bluuebunny/crossref_metadata_2025 huggingface dataset:
Porous Composites for Adhering Artificial Cartilage to Bone
Authors: Zhang Kai , Grimm Mary E. , Lu Qiwei , Oegema Theodore R. , Francis Lorraine F.
Published: April 2011

Artificial cartilage can be grown from cultured chondrocytes, but adhering this tissue to bone presents a challenge. Porous polymer/bioactive glass composites are candidate materials for engineering the artificial cartilage/bone interface and possibly other soft-to-hard tissue (ligament/bone, tendon/bone) interfaces. A phase separation technique was used to make porous polymer/bioactive glass composites. The composites (thickness: 200-500 μm) have asymmetric structures with dense top layers and porous structures beneath. The porous structures consist of large pores (>100 μm) in a network of smaller (<10 μm) interconnected pores. The dense layers were removed and large pores exposed by abrasion or salt leaching from the casting surface. The tissue bonding abilities of the composites were studied in vitro in simulated body fluid (SBF) and in rabbit chondrocyte culture. Culture studies revealed that composite surfaces were suitable for attachment, spreading and proliferation of chondrocytes. The growth of hydroxycarbonate apatite (HCA) inside and on the composites after soaking in the SBF for two weeks demonstrates their potential for integration with bone. The results indicate the potential for the composites to facilitate growth and attachment of artificial cartilage to bone.
Formation of Supramolecular Assemblies by Modulating Self-Assembling Properties of Diacetylenic Phosphocholines
Authors: Singh Alok , Wong Eva M. , Spector Mark S. , Schnur Joel M.
Published: April 2011

Diacetylenic phospholipid dispersions in water produce tubules (500 nm diameter) and helices from their initial vesicular morphology as a function of temperature and concentration. A binary mixture consisting of diacetylenic phospholipid, 1, 2 bis (tricosa-10, 12-diynoyl)-sn-glycero-3-phosphocholine and a short chain phospholipid, 1, 2-dinonanoyl -sn-glycero-3-phosphocholine was studied to explore the morphological transformation of lipids into tubules to develop an approach to control and produce tubules of different diameters. Circular dichroic spectra not only indicated the chiral nature of these tubules, but also provided distinct spectral signatures differentiating micro- and nanotubules. The effects of temperature and lipid concentration on the formation and stability of tubules were also explored. An equimolar lipid mixture provided structures with uniform morphology, which were stable for several hours up to 36 °C. The thermal stability of nanotubules makes them an attractive candidate for many practical applications including controlled release technology.
Immunoreactivity and Characterization of Histidine-Rich Peptide Encapsulated Nanoclusters
Authors: Slocik Joseph M. , Moore Joshua T. , Wright David W.
Published: April 2011

Histidine-rich proteins (HRP), which function in the biological control of inorganic materials, have been identified in the liver fluke Fasciola hepatica, marine polychaetes, humans, and the malarial parasite Plasmodium falciparum. For example, the malarial parasite contains HRP II composed of repeating peptide sequences of Ala-His-His-Ala-His-His-AlaAla-Asp. This peptide was screened as a stabilizing peptide coat for a variety of nanoclusters of Ag0, Au0, ZnS, TiO2, and Ag2S, and characterized by UV-Vis spectroscopy, fluorescence, IR, XRD, and TEM. The resulting nanoclusters were examined for immunoreactivity against a commercial monoclonal antibody for HRP II of P. falciparum.
Technical Studies on Renaissance Bronzes
Authors: Weisman Billie Milam , Reedy Chandra L.
Published: April 2011

The merging of art production and technological innovation during the Renaissance in Europe led to some of the world's most renowned master works in bronze. Published technical studies of such bronzes are still relatively few in number. The objective of the present study was to conduct a comprehensive investigation of comparative examination and analysis on fifty-two bronze sculptures which were attributed to a wide variety of workshops and individual artists. The sculptures are housed in the permanent collection of the Kunsthistorisches Museum in Vienna, Austria, and were shown in the museum's 1987 exhibition, Renaissance Master Bronzes. Technical analysis included identifying and characterizing casting and fabricating techniques through visual surface examination; studying x-radiographs; and identifying clay core materials through thin-section petrography. The results of these studies were subsequently compared to technical treatises/accounts of bronze techniques by three Renaissance artist-scholars: Biringuccio (ca. 1540), Vasari (ca. 1550), and Cellini (ca. 1568). The present investigation shows a strong correlation between its technical results and those set forth by the above scholars from the Renaissance period. The findings of this research and comparison indicate that many methods and procedures in Renaissance bronze production were not standardized. Rather, there is shown to have been a wide range of technical variation. The broad variance is demonstrated through numerous processes, including: modes of separate cast-piece attachment, armature construction, chaplet insertion, selection of clay core and additive materials, and removal of clay core portions after casting. The variance is also evident in the quality and extent of surface tooling and/or chasing, and in the visual appearance of patinas. One result of this study is a better understanding of the nature of bronze sculpture technology during the Renaissance period.
Early Historic Period Ceramic Smoking Pipes from Budhigarh, in the Kalahandi District of Orissa, India
Authors: McCarthy Blythe , Downie Christine , Mohanty Pradeep
Published: April 2011

