bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Hydrostatic Pressure on Indentation Modulus
Authors: Mook William M. , Gerberich W. W.
Published: April 2011

The high pressures generated at a contact during nanoindentation have a quantifiable effect on the measured indentation modulus. This effect can be accounted for by invoking a Murnaghan equation of state-based analysis where the measured indentation modulus is a function of the hydrostatic component of the stress state which is generated beneath the indenter tip. This approach has implications pertinent to a range of mechanical characterization techniques that include instrumented indentation and quantitative atomic force microscopy (AFM) since these techniques traditionally consider only zero-pressure modulus values during data interpretation. To demonstrate the validity of this approach, the indentation modulus of four materials (fused quartz, sapphire, rutile and silicon) is evaluated using a 1 μm radius conospherical diamond tip to maximum contact depths of 30 nm. The tip area function is independently determined via AFM while the unloading stiffness from the load-displacement data is determined using standard Oliver-Pharr analysis.
Mechanical Properties of 3C-SiC Films for MEMS Applications
Authors: Reddy Jayadeep Deva , Volinsky Alex A. , Frewin Christopher L. , Locke Chris , Saddow Stephen E.
Published: April 2011

There is a technological need for hard thin films with high elastic modulus and fracture toughness. Silicon carbide (SiC) fulfills such requirements for a variety of applications at high temperatures and for high-wear MEMS. A detailed study of the mechanical properties of single crystal and polycrystalline 3C-SiC films grown on Si substrates was performed by means of nanoindentation using a Berkovich diamond tip. The thickness of both the single and polycrystalline SiC films was around 1-2 μm. Under indentation loads below 500 μN both films exhibit Hertzian elastic contact without plastic deformation. The polycrystalline SiC films have an elastic modulus of 457 GPa and hardness of 33.5 GPa, while the single crystalline SiC films elastic modulus and hardness were measured to be 433 GPa and 31.2 GPa, respectively. These results indicate that polycrystalline SiC thin films are more attractive for MEMS applications when compared with the single crystal 3C-SiC, which is promising since growing single crystal 3C-SiC films is more challenging.
Theory of Lubrication due to Poly-Electrolyte Polymer Brushes
Authors: Sokoloff Jeffrey B.
Published: April 2011

It is shown using a method based on the mean field theory of Miklavic Marcelja that it should be possible for osmotic pressure due to the counterions associated with the two polyelectrolyte polymer brush coated surfaces to support a reasonable load (i.e., about 105Pa) with the brushes held sufficiently far apart to prevent entanglement of polymers belonging to the two brushes, thus avoiding what is likely to be the dominant mechanisms for static and dry friction.
PLASTICITY CHARACTERISTICS OBTAINED THROUGH INSTRUMENTAL INDENTATION
Authors: Milman Yuliy , Dub Sergey , Golubenko Alex
Published: April 2011

The nanohardness and microhardness testing of crystalline materials with different types of interatomic bonds and different crystal structures was performed with Berkovich indenter.

The plasticity characteristics for crystalline materials with different types of interatomic bonds and different crystalline structures were determined by microindentation and by nanoindentation. The relation between these characteristics and parameters of material (Meyer hardness, Young's modulus and Poisson's ratio) was assigned. Plasticity characteristic may be used for characterization of mechanical behavior of materials which are brittle at standard mechanical tests and for coatings.
Tip-Induced Calcite Single Crystal Nanowear
Authors: Gunda Ramakrishna , Volinsky Alex A.
Published: April 2011

Wear behavior of freshly cleaved single crystal calcite (CaCO3) was investigated by continuous scanning using the Hysitron Triboindenter in ambient environment as a function of scanning frequency (1 Hz – 3 Hz) and contact load (2 µN – 8 µN). At lower loads below 4 µN, initiation of the ripples takes place at the bottom of the surface slope, which continue to propagate up the slope as scanning progresses. The orientation of these ripple structures is perpendicular to the long scan direction. As the number of scans increases, ripples become fully developed, and their height and periodicity increase with the number of scans. At 6 µN normal load, tip-induced wear occurs as the tip begins removing the ripple structures with increased number of scan cycles. As the contact load increased further, ripples did not initiate and only tip-induced wear occurred on the surface, and saturated after 20 scans. At 1 Hz frequency wear takes place as material slides towards the scan edges when the tip moves back and forth. Material removal rate increased with contact load and it is observed that the number of scans required to create a new surface is inversely proportional to the contact load. Possible mechanisms responsible for the formation of ripples at higher frequencies are attributed to the slope of the surface, piezo hysteresis, system dynamics, or a combination of effects. The wear regime is due to abrasive wear. Single crystal calcite hardness of 2.8±0.3 GPa and elastic modulus of 75±4.9 GPa were measured using nanoindentation and used to determine the wear mode.
Determination of Residual Stress and Yield Stress Simultaneously by Indentation Method with Dual Indenters
Authors: Baoxing Xu , Wang Xinmei , Yue Zhufeng
Published: April 2011

