We propose a novel technique for electroless plating on polymer substrates using a dense CO2 beyond the critical point. Ni-P thin films were fabricated by a novel, hybrid technique consisting of two processes: catalyzation in... more
We propose a novel technique for electroless plating on polymer substrates using a dense CO2 beyond the critical point. Ni-P thin films were fabricated by a novel, hybrid technique consisting of two processes: catalyzation in supercritical CO2 with Pd bis-acetylacetonate and electroless plating in emulsion with dense carbon dioxide. Catalyzation in supercritical CO2 enabled the nucleation of a large number
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The development of strong, tough, and damage-tolerant ceramics requires nano/microstructure design to utilize toughening mechanisms operating at different length scales. The toughening mechanisms so far known are effective in micro-scale,... more
The development of strong, tough, and damage-tolerant ceramics requires nano/microstructure design to utilize toughening mechanisms operating at different length scales. The toughening mechanisms so far known are effective in micro-scale, then, they require the crack extension of more than a few micrometers to increase the fracture resistance. Here, we developed a micro-mechanical test method using micro-cantilever beam specimens to determine the very early part of resistance-curve of nanocrystalline SiO2 stishovite, which exhibited fracture-induced amorphization. We revealed that this novel toughening mechanism was effective even at length scale of nanometer due to narrow transformation zone width of a few tens of nanometers and large dilatational strain (from 60 to 95%) associated with the transition of crystal to amorphous state. This testing method will be a powerful tool to search for toughening mechanisms that may operate at nanoscale for attaining both reliability and strength of structural materials.
A novel electroless plating method, which is a hybrid of supercritical fluid technology and electroless plating, has been proposed. In this technology, electroless plating reactions are carried out in emulsion of supercritical carbon... more
A novel electroless plating method, which is a hybrid of supercritical fluid technology and electroless plating, has been proposed. In this technology, electroless plating reactions are carried out in emulsion of supercritical carbon dioxide (CO2) and electroless plating solution with surfactants. The Ni-P film obtained by this proposed technique became a uniform and conformal film without pinholes, which originated from
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This paper proposes a novel coating method combining supercritical fluid technology and electroless plating in a hybrid technique. The electroless plating reactions are carried out in an emulsion of supercritical carbon dioxide (sc-CO2)... more
This paper proposes a novel coating method combining supercritical fluid technology and electroless plating in a hybrid technique. The electroless plating reactions are carried out in an emulsion of supercritical carbon dioxide (sc-CO2) and an electroless plating solution with surfactants. The Ni-P film obtained by this proposed technique was a uniform and conformal film without the pinholes and nodules. The
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ABSTRACT In the present study, the micro-sized cantilever-beam type specimens containing only one block of lath martensite were fabricated, and change in deformation microstructure inside a block with strain was observed directly by... more
ABSTRACT In the present study, the micro-sized cantilever-beam type specimens containing only one block of lath martensite were fabricated, and change in deformation microstructure inside a block with strain was observed directly by scanning electron microscopy and transmission electron microscopy. A number of slip bands appeared in the fixed end of the specimen by deformation. The propagations of slip bands, however, terminate due to the gradient of strain inside the specimen. The direction of slip bands changed during the propagation by the low angle boundaries inside the block. The shear localized region becomes narrow with an increase in strain. Furthermore, the width of laths increases greatly at the large strain region. The increase in width of laths is attributed to the disappearance of some initial lath boundaries by deformation.
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ABSTRACT This paper reports an investigation of deformation-induced structural changes of Pd78Cu6Si16 metallic glass observed after the exact positions of the shear bands were identified. The propagation of shear bands induced... more
ABSTRACT This paper reports an investigation of deformation-induced structural changes of Pd78Cu6Si16 metallic glass observed after the exact positions of the shear bands were identified. The propagation of shear bands induced nanocrystallization not inside the shear bands, but around them. We conclude that the nanocrystal formation results from the accumulating temperature rise caused by the propagation of numerous shear bands. The extremely large temperature rise inside the shear bands may have led to the re-formation of an amorphous structure.
