Experiments Prove Existence of Atomic Chain Anchors

February 3, 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: Using an electron to probe the tiny magnetic core of an atom

Related Stories

Using an electron to probe the tiny magnetic core of an atom

August 12, 2015

Precise information about the magnetic properties of nuclei is critical for studies of what's known as the 'weak force.' While people do not feel this force in the same way they feel electricity or gravity, its effects are ...

The protein problem

June 17, 2015

The importance of proteins is difficult to overstate; they play a critical role in countless biological processes. An enhanced understanding of their structure and function is essential to advancing the state of the art in ...

A controversial theory of olfaction deemed implausible

June 5, 2015

Humans can discriminate tens of thousands of odors. While we may take our sense of smell for granted, it adds immeasurably to our quality of life: the aroma of freshly brewed coffee; the invigorating smell of an ocean breeze ...

Recommended for you

For 2-D boron, it's all about that base

September 2, 2015

Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.

0 comments

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.