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We report an ohmic contact metallization scheme for n-GaN based on a Re–Al–Ni–Au multilayer stack that offers low-resistivity and provides better edge sharpness and lower surface roughness at reduced annealing temperature compared to standard Ti–Al-based metallization. We studied three sets of samples with Re thicknesses of 10, 30, and 60 nm and measured specific contact resistances using the circular transmission line method. We obtained reliable ohmic contacts with specific contact resistance of the order of 10−6 Ω cm2 at 550 °C temperature with the contact stack having a large annealing temperature window of >300 °C for resistivity below 5 × 10−6 Ω cm2. The lowest contact resistivity, below 10−7 Ω cm2, is achieved at annealing temperature around 650–700 °C. A reduction in surface roughness by a factor of 4, with excellent edge definition for Re >30 nm thickness is observed as compared to Ti–Al contacts. Grazing incidence x-ray diffraction and electron dispersive x-ray spectroscopy (EDS) show intermetallic phases of RexNy, Re–Al–Ni, Al–Re, and Al–Au being formed. Atomic force microscope and EDS measurements show the formation of crystalline Re–Al–Ni agglomerates, surrounded by phases of AlAu2 and Al2Au5. The presence of Re seems to suppress the formation of viscous AlAu4 phase, thus minimizing the lateral flow of the metals and providing better edge acuity. The temperature dependence of contact resistivity suggests a field-emission mechanism for current transport across the contact. Our results show that Re-based ohmic contacts, with their lower annealing temperature and excellent edge definition, may offer a promising alternative to Ti–Al contacts. [ABSTRACT FROM AUTHOR]

The formation of dust particles in low-pressure plasmas is a 3-step process. The first one corresponds to nucleation and growth of nanoparticles by chain reactions between ions and gas molecules, the second one is agglomeration of the nanoparticles to form larger particles, and finally, the particles grow by radical deposition on their surfaces. In this work, the nucleation time for carbon dust particles was studied in low pressure acetylene/argon radio frequency (RF) plasmas. Since the self-bias voltage on a powered electrode was drastically affected by the transition from the nucleation to the agglomeration phases, the nucleation time was measured by observing the self-bias voltage time evolution. The nucleation time increases with the gas temperature and decreases when the gas pressure and the RF power are increased. A kinetic model, involving balance between diffusion and charging times of the nanoparticles as well as the chain reactions, is used to explain the exponential dependence of the nucleation time on the gas temperature. The balance between the times was especially indispensable to get good agreement between the model and the experimental results. [ABSTRACT FROM AUTHOR]

Single-phase Ba1.5Sr1.5Co2Fe24O41 (Ba1.5Sr1.5Z) hexaferrite flakes were synthesized using a two-step grain growth process, involving a calcination process and molten salt synthesis. Geometric parameters such as aspect ratio and the degree of agglomeration can be controlled by tuning this calcination-molten salt method. The morphological evolution of the flakes was explained using the concept of mixed-control grain growth, i.e., a combination of diffusion for growth and interface reactions, which is a growth mechanism for a faceted interface. The single-phase Ba1.5Sr1.5Z flake particle with high aspect ratio turned out to be a good candidate of soft magnetic inclusion, through an investigation of the correlation between material composition, magnetic behavior, and particle morphology. [ABSTRACT FROM AUTHOR]

