Atomic Force Microscopy Methods Research Articles

An integrated microscopical study of surface properties and surface effects in superprotonic (K1-x(NH4)x)3H(SO4)2 crystals

Surface properties of superprotonic (K1-х(NH4)x)3H(SO4)2 (x ≥ 0.57) single crystals and their evolution under humidity were studied by optical polarization microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDXS). Traditional method of atomic force microscopy (AFM) and sophisticated methods such as Kelvin probe force microscopy (KPFM) and scanning capacitance force microscopy (SCFM) were also used. Fresh and aged cleavage surfaces perpendicular and parallel to the c axis of the trigonal superprotonic phase were examined. The effect of air humidity on the surface morphology, surface conductivity, surface potential and surface capacitance was studied. The influence of material composition and surface orientation was considered. During ageing for 430 h, the (001) sample surfaces, initially stepped, were smoothened, surface electric potential changed from negative greater than a hundred of millivolts in absolute value to positive of about 80 mV, and a modified layer containing new crystal phases was formed.

Conductivity, its anisotropy and changes as a manifestation of the features of the atomic and real structures of superprotonic [K1-x(NH4)x]3H(SO4)2 crystals.

Single crystals of [K1-x(NH4)x]3H(SO4)2 (x ≥ 0.57) grown in the K3H(SO4)2-(NH4)3H(SO4)2-H2O water-salt system are studied. The atomic structure including H atoms was determined at room temperature using X-ray structural analysis. [K1-x(NH4)x]3H(SO4)2 (x ≥ 0.57) crystals have trigonal symmetry and disordered hydrogen-bond networks at ambient conditions similar to the high-temperature phases of K3H(SO4)2, (NH4)3H(SO4)2 and other superprotonic compounds M3H(AO4)2. Impedance measurements performed on single crystals show high values of conductivity characteristic for superprotonic phases. Using the methods of impedance spectroscopy and atomic force microscopy, a significant anisotropy of the conductivity of crystals has been detected. It was also shown that there is a qualitative correlation of bulk and local conductivity measured for samples of the same composition and orientation at room temperature, which is due to the peculiarities of their crystal structure.

Atomic force microscopy of anisotropic silicone magnetoactive composites

New anisotropic magnetically active elastomers using carbonyl iron micrometer size ferromagnetic fillers in the silicone matrix were synthesized. Samples with orientation of the outer magnetic field strength vector applied in perpendicular or in parallel direction to the mold surface during polymerizing composite mass were investigated. These composites surface structure was studied using the topography and phase contrast images in the atomic force microscope. Significant surface magnetodeformation effects in these composites, comparable with Terphenol-D, under the application of small external magnetic fields were visualized by atomic force microscopy methods. The transverse magneto-deformation constant value was determined for both samples. Greatly periodically deformed surface structure background was observed in these composites. The obtained experimental results analysis show that significant component of these materials unique properties is due to the ferromagnetic fillers restructuring in both isotropic and anisotropic magnetically active composites under small external magnetic fields influence.

ВЛИЯНИЕ МОЩНОГО ИОННОГО ПУЧКА НА МОРФОЛОГИЮ ПОВЕРХНОСТИ И СВОЙСТВА ИЗДЕЛИЙ ИЗ СЕРЕБРА

In this work, using a combination of optical, electron and atomic force microscopy methods, we study the effect of modifying silver products with a powerful nanosecond ion beam or changing the morphology of their surface layers and operational properties (susceptibility to blackening and scratching). It has been established that exposure to an ion beam contributes to a significant reduction in the number of scratches on the surface of silver items while they are worn, which is presumably due to a change in the morphology of the surface of the irradiated samples. In addition, it was discovered that exposure to a powerful ion beam reduces the rate of blackening of silver.

Study of microgeometry of hardened surfaces of lathe teeth of loom using atomic force microscopy method

The article presents the results of an experimental study of the microgeometry of the surfaces of the teeth of the lathe of looms, the working surfaces of which are hardened by shot-blasting with microballs in order to increase the resistance of the contact surfaces to wear. Atomic force microscopy was used to study the height parameter of roughness and the transformation of the microrelief in comparison with the initial state in the course of operating time under operational loads.