Among ceramics found at early historic sites in the Kalahandi district of India are a great variety of terracotta smoking pipes or hukka. The pipes are fashioned from fine, iron-rich clay with extensive surface decoration. Their intricacy makes them the most distinctive art form of the area. Found at the majority of sites in the region, they are of special interest, both due to the care used in their execution and as they predate the introduction of tobacco to the area, leaving the plant being smoked a question. To determine their method of manufacture, and investigate the possibility of local manufacture, an initial study was conducted of a small number of pipes from the site of Budhigarh. The pipes, along with clay from the site (used extensively by modern potters), were studied using x-ray radiography, petrography, and inductively coupled plasma spectroscopy (ICP).
The Relationship Between Microstructure and Mechanical Properties of Late 19th/Early 20th Century Wrought Iron Using the Generalized Method of Cells Model
Authors: Hooper Jennifer J. , Graham Lori , Foecke Tim , Weihs Timothy P.
Published: April 2011

The discovery of the RMS Titanic has led to a number of scientific studies, one of which addresses the role that the structural materials played in the sinking of the ship. Chemical, microstructural, and mechanical analysis of the hull steel suggests that it was state-of-the-art for 1912 with adequate fracture toughness for the application. However, the quality of the wrought iron rivets may have been an important factor in the opening of the steel plates during flooding. Preliminary studies of Titanic wrought iron rivets revealed an orthotropic, inhomogeneous composite material composed of glassy iron silicate (slag) particles embedded in a ferrite matrix. To date, very little is understood about the properties of wrought iron from that period. Therefore, in order to assess the quality of the Titanic material, contemporary wrought iron was obtained from additional late 19th/early 20th century buildings, bridges, and ships for comparison. Image analysis completed on the Titanic wrought iron microstructure showed a high slag content that is very coarse and unevenly distributed. To investigate how microstructure impacts the mechanical properties, and hence the quality of late 19th/early 20th century wrought iron, a detailed analysis of the relationship between the microstructural features and the mechanical behavior was completed. Here we present the first step in that process: the use of the Generalized Method of Cells (GMC) to predict the mechanical response of composites with variable microstructural properties. The GMC tool is used to generate the effective inelastic behavior of the composite from the individual constituent properties.
Analysis of CizhouMonochrome Green Enamels and Lead Glazes From Guantai Kiln in Northern China, Song to Jin Dynasty
Authors: Liu Wei , McCarthy Blythe
Published: April 2011

The composition and microstructure of Cizhou monochrome overglaze enamels, the first known form of overglazed enamels in China, and green lead glazes from Guantai kiln were determined. Although microstructure and thickness of the enamels were very similar to those found for the single layer lead glazes, lead contents were lower. Enamels from the later part of the twelfth century formed a narrower compositional grouping than the lead glazes, indicating that increased control of the technology was attained. The monochrome enamels are thicker and have a composition distinct from that published for later painted enamels from sites other than Guantai. Increased viscosity and decreased values of thermal expansion coefficients were calculated for Guantai enamels relative to the glazes. An attempt to promote adhesion and reduce crawling may have caused the use of lower lead in the enamels relative to the single layer lead glazes.
Painted Qero Cups from the Inka and Colonial Periods in Peru: An Analytical Study of Pigments and Media
Authors: Newman Richard , Derrick Michele
Published: April 2011

Qero cups, made from wood, ceramics and precious metals, have been used for millennia in the Andean region for ritual consumption of maize beer. From the cusp of the Inka-Colonial period, painted decoration became more common on qero cups. Most of the painted decoration actually consists of thin layers of a pigmented rubbery material that was cut and inlaid into shallow carved cavities in the wood substrate. For this project, 312 paint samples from 53 qerocups in collections of the Brooklyn Museum of Art, National Museum of the American Indian/Smithsonian Institution, Metropolitan Museum of Art, and American Museum of Natural History were analyzed. The study of paints is part of larger study of the technology of over 150 qero cups from these four collections. Samples from seven qeros in Peruvian collections have also been analyzed. Nearly two dozen pigments have been identified, including mineral, synthetic inorganic compounds, and natural dyestuffs. The binder consisted of an unusual natural resin (commonly called ‘mopa mopa’) usually mixed with a nondrying or semidrying oil. This resin, which was used at least locally during the pre-Inka period and continued to be used through the Colonial period and later, came from a tree that grows in the montana of southwest Colombia, a region that was part of the northernmost extension of the Inka empire.
Crystal Structure of and Defects in the Pentacene Thin Film Phase
Authors: Drummy Lawrence F. , Miska Paul K. , Martin David C.
Published: April 2011

The aromatic hydrocarbon pentacene is currently under investigation for use as the active layer in electronic devices such as thin film field effect transistors. We have used X-Ray Diffraction (XRD), Electron Diffraction (ED), Low Voltage Electron Microscopy (LVEM), High Resolution Electron Microscopy (HREM) and molecular modeling to investigate the thin film phase of pentacene. We will report the orthorhombic symmetry and lattice parameters of the thin film phase measured experimentally from these techniques. The structure of extended defects such as dislocations and grain boundaries will influence the electrical and mechanical characteristics of the films. Here we show a direct image of an edge dislocation in the thin film phase and discuss the way in which the lattice accommodates the defect.
High frequency contact mechanics based on quartz crystal resonators: application to polymer surfaces
Authors: Berg Steffen , Johannsmann Diethelm
Published: April 2011

