bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Characterization and Morphology Control of Electrospun Nanofibers of Pani/Pmma Blends
Authors: Desai K. , Sung C.
Published: April 2011

Electrospinning derived from electro spraying is a process by which sub-micron polymer fibers can be produced using an electrostatically driven jet of polymer solution. The fibers are collected as non-woven mat and offer a high surface to volume ratio. Polyaniline is an organic conducting polymer and can be used to fabricate conducting nano fibers by blending with suitable polymers like poly methyl methacrylate. In this present work we have explored the effects of electrospinning parameters on the formation of PANI/PMMA fibers and the phase morphology of the electrospun fibers using advanced electron microscopy and scanning probe microscopy techniques.
Self assembled gold and silver nanoparticulates on silicon nanotips as surface enhanced Raman active substrates
Authors: Chattopadhyay S. , Lo H. C. , Chen K. H. , Hsu C. H. , Chen L. C.
Published: April 2011

Silicon nanotips, grown via electron cyclotron resonance plasma chemical vapour deposition, with apex diameters of ∼2nm and lengths of 1000 nm and densities of 1011/cm2 were used as a new substrate for surface enhanced Raman spectroscopy. Ion beam sputtered gold and silver self assemble on these substrates as nanoparticulates of 4–10 nm diameter and these metallic nanoparticulates assist in the surface enhancement of Raman signals of analytes. Molecules such as Rhodamine 6G and bis-Pyridyl ethylene of varied concentrations, in the range of 10-6-10-10 M, has been studied on these substrates and enhancements in the range of 106-108 were observed.
Growth of Carbon Nanotubes Using Uniformly Distributed Cobalt Nanoparticles as Catalyst: Controlled Growth and Structural Characterization
Authors: Huh Yoon , Lee Jeong Yong , Choi Sang Kyu , Lee Cheol Jin
Published: April 2011

We have controllably grown carbon nanotubes using uniformly distributed cobalt nanoparticles as catalyst. Cobalt nanoparticles with a uniform size were synthesized by chemical reaction and colloidal solutions including the cobalt nanoparticles were prepared. The cobalt nanoparticles were uniformly distributed on silicon substrates by a spin-coating method. Carbon nanotubes with a uniform diameter were synthesized on the cobalt nanoparticles by thermal chemical vapor deposition of acetylene gas. The density and vertical alignment of carbon nanotubes could be controlled by adjusting the density of Co nanoparticles.
Incorporation of Functional Metal Oxide Materials in Chemical Microsystems
Authors: Yao Nan , Yeung King Lun
Published: April 2011

TiO2-SiO2 aerogel with various TiO2 contents was successfully deposited into a microchannel. SEM, XPS and liquid-phase photocatalytic oxidation reaction of phenol were used to examine the TiO2-SiO2 aerogel's microstructure and reactivity. The TiO2 content has a significant effect on the aerogel network and its adhesion on the microchannel. High open and cross-linking or ordered macroporous structure can be formed in TiO2-SiO2 aerogels with lower TiO2 content (5wt% or 10wt%). The conversion of phenol is around 36.6% during the reaction when this aerogel incorporated microchannel is used as microreactor.
Nanocrystalline Mixed Metal Oxides – Novel Oxygen Storage Materials
Authors: Sarkas Harry , Murray Patrick G. , Fay Aaron , Brotzman R. W.
Published: April 2011

Nanophase Technologies Corporation (NTC) employs a new physical vapor synthesis technique to manufacture ceria-based mixed rare earth oxide nanomaterials. The mixed rare earth oxide nanoparticles are nonporous, dense, discrete crystals. The compositions are solid solutions that remain thermally stable to above 1050°C.

Ceria is an active oxygen storage material. Doping ceria with other rare earth metals enhances the thermal stability of nanocrystalline particle size and increases the oxygen storage capacity (OSC). The mean particle size and OSC of ceria-based mixed rare earth oxides are presented as a function of particle composition, morphology, and thermal history.

These materials are commercially available and are being engineered for several applications including oxygen storage catalysts and polishing materials.
The Use of Mesoporous Systems for Preparation of One-Dimensional Ordered Magnetic Nanowires
Authors: Eliseev Andrei A. , Napolskii Kirill S. , Gorozhankin Dmitry F. , Lukashin Alexei V. , Tretyakov Yuri D. , Grigorieva Natalia A. , Grigoriev Sergei V. , Vorobieva A. A. , Görnert Peter
Published: April 2011

Here we report the synthesis and investigation of iron and iron oxide nanowire arrays using mesoporous silica as a host material. In the present work a novel variant of synthesis of ordered magnetic nanowires in the mesoporous silica matrix was suggested. The method is based on the incorporation of a hydrophobic metal compound into the hydrophobic part of silica-surfactant composite. The amount of iron intercalated into the mesoporous matrix was measured by chemical analysis. In all samples it corresponds well to with the molar ratio SiO2: Fe = 9:1. To provide crystallinity of nanowires additional thermal treatment was performed. Thus prepared nanocomposites were characterized by TEM, ED, SAXS, SANS, BET and magnetic measurements. The anisotropy parameters of nanowires were determined using two non-correlated methods: temperature dependence of magnetic susceptibility and small angle polarized neutron scattering. It was found that the particle length increases with the increasing of the decomposition temperature of the metal complex. Obviously it deals with crystallization and growth of metal particles inside the pores at a constant diameter of a single particle. For iron containing sample annealed at 375 °C (form factor of nanowire is about 40), the coercive force at room temperature was found to be 145 Oe at saturation magnetization of 1.2 emu/g, which is not far from modern information storage. It was shown that particles shape and size are in good agreement with that of the pores. Particles are uniform and well ordered in the silica matrix. Thus, the suggested method leads to one-dimensional anisotropic nanostructures which could find an application as high-density data storage magnetic media.
Carbon-Based Nanocomposite Materials For Cold Cathode Sources
Authors: Karabutov Alexander V. , Ralchenko Viktor G. , Gordeev Sergey K.
Published: April 2011

