Direct Imaging of Nanoparticle Embedding into PS Films
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DIRECT IMAGING OF NANOPARTICLE EMBEDDING INTO PS FILMS J.H. Teichroeb and J.A. Forrest Department of Physics and Guelph-Waterloo Physics Institute, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1. ABSTRACT Non-contact Atomic Force Microscopy (AFM) was used to study the embedding of 10 nm and 20 nm gold nano-particles into the surface of polystyrene films spin-coated onto silicon substrates. The rate of embedding was determined by measuring the apparent nanosphere height as a function of annealing time. This was accomplished by two different methods. In the first case, each image (after a specific annealing time) is acquired at a different spot on the sample surface. In this case a fairly large (~40) number of particles were imaged in order to have acceptable statistics. A second method involved the use of a kinematic mounting hot stage that allowed the same spot on the sample to be imaged at each time. This allows the same final precision without the same necessity for imaging large numbers of particles. The results indicate that sub nm resolution is easily obtainable with either technique. INTRODUCTION Despite the growing interest from both fundamental and practical viewpoints, the near surface properties of polymer materials have yet to be quantified with any degree of consensus[1-5]. Measurements using SPM techniques to do nanoscopic dynamic mechanical analysis have been used to study the properties of polymer surfaces. Unfortunately, some studies support the idea of bulk-like surface properties and some studies support the idea of surface properties different from that of the bulk material [68]. A notable advantage of SPM dynamical mechanical measurement techniques is their ability to arrive at detailed numerical predictions for the viscoelastic properties of a near surface region. On the other hand, the large stress induced on the surface, the uncertainties in tip shape, and the necessity of using a reasonably complicated analysis make it difficult to easily identify any experiment as being more correct than any other. Other techniques have also been introduced in order to study this problem. One class of experiments involves the imprinting of some surface morphology and monitoring the decay of this morphology with time. This interesting class of experiments has yet to be fully explored, but two key experiments have been performed with contradicting conclusions. Hamdorf and Johansman imposed a micron sized surface relief grating on a PS film[9]. Heating this sample did not result in any difference in the surface morphology until the temperature was greater than the glass transition temperature of the film. In contrast by using an etched CaF2 substrate to template a PS surface, Kerle et al were able to demonstrate a remarkable relaxation of surface asperities even below the bulk glass transition[10]. It is notable that in this case the local curvature of the surface morphology was large enough that the sub-Tg evolution may have been a result of plastic
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flow. A key advantage of these
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