Pyramid Height Research Articles

Electrochemical polishing of chemical vapor deposited niobium thin films

Combining chemical vapor deposition (CVD) with electrochemical polish (EP) operation is a promising route to producing performance-capable superconducting films for use in the fabrication of cost-effective components for superconducting radiofrequency (SRF) particle accelerators and superconducting quantum computers. The post-deposition EP process enables a critically necessary reduction in surface roughness of niobium (Nb) thin films to promote optimal superconducting surface conditions. This work investigated surface morphology, roughness, and crystal orientation of the CVD-grown and EP-polished Nb films. The CVD films were found to comprise steps and pyramidal features, resulting in undesirable large peak-to-valley distances. EP was demonstrated to significantly diminish the height of pyramids and effectively minimize the overall surface roughness. EP results showed a probable dependence on the crystal orientation. These understandings identify the EP principles tied to CVD-grown Nb films that allow further refinement of surface profiles for film-based SRF applications.

Secondary Flow and Heat Transfer Enhancement Characteristics of a Channel Formed by Circular Tube Bank Fins Stamped with Convex/Concave Pyramids

Thermal and flow characteristics of a channel formed by circular tube bank fins stamped with convex/concave pyramids were numerically investigated by ANSYS Fluent software, and the parametric studies on the thermal performance of the pyramid fin are examined for varying pyramid height (H p), pyramid length (L p), and pyramid width (W p) as Reynolds number (Re) ranged from 1297 to 4541. The pyramid fin provides superior thermal performance to the counterpart plain fin, which is ascribed to the punched pyramids effectively expanding heat transfer area and inducing the secondary flow to better fluid mixing, and the action of the convex/concave pyramids lead to the area of undesirable heat transfer dead zone behind the circular tube being significantly reduced. Under identical pumping power constraint, the thermal performance factor of 1.41 is achieved for H p = 1 mm, L p = 5.74 mm, and W p = 3 mm at Re = 3892, and the optimal pyramid height and width fin respectively are H p = 1 mm and W p = 3 mm for studied cases, while the optimal pyramid length is associated closely with Re. The correlations of average Nusselt number and friction factor are proposed to estimate thermal performance of the pyramid fin used in a finned circular tube heat exchanger.

Selective excitation of hyperbolic phonon polaritons-induced broadband absorption via α-MoO3 square pyramid arrays

Optical anisotropy of α-MoO3 in its reststrahlen (RS) bands provides exciting opportunities for constructing the polarization-dependent devices. However, achieving broadband anisotropic absorptions through the same α-MoO3 arrays is still challenging. In this study, we demonstrate that selective broadband absorption can be achieved by using the same α-MoO3 square pyramid arrays (SPAs). For both the x and y polarizations, the absorption responses of the α-MoO3 SPAs calculated by using the effective medium theory (EMT) agreed well with those of the FDTD, indicating the excellent selective broadband absorption of the α-MoO3 SPAs are associated with the resonant hyperbolic phonon polaritons (HPhPs) modes assisted by the anisotropic gradient antireflection (AR) effect of the structure. The near-field distribution of the absorption wavelengths of the α-MoO3 SPAs shows that the magnetic-field enhancement of the lager absorption wavelength tends to shift to the bottom of the α-MoO3 SPAs due to the lateral Fabry–Pérot (F–P) resonance, and the electric-field distribution exhibits the ray-like light propagation trails due to the resonance nature of the HPhPs modes. In addition, broadband absorption of the α-MoO3 SPAs can be maintained if the width of the bottom edge of the α-MoO3 pyramid is large than 0.8 μm, and excellent anisotropic absorption performances are almost immune to the variations of the thickness of the spacer and the height of the α-MoO3 pyramid.

