bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoindentation of Au and Pt/Cu thin films at elevated temperatures
Authors: Volinsky Alex A. , Moody Neville R. , Gerberich William W.
Published: May 2005

This paper describes the nanoindentation technique for measuring sputter-deposited Au and Cu thin films’ mechanical properties at elevated temperatures up to 130 °C. A thin, 5-nm Pt layer was deposited onto the Cu film to prevent its oxidation during testing. Nanoindentation was then used to measure elastic modulus and hardness as a function of temperature. These tests showed that elastic modulus and hardness decreased as the test temperature increased from 20 to 130 °C. Cu films exhibited higher hardness values compared to Au, a finding that is explained by the nanocrystalline structure of the film. Hardness was converted to the yield stress using both the Tabor relationship and the inverse method (based on the Johnson cavity model). The thermal component of the yield-stress dependence followed a second-order polynomial in the temperature range tested for Au and Pt/Cu films. The decrease in yield stress at elevated temperatures accounts for the increased interfacial toughness of Cu thin films.
Transparent nanocrystalline MgO by rapid and low-temperature spark plasma sintering
Authors: Chaim Rachman , Shen Zhijian , Nygren Mats
Published: May 2005

We investigated superfast densification of nanocrystalline MgO powders by spark plasma sintering (SPS) between 700 °C and 825 °C under applied pressures of 100and 150 MPa. Fully-dense transparent nanocrystalline MgO with a 52-nm average grain size was fabricated at 800 °C and 150 MPa for 5 min. In-line transmissionsof 40% and 60% were measured compared to MgO single crystal, for the yellowand red wavelengths, respectively. Densification occurs by particles sliding over each other; the nanometric grain size and pores lead to the optical transparency. The light brownish color of the nanocrystalline MgO is due to the oxygen vacancy color centers, originating from the reducing atmosphere of the SPS process.
Selective synthesis of nanosized TiO2by hydrothermal route: Characterization, structure property relation, and photochemical application
Authors: Reddy K. Madhusudan , Guin Debanjan , Manorama Sunkara V. , Reddy A. Ramachandra
Published: May 2005

By variation of reaction temperature and time during the hydrothermal synthesis process, TiO2nanoparticles in anatase, rutile, and mixture of rutile-anatase phases are formed without adding any mineralizer. Differential thermal analysis studies indicate the rutile phase crystallization at a comparatively lower temperature and a low weight loss. The material synthesized by hydrothermal reaction required no post-calcination for the crystallization. Transmission electron microscopy, selected-area diffraction, Brunauer–Emmett–Teller, and x-ray diffreaction studies confirmed the compositions to be anatase and rutile with the particle size ranging from 5 to 25 nm with surface area as high as 260 m2/g for the anatase and 65 m2/g for rutile. The prepared nanoparticles exhibited a blue shift of the absorption edge in the ultraviolet-visible spectrum greater than 10 nm. The particles with average size around 5 nm showed two band edges in the absorption spectra attributed to two different particle sizes. Simple photocatalytic reactions were tried to demonstrate the photochemical activity of the synthesized material. The synthesized nanoparticles exhibited an ultraviolet radiation simultaneous photoreduction of Cr(VI) to Cr(III) and oxidation of formic acid into carbon dioxide and water.
Nature of contact deformation of TiN films on steel
Authors: Bhowmick S. , Xie Z-H. , Hoffman M. , Jayaram V. , Biswas S.K.
Published: May 2005

Nanoindentation experiments were carried out on a columnar ∼1.5-μm-thick TiN film on steel using a conical indenter with a 5-μm tip radius. Microstructural examination of the contact zone indicates that after initial elastic deformation, the deformation mechanism of the TiN is dominated by shear fracture at inter-columnar grain boundaries of the TiN film. A simple model is proposed whereby the applied load is partitioned between a deforming TiN annulus and a central expanding cavity in the steel substrate. It is possible to obtain a good fit to the experimental load–displacement curves with only one adjustable parameter, namely the inter-columnar shear fracture stress of the TiN film. The implication of results in the context of the performance of TiN films in service is also discussed.
Relative effects of Pb and Re doping in Hg-1223 thick films grown on Ag substrates
Authors: Su J.H. , Sastry P.V.P.S.S. , Schwartz J.
Published: May 2005

The relative effects of Pb and Re doping on microstructure, irreversibility field, and electronic anisotropy of HgBa2Ca2Cu3O8+δ (Hg-1223) thick films grown on Ag substrates prepared by dip-coating were studied. Both Pb- and Re-doped films exhibit the dominant phase of Hg-1223, characterized by a superconducting transition temperature (Tc) of 133 K. Both dopants distribute homogeneously in the Hg-1223 grains and promote grain growth. Pb-doped films have larger colony size compared to the Re-doped. The irreversibility fields (Hirr) of (Hg,Re)-1223 are significantly higher than those of (Hg,Pb)-1223 at temperatures below 100 K. The logarithmic plots of Hirr versus (1 – T/Tc) show both Pb- and Re-doped have a crossover temperature reflecting a transition from two- to three-dimensional behavior with increasing temperature. Re doping significantly decreases the electronic anisotropy γ, which would enhance flux pinning and consequently improve the critical current density. The differences between Pb and Re dopants in affecting γ are explained in terms of crystal structure.
Freestanding microscale 3D polymeric structures with biologically-derived shapes and nanoscale features
Authors: Gaddis Christopher S. , Sandhage Kenneth H.
Published: May 2005

