Semi-contact Mode Research Articles

ВЛИЯНИЕ ИСКУССТВЕННОГО СТАРЕНИЯ НА ИЗМЕНЕНИЕ ШЕРОХОВАТОСТИ ГЛАЗУРОВАННОЙ И ПОЛИРОВАННОЙ ПОВЕРХНОСТИ ДИОКСИДА ЦИРКОНИЯ: ИССЛЕДОВАНИЕ IN VITRO

Aim: to evaluate the characteristics of glazed and polished surface during hydrothermal aging using different types of zirconium dioxide. 
 Materials and Methods. The same standardized samples from different types of zirconium dioxide with a diameter of 10 mm and a height of 1 mm were used for all experiments. These types included Katana (Kuraray Noritake Dental, Tokyo, Japan) HTML (control) UTML, STML, and ZirCAD Prime (Ivoclar Vivadent). Atomic force microscopy (AFM) was used to measure the roughness and to visualize the surface morphology of the samples. The Bruker Innova instrument was used as an atomic force microscope. Image acquisition was carried out in semi-contact mode. The probe sensor was TESP-V2 with a triangular-shaped probe and a tip radius of 7 nm. The scanning area was 50 x 50 μm. Frequency 0.5 Hz. The study of roughness was reduced to the processing of AFM image data. For this purpose, three arbitrary sections were made in the height map channel and the necessary roughness parameters Ra, Rz were calculated using software.
 Results. There was an increase in roughness during artificial aging of the control group of glazed surface, Prime group of polished surface, and Prime group of glazed surface. There is a decrease of roughness in the process of artificial aging of the control group of glazed surface, for STML and UTML groups of both glazed and polished surface. In the case of samples of group "polishing" it is possible to observe that roughness is formed by traces of abrasive material. From the results of the study of roughness it can be noted that for the samples of the group "Glaze" roughness is formed mainly by traces of brush or other tools used in the process of glaze application
 Conclusion. Artificial aging affects the roughness of the glazed and polished surface of zirconium dioxide with cubic phase predominance depending on the amount of yttrium content.

Electrostimulation and Nanomanipulation of Two-Dimensional MoO3-x Layers Grown on Graphite

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO3 monolayer.

Featuring exfoliated 2D stacks into fractal-like patterns in WS2/carboxy methyl cellulose nanocomposites

We report on the formation of fractal-like structures with 2D layer support derived from exfoliated WS2 stacks in cellulose environment (NaCMC, sodium carboxymethyl cellulose). Morphological features and surface topography are studied on 1–4 wt.% WS2/NaCMC nanocomposite films by employing high resolution scanning electron microscopy (HR-SEM) and atomic force microscopy (AFM) employed in semi-contact mode. The development of termite-like, fractal patterns in the nanocomposites can be visualized from the micrographs. Using a box-count method, we predict bi- and tri-modal fractals in the background of 2D, giving out asymmetric shapes in the dimension vs. frequency curves. While typical fractal dimension reduces from 1.98 to 1.6 with increasing WS2 content, the AFM images exhibited an evenly spread rough units while giving a root mean square (RMS) roughness of σ = 66.5 nm, for 4 wt.% specimen. Moreover, Raman analysis exhibited an augmented in-plane (E12g ∼350 cm−1) to out-of-plane (A1g ∼418 cm−1) intensity ratio with an increase in WS2 loading. Also, the intensities of individual Raman modes were found to vary nonlinearly with an increase in concentration of WS2(1-16%) being dispersed in cellulose-based polymer. Furthermore, the force constants are estimated using vibrational frequencies observed in the fourier transform infrared (FTIR) spectra which predict several orders of higher strength in W−S relative to S−S, depending on stretching or bending vibrations. The hexagonal, 2H phase of WS2 system with prominent (002) diffraction plane along the c-axis representing crystalline nature in the composites can be seen from the XRD patterns. Association of fractal-like textural patterns in 2D is expected to draw implications in advanced sensing, antifouling, photo-catalysis, energy storage etc.

