The building blocks of storage media have become ever smaller over the past few years. However, further miniaturization of the existing technology is hindered by essential limits of quantum mechanics. A new approach deals with the usage of spin-crossover molecules as the smallest possible storage unit. These special molecules, similar to normal hard drives, can save information through their magnetic state.
The images from the scanning tunneling microscope (STM) show the three different states of the molecule, which correspond to a trinary code for encrypting information: in a highly magnetic state (left), in a low magnetic state with atoms that have moved closer together (middle) and in an equally low magnetic state but turned by 45 degrees (right). Figure/Copyright: Manuel Gruber
In order to do this, they have to be positioned on surfaces, which is challenging without causing any damage to their ability of saving the information. A research team from
Kiel University has presently managed to successfully position a new class of spin-crossover molecules onto a surface, and they have also employed interactions which were earlier considered to be as obstructive in order to enhance the storage capacity of the molecule. The storage density of standard hard drives could thus theoretically be increased by more than one hundred fold, and it could also be possible to make data carriers significantly smaller. The findings have been featured in the scientific journal Nano Letters.
Is a switch on or off? Is an answer yes or no? Is a statement true or false? The differentiation between two possibilities refers to the smallest piece of detail that a computer can save. Bits (a word made up of ‘binary’ and ‘digit’), as the smallest electronic storage unit, are considered to be the basic building blocks for all information stored on the hard drives. They are presented as a sequence of two varied symbols like 0 and 1, which is called binary code. Storage media have become ever smaller, over the past few years, while their capacity for storing information has indeed increased. One Bit on a hard drive presently needs only a space of around 10 by 10 nanometers. However, this is still considered to be too big for miniaturizing components.
“The technology that is currently being used to store data on hard drives now reaches the fundamental limits of quantum mechanics due to the size of the Bit. It cannot get any smaller, from today’s perspective,” says Torben Jasper-Tönnies, doctoral researcher in Professor Richard Berndt’s working group at Kiel University’s Institute of Experimental and Applied Physics. He and his colleagues employed a single molecule capable of being used for encoding a Bit, and demonstrating a principle which could just allow even smaller hard drives with more storage in the future. “Our molecule is just one square nanometer in size. Even with this alone, a bit could be encoded in an area hundred times smaller than what is nowadays required,” says his colleague, Dr Manuel Gruber. This indeed could become another step towards shifting the boundaries of quantum physics in storage technology.
When Bits Become Trits
The molecule used by the interdisciplinary research team from the Kiel Collaborative Research Centre (CRC) 677 “Function by Switching” can assume two varied magnetic states, but when fixed to a special surface, it is also capable of changing its connection to the surface. Following this, it can also be switched between a high and low magnetic state, and turned by 45 degrees.
“When transferred onto storage technology, we would be able to depict information on three states - those being 0, 1 and 2,” explained Jasper-Tönnies. “As a storage unit, we wouldn’t have a Bit, we would have a Trit. Binary code would become trinary code.”
The challenge for the researchers from Physics and Chemistry was in finding a perfect molecule and an ideal surface, besides using the exact method in order to connect the two together in a manner that would still permit them to work.
“Magnetic molecules, so-called spin-crossover molecules, are very sensitive and easily damaged. We needed to find a way to firmly attach the molecule to the surface without affecting its switching ability,” explained Gruber.
Perfect Combination of Molecule and Surface
Their experiments finally paid off: A magnetic molecule of a superior class (a so-called Fe(III) spin crossover molecule) was synthesized by chemists from Professor Felix Tuczek’s working group at the Institute of Inorganic Chemistry. Physicists Jasper-Tönnies, Gruber and Sujoy Karan also succeeded in depositing this molecule on a copper nitride surface through evaporation. Using electricity, it can be switched between two varied directions (in the so-called low-spin state), and also between varied spin states. The fine tip of a scanning tunneling microscope (STM) behaves as a hard drive’s reading and writing head in their experiments. This piece of equipment permits the molecule to not only be “written” as a storage medium, but also to be “read” with the help of electricity.
Before employing these molecules as a data storage on an industrial level, additional investigation must be performed. The proof of principle is indeed demonstrated by using a rather voluminous setup (STM) and additional work is needed in order to incorporate such a molecular memory on a tiny chip.
This research was completed in the Kiel Collaborative Research Centre (CRC) 677 “Function by Switching”. Around 100 scientists from Physics, Materials Science, Chemistry, Pharmacy and Medicine are working at the CRC on a cross-disciplinary basis in order to develop switchable molecular machines. The German Research Foundation (DFG) has been financing the CRC since 2007.