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PubMed2004

Atomic force microscopy study on the stability of a surface film formed on a graphite negative electrode at elevated temperatures.

The stability at elevated temperatures of a solid electrolyte interphase (SEI) formed on a graphite negative electrode in lithium ion batteries was investigated by storage tests and in situ atomic force microscopy (AFM) observation. When the fully discharged graphite electrode was stored at elevated temperatures, the irreversible capacity in the following cycle increased remarkably. On the other hand, when the electrode was stored at the fully charged state at elevated temperatures, it was severely self-discharged during storage. AFM observation of the SEI layer formed on a model electrode of highly oriented pyrolytic graphite revealed two important facts on the stability of the SEI at elevated temperatures: (i) dissolution and agglomeration of the SEI layer at the discharged state and (ii) serious SEI growth at the charged state. These phenomena well explain the results of the charge and discharge tests. It was also shown that the addition of vinylene carbonate greatly improves the stability of the SEI at elevated temperatures, and gives good charge and discharge performance after storage.

Journal Article↗

PubMed1993

Effect of probe force on the resolution of atomic force microscopy of DNA.

Experimental results are presented to show that the adhesion force is the single most important limiting factor in high-resolution atomic force microscopy of DNA in air, prepared by the cytochrome-C-assisted spreading method. It is also shown that humidity plays a minor role in the control of probe force. Using a pure carbon film as the substrate to clean the AFM tip prior to imaging, it is demonstrated that 4-6 nm resolution on DNA can be routinely obtained by the atomic force microscope with commercial Si3N4 pyramid cantilevers. We also show that in organic solvents a resolution of up to 3 nm can be obtained under optimal conditions.

DNA, Bacterial↗

PubMed2001

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy.

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.

Journal Article↗

PubMed2004

Encapsulated cells: an atomic force microscopy study.

Two types of cells--human platelets and spore cells--were encapsulated in polymer shells by adsorbing polyanions and polycations in a stepwise fashion. The encapsulated cells were attached to gold and silicon surfaces and their morphological and adhesion properties were studied in air using tapping mode atomic force microscopy (AFM). The roughness of the encapsulated cells increased upon the addition of a new polymer layer. The increase in roughness can be attributed to the formation of a shell around the cells, which is stabilized by electrostatic interactions, as well as to the drying effects associated with the immobilization and dehydration of the cells. Trigger mode was used to perform the force imaging and map out the adhesion characteristics of the cells. Systematic "maps" of the adhesion properties of the encapsulated cells to clean and amine terminated AFM tips were collected. The adhesion force data for the different tips and encapsulated cells showed dependence not only on the number and thickness of the polymer layers, but also on the interactions between these layers. The encapsulated cells' morphology and roughness characteristics remained intact over a substantial storage period. This stability and adhesion properties make them suitable building blocks for the design and construction of biomimetic templates where AFM is used as the primary tool to do the fabrication.

Adhesiveness↗

PubMed1993

Atomic force microscopy of DNA and bacteriophage in air, water and propanol: the role of adhesion forces.

We have developed a chemical treatment for the mica surface which allows biopolymers to be held in place for atomic force microscopy, even under water, using conventional, untreated force sensing tips. We illustrate the procedure with images of lambda DNA and fd phage. The phage adheres well enough to permit in situ imaging of the adsorption process in water. These experiments yield a mean length for the phage of 883 +/- 72 nm. This compares with a measured length of 883 +/- 33 nm when the phage are imaged after drying following adsorption from water, showing that the effect of dehydration is quite small. Adhesion forces between the force sensing tip and the substrate and the sensing tip and the biomolecules are very different in the three media (air, water and propanol). The apparent height of the phage and the width and height of the DNA depends upon these adhesion forces quite strongly. In contrast, changing the Hookean spring force exerted by the scanning tip makes little difference. These results suggest that the chemical factors involved in adhesion can dominate atomic force images and that the composition of the scanning tip is at least as important a factor as its geometry.

1-Propanol↗

PubMed2004

In situ atomic force microscopy investigation of the [100] face of KH2PO4 in the presence of Fe(III), Al(III), and Cr(III).