Fabrication of probe tips via the FIB method for nanodiagnostics of the surface of solids by atomic force microscopy

In this work, we carried out an investigation of commercial atomic force microscope (AFM) probes for contact and semi-contact modes, which were modified by focused ion beam (FIB). This method was used to modify the original tip shape of silicon AFM probes, by ion-etching and ion-enhance gas deposition. we show a better performance of the FIB-modified probes in contrast with the non-modified commercial probes. These results were obtained after using both probes in semi-contact mode in a calibration grating sample.

Study of Langmuir monolayers and Langmuir-Schaefer films based on symmetrical meso-aryl-substituted porphyrin derivative

This paper presents the results of a study of meso-aryl-substituted porphyrin Langmuir monolayers by the method of compression isotherms. Experimental data were used to plot the dependences of the compression modulus (C−1) on the specific area. Monolayers at specific surface pressure were transferred to solid substrates and investigated. The monolayers were transferred to the surface of monocrystalline silicon at surface pressures of 8, 25, and 60 mN/m and examined them by atomic force microscopy (AFM) in a semi-contact mode. It was found that with an increase in the transfer pressure, the coarsening of molecular aggregates occurs. The smallest roughness is observed for a porphyrin film formed and transferred at a pressure of 8 mN/m.

Exploring Nanomechanical Properties of Soot Particle Layers by Atomic Force Microscopy Nanoindentation

In this work, an experimental investigation of the nanomechanical properties of flame-formed carbonaceous particle layers has been performed for the first time by means of Atomic Force Microscopy (AFM). To this aim, carbon nanoparticles with different properties and nanostructures were produced in ethylene/air laminar premixed flames at different residence times. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. An experimental procedure based on the combination between semi-contact AFM topography imaging, contact AFM topography imaging and AFM force spectroscopy has been implemented. More specifically, a preliminary topological characterization of the samples was first performed operating AFM in semi-contact mode and then tip-sample interaction forces were measured in contact spectroscopy mode. Finally, semi-contact mode was used to image the indented surface of the samples and to retrieve the projected area of indents. The hardness of investigated samples was obtained from the force–distance curves measured in spectroscopy mode and the images of intends acquired in semi-contact mode. Moreover, the Young’s modulus was measured by fitting the linear part of the retraction force curves using a model based on the Hertz theory. The extreme force sensitivity of this technique (down to nNewton) in addition to the small size of the probe makes it extremely suitable for performing investigation of mechanical properties of materials at the nanoscale. The experimental procedure was successfully tested on reference materials characterized by different plastic behavior, e.g., polyethylene naphthalate and highly oriented pyrolytic graphite. Both hardness and Young’s modulus values obtained from AFM measurements for different soot particle films were discussed.

Semicontact AFM Mode for Fast Determining the Subsurface Structure of Filled Elastomers

Using atomic force microscopy in the semicontact AFM mode, we examined the surface of the filled elastomer obtained by the rupture method. A feature of the material is that it consists of a soft binder and hard nanofiller particles. Filler particles are usually hidden by a binder layer. In our work, we have shown that the information on the phase shift obtained during scanning makes it possible to look into the subsurface layer and obtain more information about the geometry of the filler particles and their location in the nanocomposite. It is possible to make visible the fragments of particles immersed in the binder, which are almost invisible on the surface relief. This does not require the use of special modes of the atomic force microscope for analysis. It is enough to use the reliable and fast scanning method in semicontact mode.

Indentation of soft material containing filler particles

The work is devoted to the study of the features of the interaction of the atomic force microscope probe with a soft elastomeric material containing hard particles of nanofiller. In experimental studies of materials using the nanoindentation mode of AFM, the main result is the curves describing the dependence of the cantilever bend on the probe penetration depth. The indentation can be carried out on a set of points on the material surface and a map of the stiffness distribution can be obtained. The semi-contact mode is most often used in practice to study the relief of an elastomeric nanocomposite. To obtain a correct interpretation of the data, the use of mathematical models is required. An important element of these models is the dependence of the elastic resistance force on the depth of the probe penetration into the material.The paper presents solutions to the problems of indentation of Neo-Hookean material in the formulation of plane deformations. The inclusions were presented as round particles. Solutions are obtained for the cases of indentation near filler particles of different sizes and with different depths of their location under the surface. Computational experiments have shown that by the response to the probe indentation into the material, we can obtain additional information (about the shape and depth of the inclusions), which can be used in the analysis of the material structure data maps.

