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The dielectric constant is a critical parameter in many energy-related applications. Typically, increasing the dielectric constant of soft materials involves adding high dielectric constant polar liquids or inorganic fillers, but there are limitations to this approach due to safety concerns with volatile and flammable solvents and the agglomeration of inorganic fillers. An alternative approach is to add zwitterionic liquids that exhibit exceptionally high dielectric constants with negligible volatility. Here, we report the synthesis of a series of zwitterionic liquids containing an imidazolium cation, exhibiting the highest dielectric constant among all organic molecules (∼350 at 293 K). The cation–anion linkage was tailored in a wide range between three and nine carbons, rendering the zwitterion dipole from 25 to 52 D. Comparing the dielectric constant for zwitterions with different anions (i.e., sulfonylimide, sulfonate, and carboxylate) reveals the beneficial impacts of the delocalized sulfonylimide anion vs the carboxylate anion due to the enlarged molecular dipole and more homogenous liquid morphology. Molecular dipole and liquid morphology are identified as the keys to developing high dielectric constant zwitterionic liquids. The extremely high dielectric constant accessible with the proposed molecular design paves new avenues for developing high dielectric constant zwitterions that act as dielectricizers. [ABSTRACT FROM AUTHOR]

We evaluated the effect of O atoms on the postannealed BaSi2 films grown by molecular beam epitaxy. Postannealing (PA) in an Ar atmosphere at a pressure of 1.9 × 105 Pa increased the O concentration to 7 × 1020 cm−3 in the bulk region and further increased to ∼1022 cm−3 at the BaSi2/Si interface. Cracks formed during the PA process, allowing O to enter more easily to the BaSi2 films. In the x-ray photoelectron spectroscopy spectrum of the Si 2s core level measured at 10 nm from the surface, a shift of the peak related to SiOx was detected, indicating a change in the bonding state of Si and O in this region. When PA was performed in vacuum at 10−3 Pa, the photoresponsivity in the short wavelength region was enhanced, with a maximum value of 6.6 A W−1 at 790 nm. The O concentration in the film decreased in the sample annealed in vacuum, and the PL peak intensity at 0.85 eV decreased, suggesting that this was due to a decrease in O-related defects compared to the Ar atmosphere. However, agglomeration of BaSi2 caused significant surface roughness, indicating the importance of PA conditions that minimize O uptake and keep the surface smooth for improved performance of BaSi2 solar cells. [ABSTRACT FROM AUTHOR]

In order to address the issue of magnetic agglomeration leading to poor magnetic separation efficiency and low activity enhancement, resulting in limited utilization of steel slag fine powder material, this study proposes a novel dry magnetic separator with air fluidization as the feeding method. The new separator incorporates adjustable magnetic field strength based on the material's magnetic properties, enabling individual particle separation through a magnetic mesh while simultaneously enhancing mechanical and ultrasonic composite vibration. In addition, it enhances competitiveness by incorporating negative pressure suction. Primary magnetic separation tests on a steel slag fine powder material demonstrate that the air fluidized dry magnetic separator effectively separates inert minerals from active minerals in the steel slag powder. The iron grade in the magnetic products reaches 21.81%, which is 6.88% higher than that of the original steel slag, while the iron grade in non-magnetic products decreases to 11.93%, representing a 3% reduction compared to the original steel slag composition. Further sweeping and selection processes are expected to further improve these results, ultimately achieving effective utilization of steel slag. [ABSTRACT FROM AUTHOR]

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 low melting point of room temperature ionic liquids is usually explained in terms of the presence of bulky, low-symmetry, and flexible ions, with the first two factors related to the lattice energy while an entropic effect is attributed to the latter. By means of molecular dynamics simulations, the melting points of 1-ethyl-3-methyl-imidazolium hexafluorophosphate and 1-decyl-3-methyl-imidazolium hexafluorophosphate were determined, and the effect of the molecular flexibility over the melting point was explicitly computed by restraining the rotation of dihedral angles in both the solid and the liquid phases. The rotational flexibility over the bond between the ring and the alkyl chain affects the relative ordering of the anions around the cations and results in substantial effects over both the enthalpy and the entropy of melting. For the other dihedral angles of the alkyl group, the contributions are predominantly entropic and an alternating behavior was found. The flexibility of some dihedral angles has negligible effects on the melting point, while others can lead to differences in the melting point as large as 20 K. This alternating behavior is rationalized by the different probabilities of conformation defects in the crystal. [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]

