bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of SiCN Crystals Consisting of a Predominantly Carbon Nitride Network
Authors: Bhusari D. M. , Chen C. K. , Chen K. H. , Chen L. C. , Chuang T. J.
Published: April 2011

We report here growth of thin films of Si-containing crystalline carbon-nitride by microwave plasma assisted CVD. The chemical composition of these films has been observed to be a strong function of the substrate temperature. A significant incorporation of Si into the CN network occurs for substrate temperatures exceeding 1000C. XPS analyses of these films indicate a multiple bonding structure between carbon and nitrogen and also indicate that a majority of the carbon atoms are tetrahedrally coordinated and covalently bonded with nitrogen. Investigations of the growth rate as a function of various deposition parameters revealed that Si substrates exhibit weight loss rather than deposition, suggesting that abstraction of Si atoms from the substrate surface by the chemically active radicals from the plasma is a dominant process. The species thus formed, i.e., the active radicals bonded with Si, appear to facilitate the subsequent reactions in the gas phase. A major achievement of this study is that there is no obvious deposition of any amorphous CN material.
Synthesis of Crystalline C3N4 films and the new C-N Phases
Authors: Chen Yan , Johnson D. J. , Prince R. H. , Guo Liping , Wang E. G.
Published: April 2011

Crystalline C-N films composed of α- and β-C3N4, as well as other C-N phases, have been synthesized via bias-assisted hot-filament chemical vapor deposition using a gas mixture of nitrogen and methane. Scanning electron microscopy(SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the films. Lattice constants of the α- and β-C3N4 phases obtained coincide very well with the theoretical values. In addition to these phases, two new C-N phases in the films have been identified by TEM and XRD; one having a tetragonal structure with a = 5.65 Å, c = 2.75Å, and the second having a monoclinic structure with a = 5.065 Å, b= 11.5 Å, c = 2.801 Å and β = 96°. Their stoichiometric values and atomic arrangements have not yet been identified. Furthermore, variation in growth parameters, for example methane concentration, bias voltage, etc., can yield preferred growth of different C-N phases.
Structural and Optical Properties of Electro-Chromic Nickel Oxide Films
Authors: Murai Kensuke , Sato Yoshiyuki , Tamura Shigeharu
Published: April 2011

The electro-chromic behavior of nickel oxide (NiOx) films, prepared by spin-coating, were analyzed for their structual and optical properties before and after cycling procedure in electrolyte. It was found that the chemical composition, refractive index, and thickness of the film changes significantly on hydration.
Strain Effects in Heteroepitaxial Growth: Island and Dot Formation Kinetics
Authors: Williams D. R. M. , Sander L. M.
Published: April 2011

In many situations where islands and quantum dots are formed on a growing surface strain effects are believed to play an important role. Here we present some preliminary results from a computer simulation study of a one-dimensional model system. Our system consists of an A material upon which grows a B material with a different lattice constant. We only consider the case where less than one monolayer of B has grown on the surface. At any given time the surface consists of a series of “islands” of B bounded by up and downsteps. Dispersed between these islands are mobile B atoms. In general, because of the lattice mismatch between A and B the mobile B atoms are repelled from the islands. This repulsion has an effect on the island size distribution and more particularly on the number of islands per unit length. Here we show that for a moderate repulsion there is a large effect on the number of islands per unit length. However, as the repulsion is increased the effect grows only gradually.
Analysis And Characterization Of Electrically Conductive Adhesives
Authors: Gaynes Michael A. , Matienzo Luis J. , Zimmerman Jeffrey A. , Vanhart Daniel
Published: April 2011

Electrically conductive adhesives (ECAs) are considered an alternative to solder interconnection in microelectronic circuit packaging. In an effort to understand the performance of this class of materials, several chemical analytical techniques have been employed to characterize polymer chemistry, filler morphology and surface chemistry. These techniques include fourier transform mass spectroscopy pyrolysis (FTMS), optical microscopy, confocal laser scanning microscopy (CLSM), scanning electron microscopy with energy dispersive x‐ray analysis (SEM/EDX), auger electron spectroscopy (AES) and photo‐electron spectroscopy (XPS). Samples studied were conductive adhesive layers and deposits, plated metal surfaces, cross‐sections of bonded joints and fractured bonds. Electrical contact resistance data were also taken on bonded joints. Three commercial adhesives were studied. It was found that thermal stability varied among the three adhesives with one adhesive showing degradation at as low as 200 °C. Differences were also noted in silver flake size, morphology and apparent contact area. Excellent contact resistance stability is achieved with two formulations on a palladium‐nickel alloy surface. In contrast, a hard gold surface yielded unstable contact resistance. Fractured bond surfaces were studied for both stable and unstable joints to understand mechanisms for contact resistance degradation. The increase in contact resistance is most likely caused by oxygen ingress along an interfacial bond where the adherend surface is smooth. The matrix polymer oxidized at the interface when exposed to temperatures above the glass transition temperature. Tin surfaces cause increasing contact resistance and nickel surfaces give an initial contact resistance that is more than two orders of magnitude higher than noble metal surfaces. Oxide formation in both cases is the likely cause for the unstable and high resistances. Various analytical techniques have been used to characterize and differentiate electrically conductive adhesives. Differences among three adhesives are noted and correlated to contact resistance performance.
In‐Situ Mapping and Modeling Verification of Thermomechanical Deformation in Underfilled Flip‐Chip Packaging Using Moiré Interferometry
Authors: Dai Xiang , Kim Connie , Willecke Ralf , Ho Paul S.
Published: April 2011

