bluuebunny/crossref_metadata_2025 huggingface dataset:
A Methodology for the Calibration of Spherical Indenters
Authors: Swadener J. G. , Pharr G. M.
Published: April 2011

Spherical indentation with continuous load and depth measurement is a useful technique for characterizing thin film mechanical properties. With this technique, the initial loading is in the elastic range. Therefore the elastic-plastic transition can be observed. However, the calibration of spherical indenters presents special problems. First, the radius of the indenter at the point of contact must be determined, and any deviation from a spherical radius must be evaluated. The shape of the indenter also causes mounting difficulties that can create a relatively large and nonlinear compliance in the testing machine. The calibration of spherical indenters is further complicated, because asperities on the indenter and surface roughness add to the uncertainty in locating the surface of the sample. In addition, spherical indenters are generally made of anisotropic single crystals, and the calculation of their elastic responses must include this anisotropy. To address these issues, a methodology has been developed for the calibration of spherical indenters, whereby indentation experiments are conducted on multiple ceramic materials in the elastic range. The method was used to determine the local radius of synthetic sapphire spherical indenters. The accuracy of this measurement was verified using confocal microscopy. The method was successfully applied to an indenter with a nonlinear machine compliance. Further results involving indentation in the plastic regime are also presented.
Strain Relaxation in Thin Films: the Effect of Dislocation Blocking
Authors: Goodhew Peter J
Published: April 2011

The relaxation of strained layers frequently occurs by the glide of threading dislocations. From very early on in the relaxation process, gliding dislocations will be forced to intersect a number of prior dislocations with almost-perpendicular line directions and their progress may be blocked. This effect has been widely reported in semiconductor films, and there is some experimental evidence that it is reduced when layers are grown on vicinal substrates. This implies that the blocking is sensitively dependent on the dislocation configuration and in particular on the dislocation line directions.

In this paper the interactions between gliding threading dislocations and the perpendicular or nearly-perpendicular dislocation in their path are modelled quantitatively. The differences arising from different initial dislocation configurations and different predominant line directions are found to be small. Strain relaxation, at least in its early stages, should be virtually independent of the initial dislocation configuration.
Plasma Etching Damage to Ferroelectric SrBi2Ta2O9 (SBT) Thin Films and Capacitors
Authors: Cho Jun Hee , Kwon Il Young , Park Chanro , Choi Chang Ju , Seol Yeo Song , Pyun D. S. , Choi Il Hyun
Published: April 2011

The effects of reactive ion etching damage on the electrical properties of Pt/SBT/Pt capacitors have been investigated. The plasma treated SBT/Pt layers showed a significant decrease in remanent polarization compared with that of the reference sample. The remanent polarization of the plasma treated layers varied with the gas ratios of the Cl2/Ar plasma. XPS analysis of the plasma treated SBT/Pt samples showed that the surface composition was significantly changed as the gas ratios were varied, which resulted in a polarization decrease in the plasma treated samples. Plasma treatment also caused a voltage shift of the hysteresis loops along the voltage axis. The magnitude of the voltage shift was increased for the chlorine-rich plasma. The results of surface analysis revealed that the voltage shift is caused by oxygen deficiency at the SBT surface. Based on our experimental results, reactive ion etching damage was explained in terms of physical and electrical effects of the plasma on the electrical properties of the ferroelectric Pt/SBT/Pt capacitors.
A Structural Study of SrBi2Ta2O9 - Bi3TiNbO9 Ferroelectric Thin Films
Authors: Ching-Prado E. , Pérez W. , Dobalt P. S. , Katiyart R. S. , Tirumala S. , Desu S. B.
Published: April 2011

Thin films of ferroelectric (SrBi2Ta2O9)x(Bi3TiNbO9)1-x layered structure (for x = 0.0, 0.2, … 1.0) were prepared by a metal organic solution deposition method on Pt/TiO2/SiO2/Si substrates. Raman spectroscopy, X-ray diffraction, atomic force microscopy (AFM), and electrical characterization techniques were utilized to study the inclusion of SrBi2Ta2O9 (SBT) in the Bi3TiNbO9 (BTN) system. The Raman spectra show frequency shifts and broadening of modes as x increases from 0.0 to 0.4, which are related to the nature of Sr and Bi in the A-sites, and Ta, Ti, and Nb in the B-sites. Smooth surfaces without any cracks or defects were evidenced in each of these films by AFM. These images also indicate that the grain size in the films increases with increasing SBT content in the BTN compound. Electrical measurements show that the remanent polarization (Pr) and the coercive field (Ec) values in the x=0.0 film (2 μC/cm2 and 30 kV/cm, respectively) increase to 12.5 μC/cm2 and 125 kV/cm for x=0.6. A decrease in these parameters was found for higher compositions.
Characteristics and Applications of Sr-Modified Ferroelectric Pb(Zr,Ti)O3 Thin Films
Authors: Lee K. B. , Ju B. K. , Desu Seshu B.
Published: April 2011

