bluuebunny/crossref_metadata_2025 huggingface dataset:
Colloidal Silica based High Selectivity Shallow Trench Isolation (STI) Chemical Mechanical Polishing (CMP) Slurry
Authors: Bu Kyoung-Ho , Moudgil Brij M.
Published: June 2019

Among various properties of chemical mechanical polishing (CMP) slurry, selectivity plays a key role in global planarization of high density and small pattern size shallow trench isolation (STI) process. Lack of adequate selectivity can lead to defects such as dishing and erosion. To improve the selectivity of STI CMP process, CMP characteristics of silica and silicon nitride wafer were investigated using colloidal silica slurry as a function of slurry pH. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added to increase the selectivity of the slurry. As a result, selectivity increased from 3 to 25. It was concluded that selective passivation layer formed on silicon nitride wafer surface at acidic slurry pH range was responsible for the observed selectivity increase. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by zeta potential behavior under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher han silica due to the electrostatic forces. Significantly higher SDS coating on silicone nitride seems to have resulted in lubrication layer leading to increased polishing selectivity.
A New Approach Using Artificial Substrates for Growth of High-Quality Precipitate-Free HTS Thin Films, Toward Electronic Device Applications
Authors: Endo K. , Badica P. , Sato H. , Akoh H.
Published: June 2019

High quality thin films of HTS have been grown by MOCVD on substrates with artificial steps of predefined height and width. The surface of the films grown on the steps having width equal to the ‘double of the migration length' of the atomic species depositing on the substrate is totally free of precipitates: precipitates are gathered at the step edges where the free energy is lowest. The method has several advantages: it is simple, universal (it is independent of the materials, substrates, deposition technique or application) and allows control of precipitates segregates so that the quality and growth conditions of the films are the same as for the films grown on conventional substrates. The method is expected to result in new opportunities for the device fabrication, design and performance. As an example we present successful fabrication of a mesa structure showing intrinsic Josephson effect. We have used thin films of Bi-2212/Bi-2223 superstructure grown on (001) SrTiO3 single crystal substrates with artificial steps of 20 μm.
Pulsed-Laser Deposition of Biaxially Textured YSZ/CeO2 Films on Electrodeposited Ir/Ni-W Tapes for YBCO Superconductors
Authors: Chaudhuri Tapas , Spagnol Priscila , Bhattacharya Raghu , Phok Sovannary
Published: June 2019

Iridium film is a potential candidate as a buffer layer for yttrium barium copper oxide (YBCO) coated conductors. Pulsed laser deposition (PLD) of biaxially textured CeO2/yttrium stabilized zirconium oxide (YSZ) layers on electrodeposited Ir/Ni-W is reported. Biaxial texturing is obtained by deposition of a YSZ seed layer at 800°C in 10-6 Torr vacuum. X-ray diffraction (XRD) studies of Θ-2Θ and pole figure confirmed in-plane out-of-plane biaxial texturing with Δφ = 6.5° and Δω = 8°. Atomic force microscopy (AFM) revealed a surface with roughness of about 3 nm.
Non-Vacuum Deposition of Buffer Layer for YBCO Superconductor Oxide Films
Authors: Bhattacharya Raghu , Phok Sovannary , Spagnol Priscila , Chaudhuri Tapas
Published: June 2019

Nonvacuum electrodeposition was used to prepare biaxially textured CeO2 and Sm-doped CeO2 coatings on Ni-W substrates. The samples were characterized by X-ray diffraction (including Θ/2Θ, pole figures, omega scans, and phi scans), atomic force microscopy, and Auger electron spectroscopy (AES). Pole-figure scans show that electrodeposited CeO2 and Sm-doped CeO2 on textured Ni-W (3 at.%) is cube textured. Full-width at half-maximum values of thew scan andf scan of the electrodeposited layers were better than those of the Ni-W base substrates, indicating improved biaxial texturing of the electrodeposited layers. AES analysis of the YBCO/CeO2/YSZ/ED-CeO2/Ni-W revealed that Ni interdiffusion was completely stopped at the first electrodeposited CeO2 layer.
X-ray Photoelectron Spectroscopy Study on E-beam Co-evaporated YBCO Precursors and their Post –deposition Conversion
Authors: Zhang Yifei , Feenstra Ron , Christen David K.
Published: June 2019

Electron beam co-evaporation is one of the ex situ techniques being developed for cost-effective fabrication of YBa2Cu3O7-δ (YBCO) coated conductors. To achieve high critical current (Ic) and fast conversion, further understanding is needed of the chemical and microstructural characteristics of the precursors and the phase evolution process towards the epitaxial c-axis oriented YBCO film during the post-deposition conversion annealing. In this study, X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical and compositional profiles of the precursors. Samples quenched from the processing stage were also inspected for identifying the transient elemental chemical states during the YBCO phase formation. XPS survey and detailed spectra were recorded for the surfaces and through various depths. It is suggested that XPS spectra, especially the “Auger parameters” can be used for revealing the conversion reaction. Preliminary results indicate that the copper oxidation state might have important effect on precursor conversion behaviors.
Magnetic Field Dependence of Critical Current Density of PLD RE-Ba-Cu-O (RE=Gd, Sm, Dy, Er, Y) Film on CeO2 Capped IBAD-GZO Layers
Authors: Takahashi Kazuhiro , Konishi Masaya , Ibi Akira , Watanabe Tomonori , Muroga Takemi , Miyata Seiki , Yamada Yutaka , Shiohara Yuh , Kato Takeharu , Hirayama Tsukasa
Published: June 2019