An experimental technique of environmental moiré interferometry has been developed for in‐situ monitoring and analysis of thermomechanical deformation of microelectronics packages subjected to thermal loading under a controlled atmosphere. Coupled with fractional fringe analysis and digital image processing, the environmental moiré interferometry technique achieves accurate and realistic deformation monitoring with high sensitivity and excellent spatial resolution. It has been applied to investigate the thermomechanical deformations induced by thermal loading in an underfilled flip‐chip‐on‐board packaging. The effects of temperature change in the range of 102 °C to 22 °C are analyzed for underfill and solder bumps. In addition, shear deformation and shear strains across the solder bumps are determined as a function of temperature. The experimental results are compared with the results of a finite element analysis for modeling verification. Good agreement between the modeling results and experimental measurements has been found in the overall displacement fields. Through this study, the role of underfill in the thermomechanical deformation of the underfilled flip‐chip package is determined.
In‐Situ Measurements of Thermal Properties of Dielectric Films on Metal‐Dielectric‐Substrate Structures
Authors: Bloss P. , De Reggi A.S. , Schäfer H.
Published: April 2011

We show that the thermal diffusivity of a dielectric film and the heat‐transfer coefficient between the film and the substrate to which it is adhesively bonded can be determined from the electret‐like response stimulated by laser pulses applied to the voltage‐biased dielectric. The temperature profile is calculated as a function of time from the heat‐conduction equation with boundary conditions appropriate for the model structure representing the metallic electrode/ dielectric film/ glue layer/ substrate structure. The electrode, acting as a thermal mass, and the substrate, acting as a thermal sink, affect the temperature profile in different time ranges.

The response is a convolution of the temperature and the electric‐field profiles across the dielectric. For nonideal dielectrics that acquire bulk charge under bias, deconvolution is necesssary to determine the field profile and the thermal properties. Deconvolution is accomplished using the Tikhonov‐regularization technique with a self‐consistent regularization parameter. This procedure yields information about the thermal properties of both the dielectric and the glue joint, as shown by actual measurements.
Interfacial Delamination in Plastic Encapsulated Integrated Circuits (Pics)
Authors: Strifas Nickolaos , Christou Aris
Published: April 2011

The reliability of plastic packaged integrated circuits was assessed from the point of view of interfacial mechanical integrity. It is shown that the effect of structural weaknesses caused by poor bonding, voids, microcracks or delamination may not be evident in the electrical performance characteristics, but may cause premature failure. Acoustic microscopy (C-SAM) was selected for nondestructive failure analysis of the plastic integrated circuit (IC) packages. Integrated circuits in plastic dual in line packages were initially subjected to temperature (25 °C to 85 °C) and humidity cycling (50 to 85 %) where each cycle was of one hour duration and for over 100 cycles and then analyzed. Delamination at the interfaces between the different materials within the package, which is a major cause of moisture ingress and subsequent premature package failure, was measured. The principal areas of delamination were found along the leads extending from the chip to the edge of the molded body and along the die surface itself. Images of the 3-D internal structure were produced that were used to determine the mechanism for a package failure. The evidence of corrosion and stress corrosion cracks in the regions of delamination was identified.
On Relating Thermodynamic Work of Adhesion to Interfacial Fracture Toughness
Authors: Pearson Raymond A. , Lloyd Thomas B.
Published: April 2011

Organic adhesives are commonly used in the microelectronics industry to bond silicon chips to a wide variety of substrates. The substrates include copper, silver, nickel / palladium, polyimide, and glass‐filled epoxies. The surfaces of these substrates are affected by the processing steps used in the manufacturing process used to produce the final package. The most common adhesives used in the assembly of microelectronic packages are epoxy‐based and there are numerous grades and types to chose from. Therefore, the packaging engineer is faced with the dilemma of what criterion to use to select the best adhesive for a particular package design.

At the crux of the problem is how does one predict adhesion and how does one measure it? It is proposed that the surfaces play an important role in forming the interfacial bond and that strength of the mating surfaces can be characterized in terms of the thermodynamic work of adhesion. Roughness is also a factor but will not be dealt with here. The thermodynamic work of adhesion describes the energy to reversibly separate two surfaces (elastic). Interfacial fracture mechanics may be used to quantify the strain energy release rate for separating two surfaces and contains both elastic and inelastic contributions. This talk will contain a discussion of our studies on the use of a three liquid probe method to determine the thermodynamic work of adhesion and a mixed‐mode bending method to measure interfacial fracture toughness. Moreover, we will comment on the perils of relating the thermodynamic work of adhesion to the interfacial fracture toughness.
Low Temperature Oxidation of Cu-Base Leadframe and Cu/Emc Interface Adhesion
Authors: Cho Soon-Jin , Paik Kyung-Wook
Published: April 2011

