bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Composition and Morphology of Titanium Surface Oxides
Authors: Lausmaa J. , Mattsson L. , Rolander U. , Kasemo B.
Published: June 2019

Titanium has emerged as one of the most tissue-compatible metallic materials. The high degree of biocompatibility is intimately connected with the oxide that forms on the metal surface. In the present work a broad characterization has been made of titanium samples pretreated both by presently used clinical procedures (mechanical machining, ultrasonic cleaning and autoclaving) and by alternative preparation procedures such as electropolishing and anodic oxidation. The former samples are found to have a surface oxide of TiO2 which is 30–50 Å thick, with some trace element contamination and a relatively large carbon content (30–50 % of a monoatomic layer). The anodically oxidized samples also consist of TiO2 with an oxide thickness range of 50–2000 Å, but the morphology and crystallinity of the anodic oxides are found to depend on thickness and preparation conditions.

The main methods of investigation used in the present study were ESCA, SIMS and transmission electron microscopy.
Biomaterials in Ophthalmology A Generalist's Overview
Authors: Lee J. Michael
Published: June 2019

For the biomaterials scientist, the eye presents unique problems, principally because the maintenance of optical function is paramount. This paper concentrates on some current challenges in the development of devices to be placed in the optical path: from air to tear film, cornea, aqueous humour, pupil, lens, vitreous humour, and finally to the retina. Optical clarity during contact lens wear depends on control of deposits from tear film components (by patient performed cleaning procedures) and on continuous oxygen supply to the cornea whose clarity depends on intact epithelial and endothelial cells. Intracorneal lenses of contact lens material are possible if intracorneal fluid flow is not compromised. Corneal integrity can also be affected by adhesive endothelial cell damage during intraocular lens implantation, a factor leading to the development of so-called visco-elastic media for anterior chamber use. The associated questions of photodegradation of materials and protection of the optical tissues from photo-toxicity are critical in the eye. Laser surgery is also uniquely valuable in ophthalmology since many procedures can be performed without invasive access. Finally, intraocular lenses can also incur protein adsorption, cellular adhesion, and opacification of the lens capsule which compromise optical performance.
Slow Crack Growth in Dental Composites
Authors: Montes-G. G. M. , Draughn R. A. , Simpson T. H.
Published: June 2019

The fracture properties of selected commercial composite dental restorative materials and a model composite system were studied to determine the influences of the reinforcing phase, exposure to water, and particle/polymer adhesion on crack propagation. The content of inorganic fillers ranged from 36 to 62 volume percent. In the model system the polymer phase approximated that of the commercial products, a constant size distribution of quartz fillers was used, and polymer/particle adhesion was varied. The double torsion test method was employed to measure relationships between applied stress intensity factor and velocity of crack propagation during stable crack growth. In all systems, cracks propagated through regions of high stress concentration at the low end of the velocity range studied (10−7 m/sec to 10−3 m/sec). Wet materials fractured at lower stress intensities than dry materials at all velocities. At high velocities unstable (stick-slip) growth occurred in dry materials with strong filler/matrix interfaces and in wet specimens with initially strong interfaces and less than 41 volume percent filler. In wet conditions, materials with poorly bonded fillers fractured by slow crack growth at stress intensities 10% to 30% below the levels of composites with strong interfaces.
Degradation of Rocks, Through Cracking Caused by Differential Thermal Expansion, in Relation to Nuclear Waste Repositories
Authors: Mclaren J.R. , Davidge R.W. , Titchell I. , Sincock K. , Bromley A.
Published: June 2019

Heating to temperatures up to 500°C, gives a reduction in Young's modulus and increase in permeability of granitic rocks and it is likely that a major reason is grain boundary cracking. The cracking of grain boundary facets in polycrystalline multiphase materials showing anisotropic thermal expansion behaviour is controlled by several microstructural factors in addition to the intrinsic thermal and elastic properties. Of specific interest are the relative orientations of the two grains meeting at the facet, and the size of the facet; these factors thus introduce two statistical aspects to the problem and these are introduced to give quantitative data on crack density versus temperature. The theory is compared with experimental measurements of Young's modulus and permeability for various rocks as a function of temperature. There is good qualitative agreement, and the additional (mainly microstructural) data required for a quantitative comparison are defined.
On the Mechanical Integrity of Ultra Low Dielectric Constant Materials for Use in Ulsi Beol Structures
Authors: Shaffer E. O. , Howard K. E. , Mills M. E. , Townsend P.H.
Published: June 2019

Adherence to the prescript of Moore's law continues to drive materials development for new and lower dielectric constant materials for use as back-end-of-line (BEOL) interlayer dielectric in advanced logic IC's. As is the case for the current generation of low-K materials (<3.0), these ultra-low K materials (<2.2) will need to meet the variety of integration and reliability requirements for successful product development. Excluding the incorporation of fluorine to lower the material polarity, further reductions of dielectric constant can only be achieved by reduced density. Based upon the industry's experience with the current class of full density dielectrics, process integration may be challenging for ultra-low K materials. This anticipated difficulty derives from the profound differences in material properties, e.g. mechanical integrity, as one lowers the material density, which in turn confounds existing manufacturing processes that have evolved over 35 years based on silicon dioxide.

