Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Process for 'two-faced' nanomaterials may aid energy, information tech

Selenium atoms, represented by orange, implant in a monolayer of blue tungsten and yellow sulfur to form a Janus layer. In the background, electron microscopy confirms atomic positions.

CREDIT
Oak Ridge National Laboratory, U.S. Dept. of Energy
Selenium atoms, represented by orange, implant in a monolayer of blue tungsten and yellow sulfur to form a Janus layer. In the background, electron microscopy confirms atomic positions. CREDIT Oak Ridge National Laboratory, U.S. Dept. of Energy

Abstract:
A team led by the Department of Energy's Oak Ridge National Laboratory used a simple process to implant atoms precisely into the top layers of ultra-thin crystals, yielding two-sided structures with different chemical compositions. The resulting materials, known as Janus structures after the two-faced Roman god, may prove useful in developing energy and information technologies.

Process for 'two-faced' nanomaterials may aid energy, information tech

Oak Ridge, TN | Posted on June 26th, 2020

"We're displacing and replacing only the topmost atoms in a layer that is only three atoms thick, and when we're done, we have a beautiful Janus monolayer where all the atoms in the top are selenium, with tungsten in the middle and sulfur in the bottom," said ORNL's David Geohegan, senior author of the study, which is published in ACS Nano, a journal of the American Chemical Society. "This is the first time that Janus 2D crystals have been fabricated by such a simple process."

Yu-Chuan Lin, a former ORNL postdoctoral fellow who led the study, added, "Janus monolayers are interesting materials because they have a permanent dipole moment in a 2D form, which allows them to separate charge for applications ranging from photovoltaics to quantum information. With this straightforward technique, we can put different atoms on the top or bottom of different layers to explore a variety of other two-faced structures."

This study probed 2D materials called transition metal dichalcogenides, or TMDs, that are valued for their electrical, optical and mechanical properties. Tuning their compositions may improve their abilities to separate charge, catalyze chemical reactions or convert mechanical energy to electrical energy and vice versa.

A single TMD layer is made of a ply of transition metal atoms, such as tungsten or molybdenum, sandwiched between plies of chalcogen atoms, such as sulfur or selenium. A molybdenum disulfide monolayer, for example, features molybdenum atoms between plies of sulfur atoms, structurally similar to a sandwich cookie with a creamy center between two chocolate wafers. Replacing one side's sulfur atoms with selenium atoms produces a Janus monolayer, akin to swapping one of the chocolate wafers with a vanilla one.

Before this study, turning a TMD monolayer into a two-faced structure was more a theoretical feat than an actual experimental accomplishment. In the many scientific papers about Janus monolayers published since 2017, 60 reported theoretical predictions and only two described experiments to synthesize them, according to Lin. This reflects the difficulty in making Janus monolayers due to the significant energy barriers that prevent their growth by typical methods.

In 2015, the ORNL group discovered that pulsed laser deposition could convert molybdenum diselenide to molybdenum disulfide. At the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL, pulsed laser deposition is a critical technique for developing quantum materials.

"We speculated that by controlling the kinetic energy of atoms, we could implant them in a monolayer, but we never thought we could achieve such exquisite control," Geohegan said. "Only with atomistic computational modeling and electron microscopy at ORNL were we able to understand how to implant just a fraction of a monolayer, which is amazing."

The method uses a pulsed laser to vaporize a solid target into a hot plasma, which expands from the target toward a substrate. This study used a selenium target to produce a beam-like plasma of clusters of two to nine selenium atoms, which were directed to strike pre-grown tungsten disulfide monolayer crystals.

The key to success in creating two-faced monolayers is bombarding the crystals with a precise amount of energy. Throw a bullet at a door, for example, and it bounces off the surface. But shoot the door and the bullet rips right through. Implanting selenium clusters into only the top of the monolayer is like shooting a door and having the bullet stop in its surface.

"It's not easy to tune your bullets," Geohegan said. The fastest selenium clusters, with energies of 42 electron volts (eV) per atom, ripped through the monolayer; they needed to be controllably slowed to implant into the top ply.

"What's new from this paper is we are using such low energies," said Lin. "People never explored the regime below 10 eV per atom because commercial ion sources only go down to 50 eV at best and don't allow you to choose the atoms you would like to use. However, pulsed laser deposition lets us choose the atoms and explore this energy range fairly easily."

