Composition Of Interfacial Layer Research Articles

Effect of Ti incorporation on the interfacial and optical properties of HfTiO thin films

Interfacial and optical properties of HfTiO films with different Ti concentration grown by radio frequency reactive magnetron sputtering have been investigated by x-ray photoelectron spectroscopy (XPS) and spectroscopy ellipsometry (SE). XPS spectra indicate that interfacial layer is formed unavoidably for Ti doped and undoped HfO2 thin films and the interfacial structure is stable for Ti doped films. The composition of interfacial layer is most likely silicate and SiOx. Meanwhile, SE results indicate that the band gap of HfTiO thin films decreases with the increase in Ti concentration. Further results show that the valence band offset (ΔEv) decreases from 2.32 to 1.91 eV while the conduction band offset (ΔEc) decreases from 2.05 eV to 0.99 with the increase in Ti content. The optical constants consist of refractive index and extinction coefficient have also been investigated to provide the valuable references to prepare and select the HfTiO thin films for future high-k gate dielectrics.

Adsorption of a Water Treatment Protein from Moringa oleifera Seeds to a Silicon Oxide Surface Studied by Neutron Reflection

An extract from the seeds of the Moringa oleifera tree that is principally a low molecular mass protein is known to be efficient as a coagulating agent for water treatment. The present paper investigates the adsorption of the purified protein to silica interfaces in order to elucidate the mechanism of its function as a flocculent. Neutron reflection permits the determination of the structure and composition of interfacial layers at the solid/solution interface. Dense layers of protein with about 5.5 mg m(-2) were found at concentrations above 0.025% wt. The overall thickness with a dense layer in excess of 60 A at 0.05 wt % suggests strong co-operative binding rather than single isolated molecules. An ionic surfactant, sodium dodecyl sulfate, was also seen to coadsorb. This strong adsorption of protein in combination with the tendency for the protein to associate suggests a mechanism for destabilizing particulate dispersions to provide filterable water. This can occur even for the protein that has previously been identified as being of low mass (about 7 kDaltons) and thus is unlikely to be efficient in bridging or depletion flocculation.

Fracture toughness of concentric Si 3N 4-based laminated structures

A new concentric rectangular laminated structure was designed and fabricated by slip-casting method and densified by pressureless sintering process. One class of laminates consists of layers of Si 3N 4 with 7 wt.% Y 2O 3 and 3 wt.% Al 2O 3 as sintering aids, and of interlayers consisting of 50 wt.% BN and 50 wt.% Al 2O 3 designated as SN-(BN + Al 2O 3). The other class of laminates has the same Si 3N 4 layer composition but different interlayer composition of 90 wt.% BN and 10 wt.% Si 3N 4 designated as SN-(BN + SN). The objective of this paper is to investigate the effects of the number of layers and their thickness on apparent fracture toughness of these laminates. The interfacial layer composition was discussed in terms of its role in toughening of the laminates. For the SN-(BN + Al 2O 3) laminates the highest apparent fracture toughness of 22 MPa m 1/2 was found in the samples with 7 Si 3N 4 layers and for the SN-(BN + SN) laminates the highest apparent fracture toughness of 19.5 MPa m 1/2 was found in the samples with 4 Si 3N 4 layers.

Effect of the Interfacial Layer Composition on the Properties of Emulsion Creams

We have quantified observed differences in the microstructure and rheology of creaming emulsions stabilized by protein and low molecular weight surfactants. In this study, we made two sets of emulsions from a single parent emulsion, which differed only in their interfacial composition (i.e., either protein or surfactant). The protein studied was whey protein isolate. The zeta potential of the surfactant-stabilized emulsion was controlled by mixing anionic (SDS) and nonionic (Brij 35) surfactants to match the zeta potential of the protein-stabilized emulsion. Despite this, ultrasonic creaming measurements and confocal microscopy showed that the structures within the cream layers were different between the two sets of emulsions. The protein-stabilized emulsions appeared to slow or arrest the packing within the cream, leading to a lower density network of emulsion droplets, whereas the surfactant emulsion droplets rearranged more quickly into a well-packed, concentrated cream layer. Rheological analysis of the creams showed that despite the protein-stabilized emulsions having a lower dispersed phase volume fraction, their elastic modulus was approximately 30 times greater than that of a comparable surfactant-stabilized emulsion. These differences were caused by the ability of the protein to form a highly viscoelastic interfacial network around the droplets which may include intermolecular covalent cross-links. At close range the adhesive nature of the interaction between the layers contributes to the microstructure and rheology of concentrated emulsions. This is the first time that such well-defined emulsion systems have been studied in detail both noninvasively to look at the impact on creaming and also invasively to look at the impact on bulk rheological properties.

