bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of composition on the thermal properties and spontaneous emission probabilities of Tm3+-doped TeO2–LiCl glass
Authors: özen G. , Demirata B. , öveçoğlu M. L.
Published: March 2008

The effect of composition on the thermal properties and the spontaneous emission probabilities of various 0.5 mol% Tm2O3containing (1 −x)TeO2 + (x)LiCl glasses were investigated using differential thermal analysis (DTA) and ultraviolet–visible– near-infrared (UV/VIS/NIR) absorption measurements. DTA curves of the samples were obtained in the 23–600 °C temperature range with a heating rate of 10 °C/min. The value of the glass transition temperatureTgand the crystallization temperatureTcwere found to vary with the glass composition. Melting was not observed for the glasses containing less than 50 mol% LiCl in this temperature range. However, a melting peak was observed atTm= 401 °C for the glasses having higher than 50 mol% LiCl, which were also found to be moisture-sensitive. Absorption measurements in the UV/VIS/NIR region were used to determine spontaneous emission probabilities for the 4f−4ftransitions of Tm3+ions. Six absorption bands corresponding to the absorption of the1G4,3F2,3F3,3F4,3H5, and3H4levels from the3H6ground level were observed. An integrated absorption cross section of each band, except that of3H5level, was found to vary with the glass composition. The role of the Judd–Ofelt parameters and therefore the effect of the glass composition on the radiative transition probabilities for the metastable levels of Tm3+ions are discussed in detail.
Characterization of NOx sensor using doped In2O3
Authors: Tanaka Shinichiro , Esaka Takao
Published: March 2008

To develop a highly sensitive gas sensor monitoring NOx, various kinds of n-type semiconductors made of In2O3 were prepared, and the relations between doped elements and gas sensitivities or response times were studied. Consequently, it was found that the samples doped with less than 1 at.% alkali-earth metal components have high sensitivities and responsiveness. The gas-absorbing phenomena were investigated using highly sensitive thermal analysis. From the result, it was indicated that alkali-earth component-doped In2O3 materials have higher adsorption ability of NOx than pure In2O3 has.
Eu+3 and Cr+3 doping for red cathodoluminescence in ZnGa2O4
Authors: Rack Philip D. , Peterson Jeffrey J. , Potter Michael D. , Park Wounjhang
Published: March 2008

Cathodoluminescence emission spectra and photoluminescence (PL) excitation spectra were used to evaluate Eu+3 and Cr+3 as activators for red luminescence in ZnGa2O4. In the ZnGa2O4:Eu materials red emission from Eu+3 and blue intrinsic emission were observed. The blue intrinsic emission increased relative the Eu+3 emission with increasing current density and is attributed to preferential current saturation of the Eu+3 activators. In addition, PL excitation measurements revealed that the inefficient energy transfer from the ZnGa2O4 host to the Eu+3 is due to poor spectral overlap between the ZnGa2O4 emission and the Eu+3 absorption. Cr-doping resulted in a saturated red-color, and no host emission was observed over the entire current density regime investigated. The PL excitation of the ZnGa2O4:Cr revealed good overlap between the ZnGa2O4 host and the Cr+3 absorption. Efficient energy transfer to the Cr+3 activators occurs via multipolar interactions.
Texture analysis of grain refinement in undercooled Ni99.45B0.55
Authors: Lee K. L. , Shek C. H. , Yang H.
Published: March 2008

Recently, it was demonstrated that Ni99.45B0.55 undergoes grain refinement by either remelting or dynamic nucleation at two different undercoolings. In this work, we found that the grain refinement by remelting can be characterized by a gradual disappearance of the texture of the initially formed dendrites in the transition regime while the grain refinement by dynamic nucleation is characterized by a sudden disappearance of texture.
Microwave dielectric properties of (1 − x)Cu3Nb2O8−xZn3Nb2O8 ceramics
Authors: Kim Dong-Wan , Kim In-Tae , Park Byungwoo , Hong Kug Sun , Kim Jong-Hee
Published: March 2008

The sintering behavior and microwave dielectric properties of (1 − x)Cu3Nb2O8−xZn3Nb2O8 have been investigated using dilatometry, x-ray diffraction, and a network analyzer. It was found that (1 − x)Cu3Nb2O8−xZn3Nb2O8 ceramics have a much lower melting temperature than Zn3Nb2O8 ceramics without Cu3Nb2O8 additives. Samples sintered at 900 °C for 2 h exhibited densities >97% of the theoretical density. Cu3Nb2O8 acts as a sintering aid. Two phase regions were identified with increasing Zn3Nb2O8 contents. A Cu3Nb2O8−Zn3Nb2O8 solid solution exists from 0 < x < 0.5 while a mixture of Cu3Nb2O8 and Zn3Nb2O8 exists from 0.5 < x < 1. The microwave dielectric properties correlated to the crystal structure. In Cu3Nb2O8−Zn3Nb2O8 solid solution region, the variation of dielectric properties could be explained by the structure distortion of Cu3Nb2O8 due to electronic anisotropies of Cu2+ cations.
Cracking of porcelain coatings bonded to metal substrates of different modulus and hardness
Authors: Zhao Hong , Hu Xiaozhi , Bush Mark B. , Lawn Brian R.
Published: March 2008