We have investigated the structural and electrical properties of Sr-modified Pb(Zr,Ti)O3, i.e., (Pb1-xSrx)(Zr0.53Ti0.47)O3 (PSZT), thin films. Sol-gel derived PSZT films were deposited by spin casting onto Pt/Ti/SiO2/Si substrates. Ferroelectric perovskite phases were found for all specimens (x ≤ 0.6), which implied the successful substitution of Sr for Pb. The values of dielectric constant (εr) as well as remanent polarization (Pr) of PSZT capacitors decreases monotonically with increasing Sr for x ≥ 0.1. PSZT (x=0.4) thin film was found to be applicable to high permittivity films for high density dynamic random access memories, whose Pr and εr are 5 μC/cm2 and 350, respectively, and leakage current density is low as 1×10−7 A/cm2 at a electric field of 100 kV/cm. In this paper, we also discuss the characteristics of Sr-modified PbTiO3 thin films.
High-Endurance Scalable PZT Capacitors Using Thin SRO/Pt Stacked Electrodes
Authors: Yamakawa K , Arisumi O. , Hidaka O. , Morimoto T. , Kunishima I. , Tanaka S. , Arikado T.
Published: April 2011

90nm-thick PZT capacitors using Pt/thinSRO stacked electrodes showed 2V operation capability, no remanence degradation after more than 1E10 switching cycles, and low imprint. Effects of SRO(SrRuO3) electrode have been studied for high-endurance PZT capacitors. In capacitors with only top SRO electrodes, the SRO increased polarization and improved saturation property compared to Pt electrode PZTs. Fatigue and imprint degradation was caused by Pt bottom electrode interface deterioration. It is thought that the oxygen vacancies created with Pb vacancies are important respecting endurance and retention. PZT films crystallized on SRO showed smaller coercive voltage Vc (2/3 of that for PZT/Pt) with random orientation. The SRO layers block Pb diffusion and supply oxygen, thereby resulting in less oxygen vacancy accumulation at PZT interfaces. We have improved the imprint property by the reduction of thermal budget in SRO/PZT/SRO structures.
Low Temperature Hydrogen Induced Degradation of (Ba,Sr)TiO3 Thin Film Capacitors
Authors: Baniecki J. D. , Parks C. , Laibowitz R. B. , Shaw T. M. , Lian J. , Costrini G.
Published: April 2011

We have used electrical characterization and secondary ion mass spectroscopy (SIMS) to investigate the influence of hydrogen or deuterium (H/D) on the degradation of the electrical properties of metal/Ba0.7Sr0.3TiO3/metal (M/BSTO/M) thin film capacitors after forming gas annealing (FGA). Leakage and dielectric relaxation currents increase after FGA at temperatures as low as 23C. SIMS profiling shows that at 23C H/D diffuses through thin film metal electrodes and accumulates at electrode interfaces. The location (top or bottom electrode interface) of H/D accumulation is dependent on the type of electrodes and capacitor structure. The resulting asymmetric distribution of H/D leads to large voltage offsets in the C-V characteristic, asymmetric leakage currents, and increased dielectric relaxation currents. Possible mechanisms for increased leakage and relaxation currents after FGA are discussed.
Chemical Vapor Deposition and Electrode Technologies for (Ba,Sr)TiO3 Capacitor Used in Gigabit Dram
Authors: Eguchi K. , Hieda K. , Nakahira J. , Kiyotoshi M. , Nakabayashi M. , Yamazaki S. , Izuha M. , Aoyama T. , Tsunoda K. , Lin J. , Nakamura K. , Niwa S. , Tomita H. , Shimada A. , Kohyama Y. , Ishibashi Y. , Fukuzumi Y. , Arikado T. , Okumura K.
Published: April 2011

We review our capacitor technology using (Ba,Sr)TiO3 (BST) as a capacitor dielectric for dynamic random access memory (DRAM) application. Among a number of issues for BST capacitor process integration in DRAM cells, two important technologies are discussed. As an electrode technology, we propose All PErovskite Capacitor (APEC) technology, in which conducting perovskite oxide of SrRuO3 (SRO) is used as capacitor electrodes. For chemical vapor deposition (CVD) of BST, we propose In-situ Multi-Step (IMS) process, which is a sequential repetition of low temperature deposition of ultra thin BST film and crystallization in the same chamber. By using APEC technology and IMS CVD process of BST, we can simultaneously achieve good electrical characteristics (low leakage current and high permittivity) and good step coverage. The combination of APEC technology and IMS CVD process of BST is a promising BST capacitor process technology for future DRAMs.
Interface Properties Between SrTiO3 Thin Films and Electrodes
Authors: Clark A. M. , Hao Jianhua , Si Weidong , Xi X. X.
Published: April 2011

SrTiO3 (STO) thin films were grown by pulsed laser deposition on single crystal STO substrates with a SrRuO3 buffer layer, which also serves as a bottom electrode. Measurements of the low frequency dielectric properties were performed in a parallel plate capacitor configuration for a range of temperatures using different top electrode materials. The contribution to the interfacial potential from Schottky barriers was investigated. In comparison to STO single crystals, thin films have continued dielectric non-linearity above T ∼ 70 K. This complicates conventional Schottky barrier height measurements using C-V curves because both Schottky barriers and dielectric non-linearity result in a decrease in dielectric constant under applied electric fields. However, by using I-V data, difficulties related to field dependence of the dielectric constant may be removed. Barrier height measurements for both metal and oxide electrodes were performed for T > 70 K. Calculated barrier heights from a modified Schottky equation were very low for an oxide electrode, and an order of magnitude higher for a normal metal electrode.
Domain Imaging, Polarization Hysteresis, and Switching in Nano-Size Ferroelectric Structures
Authors: Harnagea C. , Pignolet A. , Alexe M. , Hesse D. , Gösele U.
Published: April 2011