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ABSTRACT Electroplating of Cu with supercritical CO2 emulsion (SCE) is studied to clarify the effects of SCE in the electroplating reaction. Properties of the SCE can be adjusted by pressure. Size and size distribution of the dispersed... more
ABSTRACT Electroplating of Cu with supercritical CO2 emulsion (SCE) is studied to clarify the effects of SCE in the electroplating reaction. Properties of the SCE can be adjusted by pressure. Size and size distribution of the dispersed phase are reduced by increasing pressure, which is expected to promote the transfer efficiency of Cu2+ into the diffusion layer and causes a decrease in on-time of the periodic-plating-characteristic in the electroplating with SCE (ESCE). A minimum value for both surface roughness and grain size was observed for the Cu films electroplated at 15 MPa when pressure was increased from 9 to 21 MPa. The most positive potential response was observed for ESCE also at 15 MPa in chronopotentiometry. Therefore, we believed a critical size for the dispersed phase was reached at roughly 15 MPa to cause the phenomena observed.
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ABSTRACT An electroplating method with supercritical carbon dioxide (sc-CO2) suspension, which is named EP-SCS, is proposed in this study. Application of sc-CO2 emulsion in electroplating has been reported to be effective in reducing... more
ABSTRACT An electroplating method with supercritical carbon dioxide (sc-CO2) suspension, which is named EP-SCS, is proposed in this study. Application of sc-CO2 emulsion in electroplating has been reported to be effective in reducing defects found in the plated materials. However, dissolution of the Cu seed layer was observed in the attempt to fill the nanoscale holes on a hole test element group. Therefore, Cu particle was added to form a suspension to inhibit the dissolution of the Cu seed layer. In this study, we found usage of the additives in the Cu damascene process can be reduced significantly by application of EP-SCS. Complete Cu fillings were obtained in the holes with 60 nm in diameter and aspect ratio of 2 by application of EP-SCS.
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ABSTRACT Pore structure in the thin porous Ni films fabricated by supercritical CO2 emulsion was found to be affected by number of ethylene oxides (EOn) in head group of the nonionic fluorinated surfactants (PFP3-EOn) used. The pores were... more
ABSTRACT Pore structure in the thin porous Ni films fabricated by supercritical CO2 emulsion was found to be affected by number of ethylene oxides (EOn) in head group of the nonionic fluorinated surfactants (PFP3-EOn) used. The pores were formed by adhesion of micelles on the cathode surface during electroplating. Properties of the micelles, such as size, shape, and interaction with the cathode surface were influenced by EOn and surfactant concentration. Finally, dense small size pores were formed by PFP3-EO1 and discrete large size pores were formed by PFP3-EO5. Also, increasing surfactant concentration led to large size distribution of pores. (c) 2013 The Electrochemical Society. All rights reserved.
ABSTRACT This study investigates formation of abnormally large grains in a Ni layer electrodeposited using additive-free Watts bath. The Ni electrodeposited layer had bimodal structure with abnormally large grains and fine grains. Surface... more
ABSTRACT This study investigates formation of abnormally large grains in a Ni layer electrodeposited using additive-free Watts bath. The Ni electrodeposited layer had bimodal structure with abnormally large grains and fine grains. Surface morphology of the fine grains was relatively heterogeneous and composed by fine crystals with quadrangular pyramid shape, while surface of the abnormally large grain was uniform. Electron backscatter diffraction analysis was conducted for the surface, the cross section of the layer, and after polishing the Ni electrodeposited layer. Shape and crystallographic orientation of the abnormally large grains are consistent with those of the corresponding grains on surface of the Cu substrate. The large epitaxial growth occurred on the substrate only with near [100] orientation, while abnormally large grains could not be formed the substrate with [111] or [110] orientation. The abnormally large grain formation is caused by epitaxial growth on the substrate with the particular crystal orientation.
