bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Radiation-induced Defects in Fluorite Structure Oxides Formed by Electron Irradiation
Authors: Yasuda Kazuhiro , Yasunaga Kazufumi , Matsumura Syo , Sonoda Takeshi
Published: April 2011

Oxide ceramics with fluorite structure attracts considerable attention as a host of inert matrix fuels and a transmutation target for minor actinides and long life fission products. We will report the characteristic features of defect clusters in oxide ceramics with fluorite structure, such as yttria stabilized zirconia (YSZ: 13 mol% Y2O3-ZrO2), ceria (CeO2), which were investigated in situ by transmission electron microscopy under electron irradiation. Results on calcium fluorite (CaF2) will be also shown for a comparison [1]. Electron irradiation with 100 to 1000 keV was found to induce large defect clusters in YSZ, which accompany strong black/black lobes contrast and multiply dislocation networks when they grow to a critical diameter of about 1.0 ìm. The defect clusters were considered to be charged oxygen platelets formed by the selective displacement damage of oxygen sublattice. A large difference in mass of constituent ions (O and Zr/Y ions) attributes the selective displacement damage under electron irradiation [2]. Similar defect clusters with strong diffraction contrast were formed in CaF2 under 200 keV electron irradiation, and they also multiplied dislocations at a critical diameter [1]. In the case of CeO2, a higher density of defect clusters was formed compared with YSZ and CaF2. Defect clusters formed under electron irradiation less than 1250 keV were found to be faulted-prismatic-interstitial loops lying on {111} planes with Burgers vector parallel to <111> directions [3], whereas electron irradiation with 1500, 2000 and 3000 keV induces perfect dislocation loops of 1/2<110>{110} in nature. Formation of radiation-induced defects is found to depend on electron energy for crystals with fluorite structure investigated in this study. Results will be discussed through selective displacement damage and charge accumulation. This work was financially supported by the Budget for Nuclear Research of MEXT, based on the screening and counseling by the Atomic Energy Commission, and by the Grant-in-Aid for Scientific Research (B) from JSPS. [1] M. Watanabe, T. Noma, K. Yasuda, K. Yasunaga, S. Matsumura and C. Kinoshita, Proc. of 16th Electron Mmicroscopy Congress, (2006) 1854. [2] K. Yasuda, C. Kinoshita, S. Matsumura, A.I. Ryazanov, J. Nucl. Mater., 319 (2003) 74. [3] K. Yasunaga, K. Yasuda, S. Matsumura and T. Sonoda, Nucl. Instr. and Meth. B, 250 (2006) 114.
Investigation of Thermoelectric Materials: Substitution effect of Bi on the Ag1-xPb18MTe20 (M = Sb, Bi) (x = 0, 0.14, 0.3)
Authors: Han Mi-kyung , Kong Huijun , Uher Ctirad , Kanatzidis Mercouri G
Published: April 2011

We performed comparative investigations of the Ag1-xPb18MTe20 (M = Bi, Sb) (x = 0, 0.14, 0.3) system to better understand the roles of Sb and Bi on the thermoelectric properties. In both systems, the electrical conductivity nearly keeps the same values, while the Seebeck coefficient decreases dramatically in going from Sb to Bi. Compared to the lattice thermal conductivity of PbTe, that of AgPb18BiTe20 is substantially reduced. The lattice thermal conductivity of the Bi analog, however, is higher than that of AgPb18SbTe20 and this is attributed largely to the decrease in the degree of mass fluctuation between the nanostructures and the matrix (for the Bi analog). As a result the dimensionless figure of merit ZT of Ag1-xPb18MTe20 (M = Bi) is found to be smaller than that of Ag1-xPb18MTe20 (M = Sb).
Variation in the Einstein Temperature of Guest Atoms in Ba-Ge-X type-III Clathrate Compounds
Authors: Tanaka Katsushi , Kim Jung-Hwan , Kishida Kyosuke , Inui Haruyuki
Published: April 2011

Einstein temperatures of guest atoms in Ba-Ge-(Al, In) type-III clathrate compounds have been estimated from the temperature dependence of the atomic displacement parameters determined by synchrotron X-ray powder diffractions. The lowest temperature is obtained for the vibration of Ba(2) atoms along the x-direction, which corresponds to the “rattling motion” of the guest atoms in the compounds. The temperature estimated is significantly low of about 50 K, which agrees with the fact that the compounds have small lattice thermal conductivities of about 0.6 W/mK. Though the lattice thermal conductivity of Ba24Ge88Al12 is larger than that of Ba24Ge88In12, the Einstein temperature of Ba24Ge88Al12 is slightly smaller than that of Ba24Ge88In12. This discrepancy can be explained by the consideration of higher Debye temperature of Ba24Ge88Al12 than that of Ba24Ge88In12, that is, lattice thermal conductivity without “rattling motion” is larger for Ba24Ge88Al12 than that for Ba24Ge88In12.
Synthesis and Thermoelectric Properties of Y Doped SrTiO3by Modified Pechini's Method
Authors: Takenouchi Hirofumi , Imai Tomohiro , Mae Hideo , Fujimoto Masakatsu , Kineri Tohru , Iida Tsutomu , Hamada Noriaki , Watanabe Tsuneo , Nishio Keishi
Published: April 2011

