Photoelectrodes based on two-dimensional (2D) materials can undergo substantial surface reconstruction during photoelectrochemical (PEC) operation, although identifying the surface that actually mediates water oxidation remains challenging. Here, mixed-anion SnSSe nanosheets were used to determine how band-edge engineering and potential-dependent surface chemistry determine the working state of a tin-dichalcogenide photoanode. Comparison with the binary SnS 2 and SnSe 2 end members shows that SnSSe retains the layered CdI 2 -type structure after liquid-phase exfoliation while combining a visible-light optical gap of approximately 1.8 eV with a valence band maximum near −6.0 eV versus vacuum, providing the oxidative driving force required for photoanodic water oxidation. Wavelength-resolved PEC measurements in acidic, neutral, and alkaline electrolytes establish reproducible photoanodic operation with a ratiometric power-saved efficiency for OER of 1.27% in acidic electrolyte. The origin of this activity is resolved by combining density functional theory with four complementary X-ray photoelectron spectroscopy approaches, enabling operando and in situ spatially resolved analysis of individual exfoliated flakes, also under electrochemical polarization. Calculations show that pristine SnSSe is intrinsically limited by *OOH formation, whereas complete oxidation to an SnO 2 -like termination produces an energetically unfavorable OER pathway. In contrast, the formation of an under-oxidized SnO-like layer strongly alters the reaction energetics and generates the most favorable OER surface among the investigated states. Operando XPS directly identifies the corresponding SnO-like component under intermediate anodic polarization, predominantly within approximately 0.8–2.0 V versus RHE, while higher potentials promote Sn(IV)-rich SnO 2 formation and irreversible passivation. The results therefore identify a bias-selected SnO/SnSSe interface as the functional state of the photoanode and establish controlled surface reconstruction, rather than resistance to oxidation alone, as a design parameter for mixed-anion photoelectrodes for solar water splitting.
The formation of native oxide on silicon surfaces is an unavoidable phenomenon that critically influences subsequent semiconductor fabrication processes, particularly for advanced devices requiring precise interface control. While the orientation-dependent oxidation behavior has been extensively studied under thermal oxidation, the native oxide evolution formed spontaneously at room temperature has yet to be fully elucidated. In this study, the native oxide growth behavior on Si(110) and Si(100) surfaces was preliminary evaluated as a function of storage time under identical conditions. X-ray photoelectron spectroscopy (XPS) was primarily employed to investigate the evolution of intermediate suboxide species within the SiO X transition layers formed after final cleaning on both Si(100) and Si(110) surfaces. The result reveals a strong crystallographic dependence on native oxide growth, in which the oxidation behavior of both surfaces increases as a function of storage time. Notably, the Si 4+ component exhibits significantly higher relative intensity on Si(110), becoming detectable shortly after cleaning. This indicates a faster native oxide formation compared to Si(100), where the ratio of their initial oxide thicknesses (0.19 nm and 0.04 nm) is approximately 4.8 times. Spectroscopic ellipsometry measurement shows a consistent trend with the XPS data that demonstrates an increase of oxide thickness as a function of the storage time. The accelerated oxidation on Si(110) is attributed to its higher density of dangling bonds and distinct surface atomic configuration, which are rapidly promoting the oxygen adsorption and oxide formation. These findings demonstrate the higher environmental sensitivity of the Si(110) surface and provide important insights into surface preparation and native oxide control for next-generation semiconductor device fabrication.
