bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of Pt Nanoparticles Dispersed in Mesoporous Silica
Authors: Chiba Yukitoshi , Shibata Hirobumi , Nagata Daichi , Gunji Takahiro , Tamura Ryuji , Kineri Tohru , Nishio Keishi 
Published: February 2010

AbstractPlatinum nanoparticles were dispersed in mesopores of mesoporous silica using a sol-gel process with a composite template consisting of an amphiphilic triblock copolymer (Pluronic P123 or F127) and a Pt-organic complex, which was prepared with K2Pt(II)Cl4 as a Pt source and 1,10-phenanthroline as a chelating agent. The obtained Pt-1,10-phenanthroline complex did not dissolve in any of several solvents, e.g., hexane, benzene, toluene, THF, H2O, CH3OH, and C2H5OH. However, when the Pt-1,10-phenanthroline complex was reacted with ethylenediamine it dissolved in many solvents. Platinum nanoparticles dispersed in mesoporous silica were obtained using a sol-gel process with a complex template consisting of Pt-1,10-phenanthroline-ethylenediamine, and an amphiphilic triblock copolymer (Pluronic P123 or F127). A sample dried at 353 K was bright yellow. When it was subsequently heat-treated at 823 K, it turned light gray. This change indicates that Pt nanoparticles can be obtained by heat-treatment at high temperature, because, to generate Pt nanoparticles, the organics chelated to Pt ions must be removed. Measurements from small-angle x-ray scattering show that mesoporous silica obtained using a complex template has a much more highly ordered pore structure than that obtained using only an amphiphilic triblock copolymer. It has both large pores (above 8 nm) and a large surface area (about 290 m2/g). Furthermore, results of a TEM investigation showed that Pt nanoparticles were generated only in mesopores of mesoporous silica.
Structural Properties of the Bimetallic Cluster Au12Ag6 on the NOx (x=1,2,3) Adsorption Processes
Authors: Molina Bertha , Castro Jorge , Soto Jorge , Yépez Enrique , Calles Alipio 
Published: February 2010

AbstractIt has been shown that Au and Ag nanoparticles present catalytic properties of pollutant gases, product of the hydrocarbons combustion processes, whose efficiency is strongly dependant on their size, morphology and supporting material. The activity of Ag subnanometric particles supported on alumina in the NOx reduction mechanism, for the reaction HC-SCR (Hydrocarbon Selective Catalytic Reaction) is a good example of these catalytic properties. It is also well established that both Au and Ag nanoparticles are oxygen poisoning resistant and that in certain reactions the bimetallic combination may be more efficient than their isolated parts. In this work we present a DFT calculation of the NOx (x =1, 2, 3) adsorption energies on the Au12Ag6 cluster surface. It is also discussed the possible synergetic effect of the different configurations, forming small Ag islands composed of one to five atoms, on the surface of the bimetallic cluster. The analysis was done using DFT in the ZORA approximation.
Transition Pathway Analysis of Homogeneous Dislocation Nucleation in a Perfect Silicon Crystal
Authors: Saeed Hasan Aftab , Izumi Satoshi , Hara Shotaro , Sakai Shinsuke 
Published: February 2010

AbstractTransition pathway sampling was carried out for homogeneous dislocation nucleation in perfect crystal Si. The sampling algorithm employed was Nudged Elastic Band method. Results obtained were compared with corresponding results for Cu. The stress and activation barrier ranges were found to be much higher for Si than those reported for Cu. The results also showed that while for lower values of resolved shear stress the dislocation embryo approaches that of a perfect dislocation, for higher resolved shear stress values the embryo is far from perfect. That is, the shear displacement of most particles is considerably less than the Burger’s vector. This investigation also demonstrated for the first time that Athermal shear stress for homogeneous dislocation nucleation in Si does not exist, as the crystal undergoes twinning at such high stresses.
Interface Effects on the Mechanical Properties of Nanocrystalline Nanolaminates
Authors: Jankowski Alan F. 
Published: February 2010

