Atomic Force Microscopy In Conjunction Research Articles

Nanoscale visualization of high-angle misorientations in quartz-rich rocks using SEM-EBSD and Atomic Force Microscopy

High-angle misorientations can significantly influence material properties. In this study, optical microscopy, Scanning Electron Microscope-Electron Backscatter Diffraction (SEM-EBSD), and Atomic Force Microscopy (AFM) have been used to investigate high-angle misorientations in quartz-bearing crustal rocks. Thin sections of high-grade quartzofeldspathic rocks were subjected to chemical mechanical polishing (CMP) with colloidal silica. In quartz, high-angle misorientations like random high angle grain boundaries (RHAGBs) and Dauphiné twin boundaries (DTBs) could be discriminated using EBSD techniques but not optical microscopy. In nanoscale AFM images, indented channels are observed along RHAGBs but not DTBs; these result from material removal during CMP, indicating lower compactness of RHAGBs compared to DTBs. Along any RHAGB, EBSD reveals different misorientations across segments between consecutive RHAGB-DTB intersections. Grains adjacent to these RHAGB segments have angles between their c-axes varying from 61-66° with parallel {101‾2} planes, and 81–84° with parallel {112‾2} planes, respectively. These symmetries represent the Japan and Sardinian twin laws of quartz, indicating that the RHAGB segments become low-energy twin boundaries, thereby reducing the overall surface energy of the aggregate. Finally, these results suggest that apart from surface topography quantification and high-resolution nanoscale imaging, AFM in conjunction with SEM-EBSD can be used for precisely locating sites for TEM study.

Modification of a Polymer Surface by Partial Swelling Using Nonsolvents.

Surface modification without changing the physical properties in the bulk is of pivotal importance for the development of polymers as devices. We recently proposed a simple surface functionalization method for polymer films by partial swelling using a nonsolvent and demonstrated the incorporation of poly(2-methoxyethyl acrylate) (PMEA), which has an excellent antibiofouling ability, only into the outermost region of a poly(methyl methacrylate) (PMMA) film. We here extend this technology to another versatile polymer, polystyrene (PS). In this case, PS and PMEA have different solubility parameters making it difficult to select a suitable solvent, which is a nonsolvent for PS and a good solvent for PMEA, unlike the combination of PMMA with PMEA. Thus, such a solvent was first sought by examining the swelling behavior of PS films in contact with various alcohols. Once a mixed solvent of methanol/1-butanol (50/50 (v/v)) was chosen, PMEA chains could be successfully incorporated at the outermost region of the PS film. Atomic force microscopy in conjunction with neutron reflectivity revealed that chains of PMEA incorporated in the PS surface region were well swollen in water. This leads to an excellent ability to suppress the adhesion of platelets on the PS film.

Correction: Analysis of long dsRNA produced in vitro and in vivo using atomic force microscopy in conjunction with ion-pair reverse-phase HPLC.

Correction for 'Analysis of long dsRNA produced in vitro and in vivo using atomic force microscopy in conjunction with ion-pair reverse-phase HPLC' by Alison O. Nwokeoji, et al., Analyst, 2019, 144, 4985-4994.

Triboelectric Nanogenerator Based on Biocompatible and Easily Available Polymer Films

AbstractWe have fabricated robust triboelectric nanogenerators (TENGs) employing different polymer films which are biocompatible and easily available. The combination of polyurethane and PTFE layers is seen to provide the highest TENG parameters with an open circuit peak‐to‐peak output voltage of ∼33.5 V and a current value of 27.4 μA with a gentle tapping force of 0.33 N. The topography of the film surface has been characterized using atomic force microscopy in conjunction with image analysis. We find a very good, albeit non‐linear, correlation between the TENG electrical output and the surface roughness. Our studies do not support any relation between the permittivity of the medium and the TENG output. Employing cellulose acetate and Kapton as the triboelectric layers, we have constructed a simple force sensor, whose output is seen to be highly linear over a large range of force varying from 0.24 to 5.2 N, and a significantly high output of 1.5 V/N.

