bluuebunny/crossref_metadata_2025 huggingface dataset:
Conductive LaNiO3 Electrode Grown by Pulsed Laser Ablation on Si Substrate
Authors: Sun Li , Yu Tao , Chen Yan-Feng , Zhou Jun , Ming Nai-Ben
Published: March 2008

Using the pulsed laser ablation (PLA) technique, conductive LaNiO3 thin films have been successfully grown on (001) Si substrates. The XRD θ-2θ scan patterns indicate a preferential (110) orientation, and the electron probe microanalyzer (EPMA) investigations show that the three elements La, Ni, and O distribute uniformly in the films. The resistivity of the as-deposited LaNiO3 films display a metallic character. Polycrystalline PbTiO3films are deposited by metalorganic chemical vapor deposition (MOCVD) on these LaNiO3 electrodes. Ferroelectricity measurements of the PbTiO3/LaNiO3 heterostructure prove LaNiO3 to be a promising electrode material in the integration of ferroelectrics and Si wafer.
Microstructure and Homogeneity of Nanocrystalline Co–Cu Supersaturated Solid Solutions Prepared by Mechanical Alloying
Authors: Huang J. Y. , Yu Y. D. , Wu Y. K. , Li D. X. , Ye H. Q.
Published: March 2008

Mechanical alloying (MA) has been performed in the CoxCu(100-x) (x = 10, 25, 50, 60, 75, and 90) system. High resolution electron microscopy (HREM) and field emission gun transmission electron microscopy (FEG TEM) were used to characterize the microstructure and homogeneity of the nanocrystalline Co25Cu75 solid solution. After 20 h of MA, all the mixtures show an entirely face-centered cubic (fcc) phase. HREM shows that the ultrafine-grained (UFG) materials prepared by MA contain a high density of defects. Two kinds of typical defects in UFG Co25Cu75 are deformation twins and dislocations. The dislocations are mostly 60° type, and in many cases they dissociate into 30° and 90° partials. The grain boundaries are ordered in structure, curved, and slightly strained, which is similar to that observed in NC–Pd. Nanoscale energy dispersive x-ray spectroscopy (EDXS) shows that the Co concentration in both the interior of grains and the GB's is close to the global composition, which proves that supersaturated solid solutions are indeed formed. In the meantime EDXS revealed that the mixing of Co and Cu in the solid solutions is homogeneous at nanometer scale. MA in the Co–Cu system is suggested to be a diffusion-controlled process, and stress-stimulated diffusion is proposed to be the reason for the formation of supersaturated solid solutions in this immiscible system.
Similarities and Differences in the Microstructure of Attritor-milled Fe–Al–N Compositions
Authors: Rawers J. C. , Cook D.
Published: March 2008

Although numerous studies of high-energy, ball-milled metal powders have been conducted, to date few studies have characterized the mechanical processing of identical elemental compositions of prealloyed powders and of powder blends. This study reports on the mechanical processing (attritor ball milling) in argon and nitrogen gas environments of (a) iron powder and prealloyed iron–2 wt.% aluminum powder, and (b) iron-aluminum, iron-aluminum nitride, and iron-iron nitride powder blends. When nitrogen was milled into iron particles either from nitride powder or by gas infusion, the nitrogen dissolved interstitially in bcc-Fe (principally at the grain boundaries) or was present as bct-Fe nanoparticles at the bcc-Fe nanograin boundaries. The resulting nitrogen distribution was independent of how the nitrogen was added. Milled blends of iron and aluminum powder and prealloyed iron-aluminum powder resulted in similar microstructures: micrometer size particles with similar nanograin size. The aluminum in the blended powder mixture developed an ultrafine distribution on the grain boundaries, but it did not become uniformly distributed within the bcc-Fe grains. In contrast, the aluminum in prealloyed Fe–Al powder remained in solid solution during the mechanical milling
Analysis of Ball-indentation Load-depth Data: Part I. Determining Elastic Modulus
Authors: Taljat B. , Zacharia T. , Haggag F. M.
Published: March 2008

Analysis of ball-indentation process was made by the finite element (FE) method. A series of indentation FE analyses were made on materials with different elastic modulus (E), and a simple relationship between E and the load-depth (F-h) unloading data is presented. In order to check for the influence of other material properties, thorough research has been performed, introducing a combination of response surface (RS) and FE analysis. As a result, a relationship between the indentation unloading slope, E, and the strain hardening exponent was derived. Also, the indenter compliance effect has been investigated. The indenter compliance correction was calculated and applied to the experimentally measured F-h results. Experimental testing was made on three materials with essentially different elastic moduli. Comparison of the results obtained by newly developed equations with the results from other well-known equations is also presented.
Microstructure of Ruthenium Dioxide Films Grown on α–Al2O3 (0001), α–Al2O3 (1102), and SrTiO3 (100) Using Reactive Sputtering
Authors: Wang Q. , Gilmer Dave , Fan Yue , Franciosi Alfonso , Evans D. Fennell , Gladfelter Wayne L. , Zhang Xiao Feng
Published: March 2008

