bluuebunny/crossref_metadata_2025 huggingface dataset:
Stresses experienced by AlN films grown on sapphire
Authors: Bai Jie , Bai J. , Tassev V.L. , Lal Nakarmi M. , Sun W. , Huang X. , Dudley M. , Zhang H. , F. Bliss D. , Lin J. , Jiang H. , Yang J. , Asif Khan M.
Published: April 2011

The evolution of stress during the MOCVD growth of AlN thin films on sapphire substrates under both low and high temperature conditions has been evaluated. The final stress state of the films is assumed to consist of the summation of stresses from three different sources: (1) the stress which arises from residual lattice mismatch between film and substrate i.e. that which persists after partial relaxation by misfit dislocation formation. The extent of relaxation is determined from High Resolution TEM analysis of the substrate/film interface; (2) the stress arising from the coalescence of the 3D islands nucleated in this high mismatch epitaxy process. This requires knowledge of the island sizes just prior to coalescence and this was provided by AFM studies of samples grown under the conditions of interest; and (3) the stress generated during post-growth cooling which arises from the differences in thermal expansion coefficient between AlN and sapphire. The final resultant stress, comprising the summation of stresses arising from these three sources, is found to be tensile in the sample grown at lower temperature and compressive in the sample grown at higher temperature. These results are in general qualitative agreement with results of TEM and High resolution X-ray diffraction (HRXRD) studies, which show evidence for tensile and compressive stresses in the low temperature and high temperature cases, respectively.
Study of ELOG GaN for Application in the Fabrication of Micro-channels for Optoelectronic Devices
Authors: Rodak Lee E , Berry Ann N J , Kasarla Kalyan Reddy , Yang Nanying , Korakakis D
Published: April 2011

Gallium Nitride (GaN) is a promising wide band gap semiconductor material for many optoelectronic applications, especially in the near UV range. Over the past several years, an extensive technical effort has been focused on improving the quality of GaN films through various overgrowth techniques such as epitaxial lateral overgrowth (ELOG), facet controlled epitaxial lateral overgrowth (FACELO), and Pendeoepitaxy. ELOG has been shown to reduce the density of threading dislocations by up to five orders of magnitude [1], however a complete physical model describing lateral overgrowth is needed in order to take full advantage of the process. A lateral overgrowth model will allow for the design and fabrication of three dimensional structures that can lead to novel devices and also to efficient biosensors by integrating micro and nano channels on the same chip as the optoelectronic components.

A two-step process has been used to successfully control the geometry of overgrown GaN. Conditions have been identified which give a reduced lateral growth rate, in order to allow expansion of the {112n} plane to form vertical sidewalls and for the design of channel width. These geometries are being examined for possible application in laser diode and micro-channel fabrication for integrating bio-agent detection modules.
Environmental Assessment of Micro/Nano Production in a Life Cycle Perspective
Authors: Olsen Stig , Jørgensen Michael Søgaard
Published: April 2011

The concept of life cycle assessment (LCA) is build upon the object of assessment, namely the functional unit, i.e. all impacts etc. are related to a specific service or function in the society. In a LCA context, the assessment of emerging technologies like Nanotechnology is challenging due to a number of knowledge gaps. It may not be known exactly what is the function (or functional unit) or what the technology may substitute and production may still be at an experimental level, raising questions about technology or materials choice.

For prospective LCA studies methodologies like “consequential LCA” may be useful because future changes are taken into account. However, it still does not suffice for emerging technologies. In a recent “Green Technology Foresight” project a methodology was developed based on five elements: Life-cycle thinking, systems approach, a broad dialogue based understanding of the environment, precaution as a principle and finally, prevention as preferred strategy. When assessing emerging technologies three levels should be considered. First order effects are connected directly to production, use and disposal. Second order are effects from interaction with other parts of the economy from more intelligent design and management of processes, products, services, product chains etc. and the effect on the stocks of products. An example could be dematerialisation. Rebound effects may be considered as third order effects, like when efficiency gains stimulate new demands, which balances or overcompensates the savings.

In the Micro/Nano Production area a range of new possibilities arise both within applications, production technology and materials. The Department of Manufacturing Engineering and Management at The Technical University of Denmark has staked on a joint effort in manufacturing engineering and environmental assessment for eco efficiency improvement. A review of knowledge and studies on environmental assessments in the micro/nano technology area is performed and will be used to further detail the general framework for assessment outlined above to be more specific for micro/nano production.
Addressing Environmetal Issues for the Automotive Industry
Authors: Papasavva Stella
Published: April 2011

The integration of environmental, social, and economic (ESE) objectives into business decisions and future planning is the path towards sustainable development. The goal of this paper is to address the environmental component of sustainable development within the automotive industry based on the Life Cycle Analysis and Well-to-Wheels approach.

Life Cycle Analysis (LCA) is very relevant for making the concept of environmental sustainability operational because environmental impacts have to be examined from a 'cradle-to-grave' perspective. Life cycle analysis is an analytical tool that quantifies energy consumption and emissions associated with the raw material extraction, processing of materials, manufacturing, use phase, and end-of-life (reuse, recycling, and disposal) of products. The potential impact of current production and consumption patterns, on the future availability of non-renewable resources, can also be evaluated within the LCA framework. Thus, LCA provides an effective way for industry to support better management of natural resources, in order to maximize economic benefits and minimize environmental burdens.

