Synopsis: Detecting a Molecular Duet

Using a scanning tunneling microscope, researchers detect coupled vibrations between two molecules.
Synopsis figure
Zhumin Han/University of California, Irvine

Molecules vibrate in many different ways—like tiny musical instruments. Nearby molecules can even vibrate in “harmony” with each other, as observed in large molecular systems. For the first time, researchers have detected such vibrational coupling between two individual molecules. The experimental technique—based on a scanning tunneling microscope (STM)—may offer a new way to study the chemical components of complex molecules.

Molecular vibrations can be studied with so-called inelastic electron tunneling spectroscopy (IETS). This technique is based on the fact that a molecule adsorbed on the tip of an STM probe (or on the surface beneath the probe) will affect the tunneling rate of electrons between probe and surface. In particular, one can identify peaks in the tunneling current spectrum as the voltage is varied. These peaks correspond to vibrational modes of the adsorbed molecule.

Wilson Ho at the University of California, Irvine, and colleagues performed IETS experiments in which carbon monoxide (CO) molecules were allowed to adsorb on both tip and surface. Working at subkelvin temperatures, the team took tunneling spectra at various tip-sample distances. The molecules repel each other at short-range distances, and this interaction can couple their vibrations. The team detected this coupling by identifying a unique peak in the tunneling spectra. They verified this identification with density-functional calculations. The observed peak shifted in frequency as the tip moved closer to the surface. Ho’s team ascribed this shift to a tilting of the CO molecules, which altered their respective alignment and the intermolecular separation. Other molecules, like OH and SH, should have unique vibrational couplings to CO, implying that one could use a CO-functionalized tip as a sensitive chemical probe.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: Sharpening the Features of Optical Lattices
Atomic and Molecular Physics

Viewpoint: Sharpening the Features of Optical Lattices

Lasers trap cold atoms in a lattice of potential barriers much narrower than the lasers’ wavelength. Read More »

Focus: <i>Video</i>—Condensate Duo Puts on a Show
Atomic and Molecular Physics

Focus: Video—Condensate Duo Puts on a Show

Simulations of the mixing of two oppositely polarized Bose-Einstein condensates produce fingering patterns that look like those of classical fluids. Read More »

Viewpoint: Atoms Oscillate Collectively in Large Optical Lattice
Atomic and Molecular Physics

Viewpoint: Atoms Oscillate Collectively in Large Optical Lattice

By coupling atoms in an optical lattice to a thin elastic membrane, researchers have demonstrated a dynamic instability that is evidence of collective atomic motion. Read More »

More Articles