bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optical and Transport Properties of Fullerene Crystals
Authors: Byrne Hugh J. , Akselrod Lidia , Werner Andreas T. , Maser Wolfgang K. , Kaiser Mathias , RÜhle Wolfgang W. , Roth Siegmar
Published: April 2011

Picosecond time resolved photoluminescence and photoconductivity measurements are performed to investigate the influence of high intensity illumination on the properties of Fullerene crystals. A highly nonlinear dependence of both the photoluminescence characteristics and the photoconductive response of the fullerenes is seen and temperature dependent measurements indicate that the nonlinear processes are associated with an insulatormetal-like phase transition in the material, and thus that the electronic properties of the excited state are dramatically altered at high excited state densities. The observed behaviour is compared and contrasted to the changes in the optical properties upon photochemical modification of the pristine material via Raman spectroscopy. Application of a simple phenomenological model to calculate the contribution of intermolecular exchange and correlation energies in the excited state supports the proposal that the observed phenomena originate from a Mott-like phase transition. A further manifestation of this behaviour is the emergence of a broadband electroluminescent emission above a critical injection current density.
Crystalline Boron Carbide Encapsulated Into Carbon Nanoclusters from Arc-Discharge Soot
Authors: Seraphin Supapan , Zhou Dan , Jiao Jun
Published: April 2011

Using a boron-containing composite anode in an arc discharge, we found in the soot on the reactor walls graphitic multiwalled carbon clusters that contained boron carbide crystals, as identified by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and electron diffraction. The encapsulants are compounds of the lightest element that has yet been encapsulated, and the first of the non-metallic. The multiwalled graphitic cages partially encapsulating the boron compounds have rarely been observed in the soot of arc-discharge material produced from anodes not containing boron. We explain this exception by the known tendency of boron to catalyze graphitization.
The Effect of O2 Intercalation on the Rotational Dynamics and the Ordering Transition of C60
Authors: Myers S. A. , Assink R. A. , Schirber J. E. , Loy D. A.
Published: April 2011

We have used 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and rotational dynamics of C60 containing oxygen molecules located in the interstitial sites of the fcc lattice. Under normal conditions, a narrow peak at 143.7 ppm is observed for C60. When exposed to oxygen at moderate pressures, several additional resonances appear in the 13C MAS NMR spectrum. These secondary resonances are shifted downfield from the main peak at 143.7 ppm and are due to the Fermi-contact interaction of the paramagnetic oxygen molecules with the 13C nuclear spins. The presence of oxygen depresses the orientational ordering transition by ca. 20 K as observed by DSC. The spin-lattice relaxation time (T1) of each secondary peak shows a minimum near the ordering transition, indicating that this transition is not dependent on the number of oxygen molecules surrounding an individual C60 molecule. The T1 due to paramagnetic relaxation, normalized by the number of surrounding oxygen molecules, is constant. This observation demonstrates that within a given sample, the dynamics of C60 molecules are independent of the number of surrounding oxygen molecules.
High Yield Conversion of Carbon Nanotubes to Nanostraws at Mild Conditions
Authors: Hwang Kuo Chu
Published: April 2011

Several oxidants were examined for their abilities in opening carbon nanotube end caps. Up to 91% of carbon nanotubes were found to have at least one open end when treated by 0.2 M KMnO4/ 10% H2SO4 or 0.2 M KMnO4/ 0.2 M CrO3 aqueous solution at 100° C, 90 min. That is, σ82% of carbon nanotubes was converted to “nanostraws”. The morphologies of the processed carbon nanotubes reflect the relative strength of these oxidants. The mechanism of carbon nanotube end cap opening processes will be discussed.
Nuclear Reaction Probe of Oxygen Vacancy Migration in Electrically Fatigued PZT Thin Film Capacitors
Authors: Pfeffer R.L. , Wilber W.D.
Published: April 2011

The migration of oxygen vacancies and their entrapment near film-electrode interfaces has been proposed as a cause of fatigue (i.e., polarization weakening) in ferroelectric thin film capacitors. To test this idea, lead zirconate titanate (PZT) thin films were epitaxially deposited by laser ablation on LaAlO3 substrates with yttrium barium cuprate (YBCO) base electrodes. Thin film capacitors were formed by deposition of noble metal (Pt) cap electrodes; half of them were then electrically fatigued by repeated polarization reversals (108 cycles). The distributions of oxygen in the two halves were then compared by means of accelerator-based nuclear backscattering (using the narrow elastic resonance at 3.045 MeV in the scattering of 4He from 16O) throughout the bulk of the PZT films and especially right under the Pt electrodes. We were unable to detect any difference in the oxygen profiles to within the accuracy of measurement, which was about 1 % of the oxygen concentration. Compositional changes, at least involving oxygen, do not seem to be responsible for the striking electrical alterations seen in fatigued PZT.
Crystallization and Texture of Bi-Containing Layered Perovskite Thin Films
Authors: Chen S-Y. , Du X-F. , Chen I-W.
Published: April 2011

Crystallization and texture formation of a number of layered perovskite thin films prepared by the MOD method has been investigated. The crystallization temperature increases with increasing complexity of the structure, rendering it more difficult to obtain c-axis oriented films. Texture formation can be facilitated by the introduction of a seeding layer, such as PbBi2Nb2O9, which has a somewhat lower crystallization temperature, and by multiple coatings, which allow successive crystallization. Grain size is also reduced by the above practice. These results are compared with similar findings in PZT thin films to conclude that texture development in layered perovskites is nucleation controlled.
Optical Study of PbTiO3 Thin Films Grown by Sol-Gel Technique
Authors: Ching-Prado E. , Tao R.W. , Katiyar R.S. , Bhalla A.S.
Published: April 2011