We prepared REBa2Cu3O7- δ (RE= Gd, Sm, Dy, Er, Y) coated conductors on pulsed laser deposition (PLD) -CeO2/ion-beam assisted deposition (IBAD) – Gd2Zr2O7 (GZO) / metal tapes by the PLD method and measured the characteristics in magnetic fields. The GdBa2Cu3O7- σ (Gd-123) films showed superior characteristics than others in magnetic fields and showed weak anisotropy. Critical current density (Jc) value of the Gd-123 film was 3.87MA/cm2 at self-field and 0.19MA/cm2 at 3 T of perpendicular field to the tape surface in liquid nitrogen (77 K). Angular dependences in magnetic fields (Jc -Θ) of the Gd-123 and the SmBa2Cu3O7- σ (Sm-123) were superior to others and peaks in Jc -Θ were found also at 0 degree. The reduction ratios of Jc in Jc -Θ for the Gd-123 film and the Sm-123 film were smaller than other films. Transmission electron microscopy showed that the Gd-123 film had many stacking faults. It may be considered that this stacking faults naturally introduced by the PLD method contribute to improvement of anisotropy of Jc -Θ in the Gd-123 film.
AC Losses in High-TC Superconductors with Finite Thickness
Authors: Benkraouda Maamar , Mustafa M.
Published: June 2019

The structure and dynamics of magnetic vortices in high-Tc superconductors are studied. The model we use is applicable to highly anisotropic high-Tc superconductors, such as Bi and Th compounds, where the Josephson coupling is neglected between the superconducting layers. In this paper, we studied the ac losses occurring in a finite number of superconducting layers due to an applied ac current. It is found that the ac losses increase with the frequency and the amplitude of the applied current. By introducing random pinning centers in the layers, the effect of pinning on the reduction of ac losses is also studied.
Large-area Deposition of Amorphous Silicon Alloys Using a Roll-to-roll Operation
Authors: Guha Subhendu , Yang Jeffrey
Published: June 2019

Large-area deposition of thin-film amorphous silicon alloy triple-junction solar cells on lightweight and flexible stainless steel substrate is described. The proprietary roll-to-roll operation enables continuous depositions of sophisticated multi-layer structures. The deposition methods include sputtering and plasma-enhanced chemical vapor depositions. Spectrumsplitting triple-junction solar cell design, manufacturing processes, and product applications are presented.
Development Of PVDF Thick Film Interdigitated Capacitors For Pressure Measurement On Flexible Melinex Substrates
Authors: Arshak Arous , Arshak Khalil , Morris Deirdre , Korostynska Olga , Jafer Essa
Published: June 2019

In this work, a PVDF thick film paste was deposited onto interdigitated electrodes to form a capacitor. Two different substrates, alumina and Melinex® were used. Capacitors, fabricated on alumina substrates were tested as strain gauges, and showed a high sensitivity with low hysteresis. Capacitors on Melinex® substrates were tested as pressure sensors by adhering them to planar and cylindrical surfaces and subjecting them to pressures up to 300 kPa. Their sensitivity and hysteresis during cycling were examined and compared. It was found that sensors on cylindrical surfaces showed a higher sensitivity, however the hysteresis was also increased. It is thought that this is due to instabilities in the polymer film, accentuated by stretching of the substrate.
Nanocrystalline Silicon Thin Film Transistors on Optically Clear Polymer Foil Substrates
Authors: Kattamis Alex , Cheng I-Chun , Long Ke , Sturm James C. , Wagner Sigurd
Published: June 2019

We have fabricated TFTs of nanocrystalline silicon (nc-Si) at 150°C on clear polymer substrates (coefficients of thermal expansion, α∼45 to 55ppm/K), on Kapton® 200E (α=17ppm/K), and on Corning 1737 glass (α=3ppm//K) for comparison. Because thermally stable polymers, such as Kapton® 200E polyimide, have glass transition temperatures as high as 325°C, they are candidates for direct substitution of display glass. The stresses developed in the substrate and device layers, due to à, are reduced by decreasing the thickness of the active layers, by cutting the layers into islands separated by exposed substrate, and by designing stresses, via plasma conditions, into the SiNx passivating layers. By using these three techniques we have made nc-Si TFTs on high Tg, and high α, clear polymer foils with electron mobilities of up to 18cm2/Vs. When integrated with bottom-emitting organic light emitting diodes, such devices will allow for a 10x reduction in pixel TFT areas, compared to TFTs of amorphous silicon.
High Mobility Pentacene Field Effect Transistors on Plastic
Authors: Mohapatra Siddharth , Grigas Michelle , Wenz Robert , Rotzoll Robert , Olariu Viorel , Shchekin Oleg , Dimmler Klaus , Dodabalapur Ananth
Published: June 2019

