bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of a substrate pretreatment for hot filament CVD of diamond
Authors: Menningen K. L. , Childs M. A. , Toyoda H. , Anderson L. W. , Lawler J. E.
Published: September 2007

The absolute concentration of methyl radicals (CH3) and the mole fraction of acetylene (C2H2) are measured in a hot filament chemical vapor deposition (CVD) system both during and after an initial pretreatment that has been used successfully in microwave plasma and oxyacetylene torch CVD systems to produce more uniform and higher density crystal nucleation. The pretreatment technique, which consists of deposition for a relatively short time with a high input concentration of hydrocarbon in the feed gas, was studied for both methane (CH4) and C2H2 as the input hydrocarbon diluted in H2. Scanning electron micrographs of diamond films deposited under the conditions studied indicate that the pretreatment using CH4 is not effective in increasing the crystal nucleation density, but is moderately effective in increasing the crystal size. The C2H2 pretreatment has no apparent effect upon either the crystal size or nucleation density. The spectroscopie measurements suggest that the surface condition of the filament is the prominent factor affecting the gas phase chemistry both during and after the pretreatment stage.
Electrical resistance of a carbon nanotube bundle
Authors: Langer L. , Stockman L. , Heremans J. P. , Bayot V. , Olk C. H. , Van Haesendonck C. , Bruynseraede Y. , Issi J-P.
Published: September 2007

The first direct electrical resistance measurements performed on a single carbon nanotube bundle from room temperature down to 0.3 K and in magnetic fields up to 14 T are reported. From the temperature dependence of the resistance above 2 K, it is shown that some nanotubes exhibit a semimetallic behavior akin to rolled graphene sheets with a similar band structure, except that the band overlap, Δ ≈ 3.7 meV, is about 10 times smaller than for crystalline graphite. In contrast to graphite which shows a constant low-temperature resistivity, the nanotubes exhibit a striking increase of the resistance followed by a broad maximum at very low temperatures. A magnetic field applied perpendicular to the sample axis decreases the resistance. Above 1 K, this behavior is consistent with the formation of Landau levels. At lower temperatures, the resistance shows an unexpected drop at a critical temperature which increases linearly with magnetic field. These striking features could be related to the unique quasi-one-dimensional structure of the carbon nanotubes.
Effect of substrates on the growth and properties of LiNbO3 films by the sol-gel method
Authors: Hur Nam H. , Park Yong K. , Won Dong H. , No Kwangsoo
Published: September 2007

Thin films of LiNbO3 were fabricated on sapphire(012), MgO(OOl), and Si(111) substrates by the sol-gel process. Under optimized conditions, films deposited onto sapphire(012) were epitaxially grown. Preferred orientations, however, were not observed in the films on MgO(001) and Si(111) by x-ray diffraction measurements. Morphology of the epitaxial films on sapphire(012) was examined by scanning electron microscopy, which indicated that the films were smooth and had a pore-free surface. Electrical and optical measurements on the epitaxial films revealed that the properties of the films were very similar to those of the single crystalline LiNbO3, while films deposited onto Si(111) did not show any orientational behaviors. The highest quality films with epitaxy were obtained only on sapphire(012). The remaining substrates appeared to be not suitable for growing epitaxial LiNbO3 films by the sol-gel method.
Low-temperature synthesis of ultrafine La0.84Sr0.16MnO3 powder by an autoignition process
Authors: Chakraborty Amitava , Devi P. Sujatha , Roy Sukumar , Maiti H. S.
Published: September 2007

A simple and convenient method for low-temperature synthesis of La0.84Sr0.16MnO3 powder is described. The technique involves autoignition of a carboxylate (citrate + acetate)-nitrate gel resulting from a thermally induced anionie oxidation-reduction reaction to yield an ash, which upon calcination produces the desired powder. The resulting powder is pure, homogeneous, and possesses ultrafine particle size of the order of 0.3 to 0.5 μm. The autoignition is restricted to a particular range of carboxylate to nitrate ratio in the gel. Attempts have been made to understand the ignition process with the help of Thermogravimetry (TG) and Differential Thermal Analysis (DTA) of the samples. The process appears to have a higher degree of reproducibility and a good material yield (more than 96%) suitable for large-scale production.
Effects of electronic and recoil processes in polymers during ion implantation
Authors: Lee E. H. , Rao G. R. , Lewis M. B. , Mansur L. K.
Published: September 2007

It has been shown that ion implantation produces remarkable improvements in surface-sensitive mechanical properties, as well as other physical and chemical properties in polymers. To understand mechanisms underlying such property changes, various polymeric materials were subjected to bombardment by energetic ions in the range of 200 keV to 2 MeV. The magnitude of property changes is strongly dependent upon ion species, energy, and dose. Analysis indicated that hardness and electrical conductivity increased by employing ion species with larger electronic cross sections and with increasing ion energy and dose. The results showed that electronic stopping or linear energy transfer (LET, energy deposited per unit track length per ion) for ionization was the most important factor for the enhancement of hardness, while nuclear stopping or linear energy transfer for displacement generally appeared to reduce hardness.
Diamond nucleation on nickel substrates seeded with non-diamond carbon
Authors: Yang P.C. , Zhu W. , Glass J.T.
Published: September 2007

