bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Effects of Heavy Ion Irradiation on CeO2 by Using Synchrotron Radiation X-Ray Absorption Spectroscopy -as a Simulation Study for Radiation Damage in High-Burnup Light Water Reactor Fuels-
Authors: Ohno Hirotaka , Matsumura Daiju , Nishihata Yasuo , Mizuki Jun'ichiro , Ishikawa Norito , Sonoda Takeshi , Kinoshita Motoyasu , Iwase Akihiro
Published: April 2011

CeO2 thin films were irradiated with 200MeV Xe ions. Effects of the irradiation were studied by using Extended X-ray Absorption Fine Structure (EXAFS) measurement at SPring8 synchrotron radiation facility. EXAFS spectra for the irradiated thin films near the Ce K-edge show that the coordination number for oxygen atoms around Ce atom decreases and that the Ce-O Debye-Waller factor increases by the irradiation. The atomic distance between oxygen atom and Ce atom does not vary within the accuracy of EXAFS measurement. The effect of high density electronic excitation on the structure of CeO2 is discussed.
Evaluation of Mechanical Properties of Stabilized Zirconia and Zirconate Pyrochlore
Authors: Matsuo Takuya , Shimamura Keiichi , Arima Tatsumi , Idemitsu Kazuya , Inagaki Yaohiro
Published: April 2011

Mechanical properties of stabilized zirconia and zirconate pyrochlore were evaluated by experiment, MD simulation and ab initio calculation.
Progress in Out-Of-Pile Study of Low Enriched UMo/AlSi Fuel
Authors: Cornen Marilyne , Iltis Xavière , Mazaudier Fabrice , Dubois Sylvie , Lemoine Patrick
Published: April 2011

The main problem we have to face in order to improve the in-pile behaviour of the UMo/Al dispersed fuel, is the instability of the interaction zone, that is formed between the UMo particles and their surrounding Al matrix during irradiation. As the latest irradiations (e.g. IRIS 3 or RERTR 6) tend to prove, addition of Si into the Al matrix seems to be beneficial for the interaction rate decrease. To further understand the role of silicon, a wide out-of-pile interdiffusion study has been launched in CEA-France in 2006 and is still under progress. It has given promising preliminary results by showing a real effect of Si addition upon the interaction zone. The first results related to the physico-chemical aspects of the modified UMo/Al interaction as well as the kinetics aspects of the interaction layer (IL) formation are described in this paper. On a wide range of annealed couples made of UMo7 or UMo10 and Al-Si matrix (Si content ranging from 0.11 wt % to 12 wt %), the IL thicknesses have been systematically measured. Microstructures have been fully characterized by means of optical and scanning electron microscopy and the elementary compositions have been evaluated through EDX analyses. Finally, XRD characterizations and micro-hardness tests have also been performed on a few samples. On the basis of these different results, we discuss first clues about the role played by silicon on slowing down the UMo/Al interaction process.
Light Water Reactor Fuel Degradation Mechanisms at High Burnup: Implications to Generation IV Materials
Authors: Motta Arthur Thompson
Published: April 2011

The proposed designs of GenIV reactors call for high operating temperatures and long exposure times, aimed at increasing thermal efficiency, enabling hydrogen production, decreasing waste and increasing safety, among other goals. These requirements will require imply the materials will be subjected to higher radiation damage doses than seen in light water reactors, requiring an even higher degree of alloys stability. In addition the higher temperatures and exposure times in corrosive environments will require much higher corrosion resistance than current materials. One of the main challenges of designing these materials is that our ability to predict material response in the face of the synergistic effects of temperature, radiation damage and a corrosive environment is limited. However, efforts are underway to understand mechanistically the degradation processes so that they can be extrapolated to conditions beyond the experimental database.

In this context, it is interesting to consider the effort made by the nuclear power industry to qualify nuclear fuel for operation at higher burnup in existing light water reactors. In the last two decades, the average discharge burnup of nuclear fuel in light water reactors has increased almost two fold, thereby increasing the reactor exposure time and the amount of radiation damage withstood by the cladding. Experience has shown that the material degradation rates can increase at high burnup, sometimes through the synergistic operation of various processes. Two examples will be given to illustrate the complexity of the problem:

(i) The rate of irradiation growth of zirconium alloys increases significantly at high burnup. The mechanism has been shown to depend on the amorphization of intermetallic ZrCrFe precipitates with consequent release of Fe into the Zr matrix. This has been shown to help nucleate component dislocation loops which preferentially absorb vacancies, thereby increasing the net rate of growth. This causes the interstitial and vacancy fluxes both to contribute towards irradiation growth, thus increasing the rate.

(ii) One of the most significant obstacles to approval of cladding operation at high burnup is difficulty in the evaluation of the behavior of the fuel during a reactivity initiated accident (RIA). The degradation of the mechanical properties of the zirconium cladding with increasing corrosion and consequent hydrogen ingress, the radiation damage and the microstructure evolution in the fuel all have to be taken into account in evaluating the likelihood of severe fuel failure at high burnup. This problem is still being addressed in various research programs.

