bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic Constants of Diamond Like Carbon Films by Surface Brillouin Scattering
Authors: Ferrari A. C. , Robertson J. , Pastorelli R. , Beghi M. G. , Bottani C. E.
Published: April 2011

The elastic constants of thin Diamond-Like Carbon (DLC) films supply important information, but their measurement is difficult. Standard nanoindentation does not directly measure the elastic constants and has strong limitations particularly in the case of hard thin films on softer substrates, such as tetrahedral amorphous carbon on Si. Surface acoustic waves provide a better mean to investigate elastic properties. Surface Brillouin scattering (SBS) intrinsically probes acoustic waves of the wavelength which is appropriate to test the properties of films in the tens to hundreds of nanometers thickness range. SBS can be used to derive all the isotropic elastic constants of hard-on-soft and soft-on-hard amorphous carbon films of different kinds, with thickness down to less than 10 nm. The results help to resolve the previous uncertainties in mechanical data. The Young's modulus of tetrahedral amorphous carbon (ta-C) turns out to be lower than that of diamond, while the moduli of hydrogenated ta-C (ta-C:H) are considerably lower than those of ta-C because of the weakening effect of C-H bonding.
Nanomechanical Properties of Amorphous Carbon and Carbon Nitride Thin Films Prepared by Shielded Arc Ion Plating
Authors: Tajima N. , Saze H. , Sugimura H. , Takai O.
Published: April 2011

Hydrogen free amorphous carbon (a-C) and carbon nitride (a-C:N) were synthesized by means of shielded arc ion plating in which a shielding plate was inserted between a target and a substrate in order to reduce macroparticle deposition onto the substrate. Using a graphite target as a cathode, thin films of a-C and a-C:N were prepared in an arc discharge plasma of argon or nitrogen gas, respectively, at a pressure of 1 Pa. Based on nanoindentation, mechanical properties of these films were studied in relation to substrate bias voltage (VS). The a-C films prepared at VS ranging from −50 to −200 V consisted of diamond-like phase and showed hardness higher than 20 GPa with its maximum of 35 GPa at Vs = −100 V. However, hardness of the films deposited at VS < -300 V was less than 7 GPa indicating that the films were converted to graphite-like phase due to excessive ion impact in Ar plasma. Wear resistance of the a-C films was closely related to their hardness. Namely, a harder a-C film was more wear resistant. On the contrary, hardness of the a-C:N films was less dependent on VS. It remained in the range of 10 to 15 GPa and was much lower than the maximum hardness of the a-C films. Nevertheless, the wear resistance of the a-C:N films was comparable to or much better than the a-C films. In particular, the a-C:N film prepared at VS = -300 V was so wear resistant that the film showed no apparent wear when rubbed with a diamond tip less than 100 nm in tip-diameter at a contact force of 20 μN. The presence of β-C3N4 like phase characterized by a Nls XPS peak at 400.5 eV has found to be crucial for high wear resistance of the a-C:N films.
Micromechanics-Based Modeling of Interfacial Debonding in Multilayer Structures
Authors: Klein P. A. , Gao H. , Vainchtein A. , Fujimoto H. , Lee J. , Ma Q.
Published: April 2011

Classical approaches to modeling fracture have proved successful in applications for which the highly deformed region near a crack tip is small compared to any other relevant dimensions in the structure. The classical theory relies on phenomenological criteria for material failure that lack a physics-based description of the fracture process itself. Small scale, thin film structures pose difficulties for analysis by these approaches because they contain complicated geometry and many interfaces within the fracture process zone itself. Moreover, plastic flow in metal layers is often severely constrained by the surrounding structure, causing the plastic dissipation part of the overall fracture energy consumed by debonding to be a strong function of geometry. Therefore, it can no longer be regarded as an intrinsic material property. To improve the fracture characterization of these structures, one must develop a physically sound methodology capable of separating the contribution of plastic flow, and other sources of dissipation, from the work of adhesion consumed at the crack tip. In this study, we investigate the parameters affecting energy dissipation by interfacial debonding in a multilayered structure. Interlayer decohesion is modeled using the Virtual Internal Bond constitutive model. We compare our predicted variations in the macroscopic fracture energy with experimental results for varying layer geometry. We also characterize the effect of variations in material properties and other experimental uncertainties in the resulting debonding behavior.
Effect of Annealing on Microstructure and Properties of Al-Ti Multilayered Films
Authors: Mitra R. , Madan A. , Hoffman R. A. , Chiou W. A. , Weertman J. R.
Published: April 2011

Al-Ti multilayered films were deposited by magnetron sputtering of Al and Ti targets on to Si (100) or NaCl substrates. The bi-layer thickness was 16 nm with Ti constituting 12% of the total thickness. The films were subsequently annealed in vacuum at 400°C for periods between 2 and 24 h. In the course of the annealing, interdiffusion and chemical reaction between Al and Ti layers led to the precipitation of Al3Ti particles. Plan view and cross-section TEM examination of as-deposited and annealed films were performed to study the microstructural evolution, and to estimate the Al grain and AI3Ti particle size distributions. Cross-section TEM and X-ray diffraction showed a well-defined layered structure in the as-deposited films. The microstructure was found to be metastable in the first 6 h of annealing, with Al-Ti multilayers being gradually replaced by an AI-AI3Ti composite structure. The Al3Ti particles were uniformly distributed throughout the film. X-ray and electron diffraction analyses showed that Al3Ti possessed the ordered DO22 structure. The hardness of the Al-Ti films in as-deposited and annealed conditions was determined using a nanoindenter and the data have been correlated with the microstructural changes with annealing.
Microbridge Testing of Thin Films Under Small Deformation
Authors: Zhang T. Y. , Su Y. J. , Qian C. F. , Zhao M. H. , Chen L. Q.
Published: April 2011