Study of the Enhanced Efficiency of Crystalline Silicon Solar Cells by Optimizing Anti Reflecting Coating using PC1D Simulation

In this paper, simulation of a mono crystalline silicon solar cell was done using PC1D software. The impact of different solar cell parameters, with their effects on power and efficiency, has been investigated. It is seen that the textured surface reduces reflection and increases the efficiency of the solar cell at least 2–3%. From the simulation, it is seen that the optimum value of p-type doping concentration 1 × 10^16 cm^−3, n-type doping concentration 5 × 10^18 cm with pyramid height of 2–3 μm and equal angles of 54.74 degrees produces the best result in simulation. An anti-reflective coating with a refractive index of 1.38 and a thickness of 84 nm is considered optimal. By optimizing the effective parameters, a solar cell with an efficiency of 24.45% was achieved through simulation. For a p-type mono crystalline silicon wafer, with an area of 10 × 10 cm^2 and a thickness of 200 μm, initial simulation shows a 24.45% efficient solar cell.

Deformation characteristics of solid-state benzene as a step towards understanding planetary geology

Small organic molecules, like ethane and benzene, are ubiquitous in the atmosphere and surface of Saturn’s largest moon Titan, forming plains, dunes, canyons, and other surface features. Understanding Titan’s dynamic geology and designing future landing missions requires sufficient knowledge of the mechanical characteristics of these solid-state organic minerals, which is currently lacking. To understand the deformation and mechanical properties of a representative solid organic material at space-relevant temperatures, we freeze liquid micro-droplets of benzene to form ~10 μm-tall single-crystalline pyramids and uniaxially compress them in situ. These micromechanical experiments reveal contact pressures decaying from ~2 to ~0.5 GPa after ~1 μm-reduction in pyramid height. The deformation occurs via a series of stochastic (~5-30 nm) displacement bursts, corresponding to densification and stiffening of the compressed material during cyclic loading to progressively higher loads. Molecular dynamics simulations reveal predominantly plastic deformation and densified region formation by the re-orientation and interplanar shear of benzene rings, providing a two-step stiffening mechanism. This work demonstrates the feasibility of in-situ cryogenic nanomechanical characterization of solid organics as a pathway to gain insights into the geophysics of planetary bodies.

Using molecular dynamics simulation to investigate the number of wall layers and pyramidal surface roughness on atomic behavior and boiling characteristics of water/Fe nanofluid flow

In today’s heating and cooling industry, all investigators assume environmentally friendly and economic procedures because of environmental and energy crisis issues. Boiling heat transfer (BHT) is one of the impressive heat transfer (HT) procedures known in various engineering applications. The thermal conductivity of nanoparticles (NPs) is several times that of the base fluid. One way to amend a fluid’s thermophysical attributes is to utilize nanofluids (NFs) as boiling fluid. In this research, Fe NPs have been used in the water-based fluid. Fe NPs to the base fluid for reasons like enhancement of the HT surface, enhancement of the heat capacity of the fluid, enhancement of the effective thermal conductivity, and monotony of the temperature gradient in the fluid cause a substantial enhancement in HT coefficient. So far, the effect of phase change time and the effects of pyramidal surface height on the Fe/water NF have been rarely done numerically using molecular dynamics simulation (MDS). The main purpose of the current modeling is to improve the atomic behavior and pool boiling heat transfer (PBHT) of water/Fe NF. This paper investigates the effect of atomic layers and atomic pyramidal surface roughness (SR) with different heights on atomic behavior and PBHT by the MDS. The outcomes display that increasing the number of layers increases the maximum density value from 0.029 to 0.033 atom/Å3 and reduces the maximum temperature from 789 K to 653 K. The increase in the number of atomic layers in the microchannel (MC) wall corresponds to the decrease in heat flux (HF) in the MC. With addition of pyramidal SR, the HF in the MC increases.

Charge carrier localization in InAs self-organized quantum dots

We considered the problem of localization of electrons and holes taking for instance the pyramidal InAs quantum dots in GaAs. The problem of quantum mechanics was solved for the localizing potential taking into account the geometry, chemical composition and built-in fields of the mechanical stress and strain. We found that the strongest localization of both types of charge carriers can be achieved if the ratio of the pyramid height to its base is about 0.2. Keywords: quantum dots, elastic strain, charge carrier localization.

Charge carrier localization in InAs self-organized quantum dots

We considered the problem of localization of electrons and holes taking for instance the pyramidal InAs quantum dots in GaAs. The problem of quantum mechanics was solved for the localizing potential taking into account the geometry, chemical composition and built-in fields of the mechanical stress and strain. We found that the strongest localization of both types of charge carriers can be achieved if the ratio of the pyramid height to its base is about 0.2. Keywords: quantum dots, elastic strain, charge carrier localization.

