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Geometrically multifunctional structures inspired by nature can address the challenges in the development of soft robotics. A bioinspired structure based on origami and kirigami can significantly enhance the stretchability and reliability of soft robots. This study proposes a novel structure with individual, overlapping units, similar to snake scales that can be used to construct shape-morphing batteries for untethered soft robots. The structure is created by folding well-defined, two-dimensional patterns with cutouts. The folding lines mimic the hinge structure of snakeskin, enabling stable deformations without mechanical damage to rigid cells. The structure realizes multi-axial deformability and a zero Poisson's ratio without off-axis distortion to the loading axis. Moreover, to maximize areal density, the optimal cell shape is designed as a hexagon. The structure is applied to a stretchable Li-ion battery, constructed to form an arrangement of electrically interconnected, hexagonal pouch cells.

Sodium (Na) organic batteries have attracted great attention because of high abundance of Na, low-production cost, and structure diversity of organic electrode materials. Despite the efforts on organic Na-ion batteries, organic electrodes are still vulnerable to conventional electrolytes, and have a low conductivity which leads to continuous capacity fading and low-rate capability, respectively. In this study, we aimed to reduce solubility in electrolyte and enhance electrical conductivity of organic electrode by anchoring 2,5- dihydroxyterephtalic acid (DHTPA) to carbon black via esterification. Then, the sodiated DHTPA/CB powder was evaluated for an anode in Na-ion battery. The covalent-bonded organic/carbon black electrode retained 90 % of the initial capacity even after 100 cycles, and also showed excellent rate capability up to 1500 mA/g. The result sheds light on the commercialization of organic-based Na-ion batteries, and their large-scale applications to electric vehicles (EVs) and energy storage systems (ESSs) markets.

Binderless, additiveless Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si, preventing extensive pulverization, while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with a Si mass loading of 1.5 mg/cm2 were fabricated, and a high initial capacity of ∼3900 mAh/g was achieved with an excellent reversible capacity of ∼1500 mAh/g (areal capacity ∼1.7 mAh/cm2) beyond 200 cycles. A high first-cycle Coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maint...

Here, we studied the effect of thermal annealing on the microstructure and cyclic stability of a (Ti, Fe)-alloyed Si thin-film fabricated by a simple sputtering deposition method for Li-ion battery (LIB) anodes. The anode samples annealed at different temperatures (300–600 °C) were subjected to microstructure analysis and LIB performance test. The (Ti, Fe)-alloyed Si thin-film anode delivered a high capacity of 1563 mA h g−1 for 100 cycles at 0.1 A g−1 with nearly 100% capacity retention. Post-mortem analysis using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) disclosed the microstructural changes of the cycled anodes, revealing that (Ti, Fe) silicides served as a structural buffer against the large volume change of active Si during cycling for enhanced LIB performance.

Next-generation batteries require high-rate energy storage capabilities owing to the advent of fast charging electrical applications. Energy storage materials that can regulate the capacity even at high current densities must be developed. However, this is challenging owing to the limited ion transport kinetics inherent in thick electrodes. The sluggish ion transport can be mitigated by adopting nanomaterials with high specific surface areas or fabricating electrodes with structural alignment. Nevertheless, the rearrangement of materials in electrodes that facilitate fast charging with external forces and additives does not provide a satisfactory ion transport rate. In this study, for realizing a high-rate anode material, facet-controlled three-dimensional holey graphene is fabricated by transferring laser-induced graphene (LIG) to a copper tape in dry condition. This electrode exhibits a consistent capacity of ~114 mAh g−1 at an increased mass loading of 3 mg cm−2 and a high current density of 20 A g−1, implying that 95% capacity can be charged within 3 min. This exceptionally high rate is attributed to the unique structure of the transferred LIG (three dimensionally aligned macro/meso-porous LIG flakes featuring preferential surface facet directions). This fabrication is compatible with the existing manufacturing process for anode materials and can be applied to other energy materials.