Agglomeration strongly influences the stability or shelf life of nanofluid. The present computational and experimental study investigates the rate of agglomeration quantitatively. Agglomeration in nanofluids is attributed to the net effect of various inter-particle interaction forces. For the nanofluid considered here, a net inter-particle force depends on the particle size, volume fraction, pH, and electrolyte concentration. A solution of the discretized and coupled population balance equations can yield particle sizes as a function of time. Nanofluid prepared here consists of alumina nanoparticles with the average particle size of 150 nm dispersed in de-ionized water. As the pH of the colloid was moved towards the isoelectric point of alumina nanofluids, the rate of increase of average particle size increased with time due to lower net positive charge on particles. The rate at which the average particle size is increased is predicted and measured for different electrolyte concentration and volume fraction. The higher rate of agglomeration is attributed to the decrease in the electrostatic double layer repulsion forces. The rate of agglomeration decreases due to increase in the size of nanoparticle clusters thus approaching zero rate of agglomeration when all the clusters are nearly uniform in size. Predicted rates of agglomeration agree adequate enough with the measured values; validating the mathematical model and numerical approach is employed. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of carbon nanotube (CNT) agglomeration on the electrical conductivity of CNT-polymer composites by experimental characterization and theoretical modeling. The present experimental results show that the acid treatment of CNTs has significantly alleviated the CNT agglomeration in CNT-polymer composites and improved the electrical conductivity of the composites compared with CNT-polymer composites made from the same pristine CNTs. The improvement by the acid treatment is further studied by a multiscale CNT percolation network model that considers the CNT agglomeration based on experimental observation. Numerical results are in good agreement with the experimental data. The smaller the size of CNT agglomerates is in the experiments, the closer the measured electrical conductivity of CNT-polymer composites is to its theoretical limit. The current study verifies that (i) the CNT agglomeration is the main cause that leads to a lower electrical conductivity of CNT-polymer composites than their theoretical limit, and (ii) the current multiscale percolation network model can quantitatively predict the electrical conductivity of CNT-polymer composites with CNT agglomeration. The comprehensiveness of the developed modeling approach enables an evaluation of results in conjunction with experimental data in future works. VC [ABSTRACT FROM AUTHOR]

Variations in the hardness of a poly (ether ether ketone) beam electrically modified with multiwalled carbon nanotubes (MWCNT, 0.5%-3%) are investigated. It is shown that both rupture and hardness variations correlate with the changes in carbon nanotube concentration when using micro indentation and extended Raman imaging. Statistical analysis of the relative spectral intensities in the Raman image is used to estimate local tube concentration and polymer crystallinity. We show that the histogram of the Raman D band across the image provides information about the amount of MWCNTs and the dispersion of MWCNTs in the composite. We speculate that we have observed a local modification of the ordering between pure and modified polymer. This is partially supported by small angle neutron scattering measurements, which indicate that the agglomeration state of the MWCNTs is the same at the concentrations studied. [ABSTRACT FROM AUTHOR]

An in situ transmission-electron-microscopy methodology is developed to observe time-dependent dielectric breakdown (TDDB) in an advanced Cu/ultra-low-k interconnect stack. A test structure, namely a "tip-to-tip" structure, was designed to localize the TDDB degradation in small dielectrics regions. A constant voltage is applied at 25 °C to the "tip-to-tip" structure, while structural changes are observed at nanoscale. Cu nanoparticle formation, agglomeration, and migration processes are observed after dielectric breakdown. The Cu nanoparticles are positively charged, since they move in opposite direction to the electron flow. Measurements of ionic current, using the Triangular-Voltage-Stress method, suggest that Cu migration is not possible before dielectric breakdown, unless the Cu/ultra-low-k interconnect stacks are heated to 200 °C and above. [ABSTRACT FROM AUTHOR]

Large-scale, high-rate epitaxial growth technology for the second-generation superconducting wire brings unique technological challenges for the thin-film coating industry. One of the most difficult steps of the process is controlling nucleation of a complex compound over a km-long low-cost oxide template. Here, we analyze early stages of industrial-scale epitaxial metal organic chemical vapor deposition (MOCVD) growth of ReBa2Cu3Ox (REBCO, Re = rare-earth) on buffered metal substrates. The nucleation event is detected by high-flux synchrotron X-ray diffraction and confirmed by atomic force microscopy. REBCO nuclei exhibit a strong preference for edges of the buffer grain, indicating that (001) steps of the buffer grains are preferred nucleation sites. It is concluded that random nucleation of REBCO is caused by agglomerates of small buffer grains. [ABSTRACT FROM AUTHOR]

The induction of dipolar coupling has proven to allow for the initiation of self-assembled, reconfigurable particle clusters of superparamagnetic microbeads suspended in a carrier liquid. The adjustment of the interplay between magnetic and hydrodynamic forces opens various possibilities for guiding strategies of these superstructures within microfluidic devices. In this work, the formation dynamics of such particle clusters under the influence of a rotating magnetic field are studied. Different agglomeration regimes are characterized by the dimensionality of the confined objects. The growth dynamics of the obtained agglomerates are analyzed quantitatively in order to deduce the microscopic growth mechanisms. The growth of two-dimensional clusters is governed by the addition of bead chains to previously formed agglomerates. Time scales for the cluster growth are characterized by the chain dissociation rate. Based on the experimental findings, we may conclude to a linear dependence of the chain dissociation rate on the rotation frequency of the applied magnetic field. [ABSTRACT FROM AUTHOR]