This paper reports the electrical properties of thin-film transistors with pentacene active layers used in a bottom contact transistor geometry utilizing solution processed poly-4-vinylphenol (PVP) as the gate dielectric processed on a polyethylene napthalate (PEN) substrate. The transistors sometimes exhibit mobilities in excess of 1cm2/Vs. The effect of various surface treatments of the gate insulator, on the electrical properties of these transistors discussed. The development of photolithographically defined 2νm channel length bottom contact transistors is emphasized as the speed of circuit elements such as the rectifier scale inversely as the square of the channel length of the transistors. Surface cleaning and semiconductor deposition techniques that improve transistor characteristics and reduce hysteresis are evaluated and the variation of the ION/IOFF ratios with the different surface treatments is noted.
The Role of Type I Collagen Molecular Structure in Tendon Elastic Energy Storage
Authors: Freeman Joseph W. , Silver Frederick H. , Woods Mia D. , Laurencin Cato T.
Published: June 2019

In order to facilitate locomotion and limb movement many animals store energy elastically in their tendons. The formation of crosslinked collagen fibers in tendons results in the conversion of weak, liquid-like embryonic tissues into tough elastic solids that can store energy and perform work. Collagen fibers in the form of fascicles are the major structural units found in tendons. The purpose of this paper is to review the literature on collagen self-assembly and tendon development and to relate this information to the development of elastic energy storage in nonmineralizing and mineralizing tendons. Of particular interest is the mechanism by which energy is stored in tendons during locomotion. In the turkey, much of the force generated by the gastrocnemius muscle is stored as elastic energy during tendon deformation and not within the muscle. As limbs move, the tendons are strained, causing the collagen fibers in the extracellular matrices to stretch. Through the analysis of turkey tendons, collagen fibers, and a molecular model, it is hypothesized that elastic energy is stored in the flexible regions of the collagen molecule. Data from the molecular model, mineralized fibers, and turkey tendons show that the presence of calcium and phosphate ions causes an increase in elastic energy stored per unit strain. Based on the theoretical modeling studies, the increase in stress with strain is a result of the initiation of stretching of the rigid regions of collagen molecules.
Architectural changes of trabecular bone caused by the remodeling process
Authors: Weinkamer Richard , Hartmann Markus A. , Brechet Yves , Fratzl Peter
Published: June 2019

Using a stochastic lattice model we have studied the architectural changes of trabecular bone occurring while the structure is remodeled. Our model considers the mechanical feedback loop, which control the remodeling process. A fast algorithm was employed to solve approximately the mechanical problem. A general feature of the model is that a networklike structure emerges, which further coarsens while the bone volume fraction remains unchanged. Decreasing the mechanical response of the system by either lowering the external load or the internal mechano-sensitivity leads not only to a reduction of the bone volume fraction, but results in topological changes of the trabecular bone architecture, where the loss of horizontal trabeculae is the most obvious effect.
Atomic Force Microscopy Contact Mode Study on Ultra High Molecular Weight Polyethylene
Authors: Cao Yifang , Zhou Jikou , Popoola Oludele , Swarts Dal F. , Soboyejo Wole
Published: June 2019

This paper presents the results of contact mode atomic force microscopy (AFM) study on the nanoscale Young's modulus and work of adhesion of ultra high molecular weight polyethylene (UHMWPE). Cryoultramicrotomed surfaces of UHMWPE were scanned using the contact mode of AFM. Fibril regions are commonly found on the sample, however, a non-fibril particulate region was also found. AFM force displacement curves were obtained for the sample. The JKR theory and Maugis Dugdale model were used for the analysis. A good fitting between the theories and experimental data was found. The nanoscale Young's modulus and work of adhesion of UHMWPE extracted from the experimental data were in reasonably good agreement with the values reported in other literatures.
Relating Local Bone Stiffness and Calcium Content by Combined Nanoindentation and Backscattered Electron Imaging
Authors: Weber M. , Schoeberl T. , Roschger P. , Klaushofer K. , Fratzl P.
Published: June 2019

Bone is a hierarchically structured mineral-organic composite material that has to bear static and dynamic mechanical loads applied by body weight and locomotion. Bone mechanical properties are influenced by a number of factors, depending on the particular hierarchical levels. The high stiffness of bone material is mainly achieved by reinforcement with calcium phosphate mineral platelets. A model for this elementary structure level consists of an arrangement of staggered mineral bricks, embedded in collagen matrix, which provides both stiffness and toughness. The mechanical properties depend on the amount, shape and arrangement of the mineral particles but also on the properties of the collagen-rich matrix.

One of the difficulties in assessing the properties of hierarchical structures is the inherent inhomogeneity of the tissue: Parameters such as stiffness or calcium content vary throughout a bone section. Such type of investigations becomes more meaningful by a combination of two complementary methods e.g. quantitative backscattered electron imaging (qBEI) and nanoindentation. The local Ca-content, representing the degree of the mineralization, is extracted from the qBEI measurements, whereas the local mechanical properties, elastic modulus and hardness, are measured by nanoindentation, a miniaturized hardness testing using a small diamond tip. The measured correlations between local Ca-content and mechanical strength help, for example, to verify biomechanical models based on the nanocomposite structure of bone. They may also shed new light on bone diseases such as osteoporosis or osteogenesis imperfecta.
Elastic Modulus and Mineral Density of Dentine and Enamel in Natural Caries Lesions
Authors: Bembey Amanpreet K. , Oyen Michelle L. , Ko Ching-Chang , Bushby Andrew J. , Boyde Alan
Published: June 2019