AbstractNanocrystalline nanolaminate (ncnl) structures are widely used in the study of physical properties in order to engineer materials for a variety of industrial applications. Often, novel and interesting mechanical behaviours that are found in nanolaminate materials can be linked with two characteristic features of structure. These are the layer pair spacing and the grain size. For the case of nanolaminates synthesized by physical vapor deposition processes, the layer spacing corresponds with the repeating sequence of layer pairs and can be referred to as composition wavelength. The grain size is the average width of the tapered columnar structure along the growth direction. Since the mechanical properties of strength and hardness are known to functionally vary with the separation between dislocations in crystalline materials, both structural features can potentially contribute to the total interfacial area and the characteristic separation of interfaces that mitigate dislocation motion. In this investigation, the individual contribution of layer pair spacing and grain size to the total interfacial structure are each quantified in an assessment of strength and hardness. A model is proposed for the total interfacial area of the material volume under plastic deformation that can quantify the interfacial area contribution from the layer pairs and the grain size. It is anticipated that each structural feature can potentially dominate the plastic deformation of the nanolaminate as dependent upon the specific layer pair spacing, the grain size, and the extent of plastic deformation.
High-Throughput Optimization of Adhesion in Multilayers by Superlayer Gradient
Authors: Grachev Sergey Yu , Cuminatto Coraly , Søndergård Elin , Barthel Etienne 
Published: February 2010

AbstractWe used thickness gradients for high throughput optimization of adhesion in film stacks. The idea is based on the so-called superlayer test where a top layer under high compression exerts a load onto the lower interfaces and may cause delamination and buckling. Thus, on one hand, the thickness gradient of the superlayer results in the gradient of the load. On the other hand, the adhesion gradient can be realized by changing the thickness of an adhesion enhancer (or an adhesion reducer). When applied in two perpendicular directions (cross-gradient), the gradient of the superlayer in one direction and of the adhesion enhancer in the other, the plane of the sample represents a map where the line of delamination relates the interfacial toughness to the thickness of the enhancer.
In our tests we used Mo superlayers under compressive stress of the order of ˜1.5 GPa on a Si wafer with a native oxide. The adhesion reduction was observed with this methodology when Ag layer up to 10 nm thick was deposited onto the substrate prior to Mo deposition. The delamination occurred at Ag thicknesses starting from ˜6 nm. This thickness of Ag corresponds to the islands coalescence and formation of a continuous film which immediately results in adhesion reduction. The other test was performed with a step gradient of Ti enhancer placed under a 10 nm thick Ag layer in otherwise the same arrangement. A single test showed that 2.8 Å of Ti was sufficient to improve the adhesion between Ag and SiOx by several times.
Towards a Virtual Laboratory for Grain Boundaries and Dislocations
Authors: Echeverri Restrepo Sebastián , Thijsse Barend J. 
Published: February 2010

AbstractIn order to perform a systematic study of the interaction between grain boundaries (GBs) and dislocations using molecular dynamics (MD), several tools need to be available. A combination of computational geometry and MD was used to build the foundations of what we call a virtual laboratory. First, an algorithm to generate GBs on face-centered cubic bicrystals was developed. Two crystals with different orientations are placed together. Then, by applying “microscopic” rigid body translations along the GB plane to one of the crystals and removing overlapping atoms, a set of initial configurations is sampled and a minimum energy configuration is found. Second, to classify the geometry of the GBs a local symmetry type (LST) describing the angular environment of each atom is calculated. It is found that for a given relaxed GB the number of atoms with different LSTs is not very large and that it is possible to find unique geometrical patterns in each GB. For instance, the LSTs of two GBs having the same “macroscopic” configuration but different “microscopic” degrees of freedom can be dissimilar: the configurations with higher GB energy tend to have a higher number of atoms with different LSTs. Third, edge dislocations are introduced into the bicrystals. We see that full edge dislocations split into Shockley partials. Finally, by loading the bicrystals with tensile stresses the edge dislocations are put into motion. Various examples of dislocation-GB interactions in Cu are presented.
Effect of Surface Roughness on Determination of Creep Parameter using Impression Creep Technique
Authors: Yan Wuzhu , Zhao Bin , Yue Zhufeng 
Published: February 2010