A quantitative study was made of the composition and microstructure of RuO2 films deposited on three different substrates using reactive sputtering. Most of the films had a composition within 2.5 wt.% of the correct stoichiometry; the only exceptions were films grown on Al2O3 (0001) at 150 °C, which had an oxygen-to-ruthenium ratio of 1: 2.24. The excess oxygen was attributed to a thin oxygen-rich layer that encapsulated the grains. Hydrogen concentrations for the films deposited on Al2O3 (0001) were 14, 6, 6, and < 0.5 at.% for room, 150, 300, and 450 °C growth temperatures respectively. The films deposited at room temperature were amorphous on Al2O3 (0001) and SrTiO3 (100), but weakly crystalline on Al2O3 (1102). Highly oriented RuO2 (100) films were produced on Al2O3 (0001) at deposition temperatures ≥150 °C. The in-plane alignment was and a threefold mosaic microstructure was observed. The grain boundaries in these films were discontinuous until the substrate temperature was raised to 450 °C, where coherent grain boundaries were formed. The films grown on Al2O3 (1102) at 450 °C exhibited the epitaxial relationship: RuO2(101)//Al2O3 (1102). The in-plane alignment was RuO2〈101〉//Al2O3〈1101〉, and the lattice parameters were the same as found in bulk RuO2. Transmission electron microscopy indicated a large degree of imperfection in the region between coalescing grains. The RuO2 films grown on SrTiO3 (100) at room temperature were amorphous. The film grown at 450 °C showed a preferential orientation with RuO2 (100)//SrTiO3 (100), but without in-plane orientation.
In situ Sputter Deposition of PbTiO3 Thin Films on Different Substrates: Influence of the Growth Temperature and the Sputtered Lead Flux on the Perovskite Phase Formation
Authors: Jaber B. , Rèmiens D. , Thierry B.
Published: March 2008

Thin films of lead titanate were prepared in situ using radio-frequency magnetron sputter deposition. The in situ perovskite phase formation has been studied as a function of the substrate temperature, the sputtered lead flux, and the substrate nature. The incident lead flux is controlled by the lead content in the target. An equilibrium zone, i.e., a saturation effect of the lead incorporation, exists where the films are stoichiometric. The temperature at which this zone appears depends on the sputtered lead flux and the substrate type. The growth mechanism is governed by a competition between the arrival rate of Pb and their re-evaporation from the film during the growth. The in situ formation temperature of the perovskite phase increased when the incident Pb flux increased. As a result, PbTiO3 films have been prepared at low temperature with appropriate combination of the substrate temperature and the lead content in the target, i.e., the sputtered lead flux. Since the lead sticking coefficient is very sensitive to the substrate material, the perovskite phase appears at different temperatures, depending on the substrate nature. PbTiO3 films are obtained at 550 °C on Al2O3 and SrTiO3 substrates; on Si/SiO2/Ti/Pt substrates, stoichiometric films are obtained at 440 °C. The structure and the microstructure of the films were examined at various deposition conditions. The substrate temperature strongly influenced the film orientation, and the crystallinity depended on the incident lead flux. High quality thin films (FWHM = 0.2°) are obtained at 550 °C on SrTiO3 substrates. The films deposited at 440 °C on Si/SiO2Ti/Pt show ferroelectric properties. This self-controlling mechanism of the stoichiometric composition allows the growth of ferroelectric films at low temperature, compatible with semi-conductor technologies for the realization of integrated circuits
Sol-gel Synthesis of LaAlO3; Epitaxial Growth of LaAlO3 Thin Films on SrTiO3(100)
Authors: Shoup Shara S. , Paranthaman Mariappan , Beach David B. , Specht E. D. , Williams Robert K.
Published: March 2008

A LaAlO3 precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO3 powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO3 powders when fired in air at 800 °C. A partially hydrolyzed solution was spun-cast on SrTiO3 (100) single crystal substrates. Epitaxial films of LaAlO3 were subsequently formed during pyrolysis in O2 at 800 °C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM) = 0.87°, and had good in-plane texture shown by a φ scan of the (202) plane with FWHM = 1.07°.
Electrically Controlled Flame Synthesis of Nanophase TiO2, SiO2, and SnO2 Powders
Authors: Vemury Srinivas , Pratsinis Sotiris E. , Kibbey Lowinn
Published: March 2008

Nanophase particles with precisely controlled characteristics are made by oxidation of their halide vapors in electrically assisted hydrocarbon flames using needle-shaped or plate electrodes. The particle size and crystallinity decrease with increasing field strength across the flame. The field generated by the electrodes across the flame decreases the particle residence time in the high temperature region of the flame. Furthermore, it charges the newly formed particles, resulting in electrostatic repulsion and dispersion that decreases particle growth by coagulation. Electric fields reduced the primary particle size of TiO2, the agglomerate size of SnO2, and both the agglomerate and primary size of SiO2.
High Strength, Electrically Conductive Pore-free TiO2 Ceramics made by Hot Isostatic Pressing
Authors: Kishi Yukio , Ogura Katsuhiko , Kamata Kiichiro , Saitoh Hidetoshi , Uematsu Keizo
Published: March 2008

A high-purity, single-phase TiO2 ceramic with high density, strength, and electrical conduction was developed as a key structural material for the production equipment of semiconductors. Green bodies were made of high purity rutile TiO2 of very fine powder. They were sintered in air at 1200 °C for 2 h and then were hot isostatically pressed (HIPed) in argon at 1000 °C, 150 MPa for 2 h. HIPed TiO2 ceramics were found to be electrically conductive and pore free. Their relative density, specific resistance, and bending strength were 100%, 1 Ω ·cm, and 300 MPa, respectively. No strength degradation was found to the temperature up to 1000 °C. This material has high potential for use as electrically conductive structure materials in the semiconductor industry.
Adsorption of Poly(vinyl butyral) in Nonaqueous Ferrite Suspensions
Authors: Jean Jau-Ho , Yeh Shun-Fen , Chen Chi-Jen
Published: March 2008

