bluuebunny/crossref_metadata_2025 huggingface dataset:
Susceptor and Proximity Rapid Thermal Annealing of InP
Authors: Katz A. , Pearton S. J. , Geva M.
Published: March 2011

An intensive comparison between the efficiency of InP rapid thermal annealing within two types of SiC-coated graphite susceptors and by using the more conventional proximity approach, in providing degradation-free substrate surface morphology, was carried out. The superiority of annealing within a susccptor was clearly demonstrated through the evaluation of AuGe contact performance to carbon-implanted InP substrates, which were annealed to activate the implants prior to the metallization. The susceptor annealing provided better protection against edge degradation, slip formation and better surface morphology, due to the elimination of P outdiffusion and pit formation. The two SiC-coated susceptors that were evaluated differ from each other in their geometry. The first type must be charged with the group V species prior to any annealing cycle. Under the optimum charging conditions, effective surface protection was provided only to one anneal (750°C, 10s) of InP before charging was necessary. The second contained reservoirs for provision of the group V element partial pressure, enabled high temperature annealing at the InP without the need for continual recharging of the susceptor. Thus, one has the ability to subsequentially anneal a lot of InP wafers at high temperatures without inducing any surface deterioration.
In-Based Ohmic Contacts to the Base Layer of GaAs-AlGaAs Heterojunction Bipolar Transistors
Authors: Ren F. , Pearton S. J. , Hobson W. S. , Fullowan T. R. , Emerson A. B. , Yanof A. W. , Schleich D. M.
Published: March 2011

The use of AuBe-In/Ag/Au p-ohmic contacts for the base layer of GaAs-AIGaAs heterojunction bipolar transistors (HBTs) is described. Annealing at 420°C for 20 sec produces a contact resistivity of 0.095 Ω mm and a specific contact resistance of l.5 × 10-7 Ω cm2, and the surface morphology of the contact is excellent. The role of the silver is as a diffusion barrier to prevent Au spiking into the base layer which could degrade the HBT performance. The presence of the In layer is highly desirable in order to reduce the contact resistance, probably by forming an InGaAs phase at the metal-GaAs interface. Beryllium acts as the p-type dopant, and the top Au layer is used to lower the contact sheet resistance. Current transport through the structure is dominated by tunneling through the barrier due to field emission in the highly doped base layer at p-type doping levels above ∼1019 cm−3
A Novel Technique for Detecting Defects in Ulsi Metallized Systems
Authors: Pico C. A. , Aton T. , Gale R. J. , Bennett-Lilley M. , Harward M. , Mahant-Shetti S. , Weaver T.
Published: March 2011

Defect location and identification in the metallization systems of ultra-large-scale integrated (ULSI) devices is becoming increasingly important because of the demands of high device density. An understanding of the sources of defects is crucial to the fabrication of submicron devices. Typically, defect identification is accomplished by electrically testing large metal combs and serpents followed by scanning electron microscopy (SEM) investigation. In order to identify metallization defects quickly, we have fabricated a novel device that bypasses the need to electrically probe. This technique utilizes voltage contrast imaging in-situ SEM to locate defects typically found during ULSI device fabrication. While voltage contrast imaging has been used to locate defects in conjuction with externally applied voltages [1], our technique takes advantage of the SEM's own beam as a charging source and makes close resolution (<0.1μm) inspection unnecessary until appropriate. In this way, defects can be located and identified using ∼/20th the time presently required.
Interaction of Copper Film with Silicides
Authors: Shy Yow-Tzong , Murarka Shyam P. , Shepard Carlton L. , Lanford William A.
Published: March 2011

Bilayers of Cu with TiSi2 and TaSi2 were tested by furnace annealing at temperatures from 200 to 500°C. Rutherford Back Scattering (RBS) technique was used to investigate the interaction between various films and determine the stability of Cu on silicide structures. The sheet resistance was also monitored. The results show that Cu on TiSi2 and TaSi2 structures are extremely stable structures at annealing temperatures in the range of room temperature to 500 °C. In such structures, therefore, there will not be a need of any diffusion barrier between Cu and the silicide films.
Analysis of Materials from a Late 15th-Early 16th Century Polychromed Wood Sculpture
Authors: Stodulski L. P. , Dorge V. J.
Published: March 2011

During conservation, The Detroit Institute of Arts' late Gothic carved wooden sculpture, Madonna and Child, was found to have extensive, though fragmentary, remains of the original polychromy and at least four subsequent “restoration” overpaints. The materials present in the original and overpaintings were probed by polarizing microscopic and X-ray diffraction analyses of individual paint specimens, and scanning electron microscopic/energydispersive X-ray analyses of cross sections prepared using an ultramicrotome. Several sections were also studied using ultraviolet fluorescence microscopic staining techniques to determine the nature of the media used.

