Experiments Prove Existence of Atomic Chain Anchors

Feb 03, 2005
Atom Anchors

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 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.

Source: NIST

Explore further: Nanomechanical sensors detect cancer from breath

add to favorites email to friend print save as pdf

Related Stories

Converting polyethylene waste into liquid fuel

Jan 27, 2014

Researchers in India have developed a relatively low-temperature process to convert certain kinds of plastic waste into liquid fuel as a way to re-use discarded plastic bags and other products. They report full details next ...

New sorbents efficiently extract uranium from seawater

Nov 20, 2013

(Phys.org) —Uranium mining for the nuclear industry causes immense environmental damage, which becomes more severe as reserves are depleted. The isolation of uranium from seawater would be a much more environmentally ...

Anti-fraud lasers and inks for transparent electronics

Nov 05, 2013

(Phys.org) —Two prototypes – a detection device which users lasers to fight fraud, and a piano which demonstrates the potential of printed electronics – have been unveiled by Cambridge researchers.

Recommended for you

Research proves nanobubbles are superstable

18 hours ago

The intense research interest in surface nanobubbles arises from their potential applications in microfluidics and the scientific challenge for controlling their fundamental physical properties. One of the ...

User comments : 0

More news stories

Research proves nanobubbles are superstable

The intense research interest in surface nanobubbles arises from their potential applications in microfluidics and the scientific challenge for controlling their fundamental physical properties. One of the ...

Google+ boss leaving the company

The executive credited with bringing the Google+ social network to life is leaving the Internet colossus after playing a key role there for nearly eight years.