bluuebunny/crossref_metadata_2025 huggingface dataset:
Protective AlZrN film for organic photoconductors
Authors: Chan Y. C. , Miao X. S. , Pun E. Y. B.
Published: March 2008

AlZrN protective film with high transmissivity was deposited onto the organic photoconductor (OPC) surface, and the surface hardness was greatly increased by a factor of 1.5–3. The OPC surface protected by (Al100−xZrx)N (x ≤ 58.5%) film was significantly harder than that protected by AlN film. The electrophotographic properties of the OPC coated with (Al100−xZrx)N (x ≤ 37.7%) film were also better than those without coating or protected with AlN film, thus demonstrating the suitability of AlZrN film as a protective coating for enhancing the operating life of OPC.
Theoretical assessment of systematic errors in volume fraction determinations by microscopy methods
Authors: Zanotto Edgar Dutra
Published: March 2008

A set of equations were derived to estimate systematic errors in experimental determinations of volume fractions transformed by microscopy methods. For reactions that occur by continuous nucleation and growth, the experimental values of volume fractions transformed may be subjected to significant errors when the largest grain size of the distribution is close to the microscope resolution limit. For transformations occurring from a fixed number of nuclei, the systematic errors are smaller than those observed in the continuous nucleation case, but can still be significant when reflection methods are used. Transmission methods lead to smaller errors than reflection techniques.
Film/substrate interactions and superconducting properties of Tl(Ba1−xSrx)2Ca2Cu3Oy thin films on (001) SrTiO3 and SrTiO3-buffered (001) MgO substrates
Authors: Bramley A. P. , Grovenor C. R. M. , Goringe M. J. , O'Connor J. D. , Jenkins A. P. , Dew-Hughes D. , Reschauer N. , Wagner H. H. , Brozio W. , Spreitzer U. , Renk K. F.
Published: March 2008

We have developed a process for the fabrication of (001) oriented SrTiO3 buffer layers onto (001) MgO substrates by rf magnetron sputtering followed by a post-deposition heat treatment in air. Precursor films with Tl :Ba : Ca : Cu ratio 2 : 2 : 2 : 3 were deposited by dc magnetron sputtering onto both these buffered substrates and directly onto (001) SrTiO3 single-crystal substrates, and thalliated at elevated temperatures. Because of Sr diffusion from the substrate/buffer layer, and its subsequent substitution for Ba in the superconducting film, the single Tl–O layer phase Tl(Ba1−xSrx)2Ca2Cu3Oy was stabilized. Diffusion of Ba and Ca in the opposite direction led to the formation of a Ba–Ca–Ti–O compound at the interface. The Tl(Ba1xSrx)2Ca2Cu3Oy films typically have superconducting transition temperatures (Tc's) > 103 K and critical current densities (Jc's) > 2.9 × 105 A cm−2 at 77 K. Rs values measured on these films and scaled to 10 GHz were 3.0 mΩ at 80 K and <200 µΩ at 50 K for the film grown on SrTiO3 buffered MgO, and 2.0 mΩ and 1.0 mΩ at 50 K for the film grown directly onto the (001) SrTiO3 substrate. Films fabricated on (001) SrTiO3 using an in situ deposition technique with a substrate temperature around 100 °C lower than the ex situ thalliation temperature showed no evidence of an interfacial reaction layer.
Microstructural control of amorphous silicon films crystallized using an excimer laser
Authors: Viatella John , Singh Rajiv K.
Published: March 2008

A technique for microstructural control of excimer laser-annealed silicon thin films on SiO2 substrates has been developed. By using single-crystal photolithographically etched silicon seed wafers in intimate contact with the silicon films, we have shown that it is possible to spatially control nucleation. Transmission electron micrographs show the resultant microstructure to consist of large (∼1 µm) grain structures in the area surrounding the seed contact, with distinct organization not previously observed. A theoretical discussion is presented to explain the observed phenomena. Also, results from a numerical simulation are given which outline the effects of the seed wafer on the resultant microstructure of the laser-annealed film, as compared to nonseeded areas.
Investigation of the solidus boundaries and microstructure in the ZnO–PrO1.5–CoO system
Authors: Chun Sung-Yong , Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: March 2008

ZnO ceramics used as varistors are prepared with cobalt oxide as an essential additive to improve nonohmic properties. Because some of its effects during the liquid-phase sintering remain unexplained, we characterize the liquid-phase formation temperatures and phase reactions in the system ZnO–PrO1.5–CoO. Using differential thermal analysis (DTA) during sintering, we detect new thermal phenomena. An addition of cobalt oxide to ZnO–PrO1.5 mixtures (ZnO–5 mol% PrO1.5–10 mol% CoO) significantly decreases the liquid-phase formation temperature to 1272 ± 5 °C, which is about 110 °C lower compared to those in the ZnO–PrO1.5 system. Characterization of ceramics quenched during sintering allows us to describe an isoplethal section with PrO1.5 contents of 5 mol% and solubility limit of Co in ZnO.
Influence of nitrogen implantation on the properties of Ti and substoichiometric TiNx films deposited on high speed steel
Authors: Rodrigo M. T. , Jiménez C. , Váquez L. , Alonso F. , Fernández M. , Martínez-Duart J. M.
Published: March 2008