Low temperature oxidation of a Cu-base leadframe has been investigated to understand the effect of Cu oxidation on the adhesion between Cu-base leadframes (Cu L/F) and epoxy molding compounds (EMC). From the kinetic studies on the oxidation, oxide growth was found to follow the parabolic rate law in the temperature range of 150 °C to 300 °C and the activation energy for the oxidation was 17.0 kcal/mol. X-ray photoelectron spectroscopy (XPS) studies confirmed that the oxide film consisted of Cu2O, CuO, and NiO. It was shown that the early stage of oxidation improved the adhesion strength. Furthermore the optimum copper oxide thickness required for the maximum pull strength ranged between 20 nm and 30 nm. The high pull strength was presumably due to the increase of surface wettability and mechanical interlocking effects resulting from copper oxidation.
A Study of the Surface Morphological Features of the Polar Faces of ZnO by Atomic Force Microscopy (AFM) Methods and AlN Thin Films Deposited on ZnO Polar Faces by PLD
Authors: Suscavage M. J. , Ryder D. F. , Yip P. W.
Published: April 2011

The effects of both temperature and atmosphere on the resulting morphological features of the polar faces of single crystal ZnO were investigated and characterized by atomic force microscopy (AFM). In studies where ZnO was thermally processed in flowing oxygen at atmospheric conditions within the temperature range of 500°C to 900°C for 30 minutes, the Znsurface (i.e., (000 1)) showed a tendency to reconstruct with increasing temperature until terraces became evident at 900°C. Terrace heights were as small as 0.9 nm. In contrast, the O-surface (i.e., (000 ī)) was observe to change very little during the O2-atmoshere, thermal treatment and remained comparatively rougher than the Zn-surface. ZnO samples which were thermally processed under high vacuum (i.e., 5 × 10-7 Torr) conditions exhibited a more dramatic contrast. The vacuum annealed Zn-surface was observed to develop very smooth surface features (Roughness = 0.09 nm) at annealing temperatures within the 700 – 800°C range. In contrast, and as expected, the O-surface roughness increased due to surface reduction reactions. In addition to these findings, it is noted that AFM measurements may be utilized as a convenient method to distinguish between the two polar surfaces of ZnO.

Aluminum nitride was deposited on the Zn- and O- surfaces from 700 to 850°C by pulsed laser evaporation. X-ray diffraction indicated that the AIN was c-axis oriented with no interface reaction products detected between the ZnO substrate and AIN film.
X-ray Absorption and Reflection as Probes of the GaN Conduction Bands: Theory and Experiment of the N-K-Edge and Ga M2,3, Edges
Authors: Lambrecht W. R. L. , Rashkeev S. N. , Segall B. , Lawniczak-Jablonska K. , Suski T. , Gullikson E. M. , Underwood J. H. , Perera R. C. C. , Rife J. C.
Published: April 2011

X-ray absorption and glancing angle reflectivity measurements in the energy range of the Nitrogen K-edge and Gallium M2,3 edges are reported. Linear muffin-tin orbital band-structure and spectral function calculations are used to interpret the data. Polarization effects are evidenced for the N-K-edge spectra by comparing X-ray reflectivity in s- and p-polarized light.
Offsets and Polarization at Strained AlN/GaN Polar Interfaces
Authors: Bernardini Fabio , Fiorentini Vincenzo , Vanderbilt David
Published: April 2011

The strain induced by lattice mismatch at the interface is responsible for the different value of the band discontinuities observed recently for the AlN/GaN (AlN on GaN) and the GaN/AlN (GaN on AlN) polar (0001) interface. We present a first-principles calculation of valence band offsets, interface dipoles, strain-induced piezoelectric fields, relaxed geometric structure, and formation energies. Our results confirm the existence of a large forward-backward asymmetry for this interface.
Ferromagnetic Properties of Spark-Processed Photoluminescing Silicon
Authors: Hack J. , Ludwig M. H. , Geerts W. , Hummel R. E.
Published: April 2011

Magnetic properties of photoluminescing spark-processed silicon (sp-Si) have been investigated for the first time. Contrary to the diamagnetic signal known for bulk silicon, sp-Si displays a paramagnetic resonance as well as a ferromagnetic hysterisis loop. The paramagnetic resonance was studied using an EPR system and showed a high concentration of at least two distinct paramagnetic centers. One center can be eliminated by annealing in Ultra-High Purity nitrogen for 30 minutes at 600 °C. Measurements utilizing a SQUID magnetometer revealed that sp-Si displays ferromagnetic ordering with a saturization magnetization occuring at low fields. This is attributed to the high density of paramagnetic centers. Temperature dependent measurements were performed to establish possible links between magnetic properties and the luminescence of sp-Si.
Multicolor-Effects of Luminescing, Nanostructured Silicon After Spark-Processing in Pure and Composite Gases
Authors: Ludwig M. H. , Augustin A. , Hummel R. E.
Published: April 2011

Spark-processing has been shown recently to generate a silicon-based substance which intensely photoluminesces in the UV/blue or green spectral range, depending on whether the preparation was performed in flowing or stagnant air, respectively. This study reports about significant differences for the radiative properties of spark-processed silicon after preparations in oxygen, nitrogen, and mixtures of both gases. Whereas there is essentially no photoluminescence (PL) after processing in pure nitrogen, an orange PL band at 1.89 eV occurs after preparation in pure oxygen. The orange PL degrades with time and when exposed to laser light. Furthermore, it switches immediately to a more intense blue emission centered at 2.61 eV when the sample is subjected to lower gas pressures. A similar 2.6 eV PL is observed after heat treatments up to 350°C. If, however, spark-processing of Si is carried out in nitrogen and oxygen is added, a green PL arises, centered at 2.35 eV. Moreover, for a volume ratio of about 1:1 N2/O2 a PL band at 3.22 eV emerges, superimposing the green emission. Both bands are about two orders of magnitude more intense than the orange PL, when prepared under otherwise identical processing conditions.
Porous Semiconductors: A Tutorial Review
Authors: Canham L T
Published: April 2011

