Quantification of lubricant activity of magnesium stearate by atomic force microscopy

Magnesium stearate (MgSt) is commonly used in pharmaceutical formulations as a lubricant to facilitate tablet release from the die after compression. In this study, we quantify the effect of MgSt on the interaction forces between microcrystalline cellulose (MCC) and steel surfaces. A quantitative approach to better understand the mechanism by which MgSt affects powder performance will assist in improved control and formulation design. We find that the forces between MgSt and steel surface are stronger than the interactions between MgSt itself, between MgSt and an MCC particle, and an MCC particle and a steel surface. These quantitative findings offer an explanation how MgSt facilitates lubrication during tablet ejection.     

A thin subsurface layer of a polymer film studied by atomic force microscopy

A thin subsurface layer of a PMMA based resist film was studied in an atomic force microscope (AFM). An analysis of the AFM image allowed a modified subsurface layer thickness to be estimated, in which the polymer density is greater than that in the bulk of the film.     

Quantitative analysis of electrodeposited tin film morphologies by atomic force microscopy

This study of the electrodeposition of tin on steel substrates demonstrates that it is possible to obtain quantitative information on the thin film growth at industrially relevant substrates using atomic force microscopy (AFM) to monitor the film morphology and X-ray fluorescence (XRF) to measure the average film thickness. The effects of current density and electrolyte temperature on the film morphology, surface roughness, and grain size distribution (GSD) are reported. While the roughness of the substrates used in this study can vary by several hundred nanometers to a micrometer, we are interested in quantitative characterization of the tin films with thickness varying from a few tens of nanometers to several hundred nanometers. This study shows that for the range of film thickness and length scale studied, analysis of the AFM images can provide quantitative characterization of the thin film roughness and grain size distribution at various stages of growth with little interference from the substrate morphological inhomogeneities.     

Determination of nano-roughness of carbon fibers by atomic force microscopy

We present a novel approach to determine the surface roughness on varying scales using atomic force microscopy data. The key factor is to find a suitable background correction for the desired scale. Using the example of the surface of sized and unsized high-tenacity carbon fibers, we present an easy method to find backgrounds for widely varying scales and to evaluate respective topography and surface roughness with the same lateral resolution as the microscope itself. The analysis is done by subtracting a tunable background from the respective height data. By choosing an appropriate background to investigate the surface topography of a carbon fiber on a nm-scale, only small nano-structures with a width of around 20 nm remain after the background subtraction. Evaluating the mean roughness R _a of these nano-structures, sized carbon fibers show an overall value of around 0.1 nm while unsized carbon fibers a value of around 0.4 nm. Total background corrected height analysis shows an even distribution of these nano-structures along the fibrils of the unsized fibers, whereas for the sized fibers the nano-structures are not present. The presented method allows analysis and visualization of the distribution of nano-structures on a carbon fiber surface for the first time. This feature is used to visualize the distribution of the sizing and can further be used to investigate the influence of different production parameters on the fiber topography or to evaluate the contribution of mechanical interlocking to the interfacial strength.     

Dynamic behaviour of a nanoscale-patterned phospholipid thin film on mica and silicon studied by atomic force microscopy

The temporal evolution of the morphology of nanoscale-patterned phospholipid thin films on mica and silicon surfaces has been investigated with an atomic force microscope (AFM). The AFM images reveal that nanoscale scratch lines on thin films prepared on mica contract with time and eventually form roundish holes. An elevated sample temperature accelerates this morphological evolution. We model such an evolution based on the interplay of the thin-film surface line tension and the friction between the thin film and the substrate. The results show that the temperature-dependent contraction is governed by the ratio of the friction coefficient and the surface line tension. The friction at the lipid/mica interface decreases to a seventh as the sample temperature rises from 18 to 60 °C. This model is supported by experiments on silicon surfaces, on which contraction of the scratch patterns is limited because of an expected greater interfacial friction.     

Studying multilayer langmuir film structure by confocal laser scanning and atomic force microscopy techniques

Features of extracting information on the surface structure of a multilayer organic film from data on its optical properties and surface relief are considered. The object of investigation was a multilayer Langmuir-Blodgett film based on a prepolymer (polyamic acid salt). It is suggested that the formation of the film volume is influenced by inhomogeneities in the structure of layers.     

