bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fabrication of FePt/M (M=C, Ag) Nanoparticulate Thin Films with Perpendicular Anisotropy
Authors: Huang Y. H. , Wan J. , Zhang Y. , Hadjipanayis G. C. , Weller D. 
Published: April 2011

ABSTRACTMagnetic nanoparticles with perpendicular anisotropy are attractive for applications in high-density recording media. For these applications, it is highly desirable to have particles with a size below 8 nm, a uniform size distribution, and a reduced ordering temperature to avoid unwanted particle agglomeration upon the required heat treatment to obtain the high anisotropy ordered L10 structure. In this work, FePt nanoparticles embedded in non-magnetic matrices M (M=C, Ag) have been fabricated by sputtering FePt and M multilayered thin films onto single crystal MgO [100] substrates at elevated temperatures up to 650 °C. The transformation from the disordered fcc to the ordered L10 phase in FePt nanoparticles was observed at temperatures as low as 300 °C. Besides the reduced transformation temperature, the deposited material showed an improved [001] texture for FePt/Ag thin films as compared to FePt/C due to lattice parameter matching between Ag and FePt. As the deposition temperature increases, the degree of atomic ordering approaches that of the fully ordered phase as indicated by the shift in the [002] XRD peak. TEM images showed that isolated particles with smaller average particle size (around 7 nm) were formed when the thickness of sputtered film is less than 4 nm. However, with a further increase of thickness of sputtered FePt film, a continuous layer of FePt particles was observed and the coercivity decreased rapidly due to a domain wall motion mechanism.
In-situ TEM Studies of Nanoscale Cu Interconnects Under Thermal Stress
Authors: An Jin Ho , Ferreira P.J. 
Published: April 2011

ABSTRACTThermal fatigue during processing of microelectronic devices is a general reliability issue of concern in the microelectronic industry. In particular, as devices continue to be downscaled, the relaxation mechanisms operating under thermal stresses are expected to change. In this study, the microstructure of 1.8 micron and 180 nm wide Cu interconnects was identified through Transmission Electron Microscopy (TEM) imaging. In addition, In-situ TEM heating, performed in both type of specimens, is used to observe the differences in dislocation dynamics under thermal stress. In-situ TEM observations show delamination and inhibited dislocation motion in 180nm Cu lines, whereas in 1.8 micron Cu lines, grain boundaries seemed to act as dislocation sources. These different deformation mechanisms are expected to have an impact on the thermal fatigue behavior of Cu interconnects as the scale of devices is brought below 100 nm.
Suppression of Dewetting in Pulsed Laser Melting of Thin Metallic Films on SiO2
Authors: Eric Kline J. , Leonard John P. 
Published: April 2011

ABSTRACTPulsed excimer laser projection irradiation has been successfully applied to completely melt and resolidify encapsulated elemental metal films of Au, Cu, Cr, and Ni directly on amorphous SiO2 substrates. A combination of narrow irradiated lines and appropriate SiO2 capping layers was used to obtain films that do not dewet when fully melted. Detailed processing maps were generated for Au and Ni, while equivalent trends for Cu and Cr were also noted. These systems were analyzed for common behaviors, and from these the principle factors, a basic process map is proposed to describe adequately these four systems. Experimental parameters and sample preparation criteria are presented to realize such resolidification studies in other metal systems.
Self-assembled Patterns in A Polymer Thin Film
Authors: Salac David , Lu Wei 
Published: April 2011

ABSTRACTThis paper reports an experimental work using an electric field to induce morphological patterns in a thin polymer film. The film was spin-coated onto a glass wafer, and subsequently heated to above its glass transition temperature to allow viscous flow. An electric field was applied by two parallel electrodes spacing 10 mm apart. The initially flat polymer/air interface evolves into islands. The self-assembled islands exhibited a narrow size distribution and demonstrated spatial ordering. We attribute the pattern formation to the minimization of combined interface energy and electrostatic energy.
Energetics and Kinetics of Epitaxial Island Formation on Lattice Mismatched Patterned Substrates
Authors: Machtay Noah D. , Kukta Robert V. 
Published: April 2011