This paper introduces a new method to synthesize layered double hydroxides and its ultrathin nanosheets in de-ionized water. By employing pulsed laser ablation, ultrathin layered double hydroxide nanosheets of Zn-Al, Co-Fe, Co-Al, and Mg-Fe were formed with a molecular thickness, corresponding to the thickness of the exfoliated two-dimensional nanosheets. The nanosheets formed directly were well-defined with a hexagonal shape, and were stable without any chemical for preventing agglomeration or formation of three-dimensional lamellar crystals. The nanosheets are assembled layer-by-layer up to the finite thickness on solid surface by the incorporation of carbonate anions from the atmospheric CO2. Observation of the seedlike layered double hydroxide nanosheets as well as the lamellar structures shows a similar structural relationship. Consequently, the laser ablation technique is deemed to have played a critical role in the formation of nanosheets. This suggests that the contamination of the as-synthesized layered double hydroxide colloidal solutions by carbonate is considerably insignificant. [ABSTRACT FROM AUTHOR]

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices, such as nanoelectronics and reflective multilayer optics. Chemical diffusion and agglomeration at interfaces of thin Ru, Mo, Si, and B4C layers have been studied with x-ray photoelectron spectroscopy, cross section electron energy loss spectroscopy, high-angle annular dark field scanning transmission electron microscopy, and energy dispersive x-ray in relation to observations in Ru-on-B4C capped Mo/Si multilayers. Rather than in the midst of the Si layer, silicides and borides are formed at the Si-on-Mo interface front, notably RuSix and MoBx. The interface apparently acts as a precursor for further chemical diffusion and agglomeration of B, Ru, and also other investigated d-metals. Reversed "substrate-on-adlayer" interfaces can yield entirely suppressed reactivity and diffusion, stressing the influence of surface free energy and the supply of atoms to the interface via segregation during thin layer growth. [ABSTRACT FROM AUTHOR]

In this paper we present a comparative study of the agglomeration process in silicon-on-insulator (SOI), silicon germanium-om-insulator (SGOI), and strained SOI (SSOI) thin layers under thermal annealing in ultrahigh vacuum. In particular, we provide the first evidence and characterization of agglomeration in SGOI and SSOI substrates. A common agglomeration dynamics is observed in all the substrates investigated, with the semiconductor-on-insulator layer thickness being the main parameter governing it. These findings provide a better understanding of the surface-energy-driven dewetting phenomenon in semiconductor layers and allow us to single out the influence of the surface and stress energies on the void formation and evolution, as well as on the size and density of the agglomerated islands. [ABSTRACT FROM AUTHOR]

Reflective Si/Mo multilayer mirrors with protective d-metal surfaces onto a range of upper Mo and Si layer thicknesses have been grown with physical vapor deposition and investigated on diffusion and in-depth compound formation. Laterally inhomogeneous upward Si and downward d-metal diffusion occurs through Mo layers up to 2 nm thickness. Especially Ru and Rh agglomerate and form silicides such as Ru2Si3 and Rh2Si not in the midst of the Si layer but at the Si/Mo interface. This appears to be mediated by MoSi2 presence at the Si/Mo interface that acts as precursor via better lattice compatibility and lowering of formation energy. [ABSTRACT FROM AUTHOR]

In this paper, the germanium (Ge) nanocrystals (NCs) are synthesized by using the rapid-thermal annealing and are embedded into a three-layer (SiO2/NCs–Ge/SiO2) capacitor structure. The samples with/without the postmetallization annealing (PMA) treatment are investigated to compare and study the PMA affections. The charge storage characteristics of our samples are investigated with the capacitance-voltage (C-V) hystereses. The frequency independence of hysteresis windows is found and attributed to NCs as slow traps with a large characteristic time constant. The frequency-dependent C-V and conductance-voltage (G-V) experiments are further introduced to study the interface traps and the fast traps induced by the NC formation. In order to extract the related trap characteristics from the measured C-V and G-V, we propose to utilize the equivalent circuit and single-level trap model based on Shakley-Read-Hall theory. Three associated parameters including the areal trap density, trap conductance, and semiconductor capacitances are used to confirm that the single-level trap model is truly appropriate for our samples. It is then found from the model that the areal trap density is high and approaches almost uniform distribution along the valence band and bandgap but significantly reduced and then becomes decreased from valence band to the midgap after PMA treatment. In addition, after PMA treatment, the characteristic time constant becomes smaller for one order of magnitude at the same gate bias. It is attributed to the reduction of trap density and also agrees that the interface traps are dominant and has a small characteristic time constant. [ABSTRACT FROM AUTHOR]

