bluuebunny/crossref_metadata_2025 huggingface dataset:
Domain structure and electrical properties of highly textured PbZrxTi1−xO3 thin films grown on LaNiO3-electrode-buffered Si by metalorganic chemical vapor deposition
Authors: Lin C. H. , Yen B. M. , Kuo H. C. , Chen Haydn , Wu T. B. , Stillman G. E.
Published: March 2008

Thin films of highly (100) textured fine-grain (lateral grain size ≅0.1 to 0.15 μm) PbZrxTi1−xO3 (PZT) (x = 0 to 0.7) were grown on conductive perovskite LaNiO3-buffered platinized Si substrates by metalorganic chemical vapor deposition. Domain configuration and crystalline orientation were studied using x-ray diffraction and transmission electron microscopy. The predominant domain boundaries of Ti-rich tetragonal-phase PZT and Zr-rich rhombohedral-phase PZT were found to be on the (110) planes and (100) planes, respectively. The equilibrium domain widths were observed and estimated numerically on the basis of transformation strain, grain size, and domain boundary energy. The peak value of the dielectric constant was 790 near the morphotropic boundary. Hysteresis behavior of these PZT thin films was demonstrated. A decrease in coercive field with the increment of Zr content was found; this variation was attributed to domain density and the multiplicity of polarization axes. Furthermore, the low leakage current (J ≤ 5 × 10−7 A/cm2 at V = 4 V) was observed for all samples, and the involvement of several possible conduction mechanisms was suggested.
Dielectric ceramics in the BaO–Sm2O3–TiO2–Ta2O5 quaternary system
Authors: Chen X. M. , Xu Z. Y. , Li J.
Published: March 2008

Dielectric ceramics in the BaO–Sm2O3–TiO2–Ta2O5 quaternary system were prepared and characterized for five typical compositions: BaSm5Ti7Ta3O30, Ba2Sm4Ti6Ta4O30, Ba3Sm3Ti5Ta5O30, Ba4Sm2Ti4Ta6O30, and Ba5SmTi3Ta7O30. The latter three compositions tended to form the tungsten–bronze phase, and the ceramics based on these compositions had a high dielectric constant (134–175) and a low dielectric loss (on the order of 10−3) but a larger temperature coefficient of the dielectric constant. Meanwhile, the former two compositions generally had a more complex phase constitution, containing the tungsten–bronze phase combined with some unknown phase, and a relatively small temperature coefficient of the dielectric constant in the temperature range of 20 to 85 °C could be achieved in these two compositions.
Joining of silicon nitride ceramics for high-temperature applications
Authors: Xie Rong-Jun , Mitomo Mamoru , Huang Li-Ping , Fu Xi-Ren
Published: March 2008

A refractory silicon nitride joint, which contains β–Si3N4 grains and grain boundary amorphous phase in the joined layer, was developed with the aid of a ceramic adhesive based on the system Si3N4–Y2O3–SiO2–Al2O3. The similarity in chemistry and microstructure between the parent ceramic and the joint zone indicates that the joining mechanism is the same as that involved in the sintering of Si3N4. The resultant joint exhibits a high bond strength of 550 MPa at 25 °C and retains a strength of 332 MPa at 1000 °C. Post-joining hot-isostatic pressing was applied to strengthen the joint, resulting in increased strengths of 668 MPa at room temperature and 464 MPa at 1000 °C.
Role of organic solvents and surface-active agents in the sol-emulsion-gel synthesis of spherical alumina powders
Authors: Chatterjee M. , Naskar M. K. , Siladitya B. , Ganguli D.
Published: March 2008

Spherical alumina particles were prepared following the sol-emulsion-gel method by systematic variation of (i) the concentration of the surfactant Span 80 above or below the critical micelle concentration (CMC) in different organic solvents and (ii) hydrophilic–lipophilic balance (HLB) of different surfactants in cyclohexane. The experimentally determined CMC of Span 80 was found to increase with increasing dielectric constant of the organic solvent, influencing the sol droplet and alumina particle size. With an increase in the HLB value of the surfactants, the tendency of monodispersed sphere formation among the particles increased with a decrease in the size distribution and average particle size (d50).
Optimization of Ta–Si–N thin films for use as oxidation-resistant diffusion barriers
Authors: Cabral C. , Saenger K. L. , Kotecki D. E. , Harper J. M. E.
Published: March 2008

We have demonstrated that the optimum Ta–Si–N compositions for use as oxygen diffusion barriers in stacked-capacitor dynamic random-access memory structures with perovskite dielectrics are in the range Ta(20–25 at.%)–Si(20–45 at.%)–N(35–60 at.%). Twenty-two different Ta–Si–N compositions were evaluated, starting from six sputter-deposited Ta–Si alloys of which four were reactively deposited in 2–8% nitrogen in an argon plasma. The barriers were evaluated after an aggressive 650 °C/30 min oxygen anneal to determine if they remained electrically conductive, prevented oxygen diffusion and formation of low dielectric constant oxides, and had minimal interaction with the Pt electrode and underlying Si plug. Rutherford backscattering spectroscopy, four-point probe sheet resistance, through-film-resistance, and x-ray diffraction analysis techniques were used in the evaluation.
Adhesion and reliability of copper interconnects with Ta and TaN barrier layers
Authors: Lane Michael , Dauskardt Reinhold H. , Krishna Nety , Hashim Imran
Published: March 2008

