bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering of cubic boron nitride without additives at 7.7 GPa and above 2000 °C
Authors: Taniguchi Takashi , Akaishi Minoru , Yamaoka Shinobu
Published: March 2008

The sintering behavior of cBN powder with various particle sizes from 0.5 to 12 µm was investigated when sintered at temperatures from 1500 to 2500 °C and pressure of 7.7 GPa without additives. Above 2000 °C, translucent sintered bodies were obtained. Microstructure observation indicated that the optimum sintering temperature was near 2350 °C for fine powders of 0.5 to 1.2 µm and 2 to 4 µm, and slightly higher than 2350 °C for powders from 8 to 12 µm. The fracture toughness of the well-sintered bodies decreased with grain growth above the optimum sintering temperature.
Selective gas-sensing properties of surface ruthenated tin oxide
Authors: Chaudhary V. A. , Mulla I. S. , Vijayamohanan K.
Published: March 2008

Gas-sensing properties of a novel surface functionalized tin oxide material have been studied to demonstrate the possibility of selectivity control by surface state formation. Covalent anchoring of ruthenium oxide on the tin oxide surface (ruthenated tin oxide) is found to give considerable enhancement in sensitivity (320) as well as selectivity to 1000 ppm of liquified petroleum gas (LPG) at 300 °C compared to the sensitivity (4) of pure tin oxide samples. The amount and distribution of grafted ruthenium oxide on the surface of tin oxide seems to be the most important parameter controlling the change in electrical transport with LPG gas adsorption.
Processing of silicon carbide ceramics using chemically modified polycarbosilanes
Authors: Okuzaki Sachiko , Iwamoto Yuji , Kondoh Shinji , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

Chemically modified polycarbosilane (PC) which contains Si–Al–C–O component, PCOAl, was synthesized using PC and aluminum triisopropoxide. Ceramic yield was greatly improved through the modification of PC with a metal alkoxide. The phase transformation behavior and microstructure development of silicon carbide (SiC) were studied on β–SiC powders coated with chemically modified PC. The β-α phase transformation of SiC was enhanced by the coating of chemically modified PC on β–SiC powder. A unique microstructure with submicron-sized plate-like grains was developed, since the fine a phase produced at low temperature served as a nucleation site for the β-α phase transformation of SiC.
Ultraviolet patterning of KTiOPO4 thin films through metallo-organics
Authors: Noda Ken-ichi , Sakamoto Wataru , Yogo Toshinobu , Hirano Shin-ichi
Published: March 2008

Patterned KTiOPO4 (KTP) films were successfully synthesized through metallo-organics using ultraviolet (uv) patterning. A homogeneous precursor solution was prepared by the reaction control of (nBuO)2P(O) (OH), Ti(OEt)4, and KOEt in ethanol. The solubility of the KTP precursor films in ethanol changed with uv irradiation because of the polymerization of KTP precursor. The patterned KTP precursor films crystallized to single-phase KTP after heat treatment at 600 °C for 2 h. The patterned films were found to be exactly stoichiometric KTP.
Ion-beam mixing in energetic collision cascades: Thermal-spike model and experiments
Authors: Park Byungwoo , Lee Hyukjae
Published: March 2008

A phenomenological model of ion-beam mixing during energetic collision cascades is developed, based on the concept of a thermal spike, to correctly predict that the mixing rate Dt depends linearly on nuclear stopping power (instead of a power-law dependence), and is correlated with a heat of mixing (analogous to Darken's relation). Previous ion-beam mixing experiments from 25 different metallic bilayers agree well with the model's predictions: mixing rates (Dt)/(ion-dose) ∼ 1 nm4, and an activation enthalpy of approximately 1 eV for atomic diffusion in liquid-like cascades.
Distribution of intercalant in copper chloride and iron chloride graphite intercalation compounds
Authors: Tzeng Shinn-Shyong , Nien Mei-Hsueh
Published: March 2008

CuCl2 and FeCl3 graphite intercalation compounds were prepared by a gas phase reaction method using different carbon host materials. The effect of the microstructure of carbon host materials on the amount of intercalation and the distribution of intercalant was investigated using x-ray diffraction and electron microprobe analysis. For a fiber sample with a core region of onion skin structure in the cross section, a lower concentration of intercalant was measured in the core region. For fiber samples with an oriented-core transverse microtexture, different intercalant distributions along the long axis (oriented-core direction) and the short axis of the elliptical cross section were found.
The effect of lead content on the critical current density, irreversibility field, and microstructure of Ag-clad Bi1.8PbxSr2Ca2Cu3Oy tapes
Authors: Anderson J. W. , Dorris S. E. , Parrell J. A. , Larbalestier D. C.
Published: March 2008

We studied the effect of lead content (x = 0.20−0.40) on the critical current density Jc (0 T, 77 K), irreversibility field H* (77 K), and microstructure of monocore, Ag-clad Bi1.8PbxSr2Ca2Cu3Oy (2223) tapes, finding that tapes with lower lead contents (x = 0.20–0.25) required higher processing temperatures (840 and 832 °C, respectively) to complete 2223 formation, as compared to the optimum 820 °C reaction temperature of the x = 0.30–0.40 tapes. We found that both the zero-field and the in-field properties correlated strongly to the phase purity with Jc (0 T, 77 K) reaching a maximum of ˜20 kA/cm2 for x = 0.30, and then decreasing with increasing lead content to ˜12 kA/cm2 for x = 0.40. H* (77 K) increased from ˜165 mT at x = 0.20 to ˜265 mT at x = 0.30, then declined to 195 mT at x = 0.40. Optimizing the lead content at x = 0.30 maximized both the connectivity and the flux pinning contributions to the critical current density.
High temperature deformation of vertical gradient freeze method melt-textured Y1Ba2Cu3O7−x
Authors: Leenders A. , Ullrich M. , Kautschor L.-O. , Freyhardt H. C.
Published: March 2008

