Добірка наукової літератури з теми "STRUCTURAL INTERFACE PROPERTIES"

AbstractMany processes in nature and technology are based on the static and dynamic properties of solid–liquid interfaces. Prominent examples are crystal growth, melting, and recrystallization. These processes are strongly affected by the local structure at the solid–liquid interface. Therefore, it is mandatory to understand the change in the structure across the interface. The break of the translational symmetry at the interface induces ordering phenomena, and interactions between the liquid's molecules and the atomically corrugated solid surface may induce additional ordering effects. In the past decade, new techniques have been developed to investigate the structural properties of such (deeply) buried interfaces in their natural environment. These methods are based on deeply penetrating probes such as brilliant x-ray beams, providing full access to the structure parallel and perpendicular to the interface. Here, we review the results of a number of case studies including liquid metals in contact with Group IV elements (diamond and silicon), where charge transfer effects at the interface may come into play. Another particularly important liquid in our environment is water. The structural properties of water vary widely as it is brought in contact with other materials. We will then proceed from these seemingly simple cases to complex fluids such as colloids.

We present a study of type II interfaces between semiconducting materials. In this type of interface the lineup of the two semiconductor band gaps has a staggered shape. The band bending at the interface depends on the doping type and concentration of the two semiconductors involved. In most cases two triangular quantum wells appear at the interface, one for the electrons in the semiconductor having the lowest conduction band edge and one in the other material for holes. In such a case, when charges are injected, the electrons and holes are separated at the interface, so that the electron/hole recombination occurs through the interface. The main characteristic of type II interfaces is that their photoluminescent (PL) intensity is very high compared with each material forming the heterojunction. This high PL intensity can be used advantageously in optoelectronic device applications. We present semiconductor pairs for which it is possible to have type II interfaces and their optical properties. We will emphasize particularly the cases of AlInAs/InP and GaPSb/InP whose low-temperature interface recombination energies are 1.2 and 0.90 eV, respectively.

ABSTRACTElectrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2- terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.

The interface structure, electronic and optical properties of Au–ZnO are studied using the first-principles calculation based on density functional theory (DFT). Given the interfacial distance, bonding configurations and terminated surface, we built the optimal interface structure and calculated the electronic and optical properties of the interface. The total density of states, partial electronic density of states, electric charge density and atomic populations (Mulliken) are also displayed. The results show that the electrons converge at O atoms at the interface, leading to a stronger binding of interfaces and thereby affecting the optical properties of interface structures. In addition, we present the binding energies of different interface structures. When the interface structure of Au–ZnO gets changed, furthermore, varying optical properties are exhibited.

The selection of a proper metal for replacement of polycrystalline silicon as the metal gate in future generation transistors has been hampered by pinning of the metal Fermi level at the metal/dielectric interface. Using monoclinic hafnia and zirconia as the gate dielectric we compare three different metal gate/gate dielectric interface structures where the oxygen affinity of the metal gate varies from low to high under normal processing conditions. For each of the metal gate/gate dielectric combination we considered a number of interface stoichiometries and tried to identify the most likely interface composition by comparing the calculated and measured valence band offsets (VBO). Because density functional theory (DFT) underestimates the dielectric band gap, it also underestimates the VBO thus requiring a correction to the band edges, which we accomplished using GW for cubic and monoclinic hafnia. Our GW shift value for monoclinic hafnia (0.3 eV) indicates mostly reduced interfaces in all metal/dielectric combinations considered.

Heterostructures with competing magnetic interactions are often exploited for their tailored new functionalities. Exchange bias is one such outcome of interfacial coupling across ferromagnetic–antiferromagnetic, multiferroic–ferromagnetic, two antiferromagnetic, or antiferromagnetic and paramagnetic interfaces. Apart from the usual horizontal shift of the hysteresis loop (exchange bias shift), a small `vertical shift' of the hysteresis loops along the magnetization axis has also been seen, but it was always relatively small. Recently, an unusually large `vertical shift' in epitaxial bilayer heterostructures comprising ferromagnetic La0.7Sr0.3MnO3and multiferroic orthorhombic YMnO3layers was reported. Here, using polarized neutron reflectometry, the magnetic proximity effect in such bilayers has been investigated. A detailed magnetic depth profile at the interface, elucidating the intrinsic nature of the vertical shift in such heterostructures, is reported. Further corroboration of this observation has been made by means of first-principles calculations, and the structural and electronic properties of YMnO3/La0.7Sr0.3MnO3heterostructures are studied. Although in the bulk, the ground state of YMnO3is anE-type antiferromagnet, the YMnO3/La0.7Sr0.3MnO3heterostructure stabilizes the ferromagnetic phase in YMnO3in the interface region. It is found that, in the hypothetical ferromagnetic phase of bulk YMnO3, the polarization is suppressed, and owing to a large difference between the lattice constants in theabplane a strong magnetocrystalline anisotropy is present. This anisotropy produces a high coercivity of the unusual ferromagnetic YMnO3phase at the interface, which is responsible for the large vertical shift observed in experiment.

Structural features of interfaces in [Co/Cu]n superlattices obtained by magnetron sputtering have been studied by nuclear magnetic resonance (NMR). Modification of interface structural characteristics and magnetoresistive properties of the superlattices with the increase of the number of [Co/C] bilayers is analyzed. Correlation between magnetoresistance and interface structural characteristics has been revealed.

Structural ceramics are necessarily polycrystalline and their usefulness is largely determined by the interfaces between the grains. The relationship between the structure and chemistry of different interfaces and the micro-structure can be illustrated by reviewing studies of interfaces in a wide range of materials including such classical ceramics as Al2O3, the current “hightech” polyphase ceramics exemplified by ZrO2-toughened Al2O3, and the composite materials of the future. Using transmission electron microscopy is essential for a complete understanding, but limitations to its use must be recognized. Only by understanding the factors that control the behavior of these interfaces will it become possible to further extend the application of interface engineering.Structural ceramics are a group of materials that can be used for applications requiring their strength to persist at high temperatures or in conditions that would be particularly corrosive to alternative materials, which are usually metallic. Strength and strength-related properties such as toughness depend largely on the microstructural features of the processed material.The microstructure is defined by the morphology and size of the grains and the interfaces between these grains. If the grains are in intimate contact, then the interface is a grain boundary of the type familiar from studies of metals.

