bluuebunny/crossref_metadata_2025 huggingface dataset:
Combustion Synthesis of Fullerenes
Authors: Richter H. , Fonseca A. , Thiry P. A. , Gilles J. M. , Nagy J. B. , Lucas A. A.
Published: April 2011

The formation of fullerenes by combustion was investigated for nine benzene/oxygen/argon flames, one acetylene/oxygen/argon- and one toluene/oxygen/argon flame burning at 75 mbar. The flame-generated soot was Soxhlet extracted with toluene and the extract analyzed by HPLC. It was shown that the C60/C70ratio depends on the percentage of argon in the fresh gas mixture, which is directly related to the flame temperature. The use of acetylene and toluene as combustible led also to the formation of fullerenes, the yield in the toluene flame being 3.71% of the generated soot, so that toluene represents a serious alternative to benzene for fullerene fabrication in flames.
Qualitative Model for Fullerene Formation
Authors: Astakhova Tanya Yu. , Shaginyan Shagen A. , Vinogradov George A.
Published: April 2011

A new mechanism of fullerene formation is presented. The ”gas-liquid” transition in the expanding flux of carbon atoms is considered as a necessary initial stage. The transition is not terminated at the liquid phase formation as the more powerful processes of network formation predominate. The process of clusters formation starts with the transformation of three-contact structures to stable two-dimensional networks and is governed by the carbon atoms specificity: three-functionality and high rate of chemical reactions. The resulting network is a flat hexagonal lattice with pentagonal ”defects” bending the surface, the free energy minimum structures being fullerenes.
Controlling the Reactivity of C60: A Theoretical Analysis of the Electronic States Modulated by Substitutional Chemistry
Authors: Wang S.-H. , Kashani M. , Jansen S.
Published: April 2011

The availability of large amounts of Buckminsterfullerene has allowed a plethora of experimental investigations on fullerenes. The chemical and physical studies have focussed on synthesis, isomerism, magnetism, spectroscopy and high temperature superconductivity in doped materials. The chemical reactivities of fullerenes have been defined and most of the studies are dominated by C60 isomers. Some of the observed activities of fullerenes parlled those of alkeies. In our previous studies, the reactivity of the 6-6' bond with respect to eco- addition was described. Current studies have exploited the olefinic nature of the 6-6' bond and analyzed the effect of the addition on cluster stability and frontier character. In this work, we describe the mechanisms of simple substitution and analyze stability and orbital effects for the addition chemistry of C60 with multiple species. Evolving changes in orbital frontier character are analyzed with respect to site directed chemistry exhibited by C60.
Fullerenes Under Pressure Studied by 13C-NMR
Authors: Auban-Senzier Pascale , Kerkoud R. , Jerome D. , Rachdi F. , Bernier P.
Published: April 2011

High pressure is an important parameter for the study of C60 and doped fullerenes as these molecular crystals are very compressible. 13C-NMR experiments under pressure in K3C60 have given access to the determination of the 13C Knight shift and the chemical shift of this superconducting compound. These NMR data do not reveal significant effects of Coulomb correlations in K3C60 and support a pairing mechanism for superconductivity mediated by intramolecular vibrations.

We report also a 13C-NMR investigation of Rb4C60 under pressure and temperature. The temperature dependence of the spin-lattice relaxation rate clearly shows, under pressure, the increase of a linear contribution which gradually substitutes to the exponential behaviour present at ambient pressure. The activated relaxation is attributed to intrinsic spin excitations through the direct Jahn-Teller gap whereas the closing of a small indirect gap under pressure gives rise to a semimetal and a Korringa like relaxation.
The Superconducting Energy Gap of Rb3C60 as measured by IR Transmission in Thin Films
Authors: Koller Daniel , Martin Michael C. , Mihaly Laszlo
Published: April 2011

The superconducting energy gap of Rb3C60 has been measured by infrared transmission through a thin film. Resistivity measurements on the same samples in situ indicate a transition to superconductivity at the expected temperature, ∼30K, with distinct gap features appearing in the transmission below this temperature. The results are interpreted in terms of the BCS theory.
Structural Characterization of a Polymer Substituted Fullerene (Flagellene) by Small Angle Neutron Scattering
Authors: Affholter K.A. , Bunick G.J. , Desimone J.M. , Hunt M.O. , Menceloglu Y.Z. , Samulski E.T. , Wignall G.D.
Published: April 2011

Small-angle neutron scattering (SANS) can structurally characterize fullerenes1in solvents with strong SANS contrast (e.g. CS2). Deuterated solvents (e.g. toluene-d8) have a high scattering length density (SLD), which is close to that of C60and C70moieties. Hence, there is virtually no SANS contrast with the solvent and these particles are practically “invisible” in such media. On the other hand, the negative scattering length of hydrogen means that the SLD of H1-containing materials is much lower, so they have strong contrast with toluene-d8. Thus, SANS makes it possible to study the size and shapes of modified buckyballs such as the polymer-substituted fullerenes, or flagellenes2. These consist of C60cores to which 1-4 polystyrene chains (with a molecular weight, MW ≃ 2000) are attached. The extrapolated cross section at zero angle of scatter [dΣ/dΩ(0)]s is a function of the number of pendant chains, so SANS can be used to assess the number of “arms” which are covalently attached to the fullerene “sphere”. Close agreement (± 4%) between the measured and calculated values of dΣ/dΩ(0) along with independent estimates of the radius of gyration (Rg) and second virial coefficient (A2) for a calibration linear polystyrene sample serves as a cross check on the validity of this methodology.
Microdielectric Measurements of Pristine and Modified thin Fullerene (C60) Films
Authors: Pevznert B. , Hebard A. F. , Haddon R. C. , Senturiat S. D. , Dresselhaus M. S.
Published: April 2011

As developed by Senturia and co-workers [1], microdielectrometry is a technique for measuring complex permittivity utilizing microfabrication technology to incorporate both the interdigital sensing electrodes and associated circuitry on the same microchip. By covering a microdielectrometer chip with a thin layer of C60, it is possible to dynamically monitor the film's frequency response and dielectric properties as a function of doping with selected gases and other species.

