Layers Of Different Thicknesses Research Articles

Correlation of Electron Beams and Hard X‐ray Emissions in ISTTOK Tokamak

AbstractThe paper reports on experimental studies of electron beams in the ISTTOK tokamak, those were performed by means of an improved four‐channel detector. The Cherenkov‐type detector measuring head was equipped with four radiators made of two types of alumina‐nitrate (AlN) poly‐crystals: machinable and translucent ones, both of 10 mm in diameter and 2.5 mm in thickness. The movable support that enabled the whole detectors to be placed inside the tokamak vacuum chamber, at chosen positions along the ISTTOK minor radius. Since the electron energy distribution is one of the most important characteristics of tokamak plasmas, the main aim of the study was to perform estimations of an energy spectrum of the recorded electrons. For this purpose the radiators were coated with molybdenum (Mo) layers of different thickness. The technique based on the use of Cherenkov‐type detectors enabled the detection of fast electrons (of energy above 66 keV) and determination of their spatial and temporal characteristics in the ISTTOK experiment. Measurements of hard X‐rays (HXR), which were emitted during ISTTOK discharges, have also been performed. Particular attention was paid to the correlation measurements of HXR pulses with run‐away electron beams. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Effect of Cesium Carbonate Modified Layer on the Performance of Organic Solar Cells

Experiments found that the thickness of the cesium carbonate modified layer of the processing solution will affect the performance of the polymer solar cells. We dissolved cesium carbonate in an organic solvent 2-ethoxyethanol, and prepared cesium carbonate modified layer of different thickness at different rotational speed. When the rotationing speed was at 2000 r/min, the efficiency of the device was preferably 2.28%, which indicated that the thickness prepared at this speed was most advantageous to the enhancement of the performance of the device. In addition, by annealing cesium carbonate modified layer at 130°C and 150°C, we found that the performance degradation of the annealing device at higher temperature was due to the fact that too much of the energy destroyed the micro-structure of the formed active layer.

Properties of thermoelectric Ce0.09Fe0.67Co3.33Sb12/FeSb2Te multi-layered structures prepared by laser ablation

Multi-layered Ce0.09Fe0.67Co3.33Sb12/FeSb2.1Te structures composed of thin equidistant layers of different thickness were prepared by pulsed laser deposition on fused silica quartz glass substrates. The structures were prepared at substrate temperatures (230°C or 250°C) applying the same laser beam energy density (3Jcm−2). In the contribution we present some thermoelectric properties such as in-plane electrical conductivity, the Seebeck coefficient and the power factor of the multi-layered structures in the temperature range from 300K to 500K. Comparison of multi-layered structure's thermoelectric properties with single thin Ce0.09Fe0.67Co3.33Sb12 and FeSb2.1Te layers is given. X-ray diffraction patterns are shown. A cross-sectional picture of the multi-layered structure made by scanning electron microscope is given for the thicker multi-layered structure.

Double-layer microwave absorber based on CoFe2O4 ferrite and carbonyl iron composites

Abstract The microwave absorption properties of carbonyl iron (CI) and CoFe 2 O 4 ferrite with single-layer and double-layer composite absorbers were investigated based on the electromagnetic transmission line theory and the impedance matching principle in the frequency range from 2 GHz to 18 GHz. XRD and SEM were used to characterize the structure of the powdered composites. Coaxial method was used to measure the electromagnetic parameters of CI and CoFe 2 O 4 . The reflectances of the matching and absorbing layers of different thicknesses and orders were also calculated. The results show that using CoFe 2 O 4 as matching layer and CI as absorbing layer can greatly expand the coating absorption bandwidth and decrease the reflectance peak. Double-layer absorbers have much better microwave absorption properties than single-layer absorbers. The microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing and matching layers. The double-layer microwave absorbers with reflection loss less than −10 dB over the range from 8.6 GHz to 18 GHz (the absorption bandwidth is 9.4 GHz), which almost covers the X-band (8.2 –12.4 GHz) and the whole Ku-band (12.4–18 GHz) were achieved when the thicknesses of CoFe 2 O 4 and CI were 2.4 and 0.5 mm, respectively.

