Controllable selective exfoliation of high-quality graphene nanosheets and nanodots by ionic liquid assisted grinding

Bulk quantities of graphene nanosheets and nanodots have been selectively fabricated by mechanical grinding exfoliation of natural graphite in a small quantity of ionic liquids. The resulting graphene sheets and dots are solvent free with low levels of naturally absorbed oxygen, inherited from the starting graphite. The sheets are only two to five layers thick. The graphene nanodots have diameters in the range of 9-29 nm and heights in the range of 1-16 nm, which can be controlled by changing the processing time.Comment: * Corresponding authors: [email protected]; [email protected]

Colloid phenomena in surface-modified polymer systems

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Hydrodynamic methods for calibrating the normal spring constant of microcantilevers

Knowledge of the spring constants of microcantilevers is vital in atomic force microscopy and for cantilever-based devices that are, for example, employed as probes in biomedical applications. We compare two recently developed hydrodynamic methods for the determination of the normal spring constant of microcantilevers. Both approaches are non-invasive when determining the spring constant and require only knowledge of the thermal noise response of the cantilever in a fluid and its plan view dimensions. The methods do not bear the risk of damaging the cantilever and are therefore attractive for example in mass sensing applications in cases where the cantilever has been modified, e. g. with a coating. The specific strengths of the methods are discussed and the results for a variety of cantilevers are presented and compared.</p

Calibration of the normal spring constant of microcantilevers in a parallel fluid flow

We demonstrate a novel approach to determine the normal spring constant of microcantilevers. The cantilevers are placed parallel to a fluid flow thus establishing one of the walls of the flow channel. Resonance frequencies are recorded depending on the velocity of the fluid. The pressure gradient resulting from the flow causes the resonance frequency to change. This change can be exploited to deduce the cantilever spring constant with high precision. The method we present can be performed in situ and does not involve any contact of the cantilever with a surface thus having great potential for the calibration of modified probes and for being incorporated in microfluidic systems. In case the spring constant is known, the setup can also be employed to determine the velocity of fluid flows and the flow rate with high precision and up to high speeds. (c) 2007 American Institute of Physics.</p