High theoretical capacity and low-cost copper sulfide (CuxS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (NaxS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuxS with a large surface area embedded in the MOF-derived carbon network (CuxS-C) through a two-step process of sulfurization and carbonization via H2S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu1.8S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu1.8S-C/C core/shell anode materials than that of pure Cu1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu1.8S-C to accommodate the volume variation of the Cu1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaxS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities. However, questions remain regarding the large irreversible loss in capacities for the first charge-discharge cycle due to oxygen removal in lattices related to layered Li2MnO3. Herein we present detailed studies on Li-rich Mn-based layered oxides of 0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2 (Li-rich NCM) electrochemically activated between 2.5 V and 4.3 or 4.7 V vs. Li+/Li. Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) revealed unusual manganese reduction after the first charge up to a high voltage of 4.7 V. Moreover, the electronic structure did not fully recover to the original pristine of Mn4+ state after discharge. Interestingly, these phenomena were not limited to a single particle, but were observed across the entire electrode. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and electron dispersive spectra (EDS) also showed a dramatic decline in oxygen content with highly porous morphologies, associated with oxygen vacancy formation following oxidation of O2- ions to O2. Our analysis suggests that an unstable manganese valence state with severe defects due to oxygen vacancies may lead to large irreversible capacity loss during the first charge-discharge cycle of Li-rich layered oxides.

In this study, Li[Ni x Co y Mn z ]O 2 cathode composition library was fabricated using combinatorial methodology and characterized using nanoindentation to create a mechanical properties database as a function of Li[Ni x Co y Mn z ]O 2 composition. A single sputter deposition from LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 compound targets resulted in a composition range of 3–44 at.% Co, 20–80 at.% Ni, and 5–50 at.% Mn. Young’s modulus and hardness values were evaluated before and after charge–discharge cycles, and a strong dependency of the mechanical properties on composition was found; Mn-rich composition showed highest retention of its mechanical properties whereas the properties degraded more significantly for the Ni-rich composition. Electrochemical performance was analyzed and compared to mechanical properties at various Li[Ni x Co y Mn z ]O 2 compositions and a strong correlation between enhanced mechanical properties retention leading to superior discharge capacity retention was found for the Mn-rich compositions. Li[Ni 0.33 Co 0.30 Mn 0.34 ]O 2 composition showed optimized electrochemical and mechanical properties, where it retained 38% and 50% of its Young’s modulus and hardness after cycling while demonstrating 91% discharge capacity retention after 20 cycles at 1 C-rate.

We fabricated a hole transport layer (HTL) using transfer printing to fabricate high efficiency PbS quantum dot solar cell with minimized hysteresis. We applied PbS-EDT(1,2-ethanedithiol) as an HTL and controlled the adhesive properties between the donor substrate and the HTL through the UVO process in order to effectively transfer the HTL to the PbS layer, which enabled multilayer transfer printing as a result. During the transfer printing process, a gradient solid-solution layer was created at the interface with the existing PbS layer to reduce the hysteresis phenomenon, and to improve the power conversion efficiency to about 10% according to the HTL thickness optimization. In addition, the use of the EDT solvent can be remarkably reduced by using the transfer printing when forming the PbS-EDT layer. This can reduce the amount of organic solvent consumed in the process and improve the potential of environmentally friendly processes.

LTO (Li4Ti5O12) has been highlighted as anode material for next-generation lithium ion secondary batteries due to advantages such as a high rate capability, excellent cyclic performance, and safety. However, the generation of gases from undesired reactions between the electrode surface and the electrolyte has restricted the application of LTO as a negative electrode in Li-ion batteries in electric vehicles (EVs) and energy storage systems (ESS). As the generation of gases from LTO tends to be accelerated at high temperatures (40–60 °C), the thermal stability of LTO should be maintained during battery discharge, especially in EVs. To overcome these technical limitations, a thin layer of Al2O3 (~2 nm thickness) was deposited on the LTO electrode surface by atomic layer deposition (ALD), and an electrochemical charge-discharge cycle test was performed at 60 °C. The capacity retention after 500 cycles clearly shows that Al2O3-coated LTO outperforms the uncoated one, with a discharge capacity retention of ~98%. TEM and XPS analyses indicate that the surface reactions of Al2O3-coated LTO are suppressed, while uncoated LTO undergoes the (111) to (222) phase transformation, as previously reported in the literature.