Porous semiconductors constitute a class of material that exhibit surprising properties, are quite easy to fabricate, but are however fragile, complex, and difficult to characterise. This tutorial review extracts specific topics from the large knowledge base now available on porous Si that are deemed relevant to other porous semiconductors beginning to receive study. It also highlights topics where controversy is now resolved, where problems remain, and where further effort could be focused.
Effects of Mn2+ Distribution Controlled by Carboxylic Acids on Photoluminescence Intensity of Nanosized ZnS:Mn Particles
Authors: Isobe T. , Igarashi T. , Senna M.
Published: April 2011

Addition of methacrylic acid (MA) during preparation of ZnS doped with Mn2+ (ZnS:Mn) increased the photoluminescence (PL) due to 4T1-6A1 transition of Mn2+. According to X-ray fluorescence analysis and electron paramagnetic resonance spectroscopy, ion exchange between Zn2+ and Mn2+ through a preferential dissolution of Mn2+ was promoted by acidic additives. This caused that Mn ions were isolatedly incorporated into ZnS. The X-ray photoelectron spectra show that the intensity of S 2p3/2 peak due to S6+ increased relative to that of S2- by virtue of carboxylic groups. The intensities of PL peaks at 450 and 580 nm, corresponding to polymethacrylic acid and Mn2+, respectively, increased after heating at 80°C for 1 week. We conclude that MA plays important roles on selective leaching to increase the amount of isolated Mn2+ ions, chemical interaction between ZnS:Mn and MA and energy transfer to Mn2+, leading to the increase in PL intensity.
Electron and Hole Trapping Dynamics in Semiconductor Nanocrystals: Femtosecond Nonlinear Transmission and Photoluminescence Study
Authors: Klimov V. , McBranch D.
Published: April 2011

Application of two complementary femtosecond techniques (time-resolved nonlinear transmission and photoluminescence up-conversion) allows us to observe separately the electron and the hole relaxation paths in CdS nanocrystals. The obtained data indicate that hole relaxation channels are different at low and high pump fluences which is attributed to an Auger-process-assisted hole trapping at surface/interface states activated at high excitation intensities.
Synthesis and Characterization of Highly Luminescent (CdSe)ZnS Quantum Dots
Authors: Mikulec F. V. , Dabbousi B. O. , Rodriguez-Viejo J. , Heine J. R. , Mattoussi H. , Jensen K. F. , Bawendi M. G.
Published: April 2011

We report the synthesis of a series of nearly monodisperse ZnS-overcoated CdSe quantum dots whose room temperature photoluminescence quantum yield approaches 50%. This spectrally narrow (FWHM < 40nm) band edge luminescence spans the visible region from blue to red light. We use a two-step synthesis based on the high temperature decomposition of organometallic precursors in a coordinating solvent. We characterize our composite quantum dots using optical spectroscopies, wavelength dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, small angle x-ray scattering, and wide angle x-ray diffraction. The data indicate that samples displaying the highest quantum yield are those which have just achieved a closed shell of ZnS encapsulating the CdSe core. As more ZnS is added, the quantum yield decreases somewhat, possibly due to the many defects present in larger ZnS shells.
Porous Silicon from Hydrogenated Amorphous Silicon: Comparison with Crystalline Porous Silicon
Authors: Chazalviel J.-N. , Wehrspohn R. B. , Solomon I. , Ozanam F.
Published: April 2011

Device-grade, boron-doped amorphous hydrogenated silicon can be made microporous by anodization in ethanoic HF. The thickness of the porous layer is limited by an instability due to the high resistivity of the material. Amorphous porous silicon exhibits strong room-temperature photoluminescence around 1.5 eV even in samples containing a high density of non-radiative recombination centers. This demonstrates the presence of a spatial confinement effect, as opposed to quantum confinement effect for crystalline porous silicon. The temperature dependence of the luminescence intensity is also accounted for on the same grounds.
Local Structure of Indium-Plated Porous Silicon
Authors: Ito Toshimichi , Ooiwa Takashi , Nagao Takanobu , Hatta Akimitsu
Published: April 2011

The fine structure of porous silicon (PS) plated electro-chemically with indium at a low plating charge of 0.03 C/cm2 has been studied mainly using Rutherford backscattering spectrometry and a transmission electron microscope. The results obtained here show (1) that the amount of plated In atoms strongly depends on the oxidation states of the pore surfaces, (2) that the average In densities, the maximum of which is usually located near the PS - Si substrate interface, are typically larger than 1 % of the Si densities in the PS layers, and (3) that the plated In atoms are concentrated locally in pores larger in size. Two-step thermal oxidation of an In-plated PS specimen results in a structure of nm-sized Si crystallites surrounded mainly by Si oxide and In oxide.
Comparative Theoretical Study of Amorphous and Crystalline Silicon Clusters
Authors: Lannoo M. , Delerue C. , Allan G.
Published: April 2011