To find an alternative for CVD diamond films and carbon nanotubes for low-field electron emission sources and cold cathode applications, we have designed a novel class of nanomaterials with excellent field emission properties – dielectric/carbon nanocomposites, in which different insulating nanoparticles such as silicon oxide, boron nitride in cubic and hexagonal forms, and nanodiamond were used inside a pyrocarbon matrix. The thickness of pyrocarbon shells covering the dielectric particles can be controlled in a wide range during the CVD process. The best samples of the nanocomposites with all four kinds of dielectric material show excellent field emission properties with threshold fields of as low as 0.5–1 V/μm, good surface uniformity and long-term stability. An effect of post-growth treatment with oxygen and hydrogen plasma on the emission was also studied. A mechanism of the emission is discussed basing on quantum properties of nanostructured thin (two-dimensional) carbon covering the dielectric particles. The mechanism could be suitable for wide range of nanostructured sp2-bonded carbon objects.
Synthesis of Ultrafine Oxide Powders by Hydrothermal-Ultrasonic Method
Authors: Meskin Pavel E. , Kolenko Yury V. , Baranchikov Alexander E. , Ivanov Vladimir K. , Churagulov Bulat R. , Oleynikov Nikolay N.
Published: April 2011

In the present work, a novel method of synthesis has been developed to obtain highly dispersed oxide powders. This method is based on the combination of hydrothermal and ultrasonic treatment and uses the effect of acoustic cavitation.

Hydrothermal-ultrasonic treatment was carried out under the following conditions: T= 423 - 523 K, t = 10 min. -3 h. and ultrasonic frequency ν = 21.5 kHz. The control experiments (without ultrasound) were performed under the same conditions. The products were characterized by X-ray diffraction (XRD), thermal analysis (TGA), transmission electron microscopy (TEM). The specific surface area was determined by the BET method.

It was found that high-temperature hydrolysis of cobalt (II) nitrate in ultrasonic field results in formation of considerably smaller particles of Co3O4 in comparison with conventional high-temperatures hydrolysis (mean particle size decreases from 600–650 nm to 60–70 nm). It must be noted that Co3O4 samples obtained by hydrothermal-ultrasonic treatment possess mesoporous structure.

Ultrasonic-hydrothermal processing of amorphous gels of zirconyl and titanyl hydroxides leads to significant raise of the rate of crystallization process and formation of nanopowders of zirconia and titania (mean particle size 7–16 nm).

It must be pointed that the use of ultrasonic treatment during hydrothermal processing of amorphous gel of zirconyl hydroxide and 0.3 M aqueous solution of H2TiO(C2O4)2 leads to increase of the content of thermodynamically stable phases in the products of synthesis.
Dynamics of water, hydrated-ions and charged polymers in highly-confined films, and their role in friction modification
Authors: Klein Jacob , Raviv Uri , Perkin Susan , Kampf Nir , Giasson Suzanne
Published: April 2011

Recent studies have revealed that, in contrast to non-associating liquids such as oils or organic solvents, salt-free water retains a viscosity close to its bulk value even when confined to films thinner than some 3 nm, indeed down to only one or two monolayers thick [1,2]. For the case of high concentration aqueous salt solution compressed down to subnanometer films between charged surfaces, the trapped hydrated ions serve to act as molecular ball-bearings, sustaining a large load while remaining very fluid under shear [3]. This behaviour is attributed to the tenacity of the hydration sheaths together with their rapid relaxation time. Finally, a very recent study [4] has shown that when charged polymer brushes in aqueous media are compressed and slid past each other, they provide a lubrication that is considerably superior to that afforded by neutral brushes: This is attributed on the one hand to the resistance to mutual interpenetration of the chains due to entropic barriers in the good-solvent conditions, and, on the other hand, to the hydration-sheaths on the charged polymer segments which can act – as noted above – as molecular ball-bearings.
Detection of Interfacial Structures of Poly(ethylene glycol), Poly(propylene glycol) and Their Copolymers at Liquid/Solid Interfaces Using Sum Frequency Generation Vibrational Spectroscopy
Authors: Chen Chunyan , Wang Jie , Even Mark A. , Chen Zhan
Published: April 2011

We have applied sum frequency generation (SFG) vibrational spectroscopy, a submonolayer surface sensitive analytical technique, to study interfacial structures of poly (ethylene glycol) (PEG), poly (propylene glycol) (PPG), their solutions, their copolymers, and copolymer solutions while contacting different media including air, fused silica, and various polymers.

