bluuebunny/crossref_metadata_2025 huggingface dataset:
Osteogenic Cell Attachment to Degradable Polymers
Authors: Healy Kevin E. , Tsai Davis , Kim Jung E.
Published: March 2011

Modifications were made to increase osteogenic cell adhesion to homo and copolymers of lactic and glycolic acid. A synthetic peptide containing the cell attachment signal Arginine-Glycine-Aspartate (RGD) was loaded into the polymers or adsorbed to the polymers' surfaces. Cell attachment was assayed after 24 hours incubation with an osteogenic cell line (ROS 17/2.8). Statistically significant differences in cell adhesion occurred between the polymers with the adsorbed peptides and the other treatment groups. Significant differences were not observed for the peptide loaded polymers and controls. These data indicate that precoating the polymer surface with a RGD-containing peptide prior to exposure to osteogenic cells increased cell attachment. For the current materials tested, the surface modification is preferred to increase osteogenic cell adhesion to degradable polyesters.
A Collagen/DBP Sponge System Designed for in Vitro Analysis of Chondroinduction
Authors: Mizuno Shuichi , Lycette Chris , Quinto Charlene , Glowacki Julie
Published: March 2011

In response to subcutaneous implants of demineralized bone powder (DBP), cells are attracted to the DBP, are converted to chondroblasts, and produce a cartilage matrix that is resorbed and replaced by bone. In order to define the cellular mechanisms of this induction, we developed a collagen sponge model for simulating the in vivo environment and for promoting the ingrowth and viability of cells cultured in them in vitro. Reconstituted pepsin–digested type I collagen from bovine hide was neutralized. Rat DBP (75–250 εm) was added into the collagen mixture (20 mg/ml). In order to simulate the connective tissue environment, modified chondroitin sulfate, heparan sulfate, or hyaluronic acid was added into the mixture. Aliquots (0.2 ml) were placed in 3/8 inch diameter molds and freeze-dried. Human dermal fibroblasts were cultured from minced fresh tissue and inoculated at 1.5 × 105cells/sponge. Fifteen hours later, some sponges were transferred to medium which contained growth factors (PDGF or TGF-β). At intervals, samples were examined histologically. The inoculated cells attached to the collagen fibers and migrated into the sponge. Eventually the sponges contracted and acquired an oval shape. Cells on or near DBP were ovoid or stellate in shape. Cell morphology was modulated by glycosaminoglycan composition of the sponge. Increasing doses of PDGF or TGF-β promoted cellularity within the sponges. In conclusion, this system simulates the in vivo environment but allows accessibility for analysis. This three-dimensional matrix culture system will enable investigation of mechanisms of chondroinduction by morphogenic material.
Effect of Substratum Morphology on Animal Cell Adhesion and Behavior
Authors: Singhvi Rahul , Stephanopoulos Gregory N. , Wang Daniel I. C.
Published: March 2011

Glass surfaces with well defined surface morphologies have been prepared using photolithography to study the effect of surface morphology on cell adhesion and function. Using a transformed recombinant cell-line, AtT-20, as a model of shear sensitive cell, we have shown that cell-substratum adhesion strength is enhanced using a surface with uniform grooves without any loss in cellular function. Furthermore, using primary hepatocytes as a model for a cell whose function is sensitive to its shape, we have shown that surface morphology can modulate cell shape as well as its function.
In Vivo Effects of an Osteogenic Bone Extract on Cartilage of the Chick Embryo
Authors: Frenkel Sally R. , Prewett Ann B. , Finkelman Richard D.
Published: March 2011

Growth and differentiation of animal cells are influenced by a number of interacting local and circulating protein factors. Several such growth factors, or morphogenetic proteins, that affect hard tissue regeneration and repair have been isolated from bone [1–3]. Bone matrix is a complex milieu consisting of serum, cell, and hydroxyapatite binding proteins, bioactive agents, and other proteins whose functions are not yet known. Most of the growth factors can be dissociated from the decalcified collagen matrix only by using chaotropic solvents such as guanidine hydrochloride or urea [4].This extraction removes virtually all noncollagenous proteins from the matrix, producing a nonselective portfolio of proteins, of which growth factors are only a small percentage. A series of chromatographic separations are then required to isolate the morphogenetic proteins from the mixture [5]. Recently, a process has been developed that permits selective extraction of certain growth factors from demineralized bone and produces a water-soluble extract of collagenous and noncollagenous proteins. When placed in an orthotopic site in the rat, the extract exhibits pronounced osteogenic activity and has a surface-adherent property that may be exploited in the coating of allograft bone or osteoprosthetic implants to facilitate osseointegration. The objective of this study is to observe the in vivo effects of this extract on proliferation and synthetic activity of cartilage cells of the chick embryo.
Poly(Phosphoesters) as Bioabsorbable Osteosynthetic Materials
Authors: Kadiyala S. , Richards M. , Dahiyat B. , Michelson J. D. , Leong K. W.
Published: March 2011