Ti and TiNx (x < 1) thin films have been deposited on high speed steel (HSS) substrates by reactive sputtering and then N+ implanted. The increase of the N/Ti ratio of the films during deposition is related to a decrease in their roughness, and N+ implantation produces another additional slight decrease of the roughness. The hardness of samples increases with the nitrogen content in the as-deposited samples; nevertheless, N+-implanted Ti coatings show lower values of hardness than reactive sputtered TiNx films. α–Ti, ε–Ti2N, and δ–TiN phases were identified by grazing x-ray diffraction.
Plasticity in ion-irradiated austenitic stainless steels
Authors: Robertson C. , Poissonnet S. , Boulanger L.
Published: March 2008

In an attempt to take advantage of charged particle irradiation for studying the effects of irradiation on the mechanical properties of metals, we developed an experimental procedure based on the combination of transmission electron microscopy (TEM) and submicron indentation of ion-implanted layers. We applied this technique to industrial 316L steel, irradiated with krypton ions up to 10 dpa at 873 K. A domain where the penetration range of the ions and the indentation depth are compatible has been identified. The indentation tests then yielded a good estimate of hardness and bulk modulus, while the TEM observations provide microstructural information in the plastic regime. It is shown that the combination of the two techniques is necessary for rationalizing the observed results.
Formation of graphite encapsulated ferromagnetic particles and a mechanism for their growth
Authors: Setlur A. A. , Dai J. Y. , Lauerhaas J. M. , Washington P. L. , Chang R. P. H.
Published: March 2008

Graphite encapsulated nanoparticles have numerous possible applications due to their novel properties and their ability to survive rugged environments. Evaporation of Fe, Ni, or Co with graphite in a hydrogen atmosphere results in graphite encapsulated nanoparticles found on the chamber walls. Similar experiments in helium lead to nanoparticles embedded in an amorphous carbon/fullerene matrix. Comparing the experimental results in helium and hydrogen, we propose a mechanism for the formation of encapsulated nanoparticles. The hydrogen arc produces polycyclic aromatic hydrocarbon (PAH) molecules, which can act as a precursor to the graphitic layers around the nanoparticles. Direct evidence for this mechanism is given by using pyrene (C16H10), a PAH molecule, as the only carbon source to form encapsulated nanoparticles.
Chemical interaction between nitrogen and iron in silica glasses via sequential ion-implantation
Authors: Isobe Tetsuhiko , Toriyama Tamotsu , Weeks Robert A. , Zuhr Raymond A.
Published: March 2008

Silica glass plates (Corning 7940 excimer grade) were implanted sequentially with N+ at 52 keV to different doses, ranging from 0 to 1.2 × 1017 ions cm−2, and then with Fe+ at 160 keV to 6 × 1016 ions cm−2 at room temperature and 4 µA cm−2. The intensity of ferromagnetic magnetic resonance (FMR) absorption and the magnetization calculated by the angular dependence of the FMR field reach maxima at an N/Fe atomic ratio ∼0.2. Two peaks due to Fe 2p3/2 electron are observed at 707.2 ± 0.2 and 710.9 ± 0.2 eV in the x-ray photoelectron spectra. The intensity of the former relative to the latter decreases with increasing the N dose. The conversion electron Mössbauer spectrum reveals the formation of superparamagnetic iron nitride as well as the existence of Fe2+ and Fe3+ in silica when implanting N+ to 7.5 × 1015 ions cm−2 and then Fe+ to 6 × 1016 ions cm−2 at N/Fe = 0.125. These results suggest that sequential ion-implantation of N+ and Fe+ produces iron nitride in silica glasses.
Microstructure of columnar-grained SrTiO3 and BaTiO3 thin films prepared by chemical solution deposition
Authors: Jia C. L. , Urban K. , Hoffmann S. , Waser R.
Published: March 2008

The microstructure and lattice defects of SrTiO3 and BaTiO3 thin films with columnar grains prepared by a chemical solution deposition technique have been investigated by means of transmission electron microscopy. The columnar grains in the SrTiO3 films exhibit a preferential orientation with a crystallographic 〈111〉 direction parallel to the normal of film, which, in turn, follows the orientation texture of the substrate Pt layer. Cubic-to-cubic relationships have been found for the two materials. For the BaTiO3 films the columnar grains are oriented in a random way without any preferential relationship to the substrate Pt layer. Pores, lattice defects, and grain boundaries occur in either type of film, however in different configurations. This reflects the individual nature of the materials and the different formation and growth mechanisms of the films under the preparation conditions.
Microstructural factors influencing the properties of high surface area molybdenum nitride films converted from molybdenum trioxide films deposited via solution spray pyrolysis
Authors: Roberson S. L. , Finello D. , Davis R. F.
Published: March 2008

Molybdenum trioxide (MoO3) films, 15 µm thick, have been deposited on 50 µm thick polycrystalline titanium substrates from 250 to 500 °C via liquid spray pyrolysis. Molybdenum pentachloride (MoCl5) dissolved in methanol was used as the molybdenum source; ambient conditions provided the oxygen source. X-ray diffraction (XRD) data indicated that amorphous MoO3 films were produced at deposition temperatures below 400 °C. Randomly orientated polycrystalline MoO3 films were produced at 400 °C and higher deposition temperatures. The deposition temperature also influenced the surface area of the films and their average grain size. Subsequent conversion of the MoO3 films to high surface area (HSA) conductive films containing both γ–Mo2N and δ–MoN was accomplished via programmed reactions with anhydrous NH3 and involved the formation of MoO2 and MoOxN1−x as intermediate phases. The degree of crystallinity, surface area, and average grain size of the MoO3 films strongly influenced the average grain size and surface area of the resultant MoxN films.
Growth, microstructure, and resistivity of RuO2 thin films grown by metal-organic chemical vapor deposition
Authors: Vetrone J. , Foster C. M. , Bai G-R. , Wang A. , Patel J. , Wu X.
Published: March 2008

