Sublayer Thickness Research Articles

Structural evolution of thermal annealed Si(0 0 1) surface layers fabricated by plasma immersion He+ implantation

Abstract Structural evolution in Si(0 0 1) surface layers after high-dose (D = 5 × 1017 cm–2) low-energy (2 and 5 keV) plasma immersion He+ ion implantation (He+ PIII) and subsequent annealing at 853 and 1073 K was studied by complementary structural sensitive methods (TEM, XRR, RBS, and AFM). Formation of a three-layer structure (amorphous a-SiOx sublayer at the surface, amorphous a-Si sublayer with large size helium-filled bubbles, and heavily damaged crystalline c-Si sublayer containing small-size bubbles and Si nanocrystallites) was observed for both implantation energies. This three-layer structure is retained after annealing. It was shown that the thickness of the oxide sublayer does not depend on implantation energy and does not change after annealing. This amorphous oxide sublayer together with dense top part of the a-Si sublayer forms a cap layer with a thickness of 15 nm that can be considered as a protective layer for the sublayers containing He-filled bubbles and Si nanocrystallites. The Si nanocrystallites were revealed at the boundary of the a-Si and the c-Si sublayers both in as-implanted at 5 keV and annealed samples.

Templated Electrochemical Synthesis of Fe–Pt Nanopatterns for High-Density Memory Applications

We demonstrate an electrochemical deposition process suitable to form arrays of L10 Fe–Pt nanodots with hard magnetic properties via electron-beam lithography, template deposition, and thermal annealing. Synthesis parameters are selected by growing single and multilayer blanket films and investigating the effect of thermal annealing on the various films. We find that the fastest ordering transformation is achieved in eight-layer Fe–Pt multilayers with a sublayer thickness of 2.5 nm, while a single Fe–Pt layer or four- and twenty-layer multilayers exhibit a more sluggish ordering process due to the imperfect layering (twenty-layer) or to the limited mean free path upon annealing (single- and four-layer); the coercivity of the eight-layer Fe–Pt multilayer after annealing at 450 °C reached 6.6 kOe, whereas the single Fe–Pt layer showed only 1.0 kOe. TEM imaging and diffraction show that the L10 Fe–Pt nanodot arrays are single crystal with a (111) orientation, suggesting a facile L10 ordering when using a mul...

Helium Bubbles Formed in Si(001) Layers after High-Dose Implantation and Thermal Annealing

In this paper, we show that high-dose low-energy plasma-immersion ion implantation H+ (E = 2–5 keV) leads to the formation of hidden layers of helium bubbles in an Si(001) substrate. The structural studies of the bubbles’ layers are carried out by using X-ray reflectometry, small-angle scattering, and transmission electron microscopy. Changes in the structure of the layers of the bubbles during thermal annealing are also studied. We have shown that as a result of implanting helium ions with a dose of 5 × 1017 cm–2, a multilayer structure is formed in the near-surface layers of the silicon substrates that generally consists of amorphous, porous amorphous, and porous crystalline sublayers. The structural parameters of the sublayers (density, thickness, and size of the boundaries) and the concentration and size of the bubbles after annealing from 580 and 800°C are determined. It is shown that annealing leads to a bimodal distribution of the bubbles with the average size of 2 to 3 nm and 7 to 8 nm. We establish that the upper amorphous layer is 15 nm thick and can be considered as a protective layer for further processing.

Experimental study on turbulent convective heat transfer of water-based nanofluids containing alumina, copper oxides and silicon carbide nanoparticles

Nanofluids are obtained by suspending metallic or non-metallic nanoparticles in conventional base liquids and can be employed to increase heat transfer rate in various applications. In this study, the effects of adding three types of nanofluids on turbulent convective heat transfer at the entrance region of a constant wall heat flux tube were experimentally studied. The nanofluids were mixtures of aluminium oxide, copper oxide, and silicon carbide at various nanoparticle volume fractions ranging from 0.0002 to 0.002 in water. The convective heat transfer coefficient was measured at different Reynolds numbers of 10,000–50,000. At these concentrations and Reynolds numbers, a maximum of 11–18% of convection heat transfer coefficient was observed as compared to the base fluid, showing a 6–9% increase on average. In this study, it was observed that changes in the nanoparticle type had no considerable effect on heat transfer coefficient increase. According to the model proposed here, the dimensionless thickness of laminar sub-layer is specified as a functional equation of the volume fraction of nanoparticles for each material.

