Atomic Force Microscopy Characterization Research Articles

Insight and control of the chemical vapor deposition growth parameters and morphological characteristics of graphene/Mo2C heterostructures over liquid catalyst

Transition metal carbides is a family of materials with many fascinating properties, especially when studied close to the 2D limit. Molybdenum carbide (Mo2C) is a member of this group which has attracted interest especially thanks to its potential application as electrode in energy storage as well as in catalysis. The latest methods development has demonstrated the potential to grow ultrathin Mo2C domains of high quality through chemical vapor deposition (CVD) over melted substrates, together with graphene. This progress provides new routes towards the preparation of vertical Van der Waals (VdW) heterostructures. In the present work we provide a detailed study of the dominant growth mechanisms of pure Mo2C crystals as well as graphene/Mo2C heterostructures. The findings reveal that the methane flow controls the growth of graphene/Mo2C heterostructures or pure Mo2C domains, while the high growth temperature and presence of hydrogen significantly increase the growth rate. Additionally, the presence of graphene serves as a blocking diffusion layer, permitting the growth of ultrathin crystals and increasing their nucleation density. Atomic Force Microscopy (AFM) characterization demonstrates the growth of stacks of crystals which consist of individual crystals with thickness as low as ∼2 nm.

Preparation and morphology-dependent wettability of porous alumina membranes.

This article presents the preparation and study of the wetting properties of porous alumina membranes (PAMs) with a thickness of 25 to 75 μm and with a different pore sizes. The fabrication process features, scanning electron microscopy and atomic force microscopy characterization results are presented. The comparative analysis of PAM surfaces (outer and inner) and the effect of morphology of these surfaces on the wetting properties are discussed. Both alumina surfaces show significant morphology-dependent wettability. Measurements of the interfacial contact angle were made on the as-fabricated amorphous membrane and after pore widening with a range of pore diameters from 25 to 100 nm. The possible applications of PAMs for various membrane technologies is shown.

AFM nano-mechanical study of the beating profile of hiPSC-derived cardiomyocytes beating bodies WT and DM1.

Myotonic Dystrophy type 1 (DM1) is the most common form of muscular dystrophy in adults, characterized by a variety of multisystemic features and associated with cardiac anomalies. Among cardiac phenomena, conduction defects, ventricular arrhythmias, and dilated cardiomyopathy represent the main cause of sudden death in DM1 patients. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful in vitro model for molecular, biochemical, and physiological studies of disease in the target cells. Here, we used an Atomic Force Microscope (AFM) to measure the beating profiles of a large number of cells, organized in CM clusters (Beating Bodies, BBs), obtained from wild type (WT) and DM1 patients. We monitored the evolution over time of the frequency and intensity of the beating. We determined the variations between different BBs and over various areas of a single BB, caused by morphological and biomechanical variations. We exploited the AFM tip to apply a controlled force over the BBs, to carefully assess the biomechanical reaction of the different cell clusters over time, both in terms of beating frequency and intensity. Our measurements demonstrated differences between the WT and DM1 clusters highlighting, for the DM1 samples, an instability which was not observed in WT cells. We measured differences in the cellular response to the applied mechanical stimulus in terms of beating synchronicity over time and cell tenacity, which are in good agreement with the cellular behavior in vivo. Overall, the combination of hiPSC-CMs with AFM characterization can become a new tool to study the collective movements of cell clusters in different conditions and can be extended to the characterization of the BB response to chemical and pharmacological stimuli.