ABSTRACTSpontaneous self-assembly of nanostructures has been a problem of long-standing interest for fabricating advanced electrical and optical devices. One approach towards controlled self-assembly is epitaxial growth on topographically patterned substrates, where surface features act as preferred sites for island formation. The substrate shape addressed here is a periodic array of rectangular mesas. Strained-layer growth on such substrates has been observed to form as islands on the edge, in the center, or at a combination of those locations on the top of the mesa. The purpose of this investigation is to discern whether these morphologies are driven by energetic or kinetic mechanisms. An energetic analysis is done under the assumption that the system free energy consists of surface free energy and strain energy. Strain arises due to a lattice mismatch between the film and substrate materials. The film and substrate are treated as two-dimensional linearly elastic solids with similar elastic properties. Under the constraint of fixed volume, various island arrangements and shapes are compared to determine low energy configurations. Islands are assumed to have the shape of a circular arc, and island positions at the center of the mesa and on the mesa edges are considered for one, two, and three island systems. For symmetric configurations, depending on mismatch strain, surface energy, volume, and relative substrate dimensions, it is found that either the configuration with a single centered island or the configuration with two edge mounted islands may be favored. Allowing for asymmetry, a single island placed on one edge of the substrate mesa is generally the low energy configuration. This occurs because islands located near the edge of a raised mesa are most efficient at relaxing mismatch strain due to an increased compliance. Kinetic simulations of morphological evolution during combined deposition and surface diffusion are also conducted in order to identify possible metastable or slowly evolving non-equilibrium states.
Thermomechanical behavior and microstructural evolution in tantalum thin films
Authors: Knepper Robert , Jackson Katherine , Stevens Blake , Baker Shefford P. 
Published: April 2011

ABSTRACTTa films were prepared in the metastable β phase using an ultra-high vacuum sputter deposition system. The stresses that arose during thermal cycles to 750°C were measured using an in situ substrate curvature measurement system, allowing oxygen content in the films to be minimized. A phase transformation from β to the stable α phase takes place in conjunction with distinct “jumps” in stress in the tensile direction during heating at approximately 400°C and 650°C. X-ray and electron backscatter diffraction (EBSD) analyses were used to determine grain sizes, along with crystal phase and orientation information. These results indicate a significant amount of grain growth accompanying the phase transformation. It is found that the measured total stress change is in reasonable agreement with that predicted by the combination of grain growth, crystal densification associated with the phase transformation, and stress relaxation.
Thin Films Stress Aging Study using Micromachined Cantilevers
Authors: Malhaire Christophe , Andrei Alexandru , Brida Sebastiano , Barbier Daniel 
Published: April 2011

ABSTRACTThe purpose of the present work was to study the long term stress stability of thin films used in harsh environment sensors. A stress determination method, based on cantilevers curvatures measurements, checked by means of 3D finite element simulations, has been proposed. Stress measurements for dielectric (silicon oxide and nitride) and metallic (AlTi and TiW) thin films have been periodically performed at room temperature, after standard annealing (450°C / 30 min in a N2+H2 atmosphere) and after 4 weeks thermal aging at 150°C or 200°C.
Stability of WC Nanoparticles for NOx Reduction
Authors: Rumaiz A.K. , Shah S.I. , Lin H.Y. , Baldytchev I. , Chen J.G. 
Published: April 2011

ABSTRACTWC nanoparticles where synthesized using various Physical Vapor Deposition (PVD) methods such as reactive sputtering and Pulsed Laser Deposition (PLD). In both the methods the metal flux obtained is condensed in the presence of He gas. The structural properties of the samples where investigated using X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The feasibility of using nano-WC as an alternative catalyst for Pt is determined. A comparative study on two sample of WC, as-prepared and carburized W, was done. The samples were used to check for the reduction of NOx in a simple reactor. The carburized W shows activity at temperatures around 400°C whereas the as-prepared WC shows activity towards NOx reduction at a slightly higher temperature. The stability of both the sample was studied by performing the same experiment at a fixed temperature for an extended period of time. XPS and XRD confirm the formation of oxide phase after de-NOx experiments.
Temperature Dependence of Magneto-Mechanical Response in Ni-Mn-Ga Magnetic Shape Memory Alloys
Authors: Cheng Leon M. , Landry Garrett , Farrell hannon P. , Ham-Su Rosaura , Hyatt Calvin V. 
Published: April 2011

