Surface Nanomorphology Research Articles

Regulating material wettability through surface plastic deformation post-processing via friction modification

The wettability of engineering materials significantly influences their cleaning and antifreeze properties, making it a key consideration in aerospace applications. Methods for controlling surface plastic deformation can alter the wettability of materials and contribute to a certain level of strengthening effect, thereby presenting significant application potential. This study aimed to modify the wetting characteristics of aviation titanium alloys in harsh environments through adjustments in surface roughness via peening treatments (such as laser shock peening with coating and mechanical shot peening). The impact of various peening processes on wetting characteristics was investigated through comprehensive surface energy, macro, and nano morphology analyses. Static contact angle measurements were quantified, followed by evaluating other properties, such as surface free energy. Through adjustments in post-treatment processes and control of surface roughness, tailored acquisition of wetting characteristics was achieved. This study elucidates the beneficial effect of surface plastic deformation post-processing on controlling material wettability and introducing strengthening effects. Additionally, the study indicates the importance of accurately determining the sampling range for precise characterization of material wettability.

An adjustable Ar ion-beam activation strategy to achieve hydrophilic bonding of Si and diamond by deposited AlN interlayer

As a III-nitride, AlN exhibits high thermal conductivity, excellent insulation, and low thermal expansion. Therefore, AlN is an alternative to the insulating layer in conventional Si-on-insulator (SOI) systems to solve the problem of severe self-heating effects caused by the poor thermal conductivity of buried oxide (BOX, SiO2) layers. This is particularly true for high-power integrated circuit and micro-electro-mechanical system fabrication. However, heat transfer also depends on the bottom Si substrate. With the highest thermal conductivity (≥2000 W/mK) among bulk materials, diamond is a highly attractive option to replace conventional Si substrates. Herein, we describe a low-temperature vacuum-free hydrophilic bonding method based on a thin AlN interlayer to prepare a single-crystal Si layer on a polycrystalline diamond. Through suitable Ar ion-beam activation, the surface nanomorphology and chemical state can be simultaneously modified. Increasing the real contact area and removing the surface heavy oxygen layer are critical factors for achieving complete bonding. Moreover, the relatively mild deposition and bonding conditions of AlN make it compatible with the complex CMOS transistor process and could enable the more flexible integration of diamond into 3D chip packages in the future.

Adsorption behavior of serum proteins on anodized titanium is driven by surface nanomorphology.

Protein adsorption behavior can play a critical role in defining the outcome of a material by affecting the subsequent in vivo response to it. To date, the effect of surface properties on protein adsorption behavior has been mainly focused on surface chemistry, but research on the effect of nanoscale surface topography remains limited. In this study, the adsorption behavior of human serum albumin, immunoglobulin G, and fibrinogen in terms of the adsorbed amount and conformational changes were investigated on bare and anodized titanium (Ti) samples (40 and 60 V applied voltages). While the surface chemistry, RMS surface roughness, and arithmetic surface roughness of the anodized samples were similar, they had distinctly different nanomorphologies identified by atomic force microscopy and scanning electron microscopy, and the surface statistical parameters, surface skewness Ssk and kurtosis Sku. The Feret pore size distribution was more uniform on the 60 V sample, and surface nanostructures were more symmetrical with higher peaks and deeper pores. On the other hand, the 40 V sample surface presented a nonuniform pore size distribution and asymmetrical surface nanostructures with lower peaks and shallower pores. The amount of surface-adsorbed protein increased on the sample surfaces in the order of Ti < 40 V < 60 V with the predominant factor affecting the amount of surface-adsorbed protein being the increased surface area attained by pore formation. The secondary structure of all adsorbed proteins deviated from that of their native counterparts. While comparing the secondary structure components of proteins on anodized surfaces, it was observed that all three proteins retained more of their secondary structure composition on the surface with more uniform and symmetrical nanofeatures than the surface having asymmetrical nanostructures. Our results suggest that the nanomorphology of the peaks and outer walls of the nanotubes can significantly influence the conformation of adsorbed serum proteins, even for surfaces having similar roughness values.