Does Size Matter? The Case of the Courtship Pyramids in Red Sea Ghost Crabs (Ocypode saratan).

Simple SummaryMale ghost crabs (Ocypode spp.) are known to build sand structures near the entrance to their burrows. It has always been assumed that the structure played a role in sexual selection and mate attraction. We hypothesized that the larger males would make relatively larger pyramids in order to enhance fitness. We studied Red Sea ghost crabs at Eilat, Israel, and found that the larger crabs actually did not put much effort into building pyramids, and it was the medium-sized crabs that invested the most in building the pyramids.Display, wherein males attempt to maximize fitness by attracting sexually mature females to mate, is known to drive speciation by Sexual Selection. We researched the Red Sea Ghost Crab (Ocypode saratan; RSGC), in which males build display pyramids to attract females. The study was conducted at the beach in Eilat, Israel. At each session, we measured the height (in cm) of all pyramids and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the carapace width of the occupant. The mean (± SE) entrance volume was 230.8 ± 11.7 cm, and the height of the pyramid was 11.8 ± 0.49 cm (n = 54). The results of our study did not support our hypothesis because we had expected to find a linear correlation between body size and pyramid height, i.e., the larger the male, the larger the pyramid. However, our results show that the largest males in the population either built small pyramids or not at all, and the cut-off of the larger crab’s body size appears to be around 350 cm3. We discovered a step-wise function in the data in that crabs with the smallest body size of ca. 250 cm3 constructed the highest pyramids, with a declining tendency between 250–350 cm3 and extremely low pyramids beyond 350 cm3. However, our findings need to be further studied with a stress on the ambiance and elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are fast disappearing owing to anthropogenic development.

Low‐Cost Strategy for High‐Efficiency Bifacial Perovskite/c‐Si Tandem Solar Cells

Many studies have confirmed that the perovskite/crystalline silicon (c‐Si) tandem solar cells (TSCs) can achieve excellent photovoltaic performance far exceeding that of single‐junction solar cells. However, the quite thick c‐Si bottom‐cells have to be used to fully absorb near‐infrared photons, which greatly improves the cost of the TSCs. The bifacial two‐terminal TSCs not only can improve the energy output by introducing rear incident light, but also significantly reduce the Si thickness while maintaining high efficiency. Herein, the photovoltaic performance of bifacial perovskite/c‐Si TSCs under different Si thicknesses, pyramid heights, and albedos have been calculated. It is found that the thickness of the c‐Si sub‐cells can be reduced from the current 250 to 25 μm, and only the albedos need to be increased by 18.6% to cover the absorption loss in the near‐infrared. It is recommended that 100‐μm thick c‐Si is a suitable candidate and optimized the size of the Si pyramids (1.0 μm) to obtain excellent light trapping performance. This work can serve as a guidance for experimental preparation of low‐cost and high‐efficiency bifacial perovskite/c‐Si TSCs.

RETRACTED ARTICLE: Fabrication of Highly Efficient Random Pyramids on Silicon Substrate by Employing CH3COONa as Texturing Solution for Organic-Silicon Hybrid Solar Cells