Using atomistic Monte Carlo simulations, we investigated the impact of the interface on the structural properties of iron and copper (Fe/Cu) magnetic multilayers grown by Voronoi diagram. Interest in magnetic multilayers has recently emerged as they are shown to be promising candidates for magnetic storage media, magneto-resistive sensors and personalized medical treatment. As these artificial materials show large differences in properties compared to conventional ones, many experimental and theoretical works have been dedicated on shedding light on these differences and tremendous results have emerged. However, little is known about the influence of the interfaces on magnetic layers. Using numerical approaches, we show that the structure of each layer depends on its thickness and the interface morphology. The Fe and Cu layers can adopt either the body-centered-cubic (bcc) or face-centered-cubic (fcc) structure, while the interface can assume amorphous, bcc, fcc, or a mixture of bcc and fcc structures depending on the layer thicknesses. These results are in good agreement with the experiments. They could be helpful in understanding effects such as giant magneto-resistance from the structural perspective.

Für die Effektivität organischer Halbleiter spielen die Grenzflächen zwischen den konjugierten, organischen Molekülen und den Metallelektroden eine entscheidende Rolle. Inhalt dieser Arbeit ist die Untersuchung dieser Grenzflächen bezüglich ihrer strukturellen und elektronischen Eigenschaften. Besonders interessant sind dabei molekulare Systeme, welche Selbstaggregation aufweisen. Ein kritischer Parameter ist dabei das Verhältnis der inter-molekularen zu den Molekül-Metall Wechselwirkungsstärken. Um verschiedene Aspekte der molekularen Selbstaggregation zu beleuchten, wurden vier verschiedene Systeme untersucht. (i) Das defekt-gesteuerte Wachstum selbstaggregierender Molekülschichten wird betrachtet. Es wird gezeigt, dass durch Alkylierung der Moleküle das Wechselwirkungsverhältnis deutlich verändert werden kann. (ii) Weiterhin wird anhand der Orientierungsänderungen der Moleküle der mit zunehmender Schichtdicke schnell abnehmende Einfluss des Substrats nachgewiesen. (iii) Es wird gezeigt, dass durch Fluorination von Molekülen starke chemische Wechselwirkungen mit dem Substrat erzeugt werden können. (iv) Ein neuartiger Ansatz zur Entkopplung von Molekülen von dem Metall wird vorgestellt. Dies geschieht mit Hilfe einer molekularen Vorbeschichtung. Aus experimentellen und theoretischen Daten geht hervor, dass auf diese Art die Wechselwirkung zwischen Molekül und Metall verhindert wird, bei gleichzeitigem Erhalt der metallischen Eigenschaften des Substrats. Weiterhin wirkt die Vorbeschichtung auch als strukturelle Maske. Zur Erkundung der verschiedenen Eigenschaften der molekularen Systeme kamen komplementäre experimentelle Techniken zum Einsatz. Die strukturellen Eigenschaften wurden dabei mit Hilfe von Rastersondenmikroskopie (STM und AFM), Beugung niederenergetischer Elektronen (LEED) und Röntgen-Nahkanten-Absorptions-Spektroskopie (NEXAFS) ermittelt. Eine Bestimmung der elektronischen Eigenschaften erfolgte mittels Photoelektronenspektroskopie (UPS und XPS).
The interfaces between conjugated organic molecules and metal electrodes play an important role for the performance of organic devices. In this thesis the structural and electronic properties at these interfaces are investigated. In particular, the focus of this work is given to molecular systems which undergo self-assembly. The critical parameter which drives the ordering behavior at the interface is the balance between the inter-molecular and molecule-metal interaction strength. To highlight different aspects of the self-assembled growth of molecules, four different molecular systems were investigated. (i) The defect mediated growth of directed self-assembled molecular layers is explored. It will be shown, that addition of short alkyl chains to molecules leads to significant changes in the interaction balance. (ii) The fast attenuation of the substrate''s influence on the molecular ordering with increasing thickness of the molecular layer will be evidenced by the observation of changes in the molecular orientation. (iii) The initiation of strong chemical interactions with the metal substrate by fluorination of molecules is demonstrated by conducting annealing time dependent experiments. (iv) A novel attempt to decouple molecules from the metal substrate is presented. This is achieved by the insertion of a molecular template layer. Experimental and theoretical results prove the successful prevention of molecule-metal interactions, while at the same time metallic properties of the substrate are conserved. Furthermore, the inserted layer acts as a structural template. To explore the properties of the molecular systems, several complementary experimental techniques were used. Structural properties were investigated by scanning probe microscopy (STM and AFM), low energy electron diffraction (LEED) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The electronic properties were discovered by using photoelectron spectroscopy (UPS and XPS).

