bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanocomposite Scaffolds for Bone Tissue Engineering: Design,
Fabrication, Surface Modification and Sustained Release of Growth
Factor
Authors: Wang Min , Duan Bin
Published: April 2011

From the material point of view, the extracellular matrix (ECM) of bone is a
natural nanocomposite consisting of an organic matrix (mainly collagen) and
inorganic nanofillers (bone apatite) which are inserted in a parallel way
into the collagen fibrils. For human bone tissue repair or regeneration,
nanocomposites consisting of a biodegradable polymer matrix and nano-sized
fillers such as bioactive ceramics or glasses, which mimic the hierarchical
structure of bone, are considered a promising strategy. Combining living
cells with biodegradable materials and/or bioactive component(s), the
concept of tissue engineering first elucidated in the early 1990s
represented a paradigm shift from tissue grafting, with autografts being the
gold standard, or even completely from prosthesis implantation. In
scaffold-based tissue engineering, scaffolds play an important role for
tissue regeneration. Currently, acellular scaffolds with or without
biomolecules such as growth factors are considered as an effective strategy
for certain tissue repair due to their relatively low costs and easier
process to gain surgeons’ acceptance and regulatory approval. In the current
study, integrating an advanced manufacturing technique, nanocomposite
material and controlled delivery of growth factor to form multifunctional
tissue engineering scaffolds was investigated. Three-dimensional,
osteoconductive and totally biodegradable calcium phosphate
(Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite
scaffolds with customized architecture, controlled porosity and
interconnecting pores were designed and fabricated using selective laser
sintering (SLS). The surface of nanocomposite scaffolds was modified with
gelatin and then heparin, which facilitated the incorporation of a growth
factor, recombinant human bone morphogenetic protein-2 (rhBMP-2).
Experimental results demonstrated the effectiveness of this strategy in
guiding the osteogenic differentiation of mesenchymal stem cells. Together
with osteoconductive nanocomposite material and controlled growth factor
delivery, the use of SLS technique to form complex scaffolds provides a
promising route towards individualized bone tissue regeneration.
Bioinspired Artificial Protein Materials: Self-Assembly and
Order from Nano to Macroscale
Authors: Dai Min , Haghpanah Jennifer S. , Yuvienco Carlo , Montclare Jin Kim
Published: April 2011

We describe the biosynthesis and characterization of protein materials
comprised of two distinct self-assembling domains (SADs): elastin (E) found
in tissue for its elastic properties and cartilage oligomeric matrix protein
coiled-coil (COMPcc, C) predominantly locatedin joint and in bones. Based on
earlier studies on protein block polymers comprised these two SADs,
orientation and number of blocks play a crucial role in the overall
stimuli-responsive supramolecular assembly behavior. Here we fabricate a
range of EnC and CEn block polymers in which the E
domain is systematically truncated to explore the effects of the E domain on
the overall physicochemical behavior.
Cross-sectional TEM study of surface modification of nano-structure with gas cluster ion beams
Authors: Toyoda Noriaki , Yamada Isao
Published: April 2011

Surface modification effects on patterned surface with gas cluster ion beam (GCIB) were studied by observation with a cross-sectional transmission electron microscope in order to use it for planarization of patterned media such as discrete track media (DTM) or bit-patterned media (BPM) for future hard disk drives. As a model structure of patterned media, line-and-space or bit patterns were fabricated on Si substrates, and subsequently amorphous carbon films were deposited on them. After Ar-GCIB irradiations on amorphous carbon, it was shown that GCIB preferentially removed bumps or crest on the surface of amorphous carbon at normal incidence. The required thickness for planarization was close to the initial peak-to-valley. At an incident angle of 57°, line-and-space patterns became sharp-pointed shape. On the contrary, line-and-space patterns were planarized without tiny asperity formation at 77°. These results indicate that quite effective planarization of patterned surface is possible using GCIB at normal or glancing angle irradiation.
Defect doping and characterization in oxide single crystals using femtosecond laser
Authors: Kanehira Shingo , Moon Chiwon , Tochigi Eita , Shibata Naoya , Ikuhara Yuichi , Miura Kiyotaka , Hirao Kazuyuki
Published: April 2011

Defects inside oxide ceramics of magnesium oxide (MgO) and sapphire (Al2O3) were formed using femtosecond laser irradiation. The laser irradiance in these ceramics forms various defects classified as dislocations, twins, or nano cracks near the focal point due to the increase of temperature and successive generation of shockwave within several picoseconds. The morphology of defects mainly depends on the crystal structure; dense dislocations inside MgO with a rock-salt type structure, and nanocracks, dislocations, or twins in sapphire with a corundum structure. The TEM analysis revealed that the dense dislocations formed on the two slip planes {110} to form a cross-shaped pattern when the laser beam focused on the (100) plane in MgO. In case of sapphire crystal, cracks propagated from the focal point that has an amorphous structure along R-planes {11-02}, which had the lowest fracture surface energy. The nano crack transformed into the aligned void and dislocation structure during the heat treatment over 1573K, which is one of the crack healing effect.
Nanostructured Engineering Alloys for Nuclear Application
Authors: Hosemann Peter , Stergar Erich , Nelson Andrew T. , Vieh C. , Maloy Stuart A.
Published: April 2011

In advanced nuclear applications, high temperature and a corrosive environment are present in addition to a high dose radiation field causing displacement damage in the material. In recent times it has been shown that Nanostructured Ferritic Alloys (NFA’s) such as advanced Oxide Dispersion Strengthened (ODS) steels are suitable for this environment as they tolerate high dose irradiation without significant changes in microstructure or relevant mechanical properties.

