bluuebunny/crossref_metadata_2025 huggingface dataset:
Sputtered YBCO films on metal substrates
Authors: Yin E. , Rubin M. , Dixon M.
Published: September 2007

Magnetron sputtering was used to deposit superconducting YBCO thin films on four polycrystalline metal substrates. Yttrium-stabilized zirconia (YSZ) and silver were used as buffer layers. The thermal expansion coefficient of the substrate was apparently correlated to the properties of the superconductor. Auger depth profiles showed that the YSZ buffer blocked diffusion of most metal elements from the substrate. Nevertheless, contamination of the films depressed Tc to 81 K on Hastelloy × from 87 K on single-crystal strontium titanate. The films on metal substrates were c-axis oriented, but with random rotation in the a-b plane and smaller grain size than epitaxial films on single crystals. The weak links from these factors restrict Jc to 104 A/cm2 at 40 K.
Metallization of glass/ceramic from solutions of organometallic compounds by laser induced pyrolysis
Authors: Dhote A.M. , Patil S.C. , Kanetkar S.M. , Gangal S.A. , Ogale S.B.
Published: September 2007

Direct writing of iron lines on glass and Al2O3 has been achieved by CW CO2 laser-driven pyrolytic dissociation of volatile iron pentacarbonyl liquid. Since a very high organometallic molecular density is realized in the solution, use of a liquid precursor has enabled deposition of micron-thick iron films at the writing speeds of 10–400 mm s−1, which are significantly higher as compared to those achievable by the conventional CVD method. The iron stripes deposited on the glass substrate at the laser power density of 5.3 kW cm−2 and the writing speed of 100 mm s−1 are found to have a resistivity of about 580 μohm-cm. These stripes have been found to have an integral bond with the substrate due to the interface reaction.
Influence of processing on the microstructure and mechanical properties of a NbAl3-base alloy
Authors: Hebsur Mohan G. , Locci Ivan E. , Raj S.V. , Nathal Michael V.
Published: September 2007

A multiphase oxidation resistant composition (Nb–67Al–7Cr–0.5Y–0.25W) based on NbAl3 was prepared by both induction melting and rapid solidification processing (RSP), followed by grinding to 75 μm powder and consolidating by powder metallurgy techniques (hot pressing, hot isostatic pressing, and Ceracon pressing). Constant strain rate compression tests conducted on consolidated materials in the temperature range 300–1300 K indicated that the RSP material exhibited significantly higher strength and ductility than the induction melted alloy up to 1200 K. Bend strengths measured on induction melted material were significantly lower than the corresponding compressive strengths, suggesting the brittle, flaw-sensitive nature of this alloy. The NbAlCrYW alloy exhibits a brittle-to-ductile transition around 1000 K. The constant load creep tests conducted on the induction melted alloy in the 1200–1300 K temperature range indicated that this alloy shows a power law creep dependency with a stress exponent, n, of 3.2. It was found that the specific strength of this alloy is competitive with other aluminide intermetallics.
Laser processed Al3Ti-based intermetallics: Al5±XTi2±Y(Fe, Ni, or Cu)1±z
Authors: Ma Y. , Arnesen T. , Gj⊘nnes J. , Taft⊘ J.
Published: September 2007

A new processing route for intermetallics starting from elemental metal powders and using laser beam heating has been investigated, by which three Al3Ti-based ternary intermetallic systems alloyed with Fe, Ni, or Cu, respectively, have been produced. Structures and compositions of five phases found in the three systems have been analyzed using optical metallography, transmission electron diffraction and microscopy, and thin foil energy dispersive x-ray spectrometry. The structure of three matrix phases in the three systems was identified as L12 type, which is consistent with previous work. The space group of the second phases in the two systems alloyed with Fe or Ni was reconfirmed or newly determined as Fm3m, using convergent beam electron diffraction. The lattice parameter measurements of these five found phases indicated atomic size-effect on the formation of intermetallics.
Structural and thermodynamic properties of nanocrystalline fcc metals prepared by mechanical attrition
Authors: Eckert J. , Holzer J.C. , Krill C.E. , Johnson W.L.
Published: September 2007

Nanocrystalline fcc metals have been synthesized by mechanical attrition. The crystal refinement and the development of the microstructure have been investigated in detail by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The deformation process causes a decrease of the grain size of the fcc metals to 6–22 nm for the different elements. The final grain size scales with the melting point and the bulk modulus of the respective metal: the higher the melting point and the bulk modulus, the smaller the final grain size of the powder. Thus, the ultimate grain size achievable by this technique is determined by the competition between the heavy mechanical deformation introduced during milling and the recovery behavior of the metal. X-ray diffraction and thermal analysis of the nanocrystalline powders reveal that the crystal size refinement is accompanied by an increase in atomic-level strain and in the mechanically stored enthalpy in comparison to the undeformed state. The excess stored enthalpies of 10–40% of the heat of fusion exceed by far the values known for conventional deformation processes. The contributions of the atomic-level strain and the excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth in the nanocrystalline fcc metals are investigated by thermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis, and estimates of the grain boundary enthalpy are given.
Tribological characteristics of polycrystalline diamond films produced by chemical vapor deposition
Authors: Kohzaki M. , Higuchi K. , Noda S. , Uchida K.
Published: September 2007