Polycrystalline RuO2 thin films were grown by metal-organic chemical vapor deposition (MOCVD) on both SiO2/Si(001) and Pt/Ti/SiO2/Si(001) substrates. Films having a controllable and reproducible structural texture and phase purity were synthesized by carefully controlling deposition parameters. Moderate growth temperatures (∼350 °C) and low growth rates (<30 Å/min) produced highly (110)-textured RuO2 films. Highly (101)-textured RuO2 films were favored at slightly lower temperatures (∼300 °C) and much higher growth rates (>30 Å/min). The most conductive RuO3 films had resistivities of 34 to 40 µΩ−cm at 25 °C, an average grain size of 65 ± 15 nm, and a surface roughness (rms) of 3 to 10 nm. Both single-phase Ru and mixed Ru/RuO2 phase material were also fabricated at low temperatures (<350 °C) by using lower oxygen flow concentrations (<10%).
Crystallization kinetics of sputter-deposited LaNiO3 thin films on Si substrate
Authors: Lee Hsin-Yi , Wu Tai-Bor
Published: March 2008

The kinetics of in situ crystallization of LaNiO3 thin films in sputtering deposition at temperatures ranging from 250 to 450 °C and isothermal crystallization of room-temperature (RT) sputtered LaNiO3 thin films in annealing at 350–500 °C were investigated by the x-ray diffraction method. The crystallization in both cases basically followed the Johnson–Mehl–Avrami (JMA) relation. However, different crystallization kinetics were observed. The transformation index and activation energy of crystallization in high temperature sputtering were about 1.5 and 33 kJ/mole, respectively, while in the annealing of RT-sputtered films, 1.0 and 63 kJ/mole were found. From the determined transformation index, it is suggested that the crystallization rate in high temperature sputtering was determined by a diffusion-controlled process of lateral growth with a decreasing nucleation rate of crystallites in the adsorption layer. However, the annealed films crystallized by an interface-controlled and one-dimensional growth of existing nuclei.
Effect of intercalation in graphite epoxy composites on the shielding of high energy radiation
Authors: Gaier James R. , Hardebeck Wendie C. , Bunch Jennifer R. Terry , Davidson Michelle L. , Beery Dwight B.
Published: March 2008

The half-thickness and mass absorption coefficient of 13.0 keV x-rays, 46.5 keV γ-rays, and 1.16 MeV βƟ particles have been measured for pristine, bromine intercalated, and iodine monobromide intercalated pitch-based graphite fiber composites. Since these materials have been proposed to replace aluminum structures in spacecraft, the results were compared to aluminum. Pristine graphite epoxy composites were found to have about 4.0 times the half-thickness, and 40% of the mass absorption of aluminum for ionizing radiation. Bromine intercalation improved performance to 90% of the half-thickness, and 1.7 times the mass absorption coefficient of aluminum. Iodine monobromide extended the performance to 70% of the half-thickness and 3.0 times the mass absorption of aluminum. Thus, intercalation not only makes up the deficiency conventional composites have in shielding components from ionizing radiation, but actually confers advantages in mass and thickness over aluminum. The βƟ particle shielding of all the materials tested was found to be very effective. The shielding of all of the materials was found to have nearly the same mass absorption coefficient of 17.8 ± 0.9 cm2/g. Inelastic scattering processes were found to be important in βƟ particle shielding; however, the extent of inelastic scattering and thus the distribution of energies of the transmitted electrons did not vary with material.
Microstructural characteristics of conductive SrRuO3 thin films formed by pulsed-laser deposition
Authors: Lu P. , Chu F. , Jia Q. X. , Mitchell T. E.
Published: March 2008

Transmission electron microscopy and high-resolution electron microscopy have been used to study microstructural properties of conductive SrRuO3 films grown by pulsed laser deposition on (001) LaAlO3 and (001) SrTiO3 substrates. It was found that the SrRuO3 films deposited on both substrates consist of mixed domains of [001] and [110] orientations, with orientation relationships that can be described as (i) (001)f ‖ (001)s and [110]f ‖ [100]s and (ii) (110)f ‖ (001)s and [001]f ‖ [100]s, respectively. The SrRuO3 films deposited on SrTiO3, in particular, were found to have a layered domain structure, with the [110] domain grown initially on the substate, followed by growth of the [001] oriented domain with increasing thickness. The films on SrTiO3 are strained and have a coherent interface with the substrate. The SrRuO3 films deposited on LaAlO3, on the other hand, contain a high density of structural defects such as stacking faults and microtwins on the (022) planes. Microtwins as large as 50 nm in thickness are observed in the films deposited on LaAlO3. Possible causes for the observed structural defects in the films are discussed.
Growth kinetics of chemically vapor deposited SiO2 films from silane oxidation
Authors: Ojeda Fernando , Castro-García Alejandro , Gómez-Aleixandre Cristina , Albella José María
Published: March 2008