Thermoelectric properties of Sr1-xYxTiO3(x = 0-0.08) were calculated using a virtual crystal method. Using a Pechini's method, Sr1-xYxTiO3(x = 0-0.06) precursor powder was prepared. Using this method, we prepared pure SrTiO3at a lower temperature than would be using the conventional solid-state reaction method. The precursor solution was heated at 823 K for 5 h after drying at 353 K for 8 h to produce the precursor powder. The powder was sintered using a hot pressing technique. The relative densities of ceramics were more than 98%. The Seebeck coefficient and electrical conductivity of the samples were measured using the standard four-probe method in a flowing He gas atmosphere in a temperature range of 323 to 923 K. The conductivities of SrTiO3, Sr0.97Y0.03TiO3, and Sr0.94Y0.06TiO3at room temperature were 6.61 × 102, 5.61 × 103, and 1.58 × 104S/m, respectively. The Seebeck coefficients of SrTiO3, Sr0.97Y0.03TiO3, and Sr0.94Y0.06TiO3at room temperature were -548, -264, and -196 μV/K, respectively.
Fabrication of Mg2Si from a Reused-silicon Source and its Thermoelectric Characteristics
Authors: Akasaka Masayasu , Iida Tsutomu , Mito Youhiko , Omori Takeru , Oguni Yohei , Yokoyama Shigeki , Nishio Keishi , Takanashi Yoshifumi
Published: April 2011

Polycrystalline Mg2Si was fabricated from a reused-Silicon source, based on Si sludge, using Spark Plasma Sintering technique. The n-type and p-type dopants, bismuth (Bi) and silver (Ag), respectively, were incorporated into the Mg2Si. The thermoelectric properties were estimated from 300 to 873K. The power factors of undoped and Bi-doped samples from the reused-Si source were comparable to those from a solar grade Si source (99.99999%). The power factor was estimated to be 2.5 × 10-5 W/cmK2 for the Bi-doped sample from the reused-Si source. However, the power factor of the Ag-doped, p-type sample from the reused-Si source was lower than that from solar grade Si source. The dimensionless figures of merit of samples from the resused-Si source were slightly lower than those from a solar grade Si source. The dimensionless figure of merit was estimated to be 0.53 at 812 K for Bi-doped sample from the reused-Si source.
LSCO Ceramics as Possible Thermoelectric Material for Low Temperature Applications
Authors: Rodríguez Julio E.
Published: April 2011

Seebeck coefficient S(T), thermal conductivity κ(T) and electrical resistivity ρ(T) measurements on polycrystalline La1.85Sr0.15CuO4-δ(LSCO) compounds grown by solid-state reaction method were carried out in the temperature range between 100 and 290K. The obtained samples were submitted to annealing processes of different duration in order to modify their oxygen stoichiometry. The Seebeck coefficient is positive over the measured temperature range and its magnitude increases with the annealing time up to reach values close to 150 µV/K. The electrical resistivity exhibits a metallic behavior, in all samples, ρ(T) takes values less than 1mΩ-cm. As the annealing time increases, the total thermal conductivity increases up to values close to 3 W/K-m. From S(T), κ(T) and ρ(T) data, the thermoelectric power factor (PF) and the dimensionless figure of merit (ZT) were determined. These parameters reach maximum values around 25 µW/K2-cm and 0.18, respectively. The observed behavior in the transport properties become these compounds potential thermoelectric materials, which could be used in low temperature thermoelectric applications.
Investigations of Bonding in Skutterudites by Electron Energy-Loss Spectroscopy
Authors: Prytz Oystein , Saterli Ragnhild , Holmestad Randi , Tafto Johan
Published: April 2011

The local electronic structure of phosphorus in the binary skutterudites CoP3 and NiP3, and in the filled skutterudite LaFe4P12 are studied using a combination of electron energy-loss spectroscopy and ab initio calculations. Relative to CoP3 we observe a filling of phosphorus s and d states in NiP3, while for LaFe4P12 increased EELS intensity indicates more empty s and d states close to the Fermi-level.
Preparation and Characterization of High Temperature Thermoelectrics Based on Metal/Oxide Nanocomposites
Authors: Gregory Otto J. , Chen Ximing , Fralick Gustave C. , Wrbanek John
Published: April 2011

Thermoelectric devices based on “n-type” oxide semiconductors and metal/oxide nanocomposites are being considered for high temperature thermocouples, heat flux sensors and energy harvesting devices. In terms of energy harvesting, preliminary 2D thermoelectric calculations indicated that enough electrical energy can be generated from the large thermal gradients that exist within a gas turbine engine to power active wireless devices. Several promising bi-ceramic junctions based on this concept were investigated in terms of their high temperature thermoelectric properties. The most promising bi-ceramic junction was based on indium tin oxide (ITO) and a NiCrCoAlY/alumina nanocomposite. The thermoelectric responses of these individual elements were evaluated relative to a platinum reference electrode. A maximum emf of 77 mV was achieved for a NiCrCoAlY/alumina nanocomposite/platinum thermocouple for an imposed temperature gradient of 1111 °C. The thermoelectric power for this couple was 78 μV/°C. When this NiCrCoAlY/alumina nanocomposite was combined with ITO to form a bi-ceramic junction, thermoelectric powers on the order of 700 μV/°C were obtained. A maximum electromotive force of 291mV was achieved for a hot junction temperature of 1100 °C. The thermoelectric response after repeated thermal cycling to 1200 °C was both repeatable and reproducible. The ITO was prepared in varying nitrogen, oxygen and argon partial pressures, which was used to control the charge carrier concentration, stability and thermoelectric response of the bi-ceramic junctions. The thermoelectric response decreased with increasing nitrogen partial pressure and increased with oxygen partial pressure in the plasma with the argon partial pressure constant. The relationship between the sputtering parameters and thermoelectric properties was investigated and the application of these bi-ceramic junctions as thermocouples and energy harvesting devices is discussed.
Thermoelectric Properties of Nearly Single-Phase Half-Heusler NbCoSn Alloys and Importance of Microstructures for Improving Performance
Authors: Kimura Yoshisato , Tamura Yukio , Kita Takuji
Published: April 2011