Effects of surface roughness and crystallinity of polycrystalline diamond films on their tribological characteristics, as well as the effects of test environment, have been investigated. Friction and wear characteristics of the diamond films deposited on sintered SiC disks have been examined with a ball-on-disk tester in the absence of any lubricant. The friction coefficients of polished diamond films against SiC and Si3N4 balls were below 0.10 at room temperature while those of as-deposited films were around 0.20. The specific wear of counterparts on the polished film was five orders of magnitude smaller than on the as-deposited film. The friction coefficient between the polished diamond film and a AISI 52100 steel ball was about 0.20. Transfer of a small amount of AISI 52100 material to the diamond film was observed along the wear track of the polished diamond surface. Diamond films of high quality were more resistant to wear than the ones of low quality. On the other hand, the friction coefficients were not affected by the crystallinity of the diamond films in the present study. Tribological characteristics of the diamond films deteriorated with increasing sliding speed and ambient temperature. At 600 °C in dry N2, the friction coefficient of diamond films against a SiC ball was about 0.8, which was about ten times higher than that at room temperature in air.
Thermally stimulated exoelectron emission from hydrogenated amorphous carbon films
Authors: Watanabe Yoshihisa , Nakamura Yoshikazu , Hirayama Shigekazu , Yamaguchi Yoshimasa
Published: September 2007

Hydrogenated amorphous carbon (a–C:H) films on stainless steel (AISI430) substrate oxidized in air at 1273 K were prepared from a gas mixture of methane and hydrogen by an rf plasma chemical vapor deposition, and thermally stimulated exoelectron emission (TSEE) was studied for the x-ray irradiated a–C:H films. Glow curves and energy distributions of TSEE from the 80- and 280-nm a–C:H films and from the AISI430 substrate have been measured under ultrahigh vacuum conditions. It was found that the glow curve from the 80-nm a–C:H film was similar to that from the AISI430 substrate, but it was quite different from that from the 280-nm film; the values of the mean energy of exoelectrons at the glow peak temperatures from the 80-nm a–C:H film are almost the same as those from the substrate but are much lower than those of the 280-nm film. The surfaces of 80- and 280-nm a–C:H films are observed with the scanning electron microscope (SEM). Observations by SEM show that the 80-nm film has relatively large-sized clusters of films and the stainless steel substrate still appears in some places, but the surface of the 280-nm film is completely covered by the carbon films. From these results, we propose that TSEE from the 80-nm film originates mainly from the oxide films on the stainless steel substrate and TSEE from the 280-nm film originates from the film itself. Thus, TSEE can be applied to characterize the surface of thin films.
Hydrogen, nitrogen, and oxygen behavior in boron
Authors: Kervalishvili P.J. , Oganezov K.A. , Tabutsidze M.L. , Andriasova I.A.
Published: September 2007

Some of the problems of hydrogen, nitrogen, and oxygen behavior in boron, which is a promising material for the development of sensitive elements in gas sensors of improved radiation resistance, were studied. Using gas and thermal gravimetric analysis methods the interaction of these gases with boron was investigated, and the influence of temperature and annealing on the sorptivity of boron, the interaction of disperse boron powder with the environment, and thermal gas release from boron and boron-containing materials were studied.
The microstructure and stoichiometry of pyrite FeS2−x
Authors: Fiechter S. , Birkholz M. , Hartmann A. , Dulski P. , Giersig M. , Tributsch H. , Tilley R.J.D.
Published: September 2007

Both natural and synthetic crystals of pyrite, FeS2−x, have been analyzed chemically and examined structurally by transmission electron microscopy and x-ray powder diffraction. Chemical analysis and density measurements have shown the synthetic crystals, grown at 850 K, are frequently deficient in sulfur, with a composition of FeS2−x with x ⋚ 0.15. From a refinement of the pyrite structure using the integral intensities of the x-ray powder pattern, a variation in the sulfur population parameter was obtained ranging from 0.87(2) to 1.03(3). A correlation according to Vegard's rule between the population factor and the lattice parameter a0 has been proven. Transmission electron microscope examination revealed that the crystals did not contain a significant population of disorder defects which may account for this apparent sulfur deficit. Therefore the nonstoichiometry in pyrite has to be interpreted in terms of S vacancies which can be understood as the tendency of the material to reduce the high anion content in the unit cell. The structural nature of nonstoichiometric pyrite is discussed in relationship to other related disulfides.
Structural study of room temperature synthesized nickel thiophosphate a–NiPS3
Authors: Fragnaud P. , Prouzet E. , Brec R.
Published: September 2007

A structural study using x-ray diffraction and simulation calculations was performed on a–NiPS3, the highly disordered phase of the nickel thiophosphate, synthesized through a soft chemistry process. The structure of the wet gel is shown to be entirely amorphous; its x-ray pattern exhibits diffusion peaks according to the disordered anionic network. For the powdered samples, measurements of the width of the diffraction lines show that there are small crystallized c–NiPS3-type crystallites with a volume V equal to (25 × 25 × 40) Å3 (i.e., 4a × 3b × 6c in terms of volume cell). The simulation calculations of the x-ray diagrams have indicated that the stacking of these crystallites is quite imperfect: the suggested crystallite structures must contain rotated or shifted layers.
Synchrotron x-ray topography studies of twin structures in lanthanum aluminate single crystals
Authors: Yao Gong-Da , Hou Shang Yun , Dudley Michael , Phillips Julia M.
Published: September 2007