Such mechanisms and the efforts to qualify nuclear fuel for higher burnup in light water reactors will be reviewed as a means of illustrating the challenges (known and unknown) faced by GenIV reactor materials.
Thermopower Measurements of Arrays of Small Diameter (18-60 nm) Bi Nanowires
Authors: Huber Tito , Adeyeye A. , Odunfa T. , Nikolaeva A. , Konopko L. , Johnson R. , Graf M.J.
Published: April 2011

Theoretical work based on one-dimensional (1D) models indicates that Bi wires with diameter smaller than 50 nm can exhibit superior thermoelectric properties since the density of states at the Fermi level of a 1D system can be tuned to very high values. Recently, angle-resolved photoemission spectroscopy (ARPES) studies of Bi surfaces have shown that Bi nanowires support Rashba spin-orbit surface states, with high carrier densities of around 5×1012/cm−2, that have not been considered in current models of Bi nanowires. According to our estimates, the sheath of surface charge on Bi nanowires should contribute substantially to the thermopower of Bi nanowires. We carried out an experimental study of the transport properties and thermopower of bismuth nanowire arrays (NWA) with wire diameters ranging between 60 nm and 13 nm to investigate these phenomena. The Rashba interaction is a spin orbit interaction that is important for surfaces of materials consisting of heavy ion elements; thermoelectric materials frequently consist of these elements (i.e.PbTe) because they scatter phonons and form low thermal conductivity materials.
Synthesis and Optical Properties of 1D Bismuth Nanorods
Authors: Reppert Jason , Krishnan Sivaram , He Jian , Rao Rahul , Tritt Terry , Rao Apparao
Published: April 2011

The presence of a high electron density of states in low-dimensional systems such as, nanowires and nanotubes, suggests that these 1D structures can be useful thermoelectric materials. Theoretical calculations predict that: (i) Semimetallic Bi nanowires exhibit semiconducting nature when their nanowire diameter is below 50 nm, and (ii) Semiconducting Bi nanowires with diameter < 10 nm are expected to have an enhanced figure of merit (ZT > 2), when Z=S2σ/κ (S: Seebeck coefficient, σ: electrical conductivity, and κ is the thermal conductivity). We report the synthesis of ∼10 nm diameter Bi nanorods using a pulsed laser vaporization method. The high resolution transmission electron microscopy images of our Bi nanorods show (i) crystalline <012> planes in the core of the nanorods, and (ii) coated with a thin amorphous Bi2O3 layer. The infrared absorption and the surface plasmon peaks in our Bi nanorods are blue-shifted in energy when compared to the corresponding spectra in bulk Bi.
Thermoelectric properties of nanostructured (Pb1-mSnmTe)1-x(PbS)x with Pb and Sb precipitates
Authors: Girard Steven N , Sootsman Joseph R. , Lin Chia-Her , Androulakis John , Kanatzidis Mercouri G.
Published: April 2011

We report the physical characterization and thermoelectric properties of (Pb0.95Sn0.05Te)0.92(PbS)0.08 containing excess Pb and Sb prepared using the matrix encapsulation technique. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5 - 4 at. % rapidly quenched from the melt show microscale Pb inclusions that increase the thermal conductivity while slightly increasing the power factor, compared to (Pb0.95Sn0.05Te)0.92(PbS)0.08. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5%, Sb 2% prepared using the same technique show microscale Sb and Pb inclusions that upon heating cause rapid PbS and Sb segregation from the PbTe matrix. This behavior significantly alters the microstructure and degrades the transport properties of the material.
Melt Spinning Preparation of Bismuth Telluride and Partially Alloying with IV-VI Compounds for Thermoelectric Application
Authors: Boettner Harald , Ebling Dirk , Jacquot Alexandre , Kühn Uta , Schmidt Jürgen , Boettner Harald
Published: April 2011

The melt spinning technique (MST) combined with post annealing processes is evaluated for the development of thermoelectric nanocomposites. The evaluated ones are based on two components almost immiscible in solid state but with crystallographic correlation. One is taken from the V-VI-components system and the other one from the IV-VI-components system. This concept was applied to p-(Bi0,2Sb0,8)2Te3 and to p-[(Bi0,2Sb0,8)2Te3]1-xPbTex composites. MST samples of all types were characterised for some structural and thermoelectric properties. All V-VI materials are clearly textured after MST and show no deterioration concerning the thermoelectric properties even after subsequent annealing processes. Structural analysis of p-[(Bi0,2Sb0,8)2Te3]1-xPbTex composites gave significant hints for oriented precipitates of a IV-VI-rich phase incorporated into the V-VI-rich matrix. The thermoelectric figure of merit of the evaluated composites could be enhanced by suitable annealing procedures of both the quenched bulk materials and the melt spin material.
Atomic Ordering, Electronic Structure, and Transport Properties of LAST-m Systems
Authors: Mahanti S. D. , Hoang Khang , Ahmad Salameh
Published: April 2011