In order to evaluate the thermoelectric properties of n-type half-Heusler compound NbCoSn, single-phase NbCoSn alloy was prepared using directional solidification based on the phase diagram information of the Nb-Co-Sn ternary system which was investigated in this work. The isotherm at 1273 K and the reaction scheme together with the projection of liquidus surface were determined. Thermoelectric properties of NbCoSn based alloys were evaluated by Seebeck coefficient, electrical resistivity and power factor, which were measured in a temperature range from room temperature to 1073 K. NbCoSn has excellent values of Seebeck coefficient exceeding -250 μV/K at around 900 K and shows the metal-like temperature dependence of electrical resistivity.
Origin of Giant Seebeck Coefficient for High Density 2DEGs Confined in the SrTiO3/SrTi0.8Nb0.2O3 Superlattices
Authors: Mune Yoriko , Ohta Hiromichi , Mizoguchi Teruyasu , Ikuhara Yuichi , Koumoto Kunihito
Published: April 2011

Recently, we have found that high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO3 exhibits extremely large Seebeck coefficient (|S|2D) [REF], approximately five times larger than |S|3D. Here we clarify the origin of giant |S|2D using [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]20 (x = 1∼60, y = 1∼20) superlattices. The |S|2D value increased proportionally to y{0.5, indicating that the density of states of the conduction band increases with decreasing y (quantum size effect). Superlattices of [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z (x = 0∼60, y = 1∼20, z = 20) were fabricated on the (001)-face of LaAlO3 substrate by PLD using RHEED to count the number of SrTiO3 or SrTi0.8Nb0.2O3 layers. HR-XRD and HAADF-STEM studies revealed that high-quality [(SrTiO3)17/(SrTi0.8Nb0.2O3)y]z superlattices were successfully fabricated. A dramatic increase of |S|2D is seen with decreasing y-value of the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices. The slope for the plots of log |S|2D - log y is -0.5, and reached 290 μVK−1 (y = 1), which is ∼5 times larger than that of the SrTi0.8Nb0.2O3 bulk (|S|3D = 61 μVK−1). Further, the |S|2D value monotonically increases with x-value and is saturated when x-value > 16 (6.25 nm). We clarified that the critical barrier thickness for electron tunneling in [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattice is 6.25 nm (16 unit cell layers of SrTiO3). The present results give very important information to utilize the [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]z superlattices for practical application.
New Approach for the Synthesis of IV-VI Thermoelectric Thin Film Materials and Devices on Si: (211) PbSnSeTe/ZnTe/Si Heterostructures
Authors: Taylor Patrick J. , Morgan Brian , Dhar Nibir K. , Chen Y.
Published: April 2011

Low-dimensional thin-film thermoelectric materials including superlattices and quantum-dot heterostructures have shown significant potential for improving the thermoelectric properties. Highly structured thin film materials such as these would be useful for integrated microdevices such as power MEMS and thermally triggered MEMS actuators. For reasons including scalability and ease-of-integration, silicon is the choice material for the substrate, however there is a lattice and a thermal-expansion mismatch. In this work, a new approach for the synthesis of integrated PbSnSeTe based thermoelectric thin film materials on silicon is demonstrated by employing an epitaxial buffer layer of II-VI compound telluride materials (e.g., ZnTe, CdTe) to help bridge the lattice and thermal expansion mismatches with silicon. This multilayer can be used for subsequent growth of thick films having low-dimensionality structures. We report the initial results from studying the structural and thermoelectric properties of simple solid-solution alloy PbSnSeTe thin films on ZnTe/Si heterostructures. Data from transmission electron microscopy and in-situ electron diffraction will be presented that shows that despite the large lattice mismatch with silicon and the three different crystal structures, unusually high structural quality PbSnSeTe has been obtained by matching the (211) lattice symmetry and the lattice spacing along the [110] directions of the ZnTe and PbSnSeTe. The structural quality of the PbSnSeTe was studied by measuring the dislocation density through etch-pit counting and x-ray diffraction. Results presented will show that a dislocation density as low as 1.2 × 106/cm2can be achieved by strategic lattice-matching between the buffer and thermoelectric layers. Electrical resistivity, doping density, and Seebeck coefficient values for solid-solution alloys without low-dimensional structuring will be shown to approach those of high-performance bulk.
Enhanced Seebeck Coefficient of Amorphous Oxide Semiconductor Superlattices
Authors: Ohta Hiromichi , Huang Rong , Ikuhara Yuichi
Published: April 2011

We propose herein that amorphous oxide semiconductor (AOS) superlattices, which can be deposited on various substrate including glasses or plastics without any substrate heating, are appropriate for the realization of superlattice thermoelectric devices. As an example, thermoelectric properties of AOS superlattices composed of a-In-Zn-O (well) and a-In-Ga-Zn-O (barrier) layers, fabricated on SiO2 glass substrate by pulsed laser deposition at room temperature, were measured to clarify whether enhancement of Seebeck coefficient |S| occurs or not. The |S|2D value increases drastically with decreasing a-In-Zn-O thickness (dIZO) when the dIZO is < ∼5 nm, and reached 73 μV·K-1 (dIZO = 0.3 nm), which is ∼4 times larger than that of bulk |S|3D (19 μV·K-1), while it kept high electrical conductivity, clearly demonstrating that the quantum size effect can be utilized in AOS superlattices.
Formation of transition-metal-based ohmic contacts to n-Mg2Si by Plasma Activated Sintering
Authors: Oguni Yohei , Iida Tsutomu , Matsumoto Atsunobu , Nemoto Takashi , Onosaka Junichi , Takaniwa Hironori , Sakamoto Tatsuya , Mori Daisuke , Akasaka Masayasu , Sato Junichi , Nakajima Tadao , Nishio Keishi , Takanashi Yoshifumi
Published: April 2011