An extensive investigation of twin structures in lanthanum aluminate single crystals at room temperature has been undertaken using White Beam Synchrotron X-Ray Topography (WBSXRT). Twin configurations, directly observable via orientation contrast, were found to comprise both large-volume, macroscopic twins and thick twin lamellae. Positional shifts of twin domain images with respect to matrix images, arising from the mutual misorientation of diffraction vectors, were measured on x-ray topographic images recorded from the (220)rhomplanes approximately parallel to the specimen surface and compared to calculated values in order to solve the twin laws in this system. The dominant twin operations were found to be (101)rhom, (011)rhom, and (112)rhommirror reflections. The potential influence of the twins on the growth of epitaxial Ba2YCu3O7−δthin films is discussed.
Preparation of Ba(Mg1/3Nb2/3)O3 ceramics as microwave dielectrics through alkoxide-hydroxide route
Authors: Fukui Toshimi , Sakurai Chihiro , Okuyama Masahiko
Published: September 2007

Ba(Mg1/3Nb2/3)O3 powders were prepared through an alkoxide-hydroxide route. Their sintering behavior and crystallographic structures were investigated, and microwave properties of the obtained ceramics were also measured. Crystalline powder with approximately 0.5 μm in particle size was obtained by the reaction of Ba(OH)2−8H2O and Mg–Nb double alkoxide, Mg[Nb(OEt)6]2, in ethanol-acetone solution. A powder compact sintered at 1350 °C for 2 h showed >99% of relative density and >0.9 of ordering degree of the B site. The Q value of Ba(Mg1/3Nb2/3)O3 ceramics was sensitive to sintering conditions due to the formation of an impurity phase. The ceramics sintered at 1350 °C for 5 h showed a dielectric constant ∊ of 32 and Q value of > 13 000 at 11.8 GHz. The temperature coefficient of resonant frequency τf was 23.9 ppm/°C at 9.8 GHz.
Improved hardness and wear properties of B-ion implanted polycarbonate
Authors: Lee E.H. , Rao Gopal R. , Mansur L.K.
Published: September 2007

Polycarbonate (Lexan) was implanted with 100 and 200 keV B+ ions to doses of 0.26, 0.78, and 2.6 × 1015 ions/cm2 at room temperature (<100 °C). Mechanical characterization of implanted materials was carried out by nanoindentation and sliding wear tests. The results showed that the hardness of implanted polycarbonate increased with increasing ion energy and dose, attaining hardness up to 3.2 GPa at a dose of 2.6 × 1015 ions/cm2 for 200 keV ions, which is more than 10 times that of the unimplanted polymer. Wear properties were characterized using a reciprocating tribometer with nylon, brass, and SAE 52100 Cr-steel balls with 0.5 and 1 N normal forces for 10000 cycles. The wear mode varied widely as a function of ion energy, dose, wear ball type, and normal load. For given ion energy, load, and ball type conditions, there was an optimum dose that produced the greatest wear resistance and lowest friction coefficient. For polycarbonate implanted with 0.78 × 1015 ions/cm2, the nylon ball produced no wear after 10000 cycles. Moreover, the overall friction coefficient was reduced by over 40% by implantation. The results suggest that the potential of ion-beam technology for improving polycarbonate is significant, and that surface-sensitive mechanical properties can be tailored to meet the requirements for applications demanding hardness, wear, and abrasion resistance.
Photochemical modification of polytetrafluoroethylene into oleophilic property using an ArF excimer laser
Authors: Okoshi M. , Murahara M. , Toyoda K.
Published: September 2007

Photochemical modification of the polytetrafluoroethylene (PTFE) with incorporation of the CH3 radical released from the B(CH3)3 molecule excited by an ArF excimer laser has been demonstrated. The incorporation of CH3 radicals and the depletion of fluorine atoms of the polymer surface were studied by XPS analysis and infrared ATR spectrum measurement. In these photochemical reactions, the photoirradiated surface changed into oleophilic. The properties were studied by contact angle measurement. The stability of the oleophilic surface was examined at the elevated temperature of 200 °C for 6 h in O2 or N2 ambient and also by immersing in alkaline or acid water solutions.
Comment on “Plastic deformation and fracture behavior of a Fe-modified Al3Ti-base L12 intermetallic alloy” [J. Mater. Res. 6, 957 (1991)]: The importance of specimen length-to-width ratios and end constraints in compression testing of brittle and semibrittle materials
Authors: Zeuch David H.
Published: September 2007

Specimen length-to-diameter ratios and specimen/platen end conditions are important to interpretation of, and comparisons between, uniaxial compression tests on brittle materials. When differing l:d ratios and specimen/platen end conditions are used to test pressure-sensitive materials, observations may not be readily comparable owing to the different and nonuniform triaxial stress states. Specimens of brittle Fe- and Ni-modified Al3Ti intermetallic alloys having relatively low and different l:d ratios were tested in compression by Gengxiang et al. and Turner et al., respectively. Qualitative observations on the macroscopic deformation and failure modes (shear failure and distributed microcracking) indicate that the alloys are pressure-sensitive and that the results were possibly complicated in differing degrees by test configuration. Thus, direct comparison of these results with those obtained earlier for Al3Ti by Yamaguchi et al., who used a significantly greater l:d ratio, may not be altogether useful. Approaches to minimizing end effects are reviewed.
Brittle fracture of nickel by dynamic indentation
Authors: Hoehn J.W. , Foecke T. , Gerberich W.W.
Published: September 2007