In general, the method of obtaining residual stress from indentation test requires calculating the contact area of indenter and indented material, and also needs to know yield stress of indented material in advance. In this work, the dimensional analysis of indentation loading curve was first analyzed, and then a reverse numerical procedure was explored to show a possibility of determining residual stress and yield stress of materials simultaneously from indentation test. Besides, the calculation of contact area can be also avoided.
Haasen Plot Activation Analysis of Constant-Force Indentation Creep in FCC Systems
Authors: Bhakhri Vineet , Klassen Robert J.
Published: April 2011

An analysis of the length-scale and temperature dependence of Haasen plots obtained from constant-force nano- and micro-indentation creep tests performed are reported here. The operative deformation mechanism for all the systems studied involved dislocation glide limited by dislocation-dislocation interactions. Our findings illustrate the potential usefulness of Haasen plot activation analysis for interpreting data from constant-force pyramidal indentation creep tests.
Magnetic-Field-Induced Strain of Fe-based Ferromagnetic Shape-Memory Alloy in a Pulsed Magnetic Field
Authors: Sakon Takuo , Fukuda Takashi , Nojiri Hiroyuki , Kakeshita Tomoyuki
Published: April 2011

The magnetic field-induced strain (MFIS) of the martensite metallic compound Fe3Pt were studied in a pulsed magnetic field using the capacitance method at low temperatures down to 4.2 K in a martensitic phase, which is much lower than the martensitic transformation temperature TM = 85 K. After zero field cooling, pulse magnetic field with the maximum frequency of 160 Hz was applied parallel to [001]p axis. Large MFIS has been measured. The value of the MFIS is ΔL/L = −1.7 %. When the magnetic field was decreased, the recovery of the strain was observed. At the 2nd shot, the strain of about 0.6 % was observed. It means that MFIS occurs even in short-pulse magnetic fields.
Optimization of the Geometry of the MEMS Electrothermal Actuator to Maximize In-Plane Tip Deflection
Authors: Kolesar Edward S. , Htun Thiri , Least Brandon , Tippey Jeffrey , Michalik John
Published: April 2011

Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This investigation optimized the geometry of the asymmetrical electrothermal actuator to maximize its in-plane deflection characteristics. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate differential thermal expansion and movement. In this investigation, a 3-D model of the electrothermal actuator was designed, and its geometry was optimized using the finite-element analysis (FEA) capabilities of the ANSYS computer program. The electrothermal actuator's geometry was systematically varied to establish optimum values of several critical geometrical ratios that maximize tip deflection. The value of the ratio of the length of the flexure component relative to the length of the hot arm was discovered to be the most sensitive geometrical parameter ratio that maximizes tip deflection.
The Effect of Hydrophobic Patterning on Micromolding of Aqueous-Derived Silk Structures
Authors: Tsioris Konstantinos , White Robert D , Kaplan David L , Wong Peter Y
Published: April 2011

A novel micromolding approach was developed to process liquid biopolymers with high aqueous solvent contents (>90% water). Specifically silk fibroin was cast into a well-defined scaffold-like structure for potential tissue engineering applications. A method was developed to pattern the hydrophilicity and hydrophobicity of the polydimethylsiloxane (PDMS) mold surfaces. The water based biopolymer solution could then be directly applied to the desired regions on the cast surface. The variations in degree of hydrophilicity and hydrophobicity on the PDMS surfaces were quantified through contact angle measurements and compared to the outcome of the molded silk structures. Through this method free-standing structures (vs. relief surface-patterning) could be fabricated.
Design and Fabrication of an Optical-MEMS Sensor
Authors: Mathur Vaibhav , Li Jin , Goodhue William D.
Published: April 2011

A novel optical-MEMS sensor based on the AlGaAs material system is designed and fabricated. The device consists of micro-beam waveguides butt-coupled with their ends separated by approximately 2 to 4 µm. The device works on the principle that when acoustically driven by an external source, the waveguides misalign, leading to coupling loss. The device design parameters were determined using FEM (Finite Element Method) modeling. The dielectric waveguide beams were designed for single mode propagation at 785 nm and longer wavelengths. A combination of dry and wet etching process followed by precision laser cutting was used to fabricate the suspended beams. Beams ranging from 100 µm to 400 µm with fundamental frequencies of 50 KHz to 200 KHz were successfully fabricated. Initial uncut waveguide test results will be discussed along with the plan for characterizing the devices using an acoustically coupled piezoelectric driver. These devices may be utilized for vibration sensing, or optical intensity modulation.
Excimer Laser Induced Patterning of PSZT and PLZT Flms
Authors: Leech Patrick William , Holland Anthony S
Published: April 2011

The patterning of strontium-doped lead zirconium titanate (PSZT) and lanthanum-doped lead zirconium titanate (PLZT) films has been examined using excimer laser radiation. Both types of film were deposited by rf magnetron sputtering using in-situ heating and a controlled cooling rate in order to obtain the perovskite-oriented phase. The depth of laser ablation in both PSZT and PLZT films showed a logarithmic dependence on fluence. The threshold fluence required to initiate ablation was ∼1.25 mJ/cm2 for PLZT and ∼1.87 mJ/cm2 for PSZT films. The ablation rate of PLZT films was slightly higher than that of PSZT films over the range of fluence (10-150 J/cm2) and increased linearly with number of pulses. The higher ablation rate of PLZT films has been attributed to the finer grainsize (160-200 nm) than in the PSZT films (1.0-1.2 µm).
High Temperature Annealing Studies on the Piezoelectric Properties of Thin Aluminum Nitride Films
Authors: Farrell R. , Pagán V. R. , Kabulski A. , Kuchibhatla Sridhar , Harman J. , Kasarla K. R. , Rodak L. E. , Hensel J. , Famouri P. , Korakakis D.
Published: April 2011