The purpose of this study is to change the surface reflectivity of organic/inorganic hybrid silicon to increase light trapping by using CH3COONa as an etchant solution. The etching procedure is a simple and convenient way to increase light trapping to accomplish this goal. This paper reports on the surface topography of (100) P-type organic/inorganic hybrid silicon wafers modified by etching a controllable pyramid structure on the surface. Sodium acetate anhydrous (CH3COONa) solution was used to etch the silicon surface, with the concentration ratio of CH3COONa varying in the range of 22–38 wt.% ( ± 0.12 wt%) and 3.5 ± 0.1 wt of isopropyl alcohol (IPA) in a temperature range of 60–75°C ± 0.1°C. By enhancing light trapping and absorption, texturization can effectively reduce the surface reflection and improve equipment performance. Texturization time ranges from 25 to 45 min during etching, while the SEM images per case are used to calculate the mean and standard deviation of the pyramid height. The etching solution is studied with respect to the reflectivity, wetting, and surface morphology of silicon wafers. The experimental results show that the optimal etching conditions are a sodium acetate anhydrous (CH3COONa) solution of 22 ± 0.12 wt.% with IPA of 3.5 ± 0.1 wt% for 45 min at a temperature of 75°C. Therefore, from the results, it was noted that the size of the pyramids generated under this condition was 1.75 ± 0.2 µm. Correspondingly, from the results, surface reflectivity of 12 ± 0.12% was observed under optimal conditions with wavelength in the the range of 450–900 nm. The results reveal that surface reflectivity modification is an effective way to control light trapping. The potential of this etching solution is well documented and paves the way for the manufacture of an efficient and low-photovoltaic device.

Локализация носителей заряда в самоорганизованных квантовых точках InAs

We considered the problem of localization of electrons and holes taking for instance the pyramidal InAs quantum dots in GaAs. The problem of quantum mechanics was solved for the localizing potential taking into account the geometry, chemical composition and built-in fields of the mechanical stress and strain. We found that the strongest localization of both types of charge carriers can be achieved if the ratio of the pyramid height to its base is about 0.2.

Non-Planar Structures of Sterically Overcrowded Trialkylamines.

Several amines with three bulky alkyl groups at the nitrogen atom, which exceed the steric crowding of triisopropylamine significantly, were synthesized, mainly by treating N‐chlorodialkylamines with Grignard reagents. In six cases, namely tert‐butyldiisopropylamine, 1‐adamantyl‐tert‐butylisopropylamine, di‐1‐adamantylamines with an additional N‐cyclohexyl or N‐exo‐2‐norbonyl substituent, as well as 2,2,6,6‐tetramethylpiperidine derivatives with N‐cyclohexyl or N‐neopentyl groups, appropriate single crystals were generated that enabled X‐ray diffraction studies and analysis of the molecular structures. The four noncyclic amines adopt triskele‐like conformations, and the sum of the three C−N−C angles is always in the range of 351.1° to 352.4°. Consequently, these amines proved to be structurally significantly flatter than trialkylamines without steric congestion, which is also signalized by the smaller heights of the NC3 pyramids (0.241–0.259 Å). There is no clear correlation between the heights of these pyramids and the degree of the steric crowding in the new amines, presumably because steric repulsion is partly compensated by dispersion interaction. In the cases of the two heterocyclic amines, the steric stress is smaller, and the molecular structures include quite different conformations. Quantum chemical calculations led to precise gas‐phase structures of the sterically overcrowded trialkylamines exhibiting heights of the NC3 pyramids and preferred molecular conformers which are similar to those resulting from the X‐ray studies.

АНАЛИЗ АНАЛОГОВ ГЕОМЕТРИЧЕСКОЙ МОДЕЛИ ОПРЕДЕЛЕНИЯ ПАРАМЕТРОВ НЕДОСТУПНОЙ ТОЧКИ

The present work analyses of the analogues of the geometric model developed for the determination of the parameters of the inaccessible point of an object. The common issues are revealed and essential steps of their resolution are identified. The essence of the problem is that the unavoidable contradiction between the need of obtaining the exact value of the determined parameter and an error involved in any measurement. The purpose of the present work is to investigate a possibility of use of the known analogues of the geometrical model of the determination of the parameters of the inaccessible point of an object. It is achieved in two steps: 1. The analysis of the known analogues of the geometrical model of the determination of the parameters of the inaccessible point of an object. 2. The determination of a feasible variant of the geometrical model of experimental measurements. The present study considered the analogues of the geometrical model of the determination of the parameters of the inaccessible point of an object. Phales Miletsky (640/624-548/545 BC) used similarity of triangles for the determination of the distance from coast to the ship and pyramid height in Egypt. For the determination of parameters of an inaccessible point by means of a theodolite, a flat analogue is the geometrical model of two overlapped rectangular triangles. Trigonometrical relationships for the determination of the values of required parameters are discussed. The pros and cons of the known analogues are identified. It is revealed that, in the analyzed geometrical models, all the measurements of the reference values of parameters are carried out with some errors in one plane. Therefore, a theoretically correct solution of the problem is in some domain (area) of the real result. The domain of possible results takes the shape of a trapeze. Besides, result of direct measurements, as a rule, are fractional numbers. Therefore, it is virtually impossible to obtain one exact result. The feasible variant of geometrical model of performance of measurements and processing of results is defined. It is suggested to develop complex three-dimensional geometrical and analytical models of definition of area (domain) of the value of parameter of the inaccessible point of an object. Keywords: a building, a roof, the analysis, directional ray, collimating ray, measurement of coordinates of a point, geometrical model, analogue.