Well-to-Wheel (WtW) analysis is a subset of a complete LCA because it quantifies the environmental burdens associated only with the fuel production and its consumption during the driving time of a vehicle. Well-to-Wheel studies mainly provide energy use and air emissions inventories.

This paper provides the results obtained from two major studies conducted at General Motors R&D Center. The first is a LCA study that assesses the environmental emissions associated with four alternative automotive paint processes and seven different paint formulations. The second is a WtW study that addresses 18 different combinations of alternative fuels and vehicle engines.

Considering that the use phase of the vehicle contributes more than 80% of its life cycle energy consumption, and that the automotive paint process is the most energy intensive component of the manufacturing phase in any given vehicle, the results presented in this paper are noteworthy for environmental sustainability considerations relevant to the automotive industry.
Hydrogen as Fuel for Urban Transportation Environmental Footprint of Different Hydrogen Production Routes and the Influence on the Total Life Cycle of FC Powered Transportation Systems: An LCA Case Study within CUTE
Authors: Binder Marc , Faltenbacher Michael , Fischer Matthias
Published: April 2011

Fuel cells have the potential to offer an alternative propulsion system to convential internal combustion engines used in transportation at the present time. As a result fuel cells may provide consumers a cleaner and more efficient technology. Fuel cells are powered with hydrogen fuel which can be produced from various energy sources, which include renewable sources of energy or conventional fossil fuel. Thus, the emerging hydrogen infrastructure needs to be addressed carefully.

A consortium of industries, research institutes and several European cities launched the EU-project CUTE (Clean Urban Transport in Europe), whose aim is not only to develop and demonstrate 30 fuel cell busses and the accompanying infrastructure in 10 European cities, but also assess the environmental impacts. Within the project scope the potential of fuel cell powered transport systems for reducing environmental influences such as greenhouse effect, improving the quality of the atmosphere and conserving fossil resources is assessed. This first large scale test run of fuel cell transportation systems is the best possible information base to give real life numbers about environmental impacts of a fuel cell system including hydrogen used as fuel.

Meanwhile the use of hydrogen fuel is mostly considered as environmental friendly. However a statement about the actual environmental impacts is only possible by regarding the entire Life Cycle of the hydrogen, which include its production and use. Within CUTE different routes of the hydrogen production have been assessed: hydrogen production via electrolysis and steam reforming, considering different boundary conditions, e.g. country specific energy production/ supply, different ways for electricity production (e.g. wind power, geothermal energy etc.) etc.

This presentation will show the environmental footprint of these routes (Life Cycle Assessment results), which enable the comparison of the environmental impacts of the different hydrogen production routes and the transportation system considering the total life cycle (production of FC bus, operation and end of life) along with diesel and natural gas as “conventional” fuels for bus operation.
A Life Cycle Analysis of Hydrogen Production for Buildings and Vehicles
Authors: Tupper Kendra , Kreider Jan F
Published: April 2011

Aspects of the hydrogen economy are addressed by quantifying impacts and costs associated with a hydrogen-based energy infrastructure. It is recommended that hydrogen (H2) is produced from Solar Thermochemical (STC) Cycles and Wind Electrolysis, with the possible use of Steam Methane Reforming (SMR) to aid in the creation of a hydrogen infrastructure. Despite high impact assessment results from SimaPro, the external costs associated with Biomass gasification are shown to be comparable with those for Wind Electrolysis. Thus, biomass-produced hydrogen could also be a viable alternative, especially in areas ideally suited to the growth of energy crops. Finally, the most influential life cycle stages are the Construction of the FCV and Hydrogen Production (except for the environmentally benign wind electrolysis). For the Wind/Electrolysis case, the majority of impacts come from plant construction.
Grinding and Separation of The Cellular Phone Housing
Authors: Jung Woo-Hyuk , Tortorella Nathan , Beatty Charles L. , McCarthy Stephen P.
Published: April 2011

The front covers of Motorola cellular phone housings, which were composed of 62.2 wt% of polycarbonate (PC) /acrylonitrile-butadiene-styrene (ABS), were ground and separated from the undesired materials using sink-float methods. The sink-float methods in water and salt were used to remove the floating materials such as the adhesive strips and the foams, and to separate the metal parts where the recovery ratios were 92.8 and 40.5 %, respectively. The separation of residual wires and button rubbers, which could not be done by the sink-float process in water, was preformed using V-Stat Triboelectric Separator (Outokumpu Technology) of a roll separator that also provided the effective methods to separate the ground metals that had existed in the printed circuit boards where the recovery weight ratio of metal parts was 19 wt%. The separated PC/ABS’s could be compounded with the ground circuit boards or the thermoplastic elastomer called Engage®, or the reactive species of glycidyl methacrylate (GMA).
Guiding the design and application of new materials for enhancing sustainability performance: Framework and infrastructure application
Authors: Keoleian Gregory , Kendall Alissa M , Lepech Michael D , Li Victor C
Published: April 2011