With the advent of copper metallization in interconnect structures, new barrier layers are required to prevent copper diffusion into adjacent dielectrics and the underlying silicon. The barrier must also provide adequate adhesion to both the dielectric and copper. While Ta and TaN barrier layers have been incorporated for these purposes in copper metallization schemes, little quantitative data exist on their adhesive properties. In this study, the critical interface fracture energy and the subcritical debonding behavior of ion-metal-plasma sputtered Ta and TaN barrier layers in Cu interconnect structures were investigated. Specifically, the effects of interfacial chemistry, Cu layer thickness, and oxide type were examined. Behavior is rationalized in terms of relevant reactions at the barrier/dielectric interface and plasticity in adjacent metal layers.
Electron field emission from polycrystalline diamond films
Authors: Zhang Qing , Yoon S. F. , Ahn J. , Gan Bo , Rusli
Published: March 2008

The influence of the carbon network structure of polycrystalline diamond films that were prepared from a mixture of H2, CH4, and N2 using microwave-enhanced plasma chemical vapor deposition on electron field emission has been systematically investigated. With increasing nitrogen gas flow ratio of [ N2]/[H2 + CH4 + N2], the film hardness and surface roughness of the as-grown films decreased, and the concentration ratio of amorphous sp2-bonded carbon clusters and mixed sp2−sp3 carbon structures to tetrahedrally bonded amorphous carbon phases increased. Correspondingly, the turn-on voltage for electron emission decreased. After the surface post-treatment by pure hydrogen plasma exposure, the concentration ratio was clearly found to have increased dramatically and the turn-on voltage decreased significantly for the films produced at small nitrogen flow ratio. Our results suggest that the influence of the concentration ratio on electron field emission is much more significant than that of the surface roughness of the polycrystalline diamond films studied in this paper.
Effects of plasma power on the properties of low-k polymerlike organic thin films deposited by plasma-enhanced chemical vapor deposition using the toluene precursor
Authors: Joo Jongryang , Quan Yong Chun , Jung Donggeun
Published: March 2008

Effects of plasma power on the properties of polymerlike organic thin films deposited by plasma-enhanced chemical vapor deposition using the toluene precursor were studied. As the plasma power was increased from 5 to 60 W, the relative dielectric constant increased from 2.53 to 2.85. The film deposited at higher plasma power showed higher thermal stability. The film deposited at 60 W was stable up to 400 °C. All the films were insulating under applied field ≤1 MV/cm.
Effect of recrystallization on the oxidative stability of poly(butylene terephthalate)
Authors: Motori Antonio , Montanari Gian Carlo , Saccani Andrea , Giannoni Steve
Published: March 2008

The oxidative stability of poly(butylene terephthalate) was investigated over the range 175 to 220 °C by isothermal differential calorimetry. It is shown that this property is affected by a fast recrystallization process, which takes place between 200 and 220 °C, with a maximum around 208 °C. In fact, recrystallization produces an increase of the crystallinity degree of the polymer, which enhances its resistance to oxidation, as proven by the longer oxidation times detected.
The effect of NbC porosity on reaction-layer microstructure in NbC|Si diffusion couples
Authors: Woodford J. , Yang C-Y. , Chang Y. A.
Published: March 2008

Further experimental observations have allowed us to refine and confirm some aspects of our recently proposed mechanism for reactive diffusion between Si single crystal and NbC powder compact, particularly regarding the prediction of Si as the dominant diffusing species and the nature of the dependence of SiC particle morphology on the presence of voids in the NbC end member. In Si|NbC diffusion couples annealed at either 1300 or 1350 °C, a two-phase NbSi2 + SiC reaction layer formed. Although NbSi2 was the matrix in all of the reaction layers, the SiC phase morphology depended upon NbC porosity: when high-porosity NbC was used, SiC was present as discontinuous particles greater than 1-μm-across, while when low-porosity or void-free NbC was used, SiC grew cooperatively with NbSi2 in the form of lamellae less than 0.5 μm thick. We propose that this difference arises from the effect of voids both as nucleation sites for SiC particles and as channels for unrestricted SiC growth. Marker experiments conclusively show that Si is the dominant diffusing species in the reaction layer.
Deformation of catalytically grown carbon nanotubes induced by annealing under high pressure
Authors: Zhang Ming , Xu C. L. , Cao L. M. , Wu D. H. , Wang W. K.
Published: March 2008

A study of the structural transformation of catalytically grown carbon nanotubes induced by annealing under high pressure is presented in this paper, in which the atomic details of the microstructural transformations have been monitored mainly with electron microscopy. The microstructural change from the multiwalled carbon nanotubes into a quasi-spherical onion becomes obvious just at 770 °C under 5.5 GPa. The nanotubes deform and almost transform into nanographite ribbons directly when the annealing temperature is above 950 °C under 5.5 GPa. It is suggested that the pressure and temperature play an important role in the structural transformations of multiwalled carbon nanotubes described here.
Synthesis, Raman scattering, and infrared spectra of a new condensed form of GaN nanophase material
Authors: Cao Y. G. , Chen X. L. , Lan Y. C. , Xu Y. P. , Xu T. , Liang J. K.
Published: March 2008