Layered Structure and Complex Mechanochemistry Underlie Strength and Versatility in a Bacterial Adhesive.

ABSTRACTWhile designing synthetic adhesives that perform in aqueous environments has proven challenging, microorganisms commonly produce bioadhesives that efficiently attach to a variety of substrates, including wet surfaces. The aquatic bacterium Caulobacter crescentus uses a discrete polysaccharide complex, the holdfast, to strongly attach to surfaces and resist flow. The holdfast is extremely versatile and has impressive adhesive strength. Here, we used atomic force microscopy in conjunction with superresolution microscopy and enzymatic assays to unravel the complex structure of the holdfast and to characterize its chemical constituents and their role in adhesion. Our data support a model whereby the holdfast is a heterogeneous material organized as two layers: a stiffer nanoscopic core layer wrapped into a sparse, far-reaching, flexible brush layer. Moreover, we found that the elastic response of the holdfast evolves after surface contact from initially heterogeneous to more homogeneous. From a composition point of view, besides N-acetyl-d-glucosamine (NAG), the only component that had been identified to date, our data show that the holdfast contains peptides and DNA. We hypothesize that, while polypeptides are the most important components for adhesive force, the presence of DNA mainly impacts the brush layer and the strength of initial adhesion, with NAG playing a primarily structural role within the core. The unanticipated complexity of both the structure and composition of the holdfast likely underlies its versatility as a wet adhesive and its distinctive strength. Continued improvements in understanding of the mechanochemistry of this bioadhesive could provide new insights into how bacteria attach to surfaces and could inform the development of new adhesives.

Direct Correlation between Molecular Cross‐linking and Macroscopic Mechanical Properties for Green Solids of Deoxyribonucleic Acids

AbstractDouble‐stranded deoxyribonucleic acids (DNAs) were intermolecularly cross‐linked using 2,5‐hexanedione under reductive amination conditions in aqueous phase. Cross‐linking points between DNAs were directly observed by atomic force microscopy in conjunction with a conventional gel electrophoresis analysis. While DNA chains near cross‐linking points were denatured, DNA chains not near cross‐linking points maintained B‐form double strands. A transparent and self‐supported film of cross‐linked DNA (DNA‐c) was obtained by a simple solvent‐casting method. The tensile properties of DNA‐c films were much better than those of non‐cross‐linked DNA (DNA‐n) films due to the presence of the cross‐linking portions. Structural analyses based on wide‐angle X‐ray diffraction measurements revealed that the reorientation of DNA‐c was remarkably restricted by the introduction of cross‐linking points.

Atomic force microscopy and cells: Indentation profiles around the AFM tip, cell shape changes, and other examples of experimental factors affecting modeling.

We use atomic force microscopy in conjunction with a fluorescence microscope capable of optical sectioning to acquire images of white blood cells while force is applied with the AFM tip. The indentation profile within the cell is compared to the profile of the AFM tip: examples are shown for indentations at the center of the cell which are reasonable matches to the tip profile, and an additional example is shown for an indentation that is on the tilted side of a highly rounded cell and that differs from the tip shape. We also demonstrate that the AFM tip can interact with internal cell structures, we show that the contact area between the cell and the substrate can increase under applied pressure, that the main body of the cell can fuse with the extended lamellipodium, and that the cell can be displaced laterally by the AFM tip. The features illustrated here are relevant to the interpretation of indentation experiments that measure cell elasticity properties, as is discussed briefly.

Bending stiffness and interlayer shear modulus of few-layer graphene

Interlayer shear deformation occurs in the bending of multilayer graphene with unconstrained ends, thus influencing its bending rigidity. Here, we investigate the bending stiffness and interlayer shear modulus of few-layer graphene through examining its self-folding conformation on a flat substrate using atomic force microscopy in conjunction with nonlinear mechanics modeling. The results reveal that the bending stiffness of 2–6 layers graphene follows a square-power relationship with its thickness. The interlayer shear modulus is found to be in the range of 0.36–0.49 GPa. The research findings show that the weak interlayer shear interaction has a substantial stiffening effect for multilayer graphene.

