Formation Of Such Layers Research Articles

The value of charge of Fe single to multiple atoms doped in Ge: Combined experimental and density functional theory study

With the aim to find out the value of an electronic charge that the Fe atoms acquire when they are doped in Ge bulk, a set of experimental and density functional theory (DFT) studies have been carried out of the model systems consisting of intermixed Fe–Ge films. Such films were prepared by electron and thermal evaporation in ultra-high vacuum (UHV) on the surface of Mo(110) substrate by initial formation of the Ge film of a mean thickness of 7.5 nm, onto which the Fe films were subsequently deposited, maintaining certain Fe to Ge concentration ratio, namely, 0.2, 0.4, 0.7 and 1.0. Annealing of such double Fe–Ge films results in notable interdiffusion of the components with quite uniform distribution of the elements throughout the intermixed layer. The details of formation of such layers were in-situ controlled by Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), low-energy electron diffraction (LEED) and work function measurements, in combination with Ar ion depth profiling. By analyzing the Fe Auger LMM-triplet, the absolute values of the charge that Fe atoms acquire when doped in Ge, were estimated for four different Fe–Ge intermixed layers with above-mentioned different Fe to Ge concentration ratio. The corresponding plot of the charge versus Fe to Ge concentration allows to estimate the charge of a single doped Fe atom, which equals to +0.34e (electron charge units) and gradually decreases to 0.07e for high Fe concentration. To verify the experimental values of the Fe charge the calculations were done by periodic DFT as implemented in full-potential FHI-aims code. Among the used algorithms of Mulliken, Hirshfeld, and Bader's atoms-in-molecules, the latter gives good correlation between charges of Fe dopant and its concentration.

Radiative Transfer Simulations for the Observed Decrease of Radio Brightness Temperature of Venus With Increasing Decimeter Wavelengths: Possible Existence of a Reflective or Quasi‐Conductive Subsurface

AbstractRadiometric observations of Venus have revealed a monotonic decrease of brightness temperature (Tb) in the decimeter wavelength regime. Such a decrease has also been independently reported by the observations using interferometric radio‐telescopes, like the Very Large Array (VLA) in the USA and the Giant Metrewave Radio Telescope (GMRT) in India. In this work, we have carried out microwave radiative transfer (RT) simulations of thermal emission from the Venusian surface at decimeter wavelengths to examine the role of subsurface properties of Venusian regolith in the continuous reduction of Tb at the microwave‐radiowave spectral domain. These simulations are compared against spectral microwave measurements by GMRT over a wide decimeter wavelength regime ranging from ∼23–128 cm. Good agreements are obtained for simulations that consider a two‐layer Venusian surface (a low‐loss medium overlaid over a reflecting/lossy medium) a situation that would arise if the subsurface layer has high dielectric properties due to the presence of semiconducting mineral assemblages such as pyrites, ferroelectric minerals, magnetite–hematite, magnetite–pyrite or magnetite–hematite–pyrite equilibrium assemblages. The thickness of the top layer, the possibilities of the formation of such layers and their geological and chemical evolutions are also discussed.

Features of Electron Optical Systems with the Plasma Emitter Based on Stationary Double Electric Layers in the Plasma

The physical concept and the model of the construction of the plasma source of charged particles in crossed E × H fields are presented in which, due to the special configuration of the electrode structure, conditions are created for the formation of stationary double electric layers. It is shown that the formation of such layers promotes the growth of the source perveance and provides the possibility of simultaneous or alternating formation of flows of charged particles of different signs. The electrode structure and the main characteristics of the developed source are given, and the mechanism of its operation is proposed.

Особенности электронно-оптических систем с плазменным эмиттером на основе стационарных двойных электрических слоев в плазме

The physical concept and the model of the construction of the plasma source of charged particles in crossed E × H fields are presented in which, due to the special configuration of the electrode structure, conditions are created for the formation of stationary double electric layers. It is shown that the formation of such layers promotes the growth of the source perveance and provides the possibility of simultaneous or alternating formation of flows of charged particles of different signs. The electrode structure and the main characteristics of the developed source are given, and the mechanism of its operation is proposed.

