Nano-sonar uses electrons to measure under the surface

Feb 27, 2009
In a computer simulation, Jülich scientists succeeded in showing what shape these rings take on the crystal lattice of copper. Credit: Forschungszentrum Jülich

Just as sonar sends out sound waves to explore the hidden depths of the ocean, electrons can be used by scanning tunnelling microscopes to investigate the well-hidden properties of the atomic lattice of metals. As researchers from Göttingen, Halle and Jülich now report in the high-impact journal Science, they succeeded in making bulk Fermi surfaces visible in this manner. Fermi surfaces determine the most important properties of metals.

"Fermi surfaces give metals their personality, so to speak," explained Prof. Stefan Blügel, Director at the Jülich Institute of Solid State Research. Important properties, such as conductivity, heat capacity and magnetism, are determined by them. On the Fermi surfaces inside the atomic union, high-energy electrons are in motion. Depending on what form the surfaces have and what mobility is assigned to the electrons, they determine the physical properties of metals.

This is the Fermi surface of copper metal. The colors represent the curvature of the surface, which determines the propagation properties for electron waves. Credit: Martin Luther University Halle

In their latest publication, the researchers report on how they used a scanning tunnelling microscope to direct electrons into a copper sample. As electrons spread out like waves, they pass through the metal and are scattered and reflected at obstacles in the bulk, such as single cobalt atoms. "The overlap between incoming and outgoing waves is so strong," said Dr. Samir Lounis from Forschungszentrum Jülich who turned the theoretical calculations into an experiment, "that they can be measured as spherical patterns on the surface using the scanning tunnelling microscope.

The somewhat deformed rings on the surface allow us to draw direct conclusions on the shape of the Fermi surfaces and the depth of the cobalt atoms, similar to how sonar recognises the ocean floor by means of reflected sound waves. "We hope that more sophisticated methods will make it possible to gain a detailed understanding of deep impurities and interfaces between atomic lattices," explained Lounis. For his simulations of the scanning tunnelling experiment, he used the supercomputer known as JUMP in the Jülich Supercomputing Centre.

A scanning tunneling microscope recognizes spherical patterns on a copper surface (image section approx. nine times nine nanometers). These irregularities in electron distribution are caused by cobalt atoms deep inside the copper. Credit: Forschungszentrum Jülich

In a related article in the "Perspectives" section of "Science", the innovative approach is praised. A scanning tunnelling microscope is primarily used to characterise the surface of a sample. Thanks to the theoretical work in Jülich, it can now be used to gain a direct insight into the bulk of solids and to understand interesting effects in the nanoworld.

More information: Science, 27 February 2009, Vol 323, Issue 5918, Seeing the Fermi Surface in Real Space by Nanoscale Electron Focusing, Weismann et al.

Source: Helmholtz Association of German Research Centres

Explore further: 3-D images of tiny objects down to 25 nanometres

Related Stories

Development of a carnivorous pitcher leaf

Mar 16, 2015

Carnivorous plants have strange-shaped leaves, and they can grow on nutrient-poor environments by trapping and eating small animals. Charles Darwin, often called "the father of evolution", was also interested ...

Hydrocarbon photocatalysts get in shape and go for gold

Mar 10, 2015

A combination of semiconductor catalysts, optimum catalyst shape, gold-copper co-catalyst alloy nanoparticles and hydrous hydrazine reducing agent enables an increase of hydrocarbon generation from CO2 by a facto ...

Recommended for you

3-D images of tiny objects down to 25 nanometres

16 hours ago

Scientists at the Paul Scherrer Institute and ETH Zurich (Switzerland) have created 3D images of tiny objects showing details down to 25 nanometres. In addition to the shape, the scientists determined how ...

Solving molybdenum disulfide's 'thin' problem

Mar 27, 2015

The promising new material molybdenum disulfide (MoS2) has an inherent issue that's steeped in irony. The material's greatest asset—its monolayer thickness—is also its biggest challenge.

Snowflakes become square with a little help from graphene

Mar 25, 2015

The breakthrough findings, reported in the journal Nature, allow better understanding of the counterintuitive behaviour of water at the molecular scale and are important for development of more efficient techno ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Ashibayai
2 / 5 (1) Feb 28, 2009
Awesomely interesting.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.