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ABSTRACT This paper reports an electroplating method with supercritical carbon dioxide (sc-CO2) emulsion (EP-SCE) on hole test element group (TEG), which has an integrated structure of Cu seed layer on TiN barrier layer sputtered on Si... more
ABSTRACT This paper reports an electroplating method with supercritical carbon dioxide (sc-CO2) emulsion (EP-SCE) on hole test element group (TEG), which has an integrated structure of Cu seed layer on TiN barrier layer sputtered on Si substrates. The reaction is carried out in an emulsion of sc-CO2 in copper-sulfate-based electrolyte with surfactants. It was reported that Ni film obtained by EP-SCE is uniform and without pinhole, because sc-CO2 has low viscosity and compatibility of hydrogen. Thus, this method is applicable in fine Cu wiring, but dissolution of Cu seed layer in EP-SCE was observed. Therefore, Cu particle was added to form a suspension. An electroplating method with sc-CO2 suspension (EP-SCS) is proposed to inhibit dissolution of Cu seed layer. Electroplated Cu film obtained by this method was a smooth film without pinhole. Moreover, we applied EP-SCS technique into filling of hole TEG with holes having 60 and 70 nm in diameter, and complete filling of all the holes with electrodeposited Cu without any void was obtained. The Cu filled into the holes was found to be single crystal or had only a few twin boundaries parallel to the surface of TEG. We suggest that crystal growth in EP-SCS could be bottom-up growth along [111] crystallographic orientation of Cu.
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ABSTRACT Thin porous Ni films were fabricated in supercritical CO2 (Sc-CO2) emulsion with a series of nonionic fluorinated surfactants, F(CF(CF3)CF2O)(3)CF(CF3)COO(CH2CH2O)(n)CH3 (denoted as PFP3-EOn where n = 1,2 and 5). The film... more
ABSTRACT Thin porous Ni films were fabricated in supercritical CO2 (Sc-CO2) emulsion with a series of nonionic fluorinated surfactants, F(CF(CF3)CF2O)(3)CF(CF3)COO(CH2CH2O)(n)CH3 (denoted as PFP3-EOn where n = 1,2 and 5). The film morphology and size distribution of pores were studied as a function of number of ethylene oxide groups and different concentrations of surfactants. Surfactant PFPO3-EO1 from low to medium concentrations showed a narrow size distribution of shallow pores on the films, and at high concentration it showed shallow pores and some large size deep pores. Surfactant PFPO3-EO2 at low concentration showed a narrow size distribution of shallow and deep pores on the film, and from medium to high concentrations the size distribution of deep pores increased. Compared to other surfactants, for all concentrations, surfactant PFPO3-EO5 showed a broad size distribution of deep pores, and it showed shallow pores only up to medium range of concentration. The increase of ethylene oxide groups and concentration of surfactants increased the size distribution of pores and decreased the number of pores on the films. There was a significant decline in the number of pores by the surfactant PFPO3-EO5. Sc-CO2 emulsion assisted Ni deposition using a series of nonionic fluorinated surfactants and concentrations shows great promise as a method to control porous structure on the plated films. (c) 2014 Elsevier B.V. All rights reserved.
