bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of composition on the growth and morphology of zeolite A in solution
Authors: Oonkhanond Bovornlak , Mullins Michael E.
Published: May 2005

The zeolite LTA (Linde type A) framework is composed of an equal amount of silica and alumina arranged in a three-dimension tetrahedral structure. This high alumina content zeolite possesses a strong negative surface charge in a basic solution due to the substitution of aluminum atoms into a SiO4tetrahedral structure making it difficult to form a continuous layer in solution. Synthesis parameters such as synthesis duration, chemical composition, and synthesis temperature were varied. The crystallization kinetics was carried out using the particle size measurement, percent crystallinity from x-ray diffraction analysis, infrared absorption of tetrahedra using attenuated total reflectance Fourier transform infrared spectroscopy, and the exponential growth model. The results showed that the zeolite A crystallization in a solution depends on the chemical kinetics of the zeolite formation, surface charge of the substrate, and the mass transfer in the solution.
A new approach to characterization of the transition temperatures of thin film NiTi shape memory alloys
Authors: Botterill Nicholas W. , Grant David M. , Zhang Jianxin , Roberts Clive J.
Published: May 2005

A novel approach in determining the transition temperatures of NiTi shape memory alloys was investigated and compared with conventional techniques. The technique is based on microthemal analysis using a scanning thermal microscope (SThM). In particular, this method has the potential to allow the transformation temperatures of thin films to be investigated in situ. Thin film shape memory alloys have potential applications, such as microactuators, where conventional analysis techniques are either not directly applicable to such samples or are difficult to perform.
Deposition and characterization of HfO2 high k dielectric films
Authors: Lo Wai , Kamath Arvind , Kher Shreyas , Metzner Craig , Wen Jianguo , Chen Zhihao
Published: May 2005

As the scaling of complementary metal-oxide-semiconductor (CMOS) transistors proceeds, the thickness of the SiO2 gate dielectrics shrinks rapidly and results in higher gate leakage currents. High k dielectric materials are acknowledged to be the possible solutions to this challenge, as their higher k values (e.g., 15–50) raise the physical thickness of the dielectrics that provide similar equivalent thickness of a thinner SiO2 film. In order for the high k materials to be applicable in CMOS devices, there should exist deposition technologies that can deposit highly uniform films over Si wafers with diameters as large as 200 mm. This report discusses the deposition process and the correlation between the growth conditions, structural and dielectric properties of HfO2, which is one of the most promising high k dielectric materials. Judging from the thickness uniformity, surface roughness, k value, and interfacial density of state of the HfO2 films, the metalorganic chemical vapor deposition technique was identified to be suitable for growing HfO2 films targeted at applications as CMOS gate dielectrics.
Evolution of microstructure during the thermal processing of aluminum-modified titania and aluminum/vanadium co-modified titania gels
Authors: Allison Francis J. , Grant David M. , McKinlay Karen , Harrison Philip G.
Published: May 2005

Sol-gel materials of aluminum-modified TiO2 of nominal composition 5.7 wt% and 10.8 wt% aluminum and aluminum/vanadium co-modified TiO2 of nominal composition 5.7Al–3.5V wt% have been prepared by evaporation of aqueous colloidal sols obtained by the hydrolysis of aqueous solutions of titanium chloride with the appropriate amount of vanadyl oxalate and/or aqueous aluminum nitrate using aqueous ammonia followed by peptization of the resulting hydrated solids using nitric acid. The nature of the sol-gel materials and the behavior upon calcination at temperatures up to 1373 K have been investigated using x-ray fluorescence, x-ray powder diffraction, transmission electron microscopy, and electron diffraction. At 333 K, all the gels comprise small (approximately 5 ± 1 nm) particles of anatase together with traces of brookite and highly crystalline ammonium nitrate. The particle size changes little on thermal treatment at 573 K, but increases significantly at higher temperatures and is accompanied by transformation to rutile. Aluminum-modified gels stabilize the anatase phase from 923 K in unmodified TiO2 to 1023 K in the 6Al/TiO2 gel and 1173 K in the 11Al/TiO2 gel. The alumina in the co-modified gel has a dominating effect on stabilizing the anatase phase until 973 K. Only rutile is present at high temperatures, except for small amounts of phase-separated α-Al2O3 (Corundum). No substitutional incorporation of Al3+ ions in the tetragonal rutile lattice occurs at high temperatures.
Growth of aromatic molecules on solid substrates for applications in organic electronics
Authors: Witte Gregor , Wöll Christof
Published: May 2005

The growth of molecular adlayers on solid substrates is reviewed with aspecial emphasis on molecules of relevance for organic electronics. In particular,we will consider planar molecules with extended π-systems, namely acenes (anthracene, tetracene, pentacene), perylene, coronenes, diindenoperylene, 3,4,9,10-perylene-tetracarboxylicacid-dianhydride, poly-phenylenes, oligothiophenes, and phthalocyanines. Special consideration is given to the importance of the formation of ordered molecular overlayers, which are compared with the structure of the corresponding bulk crystals. Whenever possible, aspects relevant for device fabrication (morphology of deposited films, mobilities of charge carriers) will be addressed.
Influence of distributed trap states on the characteristics of top and bottom contact organic field-effect transistors
Authors: Lindner T. , Paasch G. , Scheinert S.
Published: May 2005