Ion beam irradiation is a fast and cost effective way to induce radiation damage in materials but has limited penetration depth. Therefore, small scale mechanical testing such as nanoindentation and micro compression testing in combination with FIB based sample preparation for micro structural characterization has to be performed allowing a full assessment of the materials’ behavior under radiation environment. In this work two different ODS materials have been irradiated using proton and combined proton and He beams up to 1 dpa at different temperatures. Nanoindentation and LEAP measurements were performed in order to assess the changes in properties of these alloys due to irradiation. The same techniques were applied to intermetallic nanostructured alloys in order to investigate the effectiveness of the metal-intermetallic interface to provide defect sinks for He and radiation damage. It was found that irradiation can cause the formation of intermetallic particles even at room temperature while increasing the material strength significantly.
Comparison of CVD and MOCVD-grown Al2O3 coatings in the performance of cemented carbide cutting tool inserts
Authors: Jaiswal Piyush , Sathar Abdul , Shariff Arshiyan , Saif Mohammed , Dhar Sukanya , Shivashankar S. A.
Published: April 2011

Low-pressure MOCVD, with tris(2,4-pentanedionato)aluminum(III) as the precursor, was used in the present investigation to coat alumina on to cemented carbide cutting tools. To evaluate the MOCVD process, the efficiency in cutting operations of MOCVD-coated tools was compared with that of tools coated using the industry-standard CVD process.

Three multilayer cemented carbide cutting tool inserts, viz., TiN/TiC/WC, CVD-coated Al2O3 on TiN/TiC/WC, and MOCVD-coated Al2O3 on TiN/TiC/WC, were compared in the dry turning of mild steel. Turning tests were conducted for cutting speeds ranging from 14 to 47 m/min, for a depth of cut from 0.25 to 1 mm, at the constant feed rate of 0.2 mm/min. The axial, tangential, and radial forces were measured using a lathe tool dynamometer for different cutting parameters, and the machined work pieces were tested for surface roughness. The results indicate that, in most of the cases examined, the MOCVD-coated inserts produced a smoother surface finish, while requiring lower cutting forces, indicating that MOCVD produces the best-performing insert, followed by the CVD-coated one. The superior performance of MOCVD-alumina is attributed to the co-deposition of carbon with the oxide, due to the very nature of the precursor used, leading to enhanced mechanical properties for cutting applications in harsh environment.
Responses of Carbon Onions to High Energy Heavy Ion Irradiation
Authors: Alduhaileb Raed A. , Xie Kan , Myers Joshua C. , Ayres Virginia M. , Jacobs Benjamin W. , McElroy Kaylee , Bieler T. , Crimp M. , Fan Xudong , Ronningen Reginald M. , Zeller Albert F. , Baumann Thomas , Hirata Atsushi
Published: April 2011

We report evidence for graphene layer rearrangements in heavy ion interactions with carbon onions at 140 MeV and 70 MeV per nucleon kinetic energies. Graphene layer rearrangements have been recently predicted in spherical and cylindrical multi-layer graphene systems. The implications of graphene layer rearrangement on the tribological performance of multi-layer nano-carbons in extreme environments are discussed.
Effect of Seawater on Thermal Behavior of Conventional and Nanophased Carbon/Epoxy Composites
Authors: Hossain Mohammad K , Imran Kazi A , Hosur Mahesh , Jeelani Shaik
Published: April 2011

The effect of seawater on thermal behavior of conventional and nanophased carbon/epoxy composites was investigated in this study. Composites were fabricated with 1 wt.%, 2 wt.%, and 3 wt.% nanoclay by vacuum assisted resin transfer molding (VARTM) process and compared with neat samples with and without exposure to seawater. Thermal characterization was performed by the dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Samples exposed to the seawater for 30- and 60-day periods revealed that samples with nanoclay retained better thermal properties compared to the neat samples. Storage modulus was reduced by 6.28%, 6.76%, 6.15%, and 7.05% for neat, 1 wt.%, 2 wt.%, and 3 wt.% nanoclay infused samples, respectively, after the samples were exposed to seawater for 60 days . From TGA results, it was observed that the thermal stability is not related to nanoclay content and conditoning. Optical microscope (OM) and scanning electron microscope (SEM) studies revealed no significant change in surface morphology in the 30-day conditioning samples.
Dynamics of Charge Transfer Excitons Recombination in
Polymer/Fullerene Solar Cells
Authors: Hallermann Markus , Deschler Felix , Berger Josef , von Hauff Elizabeth , Da Como Enrico
Published: April 2011

Among the different recombination mechanisms in organic solar cells the
photoluminescence (PL) of charge transfer excitons (CTEs) has been
identified has one of the most important, impacting both the open circuit
voltage and the short circuit current. Here, we study their recombination
dynamics, monitoring the decay of the PL on a time scale spanning three
orders of magnitude from nanoseconds to microseconds. As a model system we
investigate blends of the conjugated polymer
poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV)
and the fullerene derivative [6,6]-phenyl C61-butyric acid methyl
ester (PCBM). We observe that the dynamics of recombination follows a
power-law, which is independent of sample morphology. Upon application of a
transient electric field, which is capable of separating the bound charge
pairs, we observe different dynamics of recombination only for the separated
pairs. Those also follow a power-law and show a strong dependence on the
film morphology.
Krypton and Helium Irradiation Damage in Yttria-stabilised Zirconia
Authors: Gilbert M. , Davoisne C. , Stennett M. C. , Hyatt N. C. , Peng N. , Jeynes C. , Lee W. E.
Published: April 2011