A new form of transparent condensed nanophase material of GaN was synthesized directly by ammono-thermal synthetic route. Nano-sized effects and thermal stability of that material were investigated through Raman scattering and infrared spectra. Compared with bulk GaN, we observed the Raman low-energy-shift of the phonon frequency of E2(high) and the transverse optical mode [E1(TO)], the infrared high-energy-shift of, ωT, and the variation of relative intensity IE2/E1(TO). These characteristics can be attributed to the existence of the interface effects and the vacancy of N in the GaN nanophase material. This material has a high thermal stability even at 900 °C as indicated through infrared and Raman spectral investigation of annealed samples of as-synthesized nanophase material.
Fabrication of a 33-layer optical reflection filter with stepwise graded refractive index profiles
Authors: Wang Xinrong , Masumoto Hiroshi , Someno Yoshihiro , Chen Lidong , Hirai Toshio
Published: March 2008

A novel optical multilayer filter characterized by symmetrically stepwise graded refractive index profiles and high optical performance was designed. This 33-layer TiO2–SiO2 filter was fabricated by helicon plasma sputtering. The prepared filter exhibited a sharp cutoff reflection band around the central wavelength of 1340 nm and wide pass regions with high transmittance. These results correspond well with calculated estimations. Symmetrically stepwise graded refractive index profiles were demonstrated to effectively contribute to suppression of the sidelobes and to be potentially applicable in the design of other filters.
Sensitizing effect of Yb3+ on near-infrared fluorescence emission of Cr4+-doped calcium aluminate glasses
Authors: Choi Yong Gyu , Kim Kyong Hon , Han Yong Seop , Heo Jong
Published: March 2008

We have demonstrated that an efficient energy transfer takes place from Yb3+ to Cr4+ in calcium aluminate glasses. Yb3+ improves excitation efficiency at around 980 nm, enhancing emission intensity of Cr4+ fluorescence at 1.2–1.6 μm. Nonradiative energy transfer via electric dipole–dipole interaction between ytterbium and chromium ions was found to be dominant over radiative Yb3+ → Cr4+ energy transfer. A diffusionlimited energy transfer mechanism well explains the decay behavior of Yb3+/Cr4+- codoped glasses. This codoping scheme may be applicable to other Cr4+-containing crystals and glasses.
Photobleaching of sol-gel-derived germanium oxide glass thin films
Authors: Jang Jae Hyeok , Koo Junmo , Bae Byeong-Soo
Published: March 2008

Photobleaching of the optical absorption band in the 5-eV region of sol-gel-derived germanium oxide glass thin films was examined with the irradiation of the 5-eV light. The photobleaching represented by the saturated absorption coefficient change (−Δα) and the ratio of the neutral oxygen monovacancies to neutral oxygen divacancies concentrations for the germanium oxide were 175 cm−1 and 0.113, respectively. These values are larger than those of the pure germanium oxide bulk glass as well as germanosilicate thin films. The changes in bonding configuration around Ge atom by ultraviolet illumination were analyzed using x-ray photoelectron spectroscopy.
Effect of Ag on the primary phase field of the high-Tc (Bi,Pb)-2223 superconductor
Authors: Wong-Ng W. , Cook L. P. , Greenwood W. , Kearsley A.
Published: March 2008

The subsolidus equilibria and the primary phase field (crystallization field) of the 110 K high-Tc (Bi,Pb)-2223 ([Bi,Pb]:Sr:Ca:Cu) phase have been determined in the presence of Ag under a 92.5% Ar/7.5% O2 atmosphere (volume fraction). A total of 29 six-phase volumes that include both the (Bi,Pb)-2223 and Ag phases was observed. These subsolidus volumes are similar to those observed without the presence of Ag. The compositional range of initial melts of these volumes (mole fraction basis) covers BiO1.5 from 5.6% to 25.3%, PbO from 0.4% to 13.8%, SrO from 8.4% to 31.9%, CaO from 12.2% to 33.3%, CuO from 21.7% to 40.9%, and AgO0.5 from 1.2% to 6.3%. Based on these data, the primary crystallization field for the (Bi,Pb)-2223 phase in the presence of Ag was constructed using the convex hull technique. A section through this “volume” was portrayed by holding the AgO0.5, SrO, and CaO components at the median value of the 29 compositions while allowing projection on the other three axes (BiO1.5, PbO, and CuO). The net effect of Ag on the melt composition is a reduction in the PbO concentration and an increase in the SrO content. Applications of the liquidus data are also discussed.
Continuous chemical vapor deposition processing with a moving finite thickness susceptor
Authors: Chiu Wilson K. S. , Jaluria Yogesh
Published: March 2008

Chemical vapor deposition (CVD) of thin films onto a moving surface is an important material processing technique for semiconductor fabrication, optical coatings, and many other applications. Continuous CVD processing offers an attractive solution to meet high volume requirements. In this study, the deposition on a finite thickness moving susceptor, considering surface reactions, is numerically investigated. When a susceptor is in motion, the reaction zone residence time and the coupling of conduction heat transfer in the susceptor with convection heat transfer in the gas flow significantly alter the deposition rate and film quality. A model is developed to quantify continuous CVD film production for several important design parameters. The numerical model is validated for the deposition of silicon through comparisons with analytical results and experimental data available in the literature. Films produced by continuous CVD are shown to be strongly dependent on susceptor speed, material selection, and susceptor thickness. Susceptor speed is directly linked to residence time in the reaction region, with lower residence times resulting in less time for reaction and heating, hence reducing growth rates. Increased thickness and susceptor thermal diffusivity alters the thermal energy distribution, thereby reducing the susceptor surface temperature and lowering the deposition rate. These effects may be overcome by increasing the length of the heating zone. Film quality is also influenced by the susceptor temperature, since reaction-controlled deposition typically produces different film structure than deposition under diffusion-controlled conditions. Overall, the results obtained demonstrate the feasibility of employing a moving finite thickness susceptor for CVD processing. A correlation of several operational parameters is also obtained for the film thickness. This may be used for the design and optimization of continuous CVD systems. The numerical model may also be used for considering deposition of other materials.
Intrinsic reduction kinetics of cobalt- and nickel-titanates by hydrogen
Authors: Arvanitidis I. , Kapilashrami A. , Sichen Du , Seetharaman S.
Published: March 2008