Dental tissues have been reported to show a considerable decrease in both their mineral content and mechanical properties in carious lesions. The changed properties of dentine and enamel have been shown to be dependent on crystal size and not only mineral content [1], although the connectivity between the mineral crystals has been overlooked. Teeth with carious lesions were sectioned, embedded in polymethylmethacrylate (PMMA) and diamond polished. Nanoindentation and quantitative backscattered electron imaging were used to determine relationships between the elastic modulus and mineral density of sound and carious regions within dentine and enamel. The changes in elastic modulus with decreased mineralization for dentine and enamel could not be explained by simple composite mechanics expressions relating elastic modulus and mineral volume fraction. Finite element modeling of dentine and enamel as a two-phase composite material at the ultrastructure level were used to demonstrate how changes in the mineral phase connectivity can produce changes in the elastic modulus. Tissue models for enamel, in which the mineral phase is both the major component of the structure (∼ 85% by volume) and highly interconnected, were consistent with the modulus of sound enamel. The drastic change in enamel modulus with a relatively small change in mineral volume fraction could be modeled as a decrease in mineral phase connectivity at nearly constant volume fraction. The more gradual trend in the dentine data was also consistent with a structure that is initially highly connected in the mineral phase, consistent with the known structure of dentine, and for which the change in modulus is more directly related to changes in mineral content than mineral connectivity.
Microstructure and Adhesive Properties of Copal Composite in Dental Incrustations
Authors: Orta-Amaro M. N. , Rodríguez-Chávez J. A. , Belío-Reyes I. A. , Bucio L. , Arenas-Alatorre J. , Espinoza J.L. , Flores-Grajeda M. C.
Published: June 2019

There are evidences that in ancient cultures in Mexico,copalwas probably used for gluing precious stones in teeth cavities and for dental restorations as well. This is an important reason for making experiments using copal and copal-based composites in order to have more information for the potential applications of this material in modern dentistry. In our experiments concerning with dental incrustations of turquoise, we have practiced round cavities (about 1 mm depth) in the middle of incisive teeth by using a low-speed air turbine. Turquoise was cut in such a way that fits exactly on the tooth cavity. Copal and powdered apatite were used to glue the stone into the cavity. With Scanning electron microscopy we have observed that the composite copal-powdered apatite, penetrates the dentin tubules in the tooth tissue (depth of penetration from 5.6 to 41 micrometers), suggesting the existence of a micromechanical adherence. Concerning to the characterization of the adhesive properties, we have applied the ASTM D2095-72 test considering the adhesion of two cylinders of bone, and the copal composite as the adhesive. A maximum cohesive tensile strength around 0.1 MPa for elastic response was measured for hydroxyapatite compositions of 0, 25 and 75 wt%. We will discuss these results considering the reports of dental incrustations in ancient Mexico.
Mechanical Properties of the Lobster Cuticle
Authors: Raabe D. , Sachs C.
Published: June 2019

We present experiments on the mechanical and structural gradients through the cuticle of homarus americanus (lobster). The exocuticle (outer layer) is characterized by a very fine woven structure of the chitin-protein matrix (Bouligand structure) and by a high stiffness (8.5–9.5 GPa). The hardness increases within the exocuticle between the surface region (130 MPa) and the region close to the interface to the endocuticle (270 MPa). In the endocuticle which is characterized by a much coarser twisted plywood (Bouligand) structure both, the stiffness (3–4.5 GPa) and hardness (30–55 MPa) are much smaller than in the exocuticle. The transition in mechanical properties and structure between the exo- and endocuticle is abrupt.
Elasticity and Viscoelasticity of Human Tibial Cortical Bone Measured by Nanoindentation
Authors: Silva Leandro de Macedo Soares , Ebacher Vincent , Liu Danmei , McKay Heather , Oxland Thomas R. , Wang Rizhi
Published: June 2019

Bone is a composite material composed of collagen, carbonated apatite mineral, water, and other non-collagenous proteins. The bone structure inside human body is under constant remodelling. The mechanical properties of bone and their dynamic changes during remodelling are crucial to the health and quality of life.

In this study, the elastic and viscoelastic properties of a 73 year-old female cortical bone were investigated at the lamellar level. This was realized by a nanoindentation technique equipped with dynamic loading function. 325 indentations were made in individual Haversian systems and interstitial bone at both dry and wet condition, and under two different loading frequencies. The results showed no statistically significant differences in elastic modulus between Haversian systems and interstitial bone. There were no systematic differences in modulus across the cortex except for a slight drop at the periosteal site. The lamellar structure of both Haversian system and interstitial bone is viscoelastic with water playing a significant role to the properties. When dry bone is re-hydrated, elastic modulus decreases and loss tangent increases.
Constitutive Modeling of the Stress-Stretch Behavior of Membranes Possessing a Triangulated Network Microstructure
Authors: Arslan Melis , Boyce Mary C.
Published: June 2019