For the first time, conformations of polyether materials at various interfaces have been shown at the molecular level in situ. Depending on the hydrophobicity of the solid contacting media, the liquid polymers PEG and PPG show different conformations at different interfaces, which can be correlated to molecular interactions at these interfaces. The favorable interaction between hydrophobic media and the hydrophobic segments, methylene or methyl groups, of polyethers causes an ordered conformation with these groups standing up at the interface. The unfavorable interaction between hydrophilic media and hydrophobic segments of the polyethers induces interfacial methylene or methyl groups to have a random structure or to lie down at the interfaces, indicated by the weakening or even absence of SFG signals. For comparison, interfaces between aqueous PEG or PPG solutions and air, polystyrene (PS), poly(methyl methacrylate) (PMMA), and fused silica have also been investigated. In addition, we have studied conformations of pluronics at various interfaces, showing that different blocks have different interface activities. The interfaces are always dominated by the PPG segments. The studies on molecular level interfacial structures of PEG, PPG and pluronics will help us to understand and control the interfacial behavior of liquids at interfaces.
Segmental Dynamics of polymers in 1 and 2nm slit-pores
Authors: Kuppa V. , Manias E.
Published: April 2011

Molecular dynamics computer simulations are used to study the structure and dynamics of 1nm wide films of poly(ethylene oxide)(PEO) confined between mica type layered silicates of different cation exchange capacities(CEC). The simulation setup mimics the experimental systems formed by intercalation of PEO in silicate clays with differing numbers of inherent charges. Counterbalancing lithium cations are present in the interlayer gallery to offset the negative charge on the silicate platelets created by the isomorphic substitution of trivalent aluminum by divalent magnesium ions. It is seen that the presence of the lithium has a significance influence on the behavior of the system, with PEO segmental motion strongly dependent on the number of Li+ present in the slit pore. In particular, the coexistence of fast and slow modes for C-H bond dynamics is heavily affected due to the strong interaction between the Li+ ions and partially charged PEO oxygen. In conjunction with local density inhomogeneities, the coordination between lithium and oxygen is responsible for the anomalous segmental dynamics of nanoconfined PEO.
Intercalated Polymer Nanocomposites Prepared in Supercritical Carbon Dioxide.
Authors: Garcia-Leiner Manuel , Lesser Alan J.
Published: April 2011

An alternative route to prepare polymer-clay nanocomposites using supercritical carbon dioxide (scCO2) is described. The presence of clay nanoparticles significantly influences the morphology, foaming process and crystallization of a polymer when processed in scCO2. Intercalated structures are successfully produced in the presence of scCO2 even when favorable interactions between the polymer and the clay are not present. The effect of scCO2 on the intercalation process is analyzed for a variety of polymer systems both with modified and unmodified clays. By controlling the hydrophilicity of the polymer and clay systems, specific understanding of the effect of scCO2 on the structure and morphology of the nanocomposites is obtained. Experimental results show significant increases in the clays d-spacings for scCO2-treated samples. This behavior is consistent regardless of the nature of the polymer, showing significant amounts of intercalation even in purely hydrophobic polymers.
Modeling of Deformation in Nanocrystalline Copper Using An Atomistic-Based Continuum Approach
Authors: Warner D. H. , Sansoz F. , Molinari J. F.
Published: April 2011

The deformation of copper with grain size less than 10 nm is investigated using a 2D continuum model incorporating atomistically-based constitutive relations. The local constitutive response of a series of symmetric and asymmetric tilt grain boundaries is obtained using an atomistic quasicontinuum method under tension and shear. The atomistic results show that it is possible to associate a constant maximum stress with each deformation mechanism triggered in the GB vicinity, i.e. GB sliding and decohesion, atom shuffling and partial dislocation emission. The GB strength is always found weaker in shear than in tension. This information is incorporated into a continuum polycrystalline model tested under compression. This model provides useful insights, in the absence of intragranular plasticity, into the onset of macroscopic quasi-plasticity, which results from GB sliding and collective grain rotation mechanisms.
TEM Investigation on Microstructural Characteristics in Nanostructured Al-Mg Alloy
Authors: Park Young S. , Chung Kyung H. , Kim Nack J. , Lavernia Enrique J.
Published: April 2011

The microstructural evolution in a nanostructured Al-Mg alloy fabricated by cryogenic mechanical alloying (cryomilling), was investigated using transmission electron microscopy (TEM). Nanostructured Al-Mg powders were first synthesized by a mechanical alloying under liquid nitrogen media (cryomilling), and the powders were subsequently degassed, hot isostatically pressed, and extruded into a full dense, bulk form. The results showed that Si containing phases and (Fe,Ni)Al intermetallics existed in as-extruded Al-Mg alloy. In addition, the extrusion temperature has a strong influence on the formation of microstructural anisotropy. A lower extrusion temperature yields a microstructure that is more anisotropic relative to that present at the higher extrusion temperature. More specifically, at the lower temperature, the nano-sized Al grains have a tendency to rotate towards the <111> direction, along the extrusion direction.
Creep Resistance of the Directionally Solidified Ceramic Eutectic of Al2O3/c-ZrO2(Y2O3)
Authors: Yi Jin , Argon Ali S. , Sayir Ali
Published: April 2011

