bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect Of pH On Chemical-Mechanical Polishing Of Copper And Tantalum
Authors: Jindal Anurag , Li Ying , Babu S. V.
Published: April 2011

pH has a strong effect on the polish rates of copper (Cu) and tantalum (Ta) [1]. In this paper, removal rates of Cu and Ta using aqueous slurries containing alumina and silica abrasives in H2O2-glycine solution are studied at varying pH values. It is observed that variation in the Cu and Ta removal rates is a direct result of the change in surface characteristics of the films. Surface characteristics such as presence/absence of a passivating layer and hardness of such layer vary with pH and hence result in removal rate variation. It is also shown that a favorable Cu/Ta polish rate selectivity can be obtained by adjusting the pH of the slurry.
Photoacoustic spectra from copper phthalocyanine films on Si wafers
Authors: Ohmukai Masato , Kubota Hitoshi , Tsutsumi Yasuo
Published: April 2011

Copper phthalocyanine (CuPc) films were deposited on (100) silicon wafers by means of a vacuum evaporation method. We examined the films using photoacoustic (PA) spectroscopy to study their optical absorption properties. It was clarified that the PA signal from the silicon substrate can be excluded with a chopping frequency of 200 Hz when the film thickness is greater than 4.4 m. We detected an absorption band at 1.128 eV.
In Situ Biaxial Texture Analysis of Mgo Films During Growth on Amorphous Substrates by Ion Beam-Assisted Deposition
Authors: Brewer Rhett T. , Arendt Paul N. , Groves James R. , Atwater Harry A.
Published: April 2011

We used a previously reported kinematical electron scattering model1 to develop a RHEED based method for performing quantitative analysis of mosaic polycrystalline thin film in-plane and out-of-plain grain orientation distributions. RHEED based biaxial texture measurements are compared to X-Ray and transmission electron microscopy measurements to establish the validity of the RHEED analysis method. In situ RHEED analysis reveals that the out-of-plane orientation distribution starts out very broad, and then decreases during IBAD MgO growth. Other results included evidence that the in-plane orientation distribution narrows, the grain size increases, and the film roughens as film thickness increases during IBAD MgO growth. Homoepitaxy of MgO improves the biaxial texture of the IBAD layer, making X-ray measurements of IBAD films with an additional homoepitaxial layer not quantitatively representative of the IBAD layer. Systematic offsets between RHEED analysis and X-ray measurements of biaxial texture, coupled with evidence that biaxial texture improves with increasing film thickness, indicate that RHEED is a superior technique for probing surface biaxial texture.
Study of Different Phases in a-C:H:N Thin Films Deposited by Plasma- Enhanced Chemical Vapour Deposition: A comparision Between Theoretical and Experimental Data
Authors: Antoniella F. , Valentini L. , Continenza A. , Lozzi L. , Santucci S.
Published: April 2011

The electronic structure of amorphous carbon nitride (a-C:H:N) thin films prepared by radiofrequency (rf) plasma decomposition of CH4/N2 mixture was determined by soft x-ray photoe1ectron spectroscopy by the mean of synchrotron radiation source. On increasing N2 fraction, the valence band shows profound changes. The new features are identified by a comparison of the experimental spectra with theoretically weighted density of the states of graphite and C3N4 structures.
Diamond synthesis on oxide substrates
Authors: Hayashi Rie , Onishi Fumitomo , Takagi Yoshiki
Published: April 2011

Recently, many results were reported by many institutes and companies all over the world for diamond particles or thin films synthesized on crystalline substrates, such as molybdenum, silicon etc. But diamond on amorphous or oxide substrates, were rarely reported. In this study, we used material of amorphous and oxide for substrates, for example quartz glass, Alumina.

We used unique apparatus of diamond synthesis. With our apparatus, completely closed system was used, no reaction gas was introduced to the chamber and no reactant gas was evacuated from it. We used graphite rod for heater and carbon source, at the same time.

And we compared results with this unique closed system and with conventional flow system. Carbon sources of gaseous state (methane) and solid state ( graphite ), and closed and flow system result the deference of synthesized diamond particles.
Surface roughness control of the Al and Al2O3 thin films deposited by using pulsed DC magnetron sputtering
Authors: Qiu Jinjun , Li Kebin , Han Guchang , Guo Zaibing , Wu Yihong
Published: April 2011

The thickness of the Al2O3 layer used in the magnetic tunneling junctions FM1/Al2O3/FM2 is less than 2 nm, here FM1 is for the ferromagnetic layer 1 and FM2 is for ferromagnetic layer 2. In order to obtain ultra-thin Al2O3 layer with higher breakdown voltage and pinhole free, extremely smooth surface roughness of this layer is required. The influence of the sputtering gas pressure, DC pulsed frequency, DC pulsed power, substrate bias and buffer layer on surface roughness and properties of Al thin films were studied. The single layer Al films are usually amorphous, texture (111) Al films can be obtained while using thin Ta 5 nm or Ta5/NiFe2 as underlayer. Very smooth Al thin film can be sputtered on Si/SiO2 (100) wafer with Ta/NiFe buffer layer at f=15 kHz (DC pulsed frequency) and with RF substrate biasing (Vpp is about 21 V). High quality MTJs with high MR ratio up to 44.6% and high field sensitivity up to 19.3%/Oe were finally demonstrated after optimization of thin film deposition process.
In-situ study of the stiffness of alumina thin films during vapor deposition
Authors: Proost Joris , Spaepen Frans
Published: April 2011