Minimizing these material and processing differences by extending leveraged learning from previous technology nodes is essential for timely and cost-efficient development cycles. As a result, material selection of a full density low-K is somewhat influenced by the ability of that material to be extended into future generations. Understanding how the material properties will change as its density is lowered is vital to this selection process. In this paper, we present a summary of models for calculating effective properties as a function of density and apply these to current low-K materials with emphasis on mechanical integrity. We will also review experimental methods for measuring the mechanical integrity of ultra-low K materials and compare the results to the various models described herein.
The Effect of Fatigue on the Adhesion and Subcritical Debonding of Benzocyclobutene/Silicon Dioxide Interfaces
Authors: Snodgrass Jeffrey M. , Dauskardt Reinhold H.
Published: June 2019

The effect of fatigue loading on microelectronic thin film interfaces has until now been difficult to quantify. Most industrial fatigue testing uses HAST (Highly Accelerated Stress Testing) protocols, which inherently convolutes the effects of mechanical fatigue and the test environment. Our work focuses on isolating the deleterious effects of mechanical fatigue on interfaces, which we have found to be substantial. In this study, the integrity of a low-k polymer interface involving benzocyclobutene (BCB) and silica was examined under a variety of loading conditions. Critical (fast fracture) adhesion values were measured using standard interface fracture-mechanics geometries. Experiments were then conducted to measure the debond growth rate as a function of the applied strain energy release rate under both static and cyclic loading conditions. Our results show that even under room temperature conditions, debond growth rates measured under cyclic fatigue are considerably faster than those observed under static loading. Results are presented detailing the effects of interface chemistry (adhesion promoters), environmental moisture, and test temperature on the resistance of the interfaces to subcritical debonding. Strategies for increasing resistance of dielectric interfaces to fatigue debonding are outlined.
Tacticity and surface chemistry effects on the glass transition temperature of thin supported PMMA films.
Authors: Grohens Y. , Hamon L. , Carriere P. , Holl Y. , Schultz J.
Published: June 2019

The glass transition temperature (Tg) of thin supported films of stereoregular poly(methyl methacrylate) on silicon has been investigated by ellipsometry in temperature. The Tg of the spin coated layers of isotactic PMMA increases for thickness lower than 100 nm whereas a depression of the Tg is observed for the syndiotactic PMMA. This opposite trend in the Tg variation in thin layer between the two isomers evidenced a fascinating effect of the chain organization at an interacting interface. Hydrofluric acid surface etching of the silicon wafer was shown to decrease the threshold thickness at which the change in Tg occurs for both PMMA isomers. The influence of the interfacial interactions along with the tacticity dependent characteristics of the polymer will be discussed.
Simulation of Interfacial Fracture in Highly Crosslinked Adhesives
Authors: Stevens Mark J.
Published: June 2019

The fracture of highly-crosslinked networks is investigated by molecular dynamics simulations. The network is modeled as a bead-spring polymer network between two solid surfaces. The network is dynamically formed by crosslinking an equilibrated liquid mixture. Tensile pull fracture is simulated as a function of the number of interfacial bonds. The sequence of molecular structural deformations that lead to failure are determined, and the connectivity is found to strongly control the stress-strain response and failure modes. The failure strain is related to the minimal paths in the network that connect the two solid surfaces. The failure stress is a fraction of the ideal stress required to fracture all the interfacial bonds, and is linearly proportional to the number of interfacial bonds. By allowing only a single bond between a crosslinker and the surface, interfacial failure always occurs. Allowing up to half of the crosslinker's bonds to occur with the surface, cohesive failure can occur.
Adhesion Enhancement Via Crystalline-Embedded Entanglements in Melt-Processed Layered Structures
Authors: Cole Phillip J. , Macosko Christopher W.
Published: June 2019

Improving the adhesion of polyolefins to glassy polymers is complicated by the semicrystalline nature of the polyolefins. Traditional methods used in glassy polymers to increase the interlayer adhesion, including the addition of a diblock copolymer or the formation of a copolymer throughin situreaction, are still successful with semicrystalline polymers. However, melt miscibility of the adhesion promoting molecules is not the only consideration; co-crystallization can also be significant. Even when co-crystallization is achieved, the reactive method is shown to provide greater fracture toughness than the addition of a pre-made diblock copolymer. In the latter case, the formation of micelles limits the efficiency of the diblock copolymer. Finally, significant adhesion enhancement is attainable in reactive systems with contact times as short as 45 seconds as demonstrated through a multilayer coextrusion of amorphous nylon against a polypropylene-maleated polypropylene blend.
Switching of Surface Properties with Polymer Brushes
Authors: Stamm Manfred , Minko Sergiy , Goreshnik Evgeniy , Usov Denis , Sidorenko Alexander
Published: June 2019

Switchable surfaces were fabricated by grafting of two different polymers: polystyrene (PS) and poly-2-vinylpyridine (PVP) onto the surface of Si-wafers. The binary brushes of various composition, molecular weight and grafting density were synthesized via free radical polymerization initiated by the azo-initiator covalently attached to the surface of Si-wafers. Investigations showed that the binary brushes are very sensitive to the surrounding media. After exposition to a solvent selective for PVP (ethanol, water + HCl) the surface becomes hydrophilic and the top of the layer is covered by PVP. After exposition to a solvent selective for PS (toluene) the surface becomes hydrophobic and the top of the layer is enriched with PS segments. Switching kinetics depends on grafting density and layer composition and varies from several seconds to several minutes at room temperature. Surface morphology of the layers switches as well as the wetting behavior. Results show that the layer reconstruction is reversible and can be repeated many times.
Surface-attached Polymer Networks
Authors: Prucker Oswald , Müller Kristin , Rühe Jürgen
Published: June 2019