A Rapid Thermal Annealing (RTA) system was used to anneal sputtered and MOVPE-grown Aluminum Nitride (AlN) thin films at temperatures up to 1000°C in ambient and controlled environments. According to Energy Dispersive X-Ray Analysis (EDAX), the films annealed in an ambient environment rapidly oxidize after five minutes at 1000°C. Below 1000°C the films oxidized linearly as a function of annealing temperature which is consistent with what has been reported in literature [1]. Laser Doppler Vibrometry (LDV) was used to measure the piezoelectric coefficient, d33, of these films. Films annealed in an ambient environment had a weak piezoelectric response indicating that oxidation on the surface of the film reduces the value of d33. A high temperature furnace has been built that is capable of taking in-situ measurements of the piezoelectric response of AlN films. In-situ d33 measurements are recorded up to 300°C for both sputtered and MOVPE-grown AlN thin films. The measured piezoelectric response appears to increase with temperature up to 300°C possibly due to stress in the film.
Influence of Materials on the Performance Limits of Microactuators
Authors: Srinivasan Prasanna , Spearing S. Mark
Published: April 2011

The selection of actuators at the micro-scale requires an understanding of the performance limits of different actuation mechanisms governed by the optimal selection of materials. This paper presents the results of analyses for elastic bi-material actuators based on simple beam theory and lumped parameter thermal models. Comparisons are made among commonly employed actuation schemes (electro-thermal, piezoelectric and shape memory) at micro scales and promising candidate materials are identified. Polymeric films on Si subjected to electro-thermal heating are optimal candidates for high displacement, low frequency devices while ferroelectric thin films of Pb-based ceramics on Si/ DLC are optimal for high force, high frequency devices. The ability to achieve ∼10 kHz at scales < 100μm make electro-thermal actuators competitive with piezoelectric actuators considering the low work/volume obtained in piezoelectric actuation (∼ 10−8J.m−3.mV−2). Although shape memory alloy (SMA) actuators such as Ni-Ti on Si deliver larger work (∼ 1 J.m−3K−2) than electro-thermal actuators at relatively low frequencies (∼ 1 kHz), the critical scale associated with the cessation of the shape memory effect forms the bounding limit for the actuator design. The built-in compressive stress levels (∼ 1GPa) in thin films of Si and DLC could be exploited for realizing a high performance actuator by electro-thermal buckling.
Systematic Characterization of DRIE-Based Fabrication Process of Silicon Microneedles
Authors: Held Jochen , Gaspar Joao , Ruther Patrick , Hagner Matthias , Cismak Andreas , Heilmann Andreas , Paul Oliver
Published: April 2011

This paper reports on the systematic characterization of a deep reactive ion etching based process for the fabrication of silicon microneedles. The possibility of using such microneedles as protruding microelectrodes enabling to electroporate adherently growing cells and to record intracellular potentials motivated the systematic analysis of the influence of etching parameters on the needle shape. The microneedles are fabricated using dry etching of silicon performed in three steps. A first isotropic step defines the tip of the needle. Next, an anisotropic etch increases the height of the needle. Finally, an isotropic etch step thins the microneedles and sharpens their tip. In total, 13 process parameters characterizing this etching sequence are varied systematically. Microneedles with diameters in the sub-micron range and heights below 10 µm are obtained. The resulting geometry of the fabricated microneedles is extracted from scanning electron micrographs of focused ion beam cross sections. The process analysis is based on design-of-experiment methods to find the dominant etch parameters. The dependence of the needle profiles on process settings are presented and interpolation procedures of the geometry with processing conditions are proposed and discussed.
Enhanced Phonon Scattering in Oxide Superlattices to Improve Laser Induced Thermoelectric Voltages
Authors: Habermeier Hanns-Ulrich , Zhang Peng Xiang , Zhang Hui
Published: April 2011

Optimizing the figure of merit for thermoelectric applications, ZT = S2σ2T/κ is currently at the core of materials oriented research in thermoelectricity. Here, one promising approach is to reduce ther thermal conductivity without sacrificing the electrical conductivity. Constructing superlattices of structurally compatible materials is one way to accomplish this goal. We report an enhanced laser induced thermoelectric voltage (LITV) effect observed in (YBa2Cu3O7/La1-xPbxMnO3)n multilayer thin films for the first time. Two groups of multilayer thin films grown on vicinal cut LaAlO3 substrates were prepared by pulsed laser deposition technique. The first group were grown on different substrates vicinal cut at different angles, and were used for checking the mechanism of the induced voltages. The second group samples were made at different period number n and for studying the number dependence of the peak values of LITV. The substrate angle dependence proved that this is a thermoelectric effect [1]. It was found that the LITV signals were enhanced significantly for these multilayer thin films comparing with the single layer ones. It is natural that the conductivity is going to be anisotropic due to the layered structure, and the same holds for the Seebeck coefficients. The enlarged Seebeck anisotropy will lead to higher induced voltages. Another possible reason is the reduced thermal conductivity in the layered structure. The maximum enhancement of LITV signals takes place at period number of 7, which seems in agreement with the prediction of minimum thermal conductivity in superlattices by Simkin and Mahan.
3-Dimensional Al2O3 Fiber Networks using Low Temperature Atomic Layer Deposition on a Cotton Template
Authors: Hojo Daisuke , Hyde G. Kevin , Spagnola Joseph , Parsons Gregory N
Published: April 2011