The evolution of the biaxial modulus of amorphous alumina thin films has been studied insitu during electron-beam evaporation at 400°C on Si and sapphire substrates. A constant value of 197 ± 30 GPa was measured up to a thickness of 1.17 μm when depositing at 3 Å/s. This value was identical to that of films thinner than 0.30 μm deposited at an average rate of 6 Å/s. Above 0.30 μm, the modulus in these films decreased continuously to a value of 50 ± 8 GPa at a final thickness of 2.05 μm. Based on their refractive indices, the films deposited at 6 Å/s are 30% less dense than those deposited at 3 Å/s. This density deficit is insufficient to account for the modulus decrease; the remainder is probably the result of slit-like microcracks.
Calculations of Surface Structure for SrTiO3 Perovskite
Authors: Heifetsa E. , Eglitisb R.I. , Kotomin E.A. , Borstelb G.
Published: April 2011

We present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. OurSM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments.
Relation between texture and stress in thin sputtered molybdenum layers
Authors: van den Berk Ilse M. , Seijbel Léon J. , Delhez Rob
Published: April 2011

X-ray diffraction was used to measure the stress and the texture in thin molybdenum layers. The 500 nm thick layers were sputter deposited at various argon sputter pressures. All crystallites in the layers showed a strong tendency to develop a <110> direction perpendicular to the surface of the sample. Depending on the sputter pressure, a different fraction of the Mo crystallites developed a preference for a <110> direction parallel to the tangential direction of the rotating sputter table. The stresses found in the layer are best described when it is recognized that the crystallites in the layer belong to two groups: one group with both directions preferred and one group with only the out-of-plane direction preferred. For the intermediate sputter pressures the highest stresses were observed.
Formation of a Co3O4 Top Layer in SiO2 Cobalt Containing Coatings Sol-gel Obtained
Authors: Tototzintle-Huitle H. , Ramos-Mendoza A. , Mendoza-Galván A. , González-Hernández J. , Chao B. S.
Published: April 2011

SiO2 coatings containing cobalt were prepared on glass substrates using the sol-gel method. It has been found that in coatings with a Si to Co ratio of 1.3, a layer of Co3O4 is formed at the free surface of the coating upon thermal annealings in air. The properties of the coatings were studied using optical, x-ray and Auger depth profile measurements. The thermal annealings in the temperature range of 300 to 500 oC, in steps of 50 oC, were performed for 10 min. Some samples were subjected to an isothermal annealing at 400 °C for different times from 10 to 210 min. From the x-ray diffraction patterns the cubic spinel structure of Co3O4 was detected after the thermal treatments. The optical reflection and transmission spectra for each annealing temperature and annealing time, are described with an air-Co3O4-SiO2:Co2+-substrate system. From this, the cobalt oxide thickness was obtained as a function of the annealing temperature and annealing time. From the Arrhenius plots, in the temperature range studied, it was found that the activation energy for the growth of the cobalt oxide layer is 0.41 eV. The layer thickness follows a parabolic behavior with time, which suggests a diffusion-controlled process. The Auger depth profiles obtained from a sample annealed at 500 °C confirm the optical model used.
Composition-Morphology-Property Relations For Giant Magnetoresistance Multilayers Grown By RF Diode Sputtering
Authors: Zou W. , Wadley H.N.G. , Zhou X.W. , Johnson R.A. , Brownell D.
Published: April 2011

A series of experiments have been conducted to evaluate the magnetotransport properties of RF diode sputter deposited giant magnetoresistive (GMR) multilayers with either copper or copper-silver-gold nonferromagnetic (NFM) conducting layers. The study revealed that RF diode deposited multilayers utilizing Cu80Ag15Au5 as the NFM conducting layer posses significantly superior giant magnetoresistance to otherwise identical device architectures that used pure copper as the NFM conducting layer. To explore the origin of this effect, copper and Cu80Ag15Au5 films of varying thickness have been grown under identical deposition conditions and their surface morphology and roughness investigated. Atomic force microscopy revealed significant roughness and the presence of many pinholes in thin pure copper films. The surface roughness of the Cu80Ag15Au5 layers was found to be much less than that of pure copper, and the alloying eliminated the formation of pinholes. Molecular statics estimates of activation barriers indicated that both silver and gold have significantly higher mobilities than copper atoms on a flat copper surface. However, gold is found to be incorporated in the lattice whereas silver tends to segregate (and concentrate) upon the free surface, enhancing its potency as a surfactant. The atomic scale mechanism responsible for silver's surface flattening effect has been explored.
Oscillatory Angular Dependence of Exchange Bias for Epitaxial NiO-Co (001) Bilayers
Authors: Dubourg S. , Bobo J.F. , Warot B. , Snoeck E. , Ousset J.C.
Published: April 2011