Nanocomposite magnets have attracted much attention because of their ultra-high theoretical magnetic energy product and saving rare earth resources. In this study, the Fe93.5Si6.5 with higher hardness than the most common soft magnetic phase (α-Fe) was used to synthesize SmCo5/Fe-Si nanocomposite magnets, and its nanosized process was studied. The results showed that Fe-Si can be well dispersed into SmCo5 matrix through 12 hours of ball milling, and appeared in fine and evenly distributed grains in the SmCo5/Fe-Si nanocomposites, indicating it is suitable for soft magnetic phase. The nanosized process of Fe-Si phase can be summarized as from the irregular shape of agglomeration, to long chain, and finally too uniformly dispersed Fe-Si particles with increased milling time. As a result, the SmCo5/Fe-Si nanocomposite magnet with the optimal maximum magnetic energy product was 14.3 MGOe, accompanied by remanence of 9.5 kG and coercivity of 8.2 kOe. Our results show that by using Fe-Si with high hardness as the soft magnetic phase, the prepared nanocomposite magnet not only has good properties, but also can be expected that the two phases with closer mechanical properties can be deformed harmoniously. [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]

We report the formation of nanoparticles with significant diamond character after UV multi-photon laser excitation of gaseous naphthalene, buffered in static helium gas, at room temperature. The nanoparticles are identified in situ by their absorption and scattering spectra between 400 and 850 nm, which are modeled using Mie theory. Comparisons of the particles' spectroscopic and optical properties with those of carbonaceous materials indicate a sp³/sp² hybridization ratio of 8:1 of the particles formed. The particle extinction in the closed static (unstirred) gas-phase system exhibits a complex and quasi-oscillatory time dependence for the duration of up to several hours with periods ranging from seconds to many minutes. The extinction dynamics of the system is based on a combination of transport features and particle interaction, predominantly agglomeration. The relatively long period of agglomeration allows for a unique analysis of the agglomeration process of diamond-like carbon nanoparticles in situ. [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]

Room temperature ionic liquids (RTILs) have been considered an interesting alternative to stabilizers in platinum (Pt) nanoparticle synthesis because they can prevent agglomeration of nanoparticles and act as a reaction medium. In addition, since RTILs remain in a liquid state over a wide range of temperatures, Pt catalyst processing steps, such as heat treatments and surface cleaning, can be omitted, and the Pt nanoparticles are uniformly dispersed under fuel cell operating conditions. Herein, we summarize the significant works on recent advances and developments using RTILs to prepare Pt-based catalysts related to the application in oxygen reduction reaction (ORR). Moreover, peculiar attention has been paid to the role of RTILs in improving the performance and efficiency of the RTILs and their effects on catalyst structure- and composition-control, detailed by examining several aspects. Finally, we outlook the challenges and opportunities of the research in the relevant fields for the development of ORR catalysts. [ABSTRACT FROM AUTHOR]

In this work, we study the influence of polymer chain length (m), based on Lennard-Jones potential, and nanoparticle (NP)-polymer interaction strength (&eh;np) on aggregation and dispersion of soft repulsive spherically structured NPs in polymer melt using coarse-grain molecular dynamics simulations. A phase diagram is proposed where transitions between different structures in the NP-polymer system are shown to depend on m and &eh;np. At a very weak interaction strength &eh;np = 0.1, a transition from dispersed state to collapsed state of NPs is found with increasing m, due to the polymer's excluded volume effect. NPs are well dispersed at intermediate interaction strengths (0.5 <= &eh;np <= 2.0), independent of m. A transition from dispersion to agglomeration of NPs, at a moderately high NP-polymer interaction strength &eh;np = 5.0, for m = 1-30, is identified by a significant decrease in the second virial coefficient, excess entropy, and potential energy, and a sharp increase in the Kirkwood-Buff integral. We also find that NPs undergo the following transitions with increasing m at &eh;np >= 5.0: string-like → branch-like → sphere-like → dispersed state. [ABSTRACT FROM AUTHOR]