High frequency contact mechanics experiments were carried with a quartz crystal resonator, the surface of which was coated with a polystyrene film. The experiment is based on the ring-down of the resonator after the electrical excitation has been stopped. When a tip touches the quartz surface, the shear motion of the quartz is perturbed, which can be used to study force-displacement and force-speed relations in the contact zone. A nonlinear spring constant κl(x) and a nonlinear friction coefficient ξl(ẋ) are explicitly derived. When a ceramic sphere touches a polymer film the friction force depends more than linearly on lateral speed. This contrasts to metal-metal contacts or contacts between ceramic surfaces, where the friction force depends either linearly of sub-linearly on speed.
Adhesion Property of Novel Polyimides Containing Fluorine and Phosphine Oxide Moieties
Authors: Jeong K. U. , Jo Y. J. , Knag H. M. , Yoon T. H.
Published: April 2011

Novel diamine monomers, containing fluorine and phosphine oxide - bis(3-aminophenyl)-3,5-bis(trifluoromethyl)phenyl phosphine oxide (mDA6FPPO) and bis(3-aminophenyl)-4-(trifluoromethyl)phenyl phosphine oxide (mDA3PPO) - were utilized to prepare polyimides with dianhydrides such as 6FDA, BTDA or ODPA by the conventional two-step route, i.e., preparation of poly(amic-acid), followed by solution imidization. Adhesion property of the polyimides was evaluated via a peel test with bare Cu foil, as well as Cr/silane coated Cu foils, and failure surfaces were analyzed by SEM/EDX to elucidate the adhesion mechanism. The polyimides with 3FDAm exhibited the highest Tg, followed by mDAPPO-, mDA3FPPO- and mDA6FPPO-based polyimides, but the mDAPPO-based polyimides exhibited the highest adhesion properties, followed by mDA3FPPO, mDA6FPPO, mDDS and 3FDAm, attributing to phosphine oxide and fluorine moieties.
Correlation Between Nanostructure and Crystalline Morphology and Mechanical Response in Nylon 6 Nanocomposites
Authors: Reynaud E. , Shah D. , Giannelis E.P.
Published: April 2011

Several nylon nanocomposites was prepared using pristine and organically modified silicates. DSC and XRD reveal that the metastable γ phase is stabilized in the nanocomposites and the amount of γ phase scales with the silicate loading. Both storage and loss moduli of the nanocomposites increase with increasing silicate content. The overall characteristics of these systems become more solid-like before the onset of the glass transition. The increases in moduli are most pronounced in the rubbery regime. Pristine silicates have marginal effect on the mechanical response due to poor dispersion and/or lack of interactions with the polymer matrix.
Study of polymer-electrode interfaces in polymer light-emitting diodes using electrical impedance spectroscopy
Authors: van Dijken A. , Hulea I.N. , Brom H.B. , Brunner K.
Published: April 2011

Electrical impedance spectroscopy is used to show that time-dependent charge trapping processes occur in double-layer polymer light-emitting diodes based on poly(ethylene-dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) and poly(p-phenylene vinylene) (PPV). No time-dependent charge trapping processes are observed in single-layer devices based on PPV only. Furthermore, in double-layer devices based on poly(2,7-spirofluorene) (PSF) instead of PPV, such processes are also absent. Traps are probably created in the PPV layer close to the PEDOT:PSS interface due to chemical reactions that occur specifically between PEDOT:PSS and PPV.
New Surface Functional Metal Powders for Anisotropic Conductive Film Materials in Electronic Package Application
Authors: Huang Shu-Chen , Li Hsun-Tien , Chen Kai-Chi , Lee Tzong-Ming
Published: April 2011

New metal powders containing organic thin film layer with multi-functional properties are prepared and used in the manufacturing of anisotropic conductive film (ACF) material for electronic package application. The organic thin film layer possesses both insulating property and thermo-compressed flowable property. The former insulating property ensures metal powder to have good insulation property at room temperature, and the latter thermo-compressed flowable property maintains the electric conductance of ACF material after high temperature compression process. Besides, the organic thin film layer also exhibited good steric hindrance to enhance the dispersion and anti-settling of metal powers in resin matrix. The functional organic groups on the surface thin film will also improve the interface adhesion between metal powder and resin matrix. Such metal powder with surface chemical modification is suitable for electronic material application, for example, anisotropic conductive film (ACF).
An Equivalent Circuit Approach to Evaluating Conductivity of Polymer-Filler Composites
Authors: Skorokhod Vladislav
Published: April 2011

An equivalent circuit model of electrical conduction in polymer-filler particulate composites was developed in this study. The equivalent circuit was constructed for an individual composite particle with a sub-monolayer of conductive filler, where the filler particles play the role of circuit nodes, and inter-particle contacts are represented by resistors between the nodes. The mathematical representation of the equivalent circuit in the form of a linear system of equations for nodal potentials was solved numerically with Matlab software to calculate conductance of the composite as a function of the amount of conductive filler, filled fraction of the monolayer, filler-to-matrix size ratio and the degree of structuredness (non-randomness) of the filler material. Additionally, percolation concentrations and statistical distributions of composite conductance were calculated as functions of the filler-to-matrix size ratio.
Electrophysical Properties Of Polymers With Implanted Amorphous Single - Component Metals
Authors: Malkhasyan R. , Krmoyan R. , Kosyan V.
Published: April 2011

For the last years, especially after the creation of conducting polymers, much prominence has been given to the works on creation and working out the new technologies of implantation of different metals and, on the whole, inorganic components into the structure of different polymers.