A study on the scaling features for mixing and deflagration potential of stratified layer of hydrogen due to molecular diffusion

Hydrogen deflagration in confined spaces is an important safety issue. The dispersion of a stratified layer of hydrogen due to molecular diffusion is studied. It represents an important class of problems related to long term behaviour of hydrogen release in confined spaces. Diffusion being a slow process, gives an upper bound on the time taken for the stratified layer to mix with air below. A method, based on four indices, namely, average mole fraction (of hydrogen), non-uniformity index, deflagration volume fraction and deflagration pressure ratio, developed recently by the authors, is used to provide vital temporal information on mixing of the stratified layer with air below and formation of flammable cloud in the enclosure. In the present paper, stratified layers of different thickness are considered and the temporal evolutions of the above indices are plotted against diffusion Fourier number. The results in non-dimensional form provide an upper bound of the time that would be required to form a uniform mixture and to attain a state with respect to deflagration potential for enclosures of different sizes. This estimate is an important input for planning mitigation measures before the accident and for post accident investigations.

Tribological and Corrosive Properties of the Parts of Machines with Surface Alloy Layer

Abstract There are presented the results of researches conducted on the steel cast with surface alloy layer in this work. The measurement of the thickness, hardness and abrasion wear resistance was conducted in accordance with norm ASTM G 65-00. The measurement of the corrosion resistance was conducted in accordance with the potentio - dynamical method. It is shown that it is possible to obtain the alloy surface layer of different thickness by control of some factors: pouring temperature Tzal , diameter of grain of FeCrC alloy Zw and the thickness of the cast wall gśo. It is proved that the smaller diameter of ferrochromium grain, the thicker surface alloy layer. It is also said that the higher pouring temperature and thicker the cast wall, the thicker surface alloy layer. What is more - the smaller thickness of the cast wall, the bigger hardness and abrasion wear resistance.

Detection of the dynamic magnetic behavior of the antiferromagnet in exchange-coupled NiFe/IrMn bilayers

The magnetothermal behavior of antiferromagnetic IrMn layers of different thickness (3, 6, 10 nm) has been studied by exploiting the exchange coupling with a ferromagnetic 5 nm-thick NiFe layer. A procedure has been devised for the measurement of the magnetization of the NiFe/IrMn bilayers as a function of temperature and time at different values of an external magnetic field, Hinv, antiparallel to the unidirectional exchange anisotropy. This analysis allows one to probe the effective distribution of anisotropy energy barriers of the antiferromagnetic phase, as sensed by the ferromagnetic layer. Two magnetic regimes have been distinguished. At temperature T < 100 K, the interfacial IrMn spins are frozen in a glassy state and are collectively involved in the exchange coupling with the NiFe spins. At T ∼ 100 K the collective state breaks up; thus, above this temperature, only the interfacial IrMn spins which are tightly polarized by the IrMn nanograins, forming the bulk of the layer, are effectively involved in the exchange coupling mechanism. Due to that, for T > 100 K the exchange coupling is ruled by the anisotropy energy barriers of the bulk IrMn nanograins, namely by the layer thickness. The thermal evolution of the exchange field and of the coercivity in the three samples is coherently explained in the framework of this description of the dynamic magnetic behavior of the IrMn phase.

Photoluminescence modulation of ZnO via coupling with the surface plasmon resonance of gold nanoparticles

In this letter, we study how coupling between AuNPs and ZnO thin films affects their emission properties. The emission intensity of ZnO thin films changes when Al2O3 spacer layer of different thickness is included in ZnO/Au films, consistent with theoretical predictions. The emission properties are also controlled using the polarization of the excitation source. Emission properties depended on the polarization of the excitation source because of the surface plasmon resonance of AuNPs. The photoluminescence anisotropy of these systems shows that enhanced photoluminescence can be achieved through coupling of the emission from ZnO with the surface plasmon resonance of AuNPs.

