Phase change materials which are used in modern smartphones could lead to high storage capacities and increase energy efficiency. The data is recorded by switching the states between glassy and crystalline with the help of heat pulse. But till date, it has not been possible to understand what exactly happens at the atomic level.
A group of researchers from European XFEL, University of Duisburg-Essen, Germany and Lawrence Livermore National Laboratory(LLNL) described how X-ray free-electron laser at Linac Coherent Light Source (LCLS) was used to demonstrate a transition in chemical bonding mechanism, thus enabling the storage of data. The results can be used for the optimization of phase-change materials for efficient and improved data storage technologies. They also gave newer insights into the glass formation process. The study was published in the Science journal.
LLNL’s Stefan Hau-Riege, co-author of this paper told that as the current devices are used to store data more than ever, new techniques are needed for storing more information.
Phase-change materials made from elements such as antimony, tellurium and germanium are used for storing large amounts of data, efficiently and quickly. They are used as replacements for flash drives in current smartphones. These materials on applying electrical or optical pulse change from glassy to crystalline state. These two states represent the 0 and 1 in binary system for storing information. However, it has not been possible to understand this change at the atomic level until now.
Researchers used femtosecond X-ray diffraction technique for studying atomic changes when the materials switched states. The optical laser was first used for triggering the material to switch from crystalline to glassy state. The X-ray laser was used for taking images of the atomic structure. Researchers took more than 10,000 images for understanding the atomic sequence during the change of states.
For storing information in phase-change materials, they must be cooled very quickly form a glassy state without being crystallised. However for erasing the information, the same material has to be crystallised very quickly. Researchers found that when a liquid is cooled much below the melting point, it changes to form a low-temperature liquid which can be observed for a brief moment before it is crystallised. These liquids differ in behaviour as well as atomic properties. Liquid at a very high temperature has high atomic mobility for crystallisation. But below the boiling point, the chemical bonds get rigid and the disordered atomic structure of glass is held. This prevents the transformation and secures the data. This study explains how the switching process in modern technology can be both fast and reliable.