Helium 'balloons' offer new path to control complex materials

June 26, 2015, Oak Ridge National Laboratory
Inserting helium atoms (visualized as a red balloon) into a crystalline film (gold) allowed Oak Ridge National Laboratory researchers to control the material's elongation in a single direction. Credit: ORNL

Researchers at the Department of Energy's Oak Ridge National Laboratory have developed a new method to manipulate a wide range of materials and their behavior using only a handful of helium ions.

The team's technique, published in Physical Review Letters, advances the understanding and use of complex oxide materials that boast unusual properties such as superconductivity and colossal magnetoresistance but are notoriously difficult to control.

For the first time, ORNL researchers have discovered a simple way to control the elongation of a crystalline material along a single direction without changing the length along the other directions or damaging the crystalline structure. This is accomplished by adding a few into a complex oxide material and provides a never before possible level of control over magnetic and .

"By putting a little helium into the material, we're able to control strain along a single axis," said ORNL's Zac Ward, who led the team's study. "This type of control wasn't possible before, and it allows you to tune material properties with a finesse that we haven't previously had access to."

The intricate way in which electrons are bound inside means that any strain—stretching, pulling or pushing of the structure—triggers changes in many different electronic properties. This ripple effect complicates scientists' ability to study or make use of the finicky materials.

The researchers demonstrated the technique on a common oxide material known as LSMO but they anticipate the technique will be widely applicable to both functionality driven materials science research and fundamental physics studies.

"Complex oxides are where we expect an immediate impact, but this technique should be an important new tool to use on any material where crystal symmetry affects functionality," Ward said.

The team's work is a step toward bringing complex materials into commercial applications, which would greatly benefit from the ability to tune with processing similar to current semiconductor technologies.

"Our strain doping technique demonstrates a path to achieving this need, as it can be implemented using established ion implantation infrastructure in the semiconductor industry," Ward said.

The method uses a low-energy ion gun to add small numbers of helium ions into the material after it has been produced. The process is also reversible; the helium can be removed by heating the material to high temperatures in vacuum. Previously developed strain tuning methods modify all directions in a material and cannot be altered or reversed afterwards.

"We can easily control the amount of strain and how deep that strain is inside the material," Ward said. "By controlling the number of helium atoms inserted into an epitaxial film, we select a strain state in one direction while the other two directions are held in place by the substrate."

The team's experimental technique will also benefit theoretical research that seeks to model complex materials to predict and understand their behavior.

"The complexity of these requires a huge equation to explain their behaviors," Ward said. "Normal strain tuning methods require you to change many variables in that equation which means that you don't really know which one is giving you a specific reaction. In our case, there's one variable. You can feed in a single term and try to break through that complexity a little bit by simplifying it. This is a great method to experimentally probe theoretical models."

Explore further: Physicists observe magnetic 'devil's staircase'

More information: The paper is published as "Strain doping: Reversible single axis control of a complex oxide lattice via helium implantation." journals.aps.org/prl/abstract/ … ysRevLett.114.256801

Related Stories

Physicists observe magnetic 'devil's staircase'

June 24, 2015

(Phys.org)—Many hiking trails feature a "devil's staircase"—a set of steps that are often steep and difficult to climb. The devil's staircase is also the name of a mathematical function whose graph exhibits a jagged step-like ...

In Brief: Nanodots to the rescue

May 11, 2011

By applying the magnetic properties of iron nanodots to complex materials, a research team has overcome an obstacle to getting ultra-thin or highly strained films to perform on par with their bulk counterparts.

Buckle up for fast ionic conduction

June 15, 2015

ETH material engineers found that the performance of ion-conducting ceramic membranes that are so important in industry depends largely on their strain and buckling profiles. For the first time, scientists can now selectively ...

X-ray imaging reveals secrets in battery materials

June 18, 2015

In a new study, researchers explain why one particular cathode material works well at high voltages, while most other cathodes do not. The insights, published in the 19 June issue of the journal Science, could help battery ...

New research uncovers path to defect-free thin films

September 20, 2012

(Phys.org)—A team led by Oak Ridge National Laboratory's Ho Nyung Lee has discovered a strain relaxation phenomenon in cobaltites that has eluded researchers for decades and may lead to advances in fuel cells, magnetic ...

Recommended for you

CMS gets first result using largest-ever LHC data sample

February 15, 2019

Just under three months after the final proton–proton collisions from the Large Hadron Collider (LHC)'s second run (Run 2), the CMS collaboration has submitted its first paper based on the full LHC dataset collected in ...

Gravitational waves will settle cosmic conundrum

February 14, 2019

Measurements of gravitational waves from approximately 50 binary neutron stars over the next decade will definitively resolve an intense debate about how quickly our universe is expanding, according to findings from an international ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

4R0NU1
not rated yet Jun 27, 2015
wow, be interesting to see what fundamental gains can be made
rufusgwarren
not rated yet Jun 28, 2015
The steady state may be simulated with iteration to meet measured events and structure. Using only a + and - charge in a 4D space ...

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.