We have sputter-deposited NiO-Co bilayers on MgO (001) substrates. NiO grows epitaxially on MgO at 900°C and subsequently the room deposited 80 Åthick Co films have a fcc crystal structure in epitaxy with the oxide underlayer. These samples were warmed up to 300° C and then zero-field or field cooled through the NiO Néel temperature (a 300 Oe magnetic field was applied along the [100] or the [110] MgO axis). Magnetic hysteresis loops were obtained by magneto-optical Kerr effect, the magnetic field being oriented in the plane of the substrate for various angles α with respect to the [100] direction. The usually expected behavior for such experiments is a smooth angular α dependence of the exchange bias HE close to a cosine with only one sign change over 180°. The high crystallographic coherence of our NiO/Co bilayers induces a very unusual oscillatory HE (α) dependence with several sign changes according to the NiO axis field application. Despite of the Co magnetization switching mechanism which is not a pure coherent rotation, we propose a Stoner-Wohlfhart model including four fold anisotropy and unidirectional exchange anisotropy giving a realistic description of these typical magnetic properties.
Epitaxial Growth of Dilute Magnetic Semiconductors: GaMnN and GaMnP
Authors: Overberg Mark E. , Abernathy Cammy R. , Pearton Stephen J. , Sharifi Fred , Hebard Arthur F. , Theodoropoulou Nineta , von Molnar Stephan , Anane Madjid , Xiong Peng
Published: April 2011

Epitaxial growth of the dilute magnetic semiconductors GaMnP and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP films grown with < 4.5% Mn show the preferential formation of the second phases MnP and Mn5.64P3, resulting in only a slight deviation from purely diamagnetic behavior. GaMnN films grown on both Al2O3 and Metal-Organic Chemical Vapor Deposition (MOCVD) derived GaN surfaces show strong ferromagnetism when grown with either C codoping or at elevated temperatures to raise the concentration of n-type carriers. Comparable GaMnN films grown under conditions which produce highly resistive material show only paramagnetism, indicating the importance of carrier concentration on the resulting magnetic behavior. The formation of second phases was not observed in the GaMnN material for Mn concentrations less than 9%.
Ferromagnetic Resonance On Metallic Glass Ribbons
Authors: Chipara M. , Toacsen M. , Sorescu M.
Published: April 2011

Ferromagnetic resonance data on metallic glasses, at room temperature, in X band, are discussed. The spectra were decomposed into two Lorentzian lines and the angular dependence of their main parameters (line width and position) is fully analyzed. It is proved that the usual approaches are not able to describe accurately the experimental data. This behavior is ascribed to the misalignment of the magnetization with respect to the external magnetic field, and successfully tested by using a “relaxed” resonance condition that allows a small misalignment of the magnetization relative to the external magnetic field.
Nanocrystalline and Nanostructured High-Performance Permanent Magnets
Authors: Goll D. , Sigle W. , Hadjipanayis G.C. , Kronmüller H.
Published: April 2011

The rather complex correlation between the microstructure and the magnetic properties is demonstrated for two types of high-quality RE-TM permanent magnets (pms), namely nanocrystalline RE2Fe14B (RE = Nd,Pr) and nanostructured Sm2(Co,Cu,Fe,Zr)17 pms. The detailed analysis of this correlation for both pm materials leads to a quantitative comprehension of the hardening mechanism enabling the optimization of their magnetic properties and temperature dependences. In the case of RE2Fe14B, isotropic bonded pms are fabricated showing maximum energy products in the order of 90 kJ/m3. In the case of Sm2(Co,Cu,Fe,Zr)17, magnets with excellent high-temperature magnetic properties are tailored. Hereby, the investigations in addition provide important clues to the evolution of the characteristic microstructural and magnetic properties and to the role of the involved elements.
Exploring the limits of fast phase change materials
Authors: Wöltgens Han-Willem , Detemple Ralf , Friedrich Inés , Njoroge Walter K. , Thomas Ingo , Weidenhof Volker , Ziegler Stefan , Wuttig Matthias
Published: April 2011

In the last decade a number of chalcogenide alloys, including ternary alloys of GeSbTe and quaternary alloys of InAgSbTe, have been identified which enable fast phase change recording. In the quest for materials with improved phase change kinetics we present two different approaches. By comparing alloys with well-defined stoichiometries the mechanisms which govern the transformation kinetics are determined. Optical and electrical measurements determine the activation energy for crystallization to 2.24 ± 0.11 eV for Ge2Sb2Te5 and to 3.71 ± 0.07 eV for Ge4Sb1Te5, respectively. It is shown that for GeSbTe-alloys with different composition the activation energy increases linearly with increasing Ge content. Power-time- reflectivity change diagrams recorded with a static tester reveal that Ge2Sb2Te5, in agreement with previous data, recrystallizes by the growth of sub critical nuclei, while Ge4Sb1Te5 grows from the crystalline rim surrounding the bit.

To speed up the search for faster materials we employ concepts of combinatorial material synthesis by producing films with a stoichiometry gradient. Then laterally resolved secondary neutral mass spectroscopy (SNMS) combined with the static tester are used to identify the composition with superior properties for phase change applications.
Materials Issues in the Development of High Data-Transfer-Rate Phase-Change Compounds
Authors: Lankhorst Martijn H.R. , Borg Herman J.
Published: April 2011

A model is presented to calculate glass-transition temperatures. This model in combination with experimental data is used to evaluate archival-life stability of common phase change materials Ge2Sb2Te5 and doped eutectic Sb2Te compositions.

