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Pressure Assisted Crystallization of MnAl Thin Films

MRS Online Proceedings Library (OPL) 2011年第1期695卷 L13.5.1-L13.5.1页

作者： Gregory A. Fischer M. Lea Rudee Vitali F. Nesterenko Sastry Indrakanti Graduate Program in Materials Science/Center for Magnetic Recording Research University of California at San Diego La Jolla CA. 92093-0401 Graduate Program in Materials Science/Department of Mechanical and Aerospace Engineering University of California at San Diego La Jolla CA. 92093-0411

The effect of hot isostatic pressure processing (HIP) on MnAl films has been compared to vacuum annealing for the purpose of obtaining substantial amounts of tau phase MnAl in films under 200 nm. Films were deposited by dc sputtering from both MnAlNiC an MnAl targets. As-deposited films were nearly amorphous. Post deposition annealing in vacuum produced only small amounts of the ferromagnetic tau-phase in films thinner than 200 *** all instances, regardless of substrate and sputtering target, the use of HIP in place of vacuum annealing increased the degree of crystallinity of the samples when compared to those annealed in vacuum. For the 100 nm samples deposited from the MnAlNiC target, these changes in crystallinity were accompanied by changes in the M-H loops of the samples. MnAlNiC HIP samples had improved magnetic properties compared to those of equal thickness annealed in vacuum. The 100 nm HIP sample sputtered from the MnAl target also showed an increase in moment, though the changes were not as dramatic as those seen in the samples sputtered from the MnAlNiC *** 50 nm films from both targets also showed a change in crystallinity when compared to vacuum annealed samples. These films, unlike the 100 nm films, had ferromagnetic properties that were no better than those of the vacuum annealed samples. This suggests that while the 2 kbar of pressure used in this study assists in the formation of tau-phase in 100 nm films, the appropriate pressure for forming tau-phase in 50 nm films is yet to be determined.

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Processing and Creep Performance of Silicon Carbide Whisker-Reinforced Silicon Nitride

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MRS Online Proceedings Library 2011年第1期78卷 289-294页

作者： John. R. Porter F. F. Lange A. H. Chokshi Rockwell International Science Center Thousand Oaks USA Materials Program University of California Santa Barbara USA Department of Mechanical Engineering University of California Davis USA

Silicon carbide whisker reinforcement can significantly reduce creep rates in polycrystalline alumina [1], but the system SiC/Al2O3 is thermodynamically unstable in air and oxidizes to mullite during creep testing [2]. The system SiC/Si3N4 was investigated as a potentially more stable, high temperature structural composite. Silicon carbide whiskers were successfully incorporated into a silicon nitride matrix doped with alumina and yttria. Processing involved mixing dispersed slurries of silicon carbide and silicon nitride, adding the dopants as a solution of their nitrates and subsequently increasing the pH to precipitate the additive hydroxides. The resulting slurries were filter pressed at room temperature and hot pressed at 1650°C in graphite dies to full density. X-ray diffraction and transmission electron microscopy confirmed the presence of β-Si3N4, α-SiC and trace quantities of α-Si3N4, confirming that the α-β Si3N4 reaction occurred. An additional, as yet unidentified, minor phase was also detected. Whisker reinforcement was shown to increase the room temperature flexural strength and fracture toughness but high temperature creep performance was unaffected by whisker reinforcement.

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Structural Characterization of Ordered Phases in Hydrocarbon Dendrimers

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MRS Online Proceedings Library 2011年第1期351卷 413-418页

作者： Christopher J. Buchko Atisa Sioshansi Zhifu Xu Jeffrey S. Moore David C. Martin Materials Science and Engineering University of Michigan Ann Arbor USA Department of Chemistry University of Michigan Ann Arbor USA PPG Industries Inc. Advanced Research Center Allison Park USA Department of Chemistry Roger Adams Lab University of illinois Urbana USA Macromolecular Science and Engineering Center University of Michigan Ann Arbor USA

Structural characterization of phenylacetylene dendrimers (PADs) makes it possible to explore the relationship between molecular architecture and condensed phase organization. The size and geometry of the PAD series is precisely controlled, with phenylacetylene units emanating from a central phenylene in the manner of a tridendron. The branched molecule rapidly increases in size with each synthetic generation. The “shape-persistent” nature of the phenylacetylene molecule makes it ideal for use in the construction of self-assembling supramolecular systems. Transmission electron microscopy (TEM) has been used to identify the crystal structure of lower generation PADs, and wide-angle X-ray studies confirm the decrease in crystallinity with size. Hot stage optical microscopy studies of thermal transitions reveal melting points for lower generation PADs, and an apparent glass transition for the amorphous higher generations. This type of structural information is essential to the rational design of self-assembling materials.