The mechanical behavior of the membrane of the red blood cell is governed by two primary microstructural features: the lipid bilayer and the underlying spectrin network. The lipid bilayer is analogous to a 2D fluid in that it resists changes to its planar area, yet poses little resistance to planar shear. A skeletal network of spectrin molecules is crosslinked to the lipid bilayer and provides the shear stiffness of the membrane. Here, a continuum level constitutive model of the large stretch behavior of the red blood cell membrane that directly incorporates the microstructure of the spectrin network is developed. The resemblance of the spectrin network to a triangulated network is used to identify a representative volume element (RVE) for the model. A strain energy density function in terms of an arbitrary planar deformation field is proposed using the RVE. Differentiation of the strain energy density function provides expressions for the general multiaxial stress-stretch behavior of the material. The stress-strain behavior of the membrane when subjected to uniaxial loading conditions in different directions is given, showing the capabilities of the proposed microstructurally-detailed constitutive modeling approach in capturing the evolving anisotropic nature of the mechanical behavior.
Elasto-Mammography: Elastic Property Reconstruction in Breast Tissues
Authors: Wang Z. , Liu Y. , Sun L.Z. , Wang G.
Published: June 2019

Mammography is the primary method for screening and detecting breast cancers. However, it frequently fails to detect small tumors and is not quite specific in terms of tumor benignity and malignancy. The objective of this paper is to develop a new imaging modality called elastomammography that generates the modulus elastograms based conventional mammographs. A new elastic reconstruction method is described based on elastography and mammography for breast tissues. Elastic distribution can be reconstructed through the measurement of displacement provided by mammographic projection. It is shown that the proposed elasto-mammography provides higher sensitivity and specificity than the conventional mammography on its own for breast cancer diagnosis.
Indentation Micromechanics of Fibroblast-Populated Fibrin Constructs
Authors: Mooney R.G. , Costales C.A. , Curtin J.M. , Tawil B. , Shaw M.C.
Published: June 2019

During normal wound healing, a fibrin clot is formed within the first few minutes and is replaced, over several days, by collagen and other extracellular matrix components which are populated with fibroblasts [Clark, 1996]. This process leads to the rebuilding of dermal tissue on which the epidermal tissue is slowly rebuilt. In severe acute and chronic wounds dermal replacement materials that mimic these processes are needed. Current trends are to use scaffolds as structural substitutes as well as carriers for growth factors and cells for wound treatment. Fibrin-based sealants have been used over the last 30 years in hemostasis and tissue sealing applications and in the last 5 years as a scaffold. Fibrin sealant consists of two primary components, fibrinogen and thrombin which form a fibrin clot when mixed. However, a basic understanding of the microstructure/property relationships of fibrin/collagen constructs is not yet fully established. Furthermore, while previous studies showed that cells proliferate and differentiate within 3D fibrin clots, their effect on structural mechanics of the fibrin clot has not been examined.

Here, an indentation protocol was established to determine the effects of fibrin/collagen biochemistry and time-dependent cellular response on the elastic parameters of the constructs. Specifically, 4 ml fibrin/collagen constructs were prepared with varying compositions of human-derived fibrinogen (5 - 33 mg/ml), thrombin (1 or 2 U/ml) and bovine collagen (0, 25, 50, 75, 100 weight % of 2.4 mg/ml collagen). Constructs were prepared with/without the presence of human foreskin fibroblasts (ATCC NIH3T3) seeded at a density of 100K cells/ml. Using a 3-mm diameter punch indenter, the indentation load-displacement response was measured after 1, 5 and 10 days of incubation at 37°C in a humidified air/5% CO2 atmosphere. Four replicates per experimental condition were prepared, and three indentations per replicate were performed.

For the unpopulated fibrin, there was a linear (R=0.983) relationship between the indentation stiffness and fibrinogen concentration. Also, there was a nonlinear relationship between indentation stiffness and concentration of collagen in the fibrin/collagen constructs. Finally, although in most cases there was no measurable change in the stiffness of the cell-populated tissue constructs with incubation time, in one of the cell-populated formulations, however, the indentation stiffness decreased steadily with increasing incubation time. These results are analyzed within the context of existing analytical micromechanics models for the relationships between scaffold structure, e.g., porosity / fibril diameter, and stiffness.
The Influence of the Thermal Treatment of Hydroxylapatite Scaffolds on the Physical Properties and the Bone Cell Ingrowth Behaviour
Authors: Woesz Alexander , Rumpler Monika , Manjubala Inderchand , Pilz Christine , Varga Franz , Stampfl Juergen , Fratzl Peter
Published: June 2019

The material bone consists of a biopolymer matrix (collagen) reinforced with mineral nanoparticles (carbonated hydroxylapatite), forming a natural composite which builds up a dense shell on the exterior and a network of struts with a mean diameter of 200μm in the core of many bones. The architecture of the foamy inner part of bones (spongiosa) is determined by loading conditions. The architecture strongly influences the mechanical properties of cellular solids together with the apparent density and the material it consists of. In addition, the ingrowth of bone cells into porous implants depends on pore size, size distribution and interconnectivity. From this it is clear that the possibility to design the architecture of a bone replacement material is beneficial from a biological as well as a mechanical point of view. Our approach uses rapid prototyping methods, ceramic gelcasting and sintering to produce cellular structures with designed architecture from hydroxylapatite and other bioceramics.

The influence of sintering temperature and atmosphere on the physical properties of these scaffolds was investigated with x-ray diffraction and scanning electron microscopy. Furthermore, the cell ingrowth behaviour was determined in cell culture experiments, using the praeosteoblastic cell line MC3T3-E1, derived from mouse calvariae. The cell ingrowth behaviour was evaluated during a culture period of two and three weeks, by light microscopy and afterwards by histology after embedding and Giemsa-staining.

