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Graphene Molecule Interfaces for Spintronics

Periodic Reporting for period 1 - ARTEMIS (Graphene Molecule Interfaces for Spintronics)

Reporting period: 2019-09-01 to 2021-08-31

ARTEMIS aimed at exploring the potential of graphene/molecule interfaces for the development of novel hybrid organic spintronic devices. Graphene displays excellent properties for the transport of spin information, so that ARTEMIS intended to understand whether such properties can be further implemented by modifying the graphene surface with organic molecules.
ARTEMIS was developed in response to the increasing demand of new technologies and materials for the transfer and process of information. Within this context, spintronics advances are of paramount importance for conceiving a new generation of fast-computing and low-power consumption devices.
In general, ARTEMIS objectives were:
• The fabrication of spintronics devices operating through graphene/molecule interfaces
• Understanding whether the presence of organic molecules on the surface of graphene can modify the spin transport properties of graphene.
ARTEMIS’ core consisted in the fabrication and characterization of lateral spin valves (LSV) devices operating through graphene/molecule interfaces. For such a purpose, mechanically exfoliated graphene flakes were chosen, due to their excellent spin transport performance, as compared to the characteristics of graphene sheets grown by chemical vapor deposition (CVD). Manganese phthalocyanine (Mn-pc) molecules were selected for the interface design, as they demonstrated good air stability after evaporation on top of graphene. Besides, the surface characterization of the evaporated films demonstrated uniform coverage of films as thin as 5 nm. The fabrication of the LSV devices was optimized in order to be able to compare the properties of bare graphene sheets with the behavior of the graphene/molecule interfaces. Such a goal was achieved by taking advantage of a high precision stamping system for deterministic transfer of Van der Waals materials. The stamping process allowed half of the graphene channel to be protected with a flake of hexagonal boron nitride (hBN), which is an insulating Van der Waals material. In such a way half of the LSV channel was exposed to the evaporation of molecules while the other half was protected by the hBN capping. Such a strategy is particularly important in order to understand the changes induced by the evaporated molecules on the graphene channel, by comparing with the properties of the channel fabricated with the very same graphene flake. The electrical characterization of the graphene/molecule LSV showed that spin transport can be achieved through such interfaces as well as in the bare graphene channel. Yet, the results also show that the spin orbit coupling in graphene is not affected by the presence of the Mn-pc molecules. Instead, the presence of the molecules seems to affect the transport properties of graphene by inducing a sizeable charge doping.
Additionally, ARTEMIS has also focused on the optimization of graphene electrodes to be integrated in the design of organic field-effect transistor (OFET). The fabricated devices demonstrated optimal performance characteristics and constituted a positive contribution to the advance of all-organic based electronics. Such work has resulted in a published research article.
Finally, ARTEMIS resources were also dedicated to further investigation on graphene-based spintronic devices. LSV combining graphene with Van der Waals insulating (Cr2Ge2Te6) and metallic (FeGeTe3) Van der Waals magnets were designed and fabricated. The purpose of such heterostructures consisted in the achievement of injection of a spin current in graphene through all-Van der Waals interface. However, attempts to achieve electrical contacts through the Van der Waals magnets have failed, so that further optimization is needed for advancing in the measurements.
ARTEMIS demonstrated that graphene/molecule interfaces can transport spin information over several micrometers. Nevertheless, the original goal of ARTEMIS consisted in modifying the spin-orbit coupling strength in graphene by molecular functionalization. While such an effect has not been observed in the designed spin valves, it would be interesting to investigate the behavior of graphene interface built with different kind of molecules, such as single molecule magnets, for example.
The study of new materials for spintronics is of paramount importance for our society, as the demand for faster and cheaper information technology is rapidly growing. By relying on the transport of the electron spin as an alternative to its charge, spintronic technologies can contribute to reducing power consumption of the electronics available on the market and expand the present market opportunities.
The core of ARTEMIS: graphene and molecules combined for the future of spintronics and electronics.