Atomic force microscopy and direct surface force measurements (original) (raw)
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Atomic force microscopy and direct surface force measurements (IUPAC Technical Report
Pure and Applied Chemistry, 2005
Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.
Atomic force microscopy is a convenient and exceptionally rich source of information about materials on the nano-scale. The instrument can be configured to operate in a large number of modes. The main task of AFM is to produce reliable and repeatable measurement of surface and intermolecular forces, which are needed for surface analysis and provide plentiful of information regarding other features of specimen. These diverse modes measure different atomic forces that are acting between apex and specimen surface and are used for producing topographical image of the sample with high molecular resolution. The force measurement is by way of cantilever deflection measures. The cantilever can be made by piezoelectric material, whereas it is a piezoelectric stage that moves the specimen with respect to the tip. The cantilever is affected by position, tip-sample separation, it’s material, and different forces. A beam of laser focused on the force sensing/imposing lever and reflected onto a sensitive detector which is position sensing photo diode PSPD. Due to high resolution and small contact areas there is no need of vacuum and problems due to contamination and roughness are minimized.
Journal of Applied Physics, 2010
It has long been recognized that the angular deflection of an atomic force microscope ͑AFM͒ cantilever under "normal" loading conditions can be profoundly influenced by the friction between the tip and the surface. It is shown here that a remarkably quantifiable hysteresis occurs in the slope of loading curves whenever the normal flexural stiffness of the AFM cantilever is greater than that of the sample. This situation arises naturally in cantilever-on-cantilever calibration, but also when trying to measure the stiffness of nanomechanical devices or test structures, or when probing any type of surface or structure that is much more compliant along the surface normal than in transverse directions. Expressions and techniques for evaluating the coefficient of sliding friction between the cantilever tip and sample from normal force curves, as well as relations for determining the stiffness of a mechanically compliant specimen are presented. The model is experimentally supported by the results of cantilever-on-cantilever spring constant calibrations. The cantilever spring constants determined here agree with the values determined using the NIST electrostatic force balance within the limits of the largest uncertainty component, which had a relative value of less than 2.5%. This points the way for quantitative testing of micromechanical and nanomechanical components, more accurate calibration of AFM force, and provides nanotribologists access to information about contact friction from normal force curves.
The atomic force microscope (AFM) has previously been applied to the measurement of surface forces (including adhesion and friction) and to the investigation of material properties, such as hardness. Here we describe the modification of a commercial AFM that enables the " stiffness " of interaction between surfaces to be measured concurrently with the surface forces. The stiffness is described by the rheological phase difference between the response of the AFM tip to a driving oscillation of the substrate. We present the interaction between silica surfaces bearing adsorbed polymer, however, the principles could be applied to a wide variety of materials including biological samples.
Comparison between Atomic Force Microscopy and Force FeedbackMicroscopy static force curves
Atomic Force Microscopy (AFM) conventional static force curves and Force Feedback Microscopy (FFM) force curves acquired with the same cantilever at the solid/air and solid/liquid interfaces are here compared. The capability of the FFM to avoid the jump to contact leads to the complete and direct measurement of the interaction force curve, including the attractive short-range van der Waals and chemical contributions. Attractive force gradients five times higher than the lever stiffness do not affect the stability of the FFM static feedback loop. The feedback loop keeps the total force acting on the AFM tip equal to zero, allowing the use of soft cantilevers as force transducers to increase the instrumental sensitivity. The attractive interactions due to the nucleation of a capillary bridge at the native oxide silicon/air interface or due to a DLVO interaction at the mica/deionized water interface have been measured. This set up, suitable for measuring directly and quantitatively interfacial forces, can be exported to a SFA (Surface Force Apparatus).
Review of Scientific Instruments, 2005
Presented here is a novel technique for the in situ calibration and measurement of friction with the atomic force microscope that can be applied simultaneously with the normal force measurement. The method exploits the fact that the cantilever sits at an angle of about 10°to the horizontal, which causes the tip ͑or probe͒ to slide horizontally over the substrate as a normal force run is performed. This sliding gives rise to an axial friction force ͑in the axial direction of the cantilever͒, which is measured through the difference in the constant compliance slopes of the inward and outward traces. Traditionally, friction is measured through lateral scanning of the substrate, which is time consuming, and requires an ex situ calibration of both the torsional spring constant and the lateral sensitivity of the photodiode detector. The present method requires no calibration other than the normal spring constant and the vertical sensitivity of the detector, which is routinely done in the force analysis. The present protocol can also be applied to preexisting force curves, and, in addition, it provides the means to correct force data for cantilevers with large probes.
New Approach to the Study of Particle–Surface Adhesion Using Atomic Force Microscopy
Journal of Colloid and Interface Science, 2000
The colloidal probe technique is commonly employed to determine the adhesion force between a particle and a solid surface. Characterization of the adhesion of a particle across a surface can be as important, if not more so, as the determination of an average value for the adhesion. Unfortunately, the measurement of the variation in adhesion can be difficult at best. A new approach for studying particle-surface adhesion based on the force-volume technique is presented. Upon combining the force-volume technique with a colloidal probe, not only is it possible to determine the average adhesion force, but an image of the spatial variation of the adhesion can also be obtained. This method is envisioned to have great potential for examining and analyzing the adhesion behavior in complex natural and technological systems. C 2000 Academic Press
International Journal of …, 2012
The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.