Stretching to perfection of 2-D semiconductors

November 15, 2017, US Department of Energy
Stretching to perfection of 2-D semiconductors
Semiconducting films are grown on different substrates at high temperatures and then rapidly cooled to induce deformation. This process can be used to controllably modify the films’ electronic properties. If the substrate (blue) contracts the same as the semiconductor film, then the material is not stretched or compressed (referred to as having “no strain”). When the substrate (green) contracts more, the 2-D material is compressed. When the substrate (red) contracts less, the semiconductor is stretched. Stretching leads to a change in the electronic properties of the film and significantly improves its photoluminescence efficiency, which is important for developing high-efficiency lights and lasers. Credit: US Department of Energy

Compressing a semiconductor to bring atoms closer together or stretching it to move them farther apart can dramatically change how electricity flows and how light is emitted. Scientists found an innovative way to compress or stretch very thin (monolayer and bilayer) films of tungsten diselenide by placing the film on different surfaces at high temperatures. The underlying surface stretched or compressed upon cooling. Why? With few exceptions, all materials expand when heated and contract when cooled. However, this change happens at different rates. Because the films respond at a different rate than the surface, the films stretch or compress upon cooling. Excitingly, the electronic properties of the stretched films were dramatically different.

Stretching to alter how they conduct electricity could lead to brighter LED lights, more efficient lasers, and high-performing electronics. Stretching or compressing films allows for controlled modification of that can be used to explore the underlying physics of the materials. The technique has been used to make 2-D semiconducting films that can be used in different devices.

The electronic and optical properties of materials are directly related to their atomic . By bringing atoms closer to each other (compressing) or moving them apart (stretching), one can dramatically change the electronic and of materials. Now, researchers in Berkeley, California, have developed a new method to controllably induce up to 1 percent strain due to stretching and 0.2 percent strain due to compression in 2-D (WSe2). In this study, the researchers grew a semiconductor at a high temperature on different substrates with mismatched thermal properties. Upon cooling, these substrates contracted more or less than the semiconductor. If the substrate contracted more, the 2-D semiconductor film was in compression.

When the substrate contracted less, the crystal structure of the 2-D semiconductor film was stretched. Stretching the film produced a novel change in the electronic properties of the film, and the material changed from being an "indirect" to a "direct" bandgap material which resulted in the strained material emitting light with the same amount of energy (that is, an increased photoluminescence efficiency). This new method can be used to develop strain engineered 2-D semiconductors and controllably tune their electronic properties. This will allow scientists to develop a better understanding of the material's underlying physics as well as produce new for the development of highly efficient electronic devices.

Explore further: Piezoelectrics stretch their potential with a method for flexible sticking

More information: Geun Ho Ahn et al. Strain-engineered growth of two-dimensional materials, Nature Communications (2017). DOI: 10.1038/s41467-017-00516-5

Related Stories

Extra sulphur improves electronic structure of quantum dots

September 29, 2017

Quantum dots are nanometre-sized semiconductor particles with potential applications in solar cells and electronics. Scientists from the University of Groningen and their colleagues from ETH Zürich have now discovered how ...

Research team flips the switch on ferroelectrics

August 29, 2017

Many next-generation electronic and electro-mechanical device technologies hinge on the development of ferroelectric materials. The unusual crystal structures of these materials have regions in their lattices, called domains, ...

Changing semiconductor properties at room temperature

October 28, 2016

It's a small change that makes a big difference. Researchers have developed a method that uses a one-degree change in temperature to alter the color of light that a semiconductor emits. The method, which uses a thin-film ...

Recommended for you

Solving mazes with single-molecule DNA navigators

November 16, 2018

The field of intelligent nanorobotics is based on the great promise of molecular devices with information processing capabilities. In a new study that supports the trend of DNA-based information carriers, scientists have ...

A way to make batteries almost any shape desired

November 16, 2018

A team of researchers from Korea Advanced Institute of Science and Technology, Harvard University and Korea Research Institute of Chemical Technology has developed a way to make batteries in almost any shape that can be imagined. ...

'Smart skin' simplifies spotting strain in structures

November 15, 2018

Thanks to one peculiar characteristic of carbon nanotubes, engineers will soon be able to measure the accumulated strain in an airplane, a bridge or a pipeline – or just about anything – over the entire surface or down ...

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.