The pigments identified include azurite, lead white, calcite, vermilion, red lead, hematite, red lakes and glazes, smalt and Prussian blue. Gold and silver metal leafs were also detected. The deteriorated remains of the late Gothic pressed brocade technique, and the use of “bronze” paint to approximate genuine gold leaf on a later addition to the sculpture, are also discussed.
Surfactants and Adherent Silicon Resins - New Protective Agents for Natural Stone
Authors: Snethlage Rolf , Wendler Eberhard
Published: March 2011

The present paper reports investigations on the application of surfactants in the stone conservation. It is found that alkyl ammonium chlorides reduce the hygric dilatation of clay-rich sandstones to half of the original value. Polysiloxane films can be tightly bound to clay mineral basal planes using aminoalkyl silane as primer. The water uptake as well as the hygric swelling are markedly reduced. Well defined mixtures of ethanolic alkyl silane and aqueous aminoalkyl silane solutions form stable microemulsions. They can be used as commercial conservative products which are compatable with the environment.
Modification of the Physical Properties of Natural and Artificial Adobe by Chemical Consolidation
Authors: Coffman Richard L.
Published: March 2011

The use of commercially available chemical consolidants (hexamethylene diisocyanate (HDI) - derived polymers and silane esters) has been shown to increase the compressive strength of adobe and other natural building materials. Laboratory and field testing of chemically-treated adobe and sand-clay mixtures have also revealed an enhanced resistance to disintegration by water.

In HDI-treated materials this resistance to disintegration is attained without a significant loss of porosity. Because porosity is not lost and the adobe can still transmit water, the uptake of water by capillary rise is less destructive than for an adobe whose surface is sealed against moisture penetration.
Protective Coatings for Medieval Stained Glasses
Authors: Schmidt H. , Fuchs D.
Published: March 2011

The corrosion protective effect of the surface modification of corrosion sensitive glass surfaces and of ORMOCER (= organically modified ceramic) coatings is investigated. The surface modification provides a modest protection, perhaps useful for additional protection in combination with external glazing. The advantage is the “invisability” of the modification due to the thickness of several molecular layers. An effective protection can be obtained by a diffusion barrier pigmented ORMOCER coatings. First outdoor results on medieval glasses are very hopeful, but long period experience is necessary for wider application.
Venice: Stone Material Behaviour in Connection with the Environment
Authors: Biscontin G. , Fassina V. , Miaravelaki P. , Zendri E.
Published: March 2011

The present study is directed to summarize several studies carried out in the recent past on stone decay processes taking place in the lagoon environment of Venice. The behaviour of the main types of stones used in Venetian buildings has been considered.

Istrian stone, Verona red stone and Carrara marble were studied.

The knowledge of the porosity and of the pore size distribution can contribute to clarify the physical transformation of decayed materials.

The research determined the morphology of stone decay processes for the different types of stone.

As far as the morphology of deterioration is concerned, there are two main types of decay which depend on the intrinsic properties of the stone: chemical-mineralogical composition and texture-structure.
Recognizing the Limits of Archaeological Applications of Non-Destructive Energy-Dispersive X-Ray Fluorescence Analysis of Obsidians
Authors: Bouey Paul D.
Published: March 2011

Application of a non-destructive energy-dispersive XRF technique, involving use of analytc/Compton net peak ratios, has greatly increased the analytical potential for the study of obsidians in archaeological assemblages. Contrary to reported conclusions for obsidians from the Coso Volcanic Field of southeastern California, however, the method lacks the precision associated with powdered-specimen, thin film, and other more rigorous techniques. Tests have shown that changing the orientation and/or placement of an archaeological artifact in a sample slot will produce widely divergent determinations of ppm concentrations for most specimens. These results indicate that discriminating between some chemical subsources at Coso cannot be accomplished reliably.
Nondestructive Evaluation of the Mineralogy of Rock Temper in Ceramics Using X-Radiography
Authors: Carr Christopher , Komorowski Jean-Christophe
Published: March 2011

Industrial and medical x-radiography can be used in a new manner analogous to back-scattered electron microscopy to identify the approximate mineralogy of rock temper particles in ceramics, but without their destruction by thin-sectioning and at very low cost. Mineralogical traits similar to those applied in petrography to identify mineralogy are visible in a magnified radiograph. They include particle radiographic grey level contrast, which varies with specific density and mineralogy; morphology; cleavage; and internal texture. Blind tests that evaluate the specificity and accuracy of the method are presented.
The Use of Potsherds for Interpreting Alluvial Deposits: A Case Study in the Adige River Basin (Italy)
Authors: Balista C. , Levi S.T. , Vanzetti A. , Vidale M.
Published: March 2011

The paper discusses the use of a small assemblage of potsherds as evidence of fluvial erosion and indicators of microstratigraphical and geomorphological processes. The potsherds, sandwiched between 2 alluvial deposits, provide dating criteria for the two stratigraphic units, very important for understanding the geomorphology of the whole region. By integrating evidence of negative interfaces on potsherds by fluvial erosion and sedimentological evidence, it is possible to reconstruct the local stratigraphic formation processes. Furthermore, the paper discusses some theoretical implications of this case study for stratigraphic analysis. Negative interfaces produced by erosion on sediments and ceramics are considered in the same analytical framework; in both cases, they represent cumulative units preserving the record of complex stratigraphic processes. Far from being simple limits marking gaps in sedimentary deposition, erosive interfaces are very particular types of strata to be recorded and studied with geoarchaeological methods and with the same detail of traditional sedimentary units.
Patination of Ceramic Objects, Modern and Prehistoric: A Case from West Mexico
Authors: Aronson Meredith , Kingery W. David
Published: March 2011