Purification of water from dissolved gases in a film unit with discrete-rough walls

This paper analyzes the use of a highly effective film unit for water purification from dissolved corrosive gases, in order to increase the resource efficiency and reliability of various equipment using water circulation systems at industrial plants and thermal power plants. The unit consists of a vertical bundle of tubes contained in tube grids and operates in the upward co-current gas and liquid in a pipe. The gas moves at a speed of 10 – 30 m/s (strong interaction of phases) and carries a liquid film from the bottom up. In this mode, there is a significant intensification of heat and mass transfer (5 – 15 times) in comparison with counter current. In addition, the inner surface of the tubes may have artificial discrete roughness (rectangular projections), which further increases the effectiveness of the processes. The paper presents the mathematical model and the efficiency calculation results for a film contact device with rough walls at strong phase interaction. The mathematical description is based on the models of the flow structure and the diffusion boundary layer. Expressions are given for calculating the mass transfer coefficient in a turbulent film with co-current gas, as well as parameters of the flow structure model in a contact tube. The main parameters of the equation for calculation of the mass transfer coefficient are the dynamic friction velocity on the interfacial film surface and the dimensionless thickness of the viscous sublayer. The dynamic speed is calculated using the equation of balance of forces in the contact tube, and the dimensionless thickness of the viscous sublayer-based on the known values on the plate adjusted for the phase interaction conditions. The cell model of the flow structure is used, and an expression is obtained for calculating the concentration profile of gas dissolved in water at the height of the pipes. The paper also presents an expression to calculate the number of cells in a complete mixing. The paper presents the calculated and experimental dependences of decarbonization efficiency for tubes with smooth and rough walls. The influence of spacing between roughness elements (projections) on water purification efficiency is shown. Conclusions are made about the design of a unit with a rising film at higher concentrations of dissolved gases in the water.

Impact of sublayer thickness and annealing on silicon nanostructures formation in a-Si:H/a-SiNx:H superlattices for photovoltaics

In this work, we synthesized amorphous multilayered a-Si:H/a-SiNx:H superlattices with different thickness of sublayers grown on silicon and quartz substrates by PECVD method at low power density (60 mW/cm2) and substrate temperature (250 °C) using nitrogen and silane gases as reactive precursors. Subsequently, the post-deposition annealing of these structures, composed of alternating layers of a-Si:H and a-SiNx:H, was carried out up to 1100° in vacuum to form silicon nanostructures. The dependence of the structural and chemical bonding characteristics of prepared superlattices on the silicon sublayer thickness and post-deposition annealing temperature was investigated. The formation of silicon nanostructures was confirmed by transmission electron microscopy, X-ray diffraction measurement and Raman scattering spectroscopy. Changes in bonding configuration during the annealing were carried out by Fourier transform infrared spectroscopy. Optical properties were studied by UV–Vis spectroscopy. XRD, Raman and TEM measurements show that the crystallization process of a-Si:H sublayers strongly depends on the thickness of initial a-Si:H sublayers and the post-deposition treatment process. It was found that a higher crystallization temperature for the thinner a-Si:H sublayers is needed. Results clearly show that structural and optical characteristics of these systems can be controlled by deposition parameters and post-deposition annealing conditions.

Large Eddy Simulation of Liquid Metal Turbulent Mixed Convection in a Vertical Concentric Annulus

In the present study, turbulent forced and mixed convection heat transfer to a liquid metal flowing upwards in a concentric annulus is numerically investigated by means of large eddy simulation (LES). The inner-to-outer radius ratio is 0.5. The Reynolds number based on bulk velocity and hydraulic diameter is 8900, while the Prandtl number is set to a value of 0.026. A uniform and equal heat flux is applied on both walls. LES has been chosen to provide sufficiently accurate results for validating Reynolds-averaged turbulence models. Moreover, with the thermal sublayer thickness of liquid metals being much larger than the viscous hydrodynamic one, liquid metals present a separation between the turbulent thermal and hydrodynamic scales. Thus, with the same grid resolution, it is possible to perform a LES for the flow field and a “thermal” direct numerical simulation (DNS) for the temperature field. Comparison of the forced convection results with available DNS simulations shows satisfying agreement. Results for mixed convection are analyzed and the differences with respect to forced convection at the same Reynolds number are thoroughly discussed. Moreover, where possible, a comparison with air is made.

ОПРЕДЕЛЕНИЕ КОЭФФИЦИЕНТОВ ТЕПЛООТДАЧИ В КАНАЛАХ С ИНТЕНСИФИКАТОРАМИ ПРОЦЕССА

Reviewed equations for calculation of heat transfer coefficients from a smooth surface, obtained with the use of models of the turbulent boundary layer Prandtl and Deisler. It is shown that the inclusion of disturbances in the boundary layer (roughness of the walls, ledges, ring rolling) can be performed parametrically by adjusting the dynamic speed, the thickness of a viscous sublayer and boundary layer thickness. The results of calculations of the average values of heat transfer coefficients (in dimensionless form of Nusselt numbers and Stanton) and comparing with k nown experimental data.