Here, we fabricate poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) by electrospinning for a gel polymer electrolyte (GPE) for use in flexible Li-ion batteries (LIBs). As a solvent, we use N-methyl-2-pyrrolidone (NMP), which helps produce the cross-linked morphology of PVDF-co-HFP separator, owing to its low volatility. The cross-linked PVDF-co-HFP separator shows an uptake rate higher than that of a commercialized polypropylene (PP) separator. Moreover, the PVDF-co-HFP separator shows an ionic conductivity of 2.3 × 10−3 S/cm at room temperature, comparable with previously reported values. An LIB full-cell assembled with the PVDF-co-HFP-based GPE shows capacities higher than its counterpart with the commercialized PP separator, confirming that the cross-linked PVDF-co-HFP separator provides highly efficient ionic conducting pathways. In addition, we integrate a flexible LIB cell using the PVDF-co-HFP GPE with a flexible organic light emitting diode (OLED), demonstrating a fully flexible unit of LIB and OLED.

Carbon-nanotube (CNT)-based textile supercapacitors with MnO2 nanoparticles have excellent power and energy densities, but MnO2 nanoparticles can be delaminated during charge–discharge cycles, which results in significant degradation in capacitance. In this study, polypyrrole conductive polymer was coated on top of MnO2 nanoparticles that are deposited on CNT textile supercapacitor to prevent delamination of MnO2 nanoparticles. An increase of 38% in electrochemical energy capacity to 461 F/g was observed, while cyclic reliability also improved, as 93.8% of energy capacity was retained over 10 000 cycles. Energy density and power density were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in situ electrochemical–mechanical study revealed that polypyrrole–MnO2-coated CNT textile supercapacitor can retain 98.5% of its initial energy capacity upon application of 21% tensile strain and showed no observable energy storage capacity change upon application of 13% bending strain. After imposing cyclic ...

We demonstrate the fabrication of flexible micro-supercapacitors based on laser carbonization of polyimide sheets. Localized pulsed laser irradiation rapidly converts the pristine polyimide surface into an electrically conductive porous carbon structure in ambient conditions. Thus, the polyimide sheet acts as both a precursor for the carbonization and a flexible substrate. Effects of various laser parameters are examined to enhance electrical properties and morphology of the carbonized structures. The interdigitated electrode patterns are produced directly on the polyimide sheets by programmed laser scanning. A solid-state polyvinyl alcohol–phosphoric acid gel electrolyte is introduced into the active electrode area to realize a flexible all solid-state microcapacitor assembly. Cyclic voltammetry measurements exhibit the expected electrical double layer behavior. The specific capacitance of the supercapacitors reaches ∼800 μF/cm2 at a voltage scan rate of 10 mV/s with good capacitance retention under mechanical bending. The proposed laser-based approach enables facile fabrication of flexible micro-supercapacitors without tedious photolithographic patterning of porous carbon and metal current collectors.

Silicon anodes for lithium ion batteries (LiBs) have been attracting considerable attention due to a theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle causes cracks in the silicon, resulting in the degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and an unstable solid electrolyte interface (SEI) layer resulting from repeated changes in volume still block the next step forward for the commercialization of the silicon material. Herein we demonstrate the carbon nanotube (CNT) aerogel/Si nanohybrid structure for anode materials of LiBs via freeze casting followed by an RF magnetron sputtering process, exhibiting improved capacity retention compared to Si only samples during 1000 electrochemical cycles. The CNT aerogels as 3D porous scaffold structures could provide buffer volume for the expansion/shrinkage of Si lattices upon cycling and increase electrical conductivity. In addition, the nanospherical and relatively thin SEI layers of the CNT aerogel/Si nanohybrid structure show better lithium ion diffusion characteristics during cycling. For this reason, the Si@CNT aerogel anode still yielded a high specific capacity of 1439 mA h g−1 after 1000 charge/discharge cycles with low capacity fading. Our approach could be applied to other group IV LiB materials that undergo large volume changes, and also has promising potential for high performance energy applications.

We designed and fabricated a gold (Au)-coated silicon nanowires/graphene (Au–SiNWs/G) hybrid composite as a polymer binder-free anode for rechargeable lithium-ion batteries (LIBs). A large amount of SiNWs for LIB anode materials can be prepared by metal-assisted chemical etching (MaCE) process. The Au–SiNWs/G composite film on current collector was obtained by vacuum filtration using an anodic aluminum oxide (AAO) membrane and hot pressing method. Our experimental results show that the Au–SiNWs/G composite has a stable reversible capacity of about 1520 mA h/g which was maintained for 20 cycles. The Au–SiNWs/G composite anode showed much better cycling performance than SiNWs/polyvinylidene fluoride (PVDF)/Super-P, SiNWs/G composite, and pure SiNWs anodes. The improved electrochemical properties of the Au–SiNWs/G composite anode material is mainly ascribed to the composite׳s porous network structure.