Of special interest are rapidly developing researches in the field of creation and application of different nanomaterials also including metals in the processes of synthesis of different polymers.

The data on electrophysical properties of polyvinyl acetate with doping amorphous molybdenum, obtained for the first time in SPE “ATOM” of Armenia, are being presented and discussed for the first time in the given paper.

It is shown, that the dopes of amorphous nanosize molybdenum and crystalline nanosize molybdenum in the process of polymerization lead to its implantation into the structure of polymer. Amorphous molybdenum practically always lowers substantially electrical resistance of composite materials.
Blood Compatibility of Metal Oxide Layers on Stainless-steel
Authors: Tsuru Kanji , Takemoto Shinji , Yamamoto Tatsuhiro , Hayakawa Satoshi , Osaka Akiyoshi , Takashima Seisuke
Published: April 2011

We examined blood compatibility of titanium oxide layer on stainless-steel (SUS316L). The oxide layers with varied thickness were yielded on SUS316L plates by dip-coating of sol-gel solution starting from tetraethyltitanate. The blood compatibility was evaluated in term of platelet adhesion using platelet rich plasma. With increase in the thickness of the oxide layer, the number of adherent platelets decreased rapidly, reached minimum around 150nm. This indicated that the thickness of titanium oxide layer affected platelet adhesion.
Characteristics of Cu/C Films on Polymer Substrate Prepared by Room Temperature ECR-MOCVD Coupled with Periodic DC Bias
Authors: Lee Joong Kee , Ko Hyungduk , Hyun Jin , Byun Dongjin , Cho Byung Won , Park Dalkeun
Published: April 2011

Cu/C films were prepared at room temperature under Cu(hfac)2-Ar-H2 atmosphere in order to obtain metallized polymer by using ECR-MOCVD (Electron Cyclotron Resonance Metal Organic Chemical Vapor Deposition) coupled with periodic DC bias system. Room temperature MOCVD was possible when periodic negative voltage was applied on the polymer substrate. The periodic negative voltage induces ions and radicals to have nucleation reaction on the surface of the substrate. Formation of Cu/C films strongly depends on the periodic negative pattern of DC bias and the electric sheet resistance of the films was controlled from 108 to 100ohm/sq ranges by process parameters such as microwave power and magnet current. The increase in microwave power and magnet current brought on copper-rich film formation with low electric resistance. On the other hand carbon-rich films with high sheet electric resistance were prepared with decreased values for process parameters aforementioned.
Influence of Mechanical Rubbing of Polyhexylthiophene Layers on the Field-Effect Mobility using Differently Treated Isolator Surfaces
Authors: Heil H. , Finnberg T. , Schmechel R. , von Seggern H.
Published: April 2011

This paper reports on the influence of the field-effect mobility of transistors based on regioregular head-to-tail coupled poly (3-hexylthiophene) by mechanically induced alignment on differently treated insulator surfaces. It is demonstrated that on hydrophilic insulator surfaces mechanical rubbing of the polyhexylthiophene layers perpendicular to the source drain contacts can increase the field-effect mobility whereas rubbing parallel to the source drain contacts results in a reduced mobility. In contrast it is shown that in transistors with a hydrophobic insulator surfaces, which show much higher mobilities no further improvement can be achieved. The rubbing induced polymer alignment is deduced from optically polarized transmission spectroscopy on polymer-coated quartz glass substrates. The different behavior of the field-effect mobility will be explained in terms of different degrees of crystallinity.
Nanoscale 3D Chemical Mapping by Spectroscopic Electron Tomography
Authors: Möbus Günter , Doole Ron C. , Inkson Beverley J.
Published: April 2011

Electron Tomography is shown to be applicable to problems of materials science if a contrast mechanism is used which provides a projection relationship for crystals not depending on lattice plane orientation. Energy filtered TEM (EFTEM) in its mode of electron spectroscopic imaging (ESI) and STEM-EDX-Mapping are, subject to limitations, suitable image formation techniques. The spectroscopic operation not only allows to overcome Bragg scattering artefacts, but offers the possibility of recording 4-dimensional data (volume and energy) of a region of interest, otherwise only known from NMR and XAS/XANES tomography at larger length-scales and from field-ion microscopy (atom probe) under restrictive conditions.
Quantification of Displacement Fields from Lattice Images (HREM) and Electron Exit Waves in Nanostructured Composite Oxides
Authors: Calderon H. A. , Huerta A. , Kisielowski C. , Kilaas R.
Published: April 2011

Oxide composites have been produced by means of mechanical milling and sintering. Such materials consist of magnetic particles embedded in an insulating oxide matrix, which can have application as magnetic wave absorbers. Different systems have been investigated including MgO-MgFe2O4, FeO-Fe3O4 and other more complex ferrites. Milling induces the formation of a solid solution of cations and oxygen. Depending on temperature and system, sintering can produce a particle dispersion or simply the starting of the corresponding phase transformation. Spark plasma sintering was performed between 773 and 1373 K in order to reduce both processing time and temperature. High resolution (HREM) and conventional transmission electron microscopy show that an spinodal decomposition takes place in the system FeO-Fe3O4 during transformation from the solid solution.