In many cases objects lacking specific provenience are deemed inappropriate for archaeological or art historical studies. The application of analytical techniques such as thermoluminescence or carbon-14 dating have been used in conjunction with stylistic information to strengthen arguments for provenience. In the case of late-Formative figurines from West Mexico, careful study of the dark patina using morphological and chemical criteria provides a means of assessing provenience of the figurine. Comparison of modern patinas to provenienced patinas has been carried out at several levels -- visual/stylistic, morphological and chemical.
Role of Materials Analysis in the Reconstruction of Early Metal Extraction Technology: Zinc and Silver-Lead Smelting at Zawar, Rajasthan
Authors: Freestone I C , Middleton A P , Craddock P T , Gurjar L K , Hook D R
Published: March 2011

Microscopy and elemental analysis of ore, slag, ceramic and ash from a major metallurgical site have allowed insights into the ancient processes. Constraints have been placed on raw materials and smelting conditions, and aspects of technological change and development have been recognised.
Fifth Millennium BC Evidence for Metallurgical Processing of Copper and Copper Alloys in South-East Europe.
Authors: Glumac Petar D. , Todd Judith A.
Published: March 2011

Archaeological materials recovered from excavations of settlements and cemeteries of prehistoric cultures in the Middle Danube basin offer new evidence for the production of metals by the beginning of the Eneolithic (late neolithic) period. The identification of malachite, azurite and galena indicates that these minerals were extracted from the upland ore-bearing zones and transported to the lowland, alluvial river valleys for processing and smelting at settlement sites. For the first time metallurgical slags, found in association with malachite ores, crucibles, and copper/bronze artifacts, suggest that copper was smelted as early as the fifth millennium BC. Detailed analyses of these slags have identified a unique find of a tinbearing copper slag, raising the question of bronze production during the fifth millennium BC.
High-Resolution Computed Tomography and Digital Radiography of Archaeological and Art-Historical Objects
Authors: SÉGuin Fredrick H.
Published: March 2011

Recent advances in x-ray imaging and image processing are providing new options for the nondestructive physical evaluation of archaeological artifacts and works of art. Traditional film-based methods have played an important role in this field for many decades1, but digital modes developed for medical and industrial applications have been gaining ground2 and can be expected to become more important as they become more accessible and less expensive. Modes such as digital radiography (DR) and computed tomography (CT) have many advantages in terms of information content, quantitative analysis options, and image display options (including some that make image publication easier). CT, in particular, provides structural information which cannot be obtained through any other nondestructive means. From a technical point of view, the only real drawback to digital methods has been spatial resolution that hasn't compared favorably with the best available from film. That situation is changing3.

The objective here is to discuss a few of the important characteristics peculiar to digital images, to show examples of how high-resolution digital images can provide important structural information, and to illustrate useful types of image processing. The use of experimental CT and DR systems, with spatial resolution as fine as 50 microns, is illustrated in studies of three objects: an ancient terracotta sculpture, a Japanese assembledwoodblock sculpture (ca. 17th century), and an oil painting on canvas (ca. 18th century).
Why is the Japanese Sword Curved ?
Authors: Weins William N. , Bleed Peter
Published: March 2011

The history and methodology of Japanese swordmaking are reviewed with particular reference to materials and processes. In order to gain a better understanding of the structure/property relationships in Japanese swords, a 16th century katana was analyzed metallographically and by attaching strain gages and cutting to relieve the residual stresses in the blade. The results indicate that the curve in the blade can be attributed to the volumetric expansion of the untempered martensite on the cutting edge, which also causes the edge to be in a state of residual compression. The residual compressive stresses are one of the key elements of the Japanese sword which give it superior toughness and cutting ability.
The Distribution of Phosphorus in Romano-British Ironwork
Authors: Kaloyeros Alain E. , Ehrenreich Robert M.
Published: March 2011

Phosphorus is found to be a common impurity in many of the iron tools and weapons produced during the pre-Roman and Roman Iron Ages of Britain (600 BC - 300 AD). The effects of this impurity on the properties and performance of antiquarian materials is not well understood, however. This paper presents the initial findings of an in-depth study of the distribution, chemistry, and effects of phosphorus in Romano-British ironwork. For this purpose, two Romano-British iron artifacts from the site of Ircheoter, Northamptonshire, were examined using powerful techniques for archeological materials analysis that include electron microprobe, secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM) with energydispersive x-ray spectroscopy capabilities (EDXS), and Auger electron spectroscopy (AES). It was found that phosphorous was indeed present in the artifacts. The phosphorus atoms were predominantly segregated at grain boundaries and thus should have led to a lowering of grain boundary cohesion and a degradation in the performance of the tools.
Reconstructing Prehistoric Textile and Ceramic Technology from Impressions of Cloth in Figurines from Ecuador
Authors: Stothert Karen E. , Epstein Kathleen A. , Cummins Thomas R. , Freire Maritza
Published: March 2011

A method is described for using vinyl polysiloxane dental impression material to make high definition casts from ceramic objects that bear negative imprints of textiles. Casts made from impressions found on prehistoric ceramic figurines from Ecuador were examined under magnification and features of the yarns and weaves were described. The data are used to reconstruct prehistoric spinning and weaving technology. The use of cloth in figurine manufacture and the reconstructed textile technology are interpreted in spatial, temporal and cultural perspectives.
The New Netherland/New York Ceramic Chemistry Archive: Compositional Analysis of Bricks by ICP
Authors: Gilbert Allan S. , Harbottle Garman
Published: March 2011