The thermal agglomeration of ultrathin (<30 nm) single crystal silicon-on-insulator (SOI) films is a morphological evolution phenomenon with practical and scientific importance. This materials phenomenon represents both a critical process limitation for the fabrication of advanced ultrathin SOI-based semiconductor devices as well as a scientifically interesting morphological evolution problem. Investigations to date have attributed this phenomenon to a stress-induced morphological instability. In this paper, we demonstrate that SOI agglomeration is a surface-energy-driven dewetting phenomenon. Specifically, we propose that agglomeration occurs via a two-step surface-energy-driven mechanism consisting of (1) defect-mediated film void nucleation and (2) surface-diffusion-limited film dewetting via capillary edge and generalized Rayleigh instabilities. We show that this theory can explain all of the key experimental observations from the SOI agglomeration literature, including the locations of agglomeration initiation, the greater instability of patterned film edges, the destabilizing effect of decreasing silicon layer thickness and increasing temperature, the strikingly periodic silicon finger and island formation agglomeration morphology, and the scaling of agglomerated structure dimensions with the silicon layer thickness. General implications of this theory for the thermal stability of SOI and other common thin-film-on-insulator structures are also discussed. [ABSTRACT FROM AUTHOR]

Diesel soot powder generated under idle and load engine conditions was pressed into pellets at pressures ranging up to approximately 8.5 GPa. Soot powder was also immersed in acetone in order to obtain soot aggregates without agglomeration. Small-angle x-ray scattering was carried out on the powder, the pellets, and on the acetone-immersed soot. Powder and pellets show characteristic aggregate structure at small scattering vectors. Scattering curves of the pellets show a shift of the aggregate size-related scattering feature towards larger scattering vectors for increasing pressure. For the highest pressures, this aggregate structure vanished, while the suspected primary particle scattering became visible as the asymptote of the aggregate scattering structure. Soot was immersed and ultrasonicated in acetone to prevent agglomeration of aggregates, which naturally occurs in powders. This can be considered as the simulation of asymptotic behavior for vanishing pressure. Aggregate size of powder was about 290 nm for the idle soot and 240 nm for the load soot. Primary particle sizes were 14.3 and 10.2 nm, respectively. The idle soot showed a higher compressibility (0.9 GPa/nm) than the load soot (12.0 GPa/nm). Pressing the soot into pellets eliminates scattering structures from aggregation of primary particles and provides a good route to reveal the otherwise inaccessible primary particle scattering. In addition, studying the aggregate structure as a function of pellet pressure allows us to derive compacticity data of the soot. [ABSTRACT FROM AUTHOR]

The effect of Pt alloy in Ni(Pt∼5 and 10 at. %) on the agglomeration and Ge out diffusion in nickel germanosilicide formed on Si0.75Ge0.25(100) has been studied. A remarkable improvement in the agglomeration behavior with increasing Pt atomic percentage is observed by sheet resistance measurements while still maintaining Ni(Pt) monogermanosilicide phase between 400 and 800 °C. Ge out diffusion from the monogermanosilicide grains has been suppressed up to a temperature of 700 °C with the addition of Pt, evident by x-ray diffraction and micro-Raman spectroscopy. In addition, that improvement of surface morphology and suppression of Ge out diffusion with increasing Pt atomic percent is also confirmed by Rutherford backscattering and cross-sectional transmission electron microscopy. The improved morphology and agglomeration are explained by a grain-boundary model which includes kinetic effects. The suppression of Ge out diffusion from the germanosilicide grains is attributed to reduced atomic diffusion and the presence of stronger Pt–Si and Pt–Ge bonds due to the addition of Pt. [ABSTRACT FROM AUTHOR]