Suppression of superconductivity by strong magnetic fields in PbTe/PbS heterostructures with a superconducting interface

This is a comprehensive study of the effect of strong magnetic fields on superconductivity in PbTe/PbS heterostructures with semiconducting layers of different thicknesses. Metallic conductivity and superconductivity (critical temperature Tc ≤ 6.5 K) in PbTe/PbS heterostructures are caused by inversion of bands along a continuous network of misfit dislocations that develops at the interfaces between semiconductor layers of sufficient thickness (d &amp;gt; 80 nm). With decreasing d the continuity of the superconducting interface is disrupted, Tc decreases, and the metallic conductivity changes to a semiconducting type. Disruption of the continuity of the superconducting interface is found to be a necessary condition for observing a magnetic-field induced superconductor-insulator transition (SIT) and has a significant influence on its features: a fan-like set of resistance curves R(T); intersection of the R(B) curves for fields perpendicular, as well as parallel, to the interface; and, negative magnetoresistance. A scaling analysis based on Fisher's theoretical model is carried out for these samples. No evidence of a SIT was observed in heterostructures with a perfect interface. It appears that the SIT effect is related to percolation phenomena characteristic of granular superconductors.

Excitonic effects of bilayer graphene: A simple approach

The present work investigates the excitonic effects on the bilayer graphene with layers of different thickness under the influence of external electric field through a simple numerical approach. The band structure and energy gap have been calculated using a tight-binding model including parameters like the second-nearest-neighbor-hopping energies t′ (in-plane) and γ (intra-layer) and the on-site energy Δ, in details. The binding energy of exciton for bilayer graphene has been calculated by Wannier model and Hartree–Fock approximation through the Bethe–Salpeter equation. Finally the optical conductivity spectrum of bilayer graphene has been calculated by using the effective mass approximation in two band model.

Annealing of laser patterned PMMA coated with gold and gallium

Poly(methyl methacrylate) (PMMA) surface was patterned by laser scanning and Ga and Au layers of different thicknesses were sputtered onto modified polymer surface. The metal/PMMA structures were annealed at 160 °C for 1 h and the changes in the surface morphology were examined by AFM and STM techniques. It was found that sufficiently thick and continuous metal coverage protect the underlying pattern structure.

Preparation and Application of Reversed Phase ChromatorotorTM for the Isolation of Natural Products by Centrifugal Preparative Chromatography

A method of preparation of rotors with a reversed phase (RP) solid silica gel sorbent layer has been developed for centrifugal preparative chromatography (CPC), also known as rotational planar chromatography (RPC). The rotors consist of binder free RP solid SiO2 layers of different thicknesses packed between two supported circular glass discs and can be used in any appropriate device for centrifugal chromatography, like Chromatotron and CycloGraph. Polar and /or semi-polar compounds with close R(f) values, as well as extracts and column fractions were separated and/or purified in a preparative and/or semi-preparative scale using the RP rotors, eluted with mixtures of aqueous-based solvents. We herein report three examples of its application, using RP Chromatorotors, for the isolation of the diastereoisomeric alkaloids banistenosides I and II from Banisteriopsis caapi, saponins III and IV from Fagonia cretica, and the sesquiterpenes artemisinin (V) and artemisinic acid (VI) from Artemisia annua.

Mechanical spectra of glass-forming liquids. II. Gigahertz-frequency longitudinal and shear acoustic dynamics in glycerol and DC704 studied by time-domain Brillouin scattering

This paper presents and discusses the temperature and frequency dependence of the longitudinal and shear viscoelastic response at MHz and GHz frequencies of the intermediate glass former glycerol and the fragile glass former tetramethyl-tetraphenyl-trisiloxane (DC704). Measurements were performed using the recently developed time-domain Brillouin scattering technique, in which acoustic waves are generated optically, propagated through nm thin liquid layers of different thicknesses, and detected optically after transmission into a transparent detection substrate. This allows for a determination of the frequency dependence of the speed of sound and the sound-wave attenuation. When the data are converted into mechanical moduli, a linear relationship between longitudinal and shear acoustic moduli is revealed, which is consistent with the generalized Cauchy relation. In glycerol, the temperature dependence of the shear acoustic relaxation time agrees well with literature data for dielectric measurements. In DC704, combining the new data with data from measurements obtained previously by piezo-ceramic transducers yields figures showing the longitudinal and shear sound velocities at frequencies from mHz to GHz over an extended range of temperatures. The shoving model's prediction for the relaxation time's temperature dependence is fairly well obeyed for both liquids as demonstrated from a plot with no adjustable parameters. Finally, we show that for both liquids the instantaneous shear modulus follows an exponential temperature dependence to a good approximation, as predicted by Granato's interstitialcy model.

