Evolution Of Surface Morphology Research Articles

Numerical and Experimental Analysis of Dual-Beam Laser Polishing Additive Manufacturing Ti6Al4V.

Laser polishing is an emerging efficient technique to remove surface asperity without polluting the environment. However, the insufficient understanding of the mechanism of laser polishing has limited its practical application in industry. In this study, a dual-beam laser polishing experiment was carried out to reduce the roughness of a primary Ti6Al4V sample, and the polishing mechanism was well studied using simulation analysis. The results showed that the surface roughness of the sample was efficiently reduced from an initial 10.96 μm to 1.421 μm using dual-beam laser processing. The simulation analysis regarding the evolution of material surface morphology and the flow behavior of the molten pool during laser the polishing process revealed that the capillary force attributed to surface tension was the main driving force for flattening the large curvature surface of the molten pool at the initial stage, whereas the thermocapillary force influenced from temperature gradient played the key role of eliminating the secondary roughness at the edge of the molten pool during the continuous wave laser polishing process. However, the effect of thermocapillary force can be ignored during the second processing stage in dual-beam laser polishing. The simulation result is well in agreement with the experimental result, indicating the accuracy of the mechanism for the dual-beam laser polishing process. In summary, this work reveals the effect of capillary force and thermocapillary force on molten pool flows during the dual-beam laser polishing processes. Moreover, it is also proved that the dual-beam laser polishing process can further reduce the surface roughness of a sample and obtain a smoother surface.

High crystalline epitaxial thin films of NiO by plasma-enhanced ALD and their properties

NiO is an interesting transition metal oxide due to its fascinating properties. High crystalline thin films of NiO are preferred for use in a variety of device applications but are challenging to deposit at low temperatures. We have prepared epitaxial thin films of NiO with [111] as the preferred growth direction on a c-plane sapphire substrate at relatively low temperatures using plasma-enhanced atomic layer deposition (PEALD) exploiting a simple nickel precursor with oxygen plasma. The evolution of crystallinity and surface morphology of the films were studied as a function of substrate temperature. Ultra-smooth NiO films with excellent crystallinity were prepared at 250 °C without the necessity for post-annealing. Different microscopic and spectroscopic methods revealed film characteristics. The magnetic properties of (111) oriented epitaxial NiO films prepared using PEALD are explored for the first time, and they are antiferromagnetic in nature.

Simultaneous remediation of Cr and Ni from waste water using efficient Schiff-base resin bis(2-methoxy-1-napthaldehy)-O-phenylene diimine as an adsorbent

In this study, we report the synthesis of a Schiff base, bis(2-methoxy-1-napthaldehy)-o-phenylene diimine (BMNOPhen), and a Schiff-base resin, bis-2-methoxy-1-napthaldehy-o-phenylenediimine (PMBMNOPhen). The materials were characterized via different spectroscopic techniques; CHN analysis, FT-IR, TGA, EDS, SEM, and XRD to analyze the structure and surface morphology and crystallographic evolution of the polymeric resin. The synthesized resin was used for uptake studies with Ni(II) and Cr(VI) ions. The optimum conditions were determined by different parameters used to describe the effects of uptake including initial concentration, temperature, time, and pH through batch adsorption methods. Different functional groups like azomethine, OH, and amine present in the Schiff-based resin structure contain donor N and O atoms which can coordinate cationic metal ions, supported by the active adsorption of chromium(VI) and nickel(II). The isotherm data are informative and useful for calculating and modeling adsorption capacity and exploring the mechanism of removal by the adsorbent Different types of adsorption isotherms like Langmuir, Freundlich, and kinetic studies were used on environmental water samples. The polymeric resin PMBMNOPhen was used for elimination of Cr(VI) and Ni(II) ions in real water samples from different agricultural cities of Sindh (Province of Pakistan) such as Sanghar, Tando-Adam, Kotri, and Jamshoro.