The creep resistance of the directionally solidified ceramic eutectic of Al2O3/c-ZrO2(Y2O3) was studied in the temperature range of 1200–1520°C both experimentally and by mechanistic dislocation models. The creep of the eutectic in its growth direction exhibits an initial transient that is attributed to stress relaxation in the c-ZrO2(Y2O3) phase, but otherwise in steady state shows many of the same characteristics of creep in sapphire single crystals with c-axis orientation. The creep strain rate of the eutectic has stress exponents in the range of 4.5–5.0 and a temperature dependence suggesting a rate mechanism governed by oxygen ion diffusion in the Al2O3. A detailed dislocation model of the creep rate indicates that much of the nano-scale encapsulated c-ZrO2(Y2O3) is too small to deform by creep so that the major contribution to the recorded creep strain is derived from the diffusion-controlled climb of pyramidal edge dislocations in the Al2O3 phase. The evidence suggests that the climbing dislocations in Al2O3 must repeatly circumvent the c-ZrO2(Y2O3) domains acting as dispersoids resulting in the stress exponents larger than 3. The creep model is in very good agreement with the experiments.
The Influence of Amorphous Nanosized Mo and MoO2 Fillers on the Tribological Properties of Polymer-based Composite Materials
Authors: R.T. Malkhasyan , A.K. Pogosian , V.K. Makaryan , A.R. Isajanyan
Published: April 2011

The problems of the creation of composite polymer-based materials with the use of amorphous nanosized molybdenum and molybdenum dioxide fillers with the particle size of less than 5 nm are considered. The copolymer of formaldehyde and dioxolane (CFD) and the polyphenylene sulphide (PPS) are chosen as polymeric matrixes. A comparative analysis of the tribological properties of composite materials with amorphous nanosized fillers and crystalline microsized analogues is made. It is determined that the use of isotropic nanosized amorphous fillers leads to improved wear-resistance up to three times for CFD-based composites and up to an order for PPS-based ones.
An Analytical Model for the Effect of Elastic Modulus Mismatch on Laminate Threshold Strength
Authors: Paranjpye Alok , Beltz Glenn E. , MacDonald Noel C.
Published: April 2011

A scheme for calculating the stress intensity factor at the crack tip in a two-dimensional bimaterial laminate composite has been developed to model the damage tolerance obtained in brittle ceramics by using this geometry. One limitation of the model is its assumption of homogenous elastic properties throughout the composite, limiting the accuracy of predictions it can make about real material systems. Finite element simulations of the same architecture that allow for elastic modulus mismatch give results that are moderately different from those obtained from the homogeneous model. We present an analytical expression for the stress intensity factor around a crack tip in a laminated composite that can take into account the elastic modulus mismatch. To make the problem tractable, the model is based on the assumption that the system behaves as a homogeneous anisotropic material when the stress field at the crack tip arises out of far field tractions applied away from the crack tip. The model improves upon the homogeneous model, giving results that are closer to those from the finite element simulations. We, however, conclude that more work is required to predict the stresses at the tip as the crack approaches a material interface before a complete analytical model can be obtained.
Simulation of Focused Ion Beam Induced Damage Formation in Crystalline Silicon
Authors: Hobler Gerhard , Lugstein Alois , Brezna Wolfgang , Bertagnolli Emmerich
Published: April 2011

Application of focused ion beams (FIB) to circuit modification during design and debugging of integrated circuits is limited by the degradation of active devices due to beam induced crystal damage. In order to investigate FIB induced damage formation theoretically, we have extended our 1-D/2-D binary collision (BC) code IMSIL to allow surface movement due to sputtering. In contrast to other dynamic BC codes, the crystal structure of the target and damage generation during implantation may be taken into account. Using this tool we simulate the milling of trenches in the gate stack of MOSFETs and compare the results with transmission electron microscopy cross sections and charge pumping data. The simulations confirm that damage tails are generated that are a factor of two deeper at relevant defect concentrations than expected by conventional BC simulations. This result is shown to be due to recoil channeling in spite of the fact that a beam-induced surface amorphous layer is present throughout the implant. In addition, we discuss the accuracy of the experimental results and the simulations.
High-Resolution Spectrochemical Analysis of Columnar Defects Formed in Bi2Sr2CaCu2Ox by Swift Heavy Ion Irradiation
Authors: Kano F. , Terasawa M. , Mitamura T. , Kambara T. , Sasaki Y. , Ikuhara Y.
Published: April 2011

Single-crystal specimen of high-temperature superconductor Bi2Sr2CaCu2Ox was irradiated with 3.5 GeV Xe ions at room temperature up to 1.0 × 1011 ion/cm2. Significant enhancement of magnetization by the irradiation was confirmed. The irradiated specimens were studied by using a high-resolution transmission electron microscope with field emission electron gun (FE-TEM), and, also, with an energy dispersive x-ray analyzer (EDS). Columnar defects with diameter of about 6 nm were observed along the incident ion tracks. By nanoscale high-resolution x-ray spectrochemical analysis across the columnar defect, enrichment of Cu and depletion of Bi, Sr and Ca in the columnar defect center, and vice versa in the outskirts of the defect, was found for the first time. Oxygen depletion in the defect, and increased distribution outside of the defect were also found by electron energy loss spectroscopy. This experimental evidence suggests that the columnar defects are formed as a consequence of Coulomb explosion induced by the electronic excitation of the high-energy heavy ions.
“Recovery” Effect of Electron Induced Damage in 4H-SiC Schottky Diodes
Authors: Castaldini A. , Cavallini A. , Rigutti L. , Nava F. , Fuochi P.G. , Vanni P.
Published: April 2011