The deformation behavior of melt-textured Y1Ba2Cu3O7-x (YBCO) prepared by the vertical gradient freeze (VGF) method was investigated by high temperature deformation experiments at temperatures ranging from 850 to 950 °C. The experiments were performed in an atmosphere of pure oxygen under uniaxial pressure with constant strain rates in the range from 1 × 10−5 to 5 − 10−4 s−1. An analysis of the dependence of the steady state flow stress on the strain rate and the deformation temperature reveals that the predominant deformation mechanism is dislocation glide and climb controlled by climb at Y-211 particles and that no significant grain boundary sliding occurs. Furthermore, transmission electron microscopy observations of deformed and undeformed samples support a deformation mechanism based on dislocation movement. The total fracture strain, however, does not depend on the temperature or strain rate. Scanning electron microscopy investigations of the fracture faces of samples deformed until fracture reveal that fracture does not occur within the Y-123 matrix but along platelet boundaries. An improvement of the fracture behavior is expected by introducing large Y-211 particles interconnecting neighboring platelets.
Precipitation behavior in the early stage of aging in an Al–Li°Cu–Mg–Zr–Ag (Weldalite 049) alloy
Authors: Lee Kap Ho , Lee Yeung Jo , Hiraga Kenji
Published: March 2008

The precipitation behavior of various phases during the aging process of an Ag–Li°Cu–Mg–Zr–Ag (Weldalite 049) alloy was investigated by high-resolution electron microscopy and in situ hot-stage microscopy. Two kinds of domains with L12-type ordered structures, which are considered to be δ′ and β′ phases, are observed with different domain sizes in the alloy quenched from 530 °C. In the early stage of aging at 190 °C, the δ′ phase is precipitated as surrounding the β' phase, and the δ′ domains appear with in-phase and antiphase relationships to the β′ lattices. In situ observations at 190 °C clearly show that the T1 phase precipitates predominantly on dislocations at subgrain boundaries and then is homogeneously formed in the matrix with increasing aging time. The nucleation of the S′ phase is associated with clustering of Cu and Mg in the matrix, and the S0 domains are grown with {210} habit planes.
Grain boundary filmlike Fe–Mo–Cr phase in nitrogen-added type 316L stainless steels
Authors: Oh Yong Jun , Ryu Woo Seog , Sung Changmo , Kuk Il Hiun , Hong Jun Hwa
Published: March 2008

The precipitates in nitrogen-added type 316L stainless steels (SS) were investigated by transmission electron microscopy (TEM) after thermal aging. Besides carbides (M23C6 and M6C) and intermetallic phases, an unknown phase of an Fe–Mo–Cr(–Si) system n a filmlike morphology precipitated at grain boundaries. In spite of the similarity in ts chemical composition to that of the Laves phase, the phase of the Fe–Mo–Cr(–Si) system exhibited five-, three-, and twofold symmetries, which are generally observed in quasicrystals having icosahedral symmetry. This phase was formed from the intergrowth of small crystalline clusters of the Laves phase. Decreasing the nitrogen content to that of commercial type 316L grade suppressed the formation of the filmlike fivefold phase. This was attributed to the dissipation of small Laves clusters by M23C6 carbides, which increased as a result of the decreased nitrogen content.
The preparation and characterization of ultrafine Fe–Ni particles
Authors: Dong X.L. , Zhang Z.D. , Zhao X.G. , Chuang Y.C. , Jin S.R. , Sun W.M.
Published: March 2008

Ultrafine Fe, Fe–Ni, and Ni particles were prepared by using the hydrogen plasma-metal reaction method in a mixture of H2 and Ar of 0.1 MPa. The particles were characterized by x-ray diffraction, transmission electron spectroscopy, energy disperse spectroscopy, chemical analysis, and Mössbauer spectroscopy. In contrast with bulk Fe–Ni alloys, the distinguishing features in corresponding ultrafine particles are that two phases with fcc and bcc structures coexist in a wide composition range. Ultrafine Fe–Ni particles have higher resistance to oxidation than Fe and Ni particles. The mechanism of forming particles was analyzed by means of structural and magnetic measurements. It was found that quenching is a dominant mechanism for forming paramagnetic particles. Hyperfine interactions were studied by Mössbauer spectroscopy in comparison with those in bulk Fe–Ni alloys.
Dielectric, piezoelectric, and pyroelectric anisotropy in KCl-modified grain-oriented bismuth vanadate ceramics
Authors: Shantha K. , Varma K. B. R.
Published: March 2008

The effect of the additive KCl, on the structural, microstructural, and polar properties of bismuth vanadate (BiV) ceramics is investigated. The scanning electron microscopic (SEM) studies reveal a remarkable modification in the microstructure and the occurrence of high grain-orientation (75%) on KCl addition. The energy dispersive x-ray (EDX) analyses indicate the presence of chemically inhomogeneous distribution of KCl, with core-shell-like grain structure. The KCl-modified BiV samples exhibit a broad and depressed phase transition, with no frequency dispersion, as a result of the increased internal stress and the formation of core-shell-like grain structure. Significant anisotropies are observed in the dielectric, piezoelectric, and pyroelectric responses of these grain-oriented ceramic samples. These samples are characterized by near rectangular ferroelectric hysteresis loops, with a significant anisotropy in the Pr (Pr┴/Pr∥ = 2.43, at 300 K) and Ec (Ec∥/Ec┴= 2.22, at 300 K) values between the directions parallel and perpendicular to the cold-pressing axis.
Fabrication and characterization of ferroelectric Pb(ZrxTi1–x)O3 thin films by metalorganic chemical vapor deposition
Authors: Song Han Sang , Kim Tae Song , Kim Chang Eun , Jung Hyung Jin
Published: March 2008