Complex-oxides have seen an enormous amount of attention in the realm of Condensed Matter Physics and Materials Science/Engineering over the last several decades. Their ability to host a wide variety of novel physical properties has even caused them to be exploited commercially as dielectric, metallic and magnetic materials. Indeed, since the discovery of high temperature superconductivity in the “Cuprates” in the late 1980’s there has been an explosion of activity involving complex-oxides. Further, as the experimental techniques and equipment for fabricating thin films and heterostructures of these materials has improved over the last several decades, the search for new and more exotic properties has intensified. These properties stem from the interfaces formed by depositing these materials onto one another. Whether it be interfacial strain induced by the mismatch between the crystal structures, modified exchange interactions, or some combination of these and other interactions, thin films and heterostuctures provide an invaluable tool the modern condensed matter community. Simply put, a “complex-oxide” is any compound that contains Oxygen and at least two other elements; or one atom in two different oxidation states. Transition Metal Oxides (TMO’s) are a subset of complex-oxides which are of particular interest because of their strong competition between their charge, spin and orbit degrees of freedom. As we progress down the periodic table from 3d to 4d to 5d transition metals, the crystal field, electron correlation and spin-orbit energies become more and more comparable. Therefore, TMO thin films and heterostructures are indispensable to the search for novel physical properties. KTaO3 (KTO) is a polar 5d TMO which has been investigated for its high-k dielectric properties. It is a band insulator with a cubic perovskite crystal structure which is isomorphic to SrTiO3 (STO). This is important because non-polar STO is famous for forming a highly mobile, 2-Dimensional Electron Gas (2DEG) at the hetero-interface with polar LaAlO3 (LAO) as a result of the so-called “polar catastrophe”. Here, I use this concept of polarity to ask an important question: “What happens at hetero-interfaces where two different polar complex oxides meet?” From this question we propose that a hetero-interface between two polar complex-oxides with opposite polarity (I-V/III-III) should be impossible because of the strong Coulomb repulsion between the adjacent layers. However, we find that despite this proposed conflict we are able to synthesize KTO thin films on (110) oriented GdScO3 (GSO) substrates and the conflict is avoided through atomic reconfiguration at the hetero-interface. SrRuO3 (SRO) is a 4d TMO, and an itinerant ferromagnet that is used extensively as an electrode material in capacitor and transistor geometries and proof-of-concept devices. However, in the thin film limit the ferromagnetic transition temperature, TC, and conductivity drop significantly and even become insulating and lose their ferromagnetic properties. Therefore, we ask “Are the transport properties of SRO thin films inherently inferior to single crystals, or is there a way to maintain and/or enhance the metallic properties in the thin film limit?” We have fabricated SRO thin films of various thickness on GSO substrates (tensile strain) and find that all of our samples have enhanced metallic properties and even match those of single crystals. Finally, we ask “Can these enhanced metallic properties in SRO thin films allow us to observe evidence of a topological phase without the complexity of off-stoichiometry and/or additional hetero-structural layers?” Recent reports of oxygen deficient EuO films as well as hetero-structures and superlattices of SRO mixed with SrIrO3 or La0.7Sr0.3MnO3 have suggested that a magnetic skyrmion phase may exist in these systems. By measuring the Hall resistivity, we are able to observer a topological Hall effect which is likely a result of a magnetic skyrmion. We find that of the THE exists in a narrow temperature range and the proposed magnetic skyrmions range in size from 20-120 nm. Therefore, the SRO/GSO system can provide a more viable means for investigating magnetic skyrmions and their fundamental interactions.

The opportunity of using the organic molecules in spintronic devices appeared challenging since these materials, having nominally high spin relaxation times, are suitable for coherent spin manipulation. The spin behaviour in these molecular spintronic devices has been demonstrated to strongly depend on the nature of the chemical bonds between the organic molecules and the magnetic electrodes affecting also the magnetic response of both molecular and metallic sides. In particular, the adsorption of an organic molecule on a ferromagnetic layer has been proved to change the local magnetism of a magnetic substrate. In spite of their technological interest, the investigation of such effect in the case of the polycrystalline magnetic thin film is still lacking. My work contributes to filling this gap by studying the structural, morphological and magnetic properties of ultrathin polycrystalline cobalt films covered by the well-known buckminsterfullerene organic molecule (C60). The combined investigation by AFM, TEM, SQUID magnetometry and anisotropic magnetoresistance allowed to correlate the sample microstructure with the magnetic response and to identify the main mechanism responsible for spin transport in these FM layers. Analysed films are composed of polycrystalline cobalt grains decoupled by non-crystalline amorphous regions. The volume ratio between crystalline grains and amorphous regions increases by increasing the film thickness. As expected, the values of saturation magnetisation decrease as the crystallinity decreases and a typical blocking behaviour is present. The cobalt layers are also subjected to oxidation at the interface with the single crystal oxide substrate. The presence of amorphous phase in polycrystalline cobalt ultrathin film impacts the analysis of transport properties: the anisotropic magnetoresistance slightly depends on the crystalline phase while it is mainly inherent to the amorphous component.

