Nanoscale Surface Morphology Research Articles

Potential-Dependent Morphology of Copper Catalysts During CO2 Electroreduction Revealed by In Situ Atomic Force Microscopy.

Electrochemical AFM is a powerful tool for the real‐space characterization of catalysts under realistic electrochemical CO2 reduction (CO2RR) conditions. The evolution of structural features ranging from the micrometer to the atomic scale could be resolved during CO2RR. Using Cu(100) as model surface, distinct nanoscale surface morphologies and their potential‐dependent transformations from granular to smoothly curved mound‐pit surfaces or structures with rectangular terraces are revealed during CO2RR in 0.1 m KHCO3. The density of undercoordinated copper sites during CO2RR is shown to increase with decreasing potential. In situ atomic‐scale imaging reveals specific adsorption occurring at distinct cathodic potentials impacting the observed catalyst structure. These results show the complex interrelation of the morphology, structure, defect density, applied potential, and electrolyte in copper CO2RR catalysts.

Effect of Fangzhu's nanoscale surface morphology on water collection

This paper suggests a fractal mathematical model for Fangzhu's water collection by taking into account its nanoscale surface morphology. A fractal variational principle is established by the semi‐inverse method, which elucidates the conservation laws in the fractal space. Additionally, the variational formulation can also reveal the structure of the solution. An approximate analytical solution is obtained via the two‐scale transform method and He's frequency formula. Some special cases of the model are discussed numerically, showing the method is remarkably simple and capable to solve nonlinear oscillators with fractal derivatives.

Lead-bismuth eutectic (LBE) corrosion behavior of AlTiN coatings at 550 and 600゜C

High performance LBE corrosion-resistant- materials have great potential for application in the future 4th generation nuclear reactor. In this paper, LBE corrosion behavior of AlTiN coating was carefully evaluated at typical working temperatures of nuclear reactor. The coating was synthesized by cathodic arc ion plating on 316L stainless steel (SS) substrates and subjected to LBE corrosion at 550 and 600 °C for 500 h. We used SEM, AFM, EDS, XRD and Raman to carefully characterize the microstructure evolutions of the coating. The results show that the coating could effectively enhance the LBE corrosion resistance of the SS at both 550 and 600 °C. The excellent corrosion resistance performance could be attributed to the in-situ formation of a dense oxide layer on the coating surface, which mainly consists of TiO2 (Anatase and Rutile) and γ-Al2O3 phases with slow growth rate and stable structure. In addition, the dense oxide layer of the coating exhibits a lower wettability to liquid LBE metal because of the nano-scale surface morphology, which further enhance the corrosion resistance. While for bare SS substrate, porous oxide was formed after LBE corrosion. These results suggested that AlTiN coating is a promising material for improving the LBE corrosion-resistant performance of the component used in the future nuclear reactor.

Roughness and bearing analysis of ZnO nanorods

It is essential to analyze the surfaces of thin films precisely to control the production process and the performance of nano-scale devices. Conventional techniques give limited information about the nano-scale surface morphology. Instead, atomic force microscopy (AFM) provides more accurate results about the surface parameters of nanostructures. Hence, in the current study, two-dimensional (2D) and three-dimensional (3D) morphological properties of zinc oxide (ZnO) nanorods (NRs) were investigated using AFM. ZnO NRs were produced via a hydrothermal method at different growth times and temperatures. The surface texture was also examined by scanning electron microscopy (SEM). The results revealed that the morphological parameters such as diameter, length, and shape of the nanorods could be tuned by changing growth time and temperature. Moreover, we analyzed the most crucial roughness and bearing analysis parameters, which affect the functional properties of ZnO in the surface engineering applications. The average roughness increased from 5.86 nm to 17.30 nm as growth time increased from 2 h to 5 h. The average roughness was obtained as 10.92 nm for the temperature of 90 °C and it reached 41.13 nm for 150 °C. In addition, height distribution and bearing area curves associated with the real contact area were reported. 90% of the area was spread at a depth of 48 nm for the growth time of 2 h while this value was obtained 183 nm for 5 h Addition, 90% of the area was spread at a depth of 88 nm and 457 nm for the temperature of 90 °C and 150 °C, respectively. We believe that our study would be a pioneering perspective on bearing analysis of ZnO nanorods.

