Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Experiments prove existence of atomic chain ’anchors’

04.02.2005


Atoms at the ends of self-assembled atomic chains act like anchors with lower energy levels than the "links" in the chain, according to new measurements by physicists at the National Institute of Standards and Technology (NIST).


The two images above show the energy levels (vertical scale) and spatial positions (white lines) of electrons within a three-atom chain. The top image shows the calculated or theoretical results; the bottom image shows the measured energy levels in a physical experiment. Electrons are most likely to be located in the red areas and least likely in the blue areas. Both images indicate that the electrons in the outermost atoms (positioned on the far left and right at the bottom) have lower energy than those within the center atom.



The first-ever proof of the formation of "end states" in atomic chains may help scientists design nanostructures, such as electrical wires made "from the atoms up," with desired electrical properties.

The NIST experiments, described in the Feb. 4 issue of the journal Science,* involved measuring and comparing the electronic properties of gold atoms in short chains assembled on silicon surfaces. Energy levels of the electrons within the end atoms of the chains were lower than those of inner atoms. This condition arises because the structural, chemical and electronic symmetry of a chain is broken at each end, and the atoms’ electrons are redistributed to lower the chain’s energy. The electronic structure of atomic chains is comparable to the electronic structure of bulk crystals, in which surface atoms have different properties than atoms inside the crystal.


"In the past three decades the study of surface states on crystals has been a major endeavor by research groups from all over the world," says Jason Crain, lead author of the Science paper. "Our study is the first to show the formation of localized states at the ends of single atom chains. The existence of end states will have implications for future studies of one-dimensional nanostructures."

The NIST measurements were made with a scanning tunneling microscope (STM) and were enabled, in part, by the self-assembly of the gold chains on a silicon surface. Unlike the metal surfaces used in previous STM studies of single-atom chains, the silicon surface behaved as an insulator, allowing scientists to better isolate the chains and improve measurements of their atoms’ electron energy levels.

The STM, which has a needle-like tip that can apply various levels of voltage, was used to make two types of measurements of numerous chains composed of three to nine atoms. First, by maintaining a constant current between the tip and the gold-on-silicon surface, the STM produced a three-dimensional image of the surface topography. As the tip scanned across the sample, it rose and fell with changes in surface features to maintain a stable current flow. Then, by holding the STM tip at a constant distance from the surface, the scientists measured changes in current as a function of tip voltage. Measures of conductivity were used to determine the energies and spatial distribution of electrons in the chains, which showed differences between the inner and end atoms.

Laura Ost | EurekAlert!
Further information:
http://www.nist.gov

More articles from Physics and Astronomy:

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

nachricht Magnetic moment of a single antiproton determined with greatest precision ever
19.01.2017 | Johannes Gutenberg-Universität Mainz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>