Electrode materials consisting of Cu, Ti and Ni were formed on Bi-doped n-type Mg2Si by means of a monobloc plasma-activated sintering (PAS) technique. Due to the difference in thermal expansion coefficients between Ti and Mg2Si, rather high residual thermal stresses gave rise to the introduction of cracks, which were mainly located in the Mg2Si layer, when Ti was used as the electrode material. In the case of the Cu electrodes, monobloc sintering could not be performed in a reproducible manner because Cu melts abruptly and effuses at around 973K, which is 100 K lower than the sintering temperature that is required for Mg2Si of good crystalline quality. When compared with the results for Cu and Ti, the monobloc PAS process for Ni was both stable and reproducible. The room-temperature I-V characteristics of Ni electrodes were considered to be adequate for practical applications, with durable Mg2Si-electrode junction properties being realized at a practical operating temperature of 600 K with ΔT = 500 K. The highest open circuit voltage (VOC) observed was 41 mV at ΔT = 500 K (between 873 K and 373 K) for Ni electrodes fabricated using the monobloc PAS process. The voltage (V) and current (I) values with a 10 Ohm load were ∼ 48 mV and ∼ 2 mA at ΔT = 500 K.
Study on the Fabrication and Characterization of LAST and LASTT Based Thermoelectric Generators
Authors: Wu Chun-I , Timm Edward J. , Ren Fei , Hall Bradley D. , Ni Jennifer , Downey Adam , D'Angelo Jonathan , Short Jarrod , Schock Harold , Case Eldon , Sootsman Joe , Han Mi-Kyoung , Kanatzidis Mercouri , Chung Duck-young , Hogan Timothy P.
Published: April 2011

Thermoelectric modules are of great interest for power generation applications where temperature gradients of approximately 500K exist, and hot side temperatures near 800K. The fabrication of such modules requires optimization of the material compositions, low contact resistivities, and low thermal loss.

AgPbmSbTe2+m (LAST) and Ag(Pb1-xSnx)m SbTe2+m (LASTT) compounds are among the best known materials appropriate for this temperature range. Various measurement systems have been developed and used to characterize bulk samples in the LAST and LASTT systems within this operating temperature range. From the characterized data, modeling of modules based on these materials and segmented legs using LAST(T) with Bi2Te3 have been used to identify the optimal geometry for the individual legs, and the length of the Bi2Te3 segments. We have segmented LAST(T) with Bi2Te3 and achieved contact resistivities of less than 10 μΩ•cm2.

Here we give a detailed presentation on the procedures used in the fabrication of thermoelectric generators based on LAST, LASTT, and segmented with Bi2Te3 materials. We also present the output data on these generators.
Volume and Enthalpy Relaxation in Bulk Metallic Glasses
Authors: Haruyama Osami
Published: April 2011

Volume and enthalpy relaxation processes in a sub-Tg region were investigated by density and enthalpy experiments for bulk Pd-P based and Zr-based metallic glasses. Most of glasses except for a Pd40Ni40P20 glass exhibited a single relaxation process for both volume and enthalpy relaxations and the relaxation process was well described by a stretched exponential relaxation function, Φ(t)=exp{-(t/τ)β}, with a Kohlrausch index β less than 1. The as-quenched sample was pre-annealed in a supercooled liquid region to homogenize the density fluctuation quenched in an as-quenched state. Then the retardation of onset time of relaxation appeared in case of volume relaxation. The proportionality between enthalpy change ΔH and volume change Δv during relaxation was good for Pd42.5Cu30Ni7.5P20 glass within experimental error.
Microscale Thermoplastic Forming of Bulk Metallic Glasses: Numerical Simulation and Experiments
Authors: Henann David , Anand Lallit
Published: April 2011

An extremely promising microscale processing method for bulk metallic glasses called thermoplastic forming has emerged in recent years. However, most of the recent experimental thermoplastic forming studies have been conducted by trial-and-error. In this paper, we use the large-deformation constitutive theory of Henann and Anand [1] as a numerical simulation tool for the design of a micro-hot-embossing process. This numerical simulation capability is used to determine appropriate processing parameters in order to carry out a successful micron-scale hot-embossing operation on the metallic glass Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vitreloy-1). By carrying out a corresponding physical experiment, we demonstrate that micron-scale features in Vitreloy-1 may be accurately replicated under the processing conditions determined by use of the numerical simulation capability.
Computational generation of disordered structures of Al-12%Si. An ab initio approach
Authors: Diaz-Celaya J. Andres , Valladares R.M. , Valladares Ariel A.
Published: April 2011

Metallic glasses are in the forefront of metallurgical research and applications. For this reason it is important to realistically model amorphous metallic systems. Some computer simulation efforts have relied on the use of parameterized classical potentials of the Lennard-Jones type or geometric hard sphere simulations, but first principles approaches have been rarely used. In this work we apply our recently developed ab initio DFT approach (A. A. Valladares et al., Eur. Phys. J. 22 (2001) 443) for the generation of amorphous semiconducting materials, to amorphize an aluminum-silicon alloy, the eutectic Al-12%Si. We report specific atomic structures and radial distribution functions (RDFs), total and partial, of one amorphous and one liquid-amorphous periodic cubic supercell of 125 atoms (15 silicons and 110 aluminums), Al-12%Si, with a volume (12.8379 Å)3, generated using the Harris functional.
Strength Measurement in Brittle Thin Films
Authors: Borrero-Lopez Oscar , Hoffman Mark , Bendavid Avi , Martin Phil J
Published: April 2011