Особенности формирования тонких пленок алюминия под воздействием ультразвуковых колебаний подложки

Atomic force and scanning electron microscopy methods were used to study aluminum thin films grown on sitallic substrates. This study is the first to show that ultrasonic vibrations of the substrate during deposition stimulate the formation of islands on the film surface. However, the average height and lateral dimensions of the islands are not significantly affected by ultrasonic perturba-tions of the substrate.

The coefficient of friction and Hamaker constants of cementitious materials

• AFM was used to directly determine the Hamaker constants of cementitious materials. • Material characteristics affected the Hamaker constant and coefficient of friction. • The higher the Hamaker constant, the higher the coefficient of friction. • The recommended values can help to accurately calculate inter-particle forces. The friction and adhesion forces between particles are key factors affecting the flowability of cementitious materials (CMs). However, typical values are absent for common CMs due to the limitations of testing methods and the complexity of material components. In this paper, the Atomic Force Microscopy (AFM) and direct shear method were proposed to measure the Hamaker constants and coefficient of friction (COF) directly. The measured Hamaker constants and COF of limestone powder, silica fume, Type I Portland cement, ground granulated blast furnace slag, and fly ash ranged from 7.59 to 18.19×10 -20 J, and 1.06 to 1.36, respectively. Results also indicate a positive relationship between the Hamaker constant and COF. These recommended values can help to accurately calculate interaction forces for single or blend CMs and optimize their storage and transportation.

Effect of 10 MeV electron irradiation on the electrical properties of bulk α-In2Se3 crystals.

In this work, the effect of 10 MeV electron irradiation on the structure and electrical properties of bulk α-In2Se3 crystals is studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray microanalysis, atomic-force microscopy, and Raman spectroscopy methods. Droplets of 200-500 nm in size were detected on the bulk α-In2Se3 crystal surface. The droplets can be formations with the γ-In2Se3 crystalline phase. The current-voltage characteristics measured by conductive atomic-force microscopy are different on and outside the droplets after electron irradiation. On the droplets, slightly better conductive properties were detected after irradiation with the electron fluence of 1015 cm-2. It is found that local resistance increases significantly for both on and outside the droplets after irradiation with the electron fluence of 1017 cm-2. Our study shows that electron irradiation can contribute to the disappearance of ferroelectric domains in the bulk α-In2Se3 crystals. Also, the distribution of surface potentials measured by Kelvin probe force microscopy becomes more uniform after electron irradiation. The results obtained in the work allow us to calculate the operating time of the device containing α-In2Se3 under conditions of long-term electron irradiation with high-energy electrons. The study shows that α-In2Se3 is a very promising material for applications in the aerospace and nuclear industries.

Атомно-силовая микроскопия растянутых резин

Atomic force microscopy (AFM) is a powerful tool for studying the structural-mechanical proper-ties of polymers and polymer composites. Modern AFM methods provide not only a 3D-image of the surface but also its physical and mechanical properties. Elastomeric vulcanizates and their composites are widely used in tire industry. In this work, unfilled and filled (5, 30, 50 wt. parts of carbon black) rubbers in the tensile state, including open cracks, were investigated by the method of rapid nanoindentation. The defects in the stretched polymer matrix in the vicinity of the inclu-sions are shown. A binder oriented along the axis of deformation in the gaps between the filler inclusions forms strand-like structures. The stress-strain state of the stretched polymer is heterogene-ous. The stiffness of the polymer in the strands exceeds that of the surrounding matrix, i.e., the strands take the main load. At the same time, weakly loaded matrix areas shielded from load by filler inclusions are present in the material. Adjacent filler aggregates retain their relative position during stretching, and the strands appear in the filler-free areas. In the notch made in the stretched rubber, the polymer is in a critically stretched state – a slightest increase in stretching will lead to further crack propagation. In this case, an overstretched area up to 10 m wide having local defects and strands appears along the axis of the crack. The stiffness of the matrix in this region is hun-dreds of times greater than in the initial material, which indicates deformations many times greater than macroscopic ones.

