Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

ORNL Researchers Make Scalable Arrays of ‘Building Blocks’ for Ultrathin Electronics

24.07.2015

Semiconductors, metals and insulators must be integrated to make the transistors that are the electronic building blocks of your smartphone, computer and other microchip-enabled devices. Today’s transistors are miniscule—a mere 10 nanometers wide—and formed from three-dimensional (3D) crystals.

But a disruptive new technology looms that uses two-dimensional (2D) crystals, just 1 nanometer thick, to enable ultrathin electronics. Scientists worldwide are investigating 2D crystals made from common layered materials to constrain electron transport within just two dimensions.


Complex, scalable arrays of semiconductor heterojunctions—promising building blocks for future electronics—were formed within a two-dimensional crystalline monolayer of molybdenum deselenide by converting lithographically exposed regions to molybdenum disulfide using pulsed laser deposition of sulfur atoms. Sulfur atoms (green) replaced selenium atoms (red) in lithographically exposed regions (top) as shown by Raman spectroscopic mapping (bottom). Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy

Researchers had previously found ways to lithographically pattern single layers of carbon atoms called graphene into ribbon-like “wires” complete with insulation provided by a similar layer of boron nitride. But until now they have lacked synthesis and processing methods to lithographically pattern junctions between two different semiconductors within a single nanometer-thick layer to form transistors, the building blocks of ultrathin electronic devices.

Now for the first time, researchers at the Department of Energy’s Oak Ridge National Laboratory have combined a novel synthesis process with commercial electron-beam lithography techniques to produce arrays of semiconductor junctions in arbitrary patterns within a single, nanometer-thick semiconductor crystal. The process relies upon transforming patterned regions of one existing, single-layer crystal into another.

The researchers first grew single, nanometer-thick layers of molybdenum diselenide crystals on substrates and then deposited protective patterns of silicon oxide using standard lithography techniques. Then they bombarded the exposed regions of the crystals with a laser-generated beam of sulfur atoms. The sulfur atoms replaced the selenium atoms in the crystals to form molybdenum disulfide, which has a nearly identical crystal structure. The two semiconductor crystals formed sharp junctions, the desired building blocks of electronics. Nature Communications reports the accomplishment.

“We can literally make any kind of pattern that we want,” said Masoud Mahjouri-Samani, who co-led the study with David Geohegan. Geohegan, head of ORNL’s Nanomaterials Synthesis and Functional Assembly Group at the Center for Nanophase Materials Sciences, is the principal investigator of a Department of Energy basic science project focusing on the growth mechanisms and controlled synthesis of nanomaterials.

Millions of 2D building blocks with numerous patterns may be made concurrently, Mahjouri-Samani added. In the future, it might be possible to produce different patterns on the top and bottom of a sheet. Further complexity could be introduced by layering sheets with different patterns.

Added Geohegan, “The development of a scalable, easily implemented process to lithographically pattern and easily form lateral semiconducting heterojunctions within two-dimensional crystals fulfills a critical need for ‘building blocks’ to enable next-generation ultrathin devices for applications ranging from flexible consumer electronics to solar energy.”

Tuning the bandgap

“We chose pulsed laser deposition of sulfur because of the digital control it gives you over the flux of the material that comes to the surface,” said Mahjouri-Samani. “You can basically make any kind of intermediate alloy. You can just replace, say, 20 percent of the selenium with sulfur, or 30 percent, or 50 percent.” Added Geohegan, “Pulsed laser deposition also lets the kinetic energy of the sulfur atoms be tuned, allowing you to explore a wider range of processing conditions.”

It is important that by controlling the ratio of sulfur to selenium within the crystal, the researchers can tune the bandgap of the semiconductors, an attribute that determines electronic and optical properties. To make optoelectronic devices such as electroluminescent displays, microchip fabricators integrate semiconductors with different bandgaps. For example, molybdenum disulfide’s bandgap is greater than molybdenum diselenide’s.

Applying voltage to a crystal containing both semiconductors causes electrons and “holes” (positive charges created when electrons vacate) to move from molybdenum disulfide into molybdenum diselenide and recombine to emit light at the bandgap of molybdenum diselenide. For that reason, engineering the bandgaps of monolayer systems can allow the generation of light with many different colors, as well as enable other applications such as transistors and sensors, Mahjouri-Samani said.

Next the researchers will see if their pulsed laser vaporization and conversion method will work with atoms other than sulfur and selenium. “We’re trying to make more complex systems in a 2D plane—integrate more ingredients, put in different building blocks—because at the end of the day, a complete working device needs different semiconductors and metals and insulators,” Mahjouri-Samani said.

To understand the process of converting one nanometer-thick crystal into another, the researchers used powerful electron microscopy capabilities available at ORNL, notably atomic-resolution Z-contrast scanning transmission electron microscopy, which was developed at the lab and is now available to scientists worldwide using the Center for Nanophase Materials Sciences. Employing this technique, electron microscopists Andrew Lupini and visiting scientist Leonardo Basile imaged hexagonal networks of individual columns of atoms in the nanometer-thick molybdenum diselenide and molybdenum disulfide crystals.

“We could directly distinguish between sulfur and selenium atoms by their intensities in the image,” Lupini said. “These images and electron energy loss spectroscopy allowed the team to characterize the semiconductor heterojunction with atomic precision.”

The title of the paper is “Patterned Arrays of Lateral Heterojunctions within Monolayer Two-Dimensional Semiconductors.”

The research was sponsored by the U.S. Department of Energy, Office of Science. A portion of the work was conducted at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL. Basile received support from the National Secretariat of Higher Education, Science, Technology and Innovation of Ecuador.

UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/ .—by Dawn Levy

Contact Information
Dawn Levy
Science Writer
levyd@ornl.gov
Phone: 865-576-6448
Mobile: 865-202-9465

Dawn Levy | newswise
Further information:
http://www.ornl.gov

More articles from Power and Electrical Engineering:

nachricht Did you know that infrared heat and UV light contribute to the success of your barbecue?
26.07.2017 | Heraeus Noblelight GmbH

nachricht Ultrathin device harvests electricity from human motion
24.07.2017 | Vanderbilt University

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

 
Latest News

CCNY physicists master unexplored electron property

26.07.2017 | Physics and Astronomy

Molecular microscopy illuminates molecular motor motion

26.07.2017 | Life Sciences

Large-Mouthed Fish Was Top Predator After Mass Extinction

26.07.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>