On the basis of this model, novel high-data-rate phase change compositions have been identified near and on the pseudo-binary line InSb-GaSb in the ternary system Ga-In-Sb.
Dynamic behavior of azobenzene polyester used for holographic data storage
Authors: Kerekes Árpád , Lörincz E. , Sajti Sz. , Várhegyi P. , Ramanujam P. S. , Hvilsted S.
Published: April 2011

Dynamic behavior of thin photoaddressable polyester films was studied. The saturation process due to Fourier holographic recording was investigated. Model experiments show an optimal intensity ratio of the object and reference beams, where the highest efficiency occurs. This ratio is inversely proportional to the reference intensity. The material has a significantly higher sensitivity at 407 nm than at 532 nm. For 1 μm thick sample an M# of 0.25 was measurable.
Endo-fullerenes and Doped Bucky Onions as Seed Materials for Solid State Quantum Bits
Authors: Park Seongjun , Srivastava Deepak , Cho Kyeongjae
Published: April 2011

Two different models for solid-state quantum bits have been investigated. Both are based on the nuclear spin of doped atoms in endo-fullerenes or bucky-onions. 1H or 31P have been tested as suitable dopant atoms because they have half nuclear spins. The thermal stability and electronic properties of the dopant atoms and the encapsulating cages have been examined with ab-initio pseudo potential density functional methods, and the results show that both models are suitable for single qubit applications.
Medium-Range Order Structures of Amorphous Diamond-Like Carbon Films
Authors: Chen Xidong , Murray Gibson J. , Sullivan John , Friedmann Tom
Published: April 2011

In this paper, we have studied medium-range order structures in amorphous diamond-like carbon films with fluctuation microscopy. Medium-range order structures are quantified by a specific form of a general four-body correlation. We name this function as a pair-pair alignment correlation function. By analyzing speckle dark-field images taken over different areas as a function of momentum transfer in reciprocal space, we measured the pair-pair alignment correlation function for both thermally annealed samples and unannealed samples. We have found that thermal annealing introduces medium-range order in amorphous diamond-like carbon films, causing more pairs of atoms to be aligned. These results agree with density-functional simulations. Larger-scale simulations will be needed to fully understand our experimental results.
Nano-Structured Amorphous Carbon Films Synthesised Using Decr Plasma
Authors: Golanski André , Grambole Dieter , Hommet Jean , Herrmann Folker , Kern Philippe , McDonnell Liam , Piazza Fabrice , Stoquert Jean-Paul
Published: April 2011

A Distributed Electron Cyclotron Resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit ta-C:H (Diamond-Like Carbon, DLC) thin films at RT. A graphite sputtering target immersed in an argon plasma was used as carbon source. The Ar plasma density was about 5×1010 cm-3. Single crystal <100> Si substrates were RF biased to a negative voltage of -80 V. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H-→ 12C + 4He + γ, elastic recoil detection analysis (ERDA) and Rutherford backscattering (RBS) were used to investigate the early phase of the growth. The morphology of the films grown at low pressure (0.3 mTorr) is shown to be dominated by stress-mediated nucleation leading to formation of basket-like clusters of circular hillocks 20 nm high surrounded by a planar, mostly sp2 bonded film ∼8 nm thick. With increasing plasma pressure the spatial frequency of the hillocks becomes random and the growth is dominated by the Stranski-Krastanov mode. The XPS data taken at decreasing emergence angles show that the structure of the hillocks is dominated by sp3 bonded carbon. The XPS argon signal disappears at 10° emergence angle indicating that integration of argon occurs mainly within the sp bonded regions. The NRA and ERDA analysis show that the amount of integrated hydrogen decreases with increasing substrate current density. RBS data indicate that increasing bias enhances argon integration.
Physical Interactions of Carbon Nanotubes and Conjugated Polymers
Authors: Dalton A.B. , McCarthy B. , Coleman J. N. , Panhuis M. , Carroll D. L. , Czerw R. , Blau W.J. , Byrne H.J.
Published: April 2011

Single walled carbon nanotubes are shown to interact with a conjugated polymer in a periodic manner. Here this interaction is probed using electron microscopy, scanning tunneling microscopy optical and vibrational spectroscopy. The spectroscopic behaviour of the polymer is seen to be dramatically affected, which is attributed to conformational changes due to the effect of the nanotubes.
Lithium Insertion in Nanoporous Carbon Materials Produced from Carbides
Authors: Kotina I.M. , Lebedev V.M. , Ilves A.G. , Patsekina G.V. , Tuhkonen L.M. , Gordeev S.K. , Yagovkina M.A. , Ekström Thommy
Published: April 2011

In this work, the results of a study of the lithium insertion process in nanoporous carbons (NPC) obtained from carbides (SiC, TiC, Mo2C) by chlorination are presented. Lithium insertion was produced in the temperature range of 30–200 °C via the vacuum deposition and diffusion. The major analytical tools for study included nuclear reaction method and X-ray diffraction. Diffusion coefficients of lithium at this temperature interval were estimated. Possible mechanism of lithium diffusion is discussed. Investigation of phase composition of lithiated samples was carried out at room temperature. Phase composition is found to be dependent on the relationship between deposition and diffusion rates.
Effect of pH on Hydrogen Evolution Yield from Water Dispersing Titania Nanoparticles Enhanced by Gamma Ray
Authors: Seino Satoshi , Yamamoto Takao A. , Fujimoto Ryosuke , Hashimoto Kensuke , Katsura Masahiro , Okuda Shuichi , Okitsu Kenji
Published: April 2011