Thin films of PbTiO3 were prepared by sol-gel method on platinum-coated-Si and Al2O3 and annealed at 600°C. The annealing time of the films, deposited on Si, were 6 and 12 hours, respectively. Micro-Raman spectra show high background in the low frequency region and the bands are broader with respect to the single crystal work, which indicates the polycrystalline nature of the samples. The film annealed for 12 hours showed more pronounced peaks in the spectra when compared to the film annealed for 6 hours. Micro-Raman measurements on different spots in the film indicate that the PT film on platinum-coated silicon substrate is highly inhomogeneous. In the case of PT/Al2O3 such studies show a homogeneous film. The frequencies of most of the modes are decreased, which is associated to grains under stress. The nature of the stress is discussed. Although film stress may not be homogeneous, a stress value around 1.2 GPa is estimated from Raman data. XRD and SEM techniques were used for structural characterization.
Photoferroelectric Effects of Undoped and Extrinsic Ion-Doped PZT Thin Films
Authors: Li Li , Lin Chhiu-Tsu , Leung Martin S. , Adams Paul M. , Lipeles Russell A.
Published: April 2011

Deposition by aqueous acetate solution (DAAS) technique was used to synthesize undoped and 5 wt% Cr-, Mn-, Eu-, or Pr-doped Pb(Zr0.53Ti0.47O3 [PZT] thin films. The dopant was incorporated into PZT either in the precursor coating solution or via thermal diffusion into undoped PZT. X-ray diffraction shows that ion-doped PZT thin films on Pt/Ti/SiO2/Si<100> (in particular, the Mn- and Eu- doped samples) display better crystallinity and smaller lattice parameters than those on sapphire substrates. The enhancement of photoconductivity at visible wavelengths measured by excitation photocurrent spectroscopy (EPS) goes as Cr-doped∼Mn-doped > Eu-doped ∼ Pr-doped. Only Mn-doped PZT perovskites have the band gap energy red-shifted to 360 nm from 330 nm. The space charge (or photovoltaic) field was estimated to be < 8 v when about 100 v was applied to ion-doped PZT thin films with 260 or 320 nm light. By using laser irradiation at selected wavelengths and switching the polarity of applied bias voltage, the expected changes in resistance (Ry) and remanent polarization (±Pr) states were observed in the P-E hysteresis loops. The possible applications of extrinsic ion-doped PZT thin films in optical memory devices are discussed.
Impact of A Ti Adhesion Layer on Pt/PZT/Pt Capacitors
Authors: Jones R.E. , Mamar P.D. , Dupuie J.L. , Kim J. , Moazzamp R. , Witowski J. , Kottke M.L. , Saha N.C. , Gregory R.B.
Published: April 2011

A five-factor, full-factorial experiment on process sensitivity of non-volatile polarization, Pnv for Pt/PZT/Pt capacitors shows the most dramatic factor is the use, or not, of a Ti adhesion layer for the bottom electrode. With the Ti layer, Pnv is generally lower and is sensitive to several factors and interactions involving the crystallization anneal, sol-gel synthesis, and Pt thickness and deposition temperature. A possible cause is Ti diffusion through the Pt as observed in Auger and XPS depth profiles of oxygen annealed Pt/Ti electrodes.
Layered Structure Oxides for Fatigue Free Ferroelectric Applications
Authors: Vijay Dilip P. , Desu Seshu B. , Nagata Masaya , Zhang Xubai , Chen Tze C.
Published: April 2011

SrBi2(TaxNb1−x)2O9 (SBTN) layered structure oxides have been investigated for possible fatigue free ferroelectric thin film applications. High quality stoichiometric thin films of these oxides have been fabricated, across the solid solution range, using the technique of pulsed laser ablation SBTN thin films with a composition close to x=0.4 showed excellent ferroelectric properties and no fatigue up to 1010 switching cycles. Typically, these films showed a 2Pr value of 22 μC/cm2, an Ec of 60 kV/cm and a resistivity close to 5 × 1012 Ω-cm. The ferroelectric properties of these films were found to depend on the orientation. Predominantly c-axis oriented films have been fabricated on MgO (100)/Pt (100) substrates. By comparison, the c-axis oriented films were found to exhibit similar Pr values but significantly lower Ec values (by 15 kV/cm) and a higher resistivity. The fatigue free behavior of these layered structure oxides has been ascribed to the absence of any volatile species in their sublattice exhibiting polarization (i.e., the perovskite-like units in the layered structure).
Epitaxial Pb(Zr0.40Ti0.60)O3/SrRuO3 and PbTiO3/SrRuO3 Multilayer Thin Films Prepared by MOCVD and Rf Sputtering
Authors: Foster C.M. , Csencsits R. , Baldo P.M. , Bai G.R. , Li Z. , Rehn L.E. , Wills L.A. , Hiskes R. , Dimos P. , Sinclair M.B.
Published: April 2011

