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Controlled oxidation of Ni for stress-free hole transport layer of large-scale perovskite solar cells
摘要： The effect of the residual thermal stress of NiO films on the performance of an inverted type perovskite solar cell was studied. In this study, NiO films were grown on fluorine doped tin oxide (FTO) substrates of different surface roughness by thermally oxidizing Ni film and were tested as a hole transport layer for large-scale perovskite solar cells. Experimental and simulation results show that it is very important to suppress the appearance of the residual stress at the NiO–FTO interface during the oxidation of the Ni film for effective hole extraction. The Ni oxidation on the flat FTO film produced in-plane compressive stress in the NiO film due to the Ni film volume expansion. This led to the formation of defects including small blisters. These residual stress and defects increased leakage current through the NiO film, preventing holes from being selectively collected at the NiO-perovskite interface. However, when Ni was deposited and oxidized on the rough surface, the residual stress of the NiO film was negligible and its inherent high resistance was maintained. Stress-free NiO film is an excellent hole transport layer that stops the photogenerated electrons of the perovskite layer from moving to FTO. The improvements in the structural and electrical qualities of the NiO film by engineering the residual stress reduce the carrier recombination and increase the power conversion efficiency of the perovskite solar cells to 16.37%.
关键词： perovskite solar cells,large scale processing,nickel oxidation,residual stress,surface roughness
更新于2025-09-16 10:30:52
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Nondestructive Estimation of the Above-Ground Biomass of Multiple Tree Species in Boreal Forests of China Using Terrestrial Laser Scanning
摘要： Above-ground biomass (AGB) plays a pivotal role in assessing a forest’s resource dynamics, ecological value, carbon storage, and climate change effects. The traditional methods of AGB measurement are destructive, time consuming and laborious, and an efficient, relatively accurate and non-destructive AGB measurement method will provide an effective supplement for biomass calculation. Based on the real biophysical and morphological structures of trees, this paper adopted a non-destructive method based on terrestrial laser scanning (TLS) point cloud data to estimate the AGBs of multiple common tree species in boreal forests of China, and the effects of differences in bark roughness and trunk curvature on the estimation of the diameter at breast height (DBH) from TLS data were quantitatively analyzed. We optimized the quantitative structure model (QSM) algorithm based on 100 trees of multiple tree species, and then used it to estimate the volume of trees directly from the tree model reconstructed from point cloud data, and to calculate the AGBs of trees by using specific basic wood density values. Our results showed that the total DBH and tree height from the TLS data showed a good consistency with the measured data, since the bias, root mean square error (RMSE) and determination coefficient (R2) of the total DBH were ?0.8 cm, 1.2 cm and 0.97, respectively. At the same time, the bias, RMSE and determination coefficient of the tree height were ?0.4 m, 1.3 m and 0.90, respectively. The differences of bark roughness and trunk curvature had a small effect on DBH estimation from point cloud data. The AGB estimates from the TLS data showed strong agreement with the reference values, with the RMSE, coefficient of variation of root mean square error (CV(RMSE)), and concordance correlation coefficient (CCC) values of 17.4 kg, 13.6% and 0.97, respectively, indicating that this non-destructive method can accurately estimate tree AGBs and effectively calibrate new allometric biomass models. We believe that the results of this study will benefit forest managers in formulating management measures and accurately calculating the economic and ecological benefits of forests, and should promote the use of non-destructive methods to measure AGB of trees in China.
关键词： nondestructive method,above-ground biomass,DBH,bark roughness,terrestrial laser scanning
更新于2025-09-16 10:30:52
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Superstructure-enabled anti-fouling membrane for efficient photothermal distillation
摘要： Photothermal membrane distillation (MD) combining solar harvesting and heat localization is a rapidly emerging technology for water purification and desalination. However, state-of-the-art photothermal MD still suffers from several issues in membrane fouling, material instability, poor long-term performance and complex synthesis. Herein, we demonstrate a multilevel-roughness membrane by immobilizing a nanoparticle-assembled superstructure on a nanofibrous membrane to obtain omniphobic surface wettability. The nanoparticle-assembled superstructure with abundant nano/micro channels and low surface energy simultaneously captures solar energy, repels chemical/oil-based contaminants and facilitates vapor flow. The unique mechanism based on the effects of multilevel-roughness structure allows effective control of surface wettability, leading to a successful photothermal MD application, highlighted by highly-efficient solar-thermal conversion, excellent anti-fouling behavior and durability. A high clean water yield of 9.01 kg m-2 h-1 is obtained at a solar intensity of 10 kW m-2, corresponding to a solar-water efficiency of 66.8%. More importantly, when operating in complex feed-water conditions, including oil contaminated and high-saline solution, the speed of clean water generation still presents excellent stability over 48 hours of consecutive operation, which significantly outperforms the commercial distillation membranes (typically 1 hour). Multiple merits of efficient solar-thermal conversion and long-term stability, supported by techno-economic and scalability analyses, make the composite membrane promising for clean water generation from diverse contaminant mixtures in the solar-driven MD system.