A preceding study of contact damage in a bilayer system consisting of a porcelain coating on a stiff Pd-alloy substrate is here expanded to investigate the role of substrate modulus and hardness. Bilayers are made by fusing the same dental porcelain onto Co-, Pd-, and Au-alloy metal bases. Indentations are made on the porcelain surfaces using spheres of radii 2.38 and 3.98 mm. Critical loads to initiate cone fracture at the top surface of the porcelain and yield in the substrate below the contact are measured as a function of porcelain thickness. Radial cracks form at the lower surface of the coating once the substrate yield is well developed. By virtue of its controlling role in the metal yield process, substrate hardness is revealed to be a key material parameter—substrate modulus plays a secondary role. A simple elasticitybased analysis for predetermining critical loads for a given brittle/plastic bilayer system is presented.
Experimental evidence for space charge segregation in Nb-doped BaTiO3
Authors: Yoon Seok Hyun , Kim Hwan
Published: March 2008

There is ample experimental evidence demonstrating space charge segregation in acceptor-doped BaTiO3. However there is still some controversy regarding donor-doped BaTiO3. Considering the space charge segregation theory in BaTiO3, the calculated driving force for space charge segregation is larger in acceptor-doped cases than in donor-doped cases. This result explains why acceptor segregation can be easily detected. However, a significant concentration of donors can also cause donor segregation. In donor and acceptor codoped BaTiO3, the grain sizes are very small, and donor segregation can be detected for compositions inducing a large space charge potential. In addition, in compositions that induced a small space charge potential, the grain sizes are very large, and donor segregation is not detected, although the total doping concentration is larger. This phenomenon means that donor segregation is caused by the space charge potential rather than misfit strain energy.
Solid-state foaming of titanium by superplastic expansion of argon-filled pores
Authors: Davis N. G. , Teisen J. , Schuh C. , Dunand D. C.
Published: March 2008

Solid-state foaming of commercial purity titanium was achieved by hot-isostatic pressing of titanium powders in the presence of argon, followed by expansion of the resulting high-pressure argon bubbles at ambient pressure and elevated temperature. The foaming step was performed under isothermal conditions or during thermal cycling around the α/β allotropic temperature of titanium. Such thermal cycling is known to induce transformation superplasticity (TSP) in bulk titanium due to the complex superposition of internal transformation stresses and an external biasing stress; TSP was found to be active during foaming, where the deviatoric biasing stress was provided by the internal pore pressure. As compared to isothermal control experiments where foam expansion occurred by creep only, TSP foaming under thermal cycling conditions led to significantly higher terminal porosity (41% as compared to 27%). The foaming rates were also higher for the TSP case before pore growth ceased. Additionally, foaming experiments were conducted under an externally applied uniaxial tensile stress of 1 MPa. This procedure resulted in foaming kinetics and porosities similar to those achieved without an external stress and, for the TSP case, led to high aspect ratio pores elongated in the direction of the applied external stress.
Photoluminescence spectra of undoped and Sm3+-doped BaAl2S4 and BaAl2Se4 single crystals
Authors: Jin Moon-Seog , Lee Choong-Il , Yoon Chang-Sun , Kim Chang-Dae , Goh Jae-Mo , Kim Wha-Tek
Published: March 2008

Undoped and Sm3+-doped BaAl2S4 and BaAl2Se4 single crystals were grown by the chemical transport reaction method. The optical energy band gaps of the BaAl2S4 and BaAl2Se4 were found to be 4.10 and 3.47 eV, respectively, at 5 K. In their photoluminescence spectra measured at 5 K, broad emission peaks at 459 and 601 nm appeared in the BaAl2S4 and at 486 and 652 nm in the BaAl2Se4. These emissions are assigned to donor–acceptor pair recombinations. Sharp emission peaks were observed in the Sm3+-doped BaAl2S4 and BaAl2Se4 single crystals at 5 K. Taking into account the ionic radii of the cations and Sm3+, these sharp emission peaks are attributed to the electron transitions between the energy levels of Sm3+ substituting with the Ba site.
Cubic silicon nitride embedded in amorphous silicon dioxide
Authors: Zhang Ming , He Hongliang , Xu F. F. , Sekine T. , Kobayashi T. , Bando Y.
Published: March 2008

A cubic silicon nitride embedded in amorphous SiO2 compound has been characterized by means of high-resolution analytical electron microscopy. The specimen was prepared from β–Si3N4 powders at a high pressure and temperature by shock wave compression. The typical high-resolution electron microscopy image from one small crystallite together with its diffractodiagram pattern indicated that the Si3N4 crystallites had a cubic symmetry. The electron energy loss spectrum from the small crystallite is very different from those of outside amorphous SiO2 phase and raw β–Si3N4 particles, and there are more N elements that were detected in this small crystallite than those in standard Si3N4.
Dye-doped sol-gel coatings for near-infrared laser protection
Authors: Kololuoma T. , Oksanen J. A. I. , Raerinne P. , Rantala J. T.
Published: March 2008

Sol-gel technology was used to fabricate two types of near-infrared absorbing dye-doped polyceram coatings for eye protection purposes against laser radiation. Tolerance of polycarbonate visors against mechanical and chemical stresses may be enhanced by using these coatings. The visible light transmission maxima of high-quality 35 and 25 μm-thick spray-coated polyceram coatings were 70% and 90% for methacrylic and propyl functionalities, respectively. Optical densities at 1064 nm were 4 and 2.
Transmission electron microscopy observation in a liquid-phase-sintered SiC with oxynitride glass
Authors: Zhan Guo-Dong , Mitomo Mamoru , Kim Young-Wook , Xie Rong-Jun , Mukherjee Amiya K
Published: March 2008