Polymeric prosthetic devices enjoy the advantage of tailor-made properties. In particular bioabsorbable polymers possess distinct advantages. In orthopedic applications, most osteosynthesis has been achieved using metallic devices to stabilize fixation of bony fragments. The different elastic moduli of the metallic implants versus that of bone often causes cortical bone to atrophy. The theoretical advantage of gradual load transfer from the fixation device to the bone and the elimination of surgical removal after the healing of a fracture make an absorbable osteosynthetic material extremely useful. A resorbable porous coating material would also have the potential of improving fixation by promoting bony ingrowth and reducing cartilage destruction. The structural support function of a polymeric device can also be integrated with the drug-carrier function to take advantage of the recently discovered growth factors such as bone morphogenic proteins in enhancing bone union.
Tissue Engineered Growth of New Cartilage in the Shape of a Human Ear Using Synthetic Polymers Seeded with Chondrocytes
Authors: Vacanti Charles A. , Cima Linda G. , Ratkowski Dianne , Upton Joseph , Vacanti Joseph P.
Published: March 2011

This report concerns the tissue-engineered growth of new cartilage in the shape of a human ear. Using synthetic biodegradable polyesters, a porous, three dimensional device in the shape of a human ear was fabricated. The polymer matrices were seeded with living chondrocytes isolated from a freshly sacrificed calf shoulder and implanted subcutaneously on the dorsum of athymic rats. This resulted in the formation of new cartilage in the shape of a human ear of approximately the same dimensions as the original implants. Histological analysis revealed the presence of mature cartilage in all specimens.
Sterilization Mode Effect on the Hydration Rate of Calcium Sulfate Hemihydrate
Authors: Devine T. R.
Published: March 2011

Plaster bandages have been found to support bacteria. The sterilization of plaster (calcium sulfate hemihydrate) for use as an implant biomaterial is, therefore, a primary concern. Heat sterilization can significantly alter material properties and the kinetics of plaster hydration. A study has been done of the effects of sterilization by gamma radiation and by ethylene oxide on the hydration rate of plaster. Three hemihydrate bases with differing water requirements and hydration rates were sterilized by each method. Adiabatic temperature rise was used to follow hydration. Five outcomes were measured and analyzed. These outcomes include the induction period, maximum rate of temperature rise (MRR), time to MRR, total temperature rise, and time to maximum temperature. Neither sterilization mode was found to significantly alter the hydration process of any of the plaster bases. From a material property standpoint, either gamma radiation or ethylene oxide treatment is preferred to heat sterization of calcium sulfate hemihydrate.
Effects of Non-Collagenous Matrix Proteins, Fatty Acid Derivatives, Etc. on the Nucleation and Growth of Calcium Phosphate on Hydroxyapatite
Authors: Wong A. T.-C. , Czernuszka J. T.
Published: March 2011

The effects of various non-collagenous bone matrix bio-chemicals on the deposition of calcium phosphate on hydroxyapatite surfaces have been studied. Guanidine-HCI bone extract, guanidine-EDTA bone extract and phosphatidylserine all showed an overall inhibitory effect on calcification. Phosphoserine promoted secondary nucleation but hindered crystal growth. Serum albumin altered the lattice structure of the crystals, thus inducing a significant calcium deficiency. This structural change also resulted in a different fracture behaviour.
Multiple Scattering Theory, A Successful Approach Towards Electromigration
Authors: Ek J. Van , Lodder A.
Published: March 2011

Both the electromigration wind valence and the residual resistivity for hydrogen in all row 5 (Y,….Ag) and row 6 (La,….Au) transition metals were calculated. Host metals with a hexagonal lattice have been treated in the FCC or BCC structure. The KKR-Green function method used to describe the multiple scattering of Bloch electrons, accounts for charge transfer and lattice deformation around the interstitial hydrogen.
Implications and Applications of Relativistic Spin-Polarized Multiple Scattering
Authors: Hörmandinger G. , Weinberger P.
Published: March 2011

The consideration of spin-orbit coupling in spin-polarized electronic structure calculations leads to magnetic anisotropies and reduces the symmetry of the problem. The theory of magnetic groups is required to make full use of the remaining symmetry, which in turn then is applied to the Green's function method.
The Muffin-Tin-Orbital Point of View
Authors: Andersen O. K. , Postnikov A. V. , Savrasov S. Yu.
Published: March 2011

We review the interpretation of multiple-scattering theory in terms of muffin-tin orbitals. The use of slightly overlapping muffin-tin wells is justified rigorously. It is shown that the structure constants may be screened for a useful range of positive and negative energies, and that the screening may be chosen to yield desirable properties of the KKR matrix. Energy linearization and the linear muffin-tin-orbital method are discussed.
Wave Propagation in Dispersed Random Media
Authors: Sheng Ping , Jing Xiaodun , Zhou Minyao
Published: March 2011

We present a generalized coherent potential approximation for the identification of quasi propagating modes in dispersed random media and the calculation of their dispersion relations. The validity of this approach is supported by multiple-scattering calculations, numerical simulation, and comparison with experimental data on acoustic excitations in colloidal suspensions. Our theory yields excellent quantitative agreement with the measured dispersion relations and provides an explanation for the observed frequency gaps in the excitations spectra.
Complex Geometry and Electric Double Layers
Authors: Duplantier Bertrand
Published: March 2011