Here we report the effects of dissolved metal complexes of Fe(III), Al(III), and Cr(III) on the step velocities of the [100] face of KH2PO4 (KDP) as observed with atomic force microscopy. The dependence of step velocity on supersaturation (sigma) exhibits a dead zone that scales with adsorbate concentration. The observed dependence varies with the metal complex. From these data, we derive values for the characteristic adsorption time (tau) for the Al(III) and Cr(III) step-pinning adsorbates as being on the order of several hundred microseconds as compared to 10-100 s for the corresponding Fe(III) step-pinning adsorbates. The values of tau are strikingly different than rates of ligand exchange but are associated with the adsorbate-induced morphology of the surface, including elementary steps that bunch into macrosteps and supersteps. The stoichiometry of the adsorbate species is assumed to be M(HxPO4)x, where M = Fe(III), Al(III), or Cr(III). KDP crystals grown in the presence of the dissolved metals were analyzed using laser ablation inductively coupled plasma mass spectroscopy. The data revealed sectoral zoning on the [100] face, with the concentrations of the incorporated adsorbates in the sector with slower moving elementary steps being 1.7-2.0 times greater than those measured on the sector with fast moving elementary steps.

Journal Article↗

PubMed1999

Quality assessment of atomic force microscopy probes by scanning electron microscopy: correlation of tip structure with rendered images.

While image quality from instruments such as electron microscopes, light microscopes, and confocal laser scanning microscopes is mostly influenced by the alignment of optical train components, the atomic force microscope differs in that image quality is highly dependent upon a consumable component, the scanning probe. Although many types of scanning probes are commercially available, specific configurations and styles are generally recommended for specific applications. For instance, in our area of interest, tapping mode imaging of biological constituents in fluid, double ended, oxide-sharpened pyramidal silicon nitride probes are most often employed. These cantilevers contain four differently sized probes; thick- and thin-legged 100 microm long and thick- and thin-legged 200 microm long, with only one probe used per cantilever. In a recent investigation [Taatjes et al. (1997) Cell Biol. Int. 21:715-726], we used the scanning electron microscope to modify the oxide-sharpened pyramidal probe by creating an electron beam deposited tip with a higher aspect ratio than unmodified tips. Placing the probes in the scanning electron microscope for modification prompted us to begin to examine the probes for defects both before and after use with the atomic force microscope. The most frequently encountered defect was a mis-centered probe, or a probe hanging off the end of the cantilever. If we had difficulty imaging with a probe, we would examine the probe in the scanning electron microscope to determine if any defects were present, or if the tip had become contaminated during scanning. Moreover, we observed that electron beam deposited tips were blunted by the act of scanning a hard specimen, such as colloidal gold with the atomic force microscope. We also present a mathematical geometric model for deducing the interaction between an electron beam deposited tip and either a spherical or elliptical specimen. Examination of probes in the scanning electron microscope may assist in interpreting images generated by the atomic force microscope.

DNA↗

PubMed1995

Atomic force microscopy of human hair cuticles: a microscopic study of environmental effects on hair morphology.

We have used an atomic force microscope to provide quantitative real-time analysis of human hair morphologic changes under ambient conditions. This form of microscopy combines the lateral resolution of an electron microscope and the flexibility of a light microscope. Three experiments were performed: a study of hair morphology in air versus water, a kinetic study of hair hydration, and a determination of how pH changes affect hair morphology. The overlapping keratinized cells that form the hair cuticle spread out between 50 and 150% when hydrated, compared to a total shaft diameter change of 10%. This hydration reaches a saturation point within the first few minutes after immersion. Also, hair swells much more at higher pH.

Adult↗

PubMed1998

Atomic force microscopy of histological sections using a new electron beam etching method.

In order to examine histological sections of the rat vomeronasal epithelium with the atomic force microscope (AFM), we developed an electron beam etching method that improves the resolution of AFM images. This method results in AFM images comparable to those obtained with the transmission electron microscope (TEM). Ultrathin tissue sections embedded in epoxy resin were observed before and after the treatment with electron beam radiation. Before electron beam treatment, epithelial structures such as the microvilli surface, dendritic processes, the supporting cell layers and the neuronal cell layers were all visible using the AFM. However, only a few subcellular structures could also be resolved. The AFM images were not as clear as those obtained with the TEM. After electron beam treatment, however, the resolution of AFM images was greatly improved. Most of the subcellular structures observed in TEM images, including the inner membrane of mitochondria, ciliary-structure precursor body, junctional complexes between the neurons and supporting cells, and individual microvilli were now visible in the AFM images. The electron beam treatment appeared to melt the embedding resin, bringing subcellular structures into high relief. The result of this study suggests that electron beam etching of histological samples may provide a new method for the study of subcellular structure using the AFM.

