Atomic Force Microscopy Observations Research Articles

Effect of a Discontinuous Ag Layer on Optical and Electrical Properties of ZnO/Ag/ZnOStructures

ZnO/Ag/ZnO nanolaminate structures were deposited by consecutive RF sputtering at room temperature.The optical transparency, sheet resistance, and figure of merit are determined in relation to the deposition time of Ag and to the film thickness of the ZnO top layer. An improved transmittance has been found in the visible spectral range of the ZnO/Ag/ZnO structure compared to ZnO multilayers without Ag. High transmittance of 98% at 550 nm, sheet resistance of 8 Ω/sq, and figure of merit (FOM) of 111.01 × 10−3 Ω−1are achieved for an optimized ZnO/Ag/ZnO nanolaminate structure. It is suggested that the good optical and electrical properties are due to the deposition of the discontinuous Ag layer. The electrical metallic type conductivity is caused by planar located silver metal granules. The deposition of a discrete layer of Ag nano-granules is confirmed by atomic force microscopy (AFM) and cross-section high-resolution transmission electron microscopy (HRTEM) observations.

Observation of mesoscopic clathrate structures in ethanol-water mixtures

Alcohol in water is one of the fundamental liquid–liquid solutions in chemical and biological processes. Water-alcohol mixtures exhibit many abnormal physicochemical properties, the origins of which remain mysterious. In addition, the presence of a high concentration of mesoscale objects in such mixtures has caused debate; many researchers attribute these objects to bulk nanobubbles because their concentration is strongly affected by the amount of dissolved air gases. To resolve these issues, here we use transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and atomic force microscopy (AFM) to study ethanol–water mixtures. TEM reveals mesoscopic clathrate structures with water molecules forming a crystalline matrix hosting a high density of tiny cells. The presence of these mesoscopic clathrate structures is further supported by a refractive index of 1.27 ± 0.02 at 405 nm measured via NTA and the hydrophilic nature of the mesoscopic structures implied by AFM observations, explaining many long-standing puzzles related to water-alcohol mixtures.

Optical Erasure and Reconfiguration of Surface‐Relief‐Gratings of Azo Polymer and Azo Molecular Glass: A Comparative Study on Soft‐Lithographic Duplicates

Surface‐relief‐gratings (SRGs) of azo polymers and azo molecular glasses have attracted considerable interest for their erasable and reconfigurable characteristics. Herein, the optical erasure of soft‐lithographically duplicated SRGs of an azo polymer (BP‐AZ‐CN) and an azo molecular glass (IAC‐4) is investigated to tackle a long‐standing problem from “memory” effect existing in optically inscribed SRGs. The optical erasure is performed by single laser beam irradiation at wavelength of 488 nm with different polarizations, and the erasing behavior is thoroughly investigated by real‐time diffraction efficiency measurement and atomic force microscopy (AFM) observation. Showing no obvious dependence on the light polarizations, the optical erasure of IAC‐4 grating is a relatively fast process, and the original one can be completely erased and recreated. In contrast, the erasure of BP‐AZ‐CN grating is not only much slower, but also strongly correlated with the light polarizations. Upon the p‐polarized light irradiation, the grating profiles are substantially distorted during the erasure with a significant difference in that of the s‐polarized light irradiation. The gratings cannot be completely erased by the lights with all the polarizations. The erasure behavior is found to be determined by the effects of surface tension and mass transfer along the light polarization direction to different extents.

Enhanced nitrogen incorporation in the 〈112̄0〉 directions on the (0001̄) facet of 4H-SiC crystals

Enhanced nitrogen doping in the 〈110〉 directions on the (000) facet of 4H-SiC crystals grown by the physical vapor transport (PVT) growth method was investigated using Raman scattering microscopy and atomic force microscopy (AFM). The enhanced nitrogen doping showed either single or double peak structure of nitrogen incorporation in the azimuthal direction around 〈110〉. AFM observations revealed that these two characteristic doping structures stemmed from different propagation morphologies of spiral steps on the (000) facet. It was also unveiled that the change in the step-flow direction was always associated with the change of the terrace-width ratio on the facet, and that the interplay between these two parameters determined the nitrogen incorporation on the (000) facet. On the basis of these experimental results, the mechanism of the azimuthal dependence of nitrogen incorporation on the (000) facet during PVT growth of 4H-SiC crystals is discussed.