Use of nanoscale architecturing that exhibits superior strength-to-weight ratio has been of recent interest, and here we demonstrate a bulk fabrication of a fully recoverable, ultralight 3D porous composite with high strength composed of Ag nanowire/cellulose nanofiber using a freeze-casting method. A one-step process for highly efficient bulk formation of 3D porous structure via ice crystal formation followed by sublimation was demonstrated that can overcome the cost and scalability associated with lithography methods. 3D porous composite with controlled geometry was fabricated by controlling the nucleation and growth kinetics of ice formation that resulted in highly anisotropic compressive strength and resilience that depends on the wall orientations and composition of composite wall. Strength of the 3D porous composite increased with an increase in the Ag nanowire content as the deformation transitioned from bending dominant toward stretch dominant behavior for the case of vertically aligned walls, and an optimized concentration of Ag nanowires resulted in the compressive strength of 100 kPa at a relative density of 0.96%, which has 1.5 times higher strength when normalized by the material density (2.3 ± 0.2 MPa ⋅ cm3/g) in comparison to that of metal microlattice (1.7 MPa ⋅ cm3/g) fabricated by lithography methods. Horizontally oriented 3D porous structure interestingly showed a fully reversible deformation while also maintaining sufficient conductivity that makes this new material well-suited for a variety of flexible electronics applications.

Binderless, additive-less Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si preventing extensive pulverization while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with Si mass loading of 1.5 mg/cm2 was fabricated and high initial capacity of ~3,900 mAh/g was achieved with excellent reversible capacity of ~1,500 mAh/g (areal capacity ~1.7 mAh/cm2) beyond 200 cycles. A high first cycle coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maintained the coalescence of SiMPs throughout extended cycling. Therefore, the Li2O/Zn matrix derived from conversion reacted nanoporous ZnO acted as an effective buffer to lithiation induced stresses from volume expansion and served as a binder-like matrix that contribute to the overall electrode capacity and stability.

Recently developed textile and paper based supercapacitors are well-suited for wearable energy storage devices due to their mechanical flexibility and stretchability. In this study, the effects of mechanical straining on carbon nanotube coated textiles are studied, and we demonstrate the pre-straining of the textile can result in an enhanced specific capacitance as well as power and energy densities. In-situ resistance measurement during mechanical straining of the textile capacitors show a decrease in resistance with tensile straining, which contributed directly to the enhancement of electrochemical performance. Two different carbon nanotube textiles based on polyester and cotton with different mechanical behaviors are examined, where the polyester textile show an increase in specific capacitance from 53.6 F g � 1 to 85.7 F g � 1 after the textile is pre-strained to 30% permanent elongation prior to electrochemical testing, constituting a 37% enhancement. Similarly, the cotton textile shows an enhancement in specific capacitance from 122.1 F g � 1 to 142.0 F g � 1 after 30% permanent elongation, which is a 22% enhancement. Specific capacitance, energy density, and power density are increased further by electroplating of MnO2 nanoparticles on the carbon nanotube coated cotton textile and then imposing a permanent elongation of 30%. Our results indicate that the simple mechanical pre-straining of the textile fibers contribute to significant enhancements in the electrochemical performance of the supercapacitors.

Applications of thin films have been widely increased especially in microelectronics industry. In order to advance the development of thin film technology, measuring mechanical properties properly becomes important for the reliability of electronic devices because the difference of mechanical properties arises in small scale [1]. Existing tensile test methods have difficulties of making and handling free-standing specimens. In this paper, a novel methodology for thin films tensile testing by floating on water surface is presented. This method is capable of investigating intrinsic material properties of thin films floating on the water surface due to negligible adhesion of metal thin films with water surface which makes water surface very suitable to be used as underlying substrate for thin films tensile test. A dog-bone-shaped specimen which is E beam evaporated gold has been tested as a model material due to its inert nature and increasing demand in electronic devices. This method consists of fabricating gold thin films floating on water surface, attaching PDMS coated grips with the thin film specimen and applying tensile load through movement of linear DC motor. Accurate real time strain monitoring is ensured by digital image correlating (DIC) set up device as shown in Fig. 1. The validation of this proposed tensile method has been examined by first testing 500 nm gold films at a constant strain rate and then comparing the results with other studies [2-4]. After validating this methodology, 50 nm thin gold films were tested to study specimen thickness effects on mechanical behavior and apply for much thinner specimens. This new method can provide the direct way to measure the mechanical properties which is closer to its intrinsic properties with the convenient of handling the thin film specimens.

