With the silicon based computing devices approaching its fundamental limit of miniaturization, quantum controlled molecular scale electronics bears the only possible hope to meet the physical challenges imposed by quantum mechanics in the ultimate miniaturization of electronic devices. Learning how to control the electron transport in molecular systems offered by electron?s spin degrees of freedom would add a new dimension to the emerging field of molecular-scale electronics. There are several advantages. First, the weak spin-orbit and hyperfine interaction in carbon based molecular systems with atoms having low atomic numbers (Z) lead them to have a longer spin coherence length than that in conventional metals and semiconductors. Second, the low cost production, chemical flexibility, and self-assembly approach offer tremendous advantages for molecules as a viable interconnects for spin transport. Third, since spin is the ultimate logic bit where we can store information, manipulating the spin in a molecular circuit for a desired device behavior would be beneficial for computing as both information storing and processing can be integrated within a single chip. The objectives of the proposed project are to explore an innovative architecture for a molecular scale spin switch and identify the basic molecular building blocks for this device. The goal is in fundamental understanding of the spin modulated electron transport which would form the basis for functional device design. Transition metals like Ni and Co will be used as spin polarizer and analyzer (filter), molecular complex with low-Z atoms will be used as a bridge between the magnetic electrodes, and organo-metallic molecule and carbon nanotube structures for possible interconnect. The reason behind the choice of organo-metallic molecular complex as the interconnect lies in the fact that it can easily tune the electronic spin state of the metal link in the molecule by gate field providing additional electrical control of spin polarized electronic current-an effect prerequisite for a spin switch. Carbon nanotube (CNT) will be another candidate for spin transport as spin-flip scattering length in CNT has been reported to be much higher. First principles density functional theory together with a parameter free single particle Green?s function approach will be used to provide predictive capability to understand the controlled transport of spin polarized electrons in this device. The role of electronic structure and magnetic configurations at the interface and at the contact points will be systematically studied to optimize maximum modulation in magneto-resistance for device design. The proposed feasibility study will guide the future theoretical and experimental endeavors towards a successful realization of such a device.
Broader Impact: This project will yield several broader impacts: a) Identify a novel architecture for a molecular spin-switch for multi-functional applications ranging from ultra-small magnetic sensors to spin logic based molecular computing that goes far beyond the technology roadmap for the year 2020; b) Develop fundamental understanding of spin modulated electron transport in this device, which will be helpful in guiding the future theoretical and experimental efforts aimed at realizing such devices; c) Stimulate multi-disciplinary research and collaborations; d) Train graduate students in getting first-hand experience in first-principles modeling; e) Provide avenues to integrate education with research; f) broad dissemination of project results (both research and education) and long-term high-reward benefits to society. Since the proposed project is expected to venture into an emerging research idea in advanced molecular spintronics, it satisfies the important criteria for EAGER grant.
With the silicon based computing devices approaching its fundamental limit of miniaturization, researchers are in search of an alternative approach to manipulate information. The focus now is on spin, which is the ultimate logic bit where one can store information. Manipulating the spin in a molecular circuit for a desired device behavior would be beneficial for computing as both information storing and processing can be integrated within a single chip. This would lead to less wastage of energy in shuttling electrons between the processing and memory units resulting in a decreased power consumption. In this project, we have successfully designed a novel three terminal molecular scales spin switch-an important component for information processing, and have identified the mechanism at the electronic structure level that is responsible for switching of spin current in this device. This basic research is expected to pave the way toward the practical realization of a molecular scale spin transistor for multi-functional applications ranging from ultra-small magnetic sensors for medical usages that operate on lower power to spin logic based molecular computing that goes far beyond the technology roadmap for the year 2020. Three peer reviewed publications resulted from this project. The project outcome is the part of the Ph.D. thesis of one graduate student.