Ferroelectric Pb(Zr, Ti)O3 (PZT) thin films were grown on Pt/Ti/SiO2/Si, RuO2/Pt/Ti/SiO2/Si, and Pt/MgO substrates at the substrate temperature of 600 °C by the metalorganic chemical vapor deposition (MOCVD) method. Pb(C11H19O2)2(Pb(DPM)2), Ti(OiC3H7)4, and Zr(OtC4H9)4 as source material and Ar and O2 as a carrier gas and oxidizing agent were selected, respectively. In order to investigate the effect of Zr and Ti component changes on the growth aspect of PZT thin films, Zr and Ti source materials were varied by controlling Zr and Ti flow rate. From the Rutherford backscattering spectroscopy (RBS) measurement, it was confirmed that the composition of the films, particularly Pb content, changed with the increasing Zr flow rate. In addition, the x-ray diffraction (XRD) spectra analysis showed the existence of a Pb-deficient pyrochlore phase as well as ZrO2 as a secondary phase. From these results, it is believed that the higher Zr partial pressure in the gas phase reduces the sticking of the Pb precursor to the substrate. The film with Pb:Zr:Ti = 1:0.42:0.58 showed a dielectric constant of 816 at 1 MHz. The spontaneous polarization, remanent polarization, and coercive field measured from the RT66A by applying 3.5 V were 44.1 μC/cm2, 24.4 μC/cm2, and 59.6 kV/cm, respectively. The fatigue analysis of PZT thin films with Pb:Zr:Ti = 1:0.42:0.58 at an applied voltage of Vp-p = 5.4 V showed 40% degradation on the basis of initial polarization value after 109 cycles.
Polaron conduction loss in microwave dielectric ceramics
Authors: Hong Seungbum , Kim Eunah , Song Han Wook , Choi Jongwan , Kim Dae-Weon , No Kwangsoo , Kim Tae-Hong , Park Jung-Rae , Han Jin-Woo
Published: March 2008

It has been generally accepted that the product of the unloaded quality factor and resonant frequency is the universal parameter for comparison of dielectric resonators with different size.1,2 However, it is suggested in this study that this universal parameter should be modified due to the presence of the polarons. From the frequency dependence of the unloaded quality factor, it is possible to extract the factor determined only by the phonon scattering effects, and we denoted this parameter by Qs. It was found that the Qs parameter for ZrxSnzTiyO4 (ZST) and Ba(Zn1/3Ta2/3)O3 (BZT) ceramics showed constancy in the frequency range of 2–12 GHz, which supports the idea of polaron conduction loss contribution to the dielectric loss.
Room temperature reduction of scheelite (CaWO4)
Authors: Welham N. J.
Published: March 2008

A mixture of scheelite and magnesium has been mechanically milled together for 100 h, either with graphite or in a nitrogen atmosphere, with the intention of forming tungsten carbide or nitride. The resultant powders were examined by thermal analysis, isothermal annealing, and x-ray diffraction to determine the effect of milling on the reduction of scheelite. With graphite, nanocrystallite W2C was the exclusive tungsten product; WC was not detected even after annealing at 1000 °C. No nitride formed in the system milled with nitrogen; however, 10 nm crystallites of elemental tungsten were formed. The unwanted phases, MgO and CaO, were readily removed by leaching in acid, leaving a fine powder composed of impact welded aggregates of either carbide or 99% pure tungsten metal.
Lattice-distortion-induced amorphization in indented [110] silicon
Authors: Wu Y. Q. , Xu Y. B.
Published: March 2008

High-resolution transmission electron microscopy (HRTEM) is used to reveal fine structures of amorphous silicon induced by Vickers indentation and its interface with unindented silicon matrix. Deformation microtwins at the interface and continuous transition from lattice structure of crystal into amorphous structure at the interface are observed. Within the amorphous silicon near the periphery of the indented region, there are many clusters characterized by distorted silicon lattice. A possible mechanism of lattice-distortion-induced amorphization at the periphery of indented silicon is suggested. All the indentations are performed at ambient temperature.
Spray pyrolysis preparation of porous polycrystalline thin films of titanium dioxide containing Li and Nb
Authors: Golego Nickolay , Studenikin S. A. , Cocivera Michael
Published: March 2008

Titanium dioxide thin films prepared with and without lithium and niobium were as follows: uniform, crack-free, and stoichiometric, amorphous as-deposited at 300 °C and below; polycrystalline anatase when deposited at 400 °C or annealed at 500−800 °C; and rutile when annealed at 900 °C. Films prepared around 200 °C were very porous, but the porosity decreased as the substrate temperature increased. Optical absorption spectra revealed an indirect bandgap of 3.0 eV for amorphous and anatase films, and a direct bandgap of the same value in rutile. Dark dc conductivity of undoped films was lower than 10−10 (Ω · cm)−1; Hall effect measurements indicated that effective electron mobility was below 1 cm2/(V · s). The presence of Nb and Li increased the conductivity by 2–3 orders of magnitude, similar to the effect of hydrogen annealing. Illumination increased the conductivity by several orders of magnitude, and the decay followed a multiexponential law extending into the 106 second range after irradiation was stopped. The electronic properties of the films were determined by oxygen-related surface states at grain boundaries. Samples containing Li exhibited considerable sensitivity to water vapor.
The effects of grain condition on magnetic properties in Nd4Fe76Co3(Hf1−xGax)B16 alloy
Authors: Youhui Gao , Jinghan Zhu , Yuqing Weng , Byung Eon , Yang Choong Jin
Published: March 2008