Epitaxial SrRuO3 thin films were deposited by RF sputtering on SrTiO3 or MgO substrates for use as underlying electrodes. On these conductive substrates, epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) and PbTiO3 (PT) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90° domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed a 70% RBS channelling reduction. Hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag or ITO glass top electrode showed: a remanent polarization of 46.2 μC/cm2 a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of ∼5.8×109 ω-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm.
Ferroelectric (Pb,La)TiO3 Thin Films Prepared by Metalorganic Chemical Deposition
Authors: C. Z. , Kwak B.S. , Erbil A.
Published: April 2011

Recently, we reported results of an investigation of the preparation of highly textured (Pb1−xLax)TiO3 (PLT) thin films grown on Si(100) by metalorganic chemical deposition (MOCVD) [1]. In this paper, we discuss an extension of this work to the growth of PLT thin films on fused quartz substrates by the MOCVD technique. A series of PLT films with x between 0 and 0.32 were prepared. Characterization by x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and Raman scattering has been performed on these ferroelectric thin films. XRD indicated the polycrystalline nature of the PLT films and the variation of their tetragonality. The film thickness and La composition were determined by RBS. Raman spectra, measured at 300 and 80 K, showed features of the PLT film and quartz substrate. By using a “difference Raman” technique, more PLT modes were shown. The variations of the PLT Raman modes with the La composition and the measurement temperature were studied. Related physical phenomena and problems are discussed.
The Characterization and Electrical Properties of DOPED PZT Thin Films Prepared by Sol-Gel Processing
Authors: Lee Wan In , Lee J.K. , Chung Elsub , Chung C.W. , Yoo I.K. , Desu Seshu B.
Published: April 2011

PZT (Zr/Ti = 53/47), PNZT (4% Nb doped PZT), PSZT (2% Sc doped PZT), and PSNZT (1% Sc and 1% Nb doped PZT) thin films were prepared by a sol-gel process. They were characterized by XRD, SEM and TEM. Both crystallographic orientation and grain size of PZT films can be changed by doping. Pt/PZT/Pt capacitors were fabricated for the measurement of ferroelectric properties. By doping with both Sc and Nb, the fatigue performance of the PZT films was considerably improved and the coercive field was decreased, while the remanent polarization was not changed. In addition, the effect of dopants on the leakage current level of PZT films was studied.
Orientation and Phase Formation of Bi4Ti3O12 Film on (100) Silicon by APMOCVD and RTA
Authors: Wang H. , Su X.J. , Zeng J.M. , Wang Z. , Shang S.X. , Wang M.
Published: April 2011

Bismuth titanate thin films have been grown on (100) silicon substrate by atmospheric pressure metalorganic chemical vapour deposition (APMOCVD). The phase formation of Bi-Ti-0 films are dependent upon the composition, growth temperature and RTA post-annealing process. The film grown at 550°C, under optimized growth condition, is single crystal film with (100) orientation, while the (001) preffered oriented films were obtained after rapid thermal annealing. The orientation of Bi4Ti3O12 films mainly depends upon the lattice match with the substrate. At 550°C, the best lattice match is (100) of Bi4Ti3O12 with (100) of silicon. At higher temperature (>675°C), the Bi4Ti3O12 has a tetragonal structure and the best lattice match is (001) Bi4Ti3O12 with (100) of silicon due to the different thermal expansion coefficient of two materials.
Physicochemical and Electrical Properties of RF Magnetron Sputtered Lead Zirconate Titanate Thin Films
Authors: Ea Kim B. , Hugon M.C. , Varniere F. , Agius B. , Achard H. , Puech M.
Published: April 2011

Due to their high dielectric constant, good chemical stability and good insulating properties, lead zirconate titanate (PZT) thin films are considered as promising materials to replace Si3N4 and Ta2O5 for use as the capacitor dielectric in future high density DRAMs. Moreover, the ferroelectric quality of PZT films also allows use of this material in non volatile memories. In this paper, we investigate the properties of PZT films deposited from an oxide target of nominal composition {Pb1.1(Zr0.55,Ti0.45)O3} in a radio frequency (rf) magnetron sputtering system. The Pt(deposited at 450°C)/[TiN/Ti/BPSG/Si] structure annealed at 450°C at 10−6 mbar (Pt(450°C)/{TiN/Ti/BPSG/Si}450°c,10–6mbar) was used as a substrate material in this work. The PZT films were deposited at different pressures, and different substrate temperatures ranging from floating temperature to 400°C; the thicknesses of the sputtered films were in the 15–720 nm range. The kinetics of the sputtering process and the effect of sputtering parameters on film composition have been studied and related to the continuously monitored optical emission of the plasma. The relative cation and oxygen compositions of the films were determined by a new method based on the simultaneous use of Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA) induced by a deuteron beam. The conditions for the deposition of stoichiometric PZT thin films were established.