In this work we have investigated the strength variability of brittle thin films (thickness ≤ 1 μm) utilising a simple test methodology. Nanoindentation of as-deposited tetrahedral amorphous carbon (ta-C) and Ti-Si-N nanocomposite films on silicon substrates followed by cross-sectional examination of the damage with a Focused Ion Beam (FIB) Miller allows the occurrence of cracking to be assessed in comparison with discontinuities (pop-ins) in the load-displacement curves. Strength is determined from the critical loads at which cracking occurs using the theory of plates on a soft foundation. This is of great relevance, since the fracture strength of thin films ultimately controls their reliable use in a broad range of functional applications.
Study on the local damage mechanisms in WC-Co hard metals during scratch testing
Authors: Ndlovu Siphilisiwe , Durst Karsten , Hoeppel Heinz Werner , Goeken Mathias
Published: April 2011

The effect of the cobalt content and WC grain size on the deformation behaviour of WC-Co hard metals was investigated by studying materials with a varying WC grain size and cobalt content. The WC grain size ranged from 2.65 to 0.25 µm and the binder content ranged from 6 to 15 wt%. Single and multiple scratch tests were conducted using a Nano indenter with a Berkovich diamond tip and the load ranged from 5 to 500 mN with a tip sliding velocity of 10 µm/s. Several damage mechanisms were observed and these show a combination of ductile and brittle wear. The bulk properties i.e. composite properties of the hard metal determine the wear in the 6 wt% Co samples on the other hand the 15 wt% Co samples exhibited a localised response to the wear i.e. the wear is determined by the individual phases in the hard metal.
Interfacial Characterization of Multiple Layer Coatings on Thermoplastic Olefins (TPO)
Authors: Forster Aaron M , Michaels Chris A. , Lucas Justin , Sung Lipiin
Published: April 2011

Thermoplastic olefins (TPO) have made significant inroads as polymeric materials for interior and exterior automotive parts. Spray applied chlorinated polyolefins (CPO) are often used to improve paint adhesion to the low surface energy TPO substrates. The penetration of the CPO into the substrate is difficult to quantify, but is critical to achieving a good paint/TPO bond. The interphase between each layer in a coated TPO coupon was investigated using a combination of instrumented indentation and confocal Raman microscopy. The degree of CPO interpenetration was Thermoplastic olefins (TPO) have made significant inroads as polymeric materials for interior and exterior automotive parts. Spray applied chlorinated polyolefins (CPO) are often used to improve paint adhesion to the low surface energy TPO substrates. The penetration of the CPO into the substrate is difficult to quantify, but is critical to achieving a good paint/TPO bond. The interphase between each layer in a coated TPO coupon was investigated using a combination of instrumented indentation and confocal Raman microscopy. The degree of CPO interpenetration was altered by using three different CPOs exposed to two different manufacturing methods for the same TPO and base/clear coat system. It was found that the interfaces, CPO/base coat or CPO/TPO, were chemically and mechanically sharp at the 1 μm lateral resolution of both techniques. A gradient in the modulus through the thickness of the clear coat was observed using instrumented indentation.
Modeling magnetoelasticity and magnetoplasticity with disconnections and disclinations
Authors: Mullner Peter , Geleynse Alan Steward , Carpenter David Robert , Hagler Michael Scott , Chmielus Markus
Published: April 2011

The magneto-mechanical properties of magnetic shape-memory alloy single crystals depend strongly on the twin microstructure which is established during the martensitic transformation, and through thermo-magneto-mechanical training. For self-accommodated martensite, twin thickness and magnetic-field-induced strain are very small. For effectively trained crystals, a single twin may comprise the entire sample and magnetic-field-induced strain reaches the theoretical limit. Furthermore, the deformation of self-accommodated martensite is pseudo-elastic (magnetoelasticity) while the deformation of effectively trained crystals is plastic (magnetoplasticity). Twin microstructures of self-accommodated martensite were modeled using disclinations which are line defects such as dislocations, however with a rotational displacement field. The defect structure was approximated in a quadrupole solution where two quadrupoles represent an elementary twin double layer unit. The twin boundary was inclined to the twinning plane which required the introduction of twinning disconnections. The shear stress-shear strain properties of self-accommodated martensite were analyzed numerically for different initial configurations of the twin boundary (i.e. for different initial positions of the disconnections). The shear stress-shear strain curve is sensitive to the initial configuration indicating that disconnection nucleation is controlling the magneto-mechanical properties of self-accommodated martensite.
Reliability of MEMS Materials: Mechanical Characterization of Thin-Films using the Wafer Scale Bulge Test and Improved Microtensile Techniques
Authors: Gaspar Joao , Schmidt Marek , Held Jochen , Paul Oliver
Published: April 2011