Formation mechanism of alumina layer in protecting cubic boron nitride inserts in turning cast irons

Among many cast irons, compacted graphite iron (CGI) has recently been gaining more attention due to its superior mechanical properties over the currently more popular flake graphite iron (FGI), aka gray cast iron. However, the poor machinability has prevented CGI to be used in a wider range of potential applications. The resulting tool life difference between FGI and CGI is staggeringly different to be simply explained by the difference in their physical properties. In particular, the excellent machinability of FGI is claimed to be due to the presence of the MnS layer at the interface between cubic boron nitride (cBN) inserts and FGI at high cutting speed. This paper presents the results of our experimental investigation in an attempt to explain the tool wear difference between FGI and CGI while reexamining the formation of such layers. Straight turning experiments were performed with both FGI and CGI with various cBN inserts in dry condition at high cutting speeds (mostly >400 m/min). The flank and crater surfaces of the inserts during turning experiments were investigated and the difference in both flank and crater wear among various cBN inserts are reported as a function of cutting speed. When turning FGI, speckles of MnS, not as a layer, were present based on our EDS/SEM measurement on the cBN inserts, mainly from the MnS inclusions in FGI smearing on the cBN inserts. However, the total area of MnS speckles did not increase as the turning process continues, questioning the formation of the extensive MnS layer protecting the inserts. When turning CGIs, both Mn and S were present individually, not as MnS, on the cBN inserts. Intriguingly, instead of MnS layer, the extensive Al2O3 layer is formed on the rake side on the certain grades of cBN inserts with the Al2O3 binder phase when cutting at high cutting speeds, which functions as the solubility barrier for certain grades of cBN inserts. The crucial difference between FGI and CGI is that the Al2O3 layer is not only larger in coverage but also significantly more stable after turning FGI. Therefore, the tool wear difference between FGI and CGI mainly comes from the formation of the stable Al2O3 layer on the cBN inserts with Al2O3 binder phase when turning FGI. A few additional mechanisms are introduced to make the complete argument behind the remarkable difference in tool wear.

A Novel Laser‐Stimulated Technique for Direct Formation of Few‐Layer Phosphorene on Silicon Substrates

Direct formation of few‐layered phosphorene flakes through a laser stimulated crystallization on silicon substrates is reported. The formation of such layers is initiated by depositing red phosphorus (RP) on silicon followed by laser‐induced crystallization. After deposition, a glass plate is used to encapsulate the amorphous layer on the substrate. Being capable of a programmable scanning, a 1064‐nm laser is used as the source to impart energy onto the RP layer and to achieve the desired allotrope transformation. Exposure to laser beam at the presence of temperature and local pressure exerted by argon ambient leads to the conversion of amorphous material into crystalline flakes. Furthermore, interesting core‐shell, flower‐like and vertical structures are achieved. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy and energy dispersive X‐ray spectroscopy (EDS) are used to examine the conversion of red phosphorus into few‐layer phosphorene flakes. These flakes are used to fabricate a photodetector with a reasonable response to green laser and a field‐effect transistor with a mobility of 12 cm2 V−1 s−1, further indicating the evolution of well‐crystalline layers. The fabricated transistors demonstrate triode and saturation regimes in their electrical response, evidencing their high quality.

Pulsed laser annealing of highly doped Ge:Sb layers deposited on different substrates