A fundamental issue in the physics of ferroelectric memories and piezoelectric devices is to study how their properties scale with the size of the ferroelectric structure. In this work we present results concerning the ferroelectric behavior of structures with lateral sizes in the range 100 nm to 1 μm. The ferroelectric characterization was achieved using the piezoresponse mode of a scanning force microscope. 100 nm patterned PZT polycrystalline structures as well as 200 nm epitaxial SrBi2Ta2O9 grains exhibit distinct ferroelectric hysteresis loops. Fatigue measurements on 500 nm structures of PZT were also performed and are discussed.
Investigation of the Structural and Microstructural Characteristics of Sol-Gel Derived Lead Lanthanum Titanate Thin Films
Authors: Majumder S. B. , Bhaskar S. , Dobal P. S. , Cruz A. L. Morales. , Katiyar R. S.
Published: April 2011

In the present work we have studied the characteristics of Pb1.05-xLaxTil-x/4O3 ( x= 0 to 30 at%) thin films prepared by acetic acid and methoxy-ethanol based sol-gel techniques. We have found that higher intermediate temperature fired films (x=0.15), prepared by acetic acid modified technique yielded (100) textured growth with improved dielectric properties. It has been argued that homogeneous mixing of the film constituents in the sol is influenced by the choice of the precursor materials and preparation methodology which in turn controls the growth characteristics and electrical properties. Lanthanum as a dopant has a pronounced influence on the structure, microstructure and electrical properties of the deposited films. In the Raman spectra, the soft E(1TO) phonon shifts towards the lower frequency with a sharp decrease in its intensity and a tetragonal to cubic structural transformation (for 26.5 at % La) was observed at room temperature. In the ferroelectric composition range (up to 15 at % La doping), we have observed a significant improvement of ferroelectric properties with the La addition.
Evaluation of Ferroelectricity in MFIS Type Capacitor Using Pulsed C-V Measurements
Authors: Fujimura Norifumi , Yoshimura Takeshi , Ito Taichiro
Published: April 2011

We have been proposing YMnO3 with low remanent polarization and dielectric permittivity as a transistor type FeRAM. Conventional C-V measurements are normally used to evaluate the ferroelectricity of ferroelectric thin films on Si substrates. For ferroelectric thin films with low polarization, however, there are some issues to understand the C-V hysteresis. For example, interfacial polarization and space charge affect the C-V hysteresis. The effect of interfacial polarization on C-V behavior was calculated assuming the connection of ferroelectric and dielectric layers with different resistivity. If a ferroelectric layer with a leakage current of 1×10-6 A/cm2 is connected to the dielectric layer with a leakage current of 1×10-9 A/cm2, a charge density of 10-9 C/cm2 should be generated in the period of 0.2 sec. Space charge should have a longer time constant for accumulating the charge. Pulsed C-V measurement must be effective to avoid these issues. This paper proposes a simple method to evaluate the real component of ferroelectricity in the C-V hysteresis using YMnO3 or ZnO:Li with very low remanent polarization.
Deposition of Pb(Zr,Ti)O3-Thin Films on Substrates with Shape Memory Effect
Authors: Biegel W. , Klarmann R. , Kuhn M. , Wörz B. , Stritzker B.
Published: April 2011

Pulsed Laser Deposition (PLD) was used to deposit La-doped Pb(Zr,Ti)O3 (PZT) thin films onto NiTi foils. The substrate alloy with composition Ni50Ti50 shows a strong shape memory effect with a transition temperature of about 80°C. This simple bicomponental system could have the potential of an actuator device (NiTi shows a strain up to 5 % during thermal cycling) with an inherent sensorial component (PZT) for the generated elongation. The deposited ceramic films were characterized with respect to their structural properties (XRD) and their ferroelectric behavior (P-E hysteresis). Under certain deposition conditions the growth of pure perovskite PZT on the polycrystalline shape memory alloy was observed. The growth morphology of PZT on NiTi was compared to the one of PZT on single crystalline substrates whereas no distinctive texture of the films on NiTi could be found. The ferroelectric behavior of the PZT films depend on the stage of bending of the film-substrate compound.
Low Temperature Crystallization of PbTiO3 Thin Film by Excimer Laser Irradiation
Authors: Mihara T. , Mochizuki S , Ishida T. , Sato Y , Nishii J.
Published: April 2011

Lowering the fabrication temperature for ferroelectric films is very important not only for silicon monolithic circuits but also for various substrates. Amorphous PbTiO3 thin films were prepared on glass substrates using ArF pulsed laser deposition (PLD). They were subsequently treated by a laser-induced phase transformation technique to achieve a perovskite structure. After irradiation by an ArF pulsed laser with an energy density 50mJ/cm2 in air, the films crystallized into the perovskite structure. It was possible to maintain the substrate at room temperature during the whole fabrication process. The structure, morphology and composition of the films were characterized by X-ray diffraction diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. The surface of film irradiated with a laser was often rather rough and peeled off everywhere. It was necessary to control the number of laser pulses to avoid damaging the films. The effects of chemical composition and fabrication temperature are also discussed.
Heteroepitaxial Growth of Ir/ZrN Layered Electrode on (100)Si Substrate for Ferroelectric Capacitor
Authors: Horii Sadayoshi , Yokoyama Seiji , Horita Susumu
Published: April 2011