A candidate matrix material for inert matrix fuel (IMF), yttria-stabilised zirconia (YSZ) has been doped with Nd3+ as a surrogate for Pu3+. To simulate and assess the effects of fission gas accommodation and alpha decay on the microstructure, samples of (Y0.1425,Nd0.05,Zr0.8075)O1.904 have been irradiated with 2 MeV 36Kr+ ions, at fluences of 1×1014 and 5×1015 cm−2, and 200 keV 4He+ ions at fluences of 1×1014, 5×1015 and 1×1017 cm-2. Analysis by transmission electron microscopy (TEM) of thin sections prepared by focussed ion beam (FIB) milling revealed damage was only observed at the highest 36Kr+ and 4He+ fluences. Monte Carlo simulations using the TRIM code showed that it is only at these fluences that the level of atomic displacements was sufficient to result in observable defect cluster formation within the material.
PEG-Assisted Hydrothermal Synthesis and Photocatalytic Activity of Bi2Fe4O9 Crystallites
Authors: Cai Dengrong , Li Jianmin , Bu Shundong , Yu Shengwen , Jin Dengren , Cheng Jinrong
Published: April 2011

A facile hydrothermal route assisted by polyethylene glycol (PEG) 400 was utilized to synthesize single-phase Bi2Fe4O9 crystallites. X-ray diffraction results showed the products with PEG 400 of 30 g/L exhibited a preferred growth along the (001) plane. Transmission electron microscopy indicated that the morphology of the as-prepared Bi2Fe4O9 crystallites with PEG 400 were plake-like and rod-like. Strong absorption in visible-light region of the products was characterized by UV-vis diffuse reflectance spectrum (UV-DRS). The photocatalytic activity of Bi2Fe4O9 crystallites was evaluated on degradation of methyl orange (MO) under visible light irradiation. For 3 h irradiation, the degradation ratio was increased to 93% with the aid of a small amount of H2O2. The analysis of FT-IR spectra proved that the Bi2Fe4O9 catalysts were remained stable after the photocalytic reactions.
Atomistic study of the mechanical properties of metallic-glass nanowires
Authors: Koshiyama K. , Shintani K.
Published: April 2011

Melt-growth simulations based on the molecular-dynamics method for both the Cu-Zr and Ni-Al crystalline nanowires of B2 structure are performed to produce metallic-glass nanowires of amorphous structure. Next, tensile deformations of these nanowires are simulated at various temperatures. For the sake of comparison, Cu-Zr and Ni-Al crystalline nanowires of B2 structure are also elongated. It is revealed that the tensile strength of the metallic-glass nanowires is third or fourth of the tensile strength of the crystalline nanowires. Increasing tensile strain, the Cu-Zr crystalline nanowires of B2 structure change their structure twice, whereas the metallic-glass nanowires only decrease their thicknesses locally, and necking takes place.
Large Self-Assembled Peptide Fibers
Authors: Barone Justin R. , Athamneh Ahmad
Published: April 2011

Many systems, including peptide systems, have been identified that
self-assemble into nanometer sized structures. However, continued
self-assembly to the macroscopic scale has remained elusive even though
nature routinely does it. Here, a unique hierarchical peptide self-assembly
process is described from the nanometer to the micrometer scale.
Anomalous Behavior of Polystyrene Blends Using Thermally Induced
Surface Wrinkling
Authors: Torres Jessica M. , Vogt Bryan D.
Published: April 2011

The wrinkling of a 50:50 blend of a high molecular mass (Mn = 990
kg/mol) and low molecular mass (Mn = 1.3 kg/mol) polystyrene (PS)
film is studied as a function of annealing temperature and film thickness.
Both thermal and mechanical wrinkling are utilized to elucidate the apparent
modulus of these PS blend films. The PS blend shows a modulus comparable to
the high molecular weight PS, ≈ 3.2 GPa for mechanical wrinkling at ambient
and thermal wrinkling for T ≤ 50 °C. A sharp decrease in the apparent
modulus of the film occurs when thermal wrinkling occurs at 60 °C or higher.
The calculated modulus in this case is 0.5 GPa, which is significantly below
the modulus determined the neat PS for either Mn when thermally
wrinkled at T > 60 °C. This behavior is attributed to a combination of
surface segregation of the low molecular weight PS as well as the large
difference in bulk glass transition temperature (Tg) of each
component. During thermal wrinkling, the high Mn PS vitrifies
first, while the surface containing primarily low Mn PS is
rubbery; this leads to only the underlayer of PS wrinkling initially and
selection of a shorter wavelength due to the effective thickness. The
increased thermally induced stresses during cooling when the low
Mn PS is vitrified do not change the selected wavelength and
instead only leads to an increase in the wrinkle amplitude. These results
illustrate a potential method to modulate the wrinkle wavelength without
changing the overlayer, which could be useful for patterning
applications.
Sharp Tips from Crumples and Capillary Bridges
Authors: Sambandan Sanjiv
Published: April 2011

