Formation Of Intermediate Layers Research Articles

Comparison of thermal stabilities of p+-Si/p-diamond heterojunction and Al/p-diamond Schottky barrier diodes

Abstract We evaluate the current–voltage (I–V) and temperature-dependent I–V characteristics of p+-Si/p-diamond heterojunction diodes (HDs) fabricated using surface-activated bonding and compare their characteristics with those of Al/p-diamond Schottky barrier diodes (SBDs) fabricated on the same diamond substrate. The ideality factor, reverse-bias current, and on/off ratio of HDs are improved by annealing them at temperatures up to 873 K, which is in good contrast to the characteristics of SBDs. The barrier height at Si/diamond bonding interfaces is decreased by annealing. The difference in response to annealing between HDs and SBDs implies that the density of interface states formed during the surface activation process is decreased by annealing HDs. The characteristics of HDs are degraded by annealing them at 1073 K, which is assumed to be due to the formation of intermediate layers or the occurrence of local strain at Si/diamond bonding interfaces.

Two-stage PVD method for protective coating formation

The CVD methods are typically used for the formation of aluminum oxide coatings since aluminum oxide is a dielectric. The adhesion between the protective coating and the substrate material is normally improved by growing thin intermediate layers based on titanium oxides and nitrides. These intermediate layers are mainly formed using the PVD methods. In this paper, we propose a two-stage PVD method for forming a layered structure on the titanium substrate. The formation of intermediate layers was carried out by the magnetron method (first stage), and the main protective layer was deposited at the second stage using a fore-vacuum electron source. The dense beam plasma generated during the electron beam transport in a fore-vacuum gas medium compensates for the negative electrical charge accumulating on the surface of the aluminum oxide target and facilitates its effective evaporation. The electrical properties of the intermediate layers and the resulting layered coatings have been investigated, including the tangent of dielectric loss angle, the real and imaginary parts of the conductivity and the dielectric constant dependencies on frequency.

Studying the formation of intermediate layers during the destruction of an oil-water emulsion on the example of the Priobskoye field

During oil production, as well as its transportation, the formation of persistent oil-water emulsions is inevitable. Their occurrence is associated with the ingress of water into the bottomhole zone, mixing of oil with water in the well, as well as the negative impact of water on electric submersible and sucker rod pumps. As a result, when rising to the surface, oil degassing occurs. The settling of an emulsion of water and oil leads to the formation of “intermediate layers”. Within the framework of this study, it was considered what the intermediate layer is and methods of mitigating with it. The amount of sulfate-reducing and hydrocarbon-oxidizing bacteria in the samples was determined.

The formation of intermediate layers in covered Ge/Si heterostructures with low-temperature quantum dots: a study using high-resolution transmission electron microscopy and Raman spectroscopy

The method of software analysis of high-resolution TEM images using the peak pairs algorithm [Galindo P L et al 2007 Ultramicroscopy 107 1186–93] in combination with Raman spectroscopy was employed to study lattice deformations in Ge/Si(001) structures with low-temperature Ge quantum dots. It was found that the stresses do not spread in a thick Si layer above quantum dots, but completely relax via the formation of a thin boundary layer of mixed composition. However, intermixing of Ge and Si is absent beneath the Ge layer in samples with a Ge coverage of 10 Å. Besides intermixing was not observed at all, both beneath and above the Ge layer, in samples with a Ge coverage of 6 Å or less. This may be due to the predominance of Ge diffusion into the Si matrix from the {105} facets of Ge huts, not from the Ge wetting layer, at low temperatures of the Ge/Si structure deposition. The critical thickness of Si coverage at which the intense stress-induced diffusion takes place is determined to lie in the range from 5 to 8 nm.

CuF2 as Reversible Cathode for Fluoride Ion Batteries

In the search for novel battery systems with high energy density and low cost, fluoride ion batteries have recently emerged as a further option to store electricity with very high volumetric energy densities. Among metal fluorides, CuF2 is an intriguing candidate for cathode materials due to its high specific capacity and high theoretical conversion potential. Here, the reversibility of CuF2 as a cathode material in the fluoride ion battery system employing a high F− conducting tysonite‐type La0.9Ba0.1F2.9 as an electrolyte and a metallic La as an anode is investigated. For the first time, the reversible conversion mechanism of CuF2 with the corresponding variation in fluorine content is reported on the basis of X‐ray photoelectron spectroscopy measurements and cathode/electrolyte interfacial studies by transmission electron microscopy. Investigation of the anode/electrolyte interface reveals structural variation upon cycling with the formation of intermediate layers consisting of i) hexagonal LaF3 and monoclinic La2O3 phases in the pristine interface; ii) two main phases of distorted orthorhombic LaF3 and monoclinic La2O3 after discharging; and iii) a tetragonal lanthanum oxyfluoride (LaOF) phase after charging. The fading mechanism of the cell capacity upon cycling can be explained by Cu diffusion into the electrolyte and side reactions due to the formation of the LaOF compound.