The key to tuning the kinetic energy, Lin said, is to controllably slow the selenium clusters by adding argon gas in a pressure-controlled chamber. Limiting the kinetic energy restricts the penetration of atomically thin layers to specific depths. Injecting a pulse of atom clusters at low energy temporarily crowds and displaces atoms in a region, causing local defects and disorder in the crystal lattice. "The crystal then ejects the extra atoms to heal itself and recrystallizes into an orderly lattice," Geohegan explained. Repeating this implantation and healing process over and over can increase the selenium fraction in the top layer to 100% to complete the formation of a high-quality Janus monolayer.

Controllably implanting and recrystallizing 2D materials in this low-kinetic-energy regime is a new road to making 2D quantum materials. "Janus structures can be made in mere minutes at the low temperatures that are required for semiconductor electronic integration," Lin said, paving the way for production-line manufacturing. Next the researchers want to try making Janus monolayers on flexible substrates useful in mass production, such as plastics.

To prove that they had achieved a Janus structure, Chenze Liu and Gerd Duscher, both of the University of Tennessee, Knoxville, and Matthew Chisholm of ORNL used high-resolution electron microscopy to examine a tilted crystal to identify which atoms were in the top layer (selenium) versus the bottom layer (sulfur).

However, understanding how the process replaced sulfur atoms with larger selenium atoms -- an energetically difficult feat -- was a challenge. ORNL's Mina Yoon used supercomputers at the Oak Ridge Leadership Computing Facility, a DOE Office of Science user facility at ORNL, to calculate the energy dynamics of this uphill battle from theory using first principles.

Further, the scientists needed to understand how energy transferred from clusters to lattices to create local defects. With molecular dynamics simulations, ORNL's Eva Zarkadoula showed clusters of selenium atoms collide with the monolayer at different energies and either bounce off it, crash through it or implant in it -- consistent with the experimental results.

To further confirm the Janus structure, ORNL researchers proved structures had predicted characteristics by calculating their vibrational modes and conducting Raman spectroscopy and X-ray photoelectron spectroscopy experiments.

To understand that the plume was made of clusters, scientists used a combination of optical spectroscopy and mass spectrometry to measure molecular masses and velocities. Taken together, theory and experiment indicated 3 to 5 eV per atom was the optimal energy for precise implantation to form Janus structures.

####

About Oak Ridge National Laboratory
The DOE Office of Science supported the synthesis science, electron microscopy, and computational studies. This research was conducted as a user project at the Center for Nanophase Materials Sciences and used resources of the Oak Ridge Leadership Computing Facility; both are DOE Office of Science User Facilities at ORNL.

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 https://www.energy.gov/science.

For more information, please click here

Contacts:
Dawn Levy

865-202-9465

@ORNL

Copyright © Oak Ridge National Laboratory

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

The title of the paper is "Low-energy implantation into transition metal dichalcogenide monolayers to form Janus structures.":

Related News Press

News and information

Phytoplankton disturbed by nanoparticles: Due to its antibacterial properties, nanosilver is used in a wide range of products from textiles to cosmetics; but nanosilver if present at high concentrations also disrupts the metabolism of algae that are essential for the aquatic food November 27th, 2020

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

New insights into memristive devices by combining incipient ferroelectrics and graphene November 27th, 2020

Quantum Physics

NIST sensor experts invent supercool mini thermometer November 17th, 2020

CCNY & partners in quantum algorithm breakthrough November 13th, 2020

Smaller than Ever—Exploring the Unusual Properties of Quantum-sized Materials November 13th, 2020

A new candidate material for quantum spin liquids November 12th, 2020

Laboratories

NIST sensor experts invent supercool mini thermometer November 17th, 2020

Govt.-Legislation/Regulation/Funding/Policy

NIST sensor experts invent supercool mini thermometer November 17th, 2020

Arrowhead Interim Clinical Data Demonstrate ARO-AAT Treatment Improved Multiple Biomarkers of Alpha-1 Liver Disease November 13th, 2020

Making 3-D Nanosuperconductors with DNA: Complex 3-D nanoscale architectures based on DNA self-assembly can conduct electricity without resistance and may provide a platform for fabricating quantum computing and sensing devices November 10th, 2020

Face mask aims to deactivate virus to protect others: Antiviral layer attacks respiratory droplets to make mask wearer less infectious October 30th, 2020

Possible Futures

Russian scientists improve 3D printing technology for aerospace composites using oil waste November 27th, 2020

