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Super304H steel is a promising candidate for boiler tube materials in thermal power plants operating under ultra-supercritical conditions, and the fatigue properties of its welded joint play a key role in the structural reliability of the thermal power plants. Herein, we report that there is a transition in the fatigue failure location (i.e., fatigue failure mechanism) from the base metal at a high strain amplitude (≥~0.4%) to the weld metal at a low strain amplitude (≤~0.3%) at a constant temperature in the operating range of 500–700 °C, and this leads to a significant reduction in the fatigue resistance of the welded joint as compared to that of the base metal. We found that a longer fatigue test time at a low strain amplitude induces a thermal aging effect that promotes different microstructural evolutions in the base metal and weld metal, deepening material inhomogeneity in the welded joint, and thereby triggering strain localization in the weld metal. With increasing fatigue test time (i.e., thermal aging time), Cr23C6 carbides precipitated in the interdendritic region of the weld metal and at the austenitic grain boundary of the base metal, and Nb (C, N) phases precipitated in the interior of austenitic grain in the base metal, which increased local hardness, whereas there was no significant microstructural change in the dendrite core of the weld metal, retaining its initial hardness. The intensified local hardness inhomogeneity caused the softest zone in the welded joint, wherein strain localization occurred, serving as a crack nucleation site and propagation path, to shift from the base metal to the weld metal (dendrite core). This induced a shift in the fatigue failure location from the base metal to the weld metal with decreasing strain amplitude.

Super304H is a promising candidate for heat exchangers in boiler systems used in thermal power plants operating at ultra-supercritical conditions, and the mechanical properties of its welded joint play a decisive role in the reliability of the thermal power plant. Herein, we report the tensile and fatigue properties of Super304H welded joint at elevated temperatures up to 750 °C, focusing on the operating temperature range of 500–700 °C. Our results showed that the tensile strength of the welded joint was almost the same as that of the base metal at all test temperatures, meeting the requirement for weld integrity, but a significant reduction in the elongation was induced in the welded joint due to non-uniform deformation that promotes deformation localization, leading to an early occurrence of necking. As for fatigue resistance, both the welded joint and base metal had comparable fatigue lives at high strain amplitudes (≥~0.4%) in the temperature range of 500–700 °C, whereas a drastic reduction in the fatigue resistance was observed in the welded joint at low strain amplitudes (

We propose a Vickers indentation cracking-based method for evaluating the fracture toughness of brittle materials exhibiting strain hardening. The approach is an extension of the recent method by Hyun et al. (2015) for non-hardening materials to hardening materials. The hardening material is simplified by an equivalent non-hardening material with an elevated modified yield strain so that the fracture toughness of a hardening material can be evaluated with the formula proposed by Hyun et al. The proposed extension is verified by comparison with experimental results from nanoindentation tests on Ge(1 0 0) and Si(1 0 0).

Characterization and the reduction of residual stress and its gradient in thin films are important for improving the reliability of microelectromechanical systems (MEMS) devices. This study examined the room-temperature control of the residual stress gradient in sputtered titanium (Ti) films by helium (He) ion implantation. Ti micro-cantilever beam arrays were fabricated by surface micromachining and used to evaluate the residual stress gradient of the film by measuring the tip deflection of the cantilever beams. The as-fabricated Ti cantilever showed downward bending deformation as a result of the negative residual stress gradient in the film. To release the residual stress gradient, helium ions were implanted at various doses and energies into the Ti cantilever before releasing it from the substrate. The residual stress gradient could be controlled effectively by adjusting the implantation conditions. Almost straight Ti micro-cantilever beams with no residual stress gradient were achieved using the optimal implantation condition of He ions with a dose of 2.0 × 1015 at 80 KeV. The effects of He implantation on the surface properties, such as surface roughness and optical reflectance, were also investigated.