Historical archaeologists investigating early American production and trade must work with the written record as well as the evidence from controlled excavation. Both kinds of data have their place in the inquiry, yet the details they furnish are not necessarily congruent or applicable to the solution of all historical questions. To illustrate, artifacts were not always manufactured in the places where they are found, but in order to resolve this uncertainty accurately and directly, the origins of excavated materials must often be determined by means that are independent of historic documentation. If sources can be shown to be distant, then despite any similarity to items of known local manufacture or written evidence suggesting otherwise, long-range exchange structures must have been present. The interpretation of archaeological and historical data can then be guided by more informed judgment.
Thermal Analysis of Fresh and Mature Oil Paint Films: The Effect of Pigments as Driers and the Solvent Leaching of Mature Paint Films
Authors: McGlinchey Christopher W.
Published: March 2011

The effect of titanium white, zinc white and lead white on the drying properties of poppy, walnut and linseed oil are analyzed by differential scanning calorimetry (DSC). All of the fresh films undergo complex thermal transitions between -100 and O°C. For some of the dried films subambient transitions that resemble glass transitions occur at about -30 O°C. After exposure to certain solvents, these sub-ambient transitions disappear or are reduced significantly. It is suggested that samples with diminished sub-ambient transitions become more brittle as a result of the loss of materials that act as plasticizers.
A Mathematical Model for Microwave-Assisted Chemical Vapor Infiltration
Authors: Evans James W. , Gupta D.
Published: March 2011

A model for microwave heating of a ceramic preform is presented. Microwave power and external cooling are manipulated to obtain desired temperature profiles for effective chemical vapor infiltration (CVI) of the preform. A mass transport and chemical reaction model is developed to demonstrate preform densification. Conditions affecting matrix deposition are evaluated.
Preliminary Thermal Model for High Temperature Processing Using Microwave Energy
Authors: Eves E. Eugene , Snider Ronald L.
Published: March 2011

Ceramics processing with microwave energy is dominated by empirical testing of small samples. Concepts and models for reconciling information between different types of heatingtrials, and for predicting heating performance for large parts are discussed.
Generalized Pulse—Spectrum Technique for Solving Inverse Problems in Microwave Heating
Authors: Chen Y. M. , Wang Franklin F. Y.
Published: March 2011

The Generalized Pulse—Spectrum Technique (GPST), a versatile, efficient and stable Newton-like iterative numerical inversion algorithm with Tikhonov regularization. GPSThas been been successfully applied to many practical inverse problems, including the inverse problems of equations of the diffusion type. Methodology in applying GPST for solving the inverse problems in microwave heating of ceramic samples is described.
Microwave Industrial, Scientific and Medical Applications in Brazil
Authors: Andrade Octavio M.
Published: March 2011

Microwave ISM applications in Brazil are reviewed, with special emphasys on industrial. applications and measurement techniques of the dielectric properties of materials, where developments have been most sicgnificant.

Special techniques for measuring the properties of typical Brazilian soils for radiometric applications in satellite remote sensing are discussed.

High power microwave techniques are presented and analyzed.

Industrial applications in ceramics, chemical products, food processing, sterilization, production of alcohol, and many others are explained. The design of special applicators for the above techniques, including continuous processing apparatus, detectors, special loads and waveguide configurations are reviewed.

Various methods for obtaining the dielectric constant of solid and liquid substanlces are presented, and experimental techniques are analyzed.

Biological and medical applications are in early stages of development, but present a great potential in the coming years at various well equipped medical institutions.

In conclusion, the great potential of microwave non-communications applications in Brazil is explained, with promising achievements in the years ahead.
Estimates for Diffusion Barriers and Atomic Potentials in Mgo: Cndo/2 Calculations for the Study of Microwave Effects in Sintering
Authors: Skala L. , Kenkre V.M. , Weiser M.W. , Katz J.D.
Published: March 2011

As part of a program of investigation of microwave sintering, self-consistent CNDO/2 calculations are presented for diffusion barriers and potentials for the motion of interstitial atoms and vacancies in MgO. Clusters of 30 atoms are used in the calculations. Activation energies, diffusion barriers, shape of the potentials and electron densities are obtained.
Processing of Silicon Wafers Followed by Microwave Photoconductivity Measurements
Authors: Sanders A. , Wetzel H. , Kunst M.
Published: March 2011

The characterization of single crystalline silicon wafers for application in (opto)electronic devices by transient photoconductivity measurements is investigated. To this aim is the transient photoconductivity in Si wafers after different treatments determined by the Time Resolved Microwave Conductivity ( TRMC ) method. This technique is non-evasive and contactless and so in-situ measurements are possible. Application of TRMC measurements for process control and quality control of relevant process steps in the production of (opto)electronic devices is discussed in view of the experimental results presented.
Features of Microwave Processing of Inorganiciorganic Hybrid Networks (Ceramic) Materials.
Authors: Rodrigues D. E. , Wilkes G. L.
Published: March 2011