Generally the oxygen lattice is unique throughout the material but there is a distinctive distribution of cations giving rise to a particle dispersioGn having an spinel structure in a insulating matrix with a NaCl cubic structure.
Micro Raman Spectroscopy of Silicon Nanocrystals Produced by Picosecond Pulsed Laser Ablation
Authors: Wu M. H. , Mu R. , Ueda A. , Henderson D. O. , Vlahovic B.
Published: April 2011

Pulsed laser ablation has been used to produce silicon nanocrystals. Variation of the laser fluence, backing gas type and pressure result in nanocrystals with controllable size distributions. Properties of nanocrystals produced with this method also depend on the distance of the nanocrystal from the center of the laser plume. Correlated atomic force microscopy and in-situ micro-Raman measurements confirm that particle size decreases as distance from the plume center increases. Silicon peaks in the micro raman spectra taken at increasing distance from plume center show considerable differences in both center energy and width. Confocal micro raman spectra from thicker (> 10 micron) samples show little variation with depth, in contrast with porous silicon samples.
Design and Analysis of Microcantilevers for Biosensing Applications
Authors: Zhang Xuan , Yang Mo , Ozkan Cengiz S.
Published: April 2011

The primary deflection due to the chemical reaction between the analyte molecules and the receptor coating, which produces surface stresses on the receptor side is analyzed. The resonance frequency of microcantilevers is very sensitive to the properties of the microcantilever surface. Biosensing experiments based on resonance frequency shift are presented, which show that the results strongly depend on the interaction of specific analyte molecules with the receptor surface.
Reproducibility of Nano- and Micro-Scale Multi-Point Probe Sheet Resistance Measurements
Authors: Petersen Christian L. , Worledge Daniel , Petersen Peter R. E.
Published: April 2011

We have investigated the reproducibility of micro- and nano-scale measurements of sheet resistance performed with micro-fabricated multi-point probes. The probes consisted of Au coated SiO2 cantilevers extending from a Si base. The measurements were done with a four-point probe technique on thin Au films, the probe electrode spacing ranging from 18 μm to 1.5 μm. We find that the standard deviation of repeated sheet resistance measurements ranges from 0.2% at 18 μm spacing to 2.6% at 1.5 μm spacing. It is inversely proportional to the probe electrode spacing. This behaviour is expected if the resolution of the measurements is governed by the positional errors of the probe electrode tips. The corresponding standard deviation of the probe tip positions (in both lateral directions) is calculated to be approximately 20 nm. We argue that these positional errors depend on the probe cantilever amplitude at the time of contacting the surface. The amplitude is inversely proportional to the square root of the cantilever spring constant, indicating that stiff cantilevers give the best reproducibility. We estimate the limiting reproducibility of multi-point probes with nano-scale electrode spacing.
Analytical and High-Resolution TEM Characterizations for Nanoscale Fractured Interfaces in Deep-Subquarter-Micron 256MBit DRAM Devices
Authors: Zhao Wei
Published: April 2011

Interfaces, contacts, and homo- or hetero-junctions are critical components in nanometer dynamic random access memory (DRAM) semiconductor devices. With shrinkage in device dimensions, interfacial analysis by TEM becomes more and more challenging, especially in the case of investigating failure mechanisms for nanoscale FRACTURED INTERFACES where electronic signatures found to be open. In this article, fractured interfaces at several C1-type contacts (a path between a Bitline and a Metal 1 interconnector) in a deep-subquarter-micron 256Mbit DRAM device were investigated by a JEOL 2010F analytical transmission electron microscope (TEM) with field-emission gun (FEG) running at 200KV. Considering the difficulty to exactly focus the fractured nano-scale interfaces at sufficiently high magnifications, high-resolution TEM (HR-TEM) and analytical scanning transmission electron microscopy (STEM) coupled with x-ray energy dispersive spectroscopy (XEDS) elemental linescan techniques were employed to provide supplemental information from difference prospects. An in-depth understanding for the nanoscale interfacial fracture mechanisms was established, and a simple model is initiated accordingly.
A scanning tunneling microscopy and potentiometry study of epitaxial thin films of La0.7Ca0.3MnO3
Authors: Paranjape Mandar , Shantha Shankar K. , Raychaudhuri A.K. , Mathur N.D. , Blamire M.G.
Published: April 2011

To investigate the role of grain boundaries and other growth related microstructure in manganite films, a scanning tunneling microscope is used to simultaneously probe surface topography and local potential distribution under current flow at nanometer level in films of epitaxial thin films of La0.7Ca0.3MnO3deposited on single crystal SrTiO3and NdGaO3substrate by laser ablation. We have studied two types of films strained and strain relaxed. Thin (50nm) films (strained due to lattice mismatch between substrate and the film) show step growth (unit cell steps) and have very smooth surfaces. Relatively thicker films (strain relaxed, thickness 200nm) do not have these step growths and show rather smooth well connected grains. Charge transport in these films is not uniform on the nanometer level and is accompanied by potential jumps at the internal surfaces. In particular scattering from grain boundaries results in large variations in the local potential resulting in fields as high as 104-105V/cm located near the grain boundaries. We discuss the role of local strain and strain inhomogeneties in determining the current transport in these films and their resistance and magnetoresistivity. In this paper we attempt to correlate between bulk electronic properties with microscopic electronic conduction using scanning tunneling microscopy and scanning tunneling potentiometry.
Surface Modification and Optical Behavior of Tio2 Nanostructures.
Authors: Prokes S.M. , Carlos W.E. , Gole James L. , She Chunxing , Lian T.
Published: April 2011