Numerical simulations of organic field-effect transistors (OFET) of bottom and top contact (BOC, TOC) design with different source/drain contacts were carried out considering an exponential distribution of trap states in the gap of the active layer (a-Si model). For ohmic contacts, the current-voltage characteristics are similar to the trap-free case and there is not much difference between the two designs. However, the currents are lower due to immobile trapped charges, the threshold voltage is shifted, and the inverse subthreshold slope increases due to trap recharging. An analytical approximation for the effective mobility deviates from the simulation up to 20%. For low source/drain work function, there occur particular dependencies of the current on the gate voltage for the two designs, which are explained with the internal concentration and field profiles. A series resistance between source and channel causes in the TOC structure an abrupt transition from the gate voltage independent active region into saturation. In the BOC case, the reverse-biased Schottky-type source contact dominates the current. Through simulation of measured characteristics of prepared OFETs based on a modified poly-(phenylene-vinylene), the observed hysteresis is analyzed.
Organic n-channels of substituted phthalocyanine thin films grown on smooth insulator surfaces for organic field effect transistors applications
Authors: Michaelis W. , Wöhrle D. , Schlettwein D.
Published: May 2005

Thin films of the perfluorinated phthalocyanines F16PcVO and F16PcCu were grown on insulator substrates by physical vapor deposition under high vacuum conditions to study their growth and electrical properties, analyzing them as possible candidates for n-type channel materials in organic field effect transistors. As insulator substrates, mica, amorphous SiO2, poly(styrene), poly(vinylchloride), poly(vinylcarbazole), poly(methylmetacrylate) and poly(vinylidenefluoride) were chosen, offering chemically different interactions with the molecules, degrees of order, and tribological characteristics. Optical absorption spectroscopy was used to analyze the alignment of the molecules relative to the substrates and the electronic coupling to adjacent molecules in the films. Electrical conduction measurements served to analyze the electronic coupling of the molecules parallel to the insulating substrates and to discuss the growth mode of films. Atomic force microscopy and scanning electron microscopy were chosen to study the morphology of the films. An inclined orientation at an average surface angle between 58° and 86° dependent on the different substrates was found for both F16Pc. In particular, on mica, thin conductive channels of the organic n-semiconductors could be formed at an average film thickness well below 10 nm at conductivities of up to 1.3 × 10-2 S cm-1. Conductive channels could also be formed on the different polymer substrates at, however, at least an order of magnitude smaller conductivity. Before these layers were formed on the polymers, semiconductor material diffused into the polymer substrates, dependent upon the substrate temperature during deposition relative to the glass transition temperature of the polymers. An influence of the viscous state of the polymer substrates was also seen on the intermolecular coupling detected in optical spectra. Based on these results, implications for the applicability of F16Pc as organic n-channels in organic field effect transistors are discussed.
Microstructure analysis of carbon–carbon preform
Authors: Liu Zhenyi , Zhang Guoding , Sun Jinliang , Li Hong , Ren Musu
Published: May 2005

The microstructure of three kinds of porous carbon–carbon preforms prepared for carbon–carbon/aluminum composites was identified by x-ray diffraction, Raman spectroscopy, and field emission scan electronic microscope. Although manufactured at same processing conditions, including the temperature, type of organic gas, and pressure of pyrolysis, the structure of the pyrolytic carbon (Cpy) in three kinds of preforms is different. The morphology of the Cpy is influence by the topology of the preforms greatly, and the crystal structure of the Cpy is influenced by the crystal structure of the carbon fiber greatly, on which surface the Cpy was deposited. The degree of graphitization of the Cpy had been enhanced and the structure of the Cpy changed to more anisotropic form when the preforms were annealed at 2773 K.
Fabrication of heteroepitaxial thin films of layered oxychalcogenides LnCuOCh (Ln = La–Nd; Ch = S–Te) by reactive solid-phase epitaxy
Authors: Hiramatsu Hidenori , Ueda Kazushige , Takafuji Kouhei , Ohta Hiromichi , Hirano Masahiro , Kamiya Toshio , Hosono Hideo
Published: May 2005

Processes and preparation conditions for growing epitaxial thin films of Cu-based, layered oxychalcogenides LnCuOCh (Ln = La, Ce, Pr or Nd; Ch = S1-xSex or Se1-yTey) are reported. Epitaxial thin films on MgO (001) substrates were prepared by a reactive solid-phase epitaxy method. Four-axes high-resolution x-ray diffraction measurements revealed that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO and the internal stress of the crystalline lattices in the films are relaxed during thermal-annealing process of the reactive solid-phase epitaxy. Furthermore, except for CeCuOS, systematic variations in the lattice constant by chalcogen or lanthanide ion substitutions were observed. These results demonstrated that the reactive solid-phase epitaxy is an efficient technique for fabricating LnCuOCh epitaxial films.
New relationship between Young's modulus and nonideally sharp indentation parameters
Authors: Ma Dejun , Ong Chung Wo , Wong Sing Fai
Published: May 2005

Both analysis and numerical calculations have been carried out to investigate the relationship between Young’s modulus and nonideally sharp indentation parameters. The results confirm that there exists an approximate one-to-one correspondence between the ratio of nominal hardness/reduced Young’s modulus (Hn/Er) and the ratio of elastic work/total work (We/W) for any definite bluntness ratio (Δh/hm) of a nonideally sharp indenter. Based on this relationship, the Young’s modulus of the indented material can be determined just from the values of Hn, We, and W, which are directly measurable quantities in an indentation test.
Tellurium nanotubes and nanorods synthesized by physical vapor deposition
Authors: Métraux C. , Grobéty B.
Published: May 2005