This paper reports the results of a study on the microstructure evolution of sputtered BiSb–Te thermoelectric films during post-annealing and its effects on their electronic transport and thermoelectric properties. Combining X-ray diffraction, transmission electron microscopy, and Raman spectroscopy, we illuminate the fundamental aspects of the microstructure evolution: the as-deposited film was Bi0.5Sb1.5Te3 compound in the Bi2Te3-type phase with a nano-crystalline microstructure and the post-annealing prompted a drastic grain growth. The electrical and thermoelectric properties also closely changed following the trend of the grain growth. The Seebeck coefficient, electron mobility, and thermal conductivity increase while the carrier concentration remains flat. The ZT value escalates systematically with the annealing time increasing, reaching around 0.94 after 12 h annealing.

Thermoelectric power waves, where multiwalled carbon nanotubes coated with cyclotrimethylene trinitramine (MWCNT/TNA) directly convert chemical energy to electricity, have received considerable attention recently. However, the low Seebeck coefficient of carbon nanotubes has been regarded as a hurdle to increasing the electrical potential. Here, we present Sb2Te3-coated MWCNT arrays prepared by a sputtering method. An analytical model predicts an increase in Seebeck coefficient of the annular multishell structure by ∼75%. The heterostructure coupled with exothermic chemical reaction of TNA demonstrates an increase in peak electrical potential of 175% (∼198 mV), compared with typical outputs of bare MWCNT/TNA (∼72 mV). A serial connection of two repeating units increased the peak potential by up to 406 mV.

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO3 -composite electrode that is capable of undergoing "smart" reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm2 C-1 and electrochemical performance with specific capacitance of 406.0 F g-1 , energy/power densities of 40.6-47.8 Wh kg-1 and 6.8-16.9 kW kg-1 . The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge-discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.

Using resonance and bulge techniques, the mechanical properties of free standing Si-rich SiN"x membranes were precisely measured to evaluate the effect of deposition conditions on them over a narrow range of particular technological interest. Values of the elastic modulus, the residual stress and the thermal expansion coefficient were obtained. It was found that even small differences in gas composition in low pressure CVD deposition make substantial changes in residual stress and significant but much smaller changes in the elastic modulus.

We have evaluated the effect of wet chemical treatment on the interfacial bonding strength of Cu-to-Cu direct bonding. The oxide on a Cu-deposited wafer can be removed by a solution made of hydrofluoric acid and sulfuric acid (HF/H2SO4) or diluted hydrochloric acid (HCl/H2O), which can also improve the bonding quality of Cu-to-Cu bonds. Two 4-inch Cu-deposited wafers were bonded at 250 degrees C via the thermo-compression method. The interfacial adhesion energy of Cu-to-Cu bonding was quantitatively measured by the four-point bending method. After chemical pretreatment for 30 seconds with HF/H2SO4 and HCl:H2O solutions, the measured interfacial adhesion energies were 4.91 J/m2 and 5.51 J/m2, respectively. Microstructural examination of the Cu bonding interfaces showed that the interfacial bonding quality of Cu-to-Cu bonds improved under proper wet chemical etching conditions. Wafer-level cleaning by wet chemical treatment of the Cu surface was found to be a very effective way to improve the bonding quality of Cu bonds, even at bonding temperatures lower than 300 degrees C.