Microscale polymeric structures with intricate three-dimensional (3D) shapes and nanoscale features were synthesized by using silica-based microshells of diatoms (unicellular algae) as transient scaffolds. Diatom microshells were immersed in dilute solutions of polymer precursors in volatile solvents. After extraction and solvent evaporation, the resulting thin films on the microshells were cross-linked to form rigid polymer coatings. Selective silica dissolution then yielded freestanding polymeric structures that retained the microshell shapes and fine features. By utilizing bioscaffolds capable of genetically precise and massively parallel replication, enormous numbers of polymeric micro/nanostructures with identical 3D shapes may be generated for various applications.
Lu2O3:Eu3+ nanoparticles and processed ceramics: Structural and spectroscopic studies
Authors: Zhang Kai , Pradhan A.K. , Loutts G.B. , Roy U.N. , Cui Y. , Burger A.
Published: May 2005

Europium-doped lutetium oxide (Lu2O3:Eu3+) nanophosphors were synthesized via modified combustion technique using urea as the fuel and metal nitrates as oxidants. The pellets prepared from the calcined nanocrystalline powders were vacuum sintered up to 1750 °C leading to very translucent ceramic. The products were characterized by x-ray diffraction to ascertain phase purity. The microstructures reveal the nanocrystalline nature of the powders. We have illustrated the crystallite size dependence and the influence of Eu3+ activation of Lu2O3:Eu3+ nanophosphors on Raman scattering. We have also demonstrated the particle size dependence of emission characteristics of nanophosphors and ceramics. Our results suggest that although the processed ceramics display superior emission characteristics, the nanocrystalline phosphor powders calcined at 1100 °C also display reasonably good emission characteristics, illustrating the possibility of their applications in display technology.
Thermal quenching behavior of Er-doped silicon-rich SiO2 prepared by ion implantation
Authors: Zhang C.S. , Xiao H.B , Wang Y.J. , Chen Z.J. , Cheng X.L. , Zhang F.
Published: May 2005

Erbium and silicon were dual implanted into thermally grown SiO2 film on Si (110) substrates, followed by thermal treatment at 700–1200 °C for 30 min. The microstructure was studied by transmission electron microscope and x-ray diffraction. When the implanted films were annealed at T > 900 °C, the silicon nanocrystals (nc-Si) enwrapped by amorphous silicon (a-Si) could be observed. The thermal quenching behavior at λ = 1.535 μm and its relation with the annealling temperature were also investigated. With increasing annealing temperature, the portion of a-Si and the thermal quenching both decreased. Efficient luminescence from Er ions and weak intensity thermal quenching were obtained from the sample annealed at 1100 °C. The role of a-Si in non-radiative processes at T > 100 K is discussed.
Interfacial structures of Y123 and Nd123 films formed on MgO(001) substrates by liquid phase epitaxy
Authors: Matsuda J.S. , Oba F. , Murata T. , Yamamoto T. , Ikuhara Y. , Mizuno M. , Nomura K. , Izumi T. , Shiohara Y.
Published: May 2005

Interfacial structures of c-axis-oriented YBa2Cu3O7–y (Y123) and Nd1+xBa2–xCu3O7–y (Nd123) films were investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with geometrical lattice matching and molecular orbital calculations. These films were formed on MgO(001) substrates by liquid-phase epitaxy. Despite the similarity in lattice constants between Y123 and Nd123, the in-plane orientation relationship (OR) to the substrates is different: [100]film//[100]substrate(I) for Y123 and [110]film//[100]substrate(II) for Nd123. From the results of HRTEM observations and image simulations, it was found that the Y123 and Nd123 films are terminated by BaO and CuO-chain layers at the interfaces, respectively. For both the Y123/MgO and Nd123/MgO systems, the OR(I) is assessed to be the most favorable in point of geometrical matching and the OR(II) is the second among the rotational misorientations on the [001]film and [001]MgO. The molecular orbital calculations reveal that the interface with the OR(II) and the CuO-chain layer termination is preferable in terms of covalent bonding for both the systems. Consequently, we suggest that the preferential interfacial structures are delicately determined by a balance of the geometrical and chemical factors at the interfaces, resulting in making the lowest interfacial free energies.
Investigation of vibration fracture behavior of Sn–Ag–Cu solders under resonance
Authors: Song Jenn-Ming , Li Fang-I , Lui Truan-Sheng , Chen Li-Hui
Published: May 2005

This study investigated the vibration fracture properties of Sn–Ag–Cu alloys with various Cu contents. Results show that the microstructure becomes finer with a higher Cu content. This leads to a lower damping capacity, higher deflection amplitude, and thus inferior vibration fracture resistance under a constant vibration force. It is of interest that when the Cu content reaches 1.5 wt%, the specimen possesses the highest damping capacity and greatest vibration life. The presence of massive primary Cu6Sn5 intermetallics probably accounts for this phenomenon.
Time-dependent uniaxial piezoresistive behavior of high-density polyethylene/short carbon fiber conductive composites
Authors: Zheng Q. , Zhou J.F. , Song Y.H.
Published: May 2005