Palladium-Coated Platinum Powders with Tunable, Nanostructured Surfaces for Applications in Catalysis

Simultaneous control of nanoscale surface morphology and composition remains a challenge in preparing bimetallic catalysts, particularly at the large scale required for industrial application and with high-surface-area substrates. Atomic layer electroless deposition (ALED) is a scalable approach to prepare surface-modified metal powders in which elements more noble than the surface hydrides of the substrate metal are deposited layer-by-layer in a surface-limited fashion. Herein we demonstrate that high-surface-area Pt powder is a viable substrate for controlled deposition of Pd adlayers using this technique, with the potential for large-scale preparation, for use in electrocatalytic and catalytic applications such as fuel cells and functionalization of petrochemical feedstocks. Two different growth mechanisms have been proposed based on bulk and surface Pd atomic fractions obtained from atomic absorption spectroscopy and X-ray photoelectron spectroscopy, respectively. Further, spectral simulations were pe...

Silicalite-1 Layers as a Biocompatible Nano- and Micro-Structured Coating: An In Vitro Study on MG-63 Cells.

Silicalite-1 is a purely siliceous form of zeolite, which does not contain potentially harmful aluminum in its structure as opposed to ZSM-5 aluminosilicate types of zeolite. This paper reports on a study of a silicalite-1 film, deposited on a silicon Si(100) substrate, as a potential anti-corrosive and biocompatible coating for orthopaedic implants. Silicalite-1 film was prepared in situ on the surface of Si(100) wafers using a reaction mixture of tetrapropyl-ammonium hydroxide (TPAOH), tetraethyl-orthosilicate (TEOS), and diH2O. The physico-chemical properties of the obtained surface were characterized by means of X-ray photoelectron spectroscopy, water contact angle measurement, atomic force microscopy, and scanning electron microscopy. The biocompatibility was assessed by interaction with the MG-63 cell line (human osteosarcoma) in terms of cell adhesion, morphology, proliferation, and viability. The synthesized silicalite-1 film consisted of two layers (b- and a, b-oriented crystals) creating a combination of micro- and nano-scale surface morphology suitable for cell growth. Despite its hydrophobicity, the silicalite-1 film increased the number of initially adhered human osteoblast-like MG-63 cells and the proliferation rate of these cells. The silicalite-1 film also improved the cell viability in comparison with the reference Si(100) substrate. It is therefore a promising candidate for coating of orthopaedic implants.

Surface layer morphology of the high fluence Fe implanted polyethylene - Correlation with the magnetic and optical behavior

Fe/Polyethylene nanocomposite was synthesized by ion beam implantation of 56Fe+ into bulk high-density polyethylene. Nanoscale surface morphology along with magnetic and optical behavior was investigated. The aim of the research was to investigate changes of polyethylene's surface layer morphology with the change of Fe implantation fluence in the high fluence range and to find correlations with the magnetic and optical behavior. Four implantation fluences were applied: 5 × 1016, 1 × 1017, 2 × 1017 and 5 × 1017 cm−2, while the implantation energy was 95 keV. Concentration profiles of implanted Fe were analyzed by Rutherford backscattering spectrometry, showing Fe concentration profile maxima closer to the surface with increasing implantation fluence. Cross-sectional transmission electron microscopy showed the formation of metallic nanoparticles with sizes in a range from below 1 nm up to few tens of nanometers, depending on the fluence, and for the highest implantation fluence, a continuous layer was formed. Magneto-optic Kerr effect magnetometry demonstrates weak ferromagnetic behavior for the 2 higher fluences, and superparamagnetic for the 2 lower fluences. The UV-VIS remission function spectra show the peak in the UV region, which we attribute to iron nanoparticles.