The isothermal reduction of synthetic CoTiO3 and NiTiO3 in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928–1287 K (CoTiO3) and 884–1387 K (NiTiO3). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H2 were very fast during the reduction of Co2+, Ni2+, or Fe2+ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO3 by hydrogen to Co and TiO2 was evaluated to be 151 ± 1 kJ/mol, and the activation energy for the reduction of NiTiO3 by hydrogen to Ni and TiO2 was evaluated to be 153 ± 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO2 (rutile). The results were also compared with the hydrogen reduction of FeTiO3.
Thermoelectric properties of (Bi,Pb)–Sr–Co–O oxide
Authors: Shin Woosuck , Murayama Norimitsu
Published: March 2008

Electrical conductivity and thermopower of Bi2Sr3Co2Ox sintered bodies were first investigated in the temperature range 440–1060 K in air for high-temperature thermoelectric application. The samples fabricated by the sinter-forging method increased their bulk densities and electrical conductivity. The value of thermopower and the temperature dependence of electrical conductivity of the sinter-forged samples were close to that of the single crystal. Evaluating the thermal conductivity of the polycrystalline sample, we calculated a thermoelectric figure of merit Z to be 0.107 × 10−3 K−1 at 1060 K.
Preparation and coating of molybdenum oxide on alumina submicrospheres by sonochemical method
Authors: Zhong Z. Y. , Mastai Y. , Salkar R. A. , Koltypin Y. , Gedanken A.
Published: March 2008

In this work, we coated molybdenum oxide on submicrospheres of amorphous alumina and crystalline alumina, using a sonochemical method. The sonication products were characterized by transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, ultraviolet–visible, Raman, Fourier transform infrared spectroscopy, and surface area (Brunauer–Emmett–Teller) measurements. We found that on crystalline alumina, the blue oxide of molybdenum was formed, while on amorphous alumina, the presence of an isolated tetrahedrally coordinated Mo oxide species was confirmed. It seems that the amount and types of surface hydroxyl groups on the surface of alumina play an important role in both the oxidation of Mo and the relative content of Mo species in the sonication product. The surface area of the alumina-coated Mo oxide is about 11 times larger than that of the bare alumina. An explanation for this change is offered.
Liquid-phase sintering and chemical inhomogeneity in the BaTiO3–BaCO3–LiF system
Authors: Wang Sea-Fue , Yang Thomas C. K. , Huebner Wayne , Chu Jinn P.
Published: March 2008

An ongoing goal of multilayer capacitor research is to lower the firing temperature of the dielectric. This paper gives a detailed study of sintering BaTiO3 with LiF flux, which lowers the firing temperature through liquid-phase sintering. A detailed set of experiments is discussed concerning microstructural evolution and corresponding dielectric properties under a number of processing variables, including amount of LiF, sintering temperature, and particle size. Different scales of chemical inhomogeneity were observed in this system, which reflect two underlying mechanisms: solution reprecipitation with limited grain growth at low temperatures, which resulted in distinct core–shell structures, and flux volatility, which gave rise to microscopic chemical inhomogeneity at higher sintering temperatures.
Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation
Authors: Zhang Hengzhong , Banfield Jillian F.
Published: March 2008

The kinetics of phase transformation of nanocrystalline anatase samples was studied using x-ray diffraction at temperatures ranging from 600 to 1150 °C. Kinetic data were analyzed with an interface nucleation model and a newly proposed kinetic model for combined interface and surface nucleation. Results revealed that the activation energy of nucleation is size dependent. In anatase samples with denser particle packing, rutile nucleates primarily at interfaces between contacting anatase particles. In anatase samples with less dense particle packing, rutile nucleates at both interfaces and free surfaces of anatase particles. The predominant nucleation mode may change from interface nucleation at low temperatures to surface nucleation at intermediate temperatures and to bulk nucleation at very high temperatures. Alumina particles dispersed among the anatase particles can effectively reduce the probability of interface nucleation at all temperatures.
Interdependence of stress and interdiffusion during solid-state amorphization in Ni–Hf
Authors: Boyer W. S. L. , Atzmon M.
Published: March 2008

The evolution of stress in a Ni–Hf diffusion couple during solid-state amorphization reaction has been monitored by substrate curvature measurements and x-ray diffraction. The latter technique allowed an independent determination of the contribution of changes in stress-free lattice parameter to the stress in the crystalline layers. The results indicate that the amorphous phase forms under a large tensile stress, which relaxes as the reaction progresses. This stress in the amorphous phase is consistent with the volume change associated with the reaction. Stresses in the crystalline, elemental phases are considerably smaller and not affected by the reaction. Low-temperature Ni ion irradiation increases the tensile stress in the diffusion couple. The large observed stress variations are not accompanied by variations in the effective interdiffusion coefficient.
Raman and magnetization studies of barium ferrite powder prepared by water-in-oil microemulsion
Authors: Chen M. S. , Shen Z. X. , Liu X. Y. , Wang J.
Published: March 2008