Using a pure α–SiC starting powder and an oxynitride glass composition from the Y–Mg–Si–Al–O–N system as a sintering additive, a powder mixture was hot-pressed at 1850 °C for 1 h under a pressure of 20 MPa and further annealed at 2000 °C for 4 h in a nitrogen atmosphere of 0.1 MPa. High-resolution electron microscopy and x-ray diffraction studies confirmed that a small amount of β–SiC was observed in the liquid-phase-sintered α–SiC with this oxynitride glass, indicating stability of β–SiC even at high annealing temperature, due to the nitrogen-containing liquid phase.
Highly (111)-oriented and conformal iridium films by liquid source metalorganic chemical vapor deposition
Authors: Goswami Jaydeb , Wang Chang-Gong , Majhi Prashant , Shin Yong-Wook , Dey Sandwip K.
Published: March 2008

Highly (111)-oriented and conformal iridium (Ir) films were deposited by a liquid source metalorganic-chemical-vapor-deposition process on various substrates. An oxygen-assisted pyrolysis of (methylcyclopentadienyl) (1,5-cyclooctadiene) Ir precursor at a wide range of substrate temperatures (Tsub) between 300 and 700 °C was used. At a low Tsub of 350 °C, the randomly oriented polycrystalline films exhibited an I111/I200 x-ray intensity ratio of 6. However, the films deposited at Tsub = 700 °C on native SiO2 and amorphous SiO2 surfaces were highly oriented with the I111/I200 ratios of 277 and 186, respectively. The transmission electron microscopy study revealed continuous, dense, and faceted microstructures of Ir films. Also, the step coverage of Ir on TiN (64%) was higher than that on amorphous SiO2 (50%) surfaces.
Characterization of mechanical properties of tungsten carbide/carbon multilayers: Cross-sectional electron microscopy and nanoindentation observations
Authors: Carvalho N. J. M. , De Hosson J. Th. M.
Published: March 2008

Multilayers of tungsten carbide/carbon (WC/C) deposited by physical vapor deposition onto steel substrates were subjected to depth-sensing indentation testing. The investigation aimed at probing the influence of dissimilarities between the microstructure of the multilayers and substrate on the system mechanical properties. The resultant load-displacement data were analyzed both by conventional load-displacement (P-δ) and load-displacement squared (P-δ2) plots. Furthermore, it was demonstrated that the occurrence of annular through-thickness cracks around the indentation sites can be identified from the load-displacement curve. Also, analysis of the lower part of the unloading curve permitted us to identify whether the coating had popped up by localized fracture. The cracking mechanism was characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. The information retrieved with this technique eliminates the problems, inherent in assessing at this small contact scales, whether the fracture is by coating decohesion or by interfacial failure. In our case, it was demonstrated that the failure mechanism was decohesion of the carbon lamellae within the multilayers. The mechanical properties (hardness and effective Young's modulus) were also assessed by nanoindentation. The hysteresis loops were analyzed and discussed in terms of the method developed by Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)].
Methods of correction for analysis of depth-sensing indentation test data for spherical indenters
Authors: Fischer-Cripps A. C. , Bendeli A. , Bell T. J. , Field J. S. , Jamting A. K.
Published: March 2008

Depth-sensing indentation testing has proven extremely useful in the determination of mechanical properties of thin films and small volumes of material. However, the validity of the results obtained depend largely on the corrections made to the experimentally recorded data to account for initial penetration depth, nonuniformities in indenter shape, and compliance of the loading frame. The present work examines each of these issues and presents potential methods of correction for them. The present work also highlights limitations inherent in the data analysis methods and the significance of these in terms of experimental test parameters.
Thermal expansion and high-temperature phase transformation of the yttrium silicate Y2SiO5
Authors: Nowok J. W. , Kay J. P. , Kulas R. J.
Published: March 2008

The linear thermal-expansion coefficients of yttrium silicate Y2SiO5, [Y2(SiO4)O] were measured in the temperature range from 20 to 1400 °C using x-ray diffraction. The anomalous behavior of thermal expansion was observed above Tc = 850 °C and was attributed to the displacive phase transformation. The transformation was reversible and resulted from the local order °C the compositional disorder and local fluctuation in the elastic free energy constrained a secondary transformation related to the polymorphic twin transformation. This created an additional peak in x-ray diffraction patterns at 2 's intensity. The characteristic of phase transformation both on heating and on cooling of the sample was also investigated using the differential thermal analysis method. The thermogravimetric technique did not indicate on a change of weight at Tc.
Effect of α/β phase ratio on microstructure and mechanical properties of silicon nitride ceramics
Authors: Kawaoka Hirokazu , Adachi Tomohiko , Sekino Tohru , Choa Yong-Ho , Gao Lian , Niihara Koichi
Published: March 2008

Highly densed silicon nitride ceramics with various α/β phase ratios were produced by pulse electric current sintering process. The β-phase content of Si3N4 in sintered materials varied from 20 to 100 wt% depending on the sintering condition. The microstructure was observed by scanning electron microscopy and investigated by image analysis. Young's modulus, hardness, fracture toughness, and strength were strongly dependent on the α/β phase ratio. The fracture toughness increased from 4.6 MPa m1/2 for 20-wt% b-phase content to 8.2 MPa m1/2 for 95-wt% β-phase content, and the fracture strength showed a maximum value of about 1.6 GPa at 60-to-80-wt% β-phase content.
Highly textured nanostructure of pulsed laser deposited IrO2 thin films as investigated by transmission electron microscopy
Authors: Serventi A. M. , El Khakani M. A. , Saint-Jacques R. G. , Rickerby D. G.
Published: March 2008