Micro-scale woven structures were replicated 3 dimensionally by conformal coating onto natural woven cotton using a binary reaction of trimethylaluminum and water at 100°C. Even after the woven cotton was removed at 450°C, the woven structures completely remained. Results demonstrate the capability of ALD to penetrate into the complex 3D network structure of natural woven cotton to form uniform coating at low temperature and give insight into general understanding of methodology to translate deposition processes from 2D surface to a 3D network to obtain a uniform coating throughout the sample network bulk. It also shows the possibility of replication of micro-scale structures from highly conformal coatings to give the unique synthesis root of hollow structures.
Functionalised Nanostructured Polyaniline – A New Substrate for Building Adaptive Sensing Surfaces
Authors: Lahiff Emer , Bell Steven , Diamond Dermot
Published: April 2011

A new method for covalently binding side-chains to the surface of solution based conducting polymer nanostructures is introduced in this paper. Modification of the structures is achieved by convenient reflux in the presence of a nucleophile, and post-functionalization purification is subsequently carried out by centrifugation. The entire process is easily scalable and hence suitable for bulk production of functionalized nanomaterials. In particular we focus on the modification of polyaniline nanofibres which can be synthesized by interfacial polymerization. Mercaptoundecanoic acid side-chains are attached to the polymer nanostructures, with the intrinsic nano-morphology of the material being maintained during the process. The modified PAni nanofibres provide a template for the attachment of other specific functional groups which could be used to target a particular species.
Improvement of Impact Strength for Transparent Inorganic Glass by Electron Beam Irradiation
Authors: Iwata Keisuke , Tonegawa Akira , Nishi Yoshitake
Published: April 2011

Low-energy electron beam (EB) irradiation, generally applied to enhance hardening and wear resistance of polymer, was a successful surface treatment. Effect of EB irradiation was the homogeneous activation of surface atoms and the breaking of the chemical bonds in the network structure of a surface layer of inorganic glasses. When EB irradiation generated dangling bonds at the weaker-bonded metal-oxygen atomic pairs in the glass network structure, partial relaxation occurred at points of residual strain in the network structure. It was clear that the increased rigidity was mainly due to an increase in the bonding energy of the stronger-bonded metal-oxygen atomic pairs in the atomic network structure. The possible beneficial effects of EB irradiation on the impact value of transparent inorganic glass was investigated. To clarify the results, ESR observations were used to confirm the existence of dangling bonds. The EB irradiation increased the impact value of the transparent inorganic glasses. Based on the ESR signals of transparent glasses before and after EB irradiation, the high density of dangling bonds was obtained.
Enhanced Light Emission by Exciton-Surface Plasmon Coupling
Authors: Okamoto Koichi , Scherer Axel , kawakami Yoichi
Published: April 2011

Surface plasmon coupling technique was performed to enhanced green light emissions from InGaN/GaN quantum well. We found that photoluminescence intensities were increased by fabricated nano-grating structures on the gold layers and enhancement ratios depend on the grating periods. We also simulated the localized SP modes by 3D-finite difference time domain (FDTD) calculation. The experimental results were well correlated to the calculated results, and we found that the both exciton-SP coupling and light extraction process can be controlled by the nano-structures of the interfaces. This suggests that even more efficient emission should be obtainable by optimizing the nanostructure geometries.
Interaction of Spherical Nanoparticles with a Highly Focused Beam of Light
Authors: Sendur Ibrahim Kursat , Challener William , Mryasov Oleg
Published: April 2011

Interaction of a highly focused beam of light with spherical nanoparticles is investigated for various incident field polarizations. First, an analytical solution is obtained to calculate the interaction of a highly focused beam of light with a spherical particle. To accurately express the incident electric field near the focus of an aplanatic lens, the technique established by Richards and Wolf is used. Using this analytical solution, electric field distributions of various spherical nanoparticles made of silver are investigated for highly focused linearly and radially polarized beams. The effect of the half angle of the focused beam is investigated. In addition a three-dimensional finite element method based solution is obtained and compared with the analytical solution for problems involving a highly focused beam of light interacting with a spherical particle.
Arrays of Well-Defined Size-Tunable Metallic Nano-Cones for Plasmonic Applications
Authors: Fleischer Monika , Stade Florian , Heeren Andreas , Haeffner Michael , Kern Dieter P. , Braun Kai , Stanciu Catrinel , Meixner Alfred J.
Published: April 2011