Oriented diamond films have been nucleated on single crystal nickel substrates seeded with non-diamond carbon and annealed at high temperatures in atomic hydrogen. The non-diamond carbon seeds included graphite powders, fullerene (60) powders, and gaseous carbon species. It was found that these different non-diamond carbon powders or species were effective in the enhancement of oriented nucleation of diamond. The morphologies of diamond films were similar regardless of the types of carbon used, suggesting a common nucleation mechanism involved. Based on the experimental observations, a revised model was developed for the oriented nucleation of diamond on Ni.
Microanalysis of crystalline phases in Tl-1223 superconducting wire using an x-ray microdiffractometer
Authors: Hirano Tatsumi , Usami Katsuhisa
Published: September 2007

We developed an x-ray microdiffractometer using synchrotron radiation with which we analyzed microcrystal structures of heterogeneities in Tl-1223 superconducting wires prepared by different processes, i.e., partial melt and solid/liquid phase reaction. Samples with the nominal composition (Tl0.5Pb0.5)1(Sr0.8Ba0.2)2Ca2Cu3O9 were irradiated by focused SR x-rays of 6 μm × 8 μm size. The diffracted x-rays were two-dimensionally detected with an imaging plate. From crystal structure analysis, we identified the heterogeneities as BaPbO3 and (CaSr)2Cu1O3 which are present in Tl-1223 superconducting wires prepared by both processes. This suggested that these heterogeneous phases coexist with the stable phase in the Tl-1223 phase diagram. Consequently, it is necessary to develop a new processing method such as low temperature annealing or a suitable O2 pressure control method.
Magnetoresistance in a deformed Cu-Ni-Fe alloy with ultrafine multilayer structure
Authors: Chen L.H. , Jin S. , Tiefel T.H. , Ramesh R.
Published: September 2007

The creation of a giant magnetoresistance (GMR) effect in a spinodally decomposed and deformed Cu-20% Ni-20% Fe alloy is reported. The alloy is processed to contain a locally multilayered superlattice-like structure with alternating ferromagnetic and nonmagnetic layers with a size scale of 10-20 Å. The microstructural modification produced a dramatic improvement in room-temperature magnetoresistance ratio from ∼0.6 to ∼5%. The observed magnetoresistance is most likely related to the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase, although the exact mechanism involved may be qualitatively different from the usual GMR picture. A rather unusual temperature-dependence of magnetoresistance ratio, i.e., the room-temperature value being greater than that at 4.2 K, was found.
Thermal transfer printing technique for electrode patterning in cofired ceramic multi-layer devices
Authors: Okuwada Kumi , Okuyama Tetsuo
Published: September 2007

A new mask-less electrode patterning method using a thermal transfer printing technique was investigated. Thermal ink ribbons were prepared, which included more than 50 vol. % conductive metal powder. Arbitrary electrode patterns were designed with a computer and printed out on a ceramic green sheet with a serial thermal printer. The ceramic green sheets with printed electrode patterns were stacked up and cofired to obtain a multi-layer ceramic capacitor.
Microstructural variations as a function of δ in La2−xSrxNiO4+δ
Authors: Sayagués M.J. , Caneiro A. , González-Calbet J.M. , Vallet-Regí M.
Published: September 2007

A microstructural characterization of the La2−xSrxNiO4+δ (0 ⋚ x ⋚ 1) system, prepared with accurate control of the oxygen content, has been performed. The electron diffraction study shows the evolution of the accommodation of compositional variations as a function of δ. For δ > 0.06, interstitial oxygens are ordered, leading to new K2NiF4 superstructural types. Samples with δ < 0.06 accommodate the nonstoichiometry by means of random distribution of anionic vacancies.
Hydration of sodium phosphate-modified high alumina cement
Authors: Ma Weiping , Brown Paul W.
Published: September 2007

High strength can be achieved in high alumina cement (HAC) through the incorporation of phosphate-based additions at levels of 10 and 20 wt. %. In order to establish the mechanism that results in higher strength, the effects of a variety of condensed sodium phosphates (NaPO3)n, (NaPO3)n · Na2O, Na5P3O10, and (NaPO3)3 were studied. The influence of these additions on the kinetics of hydration was studied using isothermal calorimetry. The phosphatic additions enhanced reactivity, but x-ray diffraction analyses did not reveal evidence of new crystalline phosphate-containing hydration products. Microstructural evolution was examined in real time using environmental SEM, and hydration products exhibiting distinct morphologies were observed. The features exhibited ranged from amorphic to polygonal shapes, plates, and fibers. These frequently formed between crystalline calcium aluminate hydrate grains and by doing so appear to provide a means to enhance the strengths of these cements. In spite of the morphological variations, companion energy dispersive x-ray analysis showed that the compositions of these products did not vary widely. Their ranges of compositions are 52-60 wt. % Al2O3, 20-26 wt. % P2O5, and 20-24 wt. % CaO.
Erratum
Authors: Vaidya K.J. , Yang C.Y. , DeGraef M. , Lange F.F.
Published: September 2007

“Heteroepitaxy of rare-earth hexa-aluminates on sapphire” [J. Mater. Res. 9, 410-419 (1994)]
Effect of silver addition on the microstructure of YBa2Cu3O7−x
Authors: Yun Jondo , Harmer Martin P. , Chou Ye T.
Published: September 2007