Aluminum (Al) thin films are used widely as an electronic material in a variety of applications because of their high conductivity, optical reflectance and low cost. In the present study, helium (He) and nitrogen (N2) ions were implanted in sputter-deposited Al thin films with different doses and energies, and the changes in the film properties, such as the surface roughness, optical reflectance, hardness and Young’s modulus, were investigated. The results showed that the implantation of both ions smooth the surface of Al thin films by decreasing the hillock density, resulting in low global surface roughness. In particular, in the case of He ion implantation, the moderated degradation of optical reflectance was observed compared to the film implanted with nitrogen ion. On the other hand, excessive ion implantation increased the local (short-range) surface roughness, which deteriorated the optical reflectance of the Al films. The continuous stiffness measurement technique in nano-indentation showed that ion implantation increased the hardness near the surface. He ion implantation hardened the surface of the Al thin film, and almost 2 times higher surface hardness was achieved with an ion dose of 1018 ions/cm2 at 40 KeV.

We report here a new dual-coating method for the deposition of SiCOH (elementally descriptive but not representing the stoichiometry) ATMS (allyltrimethylsilane) low-k films on mesoporous SiO2 (SBA-15)/PEG (polyethylene glycol) composite films to improve the dielectric constant and mechanical properties of SiCOH/SBA-15 dual forms. The deposition was achieved via a two-step process: (i) pre-treatment, where SBA-15 was mixed with a dispersion of PEG in DI water, and SBA-15/PEG composite films were formed by spin-coating; and (ii) post-treatment, involving the deposition of SiCOH films on SBA-15s functionalized with PEGs and post-thermal annealing. In comparison with SiCOH-only films, SiCOH/SBA-15 dual forms exhibited a 20% reduction in the dielectric constant without a significant loss of mechanical properties after post-thermal annealing. SEM, TEM, XRD, BET, FT-IR, EP, and XPS results show that the enhanced electrical properties can be attributed to mesoporous SiO2 and additional porosity gained through the removal of PEG and CxHy (thermally labile phases in SiCOH films) after post-thermal annealing. In the SiCOH/SBA-15 dual forms, the SBA-15 layer is expected to function as a soft layer which acts as a buffer layer to prevent the rapid decay of the modulus and hardness.

In this study, we investigated the effect of the indenter geometry on the crack characteristics by indentation cracking test and FEA. We conducted various cohesive finite element simulations based on the findings of Lee et al. (2012), who examined the effect of cohesive model parameters on crack size and formulated conditions for crack initiation and propagation. First, we verified the FE model through comparisons with experimental results that were obtained from Berkovich and Vickers indentations. We observed whether nonsymmetrical cracks formed beneath the surface during Berkovich indentation via FEA. Finally, we examined the relation between the crack size and the number of cracks. Based on this relation and the effect of the indenter angle on the crack size, we can predict from the crack size obtained with an indenter of one shape (such as Berkovich or Vickers) the crack size for an indenter of different shape.

A modified thermal noise method was proposed to measure the normal spring constants of the colloidal probes for an atomic force microscope. We used commercial tipless cantilevers (length 150, width 30, nominal k 7.4 N/m) and borosilicate spheres with a diameter of 20 to fabricate colloidal probes. The inverse optical lever sensitivity of both the tipless cantilever and colloidal probes were used to measure the normal spring constant of the colloidal probes. We confirmed the accuracy and usefulness of our method by comparing the measurement results with those obtained using the nanoforce calibrator (NFC), which reportedly has an uncertainty of 1.00%. The modified thermal method showed a good agreement (~10% difference) with the NFC, allowing us to conclude that the modified thermal method could be employed for the effective measurement of the normal spring constants of colloidal probes.

A blunted height of a sharp indenter can be elucidated by fitting the indentation load versus the indentation depth data into Kick's law. Nanoindentations adapting two Berkovich indenters with different bluntnesses were performed on fused silica and then resulting nanoindentation loading curves were analyzed from a linear proportional fitting between the square root of the indentation load and the indentation depth modified with the blunted height; the blunted heights of 4.1 ± 0.5 and 38.4 ± 1.9 nm were estimated for the new and the severely worn indenters, respectively. In addition, the validity of this bluntness prediction was confirmed by a direct observation with an atomic force microscope; the blunted height measured for the indenter B was 45 nm comparable with the predicted value. The bluntness correction applied to the indentation data for a 200 nm-thick SiO 2 coating on Si substrate yielded not only roughly overlapped nanoindentation curves but also discrete discrepancies at low and peak load regimes. These phenomena are discussed from a geometrical difference of both indenters within the blunted regime and an extensive deformation of the hard substrate at deep indentations.