Influence of growth temperature on structural and optical properties of laser MBE grown epitaxial thin GaN films on a-plane sapphire

Epitaxial thin GaN films (∼60 nm) have been grown on a-plane sapphire substrates at different growth temperatures (500–700 °C) using laser molecular beam epitaxy (LMBE). The effect of growth temperatures on the structural and optical properties of GaN layers grown on low temperature (LT) GaN buffer on prenitridated a-sapphire have been studied systematically. The in situ reflection high energy electron diffraction pattern revealed the three-dimensional epitaxial growth of GaN films on a-sapphire under the adopted growth conditions. The full width at half maximum (FWHM) value of x-ray rocking curves (XRCs) along GaN (0002) and (10-12) planes decreases with increasing growth temperature. The FWHM values of (0002) and (10-12) XRC for the 700 °C grown GaN film are 1.09° and 1.08°, respectively. Atomic force microscopy characterization showed that the grain size of GaN increases from 30–60 to 70–125 nm with the increase in growth temperature as GaN coalescence time is shorter at high temperature. The refractive index value for the dense GaN film grown at 600 °C is obtained to be ∼2.19 at the wavelength of 632 nm as deduced by spectroscopic ellipsometry. Photoluminescence spectroscopy confirmed that the epitaxial GaN layers grown on a-sapphire at 600–700 °C possess near band edge emission at ∼3.39 eV, close to bulk GaN. The GaN growth at 700 °C without a buffer still produced films with better crystalline and optical properties, but their surface morphology and coverage were inferior to those of the films grown with LT buffer. The results show that the growth temperature strongly influences the structural and optical quality of LMBE grown epitaxial GaN thin films on a-plane sapphire, and a growth temperature of >600 °C is necessary to achieve good quality GaN films.

Transforming Monolayer Transition-Metal Dichalcogenide Nanosheets into One-Dimensional Nanoscrolls with High Photosensitivity.

One-dimensional (1D) nanoscrolls derived from two-dimensional (2D) nanosheets own unusual physical and chemical properties that arise from the spiraled 1D morphology and the atomic thin 2D building blocks. Unfortunately, preparation of large-sized nanoscrolls of transition-metal dichalcogenides (TMDCs) remains a big challenge, which greatly restricts the fabrication of single-scroll devices for their fundamental studies and further applications. In this work, we report a universal and facile method, by making use of the evaporation process of volatile organic solvent, to prepare TMDC (e.g., MoS2 and WS2) nanoscrolls with lengths of several tens to one hundred micrometers from their 2D precursors presynthesized by chemical vapor deposition on Si/SiO2. Both atomic force microscopy and electron microscopy characterizations confirmed the spirally rolledup structure in the resulting nanoscrolls. An interlayer spacing of as small as ∼0.65 nm was observed, suggesting the strong coupling between adjacent layers, which was further evidenced by the emergence of new breathing mode peaks in the ultralow frequency Raman spectrum. Importantly, compared with the photodetector fabricated from a monolayer MoS2 or WS2 nanosheet, the device based on an MoS2 or WS2 nanoscroll showed the much enhanced performance, respectively, with the photosensitivity greatly increased up to 2 orders of magnitude. Our work suggests that turning 2D TMDCs into 1D scrolls is promising in achieving high performances in various electronic/optoelectronic applications, and our general method can be extended to the preparation of large-sized nanoscrolls of other kinds of 2D materials that may bring about new properties and phenomena.

Thermally triggered transition of fluid atomized micro- and nanotextured multiscale rough surfaces

Evaluation of fluid atomized spraying process parameters for poly(1,1,2,2-tetrafluoroethylene) coating such as ‘patternation’ influencing on the distribution of droplets inside the spray boundary, air pressure affecting the ‘nozzle flow-rate’, air pressure assisted nozzle flow rate dependent ‘droplet size’, etc. gives state-of-the-art hydrophobicity. The fabricated coating shows the transition from hydrophilic surface to hierarchical rough hydrophobic surface (WCA = 139° ± 3°) at a temperature of 130 °C. Furthermore, the reflex of transition temperature on the hydrophobicity of coated system triggers the fabrication of hierarchical surface morphology culminating the maximum static water contact angle (147° ± 3°) at an optimized temperature of 220 °C. Tailoring of nano-spindles over the multiscaled hierarchical rough surface by the synergistic effect of air-pressure assisted atomization parameters and thermally triggered transition temperature endowing ultimate hydrophobicity. Atomic force microscopy (AFM) characterization of the coating morphology confirms the triggered temperature by demonstrating the nano-spindled structure with RMS roughness (78 nm). Anti-corrosion performance of thermally triggered hydrophobic coating containing ‘air valleys’ has been evaluated by using Tafel polarization curves proclaiming reduction in corrosion rate (0.001 mmpy) in the coated system. The results obtained by the following study possess tremendous potential to tailor-wet characteristics of the nano-textured atomized PTFE coating for diversified naval applications.