The adsorption of poly(vinyl butyral) (PVB) on NiCuZn ferrite powder in binary solvent systems of 1-butanol and toluene has been investigated. The adsorption isotherms of different PVB's on ferrite powder from various solvent mixtures follow closely the Langmuir monolayer types and can be explained by adsorption competition between solvents and PVB. A relatively poor solvent for PVB increases its adsorption on ferrite powder and thus improves the dispersion of the powder in the nonaqueous suspension. The adsorbance of PVB increases with increasing hydroxyl content in PVB suggesting that PVB is bonding strongly to the protruding surface hydroxyl groups on ferrite powder.
Magnetic Properties of Graphitically Encapsulated Nickel Nanocrystals
Authors: Hwang J.-H. , Dravid V. P. , Teng M. H. , Host J. J. , Elliott B. R. , Johnson D. L. , Mason T. O.
Published: March 2008

Graphitically encapsulated ferromagnetic Ni nanocrystals have been synthesized via a modified tungsten arc-discharge method. By virtue of the protective graphitic coating, these nanocrystals are stable against environmental degradation, including extended exposure to strong acids. The magnetic properties of the encapsulated particles are characterized with regard to the nanoscale nature of the particles and the influence of the graphitic coating which is believed to be benign insofar as the intrinsic magnetic properties of the encapsulated nanocrystals are concerned. The Curie temperature of graphitically encapsulated Ni nanocrystals is the same as that of microcrystalline Ni. However, saturation magnetization, remanent magnetization, and coercivity of these particles are reduced, for a range of temperatures. The unique features are compared with those of unencapsulated nanocrystalline and coarse microcrystalline nickel particles.
Investigation of NiAl–TiB2in situcomposites
Authors: Guo J. T. , Xing Z. P.
Published: March 2008

A hot-pressing aided exothermic synthesis (HPES) technique to fabricate NiAl matrix composites containing 0 and 20 vol.% TiB2 particles was developed. The conversion of mixtures of elements to the product was complete after processing, and TiB2 particles in the matrix were uniformly dispersed. The microstructure and interfaces were very thermally stable. The interfaces between NiAl and TiB2 were atomically flat, sharp, and generally free from interfacial phases. In some cases, however, thin amorphous layers existed at NiAl/TiB2 interfaces. At least three kinds of orientation relationships between TiB2 and NiAl were observed. The compressive yield strengths at room temperature and at 1000 °C of the composite were approximately three times as strong as those of the unreinforced NiAl. The tensile yield strength at 980 °C of the composite was about three times stronger than that of NiAl. The ambient fracture toughness of the composite was slightly greater than that of the monolithic NiAl.
Optically Transparent Polymethyl Methacrylate Composites made with Glass Fibers of Varying Refractive Index
Authors: Kang Seunggu , Lin Hongy , Day Delbert E. , Stoffer James O.
Published: March 2008

The dependence of the optical and mechanical properties of optically transparent polymethyl methacrylate (PMMA) composites on the annealing temperature of BK10 glass fibers was investigated. Annealing was used to modify the refractive index (R.I.) of the glass fiber so that it would more closely match that of PMMA. Annealing increased the refractive index of the fibers and narrowed the distribution of refractive index of the fibers, but lowered their mechanical strength so the mechanical properties of composites reinforced with annealed fibers were not as good as for composites containing as-pulled (chilled) glass fibers. The refractive index of as-pulled 17.1 μm diameter fibers (R.I. = 1.4907) increased to 1.4918 and 1.4948 after annealing at 350 °C to 500 °C for 1 h or 0.5 h, respectively. The refractive index of glass fibers annealed at 400 °C/1 h best matched that of PMMA at 589.3 nm and 25 °C, so the composite reinforced with those fibers had the highest optical transmission. Because annealed glass fibers had a more uniform refractive index than unannealed fibers, the composites made with annealed fibers had a higher optical transmission. The mechanical strength of annealed fiber/PMMA composites decreased as the fiber annealing temperature increased. A composite containing fibers annealed at 450 °C/1 h had a tensile strength 26% lower than that of a composite made with as-pulled fibers, but 73% higher than that for unreinforced PMMA. This decrease was avoided by treating annealed fibers with HF. Composites made with annealed and HF (10 vol. %)-treated (for 30 s) glass fibers had a tensile strength (∼200 MPa) equivalent to that of the composites made with as-pulled fibers. However, as the treatment time in HF increased, the tensile strength of the composites decreased because of a significant reduction in diameter of the glass fiber which reduced the volume percent fiber in the composite.
Fatigue of in situ Reinforced Ti–8.5Al–1B–1Si
Authors: Rangarajan S. , Aswath P. B. , Soboyejo W. O.
Published: March 2008

The effect of temperature on the fatigue and fracture properties of an in situ reinforced super α alloy Ti–8.5Al–1B–1Si (wt. %) was investigated. At room temperature the as-extruded composite has a strength of 631 MPa with limited ductility. On increasing the temperature to 700 °C only a marginal drop in strength to 610 Mpa was observed along with a significant improvement in ductility to 5.9%. Low-cycle fatigue results indicate a marginal decrease in fatigue life as temperature is increased from room temperature to 700 °C. Fatigue crack growth studies in the as-extruded microstructure indicate a strong influence of R-ratio on both the threshold for fatigue crack growth and crack growth rates in the Paris regimes. At elevated temperatures, the resistance to fatigue crack growth increases with temperature below approximately 500 °C. At 600 °C, however, there is an increase in the near threshold crack growth rate due to embrittlement effects. At higher δK values , the resistance to fatigue crack growth at elevated temperatures is always better than that at room temperature. This improvement is attributed to the increase in the inherent resistance
Excimer laser deposition of c-axis oriented Pb(Zr, Ti)O3 thin films on silicon substrates with direct-current glow discharge
Authors: Zheng Lirong , Hu Xuhong , Yang Pingxiong , Xu W-ping , Lin Chenglu
Published: March 2008