The growth kinetics of SiO2 thin films obtained by low-pressure chemical vapor deposition (CVD) from SiH4/O2/N2 gas mixtures has been determined at different temperatures and flow rates. The results show that the film growth is originated by some intermediate species (e.g., SiOxHy) produced in the gas phase. At low temperatures the deposition rate is limited by some homogeneous reaction with an apparent activation energy of 1.42 eV. Furthermore, the observation of critical limits when total pressure, oxygen/silane flow ratio, and temperature are decreased gives support to a branching-chain mechanism of deposition. Finally, we have observed that the deposition rate shows a hysteresis behavior when varying the temperature within the 300–400 °C range, which has been attributed to the inhibition of silane oxidation by the Si–OH surface groups of the films grown on the reactor walls.
Nonlinear physical properties of some nonconventional semiconducting Bi–Pb–Ba–O glasses
Authors: Modak D. K. , Banerjee G. , Karar M. , Sadhukhan M. , Bera A. K. , Chaudhuri B. K. , Pal P. K.
Published: March 2008

Semiconducting Bi1−xPbxBaO3−δ (or BPB) glasses with x = 0 to 0.8 have been prepared by fast quenching from the melt. Interesting anomalies in the temperature-dependent polaronic conductivity and dielectric constant have been observed in all these glass compositions at temperatures, Tp, varying from 310 to 330 K (depending on Pb concentration). This nonlinear behavior is considered to be associated with the local ordering or the displacements of the BiO3 type pyramidal structural units present in the glass matrix (observed from the infrared spectra of these glasses). This type of ordering/displacement gives rise to a local instability in the glass network structure which is also supported by the observed heat capacity anomaly around the same temperatures Tp.
Preparation, morphology, and microstructure of diameter-controllable vapor-grown carbon nanofibers
Authors: Fan Yue-Ying , Li Feng , Cheng Hui-Ming , Su Ge , Yu Ying-Da , Shen Zu-Hong
Published: March 2008

Pure vapor-grown carbon nanofibers (VGCNF's) with controllable diameters of 10–200 nm were prepared by an improved floating catalyst method. Through transmission electron microscopy (TEM) observation, it was found that VGCNF's have a duplex structure, a hollow and high-crystallinity graphite filament called primary carbon fiber surrounded by a pyrocarbon layer with low graphite crystallinity. It was observed using high-resolution TEM that VGCNF's have excellent graphitic crystallinity with graphite layers stacked neatly parallel to fiber axis. Moreover, x-ray diffraction results showed that the graphitic crystallinity of carbon fibers became higher with decreasing diameter of carbon fibers.
Photovoltaic silicon produced by thermal plasma: Influence of atomic hydrogen on oxygen elimination and passivation of the crystal defects
Authors: Morvan D. , Cazard-Juvernat I. , Amouroux J.
Published: March 2008

The photovoltaic properties of the polycrystalline silicon depend on the crystallinity and the purity of the material. The thermal plasma process gives us an alternative method of silicon preparation since it is possible to produce an ultrahigh purity with simultaneously a passivation of crystalline defects and active impurities. We demonstrate the efficiency of the plasma purification process and particularly the influence of the atomic hydrogen in an argon thermal plasma on the photovoltaic properties of silicon. The results of the diffusion lengths measured by the photoelectrochemical method show that locally it rises up to 200 μm. We correlate these photovoltaic measurements with the properties of the crystal (defects and purity) by means of measurements by Fourier transform infrared spectroscopy (FTIR) at low temperature (6 K), four probes resistivity technique, scanning electronic microscopy, inductively coupled plasma (ICP), and neutronic activation analyses. We show that the increase of the purity explains the high me asured diffusion lengths. Nevertheless, the thermal conditions of the crystallization of the silicon, due to the specificity of the plasma, lead to defects such as dislocations for which density is particularly high (>106 dis/cm2). The results show that chemical reactions between the atomic hydrogen of the plasma and the oxygen of the silicon occur. They decrease the oxygen content in silicon from 3 × 1017 at./cm3 down to 2 × 1016 at./cm3, while the residual hydrogen in silicon is close to 2 × 1015 at./cm3. This passivates the dangling bonds of ultrapure silicon with a high thermal stability up to 1000 K. The objective of this paper is to demonstrate that the hydrogen in the plasma modifies the electronic properties of the material to achieve a very good photocurrent even though the dislocation density of the silicon is very high.
Multicrystalline silicon material: Effects of classical and rapid thermal processes
Authors: Muller J. C. , Martinuzzi S.
Published: March 2008

For photovoltaic applications silicon is still the predominant material. Besides monocrystalline Czochralski wafers (Cz-Si), multicrystalline sheets (mc-Si) play an important role in terrestrial power applications (almost 50%). Large mc-Si ingots (up to 250 kg) are now produced in large scale by the industry using various directional solidification methods in appropriate crucibles (or molds). However, if the crystallographic properties are now quite satisfactory (columnar structure with large grains of more than 1 cm2, dislocations and intragrains defects), multicrystalline silicon contains larger quantities of impurities than single crystalline silicon which can have detrimental effects on the bulk minority carrier diffusion length (Ln,p). These impurities, including metals as well as high concentrations of carbon and/or oxygen, can degrade the photovoltaic properties of solar cells. Thermal treatments such as gettering, performed in a classical or rapid thermal furnace, studied separately or in conjunction with the doping steps can limit or avoid the degradation of the bulk diffusion length, but its efficiency is strongly dependent on the presence of these impurities in Si.
Probing of microvoids in high-rate deposited a-Si: H thin films by variable energy positron annihilation spectroscopy
Authors: Zou X. , Webb D. P. , Chan Y. C. , Lam Y. W. , Hu Y. F. , Fung S. , Beling C. D.
Published: March 2008