TiO2 is a very important material from the perspective of photocatalytic applications, but due to its 3.2 eV bandgap, it is not possible to make this material efficient under visible illumination. Anatase TiO2 nanoclusters in the 3 – 30 nm range have been formed by a wet chemical technique and surface modified in order to enhance the absorption of visible light. Nitridation of the highly reactive TiO2 nanosphere surface has been achieved by a quick and simple treatment in alkyl ammonium compounds and the metallization of this surface has been achieved by electroless plating. Although the structure of the resultant material remains anatase, some of the treated material exhibits strong emission between 550–560 nm, which red shifts and drops in intensity with aging in the atmosphere. Electron Spin Resonance performed on these samples identify a resonance at g=2.0035, which increases significantly with the nitridation step. This resonance is attributed to an oxygen hole center created near the surface of the nanoclusters, which correlates well the noted optical activity.
Formation, Mechanical and Electrical Properties of Ni-based Amorphous alloys and their Nanocrystalline Structure
Authors: Sun Xiangcheng , Zhao Tiemin
Published: April 2011

A Ni-based amorphous alloy in Ni60Ti20Zr20 system was prepared by melting spinning. The glass transition temperature (Tg) was as high as about 760 K, the supercooled liquid region was quite wide, ΔTx = 50 K (ΔTx= Tx-Tg, Tx crystallization temperature), and the reduced glass transition temperature (Tg/Tm) was 0.60. The amorphous alloys exhibited a high tensile strength (of= 1015 MPa) at room temperature. The electrical conductivity obeyed a T12 law over the range of 15 K< T < 300 K, which can be explained by an electron-electron interaction model. After annealing the amorphous alloy into primary crystallization, a nanocomposites consisted of metastable Ti2Ni and Zr2Ni nanophases with size less than 15 nm embedded in the amorphous matrix was appeared.
Simulation of Morphology and Surface Vibration in Copper and Gold Nanoparticles
Authors: Kogure Y. , Kato Y. , Nozaki T. , Doyama M.
Published: April 2011

Formation and vibrational states in nanoparticles have been investigated by means of molecular dynamics simulation. The embedded atom method potentials for Cu and Au were adopted to express the interaction between atoms in the crystals. The nanoparticles were formed by cooling the atomic systems of molten states. Surface morphology of the nanoparticles were represented by highlighting the surface atoms, which were distinguished by the potential energy. Simulated surface morphology is not so symmetric as natural nanoparticles. The radial distribution function and the cross sectional view of the particles were also derived to characterize the internal structure. Thermal vibration of sample atoms at elevated temperatures was analyzed and the power spectra were calculated. Excitation of phonon mode is seen in the spectra.
A Study of Hydrogen Adsorption in Pretreated Nanocarbon
Authors: Lee Sang Moon , Ohshima Satoshi , Uchida Kunio , Yumura Motoo
Published: April 2011

A thermal treatment was applied with CO2 and air for the development of a porous structure. Adsorption isotherms of nitrogen were measured on well-characterized Ni-C nanoparticles. The thermal treatment with CO2 increased the total surface area and micropore volume. In addition, the thermal treatment with CO2 increased the hydrogen adsorption.
Synthesis and Characterization of Metal Nanoparticles and the Formation of Metal-Polymer Nanocomposites
Authors: Pradhan Anshu A. , Ismat Shah S. , Pakstis Lisa
Published: April 2011

Metal nanoparticles are highly prone to oxidation due to their high surface energy and affinity for oxygen which can lead to the complete oxidation of the particles. Studying and utilizing the unique properties of metal nanoparticles requires minimizing their interaction with the atmosphere. We have used the co-condensation technique to synthesize suspensions of metal nanoparticles in isopropanol. The solvent protects the nanoparticles from the atmosphere and minimizes agglomeration of the nanoparticles. The particles showed a lognormal distribution and the average particle size was below 20nm. Polymer-metal nanocomposites were made by dispersing the metal nanoparticles in PMMA matrix by spin coating and solution casting. Adherent films, fibers and free standing films could be obtained by varying the process conditions. The SEM images show that the nanoparticles in the spun coated films were non-agglomerated and well dispersed over a wide area. Morphology of the spun coated films was different from the solution cast films. Electrically conducting films having interconnected silver particle network could be obtained. Cytotoxicity studies show that the silver nanoparticles and the PMMA-Ag nanocomposite films are antibacterial in nature. We have also dispersed the nanoparticle into pump oil and measured the thermal conductivity of the resultant mixture. The thermal conductivity of the oil could be increased by over 50% by adding an extremely small fraction of the silver nanoparticles.
Multilayers by Self-Assembly
Authors: Toprak M. , Kim D.K. , Mikhaylova M. , Muhammed M.
Published: April 2011

Nanoparticles, as building blocks, are important for the development of advanced, functional composite materials. Recent developments have shown that self-assembly of nanoparticles is a promising technique for the fabrication of complicate nanostructured materials. Self assembly of the nanoparticles into ordered structures on a substrate can be achieved through chemical treatment of the particle and/or substrate surface. The assembled nanoparticles can have a dramatic effect on the physical properties of the composite. A μCP technique has been employed to form a SAM of bifunctional silane (APTMS) in the region of contact. The stamps for the μCP are prepared by polymerization of polydimethysiloxane (PDMS) on a flat surface. Glass substrates have been used for optical absorption measurements. Oxide or metallic particles have been assembled on the patterned surface after a surface treatment. The self-assembled layer was subsequently treated with bifunctional molecules and multilayers of the same material or composites have been thus obtained.
Interfacial Control of Creep Deformation in Ultrafine Lamellar TiAl
Authors: Hsiung L. M.
Published: April 2011