Anodic Electrophoretic Deposition of Graphene Oxide on 316L Stainless Steel with pH-Dependent Microstructures

This paper describes anodic electrophoretic deposition of graphene oxide (GO) on 316L SS with pH-dependent microstructures. GO flakes were synthesized by modified Hummers’ method. Detailed studies on structural characteristics, thermal stability, and elemental composition of the GO flakes were carried out using advanced characterization techniques. Results showed successful oxidation and exfoliation forming GO flakes that are hydrophilic in nature. Acidic (pH 3.4) and basic (pH 11) aqueous GO suspensions were prepared, and the zeta potential as well as the average particle size distribution of the suspensions was ascertained. The GO suspensions were exhibiting zeta potential values of −32.9 and −36.8 mV and average particle size of 1–2 µm and 800–900 nm at acidic pH of 3.4 and alkaline pH of 11, respectively. Using anodic electrophoretic deposition (EPD) methods, GO was coated on 316L SS substrate from acidic and alkaline suspension and coatings were characterized. The increased value of ID/IG by Raman spectra analysis, partial restoration of C = C skeleton in the de-convoluted C 1s XPS spectra analysis, and the presence of C–C and C–H stretching bands in ATR-FTIR spectra were correlated with partial reduction of GO during the deposition on 316L SS surface. Though there was no difference in the chemical composition of the coatings formed from the acidic and alkaline pH suspension, atomic force microscopy and field emission scanning electron microscopy characterization showed difference in topography and morphology of the coatings. 316L SS substrates coated with GO in acidic pH showed higher RMS and average roughness and dense agglomerated wrinkled microstructure compared to substrates coated with alkaline pH suspension. Again GO coating from acidic pH suspension showed hydrophobicity. The present study showed that the microstructures of the GO coatings on 316L SS can be tuned by varying the pH of the GO suspension during EPD process.

Crosslinking induces high mineralization of apatite minerals on collagen fibers

Type I collagen, as the critical organic component of bone matrix, plays a template role in mineralization. Gamma-ray irradiation is used to prepare collagen with different crosslinking degrees without introducing foreign substances for mineralization. Significant improvement in crosslinking degree of collagen can be inferred by enzymolysis and differential scanning calorimetry analysis. Scanning electron microscopy observation reveals that, as crosslinking degree increases, the pore structure of collagen becomes more compact. Fourier transform infrared spectroscopy analysis shows the intact retention of classical triple-helical structure of collagen after crosslinking and the following mineralization. Atomic force microscopy characterization, calcium and phosphorus assay kit tests and thermogravimetry measurements indicate that the more compact the collagen structure, the more hydroxyapatite can attach on collagen fibers. These findings reveal the high crosslinking degree of collagen is favorable for the improvement of mineralization ability by providing a more stable and compact network structure. Such crosslinked collagen may provide a more potential way for the preparation of bone substitute materials.