Hydrogen gas evolution from water dispersing nanoparticles induced by 60Co gamma-ray irradiation was studied. Nanoparticle of TiO2 with average size of 30 nm was examined. It was indicated that the hydrogen yields were affected significantly by pH of the dispersion. Difference in agglomeration could explain the difference in hydrogen yields. Reactions that enhance the hydrogen yields were discussed, and it was concluded that the radiolysis process is dominant in the total enhancement mechanism.
A Magnetically Ordered Non-Stoichiometric Zinc Ferrite for the Oxidative Dehydrogenation Reactions.
Authors: Toledo J. A. , Nava N. , Sun X. C. , Bokhimi X.
Published: April 2011

ZnFe2O4nanoparticles were prepared by hydrothermal reduction approach. A considerable amount of α-Fe2O3was segregated in the as-synthesized sample, which diffused into the tetrahedral and octahedral sites of the ZnFe2O4spinel structure with increasing the annealing temperature. The introduction of Fe3+into the tetrahedral positions was observed by Mössbauer spectra. Magnetization measurements showed an unusual ferrimagnetic behavior of the ZnFe2O4phase, even at room temperature, confirming the introduction of Fe3+into the tetrahedral sites of the spinel structure. Catalytic activity measured in the oxidative dehydrogenation of 1-butene reaction increased with increasing annealing temperature, indicating that those interactions of Fe3+in tetrahedral and octahedral positions also promotes the activity and selectivity to butadiene formation.
Bioceramics and Biominerals and Their Nanostructures
Authors: Wen Shulin , Feng Jingwei
Published: April 2011

Artificial hydroxyapatite with chemical formula of Ca10(PO4)6(OH)2 is the best as bioceramics due to its composition and structure being similar with inorganic part of hard tissues. The alloys especially with Ti, Ni and Co contents are very promising as a kind of biomaterials due to their high strength and high toughness. The alloys as biomaterials need good final surface properties by proper surface treatment. By using clinical treatment with machining, cleaning, sterilization, we obtained Ti-oxides surface with 4-6 nm in thickness which are very good in property with chemical composition of TiO2 + Ti2O3 + TiO. However, the Ti-alloy with an artificial hydroxyapatite surface is even much better than that with the surface of Ti-oxides due to its high bioactivity. Human bones and human teeth with a chemical composition of Ca10(PO4)6(OH)2 and the structure of hydroxyapatite are commonly considered as bio-mineral. In nature the pears and shells are also a kind of bio-minerals. Our observations showed that human bone is a complex material with a layered composite structure. The hydroxyapatite mineral crystals that reinforce the organic proteinceous component are about 35 nm wide, irregular, plate-like crystals reside initially in the hole zones of the collagen microfibris: later fill available space within the collagen fibrils. At present paper nanostructure features of both bioceramics and biominerals have been characterized with comparison between each other's.
Nanocrystalline Mg-based hydrides for hydrogen storage
Authors: Oelerich W. , Klassen T. , Bormann R.
Published: April 2011

Hydrogen is the ideal means of energy storage for transportation and conversion of energy in a comprehensive clean-energy concept. However, appropriate storage facilities, both for stationary and for mobile applications, are complicated, because of the very low boiling point of hydrogen (20.4 K at 1 atm) and its low density in the gaseous state (90 g/m3). Furthermore, the storage of hydrogen in liquid or gaseous form imposes safety problems, in particular for mobile applications, e.g. the future zero-emission vehicle. Metal hydrides are a safe alternative for H-storage and, in addition, have a high volumetric energy density that is about 60% higher than that of liquid hydrogen. Mg hydride has a high storage capacity by weight and is therefore favoured for automotive applications. However, so far light metal hydrides have not been considered competitive because of their rather sluggish sorption kinetics. Filling a tank could take several hours. Moreover, the hydrogen desorption temperature of about 300 °C is rather high for most applications. A breakthrough in hydrogen storage technology was achieved by preparing nanocrystalline hydrides using high-energy ball milling. These new materials show very fast aband desorption kinetics within few minutes, thus qualifying lightweight Mg-based hydrides for storage application. In this paper recent detailed results on the sorption behaviour of nanocrystalline Mg and Mg-based alloys are presented. In a following research effort the sorption kinetics of nanocrystalline Mg has been further enhanced by catalyst additions. Furthermore, different transition metals have been added to Mg to achieve a thermodynamic destabilisation of the hydride, thus lowering the desorption temperatures to about 230 °C. The newly developed materials are currently being tested in prototype storage tanks.
Investigation of Nanoelectrodes by Transmission Electron Microscopy
Authors: Kabir M. S. , Magnus Persson S. H. , Yao Yimin , Bourgoin Jean Phillippe , Palacin Serge
Published: April 2011

Electrodes for making connections to single molecules and clusters must have separations smaller than 10 nm. They are therefore difficult or impossible to image with atomic force microscopes (AFM) or Scanning Electron Microscopes (SEM). We have fabricated nanoelelectrodes by different methods to contacts nanoclusters and conjugated molecules and investigated their properties in transmission electron microscope (TEM) and their electrical characteristics at room temperature and at 4.2K. The electrodes are made on SiN4 membranes, which is transparent to high energy electrons and which make it possible to image features of a few nanometers in TEM.
Magnetic behavior of coated superparamagnetic iron oxide nanoparticles in ferrofluids
Authors: Voit W. , Kim D. K. , Zapka W. , Muhammed M. , Rao K. V.
Published: April 2011