This study provides a framework for evaluating the drop reliability of solder joints using a high-speed lap-shear test. The test specimens employed here were Sn-37Pb/Cu under bump metallization (UBM) solder joints and were aged for 120h at different temperatures (120, 150, and 170^[email protected]?) to examine the effects of aging. We tested them at different loading speeds in the range of 0.01-500mm/s. A careful analysis of the stress-strain graphs attained from the tests, coupled with characterization of the fracture surfaces, discloses that the fracture mode shifts from ductile to brittle as the loading speed escalates. A map of the fracture mode shows that how readily the mode transition with the loading speed occurs can be directly translated into the drop reliability of the solder joint, disclosing that the drop reliability would deteriorate as the aging temperature increases possibly due to the increased IMC thickness. These results underscore the utility of the experimental methodology adopted in this study to evaluate the drop reliability of solder joints.

This study examined the sensitive effects of composition on the microstructure evolution and thermoelectric properties of sputtered Bi-Te films. Bi-Te films of various Te compositions (49 at.% to 60 at.%) were grown by cosputtering deposition and annealed at 200°C for different durations. We examined the microstructure of the films using x-ray diffraction (XRD) and transmission electron microscopy (TEM), and measured the electronic transport and thermoelectric properties. As the Te composition of the films changed from 49 at.% to 60 at.%, the phase of the as-sputtered film changed from the rhombohedral BiTe-type phase to the metastable rock-salt phase, which eventually transformed to the Bi2Te3-type phase upon annealing, instigating microstructure evolution. This phase transformation profoundly influenced the electrical and thermoelectric properties of the films.

In ultraviolet (UV) nanoimprint lithography, the adhesion between the UV-curable resin and the stamp must be carefully controlled to avoid deformation and breakage of the imprinted patterns during the stamp separation process. In this work, UV-curable resins with different amounts of release agent were prepared, and the adhesion properties of the resins were characterized quantitatively using a four-point bending test. The interfacial fracture energy between the UV-curable resin with a release agent and a glass wafer was measured based on the concept of interfacial fracture mechanics. The results were used to investigate the effect of the release agent on the reduction of the interfacial adhesion. The interfacial fracture energy between the resin containing the release agent and the glass wafer decreased with increasing concentration of the release agent. After the test, the fractured surfaces were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectro...

This paper reports the microstructure evolution of Bi-Te thermoelectric films upon post-annealing and its effects on the thermoelectric properties. Bi-Te films with the composition of around 61at.% Te and the thickness of 300nm were deposited onto SiO"2-coated Si substrates by using bismuth and tellurium targets in a radio frequency (RF) magnetron sputtering system. We annealed the films at different temperatures (100, 150 and 200^oC) under N"2 ambient for 8h, and characterized the crystallinity and morphology of the Bi-Te films. Microstructure characterization using X-ray diffraction and scanning electron microscopy disclosed that the post-annealing treatment entailed a drastic microstructural evolution by inducing the development of a strong texture of grains with their c-axis oriented normal to the substrate. In addition, we measured the electrical transport and thermoelectric properties of the films to reveal their close link with the microstructure changes. The electron mobility and Seebeck coefficient increase significantly, leading to a remarkable improvement in the power factor from [email protected]/K^2cm for the as-deposited sample to [email protected]/K^2cm for the 200^oC-annealed sample.

It was studied that FePt-Ta thin films prepared on MgO (100) buffer-layer by DC/RF magnetron co-sputtering have shown better magnetic properties and micro structural improvement. The Ta-doped FePt-Ta films indicate somewhat differences in micro structural ordering and the aspect of grain growth after annealing. With respect to magnetic property, the sample having 30% increased coercivity was obtained after a heat treatment at 700^oC. In particular the addition of Ta (5.5%) enhances the L1"0 ordering of FePt at relatively high temperature (above 500^oC).

Bismuth-telluride-based materials have excellent room-temperature thermoelectric properties. In this study, the composition of Bi-Te thin films deposited by RF-magnetron sputtering was systematically varied across a single wafer. X-ray diffraction, field emission-scanning electron microscopy (FE-SEM, JEOL, JSM-7000F) and energy dispersive X-ray spectroscopy (EDS) were then used to investigate the thermoelectric properties of the Bi-Te films as a function of the Te fraction. The Te content of the films ranged from 38% to 81%, and their microstructure and crystal structure varied depending on the Te content. The Seebeck coefficients of the Bi-Te thin films were in the range -10 to 153@mV/K, and the maximum power factor of the films was 3.7x10^-^4W/K^2m, without post annealing.