Development of a Perchlorate Chemical Sensor Based on Magnetic Nanoparticles and Silicon Nitride Capacitive Transducer

AbstractWe report in this work the development of a novel capacitance electrochemical sensors based on silicon nitride substrate (Si3N4) chemically modified with a structure of Cobalt phthalocyanine, C,C,C,C‐tetracarboxylic acid‐Polyacrylamide (Co(II)Pc‐PAA). This sensitive layer was tested with and without magnetic nanoparticles (MNP) for perchlorate ( ) detection. The developed chemical sensor with Si3N4/APTES‐MNP/Co(II)Pc‐PAA structure has shown a better performance when compared to the other structure based on Si3N4/Co(II)Pc‐PAA. Contact angle measurements (CAM) and atomic force microscopy (AFM) characterizations have been performed to characterize the functionalization of the chemical sensors surface. Under the optimized structure of the chemical sensor, electrochemical measurements were carried out using Mott‐Schottky analysis for detection within the large range of 10−10 to 10−4 M with a very low detection limit of 2×10−10 M. The chemical sensor has demonstrated a high selectivity toward when compared to other interfering anions such as Cl−, SO42−, and CO32−. The present capacitive chemical sensor is very promising for sensitive and rapid detection of for environmental applications.

Microwave-Assisted Regeneration of Single-Walled Carbon Nanotubes from Carbon Fragments.

Direct growth of chirality-controlled single-walled carbon nanotubes (SWNTs) with metal catalyst free strategy, like cloning or epitaxial growth, has suffered from the low efficiency. The underlying problem is the activation of seed edge. Here an unexpectedly efficient microwave-assisted pathway to regenerate SWNTs from carbon fragments on SiO2 /Si substrate is demonstrated via Raman spectroscopy and atomic force microscope (AFM) characterization. In this attempt, microwave irradiation provides fast heating to remove polar groups bonded to carbon nanotubes and reduce the spontaneous closure of tubes' open ends. The survived SWNT and carbon fragments connected to it after plasma treatment are simply microwaved and then they serve as the template for regeneration. Scanning electron microscope and AFM characterizations indicate that the efficiency of the regeneration can reach 100%. And the regenerated SWNT has been proved without any change in chirality compared to the original SWNT. Electrical measurements on regenerated carbon nanotube films indicate 1 and 2 times increase in on/off ratio and on-state current respectively than original carbon nanotube films obtained from solution-phase separation, confirming the improvement of SWNT's quality. The microwave-assisted regeneration is found to be highly effective and would be applied to improve the cloning efficiency of carbon nanotubes potentially.

Controlling of green nanocellulose fiber properties produced by chemo-mechanical treatment process via SEM, TEM, AFM and image analyzer characterization

Nanocellulose fibers were extracted from Oil Palm Empty Fruit Bunch (OPEFB) fibers by a chemo-mechanical treatment process. The aim of this study is to observe and investigate the morphological structure and fiber dimension characteristic of each stage in the nanocellulose production. The fiber structure characterization of the raw, purified pulps, extracted cellulose and nanocellulose fibers were controlled by observation and investigation under Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Image Analyzer. The morphological observation illustrated that the isolation of nanocellulose fibers had greatly decreased from micron to nanoscale, up to 5-10 nm in diameter, and therefore suitable to be used as quality nano-reinforcement in the polymer matrix for a potential environmental green nanobiocomposites development.

Atomic force microscopy characterisation of alkali-silica reaction products to reveal their nanostructure and formation mechanism

Microscopic studies on alkali-silica reaction (ASR) products revealed two distinct forms of solid ASR products. However, their chemical and morphological aspects have not been adequately understood. This study provides a new insight into the nanostructure of ASR products as examined by atomic force microscopy (AFM). Results reveals that the surface microscale morphology of the rosette-like ASR product is associated with the loss of surface water, and the granular ASR product is formed by the accumulation of nanoscale particles with a typical size of around thirty nanometers. Moreover, the application of AFM provides evidence for the fluid nature of the granular ASR product at high moisture content.

Single-Step Binary Electrostatic Directed Assembly of Active Nanogels for Smart Concentration-Dependent Encryption.