Investigation into the compaction of nanopowders and micropowders of silicon carbide in high-pressure apparatus

The results of the investigation into the compaction (sintering) of silicon carbide nanopowders and micropowders in a DO-138 high-pressure apparatus are presented. Compaction modes for both types of materials are identical (a pressure of 3.5–4.0 GPa, a temperature of 1600—1700°C, and a holding time of 10 s). The influence of cladding of SiC nanopowders and micropowders with titanium and titanium nitride on the properties of compacts (cakes) formed under the same sintering modes is investigated. It is established that, when compacting the silicon carbide nanopowder, cakes differ in regards to higher density, hardness, and lower porosity compared with the samples made of finely dispersed technical silicon carbide. A higher activity of titanium relative to SiC makes it possible to chemically associate the grains of the latter due to the formation of intermediate layers of titanium carbide between them. The resulting ceramics possesses a higher density, hardness, and wear resistance. The wear resistance of synthesized composites based on nano-SiC is higher than for a polycrystalline material based on silicon carbide micropowder by a factor of 4.5.

Reduction of magnetite to metallic iron in strong alkaline medium

This work focuses on assessing the feasibility of cathodic iron extraction from the magnetite based precursors. For this, electrochemical processes at Fe3O4/alkaline electrolyte interface were screened by cycling voltammetry. Based on these results, one obtained guidelines for selecting the conditions (i.e., potential and temperature) where efficient direct electrochemical reduction of magnetite ceramics to metallic iron occurs. Electrochemical conversion of relatively dense magnetite samples yields a polycrystalline Fe scale, formed at the surface of the magnetite pellet in direct contact with the bulk electrolyte. Still, the onset of slightly open porosity results in formation of intermediate layers with coexisting magnetite and metallic Fe; this is ascribed to gradual development of additional porosity, which promotes sample impregnation with the electrolyte, extends the effective electrochemically active area, and facilitates dissolution of soluble species in the inner pores. This is clearly demonstrated by transient response behavior, with remarkable increase in the current density. The key roles of porosity and effective Fe3O4/electrolyte area are also emphasized by the enhanced kinetics of electrochemical reduction observed for highly porous magnetite samples, with nearly homogeneous distribution of reactant (Fe3O4) and product (metallic Fe), without a clear surface scale of metallic iron. In this case, the final product is very porous and fragile. The conversion of highly porous magnetite samples also proceeds with much higher Faradaic efficiency compared to nearly dense ceramics.

Investigation into Compacting the Nanopowders and Micropowders of Tungsten Carbide in a High-Pressure Apparatus

The results of the investigation into compacting (sintering) in high-pressure apparatus of the DO-138 model of nanopowders and micropowders of silicon carbide are presented. Compacting modes for both types of materials were identical (pressure of 3.5–4.0 GPa, temperature of 1600–1700 °C, and holding time of 10 s). The influence of cladding the SiC nanopowders and micropowders with titanium and titanium nitride on the properties of compacts (cakes) fabricated in the same sintering modes is also considered. It is established that when compacting the silicon carbide nanopowder, the formed cakes differ by the higher density, hardness, and lower porosity compared with the samples of finely dispersed silicon carbide of technical grade. High activity of titanium with respect to SiC allows one to bond chemically the grains of the latter due to the formation of intermediate layers of titanium compounds between them. This is resulted in that the formed ceramics possesses high density, hardness, and wear resistance. Wear resistance of synthesized composites based on nano-SiC is higher by a factor of 4.5 than that one of polycrystalline material made of silicon carbide micropowder.

