Synopsis: A van der Waals Tuning Knob

By adding dopant atoms to a graphene sheet, researchers are able to control the van der Waals attraction that the surface exerts on molecules.
Synopsis figure
Nicolae Atodiresei/Forschungszentrum Jülich

The van der Waals attraction occurs when two objects come close enough to induce an electric polarization in one another. Researchers have now demonstrated a way to tune the van der Waals force exerted by graphene on a molecule. The technique, which is based on doping the graphene from the back side, could be used to control adsorption to graphene for a wide range of molecules and raises the prospect of electrical control of adsorption.

Tunability is nothing new to graphene. Its unique cone-shaped electronic band structure allows one to control the potential energy (or Fermi level) of its electrons by simply adding a gate electrode or dopant atoms. Recent work has used this Fermi-level tuning to manipulate the strength of ionic bonding between atoms and the graphene surface. Felix Huttmann from the University of Cologne, Germany, and his colleagues have extended this surface control to the weaker, but more general, van der Waal interactions.

The researchers produced a graphene sheet on a metal substrate and then added either electron-donor atoms (n-type dopants) or electron-acceptor atoms (p-type dopants). In both cases, the dopants nestled between the graphene and metal, leaving a “clean slate” on the top surface of the graphene. To explore van der Waals interactions, the team exposed the graphene to naphthalene molecules and observed their adsorption on the surface with scanning tunneling microscopy. When the samples were heated, the temperature at which naphthalene desorbed was higher for n doping than for p doping, implying that the van der Waals attraction was stronger in the former. Theoretical calculations confirmed this picture by demonstrating that n doping causes the electron orbitals around carbon atoms to extend out further spatially, making the atoms more easily polarizable.

This research is published in Physical Review Letters.

–Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

GrapheneChemical PhysicsMaterials Science

Previous Synopsis

Soft Matter

Down to Friction

Read More »

Next Synopsis

Particles and Fields

Black Hole Tests of Fermionic Dark Matter

Read More »

Related Articles

Synopsis: How Diamond-Like Carbon Films Grow
Materials Science

Synopsis: How Diamond-Like Carbon Films Grow

Machine-learning-based molecular dynamics simulations explain the growth mechanism of diamond-like amorphous carbon films. Read More »

Synopsis: Hidden Structure of Plasmons
Plasmonics

Synopsis: Hidden Structure of Plasmons

Calculations of the current density within collective charge oscillations called plasmons reveal a complicated structure that could affect how plasmons reflect off a boundary. Read More »

Synopsis: Stretching Graphene Localizes its Electrons
Graphene

Synopsis: Stretching Graphene Localizes its Electrons

The electrical properties of a graphene bilayer can be tuned by stretching and rotating one of the bilayer’s sheets. Read More »

More Articles