Bismuth-telluride-based materials have excellent room-temperature thermoelectric properties. In this study, the composition of Bi-Sb-Te thin films deposited by RF magnetron sputtering was systematically varied across a single wafer. X-ray diffraction, field emission-scanning electron microscopy (FE-SEM, JEOL, JSM-7000F), energy dispersive x-ray spectroscopy (EDS) and an electron probe x-ray micro analyzer (EPMA, JEOL, JXA 8800R) were then used to investigate the thermoelectric properties of the Bi-Te films as a function of the Te fraction. The Te content of the films ranged from 45% to 87%, and their microstructure and crystal structure varied depending on the Te content. The Seebeck coefficients of the Bi-Sb-Te thin films range from +88 μV/K to +375 μV/K, and the maximum power factor of the films was 105 × 10−5 W/K2 m without post annealing.

The increase of electrical resistance during the strain-controlled bending fatigue of 2 μm-thick inkjet-printed or vacuum deposited metallic films (Cu, Ag) on flexible substrates (BT: Bismaleimide Triazine, PI: Polyimide) was investigated. Electrical resistance increased with an increase in the number of fatigue cycles. The rate of increase in the electrical resistance of inkjet-printed Cu films was lower than that of thermally evaporated films. This phenomenon is attributable to the porous microstructure of inkjet-printed Cu films. The porous structure contains a lot of free volume and a large area of free surface, which can be a sinking site for vacancies formed during the cyclic deformation. It was confirmed that a smaller grain size leads to a lower rate of increase in the electrical resistance, which was ascribed to the easy vacancy annihilation due to a short diffusion length of the vacancy to the grain boundary which is a vacancy sinking site. The rate of increase in the electrical resistance was also influenced by the grain boundary geometry. The lower rate of the evaporated Ag film on a BT substrate was attributed to the crack-like grain boundaries, which were expected to behave like pores.

Four-point bending tests were performed to investigate the interfacial adhesion of Cu-Cu bonding fabricated by thermo-compression process for three dimensional packaging. A pair of Cu-coated Si wafers was bonded under a pressure of 15 kN at 350 °C for 1 h, followed by post annealing at 350 °C for 1 h. The bonded wafers were diced into 30 mm × 3 mm pieces for the test. Each specimen had a 400-�m-deep notch along the center. An optical inspection module was installed in the testing apparatus to observe crack initiation at the notch and crack propagation over the weak interface. The tests were performed under a fixed loading speed, and the corresponding load was measured. The measured interfacial adhesion energy of the Cu-to-Cu bonding was 9.75 J/m 2 , and the delaminated interfaces were analyzed after the test. The surface analysis shows that the delamination occurred in the interface between SiO2 and Ti.

FeRh/FePt bilayers on MgO (100) substrates were fabricated by rf-magnetron sputtering, and the magnetic properties and microstructures of the bilayers were studied in terms of Ta addition to the storage layer. Compared to undoped FeRh/FePt bilayers, FeRh/FePt-Ta bilayer films showed improved magnetic properties and lower degree of interdiffusion. The FeRh/FePt-Ta bilayers clearly demonstrated the AFM-FM transition. Reduced interdiffusion by Ta segregation along grain boundaries was speculated to be a possible cause for the observed improvement in magnetic properties when fabricated at high temperature.

LTO (Li4Ti5O12) has been highlighted as anode material for next-generation lithium ion secondary batteries due to advantages such as a high rate capability, excellent cyclic performance, and safety. However, the generation of gases from undesired reactions between the electrode surface and the electrolyte has restricted the application of LTO as a negative electrode in Li-ion batteries in electric vehicles (EVs) and energy storage systems (ESS). As the generation of gases from LTO tends to be accelerated at high temperatures (40–60 °C), the thermal stability of LTO should be maintained during battery discharge, especially in EVs. To overcome these technical limitations, a thin layer of Al2O3 (~2 nm thickness) was deposited on the LTO electrode surface by atomic layer deposition (ALD), and an electrochemical charge-discharge cycle test was performed at 60 °C. The capacity retention after 500 cycles clearly shows that Al2O3-coated LTO outperforms the uncoated one, with a discharge capacity retention of ~98%. TEM and XPS analyses indicate that the surface reactions of Al2O3-coated LTO are suppressed, while uncoated LTO undergoes the (111) to (222) phase transformation, as previously reported in the literature.