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ABSTRACT Physical properties of supercritical carbon dioxide emulsion (Sc–CO2–E) were controlled to evaluate the effects on properties of nickel film electroplated. Additive-free Watts bath was used to study sole-effect of Sc–CO2–E on... more
ABSTRACT Physical properties of supercritical carbon dioxide emulsion (Sc–CO2–E) were controlled to evaluate the effects on properties of nickel film electroplated. Additive-free Watts bath was used to study sole-effect of Sc–CO2–E on nickel electroplating reaction. Experimental pressure, volume fraction of CO2 and surfactant were adjusted to control physical properties of Sc–CO2–E. Influence of current density was also studied. Surface roughness (Ra) was found to decrease with increase in pressure, volume fraction of CO2, volume fraction of surfactant and current density. Reduction in Ra was believed to be caused by improved homogeneity of Sc–CO2–E, enhanced desorption of hydrogen bubbles from surface of cathode, and increased nickel nuclei density. Grain refinement was observed when increasing pressure, volume fraction of CO2 and surfactant, which was believed to be caused by periodic plating characteristic of electroplating with Sc–CO2–E. On the other hand, grain coarsening was observed with increase in current density.Research highlights►How does supercritical CO2 emulsion (Sc–CO2–E) influence on electroplating? ►Additive-free Watts bath was used to study sole-effect of Sc–CO2–E. ►The grain refinement is caused by periodic plating characteristic with Sc–CO2–E. ►The smoother surface is caused by improved homogenous reaction Sc–CO2–E. ►A model is proposed to demonstrated effects of Sc–CO2–E on electroplating.
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This study was conducted to examine how catalyzation in supercritical CO2 with Pd-bis(acetylacetonate) influences electroless plating on polymer substrates. Catalyzation in supercritical CO2 enabled the nucleation of abundant Pd nuclei on... more
This study was conducted to examine how catalyzation in supercritical CO2 with Pd-bis(acetylacetonate) influences electroless plating on polymer substrates. Catalyzation in supercritical CO2 enabled the nucleation of abundant Pd nuclei on a polyimide substrate without chemical pretreatment, ultimately leading to the deposition of a uniform Ni–P metal film. Conventional catalyzation without chemical pretreatment led to the deposition of only a
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ABSTRACT Supercritical CO"2 emulsion (SCE) was found to be effective in removal of epoxy-type SU-8 photoresist. The ability to remove SU-8 was compared between a commercially available Remover PG (RPG) solution and SCE. Both RPG... more
ABSTRACT Supercritical CO"2 emulsion (SCE) was found to be effective in removal of epoxy-type SU-8 photoresist. The ability to remove SU-8 was compared between a commercially available Remover PG (RPG) solution and SCE. Both RPG and SCE were effective in removing not-hard-baked SU-8 dots, with height of ~50@mm and diameter ranged from 50 to 125@mm. When the SU-8 dots were hard-baked at 150^oC for 10min, RPG could not remove any of the SU-8 dots. On the other hand, SCE could still remove 42.11% of the O50@mm SU-8 dots. When the SU-8 dots were hard baked at 200^oC for 10min, 5.75% of the O50@mm SU-8 dots could be removed by SCE.
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ABSTRACT This paper reports mechanical properties of nickel films fabricated by high pressure electroplating (HPE) and electroplating with supercritical CO"2 emulsion (ESCE). Structures and mechanical properties of the plated... more
ABSTRACT This paper reports mechanical properties of nickel films fabricated by high pressure electroplating (HPE) and electroplating with supercritical CO"2 emulsion (ESCE). Structures and mechanical properties of the plated films were examined by TEM, electron backscattered diffraction analysis and micro-compression test using a non-tapered micro-sized pillar. The films were electroplated in an electrolyte composed of Watts bath, supercritical CO"2 and surfactant. Agitation in ESCE leads to the formation of many CO"2-in-water type micelles. The micelles would cause an effect called periodic plating characteristic, and this effect refined the microstructure of the plated nickel from 3@mm of columnar grained structure to 8nm diameter of equiaxial grained structure. Mechanical properties were also improved to 3.5GPa of compressive strength, which was five times higher than the HPE nickel. The high strength in ESCE is believed to be largely a result of grain refinement and carbon impurity.