The occurence of confinement effects for amorphous Si and Si:H clusters is investigated theoretically in an empirical tight binding treatment. The results show that one must consider three categories of states: strongly localized, weakly localized and delocalized. In all cases a substantial blue shift with reduction in size is obtained, of comparable magnitude for amorphous a-Si:H and crystalline clusters. These results are compared with available experimental data
«Holographie grating in Porous Silicon»
Authors: Lérondel G. , Thönissen M. , Setzu S. , Romestain R. , Vial J. C.
Published: April 2011

We have produced lateral porosity modulation in porous silicon layers on a micron scale. Using the photosensitivity of the etching process and optical interferences, stripes are formed periodically on the top but also in the depth of the layer depending on the illumination wavelength. The periodicity of the structure is easily modified by changing the wavelength or the incident angles of the two laser beams used to create the modulated illumination. By rotating the sample, two dimensional structures have also been obtained. The samples formed by this procedure are characterised by light diffraction and photoluminescence both of which show the alternance of high and low porosity ranges. With this kind of in-depth lithography, easy and very cheap fabrication of porous silicon gratings promises a large potential range of applications of this material to integrated optics and photonics.
Structural Analysis of Nanocrystals Embedded in Amorphous Si Films
Authors: Garrido B. , Achiq A. , Macía J. , Morante J. R. , Pérez-Rodríguez A. , Ruterana P. , Rizk R.
Published: April 2011

Silicon nanocrystals embedded in amorphous silicon films have been obtained by RF sputtering using two approaches : i) with a pure H2 plasma at different substrate temperatures (between 50° and 250°C) and ii) with the substrate at 250°C, from a mixture of Ar and a variable partial pressure of H2, and annealing at 750°C. In the first case (i) Raman spectra show strong phonon confinement effects and an increase in the crystalline fraction as temperature increases. In the second case (ii), a higher compressive stress is estimated and a close correlation is found between the optical band gap E0 and the hydrogen content in the basic amorphous layer a-Si:H (i.e. before annealing). These results correlate with the TEM data, which corroborate an enhancement of the crystallinity of the layers and an increase in the particle size when the substrate temperature increases. Furthermore, the crystalline fraction remains nearly constant with the H2 partial pressure. The role of hydrogen and voids in the structure of the films is presented and discussed.
Crystalline and Electrical Properties of ITO Semiconductive Films deposited by Atmospheric RF Plasma Technique
Authors: Moss R. W. , Misture S. , Lee D. H. , Condrate R. A. , Wang X. W.
Published: April 2011

Indium tin oxide (ITO) semiconductive films were deposited by an atmospheric RF plasma technique. Indium-to-tin (In:Sn) ratios varied from 10:0 to 0:10. A small amount of antimony was doped into some ITO samples for comparative studies. Substrate materials were soda-lime-silicate (SLS) float glass and fused silica glass. Structural, electrical, and optical properties were dependent on the In:Sn ratio, precursor material feeding rate, oxygen feeding rate, and other deposition conditions.
Morphotropic Phase Boundary in the Nanocrystalline PbZrxTi1-xO3 System
Authors: Katiyar R. S. , Meng J. F.
Published: April 2011

Micro Raman spectra for PbZrxTi1-xO3 (PZT) with a grain size of 60 nm have been recorded. The results show that the lowest E(TO) phonon mode of PbTiO3 (soft mode) displays a decrease in frequency and increase in linewidth with increasing Zr concentration. A discontinuous behavior of the phonon energy of the soft mode occurs at x=0.4 and it can be attributed to a phase transformation from the tetragonal ferroelectric to rhombohedral ferroelectric phase in PZT. The coupling between the soft mode and an additional impurity mode, has been observed, which plays an important role in the phase transformation. A lowest phonon mode at 10 cm−1 is detected and it is found to exhibit an increase in intensity for x above 0.2. The grain size dependence of the mode seems to be associated with the effect of grain size on the microstructure in PZT. The mechanism of grain size - induced new morphotropic phase boundary, which is lower than that of the corresponding bulk materials, is discussed.
N-I-P Micromorph Solar Cells on Aluminium Substrates
Authors: Goetz M. , Torres P. , Pernet P. , Meier J. , Fischer D. , Keppner H. , Shah A.
Published: April 2011

The first successful deposition of ‘micromorph’ silicon tandem solar cells of the n-i-p-n-i-p configuration is reported. In order to implement the ‘micromorph’ solar cell concept, four key elements had to be prepared: First, the deposition of mid-gap, intrinsic microcrystalline silicon (μc-Si:H) by the 'gas purifier method', second, the amorphous silicon (a-Si:H) n-i-p single junction solar cell, third, the microcrystalline silicon n-i-p single junction solar cell and fourth, the ability of depositing on aluminium sheet substrates.

All the solar cells presented have been deposited on flat aluminium sheets, using a single layer antireflection coating to couple the light into the cell. It is shown, that this antireflection concept- together with a flat substrate- holds for amorphous single junction solar cells, but it reaches its limit with the extended range of spectral response of the ‘micromorph’ cell.

