Origin of resistance hysteresis in graphene layers on ferroelectric substrates


Project Director: Dr. Apostol Nicoleta

This Project aims to elucidate the nature of the anti-hysteretic behavior for the variation of the in-plane resistance of graphene, as function on a gate voltage applied through a ferroelectric separator with out-of-plane polarization. Such structures should exhibit a („normal”) hysteresis due to the screening of the depolarization field by charge carriers from graphene: when the ferroelectric polarization is reversed, the type of charge carriers changes from electrons to holes or viceversa, yielding resistance peaks. When the graphene is pre-doped, the resistance exhibits two different stable states, enabling one to design easily and rapidly accessible, non-volatile memory elements. In practice, the sense of the hysteresis is reversed; the cause of this „anomal” hysteresis is attributed to contaminants on graphene or at the interface between graphene and ferroelectrics, however with no explicit demonstration sofar. This problem will be investigated in this Project on atomically clean, single crystal ferroelectrics with graphene grown by carbon molecular beam epitaxy. A first characterization by X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption spectroscopy certified that carbon layers exhibit two dimensional character, have similar XPS as graphene, the chemical interaction with the ferroelectric is minimal and the polarization state is not changed by carbon deposition. The continuation of this work supposes the proof  by scanning tunneling microscopy (STM) and by angle resolved photoelectron spectroscopy  that graphene is formed, then the analysis of electrical transport properties, together with the development of new models, if necessary. Further, one will dose these structures with molecules and follow by correlated XPS, STM and electrical measurements their behavior as function on the quantity and nature of dosed molecules. Besides fundamental knowledge, the Project’s outcomes will consist in new models for memory elements and gas sensors.

Dr. Nicoleta G. Apostol - Project Director

Dr. Cristian M. Teodorescu  - Mentor

 

The main Objective of this project is to analyze the resistance hysteresis behavior of graphene layers synthesized on ferroelectrics, as function of the voltage applied on the substrate, in the following conditions: (i) flat, single-crystal surfaces; (ii) lack of contaminants; (iii) well-defined polarization state of the substrate, externally adjustable; (iv) minimal chemical interaction between the ferroelectric and the graphene layers, in order to reduce accidental doping or even breaking of the C–C bonds.

I.C. Bucur, N.G. Apostol, L.E. Abramiuc, L.C. Tănase, C.A. Tache, G.A. Lungu, R.M. Costescu, C.F. Chirilă, L. Trupină, L. Pintilie, C.M. Teodorescu, Room temperature ferromagnetism and its correlation to ferroelectricity of manganese embedded in lead zirco-titanate, Thin Solid Films 669, 440–449 (2018).  Bucur et al TSF 2018

Nicoleta G. Apostol

Scientific Researcher II
National Institute of Materials Physics
Atomistilor Str. 405A
077125 Magurele-Ilfov
Romania


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