Atomic Force Microscope Phase Images Research Articles

Separation performance enhancement of PEEKWC/PEI cross-linked ultrafiltration membranes by poly(ethylene glycol) and polyvinylpyrrolidone as polymeric additives

In order to improve both pure water flux and retention rate of the cross-linked ultrafiltration membranes based on phenolphthalein-based poly(ether ether ketone) (PEEKWC) and polyethyleneimine (PEI), poly(ethylene glycol) (PEG) and polyvinylpyrrolidone (PVP) were used as polymeric additives in non-solvent-induced phase separation process. The characterizations, separation effectiveness, and anti-fouling performance of membranes were investigated. Compared with n-butanol additive, the PEG and PVP could accelerate the phase separation rate and form thinner and denser skin layer, and then that led to an increase in the fluxes of pure water and better dye retention performance. In addition, the impact of variable additive dosage on the pure water flux and retention for dye solutions was investigated, and the pure water flux of membranes could reach 3270.8 L·m−2·h−1 and 2494.5 L·m−2·h−1 at a PEG or PVP concentration of 0.5 wt%, respectively. These membranes also exhibited excellent retention performance for Coomassie brilliant blue and Congo red greater than 98%. The simultaneous improvement of pure water flux and retention performance also could be related to the more efficient water transmission channel forming which was investigated by atomic force microscope phase images. In anti-fouling performance tests, the membranes demonstrated effective anti-fouling properties with a high flux recovery ratio after external cleaning with water only.

Modulation of magnetic anisotropy through self-assembled surface nanoclusters: Evolution of morphology and magnetism in Co–Pd alloy films

In this study, the self-assembly of surface nanoclusters on 10–20-nm-thick Co50Pd50 (Co–Pd) alloy thin films deposited on the Al2O3(0001) substrate was systematically investigated. The time-dependent evolution of the nanocluster size and magnetic properties was monitored using an atomic force microscope (AFM) and the magneto-optical Kerr effect. When the Co–Pd alloy films were stored in an ambient environment, small nanodots gradually gathered to form large nanoclusters. Approximately 30 days after growth, a nanocluster array formed with an average lateral size of 100±20nm and average height of 10±3nm. After 100 days, the average lateral size and average height had increased to 140±20 and 25±5nm, respectively. The AFM phase image exhibited a structured contrast on the nanocluster surface, indicating the nonuniform stiffness distribution of the nanoclusters. A microscopic Auger spectroscopy measurement suggested that in contrast to the Pd-rich signal in the flat area, the nanoclusters were cobalt- and oxygen-rich areas. Cross-sectional investigation through transmission electron microscopy coupled with energy dispersive spectroscopy showed that the nanoclusters were mostly composed of Co oxide. A uniform Pd-rich underlayer had been maintained underneath the self-assembled Co-oxide nanoclusters. With the formation of a Co-oxide nanocluster array and Pd-rich underlayer, the magnetic easy axis of the Co–Pd film gradually altered its direction from the pristine perpendicular to in-plane direction. Because of the change in the magnetic easy axis, the hydrogenation-induced spin-reorientation transition was suppressed with the evolution of the surface Co-oxide nanoclusters.

Centimeter-Scale CVD Growth of Highly Crystalline Single-Layer MoS2 Film with Spatial Homogeneity and the Visualization of Grain Boundaries.

MoS2 monolayer attracts considerable attention due to its semiconducting nature with a direct bandgap which can be tuned by various approaches. Yet a controllable and low-cost method to produce large-scale, high-quality, and uniform MoS2 monolayer continuous film, which is of crucial importance for practical applications and optical measurements, remains a great challenge. Most previously reported MoS2 monolayer films had limited crystalline sizes, and the high density of grain boundaries inside the films greatly affected the electrical properties. Herein, we demonstrate that highly crystalline MoS2 monolayer film with spatial size up to centimeters can be obtained via a facile chemical vapor deposition method with solid-phase precursors. This growth strategy contains selected precursor and controlled diffusion rate, giving rise to the high quality of the film. The well-defined grain boundaries inside the continuous film, which are invisible under an optical microscope, can be clearly detected in photoluminescence mapping and atomic force microscope phase images, with a low density of ∼0.04 μm-1. Transmission electron microscopy combined with selected area electron diffraction measurements further confirm the high structural homogeneity of the MoS2 monolayer film with large crystalline sizes. Electrical measurements show uniform and promising performance of the transistors made from the MoS2 monolayer film. The carrier mobility remains high at large channel lengths. This work opens a new pathway toward electronic and optical applications, and fundamental growth mechanism as well, of the MoS2 monolayer.

Constructional details of polystyrene-block-poly(4-vinylpyridine) ordered thin film morphology

One of the most important issues for spin-coated diblock copolymer thin films is to distinguish the blocks by common techniques, especially for the diblock copolymers containing one block could form active domain. Aiming different estimations on the composition of surface microdomains in polystyrene-block-poly (4-vinylpyridine) (PS-b-P4VP) atomic force microscope (AFM) phase images, AFM, transmission electron microscopy, and droplet shape analyzer were used to identify the constructional details of the polymer thin film morphology. It was confirmed that PS block is harder than P4VP block in symmetric PS-b-P4VP films and corresponds to brighter regions in AFM phase image. It is helpful to distinguish the nanodomains that originate from the different blocks in PS-b-P4VP thin films. The structure evolutions of PS-b-P4VP film annealed with different selective solvents were studied and discussed. The results indicated that the core-corona inversion process is due to the cores of micelles swell and coalesce together rather than local reorganization of the chains.