This paper reports on recent improvements of the bulge and microtensile techniques for the reliable extraction of material parameters such as the Young's modulus E, Poisson's ratio ν, plane strain modulusEps=E/(1–ν2), prestress σ0, fracture strength μ, Weibull modulusmand strain hardening coefficientsn, and on the direct comparison between the two methods. The bulge technique is extended to full wafer measurements enabling throughputs of data with statistical relevance whereas key improvements of a previous fabrication process of microtensile specimens lead now to much higher yields, approaching 100%. Both techniques are applied to an extensive set of materials, brittle and ductile, typically used in MEMS applications. These include thin films of silicon nitride, silicon oxide, polycrystalline silicon and aluminum deposited by techniques such as thermal oxidation, LPCVD, PECVD and PVD.
Microstructural and Geometrical Factors Influencing the Mechanical Failure of Polysilicon for MEMS
Authors: Jonnalagadda Krishna , Chasiotis Ioannis
Published: April 2011

The failure strength of polycrystalline silicon is discussed in terms of activation of critical flaws, as well as the material microstructure and inhomogeneity. The Weibull probability density function parameters were obtained to deduce the scaling of material and component strength and to identify critical flaw populations, especially when two or more flaw sets are concurrently active. It was shown that scaling of strength changes for small feature sizes, which limits the applicability of strength data from large MEMS components to self-similar small MEMS components. On the other hand, the probability of failure of small components is described by a larger Weibull material stress parameter, which makes uniaxial strength data a conservative design approach. Furthermore, according to mode I and mixed mode I/II fracture studies for polysilicon, it is concluded that microstructural inhomogeneity alone accounts for 50% scatter in strength (with reference to the minimum recorded value). Thus, the conditions for applicability of the Weibull probability density function are rather weak in polycrystalline silicon, because flaws of the same length that are subjected to the same macroscopic stresses are not always critical.
Mechanical Stress Sensors for Copper Damascene Interconnects
Authors: Delamare Romain , Blayac Sylvain , Kasbari Moustafa , Inal Karim , Rivero Christian
Published: April 2011

We propose embedded microsensors to investigate the mechanical stress in copper damascene lines in a standard CMOS microelectronic technology. Those sensors are based on silicon piezoresistive effect where strain in the active silicon is induced by orientated copper lines. The challenge is to correlate the electrical sensors signal directly to stress variation in lines.

We have performed electrical measurements of the structures as a function of temperature. A coupled analytical and Finite Element thermomechanical Model of the structure was developed and a good agreement with measurements was obtained.
Variation in Dislocation Pattern Observed in SCS Films Fractured by Tensile Test: Effects of Film Thickness and Testing Temperature
Authors: Nakao Shigeki , Ando Taeko , Arai Shigeo , Saito Noriyuki , Sato Kazuo
Published: April 2011

This paper reports a transition in the fracture behavior of micron-sized single-crystal-silicon (SCS) film in an MEMS structure for various film thicknesses and ambient temperatures. The mean fracture toughness of 4-µm-thick SCS films was 1.28 MPa at room temperature (RT), and the value increased as the film thickness decreased, reaching 2.91 MPa for submicron-thick films. The fracture toughness of 4-µm-thick film did not change for ambient temperatures ranging from RT to 60ºC. However, it drastically increased at 70ºC and reached 2.60 MPa at 150ºC. Enhanced dislocation activity in the SCS crystal near the fracture surface was observed on 1-µm-thick film at RT and 4-µm-thick film at 80ºC by high-voltage electron microscopy. This change in dislocation activity seemed to correlated with the transition in fracture behavior.
Novel Differential Surface Stress Sensor for Detection of Chemical and Biological Species
Authors: Kang Kyungho , Shrotriya Pranav
Published: April 2011

A miniature sensor consisting of two adjacent micromachined cantilevers (a sensing/reference pair) is developed for detection of chemical and biological species. A novel interferometric technique is utilized to measure the differential bending of sensing cantilever with respect to reference. Presence of species is detected by measuring the differential surface stress associated with adsorption/absorption of chemical species on sensing cantilever. Surface stress associated with formation of alkanethiol self-assembled monolayers (SAMs) on the sensing cantilever is measured to characterize the sensor performance.
A Comparative Study of the Strength of Si, SiN and SiC used at Nanoscales
Authors: Alan Tuncay , Sarro Pasqualina M.
Published: April 2011

Microelectromechanical systems (MEMS) are being used in many critical applications that require very high stress levels. To properly design MEMS components, mechanical properties should be characterized testing relevant sized samples that are fabricated with the same procedures as the final structure. In this paper we use atomic force microscopy (AFM) experiments to study the fracture strength statistics of polycrystalline SiC and SiN nanobeams, and compare their mechanical performance with the performance of previously tested Si nanostructures. Using the same AFM method and similar sample shape and sizes, allows a direct comparison to be made, which will be useful in determining the best material for different mechanical applications and also to validate the theoretical limits.
Spectroscopy of Chromium Doped Garnets in a Wide Temperature Range
Authors: Orucu Humeyra , Ozen Gonul , Collins John , Di Bartolo Baldassare
Published: April 2011

Chromium doped garnets are tunable solid state laser materials which emit in the red and near infrared. We have studied the emission spectra of Y3Al5O12:Cr3+ (YAG:Cr), Gd3Ga5O12:Cr3+ (GGG:Cr) and Gd3Sc2Ga3O12:Cr3+ (GSGG:Cr) in a wide range of temperatures 25-800 K and have related their spectroscopic properties to the interaction between the 2E and 4T2 energy levels of the chromium ion. The measurements included absorption, lifetime, luminescence under continuous and pulsed excitations, and thermal effects on sharp lines.
Performance and Modeling of a Nanostructured Relative Humidity Sensor
Authors: Taschuk Mike , Steele John , Brett Mike
Published: April 2011