We used contact resonance force microscopy (CRFM) technique to determine the quantitative elastic properties of multiple materials integrated on the sub micrometer scale. The CRFM approach measures the frequencies of an AFM cantilever`s first two flexural resonances while in contact with a material. The plain strain modulus of an unknown or test material can be obtained by comparing the resonant spectrum of the test material to that of a reference material. In this study we examined the following bumping materials for flip chip by using copper electrode as a reference material: NiP, Solder (Sn-Au-Cu alloy) and under filled epoxy. Data were analyzed by conventional beam dynamics and contact dynamics. The results showed a good agreement (~15% difference) with corresponding values determined by nanoindentaion. These results provide insight into the use of CRFM methods to attain reliable and accurate measurements of elastic properties of materials on the nanoscale.

The effects of the indenter shape on hardness were studied from thin-film nanoindentations. Two Berkovich indenters with different operating histories were prepared and their morphologies were measured with an atomic force microscope. The curvature radii of both indenters that were measured through an image analysis were 58.8 nm and 732.2 nm, respectively. The nanoindentations were carried out on a 1.2 microm-thick Au thin-film with a Nanoindenter XP system with both indenters. Various nanoindentation data with indenter exchanges were surveyed, and they showed that the peak indentation loads under the blunter indenter were higher than those of the sharper indenter at the same indentation depths. The indenter sharpness parameter was used to correct the raw nanoindentation curves. The corrected curves overlapped well and the resulting hardness values were consistent regardless of the indenter sharpness. The intrinsic hardness values of the Au thin-film from both indenters agreed with each other, with only a 0.6% difference. This means the indenter sharpness was properly corrected and that the sharpness must be considered when the contact properties are measured at shallow indentations.

Friction behavior of nanoporous anodic aluminum oxide(AAO) film was investigated. A 60 thick AAO film having nanopores of 45 nm diameter with 105 nm interpore-diatance was fabricated by mild anodization process. The AAO film was then saturated with paraffinic oil. Reciprocating ball-on-flat sliding friction tests using 1 mm diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 N to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient significantly increased with the increase of load. The boundary lubrication layer of paraffinic oil contributed to the lower friction at relatively low load (0.1 N), but it is less effective at high load (1 N). Plastic deformed layer patches were formed on the worn surface of oil-enriched AAO at relatively low load (0.1 N) without evidence of tribochemical reaction. On the other hand, thick tribolayers were formed on the worn surface of both oil-enriched and as-prepared AAO at relatively high load (1 N) due to tribochemical reaction and material transfer.

Friction and wear properties of nanostructured anodic aluminum oxide (AAO)) films were studied in relation to contact load and pore size (pore diameter). Uniformly arrayed nanoporous aluminum oxide films (pores of 28 nm, 45 nm, 95 nm, and 200 nm diameter and 60–100 μm thick) were synthesized by anodization. Reciprocating wear tests using 1 mm diameter steel balls as counterpart were carried out for a wide range of load (from 1 mN to 1 N) at ambient environment. The friction coefficient reduced with the increase of load. The friction coefficient decreased by approximately 30% when the load increased by 3 orders of magnitude. The pore density marginally affected the frictional properties of AAO films. The influence of pore size on the friction coefficient was significant at relatively high loads (0.1 N and 1 N) whereas it was negligible at low loads (1 mN and 10 mN). The worn surface of AAO films tested at low loads did not experience tribochemical reaction and exhibited only mild plastic deformation. Dispersed thick smooth films were formed on the worn surface of all samples at relatively high loads whereas only extremely thin smooth film patches were rarely formed at low loads. These thick smooth films were generated by combined influence of tribochemical reaction at the contact interface and plastic deformation of compacted debris particles as evidenced by energy-dispersive spectroscopy analysis. We suggest that these thick films mainly contributed to the decrease of friction regardless of the pore size.