Molten salts attracted the attention of the scientific community several times during the last century. This interest is motivated by the physico-chemical properties of these systems. In fact, usually molten salts show chemical and thermal stability, i.e. they do not easily decompose or react. Furthermore, these compounds remain liquid over an extended range of temperatures, in which they show also a remarkably low volatility. The fact that molten salts are composed solely by ions, and can have a quite wide electrochemical window, make them very interesting as electrolytes[1]. The main disadvantage in the usage of molten salts in any practical process, is their high melting point (for example as high as 800°C for NaCl), which severely limits the number of reactions that can be done in these media and reduces the possibility of industrial scaling, due to the high energy required to maintain those high temperatures. Since the '70s lower temperature molten salts has been synthesised, like chloroaluminate eutectic mixtures, having melting points around 100°C or even lower, but the real turning point that boosted the research field has been the development of the first water-stable low melting point molten salts, that is what are now usually named room temperature ionic liquids, or simply ionic liquids. Ionic liquids are usually composed by a big organic cation and a bulky inorganic, water stable, anion: the bulkiness and the complex asymmetric structure of the ions prevent an efficient packaging, leading to a lowering of the coulombic cohesive energy and so of the melting point. Ionic liquids maintain all the characteristics of the high temperature molten salts, but they are usually liquid at room temperature. This fact induced a renewed interest in the field, as is proved by the several thousand papers published on the topic in 2011. The community of chemists devoted a great effort to the study of ionic liquids, because of the potential use of those liquids as solvents. Ionic liquids are complex systems, that usually are organised in polar and apolar domains, and can dissolve both polar and apolar species. In addition, there are virtually unlimited choices of ions, and each choice changes the physico-chemical characteristics of the systems: this allows to tailor the properties of the ionic liquids (like miscibility, density, viscosity...), in order to match specific tasks. The characteristics of ionic liquids, last but not least their low vapour pressure, promote them as good solvents for the growing field of the Green Chemistry, in substitution of the volatile organic compounds. Ionic liquids are also promising as lubricants, in particular in micro- and nano- -electromechanical devices (NEMSs and NEMSs)[2, 3] as well as electrolytes in photoelectrochemical devices used for energy storage and energy production such as supercapacitors[4, 5] or Grätzel solar cells[6]. In all these cases, the most relevant processes determining the performance of the devices, take place at the liquid/solid interface between ILs and solid surfaces: this is a region only a few nanometers thick where the properties of ILs can be significantly different from those of the bulk. The investigation of the interfacial properties of ILs is therefore of primary importance for their technological exploitation. To date, the (bulk)liquid-vapour and solid- (bulk)liquid ILs interfaces have been studied, mostly by sum-frequency generation spectroscopy[7, 8] and by X-ray photoemission spectroscopy[9]. For imidazolium-based ILs, ordering of the ions at the solid/liquid or liquid/ vapour interface has been inferred from vibrational spectroscopy data. For example Mezger et al.[10] performed a study of the (bulk)liquid/solid interface between a negatively charged sapphire substrate and imidazolium and pyrrolidinium-based ILs. They found strong interfacial layering, with repeated spacing of 0.7-0.8 nm, decaying exponentially into the bulk liquid. Recently the ionic liquid/solid interface has been studied with the surface force apparatus (SFA)[11, 12, 13]. In those experiments thin layers of ionic liquids are compressed between two approaching sheets of mica, while the normal force is recorded. The force vs. distance curves show a characteristic oscillatory profile, extending for few nanometers from the interface and exponentially decaying into the bulk. Only very recently, in order to explore in details the ionic liquid/solid interfaces, more local approaches has been used, i.e. scanning probe microscopies and numerical simulations. Layering at the solid/(bulk)liquid have been found by Atkin[14, 15] performing force spectroscopy with atomic force microscope (AFM). In these kind of measurements, in which the AFM tip is ramped against the interface while measuring the force acting on it, as in SFA experiments, subsequent ruptures of solvation layers are seen, beginning few nanometers above the surface. The group of Atkin, in collaboration with other groups, performed also scanning tunneling microscopy (STM)/AFM study on ionic liquid/Au(111) interface, finding a dependence of the behaviour of the solvation layers upon potential changes[16]. In simulation studies is again evidenced the formation of strong interfacial layering on different surfaces[17, 18], where moreover, the preferential orientation of the ions at the interface can be analysed. The studies previously cited about the interfacial behaviour of the ionic liquids, are mainly focused to the analysis of the bulk ionic liquid/solid interface. To date, a little effort has been devoted to what happens when thin layers of an ionic liquid are put in contact with a solid substrate. In those kind of situations, where the surface/volume ratio is high, it can been argued that the interaction with the surface can greatly change the physico-chemical and structural properties of the ionic liquid. The study of systems with high surface/volume ratio is directly relevant in all those applications in which a thin _lm of ionic liquid is used, e.g. in tribological applications, as well as in photoelectrochemical devices, where the liquid is soaked into a nanoporous matrix: a change of the properties of the ionic liquid in this case can heavily modify the final performance of the devices. My PhD work has been devoted to improving further extend the understanding of the behaviour of thin films of ionic liquids in contact with solid surfaces. At the time when I begun my work, very few studies regarding such systems were published. A pioneering study on thin _lm of [Bmim][PF6] on mica has been published in 2006 by Liu et al.[19]. In this work, performed using an AFM, the ionic liquid has been found to structure in two different ways on substrate: as droplets and as at layers, qualitatively referred to as solid layers. Inspired by the approach of Liu, I decided to study more quantitatively the thin-layer/solid interface, in particular using atomic force microscopy, because this instrument can acquire morphologies with vertical sub-nanometer and lateral nanometric resolution, so giving access to very localised information. Furthermore other kind of maps regarding different physico-chemical properties can be acquired simultaneously to the topography and moreover, force spectroscopy studies can be performed ramping the AFM tip against the surface. In particular I focused my investigation on the interaction of [Bmim][Tf2N], a hydrophobic and almost water-stable liquid, with different substrates, i.e. mica, amorphous silica, single crystal silicon covered by its native oxide, and HOPG graphite. The main part of the work has been performed on those test substrates, because their properties are well known and because they are at, so very suitable for an accurate AFM investigation. With the experience gained on those systems and the results obtained, on the last part of my PhD, the attention has been moved to surfaces more relevant for applications, as the nanostructured silicon oxide, directly synthesised in our lab with supersonic cluster beam deposition (SCBD). In order to perform my investigation, I first obtained very thin ionic liquid layers on the surface, diluting the liquid into a solvent, (methanol, ethanol, chloroform), and then drop-casting few μl of the solution onto a freshly cleaned substrate, letting the evaporation to proceed in air. On all the insulating surfaces studied, the [Bmim][Tf2N] coexists in 2 forms: as liquid micro- and nano- droplets and in at ordered domains. The melting temperature of this particular ionic liquid is ~-4°C, so a fundamental role in the liquid to solid transition has to be played by the interaction with the solid surface. The solid-like terraces appear as at layers, often growing one on top of the other. The hypothesis is that each layer is composed by several layers of cations and anions. By a statistical analysis of the morphological maps acquired, I extrapolated that the height of the best sub-multiple of the solid-like terraces is δ=0.6nm, in good agreement with the result of the simulations. The AFM has also been used to study the mechanical behaviour of the solid-like structures. If imaged in contact mode, the layers tend to be eroded after repeated scans, and in some cases the terraces are removed one by one, as in a lamellar solid. Investigating the resistance to normal loads, saw tooth profiles in force vs. separation curves have been found, highlighting a sequence of ruptures, separated by 1.8-2nm, where the average rupture pressure is ~2-3KBar, very similar to