This paper presents a framework for guiding the design of new materials to enhance the sustainability of systems that utilize these materials throughout their production, use and retirement. Traditionally, materials engineering has focused on the interplay between material microstructure, physical properties, processing, and performance. Environmental impacts related to the system’s life cycle are not well integrated into the materials engineering process. To address this shortcoming, a new methodology has been developed that incorporates social, economic, and environmental indicators – the three dimensions of sustainability. The proposed framework accomplishes this task and provides a critical tool for use across a broad class of materials and applications. Material properties strongly shape and control sustainability performance throughout each life cycle stage including materials production, manufacturing, use and end-of-life management. Key material parameters that influence life cycle energy, emissions, and costs are highlighted. The proposed framework is demonstrated in the design of engineered cementitious composites, which are materials being developed for civil infrastructure applications including bridges, roads, pipe and buildings. This research is part of an NSF MUSES (Materials Use: Science, Engineering and Society) Biocomplexity project on sustainable concrete infrastructure materials and systems (http://sci.umich.edu).
On-Chip Initiation and Burn Rate Measurements of Thermite Energetic Reactions
Authors: Apperson Steven , Bhattacharya Shantanu , Gao Yuanfang , Senthil Subramanian , Hasan Shameem , Hossain Maruf , Shende Rajesh , Redner Paul , Kapoor Deepak , Nicolich Steven , Gangopadhyay Keshab , Gangopadhyay Shubhra
Published: April 2011

Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses.
Energy Release Characteristics of Impact-Initiated Energetic Materials
Authors: Ames Richard
Published: April 2011

Impact-initiated energetic materials are a class of energetic materials that are formulated to release energy under highly dynamic loads. Under quasi-static or static loads, however, the materials are intended to be inert and carry a material classification of 4.1 flammable solid. In general, these materials are formed by introducing metal powders into a polymer binder but a number of binderless varieties exist (primarily pressed/sintered intermetallics and thermites). Most of the materials are sufficiently insensitive so as not to produce a self-sustaining reaction; as such, they require the mechanical work of a high-strain-rate plastic deformation process to provide the energy required to drive the reaction. Traditional initiation techniques such as exploding bridge wires or flame initiation are not sufficient to maintain a reaction in this class of materials. This paper presents a brief overview of the energy release characteristics of this class of materials, including a discussion of the material formulations, initiation phenomena, and a discussion of the manner in which the material properties affect the energy release characteristics.
Influence of Activating Compounds on Oxidation Mechanisms of Aluminum Powders
Authors: Johnson Curtis , Foley Timothy J. , Higa Kelvin T.
Published: April 2011

This study involves an investigation of the mechanism underlying activating effects of inorganic additives on the oxidation of aluminum. The oxidation of nano aluminum powders in air was characterized by variable temperature x-ray powder diffraction and thermogravimetric analysis. For a 33-nm aluminum powder the aluminum oxide produced by air oxidation was poorly crystallized until the sample was heated to above 1050°C, where the alpha-alumina phase crystallized. For a mixture of the aluminum with cryolite, crystallization of oxide phases is enhanced, with Na-Al-O phases evident at 550°C and above. Fluorine is lost from the sample between 550 and 850°C, presumably due to reaction with moisture to produce HF. In a similar experiment with aluminum and silver molybdate, the only crystalline product was alpha-alumina, which was observed at 550°C and higher. The general result is that alpha-alumina, the ultimate product in most cases, crystallized at a lower temperature when activating agents were present.
Melting and Oxidation of Nanometer Size Aluminum Powders
Authors: Trunov Mikhaylo A , Umbrakar Swati , Schoenitz Mirko , Mang Joseph T , Dreizin Edward L
Published: April 2011

Recently, nanometer-sized aluminum powders became available commercially and their use as potential additives to propellants, explosives, and pyrotechnics has attracted significant interest. It has been suggested that very low melting temperatures are expected for nano-sized aluminum powders and that such low melting temperatures could accelerate oxidation and trigger ignition much earlier than for regular, micron-sized aluminum powders. The objective of this work was to investigate experimentally the melting and oxidation behavior of nano-sized aluminum powders. Powder samples with three different nominal sizes of 44, 80, and 121 nm were provided by Nanotechnologies Inc. The particle size distributions were measured using small angle x-ray scattering. Melting was studied by differential scanning calorimetry where the powders were heated from room temperature to 750 °C in argon environment. Thermogravimetric analysis was used to measure the mass increase indicative of oxidation while the powders were heated in an oxygen-argon gas mixture. The measured melting curves were compared to those computed using the experimental particle size distributions and thermodynamic models describing the melting temperature and enthalpy as functions of the particle size. The melting behavior predicted by different models correlated with the experimental observations only qualitatively. Characteristic step-wise oxidation was observed for all studied nanopowders. The observed oxidation behavior was well interpreted considering the recently established kinetics of oxidation of micron-sized aluminum powders. No correlation was found between the melting and oxidation of aluminum nanopowders.
Patterning PETN and HMX using Dip Pen Nanolithography
Authors: Nafday Omkar , Weeks Brandon , Haaheim Jason , Eby Ray
Published: April 2011