The effects of electron irradiation on the defects associated electronic levels in Schottky diodes on 4H silicon carbide epilayers grown by chemical vapour deposition were investigated by Deep Level Transient Spectroscopy (DLTS) and Capacitance-Voltage (C-V) characteristics. These investigations were performed before and after irradiation with 8.6 MeV electrons at different doses. After irradiation four new traps with enthalpies equal to (Ec-0.23 eV), (Ec-0.39 eV), (Ec-0.63 eV) and (Ec-0.75 eV) were detected. Their thermal stability, a key point to determine their structure on the basis of recent theoretical and experimental results, was carefully investigated since it was earlier observed that during DLTS temperature runs up to 500 K a slight but significant recovery of a few irradiation-induced levels occurs. This effect was previously observed in literature for the level (Ec-0.70 eV) after thermal treatment at 500 °C [1], but the present results indicate that it involves more than a single level and is also effective at lower temperature. DLTS analyses were also performed from room temperature to liquid nitrogen temperature and vice versa up to 500 K.The annealing kinetics is reported and a few conclusions on the structure of the defects involved in the recovery are drawn. The correlation with the diode charge collection efficiency is also reported.
Ion Beam Processing for Silicon - Based Light Emission
Authors: Skorupa W. , Dekorsy T. , Gebel T. , Helm M. , Lysenko V.S. , Nazarov A.N. , Osiyuk I.N. , Rebohle L. , Schmidt B. , Sun J. M.
Published: April 2011

The development of novel devices for optical communication and integrated sensor applications is mainly focused on their possible integration into dedicated integrated circuits. The main problem concerning integrated optical systems in silicon technology has always been the realization of a highly efficient silicon-based light emitter which is a key requirement to make a real step into the world of integrated optoelectronics.

One of the most promising approaches to form such a silicon based light emitter is ion beam processing. In this paper we will report on recent results regarding blue-violet (∼400 nm) and infrared (∼1100 nm) electroluminescence (EL) from ion beam synthesized Ge-rich silicon dioxide layer and Boron-implanted pn-junctions in silicon showing remarkable power efficiencies of 0.5 and 0.12%, respectively. The main effort is devoted to the achievement of a deeper insight into the mechanism of the EL.
RBS, TEM and SEM Characterization of Gold Nanoclusters in TiO2(110)
Authors: Shutthanandan V. , Zhang Y. , Wang C. M. , Young J. S. , Saraf L. , Thevuthasan S.
Published: April 2011

Nucleation of gold nanoclusters in TiO2(110) single crystal using ion implantation and subsequent annealing were studied by Rutherford backscattering spectrometry /channeling (RBS/C), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Approximately 1000 Au2+/nm2 were implanted at room temperature in TiO2(110) substrates. TEM and SEM measurements reveal that rounded nanoclusters were formed during the implantation. In contrast, subsequent annealing in air for 10 hours at 1275 K promoted the formation of faceted (rectangular shaped) Au nanostructures in TiO2. RBS channeling measurements further reveled that Au atoms randomly occupied the host TiO2 lattice during the implantation. However, it appears that some Au atoms moved to the Ti lattice positions after annealing.
Ion Beam Assisted Deposition
Authors: Hirvonen James K.
Published: April 2011

The beneficial roles energetic ions play in thin film vacuum processes have long been recognized by the vacuum coating community. Optical coaters were among the first to adopt the process in the form of concurrent, low energy, directed ion beam bombardment of physical vapor deposition [electron beam] coatings for producing dense, adherent, robust, and environmentally resistant optical coatings. The international research and development community has also been actively pursuing the study of ion beam assisted deposition (IBAD) for both studying the mechanisms of ion/solid interactions during thin film growth as well as for developing coating protocols for specific application areas, including: tribological coatings, anti-corrosion coatings, optical coatings, superconducting buffer layers and coatings for temperature sensitive substrates such as polymers. This paper will review selected areas of this active field and will attempt to identify emerging application areas.
Radiation-induced Defects in Nonradioactive Natural Minerals: Mineralogical and Environmental Significance
Authors: Calas Georges , Allard Thierry , Balan Etienne , Morin Guillaume , Sorieul Stéphanie
Published: April 2011

Natural short-lived radionuclides generate electronic defects in minerals, such as trapped electrons and positive holes, often associated with element impurities, which act as final traps over geological periods. Two main examples will be illustrated. The first example will concern the point defects, which are observed in clay minerals. The high specific surface area makes clay minerals sensitive to the geochemical radiation background and provides a record of the past occurrence of radionuclides in geological systems. In kaolinite, three types of hole-centers are trapped by oxygen atoms linked to Si- or Al-sites. An experimental dosimetry gives the paleodose, which can be used either to assess mean past U-concentration or for kaolinite dating, depending on the available geochemical parameters. The detection of past migrations of radioelements in natural analogues may be used in the safety assessment of radioactive waste disposals. The second example will concern the role of mineral impurities in defect formation and stabilization. Natural fluorites (CaF2) exhibit hole-and electron-centers trapped on several rare earths and oxygen impurities, often present at the ppm level, which are responsible for the wide range of coloration observed in natural fluorites. Ca colloids may form under severe irradiation and give rise to a characteristic absorption. The thermal stability of radiation-induced defects gives constraints on the evolution of fluorites as a function of temperature and time. Other minerals, such as apatite, confirm the importance of impurities in stabilizing radiation-induced defects over geological periods.
Modification of lattice structure and magnetic properties of Fe-Rh alloys by energetic electron irradiation
Authors: Fukuzumi Masafumi , Taniguchi Ryoichi , Komatsu Seiji , Ono Fumihisa , Iwase Akihiro
Published: April 2011

In order to modify the lattice structure and magnetic properties, we irradiate Fe-50at.%Rh alloys with 8 MeV electrons at room temperature. Effects of irradiation are investigated by using Superconducting QUantum Interference Device (SQUID) and X-Ray Diffractometer (XRD).