the maximum pressure found in a MD simulation of a tip penetrating in 4nm of [Bmim][Tf2N] on silica[20]. Moreover, the observation that supported IL islands were not disrupted by intense electric fields up to 108-109V/m (applied biasing the AFM with respect to sample during imaging) and that Scanning Nanoscale Impedance Microscopy[21] measurements highlighted a dielectric insulating character of the ordered domains (εr = 3-5 was measured[22]) is consistent with the idea that IL ordered domains behave as solid materials in which the ions are tightly bound. To understand what is the influence of the nanostructure on the formation of the solid-like layers, I realised [Bmim][Tf2N] depositions on nanostructured silica deposited on oxidised silicon by SCBD in our lab. Of particular interest is the case of IL coating on a sub-monolayer deposition of silica nanoparticles. The preliminary results show that the presence of a dense distribution of nanoparticles on the surface of oxidised silicon actually doesn't prevent the growth of multilayered solid-like domains, that are as thick as on at surfaces and densely distributed. The liquid part of the deposition is pinned to the silica clusters, fact that evidences the strong affinity of [Bmim][Tf2N] with silica. The results suggest that the formation of immobilised, possibly solid-like, layers of ionic liquids in contact with nanoporous matrices, is not unlikely and such structures and can strongly affect the properties of the devices in which those interfaces are present. This possibility is also supported by the fact that a small percentage of silica nanoparticles (5 wt%) is enough to induce the gelation in an IL-based electrolyte used for dye sensitised solar cells[23]. The findings of my PhD work highlight the potentialities of scanning probe techniques for the quantitative investigation of the interfacial properties of thin ionic liquid films. My AFM investigation highlights how heterogeneous can be the IL/solid interfaces and so how is of fundamental importance to deal with local and not with average properties. The results of my work show that the behaviour of thin layers of ionic liquid is greatly modified by the influence of the substrate. In particular, I found a coexistence of liquid domains and terraces with elevated structural order. The formation of those structures, not present in the bulk liquid, is clearly induced by the contact with the solid surface. The solid-like terraces are very resistant to normal loads and to intense electric fields and, differently from the bulk, they tend to behave as insulating layers: the development of those structures can then have a crucial influence in the performances of photoelectrochemical devices. The importance of this field of research and the validity of my work, are witnessed by the increasing number of papers studying thin ionic liquid layers appeared just before, but especially during the course of my PhD[24, 25, 26, 27, 28, 15, 16]; in many of these works, the AFM is the instrument of choice for the interfacial investigation because it allows to access to the physico-chemical properties of the system with nanometric or sub-nanometric resolution in all the three dimensions. In the next future the structural behaviour of the ionic liquids in contact with nanostructured surfaces will be further studied, making use of the experience of our group in synthesise the nanostructured oxides and metals. Moreover, we will explore in more details the dielectric properties of thin fillm of ionic liquids, in particular selecting those ILs directly used in supercapacitors and solar cells. Another interesting field that to date is still poorly explored is the interaction of ionic liquids with biological tissue. For this reason, we are going to begin to study the effects of ionic liquids on supported lipid bilayers. Bibliography [1] Wilkis, J. S., Green Chem 4, 73-80, (2002). [2] Qu, J., Truhan, J. J., Dai, S., Luo, H., Blau, P., J. Tribol. Lett. 22, 207-214, (2006). [3] Bhushan, B., Palacio, M., Kinzig, B., J. Coll. and Inter. Sci. 317, 275-287, (2008). [4] Simon, P. and Gogotsi, Y., Nature Materials 7, 845-854, (2008). [5] Appetecchi, G. B., Montanino, M., Carewska, M., Moreno, M., Alessandrini and F., Passerini, S., Electrochimica Acta 56, 1300-1307, (2011). [6] Grätzel, M., Journal of Photochemistry and Photobiology A: Chemistry 164, 3-14, (2004). [7] Santos, C. S., Baldelli, S., J. Phys. Chem. B 111, 4715-4723, (2007). [8] Rollins, J. B., Fitchett, B. D. and Conboy, J. C., J. Phys. Chem. B 111, 4990-4999, (2007). [9] Lovelock, K. R. J., Villar-Garcia, I. 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Amorphous silicon carbide (a-SiC) and silicon carbonitride thin films have been deposited onto a variety of substrates by Polymer-Source Chemical Vapor Deposition (PS-CVD). The interfacial interaction between the a-SiC films and several substrates including silicon, SiO[subscript 2], Si[subscript 3]N[subscript 4], Cr, Ti and refractory metal-coated silicon has been studied. The effect of thermal annealing on the structural and mechanical properties of the prepared films has been discussed in detail. The composition and bonding states are uniquely characterized with respect to the nitrogen atomic percentage introduced into the a-SiCN:H films. Capacitance-voltage (C-V) measurements were systematically used to evaluate the impurity level of the deposited a-SiC films. The chemical bonding of the films was systematically examined by means of Fourier transform infrared spectroscopy (FTIR). In addition, elastic recoil detection (ERD) and X-ray photoelectron spectroscopy (XPS) techniques were used to determine the elemental composition of the films and of their interface with substrates, while X-ray reflectivity measurements (XRR) were used to account for the film density. Spectral deconvolution was used to extract the individual components of the FTIR and XPS spectra. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were also employed to characterize the surface morphology of the films. In addition, their mechanical properties [(hardness (H) and Young's modulus (E)] were investigated by using the nanoindentation technique. The impurity levels of the a-SiC films were found to be clearly correlated with the nature of the underlying substrates. The Pt-Rh and TiN-coated Si substrates were shown to lead to the lowest impurity level (~ 1×10[superscript 13] cm[superscript -3]) in the PS-CVD grown a-SiC films, while Cr and Ti-coated Si substrates induced much higher impurity concentrations. Such high impurity levels were shown to be a consequence of a strong metallic diffusion of the metallic species (Cr or Ti). In contrast, no diffusion was observed at the interface of a-SiC with either Pt-Rh or TiN. Our results pinpointed TiN-coated Si as the electrode material of choice that satisfied best all criteria required for the integration of a-SiC into opto-electronic devices. FTIR measurements revealed that not only the intensity of a-SiC absorption band linearly increased, but also its position is found to shift to a higher wave number as a result of annealing. In addition, the bond density of Si-C is found to increase from (101.6-224.5)×10[superscript 21] bond[dot]cm[superscript -3] accompanied by a decrease of Si-H bond density from (2.58-0.46)× 10[superscript 21] bond[dot]cm[superscript -3] as a result of increasing the annealing temperature (T[subscript a]) from 750 to 1200 [degrees]C. Annealing-induced film densification is confirmed by the XRR measurements, as the a-SiC film density is found to increase from 2.36 to ~ 2.75 g/cm[superscript -3] when T[subscript a] is raised from 750 to 1200 [degrees]C. In addition, as annealing temperature T[subscript a] is increased from 750 to 1200 [degrees]C, both hardness and Young's modulus are found to increase from 15.5 to 17.6 GPa and 155 to 178 GPa, respectively. On the microstructural level, the increase incorporation of N in the a-SiCN:H films is found not only to lead to C atoms substitution by N atoms in the local Si-C-N environment but also to the formation of a complex structure between Si, C and N. For instance, the FTIR spectra show a remarkable drop in the intensity of Si-C vibration accompanied by the formation of further bonds including Si-N, C-N, C=N, C[identical to]N and N-H with increasing NH[subscript 3]/Ar ratio. Moreover, the XPS spectra showed the existence of different chemical bonds in the a-SiCN:H films such as Si-C, Si-N, C-N, C=N and C=C. Both FTIR and XPS data demonstrate that the chemical bonding in the amorphous matrix is more complicated than a collection of single Si-C, Si-N, or Si-H bonds. Furthermore, the increase incorporation of N in the a-SiCN:H films resulted in an increase of the average R[subcsript rms] surface roughness from 4 to 12 nm. Moreover, the films became porous with pore size and density increase as a result of increasing N at.%. Ultimately, both H and E of the a-SiCN:H films were found to be sensitive to their N content, as they decreased (from ~17 GPa and 160 GPa to ~13 GPa and 136 GPa, respectively) when the N content was increased from 0 to 27 at.%. The formation of Si-N, Si-H, and N-H bonds at the detriment of the more stiffer Si-C bonds are thought to account for the observed lowering of the mechanical properties of the a-SiCN:H films such as their N content increased. Our results confirmed the previously-established constant-plus-linear correlation between the mechanical properties of the a-SiC films and their bond densities.