Over the last two decades the sol gel technique has become very popular because of its ability to yield a multicomponent inorganic glass at low temperatures[1,2]. More recently, techniques to incorporate organic species into a sol gel network of metal alkoxides has been developed and studied[3-7]. One technique developed in our laboratory is to incorporate oligomers endcapped with metal alkoxide functionalities into a reaction mixture of TEOS, water and acid catalyst. The resulting materials, often cured at ambient temperatures, can be tough and transparent monoliths. This technique is important in that it helps to overcome some of the defects of pure sol gel silicate structures such as cracks, voids and brittleness. The high temperature structural properties of these materials, however, are limited because of the organic component. This approach provides the ability to make a wide range of materials with vastly different properties depending upon the polymer and metal alkoxide chosen. Novel properties displayed by these materials make them attractive for certain technological applications such as coatings, films and fibers. One of the main drawbacks of the ambient temperature curing process is the relatively long reaction time which hinders immediate utilisation of the product. As would be expected, the extent of reaction has been found to be dependent on the T, of the oligomer under consideration. In the case of high Tg oligomers (e. g. polysulfones) the reaction has to be completed at elevated temperatures (above the Tg.) in order to acheive a high extent of reaction. In the case of ceramers containing functionalized poly(tetramethyleneoxide) (PTMO) oligomer, curing time can vary between 48 to 100 hours before the final gel can be successfully handled and tested. In order to enhance the rates of reaction and determine the effect of such an acceleration on the physical properties, samples were reacted at elevated temperatures using microwave heating and conventional oven curing. When microwaves were used the curing time has been found in some cases to be reduced dramatically from 60 hours to twenty minutes. In this paper structure-property relationships of these "microwaved" materials will be compared and contrasted with similar materials cured in a conventional oven at equivalent elevated temperatures as well as room temperature cured materials. Time-temperature studies of the reactants were also conducted in a travelling wave guide. These studies were done primarily to gain some insight as to the effect of microwaves on specific reactants. analyzer.
An Amplitude-Only Measurement Technique for the Evaluation of the Complex Permittivity Of Composite Materials in the Microwave Range.
Authors: Bisceglia B. , Ciliberto A. , D'Ambrosio G. , Ferrara G. , Massa R. , Sabatino C.
Published: March 2011

The basic transmission line and rectangular waveguide equations, with reference to different loading conditions, are firstly reviewed. Amplitude and phase, amplitudeonly, and phase-only permittivity measurement techniques are briefly discussed. Two very naive graphical and numerical calculation procedures are presented, together with the results of measurements on some composite materials.
Detoxification of Hazardous Waste Streams Using Microwave-Assisted Fluid-Bed Oxidation
Authors: Varma R. , Nandi S. P. , Katz J. D.
Published: March 2011

Microwave-assisted oxidation of trichloroethane (TCE) performed at 500-580°C has been found to be significantly more efficient than conventional oxidation methods. Experiments were conducted using a 6 kW, 2.45 GHz power supply and a 6 inch bed of silicon carbide granules in a 1 inch diameter quartz reactor tube which in turn was placed in a microwave cavity. After heating the reactor to a given temperature a TCE-air stream was passed through the silicon carbide bed. TCE was almost completely detoxified (98-99%) in a single pass through the silicon carbide bed at 500-580°C. The oxidation products are HC1, CO2 and CO. By comparison the corresponding single-pass detoxification using conventional thermal methods results in only partial conversion. The principal products being dichloroethylene (C2H2C12) and HCl.
Acidic Biopolymers as Dispersants for Ceramic Processing
Authors: Pellerin N. , Staley J. T. , Ren T. , Graff G. L. , Treadwell D. R. , Aksay I. A.
Published: March 2011

Some acidic biopolymers serve as dispersants for colloidal processing of ceramics. One biopolymer we tested was alginate, a heteropolysaccharide containing two carboxylic sugar acids, D-mannuronic and D-guluronic. Kelp alginate was a suitable dispersant, provided that its viscosity was reduced by partial acid hydrolysis. Low molecular weight polymers rich in guluronic acid proved to be better dispersants than those rich in mannuronic acid, perhaps due to their greater charge density caused by their buckled molecular configuration. In situ processing of ceramic materials was tested by growing the alginate-producing bacterium, Azotobacter vinelandii, in the presence of alumina particles. Growth occurred at 15 vol% alumina in medium. Alumina particles which were exposed to such treatment showed a high packing density comparable to that with purified polymer. We also tested polypeptide polymers of the dicarboxylic amino acids, glutamate and aspartate, which also served as excellent dispersants for small alumina particles.
Mimicking Photosynthetic Electron Transfer
Authors: Gust Devens , Moore Thomas A. , Moore Ana L.
Published: March 2011

The photosynthetic reaction centers of plants and bacteria are photovoltaic devices on the molecular scale which convert light energy into chemical potential energy in the form of long-lived, energetic charge separated states. It is now possible to prepare synthetic multicomponent molecules which mimic important aspects of this process. For example, one of the keys to reaction center function is a multistep electron transfer strategy. In this paper, two general types of multistep electron transfer, sequential and parallel, are described and illustrated with several synthetic triad and pentad molecules.
Parallel Fibres Control Fracture in Biological Systems
Authors: Vincent Julian F. V.
Published: March 2011