In this paper we present three novel routes for the preparation of surface-attached polymer networks. In one system the network is formed in situ at the surface by thermal polymerization in solution and from the surface. Another synthetic route starts with a surface that carries photoreactive groups. Onto this surface a polymer is deposited that also carries photoreactive groups and both the crosslinks of the network and the covalent bond to the surface are formed by UV illumination. The third approach start with the in situ formation of surface-attached copolymers that again carry photoreactive groups that are subsequently linked together by UV light. We present evidence for the successful synthesis of these networks and their superior adhesion on glass surfaces.
Low Temperature Shallow Junction Formation For 70nm Technology Node And Beyond
Authors: Borland John O.
Published: June 2019

Low temperature shallow junction formation is an attractive activation technique for 70nm technology node and beyond as it can easily be integrated into device structures that are formed using disposable spacer (reverse source drain extension formation) or low power CMOS devices using high-k/metal gate stack structures. Therefore, this paper will first review the shallow junction requirements as stated in the 2001 ITRS (international technology roadmap for semiconductors) and it's interpretation to ion implantation shallow junction formation for various dopant activation and annealing techniques. First high temperature (>1000°C) RTA spike, flash or sub-melt laser annealing techniques with oxide or oxynitride/polysilicon electrode gate stack structures will be discussed and its limitations to >8E19/cm3 boron electrically active dopant level due to boron solid solubility limit in silicon satisfying only the 100nm technology node requirement (2003). Next, higher temperature laser melt annealing (1200°C to 1400°C) will be discussed and it's applicability beyond 70nm node technology (2006) to 25nm node (2016) where boron solid solubility limit is up to 5E20/cm3. However, if high-k (HfO) dielectric/metal electrode gate stack structures are to be used starting at sub-100nm node in 2005 for low power CMOS then low temperature (>700°C) annealing must be used for shallow junction formation to prevent recrystallization and dielectric constant degradation. Using low temperature SPE (solid phase epitaxial regrowth) annealing techniques in the 550°C to 750°C for short anneal times of >5mins., shallow & abrupt junctions 8.0nm deep, >2.0nm/decade with up to 2.5E20/cm3 boron electrical active dopant level can be achieved satisfying the 25nm technology node (2016) requirements.
The Influence of Low Temperature Pre-Annealing on the Defect Removal and the Reduction of Junction Depth in Excimer Laser Annealing
Authors: Baek Sungkweon , Jang Taesung , Hwang Hyunsang
Published: June 2019

The influence of low temperature pre-annealing on p+/n ultra-shallow junction was investigated. An ultra-shallow junction was formed by means of B2H6 plasma doping at an energy of 500V. The activation was performed by excimer laser annealing. To study the low temperature annealing prior to laser annealing, furnace annealing at 300°C∼500°C for 5min was performed. Compared with control samples with no pre-annealing, the low temperature preannealing significantly improves junction characteristics, resulting in a reduction of junction depth and a lower leakage current density. A cross-sectional transmission electron microscopy analysis confirmed the lower defect density, which explains the lower leakage current. By optimizing the process conditions, excellent electrical characteristics of the p+/n ultra-shallow junction such as a junction depth of 28nm and a sheet resistance of 250Δ/sq. can be obtained.
Single-Shot Excimer Laser Annealing and In Process Ellipsometry Analysis for Ultra Shallow Junctions
Authors: Noguchi T. , Kerrien G. , Sarnet T. , Débarre D. , Boulmer J. , Zahorski D. , Hernandez M. , Defranoux C. , Laviron C. , Semeria M.N.
Published: June 2019

Single-shot Excimer Laser Annealing (ELA) was performed onto Si surface that was previously B+ implanted with or without Ge+ pre-amorphization. As a result, p+ type USJ (Ultra-Shallow Junction) has been formed. In process analysis, using Infrared Spectroscopic Ellipsometry (IR-SE) has been performed and compared with conventional 4-point probe method. Also, the corresponding crystallinity for the USJ of Si surface has been studied using Ultraviolet-Visible (UV-Vis) Spectroscopic Ellipsometry. In the case of pre-amorphization by Ge+ implantation, the laser energy density threshold required for melting the surface, and therefore for electrical activation, decreased drastically because of the difference in the thermodynamic properties of the amorphized Si. Estimation of the junction depth shows a shallower junction when using UV-SE, as compared to IR-SE. This can be explained by the fact that, in the UV range, the crystallinity of the top layer is predominant while IR-SE is more sensitive to dopant activation. This efficient single-shot ELA is a candidate for the USJ formation for sub-0.1 νm CMOS transistors. The effective method for investigating the activation state related to the crystallinity by using UV-SE and IR-SE is expected to apply as a non-contact analytical tool for USJ formation.
Structural and Optical Properties of the Multilayer Structures Formed by Ge Sub-Critical Insertions in a Si Matrix
Authors: Cirlin George E. , Zakharov Nikolai D. , Werner Peter , Makarov Alexander G. , Tsatsul'nikov Andrei F. , Ustinov Victor M. , Ledentsov Nikolai N. , Egorov Vyatcheslav A. , Gösele Ulrich
Published: June 2019