The present work proposes a novel microbridge testing method to simultaneously evaluate the Young's modulus, residual stress of thin films under small deformation. Theoretic analysis and finite element calculation are conducted on microbridge deformation to provide a closed formula of deflection versus load, considering both substrate deformation and residual stress in the film. Silicon nitride films fabricated by low pressure chemical vapor deposition on silicon substrates are tested to demonstrate the proposed method. The results show that the Young's modulus and residual stress for the annealed silicon nitride film are respectively 202 GPa and 334.9 MPa.
Evaluation of Conductive Region in PZT film Induced by Low Temperature Hydrogen Treatment on PT/PZT/PT Capacitor
Authors: Kanaya Hiroyuki , Kumura Yoshinori , Kunishima Iwao , Tanaka Shin-Ichi , Iwamoto Tsuyoshi , Takahagi Yukio
Published: April 2011

A conductivity difference in a PZT film in a Pt/PZT/Pt capacitor was found by novel charged-up SIMS analyses for the first time. The charged-up SIMS technique was useful for evaluating the conductivity profile in the PZT film. It was found that the conductive region existed in an as-prepared PZT film near the bottom Pt electrode. After hydrogen plasma treatment at 45°C, the conductive region increased in the PZT film near the top electrode. Electrical measurements showed that the leakage current of the capacitor increased after hydrogen treatment. The hydrogen was expected to reduce PZT both at grain boundaries and the electrode-PZT interfaces, and to form the conductive region, which induced an increase in leakage current.
Relationships Between Bi/Ti Composition Ratio and O2 Concentration for Orientation Control of Bi4Ti3O12 Thin Film Using Mocvd Method
Authors: Kijima Takeshi
Published: April 2011

Pt/Bi2SiO5/Si (MIS) and Pt/200nm-Bi4Ti3O12/Pt/30nm-Bi2SiO5/Si (MFMIS:Metal/ Ferroelectric/ Metal/Insulator/Semiconductor) structures were prepared by MOCVD. Oxygen concentration and the Bi/Ti composition ratio determine Bi4Ti3O12 orientation and Bi4Ti3O12 volume in the film, respectively. When the oxygen concentration and the Bi/Ti composition ratio was 33% and 0.65, (001) Bi4Ti3O12 film with the dielectric constant of 40 was obtained. In addition, the capacitance-vs-voltage (C-V) measurement of the Pt/Bi2SiO5/Si structure exhibits normal MIS C-V characteristics. The C-V characteristics of Pt/Bi4Ti3O12/Pt/ Bi2SiO5/Si structure have ferroelectric switching properties with a memory window of about 2.OV Moreover, it is found that the capacitance at zero-bias remains constant for over 24 h.
Displacement Charge Patterns and Ferroelectric Domain Wall Dynamics Studied by In-Situ Tem
Authors: Krishnan A. , Treacy M. M. J. , Bisher M. E. , Chandra P. , Littlewood P. B.
Published: April 2011

We have observed the growth of domains in ferroelectric barium titanate and potassium niobate using a transmission electron microscope. When domains move in response to electric fields we see a scaling effect where the fine scale domain structure is activated first, followed by larger length-scale patterns. Curvature and tilting of domain walls leads to local uncompensated displacement charge and external fields can interact with these charged walls. In this paper, we posit that the presence of displacement charge on domain walls is important for polarization switching. Charge-neutral domain configurations are in a lower energy state and are harder to switch. We argue that the number of charge-neutral, low energy domain configurations can increase with time. This mechanism provides an intrinsic contribution to ferroelectric fatigue.
Electrical Properties of Low-Temperature Processed PZT Thin Films with Preferred Orientations
Authors: Suzuki H. , Kondo Y. , Kaneko S. , Hayashi T.
Published: April 2011

Ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) thin films with preferred orientations were successfully deposited on the Pt/Ti/SiO2/Si wafer at low temperature of 525°C by the chemical solution deposition from molecular-designed precusor solution with 20 mol % excess lead than a stoichiometric composition. The composition of the resultant PZT thin films showed slightly lead excess than a stoichiometric composition. In addition, orientation of the resultant PZT thin films could be controlled by changing the pre-annealing temperature or insertion of thin PbO layer, which affected the interfacial state between Pt electrode and PZT thin films. The electrical properties of the resultant PZT thin films were also affected by the orientation of the resultant films. As a result, orientation of the low-temperature processed PZT thin films had large effect on the electrical properties of the resultant films.
Effects of Active Ammonia Gas Cracked in Catalytic-CVD on PZT Ferroelectric Capacitors
Authors: Minamikawa Toshiharu , Yonezawa Yasuto , Fujimori Yoshikazu , Nakamura Takashi , Masuda Atsushi , Matsumura Hideki
Published: April 2011

