Phonon gated electronics: Changing the electrical transport in molecular devices with vibrations generated via magnetic power absorption

The size and speed of electronic appliances have improved exponentially in the last few decades thanks to the advances in materials science and fabrication processes. Nonetheless, these ever smaller and faster components are pushing at the fundamental boundaries of quantum mechanics, which will soon result in excessive heating, defective elements and/or impaired processing. Furthermore, performance limitations are not the only problem for conventional electronics. There is an increasing concern about the environmental and health repercussions for a society that depends on electronics in almost every aspect of our life, with an ever-expanding product range and market base. Many of the materials used in electronic devices are harmful, and the wasteful methods employed for their fabrication, together with the unstoppable updating of electronic gadgets every few years mean that large amounts of hazardous waste is produced.Molecular electronics has the advantages over conventional semiconducting devices of small intrinsic size and potentially biodegradable components. However, the research has so far focused in emulating the operation of standard devices and p-n junctions, rather than developing new functionalities based on the unique properties of molecular structures. Added to metal-molecular contact problems, and the chemical and structural degradation that organic structures undergo during operation, molecular devices still lag the efficiency and durability of conventional structures. Therefore, the electronics industry cannot profit from adopting a new generation of hybrid electronics. This project aims to address these drawbacks by using the intrinsic properties of molecules and molecular dynamics, instead of mimicking semiconductor devices.To bring molecular electronics to fruition as an independent field with intrinsic features, a qualitative conceptual step in hybrid electronics is required. Molecular dynamics, where the atoms vibrate at a characteristic frequency due to the thermal energy, are usually considered a nuisance for molecular devices aiming to emulate semiconducting structures. However, the rich range of vibrational properties in molecules, from low-frequency breathing modes to ultrafast hydrogen bond vibrations, is an attractive possibility to develop new paradigms if we could generate or even artificially control the vibrations at chosen chemical bonds without changing the macroscopic temperature. For this purpose, we can use the power dissipated by magnetic materials during exposure to alternating magnetic fields to generate or quench normal modes in molecules functionalized to, or in contact with the magnet. This power is dependent on an external DC magnetic field, the frequency of the AC magnetic field and the magnetic anisotropy, parameters which can be controlled by external fields or modifying the material composition or shape. This will allow us to study the interaction between electronic transport and molecular dynamics by having control over both voltage andvibrational spectrum.From the point of view of applications to electronic devices, rather than just changing the temperature of the system, the method I put forward will not be hampered by the long relaxation times associated with structural changes in the molecules and the macroscopic cooling of the electrodes. This is because the phonons will be injected directly to the molecules through a third insulating magnetic terminal not in contact with the electrodes. As compared with simply irradiating the molecules with microwave fields, the technique will also allow us to overcome the low microwave absorption of organic molecules, and extend the operation to arbitrary molecular systems, where we will generate vibrational modes in the optical range with exposure to microwave fields. We can then fabricate transistors operating at the molecular scale and with driving magnetic fields at frequencies of several GHz.

Microelectronics companies such as Intel, Siemens and others have extensive research programmes aiming to push the limits in size and speed of semiconducting devices. Thanks to this research, devices with billions of transistors with nominal size of 45 nm operating at 3 GHz are now widely distributed. However, pushing the limits of the semiconductor technology has given rise to regular faulty operations in many of our state of the art electronic appliances caused by overheating, radiation and/or imperfect nano-components. In addition to performance limitations, the environmental and health effects of large scale production are also urgent issues. Our society discards millions of appliances every year, almost one million tonnes in the year 2000 in the UK, and only about 50 % of those are recycled or exported for re-use, which leads to vast amounts of hazardous waste that includes heavy metals and other poisonous materials. In the local economy, the electronics industry in the UK has been brought to a standstill, with the international trade going from a balance shortfall of 282 million in the year 1995 to 1302 million in 2001, while the total number of companies in the sector fell by 1500, and the computer industry lost 12000 jobs during that period. This proposal offers an answer to some of these problems. So far, research in molecular electronics has been difficult to translate into actual industrial applications, partly due to the fast degradation of molecular devices over short times. Manipulating phonons to gate electronic devices will resolve problems on reproducibility and degradation. By using the same quantum effects that hamper conventional electronics, phonon gating will produce new molecular-size devices operating at clock times faster than 3 GHz. The results will increase the industrial benefits to adopt organic materials for nanoelectronics, making possible a more sustainable process that counterbalances the wasteful lithographic technique through self-assembly and other chemical methods, and relies more in biodegradable materials. It will also trigger a new technology that, to be developed, will require advanced equipment and highly skilled personnel formed in top class institutions, rather than cheap labour. The industry will then profit through investment for technological development and new jobs, whereas the consumers will benefit from faster, smaller and more reliable electronics. To achieve a maximum output from the results of this proposal, we will take action at three levels: i) Regarding the dissemination of our results within the scientific community, we will submit our publications to highly respected journals with high impact factor (e.g. Nature Materials, Nano Letters, etc.). At the local level, we will collaborate with the Microwave Institute and the Centre of Molecular Nanoscience to expand the possibilities of our research. We will contact our past collaborators in Ireland, France and Japan to present them our results so we can explore new possibilities for our method. Finally, we will also present our results in the 56th Conference on Magnetism and Magnetic Materials (November 2011) and the American Physical Society meeting (June 2012), where thousands of scientist gather to communicate their latest achievements. ii) At an industrial level, we will contact electronic companies through the National Microelectronics Institute in the UK and the Enterprise & Knowledge Transfer office of the University of Leeds. Patents and applications will then be discussed with potential industrial partners to maximize the outcome and distribution of the new technology. iii) For the results to reach their full potential rather than being limited to technical publications, it is essential to make them accessible to the wider public. For this purpose, we will contact the appropriate broad diffusion media through the Media Relations office of the University of Leeds and its press officers