Gravity wave effects on postsunset equatorial F region stability

AbstractThe influence of gravity waves on the stability of the postsunset equatorial F region ionosphere is investigated numerically. For this investigation, we use the output of a direct numerical simulation of waves and turbulence in the mesosphere and lower thermosphere to force a simulation of ionospheric dynamics. Both simulations are cast in three dimensions. The effectiveness of the neutral‐plasma coupling involved is generally thought to depend on the dynamo efficiency and spatial resonance of the forcing, which we evaluate. In our simulations, the postsunset equatorial ionosphere could be deformed by neutral waves after 5–15 min most severely when the wavefronts were aligned approximately with the magnetic meridian, despite the fact that the dynamo efficiency is modest even in that case. However, poor spatial resonance limits the subsequent growth of the deformations in our simulations, and the seeding of interchange instabilities does not occur. The coupled simulations predict the formation of intermediate layers in the equatorial valley region (150–250 km apex altitude) under some circumstances that could serve as telltales in nature of the presence of the kind of neutral forcing we simulate.

Formation of Intermediate Layers for Immobilization of Biomacromolecules by Self‐Assembling and Reduction of Phenyldiazonium Salts. A Comparative Study

AbstractTwo types of biomolecules were tested in the comparison of usefulness of two ways of formation of the intermediate layers at electrodes: a 20‐nucleotide DNA sequence and glucose oxidase. Chronocoulometric, amperometric, electrochemical impedance and PM‐IRRAS experiments proved that the layers obtained by electroreduction of diazonium salts are much more stable and more efficient in the accumulation of biomolecules compared to layers obtained by self‐assembling of appropriate thiols.

Surface engineering of titanium with potassium hydroxide and its effects on the growth behavior of mesenchymal stem cells

To improve the corrosion resistance and biological performance of commercially pure titanium (cp-Ti) substrates, potassium hydroxide was employed to modify the surfaces of titanium substrates, followed by biomimetic deposition of apatite on the substrates in a simulated body fluid. The morphologies of native and treated titanium substrates were characterized by field emission scanning electron microscopy (FE-SEM). Treatment with potassium hydroxide led to the formation of intermediate layers of potassium titanate on the surfaces of titanium substrates, while apatite was subsequently deposited onto the intermediate layer. The formation of potassium titanate and apatite was confirmed by thin-film X-ray diffraction and FE-SEM equipped with energy dispersive spectroscopy, respectively. Electrochemical impedance spectroscopy showed that the formed potassium titanate layer improved the corrosion-resistance properties of titanium substrates. The influence of modified titanium substrates on the biological behavior of mesenchymal stem cells (MSCs), including osteogenic differentiation, was investigated in vitro. Compared with cp-Ti substrates, MSCs cultured onto alkali- and heat-treated titanium substrates and apatite-deposited titanium substrates displayed significantly higher ( P < 0.05 or P < 0.01) proliferation and differentiation levels of alkaline phosphatase and osteocalcin in 7 and 14 day cultures, respectively. More importantly, our results suggest that the modified titanium substrates have great potential for inducing MSCs to differentiate into osteoblasts. The approach presented here may be exploited to fabricate titanium-based implants.

Effect of refractory nanoparticles on the structural modification of metal-matrix composites

The structure and tribological behavior of composite materials (CMs) filed by dispersed particles and based on aluminum alloys grown by reactive casting with titanium microparticles and SiC nanoparticles or synthetic diamond mixed to the melt have been studied. The composition, size, and volume fraction of the strengthening phases are determined by optical microscopy and x-ray diffraction. The hardness of the CMs is measured. The tribological properties of the CMs are tested during dry friction on a rider made of grade 45 steel. Alloying nanoparticles are shown to affect the morphology, volume fraction, and sizes of the strengthening phases formed in the CMs. The main phases in the CMs are intermetallic compounds Al3Ti, Al24Ti9, and AlTi. The introduction of SiC nanoparticles in a CM causes the formation of TiSi2 (<1%) particles, whereas TiC carbides (<1%) form in a CM containing diamond nanoparticles. CM-steel friction interaction causes the formation of intermediate layers consisting of mechanical mixtures with an ultrafine-grained structure between the sliding surfaces. Their effect on the stable-friction range is discussed.

Determination of the layered structure in Mo/Si multilayers by grazing incidence X-ray reflectometry

The formation of intermediate layers was investigated in Mo/Si multilayers produced by e-beam evaporation and ion-beam smoothening. A model of a four-layer step profile structure of the multilayer period was applied successfully to account for grazing incidence X-ray reflectivity of the structures. We have used a special method to determine the multilayer period composition, namely the use of a laterally graded multilayer of which only the thickness of the spacer layer was varied. The well-known modulation of the Bragg peak intensities of 0.154 nm X-rays was then used to determine the thickness and the composition of the silicides formed at the boundaries. The impact of the polishing conditions on the thickness and composition of the intermediate layers was investigated. The study allowed optimization of the composition of Mo/Si multilayer for use at near-normal incidence in the 12.5–15 nm wavelength area for Extreme UV Lithography.