It is known that solid C60 has a substantial amount of interstitial volume. The presence of mobile ions in these spaces compromises the breakdown voltage and makes pure C60 unsuitable for applications requiring high-quality dielectric films. However, various immobile ions or neutral species (e.g. oxygen) can be made to fill the interstitial volume, changing the characteristics of the C60 films and, in some cases, improving the dielectric properties. In-situ microdielectric measurements of pristine and modified C60 films were performed for frequencies ranging from 0.005 Hz to 100 kHz. Based on the low-frequency behavior of the dielectric constant, a model is proposed for the mechanism of oxygen diffusion into the interstitial spaces of the fullerene material.
Fragmentation of C60 Molecules in Partially Ionized Fullerene Beam Deposition
Authors: Ren Zhong-Min , Xiong Xia-Xing , Du Yuan-Cheng , Ying Zhi-Feng , Chen Liang-Yao , Li Fu-Ming
Published: April 2011

C60 films have been deposited using a partially ionized cluster beam deposition (PIBD) technique. The experimental results show that as Va. exceeds about 400 V almost all the C60 molecules fragmentate at collision with the substrate and the obtained films turn to be amorphous carbon layers at elevated Va, indicated by measurements of Raman spectra, X-ray diffraction, and ellipsometry.
Doping of C60 Films Using High Energy Boron Ion Implantation
Authors: Ren Zhong-Min , Du Yuan-Cheng , Xiong Xia-Xing , Ying Zhi-Feng , Li Fu-Ming , Xu Xing-Long
Published: April 2011

C60 films, which are deposited by partially ionized beam deposition (PIBD), are doped by 100 keV boron ion implantation at dose ranging from 3*1014 to 1*1016 cm2 The implantation process has been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) analyses. Almost all C60 soccer-balls in the doped region in the films are found to be broken at dose of 1*1016 cm2, while at dose less than 6*1014 cm2 a few C60 molecules remain undestroyed and maintain the original structural properties.
Structural and Electronic Properties of Damaged Fullerite Crystals
Authors: Manfredini M. , Serra S. , Colombo L. , Milani P.
Published: April 2011

A structural tranfsormation of C60 crystals has been induced by high fluence laser irradiation under various chemical environments. The role of oxygen in driving fullerene cage opening reactions is investigated. The resulting material, showing features typical of low density amorphous carbon, has been characterized by Raman spectroscopy. In order to provide an atomistic model of the damaged sample, we have simulated the irradiation process by a tight binding molecular dynamics calculation on a 240-atoms system. We have carefully investigated the structural and electronic properties. In particular, the short- and medium-range features have been related to the cage opening, which is here modeled as a sequence of bond breakings.
Multiphoton Ionization Mass Spectroscopy of Fullerenes in Methane Diffusion Flames
Authors: Hepp H. , Siegmann K. , Sattler K.
Published: April 2011

Multiphoton ionization time-of-flight mass spectrosocopy is used as an on-line technique to investigate polycyclic aromatic hydrocarbons (PAH) and fullerenes in atmospheric pressure flames. We have recorded height profiles of neutral PAH and fullerenes in methane/argon diffusion flames. Fullerenes ranging from C32 to at least C150 are found in a region where PAH concentration starts to decrease. Uniformity of the profiles indicates that the fullerenes do not grow from smaller to larger ones. The influence of the amount of argon additive is discussed.
Physical Phenomena in Ferroelectric Thin Films: Study and Modeling
Authors: Petrovsky Vladimir I. , Pevtsov Eugeniy Ph. , Sigov Alexsander S.
Published: April 2011

An impact of different factors on the shape of dielectric hysteresis loop in ferroelectric thin films is discussed. They include: polycrystallinity and disorientation of polarization axis, polarization nonuniformity and depolarization fields, interface contact layer and series capacity, contact potential difference and interaction of volume impurity centers with polarization field. A comparison between models and experiment show that compromise of interface layer and space charge permits to explain all main distortions of dielectric hysteresis loop in thin films at realistic parameters of the layers. The obtained results permit to explaine the distortions of real hysteresis loop and also to obtain quality parameters of samples, which are important for improving of film preparation techniques.
Ferroelectric Film Self-Polarization
Authors: Sviridov E. , Sem I. , Alyoshih V. , Biryukov S. , Dudkevich V.
Published: April 2011

In the present paper three mechanisms of self-polarization of ferroelectric crystals are discussed: polarization by the crystal bending, that by the “organized” Phase transition and that by the internal field. It is shown that these mechanisms operate also in the case of films. However, the using of cathode sputtering leads to the appearance of two new mechanisms: polarization by the field biasing the substrate with respect to the gas discharge at the film deposition temperature Ts below the Curie point temperature Tc (Ts < TO; and polarization by the field captured by the traps of the negative charge having no time to relax for the time of cooling the film to Tc (Ts > Tc).
Deposition of Strontium Barium Niobate Thin Films by Metal-Organic Chemical Vapor Deposition and Their Nonlinear Optical Properties
Authors: Nystrom M.J. , Wessels B.W. , Neumayer D.A. , Marks T.J. , Lin W.P. , Wong G.K.
Published: April 2011