We investigated the effects of exposure to active ammonia (NH3) gas generated by catalytic chemical vapor deposition (Cat-CVD) apparatus on ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitors. It is very important to know these effects in order to apply Cat-CVD SiNx films to passivation films for ferroelectric FRAMs. The exposure to active NH3 was carried out for PZT film capacitors with two types of bottom electrodes on Si wafer at various substrate temperatures. The capacitor with Pt/IrO2 bottom electrode peeled off from substrate during exposure over 200°C. On the other hand, the ferroelectricity of the capacitors with IrO2 bottom electrodes gradually degraded from 200°C to 300°C. As a result, it is found that no degradation of the ferroelectricity is detected for exposure below 200°C. It is concluded that the Cat-CVD method is a promising candidate for preparation of the SiNx passivation film on ferroelectrics, since it is a low stressed film with low hydrogen content.
Reversible and Switching Parts of Polarization in PZT Films
Authors: Petrovsky Vladimir , Anderson Harlan U. , Petrovsky Tatiana , Grishin Alexander
Published: April 2011

A pulsing technique was used for more detailed investigation of the switching process in ferroelectric PZT films. This technique allows for the separation of the switching and reversible parts of the polarization and an estimation of the impact of the different effects in the hysteresis loop such as domain structure, depolarizing field and space charge distribution. It is shown that it is possible to provide nondestructive readout of the information stored as the polarization state by measuring the nonlinearity of the reversible polarization. Theoretical limit for the nondestructive readout signal is 20% of the remanent polarization in the differential regime and 12% in the direct regime. The experimental value of the signal is 10% in the both regimes and does not depend on time or the number of readings.
Effects of Grain Boundary on the Ferroelectric Properties of Selectively Grown PZT Thin Films
Authors: Lee Jang-Sik , Park Eung-Chul , Park Jung-Ho , Lee Byung-Il , Joo Seung-Ki
Published: April 2011

The effects of grain boundaries on the characteristics of the PZT thin films using single-grained PZT array by selective nucleation and growth method were investigated by locating the upper Pt electrode of 8 μm× 8 μm sized square directly on the single grains, 1 grain boundary and 4 grain boundaries in a controlled manner. It turned out that when there was no grain boundary, the best ferroelectric and electrical performance were obtained as expected. However, serious degradation was observed in polarization, leakage current, breakdown field and fatigue characteristics when grain boundary was contained in the area measured. This is the first qualitative investigation about the effects of the grain boundaries on the ferroelectric and electrical performance of the PZT thin films. It was found that degradation of the PZT thin films was accelerated with increasing the length of the grain boundaries within the top electrode and the main source of degradation in PZT thin films is grain boundary.
Current Status of Fabrication and Integration of Ferroelectric-Gate Fet's
Authors: Ishiwara Hiroshi
Published: April 2011

Current status of fabrication and integration of ferroelectric-gate FET's is reviewed. Novel applications of ferroelectric-gate FET's are first discussed, which include a single-transistor-cell-type digital memory, reconfigurable LSI's, and an analog memory for an artificial neural network. In the neural network application, fabrication and basic operation of a pulse-frequency-modulation-type adaptive-learning neuron circuit are described as well as an SOI (silicon-on-insulator)-type FET array for synaptic connection is proposed.

Then. data retention characteristics of ferroelectric-gate FET's with MFIS (M : metal, F : ferroelectric, I : insulator (buffer layer), S : semiconductor) and MFMIS structures are discussed. It is shown that the important factors to improve the retention characteristics are (1) increase of the buffer layer capacitance, (2) decrease of the leakage current of both the ferroelectric film and buffer layer, and (3) optimization of the area ratio between the MFM and MIS parts in the MFMIS structure. Based on these considerations, MFMIS-FET's were fabricated using a stacked buffer layer of SrTa2O6/SiON; a current on/off ratio larger than 103 was obtained at a retention time of 10 hours.
Thin Film Decoupling Circuits, Making Use of a Three-dimensional Integration of Thin Film Passive Components
Authors: Klee M. , Löbl P. , Kiewitt R. , Brand W. , van Oppen P. , Lok P.
Published: April 2011

In electronic circuits besides active devices a major part of the components are discrete passive components such as capacitors, resistors and inductors. Especially in the telecommunication circuits, miniaturisation is a major issue. To achieve a high degree of miniaturisation of passive components, thin film processes have been applied. A thin film module for high frequency applications has been demonstrated with a three-dimensional integration of a thin film resistor, a thin film X7R capacitor and a thin film NP0 capacitor processed on top of each other.
Origin of Leakage Current of YMnO3 Thin Films Prepared by the Sol-Gel Method
Authors: Kitahata Hiroya , Tadanaga Kiyoharu , Minami Tsutomu , Fujimura Norifumi , Ito Taichiro
Published: April 2011

The preparation conditions of YMnO3 thin films by the sol-gel method using yttrium alkoxide were optimized to decrease the leakage current of the films. The leakage current of the films was decreased due to the dense microstructure of the films. Moreover, the heat treatment in hydrogen atmosphere and the zirconium doping resulted in a further decrease of the leakage current. The heat treatment in hydrogen atmosphere and the zirconium doping were effective in the decrease of carriers originating in the valence fluctuation of the Mn ions in YMnO3
Photo-Assisted Mocvd Growth of High Dielectric (Ba,Sr)TiO3 Thin Films on Ni/TiN/Si Substrate for Dram Application
Authors: Chen Y. M. , Wu N. J. , Ignatiew A.
Published: April 2011