The phase composition of the material was found to change with increasing sintering temperature and its surface characteristics was influenced by the sintering atmosphere. These changes also affected the cell ingrowth behaviour. In some experiments, the osteoblasts-like cells were found to cover the whole external and internal surface of the scaffold. The cells produced extracellular matrix consisting of collagen, which eventually filled nearly all the pores. In particular, the cells had the tendency to fill any crack or opening in the scaffolds, and to generally smooth the surfaces.

In conclusion, rapid prototyping and ceramic gelcasting allows the freeform fabrication of porous bioceramics with controlled architecture. Such structures made of hydroxylapatit were found to support the growth of mouse osteoblasts.
Domain Switch Toughening in Polycrystalline Ferroelectrics
Authors: Landis Chad M. , Wang Jianxin
Published: June 2019

Mode I steady crack growth is analyzed to determine the toughening due to domain switching in poled ferroelectric ceramics. A multi-axial, electromechanically coupled, incremental constitutive theory is applied to model the material behavior of the ferroelectric ceramic. The constitutive law is then implemented within the finite element method to study steady crack growth. The effects of mechanical and electrical poling on the fracture toughness are investigated. Results for the predicted fracture toughness, remanent strain and remanent polarization distributions, and domain switching zone shapes and sizes are presented. Finally, the model predictions are discussed in comparison to experimental observations.
Simulation of a Ferromagnetic Shape Memory Actuator in a Magnetic Field
Authors: Krevet B. , Kohl M.
Published: June 2019

In this work, we present simulations of the thermo-magneto-mechanical performance of a ferromagnetic SMA microactuator in the inhomogeneous field of a CoSm permanent magnet and compare it with experimental results. For the simulations, a combination of different finite element (FEM) programs is used allowing the coupling of electrical, thermal, magnetic and mechanical properties. The field of a permanent magnet is calculated along the trajectory of the microactuator, from which the magnetic forces Fmag and their gradients are derived. Shape memory forces FSME are calculated based on a two-phase macromodel. Both forces, Fmag and FSME, determine the quasi-static behavior of a NiMnGa microscanner, which has been proposed recently.
Internal Stress Generation During Switching of Ferroelectrics
Authors: Haug Anja , Onck Patrick R. , Giessen Erik Van der
Published: June 2019

Progressive switching of grains in ferroelectric materials leads to internal stresses, which may give rise to degradation of the material or even fracture. Here we propose a two-dimensional multigrain model for ferroelectric polycrystal. The numerical computations employ the nonlinear micromechanics model of Huber et al. [1] for each grain. Results for the macroscopic response, butterfly and hysteresis loops, as well as internal stress and electric field distributions are presented.
Finite Element Modeling of Piezoelectric Actuators and Sensors: Local Analysis of the Ferroelectric and Ferroelastic Effects
Authors: Elhadrouz M. , Zineb T. Ben , Patoor E.
Published: June 2019

A new electromechanical finite element is implemented in the Abaqus F.E. code. It takes into account the ferroelectric and ferroelastic behavior. It is represented by a developed phenomenological constitutive law using two internal variables (remnant ferroelastic strain and remnant polarization) and two loading surfaces (electrical and mechanical ones). Saturation phenomena and depolarization under compression mechanical loading are taken into account.

In order to lead to a more accurate description of the domain switching mechanisms, a micromechanical single-crystal ferroelectric and ferroelastic constitutive law was also developed.

The self consistent scale transition technique will be adopted to derive the polycristalline behavior. The results that were obtained by the micromechanical and phenomenological approaches will be compared in order to identify material parameters that will be introduced in the F.E. modeling.
Fully Coupled 3-D Modelling of Ferroelectric Polycrystalline Material Behavior
Authors: Mehling V. , Tsakmakis Ch. , Gross D.
Published: June 2019

A thermodynamically consistent phenomenological model for the material behavior of polycrystalline ferroelectric ceramics is presented. The internal state of the material is described by two internal state variables. The first one is a second-order texture tensor, determining a simple orientation distribution function (ODF) for the axes of the crystal unit cells. The second is the vector of relative irreversible polarization. The irreversible strains are derived from the ODF by volume averaging. The polarization saturation states are calculated by summing up the possible contributions of all cells to the overall polarization. An invariant formulation of the piezoelectric law is applied. Analogous to the thermodynamical framework of rate-independent plasticity, driving forces and evolution laws for the internal state variables are established. Saturation and coupling of the switching behavior are governed by energy barrier functions introduced in the electric enthalpy function. Numerical examples illustrate the models capabilities.
A Density Functional Theory Study of the Catalytic role of Ti atoms in Reversible Hydrogen Storage in the Complex Metal Hydride, NaAlH4
Authors: Chaudhuri Santanu , Muckerman James T
Published: June 2019

Presence of ∼2-4 % Ti is critical for reversible hydrogenation/rehydrogenation in NaAlH4. We have investigated the probable catalytic role of Ti in this complex multi-step process. The present part of our study concentrates on the rehydrogenation reaction, i.e., the reverse reaction that forms NaAlH4 from its constituent binary hydrides. First principles calculations using density functional theory (DFT) show that a particular arrangement of Ti atoms on the surface of Al metal promotes the chemisorption of molecular hydrogen. We also present comparisons with existing experimental data (EXAFS and TEM) to support the existence of such an arrangement on the surface.
Transmission Electron Microscopy Studies of 5-cycled Na Alanate with Ti Based Additive
Authors: Andrei Carmen M. , Walmsley John C. , Holmestad Randi , Botton Gianluigi A. , Srinivasan Sesha S. , Jensen Craig M. , Hauback Bjorn C.
Published: June 2019