We present a study on the magnetic behavior of nanosized iron oxide particles coated with different surfactants (sodium oleate, PVA and starch) in a ferrofluid. The effect of the coating material, and different particle concentrations in the ferrofluid have been magnetically investigated to determine the effective magnetic particle size and possible interaction. The superparamagnetic iron oxide particles, synthesized by a controlled co-precipitation technique, are found to contain magnetite (Fe3O4) as a main phase with a narrow physical particle size distribution between 6 and 8 nm. The mean effective magnetic size of the particles in different ferrofluid systems are estimated to be around 4-5 nm which is smaller than the physical particle size. On a 10% dilution in the starch coated ferrofluid we observe a decrease in the blocking temperature.
Current induced organization in thin nanocrystalline gold films during deposition
Authors: Chaoguang P. , Ederth J. , Kish L. B. , Granqvist C. G.
Published: April 2011

Nanocrystalline gold films were prepared by advanced gas deposition. Electric field induced effects on the film structure during and after deposition was investigated. A dc electric field in the range 2 ≤Ua ≤ 8 V/cm, was applied parallel to the substrate surface and led to changes of film microstructure and resistivity. In another set of experiments, films deposited at Ua = 0 were exposed to electric fields of similar strength after deposition. Film degradation could be understood from a mechanism consistent with a biased-percolation effect. Our results show that it is possible to control the film structure by varying the strength of an applied electric field.
Control and Assessment of Structure and Composition in Bismuth Telluride Nanowire Arrays
Authors: Sander M. S. , Prieto A. L. , Gronsky R. , Sands T. , Stacy A. M.
Published: April 2011

Due to effects of reduced dimensionality, Bi2Te3 nanowires are predicted to have increased thermoelectric efficiency relative to bulk Bi2Te3, one of the most efficient thermoelectric materials known. High-density arrays of nanowires have desirable characteristics for accessing nanowire properties in potential applications and also allow for facile nanowire property assessment. Here we describe a fabrication method to produce Bi2Te3 nanowire arrays by direct current electrochemical deposition into porous anodic alumina templates. The characteristics of the arrays have been assessed to determine the composition and structure in the arrays as well as in individual nanowires. Thefabricated arrays have a high-density of uniform diameter (∼40nm), high aspect ratio wires that are stoichiometric, polycrystalline Bi2Te3.
Increased Osteoblast and Decreased Smooth Muscle Cell Adhesion on Biologically-inspired Carbon Nanofibers
Authors: Price Rachel L. , Haberstroh Karen M. , Webster Thomas J.
Published: April 2011

Osteoblast (the bone-forming cells) and smooth muscle cell adhesion was investigated on carbon nanofiber formulations of various diameters (specifically, from 60 to 200 nm) and surface energies (from 25 to 140 mJ/m2) in the present in vitro study. Results provided the first evidence that osteoblast adhesion increased with decreased carbon nanofiber diameter after 1 hour. In contrast, smooth muscle cell adhesion was not dependent on carbon nanofiber diameter. Moreover, the present study demonstrated that smooth muscle cell adhesion decreased with increased carbon nanofiber surface energy after 1 hour. Alternatively, osteoblast adhesion was not affected by carbon nanofiber surface energy. Since adhesion is a crucial prerequisite for subsequent functions of cells (such as the deposition of bone by osteoblasts), the present results of controlled adhesion of both osteoblasts and a competitive cell line (i.e., smooth muscle cells) demonstrate that carbon nanofibers with small diameters and high surface energies may become the next-generation of orthopedic implant materials to enhance new bone synthesis. These criteria may prove critical in the clinical success of bone prostheses.
Computational model for multiscale simulation of laser ablation
Authors: Zhigilei Leonid V.
Published: April 2011

Multiscale computational approach that combines different methods to study laser ablation phenomenon is presented. The methods include the molecular dynamics (MD) breathing sphere model for simulation of the initial stage of laser ablation, a combined MD - finite element method (FEM) approach for simulation of propagation of the laser-induced pressure waves out from the MD computational cell, and the direct simulation Monte Carlo (DSMC) method for simulation of the ablation plume expansion. The multiscale approach addresses different processes involved in laser ablation with appropriate resolutions and, at the same time, accounts for the interrelations between the processes. A description of the ablation plume appropriate for making a connection between the MD simulation of laser ablation and the DSMC simulation of the ablation plume expansion is discussed.
Electronic Excitations in Initiation of Chemistry in Molecular Solids
Authors: Kuklja Maija M.
Published: April 2011

An ab initio study is performed for the initiation of chemistry in high explosive crystals from a solid-state physics viewpoint. Specifically, we are looking for the relationship between the defect-induced deformation of the electronic structure of solids, electronic excitations, and chemical reactions under shock conditions. Band structure calculations by means of the Hartree- Fock method with correlation corrections were done to model an effect of a strong compression induced by a shock/impact wave on the crystals with and without edge dislocations. Based on the results obtained, an excitonic mechanism of the earliest stages for initiation of high explosive solids is discussed with application to cyclotrimethylene trinitramine (also known as RDX) crystal. Experimental verification of the validity of the proposed model is reported for RDX and heavy metal azides. Thus, the key role of electronic excitations facilitated by edge dislocations in explosive solids is established and analyzed. Practical applications of the suggested mechanisms are discussed.
First Principles Simulations of Phase Stability in Stoichiometric and Doped LiMnO2
Authors: Landa Alexander I. , Chang Chun-Chieh , Kumta Prashant N. , Magyari-Köpe Blanka , Vitos Levente , Ahuja Rajeev , Abrikosov Igor A.
Published: April 2011