Highly conductive iridium dioxide (IrO2) thin films have been deposited onto in situ oxidized Si(100) substrates by means of a reactive pulsed laser deposition (PLD) process. The polycrystalline IrO2 films were obtained by ablating a metal iridium target under an optimal oxygen background pressure of 200 mtorr and at different substrate deposition temperatures (Td ) ranging from 350 to 550 °C. Conventional and high-resolution transmission electron microscopy (HRTEM) techniques were used to investigate the micro- and nanostructural changes of the PLD IrO2 films as a function of their deposition temperatures. The microstructure and the morphology of the PLD IrO2 films was found to change drastically from an irregular and loosely packed columnar structure at Td = 300 °C to a uniform and densely packed columnar structure for higher Td (≥350 °C). For IrO2 films deposited in the 350 ≤ Td ≤ 550 °C range, HRTEM have revealed the presence of highly textured arrangements of almost spherical IrO2 nanograins (of 3–5 nm diameter, regardless of Td) in the columns (of which diameter was found to increase from 85 ± 15 to 180 ± 20 nm as Td increases from 350 to 550 °C). Lattice resolution and dark-field imaging have pointed out the presence of large IrO2 crystallites made of many similarly oriented nanograins (i.e., under the same Bragg diffraction conditions). Moreover, a high continuity of the lattice planes across the entire crystallite was clearly observed. This latter aspect together with the highly textured nanostructure of the IrO2 films correlate well with their high conductivity (42 ± 6 μω cm for Td ≥ 400), which was found to be comparable with that of bulk single-crystal IrO2.
Effect of the calcium dopant on oxide ion diffusion in yttria ceramics
Authors: Saito Noriko , Haneda Hajime , Sakaguchi Isao , Ikegami Takayasu
Published: March 2008

Tracer oxygen diffusion coefficients, D*, in polycrystalline yttria doped with Ca have been determined by a gas–solid exchange technique and secondary ion mass spectrometry. Samples containing few pores were used to avoid their influences on diffusion profiles. The resulting profiles were assigned only to volume diffusion; no grain boundary diffusion was observed. According to the effects of Ca doping on D*, the Ca contents are divided into three regions. In a Ca content region of 0–0.17 mol%, D* changed a little with Ca doping and took a minimum experimentally at 0.02 mol%. D* increased significantly within a range of 0.17–0.54 mol% and saturated at 0.54 mol% or above because of a solubility limit. The activation energies of oxygen diffusion were estimated at 249–282 kJ/mol.
Coherent island formation of Cu2O films grown by chemical vapor deposition on MgO(110)
Authors: Markworth P. R. , Liu X. , Dai J. Y. , Fan W. , Marks T. J. , Chang R. P. H.
Published: March 2008

Cuprous oxide (Cu2O) films have been grown on single-crystal MgO(110) substrates by a chemical vapor deposition process in the temperature range 690–790 °C. X-ray diffraction measurements show that phase-pure, highly oriented Cu2O films form at these temperatures. The Cu2O films are observed to grow by an island-formation mechanism on this substrate. Films grown at 690 °C uniformly coat the substrate except for micropores between grains. However, at a growth temperature of 790 °C, an isolated, three-dimensional island morphology develops. Using a transmission electron microscopy and atomic force microscope, both dome- and hut-shaped islands are observed and are shown to be coherent and epitaxial. The isolated, coherent islands form under high mobility growth conditions where geometric strain relaxation occurs before misfit dislocation can be introduced. This rare observation for oxides is attributed to the relatively weak bonding of Cu2O, which also has a relatively low melting temperature.
Study of the mechanism for controlled crystallization of BaF2 under two kinds of monolayers
Authors: Lu L. , Cui H. , Li W. , Zhang H. , Xi S.
Published: March 2008

Controlled crystallization of BaF2 under two different kinds of monolayers, octadecylamine [CH3(CH2)17NH2] and hexadecanol [CH3(CH2)14CH2OH], has been studied by using x-ray diffraction (XRD) and scanning electron microscope. It was found that the monolayer headgroup, the degree of ionization of the headgroup, etc., had a complicated effect on the selectivity of monolayers for crystal and on the morphology and orientation of crystals grown under the compressed monolayers. At pH = 7.0, XRD analysis showed that (100)-oriented BaF2 crystals were formed under the octadecylamine monolayer, while several kinds of crystals were found under the hexadecanol monolayer. In comparison, at pH = 8.5, both (100)-oriented BaF2 and (111)-oriented Ba(NO3)2 crystals were obtained under the monolayer of octadecylamine. However, crystals formed under hexadecanol monolayer consist of BaF2, Ba(NO3)2, etc. The detailed mechanism for crystallization was discussed in terms of the specific interaction and lattice matching between the monolayer headgroup and the nucleating species.
Moving the pulsed heating technique beyond monolithic specimens: Experiments with coated wires
Authors: Josell D. , Basak D. , McClure J. L. , Kattner U. R. , Williams M. E. , Boettinger W. J. , Rappaz M.
Published: March 2008

Pulsed heating experiments that measure high-temperature thermophysical properties using pyrometric measurement of the temperature–time history of metal specimens rapidly heated by passage of electric current have a 30-year history at the National Institute of Standards and Technology. In recent years, efforts have been made to move beyond the limitations of the standard technique of using costly, black-body geometry specimens. Specifically, simultaneous polarimetry measurement of the spectral emissivity has permitted study of sheet and wire specimens. This paper presents the results of two efforts to expand beyond the macroscopically monolithic, single-phase materials of all previous studies. In the first study the melting temperatures of coatings, including Ti and Ti(Al) alloys, deposited on higher melting Mo substrates are measured. In the second study the melting temperatures of substrates, Ti and Cr, covered by higher melting W and Mo coatings are measured.
Interface structure and solute segregation behavior in SiC/2124 and SiC/6061 Al composites exhibiting high-strain-rate superplasticity
Authors: Kim Woo-Jin , Kum Dong-Wha , Jeong Ha-Guk
Published: March 2008