Scanning tunneling microscopy under chemical reaction at solid–liquid and solid–gas interfaces

The task of bridging the pressure gap between ideal ultrahigh vacuum conditions and more realistic reaction conditions involving gas and liquid phases is crucial in surface and interfacial chemistry. Scanning tunneling microscopy (STM) has played a key role in addressing this challenge by enabling atomic-scale probing of the interface. STM enabled us to study surface structure, electronic structure, atomic manipulation, dynamics of molecules and atoms, and chemical properties of the surface at the atomic scale. Over the past four decades, the field of STM has undergone explosive growth. This review article focuses on recent advances in operando STM, specifically in the study of solid–liquid and solid–gas interfaces. It highlights the latest works in ambient-pressure STM, which has enabled the observation of atomic features under various gas and reaction conditions. This information sheds light on the surface mobility of adsorbates and atomic structures of reaction intermediates. The review also addresses research on electrochemical STM, which investigates the evolution of surface morphology under electrochemical processes and provides insights into atomic-scale reaction mechanisms. Finally, the article outlines future challenges and perspectives for operando STM techniques.

Fractal characteristics of coal surface structure during low-temperature oxidation and its effect on oxidizability

Pore structure and surface morphology are the key factors affecting coal spontaneous combustion. However, there are few studies that focus on quantitative descriptions of them. This paper presents an investigation into the evolution of the surface physical structure of different metamorphic coal during low-temperature oxidation. Specific surface area analyzer and atomic force microscopy were used to quantify the physical structure. The results indicate that the average pore size of coal decreases as the temperature increase, with low-metamorphic coal demonstrating a more pronounced reduction. Conversely, the specific surface area exhibits a gradual increase with temperature, particularly for the lignite. The evolution of surface morphology gradually changes from the fluctuation of low temperature to a flat surface with fewer high peaks. Meanwhile, the fractal dimension increasing with temperature also explain that the pore structure and surface morphology tend to become more complex during coal oxidation, especially the lignite. That is, the slopes of the fitting lines of fractal dimension vs temperature are higher for XLT coal than for YL coal and SG coal. The effect of coal surface structure on oxidizability is interpreted by the pore connectivity and oxygen adsorption on the surface during the coal oxygen compound reaction.

Preparation and characterization of wear resistant TiO layer on Ti alloy

Titanium monoxide (TiO) is golden in color, and of good chemical inertness and high hardness, making it a potential candidate for decorative and protective coatings. In this study, a TiO layer was coated on Ti alloy substrate through a combination of cathode plasma electrolysis (CPE) and comproportionation between the Ti substrate and Ti4+ from the electrolyte. The thickness of the obtained TiO layer was around 500 nm, with a hardness of 11 GPa, a modulus of 220 GPa and a critical load of 55 N. The coefficient of friction of the CPE-treated sample vs. ZrO2 ball was decreased from 0.4 to 0.6 to around 0.2 when the Hertz pressure was less than 885 MPa. The wear rate of the CPE-treated sample was reduced by ~450 times compared with that of the untreated Ti alloy. Correspondingly, the wear rate of the ZrO2 ball was reduced by ~170 times. In addition, wear resistance of the CPE-treated samples was also significantly improved for common metallic materials (such as stainless steel, carbon steel, or copper alloy) as the counterpart. The surface morphology evolution and the mechanical properties of the TiO layer can avoid the severe abrasive wear as well as adhesive wear, and contribute to the excellent antiwear effects. CPE demonstrates a technologically relevant capability, especially in forming a TiO antiwear layer on Ti alloy.

Operando Imaging of Over-Discharge-Induced Surface Morphology Evolutions of LiMn2O4 Submicron-Sized Particles by Electrochemical High-Speed Atomic Force Microscopy.

Spinel LiMn2O4 is a promising cathode material but suffers from severe capacity fading during battery operation. One of capacity fade mechanisms results from changes in its morphology and structure due to over-discharge. In this work, for the first time, we successfully tracked the morphologic evolution of LiMn2O4 submicron-sized particles during over-discharging by our home-made electrochemical high-speed atomic force microscopy (EC-HS-AFM). Seven hundred and sixty successive EC-HS-AFM images were stably captured at an imaging speed of ∼0.85 fps at corresponding potentials during over-discharging in ∼15 min, from which evolutions of nanoscale wrinkle-like and step-like structures on the particle surface were clearly observed. The phenomena could be resulted from the complex stresses due to structural distortion during the phase transformation from cubic (LiMn2O4) to tetragonal (Li2Mn2O4), and the formation of the Li2Mn2O4 phase was confirmed by ex situ XRD. Moreover, the particle surface area as a function of the potential was quantitatively extracted from the EC-HS-AFM images, revealing the irreversible expansion/contraction of the particles, and this finding obtained at the nanoscale was consistent with the macroscopic results tested by cyclic voltammetry and galvanostatic charge/discharge methods. These results demonstrate that the EC-HS-AFM is a powerful tool to establish the correlation between the over-discharge-induced surface morphology changes and irreversibility of the Li-ion insertion/extraction as well as capacity fading.

