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Surface Properties of Beech Wood after CO2 Laser Engraving
摘要： The paper deals with the properties of a beech wood surface treated by CO2 laser engraving. The studied concerns were the discoloration, changes to morphology assessed through roughness and waviness parameters, and surface wetting with standard liquids (water and diiodomethane), with the aim of determining the wood surface free energy. The results have confirmed that the studied properties of the beech wood surface varied significantly, which were affected by the laser beam power P and raster density n. With increasing P and n, the lightness L* (expressed in CIE L*a*b* color space) decreased significantly. We also observed significant variation in the color coordinates a* and b*. At 8% laser power, the roughness and waviness parameters measured parallel as well as perpendicular to the grain increased proportionally with the increasing raster density. However, 4% laser power was not associated with distinct changes. Increasing the raster density reduced beech wood surface wetting equally with water and with diiodomethane. This was reflected in the higher contact angle values. The wood surface exhibited higher hydrophobicity at 4% laser power. At this power, the increasing raster density was reflected in the decreasing surface free energy, due to its polar component decrease. At 8% laser power, the changes in surface free energy were very minor from the practical viewpoint. The results suggest a potential good adhesion between film-forming materials and wood. However, the gluing performance may be negatively affected by the high roughness attained at 8% laser power and at higher raster densities.
关键词： color,wetting,surface properties,CO2 laser,roughness,contact angle,beech wood,surface free energy
更新于2025-09-19 17:13:59
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Wetting angle stability of steel surface structures after laser treatment
摘要： In this work, we have used a nanosecond pulsed fiber laser to modify the wettability characteristics of AISI 430 steel. For this, various surface morphologies were created on the samples by laser irradiation with different overlapping and intensity parameters. Immediately upon laser treatment, all the structured samples acquired either hydrophilic or superhydrophilic wetting angles. All the samples were also analyzed with XRD. Then, laser-treated samples were kept in ambient air and/or low-temperature annealing was applied to reach hydrophobic surface properties. Interestingly, these surfaces returned back practically to their initial wetting state by cleaning in an ultrasonic bath. The obtained results are analyzed based on the existing wettability models.
关键词： Nanosecond laser structuring,Hydrophobic and hydrophilic surfaces,Wettability transition,Wetting angle stability
更新于2025-09-19 17:13:59
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Metal-Assisted Silicon Chemical Etching Using Self Assembled Sacrificial Nickel Nanoparticles Template for Anti-Reflection Layers in Photovoltaic and Light-Trapping Devices
摘要： Thin film de-wetting is a simple patterning approach that provides a straight forward method for fabricating silicon structures using metal-assisted chemical etching (MacEtch). Currently, this has been mainly demonstrated with gold (Au) or silver (Ag) catalyst for MacEtch and to accomplish this, an extra Au or Ag nanoparticles lift-off step is required. The uncertain success with the lift-off process is potentially a major hindrance to achieve low-cost, large-scale and uniform Si nanostructures. In this work, we report on the use of nickel (Ni) as an alternative sacrificial metal for the de-wetting process. The de-wetting phenomenon of Ni on silicon dioxide is investigated to show that controllable sizes and density are achievable for this material system. A physical model to describe the relationship among Ni film thickness, particle interspacing and density is proposed. Using the Ni nanoparticles as a starting mask template, an improved approach for the large scale fabrication of silicon nanowires without the use of lithography methods is demonstrated. This not only eliminates problems associated with lift-off but also allows for scaling up of such fabrication using the proposed self-assembly approach, which holds great potential in furthering the versatility of the MacEtch technique in anti-reflection surfaces and light-trapping devices applications.
关键词： MacEtch,Nickel nanoparticles,Silicon,MACE,De-wetting,Metal-assisted chemical etching
更新于2025-09-19 17:13:59
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Evolution of InAs quantum dots and wetting layer on GaAs (001): Peculiar photoluminescence near onset of quantum dot formation
摘要： InAs quantum dots (QDs) have been grown on a GaAs (001) substrate in the subcritical region of InAs coverage for transition from a 2-dimensional (2D) to a 3-dimensional growth mode. Evolution of QDs and the corresponding wetting layer (WL) with InAs coverage has been investigated. Under specific growth conditions, quantum dot formation was observed only in samples where InAs coverage is more than 1.48 ML. The QD density increases sharply with InAs deposition initially but slows down with increased coverage. Photoluminescence (PL) shows the existence of a third peak, other than QD and WL peaks, at the low energy side of the WL peak, which is named the precursor peak. Evidence is presented supporting the theory that this peak is due to 2D InAs islands on a monolayer of InAs, which are small enough to localize excitons. Meanwhile, the WL peak is due to larger InAs islands under high compressive strain. During QD formation, the WL peak energy increases with the increase in InAs deposition. This is due to the sudden transfer of material from the bigger size of InAs islands to the QD. Our results show that the QD, WL, and precursor peaks coexist near the onset of QD formation. The power dependence of the three PL peaks is evident, which supports to our conclusion.
