For more than a decade, the workhorse sensors for MRFM have been silicon cantilevers with a resonance frequency of 3-5 kHz. They reach a force sensitivity of a few aN per root Hz when cooled to liquid He temperatures. Recently, several groups started investigating the use of silicon nitride membranes as improved force sensors. These devices are typically in the MHz range and feature quality factors beyond 100 millions, which may allow the detection of forces below 100 zN. In ...
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