Ferroelectric thin films of Pb(Zr, Ti)O3 (PZT) were fabricated on platinum-coated silicon using the process of direct-current glow discharge assisted laser deposition, where the substrate was electrically grounded. The films deposited at 730 °C with +800 V discharge voltage are oriented mostly with the c-axis perpendicular to the substrate surface, and exhibit good ferroelectric hysteresis loops. A possible mechanism for the improvement of the deposition process has been proposed.
The syntheses of SiCp/Al nanocomposites under high pressure
Authors: Liu Haozhe , Wang Aimin , Wang Luhong , Ding Bingzhe , Hu Zhuangqi , Peng Hongying
Published: March 2008

The SiCp/Al nanocomposites were synthesized under high pressure. The reaction behavior between SiC particles and Al matrix within 2–6 GPa pressure range was determined. The high resolution electron microscopy (HREM) observation and the Vickers microhardness measurement show that the reaction is slight and that the adhesion of SiC particles to the Al matrix is good whether the reaction between them occurred or not. This offers an opportunity to tailor the nanocomposite mechanical properties by adjusting the synthesis temperature, pressure, and volume fraction of SiC particles.
Two-stage sintering of dense superconducting YBa2Cu4O8 ceramics
Authors: Matsuda Motohide , Ogawa Yoshihisa , Yamashita Kimihiro , Umegaki Takao , Miyake Michihiro
Published: March 2008

Dense YBa2Cu4O8 (124) ceramics were prepared by the following two-stage sintering: compressed 124 powders were heated to 1203 K for decomposition to YBa2Cu3O7−x (123) and CuO, and then cooled down to 1073 K and annealed for the re-formation of 124 single phase. The relative densities thus obtained were 93–95%, as high as those prepared under high oxygen pressure. The densification was considered to take place due to the liquid phase. In the sintered 124, the island-like fine grains of CuO were observed within the 123 matrix. As a result, it was considered that the re-formation of 124 proceeded in each grain. The geometrical phase distribution in the grains is discussed on the basis of superconducting properties from resistivity measurements.
Single crystal growth of cuprates from hydroxide fluxes
Authors: Sunshine S. A. , Siegrist T. , Schneemeyer L. F.
Published: March 2008

Barium and potassium hydroxide have been investigated as fluxes for the growth of cuprate single crystals. The relatively high solubility of transition metals and lanthanoids in these salt fluxes at moderate temperatures allows significant lowering of the growth temperatures required for many phases. Also, phases not stable at high temperatures become accessible. Two new cuprates have been prepared in the Ba–Ca–Cu–O and Ba–Y–Cu–O systems from a Ba(OH)2 · H2O flux. The compounds Ba3(Y0.23Cu0.77)2O5.78 and Ba3(Ca0.24Cu0.76)2O4.43 crystallize in a tetragonal (space group I4/mmm) oxygen deficient Sr3Ti2O7-type structure with lattice parameters a = 4.069(2) Å, 4.022(1) Å and c = 21.61(2) Å, 21.63(2) Å, respectively. The compound (Ba0.92Sr0.08) (Ca0.38Cu0.62)O2.1 crystallizes with a doubled perovskite unit cell along all three axes, a = 8.116(4) Å. In addition, single crystals of Ba2Ycu3O7–δ have been prepared from a KOH flux at 750 °C.
Optimizing diamond growth for an atmospheric oxyacetylene torch
Authors: Zeatoun Lua'y A. , Morrison Philip W.
Published: March 2008

Diamond growth conditions for an atmospheric combustion flame have been optimized using statistical experimental design. Films are grown on a molybdenum bolt for 40 min at a distance of 1 mm from the flame cone. The diamond films have been characterized using Raman spectroscopy, x-ray diffraction, and scanning electron microscope. The input process variables are varied over a range of conditions: total gas flow rate Q = 2–4 standard liter/min, substrate surface temperature Ts = 800–1000 °C, and flow ratio of O2/C2H2 = R = 0.93–0.99. The experimental response outputs are growth rate, full width half maximum (FWHM) of the diamond Raman peak, Raman diamond fraction (β) in the film, ratio of luminescence to diamond peak height (LR), and the relative intensity of the {220}, {311}, {400}, and {331} orientations. The film quality indices FWHM, β, and LR improve by increasing the gas ratio (R), by increasing substrate surface temperature (Ts), and lowering the growth rate by decreasing total gas flow rate. Diamond film shows a small amount texturing in {220} and {400} orientation at low R and Ts. At high R and low Ts crystals are oriented with the {111} direction normal to the substrate surface. Jet and boundary layer theory have been applied to understand the growth rate, the thickness profile, and the morphological instability of the diamond films. Surface Damkühler calculation shows that the deposition process is marginally controlled by mass transfer. Growth rate of an open flame is higher than for an enclosed flame, while the Raman quality measurements of the enclosed flame are more uniform than open flame over the range of the comparison.
Graphite encapsulated nanocrystals produced using a low carbon : metal ratio
Authors: Host Jonathon J. , Teng Mao H. , Elliott Brian R. , Hwang Jin-Ha , Mason Thomas O. , Johnson D. Lynn , Dravid Vinayak P.
Published: March 2008