Tellurium nanotubes and nanorods were synthesized by physical vapor deposition (PVD) in an induction furnace for reaction times between 25 and 35 min. The growth morphologies depended on the reaction times and the atmosphere in the induction furnace. Nanotubes grew only under argon atmosphere (1 mbar). Under vacuum, tellurium blades and nanorods were observed. Of particular interest are the dense carpets of nanorods observed on polycrystalline aluminum. PVD experiences in a conventional high vacuum coating system did not lead to the formation of nanotubes nor nanorods. The interesting electrical properties of tellurium and tellurium compounds combined with the observed growth morphologies are promising for the fabrication of nanoscale functional devices.
Anisotropies in the electrical properties of rod-like aggregates of liquid crystalline phthalocyanines: Direct current conductivities and field-effect mobilities
Authors: Donley Carrie L. , Zangmeister R.A.P. , Xia Wei , Minch Britt , Drager Anthony , Cherian Samir K. , LaRussa Lynn , Kippelen Bernard , Domercq Benoit , Mathine David L. , O’Brien David F. , Armstrong Neal R.
Published: May 2005

The direct current (dc) conductivities and organic field-effect transistor (OFET) characteristics of a class of octa-substituted liquid crystalline (discotic mesophase) phthalocyanines (Pcs) are discussed. These molecules self-organize into columnar aggregates with large coherence lengths (up to approximately 300 nm). Langmuir–Blodgett films of these molecules were horizontally transferred to either interdigitated microelectrodes (IME) or OFET substrates, so that current flow could be measured either parallel or perpendicular to the column axis. Twenty-eight bilayer films of these Pcs on the IME substrates showed anisotropies in dc conductivity up to 50:1, whereas similar Pc films showed anisotropies in field effect mobilities of approximately 10:1, for a variety of W/L ratios (source/drain dimensions and spacing). Field-effect mobilities of 1 to 5 × 10-6 cm2·V-1·s-1 were determined from OFET measurements, along the Pc column axis, whereas charge mobilities measured from the space charge limited current regime on the IME substrates were in the range of 10-4 cm2·V-1·s-1. Conductive tip atomic force microscopy measurements on the apprximately 500-nm length scale showed that the conductivity anisotropy can be as high as 1000:1 when the Pc columns are intimately contacted to an adjacent Au bond pad.
Thermochemistry of the alkali rare-earth double phosphates, A3RE(PO4)2
Authors: Ushakov Sergey V. , Navrotsky Alexandra , Farmer J. Matt , Boatner Lynn A.
Published: May 2005

The formation enthalpies for alkali rare-earth compounds of the type K3RE(PO4)2where RE = Sc, Y, Lu, Er, Ho, Dy, Gd, Nd, or Ce and for A3Lu(PO4)2compounds with A = K, Rb, or Cs were determined using high-temperature oxide-melt solution calorimetry. Structural phase transitions were observed and characterized using differential scanning calorimetry and high-temperature x-ray diffraction. The formation enthalpy of the K3RE(PO4)2phases from oxides becomes more exothermic with increasing rare-earth radius for the K3RE(PO4)2series and with increasing alkali radius for the A3Lu(PO4)2compounds. The K3RE(PO4)2phases are stable with respect to anhydrous K3PO4and REPO4. The monoclinic K3RE(PO4)2compounds undergo a reversible phase transition to a hexagonal (glaserite-type) structure with a phase transition temperature that increases from −99 to 1197 °C with increasing RE ionic radius going from Lu to Ce.
Bulk glass formation in the Ni–Zr–Ti–Nb–Si–Sn alloy system
Authors: Lee J.Y. , Bae D.H. , Lee J.K. , Kim D.H.
Published: May 2005

In this study, the effect of addition of Nb on glass formation in Ni–Ti–Zr–Si–Sn alloys has been studied. The composition range for bulk glass formation with Dmax > 2 mm (Dmax, maximum diameter for glass formation by injection cast method) becomes wider when compared with the non-Nb–containing alloy. The ΔTx (= Tx – Tg; Tx, crystallization onset temperature; Tg, glass transition temperature), Trg (= Tg/Tl; Tl, liquidus temperature) and γ [= Tx/(Tl + Tg)] values for the alloys Dmax > 2 mm are in the range of 40–59, 0.638–0.651, and 0.410–0.419, respectively. The compositions of the alloys (Dmax > 2 mm) are closer to pseudo-eutectic composition than that of the alloy without Nb, showing an improved glass forming ability. The critical cooling rate for glass formation (Dmax = 5 mm) is estimated to be order of approximately 40 K/s.
Effects of nitrogen flow rates on reactively sputtered nanocrystal-(Ti,Al)xN1-x/amorphous-SiyN1-y nanolaminate films
Authors: Yau Bao-Shun , Huang Jow-Lay , Lii Ding-Fwu
Published: May 2005

Nanocrystal-(Ti,Al)xN1-x/amorphous-SiyN1-y nanolaminate films were deposited periodically under different nitrogen flow rates. The composition, microstructure and mechanical properties of nanolaminate films were investigated by x-ray photoelectron spectroscope, x-ray diffractometer, scanning and transmission electron microscopy, atomic force microscope, and nanoindentation apparatus. Results indicated that the formation of the compound on the target surface was substantially influenced by the deposition rate, composition and crystallite size of the nanolaminate films. Nanolaminate structure with periodic compositional modulation and sharp interfaces were deposited at different nitrogen flow rate. Smaller nanocrystallite size, round-shaped grain features, smoother surface morphology, higher hardness, and reduced elastic modulus were obtained for nanolaminate films with increasing the nitrogen flow rate.
Improvement of Young's modulus and tensile strength of polymer impregnation and pyrolysis processed SiC/SiC composite by improved continuity of matrix
Authors: Ochiai S. , Okuda H. , Kimura S. , Morishita K. , Tanaka M. , Hojo M. , Sato M.
Published: May 2005