Cr2O3 Doping Effect on Silica Glass Cooling Rate

In this paper we present the results on the effect of the SiO2 melt cooling rate on the morphology of its surface. The method of atomic force microscopy explores a surface roughness of the silica glass cooled at different rates after its heating up to more than 2100 °C. The study compares three modes of cooling glass rods with a diameter of 14 mm: convective heat exchange with the surrounding air, quenching with dropping the sample into a vessel with water, and radiation of silica glass doped with 0.1 wt% Cr2O3. The surface roughness of silica glass in the second and third modes of cooling was significantly less than in the conditions of convective heat exchange. Doping the silica glass with Cr2O3 increases the heat exchange coefficient by 2 times and decreases the surface roughness. The results of the research can contribute to improving the mechanical and optical properties of silica glass light guides.

Microstructural Analysis of Collagenous Structures in Relapsed Clubfoot Tissue

Abstract Talipes equinovarus congenitus (clubfoot) is frequently defined as a stiff, contracted deformity, but few studies have described the tissue from the point of view of the extracellular matrix, and none have quantified its mechanical properties. Several researchers have observed that clubfoot exhibits signs of fibrosis in the medial side of the deformity that are absent in the lateral side. Our study aims to quantify the differences between the medial and lateral side tissue obtained from relapsed clubfoot during surgery in terms of the morphological and mechanical properties of the tissue. Combining methods of optical and atomic force microscopy, our study revealed that the medial side has a higher Young’s modulus, contains more collagen and less adipose tissue and that the collagen fibers propagate at a higher frequency of the crimp pattern after surgical dissection of the tissue. Our study offers a multi-correlative approach that thoroughly investigates the relapsed clubfoot tissue.

Laser Cladding Treatment to Enhance the Corrosin Resistance and Surface Hardness by Electrophoretic Coatings to A283 Steel

Laser cladding (LC) is a laser-based surface modification technology that has been widely adopted for the development of thin layers that operate under harsh conditions. Corrosion contributes to approximately 50% of oil and refinery equipment failures. These major risks require sophisticated methods to improve oil equipment performance. LC promotes the generation of superior properties on the substrate surface, which improves service life. To reduce corrosion failure and enhance life cycles, we conducted electrophoretic deposition (EPD) of Ti and Ni powders and directly coated them on A283 steel alloy, which was alloyed by ND-YAG LC and the remelted surface of A283 steel alloy. The microstructure, element distribution and phase analysis of the cladding sample were studied by optical microscopy, field-emission scanning electron microscopy, X-ray energy-dispersive spectrometry, atomic force microscopy and X-ray diffraction methods. The results indicated that the coatings with fine metallurgical bonding to the substrate comprised major stable FeTi and FeNi and illustrated two different regions of solidification microstructures. The LC process and powder feeding by EPD were applied, which improved the mechanical properties, corrosion behaviour, phase transformation and structural optimisation of the surface microstructure of the laser mixed zone. Melting of the coated sample showed that the coating produced by laser treatment had a smooth top surface. In addition, we have a proven case of surface treatment with a laser that delivered the required performance. Moreover, this treatment is a more environmentally friendly alternative to traditional surface preparation treatments.

Polygalacturonates of Biogenic Metals - Prospective Components of New Composite Preparations for Wheat

New bi- and polymetallic complexes of polygalacturonic acid with essential trace elements for pre-sowing treatment of winter wheat seeds were created.
 Aims: The goal of the research was to create effective environmentally safe preparations of multifunctional action, with low cost rates for grain crops based on natural polymers of pectin nature and to determine the effectiveness of their use for pre-sowing treatment of winter wheat seeds.
 Methodology: Methods of chemical synthesis of products, research of their structure by atomic force microscopy were used in the work. Laboratory and vegetative experiments were carried out. The substrate is quartz sand. Physiological and biochemical methods were used to determine the working absorbing surface of the roots and its absorbing activity, amylolytic activity, the content of photosynthesis pigments according to Wellburn. The results were processed using the methods of mathematical statistics.
 Results: The atomic force microscopy method made it possible to detect a mixture of individual polymer molecules and their aggregates in pectin fractions. Depending on the concentration of pectins in the solution, they form different structures. New bi- and polymetallic complexes of polygalacturonic acid with essential trace elements for pre-sowing treatment of winter wheat seeds were created. According to the results of laboratory and vegetation experiments, the growth-stimulating activity of polygalacturonates of copper, iron, calcium, and nickel, which were used for pre-sowing processing of Smuhlyanka variety winter soft wheat seeds was determined. Preparations contribute to the active development of the root system of plants, strengthening their physiological activity. The investigated compounds are effective promising components of complex compositional preparations for modern agrotechnologies of winter wheat cultivation. 
 Conclusion: The use of such metal complexes at an insignificant rate of expenditure should contribute to the increase of economic and ecological indicators of crop production — the reduction of the cost price of wheat grain due to the increase in yield and grain quality.