High-quality bulk MgB2 exhibits a structure of voids and agglomeration of crystals on different length scales. Because of this, the superconducting currents percolate between the voids in the ensuing structure. Magnetic measurements reveal that the superconducting currents circulate on at least three different length scales, of ∼1 μm, ∼10 μm, and whole of the sample (∼millimeter). Each of these screenings contributes to the measured irreversible magnetic moment (Δm). The analysis of the field dependence of Δm for samples of subsequently decreasing size showed that the critical current obtained using the simple critical state model is erroneous. This leads to the artifact of the sample size-dependent critical current density Jc and irreversibility field. Our data analysis enables the separation of the contribution of each of the screening currents to Δm. The field dependence of each of the currents follows a stretched exponential form. The currents flowing around whole of the sample give a dominant contribution to Δm in the intermediate fields (1 T

The influence of carbon and germanium on phase transformation and sheet resistance of Ni on epitaxially grown Si[sub 1-x-y]Ge[sub x]C[sub y] (0<=x<=0.24 and 0<=y<=0.01) layers annealed in a temperature range of 360 to 900 °C has been investigated. The role of strain relaxation or compensation in the reaction of Ni on Si[sub 1-x-y]Ge[sub x]C[sub y] layers due to Ge or C out-diffusion to the underlying layer during the phase transformation has also been investigated. The formed NiSiGe layers were crystalline, with strong (020)/(013) growth orientation in the direction, but the thermal stability decreased rapidly with increasing Ge amount due to agglomeration. However, this thermal behavior was shifted to higher annealing temperatures when carbon was incorporated in the SiGe layers. A carbon accumulation at the interface of NiSiGeC/SiGeC has been observed even at low-temperature annealing, which is suggested to retard the phase transformation and agglomeration of Ni/SiGeC system. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The agglomeration behavior of Cu and Au films each with a thickness of 5 and 50 nm, deposited on thermally grown SiO[sub 2] by dc magnetron sputtering, was investigated with scanning electron microscopy. The size of Cu islands formed by agglomeration increased with increasing annealing temperature. Also, the agglomeration of Cu films seem to follow the grain boundary grooving process. On the other hand, Au islands have an identical size at different annealing temperatures. Au films were observed to agglomerate via nucleation of voids followed by the fractal growth of voids. The fractal dimension was determined to be 1.7 indicating that the fractal growth of voids can be described with a diffusion limited aggregation model. Finally, the kinetics of agglomeration of the Au films was described with an Avrami-type equation. [ABSTRACT FROM AUTHOR]

Presents information on a study which produced films from monodispersed cobalt clusters and analyzed their morphological and magnetic features. Importance of nanometer-scale geometrical and chemical controls; Methodology; Results and discussion; Conclusion.

Presents information on a study which investigated the effect of C49-to-C54 conversion behavior on the agglomeration of titanium-silicide fabricated on subquarter micro polycrystalline silicon lines. Experimental details; Results and discussion; Conclusions.

Studies carbon clustering kinetics in detonation wave propagation. Adaptation of an analytic solution of the Smoluchowski rate equations for the evolution of the cluster size distribution function; Reactive flow equations; Detonation velocity versus curvature relation; Conclusion.

Presents information on a study which described the application of sonoluminescence technique to detect spatial agglomeration patterns produced in powder mixtures subjected to acoustically driven plate. Experimental procedure; Results and discussion; Conclusions.

Evaluates alloy clustering in liquid-phase epitaxial GaInAsP layers using transmission electron microscope and transmission electron diffraction. Results of the study; Discussion of findings; Conclusions.

Presents information on a study which examined the usage of dust particles for microelectronics fabrication. Details on the particles being generated in low temperature plasmas; Transport of the agglomerates; Information on local electric fields; Methodology used to conduct the study; Results of the study.

Investigates the process of agglomeration of TiSi2 thin films on silicon substrates as a model system for the geometrical model of agglomeration based on the spheroidization. Occurrence of agglomeration by nucleation of holes at grain-boundary vertices; Ratio of the grain size to film thickness.

Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogous to the diffusive regime in neutral agglomeration. Large particles in high powered plasmas generally produce compact agglomerates of high fractal dimension, analogous to ballistic agglomeration of neutrals. [ABSTRACT FROM AUTHOR]

Presents a study that determined the time evolution of particle size and their number density through the use of in situ multi-angle polarization-sensitive laser light scattering. Discussion on the coagulation model; Comparison of multi-angle polarization-sensitive laser light scattering with other laser scattering methods; Demonstration on the existence of nonspherical agglomerates during the early phase of agglomeration.

Presents a study which described a simple quasi-in situ resistivity technique and its application to the study of C49 to C54 TiSi[sub2] conversion in narrow lines. Description of the silicide samples used in the experiment; Investigation of agglomeration; Conclusion.

Details a study which investigated the growth, morphology and surface atomic structure of ultrathin silicide films on silicon substrates. Experimental procedures; Agglomeration of ultrathin titanium silicide; Temperature dependence of crystalline formation; Correlation between silicide agglomeration and crystalline growth.

Presents a study which determined the density of nanometer sized particles of different materials suspended in a carrier gas as a function of particle radius via the measurement of particle mobility and inertia using a differential mobility analyzer and a low pressure impactor. Structure of the agglomerates; Densities of carbon particles and of particles in oil burner exhaust; Findings of the study regarding the fractal-like dimensions of ferromagnetic cobalt agglomerates.

Presents a study which measured small- and large-angle x-ray scattering from epitaxial iron (001) on a magnesium oxide (001) surface as a function of film thickness, using grazing incidence x-ray scattering. Details on strain relaxation subsequent to agglomeration; Description of epitaxial film preparation; Information on the elastic homogeneous biaxial strain energy in an island.

Studies boron diffusion at high concentrations under predeposition conditions. Information on the kinetic model without clustering reaction; Details on the dynamic clustering model; Discussion of findings.

Presents an equilibrium model for agglomeration in polycrystalline thin films which considers the energy balance between the grain boundary energy and both surface and substrate interface energies. Energy balances at upper and lower grain boundary grooves; Forecast on critical grain size limiting agglomeration using the measured grooving angles; Energy balance after island formation.

Fe79.7-xNb0.3CrxB20 (x = 11.5-13.5 at. %) submicron powders with glassy structure and sizes between a few tens of nm and 1 μm have been prepared by high-energy ball milling from glassy melt-spun ribbons (MSRs) precursors. The glassy structure existing in the MSRs, and consisting of Fe-Cr clusters embedded within the (Fe,Nb)3B residual amorphous matrix, is preserved by milling the annealed MSRs in oleic acid and n-heptane. The glassy structure of the submicron powders confers the specific magnetic properties and allows tuning the Curie temperatures in the range of 15-50 °C. The precipitation of α-Fe in excess shifts the Curie temperature to 780 °C. The use of surfactants (oleic acid or heptane) avoids partially the agglomeration of powders, and their individual size goes down to 25-40 nm. The heating efficiency of the submicron powders in a.c. fields (H = 350mT and f = 153 kHz) evidences a working regime in the range of 33-45 °C, depending on Cr content, indicating the suitability of using the Fe-Cr-Nb-B powders for hyperthermia applications. [ABSTRACT FROM AUTHOR]

High-moment monodisperse disk-shaped Co–Fe magnetic nanoparticles, stable in aqueous solution, were physically fabricated by using nanoimprinted templates and vacuum deposition techniques. These multilayer synthetic antiferromagnetic nanoparticles exhibit nearly zero magnetic remanence and coercivity, and susceptibilities which can be tuned by exploiting interlayer magnetic interactions. In addition, a low cost method of scaling up the production of sub-100 nm synthetic antiferromagnetic nanoparticles is demonstrated. [ABSTRACT FROM AUTHOR]

Maghemite-silica nanocomposites were prepared from water-based magnetic fluids through the sol-gel method. X-ray diffraction revealed that the maghemite nanoparticles had a size of 5 nm. Electron magnetic resonance of the composites was studied as a function of temperature and nanoparticle concentration. The resonance field was found to decrease upon increasing the maghemite concentration, while the linewidth increased. The effect was interpreted in terms of interparticle as well as intraparticle magnetic interactions. The data analysis suggests the presence of small agglomerates in the maghemite-silica nanocomposite for higher particle concentrations. [ABSTRACT FROM AUTHOR]