The adsorbed layer morphology of a series of surfactants under different conditions has been examined primarily using atomic force microscopy (AFM). The morphologies of single and double chained quaternary ammonium surfactants adsorbed to mica have been characterised using AFM at concentrations below the cmc. Mixing these different types of surfactants systematically allowed a detailed examination of the change in adsorbed film curvature from the least curved bilayers through to most curved globules. From this study a novel mesh structure was discovered at curvatures intermediate to bilayers and rods. A mesh was again observed in studies examining the morphology change of adsorbed nonionic surfactant films on silica with variation in temperature. Other surfactant mixtures were also examined including grafting non-adsorbing nonionic surfactants and diblock copolymers into quaternary ammonium surfactant films of different morphologies.

The adsorbed layer morphology of a series of surfactants under different conditions has been examined primarily using atomic force microscopy (AFM). The morphologies of single and double chained quaternary ammonium surfactants adsorbed to mica have been characterised using AFM at concentrations below the cmc. Mixing these different types of surfactants systematically allowed a detailed examination of the change in adsorbed film curvature from the least curved bilayers through to most curved globules. From this study a novel mesh structure was discovered at curvatures intermediate to bilayers and rods. A mesh was again observed in studies examining the morphology change of adsorbed nonionic surfactant films on silica with variation in temperature. Other surfactant mixtures were also examined including grafting non-adsorbing nonionic surfactants and diblock copolymers into quaternary ammonium surfactant films of different morphologies.

This chapter deals with the interface between Syntax and Pragmatics by examining argument fronting in Old Irish non-poetic Glosses. Relying on lexical and contextual indicators of discourse function, three Information Structure patterns can be identified: aboutness topic; contrastive topic; and focus. Aboutness and contrastive topic are often resumed and do not mark relativization on the verb, suggesting that they are left dislocation structures. Focus is most commonly expressed through clefts, although clefts in Old Irish can be morphologically opaque. Modern Irish has all these structures besides a non-clefted focus structure, which is likely derived from interpreting morphologically opaque clefts as topicalization. In sum, this paper argues that Old Irish has a set of productive argument fronting positions with distinct and conventional information structural properties that can be analysed in terms of an articulated left periphery, and that these fronting positions are the direct ancestors of fronting positions in Modern Irish.

AbstractRedispersible polymers such as ethylene–vinyl acetate copolymer (EVA) have attracted attention in construction due to their enhanced flexural strength, adhesion, flexibility and resistance against water penetration. However, EVA particles cluster in a highly alkaline cementitious matrix and exhibit poor interaction with the cement matrix. The underlying mechanism of poor dispersibility of EVA is attributed to hydrophobic groups of polymers, a variation in the adsorption rate and molecular diffusion to the interface where they cluster together. This phenomenon can negatively affect the fresh properties of cement and produce a weak microstructure, adversely affecting the resulting composites’ performance. This study highlights how graphene oxide (GO) nanomaterial alters the nano- and microscale structural characteristics of EVA to minimize the negative effects. Transmission electron microscopy (TEM) revealed that the GO sheets modify EVA’s clustered nanostructure and disperse it through electrostatic and steric interactions. Furthermore, scanning electron microscopy (SEM) confirmed altered microscale structural characteristics (viz. surface features) by GO. The altered and enhanced material scale engineering performance, such as the compressive strength of the resulting cement composite, was notable.

Abstract This paper presents an inverse problem methodology for the identification of structural joint characteristics. The underlying theory employs a substructural flexibility method that allows statistical uncertainties in joints and interfaces. The method partitions structures into continuum and localized joint/interface substructural regions. The former are modeled by continuum finite elements and built up with the standard direct-stiffness method. Joint and interface regions are constructed from continuum and/or special elements. The novel aspect of the method is that the coupling of substructures is effected in terms of node-collocated Lagrange multipliers, which leads naturally to a boundary-flexibility formulation. Coupling through interaction forces addresses the concern that delicate localized effects are not masked out in the overall structural model. This heightened sensitivity is significant for inverse problems in which localized properties and uncertainties are deduced indirectly, through a hierarchical “peeling off” process. The method is applied to identify joint flexibilities in a model engine mount, which demonstrates key features of the method and its high-fidelity capability.