Influences of the continuity of the matrix on Young's modulus and tensile strength of unidirectional SiC/SiC mini-composite prepared by the polymer impregnation and pyrolysis method were studied experimentally by observation of appearance of matrix and tensile test and analytically by a shear lag–Monte Carlo simulation. The continuity of the matrix was improved by the addition of particles such as ZrSiO4, barium magnesium aluminosilicate, and Pyrex (borosilicate glass) into the matrix. The improved continuity of the matrix led to the increase in stress carrying capacity of the matrix and therefore to the increase in Young's modulus and tensile strength of the composite. Such a correlation between the continuity of the matrix and the property of the composite was verified numerically by the shear lag–Monte Carlo simulation.
Photoluminescence at 1540 nm from erbium-doped amorphous silicon carbide films
Authors: Gallis Spyros , Efstathiadis Harry , Huang Mengbing , Nyein Ei Ei , Hommerich Uwe , Kaloyeros Alain E.
Published: May 2005

Room-temperature photoluminescence (PL) was observed at 1540 nm in erbium-implanted amorphous silicon carbide (a-SiC:Er) films grown by thermal chemical vapor deposition at 800 °C. The PL spectra of the a-SiC:Er samples did not exhibit any defect-generated luminescence, with the PL intensity at 1540 nm dropping only by a factor of 3.6 as the sample temperature was increased from 14 K to room temperature. Time-resolved PL measurements showed that the Er3+ luminescence lifetime of approximately 0.6 ms was nearly independent of sample temperature. In addition, luminescence quenching was observed as implanted Er dose exceeded 7 × 1015 ions/cm2. It is suggested that the lower density of Si and C vacancies in the stoichiometric a-SiC:Er, as compared to its non-stoichiometric a-Si1-xCx counterpart, along with the incorporation of a higher Er dopant concentration, can effectively quench defect-produced luminescence and lead to a significant improvement in PL performance. These properties indicate that stoichiometric a-SiC is potentially a viable candidate for optoelectronic devices operating in the 1540 nm region.
Phase equilibria of the Ag–Sn–Cu ternary system
Authors: Yen Yee-wen , Chen Sinn-wen
Published: May 2005

Phase equilibria of the Ag–Sn–Cu ternary system have been determined experimentally as well as using the calculation of phase diagram (CALPHAD) method. Various Ag–Sn–Cu alloys were prepared to study the isothermal sections of the Ag–Sn–Cu ternary system at 240 and 450 °C. No ternary compounds were found and all the binary compounds had only limited ternary solubility. The ∈1–Cu3Sn phase is a very stable phase. It is in equilibrium with the Ag, ζ–Ag4Sn, ∈2–Ag3Sn, η–Cu6Sn5, and Cu phases at 240 °C, and is in equilibrium with the Ag, ζ, ∈2, L, and δ–Cu4Sn phases at 450 °C. Thermodynamic models of the Ag–Sn–Cu ternary system were developed based on available thermodynamic models of the constituent binary systems without introducing ternary interaction parameters. The isothermal sections at 240 and 450 °C were calculated, and the results were in good agreement with those determined experimentally. In addition to the isothermal sections, stability diagrams of Sn and Cu were calculated as well.
Synthesis and characterization of ultraviolet-emitting cerium-ion-doped SrBPO5 phosphors
Authors: Lu Chung-Hsin , Godbole S.V.
Published: May 2005

The synthesis and characteristics of strontium borate phosphate phosphors doped with cerium ions were investigated in this study. The synthesis of Sr0.95Ce0.05BPO5 in oxidizing atmosphere results in partial conversion of Ce4+ ions into Ce3+ ions. The luminescent characteristics reveal that Ce3+ ions occupy two principal sites in the host. The dominant emission at 317 nm on 275-nm excitation is attributed to Ce3+ ions located at Sr2+ sites without local charge compensation. The weak emission at 330 nm due to 295-nm excitation is ascribed to Ce3+ ions located at Sr2+ sites in association with charge compensatory vacancy. The reduction of Ce4+ ions to Ce3+ ions occurs in Sr0.95Ce0.05BPO5 heated in the reducing atmosphere. For Sr0.9Ce0.05Na0.05BPO5 and Sr0.9Ce0.05Li0.05BPO5 phosphors, enhancement in luminescence is observed due to the codoping of monovalent ions. The increased luminescence of these phosphors is attributed to the decrease in non-radiative energy transfer.
Microstructure evolution during electromigration in eutectic SnPb solder bumps
Authors: Lu C.M. , Shao T.L. , Yang C.J. , Chen Chih
Published: May 2005

A technique has been developed to facilitate analysis of the microstructural evolution of solder bumps after current stressing. Eutectic SnPb solders were connected to under-bump metallization (UBM) of Ti/Cr-Cu/Cu and pad metallization of Cu/Ni/Au. It was found that the Cu6Sn5 compounds on the cathode/chip side dissolved after the current stressing by 5 × 103 A/cm2 at 150 °C for 218 h. However, on the anode/chip side, they were transformed into (Nix,Cu1-x)3Sn4 in the center region of the UBM, and they were converted into (Cuy,Ni1-y)6Sn5 on the periphery of the UBM. For both cathode/substrate and anode/substrate ends, (Cuy,Ni1-y)6Sn5 compounds were transformed into (Nix,Cu1-x)3Sn4. In addition, the bumps failed at cathode/chip end due to serious damage of the UBM and the Al pad. A failure mechanism induced by electromigration is proposed in this paper.
Uniqueness of reverse analysis from conical indentation tests
Authors: Tho K.K. , Swaddiwudhipong S. , Liu Z.S. , Zeng K. , Hua J.
Published: May 2005