High Speed Atomic Force Microscope Observation of Polyethylene Glycol Adsorption on Au(100)

Polyethylene glycol (PEG) plays an important role as an inhibitor of the electrodeposition. In this study, we investigated the potential dependence of PEG (molecular weight: 3000) adsorption and desorption processes on the gold single crystal substrate. High speed atomic force microscope (HS-AFM) was applied for observing the dynamic behaviors of the nucleation and the growth of PEG adsorption. The in situ observation was conducted at the several potentials where the cyclic voltammogram measurement showed the broad peak of the reduction current. As the applied potential became more cathodic, the adsorption morphology changed from film-like, through the sphere, to the large irregular cluster. When the potential was switched to anodic potential, HS-AFM could show the dissolution process of PEG. Finally we demonstrated the effect of the tip force by modifying the feed-back circuit of AFM.

Inhibitive performance of novel/eco-friendly pyrimidine derivative for Q235 steel protection in 15% HCl under hydrodynamic condition: Combination of experimental, surface and computational approach

The developing effective and eco-friendly corrosion inhibitor plays a vital role in protecting Q235 steel in acid solution. Accordingly, novel pyrimidine derivatives, namely 4-Amino-2-phenyl-1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitrile (APC), were synthesized and applied as the corrosion inhibitor under hydrodynamic conditions in 15% HCl. The inhibition performance was investigated by weight-loss experiment, potentiodynamic polarization curve, electrochemical impedance test, scanning electron microscope (SEM), atomic force microscopy (AFM), contact angle measurement, and X-ray photoelectron spectroscopy. The research showed that APC exhibited good inhibition nature for Q235 steel in 15% HCl medium, and the inhibition efficiency is correlated with APC concentration. The change of impedance parameters showed that the corrosion inhibitor adsorbs on the surface of Q235 steel in forming a protective film. The protective performance results come to 92.83% at 400 mg/L. Langmuir isotherm represents the excellent fitting. SEM, AFM, and XPS observation on the surface of Q235 steel showed that the metal matrix has a good anti-corrosion effect in the corrosion inhibitor solution. Density functional theory (DFT) and Molecular dynamic simulation (MD) were used to determine the inhibitor's and metal interactions' relationship.

Harmonizing Topological Features of Self-Assembled Fibers by Rosette-Mediated Random Supramolecular Copolymerization and Self-Sorting of Monomers by Photo-Cross-Linking.

Random copolymerization is an effective approach to synthesize the desired polymers by harmonizing distinct properties of different monomers. For supramolecular polymers in which monomer binding is inherently dynamic, it is difficult to achieve random copolymerization of monomers with distinct molecular structures and properties due to an enthalpic advantage upon self-recognition (self-sorting). Herein, we demonstrate an example of thermodynamically controlled random supramolecular copolymerization of two monomers functionalized with barbituric acid via the formation of six-membered hydrogen-bonded rosette intermediates to exhibit structural harmonization of the two main-chain motifs, i.e., intrinsically curved and linear motifs. One monomer based on naphthalene chromophore exclusively forms toroidal fibers, whereas another one bearing additional photoreactive diacetylene moiety affords linearly elongated fibers. Supramolecular copolymerization of the two monomers is achieved by cooling hot monomer mixtures in a nonpolar solvent, which results in the formation of thermodynamically stable spirally folded yet elongated fibers. Atomic force microscopic observations and theoretical simulations of the experimental data obtained by absorption spectroscopy reveal the homopolymerization of the diacetylene-functionalized monomer in the high-temperature region, followed by the incorporation of the naphthalene monomer in the medium-temperature region to form supramolecular copolymers with random monomer sequence. Finally, we demonstrate that the random copolymerization process can be switched to a narcissistically self-sorting one by deactivating monomer exchange through the photo-cross-linking of the diacetylene-functionalized monomers.