The best linear fit of Hc(T)/Ms(T) versus implies that Hc is determined by a nucleation process in nanocrystalline two-phase magnets. The condition of the grain shapes is improved after adding Hf and Ga, but the surfaces are deteriorated by some precipitates on the boundary. Taking into account the values of α, Neff, the results of transmission electron microscopy (TEM), and Mössbauer spectroscopy, the magnetic field heat treatment not only induces grain refinement but also causes a uniform distribution of the soft and hard phases. Both the remanence and energy product values are increased by 20–30% for all ribbons after annealing with magnetic field. The magnetic interaction in Nd2Fe14B/Fe3B + αFe-based nanocrystalline two-phase magnets is studied using δM plots in this paper. It is found that the exchange-coupled interaction is greatly enhanced in the sample annealed with magnetic heat treatment, especially Nd4Fe76Co3Hf0.5Ga0.5B16, which achieves the highest energy product (BH)max = 15.8 MGOe.
In situ scanning electron microscopy study of eutectic SnPb and pure Sn wetting on Au/Cu/Cr multilayered thin films
Authors: Zheng D. W. , Wen Weijia , Tu K. N. , Totta P. A.
Published: March 2008

Wetting behavior of eutectic SnPb and pure Sn on Au(500 Å)/Cu(1 μm)/Cr(800 Å) layered thin films were monitored in situ in a ramping temperature profile using a scanning electron microscope (SEM) with a vacuum of 10−5–10−6 Torr. We found that the wetting behavior of these two solders in SEM was dramatically different from their behavior in RMA soldering flux; a smaller wetting angle and rough wetting front morphology were observed. Very surprisingly, no dewetting could be observed inside the SEM chamber, yet dewetting happened to the same sample when it was removed from the SEM and immersed in RMA soldering flux. We estimate the interfacial energy between liquid Sn and solid Cr and assume the reduction of surface and interfacial energies caused by possible oxidation of Cr and liquid Sn surface in the SEM in order to explain the above-mentioned wetting and dewetting behaviors.
Strain sensing using carbon fiber
Authors: Wang Xiaojun , Fu Xuli , Chung D. D. L.
Published: March 2008

Carbon fiber provides strain sensing through change in electrical resistance upon strain. Due to piezoresistivity of various origins, a single carbon fiber in epoxy, an epoxy-matrix composite with short carbon fibers (5.5 vol%), a cement-matrix composite with short carbon fibers (0.2–0.5 vol%), and an epoxy-matrix composite with continuous carbon fibers (58 vol%) are strain sensors with fractional change in resistance per unit strain up to 625. A single bare carbon fiber is not piezoresistive, but just resistive.
Low volume fraction SiCp/AA 380.0 composites fabricated by vacuum infiltration
Authors: Chung Wen-Sheng , Chang Shou-Yi , Lin Su-Jien
Published: March 2008

A vacuum infiltration process has been developed to fabricate the aluminum matrix composites reinforced with low volume fraction (<50 vol%) of SiCp. Generally, it is difficult to fabricate low volume fraction particulate composites by traditional infiltration processes because the particles always pack up to about 50 vol% in the preforms or compacts. In this study, the powder compacts were prepared of the well-mixed Ni-coated SiCp and pure aluminum powders and then were packed in quartz tubes. An aluminum alloy (Al–8.7% Si–2.6% Cu) with a composition similar to AA 380.0 was used to infiltrate these compacts. Experimental results showed that the infiltration temperature of 640 °C is favorable for the fabrication of these composites. Infiltration behavior, microstructure, nickel distribution, bending test, and fractography of the composites were investigated.
Interfacial characterization using transmission electron microscopy examination of the diffusion bonding of SiC whisker-reinforced aluminum alloys
Authors: Ureña-Fernandez A. , Gómez de Salazar J. M. , Escalera M. D.
Published: March 2008

This paper describes the microstructural characterization, using transmission electron microscopy (TEM), of the solid-state, diffusion-bonded interfaces generated in a SiC whisker-reinforced, aluminum composite. Diffusion bonding was carried out using an aluminum-lithium alloy as the bonding interlayer. Two kinds of bonded interface were studied: those generated between the composite matrix and the metallic interlayer (metallic-metallic) and other ceramic-metallic interfaces formed between the interlayer and the SiC whiskers. The first showed the formation of zones of recrystallization across the original bond interface, and the second generally presented a high degree of continuity without the formation of interface reaction layers between the SiC whiskers and the interlayer. However, the formation of a degradation oxide layer was detected in some of the whisker/interlayer diffusion bonds. Its presence is due to the reaction between the alloying elements of the Al–Li interlayer and the SiO2 layer which surround some of the whiskers of the parent composite.
The interfacial reaction in Cr3C2/Al2O3 composites
Authors: Lii Ding-Fwu , Huang Jow-Lay , Huang Jin-Jay , Lu Horng-Hwa
Published: March 2008

This study investigates the effects of sintering atmosphere and temperature on the interfacial properties of Cr3C2/Al2O3 composites. Thermodynamic considerations and calculations with computer-assisted methods for the equilibrium compositions in the Al–O–Cr–C system were used to simulate the interfacial reaction in Cr3C2/Al2O3 composite during sintering. The results were in good agreement with the experimental analysis. Cr3C2 is more stable during sintering in a system with carbon due to the lower equilibrium oxygen partial pressure. Controlling CO and O2 gas concentration, Cr3C2 first oxidized, decarbonized, and then transformed to Cr7C3 before reacting with Al2O3. An interfacial reaction between Cr3C2 and Al2O3 was not observed.
Synthesis, structural, and morphological characterization of ceramics in the system Bi2O3–TiO2–CuO
Authors: Pérez-Arrieta L. , Mendoza-Alvarez M. E. , Silva-González R. , Alvarez-Fregoso O. , Tabares-Muñoz C.
Published: March 2008