The curvature of the loading curve, the initial slope of the unloading curve, and the ratio of the residual depth to maximum indentation depth are three main quantitiesthat can be established from an indentation load-displacement curve. A relationship among these three quantities was analytically derived. This relationship is valid for elasto-plastic material with power law strain hardening and indented by conical indenters of any geometry. The validity of this relationship is numerically verified through large strain, large deformation finite element analyses. The existence of an intrinsic relationship among the three quantities implies that only two independent quantities can be obtained from the load-displacement curve of a single conical indenter. The reverse analysis of a single load-displacement curve will yield non-unique combinations of elasto-plastic material properties due to the availability of only two independent quantities to solve for the three unknown material properties.
Growth of heteroepitaxial GaSb thin films on Si(100) substrates
Authors: Nguyen Thang , Varhue Walter , Adams Edward , Lavoie Mark , Mongeon Stephen
Published: May 2005

The heteroepitaxial growth of GaSb thin films on Si(100) and GaAs(100) substrates is presented. The growth technique involves the use of atomic Ga and Sb species, which are provided by thermal effusion and radio frequency sputtering, respectively. The crystalline quality of the heteroepitaxial GaSb film on the Si substrate is high despite the larger lattice mismatch. Epitaxial quality is determined by high-resolution x-ray diffraction and Rutherford backscatter spectrometry channeling. Atomic-force microscopy is used to monitor the evolution of surface morphology with increasing film thickness. Transmission electron microscopy shows the formation of stacking faults at the Si/GaSb interface and their eventual annihilation with increasing GaSb film thickness. Annihilation of stacking faults occurs when two next-neighbor mounds meet during the overgrowth of a common adjacent mound.
Indentation responses of time-dependent films on stiff substrates
Authors: Oyen Michelle L. , Cook Robert F. , Emerson John A. , Moody Neville R.
Published: May 2005

A viscous-elastic-plastic indentation model was extended to a thin-film system, including the effect of stiffening due to a substrate of greater modulus. The system model includes a total of five material parameters: three for the film response (modulus, hardness, and time constant), one for the substrate response (modulus), and one representing the length-scale associated with the film-substrate interface. The substrate influence is incorporated into the elastic response of the film through a depth-weighted elastic modulus (based on a series sum of film and substrate contributions). Constant loading- and unloading-rate depth-sensing indentation tests were performed on polymer films on glass or metal substrates. Evidence of substrate influence was examined by normalization of the load-displacement traces. Comparisons were made between the model and experiments for indentation tests at different peak load levels and with varying degrees of substrate influence. A single set of five parameters was sufficient to characterize and predict the experimental load-displacement data over a large range of peak load levels and corresponding degrees of substrate influence.
Bismuth titanate nanoparticles dispersed polyacrylates
Authors: Su Wei-Fang , Lee Jiann-Fong , Chen Ming-Yao , Ho Ron-Ming
Published: May 2005

We successfully dispersed amorphous bismuth titanate nanoparticles (<50 nm)in situ in poly-hydroxy ethyl methacrylate via a sol-gel process. Since less than 20% of the polymer composition is bismuth titanate by weight, the material exhibits high refractive indices (>1.6) and good optical transparency (>90% transmittance from 530 to 800 nm). Furthermore, this highly cross-linked material has an improved thermal stability and a lower coefficient of thermal expansion than that of neat polymers. The material also displays a high dielectric constant (>10) without ferroelectricity. Thus the material has potential applications in optical lenses, optical waveguides, and capacitors.
Growth and characterization of c-axis oriented LiNbO3 film on a transparent conducting Al:ZnO inter-layer on Si
Authors: Gupta Vinay , Bhattacharya P. , Yuzyuk Yu. I. , Katiyar R.S. , Tomar Monika , Sreenivas K.
Published: May 2005

C-axis oriented lithium niobate (LiNbO3) films were deposited by pulsed-laser deposition on silicon using a transparent conducting interlayer of aluminum (Al)-doped zinc oxide (ZnO). Only two x-ray diffraction reflections corresponding to (006) and (0012) planes of LiNbO3 were observed in the films deposited at a 100-mTorr oxygen pressure and a 450–500 °C substrate temperature. Presence of sharp modes corresponding to E(TO) and A(LO), and absence of any superfluous peaks mainly around 900–905 cm−1 in the Raman spectra confirmed the formation of textured LiNbO3 film. Measured value of direct current and alternate current (AC) conductivities and dielectric constant are 8.6 × 10-12 Ω−1cm-1, 1.16 × 10-6 Ω−1cm-1, and 29.3, respectively, at room temperature. Behavior of dielectric constant and AC conductivity with frequency and temperature are close to the reported single-crystal data.
Possible influence of quenched-in nuclei on quasicrystal formation in mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powder
Authors: Scudino S. , Eckert J. , Schultz L.
Published: May 2005

The influence of quenched-in nuclei of icosahedral short range order, proposed as a possible explanation for quasicrystal formation, has been investigated by producing a melt-spun ribbon from previously mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powder. A ribbon prepared from highly pure materials forms a quasicrystalline phase during the first stage of the crystallization process, whereas no quasicrystal formation has been detected in the devitrification of the ribbon produced from the mechanically alloyed powder. This finding indicates that the absence of quenched-in nuclei may not be the only reason for the lack of quasicrystal formation in mechanically alloyed powders.
Structure–property correlation of nanostructured WO3 thin films produced by electrodeposition
Authors: Deepa M. , Srivastava A.K. , Singh S. , Agnihotry S.A.
Published: May 2005