Si/Ge multilayer structures formed by the deposition of relatively small amounts of Ge layers (less then the critical thickness for 3D islands formation) are obtained by molecular beam epitaxy. Their structural and optical properties are investigated in detail. Appropriate growth parameter of the stacked island structures lead to significant increasing of the luminescence efficiency even at room temperature.
Junction and Profile Analysis using Carrier Illumination
Authors: Clarysse T. , Vandervorst W. , Lindsay R. , Borden P. , Budiarto E. , Madsen J. , Nijmeijer R.
Published: June 2019

Carrier Illumination™ (CI) is an optical technique for non-destructive in-line monitoring of post-anneal junction depth and pre-anneal PAI depth and dose with wafer mapping capabilities. This work intends to extend the use of the CI-measurements from a range-specific quantitative measurement towards a more universal quantitative analysis of junction depth, profile abruptness and implant dose. For that purpose this paper presents a systematic study of the CI response to a wide variety of post anneal implant processes, varying parameters including implant species, dose and energy, annealing condition, and surface preparation.

Samples containing B, BF2 and As-implants with and without Ge PAI layers, with junction depths between 10-120 nm, were measured. In addition near-ideal box-like profiles (as obtained with CVD-growth) were fabricated and measured. For the abrupt CVD profiles, CI measures the junction position with sub-nm resolution independent of the CI-analysis conditions. For more graded profiles resulting from annealed implants, the correlation to the SIMS junction depth becomes a function of generation laser current (which is proportional to the applied power). As the concentration level, at which the correlation is made, can be adjusted over a concentration range of approximately 2x1018 to 2x1019/cm3 by changing the laser current, a route towards correlating the CI measurement with profile abruptness becomes feasible.
A New Ferroelectric Varactor From Water Based Inorganic Precursors
Authors: Dougherty T. Kirk , Drab John , Brand Mike , Kehle Kathleen
Published: June 2019

Solution deposition processes for the production of thin multi-element metal oxide films continue with great interest and varied success. Solution deposition via either sol-gel or MOD (Metal Organic Decomposition) methods are of interest due to the ability to produce a wide variety of compositional products at low capital investment cost. The sol-gel method generally uses hydrolytically sensitive metal alkoxides as the starting materials. Manipulation of the reagents and different hydrolysis rates for multi-element mixtures are issues. The MOD method utilizes large organic acid metal salts as the starting materials. In general, MOD solutions are more hydrolytically stable than the sol-gel solutions. MOD process challenges include large quantities of carbon to be decomposed during the firing, shrinkage and stress of the thin films, variable chemistry in synthesis of the starting materials (especially when the starting materials for the MOD precursors are metal alkoxides), and long reaction times for the synthesis. For both the sol-gel and MOD precursors, toxic and volatile organic chemical (VOC's) solvents are employed as the vehicle.

This paper will review the chemistry-related issues to production of consistent highquality metal oxide films via the MOD process. The fabrication of thin BaxSr(1-x)TiO3 (BST) films is described. A new class of MOD precursor has been implemented using polyether acids as the organic vehicle. These new materials are both water stable and water soluble. High quality BST thin films made from these precursors are described and capacitors made from these films are compared to the aliphatic acid MOD materials. Improved capacitors using lower resistance electrodes and interconnects are described, as well as devices designed specifically for our specific application.
Characteristics Analysis of Saw Filter Using Al0.36Ga0.64N Thin Film
Authors: Kim Sun-Ki , Park Min-Jung , Jang Cheol-Yeong , Choi Hyun-Chul , Lee Jung-Hee , Lee Yong-Hyun
Published: June 2019

AlxGa1-xN sample with x=0.36 was epitaxially grown on sapphire by MOCVD. SAW velocity of 5420 m/s and TCF (temperature coefficient of frequency) of -51.20 ppm/°C were measured from the SAW devices fabricated on the AlxGa1-xN sample, when kh value was 0.078, at temperatures between –30 °C and 60 °C Electromechanical coupling coefficient was ranged from 1.26 % to 2.22 %. The fabricated SAW filter have shown a good device performance with insertion loss of -33.853 dB and side lobe attenuation of 20 dB.
Sub 0.1 μm Asymmetric Γ-gate PHEMT Process Using Electron Beam Lithography
Authors: Sul W. S. , Shin D. H. , Rhee J. K.
Published: June 2019