The variation of grain morphology in silver-doped YBa2Cu3O7−xwas investigated as a function of sintering temperature, atmosphere, and amount of Ag addition. In the presence of the liquid phase formed at 925 °C for undoped samples, and at 910 °C for silver-doped samples, the grain shape and size changed drastically from small and nearly equiaxed to large and elongated. The anisotropy in the grain shape was sensitive to both the silver content and the atmosphere. On the other hand, while the grain size was generally insensitive to the atmosphere, it decreased as the silver content increased. The silver phase, if sufficiently large, would block the grain growth in the matrix. The amount of silver for effective blocking was predicted from a microstructural model, and the prediction was in agreement with experimental results.
Effect of substrate materials on laser deposited Nd1.85Ce0.15CuO4−y films
Authors: Prasad Beesabathina D. , Salamanca-Riba L. , Mao S.N. , Xi X.X. , Venkatesan T. , Wu X.D.
Published: September 2007

The growth morphology and interface structure of Nd1.85Ce0.15CuO4−y (NCCO) films grown by pulsed laser deposition on two different types of substrates, “perovskite” LaAlO3 (LAO) and SrTiO3 (STO) and “fluorite” Y2O3-stabilized ZrO2 (YSZ), were studied using cross-sectional electron microscopy. Structurally, the NCCO films are different when grown on the two types of substrates in three aspects: (i) epitaxy, (ii) substrate-film intermixing, and (iii) substrate-film interface roughness. In general, films deposited on “fluorite” substrates showed better superconducting properties than the films grown on “perovskite” substrates, especially for thinner films. Lattice mismatch considerations are not sufficient to explain the observed differences since films grown on the YSZ substrate showed sharp substrate-film interface in spite of their large lattice misfit. The atomic arrangements at the interface were analyzed in terms of electrostatic energy (charge balance) and matching of the oxygen sublattices in order to account for the experimental results.
Grain growth behavior in Fe3Al alloys fabricated by different methods
Authors: Rabin B.H. , Wright J.K. , Wright R.N. , Sellers C.H.
Published: September 2007

Grain sizes were measured after various heat treatments in three Fe3Al alloys having similar composition that were fabricated using the techniques of ingot metallurgy (cast and wrought), hot extrusion of prealloyed powder, and hot isostatic pressing (HIP) of elemental powders. The ingot metallurgy (I/M) material exhibited normal grain growth behavior at temperatures above 750 °C, in agreement with previous observations. Both powder metallurgy (P/M) materials displayed unusual resistance to grain growth compared to the I/M alloy. In the case of the prealloyed P/M material, the initial (recrystallized) grain size was larger than the initial grain size of the I/M material, although little grain growth was observed for heat-treatment temperatures up to 1100 °C. At higher temperatures grain growth occurred at a rate comparable to that observed to the I/M alloy. The elemental powder P/M material exhibited similar grain growth behavior to the prealloyed P/M material, although the initial (as-HIPed) grain size was considerably smaller. Transmission electron microscopy (TEM) indicated that the grain growth resistance of the P/M materials could be attributed to grain boundary pinning by oxide particles presumed to originate from the powder particle surfaces. The difference in the stable grain size between the prealloyed and elemental powder P/M materials was attributed to the nature of the particle dispersions resulting from processing.
Current-voltage characteristics of ultrafine-grained ferroelectric Pb(Zr, Ti)O3 thin films
Authors: Hu H. , Krupanidhi S.B.
Published: September 2007

Room-temperature current-voltage dependence of ultrafine-grained ferroelectric Pb(Zr, Ti)O3 thin films has been investigated. Both strong varistor type behavior and space charge limited conduction (SCLC) were observed. Differences in the current-voltage characteristics are attributed to differences in the nature of the grain boundaries resulting from variations in processing conditions. The strong varistor type behavior is believed to be due to the presence of highly resistive grain boundaries and thus may be termed grain boundary limited conduction (GBLC). A double-depletion-layer barrier model is used to describe the origin of high resistivity of the grain boundaries. It is suggested that the barrier height varies significantly with the applied field due to the nonlinear ferroelectric polarization, and that the barrier is overcome by tunneling at sufficiently high fields. In some other cases, the resistivity of the grain boundaries is comparable to that of the grains, and therefore the intrinsically heterogeneous films degenerate into quasi-homogeneous media, to which the SCLC theory is applicable. As such, a unified grain boundary modeling reconciles different types of conduction mechanisms in the ultrafine-grained ferroelectric thin films. This grain boundary modeling also well accounts for some other dc-related phenomena observed, including abnormal current-voltage dependencies, remanent polarization effect, electrode interface effect, and unusual charging and discharging transients. In addition, many other electrical properties of the ferroelectric films may be better understood by taking the effect of grain boundaries into account.
Crystal growth, morphology, structure, and properties of HNaMP2O7 crystals where M = Co and Ni
Authors: Byrappa K. , Dutt Umesh B.V. , Clearfield A. , Poojary Damodara M.
Published: September 2007

The HNaMP2O7 (where M = Co and Ni) new Na+ superionic pyrophosphates were obtained by the hydrothermal method at lower PT conditions (T = 250 °C, P = 100 atm). The solubility, complexation with reference to the solvent-solute interaction, and the growth process have been studied in detail. A new investigation on the crystal structure of these compounds showed that the title compounds do not contain Zr as reported previously. The crystal morphology and properties have also been studied.
The effect of ballpoint pen ink coating on the nucleation enhancement of low-pressure diamond
Authors: XiLing Peng
Published: September 2007