Although the crystal structure is not changed by the irradiation and remains the B2 structure, the lattice parameter increases by about 0.1–0.3 % and the antiferromagnetic(AF)-ferromagnetic(FM) transition temperature decreases by 3–18 deg. with increasing the electron fluence. The present result shows that energetic electron irradiation can be used for the precise control of AF-FM transition temperature of Fe-50at.%Rh alloy.
Proton Beam Irradiation Effects on Magnetic Nanocomposites
Authors: Chipara M. , Zaleski M. J. , Hui D. , Pelecky D. L. , Balascuta S.
Published: April 2011

A magnetic nanocomposite material has been obtained by dispersing ball milled magnetic nanoparticles of barium ferrite within a styrene- isoprene- styrene block copolymer, sonicating the solution, and spin coating it onto a quartz crystal. Ferromagnetic resonance spectra of pristine and irradiated magnetic nanocomposites are reported. Although the flux of incoming protons was not large, modifications in the ferromagnetic resonance spectra were noticed. This suggests that the future ultra high-density media would present an enhanced sensitivity to the radiation component of the space environment.
Small-angle x-ray scattering characterization of self-irradiated zircon
Authors: Ríos Susana , Salje Ekhard K. H.
Published: April 2011

Small-angle x-ray scattering (SAXS) measurements were performed on two natural zircons: one with an amorphous content close to 85 %, and the second one x-ray amorphous. Electron density fluctuations were observed in the untreated samples, and studied as a function of various heat-treatments. In the starting material, density fluctuations were found to have a characteristic length-scale of approximately 1 nanometer diameter. Below 800 °C, the SAXS contribution (Q<10 nm-1) showed only a small variation as a function of temperature. Above 800 °C, a strong increase in intensity is observed, accompanied by the precipitation of 2–3 nm zirconia domains. At high enough temperatures, >1000 °C, when the amorphous phase recrystallizes into the starting zircon structure, characteristics of surface-scattering are observed, associated to large zircon regions.
Effects of High-Energy Ion Irradiation in Bismuth Thin Films at Low Temperature
Authors: Chimi Yasuhiro , Ishikawa Norito , Iwase Akihiro
Published: April 2011

We have studied high-energy ion irradiation effects in bismuth by measuring the electrical resistivity at low temperature in relation to its structural change. Bismuth thin films (330–520 Å thick) are irradiated below ∼10 K with energetic (150–200-MeV) heavy ions. The resistivity of the specimen is measured in situ below ∼7.2 K during the irradiation. After the irradiation, annealing behavior of the resistivity is observed up to ∼30 K. The temperature dependence of the resistivity during annealing shows an abrupt increase around 20 K, implying re-crystallization of irradiation-induced amorphous regions. We have tried to detect a superconducting transition which may take place as a result of irradiation-induced amorphization. In the range of the measuring temperature down to ∼4.9 K, resistivity decrease due to superconducting transition has not been observed in the temperature dependence of the resistivity after 200-MeV 197Au ion irradiation up to a fluence of 3.1×1012 cm-2.
Atomic-scale simulations of radiation effects in GaN and carbon nanotubes
Authors: Nordlund K. , Nord J. , Krasheninnikov A. V. , Albe K.
Published: April 2011

Gallium nitride and carbon nanotubes have received wide interest in the materials research community since the mid-1990's. The former material is already in use in optoelectronics applications, while the latter is considered to be extremely promising in a wide range of materials. Common to both materials is that ion irradiation may be useful for modifying their properties. In this paper we overview our recent molecular dynamics simulations results on ion irradiation of these materials. We employ such potentials to study the basic physics of how ion irradiation affects these materials. In particular we discuss the reasons for the high radiation hardness of GaN, and the surprising nature of vacancies and interstitials in carbon nanotubes.
Correlation and Spectral-Density Roughness Analysis of Surfaces Processed With Gas-Cluster Ion Beams
Authors: Fenner D. B.
Published: April 2011

Autocorrelation, height-difference correlation, and power spectral density are used to characterize various surfaces exposed to gas-cluster ion beams (GCIB), as well as for detailed comparison with simulated surfaces which are based on models with stochastic impact and surface mobility mechanisms. This work demonstrates a close correspondance between detailed statistical analysis of AFM images from actual surfaces and the results of the same types of analysis of simulated surfaces. Surface roughness prior to and after GCIB treatment is always found to be essentially fractal in nature. Phenomenological models with both continuum surface mobility and Monte Carlo impact accumulations are presented. Accurate simulation of smoothing requires a combination of these models.
Radiation Damage Characterization in Ar+ Implanted GaN
Authors: Usov I. , Kvit A. , Reitmeier Z. , Davis R.
Published: April 2011

