Formation Of Surface Features Research Articles

Photochemical Design for Diverse Controllable Patterns in Self-Wrinkling Films.

Harnessing the spontaneous surface instability of pliable substances to create intricate, well-ordered, and on-demand controlled surface patterns holds great potential for advancing applications in optical, electrical, and biological processes. However, the current limitations stem from challenges in modulating multidirectional stress fields and diverse boundary environments. Herein, this work proposes a universal strategy to achieve arbitrarily controllable wrinkle patterns via the spatiotemporal photochemical boundaries. Utilizing constraints and inductive effects of the photochemical boundaries, the multiple coupling relationship is accomplished among the light fields, stress fields, and morphology of wrinkles in photosensitive polyurethane (PSPU) film. Moreover, employing sequential light-irradiation with photomask enables the attainment of a diverse array of controllable patterns, ranging from highly ordered 2D patterns to periodic or intricate designs. The fundamental mechanics of underlying buckling and the formation of surface features are comprehensively elucidated through theoretical stimulation and finite element analysis. The results reveal the evolution laws of wrinkles under photochemical boundaries and represent a new effective toolkit for fabricating intricate and captivating patterns in single-layer films.

Phase-field modeling and n-point polytope characterization of nanostructured protuberances formed during vapor-deposition of phase-separating alloy films

The formation of surface features, such as grooves, protruding grains, or hillocks, in vapor-deposited phase-separating films is typically attributed to internal residual stresses arising due to a difference in thermal expansion coefficients of the film and the substrate. Even though such protuberances are typically observed on the film’s surface, the current understanding of how interfacial energies and surface contact angles influence this nanostructural evolution is very limited. In view of this knowledge gap, we adopt a three-dimensional phase-field approach to numerically investigate the role of seed morphology and contact angles on the morphological evolution of surface protuberances in phase-separating alloy films. Film nanostructures are quantified using a statistical morphological descriptor, namely, n-point polytope functions, which provides a host of insights into the kinetic pathways while unraveling a hidden length scale correlation present at all contact angles. Finally, we also apply this characterization technique on previously reported micrographs of Cu–Ta and Cu–Mo–Ag films to highlight similarities between our simulation-based findings with those obtained from co-deposition experiments.

Effect of magnetic field on corrosion behavior of Indian reduced activation ferritic/martensitic steel in liquid Pb–Li

In the present study, the effect of a magnetic field on the corrosion of Indian reduced-activation ferritic/martensitic steel (IN RAFMS) in flowing lead–lithium eutectic (Pb–Li) has been studied in an electromagnetic-pump-driven loop (EMPPIL-M). The loop was operated for 2800 h at an average flow velocity of 1.5 m s−1 with a 0.5 T magnetic field over the IN RAFMS samples. The corrosion rate in the presence of a magnetic field at a temperature of 773 K was found to be 1.3 times higher than that observed in the absence of a magnetic field. Non-uniform corrosion, resulting in the formation of distinct surface features, was observed over the surface of the sample located inside the magnetic field. Pb–Li attack in the presence of a magnetic field was not only confined to the prior austenite and martensitic lath boundaries (as in the absence of magnetic field), but also occurred in the intra-lath regions resulting in the formation of substructures. The development of electric potential over metallic samples and significant gradients in Pb–Li flow due to the magnetohydrodynamic effect played a major role in the formation of surface features and accelerating the corrosion rate within the magnetic field. On the other hand, the increase in the depletion of iron from the steel matrix observed in the presence of the magnetic field was a result of its direct interaction with the field parameters.

Frozen debris lobe morphology and movement: an overview of eight dynamic features, southern Brooks Range, Alaska

Abstract. Frozen debris lobes (FDLs) are elongated, lobate permafrost features that mostly move through shear in zones near their bases. We present a comprehensive overview of eight FDLs within the Dalton Highway corridor (southern Brooks Range, Alaska), including their catchment geology and rock strengths, lobe soil characteristics, surface movement measurements collected between 2012 and 2015, and analysis of historic and modern imagery from 1955 to 2014. Field mapping and rock strength data indicate that the metasedimentary and metavolcanic bedrock forming the majority of the lobe catchments has very low to medium strength and is heavily fractured, thus easily contributing to FDL formation. The eight investigated FDLs consist of platy rocks typical of their catchments, organic debris, and an ice-poor soil matrix; massive ice, however, is present within FDLs as infiltration ice, concentrated within cracks open to the surface. Exposure of infiltration ice in retrogressive thaw slumps (RTSs) and associated debris flows leads to increased movement and various stages of destabilization, resulting in morphological differences among the lobes. Analysis of historic imagery indicates that movement of the eight investigated FDLs has been asynchronous over the study period, and since 1955, there has been an overall increase in movement rates of the investigated FDLs. The formation of surface features, such as cracks, scarps, and RTSs, suggests that the increased movement rates correlate to general instability, and even at their current distances, FDLs are impacting infrastructure through increased sediment mobilization. FDL-A is the largest of the investigated FDLs. As of August 2015, FDL-A was 39.2 m from the toe of the Dalton Highway embankment. Based on its current distance and rate of movement, we predict that FDL-A will reach the Dalton Highway alignment by 2023.