关键词： Multilevel roughness,Omniphobicity,Solar energy,Water purification,Anti-oil-fouling,Photothermal membrane
更新于2025-09-16 10:30:52
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Research and Optimization of Surface Roughness in Milling of SLM Semi-Finished Parts Manufactured by Using the Different Laser Scanning Speed
摘要： The paper studies the potential to improve the surface roughness in parts manufactured in the Selective Laser Melting (SLM) process by using additional milling. The studied process was machining of samples made of the AlSi10Mg alloy powder. The simultaneous impacts of the laser scanning speed of the SLM process and the machining parameters of the milling process (such as the feed rate and milling width) on the surface roughness were analyzed. A mathematical model was created as a basis for optimizing the parameters of the studied processes and for selecting the sets of optimum solutions. As a result of the research, surface with low roughness (Ra = 0.14 μm, Rz = 1.1 μm) was obtained after the face milling. The performed milling allowed to reduce more than 20-fold the roughness of the SLM sample surfaces. The feed rate and the cutting width increase resulted in the surface roughness deterioration. Some milled surfaces were damaged by the chip adjoining to the rake face of the cutting tool back tooth.
关键词： face milling,surface roughness,AlSi10Mg,SLM
更新于2025-09-16 10:30:52
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Analysis of the topographic roughness of the Moon using the Wavelet Leaders Method and the Lunar Digital Elevation Model from the Lunar Orbiter Laser Altimeter and SELENE Terrain Camera
摘要： The Wavelet Leaders Method (WLM) is a wavelet-based multifractal formalism that allows the identification of scale breaks (thus scaling regimes), the definition of scaling properties (mono versus multi fractality of the surface) and the calculation of the H?lder exponent that characterizes each pixel, based on the comparison between a theoretical wavelet and topographic values. Here we use the WLM and the SLDEM2015 digital elevation model to provide a near-global and a local isotropic characterization of the lunar roughness. The near-global study of baselines between 330 m and 1,350 km reveals scale breaks at ~1.3, 42.2 and 337.6 km. Scaling properties and H?lder exponent values were calculated for the three corresponding scaling regimes: 330–659 m, 1.3–21.1 km, and 42.2–168.8 km. We find that the dichotomy between the highlands and the maria is present at all scales. Between 330–659 m, the H?lder exponent map shows the unique signature of Orientale basin, rilles and a correlation with the age of mare units. Between 1.3–21.1 km, it shows the unique signature of the Orientale basin and a relationship with the density of 5-20 km diameter craters. Scaling properties and H?lder exponent values were also calculated locally for complex craters, basins, rilles and light plains, for two scaling regimes: 165–659 m, 1.3–21.1 km. Relationships between the H?lder exponent values at 165–659 m , the density of <500 m diameter craters and different geologic units were found and a potential scale break near 165 m was identified.
关键词： scaling regimes,Wavelet Leaders Method,SLDEM2015,lunar roughness,H?lder exponent
更新于2025-09-16 10:30:52
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In-Process Laser Re-Melting of Thin Walled Parts to Improve Surface Quality after Laser Metal Deposition
摘要： Laser metal deposition (LMD) is an additive manufacturing process highly adaptable to medium to large sized components with bulky structures as well as thin walls. Low surface quality of as-deposited LMD manufactured components with average roughness values (Ra) around 15-20μm is one of the main drawbacks that prevent the use of the part without the implementation of costly and time-consuming post-processes. In this work laser re-melting is applied right after LMD process with the use of the same equipment used for the deposition to treat AISI 316L thin walled parts. The surface quality improvement is assessed through the measurement of both areal surface roughness Sa(0.8mm) and waviness Wa(0.8mm) parameters. Moreover, roughness power spectrum is used to point out the presence of principal periodical components both in the as-deposited and in the re-melted surfaces. Then, the transfer function is calculated to better understand the effects of laser re-melting on the topography evolution, measuring the changes of individual components contributing to the surface roughness such as the layering technique and the presence of sintered particles. Experiments showed that while low energy density inputs are not capable to properly modify the additive surface topography, excessive energy inputs impose a strong periodical component with wavelength equal to the laser scan spacing and directionality determined by the used strategy. When a proper amount of energy density input is used, laser re-melting is capable to generate smooth isotropic topographies without visible periodical surface structures.