Electrical characterizations of the PZT films including resistivity, dielectric constant, dissipation factor were studied as a function of the temperature. From initial electrical measurements, it appears that a dielectric constant of 740 can be obtained for PZT 55/45 films deposited on a previously annealed Pt/TiN/Ti/BPSG/Si structure.
Microstructure Evolution of Epitaxial (Ba, Sr) TiO3/ (001) HgO Thin Films
Authors: Alyoshin V.A. , Sviridov E.V. , Hukhortov V.I.M. , Zakharchenko I.H. , Dudkevich V.P.
Published: April 2011

Surface and cross-section relief evolution of ferroelectric epitaxial (Ba,Sr)TiO3 films rf-sputtered on (001) HgO crystal cle-avage surface versus the oxygen worKing gas pressure P and subst-rate temperature T were studied. Specific features of both three-dimensional and two-dimensional epitaxy mechanisms corresponding to various deposition conditions were revealed. Difference between low and high P-T-value 3D epitaxy was established. The deposition of films with mirror-smooth surfaces and perfect interfaces is shown to be possible.
Structure and Ferroelectric Behaviour of Step-Crystallized PbZr0.5Ti0.5O3 Thin Films Prepared by Electron Beam Evaporation of Multi-Component Oxides
Authors: Darvish Shaban R. , Rastogi A.C.
Published: April 2011

Preparation of ferroelectric lead zirconate titanate (PZT) thin film by electron beam evaporation of multicomponent oxides followed by a post-deposition synthesis of PZT films by step-annealing under O2 ambient is described. Incipient formation of Pb3O4-ZrO2-PbTiO3 solid solution by a 600°C annealing is required for crystallization of PZT phase. Two morphotropic phase boundary reactions between solid solution phase with TiO2 and PbTiO3 with ZrO2 are proposed for PZT growth. Polarization and capacitance-voltage hysteresis data are presented to establish ferroelectric behaviour.
Mechanism(s) for the Suppression of the Switchable Polarization in PZT and BaTiO3
Authors: Warren William L. , Dimos Duane , Tuttle Bruce A. , Pike Gordon E. , Raymond Mark V. , Nasby Robert D. , Ramesh R. , Evans Joseph T.
Published: April 2011

Switchable polarization can be significantly suppressed in ferroelectric (FE) materials by optical, thermal, and electrical processes. The thermal process can occur by either annealing the FE in a reducing environment or by heating it in air to 100°C while impressing a bias near the switching threshold. The optical process occurs while biasing the FE near the switching threshold and illuminating with bandgap light. And the electrical suppression effect occurs by subjecting the FE to repeated polarization reversals. Using electron paramagnetic resonance, polarization-vol tage measurements, and charge injection scenarios, we have been able to elucidate both electronic and ionic trapping effects that lead to a suppression in the amount of switchable polarization in FE materials. The relative roles of electronic and ionic effects in the same material can depend on the stress condition. For instance, in oxidized BaTiO3 crystals, optical and thermal suppressions occur by electronic domain pinning; electrical fatigue in the BaTiO3 crystals also appears to involve electronic charge trapping, however, it is suggested that these electronic traps are further stabilized by nearby ionic defects. In sol-gel PZT thin films with either Pt, RuO2, or La-Sr-Co-O electrodes it appears that the polarization suppression induced by electrical fatigue, a temperature/bias combination, or a light/bias combination are all primarily due to the trapping of electronic charge carriers to first order.
Properties of Reactively Sputter Deposited SrTiO3 Films for IR Detector Readout Electronics
Authors: Bernstein S.D. , Wong T.Y. , Rawson J.K. , Tustison R.W.
Published: April 2011

The effects of film thickness, oxygen partial pressure, electrode type, substrate temperature, and position on the room temperature and 77 K dielectric properties of SrTiO3 (ST) films were studied. The film composition and properties vary with radial position and oxygen partial pressure. A maximum in dielectric constant occurs near the same position where stoichiometric films are obtained. The room temperature and 77K dielectric constants increase with increasing thickness, while the capacitance density decreases. Capacitance densities as high as 4 fF/μm2 were observed for films deposited at low temperature and subsequently crystallized. Elevated temperature deposition, however, results in better properties than room temperature deposition followed by annealing. Dielectric constants as high as 200 with capacitance densities up to 9 fF/μ2 were observed. For optimized deposition conditions, no dielectric break-down of the capacitors was observed at 20V after 111 days of testing. The properties of capacitors with n+Si bottom electrodes were not as good as those with Ti/Pt electrodes, however, integration with Si integrated circuit processing is expected to be much simpler.
Heteroepitaxial Growth of Ba0.5Sr0.5TiO3/SrRuO3 on YSZ/Si by Off-Axis Sputtering
Authors: Hou S.Y. , Kwo J. , Watts R.K. , Cheng J.-Y. , Cava R.J. , Peck W.F. , Fork D.K.
Published: April 2011

We demonstrate an epitaxial heterostructure of Ba0.5Sr0.5 TiO3/SrRuO3/YSZ on Si for potential charge storage applications. The dielectric Ba0.5Sr0.5TiO3 (BST) and conductive oxide SrRuO3 are both grown (110) oriented on YSZ (100) buffered Si by 90° off-axis sputtering. These films showed a high degree of crystallinity with minimal interdiffusion at the interfaces as examined by X-ray diffraction, Rutherford backscattering spectroscopy, and cross-section transmission electron microscopy. The in-plane epitaxial alignment of the films is BST/SRO 〈111〉 // YSZ 〈110〉 with a four-fold degeneracy. The dielectric constant and loss tangent of the epi-BST films are 360 and 0.01 at 10 kHz. The leakage current density is < 4×10∼−7 A/cm2 at 1 V. The room temperature dielectric constant (ε) of the BST films shows a roll-off in the 1–10 MHz range. This is attributed to the existence of a series resistance in the measurement circuit, which likely arises from the SrRuO3 electrode.
Effects of Antiphase Domain Size and Twin Platelet Width on the Hardness of an Ordered CuAu Alloy
Authors: Shiraishi Takanobu , Ohta Michio , Nakagawa Masaharu
Published: April 2011