Anionic and cationic (N-isopropylacrylamide derivatives) active colloidal hydrogel nanoparticles, i.e., nanogels, are electrostatically assembled on surfaces to form microscale patterns with complex geometries. While using mixed dispersions of these two kinds of nanogels, we demonstrate the capability of sorting the nanogels in one step to form binary nanogel patterns on a surface. These patterns appear independently or simultaneously depending on the relative proportion of each nanogel type in the mixture. Hence, the resulting nanogel patterns provide quantitative information regarding the dispersion composition and can be used to achieve smart concentration-dependent nanogel encryption. Moreover, atomic force microscopy characterization measurements performed in liquid prove that the assembled nanogels maintain their swelling/deswelling properties once attached to the surface. Consequently, this method paves the way for applying such active nanogel patterns to produce smart coatings and sensors.

Amyloid Beta Peptide VHHQ, KLVFF, and IIGLMVGGVV Domains Involved in Fibrilization: AFM and Electrochemical Characterization.

The time-dependent structural modifications and oxidation behavior of specifically chosen five short amyloid beta (Aβ) peptides, Aβ1-16, Aβ1-28, Aβ10-20, Aβ12-28, and Aβ17-42, fragments of the complete human Aβ1-40 peptide, were investigated by atomic force microscopy (AFM) and voltammetry. The objective was to determine the influence of different Aβ domains (VHHQ that contains electroactive histidine H residues, KLVFF that is the peptide hydrophobic aggregation core, and IIGLMVGGVV that is the C-terminus hydrophobic region), and of Aβ peptide hydrophobicity, in the fibrilization mechanism. The short Aβ peptides absence of aggregation or the time-dependent aggregation mechanisms, at room temperature, in free chloride media, within the time window from 0 to 48 h, were established by AFM via changes in their adsorption morphology, and by differential pulse voltammetry, via modifications of the amino acid residues oxidation peak currents. The first oxidation peak was of tyrosine Y residue and the second peak was of histidine H and methionine M residues oxidation. A correlation between the presence of an intact highly hydrophobic KLVFF aggregation core and the time-dependent changes on the Aβ peptides aggregation was found. The hydrophobic C-terminal domain IIGLMVGGVV, present in the Aβ1-40 peptide, also contributed to accelerate the formation of Aβ1-40 peptide aggregates and fibrils.

Electrochemical and AFM Characterization of G-Quadruplex Electrochemical Biosensors and Applications.

Guanine-rich DNA sequences are able to form G-quadruplexes, being involved in important biological processes and representing smart self-assembling nanomaterials that are increasingly used in DNA nanotechnology and biosensor technology. G-quadruplex electrochemical biosensors have received particular attention, since the electrochemical response is particularly sensitive to the DNA structural changes from single-stranded, double-stranded, or hairpin into a G-quadruplex configuration. Furthermore, the development of an increased number of G-quadruplex aptamers that combine the G-quadruplex stiffness and self-assembling versatility with the aptamer high specificity of binding to a variety of molecular targets allowed the construction of biosensors with increased selectivity and sensitivity. This review discusses the recent advances on the electrochemical characterization, design, and applications of G-quadruplex electrochemical biosensors in the evaluation of metal ions, G-quadruplex ligands, and other small organic molecules, proteins, and cells. The electrochemical and atomic force microscopy characterization of G-quadruplexes is presented. The incubation time and cations concentration dependence in controlling the G-quadruplex folding, stability, and nanostructures formation at carbon electrodes are discussed. Different G-quadruplex electrochemical biosensors design strategies, based on the DNA folding into a G-quadruplex, the use of G-quadruplex aptamers, or the use of hemin/G-quadruplex DNAzymes, are revisited.

