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Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-iblock/i-poly(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

Tin whisker growth, which may lead to short circuits and current leakage, is a serious issue in electronics components. Polyurethane-based conformal coatings have been seen as an effective candidate to mitigate the tin whisker growth. To better understand the effect of such coatings, this study exposed the tin-plated copper coupons coated with i) moisture cured polyurethane (PU) and ii) dual UV/moisture cured polyurethane acrylate (PUA), for long-term (up to 5000 h) high-temperature and high-humidity (HTHH) storage (85 °C and 85%RH, respectively). After HTHH storage, microstructural developments in the tin layer, coating degradation, tin surface reaction, and coating adhesion to tin surface were analyzed to compare the tin whisker mitigation behavior. In order to improve the coating adhesion, tin surface was also treated with a silane adhesion promoter before coating was applied. Furthermore, the effect of electron beam irradiation was investigated as it degraded the coating properties and adhesion. The results show that maintaining good adhesion and suppressing the degradation of mechanical properties of conformal coatings during various environmental exposures are essential for enhanced tin whisker mitigation.

Stimuli-responsive self-assembly of functional amphiphilic molecules by specific chemical stimulants is a promising strategy for sensor application. Herein, we demonstrate a fast optical detection of urea in human urine by exploiting bolaform perylene diimide functionalized with imidazoles (PDI-Hm), whose aggregation is induced by urea hydrolysis. The hydroxides produced from the enzymatic urea hydrolysis deprotonate the imidazoles to reduce electrostatic repulsion between PDI-Hm molecules in a HCl-methanol mixture, thereby leading to aggregation and consequent fluorescence quenching. The molecular interaction of PDI-Hm was further scrutinized to understand the aggregation behavior driven by the screening of electrical repulsion. As an optical sensing probe, PDI-Hm displays a prompt response (

Polyurethane (PU)—based conformal coatings which protect electronic components and boards from harsh environmental exposures were further developed to mitigate the tin (Sn) whisker growth in lead (Pb)—free electronics. As a means of achieving this goal, the adhesion mechanics of PU-based conformal coating on tin surfaces was investigated. We attempted to improve the interfacial adhesion between PU-based conformal coatings and tin (Sn) as it slows down the formation of tin whisker growth. A multi-layer sandwiched specimen made between two Si beams was employed to create an interface between PU coating and Sn for four-point bending testing (4PBT). The result shows that PU has strong adhesion to Sn while polyurethane acrylate (PUA) has much weaker adhesion to Sn. The PUA adhesion, however, increased by introducing a silane agent ((3-Aminopropyl)triethoxysilane) on the tin surface, which is covalently bonded to PUA. The adhesion improvement of a modified tin surface was also confirmed by a simple cross-cut tape peeling test. Post fracture analysis suggested that blocking the reaction between bare Sn surface and the acrylate component contribute to improved adhesion.

Conformal coatings with higher adhesion strength is crucial for mitigating the growth of whiskers from the pure tin (Sn) or Sn-rich surfaces of the Pb-free electronics. Silane coupling agents have the ability to form a durable bond between polymeric coatings and metallic materials. The main goal of this paper is to investigate the effect of silane agents on the adhesion behavior of polyurethane (PU), polyurethane acrylate (PUA) and both coatings filled with silicone rubber (SR) nanoparticles on the tin solder pads. It was found that an isocyanate-based silane provided excellent adhesion for PU and PU + SR coatings and an acrylic-based silane for PUA and PUA + SR coatings on the tin surface. This was due to the reaction bond formation between the silane coupling agent and the coating. Hence, the selection of silane coupling agents with the organofunctional group similar to the coating material is crucial to improve the adhesion properties of the coating.