Humidity-Dependent Surface Structure and Hydroxide Conductance of a Model Quaternary Ammonium Anion Exchange Membrane

Anion exchange membrane (AEM) fuel cells (AEMFCs) are a promising cost-effective alternative energy conversion technology because of the potential implementation of earth-abundant catalysts, obviating the need for precious metals. AEMs, however, have low conductivity and suffer from poor stability. The conductivity of the AEM is inherently tied to the complex phase-separated morphology, as its dependence on the hydration level is not well understood. In this report, we employ phase-contrast tapping mode and conductive-probe atomic force microscopy (cp-AFM) to study the nanoscale surface morphology and hydroxide conductance of a commercially available quaternary ammonium (QA) AEM by FuMA-Tech GmbH (Fumapem FAA-3). The chemical structure of FAA-3 consists of a poly(phenylene oxide) backbone with QA functionality. The morphology of FAA-3 was observed in the bromide (FAA-3-Br-) and hydroxide form (FAA-3-OH-) in dehydrated and hydrated conditions. Under dehydrated conditions, both membranes showed no phase contrast, indicating the absence of phase-separated hydrophilic domains at the surface. At hydrated conditions, FAA-3-Br- shows randomly dispersed isolated clusters, while FAA-3-OH- shows elongated fibrillar structures extending microns in length. cp-AFM of hydrated FAA-3-OH- showed that these elongated regions were insulating. These results provide morphological evidence for the conduction of hydroxide at the surface and its dependence on the hydration level.

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.

Morphology and Surface Properties of Roach Water Transport Arrays.

We report on morphological studies of wharf roaches, Ligia exotica, which can passively absorb and transport water through the microscopic protrusions on their legs. We systematically investigated the geometrical variables of the protrusions on each podite of legs to reveal a particularized structural complexity. For the morphological analysis, each podite was split into nine different zones by grouping the protrusions with similar shapes and organization. The protrusions are shown to possess three different types of shapes located on each specific zone of the podite. In addition, the nanoscale surface morphologies of the protrusions on the wharf roach legs were probed by using atomic force microscopy, and the surface properties of the hairy arrays were determined for identifying the localized hydrophobicity distribution. The protrusion surface possessed a nanoscale periodic patterned texture, and both the valley and ridges of a periodic pattern on the protrusion surface exhibited an identical low surface energy. We suggest that the structural morphologies and distinct hydrophobicity of the protrusions can be critical in determining the directional wettability of an entire leg and important for designing a sturdy water transport and passive water-absorbing system without external energy consumption.

Titania nanotube interface to increase adhesion strength of hydroxyapatite sol-gel coatings on Ti-6Al-4V for orthopedic applications

Sol-gel coating hydroxyapatite (HA) allows for non-line-of-sight coatings on metallic implants that enhance biocompatibility and osseointegration, but coatings are on the order of a few microns thick and have poor adhesion, especially at low sintering temperatures; Both issues can limit implant longevity. In order to improve coating adhesion strength, a titania nanotube interface was used to reduce thermal mismatch and provide a nano-scale surface morphology for mechanical interlocking, while multiple dip-coatings achieved coating thicknesses >70 μm. In this study, Ti-6Al-4V disks were anodized to produce self-assembled titania (TiO2) nanotubes (NTs) on the surface of the substrates, while HA sol-gel was used to dip-coat the samples. The titania layers measured 800–900 nm thick, with nanotube pore widths of 90 ± 12 nm. Pure HA coating thicknesses were measured at 73.3 ± 10.5 μm and 84.97 ± 18.1 μm for polished Ti-6Al-4 V and anodized Ti-6Al-4V, respectively. The adhesion strengths of pure HA coatings on anodized (NT) surfaces were significantly higher (P < 0.05, N = 7) than polished surfaces at 19.02 ± 3.36 MPa and 13.8 ± 3.28, respectively. Strontium was doped into sol-gel coatings (Sr-Sol) to enhance bioactivity and showed a significant increase in preosteoblast MTT optical density after 3 days of culture compared to pure HA sol-gel, and plasma sprayed pure HA and strontium-HA (Sr-HA). SEM imaging showed well attached osteoblast cells with a similar morphology of multiple, long filopodia across all samples. This study shows that forming titania nanotubes through anodization is a viable approach to increase the adhesion strength of sol-gel coatings sintered at low temperatures, and demonstrates a facile method to incorporate dopants that enhance the osteoconductivity of HA sol-gels.