Interface structure and solute-segregation behavior in the high-strain-rate superplastic SiCp/2124 and SiCp/6061 Al composites were investigated. Evidence for interfacial reaction between reinforcement and Al matrix, which was evident in the superplastic Si3N4p,w/2124 Al and Si3N4p,w/6061 Al composites, could not be detected in the current SiC-reinforced Al composites. Instead, strong solute segregation was observed at SiC/Al interfaces. Extensive formation of whiskerlike fibers was observed at the fractured surface of tensile samples above the critical temperature where particle weakening began to be seen. These results suggest that partial melting occurs at the solute-enriched region near SiC interfaces and is responsible for the particle weakening. The absence of reaction phase in the SiC-reinforced composite may explain why no endothermic peak for partial melting appears in its differential scanning calorimetry curve and why its optimum temperature for superplasticity is generally higher than that of the Si3N4-reinforced composite.
Low-temperature growth of c-axis-oriented Y-type hexagonal ferrite thin films by the polymeric precursor method
Authors: Fujii Tatsuo , Harano Aiko , Nakanishi Makoto , Takada Jun
Published: March 2008

Well-crystallized Ba2Zn2Fe12O22 (Zn2–Y) films with high c-axis oritentation were successfully formed on Ag substrates at low temperature by the polymeric precursor method. A precursor solution with stoichiometric Ba2+, Zn2+, and Fe3+ ions was deposited on the substrates by a dip-coating. The films were then heat-treated at temperatures ranging from 700 to 900 °C. The crystallization process of c-axis-oriented Zn2–Y films occurred at the considerably low temperature of 750 °C, though a small amount of spinel oxides contaminated them. The films had hexagonal grain structures which were developed by increasing the heat-treatment temperature. Magnetization curves of the Zn2–Y film heated at 900 °C clearly indicated that the film had large in-plane magnetic anisotropy and had small in-plane coercivity.
Model for the robust mechanical behavior of nacre
Authors: Evans A. G. , Suo Z. , Wang R. Z. , Aksay I. A. , He M. Y. , Hutchinson J. W.
Published: March 2008

The inelastic deformation of nacre that leads to its structural robustness has been characterized in a recent experimental study. This article develops a model for the inelastic behavior, measured in tension, along the axis of the aragonite plates. The model is based on observations for abalone nacre that the inelasticity is associated with periodic dilatation bands. These bands contain coordinated separations at the periphery of the plates. The separations open as the material strains. The response is attributed to nanoscale asperities on the surfaces of the plates. The model calculates the stresses needed to displace the plates, resisted by elastic contacts at the asperities. The results are compared with the measured stress/strain curves.
Chemical structure evolution and orientation selection in sol-gel-prepared ferroelectric Pb(Zr,Ti)O3 thin films
Authors: Fè L. , Norga G. J. , Wouters D. J. , Maes H. E. , Maes G.
Published: March 2008

We studied in detail the chemical structure evolution of Pb(Zr1−x, Tix)O3 (PZT) thin films on Pt electrodes during the initial thermal steps of their preparation using an alkoxide-based sol-gel process. Absorption-reflection Fourier transform infrared spectroscopy (AR-FTIRS) was used to monitor chemical reactions occurring in the films on a real temperature scale. We demonstrate that the chemical state of the pyrolyzed film strongly depends on pyrolysis conditions and can have a large effect on the orientation selection in the film. First, residual acetate groups, resulting from incomplete decomposition of the Pb acetate precursor, strengthen the (111) PZT texture component after crystallization. Second, OH bonds, which are seen to remain in the film after pyrolysis under specific conditions, are seen to strengthen the intensity of the PZT(100) reflection. Possible mechanisms behind these observations are discussed.
In situ transmission electron microscopy studies of shear bands in a bulk metallic glass based composite
Authors: Pekarskaya E. , Kim C. P. , Johnson W. L.
Published: March 2008

In situ straining transmission electron microscopy (TEM) experiments were performed to study the propagation of the shear bands in the Zr56.3Ti13.8Cu6.9Ni5.6Nb5.0Be12.5 bulk metallic glass based composite. Contrast in TEM images produced by shear bands in metallic glass and quantitative parameters of the shear bands were analyzed. It was determined that, at a large amount of shear in the glass, the localization of deformation occurs in the crystalline phase, where formation of dislocations within the narrow bands are observed.
Purification of single-walled carbon nanotubes synthesized by the hydrogen arc-discharge method
Authors: Hou Pengxiang , Liu Chang , Tong Yu , Xu Shitao , Liu Min , Cheng Huiming
Published: March 2008

A simple procedure for the purification of the single-walled carbon nanotube (SWNT) product synthesized by the hydrogen arc-discharge method was proposed and discussed. The procedure involves ultrasonication in alcohol, oxidation in fixed air, and soaking in hydrochloric acid. Most of the amorphous carbon and carbon nanoparticles as well as metal particles in the product was successfully removed, according to the results obtained from transmission electron microscopy, thermogravimetric analysis, and resonant laser Raman measurements. With this procedure, a 41 wt% yield of the SWNTs with a purity of about 96% was achieved after purification.
Synthesis of nanoscale particles of Ta and Nb3Al by homogeneous reduction in liquid ammonia
Authors: Zhu Hongmin , Sadoway Donald R.
Published: March 2008