Single phase, highly textured strontium barium niobate (SBN) thin films were deposited by low pressure metal-organic chemical vapor deposition on both crystalline and amorphous substrates. The metal precursors employed were niobium pentaethoxide as well as barium and strontium (hexafluoroacetylacetonate)2•tetraglyme. SBN thin films with compositions across the entire solid solution range were deposited. The nonlinear optical properties of the SBN films were also measured. Nonlinear optical coefficients approaching bulk values were obtained for as-deposited oriented films. The room temperature, effective second-order nonlinear coefficient was 3.0 pm/V. Films with the highest degree of crystalline perfection had the largest effective nonlinear coefficient. The second harmonic intensity was strongly temperature dependent with a maximum at the ferroelectric transition.
Light Influence on Fatigue in PZT Films with Planar Electrodes
Authors: Dudkevich V.P. , Sem I.M. , Sviridov E.V. , Surowiak Z.
Published: April 2011

A set of fatigue measurements has been performed on RF-sputtered PZT films of about 2 urn in thickness. Polarization switching characteristics with the sinusoidal ac electric field applied were studied both with sandwich and planar electrodes. Planar structure has allowed one to study the influence of the free charge carriers induced by UV -illumination in the planar capacitor gap. The fatigue became noticeable after 106 switching cycles for a sandwich structure and after 109 cycles for the films with planar electrodes. Illuminating the film during polarization switching greatly accelerates the fatigue process. The additional fatigue induced by the photoactive light was completely reversible.
Photoferroelectric Phenomena in Sn2P2S6 Single Crystals and Thin Films
Authors: Arnautova E. , Kosonogov N. , Rogach E. , Pavlov A. , Protsenko N. , Grekov A.
Published: April 2011

Tne present paper is devoted to the experimental study and the analysis of photoferroelectric phenomena in ferroelectric-semiconductor Sn2P2S6 crystals and films. These photoactive light-induced phenomena observed in polarized Sn2P2S6 samples are described by the model of screening the depoling field of remanent polarisation by free charge carriers fixed at the deep energy levels.
Structural and Ferroelectric Properties of SrBi2Ta2O9 Thin Films
Authors: Amanuma Kazushi , Hase Takashi , Mtyasaka Yoicht
Published: April 2011

Structural and electrical properties were investigated for chemically prepared SrBi2Ta2O9(SBT) thin films on Pt/Ti/SiO2/Si substrates. Good ferroelectric properties were obtained with a Pt top electrode: Pr=10.0μC/cm2 and Ec-34kV/cm. Au top electrodes resulted in smaller Pr. However, no fatigue was observed up to 109 switching cycles regardless of the top electrode material. Grains were spherical, not columnar, and the average grain size was 200nm. A marked structural change took place in the bottom Pt/Ti electrode during film preparation. The SIMS analysis indicates the reaction between Bi and Pt
Microstructural and Electrical Properties of Ferroelectric Capacitors with Pt/RuO2 Hybrid Electrodes
Authors: Al-Shareef H.N. , Chen Y.L. , Auciello O. , Kingon A.I.
Published: April 2011

Thin films of pb(Zr0.53Ti0.47)O3 (PZT) grown in our laboratory on RuO2 electrodes by the sol-gel process are characterized by high leakage currents and by the presence of a pyrochlore-type second phase. We have used a thin Pt interlayer between the PZT film and RuO2 bottom electrode to produce RuO2/PZT/100ÅPt/RuO2/SiO2/Si capacitor structures. It is found that use of such a Pt interlayer significantly reduces or eliminates the second phase in the PZT films, and lowers their leakage currents by more than four orders of magnitude. At the same time, the excellent resistance to polarization fatigue characteristic of the RuO2/PZT/RuO2 capacitors is maintained. The microstructures of PZT films grown on RuO2 electrodes with and without the 100Å Pt interlayer are compared. In addition, the voltage, temperature, and polarity dependence of the leakage current in these samples was measured. The data suggest that leakage current in these samples is most likely Schottky emission controlled. The barrier heights are determined to be about 0.80 and 0.73 eV for the top and bottom interfaces, respectively.
Effects of Annealings on Pt/TiN/Ti Interfacial Reactions
Authors: Varniere F. , Eakim B. , Agius B. , Bisaro R. , Olivier J. , Chevrier G. , Achard H. , Mace H. , Peccoud L.
Published: April 2011

The selection of a suitable electrode and barrier layer is important in the integration of lead zirconate titanate (PZT) into memory circuits. Processing at elevated temperatures of up to 800°C can give rise to diffusion processes and therefore to formation of poor quality layers.

In this paper we used Rutherford Backscattering Spectrometry (RBS), Auger Electron Spectrometry (AES), and X-ray Diffraction (XRD) to study the effects of annealings on the interdiffusion of Pt/TiN/Ti trilayers deposited on BPSG/Si substrates. The wafers were annealed in Ar, N2 or O2 ambients with temperatures ranging from 550 to 700°C for 60 min, 30 min or 30 sec. Drastic changes occur when the as deposited Pt/TiN/Ti layers on BPSG/Si structures are exposed to classical heat treatment: oxidation induces diffusion of Ti into Pt and oxidation of Ti is also observed. Regardeless of annealing proceedure used, significant improvement in the interdiffusion of Pt, Ti and O have been achieved when the TiN/Ti/BPSG/Si structure was heated up to 450°C in vacuum. Platinum films deposited on such a structure seem to be a promising barrier layer for PZT film elements as there was no indication of Pb diffusion into the underlying layers and furthermore the desired crystal structure was obtained.
Influence of Ti Sources on Properties of (Ba,Sr)TiO3 Films Prepared by Liquid Source CVD
Authors: Kawahara T. , Yamamuka M. , Makita T. , Yuuki A. , Mikami N. , Ono K.
Published: April 2011