Nanocrystalline tungsten oxide (WO3) films were electrodeposited potentiostatically at room temperature on transparent conducting substrates from an ethanolic solution of acetylated peroxotungstic acid prepared from a wet chemistry process. The changes that occur in the microstructure and the grain size of the as-deposited WO3 films as a function of annealing temperature are simultaneously accompanied by a continually varying electrochromic performance. X-ray diffraction studies revealed the transformation of a nanocrystalline as-deposited WO3 film into a highly crystalline triclinic WO3 as the annealing temperature was raised from room temperature to 500 °C. The microstructural evolution with the increasing annealing temperature of the as-deposited film was further exemplified by transmission electron microscopy (TEM) studies. While the as-deposited film was composed of uniformly distributed ultra fine nanograins, the most noticeable feature seen in these films annealed at 250 °C was the presence of open channels which are believed to promote lithium ion motion. Films annealed at 400 °C exhibited coarse grains with prominent grain boundaries that hinder lithium ion movement, which in turn reduces the film’s ion insertion capacity. In concordance with the TEM results, the 250 °C film had the highest ion storage capacity as it exhibited a charge density of 67.4 mC cm−2 μm−1. The effect of microstructure was also reflected in the high transmission modulation (64%) and coloration efficiency (118 cm2 C−1) of the 250 °C film at 632.8 nm. Contrary to the superior electrochromic performance of the 250 °C film, the optical switching speeds between the colored and bleached states of the as-deposited WO3 film declined considerably as a function of annealing temperature. Also, the diffusion coefficient for lithium ions was greater by at least an order of magnitude for the as-deposited film as compared to the 250 and 500 °C films. In this report, the influence of microstructural changes that are brought about by the annealing of the as-deposited WO3 films on their coloration-bleaching dynamics is evaluated in terms of their structural, electrochromic, and electrochemical properties.
New perspective in degradation mechanism of SrTiO3:Pr,Al,Ga phosphors
Authors: Kim Jin Young , You Yong Chan , Kang Jong Hyuk , Jeon Duk Young , Weber Jörg
Published: May 2005

Under prolonged electron-beam exposure, perovskite-structured SrTiO3:Pr,Al,Ga (STO) phosphor can be easily reduced due to oxygen loss. In particular, it is well known that dissociative H2O molecules are well adsorbed on reduced STO surfaces. The hydroxyl species produced by such dissociative adsorption of H2O strongly decompose organic compounds chemisorbed on the surface from vacuum ambient used in display devices into carbon species due to the photocatalytic properties of STO. Consequently, it is very likely that this mechanism attributes to the larger amounts of carbon adsorption by electron-stimulated chemical reactions on the STO phosphor surface than other phosphors.
Fatigue crack growth in micro-machined single-crystal silicon
Authors: Renuart Emily D. , Fitzgerald Alissa M. , Kenny Thomas W. , Dauskardt Reinhold H.
Published: May 2005

Although crystalline silicon is not generally considered susceptible to fatigue crack growth, recent studies suggest that there may be fatigue processes in silicon micro-machined structures. In the present study, a micro-machined fracture specimen geometry was used to examine stable crack growth under fatigue loading. Crack length and loads were carefully monitored throughout the test to distinguish between environmentally assisted crack growth (stress corrosion) and mechanically induced fatigue-crack growth. Results revealed similar steplike crack extension versus time for the cyclic and monotonic tests. The fatigue crack-growth curve extracted from the crack extension data exhibited a nearly vertical slope with no evidence of accelerated crack-growth rates. Fracture surfaces for the monotonic and cyclic tests were similar, further suggesting that a true mechanical fatigue crack-growth mechanism did not occur. Explanations for the observed lack of fatigue crack growth are presented and discussed with respect to reported stress-life behavior.
Half-metallic ferromagnetism in hypothetical wurtzite structure chromium chalcogenides
Authors: Zhang Ming , Brück Ekkes , Boer Frank R. de , Liu Guodong , Hu Haining , Liu Zhuhong , Cui Yuting , Wu Guangheng
Published: May 2005

The hypothetical wurtzite structure chromium chalcogenides were investigated through first-principle calculation within density-functional theory. All compounds are predicted to be true half-metallic ferromagnets with an integer Bohr magneton of 4 μB per unit. Their half-metallic gaps are 1.147, 0.885, and 0.247 eV at their equilibrium volumes for wurtzite-type CrM (M = S, Se, and Te), respectively. The half-metallicity can be maintained even when volumes are expanded by more than 20% for all compounds and compressed by more than 20%, 20%, and 5%, for CrS, CrSe, and CrTe, respectively.
Effects of mesoporous structure on grain growth of nanostructured tungsten oxide
Authors: Teoh Lay Gaik , Shieh Jiann , Lai Wei Hao , Hon Min Hsiung
Published: May 2005

The effects of mesoporous structure on grain growth were investigated in this study. The synthesis was accomplished using block copolymer as the organic template and tungsten chloride as the inorganic precursor. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, x-ray diffractometry (XRD), transmission electron microscopy, and N2 adsorption/desorption isotherms were used to characterize the microstructures obtained for different temperatures. TGA and XRD analyses demonstrate that copolymers were expelled at 150–250 °C, and mesoporous structure was stable up to 350 °C. The pore diameter and the surface area evaluated from the Barrett-Joyner-Halenda model and Brunauer–Emmett–Teller method indicated that the average pore diameter is 4.11 nm and specific surface area is 191.5 m2/g for 250 °C calcination. Arrhenius equation used to calculate the activation energy for grain growth demonstrates that the activation energy for grain growth was about 38.1 kJ/mol before mesostructure collapse and 11.3 kJ/mol after collapse. These results show evidence of two different mechanisms governing the process of grain growth. The presence of the pore can be related to the obstacle for grain growth.
Degradation resistance of silicon carbide diesel particulate filters to diesel fuel ash deposits
Authors: O’Sullivan D. , Pomeroy M.J. , Hampshire S. , Murtagh M.J.
Published: May 2005