Investigating and understanding the effects of multiple femtosecond laser scans on the surface topography of stainless steel 304 and titanium

The majority of studies performed on the formation of surface features by femtosecond laser radiation focuses on single scan procedures, i.e. manipulating the laser beam once over the target area to fabricate different surface topographies. In this work, the effect of scanning stainless steel 304 multiple times with femtosecond laser pulses is thoroughly investigated over a wide range of fluences. The resultant laser-induced surface topographies can be categorized into two different regimes. In the low fluence regime (FΣline,max<130J/cm2), ellipsoidal cones (randomly distributed surface protrusions covered by several layers of nanoparticles) are formed. Based on chemical, crystallographic, and topographical analyses, we conclude that these ellipsoidal cones are composed of unablated steel whose conical geometry offers a significant degree of fluence reduction (35–52%). Therefore, the rest of the irradiated area is preferentially ablated at a higher rate than the ellipsoidal cones. The second, or high fluence regime (FΣline,max>130J/cm2) consists of laser-induced surface patterns such as columnar and chaotic structures. Here, the surface topography showed little to no change even when the target was scanned repeatedly. This is in contrast to the ellipsoidal cones, which evolve and grow continuously as more laser passes are applied.

Formation of surface features on ventifacts: Modeling the role of sand grains rebounding within cavities

Surface textural features – pits, grooves, flutes, and scallops – of sand-blasted ventifacts have been attributed to various erosional mechanisms and to variations in material hardness. This study develops a numerical model of abrasion to examine feature formation by direct grain impacts. We demonstrate that abrasion by a continuous supply of impactors arriving from a single direction, each hitting the surface once, transforms existing cavities into transient features (similar to scallops, flutes, and pits), which shrink and eventually vanish. However, by incorporating additional impacts within the features from rebounding particles, persistent, continuously growing features emerge. We conclude that: (1) rebounding particles concentrate their effect within features, and therefore increase their size; (2) the development of features is sensitive to material type; and (3) the ultimate maximum feature scale is related to the size of the rock, and the size and velocity of impactors. Our model helps organize diverse ventifact field observations into an initial framework of pattern formation and confirms field and laboratory observations that the most common features are linear in wind-parallel directions.

Impurity incorporation and the surface morphology of MOVPE grown GaAs

The impact of impurity incorporation on the development of the surface morphology of GaAs epilayers, grown by metalorganic vapor phase epitaxy (MOVPE), has been systematically investigated. A variety of different doping elements, including Mg, Zn, C, Si, O, and Se, were used to study the interaction between the impurity atoms and GaAs surface. Impurity atoms with smaller atomic weight, belonging to group II and VI, have a larger influence on the surface morphology than the other dopants. Different chemical sources for carbon doping were also used to explore the effect of surface growth chemistry on the formation of surface features. The epilayer surface morphology was affected by the combination of several physical and chemical factors. Factorsinfluencing the impact of an impurity on the growth front evolution are presented based on the interaction between the impurity atoms and the surface step structures.

Atomic Force Microscopy and Grazing Incidence Diffraction Investigation of the Gas-Solid Diazotation of Sulfanilic Acid

The solid state diazotation of sulfanilic acid monohydrate (1) on (010) gives island features and craters on the surface. The remaining surface roughness stays low enough to permit depth dependent grazing incidence X-ray diffraction (GID) measurements, but only when the gas applications are slow. The theoretical background of the unprecedented GID measurements is given. GID measurements were undertaken below, at and above the critical angle of incidence to differentiate the processes at the surface and in the crystal bulk. The phase rebuilding and phase transformation processes could be directly detected in the bulk of the crystal supporting the common AFM interpretations which are derived from the formation of surface features in correlation with crystal packing data. The combined consideration of depth resolved in-plane GID and AFM experiments leads to a comprehensive description of the gas-solid process.

Formation of surface features on niobium during high temperature hydrogen irradiation

Formation of surface features on niobium during high temperature hydrogen irradiation

Trace Impurity Effects on Growth Hillocks during Epitaxial Electrodeposition from Copper Perchlorate Solutions

Growth hillocks ordinarily cover the surface of copper electrodeposits from reagent grade solutions. A 75% decrease in the number of hillocks was observed when the plating baths were purified by pre‐electrolysis and oxidation. When gelatin or Pb++ were added in parts per million or parts per billion concentration to the purified solutions, the surfaces of new electrodeposits were then completely covered with growth hillocks. It is concluded that the formation of surface features during electrodeposition from reagent grade solutions is affected by the presence of trace impurities.