We have investigated influences of Ti sources on properties of (Ba,Sr)TiO3 [BST] films prepared on Pt/SiO2/Si substrates by liquid source chemical vapor deposition (liquid source CVD): TiO(DPM)2 [titanyl bis (dipivaloylmethanato), TiO(C11 H19O2)2], Ti(O-i-Pr)2 (DPM)2 [bis (isopropoxy) bis (dipivaloylmethanato) titanium, Ti(o-i-C3H7)2(C11H19O2)2], and TTIP [titanium tetraisopropoxide, Ti(O-i-C3H7)4]. Improved electrical properties and step coverage were obtained using TiO(DPM)2 at a substrate temperature TS=420'C and a reactor pressure P=1.5Torr as follows: a dielectric constant ε=210, equivalent SiO2 thickness teq=0.51nm, leakage current density JL=6.6×10∼−8A/cm2 at +1.1V, dielectric loss tan δ=0.007, and coverage of 0.8. However, hillocks appeared on the BST film surface under these conditions, while the film surfaces were relatively smooth using TTIP. The density of these hillocks appeared to be related to the BST(110) peak intensity of the X-ray diffraction pattern.
Autostoichiometric Vapor Deposition of Multicomponent Oxides
Authors: Chour K.W. , Xu R.
Published: April 2011

The theoretical basis of an autostoichiometric vapor deposition method is discussed. We try to define and analyze through the stagnant film model for vapor deposition, the mechanism through which the stoichiometry of a multicomponent oxide film can be precisely controlled. It is found that the utilization of a thermally stable, heterometallic molecular precursor, and a chemical reaction scheme which partially protects the integrity of the precursor molecule during deposition are essential for autostoichiometric vapor deposition. An ideal deposition reaction is the vapor phase hydrolysis, substrate surface polycondensation of volatile double alkoxides. A simple low pressure apparatus can be used to realize autostoichiometric vapor deposition.
Preparation and Characterization of Metal Alkoxide Derived Epitaxial Lead Titanate Based Thin Films
Authors: Nashimoto Keiichi , Nakamura Shigetoshi
Published: April 2011

Epitaxial and highly oriented lead titanate based thin films were prepared by a sol-gel process using non-hydrolyzed methoxyethoxide precursors and RTA process. PbTiO3 crystallized with preferred (001) or (100) orientation on SrTiO3 (100) and MgO (100). Solid phase (001) oriented epitaxial growth of PZT on SrTio3 was observed at 425°C, directly from the amorphous phase. That of PZT on MgO was observed at temperatures above 550°C, after the formation of pyrochlore phase. The PZT on SrTiO3 had a single (001) orientation and rocking curve full width at half maximum less than 0.08°. PZT showed a weak preferred (111) orientation on sapphire (0001) substrates, while highly (111) oriented PLT thin films were obtained on them. The guided wave modes were excited by a prism coupling for PZT thin films crystallized on SrTiO3 and MgO. Electrical properties of epitaxial PZT and PLT thin films on Nb-SrTiO3 substrates were characterized.
Dielectric and Ferroelectric Properties of Sol-Gel Derived PLZT Films
Authors: Teowee G. , Quackenbush E.L. , Baertlein C.D. , Boulton J.M. , Kneer E.A. , Uhlmann D.R.
Published: April 2011

There has not been much exploration of PLZT film properties as a function of compostion reported in the literature. A survey of numerous PLZT films covering a wide spectrum of the PLZT phase diagram was undertaken to explore the dependence of film properties on composition. A series of sol-gel derived PLZT films were prepared on platinized Si wafers and fired to 700C to obtain the perovskite phase. The film compositions include PLZT x/65/35, x/20/80, x/53/47 for x = 0, 2, 4, 6, 8, 10 and 12 and 7.5/x/y where x/y = 70/30, 53/47, 20/80 and 0/100. These films were characterized for their dielectric and ferroelectric properties. The films definitely showed a strong dependence of final film properties on composition, providing a valuable tool for the material engineering of ferroelectric film properties.
The Influence of the Crystalline Structure on the Electrical Properties of BaTiO3/SrRuO, Heterostructures
Authors: Wills L.A. , Amano Jun
Published: April 2011

Epitaxial BaTiO3/SrRuO3 heterostructures were deposited on MgO and SrTiO3 substrates by 90° off-axis, rf-magnetron sputtering. A template layer growth was required to obtain epitaxy on MgO. The crystalline structure of the films was analyzed with x-ray diffraction. The leakage current and remanent polarization depended on the crystalline structure and processing parameters. The BaTiO3 thin films displayed remanent polarizations of 13 μC/cm2 and leakage current densities of 107 Amps/cm2 at 2 volts. The BaTiO3 thin films grown under optimal conditions displayed very little fatigue up to 5×108 cycles.
Enhancement of the Electrical Properties of BaTiO3 Films on GaAs Using Double Layer Structures
Authors: Chang L.H. , Anderson W.A.
Published: April 2011

