Atomic Force Microscopy Observations Research Articles

Air-water interfacial properties and quantitative description of pea protein isolate-Tween 20

The air-water interfacial properties of pea protein isolate (PPI) and Tween 20 (T20) were investigated in this study. The result of dynamic foam analyzer showed that the foam prepared by 0.5%PPI-0.1%T20 exhibited higher foam stability at 30 min and uniform bubble size distribution. The protein displacement by Tween 20 at the air-water interface was observed by atomic force microscopy (AFM) through the imaging of Langmuir-Blodgett (LB) films. During the displacement of pea protein isolate by the nonionic surfactant Tween 20, the surface pressure was increased while the complex surface dilatational modulus was decreased. Based on the AFM observations of the LB films, the quantitative analysis indicated the increased protein quantity in the foam network. To be emphasized, the formation of protein network at the plateau border of foams contributed to the increased foam stability. The AFM results showed that the protein at the air-water interface could be replaced by T20, but comparing with the PPI-stabilized foam, the addition of 0.1% T20 could increase the relative quantity of vicilin, thus leading to the increase of interconnected protein network at foam film to improve the foam stability. The research could promote the understanding of protein displacement by Tween 20 at the air-water interface, which could improve the quality of protein-surfactant stabilized foam-based foods.

Investigation of optical properties of zinc oxide nanofilms deposited by electrodeposition technique

Zinc oxide (ZnO) nanofilms were synthesized by electrochemical deposition from a simple aqueous zinc chloride onto indium tin oxide (ITO) substrate. Chronoamperometry experiments were performed to deposit nanofilms at the cathodic potential −1.0 V and time 5000 s at 70°C. Diffraction measurements of x-ray showed the hexagonal wurtzite structure of the as-grown nanofilms and the preferred orientation was along the (002) axis. A well-defined ZnO morphology was generated under −1.0 V for 1000 s on ITO glass. Atomic force microscopy observations explored the effect of electrode coating technique on the microscale ZnO nanofilms. The optical constants and thickness of nanofilms were determined with high precision using spectroscopic ellipsometry. The measurements of photoluminescence demonstrated two emission peaks; the first of which was related to excitonic emissions at about 392 nm, referring to the band gap of ZnO, and the second was related to oxygen vacancies ionized singly at about 490 nm.

Self-oriented anisotropic structure of G-hydrogels as a delicate balance between attractive and repulsive forces.

Guanine (G) hydrogels are very attractive materials made by the supramolecular organization of G-derivatives in water. In this paper, hydrogels composed of guanosine 5'-monophosphate (GMP) and guanosine (Gua), that make long, flexible and knotted G-quadruplexes, were investigated by small- and wide-angle X-ray scattering (SAXS and WAXS) to comprehend the origin of their unique orientational properties. The SAXS intensity, analysed at a fixed scattering vector modulus Q as a function of polar angle, allowed us to derive the Maier-Saupe orientation parameter m. The strong dependence of m on hydrogel composition and temperature demonstrated that the preferred orientation is controlled by the quadruplex surface charge and flexibility. Indeed, a possible correlation between the orientation parameter m and the quadruplex-to-quadruplex lateral interactions was explored. Results confirmed that the balance between attractive and repulsive interactions plays a main role in the orientational anisotropy: quadruplex clusters lose their orientational properties when attractive interactions decrease. The key role of the number of negative charges per unit length of the G-quadruplex filaments was confirmed by Atomic Force Microscopy (AFM) observations. Indeed, directionality histograms showed that in the presence of a large amount of Gua, G-quadruplexes follow preferential orientations other than those related to the strong interactions with the K+ pattern on the mica surface. The fact that lateral quadruplex-to-quadruplex interactions, even in the presence of external (opposing) forces, can tune the hydrogel alignment in a given preferred direction provides novel possibilities for scaffold/3D printing applications.

Metallogels: a novel approach for the nanostructuration of single-chain magnets.