The properties of electric double layers near curved surfaces of arbitrary shape and genus are obtained exactly within the Debye-Hückel theory by means of multiple-scattering expansion. For smooth membranes, geometric and topological feature of the electrostatic free energy then emerge through convergent expansions in inverse powers of the principal radii of curvature. Some consequences for the electrostatic stability of various membrane shapes are considered. We also study the effects of surface singularities, e.g., wedges, on the thermodynamics of electric double layers near a rough colloid. Each wedge yields an additive contribution to the free energy that is a functionof the angle. A probabilistic Brownian representation of is given, which is entirely similar to that of vibration eigenmodes given by M. Kac long ago in “Canone hear the shape of a drum?” [Amer. Math. Monthly 73S, 1 (1966)]. The analysis yields a universal scaling law for the free energy of a rough colloid with its fractal Minkowski dimension.
Optical Response of Rough Metal Surfaces and Island Films
Authors: Urbakh M.
Published: March 2011

This study treats the optical properties of different two-dimensional inhomogeneous systems in which localized and delocalized surface modes excited by incident light can exist. The optical response is described with the use of kinetic equations linking together different types of surface and bulk modes. It is important that both electromagnetic interactions between local modes and the dependence of the optical characteristics of centers on the local geometrical structure are taken into account.

It is shown that the behavior of experimentally observable quantities (enhancement ratioof the electric field at the surface, surface absorption, etc.) as functions of the frequency and concentration of local centers depends essentially on the excitation mechanismof local modes.
Applications of Multiple Scattering Theory to Electron Spectroscopy
Authors: Durham P J
Published: March 2011

Because it gives direct and convenient access to the Green's function, multiple scattering theory (MST) provides a powerful machinery for the calculation of I particle observables in general and electron spectroscopies in particular.

The two techniques in which multiple scattering methods have made the biggest impact areangle-resolved photoemission and x-ray spectroscopy (absorption and emission); here the essential point is that MST allows experimental data to be analysed and modelled on the same footing as calculations of the underlying electronic structure, for both ordered and disordered systems. Applications in these areas are briefly reviewed, drawing attention to the two outstanding current deficiencies of the methodology (the use of density functional theory to describe excited states and the approximate — muffin-tin — form of the effective 1—electron potential) as well as its successes.

Current developments, particularly the treatment of relativistic and magnetic systems, the possibilities opened up by third-generation synchrotron radiation sources, and the use of parallel computing techniques, are mentioned.
Charge and Spin Selfconsistent Kkr-Cpa Methodology for Complex Multi-Component Alloys
Authors: Bansil A. , Kaprzyk S. , Tobola J.
Published: March 2011

We have developed the charge and spin selfconsistent KKR-CPA approach for a first-principles parameter free treatment of disorder effects in complex multi-component alloys. Thenature of the KKR-CPA Green's function in the complex energy plane is discussed. A generalized Lloyd formula for the density of states is obtained and some subtle features of the formalism are pointed out. We illustrate our KKR-CPA methodology by giving a number of examples of magnetic as well as non-magnetic systems. The non-magnetic cases considered are the simple cubic perovskites BaxK1−0BiO3 and BaPb—1BixO3, and the high-Te superconductor La2—xSrxCuO4 for the body-centeredtetragonal phase. The examples of magnetic systems discussed are, the the Heusler alloys Co2—xFexMnSi (L21 structure), and the semi-magnetic semiconductor Cdl—xMnxTe in the zincblende structure.
Mechanical Behavior of Hierarchical Synthetic Composites
Authors: Mayer George
Published: March 2011

Diverse microstructures observed in rigid natural composites have been linked to mechanical properties that are equal to and, at times, superior to those which have been designed into synthetic composite materials comprised of organic, metallic, and ceramic constituents. The constitution, properties, and microstructures of the natural and synthetic materials are described, along with what is known and what is unknown about the constituent components, and interfaces. Hierarchical approaches to designing with and the mechanical analyses of both natural and synthetic composites will be described.
The Influence of Reinforcing Fibers on the Morphology and Crystallization of Thermoplastic Polymer Composites
Authors: Rebenfeld Ludwig , Desio Glenn P. , Reinsch Veronika E.
Published: March 2011

Semi-crystalline thermoplastic polymers are being used increasingly as matrices in high performance fiber reinforced composites. The crystallization kinetics and morphology of these polymers have been studied extensively, but relatively little attention has been given to the effects of the reinforcing fibers on the crystallization process.

We have studied the effects of glass, carbon and aramid fibers on the rates of crystallization, the degree of crystallinity, and the glass transition temperature of such typical thermoplastics as poly(phenylene sulfide) and poly(ethylene terephthalate). Based on the isothermal crystallization studies using DSC, we find that, in general, reinforcing fibers increase the rates of crystallization and decrease the degree of crystallinity, the extent of these effects being dependent on the weight fraction of fiber in the composite, the specific type of fiber, and the nature of surface finishes (sizes) that may have been applied.