A series of experiments were conducted to investigate chemical interactions between silicon carbide (SiC) and synthetic ash compositions expected to be deposited on the surfaces and within the pore structure of a diesel particulate filter. The chosen ash compositions simulated those arising from lubricants and three fuel types: standard diesel, diesel containing ferrocene as a catalytic additive, and diesel containing a cerium-based catalyst. Results demonstrated that SiC suffered little chemical or oxidative degradation in the presence of the ashes at 900 °C. For the ash not containing Fe or Ce, ash sintering effects were a possible mechanism causing filter blockage at temperatures above 970 °C. For ashes containing Fe or Ce, appreciable sintering effects were not observed below 1100 °C. Based upon the work conducted the suitability of SiC as a construction material for diesel particulate filters is not compromised by chemical degradation in the presence of lubricant/additive derived ash at temperatures less than 1100 °C.
Synergism of nano ZnO for improvement of hydrogen absorption performance of Ti–V-based alloys
Authors: Yu X.B. , Wan Q. , Wu Z. , Xia B.J. , Xu N.X.
Published: May 2005

Effect of nano ZnO on the hydrogen absorption performance of Ti-30V-15Mn-15Cr alloy was investigated. It was found that a small amount addition of nano ZnO (3 wt%) drastically improves the hydrogen absorption property of this alloy powder. The modification enables the air-exposed powder to absorb hydrogen quickly without activation. It could be attributed to the synergetic action of nano ZnO, which might expedite the dissociation of hydrogen on the oxidized alloy surface and play as entrance for hydrogen into the bulk alloy. The fact that nano ZnO addition improves the hydrogen absorption performance of Ti-30V-15Mn-15Cr alloy pioneers a new way for developing highly active Ti-V-based body-centered-cubic phase alloys.
Analytical solution for shape evolution of a coherent precipitate in triaxially stressed solid
Authors: Wang Hua , Li Zhonghua
Published: May 2005

An analytical solution for shape evolution of a coherent misfit precipitate in triaxially stressed solid has been proposed based on Eshelby inclusion theory. With complete energy consideration, the free energy that controls the shape evolution of the precipitate is a function of the precipitate shape, size, triaxially applied stresses, misfit strains, and Young’s moduli of the precipitate and the matrix. Based on the energy analysis, a comprehensive picture of shape evolution of the precipitate is presented.
Interfacial reactions of Sn–Cu and Sn–Pb–Ag solder with Au/Ni during extended time reflow in ball grid array packages
Authors: Islam M.N. , Chan Y.C. , Sharif A.
Published: May 2005

Lead-free solders with high Sn content cause excessive interfacial reactions at the interface with under-bump metallization during reflow. The interface formed after reflow affects the reliability of the solder joint. For this paper, we investigated the interfacial reactions of Sn0.7Cu and Sn36Pb2Ag solder on electrolytic Ni layer for different reflow times. The traditionally used Sn36Pb2Ag solder was used as a reference. It was found that during as-reflowed, the formation of Cu-rich Sn–Cu–Ni ternary intermetallic compounds (TIMCs) at the interface of Sn0.7Cu solder with electrolytic Ni is much quicker, resulting in the entrapment of some Pb (which is present as impurity in the Sn–Cu solder) rich phase in the TIMCs. During extended time of reflow, high (>30 at.%), medium (30-15 at.%) and low (<15 at.%) Cu TIMCs formed at the interface. The amount of Cu determined the growth rate of TIMCs. Cu-rich TIMCs had higher growth rate and consumed more Ni layer. By contrast, the growth rate of the Ni–Sn binary intermetallic compounds (BIMCs) in the Sn36Pb2Ag solder joint was slower, and the Ni–Sn BIMC was more stable and adherent. The dissolution rate of electrolytic Ni layer for Sn0.7Cu solder joint was higher than the Sn36Pb2Ag solder joints. Less than 3 μm of the electrolytic Ni layer was consumed during molten reaction by the higher Sn containing Sn0.7Cu solder in 180 min at 250 °C. The shear strength of Sn–Pb–Ag solder joints decreased within 30 min of reflow time from 1.938 to 1.579 kgf due to rapid formation of ternary Ni–Sn–Au compounds on the Ni–Sn BIMCs. The shear strength of Sn0.7Cu solder joint is relatively stable from 1.982 to 1.861 kgf during extended time reflow. Cu prevents the resettlement of Au at the interface. The shear strength does not depend on the thickness of intermetallic compounds (IMCs) and reflow time. Ni/Sn–Cu solder system has higher strength and can be used during prolonged reflow.
Influence of residual stress on elastic modulus and hardness of soda-lime glass measured by nanoindentation
Authors: Kese K.O. , Li Z.C. , Bergman B.
Published: May 2005