An Ir film was grown heteroepitaxially on the epitaxial (100)ZrN film deposited on the (100)Si substrate by sputtering. Further, we obtained a heteroepitaxial (001)PZT film on the epitaxial (100)Ir/(100)ZrN/(100)Si substrate structure by reactive sputtering. The crystallographic relationship was cube-on-cube. The polarization-electric field hysteresis loop of the 300-nm-thick epitaxial PZT film with a top electrode of IrO2 showed a saturated square shape at an ac amplitude of 5V, and the remanent polarization, 2Pr, and coercive field, 2Ec, were 60 μC/cm 2 and 80 kV/cm, respectively. The Pr was not reduced up to 5×1010 switching cycles with a ±10 V bipolar pulse train. The leakage current of the PZT film at +5 V and –5 V was about 8.0× 10−8 and 2.5 ×10−7 A/cm2, respectively.
Laser-Based Flat Panel Displays
Authors: Bischel W. K.
Published: April 2011

Gemfire is developing a novel wall-mounted display technology called Polymer Switch Matrix (PSM). Featuring significant advantages in performance, manufacturability and scalability, it represents a fundamental change in the way flat panel displays are designed and manufactured. The perceived market opportunity, operating principle, system architecture and feasibility demonstration of this radically new laser based technology are described.
Optical and Electro-Optic Properties Of Highly Oriented (Sr,Ba)Nb2O6 Thin Films Prepared by Sol-Gel Process
Authors: Koo Junmo , Jang Jae Hyeok , Bae Byeong-Soo
Published: April 2011

Highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. The anisotropy of refractive indices (no and nc) of c-axis preferred oriented films on MgO(100) substrates decreases certainly as Sr content in the film composition increases. The optical propagation loss of the films decreases with increasing Sr content due to the reduction of the optical scattering by the anisotropy of refractive indices. The oriented films show the linear electro-optic effect with large electro-optic coefficients. The coefficient of the films increases as the Sr content increases because the linear electro-optic coefficient is dependent on the spontaneous polarization and the dielectric constant of the films.
Nonlinear Fiber Core Liquid and Nematic Liquid Crystal Film for Wide Temporal Bandwidth Optical Limiting Application
Authors: Khoo I. C.
Published: April 2011

Nonlinear absorption processes in an extremely nonlinear optical fiber core liquid, and recently observed supra-optical-nonlinearity in dopant modified nematic liquid crystals, are discussed in the context of optical limiting and anti-laser dazzling application.
Maximum Cross Sections for Excited State and Two-Photon Absorption
Authors: Becker Roger J.
Published: April 2011

There is a maximum value for any nonlinear process, which can be found on the basis of fundamental quantum mechanics. With regard to single photon processes, there is a maximum absorption cross section, σa, which any molecule may reach. The maximum is 1.13 × 10-17 λ is the wavelength of the light, n is the refractive index of the host medium, and Q is the quality factor ascribed to the absorption line width. Thus large cross sections can only be obtained at the expense of a narrow operating range. The maximum is set by fundamental physics. Since nonlinear phenomena are highly resonant, the maxima of higher-order processes are also a strong function of the width of the resonance and the peak wavelength. In the case of twophoton absorption the peak value of the maximum cross section, σ2N or δ, is roughly 3.5 × 10-32 λ4nQ cm4/GW, or about 7 × 10-57 λ3 nQ cm4/photon. No value for a nonlinear coefficient is meaningful in the absence of the width of the resonance, the wavelength, and the refractive index of the medium at the wavelength of the measurement.

The basic quantity of interest is the linear electronic polarizability. This fundamental quantity determines not only the absorption for the various processes of interest, but also the surface tension and the closely related solubility parameter. All scale with the polarizability a. The polarizability has a maximum value of e2/mω2; consequently the absorption cross sections have a corresponding ceiling. The maximum value for the peak in a resonant polarizability curve is set by a balance between the Coulomb potential energy of the electron and its kinetic energy. Hence it is an inherent property of the electron itself, irrespective of the molecular orbital in which it finds itself. All that the particular quantum configuration of the molecule does is partition the line strength for absorption among various possible transitions. The extreme case is when virtually all the strength is concentrated in a single transition, an inherently resonant condition.
Calculations of the Macroscopic Linear and Nonlinear Optical Properties of Nematic Liquid Crystals
Authors: Risser Steven M. , Ferris Kim F. , Exarhos Gregory J. , Morgan J. Corey
Published: April 2011

Many studies have focused on the computation of the structural and electronic properties of liquid crystal molecules in a single static conformation. However, a complete and quantitatively accurate description of the macroscopic optical properties of liquid crystals must also include effects due to the long-range nematic order, the anisotropic local environment surrounding the molecules, and the dynamical fluctuations of the molecules. In this paper, we explore methods to simplify computation of the molecular average second hyperpolarizability of the nematogen 4-n-pentyl-4-cyanobiphenyl (5CB). The model we develop relates changes in the geometrical parameters of the molecule to corresponding changes in the hyperpolarizability. The model is first applied to a simple donor-acceptor substituted polyene, and then to 5CB. Use of a small set of geometrical variables results in a slight increase in the RMS deviation of the predicted hyperpolarizability over the deviation obtained from a complete set. We then discuss the importance of this work for the development of means to calculate macroscopic optical properties.
Ab Initio Design of Two-Photon Absorbing Materials
Authors: Day Paul N. , Nguyen Kiet A. , Pachter Ruth
Published: April 2011