Graphite encapsulated nanocrystals produced by a low carbon tungsten arc were analyzed to determine their chemistry, crystallography, and nanostructural morphology. Metallic nanocrystals of Fe, Co, and Ni are in the face-centered cubic (fcc) phase, and no trace of the bulk equilibrium phases of body-centered cubic (Fe) and hexagonal close-packed (Co) were found. Various analytical techniques have revealed that the encased nanocrystals are pure metal (some carbide was found in the case of Fe), ferromagnetic, and generally spherical. The nanocrystals are protected by turbostratic graphite, regardless of the size of the nanocrystals. The turbostratic graphite coating is usually made up of between 2 and 10 layers. No trace of any unwanted elements (e.g., oxygen) was found. The low carbon: metal ratio arc technique is a relatively clean process for the production of graphite encapsulated nanocrystals.
Domain structure of epitaxial PbTiO3 films grown on vicinal (001) SrTiO3
Authors: Theis C. D. , Schlom D. G.
Published: March 2008

Epitaxial PbTiO3 films have been grown on vicinal (001) SrTiO3 substrates by pulsed laser deposition. Vicinal SrTiO3 substrates with misorientations up to 9° from (001) were used, and the influence of the direction of misorientation on the resulting domain structure was studied. 4-circle x-ray diffraction analysis indicates that thin (40 nm) PbTiO3 films are completely c-axis oriented [rocking curve full-width-at-half-maximum (FWHM) of 0.25° for the 002 reflection] and that thicker films (∼ 200 nm) contain mixed a-axis and c-axis PbTiO3 domains due to twinning along {011} planes. The [100] axis of the a-axis domains is misoriented by 2.1° to 3.3° toward 〈100〉 substrate directions with respect to the substrate normal. In contrast to growth on well-oriented (001) SrTiO3 surfaces where the four equivalent tilts of the [100] axis of the a-axis domains are equally likely, on vicinal SrTiO3 the a-axis domains are preferentially oriented in an uphill direction with respect to the crystallographic miscut.
Nucleation and growth of oriented diamond on Si(100) by bias-assisted chemical vapor deposition
Authors: Nishitani-Gamo Mikka , Ando Toshihiro , Yamamoto Kazuo , Dennig Paul A. , Sato Yoichiro
Published: March 2008

In order to clarify the effect of bias treatments on the highly oriented growth of diamond, we investigated the relation between the silicon surface morphology changes after applying a bias voltage, and the orientation of the diamond crystallites after growth. We report two major findings. First, a textured structure on the Si surface after the bias pretreatment was found to be a necessary but insufficient indicator for the subsequent growth of highly oriented diamond. Second, although bias pretreatments effectively enhance nucleation, we did not find a clear relationship between the nucleation density and the percentage of oriented crystallites. The highest nucleation densities resulted in randomly oriented films. We conclude that bias pretreatments affect the nucleation enhancement and the diamond orientation through different mechanisms.
Effect of lattice mismatch on the epitaxy of sol-gel LiNbO3 thin films
Authors: Derouin T. A. , Lakeman C. D. E. , Wu X. H. , Speck J. S. , Lange F. F.
Published: March 2008

A solution precursor method based on metal alkoxides was used to produce epitaxial LiNbO3 thin films, ≈200 nm thick, on (0001) sapphire substrates. Transmission electron. microscopy revealed that the major cause of surface roughness in these films was grain boundary grooves between mosaic grains with misorientations ≤5°. It is postulated that these low angle boundaries directly result in surface grooving and roughness. The epitaxial films also contained two distinguishable variants in the film/substrate interfacial plane, namely, an aligned variant, and a 60° rotated variant, . A seeded grain growth method was used to minimize the presence of the 60° rotated variant. An epitaxial buffer layer of Fe2O3 was used to lower the mismatch strain, eliminate the 60° rotated variant, and reduce the mosaic nature of the LiNbO3 film. X-ray rocking curve full-width-at-half-maximum (FWHM) values measured on the film peak indicate that the mosaic character can be reduced from 1.5° to 0.76° by using a buffer layer.
Lattice site and photoluminescence of erbium implanted in α–Al2O3
Authors: van den Hoven G. N. , Polman A. , Alves E. , Silva M. F. da , Melo A. A. , Soares J. C.
Published: March 2008

Single-crystal sapphire (α–Al2O3) was implanted at room temperature with 200 keV erbium ions to a fluence of 8 × 1013 cm–2. Ion channeling using 1.6 MeV He+ shows that the crystal suffers little damage for this low dose implant. Angular scans through axial and planar directions in the crystal indicate that 70% of the Er atoms reside on displaced octahedral sites in the α–Al2O3 lattice. As pure Al2O3 has a high density of free octahedral sites, this explains why high concentrations of Er can be dissolved in this material. Smaller fractions of Er are found on tetrahedral (20%) and random (10%) sites. The samples exhibit strongly peaked photoluminescence spectra around 1.5 μm, due to intra-4f transitions in Er3+, indicating the existence of well-defined sites for the luminescing Er3+ ions. It is concluded that the octahedral site is the dominating optically active site in the lattice.
Agglomeration of silica spheres under ultrasonication
Authors: Enomoto Naoya , Maruyama Shingo , Nakagawa Zenbe-e
Published: March 2008

Power ultrasound of 20 kHz was applied to the synthesis of silica spheres via the controlled hydrolysis of tetraethoxysilane (TEOS). Silica spheres of about 0.3 μm were agglomerated to form tolerably uniform, dense particles of about 2 μm through 90 min sonication. This agglomeration behavior was examined by laser diffraction particle size analysis and transmission electron microscopy. It was found that the agglomeration process involves (I) an incubation period in which no agglomeration occurs, (II) rapid formation of ramified particles, and (III) their densification. It was inferred that sonication enhances collision among silica spheres.
Anomalous behavior of the optical band gap of nanocrystalline zinc oxide thin films
Authors: Srikant V. , Clarke D. R.
Published: March 2008