The analysis of metallothermic reduction as an electronically mediated reaction predicted that the particle size of solid product could be reduced if the reaction were conducted in a medium that is a mixed conductor (ionic and electronic). This prediction was confirmed by reacting TaCl5 with sodium, each dissolved in liquid ammonia, to produce tantalum powder having an average particle size over an order of magnitude finer than the micron-sized powders produced commercially today. Metallothermic reduction in a mixed conducting medium has been extended to a multicomponent system in order to synthesize nanosized powder of Nb3Al by co-reduction of NbCl5 and AlCl3 both dissolved in liquid ammonia.
Threading dislocations with edge components in GaN epilayers grown on Al2O3 substrates
Authors: Kang Junyong , Ogawa Tomoya
Published: March 2008

Two types of threading dislocations with edge components were investigated by a high-resolution transmission electron microscope in undoped GaN epilayers grown on Al2O3 substrates. One is a fully filled core with regular contraction and stretch of bright dots, and the other is incompletely filled with one bright dot less and irregular contraction and stretch of bright dots. The bright dots were distorted and degenerated into bright line segments at cores in areas with smaller local dislocation intervals. The calculated results suggested that the distorted bright regions are attributable to the glide and/or climb caused by nearby dislocation interactions.
X-ray reflectivity spectra of ultrathin films and nanometric multilayers: Experiment and simulation
Authors: Bontempi E. , Depero L. E. , Sangaletti L. , Giorgis F. , Pirri C. F.
Published: March 2008

Amorphous silicon–nitrogen (a–Si1−xNx:H) alloys, thin films, and multilayers deposited by ultrahigh-vacuum plasma-enhanced chemical vapor deposition were studied and modeled by x-ray reflectivity (XRR) measurements. The analysis of XRR data obtained from the single-layer samples allowed us to calculate the density, thickness, and interface roughness of each layer. To check the deposition parameters, the deviation (tnom–texp)/(tnom) of the measured thicknesstexpfrom the nominal thicknesstnomwas evaluated. Based on these results, a simulation of a multilayer film, obtained by deposition alternating stoichiometric and substoichimetric layers was carried out. It is shown that the best fitting is obtained by introducing into the XRR calculation a thickness distribution with a standard deviation related to the deviation (tnom–texp)/(tnom) estimated for the single layers.
Control growth of PbS quantum dots doped sono-ormosil
Authors: Erce-Montilla R. , PiÑero M. , Rosa-Fox N.de la , Santos A. , Esquivias L.
Published: March 2008

Semiconductor PbS quantum dots doped-SiO2 organically modified silicate (ormosil) gels were synthesised via sol-gel by using high-power ultrasounds (sonogel). The effect of PbS crystal concentration and the addition of (3-mercaptopropyl)trimethoxysilane acting as surface capping agent (SCA) were investigated. By adjustment of the SCA to lead ratio, PbS nanoparticles of different sizes and morphologies were obtained. Textural parameters were calculated from N2 physisorption isotherms. The PbS galena phase was identified by x-ray diffraction, the crystal size by high-resolution transmission electron microscopy, and the exciton confinement by ultraviolet–visible–near-infrared spectrophotometry. Crystallite mean sizes of spheres and cubes ranging from 6.5 to 10.5 nm and needles 7-nm wide and 15–20 nm long, for different PbS and SCA concentrations, were obtained. These results differ from those predicted by the effective mass approximation corroborating the band gap modifications in the smallest nanocrystals. The method allows the control of the crystal size and improves the stabilization of the PbS nanocrystals.
Effect of pressure on the structure of Fe–N alloys formed by solid-state reaction
Authors: Yao B. , Liu L. , Liu S. E. , Hu X. , Su W. H.
Published: March 2008

Fe–N alloys with crystalline structures different from those obtained at atmospheric pressure were produced by solid-state reaction between Fe and amorphous boron nitride under high pressure. Two new paramagnetic Fe–N phases were obtained at temperatures above 800 K under pressures between 2.0 and 4.0 GPa. One is of cubic structure with lattice constant of 6.114 Å, and another is of orthorhombic structure with lattice constants of a = 4 8.443, b = 4 4.749, and c 4 3.993 Å. ε–Fe3Nx with N contents of 18.1 to 21.4 at.%, which could not be obtained at atmospheric pressure, was produced at pressures of 3.0 to 4.0 GPa and temperatures of 690 to 800 K. The mechanism of formation of ε–Fe3Nx under high pressure is discussed.
18O study of the oxidation of reactively sputtered Ti1−xAlxN barrier
Authors: Hugon M. C. , Varniere F. , Letendu F. , Agius B. , Vickridge I. , Kingon A. I.
Published: March 2008

The preparation of high-permittivity perovskite materials requires high-temperature (550–750 °C) oxidizing environments, providing stringent limitations on the choice of electrode materials. To minimize interdiffusion and oxidation reactions, an electrically conductive diffusion barrier such as Ti1−xAlxN is needed below the electrode material (Pt, IrO2, RuO2…). Ti1−xAlxN films were deposited by multitarget reactive sputtering in a mixture of Ar and N2. The stability of these films has been investigated under typical conditions for crystallization of perovskite dielectrics. Sample composition was characterized using Rutherford backscattering spectroscopy and nuclear reaction analysis. In particular, the concentration depth profiles of both 18O and 27Al were measured before and after RTA treatments via the narrow resonances of 18O(p,α)15N at 151 keV (FWHM = 100 eV) and 27Al(p,γ)28Si at 992 keV (FWHM = 100 eV). The different 18O excitation curves show that the oxidation resistance increases with Al incorporation. The Al excitation curves indicate a uniform Al content for as-deposited TixAl1−xN and reveal Al diffusion to the surface during the oxidation process which indicates the formation of an Al-rich oxide layer at the TixAl1−xN surface, leaving a layer depleted in Al below it.
Effect of in situ boron doping on properties of silicon germanium films deposited by chemical vapor deposition at 400 °C
Authors: Sedky Sherif , Witvrouw Ann , Saerens Annelies , Houtte Paul Van , Poortmans Jef , Baert Kris
Published: March 2008