Capacitive humidity sensors were fabricated using interdigitated electrodes coated with amorphous nanostructured TiO2 thin films grown by glancing angle deposition. The sensor exhibited a large change in capacitance, increasing exponentially from ∼ 1 nF to ∼ 1 μF for an increase in relative humidity from 2 % to 92 %. A simple model of the capacitive response and dielectric constant of the devices has been developed and compared to the experimental results. From this comparison, it is clear that the magnitude of the device response observed cannot be explained with bulk dielectric constants or literature values.
Implantation and Sputtering of Ge and Si Ions into SiO2 Substrates using Electric Fields for Acceleration and Optimisation of Laser-produced Ion Streams used for Modification of Semiconductor Materials
Authors: Rosinski Marcin , Wolowski Jerzy , Yerci Selcuk , Parys Piotr , Turan Rasit , Badziak Jan , Czarnecka Agata , Gasior Pawel , Pisarek Marcin
Published: April 2011

Laser plasma has been proved to be a potential source of multiply charged ions which could support the growing demands for high-current ion beams. To optimize efficiency of the ion implantation technology selection of proper laser beam characteristics is very important and should be investigated. With LIS, several variables can and must be controlled. The properties of ions (current densities, the ion charge state, angular and energy distributions) depend on target material and the laser energy, pulse duration and intensity on the target surface. So, the characteristics of laser-produced ion streams should be determined with the use of precise ion diagnostic methods.

Based on the preliminary results for acceleration of ions produced with the use of a repetitive laser system at IPPLM the special electrostatic-acceleration system has been designed and prepared. This device permits to accelerate ions having charge states of 1+ to energies up to ∼40 keV. The movable target holder was located inside the cylindrical box connected with a high-voltage source (up to 50 kV at 50 mA). The accelerated Ge and Si ions was implanted to SiO2/Si substrates and analyzed.

This contribution is concerned mainly on the analysis and optimization of laser-produced Ge and Si ion streams as well as on investigation of the direct implantation of these ions into SiO2 substrates. Targets were irradiated with the use of repetitive (up to 10 Hz) laser with energy up to 700 mJ in one pulse, at radiation intensities of ∼1011 W/cm2. The ion stream parameters were measured using the time-of-fight method. The depth of ion implantation was determined by X-Ray Photoelectron Spectroscope (XPS). After the implantation the samples were annealed in different temperatures in range of to create nanocrystal structures and then analyzed by means of Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The work has been performed within SEMINANO project supported by EC (within 6FP).
Interface Stability between Ni-P film plated by Supercritical Electroless Plating and the Polymer Substrate
Authors: Woo Byung-Hoon , Sone Masato , Shibata Akinobu , Ishiyama Chiemi , Yamagata Masahiro , Masuda Kaoru , Higo Yakichi
Published: April 2011

We propose a novel technique for electroless plating on polymer substrates using a dense CO2 beyond the critical point. Ni-P thin films were fabricated by a novel, hybrid technique consisting of two processes: catalyzation in supercritical CO2 with Pd bis-acetylacetonate and electroless plating in emulsion with dense carbon dioxide. Catalyzation in supercritical CO2 enabled the nucleation of a large number of Pd nuclei on a polyimide substrate without chemical pretreatment, and the deposition of a uniform Ni-P metal film. The electroless plating in emulsion with dense carbon dioxide produced a uniformly plated film without peeling or nodules. The improved uniformity was attained by the solubility and diffusivity of the dense CO2 beyond the critical point in the emulsion.
UV Resistant Poly(3,4-ethylenedioxythiophene) Thin Films: Layer-by-Layer Assembly with Absorbing Nanoparticles
Authors: Dawidczyk Thomas , Grunlan Jaime
Published: April 2011

Layer-by-layer (LbL) assembly is used to create thin films by alternately exposing a substrate to positively- and negatively-charged molecules or particles in water. In recent years, LbL assemblies containing poly(3,4-ethylenedioxythiophene) (PEDOT) have been heavily studied, but little work has focused on improving the environmental stability of these thin films. Most intrinsically conductive polymers suffer from increasing resistance with exposure to ultraviolet light. In the present work, photolytic stability is improved by adding UV-absorbing nanoparticles to PEDOT assemblies. Films made by alternately depositing PEDOT-PSS and polyethylenimine (PEI) show an order of magnitude increase in sheet resistance after just 28 hours of exposure to 365 nm light. This degradation is cut in half by incorporating UV-absorbing nanoparticles, carbon black or titanium dioxide, into these assemblies. After more than 200 hours of exposure, films containing TiO2 nanoparticles have sheet resistance that is one fifth that of the unprotected PEDOT. In addition to adding UV-absorbing particles, the influence of doping and type of polycation on bulk resistivity and film growth were evaluated. These films are able to achieve bulk resistivity values below 1 Ohm cm with a thickness below 100 nm. When combined with transparency greater than 90%, these films may be useful for electrostatic dissipation layers or low conductivity electrodes in film or flexible display applications.
TEM Investigation of Epitaxial Assembly in Aggregates of BaTiO3 and CaTiO3 Nanocrystalline Particles Synthesized under Hydrothermal Conditions
Authors: Iwaji Naoki , Takebe Hiromichi , Kuwabara Makoto
Published: April 2011

We investigated epitaxial assembly in aggregates of BaTiO3 and CaTiO3 nanocrystals, which were synthesized under a hydrothermal condition at 150°C using distilled water-ethanol solvent, by transmission electron microscopy analysis. The volume ratio of distilled water-ethanol used as the solvent gives a significant influence on the crystal growth of the nanocrystals. The obtained results indicate that epitaxial assembly is surely involved in the crystal growth of BaTiO3 and CaTiO3 nanocrystals under the present thermal condition.
Enhancement of light transmission through nanoslit in a circular metallic film flanked by parallel periodic gratings
Authors: Kumar Dinesh , Asakawa Kiyoshi
Published: April 2011