Recently there has been a focused effort to develop reliable nanoscopic writing and reading capabilities. Dip-pen nanolithography (DPN) has emerged as a convenient method to deliver nanoscale materials onto a substrate by leveraging scanning probe microscopy capability. A new application for the DPN method is the field of microdetonics which is the microscale decomposition and study of reactions of explosives. Results are presented for patterning pentaerythritol tetranitrate (PETN) and cyclotetramethylene tetranitramine (HMX) on silicon and mica substrates. The ultimate goal is to pattern both energetic materials in nanoscale registry and investigate their reaction and decomposition at the nanoscale due to heating or shock initiation. In addition to patterning of high explosives, a discussion on the effect of surface energy on patterning rates is investigated. This knowledge will be applicable to inks beyond high explosives.
Understanding the Structure of the Mammalian Mineralised Tissues Through Their Development
Authors: Boyde Alan
Published: April 2011

Most aspects of the structure and composition of the principal mineralised tissue types [in teeth = enamel, dentine and cementum; in bone organs = woven and lamellar and extrinsic (Sharpey) fibre bone and calcified growth plate cartilage and articular calcified cartilage and calcified fibrocartilage and calcified ligament or tendon] and of the all-important junctions between them can be best understood from a knowledge of developmental mechanisms and the rules and constraints that these generate. We should consider the interface between formative cells and the organic matrices where these are secreted by an appositional mechanism; possible influences of cell movements; mineral crystal orientation and size and maturation; junctions formed by simple apposition of one tissue upon another; junctions involving a prior resorptive (partial destruction and 'etching') step; and interstitial matrix expansion, NB in cartilage.
Crush Absorbing Energy of White Spot Lesion Measured by Indentation Tests
Authors: Fallgatter Alison M. , Ko Ching-Chang , Chou C-H
Published: April 2011

White spot lesions are clinically detectable areas of demineralized enamel that often form during orthodontic treatment. Fluoride has been shown to prevent demineralization from occurring. Mechanical properties of white spot lesions are not well characterized. Bovine enamel slabs, with and without fluoride treatment, were placed under demineralization conditions. Through a series of microindentations at incremental loads, mechanical strength was measured using a novel method, SVAE. Specific Volume Absorbing Energy (SVAE) is equal to work energy divided by the indentation volume. The supra-surface area (outmost 5 μm) of enamel slabs with fluoride demonstrated decreased mechanical strength compared to those without fluoride. Fluoride may not impart protection over long periods of demineralization.
Multi-scale Characterization and Modelling of Human Cortical Bone
Authors: Ho Ba Tho Marie-Christine , Stolz Claude , Vanleene Maximilien , Bensamoun Sabine , Treutenaere Jean-Marc , Rey Christian
Published: April 2011

Mechanical properties of cortical human bone have been investigated for more than over three decades. The objectives of the present study were 1) to investigate the influence of multiscale structural characteristics of the bone tissue on its mechanical behavior and 2) to perform a micro-macro numerical modelling based on the experimental data. It should be noted that variations of the osteon lamellae elastic properties are higher (40%) at the microstructural level than those found at the macroscopic level (about 15%) for measurements performed in the same anatomical direction. Physico-chemical analyses found that organic components were found to be higher for femurs exhibiting lower mechanical properties. There is a consistency between changes observed at the different levels. These results contribute to a basic understanding of the multiscale mechanical behavior of human cortical bone.
Microaligned collagen matrices by hydrodynamic focusing: controlling the pH-induced self-assembly
Authors: Köester Sarah , Leach Jennie B , Pfohl Thomas , Wong Joyce Y
Published: April 2011

The hierarchical structure of type I collagen fibrils is a key contributor to the mechanical properties of the extracellular matrix (ECM). It is known that the process of in vitro fibrillogenesis strongly depends on the pH of the collagen solution. To date, there are few methods available for precisely controlling and investigating the dependence of collagen fibril assembly on the local pH. The objective of this work was to create highly defined pH gradients to systematically determine the effects of local pH on microscale collagen fibrillogenesis and alignment. We use a microfluidic mixing device to create a diffusion controlled pH gradient, which in turn initiates the self-assembly and concurrent flow-alignment of soluble collagen. Finite element method simulations of the hydrodynamic and diffusive phenomena are used to calculate the local concentrations of the components involved in the reaction. We develop a model to analytically calculate the local pH in the microfluidic device from these concentrations. A comparison with the experimental results from polarized light microscopy are in good agreement with the simulations.
Atomistic modeling of elasticity, plasticity and fracture of protein crystals
Authors: Buehler Markus J.
Published: April 2011