One important type of structural imperfection that can affect the properties of multilayer (ML) structures is interfacial roughness. In x-ray optical ML, roughness both decreases the reflectivity and introduces a background halo that can degrade the resolution of imaging optics. A promising technique for characterizing the roughness of surfaces and interfaces in ML structures is x-ray scattering. The use of x-ray scattering as a structural probe has several important advantages. It is inherently a non-invasive technique, well-suited for dynamic measurements including in situ growth studies. The penetration of x-rays allows both surfaces and buried interfaces to be directly probed. Furthermore, due to the short wavelength of x-rays, x-ray scattering can provide structural information on spatial scales ranging down to atomic dimensions. There is increasing interest to use nonspecular x-ray scattering to study the roughness of interfaces in x-ray ML structures. The first experimental results indicate that the x-ray scattering can exhibit a rich variety of behavior associated with the structural correlations between interfaces1-4. We present a simple theory that, within the limitations imposed by certain simplifying approximations, can provide a straightforward means of relating realistic interface structures to measurements of nonspecular scattering.

Thermally conductive composites as compared to metals have reduced density, decreased corrosion, oxidation, and chemical resistance, as well as adjustable properties to fit a given application. However, there are several challenges that need to be addressed before they can be successfully utilized in heat sink design. The interface between the device and thermal product that is used to cool it is an important factor in the thermal network designs of microelectronics cooling. Depending on the thermal interface conditions and material properties, the contact pressure and thermal stress level can attain undesirable values. In this paper, we investigate the effect of thermal interface between the fin and base plate on thermalstructural behavior of heat sinks. A coupled-field (thermal-structural) analysis using finite element method is performed to predict temperature as well as stress fields in the region of interface. In addition temperature and heat transfer rate predictions is supported through analytical results. Effect of various interface properties (such as air gap with rough surface and gaps filled with interface material) on the resulting thermal-structural response of the pin fin is investigated with respect to four interface materials combinations.

The design of buried pipes, in terms of the allowable minimum and maximum cover heights, requires the use of both geotechnical and structural design procedures. The geotechnical procedure focuses on estimating the load on the pipe and the compressibility of the foundation soil. The focus of the structural design is choosing the correct cross-section details of the pipe under consideration. The uncertainties of the input parameters and installation procedures are significant. Because of that, the Load Resistance Factor Design (LRFD) method is considered to be suitable for the design of buried pipes. Furthermore, the interaction between the pipe structure and surrounding soil is better captured by implementing soil-structure interaction in a finite element numerical solution technique. The minimum cover height is highly dependent on the anticipated traffic load, whereas the maximum cover height is controlled by the section properties of the pipe and the installation type. The project focuses on the determination of the maximum cover heights for lock-seam CSP, HDPE, PVC, polypropylene, spiral bound steel, aluminum alloy, steel pipe lock seam and riveted, steel pipe and aluminum arch lock seam and riveted, non-reinforced concrete, ribbed and smooth wall polyethylene, smooth wall PVC, vitrified clay, structural plate steel or aluminum alloy pipe, and structural plate pipe arch steel, or aluminum alloy pipes. The calculations are done with the software CANDE, a 2D plane strain FEM code that is well-accepted for designing and analyzing buried pipes, that employs the LRFD method. Plane strain and beam elements are used for the soil and pipe, respectively, while interface elements are placed at the contact between the pipe and the surrounding soil. The Duncan-Selig model is employed for the soil, while the pipe is assumed to be elastic. Results of the numerical simulations for the maximum fill for each type and size of pipe are included in the form of tables and figures.

Polyamide 6 (PA6) is a semi-crystalline thermoplastic used in many engineering applications due to good strength, stiffness, mechanical damping, wear/abrasion resistance, and excellent performance-to-cost ratio. In this report, two structure-property relationships were explored. First, carbon nanotubes (CNT) and graphene (G) were used as reinforcement molecules in simulated and experimentally prepared PA6 matrices to improve the overall mechanical properties. Molecular dynamics (MD) simulations with INTERFACE and reactive INTERFACE force fields (IFF and IFF-R) were used to predict bulk and Young's moduli of amorphous PA6-CNT/G nanocomposites as a function of CNT/G loading. The predicted values of Young's modulus agree moderately well with the experimental values. Second, the effect of crystallinity and crystal form (α/γ) on mechanical properties of semi-crystalline PA6 was investigated via a multiscale simulation approach. The National Aeronautics and Space Administration, Glenn Research Center's micromechanics software was used to facilitate the multiscale modeling. The inputs to the multiscale model were the elastic moduli of amorphous PA6 as predicted via MD and calculated stiffness matrices from the literature of the PA6 α and γ crystal forms. The predicted Young's and shear moduli compared well with experiment.

Riprap rock and aggregates are commonly used in various engineering applications such as structural, transportation, geotechnical, and hydraulic engineering. To ensure the quality of the aggregate materials selected for these applications, it is important to determine their morphological properties such as size and shape. There have been many imaging approaches developed to characterize the size and shape of individual aggregates, but obtaining 3D characterization of aggregates in stockpiles at production or construction sites can be a challenging task. This research study introduces a new approach based on deep learning techniques that combines three developed research components: field 3D reconstruction procedures, 3D stockpiles instance segmentation, and 3D shape completion. The approach is designed to reconstruct aggregate stockpiles from multiple images, segment the stockpile into individual instances, and predict the unseen sides of each instance (particle) based on the partially visible shapes. The approach was validated using ground-truth measurements and demonstrated satisfactory algorithm performance in capturing and predicting the unseen sides of aggregates. For better user experience, the integrated approach has been implemented into a software application named “I-RIPRAP 3D,” with a user-friendly graphical user interface (GUI). This stockpile aggregate analysis approach is envisioned to provide efficient field evaluation of aggregate stockpiles by offering convenient and reliable solutions for on-site quality assurance and quality control tasks of riprap rock and aggregate stockpiles. This document provides information for users of the I-RIPRAP 3D software to make the best use of the software’s capabilities.