To transfer face-centered-cubic (fcc) FePt nanoparticles to the face-centered-tetragonal (fct) phase with high magnetic anisotropy, heat treatments are necessary. The heat treatments lead to agglomeration and sintering of the nanoparticles. To prevent the particles from sintering, salts as the separating media (matrix) have been used for annealing the nanoparticles in our experiments. The fcc nanoparticles produced by chemical synthesis were mixed with NaCl powders. The mixture was then annealed in forming gas (93%H2+7%Ar) in different conditions to complete the fcc to fct phase transition. After the annealing, the salt was washed out by water and monodisperse fct FePt nanoparticles were obtained. Detailed studies on the effect of the NaCl-to-FePt weight ratios (from 1:1 to 400:1) have been performed. It was found that a suitable NaCl-to-FePt ratio is the key to obtain monodisperse fct FePt nanoparticles. A higher NaCl-to-FePt ratio is needed for larger particles when the annealing conditions are the same. Increased annealing temperature and time should be accompanied by a higher NaCl-to-FePt ratio. Magnetic measurements show very high coercivity (up to 30 kOe) of the monodispersed fct nanoparticles by the salt-matrix annealing. [ABSTRACT FROM AUTHOR]

The charging characteristics of metal-oxide-semiconductor (p-type) structures containing Au nanocrystals in SiO2 gate oxide were studied. The Au nanocrystals of 2–3 nm in diameter are self-assembled from the agglomeration of an ultrathin Au layer embedded in SiO2 matrix by annealing at 600 °C. A large hysteresis loop is found in the capacitance-voltage (C-V) relation even at a low operating voltage (2 V), indicating its significant charge storage effect. Different charging rates for two kinds of trapped carriers (electron and hole) were found from C-V measurement under various scan rates. The relatively stable retention characteristic for holes trapped in the Au nanocrystals at room temperature was also demonstrated. [ABSTRACT FROM AUTHOR]

Presents a study which examined the agglomeration of γ-Fe[sub2]O[sub3] acicular magnetic particles in concentrations of approximately 0.005 percent by weight in water. Introduction to agglomeration effects in fluid dispersion of magnetic particles; Materials and methods used; Results and discussion.

The electrical contact of the source and drain regions in state-of-the-art CMOS transistors is nowadays facilitated through NiSi, which is often alloyed with Pt in order to avoid morphological agglomeration of the silicide film. However, the solid-state reaction between as-deposited Ni and the Si substrate exhibits a peculiar change for as-deposited Ni films thinner than a critical thickness of tc = 5 nm. Whereas thicker films form polycrystalline NiSi upon annealing above 450 ° C , thinner films form epitaxial NiSi2 films that exhibit a high resistance toward agglomeration. For industrial applications, it is therefore of utmost importance to assess the critical thickness with high certainty and find novel methodologies to either increase or decrease its value, depending on the aimed silicide formation. This paper investigates Ni films between 0 and 15 nm initial thickness by use of “thickness gradients,” which provide semi-continuous information on silicide formation and stability as a function of as-deposited layer thickness. The alloying of these Ni layers with 10% Al, Co, Ge, Pd, or Pt renders a significant change in the phase sequence as a function of thickness and dependent on the alloying element. The addition of these ternary impurities therefore changes the critical thickness tc. The results are discussed in the framework of classical nucleation theory. [ABSTRACT FROM AUTHOR]

Positron annihilation was used to probe vacancy-type defects in electrodeposited Cu films with capping layers. For as-deposited Cu films, two different types of vacancy-type defects were found to coexist: vacancy aggregates (V2-V4) and larger vacancy clusters (∼V10). During the fabrication processes of the capping layers, these defects diffused towards the interface between the capping layers and Cu. On the sample with the capping layers consisting of TaN and SiCN, a vacancy-rich region about 40 nm wide was introduced below the TaN/Cu interface, which was attributed to the blocking of vacancies by the TaN layer, and resulted in their agglomeration. The SiCN layer started degrading at annealing temperatures above 270 °C. Above 570 °C, the size of open spaces and their concentration in the SiCN layer decreased, which can be attributed to the diffusion of Cu atoms into the SiCN layer. Positron annihilation was shown to have a high potential to detect vacancy-type defects and open spaces near the interface between barrier metals and electroplated Cu. [ABSTRACT FROM AUTHOR]