Germanium (Ge) is a promising material for micro- and optoelectronics to produce high speed field-effect transistors, photodetectors, light-emitting diodes and lasers. For such applications tensile-strained and/or highly n-doped Ge layers are needed. The authors have performed the formation of such layers by ion-beam sputtering of composite Sb/Ge target, deposition of thin amorphous Ge:Sb films (~200 nm thick) on different substrates (c-Si, c-Al2O3, α-SiO2) followed by pulsed laser annealing (PLA) for their crystallization and Sb dopant activation. Structural, electrical and optical characterization of Ge:Sb films was carried out using scanning electron microscopy, x-ray diffraction, micro-Raman spectroscopy, secondary ion mass spectrometry methods and by measuring sheet resistance, carrier concentration and photoluminescence. The obtained polycrystalline n-Ge:Sb layers (NSb ~ 1 at.%) are characterized by increased values of tensile strain (up to 1%) and homogenious Sb dopant distribution within layer thickness. The electrical measurements at 300 K revealed the low sheet resistance (up to 40 Ω/□) and extremely high electron concentration (up to 5.5 × 1020 cm−3) in Ge:Sb/SiO2 samples that indicated full electrical activation of Sb dopant on SiO2 substrate. The increased values of tensile strain and electron concentration of Ge:Sb films on α-SiO2 are explained by low values of thermal conductivity and thermal expansion coefficients of quartz substrate.

Colloidal binary mixtures at fluid-fluid interfaces under steady shear: structural, dynamical and mechanical response.

We experimentally study the link between structure, dynamics and mechanical response of two-dimensional (2D) binary mixtures of colloidal microparticles spread at water/oil interfaces. The particles are driven into steady shear by a microdisk forced to rotate at a controlled angular velocity. The flow causes particles to layer into alternating concentric rings of small and big colloids. The formation of such layers is linked to the local, position-dependent shear rate, which triggers two distinct dynamical regimes: particles either move continuously ("Flowing") close to the microdisk, or exhibit intermittent "Hopping" between local energy minima farther away. The shear-rate-dependent surface viscosity of the monolayers can be extracted from a local interfacial stress balance, giving "macroscopic" flow curves whose behavior corresponds to the distinct microscopic regimes of particle motion. Hopping regions reveal a higher resistance to flow compared to the flowing regions, where spatial organization into layers reduces dissipation.

Irreversible fouling of membrane bioreactors due to formation of a non-biofilm gel layer.

Extra-cellular polymeric substances (EPS), known to contribute to fouling in membrane bio-reactors (MBRs), are generally divided into bound and free EPS. The free EPS are able to form a gel layer on the membrane active surface. The mechanisms involved in formation of such layer and its effects on performance of the MBR membranes were studied. The free EPS, extracted by centrifugation and microfiltration, contained a significant amount of humic-like substances. Under static contact to the membrane, adsorption of humic-like substances to the membrane occurred and could be explained by conventional adsorption kinetics. Due to static adsorption, surface roughness of the membrane declined significantly, indicating that adsorbed matters to the membrane filled the cavities of the membrane surface. Filtration of the free EPS caused 50% water flux decline. The fouling resistance linearly increased with the amount of the humic-like substances retained during filtration as predicted by gel growth theory. A low pressure backwash could re-establish the water flux only up to 70%.

One-Step to Prepare Self-Organized Nanoporous NiO/TiO2 Layers and its Use in Non-Enzymatic Glucose Sensing

A highly ordered nanoporous NiTi oxide layers were fabricated on Ti alloys with high Ni contents (50.6 at.%) by a combination of self-organizing anodization at 0°C and subsequent selective etching in H2O2. The key for successful formation of such layers is to sufficiently suppress the dissolve of NiO by applying lower temperature during anodization. The resulting nanoporous structure is connected and well-adhered, which exhibits a much higher electrochemical cycling stability in 0.1 M NaOH. Without further surface modification or the use of polymer binders, the layers can be behave as a low-cost, stable and sensitive platform in non-enzymatic glucose sensing.

Galling mechanisms during interaction of tool steel and Al–Si coated ultra-high strength steel at elevated temperature

Occurrence of galling in hot forming is detrimental to the quality of produced parts and process economy. Material transfer from Al–Si coated work-piece to the tool material has been studied in this work. PVD coatings (AlCrN, TiAlN and DLC) on tool steel substrate have been considered as well as plasma nitriding and their tribological behaviour was compared to the case of an untreated tool steel. Galling initiates through accumulation and compaction of wear debris when untreated tools are used whereas the PVD coatings resulted in increased galling due to adhesion. Plasma nitrided tool steel showed negligible galling due to formation of glaze layers and the formation of such layers depends on the occurrence of wear of the nitrided tool steel.