The spherulitic morphology that develops in these polymers during the crystallization process, as characterized by polarized light microscopy, is also affected by the reinforcing fibers. In many cases, transcrystalline regions develop near the fiber surface due to nucleation effects.
Structure-Mechanical Property Relationships In A Biological Ceramic-Polymer Composite: Nacre
Authors: Gunnison Katie E. , Sarikaya Mehmet , Liu Jun , Aksay Ilhan A.
Published: March 2011

The structure-mechanical property relationships were studied in nacre, a laminated ceramicpolymer biocomposite found in seashell. Four-point bending strength and three-point bend fracture toughness tests were performed, and the results averaged 180 ± 30 MPa and 9 ± 3 MPa·m1/2, respectively, indicating that the composite is many orders of magnitude stronger and tougher than monolithic CaCO3,, which is the primary component of nacre. Fractographic studies conducted with a scanning electron microscope identified two significant toughening mechanisms in the well-known “brick and mortar” microstructure of nacre: (i) sliding of the aragonite platelets and (ii) ligament formation in the organic matrix. These toughening mechanisms allow for high energy absorption and damage tolerance and thereby prevent catastrophic failure of the composite. The structure of the organic matrix and the interfacial structure between the organic and inorganic components were studied with transmission electron microscopy by using both ion milled and ultramicrotomed sections with and without the intact aragonite platelets. We found that the organic matrix is indeed a multilayered composite at the nanometer scale but is thinner (about 100 Å) than reported in the literature. The morphology of the interfacial region between the organic and the inorganic layers suggests the presence of a structural “transitory” region that interlocks the two dissimilar phases.
DNA Binding To Conducting Polymer Films
Authors: Lim Jeong-Ok , Minehan Daniel S. , Kamath M. , Marx Kenneth A. , Tripathy Sukant K.
Published: March 2011

The polycation conducting polymers, oxidized polypyrrole and polyalkylthiophene, possess the ability to form complexes with polyanionic DNA molecules through largely electrostatic interactions. This study demonstrated the solution uptake and binding of 32p radiolabeled DNA by conducting polymer thick films (50–100μm). Polypyrrole (PPy) was synthesized by electrochemical methods and poly(3-hexylthiophene) (PHT) and poly(3-undecylthiophene) (PUT) were synthesized by chemical methods. The DNA binding rates on PPy films were affected by DNA concentration and the oxidation state (measured as conductivity). The DNA kinetics support a diffusion limited model for binding. We measured DNA binding levels onto all three polymer films; PUT, PHT, and PPy. The binding levels increased in the same order as the conductivities of the polymer films. DNA binding onto oxidized PPy film was diminished upon electrochemical reduction. These observations showed, therefore, the binding may be linked with the positive charge sites responsible for conduction in the polymer films.
α-Hemolysin: A Self-Assembling Protein Pore With Potential Applications In The Synthesis of New Materials
Authors: Bayley Hagan , Krishnasastry Musti , Walker Barbara , Kasianowicz John
Published: March 2011

A selection of nanoscale membrane pores is being constructed by genetic manipulation of α-hemolysin (αHL), a 33.2 kDa polypeptide secreted by the bacterium Staphylococcus aureus, which can self-assemble into hexameric cylindrical channels -1 to 2 nm In Internal diameter. Ultimately, the new pores will be used to confer novel permeability properties upon materials such as thin films utilizing, for example, monolayer sheets of the hexamer. Recombinant αHL (r-αHL) has now been obtained in multimilligram amounts and purified to homogeneity after overexpression of the αHL gene in Escherichia coli. The properties of r-αHL are closely similar to those of αHL purified from S. aureus. Recent deletion mutagenesis experiments have given us new insight into the assembly mechanism of the pore. Three intermediates have been identified: a membrane-bound monomer; an oligomeric pore precursor; and the hexameric pore itself. Currently, point mutogenesis combined with chemical modification is being used to produce new pores of different internal diameter, with selectivity for the passage of molecules and Ions, and with gating properties (the ability to open and close in response to a physical stimulus, e.g. an electric field or light).
Design and Synthesis of Metals (Tungsten) with Structural Hierarchy for Very High Temperatures
Authors: Welsch G.
Published: March 2011

The strength of metals is limited by the weakest link in their microstructures. At high temperature, the weakest link is usually a grain boundary. Mobile dislocations represent another type of weak link. The strength-limitation by this two-level hierarchy of crystal defects can be minimized through microstructure design. Although the strengthening mechanisms differ for grain boundaries and dislocations, it is possible to design microstructural architectures that strengthen both. The design must take the stress state into consideration that the component will encounter during its later use. Processing strategies can then be devised for the synthesis of such components. It is imperative to stabilize the designed microstructure at high temperature because this will determine how well and how long the material will be able to perform. Design, synthesis and stabilization are discussed in the present paper. The lamp filament wire technology is the basis for a new method that enables the synthesis and stabilization of artificial microstructures in high-temperature materials.
Nonlinear Optical Properties of Hierarchical Systems
Authors: Prasad Paras N.
Published: March 2011

Nonlinear optical processes provide many of the functions needed for Photonics Technology. Molecular materials are hierarchical systems in which the structure can be controlled from the angstrom level to macroscopic scale to optimize the nonlinear optical properties. In this article basic concepts of nonlinear optics and photonics are reviewed. Multifunctional molecular hierarchical systems are discussed which involves heterostructure design at molecular and bulk levels. For optimization of nonlinear response at the molecular level, guidance from theoretical modeling and study of sequentially built and systematically derivatized structures has proven to be useful. The use of Langmuir-Blodgett film approach to control the order and conformation with monolayer resolution is discussed. Examples of our approach to optimize the response at the bulk level involve the use of orientation control by electric field poling and use of composite heterostructures. An important advancement in heterostructure design is the use of sol-gel processing to make organic-inorganic composites which have successfully exhibited electro-optic modulation and femtosecond Kerr gate operations. Finally, novel photorefractive molecular materials are discussed.
Morphology Control Of The Electrochromic Effect In Tungsten Oxide Thin Films
Authors: Witham H. S. , Chindaudom P. , Messier R. , Vedam K.
Published: March 2011