Grass and horn keratin are presented as examples of biological materials which are notch-insensitive due to the presence of strong and stiff parallel fibres in a weaker more compliant matrix. A simple Voigt model is adequate to account for most of these properties. The biological significance of this morphology is explored: with grasses it affects the way animals graze, with horn keratin the behaviour of the horned animal maximises fracture control.
The Role of Ashed Bone in Hard Tissue Implants
Authors: Nash Alexis S. , Dahl Laura , Shepler Mark , Choo Hahn , Choi Sun W. , Nash Philip
Published: March 2011

A novel composite consisting of Ultra-High Molecular Weight Polyethylene, UHMWPE, and ashed bone has been evaluated for human implant applications. The structure and mechanical properties of this composite have been studied using x-ray diffractometry (XRD), scanning electron microscopy (SEM) and dynamic torsion tests. Dynamic properties of the composite and its role in the enhancement of bone ingrowth and damping of vibrations at bone-implant interface are discussed. The new composite offers a novel technique that can provide the desired biological and mechanical fixation in a total hip surgery.
Carbohydrate Protein Conjugates (CPC): The Design of New Materials to Stabilize Enzymes
Authors: Hill Tara G. , Wang Peng , Oehlert Lynn M. , Huston Michael E. , Wartchow Charles A. , Smith M. Bradley , Bednarski Mark D. , Callstromt Matthew R.
Published: March 2011

Intense efforts have been directed at the stabilization of proteins because of their potential uses in organic synthesis, diagnostics, and the pharmaceutical industry. These efforts have resulted in a number of methods to stabilize enzymes including adsorbtion on inert supports or ion exchange resins, entrapment within a gel (with or without crosslinking of the gel or protein), covalent attachment to beads or polymeric supports, inclusion in micelles, chemical derivatization of the protein and mutagenesis. However, these methods do not provide a general approach to solving the problem of protein stability. We believed that the multi-site attachment of a carbohydrate-based macromolecule to the surface of a protein would provide structural stability and a water-like microenvironment for the protein under harsh reaction conditions.
Structure, Morphology and Growth of Biogenic Greigite (Fe3S4)
Authors: Heywood B. R. , Manna S. , Frankelb R. B.
Published: March 2011

Several species of aquatic bacteria are known to exploit the earth's geomagnetic field as a means of directing their motion towards suitable habitats. A feature common to these bacteria is the presence of discrete intracellular magnetic inclusions, magnetosomes, aligned in chains along the long axis of the organism. The size and orientation of the individual magnetic particles imparts a permanent magnetic dipole moment to the cell which is, in turn, responsible for the magnetotactic response. In all species examined to date the magnetic particles have been found to be well-ordered, single domain, membrane-bounded crystals with reproducible, species-specific morphologies. Until recently, however, only crystals of the mixed valence iron oxide, magnetite (Fe3O4), were identified in these magnetotactic bacteria. We have now identified three species of bacteria from sulphidic environments which contain crystals of the mixed valence ferrimagnetic iron sulphide, greigite (Fe3S4). High resolution electron microscopical studies of the biogenic greigite crystals showed that they also exhibit the narrow size range (50–90nm) and unique crystallographic habits (e.g. cubo-octahedral, rectangular prismatic) which characterized and distinguished the inclusions in other magnetotactic species. Thus, it would appear that the bio-precipitation of iron sulphides in magnetotactic bacteria is a highly regulated process which is directed and controlled at the molecular level. These findings are not only important to our understanding of biomineralization in unicellular organisms but may also be significant to studies of paleomagnetism. Furthermore, the controlled synthesis of greigite presents an interesting challenge to material scientists and solid state chemists.
Beam Assisted Atomic Layer Controlled Epitaxy and Etching of GaAs
Authors: Meguro T. , Aoyagi Y.
Published: March 2011

Atomic layer epitaxy (ALE) using laser irradiation and digital etching of GaAs are described herein.

Epitaxy: We have succeeded in the laser-assisted ALE (laser-ALE) of GaAs using visible wavelength Art laser irradiation and an alkylgallium source. Visible wavelength photon irradiation induces surface decomposition but not volume decomposition of alkylmetal molecule source gases. ALE is realized by the enhancement of decomposition of alkylgallium molecules only on the As-terminated surface but not on the Ga-terminated surface. This site-selectivity of alkylgallium decomposition is induced by the optical absorption band broadening, which is due to the chemisorption of alkylgallium at the As-terminated surface.

Etching: In ditigal etching, etchant gas pulses and an energetic beam sequentially impinge onto the substrate surface. In the Ar+/Cl2 system, the etch rate is found to be independent of both Cl2flux and Ar+ beam density, and the etch rate saturates at a level below one monolayer per cycle. By using Cl radicals as etchants instead of Cl2, the self-limited etching characteristics of digital etching are obtained within both the Ar+ incidence time and Cl feed time of the etching cycle.
Growth Rate Limiting and Carbon Reduction Processes for GaAs Grown by Alternate Gas Supply using H2 and N2 Carrier Gases
Authors: Shinohara M. , Yokoyama Y. , Inoue N.
Published: March 2011