The best initial efficiencies for each category of n-i-p cells on flat substrates were: 8.7% for the amorphous silicon single junction cell, 4.9% for the microcrystalline silicon single junction cell and 9.25% for the ‘micromorph’ tandem cell.
Synthesis of Nanophase Noble Metal Systems Utilizing Porous Silicon
Authors: Coulthard I. , Sham T. K.
Published: April 2011

Apart from its well known ability to luminesce very intensely at room temperature in the visible range, porous silicon is also an effective reducing agent. We report the formation of several noble metal (Pd, Ag, Au, Pt) nanostructures by reductive dispersion of metal ions from aqueous solutions onto the surface of porous silicon. The nanophase systems produced by reductive deposition vary with the element deposited and the metallic salt utilized in the process. The resulting nanophase systems were studied using a variety of techniques including: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spectroscopie methods using synchrotron radiation.
Ferromagnetic Nanocomposite Films from Thermally Labile Nitride Precursors
Authors: Maya L. , Paranthaman M. , Thompson J. R. , Thundat T. , Stevenson R. J.
Published: April 2011

A series of nanocomposite films containing nickel or cobalt nitride dispersed in a ceramic matrix of aluminum nitride, boron nitride or silicon nitride, were prepared by reactive sputtering of selected alloys or compounds such as nickel aluminide or cobalt suicide. Thermal treatment of the nitride composites in vacuum at ≤ 500 °C leads to selective loss of nitrogen from CoN or Ni3N to generate dispersions of the metal in the ceramic matrix. This treatment may be performed in a localized manner by means of a focused laser beam to generate microscopic features that are imaged by magnetic force microscopy. The films are potentially useful for data storage with superior chemical and mechanical stability provided by the ceramic matrix and high encoding density made possible because of the size of the magnetic particles of less than 10 nm generated in the thermal treatment. The films were characterized by chemical and physical means including FTIR, TEM, MFM and magnetic measurements. Preliminary results on similar iron composites are also described.
Microstructural Valuation of Iron-Based Composite Materials as an Ecomaterial
Authors: Itsubo Norihiro , Halada Koumei , Minagawa Kazumi , Yamamoto Ryoichi
Published: April 2011

One of an important method to realize is said that we should take recycle processes into consideration and select the material without the mixture of particular elements that make it difficult to recycle. Therefore, it is useful to control of microstructure for improvement.

From this point of view, we paid attention to “SCIFER (that is made from Kobe Steel Ltd.)” that has a recyclable formation (Fe-C-Si-Mn) and superior characteristic (tensile strength is 5000MPa). The grain size of this fiber is nano-size. In this study, we used this material and compounded it together with iron-matrix to make an iron-based composite for recycle and investigated the possibilities of realization. The difficulty of this study is to make this composite without injuring the fiber's microstructure. Therefore, we have adopted powder metallurgy which could fabricate composite at low temperature comparatively. Especially, Ultra Fine Particles (UFP) that would sinter at low temperature to bond the interface between fiber and matrix with keeping fiber's capacity. This method is useful to ascend the density of the matrix. Results are as follows. (1) Utilization of UFP slurry made it possible to adhere UFP to the surface of fiber and seed powder. Still more, this procedure enabled it to make a thin film uniformly by selecting the condition of slurry density and procedure of dryness. (2) Applying UFP to the surface of fiber and seed powder make it possible to get the bond between fiber and matrix. By the bond of interface, both fracture strength and energies have ascended remarkably due to pull out of fiber.
Synthesis, Characterization and Mechanical Properties of Nanocrystalline NiAl
Authors: Choudry M. S. , Eastman J. A. , DiMelfi R. J. , Dollar M.
Published: April 2011

Nanocrystalline NiAl has been produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100 to 300°C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range of 4 to 10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.
Structural Evolution of Fe Rich Fe-Al Alloys During Ball Milling and Subsequent Heat Treatment
Authors: Jiang H. G. , Perez R. J. , Lau M. L. , Lavernia E. J.
Published: April 2011

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been utilized to investigate the structural evolution of Fe rich Fe-Al alloys during ball milling. It is found that b.c.c. solid solutions can be formed either through ball milling alone or through ball milling together with heat treatment. Thermal diagrams of the milled Fe-Al powders reveal exothermic peaks corresponding to the formation of cc-Fe(Al) solid solution (in both Fe-4wt.%Al and Fe-10wt.%Al) and the formation of FeAl intermetallic compound (in Fe-10wt.%Al). The transformation kinetics of cc-Fe(Al) solid solution in Fe-4wt.%Al were found to follow the Johnson-Mehl-Avrami equation.
Rapid Consolidation of Nanophase Al2O3 and an Al2O3/Al2TiO5 Composite
Authors: West David A. , Mishra Rajiv S. , Mukherjee Amiya K.
Published: April 2011

A rapid consolidation technique has been utilized in producing single phase AI2O3 in less than 10 minutes at 1400°C resulting in a grain size less than 500 nm. TiO2 has been added in hopes of obtaining Al2O3/Al2TiO5 nanocomposites in sintering times less than 30 minutes. The sintering process involves resistance heating of a graphite die containing the powder at heating rates of about 10 °C/s. The resistance heating step is preceded by a preparatory step consisting of DC voltage pulses applied across a prepressed powder compact. The retention of the nanostructure is attributed to the rapid heating rate although the possible effect of the DC pulses are also discussed. An Al2O3/Al2TiO5 composite has been produced during a short anneal immediately following sintering of an Al2O3/TiO2 nanocomposite. Substantial grain growth has been observed to occur during the transformation taking the composite to the microcrystalline regime.
Percolation Threshold in Superhard Nanocrystalline Transition Metal-Amorphous Silicon Nitride Composites: The Control and Understanding of the Superhardness
Authors: Vepřek Stan , Christiansen S. , Albrecht M. , Strunk H. P.
Published: April 2011