In this paper, we have studied on the fabrication of GaAs-based pseudomorphic high electron mobility transistors (PHEMT's) for the purpose of millimeter-wave applications. To fabricate the high performance GaAs-based PHEMT's, we have developed unit processes, such as 0.1 μm Γ-gate lithography, silicon nitride passivation, and air-bridge process to achieve high performance of device characteristics. The DC characteristics of the fabricated PHEMT was measured at a unit gate width of 70 μm and 2 gate fingers, and showed a good pinch-off property (VP = -1 V) and a drain-source saturation current density (Idss) of 373.53 mA/mm. Maximum extrinsic transconductance (gm) was 522.4 mS/mm at Vgs = -0.3 V, Vds = 1.5 V, and Ids = 0.5 Idss. The RF measurements were performed in the frequency range of 1.0 ∼ 50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.3 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 4.2 dB of S21 gain were obtained, respectively. A current gain cut-off frequency (fT) of 113 GHz and a maximum frequency of oscillation (fmax) of 180 GHz were achieved from the fabricated PHEMT with a 0.1 μm gate length.
Evidence for Antiferroelectric Behavior in KNbO3/KTaO3 Superlattices
Authors: Sigman J. , Christen H. M. , Fleming P. H. , Boatner L. A. , Norton D. P.
Published: June 2019

The dielectric response in artificially layered 1x1 KTaO3/KNbO3 perovskite superlattice structures is reported. While KTaO3 and KNbO3 are ferroelectric or paraelectric, respectively, superlattices appear antiferroelectric based on an increase in dielectric constant with applied dc bias. This “positive tunability” in dielectric response occurs at the same temperature region where a structural phase transition is observed. This dielectric behavior is inconsistent with the nonlinear response for either paraelectric or ferroelectric materials. However, an increase in the dielectric constant with applied electric field is consistent with antiferroelectric behavior. The antiferroelectric ordering correlates with cation modulation imposed by the superlattice.
Review Molecular Mechanism of Bacterial Magnetite Formation and Its Application
Authors: Matsunaga Tadashi , Okamura Yoshiko
Published: June 2019

Nano-technology has been identified as an area which will bring about new evolutions in materials, devices and processes. The challenges of nano-biotechnology entail manufacturing more sophisticated and highly efficient biosensors and biomaterials at the nano-scale level for use in interdisciplinary fields. Here, we introduce a biomaterial produced by magnetic bacteria, bacterial magnetic particles (BMPs), and the molecular architecture technique we have used for its application.

Magnetic bacteria synthesize intracellular magnets which are encapsulated by lipid bilayer membranes. Sizes of BMPs vary from 50 - 100 nm in diameter, and number over 10 per cell. BMPs are composed of magnetite (Fe3O4) with a single magnetic domain. Easy aqueous dispersion of BMPs enable development of highly sensitive chemiluminescence enzyme immunoassays by the chemical coupling of antibodies on BMP surfaces. BMPs can likewise be used as drug delivery systems employing magnetoliposomes with high capture volumes. We previously reported a technique for preparing recombinant BMPs on which proteins were displayed by gene-fusion. We furthermore applied such recombinant BMPs to biotechnologically-important issues, including novel bioassay platforms for medicine and environmental management. We envisage the production of more refined chemicals and agents through expression on BMPs by gene-fusion followed by simple purification using magnet.
Poly(glycerol sebacate)—A Novel Biodegradable Elastomer for Tissue Engineering
Authors: Wang Yadong , Sheppard Barbara J. , Langer Robert
Published: June 2019

Biodegradable polymers have significant potential in biotechnology and bioengineering. However, for some applications, they are limited by their inferior mechanical properties and unsatisfactory compatibility with cells and tissues. A strong, biodegradable, and biocompatible elastomer could be useful for fields such as tissue engineering, drug delivery, and in vivo sensing [1, 2]. We designed, synthesized, and characterized a tough biodegradable elastomer from biocompatible monomers. This elastomer forms a covalently crosslinked three-dimensional network of random coils with hydroxyl groups attached to its backbone. Both crosslinking and the hydrogen bonding interactions between the hydroxyl groups likely contributes to the unique properties of the elastomer. In vitro and in vivo studies show the polymer has good biocompatibility. Subcutaneous (SC) polymer implants are absorbed completely within 60 days with restoration of the implantation sites to their normal architecture.
Nanoscale Patterning of Antigen on Silicon Substrate to Examine Mast Cell Activation
Authors: Orth Reid N. , Wu Min , Clark Theodore G. , Holowka David A. , Baird Barbara A. , Craighead Harold G.
Published: June 2019

Rat Basophilic Leukemia (RBL) cells are immobilized and stimulated on micro- and nanometer scale patterns of supported lipid bilayers. The patterns are realized as the photolithographically patterned polymer is mechanically peeled away in one contiguous piece in solution. The 0.36 μm2to 4, 489 μm2patches can contain both fluorescent lipids and lipid-linked antigen and provide a synthetic biological substrate for analysis of cell surface receptor-mediated events. 100-nm unilamellar lipid vesicles spread to form a supported lipid bilayer on a thermally oxidized silicon surface as confirmed by fluorescence recovery after photobleaching (FRAP). Aggregation of fluorescently labeled receptors is observed as their coincidence with the patterned antigen. Cell morphology is analyzed with scanning electron microscopy (SEM). Thus, a novel method has been developed for patterning antigen, capturing and immobilizing cells via specific receptors, and spatially controlling antigenic stimulus on the nanoscale.
Effects of Counterface Roughness and Conformity on the Tribological Performance of Crosslinked and Non-crosslinked Medical-Grade Ultra-High Molecular Weight Polyethylene
Authors: Chawan A. D. , Chakravartula A. M. , Zhou J. , Pruitt L. A. , Ries M. , Komvopoulos K.
Published: June 2019