Determining the Specific Activity of Anti-Rabies Sera and Immunoglobulin Using Atomic Force Microscopy of Cell Cultures.

Background:Mouse neutralization test is widely used to determine the level of anti-rabies antibodies, but it is labor-intensive and time consuming. Alternative methods for determining the neutralizing activity of anti-rabies sera and immunoglobulin in cell cultures are also known. Methods such as FAVN and RFFIT involve the use of fluorescent diagnostics. Determination of Cytopathic Effect (CPE) is often complicated due to features of rabies virus replication in cells. Atomic Force Microscopy (AFM) is able to detect the interaction of the virus with the cell at an early stage. Therefore, in this study, a method has been developed for determining the specific activity of anti-rabies sera and immunoglobulin using AFM of cell cultures.Methods:The method is based on the preliminary interaction of rabies virus with samples of rabies sera or immunoglobulin drug, adding the specified reaction mixture to cell culture (Vero or BHK-21), and then measuring the surface roughness of the cells using AFM. AFM was carried out in the intermittent contact mode by the mismatch method in the semi-contact mode. The results were compared with the values obtained in the mouse neutralization test. The consistency of the results obtained by both methods was evaluated by Bland-Altman method.Results:The increment in the surface roughness of the cells is a consequence of the damaging effect of the virus, which is weakened as a result of its neutralization by rabies antibodies. A dilution allowing 50% suppression of the increase in the surface roughness of cells was selected as the titer of rabies sera or immunoglobulin. In this case, the recommended range for determining the antibody titer is from 1:100 to 1:3000.Conclusion:For the first time, a new methodological approach in virology and pharmaceutical research is presented in this study. The use of the proposed methodological technique will reduce the time from 21 to 2 days to obtain results in comparison with the mouse neutralization test; also, fewer laboratory animals are required in this approach which is in agreement with 3 R Principle.

Investigation of the fracture structure of a composite material after bending test by atomic force microscopy

The paper presents the results of a study of the surface fracture tested for bending at negative temperatures of a ferrite-martensite composite (FMC) obtained on the basis of K 02704 structural hypoeutectoid steel by atomic force microscopy. Metallographic studies of the sample were carried out on longitudinal sections. Investigations of microstructures were performed on optical microscopes Metam RV-22 and Neophot-21. Impact bending tests were carried out in accordance with ISO 148-1:2016. The quantitative assessment of martensite was carried out using the digital imaging program and amounted to 30%. A three-dimensional image of the fracture of the sample surface was obtained by atomic force microscopy (Nanoeducator II) in the semi-contact mode. An AFM study of the fracture surface showed that the data of optical and atomic force microscopy are in agreement. The three-dimensional AFM image of the surface fracture and its profiles, extracted in different areas, as well as the roughness parameters, show the presence of a dual line structure in steel.

Морфология поверхности полимеров с молекулярными отпечатками на основе полиимида

В работе получены полимеры с молекулярными отпечатками бензоата натрия на поверхности электродов пьезосенсоров. Широкое использование консервантов в пищевой промышленности спо-собствует развитию экспресс-методов их анализа модифицированными пьезосенсорами. Цель работы: анализ морфологии поверхности полимеров с молекулярными отпечатками, полученных на основе полиимида методом сканирующей силовой микроскопии.Полимеры с молекулярными отпечатками получены на основе сополимера диангидрида 1,2,4,5-бензолтетракарбоновой кислоты с 4,4'-диаминодифенилоксидом, производства ОАО МИПП НПО «Пластик», г. Москва. В качестве темплата использовали бензоат натрия. Предполимеризацион-ную смесь наносили на поверхность электродов пьезосенсоров шпателем или методом штампования. Проводили термоимидизацию в сушильном шкафу в два этапа: первый этап проходил при 80oС, вто-рой – при 120oС. После полимеризации пленки, сенсоры охлаждали до комнатной температуры, затем помещали их в дистиллированную воду на 24 часа для удаления шаблона.Исследование морфологии поверхности полученных полимерных пленок проводили с помо-щью сканирующего силового микроскопа (ССМ) «Solver P47 PRO» производства ЗАО «НТ-МДТ» в полуконтактном режиме зондом NSG03 с жесткостью 1.74 Н/м. Обработку изображений проводили программой ФемтоСкан-001.Анализ морфологии поверхности пленок показал, что нанесение предполимеризационной смеси штампом приводит к формированию более равномерной поверхности с перепадом высот от 1.4 до 2.6 нм. Использование шпателя приводит к формированию более шероховатой поверхности с вы-сотами в диапазоне 0.9-3.4 нм. Таким образом предложенная методика нанесения смеси является пер-спективной поскольку позволяет получать более воспроизводимые по толщине и шероховатости по-верхности, что позволит повысить точность анализа веществ пьезосенсорами модифицированными этими полимерами.При этом следует учесть, что при формировании полимерной пленки молекулы-шаблона ча-стично или полностью заглубляются в матрицу полимера, а также располагаются на ее поверхности, образуя глобулярные структуры. Экстракция шаблона с поверхности полимера приводит к появлению полостей комплементарных молекулам бензоата натрия.