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ABSTRACT We propose a method of mechanical test for measuring strength of electrodeposited Ni film using micro-sized cantilever. Two cantilevers were fabricated for each beam direction parallel and vertical to grain growth direction.... more
ABSTRACT We propose a method of mechanical test for measuring strength of electrodeposited Ni film using micro-sized cantilever. Two cantilevers were fabricated for each beam direction parallel and vertical to grain growth direction. Bending tests were carried out with a test machine designed for micro-sized specimens. Bending tests of the two cantilever specimens showed that strength of the cantilever which beam direction is parallel to grain growth direction is higher than that of vertical to grain growth direction. EBSD analysis of the specimens after the bending test implies that difference in strength was caused by deformation twin.
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ABSTRACT A method to control nanostructure of metallic glass film (MGF) fabricated by electroless alloy plating (ELAP) is proposed. The nanostructure is controlled by density of catalyst core on a substrate, and which is a function of... more
ABSTRACT A method to control nanostructure of metallic glass film (MGF) fabricated by electroless alloy plating (ELAP) is proposed. The nanostructure is controlled by density of catalyst core on a substrate, and which is a function of immersion time in catalyst solution. MGF patterning was performed successfully, and the characteristic nanostructure was observed by TEM. For ELAP process, density of catalyst core was decreased with increasing immersion time, while size of the core was enlarged. Nanostructures were refined with increase in catalyst core density. These results show that nanostructure of MGF pattern can be controlled by Pd catalyst density in the ELAP process.
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ABSTRACT Self-annealing in electroplated Cu films is the dramatic evolution of the microstructure in electroplated Cu near room temperature, and it occurs during a transient period of hours following the electroplating process. This study... more
ABSTRACT Self-annealing in electroplated Cu films is the dramatic evolution of the microstructure in electroplated Cu near room temperature, and it occurs during a transient period of hours following the electroplating process. This study discusses the change of grain size and orientation in self-annealing of Cu films electroplated by an additive-free sulfate bath using X-ray diffraction and electron backscatter diffraction techniques. We found that the self-annealing started at the interface between the substrate and the electroplated Cu film. Immediately after the electroplating process, orientation of the Cu grains in the region near the interface was similar to that of the substrate. This indicates that the grain growth was affected by the substrate. Then, grain growth and change in orientation of the electroplated Cu film at room temperature became independent from the orientation of the substrate. The electroplated Cu film had many high-angle-grain boundaries (HAGBs) before incubation, and the fraction of HAGBs reduced as incubation time increased. Self-annealed Cu grains in the electroplated Cu film had many multiple twins, which came from low stacking-fault energy of Cu.
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ABSTRACT We report our investigation of the block boundary and sub-block boundary strengths of lath martensite evaluated through a micro-bending test. The sub-block boundaries contribute very little to the macroscopic strength of the lath... more
ABSTRACT We report our investigation of the block boundary and sub-block boundary strengths of lath martensite evaluated through a micro-bending test. The sub-block boundaries contribute very little to the macroscopic strength of the lath martensite. In contrast, the presence of a block boundary in the specimen greatly increased the strength. In addition, the block boundary induced a serrated flow and load drop after yielding in the load–displacement curve. The load drop and serrated flow were attributable to dislocation pile-up and subsequent propagation of dislocations across the block boundary. In a microstructural observation of specimens after deformation, we found that a block boundary significantly restricts the motion of dislocations, while a sub-block boundary does not. We concluded that the block boundary is the most effective grain boundary for strength in lath martensite.
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ABSTRACT The effect of sample size on nanocrystalline nickel with 8 nm grain size was investigated using micro-compression with non-tapered square pillars of sample size ranging from 5 to 30 μm. Nanocrystalline nickel was found to exhibit... more
ABSTRACT The effect of sample size on nanocrystalline nickel with 8 nm grain size was investigated using micro-compression with non-tapered square pillars of sample size ranging from 5 to 30 μm. Nanocrystalline nickel was found to exhibit size dependent strength with an exponent of −0.125. The decrease in the number of stress concentration sites for activation of grain boundary sliding was suggested to be responsible for the observed sample size effect.