The hardness of the recently developed novel superhard nanocrystalline composites exceeds 5000 kg/mm2 (50 GPa) and the elastic modulus 550 GPa. This is due to a special microstructure which is formed when the fraction of the amorphous component reaches the percolation threshold. Experimental data are presented and discussed.
Nano-Sized Fine Droplets of Liquid Crystals for Optical Application
Authors: Matsumoto Shiro , Houlbert Marthe , Hayashi Takayoshi , Kubodera Ken-ichi
Published: April 2011

Nano-sized fine droplets of liquid crystal (LC) were obtained by phase separation of nematic LC in UV curing polymer. The polymer composite had a high transparency in the infrared region. The fine droplets responded to an electric field causing a change in birefringence. Output power change was brought about by the generated retardation between two polarizations, parallel and perpendicular to the applied electric field. This differs from the composite containing much larger droplets, where output depends on the degree of scattering. The birefringence changed by 0.001 at the applied voltage of 7.5 V/μm.
A New Tetragonal Boride Phase in FeAl+B Type Alloys
Authors: Pierron Xavier , Baker Ian
Published: April 2011

The structure and composition of a previously unreported second phase were investigated in both Fe-43A1–0.12B and Fe-48Al-0.12B alloys. Energy dispersive x-ray and electron energy loss spectroscopy showed that the precipitates contained boron and were enriched in iron. This new boride phase had a tetragonal symmetry, with at = 4aB2 and ct = aB2, where aB2 is the matrix lattice parameter. The effect of iron content and heat treatments on the microstructure of those two boron-doped FeAl alloys are discussed.
Plasticity, Dislocation Structures and Antiphase Boundary Energies in Fe3Al Single Crystals with Chromium
Authors: Král Filip , Schwander Peter , Kostorz Gernot
Published: April 2011

The influence of Cr additions on the positive temperature dependence of the critical resolved shear stress of Fe3Al is investigated. Single crystals of binary Fe-28 at.% Al and ternary Fe-28 at.% Al-6 at.% Cr with different orientations are deformed in uniaxial compression between room temperature and 1273 K. The dislocation arrangement and the dissociation of superdislocations are studied by transmission electron microscopy using the weak-beam technique. The operative slip systems are discussed on the basis of the direct measurements of the antiphase boundary energies and of the activation volume.
In Situ TEM Observations of Cross-Slip Mechanisms in NiAl with a Soft Orientation
Authors: Vailhe C. , Douin J. , Caillard D.
Published: April 2011

In situ experiments have been conducted in NiAl single crystals in the soft orientation, at room temperature, in order to investigate the glide process of [100] dislocations. The results show that dislocations have a kinked shape in agreement with what is expected from anisotropie elasticity. Intensive cross-slip is observed, leading to slip in non-crystallographic planes and dipole formation. The ductility of the alloy is then discussed.
Powder Processing of NiAl for Elevated Temperature Strength
Authors: Daniel Whittenberger J. , Grahle Peter , Arzt Eduard , Behr Robert , Zöltzer Klaus , Hebsur Mohan
Published: April 2011

In an effort to superimpose two different elevated temperature strengthening mechanisms in NiAl, one lot of an oxide dispersion strengthened (ODS) NiAl powder has been milled in liquid nitrogen (cryomilled) to introduce A1N particles at the grain boundaries, and a second lot of ODS powder was simply roasted in gaseous nitrogen as an alternative means to produce AIN reinforced grain boundaries. Powder from both of these lots as well as the starting material have been consolidated by hot extrusion and tested at 1300 K. Both nitrogen roasting and cryomilling produced AIN within the ODS NiAl matrix which strengthened the alloy; however, based on the AIN content, cryomilling is more effective.
Strain Aging behavior In NiAI Microalloyed with Interstitial and Substitutional Solutes
Authors: Weaver M. L. , Noebe R. D. , Kaufman M. J.
Published: April 2011

Dynamic strain aging has been investigated in polycrystalline NiAl alloys containing combined additions of interstitial and substitutional impurities. The results indicate that strain aging can be enhanced in polycrystalline alloys containing concentrations of silicon or iron in excess of 0.15 at.% in addition to conventional levels of carbon. This co-doping leads to very dramatic strain aging events, comparable to those typically observed in single crystals. This effect will be discussed with respect to conventional theories of strain aging.
High-Temperature Mechanical Behavior of B2 Type IrAl Doped With Ni
Authors: Chiba A. , Ono T. , Li X. G. , Takahashi S.
Published: April 2011

Constant-velocity and constant-load compression tests have been conducted to examine the mechanical behavior of polycrystalline IrAl and Ir1-xNixAl at ambient and elevated temperatures. Although IrAl exhibits brittle fracture before or immediately after yielding below 1073K, steady-state deformation takes place at temperatures higher than 1273K. Ductility of Ir1-xNixAl is improved with increasing x. On the contrary, strength decreases with increasing x. IrAl exhibits the 0.2% flow stress of 1200MPa at 1073K and 350MPa at 1473K, about an order of magnitude higher than NiAl. Secondary creep of IrAl and Ir0.2Ni0.8Al(i.e., modified NiAl) exhibits class II and class I behavior respectively. Creep strength of binary IrAl and modified NiAl with Ir is about a magnitude of 4 higher than that of single-phase and multi-phase NiAl at a given applied stress.
Microstructure and Phase Separation of Pekk, Pekk and their Blends
Authors: Wang Wu. , Schultz Jerold M. , Hsiao Benjamin S.
Published: April 2011