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Higher-k dielectrics and conductive oxide electrodes for next generation DRAMs with a design rule of <20 nm#

Higher-k dielectrics and conductive oxide electrodes for nex...

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International Symposium Semiconductor Device Research (ISDRS)

作者： Jeong Hwan Han Woongkyu Lee Sang Woon Lee Cheol Seong Hwang WCU Hybrid Materials Program Department of Materials Science and Engineering Inter-university Semiconductor Research Center Seoul National University Seoul South Korea

Dynamic random access memory (DRAM) is used as the main memory in every personal computer, due to its high density, high speed and efficient memory function. The ever-shrinking dimensions of DRAM cells with increasing packing density made the cell's capacitor size to be smaller. For successful operation of DRAM, a large cell capacitance (~ 25 fF) and low leakage current (10 -7 A/cm 2 or 1 fA/cell) are required. In a traditional Si-based capacitor, the target cell capacitance has been achieved by increasing the surface area of the capacitor. More recently, innovations have been made by development of the component materials. A metal electrode, TiN or Ru, and a dielectric material with a moderate-k value (k is the relative dielectric constant), such as HfO 2 (k ~ 25) and ZrO 2 (k ~ 40), are being explored in giga-bit scale DRAMs. The minimum achievable t ox is ~ 0.7 nm for ZrO 2 which is being used currently in DRAM industry. However, the technology road map for memory devices states that t ox of less than 0.45 nm is necessary for the DRAMs with a design rule of 3 (STO) and (Ba, Sr)TiO 3 were reported to exhibit k values of several hundreds. However, growth of these films showed very slow growth rate and much more complicated processes than growth of binary oxide with the atomic layer deposition (ALD) technique which is a method of choice for the growth of the dielectric films and electrodes in microelectronic devices. Therefore, material and process innovations are necessary for next generation DRAM capacitors.

关键词： Films Electrodes Capacitors Random access memory Substrates Strontium

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Evaluation of rock slope stability for Yujian River dam site China by block theory analyses

45th US Rock Mechanics / Geomechanics Symposium

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45th US Rock Mechanics / Geomechanics Symposium 2011年

作者： Kulatilake, P.H.S.W. Wang, L.Q. Tang, H.M. Liang, Y. Geological Engineering Program Department of Materials Science and Engineering University of Arizona Tucson AZ 85721 United States Faculty of Engineering China University of Geosciences Wuhan Hubei province China

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used to conduct block theory analyses for the rock slopes that exist in the dam site to evaluate the stability of the slopes. The analyses were performed using mean discontinuity set orientations for each rock mass region under gravitational loading to calculate the maximum safe slope angles (MSSA) for different cut slope directions. The following conclusions have been made based on the block theory analysis results: (1) The final MSSA range between 30° and 47°, 44° and 70°, 47° and 69°for cut slope dip directions of 20°-30°, 105°-210°, and 270°-355°, respectively;(2) For cut slope dip directions of 105°-210° and 270°-355°, wide ranges of values have been obtained for the final MSSA reflecting the influence of variability of fracture orientations on MSSA;(3) Apart from the region R-d-1 for slope dip directions in the range 20°-30°, rest of the regions at the dam site seem to be stable for slope angles less than 40°. © 2011 ARMA, American Rock Mechanics Association.

