afmssgtps jt

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J.H. Teichroeb, J.A. Forrest Department of Physics, University of Waterloo, Canada Atomic Force Microscopy Results Feedback circuits maintain a constant frequency AFM basic schematic AFM Explorer Typical raw AFM image Typical region used in study Atomic Force Microscopy (AFM) uses a cantilever with a sharp tip (<50nm diameter), to probe material surfaces. Non-contact mode Cantilever oscillates near resonant frequency. Surface force gradient alters resonance. Non-contact mode Gold nanospheres become embedded into surface at 7 degrees below the bulk Tg PS surface exhibits liquid behavior even when the bulk is solid 0 min. 15 min. 120 min. T>Tg(bulk) T<Tg(bulk) Embedding occurs as expected. Embedding appears to follow some type of stretched exponential Data over extended time suggests embedding until Au-PS contact angle reached. Most interactions with solid material (including polymers) are through the surface, and not the bulk. Thin polymer films exhibit anomalous dynamics, including decreases in the glass transition temperature (where the polymer goes from being liquid-like to solid-like). Various theories put forth to explain polymer physics suggest a more mobile surface region. It is important to develop an understanding of the physical properties of polymer surfaces. Is the surface Tg the same as the bulk Tg? Use nanoparticle embedding to probe surface properties Introduction Sample Preparation Polystyrene (PS) Mn: 214 000 Mw/Mn: 1.03 Tg =97 °C. Glassy at room temperature. Sample Preparation & Measurement Materials Monodisperse Gold nanospheres Sizes used: 10, 20, 50nm Coefficient of Variation: < 10%, 15%, 20% respectively Particles/ml: 5.7x1012, 7.0x1011, 4.5x1010 HAuCl4 concentration: 0.01% Conclusions Embedding for T<Tg occurs within 50 minutes to depth of ~3.8 nm. Embedding for T<Tg occurs within 50 minutes to depth of ~3.5 nm. PS in Toluene Spin-coat onto Silicon substrate Anneal at desired temperature for some time (eg. 5 min.) Anneal film for 20h at 130oC Measure apparent height with AFM Air cool to near room temperature AFM Heating Stage Precision alignment of AFM with sample Allows repeated measurement of identical positions Constant frequency gives constant height, which is recorded as the topography of the sample. Embedding of 10nm Au Spheres on PS Apparent Height (nm) Time (minutes) Apparent Height (nm) Log(Time) Normalized 10 and 20nm Spheres at 105oC for Extended Time Spheres are no longer embedding by 24 and 48 hours for T> Tg. 0.23 0.14 Height of spheres on silicon do not change indicating embedding is not an artifact Height of spheres on silicon do not change indicating embedding is not an artifact