We describe two techniques to create sharp tips. The first involves the
buckling of thin metal films deposited on soft, stretchable substrates. The
second involves the formation of narrow necked capillary bridges.
First-Principles Investigation of Structural, Elastic and Electronic Properties of Lanthanide Titanate Oxides Ln2TiO5
Authors: Niu Hui , Gou Huiyang , Ewing Rodney C. , Lian Jie
Published: April 2011

Systematic first-principles calculations based on density functional theory were performed on a wide range of Ln2TiO5 compositions (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Y) in order to understand the correlation between structural, elastic and electronic properties. A complete set of elastic parameters including elastic constants, Hill’s bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio, were calculated. All Ln2TiO5 are ductile in nature, and analysis of densities of states and charge densities suggests that the oxide bonds are highly ionic.
HIGH FREQUENCY TOP-GATED GRAPHENE RF AMBIPOLAR FETs USING LARGE-AREA CVD GRAPHENE AND ADVANCED DIELECTRICS
Authors: Nayfeh Osama M. , Dubey Madan
Published: April 2011

Ambipolar top-gated field effect transistors (FETs) based on large area Cu catalyzed CVD-grown monolayer graphene interfaced to advanced dielectrics have been constructed and examined both for their material and electrical qualities. Interfacing of the graphene with novel insulators/substrates could be tailored for the particular application and provide for enhanced device functionality. In contrast to graphene FETs using SiO2-based top-gate dielectric, which show asymmetric electron/hole mobility (with larger hole mobility), and Dirac point shifted to positive levels, FETs constructed using advanced AlN show Dirac point almost near neutral levels and near symmetric electron/hole mobility. The DP is shifted likely due to compensation of the intrinsic p-type doping by n-type doping introduced by the AlN deposition and potentially via a contribution of polarization-induced carrier density. Finally, we demonstrate a top-gated graphene FET with the first observation of RF operation with GHz cut-off frequency based on large area CVD graphene.
Enhancing the photo-oxidation resistance of PPV-type polymers:
effect of a radical scavenger addition
Authors: Ferreira G. R. , Nowacki B. , de Azevedo E. R. , Akcelrud L. C. , Bianchi R. F.
Published: April 2011

A hindered phenol type radical scavenger (Irganox 1010®) was used to improve
the resistance to photo-oxidation in PPV-type polymers. The degradation was
performed under blue light (460 nm), and the effect of the added compound
was investigated following the intensity variation of absorbance and
photoluminescence spectra. The results showed that the addition of the
compound brought about a significant enhancement in photodegration
resistance without interfering in the electronic properties of the polymers.
These results suggest that the free radical scavenger attenuates the
decrease of the polymer conjugation length induced by the radiation. FTIR
measurements confirm this evidence.
Heterogeneous integration of Polymer Porous Photonic Bandgap
Structure with Xerogel based Biochemical Sensors
Authors: Xu Huina , Liu Ke , Yung Ka Yi , Bright Frank V. , Cartwright Alexander N.
Published: April 2011

We report the heterogeneous integration of a multifunctional sensor based on
polymer porous photonic bandgap (P3BG) structure and xerogel
based luminescence sensor technology. The P3BG structure was
fabricated using holographic interferometry. Initially, holographic
interferometry of a photo-activated prepolymer syrup that included a
volatile solvent as well as monomer, photoinitiator, and co-initiator was
used to initiate photopolymerization. Subsequent UV curing resulted in well
defined lamellae of the polymer separated by porous polymer regions that
created a high quality photonic bandgap structure. The resulting
P3BG structure was then integrated with the xerogel based
luminescence element to produce a luminescence sensor with a selective
narrow band reflector. The prototype xerogel based luminescence sensor
element consisted of an O2 sensing material based on spin coated
tetraethylorthosilane (TEOS) composite xerogel films containing tris
(4,7-diphenyl-1,10-phenanthroline) ruthenium (II)
([Ru(dpp)3]2+) luminophore. We demonstrated
enhancement of the signal-to-noise ratio (SNR) of this integrated
multifunctional sensor while maintaining the same sensitivity to
O2 sensing of the xerogel based element. The resulting
advantages and enhanced SNR of this integrated sensor will provide a
template for other luminescence based assays to support highly sensitive and
cost-effective sensor systems for biomedical applications.
Integrating Colloidal Quantum Dots with Porous Silicon for High
Sensitivity Biosensing
Authors: Gaur Girija , Koktysh Dmitry , Weiss Sharon M.
Published: April 2011

We aim to utilize the high surface area of a porous silicon (PSi) matrix
coupled with semiconductor quantum dot (QD) amplifiers for ultrasensitive
optical detection of small biomolecules using a dual-mode detection scheme.
In our system, QDs attached to the target biomolecule serve as signal
amplifiers by providing an additional refractive index increase beyond that
of the smaller target molecules. The strong photoluminescence (PL) from the
QDs serves as a secondary indication of target molecule attachment in the
pores. A resulting increase in optical thickness of ∼190 nm and detection
sensitivity of ∼700 nm/RIU have been demonstrated for attachment of
glutathione capped CdTe QDs in the porous silicon matrix. Reflectance and PL
measurements, combined with simulations, have been used to characterize the
surface area coverage of the QDs within the porous framework, which is
estimated at 10% for glutathione capped CdTe QDs.
Kinetics of crystallization of biodegradable PHA copolymers: a combined X-ray scattering and micro-indentation study
Authors: Domínguez-Díaz Maraolina , Flores Araceli , Romo-Uribe Angel , Cruz-Silva Rodolfo
Published: April 2011