Electrocatalysis-induced elasticity modulation in a superionic proton conductor probed by band-excitation atomic force microscopy.

Variable temperature band-excitation atomic force microscopy in conjunction with I-V spectroscopy was used to investigate the crystalline superionic proton conductor CsHSO4 during proton exchange induced by a Pt-coated conductive scanning probe. At a sample temperature of 150 °C and under an applied bias <1 V, reduction currents of up to 1 nA were observed. Simultaneously, we show that the electrochemical reactions are accompanied by a reversible decrease in the elastic modulus of CsHSO4, as seen by a contact resonance shift, and find evidence for superplasticity during scanning. These effects were not observed in the room-temperature phase of CsHSO4 or in the case of catalytically inactive conductive probes, proving the utility of this technique for monitoring electrochemical processes on the nanoscale, as well as the use of local contact stiffness as a sensitive indicator of electrochemical reactions.

Preparation of a polyvinylidene fluoride membrane material probe and its application in membrane fouling research

To improve the understanding and elucidate the fouling behavior of a polyvinylidene fluoride (PVDF) membrane, a PVDF membrane material probe was fabricated by sintering PVDF microspheres onto the free end of a cantilever with the aid of self-assembly devices. Foulant-coated colloidal probes were prepared by adsorbing foulants onto the surface of the PVDF microspheres that had been sintered onto the cantilever. Mixtures of the most widespread foulants of SA, HA and HA/SA were used as model organic foulants. The intermolecular forces between the membrane and the foulant and among the foulants themselves were investigated by atomic force microscopy (AFM) in conjunction with the PVDF probe and foulant-coated probe, respectively. Corresponding membrane fouling experiments were also performed to confirm the applicability of the probes made by the methods described above. The results indicate that there is a close relationship between the intermolecular adhesion forces (foulant–membrane and foulant–foulant) and the flux reduction rate and extent in the fouling filtration stage. The PVDF–foulant and foulant–foulant interaction forces measured by AFM in conjunction with the PVDF probe and the foulant-coated probe, respectively, are an effective means to provide useful information for the technology choice of membrane modification, feed water pretreatment and membrane cleaning.

Thickness dependent effects of solubility and surface phenomena on the hydrogen transport properties of sputtered Pd77%Ag23% thin film membranes

The hydrogen solubility and permeation in Pd77%Ag23% membranes have been determined as a function of temperature and membrane thickness. Unexpectedly, the solubility of hydrogen is found to systematically increase as the membrane thickness decreases from 11.2 to 2.2µm. Topography studies by atomic force microscopy in conjunction with previously reported characterization suggest linkage of the hydrogen solubility to the density of grain boundaries. A higher average grain boundary density for thinner membranes results from the nucleation and growth proceeding during membrane fabrication by sputtering. For the membranes and conditions (no membrane pretreatment; 300–400°C; ΔpH2≤200kPa) applied here, surface phenomena affect the hydrogen transport at thicknesses below ~5µm. Determination of the solubility constants hence allowed the extraction of the bulk diffusivity parameters from the permeability measurements over the thicker membranes (6.7–11.2µm), in good agreement with reported values obtained using other techniques.

Fibroblast extracellular matrix and adhesion on microtextured polydimethylsiloxane scaffolds.

The immediate physical and chemical surroundings of cells provide important biochemical cues for their behavior. Designing and tailoring biomaterials for controlled cell signaling and extracellular matrix (ECM) can be difficult due to the complexity of the cell-surface relationship. To address this issue, our research has led to the development of a polydimethylsiloxane (PDMS) scaffold with defined microtopography and chemistry for surface driven ECM assembly. When human fibroblasts were cultured on this microtextured PDMS with 2-6 µm wide vertical features, significant changes in morphology, adhesion, actin cytoskeleton, and fibronectin generation were noted when compared with cells cultured on unmodified PDMS. Investigation of cellular response and behavior was performed with atomic force microscopy in conjunction with fluorescent labeling of focal adhesion cites and fibronectin in the ECM. Changes in the surface topography induced lower adhesion, an altered actin cytoskeleton, and compacted units of fibronectin similar to that observed in vivo. Overall, these findings provide critical information of cell-surface interactions with a microtextured, polymer substrate that can be used in the field of tissue engineering for controlling cellular ECM interactions.

