Functional 2D materials and heterostructures for hybrid spintronic-memristive devices
Project Director: Dr. Velea Alin
Project Director Dr. Alin Velea
Project Type: International
Project Program: M.ERA.NET 2
Funded by: Romanian National Authority for Scientific Research, UEFISCDI
Contractor: National Institute of Materials Physics
Status: In progress
Start Date: September 1, 2019
End Date: August 31, 2022
Magnetic memories (MRAM) and memristors are amongst the most promising technologies for emerging nonvolatile memories. MRAM implement concepts developed within spintronics, which uses spin –rather than electrons– to transfer and store information. In this project we will explore hybrid spintronic-memristor devices in graphene-based heterostructures comprising 2D transition metal dichalcogenides (TMDs) and less explored group-IV monochalcogenides (IV-MCs) materials. We will perform the first ever evaluation of the potential of 2D IV-MCs as memristors and implement graphene-based heterostructures with enhanced spin-orbit coupling using both TMDs and IV-MCs. With these heterostructures we aim at controlling graphene’s spin properties by changing the memristive setting of the chalcogenides. They will be made and characterized such that new multifunctional 2D systems are generated for applications in ultradense and ultralow power nonvolatile memories and neuromorphic computer architectures.
The overarching goal of this project is to nurture a paradigm shift by developing a new generation of two dimensional functional materials (2DFM) and heterostructures that can provide a leap towards novel computing architecture technologies with potential for ultra-low power consumption, and faster and cheaper information storage. To achieve this goal, the project will initiate a new research line that feeds from two active areas in condensed matter physics, namely spintronics and memristor systems.
The project team consists of:
- Dr. Alin Velea - Project leader
- Dr. Petre Bădică - Scientific researcher I
- Dr. Mihail Secu - Scientific researcher I
- Dr. Aurelian-Cătălin Gâlcă - Scientific researcher I
- Dr. Florinel Sava - Scientific researcher II
- Dr. Iosif-Daniel Șimăndan - Scientific researcher
- Dr. Oana-Claudia Mihai - Research assistant
- Dr. Angel-Theodor Buruiană - Research assistant
Stage 1: Tests for the development of functional 2D materials
This first stage of the project aimed to perform tests for the development of functional 2D materials. In order to reach this objective, several activities have been carried out.
Tests to determine the optimum conditions for obtaining crystalline thin layers of SnSe were performed using the physical vapor transport method (PVT). The PVT method involves the transformation of the SnSe material from the condensed state (powder) into a vapor state, the transport of the vapours by the flow of argon into a quartz tube arranged horizontally and then condensation on a suitable support (positioned inside the quartz tube), as a thin crystalline layer of SnSe.
The most important parameters in the process of deposition of thin SnSe layers by PVT are the temperature of the SnSe powder and the temperature of the Si substrate, the temperature at which the thin layer is deposited, the argon flow during deposition, the time of the deposition and the residual oxygen concentration in the quartz tube during deposition.
The analysis of the obtained layers was done in the context of the influence of the deposition parameters on the quality of the obtained films. The temperature of the SnSe powder and Si substrate is an important parameter, inducing significant differences in the morphology of the obtained films. The second important parameter is the flow of argon during the deposition of the thin layers. Thus, it is found that to obtain a uniform deposition, the flow must be moderate, if it is greatly enlarged then the clusters are crowded towards the edge of the Si substrate. The third important parameter is the concentration of residual oxygen. The presence of oxygen in high concentration leads to oxidation of Tin vapors and their condensation on the "hot" substrate in the form of polycrystalline SnO2 clusters. If the residual oxygen concentration decreases, then only a part of the Sn vapors are oxidized, the rest, are condensing on the substrate as polycrystalline semispherical clusters of Sn. This difference in morphology is due to the difference in the melting temperature of Sn (231.93 °C) and SnO2 (1630 °C). If oxygen is absent, then on the surface of the substrate are formed Sn polycrystalline semispherical clusters. The Selenium vapors that are formed during deposition are partly evacuated, and another part is condensed as amorphous Selenium (melting temperature 221 °C). These results were obtained using X-ray diffraction (XRD) measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDX) and Raman spectrometry.
In conclusion, following the tests performed, valuable information was obtained which led to the identification of the most important deposition parameters and indications about the optimum values for the preparation of polycrystalline layers of SnSe. In the next step, we will improve the preparation process to have a single polycrystalline phase (SnSe) on the substrate. We will also extend the preparation process to other group IV monochalcogenides.
Project Contact Person:
Dr. Alin Velea
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