Wide Angle X-ray scattering (WAXS) and indentation hardness have been used to study the development of crystallinity at room temperature of biodegradable poly(hydroxybutyrate) (PHB) and its copolymer with hydroxyvalerate (PHB/HV) containing 12% of valerate. Measurements were carried out immediately after quenching the samples from the molten state (200 ºC) in ice water and over two weeks of storage at room temperature. WAXS showed that the crystallization of the PHB-based polymers initiated within the first minutes of storage at room temperature, the copolymer displaying a higher rate of crystallization than the homopolymer. For all samples, the degree of crystallinity,α, nearly reached a plateau value within the first hour of crystallization. Concurrently to the development of crystallinity, microhardness values,H, clearly rose as crystallization occurred. Monitoring the crystallization for over two weeks showed that after the rapid increase ofαandH, there was a slow monotonic growth of these properties. A correlation between nanostructure and microhardness is found at all stages of the crystallization process.
Computational Studies of the NiTi Alloy System: Bulk, Supercell, and Surface Calculations
Authors: Stott Amanda C. , Abel Phillip B. , DellaCorte Christopher , Pepper Stephen V. , Dixon David A.
Published: April 2011

Plane wave ab initio density functional theory (DFT) calculations of the B2 NiTi (100), (110), and (111) surfaces, the B2 and B19´ phases of NiTi, and the supercell structures of NiTi, Ni4Ti3 and Ni3Ti are reported. Electronic energies from the electronic structure calculations are used to assess relative stability of the different surface and supercell geometries.
Evaluation of Crack Growth Retardation Effect Due to Nano-scale Voids Based on Molecular Dynamics Method
Authors: Taniguchi Shin , Kameda Toshihiro
Published: April 2011

This study has investigated the crack growth retardation effect due to plural nano-scale voids in Cu single crystals using a molecular dynamics (MD) method. Focusing on an interaction between nano-scale voids and dislocations, we have evaluated the optimum placement for crack growth retardation. MD simulations showed that the dislocation activity was further enhanced due to plural nano-scale voids continuously placed on the primary slip direction. The significant ductility enhancement and slight yield stress increase due to the crack shielding effect of nano-scale voids were observed.
In Situ Spectroscopy and Modeling of Deformation Behavior of Nanoscale Interfacial Materials
Authors: Suzuki Takakazu , Suetaka W. , Suzuki A. , Sato T. , Suzuki T.
Published: April 2011

In this work, the behavior of molecules in thin-film lubricants, several tens of nanometers thick, is studied by in situ reflection infrared spectroscopy and by molecular dynamics simulations. The effect of fatty acid additives on the properties of these interfacial films is also studied. The results of these experiments are presented and interpreted, and the latest outcomes of molecular dynamics simulations are discussed. It is concluded that the molecular orientation in thin films of interfacial materials is markedly affected by the use of additives.
Accurate modeling of molecular crystal through
dispersion-corrected density functional theory (DFT-D)
method
Authors: Schatschneider Bohdan , Liang Jian-jie
Published: April 2011

Crystal structure, pressure response, and polymorph transformation were
investigated for crystalline indole through dispersion-corrected density
functional theory (DFT-D) method. An accurate, nonempirical method (as in
the latest implementations of CASTEP) is used to correct for the general DFT
scheme to include van der Waals interactions important in molecular
crystals. Ambient structural details, including space group symmetry,
density, and fine structural details, such as bicyclic angles, have been
reproduced to within experimental accuracy. Pressure response of the
structure was obtained to isostatic pressure up to 25 GPa, in increments of
1 GPa. Evolution of space group symmetry and the bicyclic angle were mapped
as a function of pressure. A previously unknown phase transformation has
been identified around 14 GPa of isostatic pressure. Total energies of the
phases before and after phase transformation are nearly identical, with a
phase transformation barrier of 0.9 eV. The study opens up the door to
reliable DFT investigations of chemical reactions of crystalline aromatic
systems under high pressure (e.g. formation of amorphous sp3
hybridized phases).
ENERGY STORAGE, RELEASE, AND DISSIPATION IN THE GECKO ADHESION
SYSTEM
Authors: Puthoff Jonathan B. , Prowse Michael , Wilkinson Matt J. , Autumn Kellar
Published: April 2011

Different types of biological adhesion can be categorized according to the
length scales, structures, and materials involved. The setal adhesion system
of the gekkonid lizards occupies a hierarchy of scales from the toes (~ 1
cm) to the terminal spatular pads on the setal branches (~ 100 nm). This
unique combination of scale and foot-hair morphology allow the animal
robust, controllable, and near-universal adhesion via van der Waals
attraction, but it is also apparent that the mechanical behavior of the
β-keratin plays an important role in an animal’s climbing ability.
Experimental results show a four-fold increase in the viscoelastic loss
tangent of β-keratin, alongside a substantial increase in adhesion of setal
arrays, over a range of relative humidity from 10 to 80%. A model of
single-spatular deformation predicts that the elastic energy stored in the
setal branches, energy which is not completely recovered on detachment, is
strongly influenced by these properties changes. The enhanced dissipation
characteristics of the system explain the effects of environmental humidity
on the clinging ability of geckos.
Characterization of Erythrocytes in the Sickle Cell Trait
Authors: Maciaszek Jamie L. , Lykotrafitis George
Published: April 2011