Damage microstructure evolution in GaN films implanted with argon ions (Ar+) as a function of implantation temperature was studied by cross-sectional transmission electron microscopy (TEM). After irradiation at room temperature, the implanted layer contained mostly isolated point defects. Implantation at elevated temperatures significantly reduced the number of isolated point defects. Numerous dislocations and regions exhibiting strain-contrast were observed after implantation at 300 °C. Bombardment at 600 °C resulted in formation of a new type of defect. Along with the partial dislocations and the strained regions, precipitates composed of carbon and nitrogen were identified by electron energy loss spectroscopy. These precipitates were formed in the vicinity of the Ar+ projected range where the amount of radiation damage was maximal. The high concentration of defects facilitated redistribution of carbon atoms introduced during the GaN film growth and resulted in the formation of precipitates. No precipitates were observed after implantation at 1000 °C. Consideration of the TEM results in conjunction with ion channeling data showed that presence of the precipitates correlated with a reverse annealing damage accumulation mode, which manifests itself as an increase of backscattering yield with increasing implantation temperature. The results of our study indicated that the carbon impurity in as-grown GaN films enhances the radiation damage accumulation rate and consequently has to be taken into account when ion implantation doping of GaN is performed.
Germanium Island Size Distribution by Atomistic Simulation
Authors: Wagner Richard J. , Gulari Erdogan
Published: April 2011

Strained epitaxial growth of Ge on Si(001) produces self-assembled, nanometer scale islands, or quantum dots. We study this growth by atomistic simulation, computing the energy of island structures to determine when and how islanding occurs. The distribution of island sizes on a surface is determined by the relation of island energy to size. Applying the calculated chemical potential to the Boltzmann-Gibbs distribution, we predict size distributions as functions of coverage and temperature. The peak populations around 80 000 atoms (35 nm wide) compare favorably with experiment.
Effects of Growth Sequence on Optical and Structural Properties of InAs/GaAs Quantum Dots Grown by Atomic Layer Molecular Beam Epitaxy
Authors: Song J. D. , Park Y. M. , Shin J. C. , Lim J. G. , Park Y. J. , Choi W. J. , Han I. K. , Cho W. J. , Lee J. I. , Kim H. S. , Park C. G.
Published: April 2011

The influence of growth sequence on optical and structural properties of InAs/GaAs quantum dots (QD) grown by atomic layer epitaxy was investigated systematically. It is found that growth interruption (GI) after In is more effective than non-GI after In in reducing the density of coalescent dots, and reducing the dot width distribution of the QDs. Meanwhile, dot densities are approximately doubled by non-GI after In. GI after As reduces dot height distribution compared with non-GI after As. Generally, GI after In plays a more critical role than GI after As does in formation of the QDs. The sample grown with In/GI/As/GI sequence shows the lowest 300 K-photoluminescence (PL) linewidth (∼30 meV), high PL peak separation between ground and 1st excited level (∼80 meV). From the result, it is known that In/GI/As/GI is the favorable growth sequence among the sample sets. Temperature dependence of PL linewidth shows that the In/GI/As/GI sample is insensitive to cryostat temperature and it is attributed to weak wetting effect. Thinner wetting layers shown in a cross-sectional TEM image supports this.
InNAs and GaInNAs self-assembled quantum dots and lasers grown by solid source molecular beam epitaxy
Authors: Sun Z.Z. , Yoon S.F. , Yew K.C. , Bo B.X.
Published: April 2011

Self-assembled Ga1−xInxNyAs1-y quantum dots were grown on GaAs by solid source molecular beam epitaxy (SSMBE). Introduction of N was achieved by a RF Nitrogen plasma source. Formation of quantum dots by S-K growth mode is confirmed by observation of standard 2D-3D RHEED pattern transition. Atomic force microscopy (AFM) and photoluminescence (PL) measurements were used to characterize the structure and optical properties of GaInNAs quantum dots. High GaInNAs quantum dot density (1010∼1011cm−2) was obtained for different In and N composition (0.3≤ x ≤1, y≤0.01). The effect of surface coverage on dot density, dot size, and optical properties was studied in detail. Adjusting the bandgap confinement by incorporating a GaNAs strain-reduction layer into the GaInNAs dot layer was found to extend the emission wavelength by 170nm. Room temperature pulsed operation is demonstrated for a Ga0.5In0.5N0.01As0.99 quantum dot laser emitting at ∼1.1μm.
First electrically injected QD-MCLED emitting at 1.3 μm, grown by metal organic chemical vapour deposition
Authors: Tasco V. , Todaro M.T. , De Giorgi M. , De Vittorio M. , Cingolani R. , Passaseo A.
Published: April 2011

We present the fabrication of a Quantum Dot Microcavity Light Emitting Diode (QD-MCLED) emitting at 1.3 μm at room temperature. The long wavelength emission is achieved by using for the first time InGaAs QDs directly grown on GaAs, by metal organic chemical vapour deposition. Electroluminescence bright emission, peaked at 1298 nm with a FWHM of 6.5 meV and a line shape independent on the applied bias is found.
Modeling of a Surface Plasmon Polariton Interferometer
Authors: Coello Victor , Søndergaard Thomas , Bozhevolnyi Sergey I.
Published: April 2011