Short carbon fiber (SCF) filled high-density polyethylene conductive composites were studied in terms of time-dependent piezoresistive behaviors. The time-dependent change of resistance under constant stress or strain was found to be the succession of the previous pressure-dependent piezoresistance. Depending on the filler volume fraction and the level of the constant stress or strain, resistance creep and resistance relaxation with different directions were observed. An empirical expression similar to the Burgers equation could be applied to fit the data for both the resistance creep and the resistance relaxation. The fitted relaxation time as a function of pressure showed that there exist two competing processes controlling the piezoresistive behavior and its time dependence. Mechanical creep and stress relaxation of the composites were also studied, and a comparison with the time-dependent resistance implied that there is a conducting percolation network attributed to the physical contacts between SCF and a mechanical network formed by the molecular entanglement or physical crosslinking of the polymer matrix and the interaction between the filler and the matrix. It is believed that the two networks dominate the electrical and the mechanical behaviors, respectively.
Effect of rare-earth species on the wear properties of α sialon and β silicon nitride ceramics under tribochemical type conditions
Authors: Jones Mark I. , Hirao Kiyoshi , Hyuga Hideki , Yamauchi Yukihiko
Published: May 2005

The wear properties under low loads of β Si3N4 and α sialon materials sintered with different rare-earth oxide sintering additives have been studied under dry sliding conditions using block-on-ring wear tests. All the worn surfaces showed an absence of fracture and smooth surfaces with the presence of an oxygen-rich filmlike debris indicating tribochemically induced oxidation of the surfaces. Extensive grain boundary removal was observed on the worn surfaces thought to be due to adhesion between this silicate phase and the tribochemically oxidized surfaces. The resistance to such oxidation and the properties of the residual grain boundary phase are thought to be important parameters affecting the wear behavior under the present testing conditions. For both the β Si3N4 and α sialon materials, there was an increase in wear resistance with decreasing cationic radius of the rare earth, thought to be due to improved oxidation resistance, and this was more remarkable in the case of the sialon materials where the incorporation of the sintering additives into the Si3N4 structure results in a lower amount of residual boundary phase.
Effects of loading rate and temperature on tensile behavior of orthogonal three-dimensional woven Si–Ti–C–O fiber/Si–Ti–C–O matrix composites
Authors: Zhu Shijie , Gomyou Takashi , Ochi Yasuo , Ogasawara Toshio , Ishikawa Takashi
Published: May 2005

Effects of loading rate and temperature on tensile behavior have been studied in air using two kinds of orthogonal three-dimensional woven Si–Ti–C–O fiber-reinforced Si–Ti–C–O matrix composites, processed by polymer infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI). Since the interphase and porosity of the two composites are controlled in as similar a manner as possible, the effect of matrix processing method is understood. The strength of the PIP composite is greater than that of the CVI composite at room temperature, but they are almost the same at high temperatures. It was found that the PIP composite is more sensitive to loading rate than the CVI composite due to more glassy phases in the PIP composite.
Nonisothermal reaction kinetics and preparation of ferroelectric strontium bismuth niobate with a layered perovskite structure
Authors: Lu Chung-Hsin , Hsu Wei-Tse , Lee Jiun-Ting
Published: May 2005

Ferroelectric layered perovskite SrBi2Nb2O9 has been successfully prepared through a new process using BiNbO4 as a precursor. The SrBi2Nb2O9 formation mechanism was investigated using a nonisothermal analysis method at constant heating rates. The weight loss recorded in thermal analysis under different heating rates was analogized to the reaction conversion. A combination of the differential and integral methods was introduced to solve the reaction mechanisms. Analysis using the differential method revealed that two kinds of diffusion-controlled models have higher linear correlation coefficients than other models. Based on the integral method principle, a new integral equation combining the Arrhenius equation and the Lobatto approximation was derived in this study. The established equation significantly simplified the conventional calculation process and improved the accuracy for predicting the reaction models. Analysis using the integral method corroborated that the SrBi2Nb2O9 formation mechanism is governed by Jander's diffusion controlled model, and the activation energy was calculated to be 192.1 kJ/mol. The proposed methods and the derived equations can be further applied to other solid-state-reaction systems to elucidate their reaction kinetics and estimate the related kinetic parameters.
Crystallization kinetics of amorphous Ga–Sb–Te chalcogenide films: Part I. Nonisothermal studies by differential scanning calorimetry
Authors: Lee Chain-Ming , Lin Yeong-Iuan , Chin Tsung-Shune
Published: May 2005

Nonisothermal crystallization kinetics of amorphous chalcogenide Ga–Sb–Te films with compositions along the pseudo-binary tie-lines connecting Sb7Te3−GaSb and Sb2Te3–GaSb of the ternary phase diagram were investigated by means of differential scanning calorimetry. Powder samples were prepared firstly by film deposition using a co-sputtering method; the films were then stripped from the substrate. The activation energy (Ea) and rate factor (Ko) were evaluated from the heating rate dependency of the crystallization temperature using the Kissinger method. The kinetic exponent (n) was deduced from the exothermic peak integrals using the Ozawa method. The crystallization temperature (Tx = 181 to 327 °C) and activation energy (Ea= 2.8 to 6.5 eV) increased monotonically with increasing GaSb content and reached a maximum value in compositions located at the vicinity of GaSb. The kinetic exponent is temperature dependent and shows higher values in the SbTe-rich compositions. Promising media compositions worthy of further studies were identified through the determined kinetics parameters.
Evaluation of elastic modulus and hardness of thin films by nanoindentation
Authors: Jung Yeon-Gil , Lawn Brian R. , Martyniuk Mariusz , Huang Han , Hu Xiao Zhi
Published: May 2005

