SFM probes design criteria

Fort e constant-. This must be matched to the operational mode and to the rigidity of the surface being scanned soft surfaces (e.g., oiganics, polymers. hioinenibranes, etc.) will be deformed and/or damaged unless a. soft lever is used. In the contact mode the usual, and most useful, spring constant is in 

The implication is that a lever with a force constant of, say, 1 N/m will exert a force at the point of contact of 1 nN, if there is a 1-nm deflection. 

Resonance frequency For contact-mode levers the resonance frequency needs to be no lower than that of the instrumental eigenmode, and preferably around 10 kh , a high resonance frequency will also allow a higher scan rate. For noncontact operation the resonance frequency needs to be at or above 1(X) khz in order to give a high Q and thus provide better respon.se for the control loop. 

Reflective coating The top surface of the lever, near its free end, must present an efficient and flat mirror. surface so as to reflect the incident laser beam without loss or divergence. Also, the thermal stability of the deflection assembly is improved by minimizing energy deposition from the laser beam. 

Radius of curvature of tip It will be shown that if the radius of curvature of the tip is larger than the radii of curvature of surface features, then the resultant image will reflect tip shape rather than reveal actual surface topography. The radius of curvature ranges from 50 nm for routine pyramidally shaped tips to less than 10 nm for high-resolution tips (e.g carbon whiskers). 

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