Cones composed of noble metals with dimensions of the order of 100 nm, especially gold cones, are extremely well suited for optical near-field investigations using visible light. Their plasmon resonance frequency lies within the range of visible light frequencies, and upon illumination, strong electric field enhancement can be observed in the direct vicinity of the cone tip. For this purpose, a method to fabricate well-controlled nanocones with sharp tips is required. We present a top-down process in which arrays of cones are dry-etched from a metal stack on silicon. During the ion milling step, patterned hydrogen silsesquioxane resist is used as an etch mask. The resulting cones have tunable base diameters around 150 nm and tip radii down to less than 10 nm. Their optical characteristics are investigated by means of apertureless optical near-field microscopy, in which field enhancement at the cone tip is observed.
Near infrared intersubband absorption in cubic GaN/AlN superlattices
Authors: DeCuir Eric A. , Fred Emil , Manasreh Omar , Schormann Jorg , As Donat J. , Lischka Klaus
Published: April 2011

Room temperature near-infrared intersubband transitions were observed in MBE grown non-polar cubic GaN/AlN superlattice structures. The peak wavelengths of these transitions were observed in the spectral region of 1.5–2.0 μm and were theoretically supported using a transfer matrix approach. All samples were unintentionally doped and grown on 3C-SiC substrates with a 100 nm GaN buffer. Each structure consisted of a 20 periods of GaN/AlN superlattice capped with 100nm of GaN. The thickness of the AlN barrier was fixed at 1.35, while the thickness of the GaN well was varied between 1.6 and 2.1nm. Electrochemical Capacitance Voltage (ECV) measurements allowed direct measurement of the intrinsic carrier concentration in a thick unintentionally doped cubic GaN layer, which confirmed sufficient population of the ground state energy level.
Surface Passivated Air and Moisture Stable Mixed Zirconium Aluminum Metal-Hydride Nanoparticles
Authors: Epshteyn Albert , Miller Joel B. , Pettigrew Katherine A. , Stroud Rhonda M. , Purdy Andrew P.
Published: April 2011

Synthesis of surface passivated Zr-Al mixed metal-hydride nanoparticles was accomplished via a multi-step process. The initial reaction to produce the zirconium aluminum hydride was via decomposition of zirconium tetrahydroaluminate (Zr(AlH4)4) while exposed to ultrasound produced by a benchtop ultrasonic bath. The particles were surface passivated using carbohydrates and were shown to be stable in air and partially stable in water. TEM imaging suggests the existence of smaller particles made of a Zr-Al alloy that range in size from 1.8 nm to 7.9 nm in diameter and are interspersed with larger particles that range from tens to hundreds of nanometers in diameter. It was also shown that the carbohydrate-derived coating of the nanoparticles is present as an aluminum alkoxide gel surrounding the core particles.
Carbon-Halide Nanocomposites for Asymmetric Hybrid Supercapacitors
Authors: Barpanda Prabeer , Fanchini Giovanni , Amatucci Glenn G
Published: April 2011

Nanostructured materials and nanocomposites have inspired many structural and functional applications in recent time. In the last decade, energy-storage devices have employed electrode materials in form of nanomaterials/nanocomposites to yield promising electrochemical performance. The current paper throws light on the application of nanostructured pristine activated carbons as well as chemically modified carbon-halide nanocomposites in practical electrochemical supercapacitors. Pristine activated carbons have been mechanochemically modified via high-energy milling and iodine doping to produce carbon-halide nanocomposites. A significant change in existing physical and electrochemical properties has been marked by introduction of iodine into carbon and the subsequent formation of nanocomposites. The effect of halides and nanoscale morphology is discussed using X-ray, Raman spectroscopy, DSC, BET analysis and electrochemical testing.
Spectroscopic Investigations of Dendrimer-Au Hybrid Nanoclusters
Authors: Tanaka Akinori , Murase Yoshiaki , Kitagawa Takanobu , Imamura Masaki , Yasuda Hidehiro
Published: April 2011

We have synthesized the dendrimer-Au hybrid nanoclusters by solution routes, and have carried out the various spectroscopic studies in order to investigate their electronic structures. From the line-shape analyses for Au 4f core-level photoemission spectra measured with hard X-ray synchrotron-radiation of Au nanoclusters with mean diameter of 2-3 nm stabilized outside the dendrimer, it is found that Au 4f core-level photoemission spectrum consists of two components. We attribute these components to interior Au atoms and surface Au atoms bonded to dendrimers. In the valence-band photoemission spectrum of these Au nanoclusters, we have observed the bandwidth narrowing of Au 5d-derived band compared to that of bulk Au crystallite. Moreover, we have observed the characteristic spectral feature in the vicinity of Fermi level due to the dynamic final-state effect in photoemission. We have also carried out the optical spectroscopic measurements of these Au nanoclusters. From these results, we discuss the electronic structures and interfacial properties of the dendrimer-Au hybrid nanoclusters.
Effect of Ligand Exchange on the Stability and Optical Properties of CdSe Quantum Dots
Authors: Siy Jacqueline T. , Leone Lindsay , Bartl Michael H.
Published: April 2011

A new post-synthesis heat/ligand-exchange treatment on CdSe nanocrystal quantum dots that allows fine-tuning the quantum dots size without losing important properties (e.g. photoluminescence) is presented. The careful control of parameters such as the reaction temperature, the quantum dot to alkyl-amine ligand mole ratio and the solvent volume is shown to provide tunable size reduction of the nanocrystals. This size reduction phenomenon provides new insights into the surface chemistry and stability of nanocrystals and can serve as a platform for designing, controlling and processing nanomaterials with tailored properties.
Synthesis and Characterization of Plasma Synthesized Nanostructured Magnesia-Yttria Based Nanocomposites
Authors: Al-Sharab Jafar F. , Sadangi Rajendra , Shukla Vijay , Kear Bernard
Published: April 2011