Effects of antiphase domain (APD) size and inter-twin spacing on the hardness of CuAu I-phase in the overaging stage were investigated by hardness testing, transmission electron microscopy, and X-ray powder diffraction. Overaging in CuAu I-phase upon progressive ordering at 300°C was found to proceed through three stages: stages I through III. In the stage I, twinning actively occurred, and most of the coherency strains were removed. Average inter-twin spacing slightly increased. These microstructural evolutions slightly decreased the hardness of the alloy. In the stage II, both APD size and average inter-twin spacing grew larger with time, leading to a continuous decrease in hardness. In the stage III, the APD size markedly grew larger, while the growth rate of average inter-twin spacing markedly slowed down. The continuous growth of APD size apparently contributed to the further decrease in hardness. Although the crystal structure changes during the CuAu I ordering, a perfectly ordered alloy with no planar defects was suggested to be not so strong as the corresponding disordered alloy.
Ultrasonic Discrimination of Samples With Differently-Distributed Grain Sizes and Equal Average Grain Size
Authors: Nicoletti Denise , Anderson Aran
Published: April 2011

Materials can have distributions of grain sizes. These distributions can have effects on the material's mechanical properties that are more complicated than an average grain-size dependence. The omission of distribution effects on properties is understandable in view of the great amount of labor required in the experimental measurement of grain volume distribution, together with the predominantly two-dimensional nature of micrography-based grain-size estimation. Ultrasonic techniques have been used to nondestructively measure the grain size of materials on a scale of microns. We suggest using ultrasonic attenuation as an alternative to micrography for three reasons. One advantage is that the ultrasonic dependence on size is a true, three-dimensional dependence. Secondly, through careful selection of wavelength, various grain-size distribution parameters can be extracted. The third justification is that ultrasonic techniques are quick and nondestructive. Previous theoretical development will be reviewed, and the experimental verification will be presented. Through numerical modeling we show the advantages of using ultrasonic techniques that are sensitive to grain-size distribution parameters. We demonstrate that samples with equal average grain size but different grain-size distributions have significantly different attenuation wavelength dependencies.
Deformation Twinning and Grain Size Aspects of Numerical Simulations of Plastic Flow
Authors: Zerilli Frank J. , Armstrong Ronald W.
Published: April 2011

The dependence of the twinning stress on grain size is similar to the dependence of the athermal part of the flow stress on grain size. Previous numerical simulations included a twinning effect based upon the premise that twinning refines the grain size and gives additional Hall-Petch strengthening. If a grain reaches the stress level given by σT = σT0+ kT ∓-1/2, it is considered twinned and a constant increment is added to the flow stress. Once twinned, the new twinning threshold stress is much higher than the original and so further twinning is unlikely to occur. The twinning model used in this work is based on the idea that enough twinning will occur in a grain to accommodate the excess by which the Von Mises equivalent stress exceeds the twinning threshold stress. The previous twinning model required knowledge of the number of twins per grain produced. With this model, the parameters for iron are known a priori (σT0 = 330 MPa and kT = 2.8 MPa m1/2) and numerical simulations of Taylor cylinder impacts produced good agreement with experimental results. For titanium and zirconium, σT0 and kT were determined by matching the computed and experimental shapes. The results here indicate that twinning hardens these metals by effectively changing the material grain size and the microstructure within the grains.
Applications of Images Digital Analysis in the Characterisation of Grains Morphology Influence in Mechanical Behaviour of Granular Soils
Authors: G Bonifazi , G Sappa , G De Casa
Published: April 2011

Preliminary results of a research aimed to identify the influence of the morphological characteristics of the grains constituting a quartz sand on the mechanical behaviour of the sand itself are presented. The tests were conducted on different size class samples resulting from a grain-size classification of the sand following the international standard classification (ASCII) procedure. For each sample traditional direct shear laboratory tests and an accurate characterisation of morphological and morphometrical properties of their constituting elements (grains) by means of digital image processing techniques were conducted. The statistical distribution of the different parameters derived following the two above mentioned procedures was studied and the results discussed.
Formation and Spatial Statistics of Spherulitic Grain Pattern in Solidified Films of Isotactic Polypropylene
Authors: Huang Tao , Rey Alejandro D. , Kamal Musa R.
Published: April 2011

Image analysis and measurements on forimation and spatial statistics of spherulitic grain pattern in solidified films of a model polymer, isotactic polypropylene (iPP), have been carried out during in-situ observation experiments under isothermnl conditions. Topological correlations and geometrical distribution fuinctions of polymer grain sides and area are reported. Some topologically unstable configurations, such as multi-vertices, “T” type vertices and two sided grain (lens), have been found. Analysis by spatial tessellations shows that the tenWal evolution and spatial distributions of nuclei point patterns play a role in all of these microstructural properties.
Kinetics of Diamond-Like Film Growth Using Filament-Assisted Chemical Vapor Deposition
Authors: Gorsuch G. , Jin Y. , Ingle N. K. , Mountziarisi T. J. , Yu W.-Y. , Petrou A.
Published: April 2011