Simple equations are proposed for determining elastic modulus and hardness properties of thin films on substrates from nanoindentation experiments. An empirical formulation relates the modulus E and hardness H of the film/substrate bilayer to corresponding material properties of the constituent materials via a power-law relation. Geometrical dependence of E and H is wholly contained in the power-law exponents, expressed here as sigmoidal functions of indenter penetration relative to film thickness. The formulation may be inverted to enable deconvolution of film properties from data on the film/substrate bilayers. Berkovich nanoindentation data for dense oxide and nitride films on silicon substrates are used to validate the equations and to demonstrate the film property deconvolution. Additional data for less dense nitride films are used to illustrate the extent to which film properties may depend on the method of fabrication.
Surfactant-assisted synthesis of lanthanide phosphates single-crystalline nanowires/nanorods
Authors: Bu Wen-Bo , Hua Zi-Le , Zhang Ling-Xia , Chen Hang-Rong , Huang Wei-Min , Shi Jian-Lin
Published: May 2005

A facile, surfactant-assisted, hydrothermal approach has been developed to synthesize lanthanide phosphate single-crystalline nanowires/nanorods with smooth surface, uniform diameter, and good crystallinity. The surfactant Pluronic P123 was found to play a crucial role on the uniform morphology of lanthanide phosphate single-crystalline nanowires/nanorods. Photoluminescence spectra of the lanthanide phosphate single-crystalline nanowires/nanorods show that these nanowires/nanorods have strong photoluminescent emissions in the ultraviolet-visible and near-infrared regions. The present work is a preliminary and significant step toward the potential luminescent and catalytic applications of lanthanide compound based one-dimensional nanostructures.
Microstructural characteristics of oxides in 5083 Al synthesized by reactive atomization and deposition
Authors: Lin Yaojun , Zhou Yizhang , Lavernia Enrique J.
Published: May 2005

A detailed study of the size, distribution, and morphology of oxide particles in as-sprayed deposited 5083 Al synthesized by reactive atomization and deposition was reported. The results indicated that the oxides exhibit thin-plate morphology and are distributed at prior droplet boundaries, grain boundaries, and grain interiors with a dimensional scale on the order of tenths of micrometers up to a few micrometers. The mechanisms involved in the formation of the observed oxide distribution were analyzed in detail.
Biomimetic synthesis of BaSO4nanotubes using eggshell membrane as template
Authors: Liu Jin-Ku , Wu Qing-Sheng , Ding Ya-Ping , Wang Shu-Yu
Published: May 2005

BaSO4nanotubes were biomimetically synthesized by the combined assembly of eggshell membrane and C12H25SH. The products were tubular structure with the external diameter of 90–140 nm and the length of 1.5–2.5 μm. The formation mechanism was also investigated. It provided a novel method for the fabrication of inorganic oxysalt nanotubes.
Supercritical CO2extraction of porogen phase: An alternative route to nanoporous dielectrics
Authors: Lubguban J.A. , Gangopadhyay S. , Lahlouh B. , Rajagopalan T. , Biswas N. , Sun J. , Huang D.H. , Simon S.L. , Mallikarjunan A. , Kim H-C. , Hedstrom J. , Volksen W. , Miller R.D. , Toney M.F.
Published: May 2005

We present a supercritical CO2(SCCO2) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO2extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450 °C) and by a SCCO2process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO2process is effective in removing the porogen phase at relatively low temperatures (<200 °C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.
In situ quasi-elastic scattering characterization of particle size effects on the hydration of tricalcium silicate
Authors: Allen A.J. , McLaughlin J.C. , Neumann D.A. , Livingston R.A.
Published: May 2005

The effects of different particle size distributions on the real-time hydration of tricalcium silicate cement paste were studied in situ by quasi-elastic neutron scattering. The changing state of water in the cement system was followed as a function both of cement hydration time and of temperature for different initial particle size distributions. It was found that the length of the initial, dormant, induction period, together with the kinetics of hydration product nucleation and growth, depends on the hydration temperature but not on the particle size distribution. However, initial particle size does affect the total amount of cement hydrated, with finer particle size producing more hydrated cement. Furthermore, the diffusion-limited rate of hydration at later hydration time is largely determined by the initial tricalcium silicate particle size distribution.
Influence of additive composition on thermal and mechanical properties of β–Si3N4 ceramics
Authors: Zhu Xinwen , Hayashi Hiroyuki , Zhou You , Hirao Kiyoshi
Published: May 2005