A novel technique to enhance the nucleation of low-pressure diamond on silicon (100) was discussed in this study. It was found that coating the silicon with ballpoint pen ink can greatly increase the diamond nucleation density when the coating was followed by heat treatment at 100 °C–400 °C. Moreover, the optimum enhancement effect was reached when the ink coating was pre-heat-treated at 300 °C × 30 min. Further SEM observation showed that heat treatment at 200 °C-400 °C produced many tiny carbonaceous particles on ballpoint pen ink-coated silicon. Particularly, the nucleation density of diamond on differently treated silicon, such as ink-coated, diamond paste scratched and polished silicon wafers, was compared using the SEM technique. The diamond structure was also characterized by Raman spectroscopy.
Superconductivity of epitaxially grown α-axis YBCO films on SrTiO3 substrate
Authors: Ito W. , Mahajan S. , Yoshida Y. , Watanabe N. , Morishita T.
Published: September 2007

The a-axis oriented YBa2Cu3Ox (YBCO) films were epitaxially grown on (100) SrTiO3 substrate by dc-100 MHz hybrid plasma sputtering. The films prepared at different temperatures with and without in situ annealing had different superconductivity, which was improved with the degradation of the crystallinity of the films. The Raman spectra for the films were very similar to each other and to that expected for YBa2Cu3O7, in spite of the different superconductivity. This indicates the importance of the symmetry of the Cu–O chains rather than the oxygen content for the superconductivity. In Rutherford backscattering measurements using a 3.05 MeV He2+ ion beam, an increase of dechanneling due to the barium atoms along the film depth was clearly observed only for the most improved superconducting film. This result suggests that the relief of the strain contained in the film is also important for improving the superconductivity in the case of a-axis oriented YBCO films.
Ultralow load indentation hardness and modulus of K – and α–Al2O3 CVD coatings
Authors: Söderlund E. , Reineck I. , Rowcliffe D.J.
Published: September 2007

Metastable k–Al2O3 often occurs as islands in thin α–Al2O3 coatings produced by CVD. In this investigation a thick single-phased K–Al2O3 coating was produced in order to determine the mechanical properties of the K-phase. As a comparison, a CVD coating as well as a sintered bulk specimen of α–Al2O3 were studied. The mechanical behavior was probed by a depth-sensing indentation (nanoindentation) system on polished taper and cross sections at several applied loads. Hardness and elastic modulus were derived and are discussed in conjunction with the crystal structure and the microstructure of the two materials. K–Al2O3 shows a marked microstructural and structural anisotropy, which is also reflected in anisotropic mechanical properties. Parallel to the c-axis, which, in this study, closely coincided with the growth direction, both the hardness and the elastic modulus are significantly higher than in the perpendicular direction. α–Al2O3 has the same hardness and elastic modulus in the coating and in the bulk form and shows no clear anisotropy in microstructure. If the two alumina materials are compared, K–Al2O3 is significantly harder than α–Al2O3 in the growth direction (on the taper section), whereas it is significantly softer in the perpendicular direction. In either of the loading directions, the elastic modulus of K–Al2O3 is significantly lower than in α–Al2O3.
Effect of precursors on the combustion synthesis of TiC-Al2O3 composite
Authors: Choi Yoon , Rhee Shi-Woo
Published: September 2007

In the combustion synthesis of TiC-Al2O3 composites from TiO2, Al, and C, different types of precursors, i.e., anatase and rutile TiO2, and graphite and carbon black were used. The measurements of combustion wave velocity showed that the reactivity was higher with graphite as a carbon source and anatase as a TiO2 source. This was also confirmed by analyzing the degree of conversion of reactants to products. For the precursors investigated, the wave propagation of the 3TiO2-4Al-3C system diluted by Al2O3 showed that the limit of wave propagation was more dependent on carbon source than on TiO2. The wave front of all the samples proceeded in unstable combustion mode. Temperature profiles in the reaction zone suggested that the heat-affected zone was broader in the case of graphite carbon source than carbon black. The microstructures and chemical composition of the products were also studied.
The effect of fiber orientation on matrix plasticity and fracture behavior of SiC fiber-reinforced titanium matrix composites
Authors: Chiu Hsing-Pang , Jeng S.M. , Yang J-M.
Published: September 2007

The effect of fiber orientation on the matrix plasticity and fracture behavior of SCS-6 fiber-reinforced Ti-15V-3Al-3Cr-3Sn composites was studied. The laminates used in this study were [0]6, [0/±45]s, and [90/±45]s. Three-point bending tests were conducted on chevron-notched specimens to determine the crack initiation energy, fracture toughness, and fracture strength as a function of notch length. The critical energy release rate was determined from the slope of the crack initiation energy versus notch length curve. The damage evolution and development of the matrix plastic deformation zone at the notch tip during the crack initiation and propagation as a function of fiber orientation were also determined. The relationships among the crack-tip matrix plastic deformation zone size, the critical energy release rate, and notch strength of the composites were discussed.
Dimensional changes in highly oriented pyrolytic graphite due to electron-irradiation
Authors: Koike J. , Pedraza D.F.
Published: September 2007