In recent years, LAST-m (AgPbmSbTem+2) and related materials have emerged as potential high performance high temperature thermoelectrics. These compounds are obtained by starting from PbTe, and replacing pairs of Pb2+ ions by (Ag1+, Sb3+) pairs. One example is LAST-18. When optimally doped, this compound has thermoelectric figure of merit ZT=1.7 at 700K. This large ZT is most likely due to very low lattice thermal conductivity, caused by phonon scattering from nanostructures. These nanostructures involve clustering and ordering of Ag, Sb, and Pb ions. Possible origins of this atomic ordering and how the presence of nanostructures affects the electronic structure near the band gap region are discussed. The temperature (T) dependence of electrical conductivity σ (∼T2.2 in the range 300K <T< 900K) in n-type PbTe is analyzed in terms of the T-dependence of different physical quantities contributing to transport. We find that the dominant contribution comes from the explicit T-dependence of relaxation time rather than its energy dependence. The T-dependence of chemical potential is also significant in the concentration range of interest. Electronic thermal conductivity for constant field (κel,E) and for constant current (κel,J) are found to differ considerably at high temperatures and the Weidemann-Franz (WF) law κel,J = LoσT, where Lo =2x10−8WΩ/K is the Lorentz number, overstimates κel,J by nearly 60% at 800K for carrier concentration n=5x1019/cm3. As a result, one tends to underestimate the lattice contribution κlatt = κexp - κel,J. We give theoretical values of effective Lorentz number L = κel.J/σT for different n and T.
Bulk Materials Research for Thermoelectric Power Generation Applications
Authors: Nolas George , Beekman Matthew , Martin Joshua , Wang Dongli , Lin Xiunu sophie
Published: April 2011

There are a variety of material systems employing different strategies in an effort to establish a new paradigm for thermoelectric materials performance. One approach is the PGEC, or “phonon-glass electron crystal”, approach were research towards optimization of the electrical properties of very low thermal conductivity materials is key. Other efforts focus on materials that exhibit high power factors via quantum-confinement or nano-scale affects. Still others focus on “engineering” metastable phases that possess properties that are distinct, if not unique, to solid state chemistry. All these approaches are valid and provide a fundamental knowledge base whereby present and future scientific materials discoveries will lead to new technological improvements. This paper focuses on bulk materials, in particular those material systems currently under investigation in the novel materials laboratory at the University of South Florida and the requirements and strategies for their optimization towards improved thermoelectric properties.
Preparation and Properties of Srn+1TinO3n+1 Ruddlesden-Popper Homologous Series by Metal-Citric Acid Complex Decomposition Method
Authors: Nishio Keishi , Fukuda Kazuhiko , Imai Tomohiro , Takenouchi Hirohumi , Mae Hideo , Fujimoto Masakatsu , Iida Tsutomu , Hamada Noriaki , Kineri Tohru , Watanabe Tsuneo
Published: April 2011

We investigated the Srn+1TinO3n+1 Ruddlesden-Popper homologous series. This material exhibits a wide range of electric behaviors, from a high-dielectric-constant tunable-paraelectric in its undoped form to a metallic superconductor when it is doped with a variety of elements.

The Srn+1TinO3n+1 and the yttrium-doped Srn+1TinO3n+1 Ruddlesden-Popper homologous series were prepared through the thermal decomposition of a metal citric acid complex. The starting solution consisted of the raw materials strontium acetate and titanium alkoxide. Citric acid was used as the chelating agent, and ethanol and distilled water were mixed and used as a solvent. Single phase Sr2TiO4 and Sr3Ti2O7 were produced without creation of SrCO3 by heat-treatment at 1073 and 1473 K, respectively, for three hours. We were unable to produce single phase Sr4Ti3O10. The samples consisted of Sr4Ti3O10 and SrTiO3 phases. Scanning electron microscopy showed that the grain shape of the Sr2TiO4 was plate-like, while those of the Sr3Ti2O7 and Sr4Ti3O10 were not and the grains had large numbers of pores. High-density Sr2-xYxTiO4 (x= 0 to 0.06) ceramic samples were produced under hot-press conditions (1823 K for one hour at a uniaxial pressure of 31.2 MPa). Although the undoped samples were insulators, the yttrium-doped samples showed high electrical conductivity (i.e. that of Sr1.98Y0.02TiO4 was ρ= 8.5×10−5 Ωcm). The Seebeck coefficient of Sr1.98Y0.02TiO4 was –160.7 μV/K, and the thermal conductivity was 3.38 W/mK.
Reduced Thermal Conductivity by Low-Frequency Optic Phonons that Give Rise to Negative Thermal Expansion: Opportunities for Thermoelectrics?
Authors: White Mary Anne , Whitman Catherine A.
Published: April 2011

We have recently found that the negative thermal expansion (NTE) materials, ZrW2O8 and HfMo2O8, show exceptionally low thermal conductivity. We surmise that the mechanism is the efficient coupling of the low-frequency optic phonons that give rise to negative thermal expansion with the heat-carrying acoustic phonons. Although neither ZrW2O8 nor HfMo2O8 has suitable electronic properties for thermoelectric applications, perhaps the principle of reduced thermal conductivity by low-frequency optic phonons in NTE materials can be used to develop more efficient thermoelectric materials.
Transport Behavior and Thermal Conductivity Reduction in the Composite System PbTe-Pb-Sb
Authors: Sootsman Joseph , Kong Huijun , Uher Ctirad , Downey Adam , D'Angelo Jonathan James , Wu Chun-I , Hogan Timothy , Caillat Thierry , Kanatzidis Mercouri
Published: April 2011