A new method for quantitative analysis of M13 bacteriophage by atomic force microscopy

Quantitative analysis is essential for virus research, especially in determining the virus titer. The classical method plaque assay is time-consuming, complex, and difficult for the phages that cannot form apparent plaque on the solid medium. In order to realize rapid and effective detection, a new method combining atomic force microscopy (AFM) observation and mathematical calculation is established. In this research, M13 phages with an appropriate dilution ratio were observed and counted by AFM. Based on the counting results, the titer of M13 phages can be calculated simply through mathematical substitution. Instead of cultivating overnight in plaque assay, this new method can be implemented within a few hours. Moreover, it is a method that can achieve visualization for titer determination and have the potential to determine the phages that fail to form apparent plaque, which is significant in virus quantitative assessment.

Atomic force microscope observation of the surfaces of natural articular cartilage

Hydrophilic and negatively charged natural cartilage surface is covered by phospholipids bilayers. These phospholipids have been demonstrated to exert highly desirable characteristics on the surface articular cartilage such as efficient lubrication, load processing, and semipermeability for nutrient transport. We examined a bovine cartilage (BC) surface using atomic force microscope. The study was performed using cartilage samples with healthy surfaces and completely depleted surface phospholipids. The artificially degraded cartilage surfaces (lipid depleted) were resurfaced with different species and combinations of synthetic bilayer of phospholipids found in human joints. Our results demonstrated that it is possible to recreate a potentially viable layer of phospholipids on the surface of degenerated cartilage. However, further studies will be required to advance the resurfacing idea developed in this paper for the potential treatment of osteoarthritis and other related orthopedic joint conditions.

Improving the solubility of myofibrillar proteins in water by destroying and suppressing myosin molecular assembly via glycation

Filamentous myosin is a self-assembling polymer that prevents myofibrillar proteins (MPs) from functioning in low ionic strength media. This study was aimed at investigating if glycation has the potential to improve the solubility of MPs in water. MPs were conjugated with monosaccharides, oligosaccharides, and polysaccharides under wet reaction conditions at 37 °C. The conjugation was verified by SDS-PAGE, FT-IR and amino acid analyses. MPs conjugated with dextran (DX) exhibited a higher solubility and dispersion stability in water, which corresponded to smaller particle size and more uniform distribution (P < 0.05). According to secondary and tertiary structure analyses, the loss of α-helix structures and unfolding of the MPs appear to be the main reasons for MP solubilization. Additionally, according to the zeta-potential, confocal laser scanning microscopy, and atomic force microscopy observation results, glycation can provide electrostatic repulsion or steric hindrance to disintegrate existing filamentous myosin aggregates and inhibit further self-assembly behavior.

Phototethering of Collagen onto Polyetheretherketone Surfaces to Enhance Osteoblastic and Endothelial Performance

Polyetheretherketone (PEEK) is a candidate material for bone implants as an alternative to metals. However, PEEK exhibits poor osseointegration and low endothelial compatibility. This study demonstrates the phototethering of collagen onto PEEK surfaces to facilitate osteoblastic and vascular endothelial performance. In particular, collagen with methacryloyl groups is covalently tethered to the PEEK surface via surface-initiated photopolymerization. This process is simpler than the conventional method of collagen-tethering and can be extended to the surface-patterning treatment of collagen. The collagen is confirmed to be tethered to the PEEK surface using attenuated total reflection Fourier transform infrared measurements, bicinchoninic acid assays, and atomic force microscopic observations. When human bone marrow-derived mesenchymal stem cells (HbmMSCs) are cultured on collagen-tethered PEEK (COL-PEEK) surfaces, the cells favorably adhere and proliferate. After inducing osteogenic differentiation, the cells on the COL-PEEK surfaces show higher expression levels of osteoblast-related genes and mineralization than those on the PEEK surface. Moreover, the tethering of collagen greatly improves endothelial proliferation. The COL-PEEK surfaces promotes endothelial networking in coculture with HbmMSCs. These results suggest that COL-PEEK is highly compatible with both osteoblasts and vascular endothelial cells. COL-PEEK is a promising implant that induces osteogenesis and angiogenesis to repair bone tissues.