In this paper, positron annihilation measurements have been carried out on a-Si: H thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at high and low rates by means of the variable energy positron beam Doppler-broadening technique. The depth profiles of microvoids in the films grown under different conditions have been determined. We found a smaller void fraction in the surface region of all films compared to the bulk, and a smaller void fraction in low rate than in high growth rate films. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature, although there appears to be a higher density of defects in the boron than phosphorus doped films. The depth profiles of the microvoid-like defects in the a-Si: H films are extracted by use of the vepfit program.
Wetting and interface microstructure between Sn–Zn binary alloys and Cu
Authors: Suganuma Katsuaki , Niihara Koichi , Shoutoku Takeshi , Nakamura Yoshikazu
Published: March 2008

Sn–Zn binary alloys have been examined as a lead-free solder. Zn distributes in a Sn matrix as platelets. The hypoeutectic alloys show two endothermic peaks in DTA, which correspond to the eutectic and the liquidus temperatures. Three reaction layers are formed at the Sn–Zn/Cu interface without containing Sn: the thick γ–Cu5Zn8 adjacent to the solder, the thin β′–CuZn in the middle, and the thinnest layer adjacent to Cu. Although many nonwetting regions and voids are formed at the interface because of poor wetting, soldering at 290 °C can form a rigid interface, and tensile strength reaches about 40 MPa.
Metal ceramic interface toughness I: Plasticity on multiple length scales
Authors: Kiely J. D. , Bonnell D. A.
Published: March 2008

The fracture toughness of Ni-sapphire interfaces was measured as a function of interfacial embrittlement. Embrittlement was controlled by segregating sulfur to the interface, by limiting the presence of moist air in the test environment, and by altering the distribution of interfacial particulates. Fracture energies scaled with the degree of embrittlement and ranged from 8.5 to 34.2 J/m2. Scanning probe microscopy revealed four distinct plasticity features, the heights of which ranged from 1 μm to 0.5 nm. Plasticity generation processes are determined based on the variation of feature height and position with fracture energy, allowing features associated with the interface decohesion process to be identified.
Metal ceramic interface toughness II: Mechanisms of fracture and energy dissipation
Authors: Kiely J. D. , Bonnell D. A.
Published: March 2008

Based on observations of plasticity on fracture surfaces, we propose two fracture mechanism for Ni-sapphire interfaces. A brittle-type mechanism is proposed for the decohesion of Ni from sapphire by which cracks advance in increments of 20 nm. When particulates that increase the interface strength are present, debonding occurs at the leading edge of the particulate, and unsteady crack advance occurs. Additionally, toughening mechanisms are proposed for each type of plasticity feature observed, and the fracture energy of each mechanism is quantified. Comparison of energy dissipated by these mechanisms with measured fracture energies indicates how the fracture energy of the interface varies with sulfur segregation and environmental embrittlement.
Annealing of mesoporous silica loaded with silver nanoparticles within its pores from isothermal sorption
Authors: Cai Weiping , Zhang Lide , Zhong Huicai , He Guoliang
Published: March 2008

Influences of annealing on the structure of mesoporous silica loaded with silver (Ag) nanoparticles, and on the coarsening of Ag particles within pores of the host were investigated from isothermal sorption. Doping a small amount of Ag nanoparticles into pores of silica and subsequent annealing decreases the measured values of specific surface area and pore volume of porous silica significantly. This is attributed to the presence and coarsening of Ag particles within pores or channels between pores, which result in more and more isolated and unmeasured free spaces. The measured value of a specific surface area for the doped samples cannot represent the real value, which is, in fact, unable to be measured directly. During additional annealing, Ag particles within silica coarsen mainly according to the mechanism of formation of Ag adatoms on pore wall and diffusion of the adatoms along with pore walls. Only the larger particles located in the larger pores can continuously grow. The smaller particles and those located in the channels or pores with smaller dimension will disappear. The activation energy of the ripening process was estimated to be about 0.60 eV, and the migration barrier of Ag adatom on the pore wall of silica is about 0.10 eV.
Tensile testing low density multilayers: Aluminum/titanium
Authors: Josell D. , van Heerden D. , Read D. , Bonevich J. , Shechtman D.
Published: March 2008

Yield stresses, ultimate tensile strengths, and specific strengths of aluminum/titanium multilayer thin films are determined from the results of uniaxial tensile tests. The plasticity in the stress-strain curves, the nature of the fracture surfaces, and the relationship of the yield stress and the bilayer thickness are discussed. Properties are compared with those of other multilayer materials published in the literature.
Synthesis and characterization of Y2O3: Eu3+ powder phosphor by a hydrolysis technique
Authors: Jiang Yong Dong , Wang Zhong Lin , Zhang Fuli , Paris Henry G. , Summers Christopher J.
Published: March 2008

A forced hydrolysis technique is used for preparing Y2O3: Eu3+ powders at low processing temperatures. The technique uses yttrium oxide, europium oxide, and nitric acid and urea, and has the potential for large-scale production for industrial applications. Several experimental conditions have been examined to optimize the luminescence efficiency. The best result was found to be at 2 mol% Eu doping and a 2 h firing of 1400 °C. Microstructural information provided by x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been applied to interpret the observed luminescent properties.
Changes in optical transmittance and surface morphology of AlN thin films exposed to atmosphere
Authors: Watanabe Yoshihisa , Sakuragi Yoshifumi , Amamoto Yoshiki , Nakamura Yoshikazu
Published: March 2008

