Pristine Surface Research Articles

Machining holes in CFRP with laser “drilling + boring” hybrid technique

ABSTRACT This paper presents a novel approach for machining carbon fiber reinforced polymer composite (CFRP), wherein a laser “drilling + boring” hybrid technique is employed. The method consists of initial high-energy pulsed laser drilling at high speeds, followed by subsequent low-energy short-pulsed laser trimming of the hole edges. A detailed examination was carried out on machining accuracy, taper angle, surface roughness, the heat affected zone (HAZ), microstructure, and mechanical properties of the CFRP samples machined with this technique. The findings revealed that the circular holes exhibit a machining accuracy of approximately 30 μm, accompanied by a taper angle measuring 0.37°. Moreover, the regions surrounding the holes display a smooth and pristine surface, devoid of burrs, fiber fractures and serrated textures. Notably, compared with laser rotary cutting method, the “drilling + boring” hybrid technique demonstrates enhancements in surface finish, HAZ control, and mechanical property of the machined holes.

Iron Impurity Impairs the CO2 Capture Performance of MgO: Insights from Microscopy and Machine Learning Molecular Dynamics.

Magnesium oxide (MgO) is a promising sorbent for direct air capture (DAC) of carbon dioxide. Iron (Fe) is a common impurity in naturally occurring MgO and minerals used to produce MgO, yet a molecular-scale understanding of Fe-doping effects on carbonation is lacking. Here, we observed reduced carbonation performance in Fe-doped MgO experimentally. The energetics of adsorbing a (bi)carbonate ion on pristine and Fe-doped MgO(001) surfaces were further investigated using ab initio and machine learning potential molecular dynamics coupled with metadynamics simulations. Both pristine and Fe-doped surfaces exhibited a basic (OH-) hydration layer, where the (bi)carbonate ion adsorption is thermodynamically favorable. However, the dissolution of surface Fe had smaller energy barriers and was more favorable than Mg. Leached Fe likely neutralized the near-surface basicity, yielding reduced reactivity on Fe-doped MgO. Our observations offer critical insights for material selection and emphasize the importance of evaluating the geologic origin of earth materials used for DAC.

Hydrogen adsorption on zinc-terminated ZnO(0001) surface at varying coverages and its effects on electronic and optical properties: a DFT+U study

Abstract Spin-polarized density functional theory implementing Hubbard corrections (DFT + U) were utilized to study H adsorption of different coverages on Zn-terminated ZnO(0001) surface. Changes in electronic and optical properties were observed upon H adsorption of varying coverages, namely with 0.25 monolayer (ML), 0.50 ML, 1 ML, and 2 ML coverage. In terms of surface structure, H atoms were found to adsorb on top of Zn forming Zn–H bond lengths ranging from 1.54–1.73 Å for certain coverages. On the other hand, O–H bond length values are 2.41 Å and 2.37 Å for 0.50 ML and 2 ML coverage respectively. Additionally, for 0.50 ML, the most stable configuration is when one H atom adsorbs on top of Zn and the other near the hollow site. At low coverage (0.25 ML and 0.50 ML), H prefers to interact with topmost layer Zn atoms resulting to shifts in the electronic bands relative to the pristine surface’s. In addition, at high coverage (1 ML and 2 ML), shifting of bands are observed and are mainly guided by Zn–H atom interaction for 1 ML and weak H–O atom interaction for 2 ML. The observed decrease in band gap as the coverage was increased from 1 ML to 2 ML is supported by the red shift in the absorption plot. However, for low H coverage adsorption, the optical plots deviate due to emergence of flat bands. Changes in electronic properties such as shifts in conduction band minimum and decrease in measured band gap occur as guided by the interaction of adsorbed H atoms with the surface atoms and are supported with obtained optical plots. These findings present the tunability of Zn-terminated ZnO(0001) polar surface properties depending on H coverage.

Luminescence Patterns on Multimillimeter Single-Crystal MAPbBr3 Microplatelets via Thermal Ablation Effects.