The molecular interactions between solvent and nanoparticles during photoactive layer formation in organic photovoltaic (OPV) cells influence the morphology of the photoactive layer and hence determine the power conversion efficiency. Prediction of optimal synthesis parameters in OPVs, such as choice of solvent, processing temperature, and nanoparticle concentration, requires fundamental understanding of the mechanisms that govern the agglomeration of nanoparticles in solvents. In this study, we used molecular dynamics simulations to simulate a commonly used organic nanoparticle, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), in various solvents to correlate solvent-nanoparticle interactions with the size of the agglomerate structure of PCBM. We analyzed the effects of concentration of PCBM and operating temperature on the molecular rearrangement and agglomeration of PCBM in three solvents: (i) toluene, (ii) indane, and (iii) toluene-indane mixture. We evaluated the agglomeration behavior of PCBM by determining sizes of the largest clusters of PCBM and the corresponding size distributions. To obtain further insight into the agglomerate structure of PCBMs, we evaluated radial distribution functions (RDFs) and coordination numbers of the various moieties of PCBMs with respect to solvent atoms as well as with respect to that of other PCBMs. Our simulations demonstrate that PCBMs form larger clusters in toluene while they are relatively dispersed in indane, which indicates the greater solubility of PCBM in indane than in toluene. In toluene-indane mixture, PCBMs are clustered to a greater extent than in indane and less than that in toluene. To correlate agglomerate size to nanoparticle-solvent interactions, we also evaluated the potential of mean force (PMF) of the fullerene moiety of PCBM in toluene and indane. Our results also show that the cluster size of PCBM molecules increases with the increase of concentration of PCBM and the processing temperature. To correlate the PCBM agglomeration with the dynamics of solvents, we evaluated the rotational correlation functions of the solvents. Our results illustrate that toluene relaxes faster than indane in the simulated systems and relaxation time of solvent molecules decreases with the decrease of concentration of PCBM and increase of processing temperature. Results presented in this study provide fundamental insight that can help to choose favorable solvents for processing PCBMs in OPV applications. [ABSTRACT FROM AUTHOR]

Ni x Fe 3 − x O4 thin films with varying Ni amount (0 ≤ x ≤ 1.5) were deposited on MgO(001) via reactive molecular beam epitaxy. The growth process was monitored during film deposition by means of X-ray diffraction. All prepared films exhibit a well-ordered structure with complete vertical crystallinity throughout the whole film growth and flat surfaces of the final films independent of the Ni amount. An enhancement of the vertical compression in the initial growth continuously decreases up to a film thickness of 8 nm. During further growth, all films exhibit residual and constant vertical compression with lateral adaption of the final films to the substrate lattice, as observed by high energy surface X-ray diffraction experiments. Hard X-ray photoelectron spectroscopy measurements of the final films reveal increasing Fe 3 + : Fe 2 + ratios for higher Ni content and point to additional NiO agglomerations within the films exceeding the stoichiometric Ni amount of x = 1. [ABSTRACT FROM AUTHOR]

The formation of agglomerates by salt-induced double layer compression of magnetic nanoparticles in the absence and presence of an external magnetic field was investigated experimentally as well as computationally in this study. The structures of the agglomerates were analyzed through scanning electron microscopy and proved to be highly porous and composed of large spaces among the branches of a convoluted network. In the absence of an external magnetic field, the branches of such a network were observed to be oriented in no particular direction. In contrast, when the agglomeration process was allowed to occur in the presence of an external magnetic field, these branches appeared to be oriented predominantly in one direction. A modified Discrete Element Method was applied to simulate the agglomeration process of magnetic nanoparticles both in the absence and presence of an external magnetic field. The simulations show that agglomeration occurred by the formation of random clusters of nanoparticles which then joined to form a network. In the presence of anisotropic magnetic forces, these clusters were rotated to align along the direction of the magnetic field and the final network formed consisted largely of elongated branches of magnetic nanoparticles. [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]

An extended particle agglomeration control model and Monte Carlo simulation methodology were used to describe the behavior of the colloidal aggregation process in presence of inhibitor as a confined fluid. In this work results about the mean cluster size, Z, with respect to different variables, temperature, inhibitor concentration and pore size, are presented and showed that Z strongly depends on the slitlike pore size. In addition, a temperature interval where the heating of the system leads to the particle clustering was found. [ABSTRACT FROM AUTHOR]