A Laser-Printed Surface-Enhanced Photoluminescence Sensor for the Sub-Nanomolar Optical Detection of Mercury in Water

Here, we report a novel, easy-to-implement scalable single-step procedure for the fabrication of a solid-state surface-enhanced photoluminescence (SEPL) sensor via the direct femtosecond (fs) laser patterning of monocrystalline Si wafers placed under the layer of functionalizing solution simultaneously containing a metal salt precursor (AgNO3) and a photoluminescent probe (d114). Such laser processing creates periodically modulated micro- and nanostructures decorated with Ag nanoparticles on the Si surface, which effectively adsorbs and retains the photoluminescent sensor layer. The SEPL effect stimulated by the micro- and nanostructures formed on the Si surface localizing pump radiation within the near-surface layer and surface plasmons supported by the decorating Ag nanoparticles is responsible for the intense optical sensory response modulated by a small amount of analyte species. The produced SEPL sensor operating within a fluidic device was found to detect sub-nanomolar concentrations of Hg2+ in water which is two orders of magnitude lower compared to this molecular probe sensitivity in solution. The fabrication technique is upscalable, inexpensive, and flexible regarding the ability to the control surface nano-morphology, the amount and type of loading noble-metal nanoparticles, as well as the type of molecular probe. This opens up pathways for the on-demand development of various multi-functional chemosensing platforms with expanded functionality.

The effect of metal surface nanomorphology on the output performance of a TENG.

In this work, the effect of charge density and nanomorphology of a metal tip on the output performance of a triboelectric nanogenerator (TENG) is studied. The basic working principle of the TENG is charge transfer after separation of a metal and a polymer. There are different charge densities on different kinds of metal surface nanomorphology, which significantly influences the output performance of the TENG. Copper samples with different nanomorphology were obtained by controlling pH value, current density, electrolyte concentration, and temperature during the electrodeposition of copper. The samples were characterized using XRD and SEM. The output performance of the TENG is closely related to the size, charge density distribution, and shape of the metal nanoparticles.

Approach to map nanotopography of cell surface receptors

Cells communicate with their environment via surface receptors, but nanoscopic receptor organization with respect to complex cell surface morphology remains unclear. This is mainly due to a lack of accessible, robust and high-resolution methods. Here, we present an approach for mapping the topography of receptors at the cell surface with nanometer precision. The method involves coating glass coverslips with glycine, which preserves the fine membrane morphology while allowing immobilized cells to be positioned close to the optical surface. We developed an advanced and simplified algorithm for the analysis of single-molecule localization data acquired in a biplane detection scheme. These advancements enable direct and quantitative mapping of protein distribution on ruffled plasma membranes with near isotropic 3D nanometer resolution. As demonstrated successfully for CD4 and CD45 receptors, the described workflow is a straightforward quantitative technique to study molecules and their interactions at the complex surface nanomorphology of differentiated metazoan cells.

A Two-Step Approach to Tune the Micro and Nanoscale Morphology of Porous Niobium Oxide to Promote Osteointegration.

We present a two-step surface modification process to tailor the micro and nano morphology of niobium oxide layers. Niobium was firstly anodized in spark regime in a Ca- and P-containing solution and subsequently treated by acid etching. The effects of anodizing time and applied potential on the surface morphology is investigated with SEM and AFM, complemented by XPS compositional analysis. Anodizing with a limiting potential of 250 V results in the fast growth of oxide layers with a homogeneous distribution of micro-sized pores. Cracks are, however, observed on 250 V grown layers. Limiting the anodizing potential to 200 V slows down the oxide growth, increasing the anodizing time needed to achieve a uniform pore coverage but produces fracture-free oxide layers. The surface nano morphology is further tuned by a subsequent acid etching process that leads to the formation of nano-sized pits on the anodically grown oxide surface. In vitro tests show that the etching-induced nanostructure effectively promotes cell adhesion and spreading onto the niobium oxide surface.

Nanocelluloses - Nanotoxicology, Safety Aspects and 3D Bioprinting.