Defect-induced wetting on BaF2(111) and CaF2(111) at ambient conditions

The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level.

Corrosion of Mg, AS31 and AZ91 alloys in nitrate solutions

The high strength to weight ratio of magnesium and its alloys makes them extremely attractive for transport and aerospace technology applications. However, their corrosion behaviour limits their general applicability compared to aluminium alloys. This study deals with the effect of nitrates on corrosion of Mg and two Mg-based alloys (AS31 and AZ91) in presence and absence of buffers (phosphate and borate) of pH 8. The results revealed that the nature of buffer has a critical effect on the protective layer formed on electrodes. When phosphate buffer used, a protective layer of magnesium phosphate formed. The rate of formation of such layer has been found to increase with increasing both nitrate concentration, in solution, and aluminium content, in the alloy. This increase continues up to a certain limit after which the protective layer may fall and a uniform corrosion is can be observed. In case of borate buffer, high rate of uniform corrosion is observed. In unbuffered nitrate solutions, localized corrosion takes place and its rate increases as the nitrate concentration or the aluminium content in the alloys increases.

Kinetic analysis of the Li + ion intercalation behavior of solution derived nano-crystalline lithium manganate thin films

In the present work, we have optimized the process parameters to synthesize nano-crystalline lithium manganate (LMO) thin films with dense surface morphology and uniform grain size distribution by a solution growth technique. These films were characterized in terms of their phase formation, surface morphology, charge–discharge capacity, rate capability, and cycleability. The films exhibited excellent discharge capacity (close to the theoretical capacity of LMO) and rate capability in a wide range of discharge current densities. However, the rapid capacity fading was observed within the first few initial charge–discharge cycles and with progressive cycling marginal capacity fading was observed. To understand these phenomena, we have investigated the kinetics of Li ion diffusion in these thin film electrodes by cyclic voltammetry (CV) as well as potential step chronoamperometry (PSCA) measurements. In case of the cycled thin film electrode, the Li ion diffusion coefficient was reduced to almost one order of magnitude as compared to its virgin counterpart. During the charge–discharge cycling of these thin film electrodes in a liquid electrolyte, a surface electrolyte interface (SEI) layer was formed on the thin film electrode. It has been argued that the formation of such layer would reduce the Li ion diffusion coefficient and led to the observed capacity fading.

Stability of Aqueous Dispersions of the Hydrated Titanium Dioxide Prepared by Titanium Tetrachloride Hydrolysis

The aggregation stability of aqueous dispersions of the hydrated anatase and rutile samples in the neutral and alkaline pH regions is related to the electrostatic stabilization factor and is described in terms of the classical DLVO theory. The abnormally high stability of the dispersions with respect to 1 : 1 and 1 : 2 coagulating electrolytes, which is exhibited in the acidic pH region, is explained by the existence of well-developed gel layers at the particle surfaces. The specific role in the formation of such layers is played by the sulfate ions.

Structure and composition of ternary carbides in carbonfibre reinforced Mg-Al alloys

Abstract The characteristics of the interlayers in metal matrix composites strongly influence the materials properties. We have investigated the formation of such layers in carbon-fibre reinforced Mg-Al alloys, produced via a gas-pressure meltinfiltration process. Results of high-voltage electron microscopy, high-resolution electron microscopy, selected area diffraction and electron energy loss spectroscopy with analysis of near-edge fine structures (ELNES) of the relevant ionization edges (Mg-L23, A1-L23, C-K, Mg-K and Ald-K) revealed that ternary carbides of approximate composition Al2MgC2 formed at the fibre/matrix interfaces. Analyses of ELNES point to a close relationship in terms of crystal chemistry between the ternary carbide Al2MgC2 and the binary carbide Al4C3. For Al2MgC2, a structure is proposed, with metal atoms in a close-packed arrangement filled with carbon atoms in octahedral and trigonal-bipyramidal interstices.