We report the synthesis of nanostructured composite PbTe with excess Pb and Sb metal inclusions. Scanning and transmission electron microscopy reveal these inclusions in both the nano- and macroscales. The electrical conductivity and Seebeck coefficient dependence on temperature show unusual trends which depend on the inclusion Pb/Sb ratio. Several ratios showed marked enhancements in power factor at 700 K. The thermal conductivity of these composites is reported.
Thermoelectric Properties of Mixed-Metal Tellurides
Authors: Powell Anthony V , Guinet Fabien , Vaqueiro Paz , Wilcock Ian M , Jones Richard L
Published: April 2011

A new series of thallium-containing materials, Tl1-xPbmATem+2 (A= Sb, Bi; m=10, 18; 0≤x≤0.3), has been prepared. Diffraction data reveal that a rocksalt-type structure is adopted at all compositions. Transport property measurements indicate n-type behaviour for the bismuth-containing materials and p-type for the antimony analogues. The reduced power factors for the latter, compared to the bismuth-containing materials, are primarily due to their more resistive nature. The highest power factors occur at a thallium deficiency in the range 0.1≤x≤0.2. Measured thermal conductivities are reduced from that of the binary telluride, suggesting that the materials may have potential as n/p-type components in device applications.
Addressing Broader Impacts through Research Center - Science Museum Partnerships
Authors: Alpert Carol Lynn
Published: April 2011

The National Science Foundation requires investigators to address the “broader impacts” of research in science, education, and society. NSF considers significant contributions in this area to include education and outreach activities designed to enhance scientific and technological understanding and to foster connections between research and service to society. Yet, organizations optimized for research and teaching often lack the expertise, tools, and resources for carrying out these activities, and lack connections to community-serving organizations and audiences intended for these kinds of engagements. It is for this reason that NSF offers the suggestion of partnering “with museums, nature centers, science centers, and similar institutions to develop exhibits in science, math, and engineering,” to “involve the public…in research and education activities,” and to provide “science and engineering presentations to the broader community.” [1] This sensible-sounding advice nonetheless offers little guidance to materials science and engineering researchers in the actual planning, design, implementation, and evaluation of effective educational outreach partnerships. This MRS Symposium proceedings briefing, preliminary to a more extensive treatment of the topic, presents particular aspects of the case for pursuing such partnerships as well as some suggestions for ensuring their effectiveness. The author is a Co-PI of the NSF Nanoscale Informal Science Education Network (NISE Net) and also manages three long-term NSF and NIH-funded research center partnership programs in place at the Museum of Science, Boston.
Inspiring 1000 Middle School Students at Princeton University's Materials Science and Engineering Expo
Authors: Steinberg Daniel , Swilley Shannon
Published: April 2011

Princeton Center for Complex Materials (PCCM) is a National Science Foundation-supported Materials Research Science and Engineering Center. The educational outreach team conducts many educational outreach programs. Since 2004, one of our largest k-12 education programs has been the Science and Engineering Expo at Princeton University (SEE Princeton) for middle school students in partnership with other outreach programs at Princeton University. The goals of the program are to allow hundreds of Princeton University scientists and engineers the opportunity to share their enthusiasm for science with middle school students, to instill excitement for science and engineering in the students, to expose the students to learning opportunities in science and engineering, and to introduce them to the field of materials science. This paper provides a brief guide to developing and conducting a science and engineering expo based on a successful model.
A Partnership Inspiring Interest in MSE Careers: The Center for Research on Interface Structures and Phenomena (CRISP)
Authors: Caragianis-Broadbridge Christine , Edgecumbe Heather , Osenko Greg , Lehman Ann , Alter Lisa , Tully John
Published: April 2011

The intent of the CRISP education and outreach effort is to use materials science as a vehicle for enhancing the scientific literacy and knowledge of kindergarten through post-graduate level students. A challenging part of our mission has been inspiring students to take the next step and consider further study (or a career) in the field of Materials Science and Engineering (MSE). The CRISP educational programs were developed through a partnership between Yale University, Southern Connecticut State University and the urban school district of New Haven, CT. An overview of the methods and results of both formal and informal educational program components will be presented for years one and two of the CRISP MRSEC. This paper will focus on two CRISP programs: 1) MRSEC Initiative for Multidisciplinary Education & Research (MIMER) and 2) “Exploring Materials Science” mobile kits. The evaluation data indicates that the approach used in developing these educational programs is important. Specifically, the impact of these programs is influenced by the students' ability to relate the acquired knowledge to real life applications and technologies. In particular, emphasizing career opportunities rather than just presenting content-based programs is a key element to increasing interest towards further study in Materials Science and Engineering.
HELICAL Learning Model Applied in a Nanotechnology for Science and Engineering Course
Authors: Peterson Eric , Reed Morgan , Gomes Jewel , Cocke David L.
Published: April 2011

In education, a popular model employed to represent the learning process is typically portrayed as a four-stage process signified by a cycle in a two-dimensional circular path. This cycle can be repeated by revisiting topics at increasing levels of sophistication in order to produce what is known as a spiral curriculum.