Electrochromic tungsten oxide thin films have been prepared by reactive dc-magnetron sputtering under different deposition conditions. Through the use of scanning electron microscopy, spectroscopic ellipsometry, and electrochromic coloration experiments, the effect of preparation conditions on film morphology and electrochromic properties has been studied. The results of this study are consistent with a previous report which found that tungsten oxide thin films are dominated by a hierarchy of dense columnar regions and less dense void regions. This morphology not only dominates the structure of tungsten oxide thin films but also strongly controls the electrochromic properties. From spectroscopic ellipsometry data and Bruggeman effective medium approximation models presented here, it seems reasonable that a cermet model of absorption can accurately describe the tungsten oxide preparationelectrochromic property relationship.
Hierarchical Tilings
Authors: Senechal Marjorie
Published: March 2011

Tiling problems arise in many areas of science, and they raise fascinating but difficult mathematical questions. Nonperiodic hierarchical tilings are particularly interesting and important. We discuss several examples of such tilings and indicate some of the unsolved problems related to them.
Hierarchically Structured Materials Generated in Membrane Mimetic Systems: Nanosized Particle Production of Cds and ZnS at Monolayers
Authors: Fendler Janos H.
Published: March 2011

The hierarchical evolution of the different mimetic systems and the concomitant level of control in the biomimetic mineralization will be critically discussed.
Toward Monodisperse Poly(γ–benzyl α,L-glutamate): Uniform, Polar, Molecular Rods
Authors: Zhang Guanghui , Fournier Maurille J. , Mason Thomas L. , Tirrell David A.
Published: March 2011

Poly(γ-benzyl α,L-glutamate) (PBLG) has been widely used in studies of the physics of rod-like polymer chains [1]. The helical structure of PBLG gives rise to considerable chain stiffness, such that the persistence length of the chain is on the order of 70 nm in helicogenic solvents [2]. This feature, coupled with the ease of synthesis and good solubility of the polymer has made PBLG the system of choice for the study of both isotropic [2,3] and liquid crystalline [4] solutions of rod-like macromolecules.
Hierarchical Structures in Liquid Crystalline Polymers
Authors: Sawyer Linda C. , Jaffe Michael
Published: March 2011

It is well known that the structure of highly oriented liquid crystalline polymers (LCPs) can be characterized by a hierarchical fibrillar structural model. Structure models were developed for the lyotropic aramid fibers and the thermotropic aromatic copolyester fibers during the last two decades showing the existence of fibrillar hierarchies. Hierarchies of structure have also been commonly observed for the biological materials. Concepts learned from the latter are useful in materials science studies today. The nature of the smallest nanostructure that aggregates, the combination of these small structures, typically microfibrils, into larger structures and the interaction of these hierarchical entities are important to understanding their behavior. The architecture of the whole of the polymer or the biological material is a further important variable as is the relation of the process with that architecture. This paper discusses details of the structure of LCPs and draws an analogy between the materials science and biological hierarchies.
A Hierarchically Structured Model Composite: A Tem Study of the Hard Tissue of Red Abalone
Authors: Liu Jun , Sarikaya Mehmet , Aksay Ilhan A.
Published: March 2011

The structure and crystallography of the nacre of red abalone, Haliotis rufescens, was studied by transmission electron microscopy imaging and diffraction. We found that the nacre structure is based upon hierarchical {110} twinning in aragonite with the following organization: (i) first generation twins between platelets having incoherent boundaries, (ii) second generation twins between domains having coherent boundaries within a given platelet, and (iii) nanometer-scale third generation twins within domains. Since the aragonite platelets nucleate and grow as separate crystals, this long-range crystallographic relationship between the inorganic units of a biological hard tissue indicates that the nucleation and growth process of crystals may be mediated by the organic matrix and that the organic template structure may also be long-range ordered. We propose a superlattice structure based on the possible twin variants and suggest that the organic matrix structure, or the arrangement of nucleation sites, is compatible with the superlattice. Multiple tiling based upon this superlattice allows all of the crystallographic and morphological platelet configurations observed in nacre.
Photoluminescence in Porous Silicon: Evidence for the Quantum Confinement Model
Authors: Naylor David L. , Lee Sung B. , Pincenti John C. , Bouma Brett E.
Published: March 2011

Photoluminescence spectra have been measured in porous silicon following electrochemical etching in dilute hydrofluoric acid (HF). The effects of HF concentration during etching on the efficiency and peak wavelength of photoluminescence have been investigated. The effects of temperature between 25°C and 200°C on PL spectra have been recorded. Photoluminescence lifetimes as a function of wavelength have been studied following ultrashort UV photoexcitation. A number of lifetime components in the decay are observed the longest in good agreement over the wavelength range of 500 to 600 nm with a silicon quantum wire model. At longer wavelengths a departure from lifetimes of the wire model is observed and two hypotheses for the discrepancy are presented.
Optical Properties of Microcrystalline Silicon in Oxide Matrix through Partial Oxidation of Anodized Porous Silicon
Authors: Ito Toshimichi , Ohta Toshimichi , Arakaki Osamu , Hiraki Akio
Published: March 2011