The full charge density exact muffin-tin orbitals method has been used to study the stability of lithium-manganese oxides exhibiting different crystallographic allotropes. Calculations have been performed for ferromagnetic and antiferromagnetic phases of LiMnO2 as well as for the phase with local moment disorder. For the ordered LiMnO2 compound we reproduced the correct ground state, the antiferromagnetic orthorhombic structure. The effect of doping LiMnO2 by Co was considered with the aim to predict the stabilization of the layered structure.
Disorder Defects Modelling for Some Ternary Crystals
Authors: Voevodin Valeriy G. , Voevodina Olga.V.
Published: April 2011

Absrtact:

The attempt to obtain the data on thermodynamic parameters and equilibrium concentra- tions of disorder defects was made. Quasi-chemical model of the defects formation with allow- ance for Schottky and Frenkel defects was used. Thermodynamic parameters were calculated based on Weiser's technique. Six types of the disorder defects in II-IV-V2 and I-III-VI2 were considered. Used models, approaches and initial parameters give that the greatest concentration (∼ 1019 cm−3) and accordingly the greatest influence on properties of the crystals have defects AB or BA.
Stoichiometry and Adhesion of Al/WC
Authors: Siegel Donald J. , Hector Louis G. , Adams James B.
Published: April 2011

We examine the relative stability and adhesion of nonstoichiometric (polar) Al/WC interfaces and WC(0001) surfaces using Density Functional Theory as implemented in a planewave, pseudopo- tential formalism. Relaxed atomic geometries and the ideal work of adhesion were calculated for six different interfacial structures, taking into account both W- and C-terminations of the carbide. Based on the surface and interfacial free energies, we find that both the clean surface and the optimal interface geometry are W-terminated. However, the largest adhesion energies are obtained with the C-termination, consistent with an argument based on surface reactivity.
Transmittance Quantities Probability Distributions of Waves through Disordered Systems
Authors: Cwilich Gabriel , Zypman Fredy R
Published: April 2011

Waves propagate through disordered systems in a variety of regimes. There is a threshold of disorder beyond which waves become localized and transport becomes restricted. The intensity I of the wave transmitted through a system has a dependence on the length L of the sample that is characteristic of the regime. For example, I decays as L−1 in the diffusive regime. It is of current interest to characterize the transport regime of a wave, from statistical studies of the transmittance quantities through it. Studies suggest that the probability distribution of the intensity could be used to characterize the localized regime. There is an ongoing debate on what deviations from the classical Rayleigh distribution are to be expected. In this numerical work, we use scalar waves to obtain the intensity, transmission, and conductance of waves through a disordered system. We calculate the intensity, by setting an incoming plane wave towards the sample from a fixed direction. The outgoing intensity is then calculated at one point in space. This process is repeated for a collection of samples belonging to the same ensemble that characterizes the disorder, and we construct the probability distribution of the intensity. In the case of transmission, we evaluate the field arriving to a series of points distributed in the far field, and repeat the same statistical analysis. For the conductance, we calculate the field at the same series of points for incoming waves in different directions. We analyze the distribution of the transmittance quantities and their change with the degree of disorder.
Screening Beneficial Dopants to Cu Interconnect by Modeling
Authors: Liu Chun-Li
Published: April 2011

Cu is currently being used as the new generation of advanced interconnects. Beneficial additives or dopants to Cu have been sought to improve the electromigration performance of the Cu interconnects primarily through experimental approaches [1]. As a vital alternative, we have established a virtual simulation procedure to screen the potential dopants to Cu by modeling. There are many factors such as film density, stress, stress- voiding, grain boundary defect / diffusion, interface adhesion / defect / diffusion, grain structures (texture, grain size and size distribution) and so on that can affect the electromigration. Here we assume that Cu diffusion along the grain boundaries (GBs) is the dominant mechanism that is responsible for the electromigration performance of the Cu interconnects. As schematically shown in Fig.1, if a dopant is added to Cu, most of the dopant will reside in bulk initially. In order for the dopant to play a beneficial role, it has to be able to segregate to the grain boundary. Then, the dopant is supposed to slow down Cu diffusion along the grain boundary and this can be achieved if the dopant can increase the overall activation energy of Cu grain boundary diffusion.
A Molecular Orbital Study on the Optical Properties of Fluorescent Dyes
Authors: Park Su-Jin , Shin Dae-Yup , Choi Seung-Hoon , Lee Han-Yong , Chung Ho-Kyoon , Kim Jung-Sik , Lee Jin-Kyu
Published: April 2011

Fluorescent dyes including Nile Red (NR), fluorescein, rhodamine and 4- (dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) derivatives were investigated to find an application for the organic light emitting device (OLED). Relationship between the molecular structure and optical property was calculated by ab initio (HF and DFT/6-31G*) and semiempirical (AM1/PM3 and INDO/S) calculation methods for the geometry optimization and for the information of electronic transition, respectively. The absorption maximum and the oscillator strength of molecules strongly depended on the molecular dipole moment, especially for the molecules having both strong electron donor and acceptor group. Since the calculated results were comparable with several experimental results, these semiempirical molecular orbital calculation methods could be used as a powerful prediction tool for optical properties of the luminescent molecules.
Simulations of long time scale dynamics using the dimer method
Authors: Henkelman Graeme , Jónsson Hannes
Published: April 2011