The formation of native oxide on silicon surfaces is an unavoidable phenomenon that critically influences subsequent semiconductor fabrication processes, particularly for advanced devices requiring precise interface control. While the orientation-dependent oxidation behavior has been extensively studied under thermal oxidation, the native oxide evolution formed spontaneously at room temperature has yet to be fully elucidated. In this study, the native oxide growth behavior on Si(110) and Si(100) surfaces was preliminary evaluated as a function of storage time under identical conditions. X-ray photoelectron spectroscopy (XPS) was primarily employed to investigate the evolution of intermediate suboxide species within the SiOX transition layers formed after final cleaning on both Si(100) and Si(110) surfaces. The result reveals a strong crystallographic dependence on native oxide growth, in which the oxidation behavior of both surfaces increases as a function of storage time. Notably, the Si4+ component exhibits significantly higher relative intensity on Si(110), becoming detectable shortly after cleaning. This indicates a faster native oxide formation compared to Si(100), where the ratio of their initial oxide thicknesses (0.19 nm and 0.04 nm) is approximately 4.8 times. Spectroscopic ellipsometry measurement shows a consistent trend with the XPS data that demonstrates an increase of oxide thickness as a function of the storage time. The accelerated oxidation on Si(110) is attributed to its higher density of dangling bonds and distinct surface atomic configuration, which are rapidly promoting the oxygen adsorption and oxide formation. These findings demonstrate the higher environmental sensitivity of the Si(110) surface and provide important insights into surface preparation and native oxide control for next-generation semiconductor device fabrication.
Powder bed fusion-laser beam (PBF-LB) is a prominent additive manufacturing technique for fabricating complex, near-net-shape components. However, the high surface roughness of as-built parts, arising from partially melted powder particles and stair-step effects, can adversely affect their fatigue performance and functional properties. This study investigates electropolishing (EP) as a post-processing strategy for improving the surface quality of PBF-LB-manufactured nickel-titanium (NiTi) cuboids. A statistically designed Design of Experiments (DoE) approach was employed to systematically investigate and optimize three key EP parameters: voltage, processing time, and electrolyte flow rate. Surface topography and chemical composition were characterized using three-dimensional optical profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS).Electropolishing substantially transformed the initially jagged, peak-dominated surface morphology into a smoother, more plateau-like topography, achieving maximum reductions of 92.85% in Sa and 94.7% in Sz. The results demonstrate that the extent of surface improvement depends on the combined effects of the EP process parameters. An appropriate processing window, characterized by elevated electrolyte flow, extended processing time, and a controlled intermediate voltage, was identified to improve surface uniformity while limiting severe pitting and localized over-etching. These findings provide a systematic optimization framework for improving the surface quality of PBF-LB NiTi components for potential biomedical and industrial applications.
Oxide layers are critical functional interfaces that determine the corrosion resistance, dielectric reliability, optical response, electronic behavior, catalytic activity, wear resistance, and biocompatibility of modern materials and devices. Even localized defects on oxide layers can accelerate degradation, disrupt functionality, and shorten its lifetime. Restoring damaged oxide regions is therefore important for maintaining structural integrity, recovering application-specific performance, and preventing progressive failure. In this review, we critically examine droplet-scale anodization as an emerging approach for the site-selective regeneration of damaged oxide films. By confining the electrolyte and electric field within micro- to millimeter-scale droplets, this method may enable oxide regrowth directly at defective regions while minimizing chemical consumption and limiting changes to surrounding intact surfaces. The review discusses the principal mechanisms that may contribute to localized healing, including field-assisted ionic migration, defect passivation, pore filling, oxide regrowth, and self-limiting growth. Material-specific opportunities and limitations are evaluated for aluminum, titanium, stainless steel, magnesium, and selected functional oxides. Current technological platforms, including open sessile droplets, scanning droplet cells, solution-flow microdroplet cells, electrolyte jets, and scanning-probe systems, are also assessed in terms of their potential for localized oxide repair. Although these systems have been widely investigated for oxide formation, patterning, and surface modification, direct demonstrations of functional oxide healing remain scarce. Major research gaps therefore persist in experimental validation, mechanistic understanding, process reproducibility, standardized recovery metrics, and long-term durability. A staged research roadmap is proposed to advance droplet-scale anodization from localized oxide fabrication toward reliable and experimentally validated oxide-layer repair systems.