Modeling the formation of intermediate layers at Arecibo latitudes

By using a modified version of the ionospheric model described by Bailey and Sellek (1990), we model the formation of intermediate ionization layers due to meridional neutral winds in the valley region between the E and F regions. The calculations are performed on a single field line with L = 1.4, in order to compare the results with observations of intermediate layers from the incoherent scatter radar at Arecibo. The winds are given a sinusoidal variation in altitude, and the effects of the wind amplitude and wavelength on layer formation are examined. Nighttime ionization rates are artificially specified to correspond with observed rates in the region. Our results show that tidal like meridional wind profiles act to deplete the apparent background ionospheric number density as well as enhance the number density in the intermediate layer. Thus the layer appears as an enhancement above a background that is much smaller than the background that would be present in the absence of a wind. In this way, layers with relatively high molecular ion concentrations can exist. Intermediate layers are seen to form at nulls in the neutral wind altitude profile, but in the altitude region above roughly 160 km this null need not coincide with a zero in the field‐aligned ion velocity.

The interfaces of NbN-MgO-NbN tunnel junctions

The chemical composition of the surfaces and interfaces of NbN-MgO-NbN trilayers has been studied by x-ray photoelectron spectroscopy during the fabrication of the trilayer without breaking the vacuum. The NbN and MgO layers were prepared by rf magnetron sputtering. The results of the chemical analysis have been correlated to the electrical characteristics of the completed NbN-MgO-NbN tunnel junctions. During the deposition of the MgO barrier layer the presence of a high amount of energetic oxygen ions and atoms in the sputtering plasma results in a strong plasma oxidation of the NbN base electrode and, hence, in mixed Nb2O5-MgO barriers. The oxygen ions and atoms are generated by the dissociation of the target material and the water of the background pressure. Their amount was found to increase with increasing argon pressure during the MgO sputtering process. Also, adsorption layers of hydroxides on the MgO-target result in the formation of an uncontrollable amount of niobium oxide components at the interface between the NbN base electrode and the MgO barrier. The current-voltage characteristics of tunnel junctions with such barriers show large subgap leakage currents. Pure MgO barriers can be prepared by reducing the oxygen bombardment of the NbN films during the MgO deposition. Pure MgO barriers are oxygen deficient and easily adsorb hydroxides. These hydroxides react with the first layers of the NbN top electrode to NbO2 and NbO thereby reducing and broadening the sumgap value of the tunnel junctions. Tunnel junctions with pure MgO barriers of a nominal thickness of less than 2 nm usually have current-voltage characteristics indicative for microshorts. A special annealing procedure of the NbN-MgO bilayers prior to the deposition of the top electrode desorbs the hydroxides, transforms Mg(OH)2 to MgO without forming metallic magnesium and prevents the formation of intermediate layers of niobium suboxides and metallic shorts.

Novel instabilities in the oxidation of a Nimonic alloy when YBaCuO is deposited upon it

When an YBaCuO film is deposited onto a Nimonic 80A alloy substrate using a plasma technique there is extensive inter-reaction. The microstructural and compositional relationships between the layered products in this interfacial scaling process are described using data obtained by conventional edge-on TEM techniques. Our results demonstrate the way in which the segregation of chromium to the YBaCuO overlayer dominates the scaling behaviour that is seen, despite the formation of intermediate layers which would normally have been expected to act as diffusion barriers, and highlight the potential difficulties in making well behaved electrical contacts for this superconductor.

Glow discharge sputtering

4. Arrival at Substrate A. Deposition rates and uniformity (i) Inert gas discharges (ii) Effect of residual gases (iii) Reactive sputtering (iv) Multi-element targets B. Substrate temperature C. Nucleation and growth (i) Nucleation (ii) Epitaxy (iii) Morphology (iv) Reactively sputtered film growth D. Crystal phases (i) Phases peculiar to thin films (ii) Effect of substrate bias (iii) Mixtures and compounds E. Crystal orientation F. Stress G. Adhesion (i) Simple interfacial adhesion (ii) Interdiffusion between two materials (iii) Formation of intermediate layers (iv) Mechanical adhesion 80 80 80 83 83 85 86 87 88 88 91 92 94 94 95 99 100 102 103 104 104 104 105