ABSTRACTIn this work, a systematic investigation is being carried out on single crystals of Ni47.8Mn27.5Ga24.7 alloy to determine the effect of temperature on the magneto-mechanical behaviour of the Ni-Mn-Ga alloys. Repeated mechanical and magnetic forces have been applied at various temperatures below the martensite finish (MF) temperature. It has been observed that twinning start and finish stresses, critical magnetic field and maximum magnetic-field-induced strain all remain almost constant within about 20K below MF and then change substantially at lower temperatures. Eventually no magnetic-field-induced strain can be observed at temperatures below 262K. It is proposed that although magnetic anisotropy constant increases with decreasing temperature, it is not sufficient to overcome the increasing twinning stresses required for twin boundary motion at lower temperatures.
Development of Field-responsive Polymeric Magnetic Composite Fibers via Electrospinning
Authors: Wang M. , Singh H. , Hatton T.A. , Rutledge G.C. 
Published: April 2011

ABSTRACTA mathematical model is developed to predict the changing stiffness of magnetic fibers within a uniform external magnetic field. Magnetite nanoparticles 16nm in diameter were synthesized by an organic route. An ultrafine PMMA fiber containing 16nm magnetite nanoparticles was produced by electrospinning. The magnetic properties of the fibers were also characterized.
Electroactive Polymer Based Micro-ElectroMechanical System as Biosensor Platform
Authors: Li Zhimin , Li Suiqiong , Cheng Z.-Y. 
Published: April 2011

ABSTRACTA micro-electromechanical diaphragm (MEMD) as micro-sensor platform is introduced. The performance of a MEMD is compared with that of a microcantilever (MC). It is theoretically found that the sensitivity of a MEMD is about 50 times higher than that of a MC. The measured resonance frequencies in air proved the validity of the MEMD design. More importantly, the quality merit factor (Q value) of MEMD is higher than that of MC. The damping effect of liquid medium on a MEMD is much smaller than on a MC. It is experimentally demonstrated that the MEMD works well in both air and liquid.
Enhanced Strain in Electrochemical Deformation of Polypyrrole Film doped with Sulfonated Polyaniline
Authors: Tanaka Akihisa , Takashima Wataru , Kaneto Keiichi 
Published: April 2011

ABSTRACTComposite films of polypyrrole (PPy) and poly(2-methoxyaniline-5-sulfonic acid) (PMAS) have been electrodeposited from aqueous electrolytes solution consisting of pyrrole and various ratios of dodecylbenzene sulfonic acid (DBS) and PMAS. The obtained PPy(DBS/PMAS) films exhibited different characteristics in water contents, surface morphology and electrochemomechanical deformations (ECMD) depending on the content of PMAS. A film having the content of PPy(95%DBS/5%PMAS) simply showed the large cathodic ECMD with the strain of 6.1% in non-aqueous electrolyte solution of 0.1M tetrabutylammonium chloride/acetonitrile electrolyte. The improvement of cathodic ECMD is conjectured to the large porosity of the composite film. The ECMD behaviors of the films operated in various electrolyte solutions including aqueous solution are also reported.
Growth of Single-Walled Carbon Nanotubes by Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Maschmann Matthew R. , Goyal Amit , Iqbal Zafar , Fisher Timothy S. , Gat Roy 
Published: April 2011

ABSTRACTSingle-walled carbon nanotubes (SWCNTs) have been grown for the first time by microwave plasma-enhanced chemical vapor deposition (PECVD) at 800°C using methane as the precursor and bimetallic Mo/Co catalyst supported on MgO dispersed on a silicon wafer. The nanotubes grown consist of bundles, each composed of individual tubes of a single diameter associated with either metallic or semiconducting SWCNTs, based on characterization by Raman spectroscopy. Field-emission scanning electron microscopy and atomic force microscopy show that the bundles are relatively thin – 5 to 10 nm in diameter – and up to a few micrometers in length. The results are compared with those obtained on recently reported SWCNTs grown by radio frequency PECVD.
Ultrafast Transient Absorption Spectroscopy Investigations of Excited State Dynamics in SWNT/Polymer Composites
Authors: Styers-Barnett David J. , Ellison Steven P. , Park Cheol , Wise Kristopher E. , Papanikolas John M. 
Published: April 2011