Nanocelluloses have good rheological properties that facilitate the extrusion of nanocellulose gels in micro-extrusion systems. It is considered a highly relevant characteristic that makes it possible to use nanocellulose as an ink component for 3D bioprinting purposes. The nanocelluloses assessed in this book chapter include wood nanocellulose (WNC), bacterial nanocellulose (BNC), and tunicate nanocellulose (TNC), which are often assumed to be non-toxic. Depending on various chemical and mechanical processes, both cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) can be obtained from the three mentioned nanocelluloses (WNC, BNC, and TNC). Pre/post-treatment processes (chemical and mechanical) cause modifications regarding surface chemistry and nano-morphology. Hence, it is essential to understand whether physicochemical properties may affect the toxicological profile of nanocelluloses. In this book chapter, we provide an overview of nanotoxicology and safety aspects associated with nanocelluloses. Relevant regulatory requirements are considered. We also discuss hazard assessment strategies based on tiered approaches for safety testing, which can be applied in the early stages of the innovation process. Ensuring the safe development of nanocellulose-based 3D bioprinting products will enable full market use of these sustainable resources throughout their life cycle.

Carbon Nanotubes Substrates Alleviate Pro-Calcific Evolution in Porcine Valve Interstitial Cells.

The quest for surfaces able to interface cells and modulate their functionality has raised, in recent years, the development of biomaterials endowed with nanocues capable of mimicking the natural extracellular matrix (ECM), especially for tissue regeneration purposes. In this context, carbon nanotubes (CNTs) are optimal candidates, showing dimensions and a morphology comparable to fibril ECM constituents. Moreover, when immobilized onto surfaces, they demonstrated outstanding cytocompatibility and ease of chemical modification with ad hoc functionalities. In this study, we interface porcine aortic valve interstitial cells (pVICs) to multi-walled carbon nanotube (MWNT) carpets, investigating the impact of surface nano-morphology on cell properties. The results obtained indicate that CNTs significantly affect cell behavior in terms of cell morphology, cytoskeleton organization, and mechanical properties. We discovered that CNT carpets appear to maintain interfaced pVICs in a sort of “quiescent state”, hampering cell activation into a myofibroblasts-like phenotype morphology, a cellular evolution prodromal to Calcific Aortic Valve Disease (CAVD) and characterized by valve interstitial tissue stiffening. We found that this phenomenon is linked to CNTs’ ability to alter cell tensional homeostasis, interacting with cell plasma membranes, stabilizing focal adhesions and enabling a better strain distribution within cells. Our discovery contributes to shedding new light on the ECM contribution in modulating cell behavior and will open the door to new criteria for designing nanostructured scaffolds to drive cell functionality for tissue engineering applications.

Adhesive Property of Aluminum Oxide Formed By High Temperature Anodizing

Aluminum and its alloys have been widely used various situations because of their light weight, specific strength, heat conductivity. Surface treatment can impart corrosion protection, hardness, coating film adhesion and others to aluminum. Anodizing is one of the most important surface finishing processes of aluminum. In recent years, technology to use multimaterials has been attracting attention to achieve the production of energy-efficient automobiles. In such activities, adhesive bonding is increasingly used in automobile manufacturing. However, the reliability and strength of the joint surface is very important to use adhesive bonding for vehicle such as car, aircraft and motorcycle. Herein, we demonstrate the fabrication of high adhesive aluminum surface via high temperature anodizing process. High-purity aluminum specimens (99.99 wt%, 300 µm thick) were ultrasonically degreased in acetone for 10 min. These specimens were immersed in a oxalic acid solution (0.3 M), and then were anodized at a constant current density using a direct-current power supply. After anodizing, the specimens were quickly removed from the electrolyte solution and then washed with distilled water. The surface nanomorphology of the anodized specimens was examined by field emission scanning electron microscopy (FE-SEM). The adhesion property of anodized specimen was measured by tape peel test using 90 degree peel test machine. Figure 1 shows the surface appearance of the specimens covered with a) typical anodic oxide formed by low-temperature anodizing and b) anodic oxide formed by high-temperature anodizing. Anodic oxide formed by high-temperature anodizing had an irregular shape numerous pores due to the chemical dissolution of anodic oxide. These photographs were taken after tape peel test. On the typical anodic oxide, the tape was easily peeled off and no adhesive remained on the surface. On the other hand, the tape adhesive remained on the irregular anodic oxide covered surface fabricated by high temperature anodizing and the strong tape peel strength was measured. High-temperature anodizing causes the intense chemical dissolution. Thus, the anodic oxide which had wide-pore outer layer and intricate inner layer was formed on the aluminum surface by high-temperature anodizing. Adhesive layer of tape might be able to penetrate such anodic oxide. Therefore, the strong peel strength by the anchoring effect was measured on the surface. Although the adhesive mechanism has not been clear in detail, this surface treatment technique has a potential for the fabrication of composite material which is consist of aluminum and another material． Figure 1