Identifying polyvinylidene fluoride ultrafiltration membrane fouling behavior of different effluent organic matter fractions using colloidal probes

The interaction forces between effluent organic matter (EfOM) fractions and membrane were measured by atomic force microscopy in conjunction with self-made membrane material colloidal probes. The inter-EfOM-fraction and intra-EfOM-fraction interactions were investigated using corresponding EfOM-fraction-coated colloidal probe. We combined this analysis with corresponding fouling experiments to identify the EfOM fractions responsible for polyvinylidene fluoride (PVDF) ultrafiltration membrane fouling. Results show that hydrophilic and hydrophobic fractions were the dominant fractions responsible for membrane fouling and flux decline in the initial and later filtration stages, respectively, which was mainly attributed to the stronger PVDF-hydrophilic fraction and intra-hydrophobic-fraction interaction forces. This phenomenon, in conjunction with the fact that each interaction force of PVDF–EfOM fraction was stronger than corresponding intra-EfOM-fraction force, suggests that the elimination of the PVDF-hydrophilic fraction interaction force is the best strategy for controlling EfOM fouling. Moreover, the inter-EfOM-fraction interaction force was mainly controlled by the corresponding intra-EfOM-fraction interaction forces. And, while the membrane–EfOM fraction and intra-EfOM-fraction interactions for each type of EfOM fraction are equivalent, the EfOM fractions with the molecular weight smaller than the molecular weight cutoff of the membranes used were mainly responsible for membrane fouling rather than the relatively high-molecular-weight fractions.

POSS-Enhanced Phase Separation in Air-Processed P3HT:PCBM Bulk Heterojunction Photovoltaic Systems

Nanoparticles have been shown in some cases to improve phase separation and morphology in bulk heterojunction organic photovoltaic cells. In this study, the effect of incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules of different structures in air processed poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) films and photovoltaic cells was evaluated. Morphology and composition of the nanoscalephase-separated domains were determined via conductive atomic force microscopy in conjunction with nanomechanical mapping and Raman imaging. UV-vis and fluorescence spectroscopy analysis of the films was performed at different stages of the process and with different levels of solvent vapor and thermal annealing. It was found that POSS molecules of selected structures provided enhancement in morphology control in films, translating to improvements in fill factor and power conversion efficiency of laboratory-scale OPV cells. The findings indicate the potential for further improvements in solar cell performance with specifically tailored POSS/polymer phase-separated systems.

Solar Cells: Effects of Impurities on Operational Mechanism of Organic Bulk Heterojunction Solar Cells (Adv. Mater. 12/2013)

The front cover shows the effect of chemical impurity on the charge generation in the donor phase and the electron transport in the acceptor phase of an organic solar cell. Using photoconductive atomic force microscopy in conjunction with transient absorption spectroscopy and charge transport study, Thuc-Quyen Nguyen and co-workers investigate on page 1706 whether differing impurity shapes may lead to different loss mechanisms.

Effects of Impurities on Operational Mechanism of Organic Bulk Heterojunction Solar Cells

Photoconductive atomic force microscopy in conjunction with transient absorption spectroscopy and charge transport study were used to investigate the effect of impurities (TCNQ and PC84 BM) on the performance of low band gap conjugated polymer and fullerene solar cells to gain insight into whether differing impurity shapes may lead to different loss mechanisms.