Helium bubble size effects on the surface morphological response of plasma-facing tungsten

Abstract We report a simulation study on the effects of helium (He) bubble size on the morphological evolution and pattern formation on the surface of tungsten used as a plasma-facing component (PFC) in nuclear fusion devices. We have carried out a systematic investigation based on self-consistent dynamical simulations of surface morphological evolution according to an atomistically-informed, 3D continuum-scale model that captures well the relevant length and time scales of surface nanostructure formation in PFC tungsten. The model accounts for PFC surface diffusion, driven by the biaxial compressive stress originating from the over-pressurized He bubbles in the near-surface region of PFC tungsten as a result of He plasma exposure, combined with the formation of self-interstitial atoms in tungsten that diffuse toward the PFC surface and the flux of surface adatoms generated as a result of surface vacancy-adatom pair formation upon He implantation; this transport of surface adatoms contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. Our detailed analysis reveals that varying the average He bubble size plays an important role in the PFC surface growth kinetics as well as the resulting surface topography. Specifically, we find that an increase in the He bubble size leads to a deceleration in the growth rate of the tungsten nanotendrils that emanate from the PFC surface. We also find that the separation distance between the resulting surface features increases with increasing He bubble size, as well as over time. This coarsening effect is a thermally activated process resulting in an accurate description of the temperature dependence of the average surface feature separation by an Arrhenius relation.

Numerical and experimental analysis of sand blasting on polymeric substrates

In view of the recent interest in modifying the surface functionality and esthetics of polymeric materials by sand blasting treatment, a numerical model was developed as a tool to predict the evolution of surface morphology as a function of blasting parameters. The wide range of shot size and shape variations, typical of blasting media, were parametrized based on microscopical observations. Thus, the developed numerical model accounts for the media inhomogeneity and also implements randomness in both the sequence and position of the multiple impacts. To make the model as realistic as possible, the velocity of individual shots was calculated based on their interaction with the airflow. Systematic experiments were performed using Polycarbonate (PC) as the substrate material and Alumina as the blasting media. A comparison of the experimental and numerical results demonstrated the ability of the developed model to successfully predict the surface roughness generated by sand blasting, as the shot arrangement and distribution were varied. This model establishes a potential basis for future studies regarding the performance of the sand blasted surfaces such as wettability using numerical approaches.

Surface evolution of fused silica hemispherical resonators and its influence on the quality factor

Investigating the surface loss mechanism of hemispherical resonators is essential to further improve the performance of hemispherical resonant gyroscopes. Although many studies have focused on the surface loss mechanism and surface treatment process of fused silica hemispherical resonators, the bulk fabrication of high-quality factor (Q factor) hemispherical resonators is still a significant factor limiting the widely applied hemispherical resonant gyroscopes. To address this practical need, this paper first analyzes the formation mechanism of surface defects and their effect on energy loss. Then, a cyclic chemical etching method using hydrofluoric acid as an etchant is proposed to significantly improve the Q factor of the hemispherical resonator by improving the surface morphology. Finally, a surface loss model was developed based on the experimental results to reveal the mechanism of the effect of surface morphology evolution on the change of the quality factor of the hemispherical resonator. The results show that the developed etching method can significantly improve surface quality with minimal damage to the substrate. The resonator’s Q factor increases to a final value of about 2 × 107 after chemical etching, which is improved by about 20 times. The developed loss model can screen hemispherical resonators with different performances according to the change of the Q factor during the etching process. The etching technique and screening method developed in this paper is essential for bulk fabricating high-quality factor hemispherical resonators.