Two-photon absorbing materials such as conjugated polyenes show promise as nonlinear optical materials. Prediction of two-photon absorption frequencies and cross-sections has been limited by the high level of ab initio calculations that must be carried out in order to accurately calculate excited state energies and transition dipole moments, by the size of many of the compounds of interest, and by the difficulty of handling condensed phase effects in the calculations. We have carried out geometry optimizations at the multi-configurational selfconsistent field level on a small polyene, hexatriene, both in the gas-phase and in solution, with the solvent effects being modeled by the effective fragment potential. The excited-state energies have been calculated by the multiconfigurational quasidegenerate perturbation theory. Transition dipole moment calculations have also been carried out, from which the two-photon absorption cross-section can be estimated. The results indicate that just one or two solvent molecules can have a large effect on the nonlinear optical properties of two-photon absorbing materials.
Surface Smoothing of Polycrystalline Si Waveguides With Gas-Cluster Ion Beams
Authors: Toyoda N. , Lee K. K. , Luan H-C. , Lim D. R. , Agarwal A. M. , Wada K. , Kimerling L. C. , Allen L. P. , Fenner D. B. , Kirkpatrick A. R.
Published: April 2011

Polycrystalline Si (poly-Si) waveguides offer design flexibility and multilayered structures in Si-integrated photonic devices. However, as-deposited poly-Si surfaces are rough compared with single-crystalline Si, and a rough surface causes significant waveguide scattering loss at the surface. In this study, surface smoothing of poly-Si waveguides with a gas-cluster ion beam (GCIB) was demonstrated as a new smoothing technique. As the GCIB process is a directional ion-beam process, in principle it can be applied not only to plane surfaces but also to three-dimensional or non-flat structures, such as waveguide ridges.

The initial average roughness of as-deposited poly-Si films (625°C, 1 μm thick) ranged from 15 nm to 22 nm, and the grain sizes were distributed from 0.2 to 0.4μm. This rough surface was dramatically smoothed to a roughness of 1.5 nm by Ar cluster ion irradiation. From the relation between the sputtered depth and the surface roughness, the sputtered depth must be greater than the height difference of the roughness (peak-to-valley) to obtain smooth surfaces. Optical transmission losses at λ =1.54 μm were measured using cutback measurement from samples before and after the smoothing by GCIB. After surface smoothing with GCIB, the optical loss decreased from 85 dB/cm to 54 dB/cm.
Two- and three-Dimensional Refractive Index Lattices Formed by Laterally Patterned Porous Silicon Layers
Authors: Uehara S. , Sasabu H. , Taira K , Hashimoto T. , Matsubara T.
Published: April 2011

Porous silicon was used to fabricate refractive index lattices. Patterned n-doping and/ or substrate etching were used to introduce lateral periodicity. By anodizing p-type substrate with an n-doped area, we realized large refractive index contrast two-dimensional lattices with underlying cladding layer. The anodization process showed an effect specific to the small dimensional patterning and this effect has significant influence on the formed refractive index structure.
Polymeric Strip Waveguides and their Connection to Very Thin Ultrafast Metal-Semiconductor-Metal Detectors
Authors: Buchal Ch. , Roelofs A. , Siegert M. , Löken M.
Published: April 2011

We present data on the fabrication process of optical waveguides from four different polymers, which have been patterned either by standard lithographical masking and reactive ion beam etching (RIE) or by direct lithographical exposure of photosensitive material. Three of the resists were directly photosensitive, they could be exposed and developed. Thereafter they can be cured and remain stable. Waveguide losses of 3.5 dB/cm had to be accepted for the photosensitive materials, while the non-sensitive polymers formed very good guides (0.8 dB/cm), but were more difficult to process. We demonstrate the coupling of the strip waveguides to optical fibers on one side and to very thin metal-semiconductor-metal (MSM) photodetectors at the other side. A beam propagation method computer code has been used to evaluate the best coupling efficiencies between the guides and the detectors, which are ultrafast (3.5 ps FWHM) due to their very thin silicon slab design (Si thickness 400 nm, sandwiched between two Schottky contacts).
Hydroxyapatite Coating on Thermal Titanium Substrate in Aqueous Solution
Authors: Okido M. , Ichino R. , Kuroda K. , Ohsawa R. , Takai O.
Published: April 2011

A hydroxyapatite, HAP, film was deposited on a titanium substrate in an aqueous solution, at an ambient temperature and ambient pressure. The solution included 3 mmoldm-3Ca(H2PO4)2and 7 mmol dm-3CaCl2at pH 5.5. The temperature of the substrate surface was controlled in both methods of applying alternative current through the Ti foil and high frequency induction heating using Ti ingot. In these methods, the substrate was heated up and the temperature gradient was formed between the substrate and the solution. The effects of surface temperature, fluoride ions, additive inhibitor and heating time on the morphology of HAP crystals formed on Ti substrate were investigated in various conditions. The morphology changed from compact layer to dendrite layer with the HAP growing time in AC current method and the HAP film with the thickness of 200 μm can be obtained on Ti foil with cross section of 30 μm × 2mm by heating for 20 min at 20 A-AC. On the other hand, the deposits consisted of algae-like whisker in the induction heating method. The HAP formation is found to take place only on the substrate surface by these substrate heating methods without HAP precipitation in aqueous solution
Calcium Phosphate Cements: Chemistry, Properties, and Applications
Authors: Chow Laurence C.
Published: April 2011

This paper reviews recent studies on self-setting calcium phosphate cements (CPC). Discussions are focused on the cement setting reactions, the products formed, those properties of the cements that contribute to their clinical efficacy, and areas of future improvements that could make CPC useful in a wider range of applications. The strengths of CPC are considerably lower than ceramic calcium phosphate biomaterials and are also lower than some of the dental cements. On the other hand, the combination of self-setting capability and high biocompatibility makes CPC a unique biomaterial. Near perfect adaptation of the cement to the tissue surfaces in a defect, and a gradual resorption followed by new bone formation are some of the distinctive advantages of CPC. In its present state CPC appears to be suitable for a number of applications. Much remains to be done to further improve its properties to meet the requirements for different applications.
Calcification Resistant Polyurethanes Modified with Geminal Bisphosphonate Groups
Authors: Alferiev I. S. , Vyavahare N. R. , Song C. X. , Levy R. J.
Published: April 2011