Micro-Raman spectroscopy was used to study the formation of BaFe12O19 (BaM) powders derived from water-in-oil microemulsion at different calcination temperatures. With increase in the calcination temperature, the Raman spectra of the BaM powders become narrower and stronger without apparent frequency shifts of the Raman bands. The calcination temperature dependence of the Raman spectra and the magnetic properties of the BaM powders result from the crystallization rather than size effect. Our results show that there is a strong correlation between the crystallinity and the magnetic properties, which could be explained in terms of the crystallization effect on the superexchange interaction between ferric ions. The γ–Fe2O3 phase occurred in the BaM precursor and the powder calcined at 500 °C. The α–Fe2O3 phase was developed in the powders calcined at 500, 600, and 700 °C, which was not detected by x-ray diffraction. With increasing calcination temperature, the γ–Fe2O3 phase can either react with oxide containing barium to form the BaM phase or transform to the α–Fe2O3 phase. The amount of α–Fe2O3 decreases due to reaction with BaCO3 to form BaM phase at higher calcination temperature.
Powder neutron diffraction studies of a carbonate fluorapatite
Authors: Leventouri Th. , Chakoumakos B. C. , Moghaddam H. Y. , Perdikatsis V.
Published: March 2008

Atomic positional disorder of a single-phase natural carbonate fluorapatite (francolite) is revealed from analysis of the atomic displacement parameters (ADPs) refined from neutron powder diffraction data as a function of temperature and carbonate content. The ADPs of the francolite show a strong disturbance at the P, O3, and F sites. When it is heat treated to partially or completely remove the carbonate, the ADPs as well as the other structural parameters resemble those of a fluorapatite (Harding pegmatite) that was measured under the same conditions. The various structural changes are consistent with a substitution mechanism whereby the planar carbonate group replaces a phosphate group and lies on the mirror plane of the apatite structure.
Effect of CuO addition on the high-field and high-pressure behavior of microwave-prepared lead vanadate glasses
Authors: Vaidhyanathan B. , Asokan S. , Rao K. J.
Published: March 2008

High-field and high-pressure behavior of microwave-prepared xCuO:(45−x) PbO: 55V2O5 (x = 0 to 20) glasses were investigated for the first time. It was found that the addition of CuO significantly alters the nonlinear I–V characteristics of these glasses; while the glasses with x = 10 exhibit a current-controlled negative resistance behavior associated with a memory type transition, glasses with x = 15 show a threshold-type behavior. Remarkable differences were also noticed in the high-pressure electrical resistivity behavior between the low- and high-CuO-containing glasses. Corroborative thermal, electrical, microscopic, and spectroscopic measurements were carried out to understand the structure–property relations. A structural model was proposed, which is based on the chemical nature of the constituents present in the glasses. The model accounts well for the various observed properties of these glasses.
Newly designed organic/inorganic film for optical second-harmonic generation
Authors: Hayakawa Tomokatsu , Imaizumi Dai , Nogami Masayuki
Published: March 2008

In this paper we report the fabrication of organic/inorganic film for optical secondharmonic generation by a sol-gel method for the purpose of the improvement of thermal stability and chemical resistance. The film contains the azo dye Disperse Orange 3 protected by poly(vinylpyrrolidone) in a reticulation of silica gel, whose structure was developed by the spinodal decomposition and the gel-forming process as temperature increased. Corona-poling at elevated temperature could successively induce the optical second-harmonic nonlinearities. The dependence of temperature and field strength on the second-harmonic intensity was also investigated.
The influence of oxide and adsorbates on the nanomechanical response of silicon surfaces
Authors: Syed Asif S. A. , Wahl K. J. , Colton R. J.
Published: March 2008

In this article we report the influence of surface oxides and relative humidity on the nanomechanical response of hydrophobic and hydrophilic Si surfaces. Depth-sensing nanoindentation combined with force modulation enabled measurement of surface forces, surface energy, and interaction stiffness prior to contact. Several regimes of contact were investigated: pre-contact, apparent contact, elastic contact, and elasto-plastic contact. Both humidity and surface preparation influenced the surface mechanical properties in the pre- and apparent-contact regimes. Meniscus formation was observed for both hydrophobic and hydrophilic surfaces at high humidity. Influence of humidity was much less pronounced on hydrophobic surfaces and was fully reversible. In the elastic and elasto-plastic regimes, the mechanical response was dependent on oxide layer thickness. Irreversibility at small loads (300 nN) was due to the deformation of the surface oxide. Above 1 μN, the deformation was elastic until the mean contact pressure reached 11 GPa, whereby Si underwent a pressure-induced phase transformation resulting in oxide layer pop-in and breakthrough. The critical load required for pop-in was dependent on oxide thickness and tip radius. For thicker oxide layers, substrate influence was reduced and plastic deformation occurred within the oxide film itself without pop-in. Elastic modulus and hardness of both the oxide layer and Si substrate were measured quantitatively for depths <5 nm.
Use of two-color array pyrometry for characterization of combustion synthesis waves
Authors: Anselmi-Tamburini U. , Maglia F. , Spinolo G. , Munir Z. A.
Published: March 2008