In this study we demonstrate that single-chain magnets (SCMs) can be assembled in gel phase and transferred intact on surface. We take advantage of a family of SCMs based on TbIII ions and nitronyl-nitroxides radicals functionalized with short alkyl chains known to form crystalline supramolecular nanotubes interacting with heptane acting as crystallizing solvent. When the radicals are functionalized with long aliphatic chains a robust gel is formed with similar structural and functional properties respect to its crystalline parent. Indeed, a small-angle X-ray scattering (SAXS) study unambiguously demonstrates that the gel is made of supramolecular nanotubes: the high stability of the gel allows the determination from SAXS data of precise nanotube metrics such as diameter, helical pitch and monoclinic cell of the folded 2D crystal lattice along the tube direction. Additionally, static and dynamic magnetic investigations show the persistence of the SCM behavior in the metallogel. Last, on-surface gelation provides thick films as well as sub-monolayer deposits of supramolecular nanotubes on surface as evidenced by atomic force microscopy (AFM) observations. This paves the road toward magnetic materials and devices made of SCMs profiting of their isolation on surface as individual chains.

Importance of annexin V N-terminus for 2D crystal formation and quick purification protocol of recombinant annexin V.

Annexin V forms trimeric structures which further assemble into two-dimensional crystal (2D crystal) lattices on negatively charged phospholipid bilayer in a Ca2+-dependent manner. It is also known that annexin V 2D crystals show two types of symmetric patterns with six-fold symmetry (p6) and three-fold symmetry (p3). The p6 lattice also contains additional trimers in the gaps between the p6 axes, which are also referred to as non-p6 trimers because they do not participate in the formation of the p6 lattice. We here show that the annexin V N-terminal has significant influence on 2D crystal formation using high-speed atomic force microscopy (HS-AFM) observations. We also present a quick purification method to purify recombinant annexin V without any residual affinity tag after protein purification in ~3h.

Beyond brewing: β-acid rich hop extract in the development of a multifunctional polylactic acid-based food packaging

Hops' (Humulus lupulus L.) phytochemicals are well known for their bioactivity. In the present study, the functional properties of hop extract rich in β-acids, as potassium-salts structures (KBA), were investigated to develop a sustainable active food packaging. Polylactic acid (PLA)-based sheets were incorporated with increasing concentrations of hop extract (0.1–5 % w/w in terms of KBA) and characterized through performance and bioactive properties. KBA-added sheets presented decreased crystallinity and affected mechanical and thermal properties, especially with higher KBA amounts. The sheets' surface hydrophobicity gradually decreased by KBA-extract addition, while the water vapor permeability was not affected. A Fickian diffuse behavior and a better fit to application in fatty foods were observed during release tests. UV-blocking and antioxidant properties were improved by KBA incorporation. Furthermore, results from antibacterial assays revealed great susceptibility of Staphylococcus aureus and Listeria monocytogenes towards sheets added with 5 % of KBA. Moreover, the atomic force microscopy (AFM) observations revealed that KBA led to strong effects on the cell membranes of both bacteria, including disruption of membrane integrity and cell death. Therefore, this study is a sign of great prospects of hop β-acids use, as KBA compound, in the production of sustainable active packaging for safe food shelf-life extension.

Surface morphology evolution of C-plane sapphire during multi-step thermal annealing

The surface morphology evolution of the C-plane (0001) sapphire surface with the 4° miscut angle towards A-plane is thermally annealed at temperatures of 1100 °C and 1200 °C for different dwell times varying between 3-12 hours in multiple steps, resulting in a total of 30 hours. Atomic Force Microscopy (AFM) observations are used to systematically study the effects of the thermal annealing process, temperature, and time on the evolution of the periodicity and step height of structures. The step-terrace structures with straight step-edges along the direction were observed over the entire surface after 3 hours of annealing at 1100 °C. The step-terrace structure morphology evolves through the step-bunching and facet coarsening mechanisms during the multi-step thermal annealing process. Step-bunching begins with the formation of contact points between the adjacent steps by diffusion of atoms. Its onset is associated with a threshold value of the periodicity of step-terrace structures. By varying the annealing temperature during the multi-step thermal annealing process, the evolution of step-terrace structures can be manipulated by delaying the process of step-bunching.