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ABSTRACT This paper reports experiments to demonstrate the effects of carbon dioxide on a Ni-P film obtained in supercritical carbon dioxide (sc-CO2) emulsion. The Ni-P film obtained by electroless plating in sc-CO2 emulsion was extremely... more
ABSTRACT This paper reports experiments to demonstrate the effects of carbon dioxide on a Ni-P film obtained in supercritical carbon dioxide (sc-CO2) emulsion. The Ni-P film obtained by electroless plating in sc-CO2 emulsion was extremely uniform, conformal, and free from pinholes and nodules. Two features of the sc-CO2 emulsion prevented defects: the stronger acidic solution attained via the dissolution of CO2 and the transport properties with the diffusive dense CO2. The phosphorus concentration and film growth rate were compared between plating films fabricated by two electroless plating techniques, one in sc-CO2 emulsion and one in Ni-P electroless solution alone. The phosphorus concentration of the film fabricated by electroless plating in sc-CO2 emulsion (22.7 wt %) was far larger than that of the film fabricated by electroless plating in Ni-P solution alone at pH 4.0-5.3. The film growth rate was lower in the electroless plating technique carried out in sc-CO2 emulsion than in that carried out in Ni-P solution alone at pH 5.3 and 4.0. On this basis, we conclude that the rate of film formation in electroless plating in the sc-CO2 emulsion was strongly influenced by the high speed agitation and the decrease in the oxidation of the reducing agent due to the lower pH.
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ABSTRACT Local deformation behavior around the block boundary of lath martensite structure was studied through a micro-bending test and microstructural observation. When the misorientation of operated slip systems across the block... more
ABSTRACT Local deformation behavior around the block boundary of lath martensite structure was studied through a micro-bending test and microstructural observation. When the misorientation of operated slip systems across the block boundary is small, the relief corresponding to the block boundary appeared by deformation. This suggested that the slip transferred directly across the block boundary. In the case of the large misorientation of operated slip systems across the block boundary, however, there is no evidence that slips were transferred directly across the block boundary. The small misorientation of operated slip systems across the block boundary also induced the obvious load drop in the load-displacement curve of micro-bending test. We considered that the flow stress at the region above the block boundary was decreased due to the transfer of pile-up dislocations across the block boundary after reaching some critical stress, resulting in the load drop in the load-displacement curve.
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The adhesive strength between microsized SU-8 columns and a silicon substrate under the bend loading condition has been studied to clarify effects of the columnar aspect ratio. The maximum tensile stresses at the root are almost the same... more
The adhesive strength between microsized SU-8 columns and a silicon substrate under the bend loading condition has been studied to clarify effects of the columnar aspect ratio. The maximum tensile stresses at the root are almost the same within the range of high aspect ratios (1.4-2.1) of the SU-8 columns, in which delamination cracks are opened by bend loading (mode
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ABSTRACT TiO2 thin films were fabricated by cathodic deposition with a supercritical CO2 (sc-CO2) emulsified TiCl3 + NaNO3 electrolyte. Morphology and average grain size were evaluated by SEM, TEM and XRD. SEM micrographs showed that the... more
ABSTRACT TiO2 thin films were fabricated by cathodic deposition with a supercritical CO2 (sc-CO2) emulsified TiCl3 + NaNO3 electrolyte. Morphology and average grain size were evaluated by SEM, TEM and XRD. SEM micrographs showed that the TiO2 films fabricated by TiCl3 + NaNO3 electrolyte were porous, and the films were composed of particles and aggregates of the particles. Also, size of the particles increased when the sc-CO2 emulsified electrolyte was used. Average grain size of the TiO2 films was calculated using Scherrer equation. The average grain size was found to increase when the sc-CO2 emulsified electrolyte was used. In addition, both particle sizes observed from SEM and average grain size calculated using Scherrer equation were found to increase when pressure was increased from atmospheric pressure to 20 MPa.