A detailed kinetic model of diamond-like film growth from methane diluted in hydrogen using low-pressure, filament-assisted chemical vapor deposition (FACVD) has been developed. The model includes both gas-phase and surface reactions. The surface kinetics include adsorption of CH3· and H·, abstraction reactions by gas-phase radicals, desorption, and two pathways for diamond (sp3) and graphitic carbon (sp2) growth. It is postulated that adsorbed CH2· species are the major film precursors. The proposed kinetic model was incorporated into a transport model describing flow, heat and mass transfer in stagnation flow FACVD reactors. Diamond-like films were deposited on preseeded Si substrates in such a reactor at a pressure of 26 Torr, inlet gas composition ranging from 0.5% to 1.5% methane in hydrogen and substrate temperatures ranging from 600 to 950°C. The best films were obtained at low methane concentrations and substrate temperature of 700°C. The films were characterized using Scanning Electron Microscopy (SEM) and Raman spectroscopy. Observations from our experiments and growth rate data from similar experiments reported in the literature [1] were used to estimate unknown kinetic parameters of surface reactions. The proposed model predicts observed film growth rates, compositions and stable species distributions in the gas phase. It is the first complete model of FACVD that includes gas-phase and surface kinetics coupled with transport phenomena.
TEM Study of Growth Defects in CVD Diamond Films
Authors: Chen Fred Y. , King Alexander H. , Salat Robert F. , Fricano Glenn J.
Published: April 2011

Transmission electron microscopy (TEM) has been used to examine defects in diamond films grown by the microwave plasma-enhanced chemical vapor deposition (CVD) method. Graphite was used as the sole carbon source during the CVD process with silicon substrates. Growth defects including twins, stacking faults, dislocations and second-phase precipitates were observed in the films. In plan-view TEM, defect clusters at the centers of diamond grains were observed, where the film is also the thickest. Cross-sectional TEM was carried out to show that the defect clusters fan out from a single nucleation site in each grain, at the diamond-silicon interface. Possible growth mechanisms of the defect clusters in diamond grains are considered.
Organometallic Chemical Vapor Deposition: the Roles of Precursor Design and Growth Ambient in Film Properties
Authors: Rees William S. , Luten Henry A. , Goedken Virgil L.
Published: April 2011

Examples of chemical control in CVD of metallic and ceramic films are highlighted. Specific attention is paid to the complexity of precursor design. The effect of reactor environment on growth chemistry is investigated. Examples where reducing or oxidizing atmospheres provide a high level of control over deposit composition are outlined. The system examined centers on yttrium and yttria. These materials are, in general, desired less for their optical or electronic properties and more for their structural properties. Thus, the rigid purity demands of the microelectronics industry are somewhat relaxed. Nevertheless, critical attention must be paid to the issues of vapor pressure and decomposition profile. Where sufficient data is available to justify it, some explaination of the issues relevent to vapor pressure is presented.
Self-Lubricating, TiN-MoS2 Composite Coatings Produced by Simultaneous Deposition from Ti((CH3) 2N)4/NH3/MoF6/H2S GAS Mixtures
Authors: Bae Y. W. , Lee W. Y. , Besmann T. M. , Blau P. J. , More K. L. , Braski D. N
Published: April 2011

Composite coatings consisting of discrete phases of TiN and MoS2 were codeposited on graphite substrates from Ti((CH3)2N)4/NH3/MoF6/H2S gas mixtures in a cold-wall reactor at 1073 K and 1.3 kPa. Chemical composition and microstructure of the coatings were characterized by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Kinetic friction coefficients of the coatings were determined by a computer-controlled friction microprobe and values less than 0.2 were obtained with a type-440C stainless-steel counterface under ambient condition.
Functionally Gradient Sic Coatings Produced by Chemical Vapor Reaction
Authors: Kowbel W. , Bruce C. , Withers J. C. , Ransone P. O.
Published: April 2011

Functionally gradient coatings have the potential to eliminate sharp interfaces between the coating layer and substrate resulting in a great ability to tailor the thermo-mechanical properties of the coating systems to a variety of substrates. Primary examples of beneficial use of the functionally gradient materials are the crack free CVD C-SiC coatings that were recently produced by a number of researchers on C-C composites. Inherent limitations of the CVD technique make it practically difficult to obtain high deposition rates on very complex and large shapes combined with good coating uniformity. A new process termed Chemical Vapor Reaction (CVR) has been employed to produce virtually crack free SiC coatings on 2–D C–C composites. Properties of this new class of functionally gradient coatings will be presented and discussed.
The Decomposition of Methyltrichlorosilane in Hydrogen and Helium
Authors: Osterheld Thomas H. , Allendorf Mark D.
Published: April 2011

Experimental measurements of the decomposition of methyltrichlorosilane (MTS), a common silicon carbide precursor, in a high-temperature flow reactor are presented. Methane, hydrogen chloride, and silicon tetrachloride are observed as products of the decomposition. Trapping experiments with acetylene and ethylene also detected SiCl3 as a decomposition product. Upper limits on the concentrations of any CH3Cl, HSiCl3, H2SiCl2, or H2C=SiCl2 which might form are provided. Quantitative measurements of product branching and MTS decomposition rates are presented. The results suggest a radical-chain mechanism for the decomposition in hydrogen but not in helium.
Understanding and Improving Materials Processing Through Interpreting and Manipulating Predictive Models
Authors: Kee Robert J. , Ting Aili , Spence Paul A.
Published: April 2011