Intense electroluminescence from Al2O3/Tb2O3 nanolaminate films fabricated by atomic layer deposition on silicon.

Intense electroluminescence (EL) from Tb3+ ions in the Al2O3/Tb2O3 nanolaminate films is achieved in a metal-oxide-semiconductor structure fabricated on silicon, utilizing atomic layer deposition. Precisely controlling of the nanolaminates enables the study on the influence of the atomic Tb layers and the distance between every dopant layers on the EL mechanism. The EL intensity decreases with excessive Tb dopant cycles due to the reduction of optically active Tb3+ ions. Cross-relaxation among adjacent Tb2O3 dopant layers depopulates the excited ions in 5D3 level and contributes to the green EL from 5D4 level, which strongly depends on the Al2O3 sublayer thickness with a critical value of ~3 nm. The 543 nm green EL from Tb3+ ions shows maximum power density of 3.37 mW cm-2 and external quantum efficiency up to 0.73%. Further promotion of efficiency is realized by adopting thicker luminescent layer and Al2O3 cladding layer.

Effect of Carrier Diffusion on the Electrical Properties of Si–Zn–Sn–O/Ag/Si–Zn–Sn–O Multilayers

Typically, a parallel circuit model is used to explain the electrical resistivity of oxide-metal-oxide (OMO) multilayers; such a model treats the top, middle, and bottom sublayers independently. However, in the case of semiconductor–metal-semiconductor multilayer systems, this model is not applicable; according to the theory of metal-semiconductor contact, carrier diffusion arising from the difference in the work functions of the materials should also be considered. In this paper, we investigate the effect of carrier diffusion on the electrical properties by changing the thickness of both the top and bottom oxide layers. We find that adjusting the thickness of the oxide sublayers realizes direct control of the carrier density in OMO multilayers.

Electro-architected porous platinum on metallic multijunction nanolayers to optimize their optical properties for infrared sensor application

Tailoring the physicochemical properties of the metallic multijunction nanolayers is a prerequisite for the development of microelectronics. From this perspective, a desired lower reflectance of infrared radiation was achieved by an electrochemical deposition of porous platinum in nonaqueous media on silver mirror supported nickel–chrome and nickel–titanium metallic films with incremental decreasing thicknesses from 80–10 nm. The electro-assembled architectures were examined by means of scanning electron microscopy and Fourier transform infrared spectroscopy and it was observed that the layer and sublayer thicknesses and resistivities have a substantial effect upon the porous platinum morphology and its optical properties. It is here reported that the augmentation of the metallic layer electrical conductivity determines the electroformation of more compact platinum nanolayers. Moreover, the platinum black coating of metallic nanolayers causes a considerable decrease of the reflectance in the region from 1000–8000 cm−1.

Wavelength Blue-Shifting and Gain Spectral Bandwidth of InAs/InP Quantum Dots for Laser Applications Around $1.55~\mu$ m

It was found experimentally that growing an ultrathin GaP interlayer/sublayer before InAs quantum dots (QDs) grown on InGaAsP barrier lattice-matched to InP (001) substrates is an efficient way to tune the emission wavelength of InAs/InP QD lasers to 1.55 μm range at room temperature (RT). However, the impact of interlayers/sublayers in InAs/InP QD lasers has not been carefully investigated and analyzed theoretically, and the existing physic model cannot predict the emission wavelength of InAs/InP QD lasers engineered by interlayers/sublayers. In this paper, an improved model, which consists of a three-step strain analysis, is applied to precisely predict measured photoluminescence emissions of various QD samples with the GaP interlayer/sublayer that have a specific thickness or chirped/varied thicknesses at both RT and low temperature. It is found that the impact of the GaP sublayers is to enhance quantum confinement instead to stop As/P exchange. Finally, a new method of emission spectrum blue-shifting and gain spectral bandwidth enhancement of an InAs/InP QD laser is proposed and found to be more efficient. By optimizing sublayer thickness and double capping, a total gain spectral bandwidth of 245.7 nm, as an example, is predicted and peak wavelength is shortened to 1500 nm.