Cracks of up to 40 μm which are either transgranular cleavage or very low energy “ductile” cracks have been introduced into large-grained fcc Ni. The mechanism for introducing this brittle fracture was dynamic indentation. Optical and scanning electron microscopy together with use of selected area channeling patterns were used to confirm that the fracture process is transgranular. The results qualitatively support the hypothesis that dynamic cracks originating in a brittle film can propagate relatively large distances into a ductile face-centered-cubic substrate by a rapid, low energy process.
Observation of a rapid amorphization reaction
Authors: Hufnagel T.C. , Brennan S. , Payne A.P. , Clemens B.M.
Published: September 2007

We have observed a rapid amorphization reaction at ambient temperature in the Gd/Co system by employing grazing incidence x-ray scattering. We find that a 135 Å crystalline Gd film is amorphized in less than 30 min by deposition of Co. We postulate that the rapidity of the reaction is due to surface diffusion of Co atoms after deposition to fast diffusion sites such as grain boundaries in the Gd film. Once the interfacial region has been amorphized these fast diffusion paths are sealed off from the surface, rapid diffusion of Co into the Gd crystalline layer is prevented, and the amorphization reaction stops.
Reversible grain size changes in ball-milled nanocrystalline Fe–Cu alloys
Authors: Eckert J. , Holzer J.C. , Krill C.E. , Johnson W.L.
Published: September 2007

Nanocrystalline FexCu100−x solid solutions (x < 60) with single-phase fcc structure have been prepared by mechanical alloying. The average grain size of the powders (8–20 nm) depends on the composition of the material. Varying the composition changes the grain size reversibly. This can be explained by the underlying mechanism of plastic deformation and solution hardening during mechanical alloying coupled with the recovery behavior of the material.
Deposition and characterization of YBa2Cu3O7−δ thin films grown in situ by sequential ion beam sputtering
Authors: Kittl J.A. , Johnson W.L. , Nieh C.W.
Published: September 2007

We investigated the in situ growth of YBa2Cu3O7−δ superconducting thin films by a sequential ion beam sputtering technique, studying the relations among deposition parameters, structural and superconducting properties. The films were deposited following the stacking sequence of YBa2Cu3O7−δ, with individual layer thicknesses nominally equal to one monolayer. O2 was supplied during deposition. Predominantly c-axis oriented films were grown on (100) SrTiO3, (100) MgO, and oxidized Si (SiO2/Si) substrates. The microstructure and film-substrate orientation relations were studied by transmission electron microscopy. X-ray studies showed the presence of homogeneous and inhomogeneous strains along the c-direction that persisted after low temperature oxygen anneals. Resistivity measurements showed correlations between the superconducting transition characteristics and the lattice distortions along the c-direction. The effect of deposition parameters on the lattice distortions was investigated, finding that the c-axis lattice parameter was larger in films grown at lower temperatures. This was interpreted in terms of the thermally activated dissociation of O2 at the film surface during growth. We assumed that the c-axis lattice expansion was due to kinetic limitations to the incorporation of oxygen into the film during growth. This led to a consistent description of the results obtained in this work and the O2 pressure dependence of the c-axis lattice expansion reported for other in situ techniques. Studies were performed on films grown by this technique as well as on films grown in situ by magnetron sputtering in an attempt to elucidate the nature of the defect structure causing the c-axis lattice distortions.
Preparation, thermal processing behavior, and characterization of YBCO from freeze-dried nitrate precursors
Authors: Coppa N.V. , Myer G.H. , Salomon R.E. , Bura A. , O'Reilly J.W. , Crow J.E. , Davies P.K.
Published: September 2007

YBCO was synthesized using atomically mixed nitrate precursors. Atomic mixing was achieved using a freeze-dried process which is fully discussed here. The thermal processing behavior of these precursors is fundamentally different from that of mechanical mixtures of the Y, Ba, and Cu oxides and it is examined in detail. Ba2Cu3O5+x (normally considered a high oxygen pressure phase) and Y2O3 formed as nitrate decomposition products at ambient atmospheric conditions. Subsequent reaction of these materials (2 h at 925 °C) produced polycrystalline YBCO. Without any post-processing of the powders, product YBCO powders consisted of 30 μm agglomerates composed of crystals 1–3 μm on an edge. The powdered products exhibited a magnetic susceptibility greater than 90% – 1/4π.
Growth kinetics of high Tc phase in Bi–Sr–Ca–Cu–O thick films
Authors: Chaudhry Sangeeta , Khare Neeraj , Gupta A.K.
Published: September 2007

Thick films of Bi–Sr–Ca–Cu–O on (100) MgO substrates have been prepared by the screen printing technique with the starting composition of 1112. The annealing process involves a two-step heat treatment. The first-step temperature is chosen between 874 °C and 898 °C for 45 min followed by slow cooling (2 °C/min) to 864 °C. In the second step, the films are kept at 864 °C for a time varying from 0 to 104 h. The Tc (R = 0) and intensity of the characteristic peaks of the high Tc and the low Tc phases in the x-ray diffraction pattern are found to be dependent on the first-step temperature and the duration of the second step. The process of crystallization and the growth of plate-like grains as a function of annealing time at the second step are studied using Scanning Electron Microscopy (SEM). Kinetics of the growth of the high Tc phase has been explained in terms of a reaction mechanism involving the first and second annealing steps.
Separation of film thickness and grain boundary strengthening effects in Al thin films on Si
Authors: Venkatraman Ramnath , Bravman John C.
Published: September 2007