Solute effect on the creep resistance of two-phase lamellar TiAl with an ultrafine microstructure creep-deformed in a low-stress (LS) creep regime [where a nearly linear creep behavior was observed] has been investigated. The resulted deformation substructure and in-situ TEM experiment reveals that interface sliding by the motion of pre-existing interfacial dislocations is the predominant deformation mechanism in LS creep regime. Solute segregation at interfaces and interfacial precipitation caused by the segregation result in an increase of creep resistance in LS creep regime.
Red Shift in Optical Absorption Tail and Superparamagnetism of γ- Fe2O3 Nanoparticles in a Polymer Matrix
Authors: Vassiliou John K. , Otto Jens W. , Mehrotra V. , Davis J. J.
Published: April 2011

Well defined spherical particles of γ- Fe2O3 have been synthesized in the pores of a polymer matrix in the form of beads by an ion exchange and precipitation reaction. The particle size distribution is a gaussian with an average diameter of 80 A. The DC magnetic susceptibility and the magnetization of the nanocomposite has been measured between 4 and 300 K using a Faraday balance and a magnetometer, respectively. The magnetic measurements demonstrate that the particles are superparamagnetic with a blocking temperature Tb about 55 K. The optical absorption edge of the mesoscopic system is red shifted with respect to single crystal films of γ-Fe2O3 with an absorption tail extended deeply in the gap. Although lattice distortion and existence of excitonic states in the gap can explain the absorption behavior, the red shift can successfully be explained by the quantum confinement of an electron-hole pair in a spherical well.
Modeling Combined Thermal, Electrical, Optical and Mechanical Response for MEMS Spectroscopic Gas Sensor Based On Photonic Crystals
Authors: Greenwald Anton C. , Pralle Martin U. , McNeal Mark P. , Moelders Nicholas , Puscasu Irina , Daly James T. , Johnson Edward A.
Published: April 2011

A new type of gas sensor was developed that combines the principles of bolometric infrared detectors with photonic crystals.1,2 This paper describes a quantitative model used to optimize the materials, geometry, and electrical properties of this suspended membrane MEMS device. Fundamentally the model is concerned with the thermal response of the device using temperature dependent thermal conductivity, specific heat, and electrical resistance to calculate conduction, convection, and radiation losses for a negative temperature coefficient of resistance material. Variations in the electrical drive circuit, dc and ac response, low and high frequency sinusoidal and random noise, along with an exacting calculation of expected signal were used to improve design. The model follows the time evolution of the system. We show how look-up tables with scaling (derived from exact, off-line finite element models for thermal conduction, spectral emission, etc.) provided sufficiently accurate estimates with rapid calculation to enable running the model on a standard PC type computer. The simulations matched the experimental results, accurately predicted the unstable operating regimes, and maximized the signal to noise ratio for the device.
Piezoelectric Micromachined Ultrasonic Transducers Based on PZT Films
Authors: Baborowski Jacek , Ledermann Nicolas , Muralt Paul
Published: April 2011

Test structures for piezoelectric micromachined ultrasonic transducers have been fabricated and investigated. The basic element consisted of a oxidized and platinized silicon membrane coated with a 2 μm thick (100)-textured Pb(Zr,Ti)O3 (PZT) thin film deposited by sol-gel techniques. SOI wafers have been applied to obtain a good definition of the silicon part of the membrane. Test devices have been characterized in air and in an insulating liquid.
A comparative microtribological investigation of diamond-like carbon films for applications in microsystems
Authors: Imad-Uddin Ahmed S. , Bregliozzi Giuseppe , Haefke Henry
Published: April 2011

This study reports on the microfrictional properties under reciprocating sliding of different types of commercially available diamond-like carbon (DLC) films, prepared using low and high frequency plasma-assisted chemical vapor deposition (PACVD) and the vacuum arc method. Silicon and sapphire balls were used as counterbodies. Friction-load curves suggest that, for applied forces in the N to mN regime, two properties have a strong influence on the microfriction: First, the chemical composition plays a dominant role and second, the film roughness. With silicon against DLC, microfriction of hydrogen-free DLC films was greater than the hydrogen containing films. With sapphire counterbodies, microfriction was inversely proportional to film roughness. For all films tested, microfriction was independent of the sliding velocity. Mild wear in the form of scratches was observed only on silicon, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in a coating development for microsystems.
Ion dose dependence on solid phase epitaxy of amorphous silicon carbide induced by ion implantation
Authors: Bae In-Tae , Ishimaru Manabu , Hirotsu Yoshihiko
Published: April 2011

Amorphous silicon carbides (a-SiC) fabricated by Xe+ ion implantation into 6H-SiC (0001) to fluences of 1015 and 1016/cm2 have been annealed at 850 °C for 1 hour. Transmission electron microscopy (TEM) observations revealed that the 1015 Xe+/cm2 implanted sample was completely recrystallized, while most of the a-SiC remains in the 1016 Xe+/cm2 implanted sample. Pair-distribution function analyses of both of the as-implanted samples show that the peak intensity of Si-C heteronuclear bonds is higher and the peak intensities of Si-Si and C-C homonuclear bonds are lower in the 1015 Xe+/cm2 implanted sample, indicating that the atomistic structure of the 1015 Xe+/cm2 implanted sample is more chemically ordered than that of the 1016 Xe+/cm2 implanted sample. This result suggests that more chemically ordered atomistic structure of 1015 Xe+/cm2 implanted a-SiC leads to complete recrystallization during thermal annealing.
Effects of Structural Defects on Diode Properties in 4H-SiC
Authors: Skromme B. J. , Palle K. C. , Mikhov M. K. , Meidia H. , Mahajan S. , Huang X. R. , Vetter W. M. , Dudley M. , Moore K. , Smith S. , Gehoski T.
Published: April 2011