High dielectric constant barium strontium titanium oxide (BST) thin films have been deposited on Ni/TiN/Si by photo-assisted metal organic chemical vapor deposition (PhAMOCVD). Planar capacitors based on the Ni/BST/Ni/TiN/Si heterostructure with BST-layer thickness of 50nm exhibited storage densities of about 30 fF/μm2 and leakage current densities of less than 10–7 A/cm2 under bias below 1.8V at room temperature. Nickel as a bottom electrode in this newly designed capacitor structure, can be easily patterned by reactive ion etching, and satisfies the requirement for integration with silicon.
Crystal Structure and Texture Effects on Piezoelectric and Dielectric Properties of PZT Thin Films
Authors: Damjanovic D. , Taylor D. V. , Setter N.
Published: April 2011

A systematic investigation of the piezoelectric and dielectric properties of Pb(Zr1-xTix,)O3 (PZT) thin films fabricated by chemical solution deposition was carried out for rhombohedral (x= 0.40), tetragonal (x=0.55) and morphotropic (x=0.47) composition. Each composition was grown with three different crystallographic orientations (textures): “random”, (111) and (100). Nonlinearity (field dependence) of d33 piezoelectric coefficient and dielectric permittivity of the films was studied in detail under subswitching conditions to reveal domain-wall related contributions to the properties. After analyzing for each texture and composition the domain-wall structure, contributions due to domain-wall displacements, and effects of film clamping by the substrate a consistent interpretation of the electro-mechanical properties and nonlinear behavior was proposed. The (100) oriented rhombohedral films show the largest piezoelectric coefficient (intrinsic effect) but limited nonlinearity (domain-wall structure effect) and should therefore be considered as potential candidates for piezoelectric devices.
Properties and Decomposition Behaviors of Reactively Sputtered Pt(O) Electrode Materials
Authors: Saenger K. L. , Rossnagel S. M.
Published: April 2011

The possibility that oxygen-containing Pt might be superior to conventional Pt as an electrode for high-epsilon (HE) and ferroelectric (FE) perovskites has led to renewed interest in the family of Pt(O) materials. Here we report on the properties and decomposition behaviors of reactively sputtered Pt(O)-PtOx electrode materials having x in the range 0 to ∼1.4. Phases of Pt(O) identified included <111>-textured cubic Pt (x < 0.2), tetragonal PtO (x ∼ 1), and amorphous platinum oxide a-PtOx (x ∼ 1.4). Film texture, morphology, resistivity, adhesion, and oxygen content were examined before and after annealing in O2 and N2 at temperatures approximating those of HE/FE deposition and processing (400 - 650°C). After annealing at 650 °C for 5 min, all Pt(O) films lost oxygen and showed growth in metallic Pt phases whose orientations were often <200> or <220> rather than the <111> orientation typically produced by physical vapor deposition of the pure metal. Pt(O) films having a PtO-like structure typically showed only surface oxygen loss, with close to original oxygen levels left in the film bulk, suggesting that the oxygen in these films may be retained long enough to have a beneficial effect on HE/FE layers at later stages in processing.
Optical Properties of a Polyimide for Waveguide Applications in On-Chip Interconnects
Authors: Agarwal N. , Huang X. , Persans P. , Plawsky J. , Ponoth S. , Zhang X. , Murarka S.
Published: April 2011

In this work. we report on characterization methods and the optical properties of a polyimide (Ultradel 9020D). The prism coupling technique was used to couple light into polyimide thin films. The scattered light from the surface was imaged to determine the optical loss at different wavelengths. The coupling angle was used to find the refractive index of the films. The stability of the polymer in terms of refractive index and absorption losses was studied by heat treatment under nitrogen at elevated temperatures. No significant change was observed in the properties of the film at annealing temperatures below 200°C. The bulk and surface losses were separated and it was found that the waveguide losses were dominated by bulk losses. Temperature stability of the polymer was evaluated by annealing the polymer at 125°C for up to 30 hours. No significant changes were seen in the optical losses for these times.
Epitaxial BaTiO3 Thin Films on Different Substrates for Optical Waveguide Applications
Authors: Siegert M. , Lisoni Judit G. , Lei C. H. , Eckau A. , Zander W. , Jia C. L. , Schubert J. , Buchal Ch.
Published: April 2011

In the process of developing thin film electro-optical waveguides we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO3 thin films. These films are grown by on-axis pulsed laser deposition (PLD) on MgO(100), MgAl2O4(100), SrTiO3(100) and MgO buffered A12O3(1102) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C). X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). BaTiO3 films on MgO(100) substrates show planar waveguide losses of 3 dB/cm and ridge waveguide losses of 5 dB/cm at a wavelength of 633 nm.
Real Time Study of Reflective H-PDLC Gratings
Authors: Natarajan L. V. , Sutherland R. L. , Pogue R. T. , Tondiglia V. P. , Tomlin D. , Bunning T. J.
Published: April 2011