The optical band gap of ZnO films on fused silica in the carrier concentration regime of 1018−1020/cm3 is reported. Contrary to theoretical predictions there is an anomalous increase in the band gap of ZnO films at a carrier concentration of 5 × 1018/cm3, followed by an abrupt decrease at a critical concentration of 3−4 × 1019/cm3 before the optical band gap rises again. Similar observations have been made before, but an explanation of these observations was lacking. We propose a model based on the existence of potential barriers at the grain boundaries, causing quantum confinement of the electrons in the small grains realized in these films. Quantum confinement leads to the initial rise in the optical band gap. On increasing the carrier concentration to the critical value, the potentials at the grain boundaries collapse, leading to the abrupt decrease in the optical band gap. Above this carrier concentration the films behave according to existing many-body theories.
Crystal structure and microwave dielectric properties of M(NbxTa1−x)2O6 solid solution (M = Mg or Zn)
Authors: Lee Hyo-Jong , Hong Kug-Sun , Kim In-Tae
Published: March 2008

The microwave dielectric characteristics and crystal structure of the Zn(NbxTa1−x)2O6 and Mg(NbxTa1−x)2O6 systems have been investigated. It was found that both systems exhibited a morphotropic phase transition. Based on the results it was suggested that permittivity and temperature coefficient of resonant frequency depend more on crystal structure rather than on chemical composition. It was also suggested that a two-phase mixture is better than a solid solution for achieving both high quality factor and good temperature stability.
Sol-gel processing of nanocrystalline haematite thin films
Authors: Armelao L. , Armigliato A. , Bozio R. , Colombo P.
Published: March 2008

The microstructure of Fe2O3 sol-gel thin films, obtained from Fe(OCH2CH3)3, was investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. Samples were nanocrystalline from 400 °C to 1000 °C, and the crystallized phase was haematite. In the coatings, the α–Fe2O3 clusters were dispersed as single particles in a network of amorphous ferric oxide.
Factors controlling carbon retention in YBa2Cu3O7−δ
Authors: Cazy Evelyne , Khalfi Ali , Smith David S. , Bonnet Jean Pierre
Published: March 2008

Natural degradation of YBa2Cu3O7−δ powders leads to trapping of CO2 by the powder. The presence of residual carbon in ceramics or textured materials can strongly affect the superconducting properties. Optimal conditions for carbon elimination during thermal treatment are defined. Amounts of carbon lower than 500 ppm are easily obtained when thermal treatment is performed in temperature, gas flowing rate, and heating ramp conditions allowing CO2 departure before pore closure. Liquid phase formation and the presence of BaCuO2 are limiting factors. An oxycarbonate formed by reaction between this latter compound and evolved CO2 is implied in the last step of the decarbonation process.
Growth of CuInSe2 crystals in Cu-rich Cu–In–Se thin films
Authors: Wada Takahiro , Kohara Naoki , Negami Takayuki , Nishitani Mikihiko
Published: March 2008

A Cu-rich CuInSe2 (CIS) thin film with an atomic ratio of Cu/In = 3.6 was characterized using high-resolution and analytical transmission electron microscopy (TEM). The film was deposited on a Mo coated soda-lime glass substrate by physical vapor deposition. Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES) showed that a secondary impurity phase such as Cu2Se segregated on the CIS surface. The three-dimensional crystallographic relationship between the Cu2Se and CIS was found to be (111)Cu2Se (111)CIS and [011]Cu2Se || [011]CIS where the Cu2Se and CIS had pseudocubic structures with a = 5.8 Å and a = 11.6 Å, respectively. CuPt type CIS could be observed near the interface between the Cu2Se and CIS. A growth model of CIS crystals under Cu and Se excess condition is proposed based on the results of TEM. The characteristics of the CIS growth model in Cu-rich CIS film are summarized as follows: (i) CIS crystals are produced from Cu2Se crystals by a “topotactic reaction,” and (ii) sphalerite and/or CuPt type CIS are produced first after the reaction, and (iii) the metastable sphalerite and/or CuPt type CIS is then transformed to the stable chalcopyrite CIS phase.
The effect of arc parameters on the growth of carbon nanotubes
Authors: Lauerhaas J. M. , Dai J. Y. , Setlur A. A. , Chang R. P. H.
Published: March 2008

The influence of starting carbon material on the generation of carbon nanotubes is investigated. Comparisons are made between oriented graphite, randomly oriented graphite, carbon black, and a polycyclic aromatic hydrocarbon as carbon sources in helium and hydrogen arcs. Transmission electron microscopy investigation of the redeposited rod formed on the cathode and the soot from the chamber walls provides evidence for the building blocks that lead to the nanostructures formed. It is postulated that polycyclic aromatic hydrocarbons are precursors for carbon nanotube growth in a hydrogen arc. While, in the case of helium, low molecular weight carbon ions and molecules have been previously hypothesized by others to be the building blocks for nanotube growth.
Investigation of growth conditions of fibrous deposits in carbon arc
Authors: Byszewski P. , Ukalski K. , Mizera E. , Kowalska E.
Published: March 2008

Carbon fibrous deposits grown in carbon dc electric arc at various buffer gas pressures and arc currents were investigated by transmission and scanning electron microscopy. The fibers contained in the deposits consisted of bundles of carbon tubes. It was found that yield and morphology were very sensitive to both parameters; sintering of the tubes could be prevented by adjusting buffer gas pressure for a given current. It is argued that these parameters control expansion of carbon gas and condensation rate, and therefore energy flow to the cathode. To purify samples by oxidation and to observe differences in resistance against oxidation of samples obtained at various conditions, the thermogravimetry method was used.
Surface reactions of low-energy carbon ions with boron nitride thin films
Authors: Montero I. , Galán L.
Published: March 2008