Opportunities provided by use of Atomic Force Microscopy for studying Invertebrates hemocytes in training biology students

Atomic Force Microscopy provides for probing of cellular characteristics, such as elasticity of cell membranes, adhesion between the probe and the sample, microrelief of cell surfaces, and linear dimensions of cells, including their height. In our study we utilized Atomic Force Microscopy to measure physical parameters of blood cells of invertebrates within the framework of the process of education of biology students. In order to measure elasticity and adhesion, we used an Atomic Force Microscope Integra Vita NT-MDT, and cells were scanned in semi-contact mode. We used NSG3 (NT-MDT) silicon tips with hardness of 1.4 N/m, curvature radius of 10 nm. Young’s modulus describes elastic properties of the cell membrane. For hemocytes of invertebrates, this parameter computed at different points of the same cell varied significantly. The difference between the greatest and the smallest values suggests that computation of mean elasticity for hemocytes of invertebrates is not informative. It is a well-known fact that Young’s moduli computed for central and peripheral portions of a cell are different, and, thus, in this study the values were grouped by their location. The experiment revealed no difference between elastic properties of central and peripheral portions of blood cells of invertebrates.

The use of the atomic force microscopy to investigate the structure of steel 14G2

In this work, we investigated the structure of doeutectoid steel 14G2, which is mainly used for welded structures. Two methods were used to analyze the structure of this steel: optical microscopy (Metam RV-22 and Neophot - 21) and atomic force microscopy (PHYWE Compact AFM) using the semicontact mode. The investigation of the microstructure of steel was carried out for two samples obtained by different heat treatment. The first sample was quenched in water and subsequent low-temperature tempering and had a uniform troost-martensitic structure. The second sample was quenched from the intercritical interval with subsequent low-temperature tempering and had a stitch structure. The results of studying the microstructure of both samples of steel 14G2 are presented. The analysis of AFM images made it possible to establish the geometric parameters of the structural components, to estimate their shape, relief, roughness, and fractal dimension of surface.

АСМ-АНАЛИЗ ПОВЕРХНОСТИ ПРОФИЛИРОВАННОЙ СУЛЬФОКАТИОНООБМЕННОЙ МЕМБРАНЫ ПОСЛЕ КОНТАКТА С ФЕНИЛАЛАНИНОМ

Методом атомно-силовой микроскопии исследована неоднородность поверхности профилированной сульфокатионообменной мембраны после химического кондиционирования и контакта с водными растворами фенилаланина. Определены микропрофили, гистограммы плотности распределения значений высот и cтaндaртные aмплитудные пaрaметры шерoхoвaтocти поверхности oбрaзцoв мембрaны МК-40пр. Установленные различия в структуре, вoзрacтaние oднoрoднocти пoверхнocти мембрaны пocле кoнтaктa c аминокислотой связано с уменьшением количества и размеров макропор и крупных дефектов поверхности вследствие сорбции аминокислоты.
 
 Работа выполнена при финансовой поддержке РФФИ (проект № 18-08-01260).
 АСМ-изображения поверхности мембраны были получены на оборудовании Центра коллективного пользования Воронежского государственного университета. URL: http://ckp.vsu.ru.