We model the operation of a micro-optical interferometer for surface plasmon polaritons (SPPs) that comprises an SPP beam-splitter formed by equivalent scatterers lined up and equally spaced. The numerical calculations are carried out by using a vector dipolar model for multiple SPP scattering. The SPP beam-splitter is simulated for different angles of the incident SPP beam, radii of the particles, and inter-particle distances in order to find a suitable configuration for realization of a 3dB SPP beam-splitter. The results obtained are in good agreement with experimental data available in the literature. The feasibility of fabricating an interferometer is thereby corroborated and the calculated intensity maps are found rather similar to those experimentally reported.
Low loss Photonic Crystal Cladding Waveguide with Large Photonic Band Gap
Authors: Yi Yasha , Bermel Peter , Akiyama Shoji , Sandland Jessica G. , Duan Xiaoman , Kimerling Lionel. C.
Published: April 2011

Light propagation in a low index core (e.g. SiO2) is realized by a Photonic Band Gap (PBG) cladding waveguide structure with large dielectric index contrast layers (Si/Si3N4). The waveguide is fabricated with a CMOS compatible process. The measured loss for the asymmetric PBG cladding waveguide is about 0.5dB/cm for both polarizations at a wavelength of 1550nm. Potential applications include optical amplification when the SiO2 core is doped with optical active materials (e.g. Er).
Optical and Crystallographic Properties of Inverse Opal Photonic Crystals Grown by Atomic Layer Deposition
Authors: King Jeffrey S. , Neff Curtis W. , Heineman Dawn L. , Graugnard Elton D. , Summers Christopher J.
Published: April 2011

We report a technique for the formation of infiltrated and inverse opal structures that produces high quality, low porosity conformal material structures. ZnS:Mn and TiO2 were deposited within the void space of an opal lattice by atomic layer deposition. The resulting structures were etched with HF to remove the silica opal template. Infiltrated and inverse opals were characterized by SEM, XRD, and transmission/reflection spectroscopy. The reflectance spectra exhibited features corresponding to strong low and high order photonic band gaps in the (111) direction (γ-L). In addition, deliberate partial infiltrations and multi-layered inverse opals have been formed. The effectiveness of a post-deposition heat treatment for converting TiO2 films to rutile was also studied.
ANGULAR ROLL-OFF DEPENDENCE OF SPECTRAL EMISSION FROM A METALLODIELECTRIC PHOTONIC CRYSTAL
Authors: Irina Puscasu , U Pralle Martin , P McNeal Mark , Nicholas Moelders , T Daly James , C Greenwald Anton , Alan Ludwiszewski , A Johnson Edward , L Schaich William
Published: April 2011

We are reporting on the analysis of a new design for a thermal source exploiting Si-based suspended micro-bridge structures. A device consists of a metal film perforated by a periodic array of apertures extending into the Si substrate and each of size on order of the wavelength of the light. This perforated film permits resonant coupling of the incident radiation from the underlying silicon photonic crystal with surface plasmons at the metal surface. The coupling provides for unusually high optical emission efficiencies when the structure is thermally excited. The radiation emitted exhibits an enhancement over a narrow wavelength range in the infrared and its spectral response is highly dependent on the direction of observation. The positions of the main resonances, for both reflection and emission from our structures, scale linearly with the periodicity of the metallo-dielectric structure. As one moves off normal incidence, a single main resonance splits into several smaller resonances whose locations scale roughly linearly with observation angle. These structures have been used as emitter/detector sensor chips to selectively detect industrial pollutants like carbon dioxide. Control of the wavelength of resonance, bandwidth and direction of emission play an important role in improving the sensitivity and selectivity of these gas sensors.
Conductive transparent probes and their application to high-density phase-change data storage by using current injection
Authors: Murashita Tooru
Published: April 2011

With the goal of producing high-density terabits/inch2 storage, we are studying a method in which nanometer-sized marks are recorded on Ge2Sb2Te5 (GST) phase-change media by current beams injected from sharpened probes. The current beams can inject powers with lower transmission losses into nanometer-sized local regions that are much smaller than the refraction limit of light. Moreover, the difference in the conductivity between amorphous and crystalline GST is orders larger than the difference in their refraction index. Therefore, the current beams are advantageous for such high-density data storage with nanometer-sized marks.

We have experimentally and numerically studied phase changes in GST using probe current injections. The structures of the media are composed of GST and a metal electrode stacked on a polycarbonate substrate. We simulated temperatures, crystallization rates, and mark sizes of GST as a function of power injection conditions. The results clarify that a small crystalline mark can be stably made in an amorphous region by injecting probe current pulses with the same beam sizes. For supplying higher injection powers to produce phase change, metal oxide, such as indium-tin- oxide (ITO), is more robust at high powers than metals. We have developed conductive transparent (CT) probes consisting of ITO coated on a fiber tapered to a point with a nanometer-scale radius. The CT probe can inject current in a nanometer-sized region and simultaneously illuminate the same local region. We also propose a new method of optical rewritable phase-change storage using the CT probes.
Thermal analysis of nonvolatile and non rotation phase change memory cell
Authors: Shi L. P. , Chong T. C. , Li J. M. , Yang H. X. , Mou J. Q.
Published: April 2011

In this paper, a three-dimensional finite-element modeling is performed for the analyses of Chalcogenide Random Access Memory (C-RAM), a non-rotation nonvolatile phase change memory cell. The thermal effect generated by an incident electric pulse was mainly discussed. Thermal performances of the cell as a result of electrical and geometrical variations were quantified. Current density distribution, temperature profiles, temperature history, heating rate, cooling rate, and heat flow characteristics were obtained and analyzed. The study is useful for the failure analysis of the C-RAM.