We have measured stress variations with temperature as a function of film thickness and a given grain size in pure Al and Al–0.5% Cu films on Si substrates. The variation in thickness for a given grain size is brought about by using the same film and the repeated controlled growth and dissolution of a barrier anodic oxide which can be grown uniformly on the film. Stress measurements were made as a function of temperature by measuring wafer curvature after successively removing each 0.1 μm of Al film. The components of strengthening due to the film thickness and the presence of grain boundaries were separated by assuming that the flow stress of the film is simply the sum of these two components. It is found that strengthening due to film thickness varies inversely with the thickness, which is consistent with results obtained by us using laser-reflowed films in an earlier work. The Hall–Petch coefficients calculated from the strengthening due to the grain boundaries are slightly higher than those reported for bulk Al. However, it is also recognized that the variation of the flow stress as g−1, where g is the grain size, is more plausible than that predicted by the Hall–Petch relation (i.e., as g−1/2). The variations of these two components with temperature, and under tension and compression, are discussed.
Ternary atom location in L12-structured intermetallic phases: Al62.5+XTi25−Y(Fe, Ni, or Cu)12.5–Z using ALCHEMI
Authors: Ma Y. , Gj⊘nnes J.
Published: September 2007

The site occupancy of ternary atoms in three L12-structured intermetallic phases, Al62.5+XTi25−Y(Fe, Ni, or Cu)12.5–Z found in three laser processed intermetallic systems was studied by the axial ALCHEMI (Atom Location by Channeling Enhanced Microanalysis). The ternary atoms in all three intermetallic phases were found preferentially to occupy the Al sublattices, although slight differences in occupancy among them were detected. A simple extrapolation method of calculating delocalization correction factors for various characteristic x-ray emissions was described, which was proved to be practically useful in ALCHEMI analyses. In order to compare the axial ALCHEMI analysis with the planar ALCHEMI in an experimental perspective, the planar ALCHEMI analysis was also carried out on the phase alloyed with Cu, which showed results in broad agreement with those of the axial ALCHEMI analysis on the same phase. Nevertheless, owing to much weaker channeling effects the planar ALCHEMI analysis gave apparently worse statistics in its results. In the end, various sources of errors in the ALCHEMI analyses at the present stage are discussed.
Superplastic behavior of a fine-grained Mg–9Li material at low homologous temperature
Authors: Taleff Eric M. , Ruano Oscar A. , Wolfenstine Jeff , Sherby Oleg D.
Published: September 2007

A fine-grained ($\overline \iota$m) laminate containing 91.0 wt.% magnesium and 9.0 wt. % lithium was prepared by a foil metallurgy technique involving rolling and pressing at low homologous temperature (0.39–0.49 Tm). The processed material exhibits superplastic characteristics above 70 °C (0.40 Tm). The strain-rate-sensitivity exponent is about 0.5 and an elongation-to-failure of 450% was obtained at 100 °C (0.43 Tm). The activation energy for plastic flow in the superplastic region is 65 kJ/mole. This value of the activation energy is related to the expected activation energy for grain boundary diffusion.
Diamond film nucleation and interface characterization
Authors: Bou P. , Vandenbulcke L. , Herbin R. , Hillion F.
Published: September 2007

A powerful micro SIMS technique coupled to a computer driven acquisition system has allowed the simultaneous recording of C−, MoO−, and Si− images of the sample surfaces, or of the transverse cross sections of the Mo-diamond interface. Diamond deposition has been shown to take place on a Mo2C layer, and the influence on the nucleation process of Si contamination, coming from the quartz tube etched by H atoms, has been investigated. Contamination can in fact occur during the shutdown procedures or during the whole experiment. This last contamination can be avoided by using suitable pressure ranges or gas combinations. Moreover, the deposition time necessary to obtain well-crystallized diamond films and the nucleation density could be optimized by an in situ pretreatment stage. This treatment reduces the delay observed before nucleation (which would correspond to the carbide formation), and increases the carbon activity at the sample surface.
Modeling of a–Si:H deposition in a dc glow discharge reactor
Authors: Orlicki Dariusz , Hlavacek Vladimir , Viljoen Hendrik J.
Published: September 2007

PECVD reactors are increasingly used for the manufacturing of electronic components. This paper presents a reactor model for the deposition of amorphous hydrogenated silicon in a dc glow discharge of Ar–SiH4 The parallel-plate configuration is used in this study. Electron and positive ion densities have been calculated in a self-consistent way. A macroscopic description that is based on the Boltzmann equation with forwardscattering is used to calculate the ionization rate. The dissociation rate constant of SiH4 requires knowledge about the electron energy distribution function. Maxwell and Druyvesteyn distributions are compared and the numerical results show that the deposition rate is lower for the Druyvesteyn distribution. The plasma chemistry model includes silane, silyl, silylene, disilane, hydrogen, and atomic hydrogen. The sensitivity of the deposition rate toward the branching ratios SiH3 and SiH2 as well as H2 and H during silyl dissociation is examined. Further parameters that are considered in the sensitivity analysis include anode/cathode temperatures, pressure, applied voltage, gap distance, gap length, molar fraction of SiH4, and flow speed. This work offers insight into the effects of all design and control variables.
Silicon cross doping and its effect on the Si or Be implantation doping of gallium arsenide grown on (100) silicon by metalorganic chemical vapor deposition
Authors: Molnar B. , Chi P. , Simons D.
Published: September 2007