关键词： precursor peak,InAs quantum dots,wetting layer,photoluminescence,GaAs substrate
更新于2025-09-19 17:13:59
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Controlled ultra-thin oxidation of Graphite promoted by cobalt oxides: influence of the initial 2D CoO wetting layer
摘要： The interaction of CoO with highly oriented pyrolytic graphite (HOPG) was studied using a set of complementary techniques. The morphology of the CoO thin film was determined using atomic force microscopy (AFM), whereas the electronic structure was investigated using x-ray absorption (XAS) and photoemission (PES) spectroscopies. The experimental spectra were analyzed using a configuration interaction CoO6 cluster model calculation. The early stages of growth are characterized by the formation of a CoO wetting layer at the CoO/HOPG interface. The electronic structure of the CoO wetting layer presents a clear 2D character, which is closer to the 2D HOPG substrate than to the 3D CoO bulk. This character of the wetting layer explains the posterior formation of CoO islands and excludes the alternative layer by layer growth mode. Further, the interaction between the CoO wetting layer and the outermost graphite layer favors the oxidation of the HOPG substrate which can be controlled by the thickness of the deposited CoO overlayer.
关键词： x-ray absorption spectroscopies,x-ray photoemission spectroscopies,wetting layers,CoO/HOPG interfaces,HOPG oxidation
更新于2025-09-16 10:30:52
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Extremely robust gas quenching deposition of halide perovskites on top of hydrophobic hole transport materials for inverted (p-i-n) solar cells by targeting the precursor wetting issue.
摘要： Lead halide perovskite solar cells afford high power conversion efficiencies, even though the photoactive layer is formed in a solution process. At the same time, solution processing may impose some severe de-wetting issues, especially if organic, hydrophobic charge transport layers are considered. Ultimately, very narrow processing windows with a relatively large spread in device performance and a considerable lab-to-lab variation result. Here, we unambiguously identify dimethylsulfoxide (DMSO), which is commonly used as a co-solvent and complexing agent, to be the main reason for de-wetting of the precursor solution on hydrophobic hole transport layers, such as polytriarylamine (PTAA), in a gas quenching assisted deposition process. In striking contrast, we will show that n-methyl-2-pyrrolidon (NMP), which has a lower hydrophilic-lipophilic-balance, can be favorably used instead of DMSO to strongly mitigate these de-wetting issues. The resulting high-quality perovskite layers are extremely tolerant with respect to the mixing ratio (NMP:DMF) and other process parameters. Thus, our findings afford an outstandingly robust, easy to use and failsafe deposition technique yielding single (MAPbI3) and double (FA0.94Cs0.06PbI3) cation perovskite solar cells with high efficiencies (~ 18.5 %). Most notably, the statistical variation of the devices is significantly reduced, even if the deposition process is performed by different persons. We foresee, that our results will further the reliable preparation of perovskite thin films and mitigate process-to-process variations that still hinder the prospects of upscaling perovskite solar technology.
关键词： gas quenching,perovskite solar cells,reproducibility,perovskite precursor wetting,perovskite deposition
更新于2025-09-16 10:30:52
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Electro-optically efficient and thermally stable multilayer semitransparent pristine Ag cathode structure for top emission organic light emitting diodes
摘要： To attain high efficiency and stability in a top-emission organic light-emitting diode (TEOLED), the semitransparent metal cathode must have high transmittance, low absorbance, and uniform surface properties under continuous driving conditions. However, conventional semitransparent metal electrodes have numerous fundamental issues. Here, we report an electro-optically efficient and stable semitransparent pristine thin Ag cathode configuration for the high performances of TEOLED. A multilayer semitransparent cathode structure is fabricated by sandwiching a thin silver (Ag) layer between new organic wetting inducer and capping layer, 1,4-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene (p-bPPhenB). A thin Ag layer in the presence of p-bPPhenB exhibits superior optical and electrical properties including a high transmittance of 83.8% at 550 nm, low absorbance of 7.65% at 550 nm, and the low sheet resistance of 2.1 Ω/□, respectively, at room temperature and even under 110 OC for 100 hours. It is observed that our organic wetting inducer and capping layer, p-bPPhenB has considerable influence on the stabilization of surface properties of the thin Ag film by forming coordination bond between the Ag atoms and nitrogen atoms of p-bPPhenB through donating unshared electrons to the Ag atom. An optically optimized phosphorescent green TEOLED with this pure Ag cathode configuration enables a low driving voltage of 5.0 V at 10 mA/cm2 and remarkably high maximum current efficiency of about 167 cd/A compared with the Mg:Ag (10:1) cathode (5.4 V and 109 cd/A).