Ferroelectric BaTiO3 thin films have been directly deposited on n-GaAs with carrier concentration of 5.3–8.2×1017/cm2. The BaTiO3 thin films with a thickness in the range of 80–120 nm were prepared by RF magnetron sputtering with a substrate temperature of 300°C. The as-deposited BaTiO3 films appeared to be amorphous with relative dielectric constants of around 15 and gave flat capacitance-voltage (C-V) curves, indicating poor interface properties and very high oxide charge density. After rapid thermal annealing (RTA) at 800°C for 60 sec, the relative dielectric constant of the BaTiO3 film increased to 82 and a sharp C-V curve was observed with oxide charge density of about 7×1012/cm2. However, the leakage current density increased from 4×10'11 A/cm2 for as-deposited BaTiO3 to 2×105 A/cm2 for RTA(800°C)-BaTiO3 at a field of 4×105 V/cm. By taking advantage of the best properties from both as-deposited amorphous BaTiO3 films (low leakage current density) and RTA(800°C)-BaTiO3 (high dielectric constant) the double layer structure was designed to enhance the electrical properties of the BaTiO3 films on GaAs. The most promising results in regards to the dielectric property and leakage current density are 76.5 and 9.7×109 A/cm2, respectively, for the double layer RTA(500°C)-BaTiO3 on RTA(800°C)-BaTiO3 structures.
Epitaxial Growth of Ba1−xSr,TiO3 Films on Si by Pulsed Laser Deposition and Their Dielectric Properties
Authors: Lee Myung-Bok , Kawasaki Masashi , Yoshimoto Mamoru , Moon Bum-Ki , Ishiwara Hiroshi , Koinuma Hideomi
Published: April 2011

Dielectric Ba1−xSrxTiO3 films were heteroepitaxially grown on Si (100) substrates by employing an epitaxial TiN interlayer. The crystallinity and surface morphology were investigated for the films prepared at various substrate temperatures and oxygen pressures. BaTiO3 and SrTiO3 films grown at 650°C and 550°C, respectively, at oxygen pressure of ∼105Torr had good crystallinity and very smooth surface morphology as observed by scanning electron microscopy and atomic force microscopy. Sharp interfaces with little interdiffusion of atoms were observed for these films by secondary ion mass spectrometry. Dielectric properties were evaluated for metal-insulator-metal capacitor structures, and revealed to be closely related to the crystallinity and surface morphology of films.
Thin Film Formation of Perovskite Type Dielectric and Ferroelectric Materials(MTiO3,M=Ca,Sr,Ba and Pb) by Pulsed Laser Deposition
Authors: Tabata Hitoshi , Tanaka Hidekazu , Kawai Tomoji
Published: April 2011

We have formed thin films of ferroelectric and dielectric materials (BaTiO3, SrTiO3 and CaTiO3) by pulsed laser deposition on various kinds of substrates such as SrTiO3, LaAlO3 and MgO(100) single crystals. All the films can be formed epitaxially on the SrTiO3 substrate with c-axis orientation by choosing suitable conditions. The electrical behavior of these films such as dielectric constant and spontaneous polarization is quite similar to that of single crystals in bulk samples. The remanent polarization of BaTiO3 and PbTiO3 films are about 15 μC/cm2 and 80 μC/cm2, respectively. The value of 80 μC/cm2 is almost the same as that theoretically predicted and have not been obtain in the bulk samples. The unique advantage of the pulsed laser deposition technique is its ability to produce highly oriented stoichiometric films that show good electrical properties.
Investigation of the Characteristics of Ferroelectric Thin Films Deposited by Pulsed Laser Ablation
Authors: Sengupta S. , Vijay D.P. , Desu S.B.
Published: April 2011

Ferroelectric thin films of barium strontium titanate (BSTO) have been deposited on bare and metallized substrates by pulsed laser ablation method under different oxygen ambients (150 mT and 50 mT). Under an oxygen pressure of 150 mT, the film composition was similar to that of its ablation target composition, viz. Ba0.4TiO3. However, when the films were deposited under the lower oxygen pressure, x-ray diffraction studies showed the presence of a secondary phase. The electrical characteristics of the films were measured to examine the effect of the stoichiometry on the dielectric constant and tunability. The results of this study will be presented.
Characterization of Post - Annealed PZT Thin Films Deposited Using Pulsed Laser Ablation
Authors: Alainen Jyrki Lapp , Frantti Johannes , Leppävuori Seppo
Published: April 2011

Pulsed laser ablation was used to deposit Nd-doped lead zirconate titanate (PZT) thin films with a thickness of from 100 to 800 nm from a Pb0.97 Nd0.02(Zr0.55Ti0.45)O3 target. The films were ablated onto sapphire and MgO substrates using a XeCl excimer laser (pulse energy 50 mJ, wavelength 308 nm, pulse duration 20 ns). The distance between the target and the substrates was 40 mm, and the angle between the target normal and the incident beam was 45 °. The films were post-annealed in air at various temperatures (600 – 900 °C) with PZT powder. It was found that the laser beam energy density on the surface of the target had a significant effect on the composition of the films, the number of particulates on the surface of the films and the growth rates of the films. Lead deficiency was found in the films in the case of high fluence (> 1.5 J/cm2) while low fluence values (< 1.0 J/cm2) gave an excess of lead and too low Zr/(Zr+Ti) ratios. The particulate number density was low for fluence values between 0.5 and 1.5 J/cm2. EDS and X-ray diffraction was used to determine the composition and the crystal structure of the annealed films. The films deposited using a low fluence showed increasing tetragonal c/a-ratio with increasing post-annealing temperatures. Raman spectra measured from annealed films were found to be typical of PZT.
Preparation of Textured Sn2P2S6 Films and Their Piezoelectric Properties.
Authors: Arnautova E. , Protsenko N. , Sandjiev D. , Zakharchenko I. , Zadorognaya L.
Published: April 2011