Buckling analysis of bilayer beam-columns with an asymmetric delamination

A general analytical model is developed to evaluate buckling behavior of a bilayer beam-column with a through-the-width asymmetric delamination under simply supported boundary conditions. Both transverse shear deformation and local deformation at delamination tip are taken into account in the model by considering two sublayers in both delaminated and intact regions as two individual shear deformable ones. Interface continuity conditions, which account for effect of interface normal and shear stresses, are also introduced in the intact regions. Furthermore, the present model is capable of dealing with the case of delamination located arbitrary through thickness and along length of beam-columns. In comparisons with the results of classical Euler-Bernoulli beam model, Timoshenko beam model (rigid joint model) and finite element analysis, better agreements are achieved for the present flexible joint model, which captures local deformation at delamination tip due to consideration of interface normal and shear stress components. Parametric studies are conducted to evaluate influences of sublayer thickness ratio, delamination length, delamination location, specimen length, and material parameters on the critical buckling strain with emphasis on transverse shear deformation and local deformation at delamination tip. The developed model can be used with confidence in buckling analysis of layered structures with an arbitrary delamination through the length and thickness.

Structures of turbulent premixed flames in the high Karlovitz number regime – DNS analysis

Lean premixed turbulent methane-air flames have been investigated using direct numerical simulations (DNS) for different Karlovitz numbers (Ka), ranging from 65 to 3350. The flames are imposed to a high intensity small-scale turbulent environment, corresponding to high Ka conditions, and the effect on the flame structure is investigated during the transition from initial laminar flame to highly distorted turbulent flame. The focus is on the internal structure of different sub-layers of these flames. The preheat layer, fuel consumption layer and oxidation layer are characterized by the distribution of formaldehyde, the fuel consumption rate and the CO consumption rate, respectively. Different measures that quantify sub-layer thickness for turbulent flames have been defined and analyzed. The flame brush is broadened with time while the local thickness (excluding large scale wrinkling) of all three layers initially show thinning due to the interaction of the flame with the turbulent flow field. As time passes, the local thickness of the preheat layer and fuel consumption layer are restored while the oxidation layer remains thinned due to suppression of CO consuming reactions. As Ka increases there is an increasing probability of finding thinned, large gradient regions in each of these sub-layers. The contribution to the evolution of flame thickness from normal strain rate, chemical reaction and normal and tangential diffusion is analyzed in terms of a gradient transport equation. The relative size of the terms changes as Ka increase and, in particular, the term due to chemical reactions loses its relative significance. The observed thinning of the local flame structure is attributed to the preferential alignment of the flame normal with the compressive strain rate eigenvectors. Such alignment provides a mechanism for the flame thinning, consistent with the behavior of non-reacting scalars. A preferred angle of about 20 degrees is observed between the flame normal and the compressive strain rate eigenvector.

Development of tuned refractive-index nanocomposites to fabricate nanoimprinted optical devices

The objective of this research is to demonstrate high-quality nanocomposites enabling convenient imprinting of nanopatterned optical devices. The nanocomposite developed contains homogeneously dispersed silicon (Si) nanoparticles in a UV-curable prepolymer host medium. Using an optical adhesive NOA73 as host eliminates surface treatment of the silicone mold due to minimal adhesion between the polymer and mold. Moreover, the chosen materials exhibit low shrinkage, enabling faithful replication of the master templates. Tunable refractive index is realized by mixtures of the host polymer with a refractive index of ~1.56 and nanoparticles with a refractive index of ~3.45. For example, using a ~28% Si fraction, an imprintable material with a refractive index of ~2.1 results. Surface functionalization of nanoparticles with polyvinylpyrolidone is shown to reduce agglomeration. Dynamic light scattering (DLS) and Fourier-transform infrared (FTIR) spectroscopy are employed to investigate the stability of nanocomposites and the efficacy of the surface treatment of nanoparticles, respectively. The quality and physical parameters of the fabricated devices are evaluated by the atomic force microscopy (AFM) and scanning electron microscopy (SEM). The thickness of a homogeneous sublayer underneath a periodic layer in the fabricated optical devices is controlled by employing a channel with precisely managed depth. The example resonant filters show acceptable response as measured in the 1600-1800 nm spectral band and reasonable agreement with theoretical predictions.

Choroidal Haller's and Sattler's Layers Thickness in Normal Indian Eyes.