Polycrystalline Y2O3 is the material of choice for IR windows since it has excellent optical properties in the visible, and near infra-red band. However, current processing methods yield polycrystalline Y2O3 with large grain size (> 100 μm), which limits the hardness and erosion resistance attainable. One way to improve strength is to develop an ultra-fine grained material with acceptable optical transmission properties. To realize a fine-grained ceramic, one approach is to develop a composite structure, in which one phase inhibits the growth of the other phase during processing. In this study, Y2O3-MgO nanocomposite with various MgO content (20, 50 and 80 mol%) were synthesized using plasma spray method. Extensive characterization techniques including x-ray diffraction, scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Energy Dispersive spectrometry (EDS) were employed to study the synthesized powder as well as the consolidated sample. Transmission Electron Microscopy, as well as EDS chemical mapping, revealed that the consolidated sample have bi-continuous MgO-Y2O3 nanostructure with an average grain size of 200 nm.
Cu Rich Nanostructured Alloys with Enhanced Mechanical Properties
Authors: Georgarakis K. G. , Ota K. , LeMoulec A. , Charlot F. , Yavari A. R. , Vaughan G.
Published: April 2011

New copper rich alloys with elemental additions of transition metals and group IIIA and IVA elements have been prepared by casting and rapid solidification. The prepared alloys show very interesting microstructures; a thick surface layer with nanocrystalline eutectic like structure, while in the bulk the microstructure is coarser lamellar or dendritic. Their microhardness was found to be exceptionally high for Cu rich alloys, reaching values of 450-550HV. Furthermore, the microhardness of the surface layer is higher than that in the bulk, indicating that these alloys can be considered for a variety of applications including tribological and structural.
CVD deposition of highly Al-rich mullite coatings
Authors: Kulkarni Tushar , Wang H Z , Basu S N , Sarin V K
Published: April 2011

Although chemical vapor deposited mullite (3Al2O3•2SiO2) environmental barrier coatings have shown promise in protecting Si-based substrates for gas-turbine applications, there is concern that the silica content within the mullite coating itself might be susceptible to hot-corrosion and recession during long term exposure to corrosive atmospheres. There is thus a strong motivation to substantially reduce or even virtually eliminate the silica from the surface of the mullite coatings that are in direct contact with atmospheres containing corrosive oxides and steam. Functionally graded mullite (3Al2O3•2SiO2) coatings have been grown for Si-based substrates and the composition has been tailored in these coatings, with the Al/Si ratio being stoichiometric (∼ 3) at the coating/substrate interface for coefficient of thermal expansion (CTE) match, and increasing monotonically towards the outer coating surface. These functionally graded coatings have some of the highest Al-rich mullite reported to date at the coating surface. At these extremely high Al/Si ratios, mullite structure breaks down and the formation of a nano-sized high-alumina rich phase occurs. High-resolution transmission electron microscopy has been used to characterize the structure and composition of high alumina mullite and will be discussed.
Fabrication of Multiwall Carbon Nanotube-nanocrystalline Copper Nanocomposite Film by Electrochemical Deposition
Authors: Yoo JungJoon , Song JaeYong , Yu Jin
Published: April 2011

A new method of fabricating nanocomposite films made up of multiwall carbon nanotube and nanocrystalline copper was developed by using an electrochemical deposition. The electroplated CNT/Cu nanocomposites have the microstructure that CNTs are well dispersed in both the planar and depth directions without any voids in the matrix. The conditions were successfully achieved by using some amphiphilic polymers, organic additives and a pulse electrodeposition method. The microstructure and CNT composition of nanocomposite films were strongly affected by the concentration of CNT in the electrolyte. The mechanical and electrical properties of CNT/Cu nanocomposite films were investigated with the variation of CNT content in the nanocomposite films.
New Core/Shell Ta2O5-PMMA Nanocomposites for Applications as Polymer Waveguides
Authors: Szabó Dorothée Vinga , Ochs Rolf , Schlabach Sabine , Ritzhaupt-Kleissl Eberhard , Hanemann Thomas
Published: April 2011