Time- and Composition-Dependent Evolution of Distinctive Microstructures in Bitumen

Bitumen’s chemistry often results in complicated intermolecular associations, which are manifested by the diverse microstructures as observed by atomic force microscopy (AFM). These microstructures largely contribute to bitumens’ bulk mechanical properties; therefore, it is essential to understand the chemical–microstructural–mechanical relationships for optimal design of bitumen-related applications. However, the complex nature of bitumen and the various influencing factors often lead to practical challenges in investigation of bitumens’ microstructures and their chemical origins. This study aims at addressing some of the main concerns related to AFM characterization of bitumens’ microstructures, namely the dependence of bitumens’ microstructures on such factors as sample preparation methods, annealing conditions and durations, and chemical composition. Our results suggest that microstructures of bitumen films of a few micrometers or thicker (i.e., the thickness of the asphalt-coating layer over the aggr...

Young’s modulus of multi-layer microcantilevers

A theoretical model for calculating the Young’s modulus of multi-layer microcantilevers with a coating is proposed, and validated by a three-dimensional (3D) finite element (FE) model using ANSYS parametric design language (APDL) and atomic force microscopy (AFM) characterization. Compared with typical theoretical models (Rayleigh-Ritz model, Euler-Bernoulli (E-B) beam model and spring mass model), the proposed theoretical model can obtain Young’s modulus of multi-layer microcantilevers more precisely. Also, the influences of coating’s geometric dimensions on Young’s modulus and resonant frequency of microcantilevers are discussed. The thickness of coating has a great influence on Young’s modulus and resonant frequency of multi-layer microcantilevers, and the coating should be considered to calculate Young’s modulus more precisely, especially when fairly thicker coating is employed.

Morphology and FT-IR analysis of anti-pollution flashover coatings with adding nano SiO2 particles

By adding nano SiO2 particles, an enhanced K-PRTV anti-pollution flashover coating had been prepared. Optical profile meter (GT-K), atomic force microscopy (AFM), infrared spectrometer (FT-IR) and EDS characterization were carried out on the coating surface analysis. Those results has been use to optimize the further design and platform of the enhanced K-PRTV pollution flash coating experiment. It is also to improve the plan formulation, formulation optimization and preparation of the hydrophobic modified K-PRTV which is based on anti-pollution coating experiment. More importantly, the anti-pollution flashover K-PRTV coating with super hydrophobic modified is the great significance for K-PRTV coating.

In situ growth of copper oxide-graphite carbon nitride nanocomposites with peroxidase-mimicking activity for electrocatalytic and colorimetric detection of hydrogen peroxide

This study reported a facile approach for the preparation of copper oxide-graphitic carbon nitride nanocomposites by an in situ growth method in aqueous solution. The powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and atomic force microscopy characterizations of the copper oxide-graphitic carbon nitride nanocomposites suggest that we have successfully synthesized a novel nanozyme. The nano-sized of copper oxide nanoparticles embedded in graphitic carbon nitride nanoparticles were evaluated focusing on the principle of horseradish peroxidase-like activity catalyzing the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine in the presence of hydrogen peroxide. Furthermore, we constructed dual sensor platforms based on copper oxide-graphitic carbon nitride nanocomposites. By constructing an electrochemical platform and a colorimetric sensor to detect hydrogen peroxide, it is shown that copper oxide-graphitic carbon nitride nanocomposites had an excellent peroxidase mimicking catalytic performance. We envision that our nanozyme have great potential in a variety of applications in catalytic field, electrochemical sensing, optical imaging, and environmental assay.

Electrical Homogeneity of Large-Area Chemical Vapor Deposited Multilayer Hexagonal Boron Nitride Sheets.

Large-area hexagonal boron nitride (h-BN) can be grown on polycrystalline metallic substrates via chemical vapor deposition (CVD), but the impact of local inhomogeneities on the electrical properties of the h-BN and their effect in electronic devices is unknown. Conductive atomic force microscopy (CAFM) and probe station characterization show that the tunneling current across the h-BN stack fluctuates up to 3 orders of magnitude from one substrate (Pt) grain to another. Interestingly, the variability in the tunneling current across the h-BN within the same substrate grain is very low, which may enable the use of CVD-grown h-BN in ultra scaled technologies.