Processes limiting the growth of GaAs grown by an alternate gas supply are investigated by kinematical analysis. Based on these results, it is shown that the atomic layer epitaxial (ALE) window is expanded on the high temperature by the suppression of the decomposition of column III gas sources using a nitrogen carrier gas and on the low temperature side by the enhancement of their chemisorption to substrate surface atoms by a new method using a cracking tube. The latter enables us to achieve ALE of AlAs for the first time. Moreover, the carbon concentration is reduced by one order of magnitude by such a reaction control.
Atomic Level Control in Crystal Growth Utilizing Reconstruction of the Surface Superstructure
Authors: Fuyuki Takashi , Yoshinobu Tatsuo , Matsunami Hiroyuki
Published: March 2011

A novel mechanism of atomic level control in crystal growth utilizing reconstruction of surface superstructures is proposed. We have found a distinguished feature of surface reconstruction during crystal growth of 3C-SiC using an alternate gas molecular beam supply of Si2H6 and C2H2. When Si2H6 is supplied, S atoms generated by thermal decomposition adsorb on the surface constructing superstructures. A fixed number of Si atoms forming surface superstructures can react with C2H2 yielding single crystalline 3C-SiC growth in the subsequent period, which realizes atomic level control in epitaxy of 3C-SiC. The reconstruction sequence is analyzed based on RHEED observations, and the obtained crystal quality is discussed.
Cadmium Telluride Thin Films Grown By Atomic Layer Epitaxy
Authors: Kytökivi Arla , Koskinen Yrjö , Rautiainen Aimo , Skarp Jarmo
Published: March 2011

Polycrystalline CdTe films up to 2 μm thick were grown by Atomic Layer Epitaxy (ALE) at 350–450°C. The growth was carried out in a lateral flow reactor, using the elements as source materials and 25 cm2 glass/ITO and glass/ITO/SnO2 as substrates. A growth of CdS film by ALE preceded the growth of CdTe.

Profilometry, X-ray diffraction analysis and scanning electron microscopy were used to characterize the films.

The relatively high vapor pressure of CdTe determined the upper limit of the processing window, while the small vapor pressure of Te2 set a practical lower limit of 390–400°C.

The CdTe films were smooth up to 100–500 nm depending on the temperature and the substrate surface. Development of surface roughness was detected as the growth process proceeded. At the same time there was an increase of the effective surface area of the film, observed as a significant increase in the macroscopic growth rate. The greater surface roughness was also evident in the reduced degree of (111) orientation.

The CdS/CdTe structure was investigated for its potential in solar cell applications.
Surface Chemistry and Mechanism of Atomic Layer Growth of GaAs
Authors: Yu Ming L. , Buchan Nicholas I. , Souda Ryutaro , Kuech Thomas F.
Published: March 2011

The success In attaining atomic layer epitaxy (ALE) of GaAs depends critically on the choice of the Ga precursor. Three systems were examined: trimethylgallium (TMGa) and diethylgallium chloride (DEGaCI) both of which give ALE, and triethylgallium (TEGa) which does not. We compared the surface reactions of these compounds on GaAs(100) and concluded that there was no evidence for reaction selectivity between Ga and As sites to cause ALE. Site blocking by the ligands on the Ga precursors alone also could not provide a self-limiting Ga deposition for ALE. We found evidence of a new mechanism by which self-limiting deposition of Ga resulted when the incoming Ga flux by the adsorption of Ga precursors was counter-balanced by an outgoing flux of Ga containing reaction product. For TMGa and DEGaCI with which ALE is successful, the products are CH3Ga and GaCl, respectively. For TEGa, the corresponding compound C2H5Ga was not formed.
Atomic Layer and Unit-Cell Layer Growth of (Ca,Sr)CuO2 and Bi2Sr2Can-1CunO2n+4 Thin Films by Laser Molecular Bean Epitaxy
Authors: Kanai Masaki , Kawai Tomoji , Matsumoto Takuya , Kawai Shichio
Published: March 2011

Thin films of (Ca,Sr)CuO2 and Bi2Sr2Can-1CunO2n+4 are formed by laser molecular beam epitaxy with in-situ reflection high energy electron diffraction observation. The diffraction pattern shows that these materials are formed with layer-by-layer growth. The change of the diffraction intensity as well as the analysis of the total diffraction pattern makes It possible to control the grown of the atomic layer or the unit-cell layer.
Self Terminating Reaction of Dipivaloylmethanate Complexes with Hydroxyl Groups on Oxide Surface
Authors: Sekine Rika , Kawai Maki , Asakura Kiyotaka , Iwasawa Yasuhiro
Published: March 2011

We have already reported that copper and calcium dipivaloylmethanates [Cu(DPM)2 and Ca(DPM)2 ] reacts selectively and stoichiometrically with surface hydroxyl groups (OH) on SiO2. In order to clarify the structure of the adsorbed species and the origin of the reaction between M(DPM)2 (M=Cu and Ca) and OH groups, the surface adsorbed species are studied by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and the extended X-ray absorption fine structure (EXAFS). As a result, it was found that H from surface OH has moved into M(DPM)2 after the adsorption, where the four oxygen coordinated structure around Cu still exists in the adsorbed Cu(DPM)2. Introducing water vapor at 673 K to this surface results in the removal of ligand DPM from the adsorbed Cu(DPM)2. At 673 K, Cu atoms decomposed from the adsorbates aggregated on the surface. This fact supports that the interaction between the adsorbed Cu(DPM)2 and SiO2 surface is originated from that between the ligands and the surface.
Real-Time Analysis Of In-Situ Spectroscopic Ellipsometric Data During Mbe Growth Of III-V Semiconductors
Authors: Johs B. , Edwards J. L. , Shiralagi K. T. , Droopad R. , Choi K. Y. , Maracas G. N. , Meyer D. , Cooney G. T. , Woollam John A.
Published: March 2011