The anti-plane vibration of a quartz plate with an additional partial non-uniform mass layer for acoustic wave sensing

The anti-plane vibration of a quartz plate having an additional partial non-uniform mass layer is solved by ignoring the effect of small c56 in comparison with other elastic constants. This analysis is based on the trigonometric series solution, and the convergence is examined. Numerical simulation is conducted for several different types of layers of different thicknesses using linear, cosine, and quadratic functions. The fre- quency spectrums, in addition to the length and mass fraction of the layer, are discussed separately. Compared with the homogeneous mass layer, the non-homogeneous layer with greater inertia leads to earlier appearance of the higher modes and more modes trapped under the same condition. Especially, there is no energy trapping in the plate with a fully covered uniform mass layer. However, this kind of energy trapping can be obtained again when the surface is non-uniform for some cases.

Effect of ZnO sacrificial layer thickness on the structure and optical properties of GaN nanoparticles prepared by RF magnetron sputtering

GaN nanoparticles were prepared on sapphire (0001) substrates with ZnO sacrificial layers by self assembly of Ga2O3 films in their reaction with NH3. ZnO sacrificial layers with different thicknesses and Ga2O3 films were deposited on sapphire substrates in turn by a radio frequency (RF) magnetron sputtering system. Nitridation of the Ga2O3 films was then carried out in a quartz tube furnace. The effect of ZnO sacrificial layer thickness on the structure and optical properties of nanoparticles prepared by RF magnetron sputtering were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL). GaN nanoparticles with ZnO sacrificial layers of different thicknesses possess hexagonal wurtzite crystal structure and have a preferred orientation with c axis perpendicular to the sapphire substrates. XRD, SEM, and AFM results reveal that the better-crystallinity, uniform, and well-dispersed GaN nanoparticles (∼30 nm) without agglomeration were obtained with a ZnO sacrificial layer 300-nm thick. The PL result reveals that the optical properties of the GaN nanoparticles are improved with a ZnO sacrificial layer 300-nm thick. Therefore, we suggest that a ZnO sacrificial layer 300-nm thick is the most suitable condition for obtaining better-quality GaN nanoparticles with good luminescence performance. Moreover, the mechanism of the formation of GaN nanoparticles with ZnO sacrificial layers is also discussed.

Copper Light-induced Plating Contacts with Ni Seed-layer for mc-Si Solar Cells after Laser Ablation of SiNx:H

This study focuses on the electrochemical Ni/Cu metallization of multi-crystalline silicon (mc-Si) without alignment steps. Selective ablation of the silicon nitride (SiNx:H) anti-reflection and passivation coating was performed prior to metallization with a frequency tripled Nd:YAG laser. Electroless nickel-phosphorous layers of different thicknesses were deposited as a seed-layer at 95°C on two batches of samples before electrolytic copper thickening. The thickening of the Ni contact by copper was done by light-induced plating (LIP). The influence of laser ablation parameters as well as chemical etching prior to metal deposition was investigated. The morphology of electrochemically deposited Ni and Cu metal layers was investigated by SEM and optical microscope. Laboratory scale solar cells were fabricated to evaluate the electrical properties of the front contacts. A copper thickness of between 9 and 16μm was necessary in order to optimize the fill factor. The best efficiency measured on 200μm thick p-type mc-Si solar cell with an area of 4.4cm2 was 15.5%. An average efficiency of 15% over 18 samples has been demonstrated. Such results were obtained without any additional thermal annealing treatment of the Ni seed-layer. The limiting factors as well as possible improvements are discussed.