Dense β–Si3N4 ceramics were fabricated from α–Si3N4 raw powder by gas-pressure sintering at 1900 °C for 12 h under a nitrogen pressure of 1 MPa, using four different kinds of additive compositions: Yb2O3–MgO, Yb2O3–MgSiN2, Y2O3–MgO, and Y2O3–MgSiN2. The effects of additive composition on the microstructure and thermal and mechanical properties of β–Si3N4 ceramics were investigated. It was found that the replacement of Yb2O3 by Y2O3 has no significant effect on the thermal conductivity and fracture toughness, but the replacement of MgO by MgSiN2 leads to an increase in thermal conductivity from 97 to 113 Wm-1K-1and fracture toughness from 8 to 10 MPa m1/2, respectively. The enhanced thermal conductivity of the MgSiN2-doped materials is attributed to the purification of β–Si3N4 grain and increase of Si3N4–Si3N4 contiguity, resulting from the enhanced growth of large elongated grains. The improved fracture toughness of the MgSiN2-doped materials is attributed to the increase of grain size and fraction of large elongated grains. However, the same thermal conductivity between the Yb2O3- and Y2O3-doped materials is related to not only their similar microstructures, but also the similar abilities of removing oxygen impurity in Si3N4 lattice between Yb2O3 and Y2O3. The same fracture toughness between the Yb2O3- and Y2O3-doped materials is consistent with their similar microstructures. This work implies that MgSiN2 is an effective sintering aid for developing not only high thermal conductivity (>110 Wm−1K−1) but also high fracture toughness (>10 MPa m1/2) of Si3N4 ceramics.
Synthesis of CdSe magic-sized nanocluster and its effect on nanocrystal preparation in a microfluidic reactor
Authors: Wang Hongzhi , Tashiro Asuka , Nakamura Hiroyuki , Uehara Masato , Miyazaki Masaya , Watari Takanori , Maeda Hideaki
Published: May 2005

CdSe magic-sized nanoclusters were synthesised at relatively low temperatures (90–150 °C) in the organometallic raw material solution by a very simple method. The variation process from nanoclusters to nanocrystals has been determined using the microreactor, and it was found that these nanoclusters could increase the CdSe nuclei number and product yield in the microfluidic reactor method. Meanwhile, the microreactor shows the advantage for studying the nanocrystal-growth process due to the precise time and temperature control and high reproducibility.
Electrical technique for monitoring crack growth in thin-film fracture mechanics specimens
Authors: Guyer Eric P. , Dauskardt Reinhold H.
Published: May 2005

An accurate and reliable electrical technique for continuous monitoring of crack growth in fracture specimens containing technologically relevant thin-film device structures has been developed. Both adhesive and cohesive crack growth measurements are reported using a SiO2passivation layer and a conducting titanium film deposited on the side face of fracture specimens. Crack velocity measurements approaching 10−12m/s were achieved, representing nearly an order of magnitude improvement over commonly used compliance-based techniques. The technique may be particularly useful for elucidating near threshold crack velocity behavior, which is important for thin-film reliability.
Correlation of stress state and nanohardness via heat treatment of nickel-aluminide multilayer thin films
Authors: Sperling Evan A. , Anderson Peter M. , Hay Jennifer L.
Published: May 2005

Heat treatment of γ-Ni(Al)/γ′-Ni3Al multilayer thin films demonstrates that multilayer hardness correlates with the magnitude of biaxial stress in alternating layers. Films with a columnar grain morphology and (001) texture were fabricated over a range of volume fraction and bilayer thickness via direct current magnetron sputtering onto NaCl (001) substrates at 623 K. The films were removed from substrates, heat-treated at either 673 K or 1073 K in argon, and then mounted for nanoindentation and x-ray diffraction. The biaxial stress state in each phase was furnished from x-ray diffraction measurement of (002) interplanar spacings. The 673 K treatment increases the magnitude of alternating biaxial stress state by 70 to 100% and increases hardness by 25 to 100%, depending on bilayer thickness. In contrast, the 1073 K heat treatment decreases the stress magnitude by 70% and decreases hardness by 50%. The results suggest that the yield strength of these thin films is controlled, in part, by the magnitude of internal stress. Further, thermal treatments are demonstrated to be an effective means to manipulate internal stress.
Dynamic nanoindentation as a tool for the examination of polymeric materials
Authors: Hayes S.A. , Goruppa A.A. , Jones F.R.
Published: May 2005

The determination of the mechanical properties of polymers is more complex than that of many other structural materials, because they display time-dependence in their response to load. Generally, dynamic analysis techniques, such as dynamic mechanical thermal analysis (DMTA), are used to characterize the viscoelastic properties of bulk polymers. However, polymers are increasingly being used as thin films, the properties of which are not readily determined using conventional techniques. Nanoindentation offers the possibility of determining the properties of thin films but has generally only been used to measure static properties. Dynamic nanoindentation equipment has recently become available, but its accuracy with soft polymers is unproven. This paper presents results of a comparison between dynamic nanoindentation, DMTA, and differential scanning calorimetry (DSC) for the determination of the thermal response of four different polymers. A favorable comparison is shown, indicating that dynamic nanoindentation is capable of measuring the time-dependent properties of small samples of polymers.
Low-temperature synthesis and characterization of GaN nanocrystals from gallium trichloride precursor
Authors: Liu F.S. , Liu Q.L. , Liang J.K. , Song G.B. , Yang L.T. , Luo J. , Zhou Y.Q. , Dong H.W. , Rao G.H.
Published: May 2005

Gallium nitride (GaN) has been synthesized by reacting gallium trichloride with ammonia (NH3) at low temperatures ranging from 500 to 1000 °C for 12 h. X-ray diffraction, transmission electron microscopy, infrared, and Raman backscattering spectra revealed that the synthesized GaN powder consists of single-phase nano-sized crystallites with the wurtzite-type structure. The average size of the crystals decreases with the reaction temperature from approximately ∼63 nm at 1000 °C to ∼5 nm at 500 °C. GaOCl and ϵ–Ga2O3are the intermediate products during synthesis of the GaN. Characteristic shifts of the Raman peaks are associated with the change in crystal size. The band-edge emission of GaN at 361 nm was observed on room temperature photoluminescence spectra exclusively for the sample synthesized at 1000 °C, while a new and broad emission band appeared with the center ranging from 827 to 765 nm for the samples synthesized between 500 and 800 °C.
Simple method and critical comparison of frame compliance and indenter area function for nanoindentation
Authors: Suganuma Motohiro , Swain Michael V.
Published: May 2005