关键词： Rock mechanics

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Estimation of rock discontinuity mean trace length and density from an outcrop in Wenchuan, China

45th US Rock Mechanics / Geomechanics Symposium

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45th US Rock Mechanics / Geomechanics Symposium 2011年

作者： Wu, Q. Kulatilake, P.H.S.W. Tang, H.M. Engineering Faculty China University of Geosciences Wuhan Hubei province China Geological Engineering Program Department of Materials Science and Engineering University of Arizona Tucson AZ 85721 United States

The equations exist in the literature to estimate corrected mean trace length and corrected two dimensional density of a discontinuity set using area sampling technique are critically reviewed. A shortcoming that exists with the equation proposed to calculate the corrected mean trace length of a discontinuity set based on a circular sampling window is pointed out. Also the major shortcomings that exist with the equation proposed to estimate the two-dimensional density of a discontinuity set using a circular window are pointed out. The discontinuity traces appearing in the outcrop in Yingxiu area are used along with rectangular windows to calculate the corrected mean trace length and two-dimensional density using Kulatilake and Wu's equations by incorporating the corrected relative frequency of each trace appearing on the two dimensional exposure. For both the corrected mean trace length and the two-dimensional density, the predictions based on the rectangular window methods are found to be quite accurate. © 2011 ARMA, American Rock Mechanics Association.

关键词： Rock mechanics

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Structure and magnetic properties characterization of electrodeposited Co37Fe63 alloys containing oxygen for magnetic recording applications

Structure and magnetic properties characterization of electr...

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作者： Elhalawaty, S. Carpenter, R.W. George, J. Brankovic, S.R. Materials Science and Engineering Graduate Program School for Engineering of Matter Transport and Energy Arizona State University 85287-6106 United States LeRoy Eyring Center for Solid State Science Arizona State University AZ 85287-9506 United States Center for Nanomagnetic Systems University of Houston TX 77204-4005 United States Electrical and Computer Engineering Department University of Houston TX 77204-4005 United States

ISBN: (纸本)9781118029473

Soft and high magnetic moment Co37Fe63 films were electro-deposited with variable additives on Cu/Ti/Si substrates. The correlation between structure and magnetic properties has been investigated. TEM showed the crystal structure of the films to be BCC with a 〈111〉 texture, and a grain size in the range of 10-20 nm. Oxygen in the deposited films has been identified by EDS and EELS using HAADF STEM. SIMS analysis revealed the presence of hydrogen and oxygen in the deposited CoFe films. Electron microscopy results showed that the oxygen was mainly distributed along the grain boundaries in the CoFe film. In regions where oxygen was present in the films, the Fe content was enhanced relative to Co. The magnetic properties of the deposits have been measured by Vibrating Sample Magnetometer (VSM), quantifying the impact of incorporated oxygen in the film on the saturation magnetization and the coercivity.

关键词： Magnetic properties

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Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization

Precise synthesis of thermo-responsive and water-soluble sta...

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作者： Hirao, Akira Inushima, Reiko Nakayama, Takefumi Watanabe, Takumi Yoo, Hee-Soo Ishizone, Takashi Sugiyama, Kenji Kakuchi, Toyoji Carlotti, Stephane Deffieux, Alain Polymeric and Organic Materials Department Graduate School of Science and Engineering Tokyo Institute of Technology 2-12-1 Ohokayama Meguro-ku Tokyo 152-8552 Japan Division of Biotechnology and Macromolecular Chemistry Graduate School of Engineering Hokkaido University Sapporo 060-8628 Japan CNRS Université Bordeaux1 UMR5629 16 Avernue Pey Berland 33607 Pessac Cedex France

A series of thermo-responsive and water-soluble 4- and 8-arm star-branched poly(2-(2′-methoxyethoxy)ethyl methacrylate) (poly(1)) with well-defined structures were synthesized by living anionic polymerization of 1, followed by a linking reaction with a core compound substituted with either four or eight benzyl bromide moieties. Furthermore, two kinds of sequentially different 4-arm star block copolymers composed of poly(1)-block-poly ((2,2-dimethyl-1,3- dioxolan-4-yl)methyl methacrylate) (poly(4)) were also synthesized by the same linking reaction of the corresponding AB or BA diblock copolymer anion with a core compound substituted with four benzyl bromide moieties. Thus, both well-defined 4-arm (AB)4 and (BA)4 star-block copolymers, whose A and B are poly(1) and poly(4) segments, were successfully synthesized. These star-block copolymers were quantitatively converted to the corresponding 4-arm (AC)4 and (CA)4 star-block copolymers with the same compositions by hydrolytic acetal cleavage of the poly(4) segment to poly(2,3-dihydroxypropyl methacrylate) (C segment). Poly(1) segments have LCST values and, on the other hand, both water-insoluble poly(4)s and water-soluble poly(2,3-dihydroxypropyl methacrylate)s are non-thermo-responsive segments. The thermo-responsive behavior of the resulting 4- and 8-arm star-branched poly(1) as well as the 4-arm (AB)4, (BA)4, (AC)4, and (CA)4 star-branched block copolymers has been extensively studied in terms of molecular weight, arm number, composition, and block sequence. As expected, such variables were observed to affect their LCST values. Interestingly, the thermo-responsive behavior of the 4-arm (AC)4 and (CA)4 stars was different from that of the block copolymers used as arm segments. © 2010 Elsevier Ltd. All rights reserved.