Stability and temporal decay of nanopatterned tribocharge on nanotextured elastomer surfaces

Contact electrification of nanotextured elastomer surfaces often generates nanopatterned tribocharges that are useful for both scientific and practical purposes. For sustained utilization of the nanopatterned tribocharge, their stability and temporal behavior must be characterized and studied. It is, however, a highly challenging task as it requires long-term, repeated probing of the tribocharge at the nanoscale spatial resolution. In this work, we performed such a comprehensive experimental study of nanopatterned tribocharges on elastomer surfaces using Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). Curve-fitting analysis of the KPFM results not only affirmed the temporally decaying nature of the tribocharge but also separated them into two distinct, fast and slowly decaying, components that could be attributed to two different tribocharging mechanisms. Through pre-constrained optimization of the curve-fitting parameters and comparison of the results, we could attribute the fast and slow decay components to the tribocharges generated by tangential sliding and surface-normal separation of the material interface, respectively. The analysis also enabled us to estimate time-invariant “pedestal” potentials from the KPFM results and predict the existence of long-term stable tribocharge on the nanotextured elastomer surface. We experimentally confirmed it by re-scanning the specimens 14 days after the initial measurements. The observations, analysis, and the mechano-triboelectric charging model will benefit not only the researchers of nanoscale tribocharges but also those interested in the study and applications of triboelectricity in general. • Observed how nanopatterned tribocharge decays in time using long-term KPFM. • Identified fast and slow decays and correlated them with surface nano-morphology. • Attributed the two tribocharges to different triboelectrification mechanisms. • Predicted long-term stable tribocharge and confirmed it via KPFM at the 14th day.

Stereometric analysis of Ta2O5 thin films

Abstract The purpose of this work is the study of the correlation between the thickness of tantalum pentoxide thin films and their three-dimensional (3D) micromorphology. The samples were prepared on silicon substrates by electron beam evaporation. The differences in surface structure of the processed and reference samples were investigated. Compositional studies were performed by energy-dispersive X-ray spectroscopy. Stereometric analysis was carried out on the basis of atomic force microscopy (AFM) data, for tantalum pentoxide samples with 20 nm, 40 nm, 60 nm, 80 nm and 100 nm thicknesses. These methods are frequently used in describing experimental data of surface nanomorphology of Ta2O5. The results can be used to validate theoretical models for prediction or correlation of nanotexture surface parameters.

Surface chemistry and morphology transition induced by critical heat flux incipience on laser-textured copper surfaces

Stability of functionalized surfaces is an often-neglected topic in phase-change heat transfer research. Here, we examine the chemical and morphological changes of textured surfaces on the molecular and atomic level after the critical heat flux incipience during saturated pool-boiling of water. SEM imaging, EDS, AES and XPS analyses are used to examine the surface changes. Copper samples were laser textured via ablation using a nanosecond fiber laser under air or argon atmosphere. Multiscale microcavities, which serve as preferential nucleation sites, were produced on the samples, which exhibited significantly enhanced heat transfer performance in pool-boiling tests. Repeated formation of a vapor film and accompanying temperatures of up to 320 °C during the tests resulted in changes of the surface chemistry and nanomorphology. It was determined that Cu (II) oxide and hydroxide transform into Cu (I) oxide and Cu metal as a result of repeated low-temperature annealing of the surface when a vapor film is formed during the transition towards film boiling. This additionally causes a wettability transition of the functionalized surfaces from hydrophilic towards hydrophobic. Both effects importantly influence the solid-liquid-vapor interface during phase-change heat transfer. Overall, surfaces functionalized via laser texturing exhibited significantly enhanced stability and boiling heat transfer performance.