Microcrystalline silicon embedded in silicon oxide has been prepared by means of partial oxidation of porous silicon produced anodically from degenerate p-Si wafers. Their optical properties such as absorption coefficients and luminescence have been characterized. Results show blue shifts in absorption and photoluminescence spectra in a visible wavelength region with decreasing size of the microcrystalline Si in the Si oxide matrix. The quantum size effect is discussed as well as possible origins of the observed visible luminescence, including light emission from as-anodized (or H-chemisorbed) porous silicon.
Analysis of the Structure of Light-emitting Porous Silicon by Raman Scattering
Authors: Sui Zhifeng , Leong Patrick P. , Herman Irving P. , Higashi Gregg S. , Temkin Henryk
Published: March 2011

Abastrac

Raman spectra from a thick porous silicon film (∼100 μm) that strongly emits in the visible (∼ 6350 Å) at room temperature are obtained. An asymmetric peak with a Raman shift of ∼ 508 - 510 cm−1 and a width of ∼ 40 cm−1 is seen in every spectrum. This Raman feature resembles that of μc-Si, suggesting that the local structure of the porous silicon is a network of interconnected crystalline silicon islands with the island size in the nanometer range., and that the, shape of the islands is more sphere-like than rod-like. The characteristic dimension of the islands in these porous silicon films is estimated to be ∼ 2.5 - 3.0 nm on the basis of an empirical model calculation of phonon confinement.
Luminescent Colloidal SI Suspensions from Porous SI
Authors: Heinrich Julie L. , Curtis Corrine L. , Credo Grace M. , Kavanagh Karen L. , Sailor Michael J.
Published: March 2011

A procedure for generating colloidal suspensions of Si exhibiting luminescence, attributed to quantum confinement effects, is described. Samples of n- or p-type Si, that have been electrochemically etched to form porous Si, can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show the Si particles to have irregular shapes, with diameters ranging from many microns to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution.
Radiative Recombination Mechanisms in Porous Silicon
Authors: Gardelis S. , Hamilton B. , Kubiak R. A. , Whall T. E , Parker E. C. H.
Published: March 2011

This paper attempts to address the question of the role played by dimensionality in the observed optical transitions of porus silicon and related material systems. The effect of the degree of porosity on the transition energies, line widths and thermal stability. In addition more subtle effects observed in the thermal behaviour of the spectra which may relate to carrier trapping in a random potential of an imperfect localised system are reported. Comparisons with the spectral behaviour which would be predicted by quantum scale confinement of electronic particles are made.
Near IR and Visible Photoluminescence Studies of Porous Silicon
Authors: Perry C. H. , Lu F. , Namavar F. , Kalkhoran N. M. , Soref R. A.
Published: March 2011

We report photoluminescence emission and photoluminescence excitation studies of porous silicon obtained from p-type Si(111) wafers over the range of 0.9–13.0 eV (∼400–1400 nm). Strong IR emission above and below the bulk silicon band gap at ∼1.09 eV (1135 nm) at 300 K was observed. This luminescence due to intrinsic band-to-band recombination, was found to be enhanced by two orders of magnitude or more over the IR spectrum from an unanodized wafer. The visible luminescence peak that has been attributed to quantum confinement effects in porous silicon was located at ∼1.8 eV (689 nm). We studied the high intensity IR and visible PL in detail as a function of temperature (4–700 K), laser excitation energy (1.96–3.80 eV), and laser power (0.1–1000 mW). The measured shift in the bulk silicon band gap was approximately linear from 300–700 K (∼−0.22 meV/K), while the visible peak red-shifted by ∼− 1.24 meV/K over the same range. Below 300 K they both had comparable temperature dependences. The visible PL was investigated at room temperature in magnetic fields up to 15 T; no discernible shift in the peak position or change in the peak intensity was observed.
Photoluminescence (PL) and Optically Detected Magnetic Resonance (ODMR) Study of Visible Light Emission from Porous Si
Authors: Lane P. A. , Swanson L. S. , Shinar J. , Chumbley S.
Published: March 2011

The photoluminescence (PL) and X-band ODMR of porous Si layers is described and discussed. The layers were prepared by anodizing the (100) face of a Si wafer at 20 mA/cm2 in 20% HF for 5 mai and passively soaking them in 36% HF for up to 10 hrs. The PL was broad and featureless, extending from ˜1.5 to ˜2.1 eV and peaking at 1.68 eV. Its intensity slightly increased upon cooling to 90 K, and then strongly decreased at lower temperatures. A ˜20 G wide asymmetric PL-enhancing ODMR was observed at g ˜2.0031 ±I 0.0009, which could be fit to a sum of two Gaussians. Their g-values were slightly temperature dependent. The ODMR intensity strongly decreased with increasing temperature, and was unobservable above ˜80 K. The results are compared to the optical properties of hydrogenated amorphous Si.
Effect of Surface Coverage on Porous Silicon Photoluminescence: Transmission FTIR Studies
Authors: Robinson M. B. , Dillon A. C. , Haynes D. R. , George S. M.
Published: March 2011