Polycrystalline Sn2P2S6 films were prepared by “hot wall” method and studied for possible electronic application. This paper deals with the determination of correlation between the preferred crystallite orientation of the film and its piezoelectric parameters. It is shown that is possible to optimize the piezoelectric properties of Sn2P2S6 films by prescribing the certainrelief of the substrate surface.
The effect of rapid solidification by spinning and laser melting On the structure of sendust-type alloys
Authors: Sheftel Elena N. , Kaputkin Dmitry E. , Stroug Raissa E.
Published: April 2011

Dispersion strengthening of the most wear-resistant soft magnetic alloy Sendust (Fe-9.5 wt.%Si -5.5 wt.% Al, HV=5000 MPa) by carbide and boride phases allowed to increase its wear-resistance by a factor of 2 to 3. Hardness of the dispersion strengthened alloys is HV=5500–6250 MPa. The changes in grain size, ordering and hardness of the Sendust and two dispersion strengthened alloys have been studied after spinning and various regimes of laser melting. Both types of rapid solidification caused a significant decrease of both the solid solution grain size and the size of carbide and boride phases. While spinning only significantly decreased the amount of ordered Fe3(Si,Al) phase in all the alloys, laser melting completely suppressed the ordering. The hardness of the boride strengthened alloy increased up to 7550 MPa after laser melting.
Impression Creep of a Sn-Pb Eutectic Alloy
Authors: Yang Fuqian , Li J. C. M.
Published: April 2011

Impression creep tests on a Sn-Pb eutectic alloy showed a hyperbolic sine stress dependence of impressing velocity and an activation energy of 55 kJ/mole which is independent of the punching stress. A finite element simulation showed that this phenomena could be explained by a constitutive law in which the creep rate is also a hyperbolic sine function of stress. This simulation also gives an impressing velocity which is proportional to the punch size for the same punching stress. Then by using lubrication theory, it is possible to relate this constitutive law to an interphase shearing mechanism in which the rate of interphase shear is a hyperbolic sine function of the shear stress. This theory gives a creep rate which depends inversely on the third power of grain size at low stresses.
Characterization of Melt Spun Cu-Nb Ribbons
Authors: Henne Mei Ling , Ebrahimi Fereshteh
Published: April 2011

Microstructure of rapidly solidified Cu-5wt%Nb ribbons produced by melt spinning was investigated by SEM and TEM techniques. Two heat treatments were done: 960°C 1 hour and 900° 3 hours. The microstructures contained three different type particles: (a)large particles located at the grain boundary, (b)small spherical particles located within the grains and at the grain boundaries, and (c)fine precipitates formed upon heat treatment. The evolution of the microstructure is discussed with regard to the previously reported studies.
Room temperature recrystallization of nanocrystalline thin copper foils
Authors: Dille J. , Delplancke J.-L. , Charlier J. , Winand R.
Published: April 2011

Thin copper foils (100 micrometers thick) are produced by electrolysis on anodized titanium substrates. A sharp distribution of grain diameter is observed around 200 nanometers. The X-ray diffraction pattern shows a slight preferential orientation of the crystals with the (111) planes parallel to the substrate. This X-ray diffraction pattern evolves at room temperature. After 60 days, a preferential orientation of the (200) planes parallel to the substrate is observed. This effect is associated with the recrystallisation of the foil with growth of large copper grains (diameter higher than 5 micrometers) as observed by high resolution transmission electron microscopy.

The structural evolution of the copper foils is studied by electron microscopy, X-ray and electron diffractions at different temperatures.

The mechanical properties of the foils are also studied as a function of time after electrodeposition.
Norman J. Petch and his Contributions to Materials Science
Authors: Armstrong Ronald W.
Published: April 2011

Norman Petch was trained in chemistry at Queen Mary College in London, in metallurgy at Sheffield, and in physics at the Cavendish Laboratory, University of Cambridge. The quantitative nature of his crystallographically-based earliest papers, dealing with the positions of iron and carbon atoms in steel, very probably contributed to the meticulous nature of his follow-on mechanical properties research, initially, into the influence of polycrystal grain size on the plastic yielding and fracturing behavior of iron and steel materials at low temperatures. This work, that was complementary to studies of the yield point behavior of steel by his Cambridge colleague, E.O. Hall, led to the well-established Hall-Petch equation for the stress dependence on reciprocal square root of average grain diameter; perhaps, the most widely quoted equation in materials science. Norman Petch's research, with students and colleagues, led on to predictive and/or interpretive Hall-Petch connected relations for the influence of carbon on the friction stress of steel, hydrogen embrittlement influences on the yield and fracture of steel, the ductile-brittle transition behavior of iron and steel and related materials, the plastic deformation properties of brass and aluminum materials, and the fracturing behavior of ceramic materials and laminated composites.
A Phenomenological Approach to the Ductility in Ultra-Fine Grain, Rapidly Solidified Materials
Authors: Otooni M. A.
Published: April 2011

Crystallization in amorphous materials produces polycrystalline materials with fine grains which can be on the order of 1–2 microns, depending on the extent of annealing. Ductility in these materials with this range of grain sizes is generally low. This paper deals primarily with the lack of ductility in these classes of materials and will present a quasi-mathematical approach to this phenomenon. It will be shown that the influence of the plastic zone, the dislocation-free zone, and the grain size can be expressed by a unique formalism from which the propagation of cracks, and the lack of ductility, can be readily predicted. These deductions will become evident from the results of recent simulation experiments which will provide evidence to support the most essential elements of the approach presented in this paper.
Effect of Ion Bombardment on the Structure and Properties of PECVD SiO2
Authors: Lee Jung H. , Kim Dong S. , Lee Young H.
Published: April 2011