Oxidation-induced stress evolutions in Ta thin films were investigated using ex situ microstructure analyses and in situ wafer curvature measurements. It was revealed that Ta thin films are oxidized to a crystalline TaO2 layer, which is subsequently oxidized to an amorphous tantalum pentoxide (a-Ta2O5) layer. Initial layered oxidation from Ta to TaO2 phases abruptly induces high compressive stress up to about 3.5 GPa with fast diffusion of oxygen through the Ta layer. Subsequently, it is followed by stress relaxation with the oxidation time, which is related to the slow oxidation from TaO2 to Ta2O5 phases. The initial compressive stress originates from the molar volume expansion during the layered formation of TaO2 from the Ta layer, while the relaxation of the compressive stresses is ascribed to the amorphous character of the a-Ta2O5 layer. According to Kissinger's analysis of the stress evolution during an isochronic heating process, the oxygen diffusion process through the a-Ta2O5 layer is the rate-controlling stage in the layered oxidation process of forming a a-Ta2O5/TaO2/Ta multilayer and has an activation energy of about 190.8 kJ/mol.

Nanoindentation studies were carried out on epitaxial ZnO thin films on (0001) sapphire substrates grown by rf magnetron sputtering technique. A single sudden discontinuity (‘pop-in’) in the load–displacement curve was observed at a specific depth (13–16 nm) of the film. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the interaction behavior of the threading dislocations during the mechanical deformation. Indentation well below the critical depth was found to be plastic deformation behavior (residual impression 4 nm). The detailed deformation behavior of ZnO thin films and the critical parameters associated with ‘pop-in’ phenomenon were also determined during indentation in correlation with the bulk ZnO single crystal.

Nanoindentation studies are carried out on epitaxial ZnO and GaN thin films on (0 0 0 1) sapphire and silicon substrates, respectively. A single discontinuity (‘pop-in’) in the load–indentation depth curve is observed for ZnO and GaN films at a specific depths of 13–16 and 23–26 nm, respectively. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It is observed that the ‘pop-in’ depth is dependent on lattice mismatch of the epitaxial thin film with the substrate, the higher the lattice mismatch the shallower the critical ‘pop-in’ depth.

Cu86Zr11Al3, a Cu-based composite, was synthesized by copper mold casting. The composite showed a unique microstructure consisting of a ductile Cu crystalline phase and a hard superlattice phase. Uniaxial compression tests revealed a high strength (1.0–1.6 GPa) and fracture strain (9.2–15.0%). We report the mechanism underlying the observed mechanical properties of the composite in relation to its unique microstructure.

Two types of porogens were tested to prepare porous low dielectric films. PCL porogens as well as Tetronic block copolymer porogens generate pores within the films thus lowering the dielectric constant. Tetronic porogens, however, yield porous films without significant matrix-porogen interactions and thus result in higher mechanical properties with lower dielectric constant, when compared with the PCL porogens.

The mechanical properties of epitaxial ZnO thin films grown on (0 0 0 1) sapphire substrate were investigated by nanoindentation with a Berkovich tip and compared with that of bulk ZnO single crystal. In all indents on ZnO film a single discontinuity (‘pop-in’) in the load versus indentation depthdatawasobservedataspecificdepthofbetween13and 16 nm.InbulkZnO,howeveronly65%ofindents showedpop-ineventat a specific depth of between 12 and 20 nm. The mechanism responsible for the ‘pop-in’ event in the epitaxial ZnO thin films as well as in bulk ZnO was attributed to the sudden propagation of dislocations, which had been pinned down by pre-existing defects, along the pyramidal 10 ¯ fg and basal {0 0 0 1} planes (cross slip). The elastic modulus and hardness of the epitaxial ZnO thin films were determined to be 154 � 5 and 8.7 � 0.2 GPa, respectively, at an indentation depth of 30 nm. # 2005 Elsevier B.V. All rights reserved.

