© 2004 Nature Publishing Group

can probe spins as deep as 100 nm below the sample surface. The magnetic tip at the end of an ultrasensitive silicon cantilever is positioned 125 nm above a polished SiO2 sample containing a low density of unpaired electron spins. The resonant slice represents those points in the sample where the field from the magnetic tip (plus an external field) matches the condition for magnetic resonance. (Reprinted with permission from Nature, 430:329–32, 2004).

Two recent advances in force-detection microscopy may one day revolutionize the science of the very small. One prototype tweaks traditional nuclear magnetic resonance (NMR) techniques; the other represents a step toward viewing single molecules directly in three dimensions.

Conventional NMR and magnetic resonance imaging (MRI) technologies work by detecting small, oscillating magnetic fields that induce a voltage in a nearby coil. Both seek to detect the spins of...

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