Cyclic voltammetry for morphological analysis of InGaN epitaxial layers and nanostructures

We introduce cyclic voltammetry (CV) with dissolved, chemically stable electrolytes as a sensitive, non-destructive and fast method for the analysis of the surface morphology of InGaN epitaxial layers and nanostructures grown on silicon. The surface area is probed by the electric double layer capacitance (EDLC) formed upon attachment of ions in solution under close-to-equilibrium conditions. The dynamics of the measured EDLC as a function of scan rate characterizes the nano-scale surface morphology. The dynamics of the measured EDLC follows a power law dependence on the scan rate. The exponent clearly correlates with the RMS surface roughness at the nano/atomic scale deduced from atomic force microscopy. CV is thus complementary to other established methods for the morphological analysis of epitaxial layers in general.

Pure and bilayer sol-gel nanolayers derived on a novel Ti surface for load bearing applications

Abstract Coating techniques of titanium (Ti) materials play a key role for increase their characteristics required for the field of the biomedical applications such as biocompatibility, mechanical as well as wear and corrosion resistances. In this regard, a serious attempt was made to develop uniform nanoscale bioceramic coatings applied on the surface of new metastable β-Ti alloy using sol-gel technique. Different bioceramic coatings, pure titania (TiO2), and bilayer composed of inner TiO2 layer and outer hydroxyapatite (HA) layer, were investigated. The surface morphology of the coated surfaces were analyzed using scanning electron microscope (SEM) and X-ray diffraction (XRD) examinations. Furthermore, the corrosion characteristics of coated Ti alloy substrates were evaluated and compared to uncoated substrate. The results showed that nano-scale surface morphology with advanced crystallization and homogeneous is obtained for bilayer TiO2/HA coating. Also, the coated Ti alloy substrates have outstanding corrosion protection comparing with uncoated Ti alloy substrate.

Hydrophobic surface modification of polymethyl methacrylate by two-dimensional plasma jet array at atmospheric pressure

Recently developed atmospheric pressure plasma jet (APPJ) is considered as a novel and efficient technique for uneven surfaces processing and APPJ array effectively expands the treatment area of a single APPJ. In this paper, a two-dimensional (2D) APPJ array in Ar/tetramethylsilane (TMS) is used to improve the surface hydrophobicity of polymethyl methacrylate (PMMA) by depositing polymerized silicalike clusters on the jet-PMMA interface. The electrical and optical characteristics of the 2D Ar/TMS APPJ array are measured to optimize experimental conditions. The wettability of jet-PMMA interface is assessed by measuring water contact angle, which increases from 65° to a maximum value of 115° after 240 s plasma treatment at 0.04% TMS content. Scanning electron microscopy is used to investigate the micro- and nanoscale surface morphology of PMMA after plasma treatment, and it is found that there are clusters of particles with diameters of hundreds of nanometers attached on the PMMA surface. The changes of the chemical composition and chemical bonding on the PMMA surface are further analyzed using Fourier transform infrared and x-ray photoelectron spectroscopies. It is found that the silicon-containing groups, such as Si-CH3, Si-H, and Si-O-Si, replace oxygen-containing hydrophilic polar groups (C—O and C=O), reduce the surface polarity, decrease the surface tension, and increase the surface hydrophobicity. For the intensive peak of Si-O-Si in FTIR spectra, the improvement of hydrophobicity of the PMMA surface is caused by the hydrophobic polymerized Si-O-Si thin film. The results demonstrate that the APPJ array as a novel atmospheric pressure plasma device provides an efficient way to modify large uneven material surfaces.

