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Ambient surface stability of thin film nanocrystalline Cu <sub/>3</sub> SbSe <sub/>4</sub> and structure-property relationships
摘要： Nanocrystalline materials have a high surface area, and hence may be significantly more reactive than their bulk counterparts under ambient conditions. This may affect device function in unexpected ways. Here, high quality crystalline Cu3SbSe4 nanocrystals are synthesized through a hot injection route, and thin films are deposited through a ligand exchange procedure. The electronic conductivity of the films increases significantly upon exposure to air, up to 80 Ω-1cm-1. This increase in conductivity is correlated to a surface oxidation as observed by XPS. The observed changes in the film upon exposure to ambient conditions are suggested to be critical for understanding the properties of these materials as they are incorporated into devices.
关键词： surface oxidation,earth abundant,copper antimony chalcogenides,hot injection,Thermoelectrics,nanoparticles
更新于2025-11-14 15:19:41
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High-throughput laser generation of Si-nanoparticle based surface coatings for antibacterial applications
摘要： High-productivity regime of nanosecond IR-laser ablative generation of silicon colloidal solutions in water for anti-bacterial applications was found in terms of GW/cm2-level laser intensity and scanning velocity by measuring multi-shot ablative mass loss and extinction coefficients of the colloids as sub-linear and third-power intensity functions, respectively. This advantageous regime implies sub-linear mass loss versus laser intensity at the simultaneous third-power yield of nanoparticles, resulting from the subcritical-density, opaque ablative plasma regulating the sample ablation rate and the related plasma-mediated dissociation (dispergation) of the ablation products. In contrast, at higher intensities, there is a drastic increase in mass loss with the corresponding increased yield of (sub) micrometer-sized particles owing to intense plasma-driven expulsion of micro-scale melt droplets and the corresponding saturation of the extinction coefficient of the colloidal solutions because of their dynamic local “self-limiting” effect during the high-rate ablation. The optimal low-intensity regime for Si nanoparticle production demonstrates the monotonous correlated increase of mass loss and extinction coefficient in terms of increasing laser scanning velocity, indicating the diminished cumulative effects. Surface coatings prepared from the generated Si nanoparticles exhibit minor surface oxidation, as acquired as their elemental composition via energy-dispersive X-ray spectroscopy, making their contact angle for water droplets (≈51°) close to that of bare Si wafer (≈58°) with its nanometer-thick native oxide layer. Owing to good wetting, the nanoparticle-based surface coatings show strong antibacterial response regarding Gram-negative Pseudomonas auereginosa bacteria even despite their minor oxidative passivation.
关键词： Silicon nanoparticles,Colloids,Surface oxidation,Extinction coefficient,Wetting,Antibacterial tests,Gram-negative bacteria Pseudomonas auereginosa,Sub-critical ablative plasma,Nanosecond laser ablation,Mass loss
更新于2025-09-23 15:21:21
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Redox Properties of Cu <sub/>2</sub> O(100) and (111) Surfaces
摘要： Intense research efforts are directed towards Cu and Cu2O based catalysts as they are viewed as potential replacements for noble metal catalysts. However, applications are hampered by deactivation, e.g. through facile complete oxidation to CuO. Despite the importance of the redox processes for Cu2O catalysts a molecular level understanding of the deactivation process is still lacking. Here we study the initial stages of oxidization of well-defined Cu2O bulk single crystals of (100) and (111) termination by means of synchrotron radiation X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Exposure of the (100) surface to 1 mbar O2 at 25 ℃ result in formation of a 1.0 monolayers (ML) CuO surface oxide. The surface is covered by 0.7 ML OH groups from trace moisture in the reaction gas. In contrast, neither hydroxylation nor oxidation was observed on the (111) surface under similar mild exposure conditions. On Cu2O(111) the initial formation of CuO requires annealing to ～400 ℃ in 1 mbar O2, highlighting the marked different reactivity of the two Cu2O surfaces. Annealing of the (100) surface, under ultrahigh vacuum conditions, to temperatures up to ～225 ℃ resulted in removal of the OH groups (0.46 ML decrease) at a rate similar to a detected increase in CuO coverage (0.45 ML increase), suggesting the reaction path 2OHadsorbed + Cu2Osolid → H2Ogas + 2CuOsolid. STM was used to correlate the observed changes in surface chemistry with surface morphology, confirming the surface hydroxylation and CuO formation. The STM analysis showed dramatic changes in surface morphology demonstrating a high mobility of the active species under reaction conditions.
关键词： XPS,surface oxidation,redox properties,hydroxylation,STM,Cu2O
更新于2025-09-23 15:21:01
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Properties of sputtered BaSi<sub>2</sub> thin films annealed in vacuum condition
摘要： Herein, BaSi2 films are deposited by the sputtering technique. A vacuum annealing process is subsequently carried out to crystallize sputtered BaSi2 films. Raman spectroscopy is used to study surface structures and crystalline quality. Elemental depth profile is measured by Auger Electron spectroscopy to understand the compositions of films. Optical and electrical properties are further investigated to reveal the effects of annealing condition. Applying vacuum annealing condition can effectively suppress diffusions of Ba and ensures a stochiometric BaSi2 layer. However, surface oxidation still occurs even in the vacuum environment owing to the high reactivity of Ba. Further attempts to prevent BaSi2 surface oxidation may focus on the combination of other methods, such as capping layer and reducing atmosphere, with vacuum (or low-pressure) annealing condition.
关键词： Auger Electron spectroscopy,vacuum annealing,BaSi2,surface oxidation,Raman spectroscopy,sputtering
更新于2025-09-12 10:27:22
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Combined effects of nanosecond laser-induced surface oxidation and nanostructure formation for selective colorization of nickel surfaces
摘要： Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.
关键词： colorization,nanosecond laser,nickel surfaces,surface oxidation,nanostructure formation
更新于2025-09-11 14:15:04
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Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation
摘要： The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 μm, 10.6 μm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650°C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.
关键词： energy coupling efficiency,absorptivity,high temperatures,surface oxidation,laser material processing
更新于2025-09-11 14:15:04
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Oxidation Induced Polymerization of InP Surface and Implications for Optoelectronic Applications
摘要： InP is among the most studied materials for energy-conversion applications including optoelectronics and photoelectrochemical devices. One of the longstanding challenges with this material—and III-V semiconductors more generally—is to understand and control surface oxide formation, which critically impacts device functionality, performance and durability. We integrate advanced in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and ab initio simulations to reveal the mechanism of the oxidation process on InP(001) surface. By interpreting the APXPS results through direct ab initio spectroscopic calculations of surface models, and by comparing calculated and measured work functions, we provide an unbiased picture of the chemical evolution of the thermal oxide. At low temperatures (< 573 K), O2 exposure leads to predominant formation of crosslinked POx units dispersed with submonolayer thickness, which grow into an amorphous 2D film that is kinetically limited to the surface layer. Increased temperature (> 573 K) leads to the polymerization of POx units and the formation of a complex, inhomogeneous 3D network of surface oxide that is progressively indium rich and phosphorus poor towards the surface. Finally, accelerated phosphorus loss via a hitherto unreported coupled charge-transfer isomer transformation mechanism leads to the formation of a thick, amorphous In2O3-like oxide at 773 K with very different optoelectronic and hot carrier transportation properties. In addition to unraveling complex mechanisms of surface oxidation, our results suggest the possibility of deliberately tuning oxide composition by leveraging competition between thermodynamic and kinetic factors.
关键词： InP,APXPS,surface oxidation,ab initio simulations,photoelectrochemical devices,optoelectronics
更新于2025-09-11 14:15:04