A study of the cross doping of GaAs layers grown by a two-step metalorganic chemical vapor deposition on Si substrates is reported. All as-grown, unintentionally doped layers of GaAs were n-type, and the carrier profiles tracked the Si atomic profiles. Furnace annealing at 850 °C for 30 min in an arsine overpressure, which is used to improve the crystalline quality of the GaAs near the heterointerface, caused additional Si to diffuse into the GaAs layer. Comparison of the Si concentration at the interface with the carrier concentration suggested the presence of compensating acceptors. Resonance Raman scattering by the SiAs local vibrational mode near the interface shows that a fraction of the Si atoms are localized at the As sites. The furnace annealing increased the Si concentration in the 1.7–1.8 μm thick initially grown GaAs layer. This, in turn, influenced the electrical profiles created with Si or Be implantation on a 2.3 μm thick GaAs layer.
Alloy clustering and defect structure in the molecular beam epitaxy of In0.53Ga0.47As on silicon
Authors: Georgakilas Alexandros , Dimoulas Athanasios , Christou Aristotelis , Stoemenos John
Published: September 2007

The MBE growth of InxGa1−xAs (x ∼ 0.53) on silicon substrates has been investigated emphasizing the effects of substrate orientation and buffer layers between In0.53Ga0.47As and Si. It is shown that growth on silicon substrates misoriented from (001) toward a [110] direction eliminates the presence of antiphase domains. The best In0.53Ga0.47As surface morphology was obtained when a 0.9 μm epitaxial Si buffer was initially grown, followed by a pre-exposure of the silicon surface to As4 at 350 °C, followed by the growth of In0.53Ga0.47As. Threading dislocations, stacking faults, low-angle grain boundaries, and spinodal decomposition were observed by TEM in the InGaAs layers. The spinodal contrast scale was shown to depend on the buffer type and the total InGaAs thickness. Thick buffers consisted of GaAs or graded InxGa1−xAs layers, and large In0.53Ga0.47As thicknesses favor the development of a coarse-scale spinodal decomposition with periodicity around 0.1 μm. Thin GaAs buffers or direct In0.53Ga0.47As growth on Si may result in a fine-scale decomposition of periodicity ∼10 nm. The principal strain direction of the spinodal decomposition appeared along the [1$\overline 1$0] direction, parallel to the vicinal Si surface step edges. InGaAs immiscibility affects the InGaAs growth process, favoring a 3-D growth mode. X-ray diffraction measurements and photoreflectance spectra indicated that the sample quality was improved for samples exhibiting a fine-scale spinodal decomposition contrast even if they contained a higher dislocation density. Threading dislocations run almost parallel to the [001] growth axis and are not affected by strained layers and short period (InAs)3/(GaAs)3 superlattices. The lowest double crystal diffractometry FWHM for the (004) InGaAs reflection was 720 arc sec and has been obtained growing InGaAs directly on Si, while the lowest dislocation density was 3 × 109 cm−2 and was obtained using a 1.5 μm GaAs buffer before the In0.53Ga0.47As deposition.
InP under high pressures
Authors: Tsai M-H. , Dow John D. , Kasowski R.V.
Published: September 2007

The direct energy gaps, Eg, and the indirect gaps at the X point, E(X), of GaAs and AlxGa1−xAs alloys are essentially linear functions of hydrostatic pressure, P. Recent photoluminescence measurements of Tozer et al. for InP under high pressures, however, found that Eg(P) is not quite linear, but bends down slightly at high pressures. Using the first-principles pseudofunction method, we have calculated Eg and E(X) as functions of pressure, as well as the zero-temperature equation of state P(V). Our calculated gap curve for InP, Eg(P), bends down slightly, as found in photoluminescence studies. The slope dEg/dP is 8.8 meV/kbar for small pressures P, and is in good agreement with the experimental value, 8.32 meV/kbar. The observed nonlinearity in the dependence of Eg on pressure for InP is attributed to a large derivative of the bulk modulus with respect to pressure. The calculated bond length, bulk modulus, and critical pressure for a phase transition from the zinc blende to a rocksalt structure, and the unit cell volume change at this phase transition are all in good agreement with the data.
Transmission infrared study of acid-catalyzed sol-gel silica coatings during room ambient drying
Authors: Parrill T.M.
Published: September 2007

Sol-gel solutions prepared from tetraethylorthosilicate (TEOS) hydrolyzed in acidic conditions were used to make thin films on Si wafers via spin coating. Solutions with H2O/TEOS ratios of 2, 5, and 10 were prepared and aged at room temperature in sealed containers for times ranging from <2.5 h to 1 month. Transmission Fourier transform infrared spectra acquired around 1 min after spinning showed peaks characteristic of both SiO2 and SiOH. Additional features at ≍580, 1093, and 1130 cm−1 were observed and possible origins are discussed. Peaks at ≍580 and 1130 cm−1, which increased in intensity with solution age time, are attributed to cyclic Si–O, e.g., 4-member rings. When films were exposed to room air, ring concentration decreased significantly within 30 min. Rings were stable for hours, however, when films were kept in N2. The feature at 1093 cm−1, most sensitive to H2O/TEOS, is attributed to residual Si–O–C.
Development of suspensions of rod-shaped β–FeOOH particles in infrared transmitting solvents for use as artificial Kerr media
Authors: Naylor D.L.
Published: September 2007