Recrystallization of Amorphous Layer in Ion Implanted GaAs - Transmission Electron Microscopy Studies

2 MeV arsenic or gallium ions were used to produce nonstoichiometric buried amorphous layers in gallium arsenide. The mechanism of thermally induced regrowth of tlese layers was investigated using transmission electron microscopy. Low-temperature annealing resulted in nucleation of high den- sities of stacking faults. This was associated with the local nonstoichiometry of the amorphous layers. After annealing at high temperatures, in arsenic as well as in gaflium implanted samples, two layers of voids, formed in result of vacancies clustering, were found in areas adjacent to the initial location of the amorphous-crystalline interfaces. A qualitative model of the formation of such layers was proposed. PACS numbers: 61.80.Jh, 6l.72.Cc, 61.72.Ff Ion implantation is a commonly used technique for electronic device process- ing. Therefore, in the past decades there have been numerous studies concerning the damage produced b y ion implantation into semiconduction and its thermal recovery. Despite all these investigations there are still many unsolved problems. In this paper, two issues will be discussed. The first concerns the influence of local nonstoichiometry of an amorphous layer on its regrowth (1, 2). The second is the mechanism of formation of layers of voids, during ligh-temperature annealing. Semi-insulating (100) gallium arsenide (GaAs) wafers were implanted with 2 MeV arsenic (As) or gallium (Ga) ions at doses of 1 x 10 16 cm -2 and 5 x 10 15 cm -2 , respectively. For both the materials cross-sectional transmission electron microscopy (TEM) showed that applied doses were high enough to pro- duce buried amorphous layers. After implantation some pieces of the materials were annealed for 20 minutes in selected temperatures between 300°C and 800°C. In order to prevent arsenic outdiffusion from the surface annealing was performed under arsine ambient in MOCVD reactor. Cross-sectional TEM samples were pre- pared afterwards.

The development of cubic-carbide-free surface layers in cemented carbides without nitrogen

In cemented carbides, the surface-region composition can be modified to provide added toughness for coated cutting-tool substrates by developing a cobalt-enriched, cubic-carbide-free surface layer. Typically, such modifications have been prepared by establishing nitrogen gradients in the cemented carbide through the additions of cubic nitrides or nitrification of the cubic carbides during sintering. Recently, methods have been developed for forming cubic-carbide-free surface layers in compositions without the intentional addition of nitrogen. In this study, the kinetics of formation of such layers are compared for compositions with and without nitrogen. The effects of sintering atmosphere and cubic-carbide composition are also discussed.

Active diagenetic formation of metal-rich layers in N. E. Atlantic sediments

Sediment cores from the Porcupine Abyssal Plain exhibit an indurated layer 0.5–3 cm thick at depths of approximately 50 cm. This is some 15–20 cm below the glacial/Holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of Ruddiman and McIntyre (1981). The layer is forming currently at the oxic/post-oxic boundary in the sediments, as revealed by pore water data: O 2 and NO − 3 are present in solution above the layer, while Fe 2+, Mn 2+, PO 3− 4 and NH + 4 are present in solution below, and all these species show concentration gradients indicating fluxes into the layer. These data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by Wilson et al. (1986a,b). The elements Mn, Ni, Co, Fe, P, V, Cu, Zn and U are all enriched to varying degrees in the vicinity of the layer. Some differential stratification of these elements in the vertical, consistent with a redox control, is observed at one site with a 0.5 cm layer, with Mn, Ni and Co above, Fe, P, V and Cu in the layer, and U below. At another site the metal-rich layer has higher Fe and P concentrations and is more indurated. Here all enrichments except Co are contained within a single layer sample, 3 cm thick.

A quantitative model for the formation of adsorption-entanglement layers

The formation of thick adsorption-entanglement layers at foreign surfaces during the flow of high molecular weight polymer solutions is now well documented. This paper presents a quantitative model which describes the formation of such layers in terms of the polymer molecular weight and radius of gyration, the solution concentration and the local flow velocity. The model is tested against experiments using capillary flow of atactic polystyrene solutions. The agreement between theory and experiment is very good.