The tribological behavior of crosslinked ultra-high molecular weight polyethylene (UHMWPE) was compared to that of non-crosslinked UHMWPE, used as control sample. A reciprocating pin-on-disk tribometer was used to determine the effects of countersurface roughness and conformity on wear mechanisms occurring during the initial stage of sliding. Pin samples of two different radii of curvature were slid against medical-grade Co-Cr alloy disks with surface roughness ranging from 0.005 to 0.04 μm in a lubricant of bovine serum. Normal loads were chosen to provide physiological contact stresses. The focus of this study was on the dependence of early wear mechanisms on surface roughness and conformity. Although a correlation between coefficient of friction data and dominant wear mechanisms was not observed, different wear mechanisms were found between control and crosslinked UHMWPE. The results of this study provide insight into the differences of the initial wear behavior of noncrosslinked and crosslinked UHMWPE used in total joint replacements.
Influence of DNA, Alginate, Lysozyme and Bovine Serum Albumin on Sodium Silicate Condensation
Authors: Coradin Thibaud , Coupé Aurélie , Livage Jacques
Published: June 2019

The interaction of DNA, alginate, Lysozyme and Bovine Serum Albumin with diluted solutions of sodium silicate was studied using the molybdosilicate method. DNA and alginate showed very weak interactions with silica precursors whereas both proteins were able to form silica gels. Both electrostatic interactions and hydrogen bonds are suggested to arise between peptide chain and polysilicates, bringing new informations on the nature of inorganic and bio-organic species involved in the natural biosilicification processes.
Colorimetric Biosensor Vesicles for Biotechnological Applications
Authors: Halevy Revital , Kolusheva Sofiya , Hancock Robert E.W. , Jelinek Raz
Published: June 2019

Supramolecular assemblies of vesicles composed of natural lipids embedded in a matrix of polydiacetylene are shown to undergo blue-to-red color changes related to specific interactions between the lipids or recognition elements and biomolecules. The colorimetric transitions observed in the vesicles are due to structural modifications within the conjugated PDA polymer backbone. This colorimetric assay could serve as a membrane-mimicking environment for detection of interfacial processes, such as peptide-membrane interactions, antibody-antigen binding, enzymatic catalysis, and detection of physiological ions. The lipid/PDA mixed vesicles are robust and can be readily applied to diagnosis of physiological molecules and rapid screening of biological and chemical libraries.
Microstructure and Thermal Expansion Properties of Ostrich Eggshell
Authors: Heredia A. , Lozano L. , Martinez-Matias C.A. , Peña-Rico M.A. , Rodriguez-Hernández A. , Villarreal E. , Martínez A. , García-Garduño M.V. , Basiuk V.A. , Bucio L. , Orozco E.
Published: June 2019

Textures of calcite crystals from ostrich (Struthio camelus) eggshells were examined with X ray diffractometry (XRD), transmission and scanning electron microscopy (TEM, SEM), and the thermal stability by thermal expansion analysis (TEA). Results showed that textures vary through the thickness of the eggshell and that expansion properties and thermal behaviour are unusual. Crystals from ostrich eggshell are arranged in two main configurations or layers; the outer layer with the c-axis of crystals oriented perpendicular to the eggshell surface and the inner layer with the c-axes of the crystals arranged almost parallel to eggshell surface; thermal expansion analysis show high stability through a wide range of temperatures until a steep growth near 450-460°C. These results show that the manipulation of crystal texture and properties is under biological control and a better understanding of this biological phenomenon will provide more and better data for improving new synthetic composite materials.
Lipid Exchange Rates of Conventional and Polymer Stabilized Liposomes
Authors: Ahmed Awad , Heldt Nicole , Slack Gregory , Li Yuzhuo
Published: June 2019

Polymer-stabilized liposome systems consisting of polyethylene glycol bound lipids (PEG-lipids) and conventional (nonpolymer stabilized) liposomes were compared in terms of their inter-membrane lipid migration rates. In order to monitor the exchange of lipids between the membranes, 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (PY-PC), a phospholipid with pyrene attached to the hydrophobic tail, was used to label the liposome. Labeled and unlabeled liposome systems were mixed and fluorescence spectroscopy was used to examine the lipid transfer. More specifically, the relative employed to deduce the exchange kinetics. After labeled and unlabeled liposome systems were mixed, the E/M ratio for PY-PC in a polymer stabilized liposome system decreased by 66% over a period of 80 minutes, while the E/M for PY-PC in a conventional liposome system decreased 70% in less than 2 minutes. This suggests that the exchange rate for lipids in polymer stabilized liposome systems is much slower than that of conventional liposome systems. In addition, the exchange rates for both conventional and polymer stabilized liposome systems are accelerated at an elevated temperature.
Biomimetic Networks For Selective Recognition of Biomolecules
Authors: Byrne Mark E. , Park Kinam , Peppas Nicholas A.
Published: June 2019