Gelling and emulsifying properties of tiger puffer (Takifugu rubripes) skin gelatin as manipulated by pH

The study investigated the modifications of gelling and emulsifying properties of tiger puffer skin gelatin (TPSG) by varying pH and the possible mechanism behind these modifications. ζ-potential analysis indicated the isoelectric point of TPSG was 6.5, and TPSG solution showed the largest particle size at pH6. Atomic force microscopy observation revealed that TPSG at pH 6 and 7 exhibited large size protein aggregates (370 and 340 nm) while TPSG at pH 4 and 9 showed small size irregular aggregates (<150 nm). FTIR analysis suggested that amide I band of TPSG at pH 6 and 7 was shifted to lower wavenumber. Secondary structure analysis suggested they contained high proportion of α-helix. The highest gel strength and gelling and cooling temperature were observed at pH 6, inconsistent with a gel microstructure characterized with dense network and small voids. Moreover, TPSG at pH 6 and 7 exhibited the lowest emulsion activity index but highest emulsion stability index. However, microscopic analysis found TPSG formed stable and small size emulsion droplets at pH 5 and 8. The results suggest that appropriate pH adjustment would provide good functional properties to TPSG.

The behavior of two indazole derivatives on the copper/sulfuric acid interface in terms of adsorption and corrosion inhibition

BackgroundTo reduce the degree of copper corrosion by the pickling solution, the introduction of organic inhibitors into the pickling solution is a reasonably effective measure.5-fluoro-1H-indazole (5-FIA) and 5‑chloro-1H-indazole (5-CIA) may act as exceptional inhibitors. MethodsBased on experimental and theoretical methods, the antiseptic ability of two indazole derivatives on copper in sulfuric acid was researched. Significant findsThe results of electrochemical experiments show that in the test solution containing 1 mM inhibitors, the corrosion inhibition efficiency (η) of 5-FIA and 5-CIA was 90.4% and 94.3%, respectively, indicating that 5-FIA and 5-CIA have outstanding corrosion inhibition capabilities and their antiseptic effects are in the order of 5-FIA < 5-CIA, which is also confirmed by observations of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Furthermore, both 5-FIA and 5-CIA are mixed-type inhibitors and their adsorption behavior follows Langmuir isothermal adsorption model. The results of X-ray Photoelectron Spectroscopy (XPS), theoretical calculations, and molecular dynamics simulations further reveal the mechanism that 5-CIA has stronger adsorption capacity than 5-FIA.

Nanoindentation hardness of Ge50In4Ga13Se33 chalcogenide glass thin films

Chalcogenide glass semiconductors are widely used in microelectronic, solar cell and other electro-mechanical applications. The mechanical characteristics of Ge50In4Ga13Se33 chalcogenide thin films were investigated using the nanoindentation technique and correlated with their structure and thickness. The amorphous nature of Ge50In4Ga13Se33 films of different thicknesses was assured using X-ray diffraction. Atomic force microscopy (AFM) measurements were performed for the structure and surface morphology analysis of Ge50In4Ga13Se33 films with thicknesses of 376, 538 and 745 nm. The thickness dependence of hardness (H) and Young's modulus (E) of Ge50In4Ga13Se33 thin films was analyzed. The results showed that the surface roughness (Ra) and root mean square roughness(Rq) decreased with increasing film thickness. The mechanical characteristics of Ge50In4Ga13Se33 amorphous films as hardness and Young's modulus increased from 2.13 ± 0.13 to 3.23 ± 0.20 GPa and from 57.99 ± 1.53 to 91.42 ± 3.12 GPa, respectively. The obtained results (H) and (E) were well correlated with the AFM observations.