A simple method has been proposed for an independent determination of the frame compliance Cf and the area function of a Berkovich indenter. Cf was determined from the unloading compliance of very large indentations in four test materials (fused silica, silicon nitride, high-carbon steel, and copper-zinc alloy) with known elastic properties, following the Oliver–Pharr method by assuming the ideal shape of Berkovich indenter. For a specific value of Cf (= 0.3 nm/mN in our case) all the specimens showed an hc (contact depth)-independent modulus, which agreed well with the expected value when the pile-up effect was taken into account. The contact area A(hc) was then estimated using fused silica as the standard specimen, according to two different procedures, i.e., the Oliver–Pharr method and the Field–Swain method. Both methods gave almost identical area functions over the whole range of the measurement. It was also found that such area functions can be described by two separate equations: A = 2πRehc for hc < Δh and A = g(hc + Δh)2 for hc ⩾ Δh, where Re is the effective tip radius, Δh the truncation depth, and g the geometrical factor for a Berkovich indenter. Based on the spherically truncated cone model, a simple procedure is presented to determine all these parameters from the analysis of a multiple partial unloading P-h curve.
Effect of excimer laser annealing on the structural properties of silicon germanium films
Authors: Sedky Sherif , Schroeder Jeremy , Sands Timothy , King Tsu-Jae , Howe Roger T.
Published: May 2005

We investigated the use of a pulsed excimer laser having a wavelength of 248 nm, a pulse duration of 38 ns, and an average fluence between 120 and 780 mJ/cm2 to locally tailor the physical properties of Si1−xGex (18% < x < 90%) films deposited by low-pressure chemical vapor deposition at temperatures between 400 and 450 °C. Amorphous as-deposited films showed, after laser annealing, strong {111} texture, a columnar grain microstructure, and an average resistivity of 0.7 mΩ cm. Atomic force microscopy indicated that the first few laser pulses resulted in a noticeable reduction in surface roughness, proportional to the pulse energy. However, a large number of successive pulses dramatically increased the surface roughness. The maximum thermal penetration depth of the laser pulse is demonstrated to depend on the fluence and the film structure being either polycrystalline or amorphous. Finally, a comparison between excimer laser annealing and metal-induced crystallization and rapid thermal annealing is presented.
Pentacene transistors with polymer gate dielectrics on metallized optical fibers
Authors: Granstrom Jimmy , Katz Howard E.
Published: May 2005

It is difficult to deposit a very thin polymer layer onto a fiber-shaped substrate from solution because the high interfacial energy can lead to dewetting. This difficulty presents itself when attempting to apply a gate dielectric to conductive fiber substrates during the fabrication of fiber transistors for use in applications such as “electrotextiles” and optical switches. In this article, we present a dip coating process that applies a gate dielectric to metal-coated optical fibers with high uniformity and reproducibility, resulting in pentacene field-effect transistors with excellent transistor characteristics including mobilities up to 0.4 cm2/Vs and on/off ratios up to 7000. In one case, a memory effect was demonstrated. Several gate dielectrics were successfully applied to the optical fibers, suggesting a baseline set of suitable materials for this purpose. A thorough study of the dip coating conditions is presented, including proposed explanations of the effects of different coating procedures and solution physical properties. Finally, alternative architectures that would provide much higher W/L ratios and on-currents are described.
Structural transition and glass-forming ability of the Ni–Hf system studied by molecular dynamics simulation
Authors: Li J.H. , Kong L.T. , Liu B.X.
Published: May 2005

A tight-binding Ni–Hf potential is constructed by fitting some of the ground-state properties, such as the cohesive energy, lattice constants, and the elastic constants of some Ni–Hf alloys. The constructed potential is verified to be realistic by reproducing some static and dynamic properties of the system, such as the melting points and thermal expansion coefficients for the pure Ni and Hf as well as some of the equilibrium compounds, through molecular dynamics simulation. Applying the constructed potential, molecular dynamics simulations are performed to compare the relative stability of the face-centered-cubic (fcc)/hexagonal close-packed (hcp) solid solutions to their disordered counterparts as a function of solute concentration. It is found that the solid solutions become unstable and transform into the disordered states spontaneously, when the solute concentrations exceed the two critical solid solubilities, i.e., 25 at.% Ni for hcp Hf-rich solid solution and 18 at.% Hf for fcc Ni-based solid solution, respectively. This allows us to determine that the glass-forming ability/range of the Ni–Hf system is within 25–82 at.% Ni. Interestingly, simulations also reveal for the first time, that two mixed regions exist in which an amorphous phase coexists with a crystalline phase, and at about 18 at.% Ni, the hcp lattice turns into a new metastable phase identified to be face-centered orthorhombic structure.
Interfacial reactions of lead-free Sn–Zn based solders on Cu and Cu plated electroless Ni–P/Au layer under aging at 150 °C
Authors: Huang Chia-Wei , Lin Kwang-Lung
Published: May 2005