The formation of holographic reflection gratings in polymer dispersed liquid crystals(H-PDLC) was investigated in real time both in reflection and transmission modes. Real time study is useful for obtaining information on the speed of grating formation, phase separation dynamics, host polymer shrinkage, polarization dependence of the reading beam, bleaching of the photointiator dye and scattering of the writing beam during grating formation. The real time studies showed that the formation of the grating is fast and reaches a maximum in a few seconds. The diffraction efficiency (DE) VS time curve shows an initial increase followed by a sharp decrease and a recovery to higher efficiencies. Variation of monomer functionality in the pre-polymer syrup resulted in a decrease of reflection efficiency as the functionality is lowered. Varying the writing power of the laser beam gave higher efficiencies at powers exceeding 10 mW/cm2. Liquid crystal (LC) loadings of >16% are needed to obtain measurable efficiencies. Varying the polarization of the probe beam (S vs P) revealed differences in the temporal evolution of DE. Morphology studies are indicative of the differences in the phase separation due to monomer functionality, LC concentration and also laser power. The growth dynamics of H-PDLC gratings are very different from the well known Du Pont photopolymer films which may be due to the phase separation process accompanying gelation in H-PDLC systems.
Optical Limiting with Lithium Niobate
Authors: Cook Gary , Jones David C. , Finnan Craig J. , Taylor Lesley L. , Vere Tony W. , Duignan Jason P.
Published: April 2011

Iron doped lithium niobate (Fe:LiNbO3) in a simple focal plane geometry has demonstrated efficient optical limiting through two-beam coupling. The performance is largely independent of the total Fe concentration and the oxidation state of the Fe ions, providing the linear optical transmission of uncoated crystals is between 30% and 60%. Fe has been found to be the best dopant for LiNbO3, giving the widest spectral coverage and the greatest optical limiting. Optical limiting in Fe:LiNbO3has been shown to be very much greater than predicted by simple diffusion theory. The reason for this is a higher optical gain than expected. It is suggested that this may be due to an enhancement of the space-charge field arising from the photovoltaic effect. The standard two-beam coupling equations have been modified to include the effects of the dark conductivity. This has produced a theoretical intensity dependence on the ΔOD which closely follows the behaviour observed in the laboratory. A further modification to the theory has also shown that the focusing lens f-number greatly affects the optical limiting characteristics of Fe:LiNbO3. A lens f-number of approximately 20 gives the best results.
Polaronic and Bipolaronic Enhancement of Second Hyperpolarizabilities in Dithienyl Polyenes from Ab Initio Quantum Methods
Authors: Trohalaki Steven , Zellmer Robert J. , Pachter Ruth
Published: April 2011

Spangler and He [1,2] have shown that dithienyl polyenes form extremely stable bipolaronic dications when oxidatively doped in solution. Previous theoretical studies applied empirical methods to predict bipolaronic enhancement of hyperpolarizabilities for simple polyenes [3,4]. Here, we employ density functional theory to optimize the gas-phase molecular conformations of neutral, cationic, and dicationic forms of a series of dithienyl polyenes, where the number of ethene units, N, is varied from 1–5. Ab initio Hartree-Fock, generalized valence bond, configuration interaction, and Møller-Plesset calculations demonstrate that the dications are farily well described with a closed shell and therefore have little biradicaloid character. Second hyperpolarizabilities, γ, are subsequently calculated using ab initio Hartree-Fock theory and a finite field methodology. As expected, γ increases with the number of ethene units for a given molecular charge. The cations also show the largest increase in γ with N. For a given value of N, the cations display the largest γ values. However, if we treat the dication as a triplet, which might be present in solution, then it displays the largest γ.
Improved Refractive Index from a Planar Leaky Wave-Guide Coupler
Authors: Liu Tao , Samuels Robert J.
Published: April 2011

Modal loss coefficients for a planar leaky wave-guide are obtained by two new methods. One is a numerical calculation combining optical thin film theory with optical wave-guide theory; another is an analytical derivation based on analogy to Beer's law. Considering the influence of the modal loss, a modified mode equation for the planar leaky wave-guide is obtained, which greatly increases the accuracy of the refractive index and thickness of the thin film in a planar leaky wave-guide coupler (prism I film I substrate).
Biomimetic Coatings on Orthopedic Implants: a Review
Authors: Groot K. De , Wen H. B. , Liu Yuelian , Layrolle Pierre , Barrere Florence
Published: April 2011

In bone replacement surgery, replacement of joints (of hip, knee, finger and jaw) is a major sub discipline, requiring mechanically strong and biologically compatible, or biocompatible, implants. Since mechanical strength can only be achieved with metals that lack the required biocompatibility, surface treatments to improve that lack have been studied extensively. Since the mineral phase of bone consists of various calcium salts, the most relevant one being (carbonated) apatite, the surface treatments of choice are coatings of such salts on orthopedic implants have been successfully developed. (Bulk ceramics of CaP are too brittle to be used for load bearing implants). Although currently used coatings as obtained by plasma spraying have been highly successful, the high temperature and line-of-sight nature of the plasma spray process prevent (1) coatings to be deposited on implants made of polymer composites, (2) coatings to be deposited on complex surfaces and/or within porous implants and (3) biological molecules such as growth factors or antibiotics to be included in the coating. Therefore, we and several other research groups have focussed our attention to so called biomimetic coatings, that are produced at ambient temperature by a precipitation process from fluids resembling body fluids in their inorganic composition. In this presentation, we will give a review of some current developments on biomimetic coatings.
Mechanism of Apatite Formation on Bioactive Titanium Metal
Authors: Kokubo T. , Kim H.-M. , Takadama H. , Uchida M. , Nishiguchi S. , Nakamura T.
Published: April 2011

