Synopsis: Separating oil from water with magnetic resonance force microscopy

An advance in magnetic resonance force microscopy enhances its chemical sensitivity and opens up the possibility of identifying different organic substances at the nanoscale.
Synopsis figure
Illustration: Alan Stonebraker

In samples that contain very few spins, random spin flips generate a fluctuating polarization that exceeds the typical thermal, or Boltzmann, polarization. Although the dominance of this statistical polarization would appear to pose a major obstacle to nanoscale magnetic resonance experiments, in fact, it can be harnessed for nuclear spin detection.

In bulk samples, the magnetic resonance signal from an ensemble of one type of nucleus can be enhanced by “cross polarizing” it with an ensemble of another species.  In simple terms, the dipolar coupling between two spin ensembles allows polarization to transfer from one ensemble to another, leaving the fingerprint of a particular species on the other. In a paper appearing in Physical Review Letters, Martino Poggio, now at the Swiss Nanoscience Institute and the University of Basel, and colleagues at IBM Almaden adapt this cross-polarization technique to a system in which statistical fluctuations dominate rather than the Boltzmann polarization.  With magnetic resonance force microscopy (MFRM) they are able to distinguish ensembles of 1H and 13C spins in 13C-enriched stearic acid (C18H36O2).

Poggio et al. are able to observe the influence of the 13C spins on the 1H spin signal (and vice versa), a result that can, for instance, allow MRFM to distinguish between organic materials and water.  This promises well for materials characterization at the nanoscale, and could eventually be applied to distinguish individual protein components in nanoscale biological structures. – Daniel Ucko


Announcements

More Announcements »

Subject Areas

MagnetismNanophysics

Previous Synopsis

Atomic and Molecular Physics

Stretching out entanglement

Read More »

Next Synopsis

Atomic and Molecular Physics

Winding up with a better clock

Read More »

Related Articles

Viewpoint: An Ultrafast Switch for Electron Emission
Condensed Matter Physics

Viewpoint: An Ultrafast Switch for Electron Emission

By firing laser pulses of two different colors at a nanosized metal tip, researchers create an interference effect that turns electron emission on and off with femtosecond timing. Read More »

Synopsis: Decoding the Light from Ten Million Quantum Dots
Photonics

Synopsis: Decoding the Light from Ten Million Quantum Dots

A spectroscopy method can identify quantum dots within an ensemble based on their size and emission frequency. Read More »

Synopsis: Coulomb Drag in a Double Dot
Nanophysics

Synopsis: Coulomb Drag in a Double Dot

Electric current passing through a quantum dot can generate current in a nearby dot through a coordinated tunneling mechanism. Read More »

More Articles