ABSTRACTWavelength-resolved femtosecond transient absorption spectroscopy is used to follow the electronic dynamics of single-walled carbon nanotubes in polymers following visible and near IR photoexcitation. Electron-hole (e-h) pairs give rise to sharp features in the transient spectra that decay in amplitude and exhibit rapid spectral shifts. The decay reflects (e-h) recombination on both short (1.3 ps) and long (35 ps) time scales. Transient spectra also exhibit a broad photobleach at early times that arises from the cooling of a hot electron gas created via excitation at the red edge of a π-plasmon band.
Light Emission from Carbon Nanotubes Induced by Field Electron Emission from Oriented MWCNT Arrays Accompanied by Re-Deposition
Authors: Nanjundaswamy R. , Zakhidov Al. A , Zhang M. , Lee S. B. , Sampson W. M. , Obraztsov A. N. , Cunningham A. , Zakhidov A. A. 
Published: April 2011

AbstractWell-ordered aligned arrays of multiwalled carbon nanotubes were synthesized by the catalytic thermal chemical vapor deposition (CVD) in acetylene gas at the atmospheric pressure. Abrupt spark–type light emission spots and release of the carbon nanotubes from the cathode and succeeding deposition onto the anode without decomposition has been detected above the threshold electron emission current. Spectral analysis of the light showed that the spectra consist of a background similar to blackbody radiation and a set of sharp lines identified with the radiative transitions of excited carbon and iron atoms. Light emission spectra were found to be essentially different depending on the type (AC or DC) of the applied bias voltage and its value. As-grown and re-deposited materials were characterized by Raman spectroscopy and scanning electron microscopy. It was found that the structural properties of the re-deposited carbon nanotubes remained intact, with only negligible amorphization. A mechanism of the spark emission and re-deposition processe is proposed and discussed in terms of fast overheating of CNT, after explosion type melting of Fe-catalyst nanoclusters, followed by CNT transfer from cathode to anode.
Carbon Nanotubes' and Silicon Carbide Whiskers' Growth on Metal Catalysts: Common Features of Formation Mechanisms
Authors: Kuznetsov Vladimir , Usoltseva Anna , Mazov Ilya 
Published: April 2011

ABSTRACTThe formation mechanisms of carbon deposits and silicon carbide whiskers on metal surface catalysts have some common steps. The most important are: (1) the formation of metal particle alloys oversaturated with carbon or silicon and carbon atoms and (2) the nucleation of corresponding deposits on the metal catalyst surface. A thermodynamic analysis of the carbon and/or silicon carbide nucleation on the metal surface was performed. The master equations for the dependence of critical radius of carbon or SiC nucleus on reaction parameters, such as reaction temperature, supersaturation degree of catalyst particles with C (or Si and C), work of adhesion of metal to carbon (or metal to SiC), were obtained. These equations combined with the phase diagram approach can be used for the description of different scenarios of carbon and/or SiC deposits formation and for the development of the main principles of catalyst and promoters design.
Growth kinetics changes of vertically aligned carbon nanostructures synthesised at low substrate temperatures
Authors: Chen G. Y. , Poa C. H. P. , Stolojan V. , Henley S. , Silva S. R. P. 
Published: April 2011

ABSTRACTCarbon nanotubes and nanofibres are typically synthesised under substrate temperatures above 600°C. Here we investigate the influence of the substrate temperature and the plasma conditions on the growth of vertically aligned carbon nanostructures using Direct Current plasma Chemical Vapour Deposition, at temperatures below 550°C. These nanostructures are produced using a C2H2 based plasma and nickel thin film as the catalyst. We found that preferential deposition of amorphous carbon takes place as the synthesis temperature is lowered below 500°C. However, lowering the carbon concentration in the gas feedstock (<2% conc.) allows for the nucleation of nanofibre-like structures, whilst balancing the buildup of amorphous carbon. This method allows for the synthesis of vertically aligned structures at low temperatures (around 230°C) without intentional heating, while still achieving reasonable average growth rates up to 27 nm/min. The only heating was provided by the plasma, which typically consumes ∼ 4 W/cm2. It was found that by varying the applied plasma bias during high temperature synthesis, we increased the growth rate up to 165 nm/min. Based on the observations of experimental process variations and the morphology of the synthesised structures, we propose a growth mechanism for such low temperature growth and examine the resulting morphology changes.
Surface characteristics and wetting behavior of carbon nanotubes
Authors: Barber Asa H. , Liu Luqi , Cohen Sidney R. , Daniel H. 
Published: April 2011