关键词： micro-cavity effect,organic wetting inducer,semitransparent pristine silver cathode,top-emitting organic light emitting diode,thermal stability
更新于2025-09-16 10:30:52
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Anomalous Stranski-Krastanov growth of (111)-oriented quantum dots with tunable wetting layer thickness
摘要： Driven by tensile strain, GaAs quantum dots (QDs) self-assemble on In0.52Al0.48As(111)A surfaces lattice-matched to InP substrates. In this study, we show that the tensile-strained self-assembly process for these GaAs(111)A QDs unexpectedly deviates from the well-known Stranski-Krastanov (SK) growth mode. Traditionally, QDs formed via the SK growth mode form on top of a flat wetting layer (WL) whose thickness is fixed. The inability to tune WL thickness has inhibited researchers’ attempts to fully control QD-WL interactions in these hybrid 0D-2D quantum systems. In contrast, using microscopy, spectroscopy, and computational modeling, we demonstrate that for GaAs(111)A QDs, we can continually increase WL thickness with increasing GaAs deposition, even after the tensile-strained QDs (TSQDs) have begun to form. This anomalous SK behavior enables simultaneous tuning of both TSQD size and WL thickness. No such departure from the canonical SK growth regime has been reported previously. As such, we can now modify QD-WL interactions, with future benefits that include more precise control of TSQD band structure for infrared optoelectronics and quantum optics applications.
关键词： wetting layer,quantum dots,tensile strain,Stranski-Krastanov growth,optoelectronics
更新于2025-09-12 10:27:22
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Laser Irradiation for Improving the Wetting of Nanoparticle Gold Inks for Printed Electronics
摘要： Digital printing technologies such as inkjet or Aerosol Jet are becoming increasingly interesting for the manufacturing of electronic devices. As a maskless and contactless process it offers the potential for low-cost deposition of functional materials onto flat, flexible or 3D-substrates. Common inks used for printed electronics are nanoparticle metal inks. Silver (Ag) is widely used because of its excellent conductivity, but also gold (Au) inks are of interest for several applications. By using nanoparticle inks it is possible to integrate conductive paths and sensors onto temperature sensitive substrate materials such as polymers. Polymers often need a pretreatment like a plasma treatment for improving the wetting. Plasma treatment usually changes the wetting behavior of the complete substrate surface. This could be critical for some applications, e.g. fluidic applications, where the original properties of the substrate should be kept. Low pressure plasma as a vacuum process is also difficult for implementation into an existing process. In this work laser irradiation for local improvement of wetting of an inkjet-printed gold ink on polymer substrates is investigated. The experiments show that laser irradiation is a very promising technique for the modification of polymer surfaces and suitable for inkjet printing nanoparticle inks on hydrophobic polymer surfaces. This offers new opportunities for printed electronics, which could be easily integrated into existing processes.
关键词： laser pretreatment,wetting,gold ink,inkjet printing
更新于2025-09-12 10:27:22
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Surface topography following pulsed laser texturing: Implications for adhesion and wettability
摘要： A model for predicting surface topography following nanosecond pulsed laser texturing of metals is applied to calculating the areal surface roughness, Sa, average ablation depth, Da, and Wenzel roughness factor or adhesion area ratio, r, for a range representative cases relating to adhesion and wettability. Optimisation of the laser scanning strategy, number of laser passes and focused spot size is performed by considering the ratio of increases in Sa and r with respect to the average ablation depth: ???? ????? values of ???? ????? focused spot size in both the scanning and lateral directions. Increases in Sa, r and ???/???? can be achieved by performing multiple laser passes, while r and ???/???? can be increased independently of Sa and ???? ????? by reducing the focused laser spot size. These results suggest that r and Sa can be optimised effectively and independently in line with a given application. Finally, laser texturing experiments are performed on AA 6082 aluminium alloy and 316L austenitic stainless steel specimens with the aim of confirming model outcomes, after which tensile tests are performed on adhesive-bonded joints prepared with the same laser treatments. Further to demonstrating the benefits of laser texturing, it is shown that optimum results are not necessarily associated with a single value of Sa or r, but are instead a compromise between maximising these parameters and limiting the ablated volume.
关键词： Adhesion,Topography,Surface Roughness,Laser Texturing,Wetting
更新于2025-09-11 14:15:04