The interfacial reactions of Sn–Zn based solder on Cu and Cu/Ni–P/Cu–plating substrates under aging at 150 °C were investigated in this study. The compositions of solders investigated were Sn–9Zn, Sn–8.55Zn–0.45Al, and Sn–8.55Zn–0.45Al–0.5Ag solders in weight percent. The experimental results indicated that the Cu substrate formed Cu5Zn8 with the Sn–9Zn solder and Al–Cu–Zn compound with Al–containing solders. However, it was detected that Cu6Sn5 formed at the Sn–9Zn/Cu interface and Cu5Zn8 formed at the Al–containing solders/Cu interface after aging for 1000 h. When it contacted with the Cu/Ni–P/Au substrate, the Sn–9Zn solder formed Au–Zn compound, and the Al–containing solders formed Al–Cu–Zn compound at the interface. After a long aging time, the intermetallic compounds existing between solders and the Cu/Ni–P/Au metallization layers almost did not grow. It was found that the interdiffusion between solders and Cu/Ni–P/Au was slower than that with Cu under aging. Furthermore, the addition of Ag to Sn–Zn solder resulted in the formation of AgZn3 particles at the interface.
Atomic layer deposition of tungsten disulphide solid lubricant thin films
Authors: Scharf T.W. , Prasad S.V. , Mayer T.M. , Goeke R.S. , Dugger M.T.
Published: May 2005

The synthesis and characterization of crystalline tungsten disulphide (WS2) solid lubricant thin films grown by atomic layer deposition (ALD) using WF6 and H2S gas precursors was studied. A new catalytic route was established to promote nucleation and growth of WS2 films on silicon surfaces with native oxide. Scanning electron microscopy with energy dispersive spectroscopy and Raman spectroscopy were used to determine the film morphology, composition, and crystallinity. The films exhibited solid lubricating behavior with a steady-state friction coefficient of 0.04 in a dry nitrogen environment.
High-strength binary Ti–Fe bulk alloys with enhanced ductility
Authors: Louzguine Dmitri V. , Kato Hidemi , Louzguina Larissa V. , Inoue Akihisa
Published: May 2005

The structure of hypoeutectic, hypereutectic, and eutectic Ti–Fe alloys produced in the shape of arc-melted ingots was found to consist of the ordered Pm-3m TiFe and disordered BCC Im3m β–Ti solid solution phase. The dimensions of the ingots were about 25–40 mm in diameter and 10–15 mm in height, and their structure was studied by x-ray diffractometry and scanning electron microscopy. The rectangular parallelepiped-shaped samples 2.5 × 2.5 × 5 mm in size cut from the central part of the ingots exhibit a high strength of about 2000 MPa, except for Ti60Fe40, and a certain ductility. The relatively low density of Ti (4.5 Mg/m3) implies high strength/density ratio for the studied alloys. These alloys are characterized by the low cost of the alloying element Fe and, compared to most of the high-strength non-equilibrium materials, do not require additional injection mold casting or rapid solidification procedures.
Structural investigations on ferroelectric Pb1−3/2xLaxTiO3 using the x-ray Rietveld method
Authors: Chen Jun , Xing Xianran , Yu Ranbo , Liu Guirong , Wu Li , Chen Xiaolong
Published: May 2005

The structures of the defect perovskite Pb1−3/2xLaxTiO3 prepared by the solid-state method were investigated in the solubility range of 0.05 ⩽ x ⩽ 0.30 with 0.05 increment by x-ray Rietveld method. In the system Pb1−3/2xLaxTiO3, the atom displacements of Ti (δTi) and Pb/La (δPb/La) along the spontaneous polarization (Ps) direction (c axis) decrease nonlinearly with increasing La content, while the value of δTi/δPb/La decreases linearly. The shape of oxygen octahedron of compounds Pb1−3/2xLaxTiO3 is independent of the La content. The calculated value of Ps decreases linearly in the solubility range of 0.05 ⩽ x ⩽ 0.30. In the refinement process, the hkl dependence of diffraction line broadening was also taken into account. The anisotropy of microstrain-like broadening observed in Pb1−3/2xLaxTiO3 might be ascribed to occurrence of compositional inhomogeneity between the crystallites.
Characterization of ballistically deformed tungsten [100]-, [111]-, and [110]-oriented single crystal penetrators by optical metallography, x-ray diffraction and transmission electron microscopy
Authors: Herring R.A. , Bruchey W.J. , Kingman P.W.
Published: May 2005

Single-crystal penetrators of tungsten having orientations of [100], [111], and [110] were ballistically deformed into targets of standard armor material and characterized by optical metallography, x-ray diffraction, and transmission electron microscopy (TEM) methods, which showed significant differences in their deformation mechanisms and microstructures corresponding to their deformation performance as measured by the penetration of the target. The [100] single-crystal penetrator, which produced the most energy efficient deformation, provided a new, alternative mechanism for ballistic deformation by forming small single-crystal blocks, defined by {100} oriented cracks, which rotated during extrusion from the interior to the side of the penetrator while maintaining their single crystal integrity. The [111] single-crystal penetrator transferred mass along allowed, high-angle deformation planes to the penetrator’s side where a buildup of mass mushroomed the tip until the built-up mass let go along the sides of the penetrator, creating a wavy cavity. The [110] penetrator, which produced the least energy-efficient deformation, has only two allowed deformation planes, cracked and rotated to invoke other deformation planes.
Effects of lanthanum nitrate buffer layer on the orientation and piezoelectric property of Pb(Zr,Ti)O3 thick film
Authors: Choi Jong-Jin , Park Gun-Tae , Park Chee-Sung , Lee Jae-Wung , Kim Hyoun-Ee
Published: May 2005

