Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

2D crystals conforming to 3D curves create strain for engineering quantum devices

04.06.2019

A team led by scientists at the Department of Energy's Oak Ridge National Laboratory explored how atomically thin two-dimensional (2D) crystals can grow over 3D objects and how the curvature of those objects can stretch and strain the crystals. The findings, published in Science Advances, point to a strategy for engineering strain directly during the growth of atomically thin crystals to fabricate single photon emitters for quantum information processing.

The team first explored growth of the flat crystals on substrates patterned with sharp steps and trenches. Surprisingly, the crystals conformally grew up and down these flat obstacles without changing their properties or growth rates.


Strain-tolerant, triangular, monolayer crystals of WS2 were grown on SiO2 substrates patterned with donut-shaped pillars, as shown in scanning electron microscope (bottom) and atomic force microscope (middle) image elements. The curvature of the pillars induced strain in the overlying crystals that locally altered their optoelectronic properties, as shown in bright regions of photoluminescence (top).

Credit: Christopher Rouleau/Oak Ridge National Laboratory, US Dept. of Energy

However, curvy surfaces required the crystals to stretch as they grew to maintain their crystal structure. This growth of 2D crystals into the third dimension presented a fascinating opportunity.

"You can engineer how much strain you impart to a crystal by designing objects for them to grow over," said Kai Xiao, who with ORNL colleagues David Geohegan and postdoctoral researcher Kai Wang (now at Intel) conceived the study. "Strain is one way to make 'hot spots' for single photon emitters."

Conformal growth of perfect 2D crystals over 3D objects has the promise to localize strain to create high-fidelity arrays of single photon emitters. Stretching or compressing the crystal lattice changes the material's band gap, the energy gap between the valence and conduction bands of electrons, which largely determines a material's optoelectronic properties.

Using strain engineering, researchers can funnel charge carriers to recombine precisely where desired in the crystal instead of at random defect locations. By tailoring curved objects to localize strain in the crystal, and then measuring resulting shifts in optical properties, the experimentalists compelled co-authors at Rice University--theorists Henry Yu, Nitant Gupta and Boris Yakobson--to simulate and map how curvature induces strain during crystal growth.

At ORNL, Wang and Xiao designed experiments with Bernadeta Srijanto to explore the growth of 2D crystals over lithographically patterned arrays of nanoscale shapes. Srijanto first used photolithography masks to protect certain areas of a silicon oxide surface during exposure to light, and then etched away the exposed surfaces to leave vertically standing shapes, including donuts, cones and steps.

Wang and another postdoctoral researcher, Xufan Li (now at Honda Research Institute), then inserted the substrates into a furnace where vaporized tungsten oxide and sulfur reacted to deposit tungsten disulfide on the substrates as monolayer crystals.

The crystals grew as an orderly lattice of atoms in perfect triangular tiles that grew larger with time by adding row after row of atoms to their outer edges. While the 2D crystals seemed to effortlessly fold like paper over tall steps and sharp trenches, growth over curved objects forced the crystals to stretch to maintain their triangular shape.

The scientists found that "donuts" 40 nanometers high were great candidates for single photon emitters because the crystals could reliably tolerate the strain they induced, and the maximum strain was precisely in the "hole" of the donut, as measured by shifts in the photoluminescence and Raman scattering.

In the future, arrays of donuts or other structures could be patterned anywhere that quantum emitters are desired before the crystals are grown.

Wang and ORNL co-author Alex Puretzky used photoluminescence mapping to reveal where the crystals nucleated and how fast each edge of the triangular crystal progressed as it grew over the donuts. After careful analysis of the images, they were surprised to discover that although the crystals maintained their perfect shapes, the edges of crystals that had been strained by donuts grew faster.

To explain this acceleration, Puretzky developed a crystal growth model, and colleague Mina Yoon conducted first-principles calculations. Their work showed that strain is more likely to induce defects on the growing edge of a crystal. These defects can multiply the number of nucleation sites that seed crystal growth along an edge, allowing it to grow faster than before.

The reason crystals can grow easily up and down deep trenches, but become strained by shallow donuts, has to do with conformity and curvature. Imagine wrapping presents. Boxes are easy to wrap because the paper can fold to conform to the shape. But an irregularly shaped object with curves, such as an unboxed mug, is impossible to wrap conformally (to avoid tearing the paper, you would have to be able to stretch it like plastic wrap.)

The 2D crystals also stretch to conform to the substrate's curves. Eventually, however, the strain becomes too great and the crystals split to release the strain, atomic force microscopy and other techniques revealed. After the crystal cracks, growth of the still-strained material proceeds in different directions for each new arm.

At Nanjing University of Aeronautics and Astronautics, Zhili Hu performed phase-field simulations of crystal branching. Xiang Gao of ORNL and Mengkun Tian (formerly of the University of Tennessee) analyzed the atomic structure of the crystals by scanning transmission electron microscopy.

"The results present exciting opportunities to take two-dimensional materials and vertically integrate them into the third dimension for next-generation electronics," said Xiao.

Next the researchers will explore whether strain can enhance the performance of tailored materials. "We're exploring how the strain of the crystal can make it easier to induce a phase change so the crystal can take on entirely new properties," Xiao said. "At the Center for Nanophase Materials Sciences, we're developing tools that will allow us to probe these structures and their quantum information aspects."

###

The title of the paper is "Strain tolerance of two-dimensional crystal growth on curved surfaces."

The DOE Office of Science supported material growth and structural and optical characterizations, which were performed at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility. This research also used resources of the National Energy Research Scientific Computing Center, also a DOE Office of Science User Facility. Work at Rice was supported by an Office of Naval Research grant.

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, visit https://energy.gov/science. --by Dawn Levy

Media Contact

Dawn Levy
levyd@ornl.gov
865-576-6448

 @ORNL

http://www.ornl.gov 

Dawn Levy | EurekAlert!
Further information:
https://www.ornl.gov/news/2d-crystals-conforming-3d-curves-create-strain-engineering-quantum-devices

Further reports about: 2D 3D Materials Sciences crystals photoluminescence quantum devices single photon

More articles from Materials Sciences:

nachricht Shell increases versatility of nanowires
26.06.2019 | Helmholtz-Zentrum Dresden-Rossendorf

nachricht Crystal with a twist: Scientists grow spiraling new material
21.06.2019 | University of California - Berkeley

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fraunhofer IDMT demonstrates its method for acoustic quality inspection at »Sensor+Test 2019« in Nürnberg

From June 25th to 27th 2019, the Fraunhofer Institute for Digital Media Technology IDMT in Ilmenau (Germany) will be presenting a new solution for acoustic quality inspection allowing contact-free, non-destructive testing of manufactured parts and components. The method which has reached Technology Readiness Level 6 already, is currently being successfully tested in practical use together with a number of industrial partners.

Reducing machine downtime, manufacturing defects, and excessive scrap

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

Im Focus: The hidden structure of the periodic system

The well-known representation of chemical elements is just one example of how objects can be arranged and classified

The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...

Im Focus: MPSD team discovers light-induced ferroelectricity in strontium titanate

Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.

Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...

Im Focus: Determining the Earth’s gravity field more accurately than ever before

Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.

The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Shell increases versatility of nanowires

26.06.2019 | Materials Sciences

Hubble finds tiny 'electric soccer balls' in space, helps solve interstellar mystery

26.06.2019 | Physics and Astronomy

New combination therapy established as safe and effective for prostate cancer

26.06.2019 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>