A two-color array pyrometer was used to investigate morphological developments on the surface of materials undergoing self-propagating high-temperature reactions. Time sequences of temperature spatial profiles during wave propagation were found to be complex in their nature and dynamics. They contain features that are interpreted in terms of morphological changes during the process. These features include formation of cracks or voids, expansion of the sample, and formation of droplets of metals on the surface. The use of the array pyrometer for determination of the activation energy of the combustion reaction between Zr and NiO is reported.
Improved adhesion of diamondlike coatings using shallow carbon implantation
Authors: Malaczynski Gerard W. , Elmoursi Alaa A. , Leung Chi H. , Hamdi Aboud H. , Campbell Albert B.
Published: March 2008

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides an excellent interface for subsequent growth of DLC. At a carbon retained dose above 1018 atoms/cm2 the DLC adhesion exceeds the coating's cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 140 MPa to separate an epoxy-coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to substantially exceed performance of DLC coatings produced by any other method.
Combined substrate polishing and biasing during hot-filament chemical vapor deposition of diamond on copper
Authors: Ali N. , Ahmed W. , Rego C. A. , Fan Q. H.
Published: March 2008

Diamond deposition on copper is problematic mainly due to the poor affinity between copper and carbon. Therefore, it becomes necessary to pretreat the substrate surfaces prior to diamond deposition. Several surface pretreatments have been investigated, such as polishing using various abrasives and substrate biasing. In this study, we report new results relating diamond nucleation on copper substrates to a combination of surface polishing and biasing pretreatments. The results show that the combined pretreatments give a higher nucleation density than the two individual treatments. It was found that an increase of 70% in the nucleation density was observed when the surfaces were polished with diamond paste and then negatively biased. Copper surfaces polished with diamond powder and then biased displayed the highest nucleation density obtained. Raman spectroscopy revealed that after negatively biasing the substrate for 30 min, broad D- and G-bands of microcrystalline graphite were present, which completely disappeared with subsequent diamond growth, leaving behind a good-quality diamond film.
Atomic structure, electrical properties, and infrared range optical properties of diamondlike carbon films containing foreign atoms prepared by pulsed laser deposition
Authors: Wei Q. , Sankar J. , Sharma A. K. , Oktyabrsky S. , Narayan J. , Narayan R. J.
Published: March 2008

We investigated the atomic structure, electrical, and infrared range optical properties of diamondlike carbon (DLC) films containing alloy atoms (Cu, Ti, or Si) prepared by pulsed laser deposition. Radial distribution function (RDF) analysis of these films showed that they are largely sp3 bonded. Both pure DLC and DLC + Cu films form a Schottky barrier with the measuring probe, whereas DLC + Ti films behave like a linear resistor. Pure DLC films and those containing Cu exhibit p-type conduction, and those containing Ti and Si have n-type conduction. Photon-induced conduction is observed for pure DLC, and the mechanism is discussed in terms of low-density gap states of highly tetrahedral DLC. Our results are consistent with relative absence of gap states in pure DLC, in accordance with theoretical prediction by Drabold et al.37 Temperature dependence of conductivity of DLC + Cu shows a behavior σ ∞ exp(−B/T1/2), instead of the T−1/4 law (Mott–Davis law). Contributions from band-to-band transitions, free carriers, and phonons to the emissivity spectrum are clearly identified in pure DLC films. The amorphous state introduces a large contribution from localized states. Incorporation of a small amount of Si in the DLC does not change the general feature of emissivity spectrum but enhances the contribution from the localized states. Cu and Ti both enhance the free carrier and the localized state contributions and make the films a black body.
Optical properties and annealing effects on the deep levels in As-doped CdTe/Cd0.96Zn0.04Te (211) B heterostructures
Authors: Han M. S. , Kang T. W. , Kim T. W.
Published: March 2008

Photoluminescence (PL) and photo-induced-current transient spectroscopy measurements on As-doped CdTe/Cd0.96Zn0.04Te heterostructures grown by molecular beam epitaxy were carried out to investigate the optical properties and the annealing effects on the deep levels. The temperature dependence of the PL spectra showed that the luminescence intensity of the exciton peak related to the neutral acceptors (A°, X) decreased with increasing measurement temperature and that the activation energy of the (A°, X) peak for the As-doped CdTe epilayer was 7 meV. Five hole-trap peaks appeared for the annealed As-doped CdTe/Cd0.96Zn0.04Te heterostructure. Two of these peaks, denoted by H1 and H2, might be related to extrinsic impurities, and the other three peaks, represented by H3, H4, and H5, might be attributed to intrinsic impurities. These results can help improve understanding for the application of As-doped CdTe/Cd0.96Zn0.04Te heterostructures in optoelectronic devices.
One-step sintering of SiGe thermoelectric conversion unit and its electrodes
Authors: Lin Jun-Shan , Miyamoto Yoshinari
Published: March 2008