Non-esterified geminal bisphosphonate groups (0.06–0.12 mmol/g) were covalently attached to elastomeric polyurethanes (PU) based on 4,4′-methylenebis(phenyl isocyanate) (MDI) and represented by a polyether-urethane (PEU), a polyurethane-urea (PUU), and a polycarbonate-urethane (PCU). Auxiliary 6-bromohexyl or carboxylic groups were attached to PU via base-induced N-alkylation of urethane NH sites either with 1,6-dibromohexane or with lithium salts of ω-bromocarboxylic acids. An alternative method to introduce carboxylic groups into the polymers via reactions of bromoalkylated PU with thiol-containing carboxylic acids was found to be more suitable than the direct carboxyalkylation. The subsequent reactions either of thiol-containing bisphosphonates with the attached 6-bromohexyl groups or of 3-amino-Ihydroxypropylidene-1,1-bisphosphonate (pamidronate) with N-hydroxysuccinimide-activated carboxylic groups of PU led to the bisphosphonate-modified PU. The polymers do not undergo a significant degradation in the course of the modification reactions, their mechanical properties and elasticity remain mostly unaffected. Water uptake of the bisphosphonate-modified PU increased up to 26% depending on the extent of modification. Bisphosphonate-modified PUU showed a significantly lower in vivo calcification compared to the non-modified polymer.
Mucin Coating on Hydrophobic Polymer Materials
Authors: Shi L. , Caldwell K. D.
Published: April 2011

In this work, the adsorption isotherm and kinetics of bovine submaxillary gland mucin (BSM) onto a hydrophobic polystyrene surface were studied by the solution depletion method, in which mucin surface concentrations were analyzed by amino acid analysis. Using a Langmuir adsorption model and non-linear curve fitting, kinetics parameters, kon and koff were determined. The coating was found to be very stable with very limited desorption (less than 2%) from a long term observation. By measuring the water contact angles, the changes in surface hydrophobicity due to mucin coating were monitored on four polymer materials, namely polymethylmethacrylate (PMMA), polyurethane (PU), polystyrene (PS), and silicone. After coating, all the hydrophobic surfaces turned into very hydrophilic. A strict correlation between mucin surface concentration and surface wettability has been found.
Formation of Calcium Phosphate on Phosphorus-Containing Groups Introduced Substrate
Authors: Yokogawa Y. , Nishizawa K. , Nagata F. , Kameyama T.
Published: April 2011

A calcium phosphate coating over chitin sample was produced by a process based on phosphorylation, Ca(OH)2 treatment and SBF immersion. Ca(OH)2 soaking of the fibers phosphorylated by urea/phosphorus acid (H3PO3) method is found to produce highly crystalline clusters lodged in the fibers which were calcium phosphite mono-hydrate (CaHPO3H2 O). CaHPO3H2O clusters were still present in chitin fibers even after 7 days of soaking, while after 17 days calcium phosphate was observed. While chitin fibers phosphorylated by urea and H3PO4 method and then soaked in saturated Ca(OH) 2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of PO4 functionalities which were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF solution for as little as 1 day. EDX analyses of the thin coating gave Ca/P ratio of 1.29, which is speculated to be OCP. The mechanism of formation of the coating is believed to involve dissolution of the CaHPO3 H2O clusters or the OCP upon introduction of the Ca(OH) 2- treated phosphorylated chitin fibers into the 1.5×SBF solution which elevates the Ca2+ ion concentration in the vicinity of the fibers so stimulating calcium phosphate formation from the soaking medium.
Bioactive Glass Stimulates the Function of Biological Signaling Molecules and Cells
Authors: Ducheyne P.
Published: April 2011

An estimated 11 million people in the United States have at least one medical device implant [1]. Orthopaedic implants account for 51.3 % of all implants. They include fixation devices (usually fracture fixation) and artificial joints, used in 77% and 23% of the cases respectively. Among the joint replacement procedures, hip and knee surgeries represent 90% of the total, and, in 1988, were performed 310,000 times in this country [1]. Currently, somewhat more than half the joint reconstruction devices are used with bone cement, which is a polymer grout that keeps the prosthesis components in place in the bone. The fixation in the other cases depends on the bone's ability to grow in contact with the device. This can be achieved by making the prosthesis surface porous, such that bone grows into the interstices; or by making the surface chemically reactive with bone tissue such that a continuous, uninterrupted transition is formed from tissue to device. Bioactive glasses and ceramics are the materials of choice to achieve this effect on bone tissue bonding [2]. Bone growth stimulation is also sought in the treatment of difficult fractures. In the U.S. alone, there are 1.23 million fractures that require a bone plate. Of that total, approximately I million require between 10 and 100 cc of graft material to stimulate bone repair. At this time, autogenous bone graft represents the gold standard: this graft is typically bone tissue taken from the patient's own iliac crest. Given the morbidity associated with this procedure and the frequently insufficient quantities available, extensive efforts for suitable alternatives are currently underway. Calcium phosphate ceramics and glasses, either by themselves or as carriers for bone (or “osteogenic”) cells or various bone growth factors, are also prime candidate materials for these applications.
Effects of Growth Factor Presence on Mineralization of Porous Poly(Lactide-Co-Glycolide) Scaffolds In Vitro
Authors: Murphy William L. , Gilhool Katherine A. , Kohn David H. , Mooney David J.
Published: April 2011