Atomic layer deposition of Er2O3 thin films from Er tris-guanidinate and water: process optimization, film analysis and electrical properties

For the first time, the combination of the homoleptic erbium tris-guanidinate metalorganic complex ([Er(NMe2-Guan)3]) simply with water yielded high quality Er2O3 thin films on Si(100) substrates employing the atomic layer deposition (ALD) process. The process optimization to grow good quality Er2O3 layers was performed by varying the Er precursor pulse time, water pulse time and purge time. The high reactivity of the Er compound towards water and good thermal stability in the temperature range of 150–275 °C (ALD window) resulted in homogeneous, stoichiometric Er2O3 layers with high growth rates (1.1 A per cycle) and the as-deposited films crystallized in the cubic phase. The saturation behavior at different temperatures in the ALD window and the linear dependence of film thickness as a function of precursor pulse time confirmed the true ALD process. The potential of Er2O3 thin films as gate dielectrics was verified by performing capacitance–voltage (C–V) and current–voltage (I–V) measurements. Dielectric constants estimated from the accumulation capacitance were found to be in the range of 10–13 for layers of different thicknesses (15–30 nm).

Erosive wear of plasma electrolytic oxidation layers on aluminium alloy 6061

Plasma electrolytic oxidation (PEO) is a process that converts the surface of light metals and alloys into a ceramic layer. In aluminium alloys, layers produced by PEO are mainly composed of oxides and other compounds which are harder, therefore, more suitable for tribological applications than the underlying base metal. The aim of this work was to study the erosive wear of PEO layers of different thicknesses and to compare it with the bare aluminium alloy 6061 base metal. PEO was conducted to produce layers 100, 125 and 150μm thick that were characterised by SEM, XRD, microhardness and stylus profiling prior to testing. Multiple impact angle (20° to 90°) erosion tests were performed in a sandblast type machine that simulates the sand blowing process to produce sand cores for castings. The erodent material was resin-bonded silica sand, jetted by compressed air at 0.69 and 1.38bar producing average particle impact velocities of 6 and 10m/s, respectively. In most cases, PEO layers wore less than the bare aluminium alloy. For the 6m/s impact velocity, the 150μm layer experienced quantitatively lower wear rates than the 125μm and the 100μm. On the contrary, for the 10m/s impact velocity the 150μm layer showed higher wear than the 125μm and the 100μm. Optical, scanning electron and confocal white light microscopy were used to elucidate the erosive wear mechanisms taking place; which are discussed in this paper.

A systematic investigation of the mechanochemical decomposition of Ag oxalate in rod drop experiments

The present work focuses on the chemical response of Ag oxalate powders to the collision of rods in controlled rod drop experiments performed by using suitably designed reactors. Powder layers of different thickness were submitted to the collision of cylindrical rods with selected radius, mass, and collision velocity. The experimental findings indicate that collisions are able to induce the partial decomposition of Ag oxalate into metallic Ag and gaseous carbon dioxide. The mass of Ag oxalate decomposed is proportional to the collision energy. Being the impact energy the same, the mass decomposed is inversely proportional to the surface area of the powder layer. In addition, it increases irregularly as the thickness of the powder layer increases. The results obtained suggest that rod drop experiments can be profitably used to promote and investigate mechanochemical transformations.

Reduced graphene oxide coated thin aluminum film as an optoacoustic transmitter for high pressure and high frequency ultrasound generation

We demonstrate that reduced graphene oxide (rGO) coated thin aluminum film is an effective optoacoustic transmitter for generating high pressure and high frequency ultrasound previously unattainable by other techniques. The rGO layer of different thickness is deposited between a 100 nm-thick aluminum film and a glass substrate. Under a pulsed laser excitation, the transmitter generates enhanced optoacoustic pressure of 64 times the aluminum-alone transmitter. A promising optoacoustic wave generation is possible by optimizing thermoelasticity of metal film and thermal conductivity of rGO in the proposed transmitter for laser-induced ultrasound applications.