Interaction between humic acid and montmorillonite in the presence of calcium ions I. Interfacial and aqueous phase equilibria: Adsorption and complexation

The organic matter content and ionic composition of soil solutions have a dominant effect on soil structure, forming gradually an aggregation of mineral particles, in which clay fractions play a determining role. The colloidal interaction of particles, including repulsion and attraction, changes with their inherent surface properties and the interfacial layer composition around them, resulting in chemical and physical equilibria between solid and aqueous phases. These interactions and their relationship were studied in model systems containing soil constituents having a definite role in the formation of soil structure and are organized into two parts, here the interfacial processes as part I, with the particle network formation in the second part. The adsorption of humic acid (HA) on montmorillonite was studied under conditions relevant to the environment at pH ∼ 6.5 and 0.0014 M NaCl. The effect of Ca loading from 0.0013 to 0.0055 M was the focus of the work. Both HA and Ca 2+ adsorption were measured. To reveal molecular insight into the interactions between HA, Ca 2+ and montmorillonite, the HA concentration was related to the molar amount of its acidic functional groups. Adsorptive fractionation of HA was characterized using spectrophotometric parameters (SUVA 254, E 3/E 4 and E 4/E 6). The fourfold increase in Ca loading resulted in more than ten times greater HA adsorption, but only three times greater Ca 2+ adsorption, during which the distribution between the solid and liquid phases changed considerably. The dominant processes were preferential Na +/Ca 2+ ion exchange and complexation by HA both in the aqueous phase and on montmorillonite (through Ca bridges on the faces and directly on Al–OH sites at the edges), causing adsorptive fractionation of organic matter and leaving the small, less humified HA fraction in the aqueous phase.

Recent Advances in Search for Suitable High-k/Metal Gate Solutions to Replace SiON/Poly-Silicon Gate Stacks in CMOS Devices for 45nm and Beyond Technologies

The criterion for a suitable high-K dielectric/metal gate stack for replacing SiON/Poly-Si stacks in conventional CMOS devices are i) Equivalent oxide thickness (EOT) of {less than or equal to} 1.1 nm, ii) Electron and hole mobilities that are comparable to conventional stacks, and iii) Near Band-Edge (BE) threshold voltages for both nFET and pFET devices. Aggressive scaling and competitive mobilities have been demonstrated using HfO2/metal gate stacks [1] through optimization of interfacial layer composition, choice of suitable metal electrodes and deposition processes, and high thermal budgets that are compatible with conventional FET fabrication. A suitable NFET BE solution compatible with gate first process flow achieved by inserting capping layers containing gp. IIA (e.g., Mg) & gp. IIIB (e.g., La) elements into proven high mobility mid-gap HfO2/TiN gate stacks thereby moving the effective work function (EWF) to nFET BE [2,3]. On the pFET front, the challenge remains that elements with high bulk workfunction exhibit Vt instability as well as inherent scaling limitations after high temperature processing that is required in a gate first process flow.

Relationship between structure and rheological properties of mixed BSA/Tween 80 adsorption layers at the air/water interface

Rheological properties of interfacial layers play a very important role for the stability of various colloidal food systems such as foams or emulsions. The ability of liquid lamellas between neighbouring elements of the dispersed phase to resist deformations upon collision can determine the coalescence rate and, therefore, the life time of the whole colloidal system. The same properties, in turn, are closely related to the structure of the interfacial layers on both sides of the liquid lamella. The composition of interfacial layers and the way in which they were formed are crucial factors influencing their structural and consequently their rheological properties. Hence, one of the most important tasks of modern food science is the development of compositions of interfacial active compounds being able to modify the structure of these layers in a controlled way. From this point of view protein/surfactant mixtures are very promising systems. In the present contribution the rheological, structural and mechanical properties of mixed adsorption layers comprised of bovine serum albumin (BSA) and Tween 80 at the air/water interface were studied by surface shear rheometry, ellipsometry and tensiometry (drop profile analysis), respectively. The dependencies of shear visco-elasticity, thickness and refractive index of the respective adsorbed layers as well as the surface tension on the total concentration and subphase composition were considered. On this basis, conclusions about possible changes in the layer structure and their relation to the rheological properties were drawn. Applicability of “orogenic” displacement model developed earlier for penetration of a spread protein layer by soluble surfactants was discussed for the current case of competitive adsorption.