Ti doped NaAlH4 hydride is proposed as a reversible hydrogen storage material. In this work, the microstructure of NaAlH4 with 2% TiCl3 additive was studied after 5 hydrogen cycles using a combination of transmission electron microscopy (TEM) techniques including energy dispersive spectroscopy (EDS) X-ray analysis. Selected area diffraction and high-resolution (HR) imaging confirmed the presence of the NaH phase in the material. Electron diffraction was dominated by Al. HRTEM showed the presence of edge dislocations, which might influence the hydrogen diffusivity process in these materials.
The Influence of Hydrogen on the Electrical and Photoelectric Properties of Photodiodes Based on Indium Monoselenide
Authors: Drapak S.I. , Kaminskii V.M. , Kovalyuk Z.D. , Netyaga V.V.
Published: June 2019

Influence of hydrogen intercalation on indium monoselenide is investigated measuring electrical properties of based on it such photosensitive structures as metal-insulator-semiconductor (MIS) and Mott diode (MD). It is established that intercalation of the basic semiconductor with hydrogen leads to the improvement of diodic properties of the MIS structures whereas those for the MD structure becomes worse. For the both structures charge transfer mechanisms are analyzed on the basis of their band diagrams.
Synthesis and Characterization of Nanoscale Transition Metal Complex for Hydrogen Storage
Authors: Srinivasan Sesha S. , Smith Matthew T. , Deshpande Deepak , Stefanakos Eias K. , Goswami Yogi , Jurczyk Michael , Kumar Arun , Kumar Ashok
Published: June 2019

The development of light weight hydrogen storage systems with high volumetric and gravimetric hydrogen densities is indeed essential for the on-board fuel cell vehicular applications [1]. Among the different hydrogen storage systems designed and developed so far, Ti- doped sodium aluminum hydrides exhibit potential promise of reversible hydrogen storage capacity (4-5 wt.%) at moderate temperatures [2,3]. However, the poor cyclic stability of these hydrides due to the partial reversibility of the two step reactions necessitates the development of exotic materials or tailoring the known hydride systems. On the other hand, transition metal complex hydrides, TMHx(T = Mg; M = Fe, Co, Ni) have also been identified as potential candidates for hydrogen storage [4-6] and/or analogous to alanates [7]. These hydrides especially Mg2FeH6, have shown excellent cyclic capacities (more than 500 cycles) even without a catalyst [8]. Besides, Mg2FeH6possesses the highest volumetric and gravimetric hydrogen densities of 150 kg/m3and 5.6 wt.% respectively [9]. However, at low temperatures, the rate of release of hydrogen and the effective reversible hydrogen capacity seems poor. Recent reports declared that the enhancement in the cycling kinetics and reduction in the operating temperature is very much possible by using a distorted nano-scale Mg structure [10, 11], doping the host lattice with Ti- species and/or lattice substitution [12]. Keeping these facts in view, the present investigation aims to improve the sorption kinetics and thermodynamics of Mg2FeH6, by 1) preparing nano-scale Mg-Fe-H system using mechano-chemical synthesis process, 2) surface localized catalyst (Ti- species) doping and 3) cationic substitution of Na+/Li+for Mg2+by incorporating NaH/LiH. The synergistic behavior of the tailored nano-scale transition metal complex for hydrogen storage is outlined.
Effect of Physical State of Carbon Nanocomposite on Hydrogen Adsorption and Desorption
Authors: Kumar Arun , Jurczyk Michael U. , Kumar Ashok , Stefanakos Elias
Published: June 2019

The inclusion of multiwalled carbon nanotubes in a conjugated polymer matrix results in extensive alterations in the polymer morphology. When the physical state of a substance is changed, heat is either absorbed or liberated but the temperature remains constant. The flexibility of chain molecules arises from rotation round the saturated chain bond moreover the potential energy barriers hindering this rotation. It is not surprising therefore that the flexibility of polymer chains is an important factor in determining their melting points and stability. If the substitution of carbon nanotube is random the primary effect is a decrease in the degree of crystallinity. These microstructures are governed by the balance of interactions between hydrodynamic forces (both viscous and elastic) and the forces working to retain the integrity of the disperse particles, such as interfacial tension or, in the case of solid filler and their mechanical strength. Carbon materials have long been shown to absorb as much as 60 wt% hydrogen due to their large surface areas as well as their high surface to volume ratios. In the present approach conducting polyaniline was doped with metal oxide, such as SnO2, as well as carbon nanotubes. The resulting carbon nanocomposite was made in both gel- and solid-state to study the effect of physical state on hydrogen adsorption and desorption by weight percentage. The morphology formation process and its impact on the rheological properties of complex polymer systems, i.e. polymer blends and composites are being studied. The materials are also compared with regard to their thermal stability using DSC, and further characterized using various techniques such as FTIR. Further experiments are in progress to better understand the nature of the hydrogen storage mechanism.
Group III-nitride Materials for High Efficiency Photoelectrochemical Cells
Authors: Ager J. W. , Walukiewicz W. , Yu K. M. , Shan W. , Denlinger J. , Wu J
Published: June 2019