The first suspensions of rod-shaped dielectric particles in an infrared transmitting solvent are reported. Specifically, micron size β–FeOOH rods have been produced in chloroform, carbon tetrachloride, and carbon disulfide. A technique to transfer the particles from water into organic solvents is demonstrated and a novel optical method to determine the degree of stability of the organosols is used. Sedimentation times vary with preparation technique over the range of minutes to hours, often being long enough to allow the use of the material as an infrared Kerr medium with large electric field induced birefringence. Dispersions in hexane, which has good microwave transmission, have also been produced.
Ultrasonically accelerated synthesis of hydroxyapatite
Authors: Fang Y. , Agrawal D.K. , Roy D.M. , Roy R. , Brown P.W.
Published: September 2007

Ultrasonic energy was used to accelerate the formation of hydroxyapatite (HAp). The experiments were carried out in aqueous systems on two different sets of reactants: (1) a mixture of Ca4(PO4)2O(TetCP) and CaHPO4 · 2H2O (brushite) and (2) α–Ca3(PO4)2 (α–TCP). The reaction systems were exposed to ultrasound of 20 kHz for various times ranging from 5 to 80 min. The products were characterized by XRD and SEM. Parallel experiments without ultrasound were carried out for calibration. The results show that the ultrasound substantially accelerates both reactions. With ultrasound, the time required for the TetCP-brushite system to complete the reaction forming HAp was reduced from 9 h to 25 min at 25 °C, and from 3 h to 15 min at 38 °C. At 87 °C, α–TCP does not hydrolyze within 1 h in de-ionized water unless the pH is adjusted. Hydrolysis of α–TCP was induced by sonication in less than 20 min, and longer treatment results in the formation of a homogeneous sol of HAp.
Tracer diffusion of Ba and Y in YBa2Cu3Ox
Authors: Chen Nan , Rothman S.J. , Routbort J.L. , Goretta K.C.
Published: September 2007

Tracer self-diffusion of Ba and Y and the diffusion of Dy, Ho, and Gd, which substitute for Y, have been measured in polycrystalline YBa2Cu3Ox over temperature and oxygen partial pressure ranges of 850 to 980 °C and 103 to 105 Pa, respectively. The diffusion of Ba is slower than that of oxygen or copper, with a high activation energy of about 890 ± 80 kJ/mole. Large anisotropy has also been observed, with diffusion along the c-axis being more than three orders of magnitude slower than diffusion in randomly oriented polycrystals. Diffusion coefficients of Ba were, within experimental uncertainty, independent of oxygen partial pressure over the range measured. The diffusion coefficients of the Y-site species were nearly identical and an activation energy of about 1.0 MJ/mole was estimated, in agreement with that for high-temperature deformation. Attempts to speed up the kinetics through creation of point defects on the Y site by doping proved to be unsuccessful. These results are compared to cation diffusion in cubic perovskites and simple oxides.
Preparation of YBa2Cu3O7−y films on SrTiO3 and MgO by the dipping-pyrolysis process under low-p(O2) heat treatment
Authors: Manabe T. , Arai K. , Kondo W. , Mizuta S. , Kumagai T.
Published: September 2007

Superconducting YBa2Cu3O7−y (YBCO) films having a thickness of 1 μm were prepared on SrTiO3(100) and MgO(100) by the dipping-pyrolysis process using a low-p(O2) annealing method. Heat-treatment conditions were varied along the upper limit of the stability region of the YBCO phase. Films on SrTiO3(100) exhibited strong c-axis orientation with sharp rocking curves (FWHM = 0.8°). The highest Tc,zero of 87 K was obtained for the film heat-treated at 750 °C. On the other hand, films on MgO(100) showed broader rocking curves and their Tc's remained lower. Moreover, Ag addition was found to enhance the Tc values (Tc,zero = 91 K) of films on SrTiO3 heat-treated at 750 °C.
Crystallinity of Y1Ba2Cu3O7−x films grown on MgO by activated reactive evaporation
Authors: Prakash Shiva , Bunshah R.F.
Published: September 2007

The film crystallinity and nature of the interface between Y1Ba2Cu3O7−x (YBCO) films and (100)-oriented MgO substrates are revealed using results from x-ray line broadening analysis, x-ray pole figure analysis, and simple models for interface types. The superconductor film was grown using Activated Reactive Evaporation (ARE) at 675 °C. The results show that the interface can be treated as semicoherent with interfacial dislocations whose spacing depends on the in-plane orientation relationship between YBCO and MgO. For the orientation relationship (100) YBCO parallel to (100) MgO, the spacings between dislocations are 9 lattice spacings of MgO in the a direction and 11 lattice spacings of MgO in the b direction. For the orientation relationship (110) YBCO parallel to (100) MgO, the spacing between dislocations is 2 lattice spacings of MgO (or 4 plane spacings of (200) MgO—see Ref. 10). The x-ray based method used here can be an addition to or a replacement for the cumbersome cross-sectional TEM technique (for the YBCO system) to view the interface.
Determination of size and distribution of second phases using nuclear microscopy
Authors: Breese M.B.H. , Romano L.T. , Salter C.J. , Grime G.W. , Watt F.
Published: September 2007

Nuclear microscopy combines a range of MeV light ion beam analytical techniques such as Proton Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS), and Scanning Transmission Ion Microscopy (STIM). One of the main advantages of using MeV light ion beams for materials characterization is the large analytical volume due to their high penetration depth. This paper shows how nuclear microscopy is used to determine the size and distribution of Pb precipitates in a 40 μm thick alloy sample with a nominal composition of Al–5 wt.% Pb.
Cracks and dislocations in face-centered cubic metallic multilayers
Authors: Lashmore David S. , Thomson Robb
Published: September 2007