Dewetting Behavior of Random Copolymer Films Induced by Solvent Vapor Annealing.

In recent years, the dewetting behavior of block copolymer films has been studied a lot, but that of random copolymer films was rarely studied. In this study, effects of film thickness and solvent vapor annealing duration (0 s-24 h) on the dewetting behavior of the spin-coated poly(styrene-co-acrylonitrile) (SAN) random copolymer films were mainly investigated by atomic force microscopy and contact angle method for the first time. The film thicknesses of the SAN films prepared at different concentrations were characterized by X-ray reflectometry to be 6-34 nm. With the annealing of acetone vapor, the SAN films first appear holes and then rupture into droplets which fuse and break periodically. The periodic evolutions of the droplets are due to the preferred affinity of acetone molecules with the AN segments and the change of surface energy. This phenomenon is different from the single evolutions in the spin-coated polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films. This illustrates the interactions between AN segments and the substrate are stronger than those between PMMA segments and the substrate in the spin-coated films.

Atomic Force Microscopic Imaging of mRNA-lipid Nanoparticles in Aqueous Medium

The efficacy of mRNA-lipid nanoparticles (mRNA-LNPs) depends on several factors, including their size and morphology. This study presents a new technique to characterize mRNA-LNPs in an aqueous medium using atomic force microscopy (AFM). This method utilizes an anti-polyethylene glycol antibody to immobilize mRNA-LNPs onto a glass substrate without corruption, which cannot be avoided with conventional procedures using solid substrates such as mica and glass. The obtained AFM images showed spherical and bleb-like structures of mRNA-LNPs, consistent with previous observations made using cryo-transmission electron microscopy. The AFM method also revealed the predominant existence of nanoparticles with a diameter < 60 nm, which were not detectable by dynamic light scattering and nanoparticle tracking analysis. As mRNA-LNPs are usually not monodisperse, but rather polydisperse, the AFM method can provide useful complementary information about mRNA-LNPs in their development and quality assessment.

Nanoscale surface dynamics of RF-magnetron sputtered CrCoCuFeNi high entropy alloy thin films

High entropy alloy (HEA) thin films of CrCoCuFeNi are grown on stainless steel substrate using radiofrequency (RF) magnetron sputtering method at different sputtering times (30, 60 and 90 minutes), substrate temperatures (room temperature, 100 and 200 deg. Celsius) and RF powers (100, 150 and 200 W). The nanoscale morphology and topography of the thin films are obtained using an atomic force microscopy (AFM) method. The average surface roughness, interface width, fractal and multifractal characteristics of the films are presented. It is shown that the average surface roughness and interface width decrease with the time of deposition while considering the combination of the other factors. The autocorrelation and height-height correlation functions reveal that these surfaces are self-affine and exhibit fractal characteristics. The increase in sputtering power, with different combinations of time and temperature, is related to large fractal dimension and small lacunarity coefficient. The increase in substrate temperature (for different combinations with time and RF power) is shown to enhance the spatial roughness of the HEA thin films. A multifractal analysis undertaken using generalized fractal dimension, mass exponent against moment order and multifractal spectrum reveal that all the films have a multifractal character; and the films deposited at high temperatures and powers exhibit the strongest multifractal behaviour.