Polyurethane (PU) is a good candidate to be used as conformal coatings for space electronic components and boards due to its manufacturability and desirable mechanical properties. It also keeps tin whiskers from growing on the tin-rich surfaces under a long-term usage that will ultimately result in electrical failure. PU coating can, however, be susceptible to the irradiation damage in space environment that ultimately alters its chemical structure and mechanical behavior. In this study, four variations of PU-based coatings (PU filled with and without nanosilica particles; polyurethane acrylate (PUA) filled with and without nanosilica particles) were investigated to understand the irradiation damage on chemical structure and the corresponding mechanical properties under three electron beam irradiation fluences (1 × 1014 cm−2, 1 × 1015 cm−2, 1 × 1016 cm−2). Infrared spectroscopy was used to examine the degradation of chemical bonding with irradiation. Microphase separation, the degree of curing, and molecule chain mobility were examined via differential scanning calorimetry (DSC) by monitoring the shift in glass transition temperatures after the irradiation. The electron beam irradiation on PU films resulted in the quinone structure formation whereas, on PUA film, microphase separation increased, thereby making both films stronger and stiffer, but less ductile and more brittle. As a result, PU and PUA coatings under a high fluence of irradiation will be more prone to tin whisker penetration. This study also shows the potential effect of nanosilica on retarding the irradiation damage in PU and PUA films.

Usage of pure tin (Sn) or Sn-rich alloy in electronics industry is growing, which makes them more susceptible to the spontaneous growth of tin whiskers. The risk of having these whiskers can be dramatically mitigated by applying a conformal coating such as parylene C. The purpose of this paper is to investigate the degradation of parylene C coating (with two thicknesses, 12.5 μm and 25 μm) during thermal aging in high humidity environment (85 °C/85% relative humidity for up to 5000 h) and its effect on the tin whisker mitigation property. It was observed that under the high temperature and high humidity (HTHH) environment, the oxidation occurs at early times, followed by bond scission, resulting in the loss in strength and modulus of the parylene coating. After 2500 h of aging, due to the degradation of the silane agent at the tin/parylene interface, the adhesion of the parylene coating on the tin surface was significantly weakened, which resulted in extensive corrosion of the tin solderpads. The loss of adhesion of the coating, along with the corrosion of the tin surface facilitated tin whisker nucleation at the interface while the loss of mechanical strength and the brittleness made the growing whiskers penetrate easily through the coating. Tin whiskers with a smaller diameter were buckled and grew along the delaminated interfacial region while those with a larger diameter penetrated and continued to grow through the coating. Although the thicker parylene coating helped delay the complete penetration and increase the critical diameter of whiskers for complete penetration, it showed more tin whisker activities and easy penetration by large diameter whiskers due to poorer adhesion. Hence, the effectiveness of the parylene coating on tin whisker mitigation will depend on its degradation kinetics of mechanical properties and adhesion under such harsh conditions.

Tin rich surfaces inside Pb-free electronics are more prone to tin whisker growth, thereby resulting in electrical failure of components. Conformal polyurethane (PU) coatings, which can be used as a mitigation strategy for such whisker growth, were investigated in this study. Nanoparticles of silica (∼20 nm in diameter) were added via liquid suspension to the PU resin to improve its mechanical properties. Four compositions of functionalized nanosilica suspensions, 10 wt.%, 20 wt.%, 30 wt.% and 50 wt.% (corresponding to the solid silica weight of 3.50%, 6.74%, 9.75%, and 15.17%, respectively) were evaluated to establish the relationship between microstructure developments and mechanical properties. Fourier-transform infrared spectroscopy (FTIR) and low-kV field emission scanning electron microscopy (FE-SEM) were used to examine the effects of nanosilica suspension addition to the PU resin. Mechanical properties of the coating were not only evaluated by nanoindentation for localized PU matrix properties but also by uniaxial tensile testing for composite properties. Results from both scales show that the addition of the particle suspension up to 20 wt.% (corresponding to 9.75 wt.% nanosilica) makes optimum mechanical performance consisting of good modulus, strength and ductility. This conclusion is also supported from microstructural, as well as chemical aspects of the PU coatings with the addition of nanosilica suspension.

We show that sandblasting can be employed to effectively enhance the oxidation resistance of copper by suppressing the interfacial delamination between copper and its oxide by modifying the surface roughness of Cu. Increasing sandblasting treatment time from 0 to 120 s increases the surface roughness of Cu from 0.12 ± 0.003 μm to 2.89 ± 0.176 μm, which results in improved oxidation resistance of the Cu surfaces and enhances the oxide/substrate interfacial fracture energy from 0.035 J/m 2 to 3.1 J/m 2 determined using nanoindentation. The sandblasting treatment has no appreciable effect on the Young's moduli of the Cu oxide film, which remain nearly constant at around 36 GPa. The improved oxidation resistance is ascribed to the enhanced interfacial adhesion of the sandblasted copper owing to the concave shape of craters generated by sandblasting, which results in a net downward force from the compressive stresses in the oxide film that forces the film to adhere to the Cu substrate.