This paper reports the formation of a solid solution in the system Bi2O3–TiO2–CuO. This solid solution seems to be isostructural with Bi4Ti3O12, according with the x-ray powder diffraction patterns. Microstructural studies done using scanning electron microscopy show the typical elongated Bi4Ti3O12 grain morphology only in samples with 2 : 2 : y molar ratios of the Bi2O3 : TiO2 : CuO oxides (y = 1, 2, or 3).
Microstructural studies of boron nitride films deposited by microwave plasma-assisted chemical vapor deposition by using trimethyl borazine precursor
Authors: Phani A. Ratna
Published: March 2008

Thin films of cubic boron nitride (c-BN) were synthesized using an organometallic precursor trimethylborazine (TMB) which contains both boron and nitrogen in 1 : 1 stoichiometric ratio. The films were deposited at different temperatures ranging from 300 to 500 °C at a pressure of 2 Torr and at 360 W microwave power, using N2 as carrier gas. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), which reveal the presence of amorphous BN and crystalline c-BN in varying proportions. The x-ray diffraction pattern of the deposited films showed a strongest peak at 2θ = 57.1° where the interplanar distance value, d = 2.06 Å, agreed well with the (111) crystallographic orientation of c-BN phase.
Preparation of a ZrO2–Al2O3 nanocomposite by high-pressure sintering of spray-pyrolyzed powders
Authors: Mishra R. S. , Jayaram V. , Majumdar B. , Lesher C. E. , Mukherjee A. K.
Published: March 2008

ZrO2–Al2O3 powders were synthesized by spray pyrolysis. These powders were sintered at 1 GPa in the temperature range of 700–1100 °C. The microstructural evolution and densification are reported in this paper. The application of 1 Gpa pressure lowers the crystallization temperature from ∼850 to <700 °C. Similarly, the transformation temperature under 1 GPa pressure for γ → α–Al2O3 reduces from ∼1100 to 700–800 °C range, and that for t → m ZrO2 reduces from ∼1050 to 700–800 °C range. It was possible to obtain highly dense nanocrystalline ZrO2–Al2O3 composite at temperatures as low as 700 °C. The effect of high pressure on nucleation and transformation of phases is discussed.
The structural transformation of anatase TiO2by high-energy vibrational ball milling
Authors: Sen Suchitra , Ram M. L. , Roy S. , Sarkar B. K.
Published: March 2008

The structural transformation of anatase TiO2by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size ∼13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2(II), which is a high-pressure phase and TiO2(B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.
Effects of PbO excess in Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics: Part I. Sintering and dielectric properties
Authors: Villegas M. , Caballero A. C. , Kosec M. , Moure C. , Duráan P. , Fernández J. F.
Published: March 2008

The influence of the presence of free PbO on densification, the perovskite/pyrochlore phase ratio, and corresponding dielectric properties has been studied for 0.9 PMN–0.1 PT-based ceramics with different added PbO excess. The sintering behavior of PMN-PT-based ceramics was basically controlled by PbO losses. However, the presence of a rich-PbO liquid phase during sintering produced pyrochlore grains, mainly located at the surface of the specimens. The dielectric properties of the PMN-PT-based materials, fabricated with different values of PbO excess, were similar when the secondary phase preferentially located at the surface was removed by polishing prior to electrode deposition. The thickness of the PbO-rich intergranular layers of the four samples with different initial PbO content was mainly independent of the amount of PbO excess because most of the free PbO was eliminated during sintering. Dielectric constant values of approximately 17,000 at 1 kHz and 40 °C were measured.
Comparison of (hexafluoroacetylacetonate)Cu(vinyltrimethylsilane) and (hexafluoroacetylacetonate)Cu(allyltrimethylsilane) for metalorganic chemical vapor deposition of copper
Authors: Park Man-Young , Son Jong-Hoon , Kang Sang-Woo , Rhee Shi-Woo
Published: March 2008

For the metalorganic chemical vapor deposition (MOCVD) of copper, (hfac)Cu(VTMS) (hfac = hexafluoroacetylacetonate, VTMS = vinyltrimethylsilane) and (hfac)Cu(ATMS) (ATMS = allyltrimethylsilane) were compared, and the effect of L ligand in (hfac)Cu–L was examined. It was found by 1H-NMR (nuclear magnetic resonance) that the thermal stability of (hfac)Cu(VTMS) was better than that of (hfac)Cu(ATMS) due to the relatively weak Cu–ATMS bond. From in situ Fourier transform infrared spectroscopy (FTIR) experiments, the formation of Cu(hfac)2, the product of disproportion reaction of Cu(hfac), was observed in the gas phase and (hfac)Cu(ATMS) was found to be more reactive to form Cu(hfac)2. The minimum temperature for the deposition of copper films from (hfac)Cu(ATMS) was as low as 60 °C, which was about 70 °C lower than from (hfac)Cu(VTMS). The grain size of the film deposited with (hfac)Cu(ATMS) was substantially larger than that with (hfac)Cu(VTMS), which showed that the chemical reactivity of the precursor had an influence on the microstructure along with the deposition temperature.
Interdiffusion in Ni80Fe20/Mo magnetic multilayers prepared by magnetron sputtering
Authors: Zhang X. Y. , Xu Y. F. , Yan M. L. , Chao L. M. , Zhang M. , Zhao J. H. , Lai W. Y. , Wang W. K.
Published: March 2008

The interdiffusion in Ni80Fe20/Mo magnetic multilayers with a repeat length of 3.4 nm has been investigated using x-ray diffraction (XRD) technology. The multilayers have been fabricated by using a magnetron sputtering system. The decay with annealing time in the intensity of the first-order x-ray satellite peak arising from the composition modulation was used to determine the effective interdiffusion coefficient Dλ. As the annealing temperature is below 483 K, the interdiffusion is found to be relatively slow (Dλ < 8.88 × 10−25 m2/s). This result suggests that the Ni80Fe20/Mo multilayers have a strong resistance to the atomic interdiffusion between sublayers. The diffusivities over the temperature range 343–683 K have an Arrhenius-type temperature dependence with a pre-exponential factor D0 = (4.02 ± 1.21) × 10−22 m2/s and an activation enthalpy of about 0.26 ± 0.08 eV. The much lower activation enthalpy is attributed to the coherence strains existing in the multilayers.
Ultraviolet laser-induced formation of thin silicon oxide film from the precursor β-chloroethyl silsesquioxane
Authors: Sharma Jaya , Berry Donald H. , Composto Russell J. , Dai Hai-Lung
Published: March 2008