The present authors previously showed that titanium metal, which was exposed to 5.OMNaOH solution at 60°C for 24 h and heat-treated at 600°C for 1 h, spontaneously forms a bonelike apatite layer on its surface in the living body, and tightly bonds to the bone through the apatite layer. In the present study, mechanism of the apatite formation on the bioactive titanium metal was investigated in an acellular simulated body fluid (SBF). A thin sodium titanate layer was formed on the surface of the titanium metal by the NaOH and heat treatments. The sodium titanate layer released Na+ ions via exchange with H3O+ ions in SBF, to form a lot of Ti-OH groups on its surface. The Ti-OH groups first combined with Ca2+ ions in SBF, and then later with PO43- ions to form the apatite. Titania and Na2O-TiO2 gels prepared by a sol-gel method as model substances of the sodium titanate layer on the surface of the titanium metal showed that Ti-OH groups of anatase structure are effective for the apatite nucleation, whereas those of amorphous structure and Na2Ti5O11 crystal are not effective.
Fast Formation of Biomimetic Ca-P Coatings on Ti6Al4V
Authors: Barrère F. , Layrolle P. , van Blitterswijk C. A. , de Groot K.
Published: April 2011

The aim of this study was to accelerate the formation of biomimetic Calcium-Phosphate (Ca-P) coatings on Ti6Al4V by using a 5 times more concentrated Simulated Body Fluid (SBFx5) than the regular SBF. The production of SBFx5 was possible by decreasing the pH of the solution to approximately 6 with CO2 gas. The release of this mildly acidic gas allowed the formation of a Ca-P film after 4h of immersion at pH=6.8. The structure of this coating was an amorphous carbonated Ca-P. In addition, our experiments showed that the presence of Mg2+ was absolutely necessary for the Ca-P coating formation on Ti6Al4V substrate. Mg2+ is a crystal growth inhibitor and favored the heterogeneous nucleation. Furthermore, depth profile X-Ray Photoelectron Spectroscopy showed that Ca-P nucleation on the passive Titanium oxide (TiO2) passive layer was initiated by Ca2+ and Mg2+. The attachment of this Ca-P coating resulted probably from chemical bonds such as P-O-Ti and Ca-O-Ti. Ca was more present at the coating/substrate interface than P. Thereby Ca-O-Ti seems to be favored.
Bone Bonding of Biomaterials And Apatite Formation On Biomaterials
Authors: Nakamura Takashi , Neo Masashi , Kokubo Tadashi
Published: April 2011

Bioactive ceramics are known, which can bind bone tissue chemically. The authors tested bone-bonding strength of biomaterials using detaching test and observed the interface between bone and bioactive ceramics with transmission electron microscopy. An intervening apatite layer was observed at the interface of bone and bioactive ceramics. This layer was distinguished from bone apatite or ceramic. This apatite layer was formed within several days after implantation before bone was observed on the materials. Bisphosphonate is well known to inhibit apatite formation. The injection of bisphosphonate to rabbits concentrationdependently decreased bone-bonding strength of ceramics. The apatite layer was formed on bioactive ceramics in vitro by immersing them in simulated body fluid that contained similar concentrations of inorganic ions as plasma did. Using this apatite layer formed in vitro, it is possible to characterize the apatite layer. This apatite layer enhanced the differentiation of rat bone marrow cells to bone cells in vitro. When osteoclasts were cultured on this layer, they absorbed the apatite layer.

These results suggested this apatite layer not only plays a key role for bone bonding but also behaved as bone-like tissues.
Improvements of Apatite-Forming Abilities on Pure and Sodium-Containing Diopside Substrates Using Porous Diopside Thin Films as Nucleating Agent
Authors: Iwata N. Y. , Tsunakawa S. , Tanaka M. , Utsu T. , Matsumoto K.
Published: April 2011

Pure diopside, CaMgSi2O6 and the partly modified new type of crystalline diopside, NaxCa1-xMgSi2O6, were prepared mainly by coprecipitation process These ceramics were synthesized from the inorganic nitrates and the metal alkoxide in ethanol solutions. The sodium contents in the crystal had remarkable effect on the apparent densities and improved the mechanical properties, especially when the hot-isostatic pressing was applied in the final process. The precise measurements of the X-ray diffraction patterns strongly suggested that the Ca positions in the unit cell were partly substituted by the Na atoms. SBF soaking tests showed that the porous sol-gel method diopside induced the higher apatite crystal growth rates than the hot-pressed surface of the pure or the Na-modified diopside.

The surface of the coprecipitation process diopside specimens was coated with the porous ceramics for the purpose of the formation of the bioactive diopside films.
Combinatorial Approaches to Peptide-Encapsulated CdS Nanoclusters
Authors: Spreitzer G. , Whitling J. M. , Wright D. W.
Published: April 2011

As many properties of group II-VI semiconductor nanocrystallites arise from their quantum confined nature, the synthesis of these clusters is of great interest. The challenge of synthesizing functional nanoclusters is, however, complicated by the limited stability of metalchalcogen surfaces under highly oxidizing conditions and Ostwald ripening. Our objectives are to develop methods for the synthesis of biogenic CdS semiconductor nanocrystallites that address the following issues: (1) What properties of the ligand peptide are important in stabilizing and producing CdS particles of any desired size? (2) Will hybrid peptides using nonnatural amino acids stabilize the nanoclusters while incorporating new surface functionality? (3) Is it possible to use novel peptides to modify the particle surface, thereby, controlling the photophysical properties of the CdS cluster? Our approach consists of parallel combinatorial techniques and computational methods for the discovery and optimization of peptide and peptidomimetic ligands to stabilize size-defined clusters of CdS. The effects of cysteine separation on CdS particle size by varying the number of bonds with rotational freedom within the spacer amino acids is examined. Furthermore, the properties of the resulting CdS nanoclusters are reported.
Hard Tissue Regeneration InStrombus Gigas, the Giant Queen Conch
Authors: Su X. , Heuer A. H.
Published: April 2011