Exploiting Plasma Exposed, Natural Surface Nanostructures in Ramie Fibers for Polymer Composite Applications.

Nanoscale surface morphology of plant fibers has important implications for the interfacial bonding in fiber-polymer composites. In this study, we investigated and quantified the effect of plasma-surface modification on ramie plant fibers as a potential tool for simple and efficient surface modification. The extensive investigation of the effects of plasma treatment of the fiber surface nano-morphology and its effect on the fiber-polymer interface was performed by Low-Voltages Scanning Electron Microscopy (LV-SEM), infrared spectroscopy (FT-IR) analysis, fiber-resin angle measurements and mechanical (tensile) testing. The LV-SEM imaging of uncoated plasma treated fibers reveals nanostructures such as microfibrils and elementary fibrils and their importance for fiber mechanical properties, fiber wettability, and fiber-polymer matrix interlocking which all peak at short plasma treatment times. Thus, such treatment can be an effective in modifying the fiber surface characteristics and fiber-polymer matrix interlocking favorably for composite applications.

Phylogenetic mapping of scale nanostructure diversity in snakes

BackgroundMany species of snakes exhibit epidermal surface nanostructures that form complex motifs conferring self-cleaning properties, and sometimes structural iridescence, to their skin.ResultsUsing confocal microscopy, we show that these specialised cells can be greatly elongated along their left-right axis and that different types of nanostructures are generated by cell borders and cell surface. To characterise the complexity and diversity of these surface gratings, we analysed scanning electron microscopy images of skin sheds from 353 species spanning 19 of the 26 families of snakes and characterised the observed nanostructures with four characters. The full character matrix, as well as one representative SEM image of each of the corresponding species, is available as a MySQL relational database at https://snake-nanogratings.lanevol.org. We then performed continuous-time Markov phylogenetic mapping on the snake phylogeny, providing an evolutionary dynamical estimate for the different types of nanostructures. These analyses suggest that the presence of cell border digitations is the ancestral state for snake skin nanostructures which was subsequently and independently lost in multiple lineages. Our analyses also indicate that cell shape and cell border shape are co-dependent characters whereas we did not find correlation between a simple life habit classification and any specific nanomorphological character.ConclusionsThese results, compatible with the fact that multiple types of nanostructures can generate hydrophobicity, suggest that the diversity and complexity of snake skin surface nano-morphology are dominated by phylogenetic rather than habitat-specific functional constraints. The present descriptive study opens the perspective of investigating the cellular self-organisational cytoskeletal processes controlling the patterning of different skin surface nanostructures in snakes and lizards.

Zinc oxide nanorod array as an inhibitory biointerface

Abstract

Surface nano structures on W surface exposed to low-energy high flux D plasma

The surface nano structures on W surface exposed to low-energy D plasma was studied by transmission electron microscopy. It was found that the surface nano structures on W surface induced by D plasma were mainly due to two reasons. First, the subsurface nano-sized bubbles will induce nano scale blistering of the surface, resulting in surface nano morphology. The nano scale blistering behaviour is most obvious on [1 1 1] surface at low temperature (500 K). Secondly, during the plasma exposure, oxide layer on W surface will be sputtered by low energy D particles, and the sputtering can also induce nano structures on some surfaces. At low temperature (500 K), the surface nano structures were formed due to the nano scale blistering behaviour and the sputtering of surface oxide layer. At high temperature (1000 K), the surface nano structures were mainly caused by the sputtering of surface oxide layer.

Fabrication of Sticky and Slippery Superhydrophobic Aluminum Surfaces Via Pyrophosphoric Acid Anodizing and SAM Modification

