Extending AFM Phase Image of Nanocomposite Structures to 3D using FIB
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Extending AFM Phase Image of Nanocomposite Structures to 3D using FIB
Russell J. Bailey1, Remco Geurts2, Debbie J. Stokes2, Frank de Jong2 and Asa H. Barber1 1
Department of Materials, School of Engineering & Materials Science, Queen Mary University of London, London E1 4NS United Kingdom. 2
FEI Company, 5651 GG Eindhoven, Netherlands.
ABSTRACT The mechanical behavior of nanocomposites is critically dependent on their structural composition. In this paper we use Focused Ion Beam (FIB) microscopy to prepare surfaces from a layered polymer nanocomposite for investigation using phase contrast atomic force microscopy (AFM). Phase contrast AFM provides mechanical information on the surface examined and, by combining with the sequential cross-sectioning of FIB, can extend the phase contract AFM into three dimensions. INTRODUCTION Nanocomposites are used in a range of applications and have been shown to be particularly effective for mechanical functions [1]. However, this mechanical function is critically related to elucidating the structural composition of the nanocomposite material. A range of techniques are available to evaluate mechanical properties of nanocomposites and can be classified into two distinct approaches. The first approach relies on measuring the mechanical behavior of the whole nancomposite and then applying varies models in order to elucidate the contribution of the smaller constituents. These approaches are limited as a number of assumptions are made in terms of the mechanical properties of the constituents and their interactions with one another. The limitations in bulk mechanical testing have led to the development of techniques suitable to measure the properties of these smaller constituents in order to evaluate composite mechanical performance more fully. Constituent evaluations in nanocomposites are relatively limited due to the constituent properties having dimensions of the order of nanometers, which are below the loading resolution of conventional engineering mechanical testing methodologies. Examples of nanocomposite constituent testing exist in the literature and range from mechanical testing of isolated individual nanomaterial constituents [2, 3] to indentation techniques [4, 5]. However, nanomaterial isolation is restricted as only one part of the nanocomposite can be considered at one time, making evaluation of a nanocomposite a lengthy process, whereas nanoindentation is able to only probe surface properties of a nanocomposite.
Phase contrast AFM is an additional technique that is able to measure the mechanical properties at surfaces but is generally infrequently used in the literature. Phase contrast AFM is a mode of amplitude modulated AFM whereby a probe attached to a cantilever is driven at its resonance frequency and periodically makes contact with the sample surface. The AFM probe is scanned over the sample surface and a predefined set-point amplitude is maintained by a feedback loop. The phase lag between the driving oscillation and the response of the cantilever whilst scann
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