Most physically based modeling software accepts input in the form of geometry definition, physical parameters, initial conditions, and boundary conditions; and then, on the basis of solving physical conservation equations, predicts the steady-state or transient behavior of a system or process. There is a growing need to create software tools that can themselves control or manipulate the physically based models in certain ways to enhance the usability of models for equipment design and process optimization. These required tools can be described broadly in the following categories: sensitivity analysis, parameter estimation, inverse problems, dynamic optimization, and real-time control. This paper discusses generally the development and application of such modeling tools, drawing examples from a specific RTP reactor design. These techniques accelerate significantly the optimal design of processes and the concurrent engineering of real-time process-control algorithms.
Dynamic Modelling of CVD for Real-Time Control of Microstructure
Authors: Gevelber M.A. , Quiñones M.T. , Bufano M.L.
Published: April 2011

A nonlinear dynamic model of the chemical vapor deposition (CVD) process has been developed and analyzed to obtain insight into the design of an appropriate control structure.
Intelligent Process Control of Silicon Nitride Chemical Vapor Deposition
Authors: Bowen Paul S. , Phelps Steve K. , Ringermacher Harry I. , Veltri Richard D.
Published: April 2011

The chemical vapor deposition of silicon nitride can be used to protect advanced materials and composites from high temperature, corrosive, and oxidative environments. Desired coating characteristics, such as uniformity and morphology, cannot be measured in-situ by traditional sensors due to the adverse conditions within the high-temperature reactor. A control strategy has been developed which utilizes a process model and an advanced laser-based sensor to measure the deposition rate of the silicon nitride coating in real-time. The control system is based on a three level hierarchical architecture which functionally separates the process control into PID, supervisory and advanced sensor-based control. Optimal setpoint schedules for the supervisory level are derived from a quasi-fuzzy logic inverse mapping of the process model. An advanced sensor utilizing laser ultrasonics provides real-time coating thickness estimates. Model bias is characterized for each reactor and is correlated on-line with the sensor's deposit thickness estimate. Deviations from model predictions may result in parametric changes to the process model. New setpoint schedules are then created as input to the supervisory control level by regenerating the inverse map of the updated process model.
Light Scattering Studies of an Electrorheological Fluid in Oscillatory Shear
Authors: Martin James E. , Odinek Judy
Published: April 2011

We have conducted a real time, two-dimensional light scattering study of the nonlinear dynamics of field-induced structures in an electrorheological fluid subjected to oscillatory shear. We have developed a theoretical description of the observed dynamics by considering the response of a fragmenting/aggregating particle chain to the prevailing hydrodynamic and electrostatic forces. This structural theory is then used to describe the nonlinear rheology of ER fluids.
Anomalous Phase Separation Kinetics Observed in a Micelle System
Authors: Wilcoxon J. P. , Martin J. E.
Published: April 2011

We report a real-time, two-dimensional light scattering study of the evolution of structure of a two component nonionic micelle system undergoing phase separation. The micelles act like molecular slug-a-beds whose domain growth is pathetically lathargic (i.e. slower than the cube root of time prediction for simple binary fluids). In fact, the growth kinetics can be empirically described as a stretched exponential approach to a pinned domain size. Although the kinetics are not yet understood, this anomalous behavior may be due to the ability of the spherical micelles to reorganize into more complex structures.
Experimental Study of Electrokinetics in Porous Media
Authors: Pengra David B. , Shi Liang , Li Sidney Xi , Wong Po-Zen
Published: April 2011

In brine-saturated porous media the existence of a space-charge layer at the solid/liquid interface leads to a coupling between fluid and electric currents. This coupling is seen as a streaming potential (STP) across a porous plug when the fluid flows through it, or conversely, as electroosmosis (ELO) of the fluid when an electric field is applied. The magnitude of these electrokinetic effects depends on the thickness of the space-charge layer relative to the pore size, which in turn depends upon the salinity of the brine. From electrokinetic measurements one can obtain an effective hydraulic radius Reff and an effective zeta-potential at the slipplane ζeff. We have developed a high-sensitivity AC technique that can detect these small coupling effects, and have measured them in a suite of natural and artificial rock samples. We find that Reff and ζeff depend on salinity in ways which may be attributed to the roughness of the pore surfaces.
Reorientational Dynamics of a Nematogenic Liquid in Porous Sol-Gel-Glasses: Surface and Pore Size Effects
Authors: Deeg F. W. , Schwalb G.
Published: April 2011

Time-resolved transient grating optical Kerr effect experiments on a nanosecond timescale were used to investigate the reorientational dynamics of pentylcyanobiphenyl (5CB) confined in the nanometer lengthscale pores of silica glasses. Pore size dependent studies (25 Å ≤ d ≤ 100 Å) over a large temperature range from the bulk phase transition temperature Tni, = 35.2 ° C up to 115 ° C demonstrate a drastic influence of geometrical restriction on the cooperative reorientational motion in the nematogenic liquid. At temperatures far above the phase transition (T ≥ 70 °C) a bulk phase and a distinct surface layer with different dynamic properties are observed. With pore size reduction to 25 Å, a decrease of the surface layer thickness and an increase of the surface layer relaxation time are found. This is associated with the modification of the surface layer structure by geometrical factors, e.g., the pore curvature. Measurements at lower temperature in the range Tni ≤ T ≤ Tni = 30 ° C show a drastic decrease of the mean relaxation time τ of the order parameter fluctuations compared to the bulk. The relaxation dynamics exhibit a pronounced pore size dependence which can be explained by a crude correlation length cutoff model as well as a modified LandaudeGennes ansatz. However, these approaches cannot reproduce the nonexponentiality of the observed decays suggesting the importance of interporous interactions.
An Undercooling Effect in Porous Glass: From Bulk to the Confined
Authors: Xue Y. , Mu R. , Henderson D. O. , Frazier D. O.
Published: April 2011