We have examined the diffusion and agglomeration of Au adatoms on the H-terminated Si(111)-(1×1) surface using periodic slab density functional theory calculations. We find that a single Au atom favorably resides atop a surface Si atom by breaking an original ≡Si–H bond while the H atom is bonded to the Au atom in the vertical direction, leading to the ≡Si–Au–H state. Starting from the most favorable on-top (T) site, a Au adatom is predicted to undergo diffusion by moving in and out of the T site without disrupting surface Si–H bonds. The predicted overall activation energy for the Au diffusion is 0.5 eV. Our calculations show that Au agglomeration leads to libration of H atoms from the Au/Si interface, while the H atoms are weakly bound to Au clusters and subsequently undergo associative H2 desorption with no significant barrier. Based on charge density analysis we also discuss bonding mechanisms for Au on H-terminated Si(111)-(1×1). Our findings are as a whole consistent with experimental results available in literature. [ABSTRACT FROM AUTHOR]

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFFAlH3 is used to study the dynamics governing hydrogen desorption in AlH3. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFFAlH3. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH4. [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]

There exist experimental evidences that the structure and extension of colloidal aggregates in suspensions change dramatically with temperature. This results in an associated change in the suspension rheology. Experimental studies of the inhibitor applications to control the particle clustering have revealed some unexpected tendencies. Namely, the heating of colloidal suspensions has provoked either extension or reduction of the colloidal aggregates. To elucidate the origin of this behavior, we investigate the influence of temperature on the stabilizing effect of the inhibitor, applying an associative two-component fluid model. Our results of the canonical Monte Carlo simulations indicate that the anomalous effect of the temperature may not be necessarily explained by the temperature dependent changes in the inhibitor tail conformation, as has been suggested recently by Won et al. [Langmuir 21, 924 (2005)]. We show that the competition between colloid-colloid and colloid-inhibitor associations, which, in turn, depends on the temperature and the relative concentrations, may be one of the main reasons for the unexpected temperature dependence of inhibitor efficacy. [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 vibrational spectroscopy of the mono- and divanadium oxide cluster cations VO[sub 1-3][sup +] and V[sub 2]O[sub 2-6][sup +] is studied in the region from 600 to 1600 wave numbers by infrared photodissociation of the corresponding cluster cation-helium atom complexes. The comparison of the experimental depletion spectra with the results of density functional calculations on bare vanadium oxide cluster cations allows for an unambiguous identification of the cluster geometry in most cases and, for VO[sub 1-3][sup +] and V[sub 2]O[sub 5,6][sup +], also of the electronic ground state. A common structural motif of all the studied divanadium cluster cations is a four-membered V–O–V–O ring, with three characteristic absorption bands in the 550–900 wave number region. For the V–O–V and V==O stretch modes the relationship between vibrational frequencies and V–O bond distances follows the Badger rule. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A systematic all electron post Hartree–Fock as well as density functional theory (DFT) based calculations for the polarizability and binding energy of sodium metal clusters have been performed and an in-depth analysis of the discrepancy between the experimental and theoretical results is presented. A systematic investigation for the assessment of different DFT exchange–correlation functionals in predicting the polarizability values has also been reported. All the pure DFT functionals have been found to considerably underestimate the calculated polarizability values as compared to the MP2 results. DFT calculations using the full Hartree–Fock exchange along with one-parameter progressive correlation functional have, however, been shown to yield results in good agreement with the MP2 and experimental results. The possible sources of error present in the experimental measurements as well as in the different theoretical methods have also been analyzed. One of the most important conclusions of the present study is that the effect of electron correlation plays a significant role in determining the polarizability of the clusters and the MP2 method can be considered to be one of the most reliable methods for their prediction. It has also been noted that the polarizability value of the lower member clusters (Na[sub 2] and Na[sub 4]) calculated by highly sophisticated methods such as, CCSD and CCSD(T) are found to be very close to the corresponding MP2 values. The polarizability and the binding energy of the clusters are found to be inversely related to each other and their correlation is rationalized by invoking the minimum polarizability principle. A good linear correlation between the polarizability and volume of the cluster has also been found to exist. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A potential energy surface for the ground electronic state of the Ar–HI van der Waals complex is calculated at the coupled-cluster with single and double excitations and a noniterative perturbation treatment of triple excitations [CCSD(T)] level of theory. Calculations are performed using for the iodine atom a correlation consistent triple-ζ valence basis set in conjunction with large-core Stuttgart–Dresden–Bonn relativistic pseudopotential, whereas specific augmented correlation consistent basis sets are employed for the H and Ar atoms supplemented with an additional set of bond functions. In agreement with previous studies, the equilibrium structure is found to be linear Ar–I–H, with a well depth of 205.38 cm-1. Another two secondary minima are also predicted at a linear and bent Ar–H–I configurations with well depths of 153.57 and 151.57 cm-1, respectively. The parametrized CCSD(T) potential is used to calculate rovibrational bound states of Ar–HI/Ar–DI complexes, and the vibrationally averaged structures of the different isomers are determined. Spectroscopic constants are also computed from the CCSD(T) surface and their comparison with available experimental data demonstrates the quality of the present surface in the corresponding configuration regions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Experimental and theoretical evidence is presented for the nondissociative chemisorption of O[sub 2] on free Au cluster anions (Au[sub n][sup -], n=number of atoms) with n=2, 4, 6 at room temperature, indicating that the stabilization of the activated di-oxygen species is the key for the unusual catalytic activities of Au-based catalysts. In contrast to Au[sub n][sup -] with n=2, 4, 6, O[sub 2] adsorbs atomically on Au monomer anions. For the Au monomer neutral, calculations based on density functional theory reveal that oxygen should be molecularly bound. On Au dimer and tetramer neutrals, oxygen is molecularly bound with the O–O bond being less activated with respect to their anionic counterparts, suggesting that the excess electron in the anionic state plays a crucial role for the O–O activation. We demonstrate that interplay between experiments on gas phase clusters and theoretical approach can be a promising strategy to unveil mechanisms of elementary steps in nanocatalysis. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A first-principles quantum chemistry method, based on the Kohn–Sham density-functional theory, is used to investigate the adsorption of CO and O[sub 2] on small gas-phase gold cluster anions. The saturated adsorption of carbon monoxide on gold cluster anions Au[sub N][sup -] (N=2–7) is discussed. The adsorption ability of CO reduces with the increase of the number of CO molecules bound to gold cluster anions, resulting in saturated adsorption at a certain amount of absorbed CO molecules, which is determined by geometric and electronic properties of gold clusters cooperatively. The effect of CO preadsorption on the electronic properties of gold cluster anions depends on the cluster size and the number of adsorbed CO, and the vertical detachment energies of CO-adsorbed gold cluster anions show a few changes with respect to corresponding pure gold cluster anions. The results indicate that the impinging adsorption of CO molecules may lead to geometry structure transformation on Au[sub 3][sup -] cluster. For the coadsorption of CO and O[sub 2] on Au[sub 2][sup -], Au[sub 3][sup -] isomers, Au[sub 4][sup -], and Au[sub 6][sup -], we describe the cooperative adsorption between CO and O[sub 2], and find that the O[sub 2] dissociation is difficult on gas-phase gold cluster anions even with the preadsorption of CO. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The C[sub s] symmetry reaction of the H[sub 2] molecule on a Pt[sub 4] (111) clusters, has been studied using ab initio multiconfiguration self-consistent field plus extensive multireference configuration interaction variational and perturbative calculations. The H[sub 2] interaction by the vertex and by the base of a tetrahedral Pt[sub 4] cluster were studied in ground and excited triplet and singlet states (closed and open shells), where the reaction curves are obtained through many avoided crossings. The Pt[sub 4] cluster captures and activates the hydrogen molecule; it shows a similar behavior compared with other Pt[sub n] (n=1,2,3) systems. The Pt[sub 4] cluster in their lowest five open and closed shell electronic states: [sup 3]B[sub 2], [sup 1]B[sub 2], [sup 1]A[sub 1] [sup 3]A[sub 1], [sup 1]A[sub 1], respectively, may capture and dissociate the H[sub 2] molecule without activation barriers for the hydrogen molecule vertex approach. For the threefolded site reaction, i.e., by the base, the situation is different, the hydrogen adsorption presents some barriers. The potential energy minima occur outside and inside the cluster, with strong activation of the H–H bond. In all cases studied, the Pt[sub 4] cluster does not absorb the hydrogen molecule. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]