The structure and behavior of proteins plays an overarching role in determining their function in biological systems. In recent years, proteins have also been proposed as basis for new materials to be used in technological applications (Langer and Tirrell, Nature, 2004). It is known that protein crystals show very interesting mechanical behavior, as some of them are extremely fragile, while others can be quite sturdy. However, unlike other crystalline materials like silicon or copper, the mechanical properties of protein crystals have rarely been studied by atomistic computer modeling. As a first step towards more fundamental understanding of the mechanics of those materials, we report atomistic studies of mechanical properties of protein crystals using empirical potentials focusing on elasticity, plasticity and fracture behavior. Here we consider the mechanics of a small protein α-conotoxin PnIB from conus pennaceus. We use large-scale atomistic simulations to determine the low-strain elastic constants for different crystallographic orientations. We also study large-strain elastic properties including plastic deformation. Furthermore, we perform systematic studies of the effect of mutations on the elastic properties of the protein crystal. Our results indicate a strong impact of mutations on elastic properties, showing the potential of mutations to tailor mechanical properties. We conclude with a study of mode I fracture of protein crystals, relating our atomistic modeling results with Griffith's theory of fracture.
Mechanical stability of collagen fibril networks
Authors: Shaw Gordon , McDaniel Dennis , Elliott John , Tona Alessandro , Plant Anne
Published: April 2011

Thin films of type 1 collagen fibril networks fabricated on alkanethiol-functionalized surfaces have been previously shown to provide an excellent protein matrix for cultured cells in applications such as drug toxicity studies and studies of cell signaling pathways. Cell phenotypic parameters, including cell morphology and rate of proliferation, can depend on the processing conditions used for fabrication of the protein films. The mechanical characteristics of the collagen fibril network appear to be particularly important, and as such, understanding the mechanical properties of individual fibrils, as well as their interactions with each other and the underlying substrate is critical for assuring a predictable response from cells. In this study, scanning probe microscopy and instrumented indentation are used in conjunction with small force metrology to examine the mechanical properties of these collagen fibrils and fibril networks.
Directed Assembly of Nanoelements Using Electrostatically Addressable Templates
Authors: Xiong Xugang , Makaram Prashanth , Bakhtari Kaveh , Somu Sivasubramanian , Busnaina Ahmed , Small Jason , Mcgruer Nick , Park Jingoo
Published: April 2011

Directed assembly of nanoparticles and single wall carbon nanotubes (SWNTs) using electrostatically addressable templates has been demonstrated. Nanoparticles down to 50 nm are assembled on the Au micro and nanowires of the templates in a DC and AC electric fields. The nanoparticles can be assembled in monolayers and thicker layers. Single wall carbon nanotubes (SWNTs) are also assembled without alignment on Au wires using the nanotemplate. As the size of the template wires is reduced to nanoscale dimensions, an AC electric field proves to be more effective for nanoparticle assembly than a DC electric field.
Nano-Structured Beta-Gallia-Rutile Surfaces as Substrates for DNA Self-Assembly
Authors: Empie Nathan , Edwards Doreen
Published: April 2011

A nano-structured beta-gallia-rutile (BGR) substrate capable of binding DNA was synthesized. Beta-gallia groups diffuse into [001] single crystal rutile along {210}rplanes, generating hexagonally shaped tunnel sites between the beta-gallia subunits (repeating ∼1 nm). The tunnel sites, approximately 2.5 Å in diameter, are preferred regions for cation incorporation. Divalent cations have been used previously to adsorb DNA to mica surfaces. For the BGR system, the site selectivity of the cations for tunnel sites could lead to controllable / tailor-able DNA adsorption. DNA buffers containing Cu (II), Fe (II), and Ni (II) cations were deposited on BGR substrates. The DNA adsorption was investigated with tapping mode atomic force microscopy (AFM) to determine the suitability of using BGR substrates as a means to self assemble DNA constructs for nano-electronic applications. At the concentrations tested, only solutions containing Ni (II) ions were capable of binding DNA sufficiently for AFM imaging; there was no evidence of site specific attachment.
Nanotubes in spray deposited Nanocrystalline HgTe: I thin films
Authors: Arnepalli Ranga Rao , Viresh Dutta
Published: April 2011

HgTe nanotubes have been prepared by spray deposition of solvothermally synthesized iodine doped HgTe nanoparticles on glass substrates at low temperature (200°C). Spray deposition was done without voltage and with an externally applied voltage (700 V) to the nozzle and it is found from TEM studies that the length of the nanotubes increases from ∼4µm in case of without voltage to ∼ 6µm in case of the applied voltage, with an average diameter of ∼ 45nm. The nanotubes are found to have cubic lattice structure having Hg:Te in stoichimetric ratio (52:48).
Nucleation of Semiconductor Quantum Dots on Nanomesas: Role of Stressors and Early Stages of Capping Process
Authors: Meynier Cyril , Priester Catherine
Published: April 2011

Here is reported, from the theoretical point of view, how a stressor layer included in a nanomesa can modify the growth process of a mismatched material : critical thickness for 2D-3D transition, and optimal location of nucleating dots by means of the induced stress field. This stress field depends on both design parameters and sign of the misfit between the stressor and the mesa material. This is exemplified by the case of InAs deposition on InP mesas which include an InGaAs stressor. A second case in which stress field plays a key role is the capping of dots on top of nanomesas . We investigate the case of Si capping of a system where one Ge dot covers the top of each mesa of a very dense array of Si nanomesas. Upon several basic assumptions, different capping processes are simulated, in order to predict the more stable one. We point out very different behaviors for pure Si capping or SiGe capping. How long it takes for recovering a flat surface strongly depends on the presence of a thin Ge surface layer.
“Smart” Defects in Colloidal Photonic Crystals
Authors: Fleischhaker Friederike , Arsenault André C. , Tétreault Nicolas , Wang Zhuo , Kitaev Vladimir , Peiris Frank , Mihi Agustin , Miguez Hernan , von Freymann Georg , Manners Ian , Zentel Rudolf , Ozin Geoffrey A.
Published: April 2011