The influence of stress on the elastic modulus E and hardness H in soda-lime glass was studied in the Vickers residual stress field by nanoindentation. The Oliver–Pharr method of analysis first gave higher values of E and H, but after correcting for the pileup contact areas around the nanoindents, results consistent with literature values were obtained at regions in the stress field where the stresses were either low or close to zero. Determination of the pileup contact areas was made possible by the use of the atomic force microscope, which has facility for generating cross-section images of the indents. The elastic modulus was found to decrease with stress, which is explained with reference to the influence of applied stresses on the Si–O–Si bond angle. The hardness on the other hand did not depend on the stresses except in the region very close to the edge of the Vickers indent where the stresses are high.
Temperature-stable microwave dielectric ceramics in the Ca5A2Ti1-xZrxO12 (A = Nb, Ta) system
Authors: Bijumon Pazhoor Varghese , Sebastian Mailadil Thomas
Published: May 2005

Ca5A2Ti1−xZrxO12 (A = Nb, Ta) ceramics were prepared through conventional solid-state ceramic route for 0 ⩽ x ⩽ 1. The crystal structures of the ceramics were studied by x-ray diffraction techniques, and dielectric properties were measured at microwave frequencies. In the Ca5Nb2Ti1−xZrxO12 system as x increases from 0 to 1, ϵr decreases from 48 to 25, Qu× f from 26,000 to 19,000 GHz, and τf from +40 to −21 ppm/°C. In Ca5Ta2Ti1−xZrxO12 ceramics, ϵr varies from 38 to 22, Quxf from 33,000 to 24,000 GHz, and τf from +10 to −26 ppm/°C as x is changed from 0 to 1. The variation of microwave dielectric properties with bond valence and electronegativity in the two systems were also investigated. Ca5Nb2Ti0.2Zr0.8O12 and Ca5Ta2Ti0.7Zr0.3O12 dielectric ceramics were found to have stable resonant frequency with temperature and are potential candidates for applications in personal and satellite communication systems in the S and C band (2–8 GHz).
Synthesis of nanometer-sized particles of barium orthotitanate prepared through a modified reverse micellar route: Structural characterization, phase stability and dielectric properties
Authors: Ahmad Tokeer , Ganguli Ashok K.
Published: May 2005

Nanoparticles of barium orthotitanate (Ba2TiO4) was obtained using microemulsions (avoiding Ba-alkoxide). Powder x-ray diffraction studies of the powder after calcining at 800 °C resulted in a mixture of orthorhombic (70%) and monoclinic (30%) phases. The high-temperature orthorhombic form present at 800 °C was due to the small size of particles obtained by the reverse micellar route. Pure orthorhombic Ba2TiO4 was obtained on further sintering at 1000 °C with lattice parameters a = 6.101(2) Å, b =22.94(1) Å, c = 10.533(2) Å (space group, P21nb). The particle size obtained from x-ray line broadening studies and transmission electron microscopic studies was found to be 40–50 nm for the powder obtained after heating at 800 °C. Sintering at 1000 °C showed increase in grain size up to 150 nm. Our studies corroborate well with the presence of a martensitic transition in Ba2TiO4. The dielectric constant was found to be 40 for Ba2TiO4 (at 100 kHz) for samples sintered at 1000 °C. The dielectric loss obtained was low (0.06) at 100 kHz.
Conditions inducing reliable transient gratings of a LaCoO3 thin film using transient grating technique
Authors: Takata Yoshiaki
Published: May 2005

First, a grating decay rate and a thermal diffusion rate of the transient gratings are determined out of the energy-time trace observed by using a transient grating technique with 266-nm laser pulse inducing transient gratings in a LaCoO3 thin film. Second, the grating models aimed at studying two different thermal diffusion phenomena in contrast with the previous paper are described. The difference between both phenomena is attributable to the volume of photon scattering to characterize induced transient gratings. It is concluded that a reliable energy-time trace is observed when the transient gratings with a thickness smaller than a film are induced on the very surface of a thin film sample.
Microstructure and mechanical properties of novel ternary electroconductive ceramics
Authors: Sciti Diletta , Guicciardi Stefano
Published: May 2005

Electroconductive ceramic composites, constituted of an insulating matrix (a composite AlN-SiC) containing 30 vol% of an electroconductive phase (MoSi2, ZrB2, or ZrC), were densified through hot-pressing. Microstructure and mechanical properties were compared to those of the AlN-SiC matrix material. All the ternary composites are good electrical conductors, with resistivities in the range 0.3 × 10-3to 4 × 10-3Ω·cm. Room temperature properties are improved by the addition of the electroconductive particles. Strength and toughness measurements at high temperature show that MoSi2-containing composite is stable up to 1300 °C (strength 611 MPa, toughness 3.7 MPa·m1/2), whereas ZrB2-containing composite is stable up to 1000 °C. ZrC-containing composite is not suitable for high-temperature applications due to poor oxidation resistance.
Cavity growth rate in superplastic 5083 Al and AZ31 Mg alloys
Authors: Chino Yasumasa , Iwasaki Hajime , Mabuchi Mamoru
Published: May 2005

The plasticity-controlled growth rate of cavities during superplastic deformationwas statistically investigated for 5083 Al alloy and AZ31 Mg alloy. When the cavity growth rate was evaluated on the basis of macroscopic strain calculated using the displacement of the specimen, the growth rate for the Al alloy was larger than thatfor the Mg alloy. However, the growth rate of the Al alloy was in agreement withthat of the Mg alloy when the cavity growth rate was evaluated on the basis of the microscopic strain due to grain boundary sliding. The results obtained lead to two conclusions: (i) the rate of cavity growth is not affected by the kind of materials,that is, the nature of the grain boundary, and (ii) the microscopic strain due to grain boundary sliding should be used to evaluate exactly the rate of cavity growth for superplastic deformation.