Controlled Synthesis of Cyclic‐Helical Polymers with Circularly Polarized Luminescence

AbstractCyclic polymers attract attention because of their endless structure and unique properties, which differ from the linear analogs. However, the synthesis of cyclic polymers is difficult and prohibits their functions and applications. In this study, we reported chiral cyclic PdII‐catalysts that initiate a living ring‐expansion polymerization of isocyanides, yielding a single‐handed cyclic‐helical poly(phenyl isocyanide), with predictable molecular weight (Mn) and low dispersity (Mw/Mn), in good yield. Using this method, cyclic bottlebrush polymers were prepared via the grafting‐onto strategy. The cyclic topology was confirmed using various spectroscopic data and atomic force microscope observation. Moreover, the cyclic polymer brushes, comprising of a one‐handed helical backbone, showed interesting photoluminescence and circularly‐polarized luminescence.

Controlled Synthesis of Cyclic-Helical Polymers with Circularly Polarized Luminescence.

Cyclic polymers attract attention because of their endless structure and unique properties, which differ from the linear analogs. However, the synthesis of cyclic polymers is difficult and prohibits their functions and applications. In this study, we reported chiral cyclic PdII -catalysts that initiate a living ring-expansion polymerization of isocyanides, yielding a single-handed cyclic-helical poly(phenyl isocyanide), with predictable molecular weight (Mn ) and low dispersity (Mw /Mn ), in good yield. Using this method, cyclic bottlebrush polymers were prepared via the grafting-onto strategy. The cyclic topology was confirmed using various spectroscopic data and atomic force microscope observation. Moreover, the cyclic polymer brushes, comprising of a one-handed helical backbone, showed interesting photoluminescence and circularly-polarized luminescence.

Dual-Silane Premodified Silica Nanoparticles-Synthesis and Interplay between Chemical, Mechanical, and Curing Properties of Silica-Rubber Nanocomposites: Application to Tire Tread Compounds.

In silica–rubber based nanocomposites, a single organo-silicon is often used to compatibilize and covalently link silica to rubber. In this work, we have investigated the impact, at micro- and macroscales, of the decoupling of the hydrophobization and the coupling activity of silane by pretreating silica with two different silane chemistries. The first one, a mercaptosilane, is the coupling agent that promotes a covalent link between silica and rubber during the sulfur-mediated vulcanization reaction. The second one, an alkylsilane, aims to improve the silica dispersion. For both kind of silanes, we have varied the chain length and studied at macroscale the dynamic mechanical properties through the key indicators that are E′′ as loss modulus, E′ as storage modulus, and their respective ratio tan δ. The shorter silanes combination yielded an improvement in terms of wet grip indicators with tan δ at 0 °C increasing from 0.205 to 0.237 while maintaining rolling resistance indicators at the same level. We have evaluated the impact of the silane chemistry onto the cross-linking reactivity within the fabricated rubber-based nanocomposites by using moving-dye rheometer measurements (MDR). By purposely using atomic force microscopy (AFM), we have studied the silica dispersion in the matrix and the rubber/silica interface and provided the rationale explanation of the mechanical properties observed at the macroscale. AFM observation pointed out the existence of a soft interface around silica fillers when long alkylsilanes were used. We infer that this interface impacts the polymer–filler dynamic and subsequently affects the mechanical properties of the composite material.

Mechanical Tuning of Aggregated States for Conformation Control of Cyclized Binaphthyl at the Air-Water Interface.