Highly oriented Pb(Zr,Ti)O3 (PZT) films were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was heat treated at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed a strong (100) preferred orientation. Regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature and heating rate, the film deposited on the buffer layer had this orientation. Thick films were also fabricated using the sol-gel multi-coating method, and the (100) texture was found to be maintained up to a thickness of 10 μm. The ferroelectric hysteresis and piezoelectric coefficient (d33) of highly oriented PZT thick films were characterized, and the (100) oriented PZT film showed higher piezoelectric property than the (111) oriented film.
Advances in local mechanoelectrochemistry for detecting pitting corrosion in duplex steels
Authors: Mary N. , Vignal V. , Oltra R. , Coudreuse L.
Published: May 2005

The goal of this study was to demonstrate that a relationship exists between surface stress and pitting corrosion. The surface stress field generated by polishing was first calculated using a thermomechanical model and a finite element code. Pitting corrosion tests performed at the microscale along the austenite/ferrite interface using the electrochemical microcell technique were then analyzed considering the microstructure, and the residual surface stress field calculated numerically under the microcapillary. Mechanical criteria are proposed leading to an enhancement of pitting corrosion of duplex steels.
Synthesis of (Y,Gd)2O3:Eu nanopowder by a novel co-precipitation processing
Authors: Chen Jiyang , Shi Ying , Shi Jianlin
Published: May 2005

Nano-sized (Y,Gd)2O3:Eu powders were synthesized by a novel co-precipitation processing in which a mixture of ammonium hydroxide and ammonium hydrogen carbonate was adopted as a complex precipitant. Evolution behaviors of precursors during calcinations were studied by means of thermogravimetry-differential scanning calorimetry-mass spectrum, Fourier transform infrared, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy in detail. Nano-sized (Y,Gd)2O3:Eu powder as prepared possessed a primary grain size of about 30 nm and specific surface area of 38 m2/g after being calcined at 850 °C for 2 h, showing much finer grains and less agglomeration. The as prepared nanopowder shows intense luminescence at 611nm under x-ray or ultraviolet excitation. Transparent (Y,Gd)2O3:Eu ceramics can also be fabricated using this high sinterable nanopowder.
Microstructural Evolution of Nanocrystalline Magnetite Synthesized by Electrocoagulation
Authors: Weng Ying-Chieh , Rusakova I.A. , Baikalov Andrei , Chen J.W. , Wu Nae-Lih
Published: May 2005

Nanocrystalline magnetite powders were synthesized by an electrocoagulation technique, in which an electric current was passed across two plate electrodes of carbon steel immersed in NaCl(aq) electrolyte, and the microstructure of the oxide powder was found to evolve in roughly three stages. The first stage involves formation and growth of severely defective colloidal crystallites. This is followed by agglomeration among the oxide crystallites to form mesoporous agglomerates containing predominantly inter-crystallite pores, and the average crystallite size was found to reach a plateau. Finally, coarsening of the crystallites within the agglomerates leads to another rapid increase in crystallite size and reduction in pore opening. The synthesized powders typically showed a saturation magnetization of ∼75 emu/g and a coercivity Hc of ∼118 Oe. A mechanism involving competition between nucleation and growth of free colloids and coarsening of the skeletal framework was proposed to explain the temporary level-off in crystallite size during the synthesis.
Influence of Electrode Modification by Ar+ Ion Beam Upon Passivation and Electrical Characteristics in Organic Light-Emitting Diodes
Authors: Jeong Soon Moon , Koo Won Hoi , Choi Sang Hun , Jo Sung Jin , Baik Hong Koo , Lee Se-Jong , Song Kie Moon
Published: May 2005

Ion-beam-assisted deposition (IBAD) was used for cathode preparation in organic light-emitting diodes to fabricate dense electrode. Dark spot growth rate was decreased by employing the IBAD process due to a highly packed aluminum structure inhibiting the permeation of H2O and O2. However, undesirable leakage current was generated because energetic particles of Al assisted by Ar+ ion may damage the organic material resulting in reduction of contact resistance. The decrease of contact resistance in the IBAD device may be caused by large contact area, increase of density of states, and Li diffusion to phenyl-substituted poly-p-phenylene vinylene.
Anisotropic Yield Behavior of Lotus-Type Porous Iron: Measurements and Micromechanical Mean-Field Analysis
Authors: Tane M. , Ichitsubo T. , Hyun S.K. , Nakajima H.
Published: May 2005

Anisotropic yield behavior of lotus-type porous iron fabricated using the continuous-zone-melting method in a pressurized nitrogen and hydrogen atmosphere has been investigated. The 0.2% offset strength (compressive yield stress) in the loading direction parallel to the longitudinal axis of pores decreases linearly with increasing porosity, while the perpendicular strength decreases steeply. The strength versus porosity curves can be expressed using a well-known power law formula. In addition, the 0.2% offset strength of lotus iron prepared in a nitrogen and hydrogen atmosphere is found to be larger than that of lotus iron prepared in a hydrogen and helium atmosphere, which is attributed to the solid solution hardening by the solute nitrogen. Furthermore, we compare the experimental results to calculations obtained by means of the extended Qiu-Weng’s mean-field method, and the comparison suggests that local stresses deviated from the average stress are dominant in the macroscopic yield behavior of lotus metals.