The evolution of hydrogen bubbles during ion irradiation and annealing in molybdenum for neutral beam injection inductively coupled plasma source

Molybdenum (Mo) is considered as a promising plasma-facing material, which is expected to be used in the manufacture of critical components for the neutral beam injection (NBI) inductively coupled plasma (ICP) source. Hydrogen isotope retention and bubble formation are regarded as the unavoidable issues that degrade the metal properties in the ion source. In this work, the evolution of hydrogen bubbles in Mo pre-irradiated by 35 eV hydrogen ion energy during different annealing processes is studied through conductive atomic force microscopy (CAFM) observation. Meanwhile, the corresponding numerical simulation is applied to analyze the mechanisms of hydrogen bubble growth. It is found that the average size and density of hydrogen bubbles are enhanced with the increase of hydrogen ion fluence at 400 K in experiments and simulations. In the subsequent annealing process, it is demonstrated that annealing temperature has a certain effect on bubble growth and evolution. No obvious changes in bubbles are observed at the annealing temperature below 573 K. The average radius of hydrogen bubbles is increased by ∼1.0-2.5 nm in Mo annealed at 673-873 K. The bubble size increases with the rise of annealing temperature, indicating that the thermal annealing promotes the growth of bubbles. When the temperature rises above 873 K, the change in bubble size is not obvious. The simulation results indicate that temperature-induced changes in the internal pressure of hydrogen bubbles leads to the growth of bubbles, but this mechanism is not significant under high annealing temperatures due to the release of hydrogen from the surface.

Ultra-low Young's modulus Zr-Nb thin films on Mg substrate for enhanced corrosion resistance

Controlling the degradation rate of magnesium (Mg) via applying the (Zr-Nb) thin films was investigated in this study. The Zr-2.5Nb coatings were deposited on the Mg with thicknesses of 250, 450, 650, and 900 nm (hereafter named [email protected], [email protected], [email protected], and [email protected]), respectively. Grazing incidence angle X-ray diffraction of (Zr-Nb) coatings revealed the alpha phase of zirconium and dominant (002) texture, with the film thickness increasing from 450 nm to 900 nm. Potentiodynamic polarization, electrochemical impedance spectroscopy, and corrosion morphology observations in Dulbecco's Modified Eagle's cell culture medium (DMEM) solution revealed the (Zr-2.5Nb)-coated mg with the thickness of [email protected] sample provides the highest corrosion resistance compared to other studied thicknesses. [email protected] sample increases the corrosion potential from −1.49 V to −1.38 V and decreases the current corrosion density and corrosion rate from 149.32 (μA.cm−2) to 39.01 (μA.cm−2) and from 3.49 (mm.y−1) to 0.912 (mm.y−1), respectively. Further studies on the surface of the [email protected] sample in terms of nano-mechanical properties demonstrated that Young's modulus and hardness are 47.95± 4.43 GPa and 2.25± 0.41 GPa, respectively, which increases the hardness to reduced Young's modulus ratio, which is known as one of the important parameters in developing of temporary orthopedic implants, of the Mg from 0.03 to 0.06. Furthermore, nano-tribological measurements and atomic force microscopy observations confirmed that detachment or breakage are not observed. Zr-2.5Nb coating, owing to the influence only on the first stage of the degradation reduced the degradation rate of Mg surafce, and therefore, can be considered as a practical strategy for further development of Mg in orthopedic applications.

Mixing Behavior of the Binary Monolayers of Fatty Acids Based on Their Cohesive Energy Differences.

The morphology involving the height difference and the surface roughness of the binary monolayers of saturated fatty acids were evaluated using atomic force microscopy (AFM) to investigate the mixing behavior of their monolayers. AFM observations revealed that the mixed monolayers of (palmitic acid/arachidic acid) and (arachidic acid/lignoceric acid), which had four methylene group differences between fatty acids, were in a molecularly mixed state. Further, the mixed monolayer of (stearic acid/lignoceric acid), which had six methylene group differences, was in a phase-separated state. From the results of the present and previous studies, it became clear that the difference in the cohesive energy between fatty acids, which corresponds to the enthalpy difference, was an important factor in determining whether the molecular aggregation state of a fatty acid mixed monolayer was in a molecularly mixed or phase-separated state. Moreover, the boundary value of cohesive energy difference was approximately 2.5 kJ mol-1 at a subphase temperature of 293 K.

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.