Hard tissue regeneration (i.e. shell repair) is an important biomineralization process in mollusks. Rapid regeneration is important in avoiding loss of fluids and preventing attacks by predators. We have studied such tissue regeneration in the Queen conch (Strombus Gigas) by inserting an abiotic glass cover slide between the mantle tissue and the shell. The glass cover slides were removed after mineralization periods extending from 6 hours to 4 days, and the deposited materials on the glass substrates (“flat pearls”) analyzed by X-ray diffraction, and scanning and transmission electron microscopy.

Although the CaCO3in native Queen conch shell is exclusively aragonite, calcite was detected in the regenerated materials grown on glass substrates. Calcite formation occurred only during the very early stage of mineralization and the initial minerals formed were soon overgrown by aragonite. The initial aragonite overgrowth had a spherulitic morphology, and was thus relatively poorly oriented; after this spherulitic transient, the microstructure was recognizable as the crossed-lamellar structure of the natural shell.

Thus, shell regeneration on abiotic substrates differs from shell formation during growth of conchs only in the very early stage. Once the crossed-lamellar microstructure has formed, further hard tissue development is identical to that occurring during natural shell growth.
Three Dimentional Finite Element Modeling of Microstructural Development of Nacre in Seashells and Implication on Mineralization of CaCO3
Authors: Katti D. R. , Katti K. S.
Published: April 2011

Three dimensional finite element models of nacre were constructed based on reported microstructural studies on the ‘brick and mortar’ micro-architecture of nacre. 3D eight noded isoparametric brick elements were used to design the microarchitecture of nacre. Tensile tests were simulated using this model at stresses of 2 MPa which occur well within the elastic regime of nacre and thus effects related to locus and extent of damage were ignored. The reported values of elastic moduli of organic (0.005 GPa) and aragonitic platelets (205 GPa) were used in our simulations and the resulting displacements were found to be extremely large and corresponding to a very low modulus of 0.011 GPa. The reported elastic modulus of nacre is of the order of 50 GPa. The large displacements can possibly result from two possibilities. Firstly. the organic layer due to its multilayered structure is possibly composed of distinct layers of different elastic moduli. A significantly higher modulus of the organic phase may be possible near the organic-inorganic interface. Simulations using variable elastic moduli for the organic phase suggest that an elastic modulus of 15 GPa is consistent with the observed elastic behavior of nacre. A second possibility for the observed higher elastic modulus may arise from localized platelet-platelet contact. Since the observed modulus of nacre lies within the above two extremes (i.e. 15 GPa and 205 GPa) it is suggested that a combination of the two, i.e. a higher modulus of the organic phase near the organic-inorganic interface and localized platelet-platelet contact can result in the observed elastic properties of nacre.
29Si NMR Chemical Shifts and Energetics of Silica-Serine and Silica-Polyalcohol Complexes as Indicators of Silica Biomineralization Mechanisms
Authors: Sahai N. , Tossell J. A.
Published: April 2011

Serine- and polysaccharide-enriched organic matrix is associated with biogenic silica such as diatom tests, sponge spicules, and phytoliths. We have used molecular orbital theory to determine the relative stability and 29Si NMR shifts of direct Si-O-C ester-like bonds versus hydrogen bonds between the monomeric silicic acid and the alcohol group on aliphatic organics such as serine and threitol (a polyacohol as proxy for polysaccharides). Preliminary results suggest that at neutral pHs, H-bonds and ester-bonds of four-fold coordinated silicon are of comparable stability. Formation of ester-like bonds with five-fold coordinated silicon is endothermic at neutral pHs but is stabilized at higher pHs. 29Si shifts of the H-bonded and ester-bonded complexes of four-fold coordinated silicon range from −55 to −73 ppm similar to monomeric inorganic silicic acid but far more positive than the −92, −102, and −110 ppm values observed experimentally in biogenic silicas. The five-coordinated silicon complexes yield shifts of −96 to −107 ppm. The latter range is within the range of inorganic, polymerized silica. If five-fold coordinated Si with direct Si-O-C bonds is present as a precursor or intermediate or stable species in biogenic silica, it could have escaped detection due to overlap with inorganic polymerized silica. Thus, 29Si NMR shifts are not necessarily diagnostic of the presence or absence of Si-O-C bonds in biogenic silica.
Effect of Calcification on The Fatigue Behavior of Fluorinated Polyurethanes
Authors: Benson R. S. , Kim H. J.
Published: April 2011