One of the main problems found in the nuclear applications of graphite is its dimensional instability under irradiation, involving both swelling and shape changes. In order to understand better the mechanisms that give rise to these changes, highly oriented pyrolytic graphite was irradiated with 300 keV electrons at temperatures between 25 and 657 °C in a transmission electron microscope (TEM). Microscopic dimensional changes and structural disordering were studied in directions parallel and perpendicular to the graphite basal plane. Changes in the specimen length were investigated by measuring the distance between two markers on the specimen surface in TEM images. Changes in the lattice parameter and the crystalline structure were studied by a TEM diffraction technique. In agreement with reported results, large increases in the specimen length and the lattice parameter were observed along the c-axis direction, whereas a relatively small decrease was observed along the a-axis. In irradiation studies conducted at room temperature, it was found that the dimensional change saturates at high dose, at an elongation along the c-axis direction of about 300%. High resolution microscopy revealed that the microstructure had become nanocrystalline. Electron energy loss spectroscopy results showed that the volume change was recovered at this stage. These observations are discussed in terms of point defect evolution and its effects on the microstructure of irradiated graphite.
Preparation and characterization of (Bi,Pb)2Sr2Ca2Cu3O10+x superconducting thick films on Ag tape using the screen-printing technique
Authors: Hornung R. , Neumüller H-W. , Wilhelm M. , Tomandl G.
Published: September 2007

Bi-Sr-Ca-Cu-O phases provide continuous manufacturing of tapes in long lengths using conventional techniques. Thick films of the BPSCCO 2223 phase [(Bi, Pb)2Sr2Ca2Cu3O10+x] were successfully prepared on Ag tapes by combining the processes of screen-printing with organic binders, cold deformation, and sintering.1 Technical and economical studies revealed that these processes have optimal properties for conductor fabrication. The effect of atmosphere and powder composition on the formation of the 2223 superconductor phase was studied on two different composites: BPSCCO/Ag (open system) and Ag/BPSCCO/Ag (closed system). For the open system, both the evaporation of lead had to be avoided and the presence of additional “catalytic” Ag grains within the layer is necessary to promote the reaction of 2223 phase. Critical current densities jc of 6–12 ± 103 A/cm2 (77 K, O T) were achieved in samples of the closed system.
Synthesis and thermal expansion behavior of Ba1+x Zr4P6−2xSi2xO24 and Sr1+xZr4P6−2xSi2xO24 systems
Authors: Huang Chi-Yuan , Agrawal D.K. , McKinstry H.A. , Limaye Santosh Y.
Published: September 2007

NaZr2P3O12 (NZP) is emerging as an important family of a large number of isostractural compounds in which several members have demonstrated very low thermal expansion characteristics. Ba1+xZr4P6−2xSi2xO24 and Sr1+xZr4P6−2xSi2xO24 crystalline solutions are two such systems belonging to the NZP family. Here, we report the bulk thermal expansion and axial thermal expansion behavior of various compositions in these systems. The low expansion behavior of these materials is attributed to their unique crystal structure, which is framework open structure, and can accommodate numerous ionic substitutions at various lattice sites.
Nucleation and growth during the chemical vapor deposition of diamond on SiO2 substrates
Authors: Rankin Janet , Boekenhauer Rachel E. , Csencsits Roseann , Shigesato Yuzo , Jacobson Matthew W. , Sheldon Brian W.
Published: September 2007

The early stages of microwave-plasma assisted CVD of diamond on fused silica and silicon substrates were investigated. Nucleation densities on fused silica were somewhat lower than on silicon; however, the diamond growth rates on fused silica were faster. These results suggest that the substrate alters the plasma chemistry near the substrate. Transmission electron microscopy showed a relatively smooth interface between the diamond grains and the SiO2 surface. At low nucleation densities, the growth kinetics on both substrates were linear (i.e., the average feature size was proportional to the deposition time), which indicates that the growth kinetics were initially controlled by reaction(s) at the growing diamond surfaces. The transition to nonlinear growth kinetics observed at higher nucleation densities was probably caused by mass-transport limits.
Erratum
Authors: Sukow C.A. , Nemanich R.J.
Published: September 2007

“Morphology of TiSi2 and ZrSi2 on Si(100) and (111) surfaces” [J. Mater. Res. 9, 1214–1227 (1994)]
Effect of trace carbon on the uv-induced behavior of aluminum nitride ceramics
Authors: Kaplan J.C. , Gerhardt R.A.
Published: September 2007

The effect of uv irradiation on the material properties of AlN containing low oxygen content (<0.3 wt. %) has been investigated. Upon irradiation with a 150 W Hg-Xe arc lamp, increases in dielectric loss and thermal conductivity drops were observed. Changes in the optical properties, including formation of an absorption band at 650 nm, and photodarkening were also observed. All samples were characterized for trace impurities including carbon, calcium, and oxygen. The magnitude of the uv-induced drops in dielectric loss and the absorption at 650 nm of samples tested were found to depend on the presence of trace levels of residual carbon. UV-induced increases in dielectric loss show an inverse relationship, and formation of an absorption band shows a direct relationship to carbon content.
Observation of fractal patterns in C60-polymer thin films
Authors: Gao H.J. , Xue Z.Q. , Wu Q.D. , Pang S.
Published: September 2007

We report the observation of fractal patterns in C60-tetracyanoquinodimethane thin films. The fractal patterns and their microscopic features are described and characterized. The fractal dimension was determined to be 1.69 ± 0.07. According to the characterization results, the observed fractals are compared to the cluster-diffusion-limited-aggregation model. The growth of the fractal patterns in the thin films is also in terms of the existing long-range correlation.
A quantitative measure of internal cavitation in superplastic alloys using photoacoustic analysis
Authors: Kim H.C. , Ahn T.H. , So C.H. , Ma Y. , Zhao X. , Langdon T.G.
Published: September 2007