Atomic force microscopy (AFM) allows for high-resolution topography studies of biological cells, measurement of their mechanical properties, and quantification of protein-protein interactions in physiological conditions. In this work, AFM was employed to investigate morphological, material, and chemomechanical properties of red blood cells from human subjects with sickle cell trait. We measured the stiffness of the cells and demonstrated that the Young’s modulus of pathological erythrocytes was three times greater than in normal cells. A single molecule AFM method was employed to report that erythrocytes from human subjects with the sickle cell trait express a greater number of the laminin receptors BCAM/Lu (p < 0.05) than erythrocytes from normal human subjects. Observed differences indicate the effect of sickle hemoglobin in the erythrocyte and possible changes in the organization of the cell cytoskeleton and membrane proteins associated with the sickle cell trait.
Hierarchical computational approaches of the effects of interstitial and vacancy loops on plastic deformation
Authors: Tsuru Tomohito , Aoyagi Yoshiteru , Kaji Yoshiyuki
Published: April 2011

Hierarchical modeling based on atomistic and continuum simulations were established to describe the fundamental characteristics of plastic deformation in irradiated materials. Typical irradiation defects of a self-interstitial atom (SIA) loop and vacancy loop are considered. At first atomic models, including a SIA loop and a vacancy as well as a straight dislocation loop in single crystals were constructed. Constant strain is applied to each model and the equilibrium configuration under deformation is calculated by a molecular statics simulation. Maximum shear stresses in various radii of irradiated defects are stored in a database for the continuum mechanics analysis. Then local interaction events between glide dislocation and irradiation defects were introduced through crystal plasticity finite element analysis. In this model the effect of radiation hardening was considered by referring to the experiment. We found that softening after the first yield event is caused by annihilation of irradiation defects resulting from unfaulting of the radiation defects.
Characterizing the Role of Deformation during Electrochemical Etching of Metallic Films
Authors: Kumar Anil , Hsu Keng , Jacobs Kyle , Ferreira Placid , Fang Nicholas X.
Published: April 2011

Electrochemical dissolution of ionic species into a solid is an area of great interest in several fields including nanoscale patterning and energy storage. Such dissolution is strongly influenced by several factors e.g., work function difference, dislocation density, grain size, and number of grain boundaries. These parameters are strongly influenced by mechanical deformation of the ionic conductor. Here we characterize such a system of silver (Ag) and silver sulfide (Ag2S), where incorporation of Ag into the solid ionic conductor, Ag2S, is dramatically influenced by mechanical deformation. We show more than three-fold dissolution rate enhancement when the polycrystalline conductor is compressed to one-third of its original size. We attribute this enhancement to increased dislocation density which is supported by the high current densities observed during dissolution. Additionally, reduced electronic currents suggest most of this contribution comes from increased reaction at the metal-conductor interface. Our studies have important applications in areas involving ionic transport including direct metal patterning and energy storage technology.
Electrical and Structural Diagnostics of Barium Strontium Titanate (BST) Thin Films
Authors: Ketkar Supriya , Ram Manoj Kumar , Kumar Ashok , Weller Thomas , Hoff Andrew
Published: April 2011

The properties of radio frequency, rf magnetron sputtered Barium Strontium Titanate (Ba1-xSrxTiO3), BST, thin films were investigated and compared with BST thin films deposited by sol-gel method with the aim of determining relationships between the oxide deposition parameters, the film structure, and the electric field dependence. This work presents noncontact electrical characterization of BST films using Corona Kelvin metrology (C-KM) which has been employed earlier only in the silicon industry. The films were structurally characterized using thickness profilometer, X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. The use of sol-gel technique to fabricate small area metal-insulator-metal (MIM) structures is found to be beneficial from the point of saving fabrication time and production costs.
Influence of Nanoindenter Tip Radius on the Estimation of the Elastic Modulus
Authors: Gadelrab Karim R. , Chiesa Matteo
Published: April 2011

Nanoindentation results are very sensitive to tip rounding and neglecting the value of the tip radius produces erroneous estimation of the material elastic properties. In this study we investigate the effect of tip radius on the estimation of the Elastic modulus by means of finite element analysis of Berkovich and conical tips with different tip radii. Our numerical results were already supported by an experimental study on fused silica with Berkovich tips with different tip radii. The use of classical Oliver Pharr equation overestimated the Elastic modulus. A new analytical model that modifies the Oliver Pharr equation to consider the value of the tip radius is employed to derive the Elastic modulus from load displacement curves yielding improved results compared to the classical Oliver Pharr equation.
Bottom-up Modeling of the Elastic Properties of Organosilicate Glasses and their Relation to Composition and Network Defects
Authors: Knaup Jan M. , Li Han , Vlassak Joost J. , Kaxiras Efthimios
Published: April 2011

