DATA: 21-07-2011

Giovedi' 21 Luglio ore 15:00 Speaker: DR. A. A. VOLINSKY (Univ. of South Florida) Abstract: The talk covers two topics related to current technical challenges in accelerators. Carbon films are considered for reducing secondary electron yield in accelerator beam lines. Different methods for carbon film deposition are being considered. Carbon-containing films formed during Cu film delamination from Si/SiO2 substrate in air. The newly formed fracture surfaces attracted carbon-containing species from the air, minimizing the surface energy. Controlled film fracture could be utilized for forming carbon films on surfaces. X-ray mirrors heat and deform during synchrotron or X-ray free electron laser operation. In-situ X-ray mirror curvature control is a challenging task. A new method for X-ray mirrors curvature control is proposed. Typically thermal expansion coefficient of thin films is different from the substrate. This effect is used to calculate residual stresses in thin films based on the substrate curvature change. Thin films bend the substrate when heated, reaching mechanical and thermal equilibrium. In case of a 5x5 cm2 cross-section 1 m long Si mirror, 200 mm thick W film will bend the mirror to desired 20 km radius of curvature when heated or cooled by 20 °C. It is feasible to utilize this mechanism for in-situ X-ray mirror curvature control in vacuum. The last portion of the talk describes electrowetting force measurement experiments. Electrowetting forces exerted on a custom-built indenter tip by salt water under electric field were measured directly. We modified the indenter by attaching a 9x9 mm2 horizontal glass plate to the tip. Salt water droplet was compressed to 400 mm height between the glass plate and two capacitors formed of metal and dielectric layers on a silicon wafer. Salt water connected these capacitors in series. Upon applying 75 V to the capacitors the constrained drop attempted to move due to the change in electrowetting force, measured by the indenter tip. This is the first time the electrowetting force was directly measured. Similar setup could be used for measuring adhesion forces exerted by live cells attaching to modified surfaces.


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