Biomimetic Super Anti-Wetting Coatings from Natural Materials: Superamphiphobic Coatings Based on Nanoclays

Superamphiphobic coatings (SAPCs) that resist wetting of water and low-surface-tension liquids have generated widespread attention in academia, but are very challenging to invent. Liquid adhesion, low stability, complicated and expensive preparation methods are the typical characteristics of SAPCs, which seriously hinder real-world applications of SAPCs. Here, we report a comprehensive study about preparation of SAPCs from abundant nanoclays with fibrous, plate-like and porous microstructures. The SAPCs are prepared simply by hydrolytic condensation of silanes in the presence of nanoclays, followed by spray-coating the as-formed suspensions onto substrates. The SAPCs feature high superamphiphobicity for various liquids down to a surface tension of 23.8 mN m−1 (n-decane), and high mechanical, chemical and thermal stability. The superamphiphobicity and stability depend on microscale and nanoscale surface morphology of the coatings, which are controllable by the microstructures of nanoclays and their acid activation. The fibrous nanoclays with moderate aspect ratio like palygorskite are the most suitable building blocks for the preparation of SAPCs by effectively forming the reentrant surface morphology. We believe that the findings will promote the progress of SAPCs, and pave the way for the development of clay-based super anti-wetting coatings.

Electrostatic Double-Layer Interaction at the Surface of Rough Cluster-Assembled Films: The Case of Nanostructured Zirconia.

Here, we investigated the influence of the nanoscale surface morphology on the electrostatic double layer at corrugated surfaces in aqueous electrolytes. For this purpose, we have produced cluster-assembled nanostructured zirconium dioxide (ns-ZrO x, x ≈ 2) films with controlled morphological properties by supersonic cluster beam deposition (SCBD) and measured the double-layer interaction by atomic force microscopy with colloidal probes. SCBD allowed tuning the characteristic widths of the corrugated interface (root-mean-square roughness, correlation length) across a wide range of values, matching the width of the electrostatic double layer (Debye length) and the typical size of nanocolloids (proteins, enzymes, and catalytic nanoparticles). To accurately characterize the surface charge density in the high-roughness regime, we have developed a two-exponential model of the electrostatic force that explicitly includes roughness and better accounts for the roughness-induced amplification of the interaction. We were then able to observe a marked reduction of the isoelectric point of ns-ZrO x surfaces of increasing roughness. This result is in good agreement with our previous observations on cluster-assembled nanostructured titania films and demonstrates that the phenomenon is not limited to a specific material, but more generally depends on peculiar nanoscale morphological effects, related to the competition of the characteristic lengths of the system.

Effect of Inhibitor Modifications on Initial Localized Dealloying of Metallic Alloy Surfaces

Despite a substantial number of reports on corrosion testing is available, only a few projects aim to understand the basic processes driving materials degradation. A special type of corrosion, localized dealloying, takes place on metallic alloy surfaces modified with self-assembled monolayers (SAMs) of organic inhibitors[1-2]. Corrosion initiation at the nanoscale can be addressed by controlling the spatial distribution and molecular organization of inhibitor-molecule SAMs at nano and micro length scales. We use micro-contact printing on model ultra-flat gold surfaces and obtain well-defined complex organic layers following a multi-step approach [3]. This approach was applied on locally atomically flat Cu3Au (100) surfaces to study initial localized dealloying which results in the initiation of localized dealloying being strongly dependent on the nanoscale surface morphology (Figure 1) [4]. In addition, different organic inhibitors containing -SH (thiol end) films were subsequently applied on polycrystalline Cu and CuZn alloys to analyse inhibitor film stabilities. Force Spectroscopy of Atomic Force Microscopy (FS-AFM) provides a stability status of such inhibitor layers by analysing AFM tip sample force interaction on inhibitor-modified metallic surfaces.

Desublimation Frosting on Nanoengineered Surfaces.