Organosilicate glasses (OSG), also known as SiCOH or carbon-doped oxide are used as low-k inter-metal dielectrics for integrated circuits. The material must fulfill two conflicting requirements: It has to have low density to reduce the dielectric constant and be mechanically stable enough to withstand mechanical stress during subsequent production steps. Experimental advances in improving their mechanical and electrical properties have not yet been theoretically examined at the ab initio level, due to the relatively large model sizes necessary for amorphous materials. We employ the density-functional based tight-binding (DFTB) method to achieve an accurate description of OSG properties at different compositions. We analyze the influence of composition and topological defects on the density and bulk modulus of non-porous OSG. We find that the dependence of density and stiffness on chemical composition is of different nature. This difference is traced to a transition between different mechanisms of elastic deformation in silica glass and in silicon hydrocarbide, which is also the reason for different sensitivity to topological defects in the two materials.
Inception of plasticity in the presence of vacancies in FCC single crystals: indenter size effect
Authors: Salehinia I. , Perez V. , Weber M. , Bahr D.F.
Published: April 2011

Atomistic simulations of nanoindentation tests were used to study the indenter radius size effect in the presence of vacancies in a (111) single crystal of nickel. For radii from 2 nm to 8 nm, the maximum shear stresses under the indenter at the onset of plastic deformation in crystals with vacancies were compared to those which cause yield in perfect crystals by placing a single vacancy in a position near the maximum shear stress underneath the indenter tip. The effect of the presence of vacancies is lowered by decreasing the indenter radius. Results obtained for several random distributions of vacancies, in the range 3.3e-4 to 0.0033, show that placing a single vacancy near a specific location produces similar results as using larger numbers of vacancies while simplifying the complexity of the simulation. Finally, visualizations of atomic configurations of a single crystal with vacancy concentration of 3.3e-4 for radii of 4 nm and 6nm show that the heterogeneous nucleation is a size dependent phenomenon.
Nondeterministic Multiscale Modeling of Biomimetic Crack Self-Healing in Nanocrystalline Solids under Mechanical Loading
Authors: Karpov Eduard G. , Grankin Mykhailo
Published: April 2011

A nondeterministic multiple scale approach based on numerical solution of the Monte-Carlo master equation coupled with a standard finite-element formulation of material mechanics is presented. The approach is illustrated in application to the long-term evolutionary processes of self-diffusion, precipitation and crack/void healing in nanocrystalline fcc and bcc solids. Effect of static and dynamic loading patterns on the crack healing rates are investigated. The approach is widely applicable to the modeling and characterization of advanced functional materials with evolutionary internal structure, as well as emerging behavior in materials systems.
Micro/Nano Structure and Morphology of Multi-Phase Polymer/Oxide Composites Prepared by Powder Melt Processing
Authors: Giancola Giorgiana , Lehman Richard
Published: April 2011

Powder polymer processing techniques were evaluated as a means to generate homogeneous immiscible polymer blends without the high residence times at elevated temperature and high shear rates required by extrusion. Using emulsion polymerized and cryogenically jet pulverized PMMA and HDPE powder precursors, blends were prepared with morphologies comparable to extruded blends. Advanced EDS imaging methods combined with SiO2 marker spheres enhanced electron imaging and analysis of all blend phases. These processing methods will be useful in producing polymer blends from fragile polymers, such as those used in biomedical applications, that cannot tolerate the temperature or shear rates of conventional melt processing.
Effect of Ag Content on Electrical Conductivity and Tensile Properties of Cu-Ti-Ag Alloys
Authors: Jung Taek-Kyun , Joh Dong-Woo , Lee Hyo-Soo , Kwon Hyuk-Chon
Published: April 2011

Effects of Ag content on microstructure, mechanical properties, and electrical conductivity in long time aged Cu-Ti-Ag alloys were investigated. In short time ageing condition, both electrical conductivity and mechanical properties were enhanced by Ag addition. On the other hand, in long time ageing condition, Ag addition showed a faster deterioration of mechanical properties than Ag free CuTi alloys.
Electroless Synthesis of 1.4 nm Pd and Pt Nanoparticles on
Self-Assembled Rosette Nanotubes
Authors: Chhabra Rahul , Fenniri Hicham
Published: April 2011

Electroless synthesis and hierarchical organization of 1.4 nm Pd and Pt
nanoparticles (NPs) on self-assembled Rosette Nanotubes (RNTs) is described.
The nucleated NPs are nearly monodisperse and reveal supramolecular
organizations guided by RNT templates. Interestingly, the narrow size
distribution is attributable to unique templating behavior of RNTs. The
resulting metal NP-RNT composites were characterized by Atomic Force
Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission
Electron Microscopy (TEM). X-ray Photoelectron Spectroscopy (XPS) was also
performed to confirm the nature and composition of RNT-templated NPs.
Deformation Mechanisms, Microstructure and Mechanical Properties of Nanoscale Crystalline and Noncrystalline Materials in Different Temperature Ranges
Authors: Milman Yuly V.
Published: April 2011

A review of the influence of nanoscale structural elements on the mechanical properties of crystals, quasicrystals, and metallic glasses (MG) is presented. Temperature ranges of cold, warm, and hot deformation are distinguished for crystalline materials, but a nanocrystalline (NC) structure may be formed by severe plastic deformation in the temperature ranges of warm and hot deformation. The plasticity characteristic obtained by indentation can be used for the characterization of low-ductile NC materials. The main features of the plastic deformation mechanisms of NC materials, including results obtained by molecular dynamic simulation, are considered.

For MG, the following two problems are discussed: the comparison of the yield stresses for NC and MG and the possibility of strengthening of MG by disperse crystalline nanoscale particles.