In this presentation, a variation of Kolb's two-dimensional learning cycle model is offered that represents the learning cycle as if it were a three-dimensional spiral or helix, with successive turns associated with increases in Bloom's Taxonomic level. This representation is explored and developed, with a specific example from a chemical engineering course offered in Industrial Electrochemistry. This more comprehensive concept-centered model for the learning cycle explicitly includes higher order thinking skills to promote creative thinking, through the application of concepts and can be used to develop more effective curricula and course instruction. Specifically, our sample class consists of four teams, each of which is responsible for becoming expert in the concepts associated with an area of science and another of application. Transfer of content is student driven while topics are explored. Students teaching each other allows for synergistic enhanced motivation to explore, with concurrent ultimate improvement in the retention of core concepts by the entire course population.
Correlation Between Thermodynamic and Kinetic Properties of Glass-Forming Liquids
Authors: Senkov Oleg N. , Miracle Daniel B.
Published: April 2011

Correlations between three characteristic temperatures: glass transition,Tg, Kauzmann,Tk, and Vogel-Fulcher-Tammann,To, were identified from the analysis of more than 60 metallic and non-metallic glass-forming materials. It was found thatTg≥Tk≥ToandTkis the geometric mean ofTgandTo. The relationTk≥Toindicates that the excess total entropy of a super-cooled liquid ΔSapproaches zero at a higher temperature than the configurational entropy ΔSconf, and such behavior was explained by the stronger temperature dependence of the excess vibrational entropy of the liquid, ΔSvib, than that of the corresponding glass,. A relationship between the fragility indexm, reduced excess heat capacity ΔCp(Tg)/Sm, and reduced glass transition temperature,Trg, was identified using the found correlation between the characteristic temperatures.
Point Defects, Recovery Kinetics and Ordering in Irradiated Bulk Metallic Glasses
Authors: Petrusenko Yuri , Bakai Alexander , Borysenko Valeriy , Barankov Dmitro , Astakhov Oleksandr , Macht Michael-Peter
Published: April 2011

The problem of structural properties and structural defects of amorphous solids is still of vital importance. To make clear whether stable point defects exist in metallic glasses (MGs) or not, we have studied the accumulation and recovery kinetics of radiation defects in ZrTiCuNiBe and ZrTiCuNiAl bulk MGs irradiated with 2.5 MeV electrons at T ∼ 80 K. The electrical resistance measurements of the irradiated samples were performed. The recovery spectrum of irradiation-induced electrical resistance was measured for the 85–300 K temperature range. The most important result of the recovery experiments is that they clearly show the annealing stages for the irradiated samples. Two annealing peaks located at T∼150 K and T∼225 K are resolved for ZrTiCuNiBe glass. Similar peaks are also revealed for ZrTiCuNiAl. It can be concluded from the data that the defect mobility is a thermally activated process, and that the activation energy is not as high as that for vacancies in crystalline alloys. Thus, the data obtained testify in favor of the structure with “perfect” local ordering of atoms. It should be noted that this property is basic in the formulation of the polycluster model of amorphous solids.
Stability of the Pd-Co-Ni-Cu-P Metallic Glasses
Authors: Fukamaki Daisuke , Takeuchi Tsunehiro , Hasegawa Masashi , Soda Kazuo , Sato Hirokazu , Mizutani Uichiro
Published: April 2011

Stability of Pd-Co-Ni-Cu-P metallic glass was investigated in terms of free energy using first principle cluster calculations, thermal analysis, and photoemission spectroscopy measurements. We found that the internal energy of the Pd-based metallic glasses is dominated by the electronic structure near the Fermi level. The analyses on the electronic structure and local atomic arrangements indicate that the substitution of cobalt or a hypothetical atom Co0.5Cu0.5 for nickel in the Pd40Ni40P20 metallic glass decreases the free energy of the Pd-Ni-P metallic glass by increasing entropy without altering significantly internal energy. On the basis of the idea mentioned above, we prepared Pd28Co24Ni24P24, Pd25Co25Ni25P25 and Pd40Co40/3Ni40/3Cu40/3P20 metallic glasses. These metallic glasses certainly showed the nearly highest TX, which directly reflect the activation energy against crystallization, among the Pd-based metallic glasses ever reported.
Processing Map for Zr-based In-situ β Phase Composites
Authors: Lee Seung-Yub , Li John J.Z. , Suh Jin-yoo , Rhim Won-Kyu , Johnson William L. , Ustundag Ersan
Published: April 2011

The processing map for Zr-based bulk metallic glasses with crystalline in-situ precipitates (â phase) has been constructed from high temperature phase information, chemical composition analysis, and â phase crystallization kinetics. The phase evolution was detected in-situ by high energy synchrotron X-ray, and kinetic information on crystalline phase was measured from electrostatic levitation facility (ESL). This processing map offers a unique opportunity to control both volume and size of the dendritic â phase through composition and processing condition manipulation. The volume fraction of â phase can be customized from 6% to 93 %, and dendrite size is controllable between 1 and 50 µm at the current stage.
Comprehensive Mechanical and Tribological Characterization of Ultra-Thin-Films
Authors: Gitis Norm , Vinogradov Michael , Hermann Ilja , Kuiry Suresh
Published: April 2011