The chemical reactions between hyperthermal species from a methane plasma and the boron nitride surface have been studied. In this work we report an x-ray photoemission study of the boron nitride with varying degrees of carburization. The carbon ions react, forming C–B and C–N bonds; for surface carbon concentration, smaller than ,∼0.30, C–B bonds are formed, while for higher surface carbon concentrations C–N bonds are also observed. In addition, the binding energy difference between the N1s and B1s core levels increases with increasing carbon content of the film. These chemical shifts are interpreted in terms of the decrease of the ionicity of the material as a consequence of the increase in the number of C–B and C–N bonds. For surface carbon concentration higher than 0.30, amorphous carbon is also formed that grows and finally forms a surface layer. The valence band spectra of the BNC compounds show that the density of states filling the gap at about 15 eV between the two characteristic peaks of the valence band of BN, marking the nitrogen 2s orbitals and the boron and nitrogen 2p electrons and the orbital hybridization between the 2s of boron and 2p states, increases with increasing carbon fluence as a consequence of the hybridization with carbon orbitals.
Low temperature growth and reliability of ferroelectric memory cell integrated on Si with conducting barrier stack
Authors: Dhote A. M. , Madhukar S. , Young D. , Venkatesan T. , Ramesh R. , Cotell C. M. , Benedetto Joseph M.
Published: March 2008

Polycrystalline LSCO/PNZT/LSCO ferroelectric capacitor heterostructures were grown by pulsed laser deposition using a composite conducting barrier layer of Pt/TiN on poly-Si/Si substrate. The growth of the ferroelectric heterostructure is accomplished at a temperature in the range of 500–600 °C. This integration results in a 3-dimensional stacked capacitor-transistor geometry which is important for high density nonvolatile memory (HDNVM) applications. Transmission electron microscopy shows smooth substrate-film and film-film interfaces without any perceptible interdiffusion. The ferroelectric properties and reliability of these integrated capacitors were studied extensively at room temperature and 100 °C for different growth temperatures. The capacitors exhibit excellent reliability, both at room temperature and at elevated temperatures, making them very desirable for HDNVM applications.
Structure and properties of carbon nitride films synthesized by low energy ion bombardment
Authors: He Xiao-Ming , Shu Li , Li Wen-Zhi , Li Heng-De
Published: March 2008

Carbon nitride films have been synthesized at low substrate temperature by Ar+ sputtering a graphite target with concurrent N+ assisted bombardment. It was disclosed that N+ bombardment with low energies of 150–400 eV and beam densities of 0.16–0.23 mA cm−2 was favorable to grow carbon nitride films with high N/C atomic composition ratios of 0.47–0.56. The spectra of x-ray photoelectron spectroscopy and infrared spectroscopy show that the low energy N+ bombardment activates nitrogen atoms to combine carbon atoms in unpolarized covalent bonds. Under the 150–300 eV and 0.16–0.23 mA cm−2 N+ assisted bombardment, the formed films are identified by transmission electron microscopy to possess the β–C3N4 microcrystalline structure. The films exhibit an extremely high hardness of 5260 kgf/mm2, a high resistivity of 4.8 × 1012 Ω × cm, and excellent optical transmittance. Friction and wear tests show that carbon nitride films on steel substrate can perform the even wear in low friction coefficients of 0.05–0.16 while raising wear loads up to 20 N.
Observations of Dislocations in Cu/Nb Nanolayer Composites After Deformation
Authors: Lu Y-C. , Kung H. , Griffin A. J. , Nastasi M. A. , Mitchell T. E.
Published: March 2008

Dislocations have been observed in deformed Cu/Nb nanolayer composites of wavelength 17 and 7 nm. The dislocations thread through the Cu/Nb interfaces even though there is a change of Burgers vector. Conventional and high resolution transmission electron microscopy studies show that the in-plane bowing direction of these dislocations in the Cu layers is opposite to that in the Nb layers, so that the dislocations appear to zig-zag. These observations are explained by the presence of residual tensile stresses in Cu and residual compressive stresses in Nb, which make dislocations bow in opposite directions in the alternating layers.
Radiation Effects in Glasses Used for Immobilization of High-level Waste and Plutonium Disposition
Authors: Weber William J. , Ewing Rodney C. , Angell C. Austen , Arnold George W. , Cormack Alastair N. , Delaye Jean Marc , Griscom David L. , Hobbs Linn W. , Navrotsky Alexandra , Price David L. , Stoneham A. Marshall , Weinberg Michael C.
Published: March 2008

This paper is a comprehensive review of the state-of-knowledge in the field of radiation effects in glasses that are to be used for the immobilization of high-level nuclear waste and plutonium disposition. The current status and issues in the area of radiation damage processes, defect generation, microstructure development, theoretical methods and experimental methods are reviewed. Questions of fundamental and technological interest that offer opportunities for research are identified.
Crystalline Phases and Electronic Structures in Superconducting Bi – Sr – Ca – Cu Oxides
Authors: Giardina M. D. , Feduzi R. , Inzaghi D. , Manara A. , Giori C. , Natali I. , Dallacasa V.
Published: March 2008