An air-water interface enables molecular assemblies and conformations to be controlled according to their intrinsic interactions and anisotropic stimuli. The chirality and conformation of binaphthyl derivatives have been controlled by tuning molecular aggregated states in solution. In this study, we have tuned molecular aggregated states of monobinaphthyldurene (MBD) by applying different mechanical stimuli to control the conformation at the air-water interface. Density functional theory calculations indicate that MBD exists essentially in two conformations, namely, 1-MBD (most stable) and 2-MBD (less stable). MBD was mechanically dissolved in appropriate lipid matrices using the Langmuir-Blodgett (LB) method, while pure MBD was self-assembled at the dynamic air-water interface in the absence of or by applying vortex motions (vortex LB method). In MBD mixed monolayer, surface pressure-molecular area measurements and atomic force microscopy observations suggest that separate lipids and MBD phases transform to mixed phases induced by the dissolution of MBD into the lipid matrices during mechanical compression at the air-water interface. Circular dichroism measurements indicate that molecular conformation changes from 1-MBD to 2-MBD in passing from a separated phase to a mixed MBD/lipid phase. In addition, the molecular aggregated states and conformations of MBD depend on the spreading volume and vortex flow rate when applying the vortex LB method. Molecular conformations and aggregated states of MBD could be controlled continuously by applying a mechanical stimulus at the air-water interface.

Nanoarchitectonics for Ultrathin Gold Films Deposited on Collagen Fabric by High-Power Impulse Magnetron Sputtering.

Gold nanoparticles conjugated with collagen molecules and fibers have been proven to improve structure strength, water and enzyme degradation resistance, cell attachment, cell proliferation, and skin wound healing. In this study, high-power impulse magnetron sputtering (HiPIMS) was used to deposit ultrathin gold films (UTGF) and discontinuous island structures on type I collagen substrates. A long turn-off time of duty cycle and low chamber temperature of HiPIMS maintained substrate morphology. Increasing the deposition time from 6 s to 30 s elevated the substrate surface coverage by UTGF up to 91.79%, as observed by a field emission scanning electron microscope. X-ray diffractometry analysis revealed signature low and wide peaks for Au (111). The important surface functional groups and signature peaks of collagen substrate remained unchanged according to Fourier transform infrared spectroscopy results. Multi-peak curve fitting of the Amide I spectrum revealed the non-changed protein secondary structure of type I collagen, which mainly consists of α-helix. Atomic force microscopy observation showed that the roughness average value shifted from 1.74 to 4.17 nm by increasing the deposition time from 13 s to 77 s. The uneven surface of collagen substrate made quantification of thin film thickness by AFM difficult. Instead, UTGF thickness was measured using simultaneously deposited glass specimens placed in an HiPIMS chamber with collagen substrates. Film thickness was 3.99 and 10.37 nm at deposition times of 13 and 77 s, respectively. X-ray photoelectron spectroscopy showed preserved substrate elements on the surface. Surface water contact angle measurement revealed the same temporary hydrophobic behavior before water absorption via exposed collagen substrates, regardless of deposition time. In conclusion, HiPIMS is an effective method to deposit UTGF on biomedical materials such as collagen without damaging valuable substrates. The composition of two materials could be further used for biomedical purposes with preserved functions of UTGF and collagen.

Low-temperature preparation of superhydrophilic coatings using tetraethoxysilane and colloidal silica by sol-gel method

In this study, a simple and facile method for producing superhydrophilic coatings by thermal curing at a low temperature of 100 °C or less for 2 h without a calcination process at high temperatures was reported. Hydrophilic coating solutions were prepared using tetraethoxysilane (TEOS) and colloidal silica as precursors by sol-gel method. After applying the prepared coating solution to a glass slide by dip-coating, a superhydrophilic coating was prepared by thermal curing at 100 °C for 2 h. In this process, the effect of the amount and concentration of colloidal silica added to the polysiloxane sol derived from TEOS on the superhydrophilicity of the coatings was observed. The coatings were characterized by water contact angle (WCA) analyzer, FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), and atomic force microscope (AFM). In the coatings prepared using 10 wt% colloidal silica, as the content of colloidal silica added increased to 8 g, 16 g, 24 g, and 40 g, the WCA of the coating decreased to 56°, 37°, 10°, and 5°, respectively. From this result, it can be seen that a superhydrophilic coating, which shows a WCA of 5° or less, can be obtained when 40 g of colloidal silica is added. The FT-IR results suggest that the superhydrophilic coating consists of more hydrophilic components than the coating using only the polysiloxane sol without the addition of colloidal silica. In addition, the superhydrophilic coating showed a rough surface morphology in SEM and AFM observations. It was considered that the superhydrophilicity of the coating was derived from the increase of hydrophilic chemical components and surface roughness by adding colloidal silica. Moreover, the superhydrophilic coating showed an excellent anti-fogging property and a self-cleaning ability.