To realize ceramic/polymer nanocomposites for polymer waveguides, PMMA-coated Ta2O5 nanoparticles are synthesized as core/shell particles. Therefor a gas-phase process is used: the Karlsruhe Microwave Plasma Process. The organic coating is supposed to reduce the agglomeration of the ceramic cores and should facilitate the incorporation into the polymer resin. TEM investigations of the nanoparticles exhibit crystalline and amorphous Ta2O5 with sizes around 3 to 6 nm, confirmed by electron diffraction. Although the polymer coating is not visible in TEM imaging, electron energy loss spectroscopy (EELS) exhibits a significant C-edge, proofing the organic coating. The Ta2O5/PMMA nanoparticles are incorporated with different weight fractions to a maximum of 1 wt% by a dissolver stirrer into PMMA resin. The optical properties (refractive index, transmission) are determined as a function of the nanoparticle content. Compared to the pure polymer, the refractive index of the modified composite, measured at 633 nm, is increased by 0.001 and 0.004 at 0.1 wt% and 0.7 wt%, respectively. A similar tendency is observed at 1550 nm. The transmission in the near infrared (NIR) is similar to that of PMMA up to a content of 0.3 wt%. At higher nanoparticle contents transmission is reduced. The reduction in transmission is due to the presence of agglomerates larger then 1/10 of the applied wavelength, confirmed by TEM. The concept of incorporating inorganic/organic hybrid nanoparticles with intrinsic high refractive index in polymer matrices is very promising. A suitable effect in refractive index for application of ceramic nanoparticle/polymer nanocomposites as polymer waveguides could be observed even with low particle concentration.
Development of a Simple Sintering Law for Fractal Aggregates Composed of Unequal Sized Primary Particles
Authors: Hawa Takumi , Zachariah Michael R
Published: April 2011

Sintering of silicon nanoparticle chain aggregates composed of unequal sized primary particles are investigated using molecular dynamics (MD) simulations at 1500 K. We consider straight chain aggregates consisting of up to 40 2.5 and 5.4 nm primary particles. The sintering time increases with increase in the total volume of the chain aggregate or with increase in the exposed initial surface area of the chain. A mathematical model was developed to describe the dynamics of sintering of such chain aggregates. The model is a power law modification of the Frenkel sintering equation with the Koch-Friedlander model to include primary particle size dependence. We found that the particle size effect is a local process, and important only at the initial stage of the sintering. Thus, the effect is not significant when the aggregate becomes large. The model is amenable for use in aerosol models that might include sintering effects.
White cast iron of network morphology-its formation and properties
Authors: Lan Yip Yeuk , Chuen Leung Ching , Ming Fuk Chung , Wah Mok Siu , Wing Kui Hin
Published: April 2011

A white cast iron of composition Fe81C14Si5 can be cast into a nanostructure with network morphology by a fluxing technique. The conventional morphology of white cast iron, which is brittle, is eutectic. The mechanical behavior of network white cast iron is attractive. Hardness tests indicate that its average hardness value is ∼770 HV. The indentations made during hardness tests have no cracks. A stylus surface profiler was employed to study the surface profile at and near the indentations. The studies indicate that there are severe plastic flows, but without cracks.
Homoepitaxial Growth of Vertical Si Nanowires on Si(100) Substrate using Anodic Aluminum Oxide Template
Authors: Shimizu Tomohiro , Xie Tian , Schmidt Volker , Nishikawa Jo , Shingubara Shoso , Senz Stephan , Goesele Ulrich
Published: April 2011

Homo-epitaxial growth of Si nanowires on Si (100) substrate was accomplished using a combination of anodic aluminum oxide (AAO) template and Vapor-Liquid-Solid (VLS) growth. We prepared two types of AAO template for epitaxial growth of Si nanowires.

We observed vertically grown epitaxial Si (100) nanowires in the AAO template. In addition, after leaving filled pores, Si nanowires changed their growth direction from [100] to <111>. This result shows that the walls of the pores forced the growth direction of Si nanowires parallel to the direction of the pores, and after complete filling, the growth direction changes to that of the Si nanowires on a bare Si substrate.
Interplay between Morphology and Surface Transport in Nanopatterns Produced by Ion-Beam Sputtering
Authors: Cuerno Rodolfo , Muñoz-García Javier , Castro Mario , Gago Raúl , Vázquez Luis
Published: April 2011

A “hydrodynamic” model has been proposed to describe nanopattern formation and dynamics on amorphous surfaces eroded by ion-beam sputtering (IBS), that relates to descriptions of pattern formation in macroscopic systems such as aeolian sand dunes. At variance with previous continuum models of the morphology of ion-sputtered surfaces, the dynamics of the species that diffuse along the surface is coupled in a natural way to that of the surface height. We report recent results for this model, considering normal and oblique ion incidence, for both fixed and rotating targets, and include comparison to recent experiments on silicon. Effective interface equations can be obtained, that generalize the anisotropic Kuramoto-Sivashinshy equation through additional conserved Kardar-Parisi-Zhang type nonlinear terms. In general dot or ripple patterns form, that later evolve exhibiting complex nonlinear dynamics. Thus, we observe interrupted coarsening behavior such that, for normal incidence, domains of hexagonally ordered structures appear, that compare favorably with those obtained in many experiments of nanodot formation by IBS. In other parameter regions, this short-range ordered patterns coexist with long range disorder and kinetic roughening. For oblique incidence, a ripple pattern is generically obtained that also shows interrupted coarsening and other nonlinear features like non-uniform transverse motion, again reproducing experimental observations.
Fabrication of SnO2 Nano Patterns Using Surface Relief Grating
Authors: Yan Fadong , Li Lian , Huh Pilho , Wang Yanping , Samuelson Lynne A , Kumar Jayant
Published: April 2011