Transmission Fourier Transform Infrared (FTIR) Spectroscopy was utilized to monitor the effect of surface coverage on photoluminescent porous silicon. These experiments were performed in situ in an ultrahigh vacuum (UHV) chamber to correlate simultaneously surface coverage and photoluminescence intensity. The goal of these FTIR and photoluminescence studies was to clarify the mechanism of the photoluminescence from porous silicon.
An Intrinsic Model for Radiative Recombination in Porous Silicon
Authors: Hybertsen Mark S.
Published: March 2011

A microcrystalline model for the light emitting portion of porous silicon is outlined. Confinement to a short length scale induces an effective direct dipole matrix element for radiative recombination. The radiative recombination time is strongly size (hence confinement induced energy shift) dependent, and in the microsecond regime for blue shifts of ˜1 eV. Trends and comparison to experiment are discussed.
Structural Characterization of Porous Silicon Fabricated by Electrochemical and Chemical Dissolution of Si Wafers
Authors: Miyazaki S. , Yasaka T. , Okamoto K. , Shiba K. , Sakamoto K. , Hirose M.
Published: March 2011

The structure of porous silicon exhibiting efficient visible photoluminescence has been characterized by using Fourier transformed infrared absorption, Raman scattering and x-ray diffraction. It is shown that the lattice spacing in the porous Si layer expands by about 0.3% in the direction perpendicular to the surface and also a partially disordered structure is existing. Electron beam irradiation causes desorption of hydrogen and fluorine bonds which terminate the surface, resulting in the quenching of the visible luminescence. The chemical etching of such layer has led to complete recovery of the luminescence intensity as well as the hydrogen and fluorine bonds termination.
Optical Characteristics of Porous Silicon
Authors: Tischler M. A. , Collins R. T. , Tsang J. C. , Stathis J. H. , Batstone J. L. , Zollner S.
Published: March 2011

The luminescent characteristics of porous silicon are affected by the preparation conditions as well as subsequent treatment. Oxidation, which easily occurs in ambient conditions under illumination, greatly reduces the luminescence efficiency. Vertical inhomogeneity, which is inherent from the preparation procedure, can complicate interpretation of results, especially following treatments which non-uniformly affect the porous material. These results point out the need to pay careful attention to the sample's structure and history, as well as the necessity of controlling this degradation in order to realize practical luminescent devices.
Heating, Laser Irradiation and Passivation Study on the Light-Emitting Porous Silicon
Authors: Chen H. C. , Wang W. , Manjularani K. N. , Snyder L. C. , Zheng X. L.
Published: March 2011

For light-emitting porous Si there has been a severe problem with instability and degradation of the light emission. We report that a stabilization of the emission intensity and the peak energy can be achieved in air by a proper laser irradiation, In-situ photoluminescence measurements were performed to monitor the degradation and stabilization process under different conditions and parameters, such as laser power, laser wavelength and environment (ambient atmosphere of certain gas or ultra high vacuum). We found oxygen is the major cause for the emission degradation in this laser enhanced adsorption process, and the laser heating effect can be excluded. For a comparison we study the reversible thermal heating and quenching process. We also discuss microwave and ECR plasma passivation results.
The Role of Silicon Monohydride and Dihydride in the Photoluminescence of Porous Silicon and Photoluminescence of Porous Silicon Buried Underneath Epitaxial GaP
Authors: Tsai C. , Li K.-H. , Sarathy J. , Jung K. , Shih S. , Hance B. K. , White J. M. , Kwong D.-L. , Sharps P. R. , Timmons M. L. , Venkatasubramanian R. , Hutchby J. A. , Campbell J. C.
Published: March 2011

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier-transform infrared (FTIR) spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures > 300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. The role of silicon hydride species on the photoluminescence intensity has been studied. The surfaces of luminescent porous Si samples were converted to a predominate SiH termination using a remote H-plasma. The as-passivated samples were then immersed in various concentrations of hydrofluouric solutions to regulate the recovery of SiH2 termination on the surface. Photoluminescence measurements and transmission Fourier-transform infrared spectroscopy have shown that predominant silicon monohydride (SiH) termination results in weak photoluminescence. In contrast, it has been observed that the appearance of silicon dihydride (SiH2) coincides with an increase in the photoluminescence intensity. To achieve electroluminescence it will be beneficial to generate carriers with sufficient energy to populate the states of the quantum-confined Si structures. A viable method to accomplish this is to utilize a wide-bandgap heterojunction injector such as GaP. Toward that end we report the successful formation of porous Si buried underneath GaP islands and we demonstrate that the buried porous Si layer exhibits strong photoluminescence.
Electroluminescent Properties of Porous Silicon Films under Electrochemical Oxidation
Authors: Billat S. , Bsiesy A. , Gaspard F. , Herino R. , Ligeon M. , Muller F. , Romestain R. , Vial J. C.
Published: March 2011

Bright visible electroluminescence has been evidenced during the anodic oxidation of ptype porous silicon films in aqueous electrolytes. It is shown that in galvanostatic conditions, two very different light emission regimes can be obtained depending on the anodic potential. At low potentials, during the progressive oxidation of the pore walls, the emission spectra present a maximum in the red-orange wavelengths : the emitted intensity increases with the oxidation level, while the maximum is shifted towards shorter wavelengths. This emission vanishes when the anodic potential starts to increase more rapidly. Upon increasing polarizations, a second regime of light emission with a spectrum centered in the green wavelength range is observed. In this case, the spectrum and the intensity are both stable under extended anodization.