Nanoindentation studies have been carried out on undoped and doped epitaxial GaN thin films with different thickness (1–4m) were grown epitaxially on c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). Multiple discontinuities (so-called ‘pop-in’ events) were observed in the load–indentation depth curve irrespective of the thickness as well as the doping condition. Atomic force microscopy (AFM) studies on the residual indentation impression revealed no micro-cracks even after the indentation beyond the critical depth. The physical mechanism responsible for the ‘pop-in’ was explained by the interaction of the deformed region, produced by the indenter tip, with the pre-existing threading dislocation in the epitaxial GaN thin films. © 2005 Elsevier B.V. All rights reserved.

Two different kinds of organic polyelectrolyte (PE)/inorganic silicate nanolaminates carrying dissimilar interfacial adhesion between the organic and the inorganic layers were prepared using the layer-by-layer self-assembly. To investigate the mechanical behavior of the prepared hybrid films, apparent modulus (E′), hardness (H), and crack length were measured by depth-sensing nanoindentation as well as a microVickers experiment. The fracture toughness of the hybrid films was then calculated based on the measured mechanical values. In the case of forming strong interfacial adhesion between the organic and the inorganic layers (A series), the fracture toughness and the crack resistance of hybrid multilayer films were significantly improved as a result of the redistribution of stress concentration and the dissipation of fracture energy by the plasticity of organic PE layers. On the other hand, samples with relatively low interfacial adhesion between the organic and the inorganic layers (T series) had little ...

In this work, a series of TiAl–Si–N films with Si content in the range from 0 to 3.6 at.% were deposited by closed field unbalanced magnetron sputtering (CFUBMS) with vertical magnetron sources. The chemical composition, crystalline structure and morphology of these films were characterized by AES, XRD, XPS and TEM. Also, their mechanical properties as a function of Si content were investigated by nanoindenter and wear tester. From our experimental results, it could be revealed that the present TiAl–Si–N films are nanocomposites, consisting of a nano-scale mixture of crystalline Ti1–xAlxN phase and amorphous Si3N4 phase. The hardness of films was strongly dependent on the Si content and the maximum hardness and elastic modulus of approximately 42 and 490 GPa, respectively, were measured for the film with the Si content of 2.1 at.%. Also, much improved wear resistance was observed compared to that of TiAlN film without Si content.

The stress gradient of gold micro-cantilever beams induced during dry-release in oxygen plasma is quantitatively studied, and the relaxation of the stress gradient by He and N2 ion implantation is investigated. An analytic model considering the finite anchor stiffness of a step-up anchor and the geometry of the beam cross-section is constructed to evaluate the induced stress gradient. Various measurements are carried out to verify the effectiveness of ion implantation in relaxing the stress gradient.

In this work, ternary Cr 1– x Zr x N films with 0 ≤ x ≤ 0.34 were synthesized by closed field unbalanced magnetron sputtering (CFUBMS) with vertical magnetron sources and their crystalline structure, morphology and mechanical properties as a function of Zr content ( x value) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and wear tests. The results reveal that the structure and mechanical properties of films were found to depend strongly on the Zr content. As the Zr content increases, the more dense and compact microstructure is developed and the surface roughness is greatly decreased. Also, the mechanical properties including hardness (maximum hardness: 34 GPa) and wear property are largely improved in comparison with CrN film. These enhancements on the mechanical properties of Cr 1– x Zr x N films could be attributed to the solid solution hardening.

The characteristics, such as deposition rate, microstructure, surface morphology and mechanical properties, of titanium aluminum nitride films synthesized by unbalanced magnetron sputtering (UBMS) and closed-field unbalanced magnetron sputtering (CFUBMS) were compared in this article. TiAlN films were deposited from an alloyed TiAl (50/50 at.%) target at various N 2 partial pressures by two types of magnetron sputtering: (i) the single UBMS and (ii) CFUBMS with four magnetron sources. The deposition rate of TiAlN films produced by CFUBMS with four magnetron sources was increased up to approximately 1.35 times in comparison with that obtained in the single UBMS. The results of AES and XRD analyses revealed that TiAlN films deposited by two types of magnetron sputtering have similar chemical composition and crystal structure as a function of the N 2 partial pressure. However, TEM analysis showed that TiAlN film synthesized by CFUBMS with four magnetron sources has a denser columnar structure and its column width and grain size were increased up to approximately two times compared with film by the single UBMS. In addition, the nanoindentation tests showed that the hardness and elastic modulus of films by CFUBMS have higher values than those of films by the single UBMS. This enhancement in the CFUBMS with four magnetron sources system on the mechanical properties could be attributed to the formation of dense and well-crystallized film by the high-level ion bombardment of growing film.