The single crystal distinguishes itself as the most outstanding representative of excellent optoelectronic performance among perovskite semiconductors due to its exceptional charge carrier properties, extraordinary optophysics, precise structural geometries, and superior material stabilities. However, it exhibits mediocre performance in light emission, which can be attributed to its excessive carrier diffusion lengths and extremely low recombination rates. To address this challenge, this study puts forward a controllable high-temperature annealing treatment strategy concentrating on multimillimeter-scale MAPbBr3 micrometer-thick platelet single crystals (MPSCs). Through the utilization of thermal ablation effects to convert the surface monocrystalline lattices into polycrystalline perovskite nanocrystals (PNCs) with a remarkably increased specific surface area, the fluorescence intensity arising from the rapid recombination of free carriers on the PNC surface is enhanced by 320 times compared to the pristine MPSC surface. These PNCs produced through surface annealing, with the characteristic of loose adhesion to surfaces, can be mechanically wiped away and regenerated in situ via reannealing the residual MAPbBr3 MPSCs, guaranteeing high intensity, durability, and standard geometric fluorescence. Moreover, by regulating the surface distributions of thermal ablation effects and carrying out embossing annealing treatment or laser direct writing, we can design and fabricate relatively complex, high-contrast (255×), and clearly resolved fluorescence patterns on MPSC surfaces.

Boron carbide biodevices for disease-specific biomarker detection: a theoretical study

An effective approach for early diagnosis of lung cancer involves detecting its biomarkers in the patient’s exhaled breath. Acetone was identified as a vital biomarker, showing significant elevation in lung cancer. Two-dimensional boron carbide materials offer benefits such as resistance to high temperatures, stability, and excellent sensitivity toward toxic gas molecules. Here, we explore acetone adsorption on the pristine and transition metal (TM)-doped (Sc, Ti, V, Cr, and Mn) boron carbide monolayers (BCMs) with density functional theory calculations. Our results revealed that the V-, Cr-, and Mn-doped BCM show larger adsorption energy values as compared to the pristine BCM surface. The change of band gap energy of surfaces after acetone adsorption is obtained between 55 and 275%. The work function variation of studied monolayers upon acetone adsorption has been also investigated and results show that V-, Cr-, and Mn-doped BCM systems are sensitive to acetone gas molecules. This work suggests that BCM-based layers can be used as a biosensor to identify VOC biomarkers such as acetone.

Altering the Solid Electrolyte Interface Through Surface-Modification of Lithium Metal Anode for High-Voltage Lithium Battery

Abstract The physical structure and chemical composition of the solid electrolyte interphase (SEI) affect the performance of the lithium metal anode. The tuning of the chemical composition and structure of the SEI through the surface modification of the lithium metal anode has been conducted. A series of dicarboxylic acids, oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid have been utilized to modify the surface of the lithium anode. Physical characterization methods have been employed to study the surface morphology and chemical composition of the SEI. Symmetrical (Li/Li) and asymmetrical (NMC622/Li) cells with pristine lithium and surface modified lithium electrodes have been assembled and tested. NMC622/Li cell with surface modified lithium shows improved performance compared to that of pristine lithium. Malonic acid-treated lithium outperforms all the electrodes by retaining 141 mAh/g specific capacity even after 100 cycles of charge-discharge. XPS depth profiling analysis reveals that the SEI on the MA-Li contains evenly distributed organic and inorganic components which are responsible for the performance of MA-Li.