Formation of silicon oxide thin films from spin-coated β-chloroethyl silsesquioxane (β-cesq) on silicon, NaCl, and quartz was induced by 193 nm laser pulses. The silicon oxide deposition is characterized by ir, uv, ellipsometry, and Rutherford backscattering spectrometry. The silicon oxide films obtained by uv irradiation were found to have much less carbon and chlorine as impurities and have a higher refractive index as compared to those obtained by annealing. The photoinduced oxide films were found to be smooth, without laser-induced microrough or periodic structures.
Thermodynamic analysis of solid-state metal/Si interfacial reactions
Authors: Lee Byeong-Joo
Published: March 2008

An attempt has been made to interpret the experimentally reported transitions of layer sequences during the Co/Si, Ti/Si, and Ni/Si interfacial reactions in a consistent way, and to build a thermodynamic calculation scheme that enables it. The basic ideas are that the silicide with the highest driving force of formation under a metastable local equilibrium state at an interface would form first at the lowest temperature, and that when several silicides can nucleate simultaneously and compete for growth at an initial stage of a high temperature reaction, the one whose composition is closest to those of surrounding phases would form a continuous interfacial layer first and grow thicker. A critical review of literature information has also been made in order to clarify the first-forming silicide and silicide formation sequence in each metalySi interfacial reaction. The observed first-forming crystalline silicides, CoSi, Ti5Si3, and Ni2Si, in each metalySi interfacial reaction were in agreement with the present prediction based on the first idea. The reason why Co2Si and C49 TiSi2 have frequently been observed in high temperature Co/Si and TiySi reactions as if they were the first-forming crystalline silicides could also be explained based on the second idea. By combining both ideas, a general thermodynamic calculation scheme that can be applied for analysis, rationalization, and even prediction of interfacial reactions between different materials could be suggested.
Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN
Authors: Smith L. L. , Davis R. F. , Liu R-J. , Kim M. J. , Carpenter R. W.
Published: March 2008

Single Ti layers, single TiN layers, and thin Ti films overlayered with Au were investigated as ohmic contacts to n-type (n 4.5 × 1017 to 7.4 × 1018 cm−3) single-crystal GaN (0001) films. Transmission line measurements (TLM) revealed the as-deposited TiN and Au/Ti contacts on n = 1.2 − 1018 cm−3 to be ohmic with room-temperature specific contact resistivities of 650 and 2.5 × 107minus;5 Ω cm2, respectively. Single Ti layer contacts had high resistance and were weakly rectifying in the as-deposited condition. The three contact/GaN systems exhibited a substantial decrease in resistivity after annealing; the value of ρc was also a function of the carrier concentration in the GaN. The Au/Ti contacts exhibited the lowest resistivity values yet observed in these contact studies, particularly for the more lightly doped n-GaN. The ρc for n = 1.2 × 1018 cm−3 reached 1.2 × 1026 Ω cm2; for n = 4.5 × 1017 cm−3, ρc = 7.5 × 1025 Ω cm2 after annealing both samples through 900 °C. X-ray photoelectron spectroscopy (XPS) and high-resolution cross-sectional transmission electron microscopy (X-TEM) analysis revealed the formation of TiN at the interface of annealed Ti layers in contact with GaN, which is believed to be beneficial for ohmic contact performance on n-GaN.
Surface textured zinc oxide films
Authors: Verghese P. M. , Clarke D. R.
Published: March 2008

Both epitaxial and crystallographically fiber-textured ZnO films can exhibit a surface texturing (“cratered”) morphology when grown by pulsed laser deposition at temperatures in the range of 350–750 °C in a background pressure of oxygen. The surface texturing is a consequence of the nucleation of oriented c axis grains that grow geometrically and impinge laterally. It is concluded that the surface texturing is due to nonequilibrium growth, being the result of a competition between the arriving flux, diffusive flux along the surface, and, possibly, concurrent ion etching from the laser-ablated plasma plume. At higher temperatures, no surface texturing occurs, presumably because of concurrent grain growth and more rapid surface smoothing by diffusion.
Characterization and optical properties of diamondlike carbon prepared by electron cyclotron resonance plasma
Authors: He Xiao-Ming , Lee S-T. , Bello I. , Cheung A. C. , Lee C. S.
Published: March 2008

Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature using electron cyclotron resonance CH4–Ar plasma. The effects of negative rf bias and reactant gas composition on the bonding structure, hardness, and resistivity of the films were systematically investigated. DLC films deposited on PMMA (polymethyl methacrylate) were examined by optical methods to determine the absorption coefficients and the optical band gap. It was found that DLC films synthesized at bias voltage of 2(80–100) V and FCH4/FAr of 0.075–0.086 exhibit extreme hardness of more than 3000 kgf mm−2, high electrical resistivity up to 1014 Ω cm, band gap larger than 2.5 eV, and excellent optical transparency. The results indicate that ECR CH4–Ar plasma with low negative rf bias and suitable CH4/Ar gas ratio can process optically transparent and hard protective DLC films on PMMA plastics.
Nonlinear optical properties of TeO2-based glasses: Li(Na and K)2O–TeO2 binary glasses
Authors: Kim Sae-Hoon
Published: March 2008