This study introduces a simple and reliable strategy, called ‘linear μ-bending method’, to measure the residual stress of surface-micromachined micro-electro-mechanical systems (MEMS). The basic theory of the linear μ-bending method relies on the fact that not only the geometry and the material, but also the residual stress contribute much to determine the linear bending stiffness of MEMS. In a reverse way, this study identifies the residual stress after obtaining the linear bending stiffness of MEMS through experimental procedure. In a first step, bending tests for the surface-micromachined cantilevers are performed so that the bending rigidity and the anchor stiffness, which play important role in altering the stiffness of suspending MEMS, are obtained as pre-data. Secondly, the bending stiffness of the surface-micromachined bridge is measured through bending tests. And, as the last step, the residual stress is achieved by putting the obtained data from the bending tests – ‘linear bending stiffness’, ‘the anchor stiffness’, and ‘the bending rigidity’ – into the analytic model presented in this study. The results from the tests about the surface-micromachined poly-silicon structures with various residual stresses demonstrate that the linear μ-bending method is reliable. The output from the linear μ-bending method is that the residual stress of as-deposited poly-silicon film is 142.7 MPa (compressive) with the standard deviation of 3.5% and that the residual stress of the poly-silicon film decreases as the annealing effect grows.

Dielectric cyclosiloxane bearing polysilsesquioxanes (CS-PSSQs) were prepared by acid catalyzed plymerization using 2,4, 6,8-tetramethyl-2,4,6,8-tetra(trimethoxysilylethyl)cyclotetrasoloxane. The molecular weight, and content of the functional end-groups of the CS-PSSQs were foud to be dependent on the process parameters, such as the molar ratio of water and catalyst to the -OCH 3 group ot the silane monomer, the amount of solvent, and the poly(e-caprolactone) (PCL) content, etc. Based on these CS-PSSQ prepolymers, nanoporous organic/inorganic hybrid thin films were fabricated by spin-coating mixtures of these prepolymers with star-shaped PLC on the silicon substrate, and subsquently heating them at 150 and 250°C for 1 minute each and the at 420°C for 1 hour. A dielectric constant as low as 2.28 was achieved for the nanoporous PCL/CS-PSSQ (3:7 v/v) film, along with low moisture absorption in ambient and water conditions, primarily due to the presence of hydrophobic moieties such as ethylene and methyl groups of the polymer and nano-sized hydrophobic pores inside the matrix, resulting in the film having stable dielectric properties. Moreover, the PCL/CL-PSSQ (3:7 v/v) nanohybrid film revealed a nanoporous structure containing ca. 1.52 nm of average-sized mesopores, as measured bye the N 2 adsorption method. The CS-PSSQ-only film showed high mechanical strenghts having an elastic modulus and hardness of 6.64 and 0.88 GPa, respectively, for the 7500 A thick film and 2.41 and 0.38 GPa, respectively, for the PCL/CS-PSSQ (3:7 v/v) film. In addition, the crack velocity of the CS-PSSQ-only film was foud to be ca. 10 -11 m.s -1 in ambient conditions and and aqueous enviroment, probably due to the enhanced hydrophobicity and mechanical toughness of the incorportated methyl group, siloxane unit and ethylene moieties in the polymer matrix.

This article reports on the mechanical properties enhanced by the variety of Cr content in the nanostructured TiN/CrN coating system. The coatings were synthesized using a closed field unbalanced magnetron sputtering method with separate Ti and Cr targets and characterized in terms of chemical composition, crystal orientation, layer structure and mechanical properties. The nanostructured TiN/CrN coatings synthesized in this work have a range of atomic concentration ratio of X =Cr/(Ti+Cr) from 0.15 to 0.59. The results from high-angle and low-angle XRD analysis show that the coating with X =0.15 is not a multi-layered film but a composite film of a mixed TiN and CrN with a grain size of approximately 16 nm. The hardness ( H ) of coatings was strongly dependent on the value of X and the maximum hardness and plastic deformation resistance ( H 3 / E 2 ) of approximately 41 and 0.36 GPa, respectively, were measured for the coating with X =0.15. These values are 1.6 and 3 times higher than those of the single TiN coating (27 and 0.12 GPa), respectively. Also, the wear resistance was largely increased than that of the single TiN coating. These enhancement of mechanical properties in the coating with X =0.15 could be attributed to the CrN doping effect, which has reduced the TiN grain size.