AbstractThe indentation creep test, especially the impression creep, exhibits a magic appealing in the determination of creep properties of small structures in industry for its simplicity, efficiency and non-destruction merits. Most of previous researches of indentation or impression creep neglect the effect of surface roughness of materials, which plays a crucial role in extracting creep properties of materials. The FE results showed that the surface roughness has no effect on the determination of creep exponent when the punching stress is larger than 150MPa. However, under a smaller punching stress the stress exponent is decreased due to the “Tuner” effect of asperities. The conclusions drawn in the present study provide an important guidance on experiment results amendment for impression creep technique.
Characterization and Control of the Wettability of Conducting Polymer Thin Films
Authors: Chang Jean H. , Hunter Ian W 
Published: February 2010

AbstractThe wettability of electrochemically deposited conducting polymer films is highly dependent on several parameters including the deposition conditions, the dopant, and the roughness of the working electrode. To produce superhydrophobic surfaces, one must be able to control the micro and nanostructure of the film. In this study, a template-free method of producing superhydrophobic (water contact angle of 154°) polypyrrole films was demonstrated. The polypyrrole was doped with the low surface-energy heptadecafluorooctanesulfonic acid and had microstructures with nanometer-scale roughness. The microstructures served to increase the roughness of the film and amplify the hydrophobicity of the surface. It is also of interest to be able to dynamically adjust the wettability of a polypyrrole surface after deposition. Applications of this functionality include microfluidics, self-cleaning surfaces, liquid lenses, and smart textiles. By oxidizing or reducing a polypyrrole film, one can change the surface morphology as well as the chemical composition, and control the wettability of the surface. This study characterizes the electrochemically-induced changes in surface energy of polypyrrole. The relationship between applied voltage, charge transferred, surface roughness, and water contact angle was investigated. Upon reduction, the polypyrrole film was switched to a superhydrophilic state and the maximum change in contact angle was observed to be 154°. Surface wettability was found to be not fully reversible, with some hysteresis occurring after the first electrochemical cycle.
Chemical Functionalization of Water-etched Si(100)
Authors: Say Carmen , Queeney Kate T. 
Published: February 2010

AbstractEtching of hydrogen-terminated Si(100) in deoxygenated water produces surfaces with a regular nanoscale topography. Surface infrared spectroscopy provides detailed information about this topography via interrogation of the silicon hydride species that populate this highly ordered surface. Here we investigate the feasibility of using siloxane chemistry to functionalize this surface while preserving the initial topography. The critical step in silanization to form high-quality organic layers is oxidative cleaning of the surface. By re-etching oxidized surfaces in hydrofluoric acid, we can repopulate surface hydride species and examine any apparent changes in topography that resulted from the oxidation step. We compare three different oxidation protocols and find that an SC-2 clean results in the least perturbation of the original topography. Preliminary results using both dynamic contact angle and atomic force microscopy suggest that the SC-2 oxidized surface can be functionalized with alkylsilane reagents to create a functionalized surface with regular, nanoscale topography, with all surface processing carried out under ambient conditions at or near room temperature.
Dislocation Arrays in Sapphire using Femtosecond Laser Irradiation
Authors: Moon Chiwon , Kanehira Shingo , Miura Kiyotaka , Tochigi Eita , Shibata Naoya , Ikuhara Yuichi , Hirao Kazuyuki 
Published: February 2010

AbstractWe investigated the formation mechanism and thermal behaviors of defects which were induced at a microscopic area inside (1120) sapphire. We used a femtosecond laser having a pulse width, wavelength, and repetition rate of 238 fs, 780 nm, and 1 kHz, respectively. Cracks were formed at the focal point along the {1102} and the {1100} planes by laser irradiation. The preferential crack formation on these planes was attributed to the different surface fracture energy between the crystallographic planes of sapphire. The cracks transformed into the array of discrete pores by the subsequent heat treatment above 1300 °C, which was due to the diffusive crack healing process. In addition, dislocations were also introduced at the interface between closed cracks.
Nanoporous Ni and Ni-Cu Fabricated by Dealloying
Authors: Hakamada Masataka , Chino Yasumasa , Mabuchi Mamoru 
Published: February 2010