关键词： laser metal deposition,direct energy deposition,Additive manufacturing,post-processing,surface roughness,laser re-melting
更新于2025-09-16 10:30:52
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Machinability of titanium alloy through laser machining: material removal and surface roughness analysis
摘要： Laser milling is a competent precision process especially when the work material is hard-to-machine such as titanium alloys. While performing the laser milling, a slight change in one of the laser parameters results in an abrupt change in the machining outcomes. A close match between the designed and the machined geometries is the essence of precision machining. A precise control over the material removal rate per laser scan is highly desirable but difficult to achieve. The difficulty level becomes higher if high surface finish is desired alongside the precision machining. In this research, the objective was set to perform the laser milling on titanium alloy (Ti-6Al-4V) with 100% control over material removal rate (MRR) per laser scan and minimum surface roughness (SR). Influence of the five laser parameters (laser intensity, pulse frequency, scan speed, layer thickness, and track displacement) on MRR and SR has been deeply investigated. Significance of each laser parameter is evaluated through ANOVA. Mathematical models for both the responses are developed to estimate the resulting responses at any parametric setting. Models have also been validated through confirmatory tests. Optimization of laser parameters is of great importance to remove the material exactly equal to the desired depth with minimum surface roughness. Therefore, the optimized combinations of laser parameters have been proposed which ensure the conformance of 100% MRR and minimum surface roughness with composite desirability > 0.9. Confirmatory experiments revealed that the optimized parameters are capable to produce the laser milling results as per the models’ predicted results. Additionally, the microstructure of the subsequent layers below the milled area has also been examined and compared with the microstructure of the bulk Ti-6Al-4V. By the use of optimized parameters, microstructure of the sub-layers remains unchanged as compared with the microstructure of the base metal. No evidence has been found altering the microstructure of the sub-layers.
关键词： Laser milling,Titanium alloy,Mathematical model,Surface roughness (SR),Optimization,Material removal rate (MRR)
更新于2025-09-16 10:30:52
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Multimode lasing in wave-chaotic semiconductor microlasers
摘要： We investigate experimentally and theoretically the lasing behavior of dielectric microcavity lasers with chaotic ray dynamics. Experiments show multimode lasing for both D-shaped and stadium-shaped wave-chaotic cavities. Theoretical calculations also find multimode lasing for different shapes, sizes, and refractive indices. While there are quantitative differences between the theoretical lasing spectra of the stadium and D-cavity, due to the presence of scarred modes with anomalously high-quality factors, these differences decrease as the system size increases, and are also substantially reduced when the effects of surface roughness are taken into account. Lasing spectra calculations are based on steady-state ab initio laser theory, and indicate that gain competition is not sufficient to result in single-mode lasing in these systems.
关键词： multimode lasing,stadium-shaped cavities,D-shaped cavities,gain competition,wave-chaotic semiconductor microlasers,scarred modes,surface roughness
更新于2025-09-16 10:30:52
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On the Effectiveness of Different Surface Finishing Techniques on A357.0 Parts Produced by Laser-Based Powder Bed Fusion: Surface Roughness and Fatigue Strength
摘要： Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technique that uses a computer-controlled laser beam as the energy source to consolidate a metal powder according to a layer-upon-layer strategy in order to manufacture a three dimensional part. This opens the way for an unprecedented freedom in geometry, but the layer-wise build-up strategy typically results in a very poor surface ?nish, which is a?ected by the staircase e?ect and by the presence of partially molten particles. Surface ?nishing treatments are therefore necessary to obtain an adequate surface ?nish, to improve the fatigue behavior and to meet mechanical and aesthetic needs. The present contribution systematically compares numerous surface ?nishing techniques, including laser shock processing, plastic media blasting, sand blasting, ceramic shot peening and metal shot peening with steel particles of di?erent sizes (φ = 0.2 mm and φ = 0.4 mm). The results show that all the proposed methods improve the surface quality and the fatigue life of A357.0 L-PBF parts. However, the achievement of the lowest surface roughness does not necessarily correspond to the best fatigue performance, thus suggesting that multiple mechanisms may be active and that besides surface roughness also residual stresses contribute to increase the fatigue strength.
关键词： laser shock processing,additive manufacturing,fatigue,shot peening,surface ?nishing,plastic media blasting,sand blasting,surface roughness,A357.0,laser-based powder bed fusion
更新于2025-09-16 10:30:52
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Micro-Mechanism of Silicon-Based Waveguide Surface Smoothing in Hydrogen Annealing
摘要： The micro-mechanism of the silicon-based waveguide surface smoothing is investigated systematically to explore the effects of silicon-hydrogen bonds on high-temperature hydrogen annealing waveguides. The effect of silicon-hydrogen bonds on the surface migration movement of silicon atoms and the waveguide surface topography are revealed. The micro-migration from an upper state to a lower state of silicon atoms is driven by silicon-hydrogen bonding, which is the key to ameliorate the rough surface morphology of the silicon-based waveguide. The process of hydrogen annealing is experimentally validated based on the simulated parameters. The surface roughness declines from 1.523 nm to 0.461 nm.
关键词： surface smoothing,silicon-based waveguide,silicon-hydrogen bonds,hydrogen annealing,surface roughness
更新于2025-09-16 10:30:52