Animals↗

PubMed2004

Electrochemical and atomic force microscopy study of carbon surface modification via diazonium reduction in aqueous and acetonitrile solutions.

Electrochemical reduction of the diazonium salts of 4-nitrobenzene and 4-nitroazobenzene-4'- has been investigated in aqueous acid and acetonitrile media at carbon surfaces. Using pyrolyzed photoresist films as the substrate, we have examined the deposited films using electrochemistry and atomic force microscopy (AFM). Film thicknesses were measured by scratching through the film with an AFM tip. The procedure employed two AFM cantilevers with different lengths, located on the one device. When the shorter cantilever engages the surface in tapping mode, the longer cantilever (which is not resonating) imbeds into the surface with a constant force. For both modifiers and modification media, film thicknesses increase with deposition time to a limiting value. With equivalent modification conditions, films prepared in aqueous acid medium have lower limiting thicknesses than those prepared in acetonitrile. For nitrophenyl (NP) films, the same trends are found when calculating surface coverages from the charge associated with the reduction of surface -Ar-NO2 groups. Lower limiting film thicknesses and surface coverages for films prepared in aqueous conditions is attributed to growth of inherently more blocking films and is supported by examination of the response of the Fe(CN)6(3-/4-) couple at NP-modified surfaces. Combination of voltammetrically determined surface coverage and film thickness data yields a surface coverage of -Ar-NO2 groups of (2.5 +/- 0.5) x 10(-10) mol cm(-2) for a film thickness equivalent to a monolayer of NP groups.

Journal Article↗

PubMed2004

Investigation of twin-wall structure at the nanometre scale using atomic force microscopy.

The structure of twin walls and their interaction with defects has important implications for the behaviour of a variety of materials including ferroelectric, ferroelastic, co-elastic and superconducting crystals. Here, we present a method for investigating the structure of twin walls with nanometre-scale resolution. In this method, the surface topography measured using atomic force microscopy is compared with candidate displacement fields, and this allows for the determination of the twin-wall thickness and other structural features. Moreover, analysis of both complete area images and individual line-scan profiles provides essential information about local mechanisms of twin-wall broadening, which cannot be obtained by existing experimental methods. The method is demonstrated in the ferroelectric material PbTiO(3), and it is shown that the accumulation of point defects is responsible for significant broadening of the twin walls. Such defects are of interest because they contribute to the twin-wall kinetics and hysteresis.

Journal Article↗

PubMed2004

Atomic force microscopy study of the adsorption and electrostatic self-organization of poly(amidoamine) dendrimers on mica.

The adsorption behavior of poly(amidoamine) dendrimers to mica surfaces was investigated as a function of ionic strength and pH. The conformation and lateral distribution of the adsorbed dendrimers of generations G8 and G10 were obtained ex situ by tapping mode atomic force microscopy (AFM). The deposition kinetics of the dendrimers was found to follow a diffusion-limited process. Fractional surface coverage and pair correlation functions of the adsorbed dendrimers were obtained from the AFM images. The data are interpreted in terms of the random sequential adsorption (RSA) model, where electrostatic repulsion due to overlapping double layers is considered. Although the general trends typical for an RSA-determined process are well-reproduced, quantitative agreement is lacking at low ionic strengths.

Journal Article↗

PubMed2005

Atomic force microscopy study of beta-substituted-T7 oligothiophene films on mica: mechanical properties and humidity-dependent phases.

The structural and mechanical properties of Langmuir-Blodgett monolayer and multilayer films of 3",4""-didecyl-5,2'; 5',2"; 5",2'''; 5''',2""; 5"",2'''''; 5''''',2"""-heptathiophene-4'''-acetic acid on mica have been studied by atomic force microscopy (AFM) as a function of humidity, temperature, and applied force. The molecules orient with the carboxylic acid group pointing toward the mica surface and expose the alkyl side chains to the air interface. As the load applied by the AFM tip increases, the film is compressed easily from an initial height of 2 to 1.2 nm. After compression the films can support much higher loads without loss of height. The state of aggregation of the molecules was found to be sensitive to the environmental humidity, which induced reversible changes. Annealing the samples with monolayer or multilayer films resulted in irreversible changes when the temperature exceeded approximately 100 degrees C.