Dense p-type and n-type SiGe thermoelectric conversion units were fabricated with a double-layer electrode of W/TiB2 or W/MoSi2 by using glass encapsulation hot-isostatic-pressing process. The TiB2 and MoSi2 layers were used to prevent the chemical reaction between the tungsten and SiGe materials. Si3N4 ceramic particles were added into the electrode materials to reduce the mismatch of the thermal expansion between the electrode and the SiGe. Finite element analysis showed that the addition of 40 vol% Si3N4 into the TiB2 layer and 55 vol% Si3N4 into the MoSi2 layer reduced the thermal residual stress to a much lower value than the strength of individual layer. Sintered units had electrical resistivities of (1.5–2.0) × 10−3 Ω cm in the SiGe zone and 10−4 Ω cm in the electrodes. The comparison of the thermoelectric properties of the SiGe sintered with and without electrodes confirmed that the electrodes did not deteriorate the Seebeck coefficient of the SiGe alloys.
Transition in high-temperature oxidation kinetics of Pd-modified aluminide coatings: Role of oxygen partial pressure, heating rate, and surface treatment
Authors: Monceau Daniel , Bouhanek Karima , Peraldi Raphaëlle , Malie André , Pieraggi Bernard
Published: March 2008

The isothermal oxidation of Pd-modified Ni aluminide coatings was studied as a function of Po2 and temperature (900–1200 °C). A kinetic transition was observed between 900 and 1000 °C. Grazing incident x-ray diffraction, thermogravimetric analysis, x-ray photoelectron spectroscopy, scanning electron microscopy/energy dispersive spectroscopy, and secondary ion mass spectrometry analyses are consistent with the growth of δ-alumina or α-alumina below or above this transition temperature. Moreover, because Po2 was established before specimen heating, an effect of heating rate was observed and analyzed. More importantly, no kinetic transition was observed for sand-blasted specimens oxidized at low Po2. Thus conditions for the direct growth of an α-alumina scale could be determined from the reported results.
Effects of microstructural evolution on the thermal conductivity of α–Al2O3 prepared from nano-size γ–Al2O3 powder
Authors: Gonzalez Eduardo J. , White Grady , Wei Lanhua
Published: March 2008

The thermal diffusivities (D) of porous α–Al2O3 specimens prepared from nano-size γ–Al2O3 powder and from conventional submicrometer-size alumina powders were measured at room temperature, and the thermal conductivity (κ) was calculated from D. Plots of κ versus the volume fraction of porosity (P) showed that the data from both sets of samples followed similar linear curves. Similarly, data of Vickers hardness versus P obtained from the same specimens also followed a single linear curve. The good correlation of thermal diffusivity with P suggests that grain boundaries have a lesser effect on thermal transport than porosity.
Thermal transport through thin films: Mirage technique measurements on aluminum/titanium multilayers
Authors: Gonzalez E. J. , Bonevich J. E. , Stafford G. R. , White G. , Josell D.
Published: March 2008

Thermal transport properties of multilayer thin films both normal and parallel to the layers were measured. Al/Ti multilayer films 3 μm thick, with individual layers systematically varied from 2.5 to 40 nm, were studied on Si substrates. Layers of Al and Ti were nominally equal in thickness, with actual composition determined for each specimen using energy dispersive spectroscopy. The thermal diffusivity both in the plane and normal to the plane of the films (thermal conductivity divided by specific heat per volume) was found to decrease significantly with decreasing bilayer thickness. Pure Ti and Al films as well as Cu films from 0.1 to 5 μm thick were also studied. In-plane electrical conductances of the Al/Ti multilayers were also measured.
Structure and thermoelectric properties of binary and Fe-doped iridium silicide thin films
Authors: Pitschke W. , Kurt R. , Heinrich A. , Schumann J. , Grießmann H. , Vinzelberg H. , Burkov A. T.
Published: March 2008

The structure-formation process and thermoelectric properties of binary and Fe-doped IrxSi1−x (0.30 ≤ x ≤ 0.41) thin films were investigated. The films were prepared by means of physical vapor deposition techniques, in particular by magnetron co-sputtering and electron beam co-evaporation. The amount of Fe dopant varied between 0 and 5 at.%. The phase-formation process depends on the volume fractions of the major components Ir and Si, whereas the small concentrations of dopant did not change the sequence of the crystalline phases formed. On the other hand, the thermoelectric transport properties correlate strongly with both the structure-formation process and the chemical composition of the films. Fe-doped iridium silicide films with useful thermoelectric power factors were successfully obtained by both magnetron co-sputtering and electron beam co-evaporation. A maximum thermoelectric power factor of 8.5 μW/(K2 cm) at 1200 K was observed for evaporated layers with thechemical composition Ir0.35Si0.63Fe0.02.
Variation of orientation and morphology of epitaxial SrBi2Ta2O9 and SrBi2Nb2O9 thin films via the coating-pyrolysis process
Authors: Nagahama T. , Manabe T. , Yamaguchi I. , Kumagai T. , Mizuta S. , Tsuchiya T.
Published: March 2008

Orientation-controlled epitaxial thin films of bismuth layer-structured ferroelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on single-crystal SrTiO3 (STO) substrates by the coating-pyrolysis process. Most of the SBT (SBN) films showed the (106) and (001) orientations on STO(110) and (001), respectively. The degree of orientation, in terms of the ratio of peak intensity to the background level in the x-ray diffraction φ-scan profile for the film, greatly increased with a decrease in the oxygen partial pressure, p(O2), of annealing atmosphere at 800 °C. Interestingly, coexistence of the (110)-oriented grains with the (106)-oriented ones on STO(110) [and the (100)-oriented grains with the (001)-oriented ones on STO(001)] was observed exclusively in the SBT films annealed at 700–750 °C under p(O2) of 10 Pa. Atomic force microscopy observations showed that the surface morphology of the SBT films remained almost unchanged, i.e., comprising round-shaped grains of submicrometer size, whereas that of the SBN films drastically changed, according to the variation in orientation of substrate surfaces or in annealing conditions, i.e., temperature, p(O2), and time.
Crystallization and nanoindentation behavior of a bulk Zr–Al–Ti–Cu–Ni amorphous alloy
Authors: Wang J. G. , Choi B. W. , Nieh T. G. , Liu C. T.
Published: March 2008