Co growth on Si(0 0 1) and Si(1 1 1) surfaces: Interfacial interaction and growth dynamics

In situ X-ray photoelectron spectroscopy (XPS) and ex situ atomic force microscopy (AFM) were used to study the growth of thin cobalt films at room temperature (RT) on both clean and H-terminated Si(0 0 1) and Si(1 1 1) surfaces. The growth proceeds by first forming an initial CoSi 2-like phase at the growth front of the Si substrate. With increasing Co coverage the interfacial layer composition becomes richer in Co and eventually a metallic Co film is formed on top. Hydrogen termination of the Si surface did not suppress the reaction of Co and Si. A pseudo-layer-by-layer growth mode is proposed to describe the growth of Co on H-terminated Si surfaces, while closed-packed small island growth occurs on clean Si surfaces. The difference in growth mode can be attributed to the increase in the surface mobility of Co adatoms in the presence of hydrogen.

Composition of Interfacial Layers in Complex Food Emulsions Before and After Aeration: Effect of Egg to Milk Protein Ratio

Whipped emulsions were prepared at pilot scale from fresh milk, whole egg, and other ingredients, for example, sugars and stabilizers (starch, polysaccharides). Egg content was varied: 4 recipes were studied differing in their egg to milk protein ratio (0, 0.25, 0.38, and 0.68). Protein and fat contents were kept constant by adjusting the recipes with skim-milk powder and fresh cream. Emulsions were prepared by high-pressure homogenization and whipped on a pilot plant. Particle-size distribution determined by laser-light scattering showed an extensive aggregation of fat globules in both mix and whipped emulsions, regardless of recipe. Amount of protein adsorbed at the oil-water interface and protein composition of adsorbed layer were determined after isolation of fat globules. Protein load is strongly increased by the presence of egg in formula. Values obtained for the whipped emulsions were dramatically lower than those obtained for the mix by a factor of 2 to 3. Sodium dodecyl sulfate-PAGE indicated a preferential adsorption of egg proteins over milk proteins at the oil-water interface, regardless of recipe. This phenomenon was more marked in aerated than in unaerated emulsions, showing evidence for desorption of some milk proteins during whipping. Egg proteins stabilize mainly the fat globule surface and ensure emulsion stability before whipping. Air bubble size distribution in whipped emulsions was measured after 15 d storage. When the egg to milk protein ratio is decreased to 0.25, large air cells appear in whipped emulsions during storage, indicating mousse destabilization. The present work allows linking the protein composition of adsorbed layers at the fat globule surface to mousse formula and mousse stability.

Fracture behavior of laminated SiC composites

Experimental investigation of the flexural properties of SiC/C laminates had been conducted. Effect of the interfacial thickness and composition on the mechanical properties of SiC laminates was characterized. The diffusion of elements from adjacent SiC layers in the carbon-based interfacial layers was studied. Accordingly, the optimal thickness and composition of interfacial layers were determined experimentally.

Tungsten silicide composition analysis by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy

While Rutherford backscattering spectroscopy (RBS) is the accepted method for determining the composition of tungsten silicide films, the systems are expensive and not widely available. Furthermore, the depth resolution of RBS is of the order of 150 Å, which does not allow for the compositional analysis of thinner films. Also, chemical information is not available from RBS. These are critical issues as the geometries of ultralarge-scale integration devices become smaller. However, with special care applied to data acquisition and reduction, both Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) provide composition agreement with RBS. Additionally, AES and in particular XPS provide chemical information about thin films that is unavailable from RBS analysis. To demonstrate that AES and XPS provide composition analysis of thin films comparable to RBS, post-anneal tungsten silicide films deposited on silicon with both chemical and vapor deposition processes were analyzed by AES, XPS, and RBS. With care taken in data acquisition and reduction, silicon-to-tungsten ratios were comparable among the three techniques. Moreover, using AES and XPS, surface oxide thickness and interfacial layer composition can be determined.