This paper reports on the role of boron in situ doping on enhancing crystallization of silicon germanium deposited at 400 °C and 2 torr. The dependence of growth rate on germanium content and boron concentration is investigated. The minimum boron concentration and the minimum germanium content required for crystallizing the as-grown layers is experimentally determined. The texture and grain microstructure of doped and undoped poly SiGe layers has been investigated by means of x-ray diffraction spectroscopy and transmission electron microscopy. The low deposition temperature coupled with the low tensile stress of the polycrystalline material enable postprocessing of surface micromachined microelectromechanical systems on top of standard complementry metal oxide semiconductor wafers with Al interconnects. Furthermore, the resistivity of the as-grown layers is as low as 1 mΩ cm, and hence, it can be used as a seeding layer for polycrystalline Si solar cells compatible with glass substrates.
Flash synthesis of zirconia nanoparticles by microwave forced hydrolysis
Authors: Bellon K. , Chaumont D. , Stuerga D.
Published: March 2008

Forced hydrolysis preparation of zirconia sols and powders by microwave heating of zirconium tetrachloride solutions at temperatures equal to 180 °C leads in a few minutes to monodispersed nanoscale zirconia particles. Synthesis was performed in a microwave reactor called the RAMO system. This microwave reactor was designed by the authors. This flash-synthesis process combines the advantages of forced hydrolysis (homogeneous precipitation) and microwave heating (very fast heating rates). The sols and powders were characterized by x-ray diffraction,photon correlation spectroscopy (PCS), small-angle x-ray scattering, and transmission electron microscopy. Sols are colloidally stable, which means that after 6 months no sedimentation is observed and the size distribution given by PCS measurements has not changed. For all synthesis conditions (with or without HCl, zirconium salt concentration, and synthesis time), zirconia polycrystalline particles were produced. According to the different analyses, these zirconia polycrystalline particles were constituted of aggregates of small primary clusters.
Thin-film fracture during nanoindentation of a titanium oxide film–titanium system
Authors: Pang M. , Bahr D. F.
Published: March 2008

Nanoindentation testing of the titanium oxide/titanium system with electrochemically grown oxide films exhibits permanent deformation prior to a yield excusion, indicating that the occurrence of this suddent discontinuity is predominantly controlled by oxide film cracking rather than dislocaton nucleation and multiplication. Observations of circumferential cracking also lend support to this explanation. A model has been developed to predict the mechanical response prior to oxide fracture for the case of a hard coating on a soft substrate. During loading contact, the hard coating undergoes elastic deflection which may include both bending and membrane stretching effects, while the substrate is elastoplastically deformed. The model works well for surface films thicker than 20 nm. Additionally, the maximum radial tensile stress in anodically grown titanium oxide, which is responsible for film cracking at the critical load, is approximately 15 GPa.
Effect of lead content on vibration fracture behavior of Pb–Sn eutectic solder
Authors: Chuang C. M. , Lui T. S. , Chen L. H.
Published: March 2008

According to resonant vibration fatigue tests, near-eutectic and Pb-rich hypoeutectic Pb–Sn specimens have higher crack-propagation resistance. The tensile flow stress of Pb–Sn solders that are near eutectic composition increases with decreasing Pb content. The solders were tested after either stabilizing at 373 K or natural aging for 20 days, which gave similar results. The naturally aged specimens show that the crack-propagation resistance increases with increasing aging time. A striated deformation was found to occur in Sn grain of the lower Pb specimen. This phenomenon is correlated with a deterioration of crack-propagation resistance.
Formation rule for Al-based ternary quasi-crystals: Example of Al–Ni–Fe decagonal phase
Authors: Qiang Jian-Bing , Wang De-He , Bao Cui-Min , Wang Ying-Min , Xu Wei-Ping , Song Mei-Li , Dong Chuang
Published: March 2008

After examining ternary Al-based quasi-crystalline phase diagrams, we pointed out that the presence of e/a-constant and e/a-variant lines is a common phenomenon. Ternary quasi-crystal compositions are located at the crossing point of these lines in ternary phase diagrams. Such an empirical rule can be used to predict the ternary quasi-crystal compositions from binary ones. We applied this rule to the Al–Fe–Ni system and clarified the decagonal phase composition zone. There are two decagonal phases, D-Al72.5Fe14.5Ni13 and D′-Al705Fe12Ni17.5, that correspond respectively to Al–Fe-based and Al–Ni-based decagonal phases in the same ternary system.
Nanocrystals in crystalline silicon: Void formation and hollow particles
Authors: Meldrum A. , Honda S. , White C. W. , Zuhr R. A. , Boatner L. A.
Published: March 2008