Manipulating Charge-to-Spin conversion via insertion layer control at the interface of topological insulator and ferromagnet

Strong spin–orbit coupling and highly spin-polarized surface states in topological insulators (TIs) are key parameters that explain their extremely high charge-to-spin conversion (CSC) efficiency at interfaces with ferromagnetic materials (FMs). This study focused on the influence of the insertion layer on the proximity effect occurring in a Co4Fe4B2/Bi2Se3 interface. Various insertion layers, including Au, MgO, and Se, were introduced to modulate the proximity effect from TI to FM and vice versa. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the Se insertion layer effectively suppresses the formation of an additional Bi layer, reducing intermixing against Co4Fe4B2. Electrical transport properties such as RXX and RXY under a vertical magnetic field show that the Se-inserted structure features the lowest anomalous Hall angle and exhibits a pristine topological surface state, indicating its potential for improving CSC efficiency. The Se-inserted structure exhibits the highest spin Hall angle among various heterostructures, according to results obtained from spin-torque ferromagnetic resonance. These findings highlight the importance of selecting an insertion layer and controlling the interface to optimize the spin-transport properties of TI-based spintronic devices and provide insights into the design of future spin devices.

Point defect distributions in ultrafast laser-induced periodic surface structures on β-Ga2O3

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices.

Hydroxylation of an ultrathin Co3O4(111) film on Ir(100) studied by in situ ambient pressure XPS and DFT

In the present work, we have studied the interaction of water with spinel cobalt oxide (Co3O4), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co3O4(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H2O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co3O4(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co3O4(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H2O dissociation and OH formation, blocking exposed Co2+ ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H2O traces in reactive feeds.

Impact of repetitive ELM transients on ITER divertor tungsten monoblock top surfaces

Abstract Owing to the high stored energy of ITER plasmas, the heat pulses due to uncontrolled Type I edge localized modes (ELMs) can be sufficient to melt the top surface of several poloidal rows of tungsten monoblocks in the divertor strike point regions. Coupled with the melt motion associated with tungsten in the strong tokamak magnetic fields, the resulting surface damage after even a comparatively small number of such repetitive transients may have a significant impact on long-term stationary power handling capability. The permissible numbers set important boundaries on operation and on the performance required from the plasma control system. Modelling is carried out with the recently updated MEMENTO melt dynamics code, which is tailored to tackle melt motion problems characterized by a vast spatio-temporal scale separation. The crucial role of coupling between surface deformation and shallow angle heat loading in aggravating melt damage is highlighted. As a consequence, the allowable operational space in terms of ELM-induced transient heat loads is history-dependent and once deformation has occurred, weaker heat loads, incapable of melting a pristine surface, can further extend the damage.

Impact of Atomic Defects on Water Contact Angle of 2D Molybdenum Disulfide Surfaces.

Interfacial dynamics within nanofluidic systems are crucial for applications like water desalination and osmotic energy harvesting. Understanding these dynamics can inform the rational optimization of two-dimensional (2D) materials and devices for such applications. This study explores the wetting behavior of realistic 2D MoS2 surfaces incorporating vacancies and atomic steps, known as atomic defects. We employ a combined density functional theory (DFT) and molecular dynamics (MD) computational approach to elucidate the influence of atomic defects on the MoS2-water interface. DFT calculations are utilized to determine the charge distribution within MoS2. Subsequently, free energy calculations are obtained through MD simulations of the MoS2-water interface. Our findings underscore the importance of incorporating atomic defects into MoS2 surfaces for accurate water contact angle (WCA) predictions in nanofluidic simulations, particularly when using Abal et al. force field parameters. However, the force field developed by Liu et al. yielded more accurate results for pristine MoS2 surfaces. While these parameters provide reliable outcomes for pristine MoS2 surfaces, their application to surfaces with defects may lead to underestimation of WCA. This highlights the critical need for realistic surface representations in nanofluidic modeling to accurately capture the complex interactions between water and MoS2 materials.