AIM:This study aims to study normative choroidal thickness (CT) and Haller's and Sattler's layers thickness in normal Indian eyes.MATERIALS AND METHODS:The choroidal imaging of 73 eyes of 43 healthy Indian individuals was done using enhanced depth imaging feature of spectralis optical coherence tomography. Rraster scan protocol centered at fovea was used for imaging separately by two observers. CT was defined as the length of the perpendicular line drown from the outer border of hypereflective RPE-Bruch's complex to inner margin of choroidoscleral junction. Choroidal vessel layer thickness was measured after defining a largest choroidal vessel lumen within 750 μ on either side of the subfoveal CT vector. A perpendicular line was drawn to the innermost border of this lumen, and the distance between the perpendicular line and innermost border of choroidoscleral junction gave large choroidal vessel layer thickness (LCVLT, Haller's layer). Medium choroidal vessel layer thickness (MCVLT, Sattler's layer) was measured as the distance between same perpendicular line and outer border of hypereflective RPE-Bruch's complex.RESULTS:The mean age of individuals was 28.23 ± 15.29 years (range 14–59 years). Overall, the mean subfoveal CT was 331.6 ± 63.9 μ. Mean LCVLT was 227.08 ± 51.24 μ and the mean MCVLT was 95.65 ± 23.62 μ. CT was maximum subfoveally with gradual reduction in the thickness as the distance from the fovea increased.CONCLUSION:This is the first study describing the choroidal sublayer thickness, i.e., Haller's and Sattler's layer thickness along with CT in healthy Indian population.

Ultra-high temperature oxidation behavior of micro-laminated ZrC/MoSi2 coating on C/C composite

A protective coating with transition inner layer of SiC and micro-laminated outer layer of ZrC/MoSi2 was prepared by packaging siliconizing and magnetron sputtering on C/C composite. The total thickness of the micro-laminated outer layer was 60 μm, and the thicknesses of ZrC and MoSi2 sublayers were 4 μm and 1 μm, respectively. Ultra-high temperature oxidation test was conducted at 1800 °C for 30 min in static air. The oxidation kinetics of coated C/C composite followed parabolic law. Such attractive ultra-high temperature oxidation resistance was attributed to the formation of a dense and spallation-free oxide scale and low oxygen diffusion coefficient of ZrCxOy.

Mechanical properties of electrodeposited amorphous/crystalline multilayer structures in the Fe-P system

Amorphous/crystalline multilayer structures of Fe-P alloys were deposited electrochemically using the single bath technique. Hall-Petch behavior of microhardness with respect to sublayer thickness was observed down to a sublayer thickness of 15nm. For thinner sublayers, a hardness plateau was obtained. The transition at a sublayer thickness of 15nm coincides with the loss of the multilayer structure as observed in transmission electron microscopy. The transition is a possible result of a change in the amorphous to crystalline sublayer thickness ratio and the interface roughness development during the deposition process. Additionally, crack deflection at the interfaces was observed for the layered structures with small sublayer thickness in microbending experiments.

Study on drag reduction mechanism of rotating disk with micro-grooves

This paper presents the drag reduction mechanism of a rotating disk with micro-grooves. The flow characteristics of the micro-grooved disk at various rotating Reynolds numbers are investigated using experiments and large-eddy simulations. The results show that fluid in the gap between the disks undergoes circumferential movement, but fluid within the micro-grooves undergoes radial movement because of the dual function of wall rejection and boundary layer blockage. As a result, fluid within the micro-grooves moves very slowly and quietly. Hence, quiet and slow-moving fluid within the micro-grooves increases the thickness of the viscous sublayer and recedes mixed layer and suppresses the unstable motion. The mean relative velocity gradient of the immersed surface on the grooved disk becomes much lower than that of a smooth disk, and the contact area between the walls and the high-speed fluid is diminished. An interaction phenomenon between the micro-grooves and the gap could be discovered due to the micro-groove unenclosed structure. The interaction phenomenon makes the quiet fluid within the micro-grooves also suppresses the outside flow. Accordingly, a micro-grooved rotating disk has an obvious drag reduction effect compared with a rotating smooth disk.

An isogeometric approach for dynamic response of laminated FG-CNT reinforced composite plates integrated with piezoelectric layers

This study proposes an extension of the isogeometric approach for the dynamic response of laminated carbon nanotube reinforced composite (CNTRC) plates integrated with piezoelectric layers. The mechanical displacement field is approximated according to the higher-order shear deformation theory (HSDT) using the formulation based on Non-Uniform Rational B-Spline (NURBS) basis functions. The single-walled carbon nanotubes (SWCNTs) are assumed to be uniformly distributed (UD) or functionally graded (FG) distributed along the thickness direction. The material properties of carbon nanotube-reinforced composite plates are estimated according to the extended rule of mixture, while the electric potential is assumed to be a linear function through the thickness of each piezoelectric sub-layer. A velocity feedback control algorithm is used for the active control of the plate through a closed-loop control with piezoelectric sensors and actuators. The reliability and efficiency of the proposed technique are verified by comparing its numerical results with available references in literature.