Phytoplankton disturbed by nanoparticles: Due to its antibacterial properties, nanosilver is used in a wide range of products from textiles to cosmetics; but nanosilver if present at high concentrations also disrupts the metabolism of algae that are essential for the aquatic food November 27th, 2020

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

Chip Technology

New insights into memristive devices by combining incipient ferroelectrics and graphene November 27th, 2020

Staying ahead of the curve with 3D curved graphene November 20th, 2020

Spintronics advances -- Controlling magnetization direction of magnetite at room temperature: Scientists develop an energy-efficient strategy to reversibly change 'spin orientation' or magnetization direction in magnetite at room temperature November 20th, 2020

NIST sensor experts invent supercool mini thermometer November 17th, 2020

Memory Technology

New insights into memristive devices by combining incipient ferroelectrics and graphene November 27th, 2020

Multi-state data storage leaving binary behind: Stepping 'beyond binary' to store data in more than just 0s and 1s October 16th, 2020

Manipulating non-magnetic atoms in a chromium halide enables tuning of magnetic properties: New approach creates synthetic layered magnets with unprecedented level of control over their magnetic properties July 24th, 2020

Photochromic bismuth complexes show great promise for optical memory elements July 24th, 2020

Discoveries

An ionic forcefield for nanoparticles: Tunable coating allows hitch-hiking nanoparticles to slip past the immune system to their target November 27th, 2020

Russian scientists improve 3D printing technology for aerospace composites using oil waste November 27th, 2020

Phytoplankton disturbed by nanoparticles: Due to its antibacterial properties, nanosilver is used in a wide range of products from textiles to cosmetics; but nanosilver if present at high concentrations also disrupts the metabolism of algae that are essential for the aquatic food November 27th, 2020

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

Materials/Metamaterials

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

Staying ahead of the curve with 3D curved graphene November 20th, 2020

Manchester group discover new family of quasiparticles in graphene-based materials: Findings to help achieve Holy Grail of 2D materials - superfast electronic devices November 13th, 2020

Announcements

Phytoplankton disturbed by nanoparticles: Due to its antibacterial properties, nanosilver is used in a wide range of products from textiles to cosmetics; but nanosilver if present at high concentrations also disrupts the metabolism of algae that are essential for the aquatic food November 27th, 2020

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

New insights into memristive devices by combining incipient ferroelectrics and graphene November 27th, 2020

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters

Russian scientists improve 3D printing technology for aerospace composites using oil waste November 27th, 2020

Phytoplankton disturbed by nanoparticles: Due to its antibacterial properties, nanosilver is used in a wide range of products from textiles to cosmetics; but nanosilver if present at high concentrations also disrupts the metabolism of algae that are essential for the aquatic food November 27th, 2020

Quantum nanodiamonds may help detect disease earlier: The quantum sensing abilities of nanodiamonds can be used to improve the sensitivity of paper-based diagnostic tests, potentially allowing for earlier detection of diseases such as HIV, according to a study led by UCL research November 27th, 2020

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

Energy

One-way street for electrons: Scientists observe directed energy transport between neighbouring molecules in a nanomaterial November 27th, 2020

Improving quantum dot interactions, one layer at a time: Scientists have found a way to control an interaction between quantum dots that could lead to more efficient solar cells November 20th, 2020

CEA-Leti to Build Quantum-Photonics Platform to Ensure Ultra-Secure Data for Finance, Energy, Defense and Other Industries : Project Will Build Demonstrators for Transmitting and Receiving Qubits and Focus on Integrating the Technology in a Unique Platform to Address Quantum Comp October 30th, 2020

Development of cost-efficient electrocatalyst for hydrogen production: Development of a highly efficient and durable electrocatalyst for water electrolysis that will lead to cost-efficient hydrogen production. Trace amounts of titanium doping on low-cost molybdenum phosphide resu October 9th, 2020

Quantum nanoscience

Pitt researchers create nanoscale slalom course for electrons: Professors from the Department of Physics and Astronomy have created a serpentine path for electrons November 27th, 2020

Improving quantum dot interactions, one layer at a time: Scientists have found a way to control an interaction between quantum dots that could lead to more efficient solar cells November 20th, 2020

NIST sensor experts invent supercool mini thermometer November 17th, 2020

CCNY & partners in quantum algorithm breakthrough November 13th, 2020

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project