The crystallization and nanoindentation behavior of a Zr–10Al–5Ti–17.9Cu–14.6Ni (at.%) bulk amorphous alloy (BAA) were studied. Resulting from the kinetic nature of phase transformation in multicomponent alloys, the crystallization path is complex. Despite the complexity of different crystallization paths, the main final crystallized product in the Zr-based BAA is Zr2Cu. Young's modulus and hardness of the BAA were found to increase with an increase in annealing temperature. The observed mechanical properties were correlated with the microstructure of the material. Also, in the present paper, both the observed crystallization and nanoindentation behavior are compared with existing data. Zr-based BAAs exhibit a ratio of hardness to Young's modulus (H/E ratio) of about 1/10, suggesting the interatomic bonding in the alloys is close to being covalent.
High-temperature heat treatment of carbon microcoils obtained by chemical vapor deposition process and their properties
Authors: Chen Xiuqin , In-Hwang Wan , Shimada Shiro , Fujii Mituhiro , Iwanaga Hiroshi , Motojima Seiji
Published: March 2008

Carbon microcoils obtained by the catalytic pyrolysis of acetylene at 770 °C were heat treated at 3000 °C for 6 h in a CO + CO2 atmosphere. The effect of the heat treatment on the morphology, microstructure, and properties was examined. The coiling morphology of the carbon coils was almost preserved even after the heat treatment, though it became brittle. The ruptured cross section of the two fibers, which form the coils, generally has either a trigonal pyramidlike form or negative pyramidal hollow. These characteristic ruptured patterns demonstrate the growth mechanism of the carbon coils. Distinct graphite layers (d = 0.339 nm) were developed by the heat treatment with an inclination of 10–40° versus the fiber axis to form a “herringbone” structure. The bulk electrical resistivity, density, and specific surface area were 10–0.1 Ωcm, 2.2077–2.087 g/cm3, and 6–8 m2/g, respectively.
Thermochemistry of microporous silicotitanate phases in the Na2O–Cs2O–SiO2–TiO2–H2O system
Authors: Xu Hongwu , Navrotsky Alexandra , Nyman May D. , Nenoff Tina M.
Published: March 2008

Microporous silicotitanates can potentially be used as ion exchangers for removal of Cs+ from radioactive waste solutions. The enthalpies of formation from constituent oxides for two series of silicotitanates at 298 K have been determined by drop-solution calorimetry into molten 2PbO · B2O3 at 974 K: the (Na1−xCsx)3Ti4Si3O15(OH) · nH2O (n = 4 to 5) phases with a cubic structure (P43m), and the (Na1−xCsx)3Ti4Si2O13(OH) · nH2O (n = 4 to 5) phases with a tetragonal structure (P42/mcm). The enthalpies of formation from the oxides for the cubic series become more exothermic as Cs/(Na + Cs) increases, whereas those for the tetragonal series become less exothermic. This result indicates that the incorporation of Cs in the cubic phase is somewhat thermodynamically favorable, whereas that in the tetragonal phase is thermodynamically unfavorable and kinetically driven. In addition, the cubic phases are more stable than the corresponding tetragonal phases with the same Cs/Na ratios. These disparities in the energetic behavior between the two series are attributed to their differences in both local bonding configuration and degree of hydration.
Microstructure and Hall–Petch Behavior of Fe–Co-based Hiperco© Alloys
Authors: Shang Chang-He , Cammarata R. C. , Weihs T. P. , Chien C. L.
Published: March 2008

The microstructure and hardness of Fe–Co-based Hiperco© alloys were investigated. Scanning electron microscopy revealed elongated grains in the as-received (cast and cold-rolled) alloys, and samples containing Nb had second phase precipitates. Annealing of alloys for 1 to 3 h at temperatures in the range 700 to 800 °C resulted in grains becoming equiaxed. In the Nb-containing alloys, the original precipitates dissolved and new precipitates appeared. The rate of grain growth decreased with increasing Nb content, suggesting that Nb or Nb-containing precipitates were responsible for a reduction in the grain boundary mobility. The hardness as a function of grain size in the annealed samples of all of the alloys could be plotted on the same Hall–Petch curve, indicating that the yield strength of these alloys is governed by the grain size, independent of the alloy composition and volume fraction of precipitates.
Sol-gel-derived Magnesium Oxide Precursor for Thin-film Fabrication
Authors: Choi Hyungsoo , Hwang Soontaik
Published: March 2008

Magnesium oxide (MgO) precursors were prepared by the sol-gel method using magnesium acetate. The reaction products and intermediates obtained during the sol-gel processing of magnesium acetate under various conditions were analyzed thermally and spectroscopically. No organic groups were detected by infrared spectroscopy after heat treating the reaction products at 400 °C. A large exothermic differential thermal analysis peak below 400 °C demonstrated the oxidation of organic moieties in each product. It was found that the presence of an acid catalyst was crucial during the sol-gel processing of magnesium acetate to produce sols suitable for depositing MgO films. The MgO films fabricated on Si(111) substrates using the precursor sol showed (200) orientation regardless of the presence of surface oxides on the substrates.