SiO2 films were deposited on silicon wafers at 25°C by plasma enhanced decomposition of tetraethoxysilane (TEOS) in a mixture of argon and oxygen. The deposition was performed in a rf-powered (13.56 MIHz) asymmetric plasma reactor. The effect of ion bombardment was evaluated by varying the ion energy flux (IEF) at the substrate surface from 0.93 to 9.94 W/cm2. On-line optical emission spectra (OES) revealed CO, CH, and H peaks whose absorption intensities increased with increasing applied power. On-line mass spectrometer data showed that the peak intensities of OC2H5, SiOH (m/e=45), and HSiOH (m/e=46) fragments decreased with increasing applied power indicating the decomposition of these species. FTIR spectra of the deposited films showed that the concentrations of Si-OH and trapped CO gases in the film decreased with increasing IEF. Also, the FTIR results and the refractive index measurements indicated that the film density increased as a function of IEF. The stoichiometry of the film did not change when IEF was below 2, but for IEF greater than 4.91 W/cm2, the film became Si-rich.
Studies of Pecvd and Ozone CVD Deposition Rate, Uniformity and Step Coverage
Authors: Guo Xin , Zhao J. , Qiao J. , Tabata A. , Pang B. , Galiano M. , Sinha A.
Published: April 2011

Chemical vapor deposition (CVD) has been used to deposit films such as silicon, silicon oxide, silicon nitride, tungsten, silicide, copper and titanium nitride in the semiconductor industry. The reaction driving forces for CVD are typically temperature for thermal CVD, plasma ionization for plasma enhanced CVD, or atomic oxygen for ozone CVD. In the recent years, plasma enhanced CVD (PECVD) and ozone CVD have found extensive applications in the semiconductor industry, due to the higher deposition rate and lower deposition temperature. For example, PECVD and ozone CVD are used to deposit almost all dielectric films such as silicon oxide and silicon nitride on a wafer. The dielectric films on wafers serve as insulating layers between conducting metal layers and as passivation layer on top of semiconductor devices.
Fabrication of Diamond and Diamond-Like Carbon by Low Pressure Inductively Coupled Plasma CVD
Authors: Okada Katsuyuki , Komatsu Shojiro , Ishigaki Takamasa , Matsumoto Seiichiro
Published: April 2011

A 13.56 MHz inductively coupled plasma(ICP) system has been applied to fabricate diamond and diamond-like carbon from a CH4/H2/Ar plasma. The characterizations of the obtained deposits by transmission electron diffraction, reflection high energy electron diffraction, and Raman scattering revealed that the deposits are diamond crystallites, with crystal sizes ∼1μm, and that they partially include disordered microcrystalline graphite. Although contamination due to etching of the quartz tube exists, this was drastically suppressed by the electrostatic shield(Faraday shield).
Achieving High Nucleation Density of Diamond Film Under Low Pressures in Hot-Filament Chemical Vapor Deposition
Authors: Chen Yan , Mei Jun , Chen Qijin , Lin Zhangda
Published: April 2011

Diamond have been deposited rapidly under low pressures (<0.1 Torr) via hot filament chemical vapor deposition (HFCVD) on either scratched or mirror-smooth single crystalline silicon and titanium with nucleation densities of 109–1011/cm2. The nucleation density increases with the pressure decreases. Hydrogen and methane were used as the gaseous source. Raman spectroscopy and scanning electron microscopy(SEM) were used to analyze the obtained films. This result breaks through the limit that diamond film can only be synthesized above 10 Torr, showing a promising prospect that, as is essential for heteroepitaxial growth of monocrystalline diamond films, diamond film can be easily nucleated on unscratched substrate via Hot Filament CVD.
Properties and Structural Characterization of the Laser Synthesized Nano-Composite Si-N-C Powders
Authors: Li Ya-li , Liang Yong , Hu Zhuang-qi
Published: April 2011

The properties and structure characteristics of the ultrafine Si-N-C powders synthesized from laser induced hexamethyldisilazane and ammonia gas phase reactions were characterized by multiple techniques. Result shows that the Si-N-C particles are uniform in diameter with narrow size distributions and less agglomerated. The powders exhibited a short distance ordered structure which was distorted at high temperature annealing. HTEM observation shows that the particles are amorphous or have nano-composite structure with SiC particles dispersed in the amorphous Si-N-C matrix. The nucleation and growth of the composite particles occurred by the polymerization of the ligand formed from the decomposition of Si-CH3and N-H bonds in hexamethyldisilazane accompanied by the release of small hydrocarbon gases.
In-Situ Formation and Characterization of α-Si3N4 Whiskers from Nano Amorphous Si-N-C Powders
Authors: Li Ya-Li , Liang Yong , Hu Zhuang-Qi
Published: April 2011

α-Si3N4 whiskers were formed from laser-synthesized nanoscale amorphous Si-N-C powders at 1873K under 1 atm N2. The as-formed whiskers were characterized by TEM, STEM, XRD techniques and the process conditions for the whisker growth were studied. The whiskers exhibit various morphologies such as the long thick straight, the prismatic, the ribbon-like, and knuckled whiskers. The gas phase reaction among N2, SiO, and CO gases leads to Si3N4 whisker growth on the pre-crystallized α-Si3N4 grains by the Vapor-Solid (VS) mechanism along specific crystal planes such as {1101}., which ensures an in-situ formation. No addition of other catalyst and the atomic combination of the elements in the Si-N-C powders ensure a high purity of the whiskers.
Modeling the GAS-Phase Chemistry of Silicon Carbide Formation
Authors: Allendorf Mark D. , Osterheld Thomas H.
Published: April 2011