The self-assembly of tyrosyl bolaamphiphiles is exploited to create a colloidal protein-like host matrix, upon which sacrificial electron-donor molecules associate to create a photosystem II (PSII) mimetic electron-relay system. This system harnesses the tyrosine phenol groups abundant on the surface of the assemblies to mediate photoinduced intermolecular electron transfer. Compared with the l-tyrosine molecules, the tyrosyl bolaamphiphile assembly facilitates electron transfer from the sacrificial electron donor to the oxidized photosensitizer. The enhanced electron relay is likely to be driven by the host function of the assembly associated with the sacrificial electron donor and by the suppression of the oxidative cross-linking of phenoxyl radicals. The tyrosyl bolaamphiphile assembly is advantageous in the construction of a PSII mimetic system with a protein-like nature and displaying biochemical functions.

We have developed a “two-step” solution-based processing to deposit high-k ceramic thin films. Electrochemically pre-coated amorphous titania layers were “hydrothermally” or “hydrothermal-electrochemically” converted to crystalline BaTiO3 films at ≤90°C. In hydrothermal process, an in situ electrochemical protection (ECP) mechanism enables utilization of common metallic substrates (e.g., Cu), which otherwise suffer corrosion from the precursor. Microstructural evolution of BaTiO3 films along with the effectiveness of ECP is discussed in this article. Derived BaTiO3 shows a dielectric constant of ~80 at 100 kHz, which makes it a promising candidate for high-density microelectronic capacitor applications.

Both the electrical and mechanical properties of silica thin films deposited by liquid phase deposition (LPD) have been evaluated in this study. Silica thin films have been prepared on glass surface by immersing it in a supersaturated Hexafluorosilicic acid (H 2 SiF 6 )-based solution at a low temperature of 50°C. The as-deposited LPD silica fihns exhibit a low dielectric constant (k) that varies from 1.7 to 2.7 depending on the film morphology and fluorine content of the film. Young's modulus of these films was measured in the range of 18.9-24.5 GPa by a nanoindentation technique. The combination of extremely low k and fairly high modulus made this low-temperature-processed LPD silica films a very promising candidate for an interlayer dielectric film for the next-generation semiconductor devices.

The fluxless solderability of pure indium on gold-coated surfaces is investigated in this study using measurements of wetting angle and joint strength. This study focuses on the effects of indium’s native oxides and those which form during heat treatment. The initial oxide thicknesses are obtained by heating indium samples at various temperatures, and then, during the reflow above the melting temperature, oxidation at the interface is either allowed in open air or prevented by reflowing in an inert environment. The testing results presented include characterization of indium oxide (In2O3), the effects of indium oxide on joint strength, and the effect of hot pressing during reflow process.

Ceramic/self-assembled monolayer (SAM) bilayer coatings can provide adequate protection for silicon devices, or act as a multipurpose coating for other electronic applications, due to synergistic effects by forming a hybrid coating structure. The organic SAM layer acts as a “template” for the growth of the ceramic layer, while the ceramic layer can provide protection from environmental and mechanical impact. Low-temperature solution-based deposition techniques, namely, an in-situ solution method (biomimetic) and a hydrothermal method, have been employed in this study. Specifically, phosphonate-based (diethyl phosphatoethyl triethoxy silane) SAMs were used as a template to generate a zirconia ceramic layer at low temperatures. Other organic templates such as -SiCl3-, -OH-, -HSO3-, or -CH3-terminated SAMs were also examined. The reactions to grow the ceramic film were found to be pH sensitive. The ceramic and SAM coatings were characterized by a variety of analytical techniques. A pathway for the formation of the ceramic coating is also discussed.