Several kinds of homogeneous organic-inor- ganic hybrid polymer thin films were designed with im- proved mechanical properties and low dielectric constants (3.0). Novel soluble siloxane-silsesquioxane hybrid poly- mers were synthesized with cyclic and/or cage silane mono- mers, which had triorganosiloxy (R3Si1/2), diorganosiloxane (R2SiO2/2), and organosilsesquioxane (RSiO3/2) moieties with ethylene bridges at the molecular level, by the hydro- lysis and condensation of 2,4,6,8-tetramethyl-2,4,6,8-tetra(t- rimethoxysilylethyl)cyclotetrasiloxane (a cyclic monomer). The electrical properties of these films, including the dielec- tric constant (2.51), leakage current (6.4 10 11 A/cm 2 at 0.5 MV/cm), and breakdown voltage (5.4 MV/cm) were fairly good. Moreover, the mechanical properties of the hy- brid films, including the hardness (7 GPa), modulus (1.2 GPa), and crack-free thickness (2 m), were excellent in comparison with those of previous spin-on-glass materials with low dielectric constants. The excellent mechanical properties were proposed to be due to the high contents of SiOOH groups (30%) and the existence of ethylene bridge and siloxane moieties in the hybrid polymer precursors. In addition, the mechanical properties of the hybrid films were affected by the contents of the cagelike structures. The more cagelike structures a hybrid film contained, the worse its mechanical properties were. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 626 - 634, 2003

By classification, two powder portions, one consisting of coarse particles and the other consisting of fine particles, were separated from a MgO-doped (1000 ppm) commercial-purity Al 2 O 3 powder. Examinations of microstructure evolution during hot pressing showed that extensive abnormal grain growth occurred for the coarse portion. For the fine portion, although there was an indication that grain-size distribution deviated from normal distribution on prolonged hot pressing, such extensive abnormal grain growth did not occur. Extensive abnormal grain growth also occurred when the coarse portion was mixed into a high-purity powder that exhibited no abnormal grain growth alone. Chemical analyses revealed that the coarse portion contained the higher concentration of impurities but lower concentration of magnesium than the fine portion. It was discussed that particle aggregates in the coarse portion might have been responsible for the higher concentration of impurities but lower concentration of magnesium and, thus, for the extensive abnormal grain growth.

BN films consisting of c-BN and h-BN phases were synthesized using an ion-beam-assisted deposition process. In contrast to conventional observations, the c-BN and h-BN phases did not form separate layers, but were distributed in the form of nano-sized grains throughout the film thickness. No distinctly aligned h-BN layer was observed before the c-BN phase. Such a mixed character of the film was attributed to a localized ion bombardment effect instead of the macro-stress. Possibly because of the presence of scattered h-BN phases, the thin film described here possessed a low hardness of about 20 GPa and a low stress of about 5 GPa, compared with other reported c-BN-containing films.

Nanoindentation studies were carried out on epitaxial ZnO thin films on (0001) sapphire substrates grown by radio frequency magnetron sputtering. A single discontinuity (‘pop-in’) in the load–displacement curve was observed at a specific depth (13−16 nm) irrespective of the film thickness. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the nucleation, propagation and interaction behavior of the glissile threading dislocations during mechanical deformation. Indentation well below the critical depth was found to be plastic deformation behavior (residual impression of 4 nm).

The Γ5 and Γ6 free excitons have been identified in GaN from emission measurements. Another emission peak is also observed which we believe to be the longitudinal free exciton. These measurements along with electrical measurements, which show the sample to have very high peak mobility, attest to the high quality of the sample.