Anodizing aluminum in a concentrated pyrophosphoric acid solution (H4P2O7) leads to the formation of numerous anodic alumina nanofibers measuring less than 10 nm in diameter. As the alumina nanofibers are modified with self-assembled monolayer (SAM), the nanofiber-covered aluminum surface exhibits a superhydrophobic behavior with a water contact angle measuring more than 150°. In the present investigation, we demonstrate the fabrication of slippery and sticky superhydrophobic aluminum surfaces covered by the anodic alumina nanofibers. The effect of the nanostructure of the anodic oxide on the adhesion interaction between the water droplet and the surface was investigated by dynamic contact angle measurements. High-purity aluminum specimens (99.99 wt%, 400 µm thick) were ultrasonically degreased in ethanol for 10 min. The specimens were electropolished in a 78 vol% CH3COOH/22 vol% 70%-HClO4 solution (T = 280 K) at a constant voltage of 28 V for 1 min. The electropolished specimens were immersed in a concentrated pyrophosphoric acid solution (74.0 wt%, T = 293 K), and then were anodized at a constant voltage of 50 V using a PC-connected direct-current power supply. After anodizing, the specimens were immersed in a 0.5 mM 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid (FOPA) / ethanol solution (T = 313 K) for 24 h to form SAM on the anodic alumina nanofibers. The surface nanomorphology of the anodized specimens was examined by field emission scanning electron microscopy (FE-SEM). The water contact angles on the anodized specimens were measured by an optical contact angle meter. The distilled water droplets were formed on the surface using an auto dispenser and a microsyringe with a flow rate of 2 µL/s, and the advancing and receding contact angles were measured by a charge-coupled device (CCD) camera (frame rate: 10 fps). Figure 1 shows the changes in the advancing and receding contact angles with the anodizing time. Here, the anodic oxide was modified with the FOPA-SAM after anodizing. The advancing contact angle rapidly increased to superhydrophobicity more than 160° by the initial stage of anodizing, and the contact angles were maintained at similar values via the long-term anodizing. In contrast, the receding contact angle was drastically changed with the anodizing time: the contact angle rapidly decreased to approximately 0° in the initial stage of anodizing, rapidly increased to 150° in the middle stage, and then gradually decreased to 0° in the final stage. This complicated behavior was due to the nanostructural surface changes via pyrophosphoric acid anodizing. Figure 2 shows the side views of the 20 µL water droplet on the superhydrophobic aluminum specimens fabricated by pyrophosphoric acid anodizing for a) 4 min and b) 20 min and subsequent FOPA-SAM modification. The water droplet was pinned on the surface anodized for 4 min when it was turned upside down (i.e. a sticky surface). Conversely, the droplet easily rolled off with a small sliding angle on the surface anodized for 20 min (i.e. a slippery surface). Figure 1

One-pot synthesis of biochar wrapped Ni/NiO nanobrick composites for supercapacitor applications

The present study demonstrates a novel approach by which porous brick like nanostructures of nickel oxide can be prepared following a combustion assisted rout. The as synthesized NiO active material is electrophoretically deposited on porous Ni foils and processed into high-surface area thin film electrodes for supercapacitor applications. A detailed study has been performed to elucidate how surface nanomorphology and porosity can impact the pseudocapacitive performances of NiO electrode. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the electrode performances and these parameters have been deduced and explained. According to single electrode studies the electrodes exhibited a specific capacitance value as high as 1058 F/g at 5 mV/s with good cyclic stability.

Structurally Oriented Nano-Sheets in Co Thin Films: Changing Their Anisotropic Physical Properties by Thermally-Induced Relaxation.

We show how nanocrystalline Co films formed by separated oblique nano-sheets display anisotropy in their resistivity, magnetization process, surface nano-morphology and optical transmission. After performing a heat treatment at 270 °C, these anisotropies decrease. This loss has been monitored measuring the resistivity as a function of temperature. The resistivity measured parallel to the direction of the nano-sheets has been constant up to 270 °C, but it decreases when measured perpendicular to the nano-sheets. This suggests the existence of a structural relaxation, which produces the change of the Co nano-sheets during annealing. The changes in the nano-morphology and the local chemical composition of the films at the nanoscale after heating above 270 °C have been analysed by scanning transmission electron microscopy (STEM). Thus, an approach and coalescence of the nano-sheets have been directly visualized. The spectrum of activation energies of this structural relaxation has indicated that the coalescence of the nano-sheets has taken place between 1.2 and 1.7 eV. In addition, an increase in the size of the nano-crystals has occurred in the samples annealed at 400 °C. This study may be relevant for the application in devices working, for example, in the GHz range and to achieve the retention of the anisotropy of these films at higher temperatures.