The Thermodynamic properties of TNT physically confined in 5, 10, and 20 nm pores were investigated by Differential Scanning Calorimetry (DSC). Depending upon the pore size and the sample condition, different aspects of the thermodynamic properties of the confined TNT were illustrated. The freezing transition of the confined TNT in 10, 20 nm pores can be triggered by excess bulk TNT on the outer surface. The sharp freezing transition of the TNT in 20 nm pores without the presence of the bulk suggests that the confined TNT maintains its interconnectivity during the transition. The confined TNT in 10 nm pores without bulk on surface failed to freeze during the cooling run up to 100 K with cooling rates ranging from 10 K/min. - 1 K/min. However, a sharp crystallization peak was observed upon heating. When the TNT is confined in 5 nm pores, the confined TNT is incapable of freezing.
Phase Separation Studies of Confined Thin Film Polymer Blends
Authors: Pan Q. , Composto R. J.
Published: April 2011

Using video-optical microscopy and image analysis software, the morphological development of phase separation of polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends is monitored for film thickness ranging from 200 to 700nm's. In the current studies, films are confined between glass slides. For blends having a PS volume fraction of 0.30 (the critical composition), the area fraction of the PS-rich minority phase, A, decreases more rapidly as film thickness decreases. At long times, the final A achieves a constant value which is less than the bulk value. The correlation length of concentration fluctuations increases more rapidly than the bulk scaling prediction, which suggests that wetting plays a significant role in the phase separation kinetics of thin films. Because of confinement, the shape of the PS-rich phase is anisotropic, flattened along the film direction. The confinement restricts the phase growth perpendicular to the film plane, and thus hinders the development of phase separation at very late stages.
A Spectroscopic and Thermodynamic Investigation of Mercuric Iodide Physically Confined in Porous Glass Hosts
Authors: Henderson D. O. , Mu R. , Ueda A. , Burger A. , Chen K. T. , Frazier D. O.
Published: April 2011

Raman and electronic spectra and results from differential scanning calorimetry (DSC) are reported for mercuric iodide (HgI2) confined in four different pore-sized glass hosts. The Raman spectra reveal peaks at 39 and 141 cm−1 that indicate the confined HgI2 is stabilized at 300 K in a modified orthorhombic (yellow) β-phase which is observed at 400 K for the bulk material. An additional band begins to appear at 145 cm−1 for pore radii smaller than 3.75 nm suggesting the presence of new phase of confined HgI2. The DSC measurements show the melting and freezing transitions of confined β-HgI2 are depressed from values reported for the bulk material and the depression increases as the pore size decreases. No transition is observed in the DSC measurement which could be attributed to the α→β transition for the confined material. Evidence supporting the new phase of HgI2 is observed in the electronic spectra of the confined HgI2 by the appearance of an energy gap transitions located at 2.7 eV.
Monte Carlo Studies of a Coupled ‘Elementary’ Reaction-Diffusion System in One Dimension
Authors: Lin Anna , Kopelman Raoul
Published: April 2011

The anomalous rate laws of diffusion limited elementary reactions in low dimensions have garnered attention over the past decade as researchers have become aware that the mean field approximation utilized in traditional kinetic rate equations is not valid in low and fractal dimensions. We use Monte Carlo simulations to study a diffusion limited system simultaneously undergoing A+B-->0 and A+A--> 0 reactions, a common situation in photochemistry. We are studying how this coupled system affects the attenuation of local fluctuations and thus the rate laws of the system in low dimensions and how these results compare to the mean field rate laws. Our results give useful guidelines for studying this type of reaction system experimentally.
Ceramic-Like Materials from Waste Industrial Gypsum
Authors: Herling E. , Cyrkiewicz Marceli , Kleszewski Jacek
Published: April 2011

This paper presents a new method for preparing composites of phosphogypsum, a chemical industry waste, and synthetic (polyester, epoxide and vinyl ester) resins. These composites, after thermal improvement of the phosphogypsum, are called CLM (ceramic-like materials). They are characterized by highly desirable physical, chemical, mechanical and strength-related properties which enable there usage as anti-corrosive coatings for storage tanks and as durable floor coatings in many branches of industry.
Local Field Effects Near Surfaces of Small Systems
Authors: Beaglehole David
Published: April 2011

The interaction of light with a system of molecules depends upon the polarisation induced by an external electric field, which depends not only upon the external field but also upon the local fields due to neighboring polarised molecules. These local fields result in the traditional Clausius-Mossotti (CM) dielectric constant for a molecule deeply imbedded in a medium. Near the surface the local fields are altered, and the dielectric constant becomes anisotropic and dependent upon depth into the medium. The local fields are shape dependent in small systems and differ substantially from the CM value.

A self-consistent computer calculation of the local fields has been implemented, and these effects will be shown using molecule positions and polarisabilities typical of liquids and crystals. The shape dependence of small systems, the reflection of light from liquids with fluctuating surfaces, and the effect of supporting substrates will be described.