Basic design requirements of scaffolds for bone tissue engineering applications include biocompatibility, temporally controlled degradability, osteoconductivity, mechanical integrity, and mass transport capabilities. A recent study has attempted to meet design criteria via the growth of a carbonated apatite (bone-like) mineral on the inner pore surfaces of a highly porous 85:15 poly(lactide-co-glycolide) scaffold using a biomimetic process. It has also been recently demonstrated that the mineralization strategy can be combined with sustained growth factor delivery to induce vascular tissue ingrowth. The present study examines the effect of protein presence on the mineralization process by measuring the amount of protein incorporated into the scaffold during the process of mineral formation. Surprisingly, vascular endothelial growth factor incorporates more readily into control scaffolds than into scaffolds subjected to mineralization treatment. This finding suggests that there is little incorporation of protein into the growing mineral film, and offers insight into the mechanism for sustained drug delivery from the mineralized scaffolds.
Effect of Post-Treatment on Dissolution and Biomineralization on Surface of ha Coatings in Simulated Body Fluid (SBF)
Authors: Chen Jiyong , Weng Jie , Zhang Qiyi , Feng Jiaming , Cao Yang , Zhang Xingdong
Published: April 2011

The HA coatings were heated separately in vacuum, air and water vapor. The dissolution of the HA coatings was investigated by immersion in Tris buffer and SBF The dissolubility of HA coatings in the solutions decreased in this order: as-received, heated in vacuum, in air and in water vapor. The nucleation of bone-like apatite on the surfaces of HA coatings after immersing a period of 11 days in SBF was observed by SEM. The microenvironment with a sufficient supersaturation of Ca and P ions was crucial for the nucleation and growth of apatite in SBF. The dissolution of amorphous phase in coatings played an important part in establishing the supersaturation of Ca and P ions.
Structural and Chemical Analysis of Crystal Enamel Nucleation
Authors: Belío-Reyes I. A. , JimÉNez-García L. F. , Reyes-Gasga J.
Published: April 2011

The aim of the present study is to obtain structural and chemical information about nucleation and growth of dental enamel as a function of location in secretory mouse foetus enamel. Then enamel tissues were obtained from 19-days-mouse foetus. TEM images show that enamel crystallites had the well-documented thin ribbons, or needles. They were found in the outermost zone in the vicinity of ameloblasts. Chemical analysis by EDS showed that, besides the elements of hydroxyapatite, Na, Cl, Al and Mg are presents from the beginning of enamel mineralization. All of these elements will play an important role on the physics and chemical properties in mature enamel.
The Control of Mineralization on Natural and Implant Surfaces
Authors: Nancollas G. H. , Wu W. , Tang R.
Published: April 2011

The generation of minerals such as calcium phosphates on the surfaces of dental and joint replacement implants is beneficial since the facilitation of bone formation permits their fixation. In contrast, the prevention of crystallization is desired on other surfaces such as kidney and cardiac valve prostheses. A key to the development of successful biomaterials is therefore an understanding of the factors that control crystal nucleation, growth and dissolution in aqueous solution. The Constant Composition method was used to investigate the influence of factors such as solution composition, ionic strength, pH and temperature on the crystallization and dissolution of the calcium phosphates, brushite (DCPD), octacalcium phosphate (OCP), hydroxyapatite (HAP) and fluorapatite (FAP). In parallel with these studies, a contact angle method along with surface tension component theory was employed to investigate the roles of interfacial free energy in mineralization and demineralization. Values of the interfacial tensions, -4.2, 4.3, 10.4 and 18.5 mJm-2obtained from contact angle measurements for DCPD, OCP, HAP and FAP, respectively, compare well with those calculated from dissolution kinetics experiments and provide information concerning the growth and dissolution mechanisms. The exploitation of these approaches is illustrated in studies of the coating of specific calcium phosphate phases on titanium metal and alloy surfaces and nucleation and growth of OCP on polymer surfaces modified by silanization to produce amine- and carboxylterminated end groups. In all these reactions involving the calcium phosphates, concomitant dissolution reactions are often involved. Constant Composition kinetic studies have shown that the rate of these reactions decrease markedly with time despite a sustained driving force, and eventually, the rates approach zero even though crystals remain in the undersaturated solutions. Dissolution can be reinitiated by exposing the crystals to the solutions of different undersaturations. These results suggest that dislocation sizes play a significant role in the dissolution kinetic processes.
Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure
Authors: Billinge S. J. L. , Petkov V. , Proffen Th. , Kwei G. H. , Sarrao J. L. , Shastri S. D. , Kycia S.
Published: April 2011

We have measured atomic pair distribution functions (PDF) of La1−xCaxMnO3 using high energy x-ray diffraction. This approach yields accurate PDFs with very high real-space resolution. It also avoids potential pitfalls from the more usual neutron measurements that magnetic scattering is present in the measurement, that the neutron scattering length of manganese is negative leading to partial cancellation of PDF peaks, and that inelasticity effects might distort the resulting PDF We have used this to address the following questions which do not have a satisfactory answer: (1) What are the amplitudes and natures of the local Jahn-Teller and polaronic distortions in the CMR region. (2) Is the ground-state of the ferromagnetic metallic phase delocalized or polaronic. (3) As one moves away from the ground-state, by raising temperature or decreasing doping, towards the metal insulator transition, how does the state of the material evolve?
New Magnetic and Ferroelectric Cubic Phase of Thin-Film Fe-Doped BaTiO3
Authors: Maier R. , Cohn J. L. , Neumeier J. J. , Bendersky L. A.
Published: April 2011