Two classes of samples, designated A and B, of layered Bi–Sr–Ca–Cu oxides having the same nominal composition 4 : 3 : 3 : 4, but different thermal histories, were investigated by using field modulated microwave absorption (ESR), powder x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and x-ray absorption near the edge structure (XANES). Previous electrical resistivity measurements showed that the B samples presented only two superconducting phases with midpoints of the transition temperatures at ∼80 K and ∼105 K. The microwave absorption technique indicated instead the presence of islands which became superconducting at the above-mentioned temperatures also in the A samples. The crystalline and electronic structures of the two types of samples are illustrated and discussed. A plausible theoretical interpretation of the experimental results, based on a quantum percolation model with Coulomb interaction, is also given.
Deformation Characteristics of Quasicrystalline Al–Cu–Fe Alloys
Authors: Shield J. E. , Kramer M. J.
Published: March 2008

The deformation characteristics of icosahedral Al–Cu–Fe quasicrystals were determined by high temperature creep experiments between 680 and 720 °C and 15 and 41 MPa. The deformation process was determined to be controlled by grain boundary mechanisms. Both the stress and grain size sensitivity exponents were found to be 2, suggesting that grain boundary sliding was the rate-controlling deformation mechanism. Microstructural analysis supported this conclusion, as no intragranular defects were produced during the deformation experiments.
Hardness and Modulus Properties in Ion-beam-modified Amorphous Carbon: Temperature and Dose Rate Dependences
Authors: Lee Deok-Hyung , Lee Hyukjae , Park Byungwoo
Published: March 2008

Ion implantation into amorphous carbon has been initiated to investigate the possibility of superhard carbon-nitride formation. Studies of implantation-temperature effects by 100 keV N+ or 80 keV C+ ions at 50 μA show a narrow temperature window at approximately −100 °C for the optimum surface hardness and elastic modulus (measured by nanoindentation), both values much higher than those for the unimplanted amorphous carbon. No distinguishable properties are found between nitrogen and self (carbon) implantations. At a dose rate of 5 μA, however, the optimum hardness and modulus are found at a lower implantation temperature, with a broader temperature window. The enhanced strengths are well correlated with the asymmetric diffuse peak at around 1500 cm−1 in Raman spectroscopy, and the increased ratio of sp3- over sp2-bonded carbon sites observed by electron energy loss spectroscopy.
Variations of Structure and Dielectric Properties on Substituting A-site Cations for Sr2+ in (Na1/2Bi1/2)TiO3
Authors: Park Seung-Eek , Hong Kug Sun
Published: March 2008

Changes in structure and phase transition behavior of (Na1/2Bi1/2)1−xSrxTiO3 were investigated using x-ray diffraction (XRD) analysis and dielectric measurements. A decrease in the degree of lattice distortion was observed when the structure was rhombohedral (x < 0.26). Further substitution of Sr2+ (x ≥ 0.26) caused (Na1/2Bi1/2)1−xSrxTiO3 to show no macroscopic lattice distortion. However, all investigated samples (0.1 ≤ x ≤ 0.5) were ferroelectric at room temperature regardless of the lack of lattice distortion found in XRD patterns. Further XRD investigations revealed that nonuniform strains caused by nonuniform polarized islands were responsible for this behavior. A-site cation substitution of Sr2+ also resulted in the decrease of Tmax (the temperature where dielectric constant is maximum). Typical relaxor ferroelectric phase transition behavior, associated with the shift of Tmax, with respect to the measuring frequencies, was found above x = 0.18. This could be also ascribed to the decrease of Tmax—this reveals the increase in the shift of Tmax with frequency, with associated decrease in ionic displacement and space charge contributions and associated increase in the relative contribution to the polarization by microdomains and domain walls at temperatures near Tmax.
Synthesis and Magnetic Properties of Nanostructured Maghemite
Authors: Vollath D. , Szabó D. V. , Taylor R. D. , Willis J. O.
Published: March 2008

Nanocrystalline maghemite, γ–Fe2O3, can be synthesized in a microwave plasma using FeCl3 or Fe3(CO)12 as the precursor. Electron microscopy revealed particle sizes in the range of 5 to 10 nm. In general, this material is superparamagnetic. The magnetic properties are strongly dependent on the precursor. In both cases the production process leads to a highly disordered material with the consequence of a low magnetization. The assumption of a disordered structure is also supported by electron energy loss (EEL) and Mössbauer spectroscopy. The structure of this material shows a nearly identical number of cations on tetrahedral and octahedral lattice sites.
Electronic Structures and Host Excitation of LaPO4, La2O3, and AlPO4
Authors: Mishra K. C. , Osterloh I. , Anton H. , Hannebauer B. , Schmidt P. C. , Johnson K. H.
Published: March 2008

We report the electronic structures and associated optical properties of three inorganic oxides, namely lanthanum oxide, aluminum phosphate, and lanthanum phosphate, calculated by the first principles augmented spherical wave (ASW) and full potential linear muffin tin orbital (FP-LMTO) band structure methods, and the self-consistent field Xα scattered wave (Xα SW) molecular orbital cluster approach. Our calculations indicate negligible effect of the choice of exchange correlation potentials on the position, shape, and relative ordering of the energy bands. The ASW energy gaps in lanthanum phosphate and aluminum phosphate agree satisfactorily with the measured values. A comparison of the electronic density of states for an isolated phosphate group from molecular orbital calculation and that of the valance band from the band structure methods indicates that the nature of bonding within the phosphate groups does not change in aluminum and lanthanum phosphates. The states near the top of the valence band and bottom of the conduction band are mostly due to the phosphate bonding and antibonding orbitals, indicating that optical absorption near the band edge involves excitation of electrons from the bonding levels to antibonding levels associated with phosphate groups. This explains why the optical gaps in many rare earth phosphates are nearly equal.