Nanophase precipitates of CdS formed in amorphous SiO2 by ion implantation and thermal processing have recently been found to exhibit a “hollow-particle” or “shell-like” microstructure. The present investigations show that this hollow-particle microstructure can be reproduced for a variety of materials other than CdS, and these results provide new insight into the mechanisms responsible for the formation of hollow precipitates embedded in solid hosts. Various elemental metal nanocrystals were formed in (100)-oriented crystalline Si hosts by ion implantation coupled with thermal treatments in which the annealing parameters were varied to investigate the “hollow-particle” formation conditions. The results indicate that depending on the melting points and vapor pressure of the precipitates or on the initial state of the host material, several processes acting either independently or in concert can lead to hollow precipitate formation. First, the implantation of materials having a high vapor pressure, either at the implant temperature or when heated during annealing, can lead to the formation of cavities in the crystalline host. Hollow precipitates can then form by a partial filling and coating of the cavity walls by the implanted species in a diffusion-based gettering/ripening process. Internal void formation can also occur or be enhanced by volume contraction during cooling if the particle solidifies from a liquid phase.
Combustion of zirconium foils in oxygen
Authors: Ewald K. H. , Anselmi-Tamburini U. , Munir Z. A.
Published: March 2008

The combustion of zirconium foils in an oxygen environment was investigated for foils ranging in thickness from about 22 to 124 μm and for oxygen partial pressures ranging from about 0.3 to 0.9 atm. Temperature profile measurements showed indications of an after-burn, which became especially significant in the combustion of thicker foils. The dependence of the combustion wave temperature and velocity on the oxygen partial pressure was determined. For any partial pressure, wave velocity decreased with an increase in foil thickness. Wave propagation in this system is a complex process and is dictated by oxide formation and oxygen dissolution. The results are examined in light of a finite difference model.
Development of a model for the prediction of the fretting fatigue regimes
Authors: Matikas T. E. , Nicolaou P. D.
Published: March 2008

parameters that govern the life of metallic materials under conditions of fretting fatigue may be divided into two broad categories. The first category concerns the material properties (e.g., yield strength, elastic modulus, and surface roughness) while the second concerns the externally imposed loading conditions and contact geometry. The two in-contact materials may either stick, slip, or stick-slip (i.e., there is a slip and a stick region on their interface) against each other. It has been shown that the fatigue life reduction is highest under partial slip. The objective of the present research effort is to develop a model that enables the prediction of the particular fretting fatigue regime (i.e., slip, stick, or mixed). The parameters that affect the fretting fatigue life of metallic components were identified and integrated into a model, which allows the prediction of the interfacial contact conditions. The model was first used to identify the sensitivity of the fretting fatigue regimes upon the materials and external, and geometrical parameters. Experimental results concerned with the fatigue life were plotted on the fretting maps; the fretting fatigue regimes indicated by the latter enabled the interpretation of the experimental data.
Growth mechanism of superconducting MgB2 films prepared by various methods
Authors: Zhai H. Y. , Christen H. M. , Zhang L. , Paranthaman M. , Cantoni C. , Sales B. C. , Fleming P. H. , Christen D. K. , Lowndes D. H.
Published: March 2008

The growth mechanisms of MgB2 films obtained by different methods on various substrates are comparably studied by transport measurements and scanning electron microscopy observations. The analyzed films include those prepared by ex situ postanneal with Tc0 ˜38.8 K and those from in situ anneal with Tc0 ˜24 K. It is clearly observed that the films obtained by the high-temperature reaction of e-beam evaporated B with Mg vapor are formed by the nucleation of independent MgB2 grains at the film surface, indicating that this approach may not be suitable to obtain epitaxial films. A significant oxygen contamination was also present in films obtained from pulsed-laser-deposition-grown precursors, which drag the Tc0 down to 24 K.
Precipitate splitting in Pb0.91La0.09Zr0.65Ti0.35O3 films
Authors: Tunaboylu Bahadir , Ring Ken , Esener Sadik C. , Ozkan Cengiz , Ata Ali
Published: March 2008

The transformation to perovskite phase of Pb0.91La0.09Zr0.65Ti0.35O3 (9/65/35) films on r-sapphire and resulting annealed microstructures were examined by transmission electron microscopy. A random equiaxed polycrystalline grain morphology (approximately 600 nm) was observed after rapid-thermal annealing or furnace annealing when the as-deposited (radio-frequency-magnetron sputtering) films were predominantly pyrochlore. However, an interesting paired-plate structure was revealed after furnace annealing when the as-deposited films were fully perovskite. The average size of such a split precipitate was 35 nm in width and 150 nm in length.
Compaction of bulk ferromagnetic Fe80P13C7amorphous alloys
Authors: Chan F. W. , Ma N. G. , Kui H. W.
Published: March 2008

When bulk ferromagnetic Fe80P13C7 amorphous rods of approximately 2-mm diameter are compacted together in a hot press, a variety of different microstructures, depending on the experimental conditions, are produced. The most intriguing microstructure is that two different bulk amorphous rods can be fused together perfectly at a temperature of 683 K and under a pressure of 2.5 to 4 GPa for a period of 5 min.
Translucent yttrium aluminum garnet: Microwave-assisted route to synthesis and processing
Authors: Panneerselvam M. , Subanna G. N. , Rao K. J.
Published: March 2008

A novel and fast microwave route is described for the synthesis of yttrium aluminum garnet (YAG) and for its sintering to translucent bodies. Precursor was made by microwave decomposition (20 min) of aluminum tri-sec-butoxide and yttrium nitrate dissolved in ethyl acetate. The precursor, conventionally calcined at 1000 °C (1 h), was sintered in microwave using SiC as secondary heater for just 35 min. Resulting translucent YAG has a microhardness (HV) of 18.1 GPa and fracture toughness (KIC) of 4.3 MPa m1/2. A 0.86-mm-thick sintered pellet exhibits approximately 45% transmission for 520-nm radiation. The entire microwave process requires less than 3 h.