Spinning the future
The August 2017 edition of the Research*EU magazine featured an interesting overview of the ACMOL project, which is working to develop graphene-based spintronics for next-gen molecular electronic devices. This article held that ‘Spintronics, molecular electronics and graphene have a common trait: they are all considered as key enablers in the future of computing beyond the limitations of Moore’s and Kryder’s laws. The ACMOL project is contributing to their joint advancement with proof-of-concept devices.’
This article, featuring the ACMOL project, is published in the "Pan European Networks" website on 20 November 2017. The article will appear in Pan European Networks: Science & Technology issue 25, which will be published in December, 2017.
Spintronics, which the article describes as ‘the development of nanoscale electronics for the fabrication of hard drives based on the detection and manipulation of electron spin,’ and molecular electronics (the use of molecules as the primary building block for electronic circuitry), were, until relatively recently, only considered separately. However, the piece reveals, ‘by developing a switchable, room-temperature spin-polariser employing electro-active and magnetic molecules and integrating them into graphene-type electrodes modified with ferromagnetic materials, ACMOL provides a new route for spintronics research.’
The question of interaction
Dr Núria Crivillers, co-ordinator of the project for ICMAB-CSIC in Spain, explained: “Despite the fast progress in spintronics, ‘molecular spintronics’ still presents great challenges. Whilst the market demands a continuous reduction of the size of the magnets forming hard disk drives, the question of how the spin of molecule interacts with an electrical current still had to be answered.”
The ‘Electrical spin manipulation in electroACtive MOLecules’ (ACMOL) project states: ‘During the last decades, society has witnessed tremendous advances in the field of semiconductor materials which have been the seed of the current information age. However, the increasing interest in miniaturising electronic devices faces the current manufacturing techniques which are reaching their physical limits, thus hindering this progression. As a consequence, the development of a new generation of electronic devices is crucial. Under this framework, the ACMOL project aims at contributing to the development of the emerging spintronics devices. The ACMOL consortium will work for the implementation of organic molecules into the devices with the aim of contributing to the catalysis of a new generation of high performance, cost effective, non-volatile, versatile, ultra-fast and low-power consuming electronic devices with applications to a broad number of different technological and societal fields, such as high-density data storage, microelectronics, (bio)sensors, quantum computing, medical technologies.’
The article explains this further: ‘ACMOL is contributing … with a proof-of-concept whereby an electrical current can interact with the spin of the molecule that can be switched between different states. The project enabled measurement and controlled charge transport across electrode-molecule-electrode junctions, developed a novel graphene-based technology for molecular spintronics, and compared its performance with that of standard technology based on coinage metals.
Crivillers added: “Gold is the preferred material for building nanometre-spaced electrodes for model experiments in molecular electronics, but these electrodes are not stable at room temperature, provide poor reproducibility and do not allow for spin injection. Graphene, on the other hand, can provide such stability. It combines high mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, and stability at room temperature and its 2D structure has the potential for more reproducible molecular junctions.
“Our devices may contribute to catalyse the development of a new generation of high performance, cost effective, non-volatile, versatile, ultra-fast and low-power consuming electronic devices in fields such as high-density data storage, microelectronics, (bio)sensors, quantum computing and medical technologies,” the co-ordinator added.
Fundamental and applied
While, initially, the project’s scope did not extend past beyond fundamental research, the understanding and control of the molecule spin/electron interaction and the development of graphene-based technology will certainly contribute to the scientific and technological revolution of molecular spintronics, the article says.
Crivillers concluded: “We believe that the ACMOL results help towards the development of new concepts guiding hybrid-technologies which might reach beyond the limits of current silicon-based technology.” In the future, the co-ordinator has also predicted applications in layered materials other than graphene, such as MoS2, BN or MoSe2.
ACMOL is not the only initiative in Europe to have made advances in spintronics in recent months. For instance, in November, researchers at the UK’s University of Cambridge have created a nanoscale magnetic circuit capable of moving information along the three dimensions of space (as opposed to the traditional way that electronic devices have to store and transmit information (bits) in two-dimensional circuits). This, it is hoped, could lead to an important increase in storage and processing capacities of electronic devices over those used today.
Amalio Fernández-Pacheco, principal investigator of the project at the Cavendish Laboratory in Cambridge, commented: “We demonstrate a new way to fabricate and use a magnetic device which, in a nanometric scale, can controllably move information along the three dimensions of space.”
To create these nano-magnets in 3D an electron microscope is used along with a gas injector to 3D print a suspended scaffold on a traditional 2D Silicon substrate. After 3D nano-printing, magnetic material is deposited over the whole ensemble to allow information transport.
The breakthrough is part of the broader field of spintronics, with spintronic technologies not only exploiting the electrical charge electrons to store and process information, but also their spin, allowing the development of electronic circuits that benefit from greater energy efficiency than current technologies.“
Projects such as this one open the path to the development of a completely new generation of magnetic devices that can store move and process information in a very efficient way by exploiting the three dimensions of space,” Fernández-Pacheco said.
Meanwhile, researchers at the UK’s University of York have discovered a new route to ultra-low-power transistors using a graphene-based composite material. Here, scientists – along with colleagues from Roma Tre University, Italy, have been working to overcome the problem of semiconductors overheating in devices. They have thus looked to composite materials built from monolayers of graphene and the transition metal dichalcogenide (TMDC). They discovered these materials could be used to achieve a fine electrical control over the electron’s spin.
Lead researcher Dr Aires Ferreira, of the University of York’s Department of Physics, said: “For many years, we have been searching for good conductors allowing efficient electrical control over the electron’s spin. We found this can be achieved with little effort when two-dimensional graphene is paired with certain semiconducting layered materials. Our calculations show that the application of small voltages across the graphene layer induces a net polarisation of conduction spins.“
We believe that our predictions will attract substantial interest from the spintronics community. The flexible, atomically thin nature of the graphene-based structure is a major advantage for applications. Also, the presence of a semiconducting component opens up the possibility for integration with optical communication networks.”
The field of spintronics is clearly one which has a lot of potential and, moreover, one in which interesting research – at both the fundamental and applied levels – is ongoing.