When flexible organic substrates are used for organic light emitting diodes (OLEDs), a barrier layer is required for the substrate to protect the enclosed functional materials from oxygen and water penetration. In this study, barrier coatings consisting of organic and inorganic films were developed for the organic substrate to ensure sufficient hermetic protection. As a model system, we chose the 'Parylene-C/TiO2' grown on the polyethylene terephthalate (PET) substrates. Parylene C films, which were vapor deposited at room temperature, have been known for a superior conformal coverage. The oxide films were biomimetically formed from in- situ precipitated particles in aqueous solutions and displayed nanoparticulate, dense structures. Since these oxides are processed at very low temperatures (< 70degC) in aqueous solutions, the processes can be applicable to organic structures, cheap and environment-friendly. Further, plasma treatments were employed to adjust the functionality of the organic surfaces and their effects on microstructure evolution of subsequent depositing layers are discussed. In order to evaluate the mechanical properties and film adhesion of the inorganic-organic hybrid coatings, in-situ AFM coupled nanoindentation techniques were introduced. Preliminary results on the dye penetration test indicated that the hermeticity of the barrier coatings was improved by having the hybrid films consisting of parylene-C and TiO2.

Protection from oxygen and moisture is crucial for organic light emitting diodes (OLED) used in flexible display applications. The surface coating is an effective way to protect the enclosed functional materials and organic substrates in order to ensure their device functionality. Parylene films, which can be vapor deposited at room temperature, are known as a superior conformal polymeric material. In fact, a few attempts have shown that the parylene can be a good barrier coating for the OLED devices. This polymer film cannot, however, provide a long-term reliability due to nature of the polymer degradation in the presence of oxygen and moisture. In order to compensate such a drawback, we have explored the ‘biomimetic’ solution processing to deposit the oxide films on the organic substrate. Oxide films can provide a better protection and more robust surface. In this study, polyethylene terephthalate (PET) commonly used for an organic substrate, is deposited with the TiO2 films with or without the parylene underlying layer. Importantly, the oxide coating is processed at very low temperatures (< 60 °C) in aqueous solution, so the process can avoid premature failure due to high-temperature processes, and is applicable to organic structures, cheap and environment-friendly. In addition, hermeticity tests are devised to measure the moisture and oxygen permeation. Interfacial structure and mechanical properties of the resultant coatings are tested via scanning electron microscope (SEM), atomic force microscope (AFM), optical microscope (OM) and nanoindentation.Copyright © 2007 by ASME

MicroElectroMechanical System (MEMS) devices often require low-temperature, fluxless soldering techniques due to their high temperature sensitivity and performance requirements of the components. While seeking the development of a soldering technology using pure indium, the major focus of this study is to assess the thermodynamics and kinetics of indium oxidation at various solder reflow environments that will ultimately provide a processing window for solder reflow and surface oxide cleaning. With a glove box employed to generate reducing environments, oxygen, moisture, and hydrogen contents were varied to examine their effects on oxidation and reduction behavior of indium. We also explored oxidation mechanisms at different regimes of temperature and time. In particular, electron transport from indium to indium oxide is shown to be the rate controlling mechanism under specific oxidizing conditions. For accurate thickness measurements, a spectroscopic ellipsometer was employed. In addition, the effect of indium oxidation on solder joint reliability was observed via wetting angle and interfacial shear strength measurements.

A bio-inspired approach is employed to deposit the oxide films on the substrates coated with self-assembled organic layers. Particularly, titania and zirconia films are grown in aqueous precursor solutions at near room temperatures. This process, directed by the nanoscale organic template, mimics the controlled nucleation and growth of the biominerals such as bones and teeth. Multiscale structural evolution resulting from initial bulk nucleation, nanoparticle aggregation, and ultimate film formation are systematically studied by adjusting the precursor solution conditions. Dynamic light scattering (DLS) is utilized to characterize initial nanoparticles and their associated aggregates/clusters formed in situ in solution. Corresponding nano- and microstructure developments of the oxide films are investigated through high-resolution transmission electron microscope (TEM) and scanning electron microscope (SEM). In addition, mechanical performance is evaluated with the aid of a dynamic nanoindentation testing to establish the structure-property relationships of the bio-inspired oxide films. The goal of this study is to have a capability to tailor microstructures and mechanical behaviors by identifying the controlling mechanisms responsible for nucleation and growth of such oxide films.