The third-order nonlinear optical susceptibilities, χ(3), of the xLi(Na and K)2O · (100 − x)TeO2 binary glasses have been measured by the third harmonic generation (THG) method. It is found that the χ(3) of each series of glasses decreases with increasing alkali oxide content. The largest χ(3) values obtained are about 1.3 × 10−12 esu for a 7.5Li2O · 92.5TeO2 glass, being about 45 times larger than that of fused silica glass for the present series samples. For the purpose of investigating the relationship between the χ(3) and the optical parameters, such as linear refractive index, polarizability per unit volume which is represented by the term (nω2 – 1)/(nω2 + 2), dispersion energy (Ed) which is related to the Abbé number, and excitation energy (E0) which is closely related to the optical band gap (Eg), we derived the equations that relate the χ(3) to optical parameters on the basis of Lines’ model. Finally, it was experimentally confirmed that the χ(3) value of alkali oxide-TeO2 glasses is proportional to the term (nω2 + 2)3 (nω2 – 1) · Ed/E02
Film microstructure-deposition condition relationships in the growth of epitaxial NiO films by metalorganic chemical vapor deposition on oxide and metal substrates
Authors: Wang Anchuan , Belot John A. , Marks Tobin J.
Published: March 2008

High-quality epitaxial or highly textured NiO thin films can be grown at temperatures of 400–750°C by low-pressure metalorganic chemical vapor deposition (MOCVD) on MgO, SrTiO3, C-cut sapphire, as well as on single crystal and highly textured Ni (200) metal substrates using Ni(dpm)2 (dpm – dipivaloylmethanate) as the volatile precursor and O2 or H2O as the oxidizer/protonolyzer. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive detection (SEM/EDX), and atomic force microscopy (AFM) confirm that the O2-derived NiO films are smooth and that the quality of the epitaxy can be improved by decreasing the growth temperature and/or the precursor flow rate. However, low growth temperatures (400–500 °C) lead to rougher surfaces and carbon contamination. The H2O-derived NiO films, which can be obtained only at relatively high temperatures (650–750 °C), exhibit slightly broader ω scan full width half-maximum (FWHM) values and rougher surfaces but no carbon contamination. Using H2O as the oxidizer/protonolyzer, smooth and highly textured NiO (111) films can be grown on easily oxidized single crystal and highly textured Ni (200) metal substrates, which is impossible when O2 is the oxidizer. The textural quality of these films depends on both the quality of the metal substrates and the gaseous precursor flow rate.
Diamond deposition on Ni/Ni-diamond coated stainless steel substrate
Authors: Sikder A. K. , Sharda T. , Misra D. S. , Chandrasekaram D. , Veluchamy P. , Minoura H. , Selvam P.
Published: March 2008

Electrodeposited Ni and Ni-diamond composite layers were used as diffusion barriers for Fe to facilitate the diamond growth on stainless steel substrates. Raman spectroscopy and scanning electron microscopy show the formation of good quality diamond crystallites by chemical vapor deposition. X-ray diffraction results indicate that the expansion of Ni unit cell has taken place due to the formation of the Ni–C solid solution. This observation is also well supported by x-ray photoelectron spectroscopy studies. The lattice constant of the expanded Ni unit cell matches closely with the diamond, and this may be helpful in explaining the epitaxial growth of diamond on single-crystal Ni observed by others.
Growth of carbon nitride thin films by radio-frequency– plasma-enhanced chemical vapor deposition at low temperatures
Authors: Lim S. F. , Wee A. T. S. , Lin J. , Chua D. H. C. , Tan K. L.
Published: March 2008

In this paper, we report our findings in the deposition of carbon nitride by radio-frequency–plasma-enhanced chemical vapor deposition (RF-PECVD) at temperatures slightly above room temperature (RT) and pressures of 800 mTorr using NH3 and C2H4 as source gases. The variation of the NH3/C2H4 source gas ratio and rf power is shown to affect the N/C ratio and sp3/sp2 ratio in a reproducible manner. An NyC ratio as high as 1.17 has been obtained under optimized growth conditions of NH3/C2H4 ratio of 7.3 and rf power of 90 W. X-ray diffraction (XRD) indicates the presence of microcrystalline carbon nitride in an amorphous CNx matrix with preferred orientation along the (100) direction. X-ray photoelectron microscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies show that our assignment of the XPS peaks and FTIR absorption bands are mutually consistent and in good agreement with published data. Both methods of analysis show the increase in the sp3 component with increase in N incorporation in the film.
Inelastic neutron scattering study of the hydration of tricalcium silicate
Authors: FitzGerald S. A. , Neumann D. A. , Rush J. J. , Kirkpatrick R. J. , Cong X. , Livingston R. A.
Published: March 2008

Inelastic neutron scattering is applied for the first time to monitor directly the concentration of calcium hydroxide formed during the hydration of tricalcium silicate. Results taken between 10 and 40 °C show that the onset of calcium hydroxide formation is delayed at lower temperatures but that the final quantity formed appears to be converging to a temperature-independent value. At 20°C, the 28 day value is 1.3 moles per mole of tricalcium silicate. Combining these results with previous measurements of the free water index made using quasielastic neutron scattering reveals that the hydrogen content of the C–S–H gel decreases significantly at increased curing temperature.
Intercalation of ε-caprolactam Ions into Inorganic Hosts
Authors: Katahira Shin-Ichiro , Yasue Kenji , Inagaki M.
Published: March 2008

The intercalation reaction of ε-caprolactam anion (ε–CL-) into hydrotalcite heated up to 500 °C to expel in its double hydroxide gallery and also that of ε-caprolactam cation (ε–CL+) into mica were successfully performed in their aqueous solutions. The intercalation reaction of ε–CL- into 500 °C heated hydrotalcite was completed within 1 h at 60 °C, and the resultant intercalation compound had the interlayer spacing of 0.77 nm. The intercalation of ε–CL+ into mica, on the other hand, proceeded rather slowly in two steps, which was due to the presence of two species, Na+ and hydrated Na+ in the mica gallery, and gave the intercalation compound with the interlayer spacing of 1.47 nm.
Microstructural and Ferroelectric Properties of a Chemical Solution Deposited Epitaxial PbZr0.5 Ti0.5O3 Thin Film on a SrRuO3/SrTiO3 Substrate
Authors: Kim J. H. , Chien A. T. , Lange F. F. , Wills L.
Published: March 2008