Based on recent studies, mechanical and tribological properties such as hardness, Young's modulus, friction, and scratch adhesion strength on various coatings and ultra-thin films are reported. These results were obtained using a Universal Nano+Micro Tester UNMT-1, suitably designed for comprehensive evaluation of mechanical and tribological properties of bulk materials, coatings and thin films. Results indicate that a substrate effect for ultra-thin films is substantial when using conventional static nanoindentation technique, while negligible with an advanced dynamic nano-indentation. Comparative results of hardness and Young's modulus obtained from various techniques are presented. Also, a means to evaluate friction and adhesion strength of thin films is highlighted, using DLC specimens as an example.
Microstructure and Mechanical Properties Characterisation of Nanocrystalline Copper Films
Authors: Tjahyono Nursiani Indah , Chiu Yu Lung
Published: April 2011

The microstructure and mechanical properties of nanocrystalline copper with grain size ranging from 50 nm to 80 nm have been investigated. Thin films of nanocrystalline copper were electrodeposited from an additive-free acidified copper sulphate solution at room temperature by employing constant current at different current density magnitudes between 20 and 80 mA/cm2. Both austenitic and ferritic steel substrates with the same surface finishing conditions have been used for the deposition. The microstructure of the thin films has been further studied using electron microscopy techniques, and the mechanical properties using nanoindentation technique. The nanoindentation study was carried out on both the plan view and cross-sectional directions to study the isotropy characteristic of the copper film. It has been noted that both the modulus and hardness measured following the Oliver-Pharr scheme show an apparent indentation size effect tested on the cross-sectional sample.
An algorithm to determine the plastic properties of materials based on the loading data in single sharp indentation
Authors: Yonezu Akio , Hirakata Hiroyuki , Minoshima Kohji
Published: April 2011

We proposed a method to determine the plastic properties of bulk materials based on data of loading curvature in indentation curve with only one sharp indenter. This method uses the dimensional analysis to solve the representative stress and effective yield stress. Indentation unloading data is only used to select the unique solution from the calculated ones obtained from representative stress and effective yield stress. We applied the proposed method to four engineering metals on an experimental basis, to verify its effectiveness, as well as its superiority to the reported methods.
Quasi-static and Oscillatory Indentation in Linear Viscoelastic Solids
Authors: Cheng Yang-Tse , Cheng Che-Min
Published: April 2011

Instrumented indentation is often used in the study of small-scale mechanical behavior of “soft” matters that exhibit viscoelastic behavior. A number of techniques have been used to obtain the viscoelastic properties from quasi-static or oscillatory indentations. This paper summarizes our recent findings from modeling indentation in linear viscoelastic solids. These results may help improve methods of measuring viscoelastic properties using instrumented indentation techniques.
Uniaxial Compression Behavior of Bulk Nano-twinned Gold from Molecular Dynamics Simulation
Authors: Deng Chuang , Sansoz Frederic
Published: April 2011

Parallel molecular dynamics simulations were used to study the influence of pre-existing growth twin boundaries on the slip activity of bulk gold under uniaxial compression. The simulations were performed on a 3D, fully periodic simulation box at 300 K with a constant strain rate of 4×107 s−1. Different twin boundary interspacings from 2 nm to 16 nm were investigated. The strength of bulk nano-twinned gold was found to increase as the twin interspacing was decreased. However, strengthening effects related to the twin size were less significant in bulk gold than in gold nanopillars. The atomic analysis of deformation modes at the twin boundary/slip intersection suggested that the mechanisms of interfacial plasticity in nano-twinned gold were different between bulk and nanopillar geometries.
A first-principles study of the martensitic instabilities in magnetic shape memory alloys
Authors: Entel Peter , Gruner Markus Ernst , Hucht Alfred
Published: April 2011

Among the magnetic shape memory Heusler alloys, Ni-Mn-Ga near stoichiometry displays the largest shape change in the martensitic 5M or 7M structure with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature nonmodulated tetragonal structures have c/a > 1. Typically, the martensitic phase changes are accompanied by a shift of a peak in the electronic density arising from the non-bonding Ni states, a reconstruction of the associated Fermi surface, and, in some cases, by pronounced phonon anomalies. These appear in the cubic high-temperature austenitic and premartensitic phases but also in the modulated phases. In addition, the modulated phases have highly mobile twins which can be rearranged under the action of an external magnetic field due to the high magnetic anisotropy, which builds up in martensite and which is at the origin of the magnetic shape memory effect. First-principles calculations confirm the overall scenario.
Determination of symmetry reduced structures by a soft-phonon analysis in Ni2MnGa
Authors: Hickel Tilmann , Uijttewaal Matthe A. , Grabowski Blazej , Neugebauer Jörg
Published: April 2011

The shape memory effect of Ni2MnGa is closely related to the fact that the material undergoes a martensitic phase transition, which results in symmetry reductions and deformations when cooling down. However, there are still substantial uncertainties about the phase diagram in the martensitic phase. Particularly challenging is the determination of those phases, which are characterized by shuffling structures. We have applied density functional theory to this problem, which allows an accurate determination of the potential energy surface as a function of the lattice constants. Based on these results we compute ab initio phonon spectra and discuss in detail how they can be used to extract detailed information about the type of shuffling structures and to systematically and efficiently identify stable atomic configurations.
Cast and Rolling Textures of NiMnGa Alloys
Authors: Chulist Robert , Poetschke Martin , Boehm Andrea , Brokmeier Heinz-Guenter , Garbe Ulf , Lippmann Thomas , Oertel Carl-Georg , Skrotzki Werner
Published: April 2011

