1064 nm, 10 Hz, 30 ps) through an axicon, was utilized to perform pulse energy-dependent (12 mJ, 16 mJ, 20 mJ, 24 mJ) laser ablation of silver (Ag) substrates in air. The fabrication resulted in finger-like Ag nanostructures (NSs) in the sub-200 nm domain and obtained structures were characterized using the FESEM and AFM techniques. Subsequently, we employed those Ag NSs in surface-enhanced Raman spectroscopy (SERS) studies achieving promising sensing results towards trace-level detection of six different hazardous materials (explosive molecules of picric acid (PA) and ammonium nitrate (AN), a pesticide thiram (TH) and the dye molecules of Methylene Blue (MB), Malachite Green (MG), and Nile Blue (NB)) along with a biomolecule (hen egg white lysozyme (HEWL)). The remarkably superior plasmonic behaviour exhibited by the AgNS corresponding to 16 mJ pulse ablation energy was further explored. To accomplish a real-time application-oriented understanding, time-dependent studies were performed utilizing the AgNS prepared with 16 mJ and TH molecule by collecting the SERS data periodically for up to 120 days. The coated AgNSs were prepared with optimized gold (Au) deposition, accomplishing a much lower trace detection in the case of thiram (~50 pM compared to ~50 nM achieved prior to the coating) as well as superior EF up to ~108 (~106 before Au coating). Additionally, these substrates have demonstrated superior stability compared to those obtained before Au coating.

Laser scribing of fluorine-doped tin oxide coated on glass substrate in air and water

Fluorine-doped tin oxide (FTO) is one of the conductive layers used in the emerging perovskite solar cell technology, and the layer is typically scribed by a laser beam. However, thermal damage induced by laser deteriorates the scribe quality and in turn reduces the efficiency of the solar panel. This paper compares five different laser scribing techniques for isolating the FTO on the film and substrate sides both in air and water environments. The width and depth of laser-scribed channels, as well as burrs height, produced by using the different techniques were examined and compared. A clean and consistent scribe with negligible burrs was achievable by ablating the FTO film in the flowing water layer. Using this technique, its burr height index was found to reduce by 62.5% compared to the laser scribing of FTO film in air. A three-dimensional transient heat transfer model was also developed in this study to simulate the temperature field of workpiece subjected to the laser scribing in air and in flowing water environments. The thermal damage region was substantially small when the ablation was performed in the flowing water film. This could be a promising technique for the P1 scribing step in the manufacturing of emerging perovskite solar modules.

Ambient air processed highly oriented perovskite solar cells with efficiency exceeding 23% via amorphous intermediate

The preparation of perovskite solar cells (PSCs) in ambient air can effectively reduce the production cost and is more conducive to commercial production. However, ambient air fabrication of perovskite film always causes rough surface and nonuniform coverage which increase non-radiative recombination in PSCs. In this work, we adopted an amorphous intermediate strategy in lead iodide (PbI2) film to prepare the oriented perovskite film under ambient air condition. This amorphous intermediate formed by the interaction force between cesium iodide (CsI) and PbI2, which promotes perovskite phase inversion in perovskite precursor film and finally the perovskite grains grow perpendicular to the substrate in the ambient air. As a result, this ambient air processed-PSCs with the perovskite film passivated with butylammonium iodide (BAI) obtained a power conversion efficiency (PCE) of 23.46%, which is equivalent to that of two-step preparation in glovebox. Furthermore, the PSC maintains 85% of its initial efficiency under more than 1000 h of continuous illumination and processes a recoverable PCE at temperatures below 65 °C under photothermal cycling stress.

Coil-to-Bridge Transitions of Self-Assembled Water Chains Observed in a Nanoscopic Meniscus.

Ten downward portions in the large oscillatory force–distance curve reported earlier are analyzed to understand a nanoscale water meniscus confined between a sharp probe and a flat substrate in air. The sigmoidal shape of each portion leads to the assumption that the meniscus is made up of n independent transitions of two states: one for a coil state and the other for a bridge state. The analysis reveals that each downward portion occurs due to a coil-to-bridge transition of n self-assembled water chains whose length ranges between 197 and 383 chain units. The transition provides novel insights into water’s unique properties like high surface tension and the long-range condensation distances.