We present a bottom-up approach for the construction of "Smart" active defects in colloidal photonic crystals (CPCs). These structures incorporate polyelectrolyte multilayer (PEM) planar defects embedded in silica CPCs through a combination of evaporation induced self-assembly and microcontact transfer printing. We show how the enormous chemical diversity inherent to PEMs can be harnessed to create chemically active defect structures responsive to solvent vapor pressures, light, temperature as well as redox cycling. A sharp transmission state within the photonic stopband, induced by the PEM defect, can be precisely, reproducibly and in some cases reversibly tuned by these external stimuli.

These materials could find numerous applications as optically monitored chemical sensors, adjustable notch filters and CPC-based tunable laser sources.
Patterning of Single-Walled Carbon Nanotubes Using Wet Chemical Self-Assembling and Photolithographic Technique
Authors: Jung Myung-Sup , Jung Sung-Ouk , Jung Hee-Tae , Kim Do Yun , Doo Seok Gwang
Published: April 2011

Single-walled carbon nanotubes (SWNTs) have been chemically attached with high density onto a patterned substrate. To form the SWNT pattern, the substrate was treated with acid-labile group protected amine, and an amine prepattern was formed using a photolithographic process with a polymeric photo acid generator. The SWNT monolayer pattern was then formed through the amidation reaction between the carboxylic acid groups of carboxylated SWNTs (ca-SWNTs) and the prepatterned amino groups. A high-density multilayer was fabricated via further repeated reaction between the carboxylic acid groups of the ca-SWNTs and the amino groups of the linker with the aid of a condensation agent. Scanning electron microscopy results show that the patterned SWNT films have uniform coverage with high surface density.
Photochemical Metal Organic Deposition of Patterned Nanostructured Oxide Films
Authors: Zhang Xin , Hill Ross
Published: April 2011

In this paper, we present examples of the use of photochemical metal organic deposition to form nanostructured metal oxide films. In the first example, we use two reactions with very different reaction rates to control the nanostructuring, utilizing tantalum (V) tetraethoxide acetylacetonate (as a thermally reactive source of tantalum oxide) and manganese (II) 2-ethylhexanoate (as a photochemically reactive source of manganese oxide). We prepare homogeneous precursor films of tantalum (V) tetraethoxide acetylacetonate and manganese (II) 2-ethylhexanoate and in the dark allow the tantalum complex to react forming tantalum oxide regions. The film is then exposed and the manganese complex is converted to a matrix surrounding the tantalum regions. The resultant structures are characterized by electron microscopy, energy dispersive X-ray spectroscopy and Auger spectroscopy. In the second example, we use two immiscible precursors, zirconium (IV) 2-ethylhexanoate and yttrium nitrate hexahydrate to form nanostructured precursor films. The nanostructuring of these films is apparent from SEM studies. Exposure of these films results in the formation of nanostructured films consisting of a zirconium oxide matrix with encapsulated yttrium oxide.
Bi-directional porous alumina templates for nanowire field-effect transistors
Authors: Wade Travis L. , Hoffer Xavier , Dayen Jean-Francois , Mohammed Al Dughaim , Humel Fahad , Wegrowe Jean-Eric
Published: April 2011

Using readily available materials and equipment we are able to sculpture aluminium wires into cylindrical, bi-directional templates for the synthesis and contacting of nanowires as field-effect transistors. The nanowire template is made by partial anodization of the wire perpendicular to its axis as an isolating layer for a gate electrode, vapour deposition of a metal on this layer as a gate, cutting the wire perpendicular to its axis, and finally anodizing the newly exposed area parallel to the wire axis as a template for nanowires. This results in a nanowire template surrounded by a gate electrode that is isolated from the template by the first anodisation layer.

The utility of this structure is demonstrated by a ZnO nanowire field-effect transistor. The ZnO was made by electrodeposition of Zn nanowires in the interior nanoporous template during which an anodic pulse was applied to form a layer of ZnO in the middle of the zinc nanowires. The IV and transfer plots indicate that the ZnO is p-type in depletion mode.