In this paper, we have demonstrated that very perfect thin multilayers of the Cu/Ni system can be prepared with coherent interfaces if the layer modulation wavelength is in the 10 nm range. At modulation thicknesses above about 60 nm, the interfaces become incoherent. We have injected a crack into a coherent interface in the 10 nm case which has generated dislocations into the interface forming the crack plane, as well as into the layers adjacent to the crack plane. The dislocations injected into the crack plane presumably form misfit dislocations on that interface, and are grouped so close to the crack tip that individual dislocations are not completely imaged. The dislocations injected into the adjacent layers are distributed rather widely. We have analyzed the dislocation emission from a crack in the fcc geometry appropriate to the multilayers using a simplified elastic theory developed for cracks in homogeneous materials. The mixed mode loading which the misfit stresses are expected to produce lead one to expect these materials to be ductile and to have high toughness. Very high dislocation densities on the crack plane near the crack, however, may lead to a brittle mode of failure, which is beyond the purview of the elastic theory. The dislocations are observed to have strong interactions with alternating interfaces in the multilayers, and this effect could be due to elastic bunching of the dislocations at alternating interfaces caused by the misfit stress.
Effect of additional elements on the mechanical and microstructural properties of copper polycrystal under dynamic compression
Authors: Ancrenaz P. , Nguy C. , Servant C.
Published: September 2007

The effect of additional elements (Si and Co) on the behavior of copper polycrystalline alloy under static and dynamic compression was studied. Relations between the deformation microstructure and the mechanical behavior have been investigated. In the Cu–Si alloys, the SFE depends on additional element content and the SFE level controls the dissociation of perfect dislocations into partial ones. In the Cu–Co alloy, Co induces precipitation and the dislocation repartition is uniform if the precipitates are coherent. When the precipitates become semicoherent, there is formation of dislocation walls around the precipitates.
Fatigue failure in Pb–Sn–Ag alloy during plastic deformation: A 3D-SIMS imaging study
Authors: Scandurra Antonino , Licciardello Antonino , Torrisi Alberto , La Mantia Antonio , Puglisi Orazio
Published: September 2007

Three-dimensional chemical maps by Secondary Ion Mass Spectrometry (3D-SIMS), XPS spectroscopy, and SEM-EDAX microscopy were employed in order to investigate the effects of accelerated fatigue tests on crack formation in 95.5% Pb–2% Sn–2.5% Ag and 95% Pb–5% Sn solder joints. These alloys are used in the die bonding of electronic power device assemblies. The results show that cracks form by Sn-depletion from the inner regions of the soldered joint. Simultaneously, there is a recrystallization of the Pb-rich phase in the same regions of the joint. The crack occurs at a critical number of cycles when a Sn-depleted region is formed, yielding weaker inner layers with lower shear strength. A possible explanation of the Sn-depletion is also discussed.
On the electronic basis of the phosphorus intergranular embrittlement of iron
Authors: Wu Ruqian , Freeman A.J. , Olson G.B.
Published: September 2007

Using the all-electron full potential linearized augmented plane wave (FLAPW) total energy method, the influence of P impurity atoms on the cohesion of the Fe Σ3[1$\overline 1$10](111) grain boundary is studied through direct comparison of phosphorus/iron interactions in the grain boundary and free surface environments. The calculated nearest P–Fe distance in P/Fe(111) is 2.14 Å—amounting to a 5% contraction compared to that (2.26 Å) measured for the Fe3P compound and assumed for the P–Fe grain boundary. The polar-covalent P–Fe chemical bonding, which is a strong function of the P–Fe interatomic distance, is thus stronger on the Fe(111) surface, while P reduces the spin polarization of the surrounding Fe atoms more efficiently in the grain boundary environment. These effects are examined in terms of the relative segregation energies affecting the work of boundary fracture.
The fcc to hcp transition induced by mechanical deformations in the Ni–Ru system
Authors: Van Neste A. , Lamarre A. , Trudeau M.L. , Schulz R.
Published: September 2007

The structural transition between the metastable fcc and hcp crystalline solid solutions in the Ni–Ru system has been studied as a function of composition using the mechanical alloying technique. At the transition point, the spacings between the close-packed planes of the metastable fcc and hcp phases are the same. No amorphization is observed at the interfaces. This mechanically induced phase transition has been studied by x-ray diffraction, transmission electron microscopy, and differential thermal analysis.
Pulsed-power volume-heating chemical vapor infiltration
Authors: Morell José I. , Economou Demetre J. , Amundson Neal R.
Published: September 2007

The dynamic behavior of a novel chemical vapor infiltration (CVI) technique called pulsed-power volume-heating CVI is investigated using a diffusion-reaction model. In this technique, a volume-heating source (e.g., RF or microwave) is used to heat the preform. The source power is modulated in time (e.g., square-wave modulation) with a specific period and duty cycle. During the low-power part of the cycle, the temperature of the composite drops, reducing the reaction rate and thus allowing the precursor gas to diffuse into the composite, essentially “refilling” the composite. This alleviates reactant concentration gradients within the composite minimizing density nonuniformities. The high-power part of the cycle is used to achieve rapid reaction rates, thereby minimizing processing time. CVI of a carbon fiber preform with carbon resulting from methane decomposition is taken as an example to illustrate the technique. The results reveal the dependence of density uniformity and processing time on relevant variables such as pulse period, duty cycle, power density level, and methane mole fraction. It is shown that pulsed-power volume-heating CVI can provide a window of operating conditions leading to rapid and complete densification.