ABSTRACTThe wetting properties and surface characteristics of individual carbon nanotubes are elucidated by immersing the nanotube into various organic liquid. The resultant force acting on the nanotube can be used to evaluate a liquid contact angle at the nanotube surface from classical methods. This technique was shown to be accurate enough to discern differences in wetting behavior due to both structural and chemical changes in the nanotube structure.
Phonon Dispersions of a Single-Wall (8,0) Carbon Nanotube: Effects of the Rotational Acoustic Sum Rule and of Surface Attachment
Authors: Mounet Nicolas , Marzari Nicola 
Published: April 2011

ABSTRACTThe lattice dynamics of single-walled carbon nanotubes (SWCNT) is studied from first-principles using density-functional perturbation theory (DFPT) at the GGA-PBE level. The phonon dispersions of a pristine, infinite zigzag (8,0) SWCNT are obtained and the effect of applying the rotational acoustic sum rule on vibrational properties is discussed. Finally we study the effects of covalent functionalizations on the SWCNT phonon frequencies by selectively increasing the effective mass of the carbon atoms that would link to the functional groups.
The Characteristics of Carbon Nanotubes with Electroless Plating Deposited Ni Catalysts
Authors: Huang C. S. , Huang B. R. , Lin C. Y. , Wu C. C. , Yu T. E. 
Published: April 2011

ABSTRACTWe have synthesized multi-walled carbon nanotubes (MWNTs) on nickel-deposited n-type silicon substrates by thermal chemical vapor deposition (Thermal CVD). The electroless plating method was adopted in the deposition of the Ni catalytic layer. Sulfuric acid solution was used as a buffer to adjust and maintain a pH value of 4.6. Both the deposition time of the nickel catalyst layer and the growth time of MWNTs were adopted to control the length and density of MWNTs. Scanning electron microscopy (SEM) images showed that the density of carbon nanotubes increased as the deposition time of nickel catalyst layer increased. The formation of nickel nucleation becomes rich as the immersion time of the substrate in electroless plating solution was longer, and this benefited the growth of carbon nanotubes. In addition, the Raman spectrum demonstrated that the ID/IG ratio of MWNTs decreases as the deposition and growth time increase, indicating that more graphene MWNT structures were formed.
Atomic-Scale Physics and Modeling of Schottky Barrier Effect in Carbon Nanotube Nanoelectronics
Authors: Xue Yongqiang 
Published: April 2011

ABSTRACTWe present an atomistic self-consistent study of the electronic and transport properties of semiconducting carbon nanotubes in contact with metal electrodes at different contact geometries. We analyze the Schottky barrier effect at the metal-nanotube interface by examining the electrostatics, the band line up and the conductance of the metal-nanotube wire-metal junction as a function of the nanotube channel length, which leads to an effective decoupling of interface and bulk effects in electron transport through nanotube junction devices.
Structure and dynamics of carbon buckyballs encapsulated into Single-Walled carbon Nanotubes
Authors: Cambedouzou Julien , Rols Stéphane , Almairac Robert , Sauvajol Jean-Louis , Kataura H. , Schober H. 
Published: April 2011

ABSTRACTThe structural and dynamical properties of C60 chains inserted inside Single Walled carbon Nanotubes (SWNT) have been investigated by x-ray and neutron diffraction, and inelastic neutron scattering (INS). The measurements have been performed on a large mass of a very high quality carbon peapods sample. We showed that powder diffraction could hardly give definitive response on the way the C60s are bonded inside SWNT. However, the comparison of the neutron-derived generalized density of states (GDOS) of the inserted C60 peas with the GDOS of the same objects derived from lattice dynamics calculations led to unambiguous results. The observation of excitations in the 8–15 meV range is a clear evidence for the presence strong bonds between C60s in the sample. In the same time, the observation of a very weak quasi-elastic signal may be related to rotational motions of C60 monomers inside the SWNT. These results suggest that peapods are made of a mixed phase of C60 monomers and C60 n-mers.