The texture of two polycrystalline NiMnGa magnetic shape memory alloys fabricated by directional solidification and hot rolling has been measured with high-energy synchrotron radiation and neutron diffraction. At room temperature the alloys used are composed of a modulated (7M) and non-modulated (NM) martensitic structure. The texture of the directionally solidified alloy for all phases is a pronounced fibre texture with <100> preferentially aligned along the growth direction. In the directionally solidified case a variant selection took place with [001] dominating. The texture of the hot rolled alloy shows a weak recrystallization texture with {111} and <112> aligned parallel to the rolling plane and rolling direction, respectively. The texture results are discussed with respect to material, processing and phase transformations including variant selection.
A Review of Tension Test Methods for Thin Films
Authors: Sharpe William N.
Published: April 2011

Test methods for mechanical property measurement of the thin films used in MEMS have been developed and refined over the last decade. This brief review considers only tensile testing since that is the preferred method for measuring Young's modulus, strength, etc. for macroscale structural materials. There are basically two kinds of tensile specimens – framed specimens whose support strips are cut after mounting and semidetached specimens fastened to the substrate at one end. The loading and force measurement systems are similar and use commercial transducers. Strain is measured either by overall grip displacement or by digital imaging in most cases. Initial works are described and followed by descriptions of some recent applications. The paper concludes with a suggested test method that could be amenable to standardization.
Passive devices for determining fracture strength of MEMS structural materials
Authors: Kahn H , Ballarini R , Heuer A H
Published: April 2011

In microelectromechanical systems (MEMS) device design and fabrication there exists a need for quick determination of fracture strength. This report describes several passive devices that use the residual stresses contained within structural MEMS materials to determine fracture strength. Stress concentrations of varying degrees are generated at micromachined notch roots, and the critical stress required for failure indicates the fracture strength. A variety of devices have been fabricated from materials, such as polysilicon, silicon nitride, and aluminum, with widely varying residual stresses, including both tensile and compressive.
Fabrication and Characterization of Normal and Shear Stresses Sensitive Tactile Sensors by Using Inclined Micro-cantilevers Covered with Elastomer
Authors: Sohgawa Masayuki , Huang Yu-Ming , Noda Minoru , Kanashima Takeshi , Yamashita Kaoru , Okuyama Masanori , Ikeda Masaaki , Noma Haruo
Published: April 2011

The tactile sensors for human support robots which can detect both normal stress and shear stress and have human-friendly surface have been proposed. Micro-cantilevers adequately inclined by Cr deflection control layer were fabricated by the surface micromachining on SOI wafer. The cantilevers were covered with the PDMS elastomer for human-friendly surface. When the stress is added to the surface of elastomer, the deformation of cantilevers along with elastomer is detected as piezoresistive layer in the cantilevers. The piezoresistive response of the cantilever is analyzed by FEM calculation. The response of the fabricated tactile sensor to normal stress and shear stress was measured by output from this resistance. The tactile sensor with PDMS elastomer can detect both normal stress and shear stress. On the other hand, it hardly has sensitivity to shear stress of orthogonal direction to the cantilever. It means that the tactile sensor can distinguish the direction of shear stress. The sensitivity of tactile sensor vary widely with cantilever pattern and relation between direction of cantilever and crystallite orientation of Si. It is suggested that the sensitivity of tactile sensor can be improved by using FEM estimation and selective ion implantation.
Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substrates
Authors: Ishiyama Chiemi , Shibata Akinobu , Sone Masato , Higo Yakichi
Published: April 2011

Adhesive bend testing for micro-sized photoresist components has been performed to clarify the effects of supercritical CO2 (ScCO2) treatment. Multiple microsized cylindrical specimens were fabricated on a silicon substrate using epoxy-type photoresist. The specimens were ScCO2 treated at a temperature of 323K at a pressure of 15MPa for 30 min, and then, decompressed to atmospheric pressure at two different rates. Double refraction appeared in the SU-8 specimens near by the interface between the SU-8 specimens and a substrate after ScCO2 treatment. Adhesive bend strength of ScCO2 treated specimen with slow decompression process is approximately 60% higher than that of non- ScCO2 treated specimens, however, the strength of the microsized photoresist was slightly degraded by ScCO2 treatment with quick decompression process. All the results suggest that ScCO2 treatment improves the adhesive strength between microsized photoresist components and a silicon substrate by control of the decompression process.
Science and Technology of Piezoelectric/Diamond Hybrid Heterostructures for High Performance MEMS/NEMS Devices
Authors: Auciello Orlando , Sumant Anirudha , Hiller Jon , Kabius Bernd , Srinivasa Sudarsan
Published: April 2011