We employ in-situ flash x-ray imaging, together with a detailed multiphase convective burn model, to demonstrate how explosives' binder characteristics influence the burning processes in thermal explosions. Our study focuses on the HMX-based explosives LX-10 and PBX 9501. While the HMX (cyclotetramethylene-tetranitramine) crystallite size distributions for these two explosives are nearly identical before heating, our experiments and simulations indicate that after heating, variations result due to differences in binder composition. Post-ignition flash x-ray images reveal that the average density decreases at late times more rapidly in PBX 9501 than LX-10, suggesting a faster conductive burning rate in PBX-9501. Heated permeability measurements in LX-10 and PBX 9501 demonstrate that the binder system characteristics influence the evolution of connected porosity. Once ignited, connected porosity provides pathways for product gas heating ahead of the reaction front and additional surface area for burning, facilitating the transition from conductive to convective burning modes. A multiphase convective burn model implemented in the ALE3D code is used to better understand the influence on burn rates of material properties such as porosity and effective thermally damaged particle size. In this context, particles are defined as gas-impermeable binder-coated crystallites and agglomerations with a set of effective radii reff. Model results demonstrate quantitative agreement with containment wall velocity for confined PBX 9501 and LX-10, and qualitative agreement with density as a function of position in the burning explosive. The model predicts a decrease in post-ignition containment wall velocity with larger radii in reff. These experimental data and model results together provide insight into the initiation and propagation of the reaction wave that defines the convective burn front in HMX-based explosives, a necessary step toward predicting violence under a broad range of conditions. [ABSTRACT FROM AUTHOR]

A combination of the effective medium and the phonon approaches is used to investigate heat conduction in heterogeneous media composed of a homogeneous matrix in which spherical particles of micro and nanosizes are dispersed. In particular, we explore the effect of different types of scattering on the particle-matrix interface, temperature dependence of the effective heat conduction coefficient, and the effect of various degrees of agglomeration of the particles. Predictions calculated explicitly for Si nanoparticles dispersed in Ge matrix agree with available Monte Carlo simulations. Our predictions show that the higher is the temperature the lower is the heat conductivity and the smaller is the influence of the details of the particle-matrix interactions. As for the influence of the agglomeration, we predict both decrease and increase of the heat conduction depending on the degree of the agglomeration. [ABSTRACT FROM AUTHOR]

Radiatively heated levitated functional droplets with nanosilica suspensions exhibit three distinct stages namely pure evaporation, agglomeration, and finally structure formation. The temporal history of the droplet surface temperature shows two inflection points. One inflection point corresponds to a local maximum and demarcates the end of transient heating of the droplet and domination of vaporization. The second inflection point is a local minimum and indicates slowing down of the evaporation rate due to surface accumulation of nanoparticles. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation, and shape deformation. In this work, we provide a detailed analysis for each process and propose two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound pressure level), droplet size, viscosity, and density. However, we show that while the agglomeration timescale decreases with initial particle concentration, the evaporation timescale shows the opposite trend. The final normalized diameter can be shown to be dependent solely on the ratio of agglomeration to evaporation timescales for all concentrations and acoustic amplitudes. The structures also exhibit various aspect ratios (bowls, rings, spheroids) which depend on the ratio of the deformation timescale (tdef) and the agglomeration timescale (tg). For tdef

Novel graphene oxide (GO) particle was introduced as an additive to soft magnetic carbonyl iron (CI) micron-sized particle based magnetorheological (MR) fluid to improve its sedimentation and agglomeration problems in which the MR fluid is a colloidal suspension of magnetizable particles dispersed in a nonmagnetic carrier. The added plate-like GO gap-fillers filled the interspaces of CI particles and improved the resistance to sedimentation. The MR properties of two systems with and without additives were evaluated and compared under different magnetic field strengths using a rotational rheometer. Morphology of pure CI and GO/CI mixture were examined via scanning electron microscopy (SEM) images, and X-ray diffraction (XRD) patterns confirm the differences between pure CI and GO/CI mixture further, the sedimentation problem was observed to be improved. [ABSTRACT FROM AUTHOR]