The properties of a new cubic perovskite phase of thin-film BaFexTi1−xO3 (0.5 ≤x≤0.75) are reported. This material is novel because the corresponding bulk compounds have hexagonal structure for comparable x. The films, grown by pulsed laser deposition on MgO and SrTiO3 substrates, are magnetic (ferro- or ferri-, with Tc > 500°C) and ferroelectric (Tc ∼ 200-300°C).
Is Magnetic Circular Dichroism Surface Sensitive in the Manganese Perovskites?
Authors: Borca C.N. , Cheng R.H. , Stadler Shane , Idzerda Y.U. , Choi Jaewu , Mcilroy D.N. , Xu Q.L. , Liou S.H. , Zhong Z.C. , Dowben P.A.
Published: April 2011

We compare the magnetization versus temperature, determined by magnetic circular dichroism, with bulk magnetization determined by SQUID magnetometry. The results for two different manganese perovskites, La0.65A0.35MnO3 systems (A=Pb, Sr), epitaxially grown on LaAlO3 substrates compared. The results suggest that the magnetic circular dichroism results may not be representative of the bulk magnetization. Similar materials, but with a different secondary electron mean free path lengths or different surface compositions, may thus be expected to have different behavior in MCD or MXLD that depends on a photoyield for detection.
Polarization Dynamics in La5/3Sr1/3NiO4
Authors: Hakim N. , Zhai Z. , Kusko C. , Parimi P.V. , Cheong S-W. , Sridhar S.
Published: April 2011

Dynamic susceptibility measurements at microwave frequencies (2 – 10GHz) are a sensitive probe of charge dynamcis in La5/3Sr1/3NiO4. Below the charge ordering temperature of 240K, a dielectric loss peak due to a relaxation mode with a large dielectric susceptibility is observed, and is associated with charge stripe formation. The dielectric response for Hω∥b (Eω ⊥ b) is well represented by ε(T) = εo/(1 – iωτ(T)), with εo, ∼ 50, and τ(T) = 2 × 10−9(sec) exp(−T/37K). Parallel conductivity σ(T) contributions dominate at higher temperatures and for Hω∥c (Eω ⊥ c). The dielectric loss peak observed indicates that the charge relaxation rates lie in the GHz frequency ranges.
High Pressure Measurements on TI2Mn2O7
Authors: Núñez-Regueiro M. , Senis R. , Cheikh-Rouhou W. , Strobel P. , Bordet P. , Pernet M. , Hanfland M. , Martinez B. , Fontcuberta J.
Published: April 2011

Transport and structural properties of the colossal magnetoresistance pyrochlore TI2Mn2O7 are studied as a function of applied pressure up to ∼20GPa. This allows us to probe the effect of structural changes on the ferromagnetic transition and the transport properties. We observe a non-monotonous pressure dependence of the ferromagnetic transition temperature. We correlate this unusual variation with the structural parameters that, according to electronic band calculations, are key in controlling the properties of these materials.
The role of strain in low-field magnetotransport properties of manganite thin films
Authors: Hu Y. F. , Wang H. S. , Wertz E. , Li Qi
Published: April 2011

Strain-induced large low-field magnetoresistance has been observed in very thin Pr0.67Sr0.33MnO3 films1. To better understand the role of strain in the low-field magnetotransport properties of manganite thin films, we have studied and compared very thin (3-20 nm) Pr0.67Sr0.33MnO3 (PSMO), La0.67Ba0.33MnO3 (LBMO), La0.67Sr 0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) films grown on different substrates, such as LaAlO3(001) (LAO), NdGaO3(110) (NGO), and SrTiO3(001) (STO). Due to the lattice mismatch between the films and the substrates ranging from -2.6% to +1%, different strains can be imposed to the films. We have found that: (1) large low-field magnetoresistance(LFMR) behaviors are observed in PSMO, LCMO and LSMO thin films on LAO substrates when a magnetic field is applied perpendicular to the film plane, but the maximum LFMR is the largest in PSMO and LCMO samples; (2) most of the films grown on STO substrates show positive MR when a magnetic field is applied perpendicular to the film plane, and when the field is parallel to the film plane all films show negative MR regardless of the substrates; (3) the large low-field MR is strongly dependent on the film thickness and the composition of the manganites. The anomalous low-field MR effect will be discussed based on strain-induced magnetic anisotropy and domain rotation and movement.
Large Magnetoresistance Anisotropy in Strained Pr0.67Sr0.33MnO3 Thin Films
Authors: Wang H. S. , Hu Y. F. , Wertz E. , Li Qi
Published: April 2011

We have studied the anisotropic magnetoresistance (AMR) of strained Pr0.67Sr0.33MnO3 thin films by measuring the MR as a function of the angle between the magnetic field direction and the substrate normal (out-of-plane). The results show that the compressive- and tensile-strained ultrathin films (5-15 nm) grown on LaAlO3 (001) (LAO) and SrTiO3 (001) (STO) substrates show unusually large out-of-plane AMR, but with opposite signs. In contrast, the almost strainfree films on the NdGaO3 (110) substrates show much smaller AMR over all the temperature and field ranges studied. Thick films on LAO and STO substrates also show much smaller AMR.