In Situ Photoelectrochemical‐Induced Surface Reconstruction of BiVO4 Photoanodes for Solar Fuel Production

BiVO4 has been widely concerned due to its great potential in photoelectrochemical (PEC) water splitting. However, low carrier mobilities and high recombination efficiency of photogenerated carriers impede its photocatalytic performance. Herein, an in situ PEC cyclic‐voltammetry‐induced surface reconstruction of BiVO4 photoanodes (BVO pristine) is developed with significantly enhanced efficiency for solar water splitting. A series of in situ characterizations (including in situ X‐ray diffraction, in situ Raman), together with electrochemical tests and density‐functional theory calculations, reveal that during the photoelectrical activation process, the BVO pristine surfaces undergo a crystal plane reconstruction with greatly increased {040} crystal face to promote the separation of photogenerated carriers. In addition, abundant vanadium vacancies and oxygen vacancies are also introduced into the BiVO4 surface during the crystal face reconstruction process with more favorable surface water adsorption and increased injection efficiency of photogenerated carriers. Therefore, the charge‐transfer resistance (Rct) between BVO pristine and electrolyte under AM 1.5G illumination substantially reduced from the original 15 200 to 2820 Ω after the activation. Moreover, the photocurrent density of activated BVO pristines increases more than 12 times, relative to the original BiVO4. In this work, a new horizon for in situ photoelectric activation of semiconductor photoelectrodes with significantly enhanced PEC water splitting is provided.

Superhydrophilic Surface Creation and Its Temporal Transition to Hydrophobicity on Copper via Femtosecond Laser Texturing

We analyzed a process to fabricate a superhydrophilic surface on copper by forming various laser-induced periodic surface structures (LIPSS) using a Ti/sapphire femtosecond laser. For these structured surfaces, the correlation between the surface structure and the wetting characteristics was analyzed by scanning electron microscopy, atomic force microscopy, and contact angle (CA) measurement. X-ray photoelectron spectroscopy (XPS) was also employed to analyze variation of the elemental composition of the surfaces. The laser treatment produced micro/nanostructures composed of ripples whose length and width are in microscale and nanoscale, respectively. At specific conditions, the CA of a water droplet was reduced to less than 1°. The superhydrophilcity is attributed to the effect of nanoholes and nanoclusters, which consist of copper (II) oxide and copper hydroxide, having a hydrophilic effect on LIPSS. However, the pristine superhydrophilic surface spontaneously became hydrophobic after being exposed to air at room temperature for about 10 days. According to XPS analysis, the surface’s transition to hydrophobic is attributed not only to the decomposition of Cu(OH)2 but also to the adsorption of oxygen molecules and/or airborne organic molecules containing carbon, which further influences the wettability.

The bone trauma and soft-tissue injury classification system in total hip arthroplasty (BOSTI Hip).

The primary objective of this study was to develop a validated classification system for assessing iatrogenic bone trauma and soft-tissue injury during total hip arthroplasty (THA). The secondary objective was to compare macroscopic bone trauma and soft-tissues injury in conventional THA (CO THA) versus robotic arm-assisted THA (RO THA) using this classification system. This study included 30 CO THAs versus 30 RO THAs performed by a single surgeon. Intraoperative photographs of the osseous acetabulum and periacetabular soft-tissues were obtained prior to implantation of the acetabular component, which were used to develop the proposed classification system. Interobserver and intraobserver variabilities of the proposed classification system were assessed. The BOne trauma and Soft-Tissue Injury classification system in total Hip arthroplasty (BOSTI Hip) grades osseous acetabular trauma and periarticular muscle damage during THA. The classification system has an interclass correlation coefficient of 0.90 (95% CI 0.86 to 0.93) for interobserver agreement and 0.89 (95% CI 0.84 to 0.93) for intraobserver agreement. RO THA was associated with improved BOSTI Hip scores (p = 0.002) and more pristine osseous surfaces in the anterior superior (p = 0.001) and posterior superior (p < 0.001) acetabular quadrants compared with CO THA. There were no differences between the groups in relation to injury to the gluteus medius (p = 0.084), obturator internus (p = 0.241), piriformis (p = 0.081), superior gamellus (p = 0.116), inferior gamellus (p = 0.132), quadratus femoris (p = 0.208), and vastus lateralis (p = 0.135), but overall combined muscle injury was reduced in RO THA compared with CO THA (p = 0.023). The proposed BOSTI Hip classification provides a reproducible grading system for stratifying iatrogenic bone trauma and soft-tissue injury during THA. RO THA was associated with improved BOSTI Hip scores, more pristine osseous acetabular surfaces, and reduced combined periarticular muscle injury compared with CO THA. Further research is required to understand if these intraoperative findings translate to differences in clinical outcomes between the treatment groups.