Riprap rock and aggregates are extensively used in structural, transportation, geotechnical, and hydraulic engineering applications. Field determination of morphological properties of aggregates such as size and shape can greatly facilitate the quality assurance/quality control (QA/QC) process for proper aggregate material selection and engineering use. Many aggregate imaging approaches have been developed to characterize the size and morphology of individual aggregates by computer vision. However, 3D field characterization of aggregate particle morphology is challenging both during the quarry production process and at construction sites, particularly for aggregates in stockpile form. This research study presents a 3D reconstruction-segmentation-completion approach based on deep learning techniques by combining three developed research components: field 3D reconstruction procedures, 3D stockpile instance segmentation, and 3D shape completion. The approach was designed to reconstruct aggregate stockpiles from multi-view images, segment the stockpile into individual instances, and predict the unseen side of each instance (particle) based on the partial visible shapes. Based on the dataset constructed from individual aggregate models, a state-of-the-art 3D instance segmentation network and a 3D shape completion network were implemented and trained, respectively. The application of the integrated approach was demonstrated on re-engineered stockpiles and field stockpiles. The validation of results using ground-truth measurements showed satisfactory algorithm performance in capturing and predicting the unseen sides of aggregates. The algorithms are integrated into a software application with a user-friendly graphical user interface. Based on the findings of this study, this stockpile aggregate analysis approach is envisioned to provide efficient field evaluation of aggregate stockpiles by offering convenient and reliable solutions for on-site QA/QC tasks of riprap rock and aggregate stockpiles.

Methods to quantify soil conditions of pore connectivity, tortuosity, and pore size as altered by compaction were done. Air-dry soil cores were scanned at the GeoSoilEnviroCARS sector at the Advanced Photon Source for x-ray computed microtomography of the Argonne facility. Data was collected on the APS bending magnet Sector 13. Soil sample cores 5- by 5-mm were studied. Skeletonization algorithms in the 3DMA-Rock software of Lindquist et al. were used to extract pore structure. We have numerically investigated the spatial distribution for 6 geometrical characteristics of the pore structure of repacked Hamra soil from three-dimensional synchrotron computed microtomography (CMT) computed tomographic images. We analyzed images representing cores volumes 58.3 mm³ having average porosities of 0.44, 0.35, and 0.33. Cores were packed with < 2mm and < 0.5mm sieved soil. The core samples were imaged at 9.61-mm resolution. Spatial distributions for pore path length and coordination number, pore throat size and nodal pore volume obtained. The spatial distributions were computed using a three-dimensional medial axis analysis of the void space in the image. We used a newly developed aggressive throat computation to find throat and pore partitioning for needed for higher porosity media such as soil. Results show that the coordination number distribution measured from the medial axis were reasonably fit by an exponential relation P(C)=10⁻C/C0. Data for the characteristic area, were also reasonably well fit by the relation P(A)=10⁻ᴬ/ᴬ0. Results indicates that compression preferentially affects the largest pores, reducing them in size. When compaction reduced porosity from 44% to 33%, the average pore volume reduced by 30%, and the average pore-throat area reduced by 26%. Compaction increased the shortest paths interface tortuosity by about 2%. Soil structure alterations induced by compaction using quantitative morphology show that the resolution is sufficient to discriminate soil cores. This study shows that analysis of CMT can provide information to assist in assessment of soil management to ameliorate soil compaction.

Our long-term goal is to develop an efficient acellular vaccine against paratuberculosis based on protein antigen(s). A prerequisite to achieve this goal is to analyze and characterize Mycobacterium paratuberculosis (Mpt) secreted and cellular proteins eliciting a protective immune response. In the context of this general objective, we proposed to identify, clone, produce, and characterize: the Mpt 85B antigen and other Mpt immunoreactive secreted proteins, the Mpt L7/L12 ribosomal protein and other immunoreactive cellular proteins, Mpt protein determinants involved in invasion of epithelial cells, and Mpt protein antigens specifically expressed in macrophages. Paratuberculosis is still a very serious problem in Israel and in the USA. In the USA, a recent survey evaluated that 21.6% of the dairy herd were infected with Mpt resulting in 200-250 million dollars in annual losses. Very little is known on the virulence factors and on protective antigens of Mpt. At present, the only means of controlling this disease are culling or vaccination. The current vaccines do not allow a clear differentiation between infected and vaccinated animals. Our long-term goal is to develop an efficient acellular paratuberculosis vaccine based on Mpt protein antigen(s) compatible with diagnostic tests. To achieve this goal it is necessary to analyze and characterize secreted and cellular proteins candidate for such a vaccine. Representative Mpt libraries (shuttle plasmid and phage) were constructed and used to study Mpt genes and gene products described below and will be made available to other research groups. In addition, two approaches were performed which did not yield the expected results. Mav or Mpt DNA genes that confer upon Msg or E. coli the ability to invade and/or survive within HEp-2 cells were not identified. Likewise, we were unable to characterize the 34-39 kDa induced secreted proteins induced by stress factors due to technical difficulties inherent to the complexity of the media needed to support substantial M. pt growth. We identified, isolated, sequenced five Mpt proteins and expressed four of them as recombinant proteins that allowed the study of their immunological properties in sensitized mice. The AphC protein, found to be up regulated by low iron environment, and the SOD protein are both involved in protecting mycobacteria against damage and killing by reactive oxygen (Sod) and nitrogen (AhpC) intermediates, the main bactericidal mechanisms of phagocytic cells. SOD and L7/L12 ribosomal proteins are structural proteins constitutively expressed. 85B and CFP20 are both secreted proteins. SOD, L7/L12, 85B and CFP20 were shown to induce a Th1 response in immunized mice whereas AphC was shown by others to have a similar activity. These proteins did not interfere with the DTH reaction of naturally infected cows. Cellular immunity provides protection in mycobacterial infections, therefore molecules inducing cellular immunity and preferentially a Th1 pathway will be the best candidate for the development of an acellular vaccine. The proteins characterized in this grant that induce a cell-mediated immunity and seem compatible with diagnostic tests, are good candidates for the construction of a future acellular vaccine.