Nano- and micro-structured SnO2 has been widely utilized as gas sensors. These SnO2 based gas sensors are often made by chemical etching, vapor deposition or lithography. Here we report a facile and vacuum-free technique to fabricate large area one-dimensional periodic SnO2 nano arrays using surface relief grating created on azobenzene functionalized polymer thin films as template. Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy characterizations confirmed the successful fabrication of SnO2 nano arrays. The fabricated SnO2 structure exhibited the same periodicity as the template with a width of a few hundred nanometers.
Reversible Nanoscale Local Wettability Modifications by Thermochemcial Nanolithography
Authors: Wang Debin , Okada Takashi , Szoszkiewicz Robert , Jones Simon C , Lucas Marcel , Lee Jungchul , King William P , Marder Seth R , Riedo Elisa
Published: April 2011

Recently, the development of a versatile thermochemical nanolithography (TCNL) technique has been reported. It allows simultaneous control of the local chemistry and topography of thin polymer films. This technique can pattern sub 15 nm chemical and topographical features at the rate of 1.4 mm per second by inducing thermally-activated chemical reactions by means of a heated atomic force microscope (AFM) tip. TCNL is achievable in different environments and can easily be adapted to a variety of substrates and chemical functionalities. Here, we demonstrate that a thin polymer film can be chemically modified twice using TCNL to tune its wettability. We are able to write hydrophilic nanopatterns over a hydrophobic polymer surface upon a first step heating and then revert back to hydrophobic surface by a second step heating. This write-read-overwrite capability is particularly useful in data storage application and complex nanofluidic device design.
Electrostatic-Directed Deposition of Nanoparticles on a Field Generating Substrate
Authors: Tsai De-Hao , Hawa Takumi , Kan Hung-Chih , Phaneuf Raymond J , Zachariah Michael R
Published: April 2011

In this paper we develop a Brownian dynamics model applied to position metal nanoparticles from the gas phase onto electrostatic-patterns generated by biasing P-N junction substrates. Brownian motion and fluid convection of nanoparticles, as well as the interactions between the charged nanoparticles and the patterned substrate, including electrostatic force, image force and van der Waals force, are accounted for in the simulation. Using both experiment and simulation we have investigated the effects of the particle size, electric field intensity, and the convective flow on coverage selectivity. Coverage selectivity is most sensitive to electric field, which is controlled by the applied reverse bias voltage across the p-n junction. A non-dimensional analysis of the competition between the electrostatic and diffusion force is found to provide a means to collapse a wide range of process operating conditions and an effective indicator or process performance.
Characterization of Kinetic Mechanisms of Three-component Photoinitiator Systems for Visible-light Free Radical Polymerizations
Authors: Kim Dongkwan , Stansbury Jeffrey W
Published: April 2011

Three-component photoinitiator systems generally include a light-absorbing photosensitizer (PS), an electron donor and an electron acceptor, which is usually an onium salt. To investigate the key factors involved with visible-light free radical polymerizations of three-component photoinitiators, we used thermodynamic feasibility and kinetic considerations with three-component photoinitiator systems containing either rose bengal (RB) or fluorescein (FL) as the photosensitizer. The Rhem-Weller equation was used to verify the thermodynamic feasibility for the photo-induced electron transfer reaction. Using the thermodynamic feasibility, we suggest three different kinetic mechanisms, which are i) photo-reducible series mechanism, ii) photo-oxidizable series mechanism and iii) parallel-series mechanism.
Novel Applications of the QCM Technique in Biomaterials Science
Authors: Silva Candida Costa , Lin David C , Horkayne-Szakaly Iren , Basser Peter J , Horkay Ferenc
Published: April 2011

A quartz crystal microbalance (QCM) has been used to investigate polymer samples. The vapor sorption of three different polymer samples (poly(vinyl acetate), polybutadiene and polydimethylsiloxane) was studied. The change in resonance frequency of the quartz sensor uniformly coated with polymer films was measured as a function of the film thickness and water absorption at different temperatures. The range of linear frequency vs. mass response was determined in the absence of absorbed water. The glass transition temperature of thin poly(vinyl acetate) films (10 nm <thickness< 1000 nm) was found to be in reasonable agreement with published values for macroscopic samples.
Dynamics and Transport of Molecules in Polymer and Colloidal-Rod Networks
Authors: Kang Kyongok
Published: April 2011

Re-orientational dynamics of liquid crystal molecules in a polymer network subjected to an electric field is studied by means of light diffraction [1]. When the optical pitch of the electric-field induced cholesteric phase is small compared to the optical wavelength of light, dynamic light scattering (DLS) can be performed to extract the relaxation dynamics of the chiral nematic molecules in the presence of the polymer network. Intriguingly, the reactive mesogenic type of polymer network exhibits a confinement effect, which can be probed within the limited range of scattering angles that comply with the structural correlation length in the system [2].

Diffusive mass transport of molecules through a rod network can be studied via fluorescence correlation spectroscopy (FCS) and DLS. Long time self-diffusion of tracer spheres (silica and proteins) in isotropic and nematic colloidal-rod networks (fd-viruses) is systematically studied for various tracer-sphere sizes as compared to the mesh size of the network [3]. In addition, by varying the salt concentration, the relative contribution of electrostatic interactions can be varied. A theory is developed where the diffusion coefficient is expressed in terms of the hydrodynamic screening length of the highly entangled rod-network. The hydrodynamic screening length of rod networks is extracted from diffusion data as a function of the rod concentration both for isotropic and nematic networks [4-5].