Aluminum nitride (AlN) thin films have been prepared by the ion-beam assisted deposition (IBAD) method, and the influence of exposure to different atmosphere on optical transmittance and surface morphology has been studied. AlN films have been prepared with the nitrogen ion beam energy of 0.1, 0.2, or 1.5 keV. Synthesized films have been exposed to the following conditions: (i) laboratory air (RT and 40–60% RH), (ii) saturated humidity air (RT and 80–90% RH), and (iii) elevated temperature air (100 °C and 10–20% RH). Optical transmission spectrum in the wavelength region from 190 to 2200 nm has been measured by a UV-visible spectrometer every week. Surface morphology of the films has been observed with an optical microscope (OM), and phase identification has been performed by thin film x-ray diffraction (TFXRD). The optical transmittance has not changed drastically after exposure both to the laboratory air and the saturated humidity air for 60 weeks and after exposure to the elevated temperature air for 48 weeks. Observations by OM showed that round-shaped substances were formed on the film surfaces after exposure to the atmosphere, and the size of the substances on the film surface exposed to saturated humidity air is much larger than those on the surface exposed to other atmosphere. The results of TFXRD revealed that the AlN diffraction peaks have gradually decreased with exposure time, but any new phase due to reaction products has not been detected for the samples exposed to the laboratory air, the saturated humidity air, or the elevated temperature air. From the present results, it is concluded that the IBAD AlN films can be applied in low humidity air without losing high transparency up to 60 weeks, and the films prepared with 1.5 keV ion beam show better durability than the films prepared with 0.1 or 0.2 keV ion beam for exposure to the saturated humidity air.
Textures of thin copper films
Authors: Kuschke W-M. , Kretschmann A. , Keller R-M. , Vinci R. P. , Kaufmann C. , Arzt E.
Published: March 2008

The textures of thin copper films were determined quantitatively by measuring (111) pole figures with x-ray diffraction. Measurements were performed on a variety of samples, differing in copper film thickness and deposition technique, diffusion barrier material, and the presence or absence of a cap layer. Texture changes due to an annealing treatment were also recorded and correlated with stress measurements by the wafer-curvature technique. It is found that the deposition method (PVD vs CVD) has a strong effect on texture, barrier layer effects range from negligible to significant depending on the barrier material, and the effect of a cap layer is insignificant.
Preparation and size evaluation of nanometer gadolinium powder
Authors: Shao Y. Z. , Shek C. H. , Lai J. K. L.
Published: March 2008

Nanometer-size gadolinium powders (nm-Gd) have been prepared by means of evaporation condensation of Gd atoms within inert gas atmosphere. Microscopic analyses, based on measurements of small angle x-ray scattering (SAXS), x-ray diffraction (XRD), Raman scattering spectrum (RSS), and observation with transmission electron microscope (TEM), have been carried out in order to evaluate the size and size distribution of the as-prepared nm-Gd powder. It turns out that the size distribution function of nm-Gd powder agrees very well with the distribution function of Rayleigh instead of logarithmic distribution. The mean size d of nm-Gd powders bears a linear relationship with the logarithm of the pressure p of the inert gas atmosphere as follows: d = a + b · ln p. A discussion concerning the influence of particle size of nm-Gd powder on nanostructured material parameters such as the size distribution, specific surface area, and the percentage of interface atoms have been given in detail.
Properties of polyimide shells made using vapor phase deposition
Authors: Alfonso E. L. , Chen S. H. , Gram R. Q. , Harding D. R.
Published: March 2008

Hollow polyimide shells, to be used in inertial confinement fusion experiments, were fabricated by codepositing monomer precursors onto spherical mandrels. Polyimide shells with 700 to 950 μm diameters and 4 to 13 μm wall thicknesses were produced. The shell wall shrunk 20–30% due to imidization. Burst and buckle pressure tests on these shells yielded estimated mechanical strength properties: ∼ 15 GPa elastic modulus and ∼ 300 MPa tensile strength. The permeability of D2 through polyamic acid at 298 K was 7.4 × 10−17 mol · m/m2 · Pa · s and increased to 6.4 × 10−16 mol · m/m2 · Pa · s upon curing the shell to 150 °C. The permeability of D2 at 298 K through vapor-deposited polyimide flat films was 240 times greater than through polyamic acid.
A study on the residual stress measurement methods on chemical vapor deposition diamond films
Authors: Kim Jung Geun , Yu Jin
Published: March 2008

Diamond films were deposited on the p-type Si substrate with the hot filament chemical vapor deposition (HFCVD). Residual stresses in the films were measured in air by the laser curvature, the x-ray diffraction (XRD) dϕψ − sin2ψ, and the Raman peak shift methods. All of the measuring methods showed similar behaviors of residual stress that changed from a compressive to a tensile stress with increasing the film thickness. However, values of residual stresses obtained through the Raman and XRD methods were 3–4 times higher than those of the curvature method. These discrepancies involved the setting of materials constants of CVD diamond film, and determination of a peak shifting on the XRD and Raman method. In order to elucidate the disparity, we measured a Young's moduli of diamond films by using the sonic resonance method. In doing so, the Raman and XRD peak shift were calibrated by bending diamond/Si beams with diamond films by a known amount, with stress levels known a priori from the beam theory, and by monitoring the peak shifts simultaneously. Results of each measuring method showed well coincidental behaviors of residual stresses which have the stress range from −0.5 GPa to +0.7 GPa, and an intrinsic stress was caused about +0.7 GPa with tensile stress.
Solidification of undercooled molten spinodal
Authors: Yuen C. W. , Kui H. W.
Published: March 2008