This 3-D transistor is unique in that it can be totally fabricated in a beaker without the need for costly clean room and lithography facilities. The ease and low cost of this new approach to nanodevices will have the effect of liberating nanoscience for scientists of moderate means. As a result this will open nanoscience to new ideas and more inputs.
A Chemical Approach to 3-D Lithographic Patterning of Si and Ge Nanocrystals
Authors: Sharp I. D. , Xu Q. , Yi D. O. , Liao C. Y. , Ager III J. W. , Beeman J. W. , Yu K. M. , Robinson J. T. , Dubon O. D. , Chrzan D. C. , Haller E. E.
Published: April 2011

Ion implantation into silica followed by thermal annealing is an established growth method for Si and Ge nanocrystals. We demonstrate that growth of Group IV semiconductor nanocrystals can be suppressed by co-implantation of oxygen prior to annealing. For Si nanocrystals, at low Si/O dose ratios, oxygen co-implantation leads to a reduction of the average nanocrystal size and a blue-shift of the photoluminescence emission energy. For both Si and Ge nanocrystals, at larger Si/O or Ge/O dose ratios, the implanted specie is oxidized and nanocrystals do not form. This chemical deactivation was utilized to achieve patterned growth of Si and Ge nanocrystals. Si was implanted into a thin SiO2 film on a Si substrate followed by oxygen implantation through an electron beam lithographically defined stencil mask. Thermal annealing of the co-implanted structure yields two-dimensionally patterned growth of Si nanocrystals under the masked regions. We applied a previously developed process to obtain exposed nanocrystals by selective HF etching of the silica matrix to these patterned structures. Atomic force microscopy (AFM) of etched structures revealed that exposed nanocrystals are not laterally displaced from their original positions during the etching process. Therefore, this process provides a means of achieving patterned structures of exposed nanocrystals. The possibilities for scaling this chemical-based lithography process to smaller features and for extending it to 3-D patterning is discussed.
Morphology Control of ZnO Nanomaterials using Double Hydrophilic Block Copolymers
Authors: Mezy A. , Gérardin C. , Tichit D. , Suwanboon S. , Ravot D. , Jean-Claude Tedenac , Bretagnon T. , Lefèbvre P.
Published: April 2011

Highly crystalline zinc oxide (ZnO) nanomaterials are synthesized using a seeded growth sol-gel method. In order to control the morphology and the organization of the ZnO nanomaterials, a double hydrophilic block copolymer has been introduced during the seeded growth synthesis: the Polyacrylic acid-Polyacrylamide (PAA-PAM). Depending on the amount of PAA-PAM copolymers, different morphologies were obtained, such as ZnO nanostructured spheres or flat hexagonal crystals. Thus, systematic studies have been done to investigate the influence of the copolymer addition on ZnO nanomaterial morphologies and explain the mechanisms of the morphological modifications.
Analysis of plasma for carbon nanotube growth by plasma-enhanced chemical vapor deposition
Authors: Ozeki Atsushi , Suda Yoshiyuki , Okita Atsushi , Nakamura Junji , Oda Akinori , Sakai Yosuke , Sugawara Hirotake
Published: April 2011

Optical emission spectra of a CH4/H2/Ar gas mixture plasma were observed during carbon nanotube (CNT) growth in RF plasma-enhanced chemical vapor deposition. CNTs with diameters of ∼10-30 nm and length of ∼6 μm were grown on double- and triple-layered films of catalyst/support materials (FexOy/TiO2 and Al2O3/FexOy/Al2O3) at the total gas pressures of 1-10 Torr with gas flow rates of CH4 = 27 sccm, H2 = 3 sccm, and Ar = 1 sccm. The number density of CNTs increased with the gas pressure, and Al2O3/FexOy/Al2O3 (each thickness of 1 nm) film yielded the thinnest CNTs with a high number density among the present catalysts. The spatial distributions of H atom relative density in the plasma were obtained by actinometry. The H relative density decreased with the pressure, and this suggests the suppression of CH3 radical generation in the plasma.
Phase Equilibria Studies of Hf44.5Ti5Cu27Ni13.5Al10 and Hf44.5Nb5Cu27Ni13.5Al10
Authors: Woodman Robert , Kecskes Laszlo
Published: April 2011

We report the equilibrium phase assemblage of two bulk-metallic-glass-forming alloys, Hf44.5Ti5Cu27Ni13.5Al10 and Hf44.5Nb5Cu27Ni13.5Al10. Using thermal analysis, scanning electron microscopy, and x-ray microanalysis, we examined the phase equilibria of the major components - Hf, Cu, and Ni. We then examined the effect of additions or substitutions of Nb, Ti, and Al on equilibrium phase assemblage and melting behavior.
Processing and Properties of Nanostructured Alloy Coatings in the Binary Ni-Cr System
Authors: Castro Pablo , Schuh Christopher A. , Liang Hong
Published: April 2011

Using a scalable electrodeposition process, nanocrystalline Ni-Cr alloy coatings have been produced on copper and steel substrates, and the roles of various processing variables on the resulting coating structure and properties have been investigated. The possibility of producing composite coatings of wear resistant nanostructured Ni-Cr alloys containing graphite or MoS2 particles has also been studied; the co-deposition of solid lubricant particles improved the tribological performance of the coatings in ball-on-disk testing. The combination of a hard material such as nanocrystalline Ni-Cr alloy with a solid lubricant has a great potential for new surface modification developments.
The Effect of As-quenched Structure on Primary Phase Crystallization in Amorphous Aluminum Alloys
Authors: Hamann Joseph , Perepezko John H
Published: April 2011