Quasicrystals with nanosize grains, which are also called nanoquasicrystals (NQC), form a separate class of materials. The mechanical properties of NQC and crystalline materials strengthened by NQC particles are analyzed. Dispersion hardening of metals by NC particles was the first application of nanoscale structures for structural materials. New possibilities of such strengthening are considered.
Fluorescence of Two-dimensional Patterned Photosynthetic Proteins onto Gold surface
Authors: Furukawa Rei A. , Yajima Shunsuke , Nozaki Shinji , Dewa Takehisa , Nango Mamoru
Published: April 2011

Photosynthetic membrane proteins convert solar light into chemical energy in a significantly high efficiency. Up-to-date reports of the photosynthetic bacterium suggest that such effective light conversion is due to the energy transfer between two light-harvesting (LH) protein complexes that are patterned in two dimensions. In this report, LH complex isolated fromRb. sphaeroideswas immobilized onto a patterned gold surface with self-assembled monolayers (SAMs) and lipid bilayers at two main objectives: (1) micron-scale patterning of LH complex, and (2) prevention of quenching for pattern observation.
FET-based biosensor incorporating a conductometric
bioreceptor
Authors: Vercik Andrés
Published: April 2011

Novel strategies of transduction may help to improve the biosensor
performance by enhancing its sensitivity or linearity or by allowing a
better integration with the electronics, which in turn favors the
miniaturization of the sensing devices. In this work, a combination of a
conductometric element containing the bioreceptor with a MOSFET is proposed
as a transduction strategy. Simulations of the gate voltage and drain
current versus conductance curves are used to confirm the feasibility of the
proposed strategy. One of the advantages of the presented device is that the
sensing element can be deposited by back-end processes compatible with
current IC technology.
Gold Nanoparticle Enlargement Coupled with Fluorescence Decrease
for Highly Sensitive Detection of Analytes
Authors: Lim Seong Yoon , Kim Jae Hong , Lee Joon Seok , Park Chan Beum
Published: April 2011

We present a versatile and facile route for highly sensitive detection of
analytes through coupling the enlargement of gold nanoparticles (Au NPs)
with fluorescence decrease. The fluorescence intensity of dye molecules
(e.g., fluorescein or rhodamine B) significantly decreased with the
increasing concentration of reducing agents, such as hydrogen peroxide and
hydroquinone. The sensitivity for the detection of reducing agents was much
higher than other detection methods based on the absorbance measurement of
enlarged gold nanoparticles or quantum dot-enzyme hybridization. We could
successfully detect acetylthiocholine with the detection limit of several nM
orders, using an enzymatic reaction by acetylcholinesterase, a key route for
the detection of toxic organophosphate compounds. The fluorescence
decreasing approach described in this work requires only a simple addition
of fluorescence dye to the reaction solution without any chemical
modification. The strategy of fluorescence decrease coupled with
nanoparticle growth will be applied on the fluorescent substrate to develop
detection templates for highly sensitive optical biosensor.
Biomolecular material systems with encapsulated interface
bilayers
Authors: Sarles Stephen A. , Leo Donald J.
Published: April 2011

In this paper we present a novel approach for interface bilayer formation in
which the uptake of an aqueous lipid vesicle solution by two polymeric
hydrogels contained in a substrate causes the gels to swell so as to come
into contact within an internal oil-filled region of the device. An
interface bilayer, similar to those formed using the droplet interface
bilayer (DIB) method, forms upon contact in oil between the lipid-encased
ends of the two gels. Experimental measurements provide initial evidence
that gel swelling enables automatic bilayer formation within a few minutes
after the addition of lipid solution. The approach presented herein works
toward the development of a new portable, easy-to-use screening platform
that features tailored interface bilayers for a wide variety of screening
applications.
Characterization on the Viscoelastic Property of PDMS in the
Frequency Domain
Authors: Du Ping , Lin I-Kuan , Lu Hongbing , lin Xi , Zhang Xin
Published: April 2011

A key issue in using Polydimethylsiloxane (PDMS) based micropillars as
cellular force transducers is obtaining an accurate characterization of
mechanical properties. The Young’s modulus of PDMS has been extended from a
constant in the ideal elastic case to a time-dependent function in the
viscoelastic case. However, the frequency domain information is of more
practical interest in interpreting the complex cell contraction behavior. In
this paper, we reevaluated the Young’s relaxation modulus in the time domain
by using more robust fitting algorithms than previous reports, and
investigated the storage and loss moduli in the frequency domain using the
Fourier transform technique. With the use of the frequency domain modulus
and the deflection of micropillars in the Fourier series, the force
calculation can be much simplified by converting a convolution in the time
domain to a multiplication in the frequency domain.
Microphase-separated block copolymer film anchored on ITO substrate with newly designed self-assembled monolayer
Authors: Goda Takenori , Hadano Shingo , Iyoda Tomokazu
Published: April 2011

The surface of Indium-tin-oxide (ITO) substrate was modified with a newly designed silane coupling molecule bearing azobenzene moiety. The silane coupling molecules formed self-assembled monolayer (SAM) on pretreated ITO surface. The SAM growth and coverage were quantified by contact angle measurement and X-ray photoelectron spectroscopy (XPS). The silane coupling molecules improved the adhesion between the ITO surface and an amphiphilic block copolymer (BC) thin film, which consists of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) with azobenzene mesogens, because the azobenzene moieties of the SAM anchor the liquid crystalline PMA azobenzene domains of BC.