Studies of protein binding domains reveal molecular architectures with specific chemical moieties that provide a framework for selective recognition of target biomolecules in aqueous environment. By matching functionality and positioning of chemical residues, we have been successful in designing biomimetic polymer networks that specifically bind biomolecules in aqueous environments. Our work addresses the preparation, behavior, and dynamics of the three-dimensional structure of biomimetic polymers for selective recognition via non-covalent complexation. In particular, the synthesis and characterization of recognitive gels for the macromolecular recognition of D-glucose is highlighted. Novel copolymer networks containing poly(ethylene glycol) (PEG) and functional monomers such as acrylic acid, methacrylic acid, and acrylamide were synthesized in dimethyl sulfoxide (polar, aprotic solvent) via UV-free radical polymerization. Polymers were characterized by single and competitive equilibrium and kinetic binding studies, single and competitive fluorescent and confocal microscopy studies, dynamic network swelling studies, DPC, and FE-SEM. Results qualitatively and quantitatively demonstrate effective glucose-binding polymers in aqueous solvent. Due to the presence of template, the template mediated polymerization process resulted in a more macroporous structure as exhibited by dynamic swelling experiments, confocal microscopy, and SEM. Recognitive networks had a more macroporous structure with absorption of water occurring via non-fickian diffusion at a faster rate and with a higher equilibrium value. Polymerization kinetic studies suggest that the template molecule has more than a dilution effect on the polymerization, and the effect of the template is related strongly to the rate of propagation. The processes and analytical techniques presented are applicable to other biologically significant molecules and recognitive networks, in which hydrogen bonding, hydrophobic, or ionic contributions will direct recognition. Further developments are expected to have direct impact on applications such as analyte controlled and modulated drug and protein delivery, drug and biological elimination, drug targeting, tissue engineering, and micro- or nano-devices.
Microcontact Printing via a Polymer-Induced Liquid-Precursor (PILP) Process
Authors: Kim Yi-yeoun , Gower Laurie B.
Published: June 2019

Our biomimetic approach for patterned crystallization is based on the combination of the Micro-Contact Printing technique and a novel mineralization process, called the Polymer-Induced-Liquid-Precursor (PILP) process, which enables the deposition of mineral films under low-temperature and aqueous-based conditions. We demonstrate that a liquid-phase mineral precursor is deposited onto specific areas templated with self-assembled monolayers of alkanethiolate on gold, and then the patterned calcitic films grow under constrained conditions via transformation of the PILP phase, leading to control over the location and morphology of calcitic films.
Polymer Nanocomposites: Molecular Dynamics Simulations of Polystyrene and Polystyrene-Polyisoprene Block Copolymer Nanocomposites
Authors: Shah D. , Bitsanis I. A. , Natarajan U. , Hackett E. , Giannelis E.P.
Published: June 2019

Molecular dynamics simulations were used to study the interlayer structure and dynamics of polystyrene (PS) and polystyrene-polyisoprene (PS-PI) block copolymers intercalated in organically modified layered silicates. In the case of PS the polymer chains displace the aliphatic surfactant chains and reside adjacent to the silicate layers. The electrostatic interactions between the aromatic rings on the PS chains and the silicate surface drive the intercalation of the polymer into the host galleries. PI, which lacks such electrostatic interactions, is immiscible (does not intercalate) with the host. There appears to be a minimum number of PS mers for intercalation of PS-PI copolymers to take place. The intercalated copolymer appears to structure inside the host galleries with the PS mers adjacent to the silicate layers and the corresponding PI away from the surface and towards the middle of the gallery. Using the mean square displacements we find that PS is the least mobile species in the galleries with the surfactant chains been the most mobile of all.
Enhanced Scratch Resistance of Nanocomposite Gelatin Films
Authors: Chen Quan , Schadler Linda S. , Siegel Richard W. , Irvin Glen C. , Mendel John
Published: June 2019

Nanocomposites were made using deionized gelatin filled with well-dispersed nanoscale alumina particles. Scratch tests on the nanocomposite films showed substantially improved scratch resistance. Tensile tests revealed increases in both modulus and tensile strength of the nano-filled gelatin films accompanied by a decrease in strain-to-failure. The increase in modulus and strength reduced the degree of plastic deformation during scratch testing, but the onset of periodic cracking in the scratch track was unaffected. Optical transmittance measurements of the gelatin composite showed that the films retained transparency in the visible light range.
Mechanical Behavior of Intercalated Polycarbonate Layered-Silicate Nanocomposites
Authors: Hsieh Alex J. , Harris Donovan , Moy Paul , Song John W.
Published: June 2019

The effect of layered-silicates on the mechanical response of intercalated polycarbonate (PC) nanocomposites subjected to quasi-static tensile, compressive and ballistic impact testing conditions has been investigated. These nanocomposites were melt-processed, in which good dispersion of nanoclays and adequate adhesive bonding between the nanoclay and PC matrix are achieved. However, their ductility upon tensile loading is significantly affected; a transition from ductile to brittle deformation occurs at clay loading of about 3 wt.%. Stress whitening is evident in the tensile- and ballistic-tested 1.5, 2.5, and 3.5 wt.% clay nanocomposites, and is attributed to the light scattering by microvoids, which are presumably formed from either crazing of PC or debonding of the nanoclay tactoids upon mechanical deformation. The effect of clay loading on the ballistic impact strength of the monolithic PC nanocomposites and layered PC/PC-nano/PC composites is determined. Compressive yield strength measurements are obtained at strain rate of 0.001/s for the monolithic PC nanocomposites and are utilized to correlate with the ballistic impact strength of the layered PC/PC-nano/PC composites. Thermal degradation is noted in these PC nanocomposites, and its effect on the mechanical deformation is briefly discussed.
Analysis of Carbon Nanotube Pull-out from a Polymer Matrix*
Authors: Frankland S. J. V. , Harik V. M.
Published: June 2019