Internal cavities often develop during the deformation of superplastic alloys. Experiments were conducted to determine whether a nondestructive photoacoustic method may be used to detect the presence of internal cavities in two different commercial Al-based alloys. An analytical procedure was developed to provide quantitative information on the volume fraction of cavitation. The results confirm that the photoacoustic signal can be used to detect the presence of cavities, and it is demonstrated that the quantitative measurements derived from the photoacoustic data are consistent with observations obtained by sectioning and standard metallographic techniques.
Thermodynamic evaluation of reaction products and layering in brazed alumina joints
Authors: Kelkar G.P. , Spear K.E. , Carim A.H.
Published: September 2007

The joints formed by brazing Al2O3to itself or to a Ti-alloy (Ti-6Al-4V) with a Ag–Cu–Ti braze filler were investigated. In the brazing process, Ti in the braze alloy reduces Al2C3to form a series of reaction products which have a layered morphology. The formation of M6X-type compounds, Ti4Cu2O or Ti3Cu3O, at the interface is characteristic of these joints. The other reaction products also belong to the Ti–Cu–O system (with the reduced Al in solution), and hence this subsystem was chosen to assess the thermodynamic stability of the joints. The Ti–Cu–O section was established experimentally at 945 °C, and activities of elements in three of the three-phase regions were estimated based on the phase boundaries of the ternary section and available binary thermodynamic data. The estimated free energies of formation of the two M6X-type compounds, Ti4Cu2O and Ti3Cu3O, are −120 kcal/mol and −122 kcal/mol, respectively. The highly negative values for the free energies of formation suggest that these compounds are thermodynamically stable. The activity data were also used to generate activity diagrams for Ti–Cu–O system. The layer sequences at the joints satisfied the stability requirements based on the ternary section and the activity diagrams, indicating that even though the interfaces formed in a matter of minutes, they were at local thermodynamic equilibrium.
Epitaxial LiNbO3 thin films on sapphire substrates grown by solid source MOCVD
Authors: Lu Z. , Hiskes R. , DiCarolis S.A. , Route R.K. , Feigelson R.S. , Leplingard F. , Fouquet J.E.
Published: September 2007

C-axis LiNbO3 epitaxial films have been grown on c-plane sapphire substrates by solid source metal-organic chemical vapor deposition (MOCVD) using the tetramethylheptanedionate sources, Li(thd) and Nb(thd)4. Stoichiometric LiNbO3 films were deposited from Li(thd)-rich source compositions. Rocking curve FWHM values as low as 0.044°were measured on films grown at 710 °C. Rocking curve peak widths became broader as films were grown at progressively lower substrate temperatures. Single prism coupling experiments revealed clearly visible optical waveguiding, with optical attenuation values as low as 2 dB/cm in the best films.
Influence of the preparing conditions on the physicochemical characteristics of glasses for thick film hybrid microelectronics
Authors: Prudenziati M. , Morten B. , Savigni P. , Guizzetti G.
Published: September 2007

Seven batches of a high-lead glass were used for the preparation of RuO2-based thick film resistors. Investigation of their electrical properties showed a lack of reproducibility of results whose origin was related to changes of the physicochemical properties of the glassy matrix. A systematic investigation of the glass batches, both in form of frit powders and screen printed and fired layers, was carried out with several spectroscopies to detect changes in composition and structure. The spectroscopic methods included x-ray Energy Dispersive Fluorescence (EDS), Scanning Electron Microscopy (SEM), Atomic Absorption (AA), diffuse optical reflection of the powders and specular reflection of the layers, optical transmission, and other complementary methods. The dissolution of Al, due to interaction between the glasses and the alumina substrate, as well as the diffusivity and solubility of Ag due to interaction with the Ag-bearing terminations were measured. The results demonstrated that, apart from small compositional differences, the various batches were characterized by differences in residual stresses, redox reactions, and “microstructure.” The latter was responsible for very notable differences in the optical properties of the glasses, which in turn are closely related with the difference in atomic solubility and diffusivity. Optical spectroscopies have been found to be a suitable means for testing reproducible preparation methods of glass frits for thick-film hybrid microelectronics.
Tetragonal-orthorhombic phase transformation and sintering behavior of KSbOSiO4 (isomorphous derivative of KTP)
Authors: Kanno Yoshinori
Published: September 2007

Fine KSbOSiO4 (KSS) powders have been prepared by a sol-gel method starting from the system of TEOS, KSb(OH)6, H2O, C2H5OH, or mechanochemical mixing method with a stoichiometric mixture of amorphous silica and KSb(OH)6. The KSS crystallized sluggishly into a tetragonal symmetry in low temperature and transformed into an orthorhombic one in higher temperature, indicating the amorphous-like powder patterns in the intermediate step. This amorphization process could be related to some redistribution of the polysilicate network structures. The mechanochemical activation energy stored in the powder surface, as well as the coexisting matrix (KSbO3), retards the transformation. It was concluded that the KSS powders composed of high molecular weight siloxane polymers, which were formed by hydrolysis in the presence of a small amount of NH3 aqueous solution, showed higher sinterability. The sintering, where the calcining process was omitted, enabled the dense tetragonal-type ceramics stabilized at lower temperature, rather than higher temperature, to fabricate.
Investigation of TiC films synthesized by low energy ion bombardment
Authors: He Xiao-Ming , Li Wen-Zhi , Li Heng-De
Published: September 2007