We fabricated nanocomposite films comprising multi- walled carbon nanotubes (MWCNTs, diameter 10~40 nm, length > 1 mum) and nanocrystalline copper using a low cost electrochemical method. Owing to pulse deposition with several additives, MWCNTs were well-dispersed in the films through thickness and the nanocomposite films showed a dense structure without any voids. For the purpose of evaluation as a candidate for electronic interconnection, elastic modulus, hardness, electrical resistivity, and thermal conductivity of MWCNT/Cu nanocomposite films were measured using nanoindentation, four probe, and time-domain thermo-reflectance methods. It was found that the mechanical properties were more or less enhanced due to the addition of MWCNTs but electrical and thermal conductivities of nanocomposite films were drastically decreased. Further studies are needed for the application of electroplated MWCNT/Cu nanocomposite films as next generation interconnecting materials of electronic devices.

Micro-tensile properties of hard and soft thin films, TiN and Au, were evaluated by directly measuring tensile strain in film tension using the micro-ESPI(electronic Speckle Pattern Interferometry) technique. Micro-tensile stress-strain curves for these films were obtained and the properties were determined. TiN thin film 1 μm thick and Au films with two different thicknesses (t=0.5 μm and 1 μm) were deposited onto the silicon wafers, respectively, and micro-tensile specimens wide 50, 100 and 200 μm were fabricated using micromachining. In-situ measurement of the micro-tensile strain during tensile loading was carried out using the subsequent strain measurement algorithm and the ESPI system developed in this study. The micro-tensile curves showed that TiN thin film was a linear-elastic material showing no plastic deformation and Au thin film was an elastic-plastic material showing significant plastic flow. Effect of the specimen dimensions on mechanical properties was examined. It was revealed that tensile strengths for both films were slightly increased with increasing specimen width. Furthermore, variations of yielding strengths for the thin film Au with change of the dimension were investigated.

A simple, easy-to-use and reliable method called nano-bending method is proposed to measure the residual stresses of surface-micromachined structures for MEMS (Micro-Electro-Mechanical Systems). The basic concept is based on the fact that the linear bending stiffness of the surface-micromachined bridge is affected by the residual stress of the consisting materials. It is preferentially necessary to know anchor stiffness and bending stiffness of the surface-micromachined cantilevers in the stress free state which are composed of the same materials as the surface-micromachined bridges. The usefulness of the method was demonstrated by poly-silicon surface-micromachined structures under various residual stresses. The results indicated that the measured residual stress of the as-deposited poly-silicon film is 142.70 MPa with standard deviation of 3.5 percent and the compressive residual stress decreases as growing the annealing effect.

This work was supported by the NANO Systems Institute-National Core Research Center (NSI-NCRC) of the Korea Science and Engineering Foundation KOSEF , the Brain Korea 21 Program endorsed by the Ministry of Education of Korea, and “System IC 2010” Project of Korea Ministry of Commerce, Industry and Energy.

A new series of photospacers has been prepared with different types of crosslinkers to improve elastic recovery. Afunctional crosslinker with six reactive groups demonstrates the best elastic recovery. As the quantity of crosslinker is increased, the elastic recovery also increases, probably due to an increase in the crosslinking density. The use of ADMS EPS® results in high resolution, good uniformity, and high production yield in the liquid-crystal-display (LCD) process. Especially, EPS® improves and solves problems such as viewing angle, crosstalk, and dark spots.

During indentation of brittle materials, cracks may be generated around the impression, depending on load conditions, material and indenter geometry. We investigate the effect of indenter geometry (centerline-to-face angle and number of edges) on crack characteristics by indentation cracking test and finite element analysis (FEA). Considering conditions for crack initiation and propagation, an FE model is employed featuring cohesive interfaces in zones of potential crack formation. After verification of the FE model through comparison with experimental results for Vickers and three-sided pyramidal indentation, we study the crack morphology for diverse indenter geometries and establish a relation between the crack length c and the number of indenter edges n c . Together with a relation between indenter angle ψ and crack length c , we can predict the length of the crack induced by other types of indenter from the crack size obtained with a reference indenter.