Quantum Conductance Probing of Oxygen Vacancies in SrTiO₃ Epitaxial Thin Film using Graphene

Abstract

The quantum Hall conductance in monolayer graphene on an epitaxial SrTiO3 (STO) thin film is studied to understand the role of oxygen vacancies in determining the dielectric properties of STO. As the gate voltage sweep range is gradually increased in our device, we observe systematic generation and annihilation of oxygen vacancies evidenced from the hysteretic conductance behavior in graphene. Furthermore, based on the experimentally observed linear scaling relation between the effective capacitance and the voltage sweep range, a simple model is constructed to manifest the relationship among the dielectric properties of STO with oxygen vacancies. The inherent quantum Hall conductance in graphene can be considered as a sensitive, robust, and non-invasive probe for understanding 2 the electronic and ionic phenomena in complex transition metal oxides without impairing the oxide layer underneath.Oxygen plays an indispensable role in determining the functional properties of transition metal oxides (TMOs), such as superconductivity, memristive behavior, and topotactic phase reversal. [1][2][3][4][5][6] In STO, a prototypical perovskite oxide, changes in both electronic and ionic behaviors were observed by introducing oxygen vacancies. [7] Oxygen vacancies in STO can be generated via the electric-field-induced redox process or the application of chemical pressure at high temperatures. They supply conducting electrons (3d 1 ) to normally insulating STO (3d 0 ), which can eventually form Cooper pairs at low temperatures (~1 K). [8] On the other hand, oxygen vacancies generated/redistributed via electric-field-induced redox reaction near the metal/oxide interface might further modify the metal/STO heterojunction and give rise to functional phenomena such as resistive switching. [1][2]6,[9][10][11][12][13] Modulation of the local conductivity using a biased conductive atomic force microscopy tip and observation of gas bubbles beneath the anodic metal electrodes indicate the electroforming of oxygen vacancies which affect the transport property of STO critically. [10][11] More recently, it has also been shown that oxygen vacancies can be created just by depositing the active metal, directly observed by the transmission electron microscopy (TEM). [14] However, the role of the ionic motion in modifying the fundamental dielectric properties of STO near the heterojunction is yet to be understood, despite its important implications in the electronic applications.In order to perceive the formation of oxygen vacancies and estimate their influence on the dielectric behavior of STO, we propose the 2D transport nature of graphene as a sensitive, robust, and non-invasive probe for examining the layer underneath. Among various 3 characteristics of graphene, linear dispersion relation and the gapless feature give rise to a delicate electronic response to an external electric field. In addition, a universal quantum Hall effect in graphene is exclusively dependent on its carrier concentration. Therefore, the position and shape of the char...

Synergetic Behavior in 2D Layered Material/Complex Oxide Heterostructures

“…Currently, high‐quality 2DLM/TMO heterostructure devices are mostly based on exfoliated 2DLM layers. In particular, characteristic physical properties such as the quantum Hall effect are only observed for such devices . On the other hand, the superconductivity in the FeSe/SrTiO 3 heterostructure is best observed for MBE‐grown samples via in situ measurement techniques such as ARPES and four‐probe transport measurements .…”

“…As shown in Figure c, the hysteretic quantum Hall conductance in a graphene/SrTiO 3 thin film was first examined by Kang et al While the graphene/SrTiO 3 thin film (90 nm) shows typical linear conductance in the low field regime, a systematic development of the hysteresis appears as the electric field exceeds the threshold of 110 kV cm −1 . The saturation behavior of the source–drain current within the graphene continues unless V G is decreased, which is the essence of the hysteresis.…”

“…e) The mapping of the relationship between dielectric constant, the thickness of oxygen vacancy layer (ε OV , d OV ) as well as the range of gate field. c–e) Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…Ionotronics image: Reproduced with permission . Copyright 2008, Elsevier Ltd. Quantum hysteretic conductance image: Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Resistance hysteresis correlated with synchrotron radiation surface studies in atomic sp2 layers of carbon synthesized on ferroelectric (001) lead zirconate titanate in an ultrahigh vacuum

“…35 Next, surface or interface sensitive characterization tools must be used to assess both the graphene layers, the presence of adsorbates or other trapping states, and the ferroelectric lm itself. Previous works mostly presented Raman spectra of graphene 9,12,17,26,27 or atomic force microscopy (AFM), sometimes with piezoresponse force microscopy (PFM) characterizations. 3,6,[10][11][12]14,18,21,23,24,[27][28][29] No surface chemical characterization in UHV such as (X-ray) photoelectron spectroscopy (XPS, PES) or X-ray absorption spectroscopy was reported previously on these kind of heterostructure.…”