Journal Article↗

PubMed2004

Direct visualization of mesh structures at solid/solution interfaces by atomic force microscopy.

The formation of adsorbed surfactant layers consisting of a mesh or network of branched cylindrical aggregates on muscovite mica by several surfactant systems is described. The curvature of the adsorbed aggregates is varied by a variety of mechanisms that all generate morphologies between adsorbed cylinders and bilayers, and the resulting lateral structure is imaged by "soft contact" atomic force microscopy. We compare the direct images and Fourier transforms of the adsorbed layer structures, and relate them to those formed in bulk solution.

Journal Article↗

PubMed1994

Stretched DNA structures observed with atomic force microscopy.

Double-stranded DNA molecules are occasionally found that appear to be straightened and stretched in atomic force microscope (AFM) images. Usually pBS+ plasmid and lambda DNA show relaxed structures with bends and kinks along the strands and have measured contour lengths consistent to about 5-7%; they also appear not to cross over each other, except in very high concentrations. The anomalous molecules observed here, compared with the majority of molecules in the preparation, show contour lengths increased by as much as 80% and have measured heights of about half that of normal relaxed DNA. Some molecules also appear to be in transition between stretched and relaxed forms. These observations are consistent with an uncoiling of the DNA helix without breakage of the covalent bonds in the deoxyribose-phosphate backbone.

Bacteriophage lambda↗

PubMed2005

Atomic force microscopy of thermally treated myosin filaments.

Heat-induced morphological change in myosin filaments was observed using atomic force microscope. The thickness of fixed native myosin filament was estimated to be 95 +/- 5 nm. When myosin filaments in 0.1 M NaCl at pH 6.0 were heated at 40, 55, and 70 degrees C for 10 min, the particulate structure appeared spirally on the surface of the filament at 40 degrees C, and the thickness of the filament was 75 +/- 10 nm. When myosin filaments were treated at 55 degrees C, several filaments were formed associated with side-by-side interaction through projected myosin heads to form a strand. The surface of the strand looked knobby. The thickness of thermally denatured filaments at 55 degrees C was 48 +/- 5 nm, and that of strands was about 80-110 nm, indicating the involvement of several filaments in a strand. The strands became to be rope-like at 70 degrees C, and the individual filaments in a strand were not distinguishable.

Animals↗

PubMed1992

Atomic force microscopy imaging of T4 bacteriophages on silicon substrates.

A new atomic force microscope incorporating microfabricated cantilevers and employing laser beam deflection for force detection has been constructed and is being applied to studies of biological material. In this study, T4 bacteriophage virus particles were deposited from solution onto electronic-grade flat silicon wafers and imaged in air with the microscope. Microliter droplets of the solution were deposited and either allowed to dry or removed with blotting paper. The images show both isolated viruses and aggregates of various sizes. The external structure as well as strands believed to be DNA streaming out of the virus could be observed. The construction of the microscope and its performance are also described.

Bacteriophage T4↗

PubMed1996

Protein tracking and detection of protein motion using atomic force microscopy.

Height fluctuations over three different proteins, immunoglobulin G, urease, and microtubules, have been measured using an atomic force microscope (AFM) operating in fluid tapping mode. This was achieved by using a protein-tracking system, where the AFM tip was periodically repositioned above a single protein molecule (or structure) as thermal drifting occurred. Height (z-piezo signal) data were taken in 1 - or 2-s time slices with the tip over the molecule and compared to data taken on the support. The measured fluctuations were consistently higher when the tip was positioned over the protein, as opposed to the support the protein was adsorbed on. Similar measurements over patches of an amphiphile, where the noise was identical to that on the support, suggest that the noise increase is due to some intrinsic property of proteins and is not a result of different tip-sample interactions over soft samples. The orientation of the adsorbed proteins in these preliminary studies was not known; thus it was not possible to make correlations between the observed motion and specific protein structure or protein function beyond noting that the observed height fluctuations were greater for an antibody (anti-bovine IgG) and an enzyme (urease) than for microtubules.

Animals↗