Methyltrichlorosilane (MTS) is a precursor commonly used in the production of silicon carbide for composites, protective coatings, and structural ceramics. Experiments suggest that MTS decomposes in the gas phase to produce a large number of species whose surface reactivity is expected to vary widely. In this work, we discuss the development of a gas-phase mechanism that describes the decomposition of MTS. Rate coefficients for the reactions were obtained from literature sources, theoretical methods, and comparisons with analogous reaction chemistry. Several unknown reaction rates were fit to experimental measurements of MTS decomposition. The results are used to predict the major reaction paths, identify reactions to which product concentrations are sensitive, and determine the rate-limiting step for MTS decomposition.
MOCVD of Yttria Stabilized Zirconia on Co-Cr
Authors: Greenwald Anton C. , Loges Peter G. , Kaloyeros Alain E.
Published: April 2011

Thin films of yttria stabilized zirconia (YSZ) were deposited by metal organic chemical vapor deposition (MOCVD) on cobalt-chromium (Co-Cr) alloys used for orthopaedic implants. TMHD derivatives were preferred for the metalorganic sources over the less expensive fluorinated beta-diketonates as the latter left up to 1% fluorine in the film, as determined by Auger spectroscopy. Crystalline cubic structure of these YSZ films was verified by X-ray diffraction. Columnar grain growth gave a rough surface on thicker YSZ films, which increased wear of the mating polyethylene component during simulation tests. YSZ films under one micron thick were mirror smooth and reduced wear of the polymer component by 70% compared to uncoated Co-Cr. Film adhesion was excellent.
The Application of the X-Ray Surface Forces Apparatus (XSFA) to Studies of Confined Complex Fluid Systems
Authors: Koltover I. , Idziak S. H. J. , Safinya C. R. , Steinberg S. , Israelachvili J. N. , Liang K. S.
Published: April 2011

We report here on the application of the new technique of the X-Ray Surface Forces Apparatus (XSFA) to the study of the smectic liquid crystal 8CB (4-cyano-4′-octylbiphenyl) and a zwitterionic polyisoprene melt. The XSFA allows one to study the structure of fluid films under confinement and flow using intense synchrotron x-ray radiation. The above systems were investigated with the distances between the confining surfaces ranging from 0.4μm to a few tens of microns. Two different kinds of confining surfaces were used leading to different structural behavior of the samples as a function of the confining gap.
Nanorheology of Polymers, Block Copolymers, and Complex Fluids
Authors: Demirel A. Levent , Cai Lenore , Dhinojwala Ali , Granick Steve , Drake J. M.
Published: April 2011

The shear rheology of molecularly-thin films of fluids has been studied experimentally as it depends on sinusoidal frequency (linear response) or on sliding velocity (nonlinear response). Building upon previous identification of a solidlike state that is induced by confinement, we find the shearinduced transition to a sliding state in which the viscous dissipation is essentially velocity-independent. The mechanism appears to involve wall slip but Fourier transforms of the response reveal fluctuations, intrinsic to the sliding state, over all accessible frequencies. Other ongoing studies involve shear-induced changes in the fluorescence of confined fluorescent probes, shear dilatancy, and the contrast between the shear of simple nonpolar fluids, and block copolymers.
Energetically and Pressure Driven Liquid-Solid Transitions in Molecularly Thin Hydrocarbon Films
Authors: Ballamudi Ravi K. , Bitsanis Ioannis A.
Published: April 2011

In this study we used molecular dynamics simulations to investigate the structural changes in nanoscopically thin n-octane films confined between smooth solid surfaces as a result of a) increasing solid-methylene unit affinity and b) increasing pressure. Increasing solid-methylene unit energetic affinity resulted in the solidification of the film at a critical value. A similar transition is observed at a critical value of pressure. Bulk n-octane was a liquid in both cases. The transition was signaled by an abrupt increase in the intermolecular order and was facilitated by a precipitous extension of the octane molecules, which adopted almost fully extended configurations. A discontinuous jump in the film density at the critical values of solid affinity and pressure was evident. The characteristics of the transitions showed that it was a mild first order transition from a highly ordered liquid to a poorly organized solid.
Probing Surface Roughness and Porosity through Adsorption of Wetting Layers
Authors: Krim J. , Panella V.
Published: April 2011

We have employed a quartz microbalance technique to record adsorption isotherms on silver and gold surfaces whose roughness has also been characterized by x-ray reflectivity or scanning tunneling microscopy. We observe strikingly different behavior for two different liquid adsorbates (oxygen and nitrogen), and attribute this to a difference in their surface tension. Our results demonstrate the impact that capillary condensation phenomena can have on the interpretation of adsorption data, particularly with regards to the fractal nature of the substrate. Valuable information on surface morphology can nonetheless be obtained from adsorption isotherms, if combined with alternate experimental techniques.
Hysteresis in a Capillary Condensation System
Authors: Lilly M. P. , Hallock R. B.
Published: April 2011

We report measurements of the hysteretic capillary condensation of liquid 4He into the porous material Nuclepore. Results are presented for global and hysteretic behavior for 300 Å diameter pores. These observations deviate from the predictions of the Preisach model of independent hysteresis domains. By modifying the Preisach model so as to restrict the ability of some of the pores to drain normally we are able to model many features of the experimental data.
Quenched Molecular Reorientation in Confinement
Authors: Korb J.-P. , Malier L. , Cros F. , Xu Shu , Jonas J.
Published: April 2011

The effect of steric hindrance on reorientational molecular dynamics has been studied both theoretically and experimentally in well-defined geometries. We show that, even for a nonwetting fluid, confinement quenches reorientation. This is unambiguously probed by the nuclear relaxation of 33S and 13C in a set of calibrated porous glasses saturated with CS2.