Molecular dynamics (MD) simulations of carbon nanotube (NT) pull-out from a polymer matrix are carried out. As the NT pull-out develops in the simulation, variations in the displacement and velocities of the NT are monitored. The existence of a carbon-ring-based period in NT sliding during pull-out is identified. Linear trends in the NT velocity-force relation are observed and used to estimate an effective viscosity coefficient for interfacial sliding at the NT/polymer interface. As a result, the entire process of NT pull-out is characterized by an interfacial friction model that is based on a critical pull-out force, and an analog of Newton's friction law used to describe the NT/polymer interfacial sliding.
Dynamic Contact Characteristics During Chemical Mechanical Polishing (CMP)
Authors: Choi Wonseop , Lee Seung-Mahn , Singh Rajiv K.
Published: June 2019

In chemical mechanical polishing (CMP), it is critical to understand dynamic contact at the pad-particles-wafer interface for desired CMP performance. The dynamic contact is dependent on process variables (platen velocity and down pressure) and particle characteristics (size and concentration), which in turn affect friction force. In this study, we have characterized the dynamic contact at the pad-particles-wafer interface as a function of platen velocity and down pressure. In situ lateral friction force measurements were carried out for silica slurry / sapphire wafer system in order to investigate the dynamic contact during polishing. As solids loading increases, the slope in the friction force vs. platen velocity curve changes from a negative to a positive value. Friction force increases with down pressure for different solids loading conditions. Consequently, friction force is determined as a function of down pressure and platen velocity, validating a dynamic contact mechanism during CMP.
Re-Examining The Physical Basis of Pattern Density and Step Height CMP Models
Authors: Xie Xiaolin , Park Tae , Lee Brian , Tugbawa Tamba , Cai Hong , Boning Duane
Published: June 2019

Our group has proposed several chip-scale CMP models, with key assumptions including the notion of planarization length in the pattern density model [1], and step height dependent polishing rate in the density step height model [2]. In the effective density model, planarization length is the characteristic length of an elliptic weighting function based on the long-range pad deformation and pressure distribution during CMP. This semi-physical model is often adequate and usually gives a fitting error of a few hundred angstroms. As ever-shrinking device size pushes for tighter control of post CMP uniformity, however, we need a chip-scale CMP model with better accuracy.

In this work, we re-examine the physical basis for averaging weighting functions and step height dependence, particularly in the context of contact mechanics based model formulations. The comparison of the two models confirms that the analytical density and step height models can be viewed as approximations to the contact wear model. The study also suggests a new dependence of contact height on line space and pattern density.
Study of Slurry Composition Transition in a Rotary Copper CMP Process
Authors: Hegde Sharath , Patri Udaya B. , Jindal Anurag , Babu S.V.
Published: June 2019

The polishing pad is one of the prime components in a typical Chemical Mechanical Polishing (CMP) process. The structure and transport properties of a polishing pad are critical in determining the particle and chemical utilization in a conventional CMP process. Our earlier paper investigated the particle retention and transport on two different polishing pads, IC-1400 and Suba-500, during copper polishing. In this paper, the results of chemical retention and transport of IC-1400 and Suba-500 pads during copper polishing are presented. The polish rate results from slurry-step-flow experiments with H2O2-glycine based slurries, where the concentrations of chemicals in the slurry are altered in steps during polishing, are correlated to the chemical retention and transport characteristics of these pads. It is found that IC-1400 has a higher chemical transport capability than Suba-500 pad, which is shown to affect the polish rates of copper.
Single Asperity Chemical Mechanical Wear Studied by Atomic Force Microscopy
Authors: Stevens Forrest , Langford Steve , Dickinson J. Thomas
Published: June 2019

Nanometer scale wear caused by a single asperity of silicon nitride was examined by measuring the wear caused by atomic force microscope tips translated against sodium trisilicate glass, soda-lime glass, or fused silica in aqueous solutions. As a function of contact force, FN, and scan duration, t, the wear to both tip and substrate scales approximately as (FNt)0.5. Substrate wear was independent of temperature from 5°C to 60°C, whereas tip wear showed a temperature dependence on soda-lime glass corresponding to an activation energy of 60 kJ/mol on soda-lime glass.
Multi-Scale Characterization of Pad Role on Material Removal Rate in CMP
Authors: Gouda Sunil D. , Bastawros Ashraf , Chandra Abhijit
Published: June 2019

A combined experimental and theoretical approach has been devised to understand the mechanical behavior of CMP pad. The pad response is examined at different length scale utilizing a nano-indentation with a conical tip and a flat-punch. The experimentally observed trends showed the competition between the local contact field of the abrasive particle and the global porous pad cell deformation. From the experiments, the local particle-level contact, cell bending, long range pad surface asperity contact as well as the bulk response of the pad can be integrated into mechanism-based models for better understanding the applied force partitioning and to predict the characteristics of the material removal rates.