The purpose of this paper is to investigate the indium joint strength with known indium oxide thickness. The indium joint strength was assessed by measuring the maximum load of indium solder with the comparison of the wetting angle. The oxide thickness was already grown in different ambient conditions, and provided for the joint strength measurement. The indium joint strength with different oxide thicknesses was tested at a fixed strain rate by tensile loading. This investigation will be very useful to characterize the indium solderability in different environment in terms of the quantitative joint strength.Copyright © 2006 by ASME

There is a growing demand in the development of small-scale devices in microelectronics and microelectromechanical systems (MEMS). Packaging and reliability of such devices are of great concern as they introduce a number of unique packaging issues that are distinct and different from typical electronic packaging applications. In addition, the packaging or encapsulation materials are often exposed to harsh environments, for which their performance is drastically degraded. Importantly, such devices become lighter and smaller, precluding the use of conventional packaging materials and schemes. Given that, surface protective coatings can provide an innovative solution for some of the aforementioned issues. Polymers have indeed shown such a potential for use either as a standalone coating, or an intermediate layer for the subsequent harder, stiffer coatings. In this study, we explore processes and properties of the three coating systems: i) PDMS, ii) Parylene (para-xylylene), iii) Parylene/PDMS. In particular, parylene coating on PDMS is a focus of this study. The parylene coating having much higher mechanical properties than PDMS provided a way to enhance the surface properties of this PDMS. Proper surface modification of PDMS via oxygen plasma seemed to be essential to generate desirable microstructures of parylene coating. Mechanical properties of such coatings are systematically examined via a nanoindenter. The dynamic nanoindentation is also employed to assess viscoelastic properties, as well as depth-dependent mechanical properties. While characterizing the films using the nanoindentation, the substrate effect influenced the indentation data. In addition, extensive surface characterizations are carried out using atomic force microscope (AFM), scanning electron microscope (SEM), and optical microscopy.Copyright © 2005 by ASME

We explore the effect of the substrate on mechanical behavior of thin films using a depth-sensing indentation. For this purpose, nanoindentation has been performed on thermally grown silicon oxide films on the silicon substrate. One primary goal of this study is to extract ‘film-only’ mechanical properties from the nanoindentation data by subtracting the substrate effect. It is also shown that elastic modulus of the film is more influenced by the substrate than hardness due to a larger elastic extension beyond a plastically deformed region, as well as a larger elastic mismatch between the SiO2 film and the Si substrate. Further, an inverse analysis of indentation data is proposed to estimate a thickness of thin films. Consequently, this study provides a fundamental understanding in mechanical phenomena of thin films occurring at nanoscales.

Zinc oxide (ZnO) films consisting of vertically aligned nanorods were hydrothermally grown on a seed layer at 90 °C using two precursors (zinc acetate, zinc nitrate). The microstructures and growth kinetics of ZnO films from various processing conditions were investigated to correlate to photovoltaic (PV) properties. For this, dye-sensitized solar cells (DSSCs) were assembled. Vertically grown nanorods exhibited the (002) out-of-plane texture and its size, alignment, density, and growth rate could be controlled by both solution and seed layer conditions. In particular, the stepwise deposition implemented by changing precursor solution every 2 h exhibited a higher power conversion efficiency (∼2.3% for 1.55-µm-thick ZnO film) than the continuous deposition. The zinc acetate seed layer cured as low as 100 °C enabled the templated growth of ZnO nanorods with an efficiency of ∼1.7% (for thickness of 1.4 µm). This will allow current low-temperature processing to be adopted for the fabrication of low-cost flexible PV devices.

Current microelectronic devices and microelectromechanical systems (MEMS) require that packaging costs be reduced with more enhanced device performance. In addition, the packaging materials are often exposed to harsh environments, for which their performance is drastically degraded. Importantly, such devices become lighter and smaller, precluding the use of conventional packaging materials and schemes. Given that, surface coatings can provide an alternative solution for some of the aforementioned issues. Polydimethylsiloxane (PDMS) is a good candidate material in many encapsulating applications but its surface must be effectively protected due to its poor surface properties. In this study, the PDMS surface is coated with the parylene C film through a vapor-phase deposition. Proper surface modification of PDMS is then essential to generate desirable interfacial adhesion and performance between the parylene C and the PDMS. Effects of plasma treatment were examined in this study to evaluate their effectiveness on the surface modification of the PDMS. In order to explore mechanical performances of the bilayer coatings, dynamic nanoindentation and feedback-control nanoindentation testings were employed. In addition, extensive surface characterizations are performed with atomic force microscope (AFM) and optical microscope (OM).