This last regime which is explained by carrier injection into the anodic oxide is not specific of the porous character of samples. On the contrary, the red-orange emission is shown to be closely related to the photoluminescence properties of the porous layer. A phenomenologic model is proposed, which analyses the electroluminescence characteristic dependence upon the oxidation level in terms of competition between the enhancement of the radiative process and the progressive electrical cut-off of the emitting crystallites.
Visible Electro- and Photoluminescence from Porous Silicon and its Related Optoelectronic Properties
Authors: Koshida Nobuyoshi , Koyama Hideki
Published: March 2011

The optoelectronic properties of porous Si (PS) are presented in terms of electroluminescence (EL), photoluminescence (PL), photoconduction (PC), and optical absorption. Observations of injection-type EL, efficient PL, band-gap widening, and photosensitivities In the visible region are consistent with the quantum size effect model in PS.
Infrared and Visible Emission from Si Layers
Authors: Kux A. , Lugli P. , Ostermeir R. , Koch F. , Deboy G.
Published: March 2011

We present an experimental study of light emission in silicon devices, mainly MOSFETs, p-i-n diodes, and MIS structures. The special analysis shows important features below as well as above the gap, indicating the type of mechanism responsible for the light emission. Striking differences we found between planar and vertical-type structures.
Structure and Composition of Luminescent Laterally Anodized Porous Si
Authors: Jung K. H. , Shih S. , Hsieh T. Y. , Campbell J. C. , Kwong D. L. , George T. , Lin T. L. , Liu H. Y. , Zavada J. , Novak S.
Published: March 2011

We have made structural and compositional studies of luminescent laterally anodized porous Si. Scanning electron microscopy reveals a surface with a network of cracks, while transmission electron microscopy shows a dual porous Si structure in which the upper layer is amorphous and the lower layer is either amorphous or crystalline, depending on anodization conditions. X-ray diffraction verified the presence of the amorphous layer. Secondary ion mass spectroscopy reveals very high concentrations of H, B, C, N, O, and F in the amorphous layer. Our results indirectly suggest that the amorphous layer is primarily responsible for luminescence.
Excitation Spectra of the Visible Photoluminescence of Anodized Porous Silicon
Authors: Motohiro Tomoyoshi , Kachi Tetsu , Miura Fusayoshi , Takeda Yasuhiko , Hyodo Shi-Aki , Noda Shoji
Published: March 2011

Porous silicon samples photoluminous in orange, pink or greenish-yellow were formed by anodization. The shapes and wave length positions of their photoluminescence peaks were not influenced by the excitation wavelength. The photoluminescence intensity at any wavelength between 520nm and 800nm varied as a function of the excitation wavelength In accordance with the imaginary part of the spectral refractive index of bulk silicon. Thus the excitation process responsible for the visible photoluminescence of porous silicon seems to be bulk-silicon-like.
Electro- and Photoluminescence from Ultrathin SImGEn Superlattices
Authors: Presting H. , Menczigar U. , Abstreiter G. , Kibbel H. , Kasper E.
Published: March 2011

P-i-n doped short-period SimGen strained layer superlattices (SLS) are grown on (100) silicon substrates by low temperature molecular beam epitaxy (300C°<∼Tg<∼400C°). The SLS's are grown with period lengths around 10 monolayers (ML) to a thickness of 250nm on a rather thin (50nm) homogeneous Si1−ybGeyb alloy buffer layer serving as strain symmetrizing substrate. Photoluminescence at T=5K is observed for various SimGen SLS samples, the strongest signal was found for a Si5 Ge5 SLS. Samples with identical SLS's but different buffer layer composition and thicknesses are grown to study the influence of strain on the PL. Electroluminescence (EL) at the same energy range is observed from mounted SimGen SLS mesa and waveguide diodes up to T=130K – for the first time reported in strain symmetrized short-period SimGen SLS. The intensity and peak positon of the EL signal was found to be dependent on the injected electrical power.
NP Heterojunction Porous Silicon Light-Emitting Diode
Authors: Kalkhoran Nader M. , Namavar F. , Maruska H. P.
Published: March 2011

We report the first demonstration of visible light emission from an all solid-state n-p heterojunction diode based on porous silicon. The p-type silicon was electrochemically etched in a hydrofluoric acid solution to form a porous silicon region; the n-p heterojunction diode was fabricated by depositing a wide bandgap n-type semiconductor, indium-tin-oxide (ITO), onto the surface of the porous silicon. With positive bias applied, electroluminescence was observed with a relatively narrow peak at about 580 nm. The device showed strong rectifying properties and no light emission was observed under reverse bias condition. Photoluminescence in the red, orange, yellow, and green was also observed in separate sample preparations.
Comparison of in Situ and Laboratory Corrosion Experiments with Borosilicate Nuclear Waste Glass
Authors: Lutze Werner , Ewing Rodney C.
Published: March 2011

The comparison of laboratory data from the corrosion of borosilicate nuclear waste glass (German SM513LW11 and French R7T7) with data from the Materials Interface Interactions Test (MIIT) and Repository Systems Simulation Test (RSST) illustrates the inherent limitations of in situ tests. Although in situ tests may confirm the short term behavior of waste forms and identify phenomena associated with the repository system, they do not provide the fundamental basis for the extrapolation of long-term behavior.