Structural, optical, electrical, and low temperature thermoelectric studies on the ordered vacancy compound AgGa3Se5

AbstractPolycrystalline thin films of the ordered vacancy compound AgGa3Se5 were prepared by a multisource vacuum coevaporation technique at a substrate temperature of 623 K. X‐ray diffraction and atomic force microscopy in conjunction with energy‐dispersive analysis of X‐rays and X‐ray photoelectron spectroscopy were used for the structural, morphological, and compositional characterization. The distortion parameter and the anion displacement deduced from the X‐ray diffraction data using the CTB plus η = ηtet rule were used for obtaining the anion–cation bond lengths. The compound manifested a slight increase in the nonideal anion displacement compared to AgGaSe2. The films with ternary chalcopyrite structure were found to possess an enhanced direct allowed bandgap of ∼1.8 eV compared to that in AgGaSe2 indicative of the slightly reduced p–d interband repulsion due to the periodic introduction of silver vacancies. The electrical resistivity was assessed to be of the order of 10−1 Ω m with n‐type conductivity and the films exhibited good photosensitivity. An unusual increase in Seebeck coefficient was manifested in the low‐temperature range 4–330 K with negligible phonon drag toward the very low and room temperature regime.

Photo-induced effects on self-organizedTiO2 nanotube arrays: the influence of surface morphology

Self-organized TiO2 nanotubes with packed, vertically aligned morphology and different lateralcharacteristics were grown on Ti metal substrates by controlled electrochemicalanodization in phosphate/HF and ethylene glycol/HF electrolytes. The wetting,photo-induced superhydrophilicity, and photocatalytic activity of the nanotubularmaterials were investigated under ultraviolet irradiation. The photoactivity of theTiO2 nanotube arrays was analysed in terms of their morphological characteristicsthat were determined by means of scanning electron microscopy and atomicforce microscopy in conjunction with geometrical modelling. The wetting andthe UV-induced superhydrophilicity could be accordingly modelled by theCassie–Baxter mode arising from the large scale roughness of the nanotubulararrays in combination with the Wenzel mode due to the small scale roughnessinduced by ridges at the outer tube surface. The photocatalytic activity of theTiO2 nanotube arrays was further found to correlate quantitatively with thevariation of the geometric roughness factor, verifying the strong impactof morphology on the photo-induced properties of the vertically orientedTiO2 tubular architecture.

Geometric Characterization of Carbon Nanotubes by Atomic Force Microscopy in Conjunction with a Tip Characterizer

An atomic force microscopy (AFM) probe tip characterizer with 14 line and space structures and two knife edges was fabricated by means of a superlattice technique. The shape of a probe tip both before and after AFM imaging was acquired by this tip characterizer with general variations <1.5 nm; depending on imaging conditions. The geometric structures of carbon nanotubes (CNTs) on a SiO2 substrate were studied by dynamic mode AFM in conjunction with this tip characterizer. Contact points between the tip and the CNTs were detected by observing changes in the AFM phase images. A modified CNT width correction model was established to calculate the estimated and upper-limit widths of two CNTs. The experimental results showed that imaging under a weak attractive force was suitable for obtaining accurate CNT height measurements, whereas a weak repulsive force provided the most accurate widths. Differing heights and widths between the two CNTs suggested that one CNT was double-walled, whereas the other had more than two walls; these results agree with transmission electron microscopy (TEM) measurements of the CNTs.

Imaging aspects of cardiovascular disease at the cell and molecular level.

Cell and molecular imaging has a long and distinguished history. Erythrocytes were visualized microscopically by van Leeuwenhoek in 1674, and microscope technology has evolved mightily since the first single-lens instruments, and now incorporates many types that do not use photons of light for image formation. The combination of these instruments with preparations stained with histochemical and immunohistochemical markers has revolutionized imaging by allowing the biochemical identification of components at subcellular resolution. The field of cardiovascular disease has benefited greatly from these advances for the characterization of disease etiologies. In this review, we will highlight and summarize the use of microscopy imaging systems, including light microscopy, electron microscopy, confocal scanning laser microscopy, laser scanning cytometry, laser microdissection, and atomic force microscopy in conjunction with a variety of histochemical techniques in studies aimed at understanding mechanisms underlying cardiovascular diseases at the cell and molecular level.