MIT researchers and their colleagues have created an ultrathin material that has ferroelectricity. This property could make the material useful in the development of computer memory, among other applications. Kenji Yasuda, MIT postdoctoral fellow and Xirui Zhang, MIT graduate student, are seen in the MIT lab key for the work. Credit: Kenji Yasuda and Xirui Wang
Ultrathin materials made of a single layer of atoms have riveted scientists' attention since the discovery of the first such materialgrapheneabout 17 years ago. Researchers at MIT, including a pioneering group, have discovered that stacking individual sheets can create new properties such as superconductivity and magnetism.
Now, MIT physicists and their colleagues have done the same with boron nitride. This is due to its atomic structure that is similar to its famous cousin. The research team discovered that if two sheets of boron nutride are placed parallel, the material can become ferroelectric. This means that the positive and negative charges in the material will spontaneously move to opposite sides or poles. The external electric field reverses the polarization by switching the charges. All of this takes place at room temperature.
This new material works in a completely different way than existing ferroelectric materials and could be used for many purposes.
Numerous 2D materials have shown a wide range of physical properties. Pablo Jarillo Herrero, the Cecil & Ida Green Professor in Physics and the leader of this work that was published in Science, says, "Now we can easily stack ferroelectric boron Nitride with other materials to generate emergent property and novel functionalities." Jarillo-Herrero also works with MIT's Materials Research Laboratory.
Jarillo-Herrero is not the only author of the paper. Kenji Yasuda is a MIT postdoctoral fellow and Xirui Zhang, a graduate student at MIT in physics. Kenji Watanabe, Takashi Taniguchi, and Takashi Taniguchi are also authors.
Potential Applications
Yasuda, the Science paper's lead author, says that among the many potential uses of the ultrathin ferroelectric materials, "one exciting opportunity is to use them for denser storage memory." Because the material's polarization can be switched to encode one-digital information and zerosdigital information, this information will remain stable over time. The material will not change if an electric field is applied. The Science paper reports that the team has performed a proof of principle experiment to demonstrate this stability.
The new material is only one billionth of a meter thick. It's one the thinnest ferroelectrics ever created. This could allow for much denser computer memory storage.
Yasuda also reported that twisting parallel sheets of boron Nitride at an angle to one another produced a new "completely different type of ferroelectric status." The Jarillo-Herrero team pioneered this general approach known as twistronics. They used it to create unusual superconductivity for graphene.
New Physics
Because it uses new physics, the ultrathin ferroelectric materials are also very exciting. It works in a completely different way than conventional ferroelectric material.
Yasuda says that the out-of-plane ferroelectric switch is caused by the in-plane sliding movement between two boron-nitride sheets. The lateral rigidity in boron nitride allows for this unique coupling of vertical polarization with horizontal motion.
Other Ferroelectrics
Yasuda points out that there are other ways to make ferroelectrics using the same process described in Science. Our method of turning non-ferroelectric materials into ultrathin ferroelectrics can be applied to other materials that have atomic structures similar boron nitride. This allows us to greatly expand our range of ferroelectrics. He says that only a handful of ultrathin ferroelectrics are available today. Researchers are working towards that goal and have seen some promising results.
Jarillo-Herrero Lab is a pioneer in manipulating and exploring ultrathin materials like graphene. However, it was not expected that ultrathin Boron Nitride could be converted to a ferroelectric.
Says Xirui Wang:
"I can still recall when we did the measurements, and there was an unusual jump in our data. We decided to repeat the experiment, and it was confirmed by doing it again and again.
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Further information: Kenji Yasuda et. al., Stacking engineered ferroelectricity for bilayer boron nitride. Science (2021). Information from Science Kenji Yasuda and colleagues, Stacking engineered ferroelectricity for bilayer boron Nitride, (2021). DOI: 10.1126/science.abd3230