AbstractMetallic nanoporous architecture can be spontaneously attained by dealloying of a binary alloy. The nanoporous architecture can be often fabricated in noble metals such as Au and Pt. In this study, nanoporous Ni, Ni-Cu are fabricated by dealloying rolled Ni-Mn and Cu-Ni-Mn alloys, respectively. Unlike conventional Raney nickel composed of brittle Ni-Al or Cu-Al intermetallic compounds, the initial alloys had good workability probably because of their fcc crystal structures. After the electrolysis of the alloys in (NH4)2SO4 aqueous solution, nanoporous architectures of Ni and Ni-Cu with pore and ligament sizes of 10–20 nm were confirmed by scanning electron microscopy and transmission electron microscopy. X-ray diffraction analyses suggested that Ni and Cu atoms form a homogeneous solid solution in the Ni-Cu nanoporous architecture. The ligament sizes of nanoporous Ni and Ni-Cu were smaller than that of nanoporous Cu, reflecting the difference between diffusivities of Ni and Cu at solid/electrolyte interface. Ni can reduce the pore and ligament sizes of resulting nanoporous architecture when added to initial Cu-Mn alloys.
Nanoimprinted Glass Substrates for Nanoscale Growth Control of Transparent Conducting Oxide Films
Authors: Sugimoto Yuki , Akita Yasuyuki , Nakasone Yuta , Mita Masahiro , Oi Hideo , Yoshimoto Mamoru 
Published: February 2010

AbstractThe crystal growth of indium tin oxide (ITO) thin films on nanoimprinted glass substrates was examined by applying pulsed laser deposition. The nanoimprinted glass was fabricated by thermal nanoimprint using a nanostriped NiO thin film mold. The nanopatterned glass had a straight nanowire array with intervals of about 180 nm, and wire height of about 30 nm. The surface morphology of the ITO thin film grown on the nanoimprinted glass accurately reflected the morphology of the glass surface nanopattern. The ITO thin film on the imprinted glass exhibited preferentially (111)-oriented polycrystalline growth, and had 35% lower resistivity in the direction perpendicular to the nanowire array than that of the film grown on the nonpatterned commercial glass.
Electron Magnetic Resonance Studies on Nanowire and Nanoparticle Arrays
Authors: Amponsah Osei K , Rakhimov Rakhim R. , Barnakov Yuri A. , Lukaszew Rosa A , Owrutsky Jeffrey C , Pomfret Michael B , Noginova Natalia 
Published: February 2010

AbstractArrays of magnetic nanowires and well-oriented chains of superparamagnetic nanoparticles were fabricated using polymer and alumina membrane templates. The systems were characterized by SQUID and studied by electron magnetic resonance methods. Comparative analysis of the obtained results for different geometries and sizes of the magnetic inclusions is presented.
Interactions Between Carbon Nanotubes and Liquid Crystals in Binary Nematic Electro-Optic Cells
Authors: Georgiev Georgi Yordanov , Gombos Erin A , McIntyre Michael B , Mattera Michael F , Gati Peter A. , Cabrera Yaniel , Cebe Peggy 
Published: February 2010

AbstractWe studied the effects of multiwalled carbon nanotubes (MWCNTs) on the Freedericksz transition of a liquid crystal (LC) and calibrated the altitudinal angle of CNTs as a function of the electric field. In addition, we directed the azimuthal angle which gave us complete control of the 3D orientation of the CNTs. We constructed anti-parallel electro-optic cells using a nanocomposite at a concentration of 0.01% CNTs with 4-Cyano-4'-pentylbiphenyl (5CB) liquid crystal. This low concentration was necessary to achieve maximum transmission of electromagnetic radiation through the cell and to minimize the Van der Waals attraction between the CNTs responsible for their aggregation. We chose two dimensional microscopic transmission ellipsometry (2D-MTE) to measure the phaseshift of the polarized electromagnetic radiation through the cell and to derive from it the altitudinal angle of the CNTs. Our results show that in the presence of CNTs the Freedericksz transition occurs at 55% of the transitional electric field as compared to the control electro-optic cell without CNTs. The width of the Freedericksz transition narrows by a similar factor. The switching time of the cell decreased in the presence CNTs by 18.5%.
Fabrication of Ga-templates Using a Focused Ion Beam
Authors: Wang Hao , Hartman Greg C. , Williams Joshua , Gray Jennifer L. 
Published: February 2010