Blade-Coated Perovskites on Textured Silicon for 26%-Efficient Monolithic Perovskite/Silicon Tandem Solar Cells

Summary Integrating perovskites onto textured silicon provides a pathway to 30% tandem solar cells. However, deposition of 0.5–1 μm thick perovskite layers from solution onto textured silicon with typical pyramid heights of 3–10 μm remains a challenge. We propose a new tandem architecture that enables scalable, solution-based blading of perovskites onto silicon wafers textured with pyramids less than 1 μm in height. These pyramids are rough enough to scatter light within the silicon nearly as efficiently as large pyramids but smooth enough to solution-process a perovskite film. A nitrogen-assisted blading process deposits both a conformal hole transport layer and a planarizing perovskite layer that fully covers the textured silicon, at a speed of 1.5 m/min. With a textured light-scattering layer added to the top of the tandem to reduce front-surface reflectance, we achieve a perovskite/silicon tandem cell with an efficiency of 26% on textured silicon.

Standard Deviation Quantitative Characterization and Process Optimization of the Pyramidal Texture of Monocrystalline Silicon Cells.

To quantitatively characterize the pyramidal texture of monocrystalline silicon cells and to optimize the parameters of the texturing process, the relative standard deviation Sh was proposed to quantitatively characterize the uniformity of the pyramidal texture. Referring to the definition and calculation of the standard deviation in mathematical statistics, Sh was defined as the standard deviation of the pyramid relative height hi after normalization of the pyramid height Hi of monocrystalline silicon wafer surfaces. Six different silicon cells, with different pyramidal textures, were obtained by applying different texturing times. The relationships between Sh and the photoelectric characteristics were analyzed. The feasibility of quantitatively characterizing the uniformity of the pyramidal texture using Sh was verified. By fitting the Sh curve, the feasibility of optimizing the texturing process parameters and predicting the photoelectric characteristics using Sh was verified. The experimental and analytical results indicate that, when the relative standard deviation Sh was smaller, the uniformity of the pyramidal texture obtained by texturing was better. The photoelectric conversion efficiency (PCE) of the silicon cells monotonically increased with decreasing Sh. The silicon cell obtained by texturing with 2% tetramethylammonium hydroxide (TMAH) solution for 18.1 min had a textured surface with a minimum of Sh, the reflectivity of the silicon cell reached its minimum value of 2.28%, and the PCE reached its maximum value of 19.76%.

Communist Party of Bolsheviks as a Soviet Social Elevator in the Context of the New Economic Policy

The authors analyze and interpret the processes that occurred during the New Economic Policy (NEP) period in the Russian Communist Party (bolsheviks) (RCP(b)) — All-Union Communist Party (bolsheviks) (AUCP(b)) as a “social elevator” from the standpoint of the theory of social mobility. The article takes into account the achievements of national historiography and is based on a wide range of published and unpublished sources. The authors reveal conditions that the party leadership imposed on those who wanted to “enter” the elevator; the number and social composition of replacements; the mechanisms, instruments, and procedures used to carry out movements between floors, as well as the volume of these movements; the transformation of the party as a social elevator; and its impact on mobility in Soviet society. The authors conclude that, thanks to the mass recruitment of workers, the height of the party pyramid quickly increased, and its structure and profile became more complex, which increased the potential for internal mobility. The forced promotion of young Communists into leading party bodies and the expansion of the number of party committees artificially caused upward intra-party mobility and the formation of a new generation of middle-level elites. The use of the nomenklatura system for appointing to the upper floors of the party hierarchy completed the process of rebuilding the RCP(b) — AUCP(b) as a social elevator controlled by Stalin’s Central Committee. As a result, by the end of NEP, the party’s influence social stratification in Soviet society became decisive.