In situ AFM and Raman spectroscopy study of the crystallization behavior of Ge2Sb2Te5 films at different temperature

Using in situ atomic force microscope (AFM) and Raman spectroscopy, the real-time crystallization properties of Ge2Sb2Te5 films at different temperature were characterized. The given AFM topograph and phase images revealed that the structure of amorphous Ge2Sb2Te5 films began to change at a temperature of as low as 100°C. When the temperature reached 130°C, some crystal fragments had formed at the film surface. Heating up to 160°C, the size of the visible crystal fragments increased, but decreased at a higher temperature of 200°C. When the Ge2Sb2Te5 film was cooled down to room temperature (RT) from 200°C, the crystal fragments divided into crystal grains due to the absence of heating energy. The Raman spectra at different temperature further verified the structure evolution of the Ge2Sb2Te5 film with temperature. This work is of significance for the preparation of Ge2Sb2Te5 films and the erasing of data.

Flexible Organic Solar Cells: Nanoscale Phase Separation and High Photovoltaic Efficiency in Solution‐Processed, Small‐Molecule Bulk Heterojunction Solar Cells (Adv. Funct. Mater. 19/2009)

The inside cover of this issue illustrates the fabrication of lightweight and flexible organic solar cells, developed by B. Walker et al. on page 3063, from a solution of fullerene and diketopyrrolopyrrole-based materials. The texture of the organic film on the substrate was taken from an atomic force microscope phase image of the high performance device (4.4% power conversion efficiency), showing the phase separation behavior of the two molecular semiconducting materials.

Magnetic force microscopy of iron oxide nanoparticles and their cellular uptake

Magnetic force microscopy has the capability to detect magnetic domains from a close distance, which can provide the magnetic force gradient image of the scanned samples and also simultaneously obtain atomic force microscope (AFM) topography image as well as AFM phase image. In this work, we demonstrate the use of magnetic force microscopy together with AFM topography and phase imaging for the characterization of magnetic iron oxide nanoparticles and their cellular uptake behavior with the MCF7 carcinoma breast epithelial cells. This method can provide useful information such as the magnetic responses of nanoparticles, nanoparticle spatial localization, cell morphology, and cell surface domains at the same time for better understanding magnetic nanoparticle-cell interaction. It would help to design magnetic-related new imaging, diagnostic and therapeutic methods.

AFM characterization of the interfacial properties of carbon fiber reinforced polymer composites subjected to hygrothermal treatments

The interface quality of Carbon Fiber Reinforced Polymer (CFRP) composites is critical to the structural integrity of composites. The environment in which composites are used also has significant effects on their performance. The objective of this work is to characterize CFRP composites, their interface and the effect of hygrothermal treatments using Atomic Force Microscope (AFM). The cross-sections of three CFRP epoxy composites were polished and investigated with AFM. AFM height images showed fibers higher than matrix caused by polishing. Hygroscopic treatment progressively reduced the height difference between fiber and matrix indicating the swelling of matrix by absorption of moisture. Thermal treatment increased the height difference, believed to be caused by matrix shrinkage resulted from additional cure under elevated temperature. The sheath-core structure of AS4 and T700 fibers manifested itself in both height and phase AFM images. AFM phase images revealed fiber/matrix interface susceptible to hygrothermal environments, implying that degradation and failures likely initiate at the interface.

Surface functionalized alumina nanoparticle filled polymeric nanocomposites with enhanced mechanical properties

Alumina nanoparticles were successfully functionalized with a bi-functional coupling agent, (3-methacryloxypropyl)trimethoxysilane (MPS), through a facile neutral solvent method. MPS was found to be covalently bound with the nanoparticles. The linked MPS was polymerized with a vinyl-ester resin monomer through a free radical polymerization. Atomic force microscope phase images showed a uniform distribution of nanoparticles. Microtensile test results revealed the Young's modulus and strength increasing with particle loading. Microscopic examinations revealed the presence of large plastic deformations at the micron scale in the nanocomposites in agreement with the observed strengthening effect of functionalized nanoparticles. Thermo-gravimetric analysis (TGA) did not show any significant change in the thermal degradation of the nanocomposite as compared with the neat resin. The polymer matrix effectively protected the alumina nanoparticles from dissolution in basic and acidic solutions.

Long-Ranged Attraction between Charged Polystyrene Spheres at Aqueous Interfaces

We report an optical and atomic force microscopic study of interactions between charged polystyrene spheres at a water-air interface. Optical observations of bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscope phase images show patchy domains on the colloidal surface, indicating that the surface charge distribution is not uniform as is commonly believed. Such surface heterogeneity introduces in-plane dipoles, leading to an attraction at short interparticle distances.

Using AFM Phase Lag Data to Indentefy Microconstituents With Varying Values of Elastic Modulus

Abstract The atomic force microscope (AFM) has allowed microscopists to observe surface topography of non-conductive samples on the atomic level. One AFM mode that scanned probe microscopists have recently shown an interest in is the phase lag imaging mode. It has already been demonstrated that the resulting phase lag data can be used to identify different densities of microlayered polyethylene. However a quantitative understanding of phase lag imaging has yet to be fully developed. With a better understanding of the phase lag data it may be possible to estimate the modulus or other material properties of a sample from an AFM phase image alone. The need for better understanding phase lag data is essential to increasing the knowledge of a how a material's microstructure behaves on the nanometer scale. This investigation focused on AFM phase lag data produced while scanning microstructures with large differences in modulus values between the compositional phases.