AbstractThere are many factors that have the potential to limit significant advances in device technology. These include the ability to arrange materials at shrinking dimensions and the ability to successfully integrate new materials with better properties or new functionalities. To overcome these limitations, the development of advanced processing methods that can organize various combinations of materials at nano-scale dimensions with the necessary quality and reliability is required. We have explored using a gallium focused ion beam (FIB) as a method of integrating highly mismatched materials with silicon by creating template patterns directly on Si with nanoscale resolution. These templates are potentially useful as a means of locally controlling topography at nanoscale dimensions or as a means of locally implanting Ga at specific surface sites. We have annealed these templates in vacuum to study the effects of ion dosage on local Ga concentration and topography. We have also investigated the feasibility of creating Ga nanodots using this method that could eventually be converted to GaN through a nitridation process. Atomic force microscopy and electron microscopy characterization of the resulting structures are shown for a variety of patterning and processing conditions.
Formation of ordered arrays of gold particles on silicon and silicon-dioxide by nanoindentation patterning
Authors: Ruffell Simon , Venkatachalam Dinesh Kumar , Shalav Avi , Elliman Robert G. 
Published: February 2010

AbstractOrdered arrays of gold particles have been fabricated on gold-coated Si(100) surfaces by pre-patterning the surface with a nanoindenter. During thermal annealing the Au is observed to accumulate within the residual indents. Once nucleated, the Au particles grow at the expense of smaller surface particles via an Ostwald-ripening process. The size of the Au particles is controlled by the initial thickness of the deposited Au layer, the size of the indentation (which is controlled with a high degree of precision), and the annealing conditions. Particles of ˜200 nm dimensions are formed in indents of ˜1 μm dimensions whilst nanoparticles of ˜20 nm are observed in the smallest indents made (˜50 nm). We have also demonstrated patterning of Au by indentation of a Au layer sandwiched between two SiO2 films deposited on Si by plasma-enhanced chemical vapour deposition. Here, cracking of the SiO2 layer occurs allowing Au to diffuse to the surface at the indented locations during post-indentation annealing.
A Concurrent Multiscale Method for Coupling Atomistic and Continuum Models at Finite Temperatures
Authors: Picu Catalin , Mathew Nithin 
Published: February 2010

AbstractA concurrent multi-scale modeling method for finite temperature simulation of solids is introduced. The objective is to represent far from equilibrium phenomena using an atomistic model and near equilibrium phenomena using a continuum model, the domain being partitioned in discrete and continuum regions, respectively. An interface sub-domain is defined between the two regions to provide proper coupling between the discrete and continuum models. While in the discrete region the thermal and mechanical processes are intrinsically coupled, in the continuum region they are treated separately. The interface region partitions the energy transferred from the discrete to the continuum into mechanical and thermal components by splitting the phonon spectrum into “low” and “high” frequency ranges. This is achieved by using the generalized Langevin equation as the equation of motion for atoms in the interface region. The threshold frequency is selected such to minimize energy transfer between the mechanical and thermal components. Mechanical coupling is performed by requiring the continuum degrees of freedom (nodes) to follow the averaged motion of the atoms. Thermal coupling is ensured by imposing a flux input to the atomistic region and using a temperature boundary condition for continuum. This makes possible a thermodynamically consistent, bi-directional coupling of the two models.
Designing Glasses with Tunable Structure and Properties by Computer Simulation
Authors: Huang Liping , Yuan Fenglin , Zhao Qing 
Published: February 2010

AbstractA normal solid becomes stiffer when squeezed and softer when heated. In contrast, silica glass behaves the opposite way: its elastic moduli decrease upon compression and increase upon heating. Silica glass is also known to densify under compression and radiations. These have been long-standing mysteries in materials science. Using molecular dynamics simulation, we uncovered the structural origins of the anomalous thermo-mechanical behaviors and mechanisms of permanent densification in silica glass. Accordingly, these anomalies can be attributed to localized structural transitions, analogous to those that occur in the crystalline counterparts. The irreversible densification in silica glass is achieved through structural transition involving bond breaking and re-formation under a combination of high pressure and temperature. We further revealed that the anomalous thermo-mechanical behaviors are inherently connected to the ability of the glass to undergo permanent densification. Our computer simulations demonstrate that by processing in ways that gradually eliminates anomalous thermo-mechanical behaviors, degree of the glass to undergo densification can be eventually eradicated. This provides the conceptual foundation for the bottom-up design of new glasses with tunable structure and properties.