Atomic force microscopy observation of the effect of laser ablation on the nanostructures of the dentin surface.

An atomic force microscope (AFM) was used to analyze the changes in organic matter in human dentin and the effects of laser irradiation with different energy densities on the surface micro-nanostructures of human dentin. Extracted human third molars were used in this study. Human dentin were scanned with an Er, Cr:YSGG laser (6.18, 8.04, 9.89, 11.1 J·cm-2). The 12 samples were randomly allocated. AFM phase imaging technology and energy-dispersive spectroscopy (EDS) were applied to detect the proportional changes in the organic components on the dentine surface before and after Er,Cr:YSGG laser irradiation. AFM was capable of observing the morphological changes of the dentine surface and hydroxyapatite crystals before and after Er, Cr:YSGG laser irradiation. After laser irradiation, the proportion of collagen with low contrast in the phase images remarkably reduced. Accordingly, the proportion of the inorganic phase significantly increased. EDS results showed that dentine was composed of Ca, P, O, and C and some trace elements of Na, Mg and Cl. After Er, Cr:YSGG laser irradiation, the C, O, and Na contents and C/Ca ratio declined significantly (P<0.05), whereas the Ca and P contents and the Ca/P ratio obviously increased (P<0.05). Irradiating human dentine with an Er, Cr:YSGG laser at varying energy densities from 6.18 to 11.1 J·cm-2 did not significantly influence the inorganic phase structure of the surface dentine layer. However, thermal ablation occurred in the organic component.

Highly effective Q235 steel corrosion inhibition in 1 M HCl solution by novel green strictosamide from Uncaria laevigata: Experimental and theoretical approaches

Traditional corrosion inhibitors are not popular due to high toxicity. Instead, green corrosion inhibitors are appearing. Here, strictosamide as a green corrosion inhibitor was firstly separated from Uncaria laevigata, showing excellent solubility in hydrochloric acid solution. By means of electrochemical test, morphology measurement, and theoretical analysis, the corrosion inhibition ability of strictosamide on Q235 steel in corrosive medium was evaluated. Electrochemical results suggested that strictosamide revealed significant corrosion inhibition efficiency of 94.25% at 25 °C. Moreover, the inhibition effect was still strong with extension of immersion time, and the highest inhibition efficiency reached up to 94.90% for 48 h at 160 mgL−1. After the samples were immersed in the inhibited solution for 24 h, scanning electron microscopy and atomic force microscopy observations indicated that strictosamide was firmly attached to Q235 steel surface by making a protective film. Then, according to X-ray photoelectron spectroscopy results, Fe-N bonds existed on the steel showed the presence of chemisorption between metal ions and strictosamide molecules. Mainly because N atoms were complexed with Fe (II) to form stable complexes attached to the active position on steel. Hence, the stability and compactness of the adsorption film on metal surface were strengthened. Additionally, the inhibition mechanism of strictosamide was illustrated by molecular dynamics. Overall, strictosamide may exhibit the potential to replace the traditional toxic corrosion inhibitors in the industry.

Line-shaped defects: Origin of leakage current in halide vapor-phase epitaxial (001) β -Ga2O3 Schottky barrier diodes

We observed line-shaped defects in halide vapor-phase epitaxial (001) β-Ga2O3 SBDs. Light emission patterns, representing the reverse leakage current, were observed at these line-shaped defects. In atomic force microscopy observations, the line-shaped defects appeared as grooves with a typical depth and width of 113 and 520 nm, respectively. Such defects corresponded to a leakage current of −0.23 μA at −200 V. Simulation results indicated that the electric field, with an intensity of 1.3 MV/cm, was highly concentrated at the bottom of the line defects. According to the cross-sectional scanning transmission electron microscopy analysis, the line-shaped defects were generated from a dislocation network beneath the crystal near the surface.