Most current micro/nanoelectromechanical systems (MEMS/NEMS) are based on silicon. However, silicon exhibits relatively poor mechanical/tribological properties, compromising applications to some devices. Diamond films with superior mechanical/tribological properties provide an excellent alternative platform material. Ultrananocrystalline diamond (UNCD®) in film form with 2-5 nm grains exhibits excellent mechanical and tribological properties for high-performance MEMS/NEMS devices. Concurrently, piezoelectric Pb(ZrxTi1-x)O3 (PZT) films provide high sensitivity/low electrical noise for sensing/high-force actuation at relatively low voltages. Therefore, integration of PZT and UNCD films provides a high-performance platform for advanced MEMS/NEMS devices. This paper describes the bases of such integration and demonstration of low voltage piezoactuated hybrid PZT/UNCD cantilevers.
Novel Fabrication Process for the Integration of MEMS Devices with Thick Amorphous Soft Magnetic Field Concentrators
Authors: Brugger Simon , Pfleging Wilhelm , Paul Oliver
Published: April 2011

This paper reports a novel fabrication process enabling the integration of mechanical MEMS devices with thick amorphous soft magnetic field concentrators. The integration process combines silicon on insulator technology for the MEMS device fabrication and epoxy-resin-based attachment of 18-µm-thick amorphous soft magnetic ribbons followed by a wet chemical structuring process. The fabrication process is reported on the basis of a field-concentrator-based resonant magnetic sensor combining an electrostatically driven micromechanical resonator and a planar magnetic field concentrator with two narrow gaps. For realization of the concentrator gaps, the integration process is extended by micro-patterning of the soft magnetic ribbons via UV-laser ablation using an excimer laser system. The characterization of the fabricated resonant magnetic sensor using a stroboscopic video microscope for in-plane motion measurement shows a high sensitivity of 390 kHz/T at a magnetic flux density of 158 µT.
Patterning of Hard Coatings for Incorporation of Solid Lubricant Microreservoirs
Authors: Guleryuz Canan G , Krzanowski James
Published: April 2011

Hard coatings containing microscopic reservoirs for solid lubricant storage have the potential to advance the development of dry, self-lubricating coatings. In the present study we have investigated several methods for fabricating hard coatings that incorporate microscopic reservoirs. These methods all involve the use of placeholders on the substrate surface that are later removed after deposition of the hard coating. One method uses a solution containing ceramic beads, while the second method uses conventional photolithography methods. Coatings using both of these methods were fabricated using TiN as the hard coating. The effectiveness of the microreservoirs for solid lubricant storage was examined by conducting pin-on-disk test using various solid lubricants, including graphite and indium. The performance of coatings with random arrangements of microreservoirs was scattered while samples with the ordered arrangements of microreservoirs all performed well. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs, the significant improvements in tribological performance can be realized.
Fiber Reinforced Multiphase Polymer Composites by In situ Fiber Alignment
Authors: Viratyaporn Wantinee , Twu Nancy , Lehman Richard
Published: April 2011

A novel approach has been explored for the efficient dispersion and uniaxial alignment of fibers in dual phase polymer matrices based on the streaming flow that occurs when two immiscible polymer blends are melt processed under high shear conditions. Such conditions improve the alignment and distribution of fibers in the matrix, a feature of particular importance when fine nanofibers are used. This self-alignment mechanism seeks to produce optimum properties from relatively small volume fractions of fiber. Recent efforts have focused on a model system containing micron-size glass fibers in immiscible polymer blends. This paper presents selected mechanical properties measured for the model system and the flow/orientation paradigm that produces the observed morphologies.
Nano-Surface Modification on Titanium Implants for Drug Delivery
Authors: Yao Chang , Webster Thomas J
Published: April 2011

The surface layer of titanium implants, i.e. titanium dioxide, is responsible for the inertness of titanium-based implants within the human body. However, their cytocompatibility properties and long-term efficacy are limited without further surface engineering since the average functional lifetime of an orthopedic implant is only 10 to 15 years. In this study, an electrochemical method known as anodization was used to create titania nanotubular structures on titanium implant surfaces. These nanotubes were about 60 nm wide (inner diameter) and 200 nm deep. In vitro studies found that anodized surfaces consisting of titania nanotube arrays were favored by bone-forming cells (osteoblasts) compared to unanodized surfaces. These titania nano-tubular structures were utilized here as novel drug release delivery systems. It is proposed that the system designed here can have multi-functional drug release to inhibit infection and wound inflammation while increasing new bone formation. For this purpose, antibiotic drugs (penicillin and streptomycin) were loaded into these nanotubular structures by physical adsorption. To mediate interactions between drug molecules and nanotube walls, anodized titanium nanotubes were modified by silanization to possess amine or methyl groups on their surface instead of −OH groups. Results showed increased hydrophobicity of chemically modified titania nanotubes (methyl > amine > hydroxyl terminated surface). These drug loaded substrates were soaked in phosphate buffered solution in a simulated body environment to determine drug release behavior. Buffer solutions were collected and replaced every day. The eluted drug amounts were measured spectroscopically. Results showed more antibiotic penicillin and streptomycin released from chemically modified nanotubes compared to unanodized titanium substrates; specifically, titania anodized nanotubes functionalized with −OH groups did quite well. In this manner, this study advances titanium currently used in orthopedics to possess drug release behavior which can improve orthopedic implant efficacy.