Two ternary alloys based on III-nitride semiconductor alloys are explored as potential components of photoelectrochemical cells (PECs) for the direct generation of hydrogen using solar energy. For In1-xGaxN, it will be shown using prior measurements of band offsets that spontaneous water splitting can occur for x up to 0.2 and potentially higher. Flat band potential and photocurrent measurements from an n-type epilayer with x = 0.37 will be presented. This initial data appears to indicate that the flat band potential lies just below the H+/H2 from pH 0 – 14. In the case of GaAsxN1-x we will demonstrate that the replacement of a few percent of As in N sublattice drives the bandgap down from the GaN value (3.4 eV) into a range that is attractive for PEC cells [1]. This band gap reduction is explained by the valence band anticrossing that pushes the valence band maximum up initially by 0.5 eV. From the point of view of a PEC cell, this reduces the gap (desirable for efficiency) without compromising the desired H+/H2 overpotential.
Indentation to Probe Atelectasis in Mammalian Lung
Authors: Silva Maricris C. , Hoyos Melissa D , Rooney Jean E , Gouldstone Andrew
Published: June 2019

Of all the internal organs, mechanical behavior of the lung is arguably most closely related to physiologic function. In inflation and deflation, lung parenchyma may be treated as an elastic material with some viscous damping. However, quasi-plasticity is observed, in the form of atelectasis, which is the localized collapse of alveoli under different conditions. General anesthesia in lung is known to increase tendency for pulmonary atelectasis, and this condition is typically removed by mechanical inflation to high pressures, which can be hazardous. The specific mechanisms of atelectasis are not fully known, one reason for this being the difficulty in developing a direct characterization method to perform causal investigations. In a previous abstract, we described the potential for controlled indentation tests to probe atelectatic tendency in lung. In this talk, we present the first results of ‘hardness testing’ on dog and rabbit lung, using different inflation schemes. Specifically, we indented excised lungs at physiologic pressures, inflated with air, pure oxygen, and 0.2% isoflurane in oxygen. Between these three conditions, we found marked differences in ‘hardness’ of the lung, when indented with tip radii comparable to that of ribs. That is to say, large contrasts in residual impressions, as well as re-inflation behavior, were observed. In addition, effects of different inflation gases occurred within a much shorter time than previously reported in other surgical experiments, indicating perhaps different, faster mechanisms controlling atelectasis than previously considered.
Fracture and Energy Partitioning in Uncooked and Cooked Noodles
Authors: Sui Zhongquan , Corke Harold , Oyen Michelle L. , Lucas Peter W.
Published: June 2019

Humans perform fascinating science experiments at home on a daily basis when they undertake the modification of natural and naturally-derived materials by a cooking process prior to consumption. The material properties of such foods are of interest to food scientists (texture is often fundamental to food acceptability), oral biologists (foods modulate feeding behavior), anthropologists (cooking is probably as old as the genus Homo and distinguishes us from all other creatures) and dentists (foods interact with tooth and tooth replacement materials). Material scientists may be interested in the drastic changes in food properties observed over relatively short cooking times. In the current study, the mechanical properties of one of the most common (and oldest at 4,000+ years) foods on earth, the noodle, were examined as a function of cooking time. Two types of noodles, each made from natural materials (wheat flour, salt, alkali and water) by kneading dough and passing them through a pasta-making machine. These were boiled for between 2–14 min and tested at regular intervals from raw to an overcooked state. Cyclic tensile tests at small strain levels were used to examine energy dissipation characteristics. Energy dissipation was >50% per cycle in uncooked noodles, but decreased by an order of magnitude with cooking. Fractional dissipation values remained approximately constant at cooking times greater than 7 min. Overall, a greater effect of cooking was on viscoplastic dissipation characteristics rather than fracture resistance. The results of the current study plot the evolution of a viscoplastic mixture into an essentially elastic material in the space of 7 minutes and have broad implications for understanding what cooking does to food materials. In particular, they suggest that textural assessments by consumers of the optimally cooked state of food has a definite physical definition.
Load Carrying Mechanisms in Wood at Different Observation Scales: A Combined Random-Periodic Multistep Homogenization Scheme
Authors: Hofstetter Karin , Hellmich Christian , Eberhardsteiner Josef
Published: June 2019

Wood exhibits a highly diversified microstructure. It appears as a solid-type composite material at a length scale of some micrometers, while it resembles an assembly of plate-like elements arranged in a honeycomb fashion at the length scale of some hundreds of micrometers. These structural features of wood result in different load carrying mechanisms at different observation scales and at different loading conditions. In this paper, we elucidate the main load carrying mechanisms by means of a micromechanical model for wood across different species, based on tissue-independent stiffness properties of cellulose, lignin, and water. The model comprises three homogenization steps, two based on continuum micromechanics and one on the unit cell method. The latter represents plate-like bending and shear of the cell walls, due to transverse shear loading and axial straining in the tangential direction Accurate representation of these deformation modes results in accurate (orthotropic) stiffness estimates, which deviate, on average, by less than 10 % from corresponding experimental results, across a variety of softwood species.