Epitaxial PbZr0.5Ti0.5O3 (PZT) thin films were grown on top of a SrRuO3 epitaxial electrode layer on a (100) SrTiO3 substrate by the chemical solution deposition method at 600 °C. The microstructure of the PZT thin film was investigated by x-ray diffraction and transmission electron microscopy, and the ferroelectric properties were measured using the Ag/PZT/SRO capacitor structure. The PZT thin film has the epitaxial orientational relationship of (001) [010]PZT ║ (001) [010]SRO ║ (001) [010]STO with the substrate. The remnant (Pr ) and saturation polarization (Ps) density were measured to be Pr ~ 51.4 µC/cm2 and Ps ~ 62.1 µC/cm2 at 5 V, respectively. Ferroelectric fatigue measurements show that the net-switching polarization begins to drop (to 98% of its initial value) after 7 × 108 cycles.
Thermoelectric Properties and Power Factor of YBa2Cu3O6+xwith Rare-earth Dopants
Authors: Kawahara T. , Tamura S. , Inai H. , Okamoto Y. , Morimoto J.
Published: March 2008

Both the thermoelectric power and the resistivity of the oxygen deficient YBa2Cu3O6+x samples were measured. The rare-earth-doped samples, such as Sm and Dy, whose magnetic moments in the +3 valence state are different, were studied. Then the power factor of the thermoelectric ability was calculated. The power factor of the Dy-doped samples is smaller than those of the other samples, especially at high temperature. This smallness of the power factor is the main reason why the Dy-doped samples have larger resistivity. We try to analyze the data by the theoretical expression under the variable range hopping conduction model. The expression of the thermoelectric power could be fit for the nondoped and Sm-doped samples, except at low temperature. In this situation, the thermoelectric power increases as temperature increases, and this temperature dependence is good for the thermoelectric materials at high temperature where the resistivity decreases with temperature increasing.
Atmospheric Pressure Chemical Vapor Deposition Growth Window for Undoped Gallium Antimonide
Authors: Subekti A. , Goldys E. M. , Paterson Melissa J. , Drozdowicz-Tomsia K. , Tansley T. L.
Published: March 2008

Metalorganic chemical vapor deposition (MOCVD) GaSb growth using trimethylgallium and trimethylantimony as a function of substrate temperature and V/III ratio was examined. These parameters were found to have a significant effect on the growth rate and surface morphology of the GaSb films. A phase diagram is used to interpret the effect of these growth parameters on the GaSb film growth. The region of single-phase growth was found to be narrow, falling between 540 and 560 °C. The optimum growth conditions for the MOCVD growth of GaSb have been determined for a TMGa flow rate of 20 sccm and a carrier gas flow of 8 l/min. The optimum substrate temperature and V/III ratio were found to be 540 °C and 0.72, respectively. In these conditions the lowest hole concentration of 5 × 1016 cm-3 and the highest room temperature mobility of 500 cm2 V-1 s-1 were achieved, accompanied by a steep, well-resolved band edge at 0.72 eV.
Stress Relaxation in Al–Cu and Al–Si–Cu Thin Films
Authors: Witvrouw A. , Proost J. , Roussel Ph. , Cosemans P. , Maex K.
Published: March 2008

Substrate curvature measurements were used to study stress changes during thermal cycling and isothermal tensile stress relaxation in 800 nm Al–0.5 wt% Cu and Al–1 wt% Si–0.5 wt% Cu films. For both compositions dislocation glide can describe the relaxation data well for temperatures up to 120 °C for Al–Si–Cu and up to 100 °C for Al–Cu. The average activation energy for Al–Si–Cu and Al–Cu is 1.7 ± 0.2 eV and 3.0 ± 0.3 eV, respectively. The athermal flow stress is the same for both and equal to 600 ± 200 MPa. This result is consistent with the obstacles for glide being Al2Cu precipitates, which, in the case of Al–Si–Cu, are fine and can be cut by the dislocations, and, in the case of Al–Cu, are strong and provide Orowan strengthening. Also, the stress changes during thermal cycling in the Al–Cu films are different from those in the Al–Si–Cu films. For Al–Cu films, the room temperature stress decreases after each thermal cycle, while for Al–Si–Cu stress changes during thermal cycling are stable from the second cycle on. These observations are supported by thorough transmission electron microscopy (TEM) studies.
Phase Evolution and Dielectric Characterization of Lead Nickel Niobate–lead Zirconate Ceramics Prepared from the Hydrothermally Derived Precursors
Authors: Lu Chung-Hsin , Hwang Wen-Jeng
Published: March 2008

The perovskite compounds with the composition of (1 – x) Pb(Ni1/3Nb2/3)O3 –xPbZrO3 have been successfully prepared from hydrothermally treated precursors. During calcination, the primary intermediate compound is pyrochlore phase in the Pb(Ni1/3Nb2/3)O3-rich composition, while it is PbZrO3 on the PbZrO3-rich side. On calcination at 800 °C, all precursors convert into perovskite phases. In the formed solid solutions, increasing PbZrO3 content results in a rise in the apparent Curie temperature as well as the maximum dielectric permittivity. The Pb(Ni1/3Nb2/3)O3-rich perovskites (x < 0.8) possess the characteristics of relaxor ferroelectrics. With increasing PbZrO3 content, the dielectric response gradually becomes less diffuse and dispersive, reflecting a reduction in the relaxor characteristics of the formed perovskites.