Simulation of chemical reactions with methanol and oxalic acid on 4H-SiC surfaces before and after nanoabrasion

Previous work by our team has shown that not only can oxalic acid added to a reactive methanol polishing solution significantly further improve SiC polishing removal rate but also surface quality. However, due to the lack of fundamental information on the nature of the interfacial reaction, the reaction mechanism involved in continuously improving SiC polishing performance remains unresolved. This study explores the chemical interactions of pristine and nano-scratched surfaces with the reaction medium using a molecular dynamics (MD) model combined with the ReaxFF reaction force field. The results show that –OH and –CHn, methanol can effectively break the Si-C bond on the surface of silicon carbide and the high amount of OH and C=O in oxalic acid favors the formation of surface silicon oxides and the softening of the silicon carbide surface. The synergistic effect of oxalic acid and methanol in the pre-scratch system indirectly supports the notion that nanoabrasion caused by nano-abrasives enhances the chemical reactivity of polishing fluid components. In conjunction with the experimental data, a proposed reaction mechanism for organic acid-containing alcohol fluids with SiC based on non-aqueous solvent systems is presented. This may stimulate ideas for better developing and applying novel non-aqueous-based polishing fluids.

How Doping Regulates As(III) Adsorption at TiO2 Surfaces: A DFT + U Study.

The efficient adsorption and removal of As(III), which is highly toxic, remains difficult. TiO2 shows promise in this field, though the process needs improvement. Herein, how doping regulates As(OH)3 adsorption over TiO2 surfaces is comprehensively investigated by means of the DFT + D3 approach. Doping creates the bidentate mononuclear (Ce doping at the Ti5c site), tridentate (N, S doping at the O2c site), and other new adsorption structures. The extent of structural perturbation correlates with the atomic radius when doping the Ti site (Ce >> Fe, Mn, V >> B), while it correlates with the likelihood of forming more bonds when doping the O site (N > S > F). Doping the O2c, O3c rather than the Ti5c site is more effective in enhancing As(OH)3 adsorption and also causes more structural perturbation and diversity. Similar to the scenario of pristine surfaces, the bidentate binuclear complexes with two Ti-OAs bonds are often the most preferred, except for B doping at the Ti5c site, S doping at the O2c site, and B doping at the O3c site of rutile (110) and Ce, B doping at the Ti5c site, N, S doping at the O2c site, and N, S, B doping at the O3c site of anatase (101). Doping significantly regulates the As(OH)3 adsorption efficacy, and the adsorption energies reach -4.17, -4.13, and -4.67 eV for Mn doping at the Ti5c site and N doping at the O2c and O3c sites of rutile (110) and -1.99, -2.29, and -2.24 eV for Ce doping at the Ti5c site and N doping at the O2c and O3c sites of anatase (101), respectively. As(OH)3 adsorption and removal are crystal-dependent and become apparently more efficient for rutile vs. anatase, whether doped at the Ti5c, O2c, or O3c site. The auto-oxidation of As(III) occurs when the As centers interact directly with the TiO2 surface, and this occurs more frequently for rutile rather than anatase. The multidentate adsorption of As(OH)3 causes electron back-donation and As(V) re-reduction to As(IV). The regulatory effects of doping during As(III) adsorption and the critical roles played by crystal control are further unraveled at the molecular level. Significant insights are provided for As(III) pollution management via the adsorption and rational design of efficient scavengers.

