Electron holography has allowed Brookhaven scientists to observe nanomaterials at the atomic level. This discovery may pave the way for a new generation of storage devices.
Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have captured images of the electric fields created by exotic ferroelectric nanomaterials with picometre precision. This trillionth of a metre resolution is crucial for understanding these materials. To achieve this they made use of a technique called electron holography on two particular ferroelectrics, insulating barium titanate and semiconducting germanium telluride. These materials were engineered at Lawrence Berkeley National Laboratory.
Brookhaven physicist Yimei Zhu said of this, “this kind of detail is just amazing – for the first time ever we can actually see the positions of atoms and link them to local ferroelectricity in nanoparticles. This kind of fundamental insight is not only a technical milestone, but it also opens up new kinds of engineering possibilities.”
Ferroelectrics are related to the better known ferromagnetics, which are found in everything from toy magnets to computer hard drives. Ferromagnetic materials have magnetic dipole moments, meaning they always orient towards north or south. On a large scale, these dipole moments align and we observe magnetisation as attraction and repulsion. With an external magnetic field, the dipole can be switched, allowing the material to be altered. This is the basis of modern storage media, as the flipping of individual dipoles is analogous to the ones and zeroes in a computer’s binary language. This enables the material to be “written” onto, and, as these materials retain their memory even when turned off, they are fundamental in our modern, computer based world.
Ferroelectrics also have a dipole moment, but with a positive or negative electric charge, rather than a magnetic charge. The polarisation of these ferroelectrics can be altered with the application of an external electric field in the same way that the magnetisation of ferromagnetics can be flipped with a magnetic field. This characteristic of the ferromagnetic materials is due to a subatomic asymmetry, which was imaged by the Brookhaven scientists.
One major possibility is a new generation of compact, high capacity storage devices. While on the surface ferroelectric devices may seem very similar to the analogous ferromagnetic devices, they have much greater potential for data manipulation. Like ferromagnetics they are non-volatile, but, according to Zhu, “ferroelectric materials can retain information on a much smaller scale and with higher density than ferromagnetics. We’re looking at moving from micrometres down to nanometres. And that’s really exciting, because we now know that on the nano scale each particle can become its own bit of information.” In the words of Brookhaven’s Myung-Geun Han, “ferroelectrics could ramp up memory density and store an unparalleled multiple terabytes of information on just one square inch of electronics.”
The next challenge is scaling up individual ferroelectric nanoparticles into useful devices. The key to this is in understanding how tightly they can be packed without compromising their individual polarisations. This is vital because ferroelectrics require some space between them to operate effectively. The work done by the Brookhaven team with electron holography will instrumental in determining how this can be achieved.