We have carried out long time scale simulations where the “dimer method” [G. Henkelman and H. Jónsson, J. Chem. Phys. 111, 7010 (1999)] is used to find the mechanism and estimate the rate of transitions within harmonic transition state theory and time is evolved by using the kinetic Monte Carlo method. Unlike traditional applications of kinetic Monte Carlo, the atoms are not assigned to lattice sites and a list of all possible transitions does not need to be specified beforehand. Rather, the relevant transitions are found on the y during the simulation. An application to the diffusion and island formation of Al adatoms on an Al(100) surface is presented.
Linear Scaling DFT Calculations with Numerical Atomic Orbitals
Authors: Ordejón P. , Artacho E. , Cachau R. , Gale J. , García A. , Junquera J. , Kohanoff J. , Machado M. , Sanchez-Portal D. , Soler J. M. , Weht R.
Published: April 2011

We have recently developed a method to perform Density Functional Theory calculations in systems with a very large number of atoms, which is based on the use of numerical atomic orbitals as basis sets. The method incorporates Order-N techniques both in the calculation of the Kohn-Sham hamiltonian matrix elements and in the solution of the wave functions, which make the CPU time and memory to scale linearly with the number of atoms, allowing calculations in very large system. In this work, we present results on several test systems to show that the approach and the basis sets used with our method are able to provide an accuracy similar to that of other standard DFT techniques.
Synchrotron X-Ray Study of Texture in Cold-Worked Shape-Memory NiTi-Wires
Authors: Schuster Andreas , Voggenreiter Heinz , Balch Dorian K. , Dunand David C.
Published: April 2011

A series of martensitic, near-equiatomic NiTi shape-memory alloy wires was deformed to strains ranging from 1 to 40% up to stresses of 920 MPa. After deformation, the wires were exposed to a monochromatic, parallel beam of high energy x-rays oriented perpendicular to the wire axis. The transmitted low index diffraction rings show that martensitic texture is increasing with prestrain up to ε=15% after twinning is complete. Further prestraining in the plastic range lowers the texture again indicating that twinning- and plasticity-textures cancel partially each other. Also, deformed NiTi-wires were heated and cooled from 20°C to 200°C under a small constant stress of 6 MPa. The strain change due to the Two-Way Shape-Memory Effect was measured and correlated to the diffraction results.
X-ray Scattering Measurements of the Ag(111) Surface Thermal Expansion
Authors: Botez Cristian E. , Elliott William C. , Miceli Paul F. , Stephens Peter W.
Published: April 2011

We have used synchrotron X-ray diffraction to study the thermal expansion of the Ag(111) surface. Throughout the temperature interval between 300 and 1100K, we observed that the separation between the first and the second atomic layers at the surface, 12 d, differs from its bulk counterpart, d, by less than 1%, indicating that the thermal expansion at the surface is similar to the one in the bulk. This result represents the first experimental confirmation of the predictions from molecular dynamics simulations, which indicate a small enhancement of the anharmonic effects at this surface.
Electronic Properties of Bismuth Nanowires
Authors: Cronin Stephen B. , Lin Yu-Ming , Rabin Oded , Black Marcie R. , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

The pressure filling of anodic alumina templates with molten bismuth has been used to synthesize single crystalline bismuth nanowires with diameters ranging from 7 to 200nm and lengths of 50μm. The nanowires are separated by dissolving the template, and electrodes are affixed to single Bi nanowires on Si substrates. A focused ion beam (FIB) technique is used first to sputter off the oxide from the nanowires with a Ga ion beam and then to deposit Pt without breaking vacuum. The resistivity of a 200nm diameter Bi nanowire is found to be only slightly greater than the bulk value, while preliminary measurements indicate that the resistivity of a 100nm diameter nanowire is significantly larger than bulk. The temperature dependence of the resistivity of a 100nm nanowire is modeled by considering the temperature dependent band parameters and the quantized band structure of the nanowires. This theoretical model is consistent with the experimental results.
A Microfabricated Device for the Characterization of Biological Entities
Authors: Chang H. , Ikram A. , Young M. , Kosari F. , Vasmatzis G. , Bhunia A. , Bashir R.
Published: April 2011

A micro-fabricated pore is constructed and tested so that it can be used to characterize biological entities. The pore is prepared by bulk micro-machining of a silicon wafer. An oxide coated silicon diaphragm with the pore is placed between two chambers containing ionic buffer solutions to mimic a bilayer system. If a voltage is applied across the pore, electrophoretic passage of charged entities can be electrically detected through changes in the ionic current flow. When the entities traverse the pore, the ionic current is blocked and a decrease in the current can be observed. As an initial test case, negatively charged polystyrene beads which were 2.38μm in diameter, were electrophoretically driven across the pore. Then the bacteriumListeria innocua, suspended in Tris-glycine buffer, was also electrophoretically driven through the pore and its effective mobility was extracted. The device can also be used to study the interactions between organisms and the micro-fabricated surfaces. Work is continuing to scale the pore to the sub-100A range to be used for characterization and possible sequencing of single molecules such as DNA.