Doping-induced spin polarization on the pristine Si surface: a Si(5 5 12)2 × 1 case

Doping-induced spin polarization on the pristine Si surface: a Si(5 5 12)2 × 1 case

Adsorption behaviour of transition metal atoms on pristine and defective two-dimensional MgAl2S4 monolayer

The electronic structures and magnetic properties of two-dimensional MgAl2S4 monolayer, as well as the adsorption configurations, adsorption energy, and charge transfer phenomena of transition metal atoms adsorbed on both pristine and defective monolayer MgAl2S4 surfaces were systematically investigated. The results show that MgAl2S4 at equilibrium is a nonmagnetic indirect semiconductor with a bandgap of 1.908 eV. The adsorption energies of the adsorbed structures on both pristine and defective MgAl2S4 surfaces are negative, indicating good stability for all configurations. The adsorption of transition metal atoms leads to the transformation of the MgAl2S4 monolayer from non-magnetic semiconductor to magnetic semiconductor, bipolar magnetic semiconductor, half-metal, and metal. In addition, there is a good modulation of the bandgap. The significant charge transfer between MgAl2S4 monolayer and the transition metal atoms implies the formation of chemical bonds. The lower work function implies that the MgAl2S4 and transition metal atom adsorption structures benefit electron emission. Thus, research has revealed that the adsorption configurations of transition metal atoms on the surface of MgAl2S4 monolayer offers new possibilities for the fabrication of spintronic devices, the design of highly efficient catalysts, and the application of emission devices.

First-principles design of PtPd bimetal dispersed WTe2 monolayer for sensing thermal runaway gases: Enhanced performance against single Pt or Pd dispersion

To conduct the early-monitoring of thermal runaway for the Li-ion battery (LIBs), this work purposes PtPd bimetal dispersed WTe2 (PtPd-WTe2) monolayer as a promising sensing material to realize the high-sensitive detection of thermal runaway gases (H2, CO, CO2, C2H2 and C2H4). The adsorption behavior of PtPd-WTe2 monolayer upon such five gas molecules are compared with single Pt- and Pd-dispersed WTe2 monolayer from the first-principles insight to highlight the combined catalytic property of two noble metal atoms. Results reveal that Pt-, Pd- and PtPd-WTe2 monolayer all behave good chemical and thermal stability at 498 K with good binding force between the noble metal atom(s) and the pristine WTe2 surface. Besides, PtPd-WTe2 monolayer behaves much enhanced adsorption performance with more negative adsorption energy and much higher sensing response with larger bandgap changing rate than Pt- and Pd-WTe2 monolayer upon five typical gas molecules. Moreover, the desorption property analysis manifests the necessity conducting the heating process to realize the reusability of PtPd-WTe2 monolayer for gas sensing. These findings manifest the strong potential of PtPd-WTe2 monolayer as a resistive gas sensor for detections of the thermal runaway gas species thus evaluating the operation status of the LIBs, which may stimulate the further deeper investigations about WTe2-based materials for gas sensing applications across multiple fields.

Improved ammonia gas adsorption of surface engineered WS2 nanoflakes

Recent investigations into nanostructured WS2 have shown promising results in the detection of reducing gases, such as ammonia. However, this material faces limitations with respect to the vital parameters such as sensitivity, recovery, and repeatability over an extended period in its purest form. To address these challenges, a low-energy (5 keV) argon ion beam was used to irradiate nanostructured WS2 nanoflakes at various fluences, leading to observable morphological and structural changes. The irradiation of WS2 resulted in a significant enhancement in its ability to detect ammonia gas. The sensing response saw a threefold increase, and both the response and recovery times were reduced significantly compared to pristine samples. Ion beam irradiation changes the overall morphology of nanoflakes and induces a certain degree of defects as apparent from electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy studies. The ion-solid interaction simulation predicts a larger amount of sulfur vacancy than tungsten due to irradiation, which is also supported by experimental results. Density functional theory predicts that sulfur vacancy leads a decisive role in better adsorption of ammonia than the pristine surface. The NH3 molecule orients towards the defective surface leading to a higher charge transfer from the NH3 molecule to the surface than the pristine surface along with a smaller adsorption height.