Microstructure and properties of Cr–AlSi12 composite coatings pre-coated on Ti–6Al–4V alloy substrate via mechanical alloying and subsequent laser cladding treatment

Cr–AlSi12 composite coating on Ti–6Al–4V alloy substrate was fabricated by mechanical alloying (MA) and subsequent laser cladding (LC). The weight ratio of the mixed powders was Cr: AlSi12 = 60:40. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to investigate the evolution of surface morphologies, cross-section microstructures and phase composition of the coatings before and after laser treatment. The results showed that Al8Cr5, AlCr2, (Si, Al)2Cr and Cr5Si3 were generated in the MA-LC coating through in-situ alloying reaction. The formation of Al3Ti and Ti5Si4 intermetallic compounds was caused by interdiffusion. Metallurgical bonding was achieved at the coating/substrate interface. Results of the scratch test indicated that laser treatment could significantly improve the bonding quality of the interface. Meanwhile, the microhardness of the MA-LC coating was about 3–4 times higher than that of the MA coating. The high-temperature oxidation resistance of the MA-LC Cr–AlSi12 coating was also studied. It was found that after 100 h of oxidation, the MA-LC coating could effectively enhance the oxidation resistance of the substrate. The oxide films and intermetallic phases formed during oxidation process could play a role of intense hindrance to the diffusion of oxygen into the internal Ti–6Al–4V substrate. The oxidation mechanism of the coating is discussed in detail.

Surface morphology evolution of N-polar GaN on SiC for HEMT heterostructures grown by plasma-assisted molecular beam epitaxy

The surface morphology evolution of N-polar GaN with growth time was investigated and compared with Ga-polar GaN. N-polar GaN directly grown on SiC substrates was found to have slower 3D-to-2D growth transformation and less coalescence than the Ga-polar counterpart, resulting in rougher surface morphology, whereas the AlN nucleation layer accelerated 3D-to-2D transformation, resulting in smoother surface morphology. N-polar GaN was found to have mound-type surface morphology with clustered atomic steps, unlike the regular screw-type dislocation-mediated step-flow growth observed for Ga-polar GaN. This was explained by the lower diffusion of adatoms on the N-polar surface due to its higher surface energy and higher Ehrlich–Schwoebel barrier. In addition, the increased III/V ratio in N-polar GaN growth was found to reduce the surface roughness from 2.4 nm to 1 nm. Without Si doping, the N-polar GaN high electron mobility transistor (HEMT) heterostructures grown under optimized conditions with smoother surface morphologies exhibited a sheet carrier density of 0.91 × 1013 cm−2 and a mobility of 1220 cm2 (V s)−1. With Si δ-doping, the sheet carrier density was increased to 1.28 × 1013 cm−2 while the mobility was reduced to 1030 cm2 (V s)−1. These results are comparable to the state-of-the-art data of plasma-assisted molecular beam epitaxy-grown N-polar GaN HEMT heterostructures on SiC substrates.

Study of surface morphology in GaAs by hydrogen and helium implantation at elevated temperature

In this work, the surface morphology and internal defect evolution process of GaAs substrates implanted with light ions of different fluence combinations are studied. The influence of H and He ions implantation on the atomic mechanism of the blister phenomenon observed after annealing is investigated. Raman spectroscopy is used to measure the surface stress change of different samples before and after implantation and annealing. Optical microscopy and atomic force microscopy are used to characterize the morphology changes of the GaAs surface under different annealing conditions. The evolution of bubbles and defects in GaAs crystals is revealed by transmission electron microscopy. Through this study, it is hoped that ion implantation fluence, surface exfoliation efficiency and exfoliation cost can be optimized. At the same time, it also lays a foundation for the heterointegration of GaAs film on Si.

Evolution of surface morphology and microstructure in reactor pressure vessel studs during triaxial rolling

Evolution of surface morphology and microstructure in reactor pressure vessel studs during triaxial rolling

Effect of in-situ Zn doping on suppression of phase separation in InxAl1−xAs epitaxial layer on InP(001) grown by MOCVD

The effect of Zn impurities on the surface morphology evolution and phase separation behavior of the InAlAs layer on InP(001) substrates is investigated using metal organic chemical vapor deposition (MOCVD). The phase separation of InAlAs occurs at a relatively low growth temperature (T < 620 °C), accompanied by surface roughening and bandgap lowering. According to the microstructural analyses, indium (In) and aluminum (Al) atoms have high reactivity with In-rich or Al-rich columns in a certain growth region. The addition of Zn impurities during InAlAs growth at the phase-separating temperature results in the suppression of phase separation, which can be attributed to a high probability of Zn incorporation into the sites, which generates an In-rich and Al-rich phase column in the phase-separated InAlAs layer. Based on atomic force microscopy (AFM) and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) analysis, we classify four types of InAlAs surface morphology as a function of the growth temperature and flow rate of Zn impurities.