When molten Pd40.5Ni40.5P19 is undercooled way below its liquidus Tl, liquid state spinodal decomposition is observed. Crystallization of this system is particularly interesting because it has plenty of interfaces. The microstructure of an as-crystallized specimen can be divided into four regions, namely, A: random spinodal; B: aligned and elongated spinodal; C: coarsened spinodal and island structure; and D: rod structure and ternary eutectics. The origin of these different microstructures is discussed.
Interfaces and properties of Al – Si alloy zircon particulate composites
Authors: Ejiofor J. U. , Reddy R. G.
Published: March 2008

Zircon-particle-dispersed Al−13.5Si−2.5Mg is a structural composite material being investigated for lightweight, tribological applications. The conventional, powder-processed material, in the temperature range of 22–100 °C, yielded a low coefficient of linear thermal expansion (CTE) of 7.8 × 10−6 °C at 0.15 volume fraction (Vf), a 64% reduction of that of the alloy. The dry sliding wear rate and the coefficient of friction measured by the pin-on-the-plate technique at 4 kg load decreased significantly by 99% and 35.5%, respectively. A significant reduction, by 29%, in wear rate of the alloy was observed to occur only when more than 0.03Vf zircon was dispersed. An x-ray study showed that the interface reaction products consist of compounds of Mg, Ce, Cu, and Nb. Tensile failure of the reaction-sintered parts revealed a ductile mode of fracture, with the path traversing both through voids and the bonded particles while interface failure was observed in parts without Mg. An analysis of both the tribological and tensile properties showed that an optimal performance of this alloy at 0.15Vf zircon is achieved when the Mg content is between 2.5 and 3.5 wt. %.
On the fractal nature of crack branching in MgF2
Authors: Mecholsky J. J. , Linhart Richard , Kwitkin Brian D. , Rice Roy W.
Published: March 2008

Nineteen disks of IR window grade, hot pressed magnesium fluoride (˜0% porosity, grain size ˜1 μm) previously loaded in ring-on-ring flexure tests were used to analyze the crack branching patterns. Fractal geometry was used to determine the crack branching fractal dimension which was named the crack branching coefficient or CBC. The failure stress was proportional to the CBC and the number of pieces generated during the fracture. Thus, the number of pieces was proportional to the crack branching coefficient. The crack branching coefficient is distinct from the fractal dimension obtained from the onset of mist and hackle on the fracture surface. The fractal dimension of the fracture surface is, in most cases for brittle materials, a constant and related to the crack tip stress field. The crack branching fractal dimension is a function of the stress at fracture and the far-field stress distribution, or in other words, related to both the type and magnitude of loading. The findings in this work have strong implications for many commercial processes such as comminution, attrition, grinding, and basic studies in crack branching.
Zirconolite transformation under reducing conditions
Authors: Begg B. D. , Vance E. R. , Hunter B. A. , Hanna J. V.
Published: March 2008

The structural behavior of zirconolite (CaZrTi2O7) under reducing conditions at high temperature has been studied, mainly by scanning electron microscopy (SEM) and x-ray diffraction (XRD), but also with x-ray absorption spectroscopy, thermogravimetry, and electron paramagnetic resonance. The partial reduction of Ti4+to Ti3+, associated with a reducing atmosphere heat treatment, led to the initial formation of perovskite (CaTiO3) as a second phase. As the concentration of Ti3+in the zirconolite increased, so did the amount of perovskite until the zirconolite was totally transformed into a fluorite structured phase. Analysis of the reduced zirconolites showed them to be consistently deficient in Ca and enriched in Zr, in proportion to the concentration of Ti3+. To determine how electroneutrality was preserved in these reduced zirconolites, a series of zirconolites were prepared in air using In3+and Ga3+as models for Ti3+. These samples were then investigated by neutron and x-ray diffraction, SEM, solid state nuclear magnetic resonance (NMR), and nuclear quadrupole resonance (NQR).71Ga MAS NMR studies of the Ga substituted zirconolite exhibited a narrow resonance at ˜13 ppm which was attributed to six-coordinate Ga incorporated in a trace perovskite phase. Broadline71Ga NMR and69/71Ga NQR were required to characterize the Ga incorporated in the zirconolite. The resultant quadrupolar parameters ofCQ= 30.0 ± 0.05 MHz and η = 1.0 ± 0.03 indicate that the Ga site is in a highly distorted environment which would suggest that it is located on the five-coordinate Ti site within the zirconolite lattice. These results were complemented by Rietveld refinement of the neutron diffraction data from the In-doped zirconolite sample, which was optimal when all the In was located on the five-coordinate Ti site with the excess Zr located on the Ca site. It would therefore appear that charge compensation for the presence of Ti3+in zirconolite is effected via the substitution of an appropriate amount of Zr on the Ca site. The Ti3+-stabilized fluorite structure was readily oxidized back to a single phase zirconolite upon heating in air.
A new hybrid two-zone/crucible furnace process for the growth of epitaxial Tl2Ba2CaCu2O8 superconducting films
Authors: Siegal M. P. , Overmyer D. L. , Venturini E. L. , Dominguez F. , Padilla R. R.
Published: March 2008