关键词： Block copolymers

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Mesenchymal stem cell differentiation by nano-engineered Si columns

Mesenchymal stem cell differentiation by nano-engineered Si ...

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Middle East Conference on Biomedical engineering (MECBME)

作者： Levent Trabzon Mustafa Ramazanoglu Huseyin Kizil Sebahattin Güvendik Department of Mechanical Engineering Materials and Manufacturing Division Istanbul Technical University Istanbul Turkey Faculty of Dentistry Istanbul University Capa Istanbul Turkey Department of Metallurgical and Materials Engineering Istanbul Technical University Maslak Istanbul Turkey Program of Materials Science and Engineering Institute of Science and Technology Istanbul Technical University Maslak Istanbul Turkey

We successfully engineered Si nano-columns with different cross-sectional geometries by e-beam evaporation with an angle between source and substrate. The Si nano-columns were grown as pillars with square, triangle and linear cross sections in in-plane. Mesenchymal stem cells (MSCs) isolated from the bone marrow stroma of young adult rats were cultured on these different Si nanosurfaces. We found that the behaviour of MSCs highly depended on the geometry of nano-topography so that mesenchymal stem cells were differentiated and induced CaP precipitation on square-cross-sectional Si nano-columns without growth factor in the culture medium.

关键词： Silicon Surface morphology Stem cells Cells (biology) Substrates Surface topography

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Effect of configurational order on the magnetic characteristics of Co-Ni-Ga ferromagnetic shape memory alloys

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Physical Review B 2011年第18期84卷 184201-184201页

作者： Navdeep Singh Ebubekir Dogan Ibrahim Karaman Raymundo Arróyave Department of Mechanical Engineering Texas A&M University College Station Texas 77843 USA Materials Science and Engineering Program Texas A&M University College Station Texas 77843 USA

In most of the ternary (and higher-order) ferromagnetic shape memory alloys (FSMAs) with compositions close to the A2BC stoichiometry, the austenite phase exhibits L21-type ordering. Recent investigations of the Co-Ni-Ga FSMA system, however, suggest that the austenite phase has B2-type ordering, although definite confirmation remains elusive. In this work, we present a theoretical investigation of the effect of configurational order on the magnetic properties of the ordered (L21) and disordered (B2) FSMA Co2NiGa. Through the use of calculations based on density functional theory, we predict the structural and magnetic properties (including magnetic exchange constants) of ordered and disordered Co2NiGa alloys. We validate our calculation of the magnetic exchange constants by extracting the Curie temperatures of the austenite and martensite structures and comparing them to experimental results. By constructing a q-state Potts magnetic Hamiltonian and through the use of lattice Monte Carlo simulation, we predict the finite-temperature behavior of the magnetization and magnetic susceptibility as well as the magnetic specific heat and entropy. The role of configurational order in the magnetic properties of the phases involved in the martensitic phase transformation is discussed, and predictions of the magnitude of the magnetic contributions to the transformation entropy are presented. The calculations are compared to experimental information available in the literature as well as experiments performed by the authors. It is concluded that in FSMAs magnetism plays a fundamental role in determining the relative stability of the austenite and martensite phases, which in turn determines the martensitic transformation temperature Ms, irrespective of whether magnetic fields are used to drive the transformation.

关键词： SHAPE memory alloys STOICHIOMETRY AUSTENITE MAGNETIC properties DENSITY functionals

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