From the reported experience, primary nanocrystallization in amorphous Al alloys involves transient kinetic behavior that is sensitive to the initial as-quenched structural arrangements. In order to examine the precursor effects, systematic studies outlining the evolving growth kinetics of primary aluminum nanocrystals (nc) during pre-crystallization annealing treatments, and investigations on the microstructure refining effect of specific alloying substitutions represent new approaches for an analysis of primary phase crystallization kinetics. In Al88Ni8Sm4 melt-spun ribbon (MSR), incremental substitutions of Cu for Ni (0 − 1at%) affect the thermal stability of the material (crystallization onset shifts to lower temperature) and refine the size of the primary phase nanocrystals. However, continuous heating calorimetry measurements indicate that the primary crystallization enthalpy remains approximately constant with increased Cu substitution. From a structural analysis standpoint, quantitative microstructure examinations applied in parallel with calorimetry measurements have been employed to characterize the as-quenched volume of MSR samples. The increased primary Al nanocrystal particle density with Cu substitution reflects the modification of local structural arrangements, necessitating an understanding of the local structure of the as-quenched sample in order to develop a description of primary phase nanocrystal growth kinetics.
Binormal Nanohelices
Authors: da Fonseca Alexandre F. , Galvao Douglas S. , Malta Coraci P.
Published: April 2011

Helical structures can be classified in accordance with the orientation of its cross-section with respect to the normal or binormal vectors. We investigate the geometric features of several nanosprings verifying the non-existence of normal nanohelices. In this work, using the VLS growth model, we explain not only the absence of normal nanosprings but also the growing process of binormal nanosprings. The dynamical stability of crystalline ZnO binormal nanohelices is also addressed.
A Study on the Tribological Properties of DLC Films Deposited with Different Reaction Gases
Authors: Cho Yong Ki , Kim Gang San , Moon Kyoung Il , Kim Sang Gweon , Kim Sung Wan
Published: April 2011

Diamond like carbon (DLC) coatings have attracted great attention for use in various applications in automobile industry and machinery because they have excellent properties such as low friction coefficient and ultra high strength. The low friction coefficient of DLC comes from anti-adhesion with other materials, smooth surface, lubrication of graphite structure at the contacting point of films, and the hydrogen content of the films. Many researches have been focused on the microstructure effects on the tribological properties of DLC films but few have been reported on the effect of hydrogen content. In this study, the effect of hydrogen content on the friction coefficient of DLC films has been investigated.

DLC films have been deposited on D2 steel by plasma enhanced CVD (Pulsed DC PECVD) method with different precursor gas of C2H2and CH4and different gas pressure. The effects of gas composition on the hydrogen content in DLC films and the resulting tribological properties have been reviewed. Si interlayer was deposited on D2 to improve adhesion of DLC on steel substrates. The characteristics of microstructure were evaluated by Raman spectroscope and composition was measured by RBS and EDS. The tribological behaviors of DLC films were investigated using ball on disk tribometer. The hardness of films was examined by nano-indenter. The failure mechanism of DLC deposited on steel substrates was examined using optical microscope and SEM/EDS. The results showed that the friction coefficient of DLC films deposited with C2H2was 0.06 and that of the film with CH4was 0.15. The friction coefficient improved with decreasing hydrogen content in DLC films.
The Role of Multiple Polytypes in Determining the Catastrophic Failure of Boron Carbide at High Shock Velocities
Authors: Fanchini Giovanni , McCauley James W , Niesz Dale E , Chhowalla Manish
Published: April 2011

The absence of a plastic phase in boron carbide and its failure at shock impact velocities just above the Hugoniot elastic limit (HEL) has been a puzzle for a long time. In the present work, using self-consistent field density functional simulations we are able to account for many experimental observations by noticing that several boron carbide polytypes [(B11C)C2B, (B12)C3, etc …] coexist without significant lattice distortions. Our analysis also indicates that above a threshold pressure all the candidate microstructures are less stable than a phase involving segregated boron (B12) and amorphous carbon (a-C) but the energetic barrier between boron carbide and B12 + 3C, is by far lower for the B12(CCC) microstructure, requiring the lowest atomic displacement for a transformation B4C→3B+a-C, occurring at pressures of 6 GPa = P(HEL). For such a configuration, segregation of free carbon occurs in layers orthogonal to the (113) lattice directions, in excellent agreement with recent transmission electron microscopy (TEM) analysis
Preparation and Nanoindentating mechanical Analyses of Porous SiO2 Low-Dielectric-Constant Films
Authors: Chang Shou-Yi , Huang Yi-Chung , Yang Bo-Kang
Published: April 2011

Porous SiO2 low-dielectric-constant films containing different porosities and sizes of pores were prepared in this study. Their mechanical properties were analyzed by a nanoindentation test. The hardness and elastic modulus of the films prepared with an ethanol molar ratio of 3 and an aging time of 16 hours reached maximum values of 2.4 and 40 GPa, respectively. With a higher ethanol ratio, the porosity increased, and the mechanical properties consequently decreased. With increasing aging time, the mechanical properties increased and then dropped due to enlarged pore sizes. The porous SiO2 films were found to yield at an ultimate stress of 3.1 GPa, and the maximum fracture energy release rate was calculated as 3.4 J/m2. The deformation and fracture behavior was observed through crack initiation and propagation along the large amount of pores.