We investigate the potential of a slit grating structure on a silver film embedded in a high index dielectric film, as a Plasmonic optical antenna in infrared region. Using FDTD calculations it is demonstrated that the transmission properties of the structure has strong dependence on the dimension of dielectric film. By tapering the height of output gratings directionality of the emitted beam has been improved. We propose the application of the Plasmonic antenna and examine its performance in axial injection of light from single mode fiber to photonic crystal waveguide.
Atomic Structure of PtRu Nanoparticle Catalysts and Their Methanol Oxidation Activity
Authors: Nitani Hiroaki , Honda Yusuke , Horioka Ryo , Ohara Kosuke , Kawaguchi Takuya , Nakagawa Takashi , Seino Satoshi , Yamamoto Takao A. , Daimon Hideo
Published: April 2011

PtRu bimetallic nanoparticles supported on carbon nanoparticle (PtRu/C) catalysts were synthesized with radiation irradiation. The samples were structural analyzed by techniques of X-ray absorption fine structure (XAFS), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results indicated that PtRu/C catalysts which prepared by an electron beam irradiation had more homogeneous atomic arrangement than that prepared by a gamma-ray irradiation. We found a clear correlation between the atomic structure and the catalytic activity of PtRu/C catalysts. These results supported the bi-functional mechanism.
Preparation and Photocatalytic Properties of TiO2/SiO2Composite Nanofibers
Authors: Lee Sung Wook , Lim Tae Ho , Kim Sang Beom , Hyun Dong Ho
Published: April 2011

(1-x)SiO2/(x)TiO2composite micro/nano scale fibers with various compositions were successfully prepared by electrospinning their sol-gel precursors of titanium(IV) isopropoxide(TiP), and tetraethyl orthosilicate(TEOS), followed by calcinations. Any gelator or binder was not used in this direct preparation process for composite fibers. The surface morphology and structure of sintered composite fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and Fourier transform infrared (FT-IR). The crystallization behavior and surface morphology of the as-spun fibers were largely influenced by the calcination temperature and the content of TiO2. The photocatalytic activity of SiO2/TiO2composite fibers was examined by UV-DRS spectra. The experiments demonstrated that the MB in aqueous solution was successfully photodegraded using SiO2/TiO2composite nanofibers under UV-visible light irradiation.
Flame Retardant Intumescent Polyamide 11-Carbon Nanofiber Nanocomposites: Thermal and Flammability Properties
Authors: Lao Si Chon , Koo Joseph H , Morgan Alexander , Jor Hung-Kai , Nguyen Khiet , Wissler Gerhardt , Pilato Louis , Luo Zhiping
Published: April 2011

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for fabricated parts that are required for performance driven applications. The introduction of selected nanoparticles such as carbon nanofibers (CNFs), combined with a conventional intumescent flame retardant (FR) additive into the polyamide 11/polyamide 12 (PA11/PA12) by melt processing conditions has resulted in a family of intumescent polyamide nanocomposites. These intumescent PA11 and PA12 nanocomposites exhibit enhanced polymer performance characteristics, i.e., fire retardancy, high strength, and high heat resistance and are expected to expand the market opportunities for resin manufacturers. The overall objective of this research is to develop improved PA11 and PA12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing. Arkema RILSAN® PA11 polymer was examined with CNFs and Clairant Exolit® OP 1230 intumescent FR additive. They were used to create a family of FR intumescent PA11-CNF nanocomposites. Transmission electron microscopy (TEM) was used to determine the degree of CNFs and intumescent FR additive dispersion in PA11. Injection molded specimens were fabricated for material properties measurements. Thermal stability of these polymer nanocomposites (PNs) was examined by TGA. Flammability and thermal properties of these PNs were obtained using the cone calorimeter, UL 94 test method, and heat deflection temperature.
Functionalized Photonic Crystal Sensor Elements based on Nanoporous Polymers
Authors: Kim Sung Jin , Nio Elizabeth , Chodavarapu Vamsy P , Titus Albert H , Swihart Mark T , Cartwright Alexander N
Published: April 2011

We report the development of oxygen sensors using polymer photonic bandgap structure and CMOS chips. These integrated sensors provide a new platform for the development of low cost, low (battery) powered, light weight, robust, fast and small sensors. We demonstrate an approach to encapsulation of chemical and biological recognition elements within the porous structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Resulting structure is nanoporous polymer 1D photonic bandgap structures that has reflection grating property and can be directly integrated into optical sensor systems that we have previously developed. For optical sensor system, CMOS (Complementary Metal Oxide Semiconductor) detectors that include phototransistors, trans impedance amplifier, and other signal processing units are used. Combining CMOS chip and nano-porous polymer reflection grating, we demonstrate an oxygen sensor as a prototype by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) using fluorescence intensity.
Optical Properties of Double-Decker-Shaped Poly (Silsesquioxane)
Authors: Watanabe Akira , Tadenuma Shohei , Miyashita Tokuji
Published: April 2011

The double-decker-shaped silsesquioxane (DDSQ) is a new family of silsesquioxanes consisting of a Si-O-Si case structure and functional organic side chains. The optical properties of a novel organic-inorganic hybrid polymer based on the DDSQ were studied. The double-decker-shaped poly(silsesquioxane) (DDPSQ) showed excellent transparency and thermal stability. The thermo-optic coefficient of the DDPSQ is 3 or 4 times larger than conventional polymers.