Precise control of nanofabrication by atomic force microscopy

With an aim of the precise control of the anodic oxidation process by atomic force microscopy, the technical improvement has been carried out based on the mechanism studies. The accuracy and reliability of the nanofabrication have been improved by the combination of ambient humidity control, improvement of instrumental performance and meniscus lifetime control. In parallel, the mechanism study has been proceeded through the detection of Faradaic current. The in situ Faradaic current detection of the nano-oxidation process can actually work as a sensitive monitor for the nano-oxidation process with a high reliability. From an engineering viewpoint with an eye to practical applications, controllable physical parameters which affect on the product size are enumerated to consider what we should do to raise the precision of nano-oxidation. Then the fast fabrication in a large area by a patchwork method, Faradaic current detection during oxidation-reduction reaction, and nanofabrication by current-control are shown as examples.     

Nanofabrication with atomic force microscopy

Atomic force microscopy (AFM) was developed in 1986. It is an important and versatile surface technique, and is used in many research fields. In this review, we have summarized the methods and applications of AFM, with emphasis on nanofabrication. AFM is capable of visualizing surface properties at high spatial resolution and determining biomolecular interaction as well as fabricating nanostructures. Recently, AFM-based nanotechnologies such as nanomanipulation, force lithography, nanografting, nanooxidation and dip-pen nanolithography were developed rapidly. AFM tip (typical radius ranged from several nanometers to tens of nanometers) is used to modify the sample surface, either physically or chemically, at nanometer scale. Nanopatterns composed of semiconductors, metal, biomolecules, polymers, etc., were constructed with various AFM-based nanotechnologies, thus making AFM a promising technique for nanofabrication. AFM-based nanotechnologies have potential applications in nanoelectronics, bioanalysis, biosensors, actuators and high-density data storage devices.     

Specific aptamer-protein interaction studied by atomic force microscopy

Aptamers are a new class of synthetic DNA/RNA oligonucleotides generated from in vitro selection to selectively bind with various molecules. Due to their molecular recognition capability for proteins, aptamers are becoming promising reagents in protein detection and new drug development. In this study, the specific interaction between the protein immunoglobulin E (IgE) and its 37-nt aptamer has been measured directly by atomic force microscopy. The single-molecule unbinding force between IgE and the aptamer is determined using the Poisson statistical method. The individual unbinding force between IgE and its monoclonal antibody has also been obtained and compared to that between IgE and the aptamer. The results reveal the high affinity of the aptamer to protein, which could match or even surpass that of the antibody to its antigen.     

Dielectric constants by multifrequency non-contact atomic force microscopy

We present a method to obtain capacitive forces and dielectric constants of ultra-thin films on metallic substrates using multifrequency non-contact atomic force microscopy with amplitude feedback in air. Capacitive forces are measured via cantilever oscillations induced at the second bending mode and dielectric constants are calculated by fitting an analytic expression for the capacitance (Casuso et al 2007 Appl. Phys. Lett. 91 063111) to the experimental data. Dielectric constants for self-assembled monolayers of thiol molecules on gold (2.0±0.1) and sputtered SiO2 (3.6±0.07) were obtained under dry conditions, in good agreement with previous measurements. The high Q-factor of the second bending mode of the cantilever increases the accuracy of the capacitive measurements while the low applied potentials minimize the likelihood of variation of the dielectric constants at high field strength and of damage from dielectric breakdown of air.     

Monitoring DNA immobilization and hybridization on surfaces by atomic force microscopy force measurements

DNA immobilization and hybridization was carried out on Au substrates that were modified with mercaptopropanoic acid and then treated with aluminum(III) solution. The positively charged AI(III) film can be used to immobilize both ds-DNA and ss-DNA. Atomic force microscopy (AFM) was used to monitor the process by force measurements between a negatively charged silica tip and the substrates while immersed in dilute electrolyte. Surface hybridization of ss-DNA produces an increase in the surface charge and surface potential of the substrates, which is reflected by the increasing repulsive force as determined from AFM force-separation curves. A single-base mismatch was detectable in surface hybridization. The AFM force measuring technique was also employed to investigate the interaction of Ru(phen)3(2+) with ss-DNA and ds-DNA. The force measurement results showed that there is a small interaction between Ru(phen)3(2+) and ss-DNA, which was ascribed to the electrostatic binding of Ru(phen)3(2+) to the ss-DNA surface. For ds-DNA, there is a strong interaction which is believed to be due to the association or intercalation of Ru(phen)3(2+) with ds-DNA.     