Self-Assembled Monolayers of Molecular Conductors with Terpyridine-Metal Redox Switching Elements: A Combined AFM, STM and Electrochemical Study

Self-assembled monolayers (SAMs) of terpyridine-based transition metal (ruthenium and osmium) complexes, anchored to gold substrate via tripodal anchoring groups, have been investigated as possible redox switching elements for molecular electronics. An electrochemical study was complemented by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) methods. STM was used for determination of the SAM conductance values, and computation of the attenuation factor β from tunneling current-distance curves. We have shown that SAMs of Os-tripod molecules contain larger adlayer structures compared with SAMs of Ru-tripod molecules, which are characterized by a large number of almost evenly distributed small islands. Furthermore, upon cyclic voltammetric experimentation, Os-tripod films rearrange to form a smaller number of even larger islands, reminiscent of the Ostwald ripening process. Os-tripod SAMs displayed a higher surface concentration of molecules and lower conductance compared with Ru-tripod SAMs. The attenuation factor of Os-tripod films changed dramatically, upon electrochemical cycling, to a higher value. These observations are in accordance with previously reported electron transfer kinetics studies.

Nanoscale chemomechanical variations of montmorillonite induced by the specificity of counterions—An in situ XRD and AFM study

The variable structural characteristics of montmorillonite (Mnt) in salt solutions depend not only on the quantity and distribution of the Mnt layer charge, but also on the specificity of counterions, including their radius, valence, concentration, and hydratability. In order to determine the nanoscale chemomechanical processes in a clay mineral–water–salt system, in situ X-ray diffraction (XRD) and atomic force microscopy (AFM) methods were used to investigate the structural variations of Mnt caused by different counterion species (e.g., Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, and Sr2+) at different concentrations (0.2–3.0 M). With an increasing concentration of counterions, separation of water molecules from the interlayer space of more weakly hydrated cations (Cs+, Rb+, and K+) is faster than for the more strongly hydrated cations (Li+, Na+, Mg2+, Ca2+, and Sr2+), water molecules are lost more slowly from the hydration shell, which remains stable even at high counterion concentrations. The sequential ion exchange in a monolayer Mnt observed by in situ AFM is consistent with the d(001) results from the real-time XRD analysis. Moreover, various defects on Mnt surfaces were visible in the high-resolution AFM images, which restrict the spatial arrangement of adsorbed cations. The water molecule partitioning between the interlayers in Mnt is controlled by the specificity of the counterions, and the cations can spontaneously form ordered structures on the surface of Mnt. These nonclassical interfacial phenomena occurred in the electric double layer (EDL) is controlled by the hydration of counterions, the surface structure and the charge distribution of Mnt.

Sol-Gel Derived Silica-Titania Waveguide Films for Applications in Evanescent Wave Sensors-Comprehensive Study.

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their optical properties are studied using ellipsometry and UV-Vis spectrophotometry. Optical losses are determined using the streak method. The material structure and chemical composition, of the silica-titania films are analyzed using transmission electron microscopy (TEM) and electron dispersive spectroscopy (EDS), respectively. The surface morphology was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods. The results presented in this work show that the waveguide films are amorphous, and their parameters are stable for over a 13 years. The optical losses depend on their thickness and light polarization. Their lowest values are less than 0.06 dB cm-1. The paper presents the results of theoretical analysis of scattering losses on nanocrystals and pores in the bulk and interfaces of the waveguide film. These results combined with experimental data clearly indicate that light scattering at the interface to a glass substrate is the main source of optical losses. Presented waveguide films are suitable for application in evanescent wave sensors.

Mechanism of Multi-Stage Degradation in Hot Bitumen of Micronized Powder Elastomeric Modifiers from Worn-Out Tire's Rubber.

For the first time, by atomic force microscopy (AFM) methods, micro- and nanofragments of micronized powder elastomeric modifier (PEM) formed at the short-term (3 min at 160 °C) interaction of PEM with hot bitumen have been demonstrated. It is the technology of high-temperature shear-induced grinding of a worn-out tire’s crumb rubber or its co-grinding with styrene–butadiene–styrene (SBS) block copolymer which provides the creation of the PEM structure inclined to rapid degradation in hot bitumen. The formation just after the preparation process of a new structure of a modified binder, more resistant to external effects, is supported by the data of rheological tests. Performance tests for a modified binder using Superpave standard adopted by the road industry for bituminous binders showed an extended temperature range, resistance to rutting, and low-temperature and fatigue cracking. The better resistance to low-temperature and fatigue cracking is certainly related to energy absorption and crack growth stopping in the presence of micron and submicron resilient PEM fragments in accordance with the mechanism of increasing impact toughness in plastics.