The present study compares the fatigue propagation behavior of a fluorinated and nonfluorinated polyurethane-calcium salt blends. The calcium salts used in this study are calcium chloride and hydroxyapatite (HAP). The fatigue crack propagation (FCP) behavior of the polyurethanes exhibited a dependence on the chemical composition of the polymer and calcium salt. The pure non-fluorinated PTMG2000 did no undergo crack propagation. While the fluorinated PTMG2003F exhibit a crack propagation rate of 7.8 × 10-6m/cycle at constant strain amplitude and tearing energy range. The incorporation of calcium chloride into PTMG2000 did not promote any changes in the FCP behavior; while the addition of HAP produced cracks with a growth rate of 3.33 × 10-6m/cycle. In the case of PTMG2003F, the addition of calcium chloride did not lead to formation of cracks; while HAP produced a material in which cracks propagated at a rate of 10.0 × 10-6m/cycle. The difference in the response the non-fluorinated and fluorinated polyurethane-calcium salt blends to cyclic loading can be attributed to molecular level variations such as domains disruption and changes in chain orientation at the crack tip.
Self-Assembled β-Sheet Architectures for Bone-Tissue Engineering
Authors: Spreitzer G. , Doctor J. , Wright D. W.
Published: April 2011

Advances in the understanding of biomineralization processes in a variety of organisms have revealed the critical role of three-dimensional scaffolding architectures to create a highly functionalized surface. These complex matrices function on a variety of length scales ranging from the macromolecular (10–100 nm) to the cellular (1–10mm) and larger. One dominant structural motif found in many of these architectures is macromolecules containing antiparallel β-pleated sheets. These “hints” from Nature have lead to the iterative design and development of a novel multipurpose platform technology based on a self-assembled periodic peptide architecture for use in bone-tissue engineering. Combining molecular modeling, structural biochemistry and synthetic techniques, we have produced a β-sheet hollow tube peptide nanoassembly. Such a synthetic approach allows for the template's designed parameters of electrostatic, geometric and stereochemical complimentarily to match those of the desired biomineral. Consequently, these templates readily nucleate calcite. Future studies will investigate the in vitro osteoconductive and osteogenic properties of these templates.
Comparison on Regulation of Calcium Phosphate by Organic Monolayer, Unilamellar Phospholipid Vesicles and Hydrothermal Self-Assembly
Authors: Cui F. Z. , Zhang Y. , Cai Q.
Published: April 2011

Biomineralization centers on the idea that organics control the nucleation, growth and final form of inorganics. The present studies investigated the deposition or precipitation of inorganics templated by organic monolayer films, unilamellar phospholipid vesicles, and selfassembled hexadecylamine, with the emphasis on the regulation of template on phase, orientation and microstructure of minerals. The obtained calcium phosphate varied from the thin layer precipitated on the organic monolayer to the confined particles formed inside the lipid vesicles to the mesolamellar structure self-organized in the precursor sol-gel. The typically regulated features of these three systems have been revealed. Consequently, the different phases of calcium phosphate can be obtained through variation of controllable parameters.
Modification of Assembled Structures of Steroids Adsorbed on Apatite Ceramic Surface by Electrical Poling
Authors: Nakamura S. , Obata A. , Yamashita K
Published: April 2011

Aggregate structures of steroids adsorbed on electrically-poled hydroxyapatite (HAp) ceramics were investigated by X-ray diffractometry (XRD) and scanning electron microscopy. Effectivity of the poled HAp on modification of the steroid assembly modes was discussed by the arrangement estimations of the steroid molecules. The dense HAp ceramics were obtained from the pelletized HAp powder precipitated from calcium hydroxide suspension and phosphoric acid using conventional sintering at 1250°C under the saturated water vapor pressure. The HAp ceramic blocks were poled in a DC electrical field of 1.0 kVcm-1 with being heated at 300°C. The HAp ceramics were immersed in ethanol solution of steroids at 37°C. The steroid crystals were overgrown onto the HAp substrates by recrystallization method. In the case of cholesterol, the tabular crystals of cholesterol monohydrate and the needle-like crystals of anhydrate were overgrown on all of the HAp ceramic surfaces. The thickness of the cholesterol layers on the positively (p) poled HAp surfaces was considerably less than those of the negatively (n) poled and non-poled (0) surfaces. The remanent chaige of the HAp ceramics altered the morphology of vitamin D3 crystals deposited on the HAp surfaces. It was revealed that the electrically-poled HAp ceramic surfaces changed the aggregate structures and the crystal growth rates of steroids.
Dip-Coating of Calcium Hydroxyapatite on Titanium Alloy (ti-6ai-4v) and Stainless Steel (316L) Substrates
Authors: Mavis B. , Tas A. C.
Published: April 2011

Titanium alloy (Ti-6AI-4V) and stainless steel (316L) are two of the most commonly used materials in the manufacture of orthopaedic implants. To achieve better biocompatibility with bone, metal implants made of 316L or Ti-6Al-4V are often coated with calcium hydroxyapatite (HA) bioceramics. This paper is to describe a new dipping solution recipe used for HA coating. Sample characterization was performed by SEM and XRD.
Inhomogeneous Magnetic Structures of La0.7Ca0.3MnO3 Investigated by ESR and Magnetization Measurements
Authors: Joh Keon Woo , Lee Chang Hoon , Lee Cheol Eui , Jeong Yoon Hee , Hong C. S. , Hur Nam Hwi
Published: April 2011

Comprehensive measurements of electron spin resonance and magnetization of La0.7Ca0.3MnO3 in the ferromagnetic as well as paramagnetic phases were carried out. From the quantitative analysis of the ESR signal, attributed to itinerant spins and localized spins in the bottleneck regime, evidences for the inhomogeneous nature of both phases, consisting of clusters of one phase embedded in the other, were found. It is suggested that the microscopic local magnetic structures above and below Tc are qualitatively similar except that the phase below Tc carries long range order.