Surface morphology evolution of GTD-450 stainless steel during laser powder bed fusion

GTD-450 is a new type of maraging stainless steel. It has a wide application prospect in the additive manufacturing of complex components such as GTD-450 compressor blades using L-PBF technology. In this study, a multi-scale numerical model was used to simulate the whole process of L-PBF forming of GTD-450 stainless steel block. This numerical model can describe the evolution process of L-PBF forming temperature field, melt flow field and melt free surface. With the help of simulation results, the surface morphology of GTD-450 stainless steel formed under different layers is clarified. The experimental and numerical data of surface morphology are in good agreement, which verifies the reliability of the numerical model. Based on the experimental results, the influence mechanism of melt pool behaviour and thermal history on melt solidification behaviour was discussed, and the development process of L-PBF block surface morphology under the influence of melt pool behaviour was explained.

Pulse-by-pulse evolution of surface morphology driven by femtosecond laser pulses

Surface morphology is a key factor that determines the quality of laser-based micromachining processes. However, the governing laws of surface morphology in the laser processing process are yet to be clarified, and optimization of processing parameters has to rely on trial and error. Specifically, under multiple-pulse irradiation, it has been difficult to quantify the evolution of the surface morphology because the surface morphology changes with each pulse irradiation, and the ablation process changes accordingly. In this study, we investigated the evolution of surface morphology under femtosecond laser irradiation. Copper and silicon were used as targets, whose surface morphology changes exhibited seemingly opposite behaviors with respect to fluence. Using thousands of datasets, we obtained an evolution equation for surface morphology in terms of surface area, which acts as a good probe of the residual surface energy after ablation. Our model successfully quantifies the cumulative effect of multiple-pulse irradiation on surface morphology changes.

Mechanism of thermoviscoelasticity driven solid-liquid interface reducing friction for polymer alloy coating

High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load, high temperature, high shock conditions due to in-sufficient supply of lubricating oil and grease. Traditional self-lubricating coatings prepared by inorganic, organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function, so that it is difficult to meet the engineering requirements of high-temperature lubrication. We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy. Polytetrafluoroethylene (PTFE, Tm = 329 °C) and polyphenylene sulfide (PPS, Tg = 84 °C, Tm = 283 °C) are used to prepare a PTFE/PPS polymer alloy coating. As the temperature increases from 25 to 300 °C, the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state, which is owing to the thermodynamic transformation characteristic of the PPS component. Additionally the friction coefficient (µ) decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300 °C. The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature (T), temperature-centrifugal force (T-Fω), temperature-centrifugal force-shearing force (T-Fω-Fτ) were investigated. The physical model of “thermoviscoelasticity driven solid-liquid interface reducing friction” is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers. The high-temperature adjusts the viscosity (η) of the coating, increases interface slipping and intensifies shear deformation (τ), reducing the friction coefficient. The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.

Laser-induced electron dynamics and surface modification in ruthenium thin films

We performed the experimental and theoretical study of the heating and damaging of ruthenium thin films induced by femtosecond laser irradiation. We present the results of an optical pump-probe thermoreflectance experiment with rotating sample allowing to significantly reduce heat accumulation in irradiated spot. We show the evolution of surface morphology from growth of a heat-induced oxide layer at low and intermediate laser fluences to cracking and grooving at high fluences. Theoretical analysis of thermoreflectance in our pump-probe experiment allows us to relate behavior of hot electrons in ruthenium to the Fermi smearing mechanism. This conclusion invites more research on Fermi smearing of transition metals. The analysis of heating is performed with the two-temperature modeling and molecular dynamics simulation, results of which demonstrate that the calculated single-shot melting threshold is higher than experimental damage threshold. We suggest that the onset of Ru film damage is caused by the heat-induced stresses that lead to cracking of the Ru film. Such damage accumulates during repetitive exposure to light.

Formation and Evolution of Surface Morphology in Overhang Structure of IN718 Superalloy Fabricated by Laser Powder Bed Fusion

Formation and Evolution of Surface Morphology in Overhang Structure of IN718 Superalloy Fabricated by Laser Powder Bed Fusion