Molecular structure and thickness of highly oriented poly(tetrafluoroethylene) films measured by atomic force microscopy

Atomic force microscopy (AFM) was used to image thin single-crystal-like layers of poly(tetrafluoroethylene) (PTFE) deposited mechanically on glass. Not only can AFM reveal details of the molecular structure, but it can also provide direct measurement of the absolute thickness and continuity of these films. High-magnification images show individual rod-like molecules with an intermolecular spacing of 0.58 nm. The helix of individual molecules is clearly resolved and fine structures along the polymer chains may indicate individual fluorine atoms. The thickness of the films varies from 7–32 nm depending on deposition temperature and mechanical pressure. The continuity of the films strongly decreases at lower temperatures. The remaining single fibres are not stable and can be modified by the imaging tip.     

Non-contact atomic force microscopy study of atomic manipulation on an insulator surface by nanoindentation

Experimental results on vertical manipulation on an insulator surface using non-contact atomic force microscopy are presented. Cleaved ionic KCl(100) single crystal is used as an insulator surface. With the nanoindentation method used, the vertical manipulation of a single atom in an ionic crystal surface is more difficult than in a semiconductor surface. Therefore, in many cases, more than one surface atom is manipulated while, in rare cases, single-atom manipulation is successfully performed. Lateral manipulation of a vacancy has occasionally succeeded on the KCl(100) surface. We have presumed that the lateral manipulation was induced by pulling.     

ESCA determination of fluorocarbon lubricant film thickness on magnetic disk media

Fluorocarbon films are in extensive use as lubricants for Winchester-type disks, to reduce disk head wear and to reduce friction during landing and start-up. This paper describes a particularly precise and simple method of measuring the average, relative thickness of such films using ESCA spectroscopy. Film thicknesses are measured with a typical precision of 5% of value (lσ), over the operational range of these films.     

FTIR determination of fluorocarbon lubricant film thickness on magnetic disk media

Fluorocarbon lubricants have been used extensively for Winchester-type media to minimize head disk interfacial wear and friction. The film thickness of these lubricants must be carefully controlled. This paper describes a non-destructive and cost-effective technique of measuring the average, relative thickness of lubricating films on rigid magnetic disks by using FTIR spectroscopy. Lubricant film thickness data obtained by FTIR correlated very well with those obtained by ESCA spectroscopy. The effect of surface roughness on lubricant retention during the lubrication process is also demonstrated.     

Measurement of interfiber friction force for pulp fibers by atomic force microscopy

Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.     

Carbon nanotube air-bubble interactions studied by atomic force microscopy

Interaction forces between a multi-walled carbon nanotube (MWCNT) and an air-bubble in pure deionized water and methyl isobutyl carbinol (MIBC) solutions were measured by atomic force microscopy (AFM). The MWCNT terminated probe was brought into contact with the bubble at controlled applied forces. The repulsive steps followed by attractive jumps recorded in the approach force curves correspond to changes in the MWCNT diameter along its length, an observation confirmed by transmission electron microscopy (TEM) data. By processing the retraction part of the force curves obtained in pure water it is possible to estimate the end diameter of the carbon nanotube with nanometer resolution using a capillary force model.     

Ultradisperse diamond cluster aggregation studied by atomic force microscopy

The structure of ultradisperse diamond (UDD) conglomerates was studied by scanning atomic-force microscopy (AFM). The UDD layers were prepared from a detonation carbon obtained by synthesis in an aqueous medium. The finest details in the AFM images of UDD layers are of the order of 10 nm, which does not allow individual 4.5-nm diamond clusters to be distinguished. The UDD conglomerates deposited and dried on a silicon substrate surface, exhibit certain deformation and differ from the initial (apparently, spherical) shape. This may imply that cohesion between the UDD nanoparticles is comparable with their adhesion to the silicon substrate.     

Chaos in dynamic atomic force microscopy

In tapping mode atomic force microscopy (AFM) the highly nonlinear tip-sample interaction gives rise to a complicated dynamics of the microcantilever. Apart from the well-known bistability under typical imaging conditions the system exhibits a complex dynamics at small average tip-sample distances, which are typical operation conditions for mechanical dynamic nanomanipulation. In order to investigate the dynamics at small average tip sample gaps experimental time series data are analysed employing nonlinear analysis tools and spectral analysis. The correlation dimension is computed together with a bifurcation diagram. By using statistical correlation measures such as the Kullback-Leibler distance, cross-correlation and mutual information the dataset can be segmented into different regimes. The analysis reveals period-3, period-2 and period-4 behaviour, as well as a weakly chaotic regime.