Low energy bombardment of CHn+ at 100-800 eV has been used to prepare TiC film at room temperature by dual ion beam sputtering. The ion bombardment energies and densities obviously affect the metallographic morphology, the crystalline orientation, and constituent ratio of TiC films. TiC films formed under 200-600 eV CHn+ bombarding with 120-190 μA/cm2 possess much finer and compact microstructure in the compressive stress state. Its hardness is in the range of 2650-2880 kgf/mm2. The tribological tests indicate that TiC films synthesized on AISI 52100 steel by DIBS with low energy bombardment exhibit low friction coefficient and good wear resistance.
Physical properties of a-C: N films produced by ion beam assisted deposition
Authors: Rossi François , André Bernard , van Veen A. , Mijnarends P.E. , Schut H. , Labohm F. , Dunlop Hugh , Delplancke Marie Paule , Hubbard Kevin
Published: September 2007

Carbon films with up to 32 at. % of nitrogen have been prepared with ion beam assisted magnetron, using a N2+/N+ beam at energies between 50 and 300 eV. The composition and density of the films vary strongly with the deposition parameters. EELS, SXS, XPS, and IR studies show that these a-C: N films are mostly graphitic and have up to 20% sp3 bonding. Nitrogen is mostly combined with carbon in nitrile (C ≡ N) and imine (C=N) groups. It is shown by RBS and NDP that density goes through a maximum as the average damage energy per incoming ion increases. Positron annihilation spectroscopy shows that the void concentration in the films goes through a minimum with average damage energy. These results are consistent with a densification induced by the collisions at low average damage energy values and induced graphitization at higher damage energy values. These results are similar to what is observed for Ar ion assisted deposition of a-C films. The mechanical properties of these films have been studied with a nanoindenter, and it was found that the hardness and Young's modulus go through a maximum as the average damage energy is increased. The maximum of mechanical properties corresponds to the minimum in the void concentration in the film. Tribological studies of the a-C: N show that the friction coefficient obtained against diamond under dynamic loading decreases strongly as the nitrogen composition increases, this effect being more pronounced at low loads.
Growth of epitaxial β-FeSi2 thin films by pulsed laser deposition on silicon (111)
Authors: Olk C.H. , Karpenko O. P. , Yalisove S. M. , Doll G. L. , Mansfield J.F.
Published: September 2007

Epitaxial films of semiconducting iron disilicide (β-FeSi2) have been grown by pulsed laser deposition. We find that pulsed laser deposition creates conditions favorable to the formation of films with the smallest geometric misfit possessed by this material system. In situ reflection high energy electron diffraction results indicate a layer by layer growth of the silicide. Analysis of transmission electron diffraction data has determined that the films are single phase and that this growth method reproduces the epitaxial relationship: β-FeSi2 (001) ‖ Si(111).
Microstructural inhomogeneities in chemically derived Ba2YCu3O7−x thin films: Implications for flux pinning
Authors: McIntyre P.C. , Cima M.J.
Published: September 2007

A gradient in the density of polytypoidal stacking faults was observed through the thickness of chemically derived epitaxial Ba2YCu3O7−x (BYC) films on (001) LaAlO3. Cross-sectional TEM studies indicated that films of less than 100 nm thickness were faulted, with a high density of polytypoidal stacking faults. A decrease in stacking fault density in thicker films (300-500 nm thick) was found with increasing distance from the most defective layer near the film/substrate interface. An abrupt transition from highly faulted material near the substrate to essentially stacking fault-free BYC in the upper part of the films was observed in several cases. The present observations are compared with the previously reported1 decrease in critical current density with increasing thickness of these films. Possible implications for flux pinning in BYC thin films are discussed.
TEM study of C70 polycrystalline films
Authors: Rusakova I. , Hamed A. , Hor P.H.
Published: September 2007

Using conventional and high resolution TEM, we have studied the microstructure of C70 polycrystalline films, prepared by sublimation of C70 powder onto glass, carbon holey film, and sapphire substrates held at 200 °C. An fcc structure with lattice parameter 1.50 nm is observed for the films on glass and amorphous carbon. A different structure and stronger adherence to the substrate was observed for the thin film grown on sapphire, suggesting a stronger molecule-substrate interaction in this case. Thicker films on sapphire, however, did have fcc structure. In all cases, the film grows in large grains about 100 nm in size, indicating high effective surface mobility of the C70 molecules. Further analysis of the films on carbon holey substrates indicates a preferred [011] film growth orientation, the existence of twins, and a high density of stacking faults. Extended exposure of the films to oxygen did not result in visible structural changes, but strong illumination for several hours in atmosphere led to partial annealing of planar defects and higher sensitivity to the electron beam, with film amorphization taking place at much shorter times under the electron beam.
A study of the pressure-temperature conditions for diamond growth
Authors: Zhang Yafei , Zhang Fangqing , Chen Guanghua
Published: September 2007

An attempt to unify the growth mechanisms and conditions for diamond formation is developed via the growth probability calculated by a barrier model between the two phases. From the distribution law of the equal growth probability lines plotted in a pressure-temperature (P-T) diagram, five regions of different growth methods and mechanisms were reasonably delineated. Many experimental results can be generalized and explained by our theory, and the unity of diamond growth mechanism was discussed over the wide region of the P-T condition.
Origins of microplasticity in low-load scratching of silicon
Authors: Morris J.C. , Callahan D.L.
Published: September 2007