The influence of two types of structural defects on Schottky diodes in 4H-SiC is investigated. First, a structural transformation that takes place during oxidation or annealing of heavily n-doped wafers is studied using X-ray diffraction, high resolution TEM, secondary electron imaging (SEI), photoluminescence, and electrical measurements on Schottky diodes. Lamellae of 3C SiC with six bilayers are introduced primarily in the heavily doped substrates, and to a lesser extent in the lightly doped epilayers. Lowered Schottky barrier heights result and are spatially correlated to the 3C phase. The 3C lamellae exhibit charge contrast in SEI images where they intersect the surface. Second, we study isolated screw dislocations and show preliminary evidence that they are not the main factor controlling Schottky barrier height and ideality in Schottky diodes in lower-doped 4H-SiC wafers.
Process Induced Extended Defects in SiC Grown via Sublimation
Authors: Yakimova R. , Syväjärvi M. , Jacobson H. , Ciechonski R. R. , Vouroutzis N. , Stoemenos J.
Published: April 2011

Three possible situations of extended defect formation during sublimation growth of SiC have been investigated: a-plane growth, occurrence and effect of irregular growth interfaces, and development of elongated open volume morphological defects. While in the first case the most preferred defects are basal plane stacking faults (SFs), in other studied samples threading dislocations and high energy SFs have been revealed, these suggesting stress accumulated in the course of the growth process. Formation of morphological defects of the above character has been observed in the presence of micropipes and step flow growth mode on vicinal surfaces. Growth on atomically flat surfaces can eliminate this type of defects but the polytype uniformity is more difficult to maintain.
Extended Defects in 4H-SiC PiN Diodes
Authors: Twigg M. E. , Stahlbush R. E. , Fatemi M. , Arthur S. D. , Fedison J. B. , Tucker J. B. , Wang S.
Published: April 2011

Using site-specific plan-view transmission electron microscopy (TEM) and lightemission imaging (LEI), we have identified SFs formed during forward biasing of 4H-SiC PiN diodes. These SFs are bounded by Shockley partial dislocations and are formed by shear strain rather than by condensation of vacancies or interstitials. Detailed analysis using TEM diffraction contrast experiments reveal SFs with leading carbon-core Shockley partial dislocations as well as with the silicon-core partial dislocations observed in plastic deformation of 4H-SiC at elevated temperatures. The leading Shockley partials are seen to relieve both tensile and compressive strain during PiN diode operation, suggesting the presence of a complex and inhomogeneous strain field in the 4H-SiC layer.
Confinement of Screw Dislocations to Predetermined Lateral Positions in (0001) 4H-SiC Epilayers Using Homoepitaxial Web Growth
Authors: Neudeck Philip G. , Spry David J. , Trunek Andrew J. , Anthony J. , Beheim Glenn M.
Published: April 2011

This paper reports initial demonstration of a cantilevered homoepitaxial growth process that places screw dislocations at predetermined lateral positions in on-axis 4H-SiC mesa epilayers. Thin cantilevers were grown extending toward the interior of hollow pre-growth mesa shapes etched into an on-axis 4H-SiC wafer, eventually completely coalescing to form roofed cavities. Each completely coalesced cavity exhibited either: 1) a screw dislocation growth spiral located exactly where final cantilever coalescence occurred, or 2) no growth spiral. The fact that growth spirals are not observed at any other position except the central coalescence point suggests that substrate screw dislocations, initially surrounded by the hollow portion of the pre-growth mesa shape, are relocated to the final coalescence point of the webbed epilayer roof. Molten potassium hydroxide etch studies revealed that properly grown webbed cantilevers exhibited no etch pits, confirming the superior crystal quality of the cantilevers.
Contact resistivity of Al/Ti ohmic contacts on p-type ion implanted 4H- and 6H-SiC.
Authors: Nipoti Roberta , Moscatelli Francesco , Scorzoni Andrea , Poggi Antonella , Cardinali Gian Carlo , Lazar Mihai , Raynaud Christophe , Planson Dominique , Locatelli Marie-Laure , Chante Jean-Pierre
Published: April 2011

Al-Ti alloys with 72 wt% Al were employed for the realisation of ohmic contacts on 4×1019 cm-3 p-type ion implanted 4H- and 6H-SiC samples. Contact resistivity characterisations by TLM measurements were done at wafer level in the temperature range 28–290°C. Analysis of the TLM measurements took into account current crowding at the metal pads. More than half of the evaluated contact resistivity reached the minimum value detectable by the used TLM devices, that was slightly higher than 1×10-6 Ωcm2. Above this limit value, contact resistivity decreased for increasing temperature and was spread over a few decades. The maximum contact resistivity at 28°C was 2×10-4 Ωcm2, which changed to 5×10-6 Ωcm2 at 290°C. The thermal behaviour of these TLM structures featured thermionic-field emission conduction.