Ice nucleation from vapor presents a variety of challenges across a wide range of industries and applications including refrigeration, transportation, and energy generation. However, a rational comprehensive approach to fabricating intrinsically icephobic surfaces for frost formation-both from water condensation (followed by freezing) and in particular from desublimation (direct growth of ice crystals from vapor)-remains elusive. Here, guided by nucleation physics, we investigate the effect of material composition and surface texturing (atomically smooth to nanorough) on the nucleation and growth mechanism of frost for a range of conditions within the sublimation domain (0 °C to -55 °C; partial water vapor pressures 6 to 0.02 mbar). Surprisingly, we observe that on silicon at very cold temperatures-below the homogeneous ice solidification nucleation limit (<-46 °C)-desublimation does not become the favorable pathway to frosting. Furthermore, we show that surface nanoroughness makes frost formation on silicon more probable. We experimentally demonstrate at temperatures between -48 °C and -55 °C that nanotexture with radii of curvature within 1 order of magnitude of the critical radius of nucleation favors frost growth, facilitated by capillary condensation, consistent with Kelvin's equation. Our findings show that such nanoscale surface morphology imposed by design to impart desired functionalities-such as superhydrophobicity-or from defects can be highly detrimental for frost icephobicity at low temperatures and water vapor partial pressures (<0.05 mbar). Our work contributes to the fundamental understanding of phase transitions well within the equilibrium sublimation domain and has implications for applications such as travel, power generation, and refrigeration.

Morphological Characteristics of Au Films Deposited on Ti: A Combined SEM-AFM Study

Deposited Au films and coatings are, nowadays, routinely used as active or passive elements in several innovative electronic, optoelectronic, sensing, and energy devices. In these devices, the physical properties of the Au films are strongly determined by the films nanoscale structure. In addition, in these devices, often, a layer of Ti is employed to promote adhesion and, so, influencing the nanoscale structure of the deposited Au film. In this work, we present experimental analysis on the nanoscale cross-section and surface morphology of Au films deposited on Ti. In particular, we sputter-deposited thick (&gt;100 nm thickness) Au films on Ti foils and we used Scanning Electron Microscopy to analyze the films cross-sectional and surface morphology as a function of the Au film thickness and deposition angle. In addition, we analyzed the Au films surface morphology by Atomic Force Microscopy which allowed quantifying the films surface roughness versus the film thickness and deposition angle. The results establish a relation between the Au films cross-sectional and surface morphologies and surface roughness to the film thickness and deposition angle. These results allow setting a general working framework to obtain Au films on Ti with specific morphological and topographic properties for desired applications in which the Ti adhesion layer is needed for Au.

Spallation-induced roughness promoting high spatial frequency nanostructure formation on Cr

Interaction of ultrafast laser pulses with metal surfaces in the spallation regime can result in the formation of anisotropic nanoscale surface morphology commonly referred to as laser-induced periodic surface structures (LIPSS) or ripples. The surface structures generated by a single pulse irradiation of monocrystalline Cr samples are investigated experimentally and computationally for laser fluences that produce high spatial frequency nanostructures in the multi-pulse irradiation regime. Electron microscopy reveals distinct response of samples with different crystallographic surface orientations, with (100) surfaces exhibiting the formation of more refined nanostructure by a single pulse irradiation and a more pronounced LIPSS after two laser pulses as compared to (110) surfaces. A large-scale molecular dynamics simulation of laser interaction with a (100) Cr target provides detailed information on processes responsible for spallation of a liquid layer, redistribution of molten material, and rapid resolidification of the target. The nanoscale roughness of the resolidified surface predicted in the simulation features elongated frozen nanospikes, nanorims and nanocavities with dimensions and surface density similar to those in the surface morphology observed for (100) Cr target with atomic force microscopy. The results of the simulation suggest that the types, sizes and dimensions of the nanoscale surface features are defined by the competition between the evolution of transient liquid structures generated in the spallation process and the rapid resolidification of the surface region of the target. The spallation-induced roughness is likely to play a key role in triggering the generation of high-frequency LIPSS upon irradiation by multiple laser pulses.