Microstructures of PEEK|PEKK blends at both structural and lamellar levels were studied using simultaneously time-resolved small-angle and wide-angle x-ray scattering (SAXS and WAXS) with synchrotron radiations. Lamellar dimensions and unit cell parameters were determined, and phase separation within the blends were observed. A suitable two-phase growth model is proposed. It is concluded that when crystallized from the melt, PEEK and PEKK lamellae formed in separate lamellar bundles within a common spherulite.
Mechanical Alloying of Pet and Pet/Vectra Blends
Authors: Balik C. M. , Bai C , Koch C.C , Spontak R.J , Saw C. K.
Published: April 2011

Mechanical alloying represents a potential method for producing finely dispersed alloys of normally incompatible polymers. In this paper, PET and blends of PET with a Vectra thermotropic copolyester have been processed via high energy ball milling at room temperature (ambimilled) and at liquid nitrogen temperatures (cryomilled). Milled powders and compacted disks have been characterized using molecular weight, density and hardness measurements, aswell as DSC, WAXS, TEM and FTIR.
Refractory Ceramics From an Iron Age Bronze Melting Workshop at Khirbet Edh-Dharih, Jordan
Authors: Klein S. , Hauptmann A. , Vandiver P.B.
Published: April 2011

An excavation at Khirbet edh-Dharih implemented by the Institut Français D'Archaéologie du Proche-Orient brought forth a few archaeometallurgical remains such as lumps of bronze, slags, and refractory ceramic fragments. Khirbet edh-Dharih is located in Jordan, near the Feinan area at Wadi Arabah. The Feinan area is well known as a major supplier of copper in the Near East's history from the Chalcolithic to the Roman period. The remains from Khirbet edh-Dharih were dated from the Iron Age II, and they are pointing to a workshop for further treatment of copper from Feinan. Khirbet edh-Dharih is the first bronze melting site excavated in the Feinan copper district.
The Pottery Technology from Bukit Tengkorak, a 3000–5000 Year Old Site in Borneo, Malaysia
Authors: Vandiver Pamela , Chia Stephen
Published: April 2011

Bukit Tengkorak (Scull Hill) is a Neolithic period rock shelter complex and prehistoric pottery production site in southeastern Sabah, about 5 miles southwest of Semporna in Borneo, Malaysia at GPS N 4 7 20.08 and E 118 37 04.3. It was excavated for a 5-week season in 1995 and another in 1994 by a joint University of Science and Sabah Museum team under the direction of S. Chia. Two areas with volcanic outcrops about 10 meters apart were excavated. A total of 6 one-meter squares, three in each area, were excavated in 5 cm layers. The three rock shelter trenches, G17, G19 and J19, were excavated to the base of undisturbed cultural deposits, about one and one half meters deep. The main archaeological materials excavated from these squares comprised pottery sherds, stone tools, molluscs and fish and animal bones. Thick layers of ash, measuring 50 to 80 cm, were associated with the pottery sherds in the three rock shelter squares, suggesting that they could have been the remnant of an open pit kiln or pit kilns used for firing the pottery. In the lower outcrop, the three trenches R13, S37 and T38, were excavated near earlier archaeological excavation by Bellwood (1). Our excavation in this area revealed large deposits of clays not found elsewhere in this locale that were probably brought to the shelter to be used as raw material for making pottery. No food remains such as animal and fish bones or unworked shells were found in this area, leading credence to the interpretation of this as a craft working area for the production of pottery and stone and shell tools.
Electron Spin Resonance Characterization and Provenance of Marbles: The Case of the “Cipollino Verde”
Authors: Armiento Giovanna , Attanasio Donato , Platania Rosario
Published: April 2011

The possibility of using Electron Spin Resonance Spectroscopy (ESR) for identifying the quarries of provenance of classical marble artifacts has been reexamined and applied to the sample case of the so-called “Cipollino Verde” marble. The method gives qualitative and quantitative information on Mn2+ and other paramagnetic impurities present in marble and the assignment is made on a statistical basis, using a properly defined database. Like other, well established, techniques, ESR seldom yields an unequivocal answer to the provenance problem. However, it provides valuable information and, coupled with other methods, reduces the existing uncertainties often leading to the final assignment.
Macro- and Micro- Non Destructive Tests for Environmental Impact Assessment on Architectural Surfaces
Authors: Moropoulou A. , Koui M. , Tsiourva Th. , Kourteli Ch. , Papasotiriou D.
Published: April 2011

Several non destructive techniques are recently applied to assess and evaluate weathering damages. In the present work several macro- and micro- non destructive tests, have been employed, in the Fortress of the Medieval City of Rhodes, for the examination of the weathering: Digital Image Processing for the mapping of the decay patterns, Fibre Optics Microscopy for the examination of the morphological characteristics of the surface, and Infra Red Thermography for the assessment of the humidity distribution within the masonries and the degradation of the stone texture. The results of the above methods are supported by porosity and humidity measurements regarding the evaluation of the microstructural characteristics of the stone and the water percolation within the masonry. It is proved that these three methods can be combined into a reliable assessment tool concerning environmental impact on architectural surfaces and particularly in the form of a thorough characterization of the materials degradation.