Microstructural characterization of silicon wafers subjected to controlled low-load scratching with a sharp indenter reveals that considerable plastic deformation occurs prior to the onset of fracture. In particular, a completely ductile response to scratching is observed at or below a Vickers load of 1 g, corresponding to penetration depths of 200 nm or less. This anomalous plasticity arises primarily as a result of a pressure-induced semiconductor-to-metal phase transition (Mott transition). Various levels of subsurface dislocation activity and cracking also contribute to the deformation. The relationships among the phase transformation, dislocation activity, and the onset of fracture are discussed. These findings can be applied to other areas of contact damage demonstrating anomalous plasticity, such as hardness testing and ductile-regime turning.
Contribution of electrodes and microstructures to the electrical properties of Pb(Zr0.53Ti0.47)O3 thin film capacitors
Authors: Al-Shareef H.N. , Kingon A.I. , Chen X. , Bellur K.R. , Auciello O.
Published: September 2007

Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitors have been fabricated with four electrode combinations: Pt/PZT/Pt/SiO2Si, RuO2/PZT/Pt/SiO2/Si, RuO2/PZT/RuO2/SiO2/Si, and Pt/PZT/RuO2/SiO2/Si. It is shown that polarization fatigue is determined largely by the electrode type (Pt vs RuO2), and microstructure has only a second-order effect on fatigue. If either the top or bottom electrode is platinum, significant polarization fatigue occurs. Fatigue-free capacitors are obtained only when both electrodes are RuO2. In contrast, the bottom electrode is found to have a major effect on the leakage characteristics of the PZT capacitors, presumably via microstructural modifications. Capacitors with bottom RuO2 electrodes show high leakage currents (J = 10−3-10−5 A/cm2 at 1 V) irrespective of the top electrode material. Capacitors with Pt bottom electrodes have much lower leakage currents (J = 10−8 A/cm2 at 1 V) irrespective of the top electrode material. At low voltage, the I-V curves show ohmic behavior and negligible polarity dependence for all capacitor types. At higher voltages, the leakage current is probably Schottky emission controlled for the capacitors with Pt bottom electrodes.
Composition and microstructural evolution of nonsuperconducting phases in silver-clad (Bi,Pb)2Sr2Ca2Cu3Ox composite conductors
Authors: Luo J.S. , Merchant N. , Escorcia-Aparicio E.J. , Maroni V.A. , Tani B.S. , Carter W.L. , Riley G.N.
Published: September 2007

The composition and microstructural evolution of nonsuperconducting phases during the course of formation of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) in a silver sheath have been investigated by x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and digital image analysis. Wire samples fabricated by the oxide-powder-in-tube technique were heat-treated under a variety of conditions (time, temperature, and oxygen pressure). Backscattered images taken on polished but unetched transverse cross sections were subjected to computerized image processing, which allowed determination of the stoichiometry and quantification of microstructural characteristics (such as area fraction, size distribution, position, and orientation) of each nonsuperconducting particle. The dominant nonsuperconducting phases observed by SEM/EDX were CuO, (Ca,Sr)2CuO3 (2/1), and (Ca, Sr)14Cu24O41 (14/24) in amounts that varied depending on the annealing temperature, time, and oxygen partial pressure. Time evolution studies performed at 825 °C in 0.075 atm O2 showed that the area fraction of 2/1 decreased with reaction time, while that for 14/24 increased. In all cases, a substantial amount (>10% area fraction) of nonsuperconducting phases was detected even after all the Bi2Sr2CaCu2Oy (Bi-2212) in the as-rolled composite conductor was fully converted to Bi-2223, as determined by XRD. High aspect ratio nonsuperconducting particles were initially randomly oriented in the composite conductor core but gradually aligned parallel to the silver/(Bi,Pb)-Sr-Ca-Cu-O interface after extended annealing. They tended to segregate and exhibited a much broader size distribution when processing was carried out at temperatures and oxygen partial pressures on the high end of the normal processing range, most likely as a result of the occurrence of partial melting in the system.
Localized epitaxy of diamond on (100) silicon
Authors: John P. , Milne D.K. , Roberts P.G. , Jubber M.G. , Liehr M. , Wilson J.I.B.
Published: September 2007

Diamond films exhibiting contiguous epitaxial crystallites (∼3-4 μm) have been grown on single crystal (100) silicon by 2.45 GHz microwave plasma deposition. The diamond films were deposited by a three-step process. In the initial stage the silicon wafer was pretreated for 3 h in a 1.8% methane in hydrogen plasma at low pressure. The subsequent nucleation stage was performed, under identical processing conditions, except that a dc bias of −340 V was applied for 25 min. During this period the current increased from 38 mA at the start to 102 mA at the end of the bias. The final growth stage was performed, with an earthed substrate, utilizing a carbon monoxide/methane/hydrogen gas mixture whose composition is conducive to uniformly faceted (100) diamond growth. Scanning electron micrographs showed that a large fraction of the (100) faces of the diamond crystallites are aligned with the (100) plane of the underlying silicon lattice with the crystallite edges parallel to the (110) direction. Raman scattering was used to confirm this finding by measuring the angular dependence of the Raman backscattering intensity at 1332 cm−1 using plane polarized excitation of individual crystallites within the diamond films.