A modular spectroscopic ellipsometer, capable of both in-situ and ex-situ operation, has been used to measure important growth parameters of GaAs/AIGaAs structures. The ex-situ measurements provided layer thicknesses and compositions of the grown structures. In-situ ellipsometric measurements allowed the determination of growth rates, layer thicknesses, and high temperature optical constants. By performing a regression analysis of the in-situ data in real-time, the thickness and composition of an AIGaAs layer were extracted during the MBE growth of the structure.
High Carrier Concentration Improved N-Type SiGe/GaP Alloys
Authors: Scoville A. Nancy , Bajgar Clara , Vandersande Jan , Fleurial Jean-Pierre
Published: March 2011

SiGe alloys have been fabricated with the hiqghest carrier concentrations achieved to date. Values in excess of 4.0 × 1020 have been observed. The thermoelectric behavior of these samples has been characterized, both in the as-pressed state and as a function of 3anneal time and temperature. Figures-of-merit between 0.85 and 0.90 × 10−3 K−1 have been reproducibly achieved. Further improvements will be achieved by reducing the carrier concentration.
On The Thermoelectric Power in Degenerate Narrow Gap Semiconductors in the Presence of a Strong Magnetic Field
Authors: Ghatak Kamakhya Prasad , De Badal
Published: March 2011

In this paper we have studied the thermoelectric power under strong magnetic field in degenerate semiconductors on the basis of fourth order in effective mass theory and taking into account the interactions of the conduction electrons, heavy-holes, light-holes and split-off holes respectively. The results obtained are then compared to those derived on the basis of the well-known three-band Kane model. It is found, taking n-Hg1-xCdxTe as an example, that the magneto-thermo power increases with decreasing electron concentration and increasing magnetic field respectively for both the models in an oscillatory way. The oscillations are due to SdH effects and the theoretical snelysis in accordance with fourth order in effective mass theory is in agreement with the experimental observation as reported elsewhere. In addition, the corresponding results for parabolic energy bands have also been obtained as special cases of our generalized foriulations.
All-Optical Switches and All-Optical Bistability by Nonlinear Optical Materials
Authors: Sasaki K. , Sasaki S. , Furukawa O.
Published: March 2011

All-optical switches and all-optical bistabili ties are realized by waveguide structures with vacuum evaporated polydiacetylene(PDA) films. The basic structure of the all-optical switches are prepared in the form of layered waveguide directional coupler with vacuum evaporated PDA top layer. Clearly switchings are observed at 1064nm of pulsed Nd:YAG laser. Furthermore ultra-high speed switching with Ti;Safire 135fs laser are recognized.

Operations of all-optical bistabilities are carried out by nonlinear coupling at grating structures in waveguides with PDA top layers. Hysterisis curves of bistability are affected by coupling parameters of gratings and parameters of waveguides.
Nonlinear Optics of Linear Conjugated Polymers
Authors: Guo D. , Mazumdar S. , Stegeman G. I. , Cha M. , Neher D. , Aramaki S. , Torruellas W. , Zanoni R.
Published: March 2011

The third order nonlinear optical properties of conjugated polymers have been considered promising since the 1970s when Sauteret et al reported large non-resonant values in PTS.[1] Although it is well-understood that the physical origin of the nonlinearities is due to the delocalization of the π-electrons, the details, and how best to calculate them have been the focus of a continuing theoretical dialogue. Until recently, experimental investigations of nonlinearities have been limited to only a few wavelengths. Now third harmonic generation (THG), which accesses only the electronic nonlinearities, can be performed over wide spectral ranges, for example from 500 to 2000 nm. The resulting third harmonic wavelength typically spans the electronic molecular transitions associated with the nonlinearities. By measuring the spectral distribution of both the amplitude and phase of the third harmonic signal, the dominant transitions (between the“essential states”) contributing to the nonlinearity can be identified. Such information is most useful for comparing with theories in which the oscillator strengths (transition dipole moments) for the various molecular transitions are calculated.
Exact Optical Susceptibilities of Three State Systems Interacting with a Single Frequency Electric Field
Authors: Kavanaugh Theresa C. , Silbey Robert J.
Published: March 2011

Using Floquet theory together with density matrix formalism, an exact, nonpertur-bative expression for the optical susceptibility of a three level system interacting with a single mode electric field is derived. By using a three state model that mimics a polymeric system, it is shown that in certain cases, using typical values for the intensity of the electric field, successive terms in the series χω=χ(1) + χ(3) E2… approach the same of order magnitude.
Damping and Third-Order Nonlinear Spectrum of Polyacetylene
Authors: Sun Xin , Fu Rong-Tang , Li Lie-Ming , Lin D. L. , George Thomas F.
Published: March 2011

Experiments have shown that the third-order nonlinear spectrum of trans- polyacetylene has two peaks at 0.6 eV and 0.9 eV respectively. None of the existing theories can give a quantitatively satisfying interpretation. A new theory is proposed in this paper by considering the excitation-dependent damping, and the theoretical results agree with the observed spectrum very well.