Epitaxial Tl2Ba2CaCu2O8 (Tl-2212) films ∼5500 Å thick are grown on LaAlO3(100) substrates using a new hybrid two-zone/crucible furnace process enabling precise control of thallination. This method combines the best features of both conventional crucible and two-zone processing for the first time: superb film properties and reduced handling of hazardous Tl-oxide powders. Single-phase, highly caxis oriented Tl-2212 films are grown with smooth morphology, Meissner transition ∼103 K, and critical current density ∼1.1 × 107 A/cm2 at 5 K for twenty consecutive runs without having to change or add to the Tl-oxide source.
Novel calcium phosphate ceramics prepared by powder sintering and crystallization of glasses in the pyrophosphate region
Authors: Kasuga Toshihiro , Abe Yoshihiro
Published: March 2008

Silica-free phosphate glasses containing small amounts of Na2O and TiO2 with the composition of Ca/P = 1 in atomic ratio were obtained. When powder compacts of the glasses were heated at 850 °C, they crystallized and subsequently sintered, resulting in glass-ceramics containing β–Ca3(PO4)2 and β–Ca2P2O7 crystalline phases. The glass-ceramics show a relatively high fracture toughness of KIC ≈ 2 MPa m0.5. By soaking in simulated body fluid at 37 °C, a calcium phosphate phase was formed newly on the surface of the glass-ceramics.
Synthesis and Na+conduction properties of the ceramics of Na5YSi4O12-type phosphate-substituted solid solutions
Authors: Yamashita Kimihiro , Matsuda Motohide , Umegaki Takao
Published: March 2008

The Na+-superionic conducting ceramics with Na5YSi4O12-type structure were synthesized using the composition formula of Na3+3x−yY1-xPySi3-yO9, in which some portions of Na+ions are considered to replace Y3+as Na(13+8x−4y/3)[Na(4x−1)/3Y(4–4x)/3] [P4y/3Si(12–4y)/3]O12according to Na5YSi4O12-type composition formula. The average ionic radius of the 6-coordinated Y3+sites [= (4x− 1)/ 3 ×rNa+ (4 - 4x)/3 ×rY] approximately covered the range ofrGdand torSm. The ionic conduction properties were strongly dependent upon the combination of composition parameters,xandy. In this report, the dependence of conduction properties on the composition is discussed on the basis of structural considerations.
A novel organothermal reduction process for producing nanocrystalline Ni2P with a circular-shaped flake morphology
Authors: Yu Shu-Hong , Yang Jian , Wu Yong-Sheng , Han Zhao-Hui , Shu Lei , Xie Yi , Qian Yi-Tai
Published: March 2008

An organothermal reduction process has been successfully developed for synthesis of nanocrystalline Ni2P in benzene at 140 °C. An x-ray powder diffraction pattern (XRD) indicated that the product was pure hexagonal Ni2P phase with a cell constants a =0.5866 and c = 0.3377 nm. Transmission electron microscopy (TEM) showed that the average particle size of the powders was 40 nm with a circular-shaped flake morphology.
Metallothermic reduction as an electronically mediated reaction
Authors: Okabe Toru H. , Sadoway Donald R.
Published: March 2008

The commonly held view that metallothermic reduction is strictly a chemical reaction and that the process is rate limited by mass transfer has been found to be incomplete. In a study of the production of tantalum powder by the reaction of K2TaF7 with sodium, it has been shown that there are two dominant kinetic pathways, both involving electron transfer. Furthermore, the overall rate of reaction is limited by electron transport between the reactants. This indicates that metallothermic reduction is an “electronically mediated reaction” (EMR). Experiments found that the location of the tantalum deposit and its morphology are governed by the reaction pathway.
The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates
Authors: Huang Y. , Vuchic B. V. , Carmody M. , Baldo P. M. , Merkle K. L. , Buchholz D. B. , Mahajan S. , Lei J. S. , Markworth P. R. , Chang R. P. H. , Marks L. D.
Published: March 2008

The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45° oriented growth to the 0° oriented growth.
Microstructural studies of PrBa2Cu3Oy during melt processing
Authors: Reddy E. Sudhakar , Rajasekharan T.
Published: March 2008

The microstructures of PrBa2Cu3Oy during melt processing have been studied for samples quenched at different stages of the thermal cycle. The absence of the Pr2BaCuO5 phase in the Pr–Ba–Cu–O phase diagram, analogous to the Y2BaCuO5 (211) phase in the Y–Ba–Cu–O system, makes it interesting to study the microstructure of PrBa2Cu3Oy (Pr-123) during melt processing. The nature and morphology of the properitectic particles, the nucleation of Pr-123, and the microstructures resulting from melt processing are investigated and discussed as compared with those in YBa2Cu3Oy. At the properitectic stage the morphology of PrBaO3 (Pr-110) particles is angular. Pr-123 is found to nucleate on all Pr-110 particles with a needle-like morphology, whereas in other 123 systems no preferred morphology for the 123 during nucleation is observed. The melt textured microstructure of Pr-123 revealed similar features like domain formation with the trapped properitectic phase. The only difference is the absence of platelet gaps within domains as observed in other 123 systems. All these observations suggest that as compared to other 123 systems the microstructure of the Pr–Ba–Cu–O system behaves differently due to the absence of the analogous 211 phase.