Investigations of reconstruction of passivation layer on stainless steel surface using AFM-based techniques

Abstract Continuous development of stainless steel technology forced by the increase in the growing demands on the operating parameters of various stainless steel alloys, is the motivation for implementation of research for understanding the complexity of electrochemical processes ongoing on the surface of a material during various technological processes and during exploitation of the finished components. In this paper, the use of atomic force microscopy (AFM) is presented as a tool for observation of reconstruction process of passivation layers on the surface of previously electropolished stainless steel. For this purpose, a technique called nanoscratching was used, in which scratches are made on the surface of a material by means of diamond scanning probe, which violates the continuity of the passivation layer. Then, the dynamics of the process of reconstruction of that layer was assessed using continuous imaging of the scratched area in AFM semicontact mode. Studies of this type can be used to evaluate the impact of various factors on the spontaneous reconstruction of the passivation layer as well as possible susceptibility of the material on the course of corrosion processes initiated as a result of mechanical defects arising during operation of the material. By using the AFM, it was possible to observe changes in the depth of scratches with a subnanometer resolution. Obtained results proved that the presented AFM application allowed observation of the dynamics of passivation layer reconstruction process in a quantitative fashion, therefore it seems to be a very useful tool in the investigation of the impact of various conditions on this phenomenon. The results showed that changes in surface modification were occurring in a continuous manner. Changing dynamics of said process was presented. It should be underlined that no such experiments have been reported so far.

New Opportunities of Atomic Force Microscopy Probes upon Polyaniline Functionalization

NSG01 industrial atomic force microscope probes were functionalized by the electrically conductive polymer, polyaniline, during in situ oxidative polymerization of aniline at the probe point, which was confirmed by scanning electron microscopy. The quality of the deposited polymer can be controlled by measuring the resonance frequency of the gauge during functionalization. The comparative test of the probes prior to and after functionalization was performed using a TGT01 calibration grate, as well as on a special polyaniline test layer with a complex nanosized morphology in the semicontact mode of surface relief study and the phase contrast mode. Local current spectroscopy showed that the functionalized probe can be converted repeatedly from the conducting to nonconducting state owing to a reversible change in the conductivity of the polymer coating.

Local Anodic Oxidation of Thin GeO Films and Formation of Nanostructures Based on Them

The process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide (R0) significantly increases and the time of starting the oxidation (t0) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.

The research of the influence of heavy metal ions on the aggregation of humic substances on the mica by atomic force microscopy

The conformation of molecules of humic substances of peats sorbed on hydrophilic mica in the absence and presence of heavy metal ions was studied by atomic-force microscopy in semi-contact mode in an aqueous medium. A model of the lignin-carbon complex is proposed, which ensures the conformation of the three-dimensional ring structure of humic substances depending on pH and allows accurate description of the surface structure of humic substances. The sizes of single globular molecules of humic substances were determined: 140-320 nm in diameter and 5-25 nm in height. Possible ways of the interaction of humic substances of peats with metal cations (Pb 2 + and Zn 2 +) with account of conformational changes of humic substances have been established. It has been proven that lead cations are sorbed mainly on the surface of humic molecules, and sorption of zinc cations proceeds with reorientation of humic substances around zinc ions.

Исследование процесса локального анодного окисления тонких пленок GeO и создание наноструктур на их основе

AbstractThe process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide ( R _0) significantly increases and the time of starting the oxidation ( t _0) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.

Formation features and AFM studies of the silicon-chitosan-containing glycerohydrogel surface

Hybrid glycerohydrogels based on silicon tetraglycerolate and chitosan were produced by means of one-pot sol-gel synthesis. The influence of the component composition (the concentration of the template and precursor), the low-molecular-weight accelerator (NaCl), and the conditions of the process (pH, temperature) on the gelling duration was estimated. The glycerohydrogel surface microrelief was visualized by AFM in the semi-contact mode and the standard roughness parameters were calculated. The silicon-chitosan-containing glycerohydrogels were established to have a complex surface relief. Their solid sol-gel matrix is characterized by a uniform distribution of elements of the inorganic phase and a developed microporous structure with amorphous-crystalline ordering. The scale of the surface irregularities, as well as their structural and morphological features and the crystallinity degree of the solid sol-gel matrix, are determined by the template/precursor weight ratio and the molecular weight of the polymer.