Validity of maxillary sinus volumetric measurements using the 3D orthogonal cone beam computed tomography images versus direct skull volumetric measurements: An in vitro study

Introduction: the total volume of maxillary sinus is important for maxillofacial reconstruction, plastic surgeries and prosthetic rehabilitation. It is important to diagnose sinus hypoplasia secondary to craniofacial syndromes, sinus obliteration caused by infections or blood dyscrasis. Aim of the study: The aim of this study was to assess the accuracy of CBCT volumetric measurements of maxillary sinus using the geometric rule of pyramid volume based on CBCT linear measurements versus real skull measurements.Materials and methods: fourteen skulls were scanned using Planmeca Promax 3D MID and the maxillary sinus pyramid height, length and width were measured in cm. The volume of 24 sinuses were calculated from pyramid volume (cm3) = 1/3 Height × Length × Width. The CBCT volumes and the reference standard were analyzed for error assessment using Dahelberg error and Relative Dahelberg Error.Results: 4.3- 4.7% was the error obtained from CBCT volumetric measurements using the rule of pyramid volume. 0.9 correlation was detected between the CBCT volume and the reference standard, between the observers and within the same observer.Conclusion: the geometric rule of pyramid volume based on CBCT linear measurements can be used to assess maxillary sinus volume.

A new uniformity coefficient parameter for the quantitative characterization of a textured wafer surface and its relationship with the photovoltaic conversion efficiency of monocrystalline silicon cells

A new parameter, the uniformity coefficient (UC), was proposed to overcome the difficulty in quantitatively characterizing the uniformity of the pyramidal textured surface of silicon wafers widely used for monocrystalline silicon cells (MSCs). The UC was defined based on the areal material ratio Smr(c) from the standard ISO 25178-2. First, the values of Smr(c) for MSC wafer surfaces with a uniform texture and an arbitrary texture were calculated. For the ideal uniform texture, Smr(c) was calculated using one pyramid assuming equal pyramids distributed over the wafer surface. For any arbitrary texture, based on the pyramidal geometrical structure, Smr(c) was calculated from the heights of pyramids extracted from their 2D projections. Second, the areas bounded by the Smr(c) curves with two coordinate axes were calculated accordingly. Then, the ratio of the two areas was defined as the UC. Fifteen kinds of monocrystalline silicon wafers were prepared by chemical texturing for 5 min, 15 min, 25 min, 35 min and 45 min with three groups of solutions, and the corresponding MSCs were fabricated. The UCs of the fifteen silicon wafers and the photovoltaic conversion efficiencies (PCEs) of the MSCs were tested. The relationships between the UC, texturing process (solution and time) and PCE were analyzed. The PCE increased monotonically with an increase in the UCs The silicon wafer obtained by texturing with 2% TMAH solution for 25 min had a textured surface with a maximum UC of 0.89, and the MSC exhibited a maximum PCE of 20.3%. The experimental results indicated that the UC is an effective parameter for the quantitative characterization of the pyramidal texture of silicon wafer surfaces and has a definite relationship with the PCE of the MSC. The UC is a useful and convenient measure for texturing process optimization.

Optimization of pyramidal radar absorber for anechoic chamber application

The pyramidal radar absorber is widely used for internal wall of an anechoic chamber. Design pyramidal radar absorber for anechoic chamber application has been done. The purpose of this study is to design and optimize the pyramidal radar absorber design. In this work, the CST Microwave Studio is operated in a simulation of the pyramidal radar absorber. A carbon material with the dielectric constant of 2.9 is implemented in simulated design. The design is investigated in broadband working frequency ranging from 0 GHz to 20 GHz. The best performance of simulation pyramidal radar absorber is obtained with for average reflection loss -45.59 dB, which pyramidal and base height of 132 mm and 20 mm, respectively. Simulation results show the reflection loss and transmission loss are satisfied for a radar absorber.