scholarly journals Electronic Structure of Oxygen-Deficient SrTiO3 and Sr2TiO4

Crystals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 580 ◽  
Author(s):  
Ali Al-Zubi ◽  
Gustav Bihlmayer ◽  
Stefan Blügel
Keyword(s):  
Density Functional ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
The Core ◽  
Atomic Force ◽  
Level Shifts ◽  
Spectroscopic Signatures ◽  
Gap States

The conductive behavior of the perovskite SrTiO 3 is strongly influenced by the presence of oxygen vacancies in this material, therefore the identification of such defects with spectroscopic methods is of high importance. We use density functional theory to characterize the defect-induced states in SrTiO 3 and Sr 2 TiO 4 . Their signatures at the surface, the visibility for scanning tunneling spectroscopy and locally conductive atomic force microscopy, and the core-level shifts observed on Ti atoms in the vicinity of the defect are studied. In particular, we find that the exact location of the defect state (e.g., in SrO or TiO 2 planes relative to the surface) are decisive for their visibility for scanning-probe methods. Moreover, the usual distinction between Ti 3 + and Ti 2 + species, which can occur near defects or their aggregates, cannot be directly translated in characteristic shifts of the core levels. The width of the defect-induced in-gap states is found to depend critically on the arrangement of the defects. This also has consequences for the spectroscopic signatures observed in so-called resistive switching phenomena.

scholarly journals Local Electric Property Modification of Ferroelectric Tunnel Junctions Induced by Variation of Polarization Charge Screening Conditions under Measurement with Scanning Probe Techniques

Nanomaterials ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3323
Author(s):  
Natalia Andreeva ◽  
Anatoliy Petukhov ◽  
Oleg Vilkov ◽  
Adrian Petraru ◽  
Victor Luchinin
Keyword(s):  
Tunnel Junctions ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Probe ◽  
Scanning Tunneling ◽  
Tunnel Barrier ◽  
Ambient Conditions ◽  
Conductive Atomic Force Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
The Difference

Scanning tunneling spectroscopy in ultrahigh vacuum conditions and conductive atomic-force microscopy in ambient conditions were used to study local electroresistive properties of ferroelectric tunnel junctions SrTiO3/La0.7Sr0.3MnO3/BaTiO3. Interestingly, experimental current-voltage characteristics appear to strongly depend on the measurement technique applied. It was found that screening conditions of the polarization charges at the interface with a top electrode differ for two scanning probe techniques. As a result, asymmetry of the tunnel barrier height for the opposite ferroelectric polarization orientations may be influenced by the method applied to study the local tunnel electroresistance. Our observations are well described by the theory of electroresistance in ferroelectric tunnel junctions. Based on this, we reveal the main factors that influence the polarization-driven local resistive properties of the device under study. Additionally, we propose an approach to enhance asymmetry of ferroelectric tunnel junctions during measurement. While keeping the high locality of scanning probe techniques, it helps to increase the difference in the value of tunnel electroresistance for the opposite polarization orientations.

scholarly journals Structure-resistive property relationships in thin ferroelectric BaTiO$$_{3}$$ films

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
N. V. Andreeva ◽  
A. Petraru ◽  
O. Yu. Vilkov ◽  
A. E. Petukhov
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Point Defects ◽  
Ferroelectric Properties ◽  
Piezoresponse Force Microscopy ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Ferroelectric Films ◽  
Force Microscopy ◽  
Atomic Force

Abstract A combined study of local structural, electric and ferroelectric properties of SrTiO$$_{3}$$ 3 /La$$_{0.7}$$ 0.7 Sr$$_{0.3}$$ 0.3 MnO$$_{3}$$ 3 /BaTiO$$_{3}$$ 3 heterostructures was performed by Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy in the temperature range 30–295 K. The direct correlation of film structure (epitaxial, nanocrystalline or polycrystalline) with local electric and ferroelectric properties was observed. For polycrystalline ferroelectric films the predominant polarization state is defined by the peculiarity of screening the built-in field by positively charged point defects. Based on Scanning Tunneling Spectroscopy results, it was found that a sequent voltage application provokes the modification of local resistive properties related to the redistribution of point defects in thin ferroelectric films. A qualitative analysis of acquired Piezoresponse Force Microscopy, tunneling Atomic Force Microscopy and Scanning Tunneling Microscopy images together with Scanning Tunneling Spectroscopy measurements enabled us to conclude that in the presence of structural defects the competing processes of electron injection, trap filling and the drift of positively charged point defects drives the change of resistive properties of thin films under applied electric field. In this paper, we propose a new approach based on Scanning Tunneling Microscopy/Spectroscopy under ultrahigh vacuum conditions to clarify the influence of point defects on local resistive properties of nanometer-thick ferroelectric films.

scholarly journals Influence of the adsorption geometry of PTCDA on Ag(111) on the tip–molecule forces in non-contact atomic force microscopy

2014 ◽  
Vol 5 ◽  
pp. 98-104 ◽  
Author(s):  
Gernot Langewisch ◽  
Jens Falter ◽  
André Schirmeisen ◽  
Harald Fuchs
Keyword(s):  
Force Spectroscopy ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Organic Adsorbates ◽  
Adsorption Geometry ◽  
Spectroscopy Studies ◽  
Tetracarboxylic Dianhydride

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) adsorbed on a metal surface is a prototypical organic–anorganic interface. In the past, scanning tunneling microscopy and scanning tunneling spectroscopy studies of PTCDA adsorbed on Ag(111) have revealed differences in the electronic structure of the molecules depending on their adsorption geometry. In the work presented here, high-resolution 3D force spectroscopy measurements at cryogenic temperatures were performed on a surface area that contained a complete PTCDA unit cell with the two possible geometries. At small tip-molecule separations, deviations in the tip-sample forces were found between the two molecule orientations. These deviations can be explained by a different electron density in both cases. This result demonstrates the capability of 3D force spectroscopy to detect even small effects in the electronic properties of organic adsorbates.

scholarly journals Structural and Nanotribological Properties of a BODIPY Self-Assembly

2021 ◽  
Vol 9 ◽  
Author(s):  
Shanchao Tan ◽  
Wendi Luo ◽  
Yongjie Zhang ◽  
Xiang-Kui Ren ◽  
Yuhong Liu ◽  
...  
Keyword(s):  
Self Assembly ◽  
Density Functional ◽  
Supramolecular Assembly ◽  
Dft Method ◽  
The Self ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Assembly Mechanism

Boron-dipyrromethenes (BODIPY) are promising functional dyes, whose exceptional optical properties are closely related to their supramolecular assembly. Herein, the self-assembly of a BODIPY derivative functionalized with uracil groups is explicitly and thoroughly investigated by using scanning tunneling microscopy (STM). Based on the simulation and calculation by density functional theory (DFT) method, it can be concluded that the construction of ordered self-assembly structure is attributed to the formation of hydrogen bonds between uracil groups. Moreover, the nanotribological property of the self-assembly on HOPG surface is measured by using atomic force microscopy (AFM). The effort on self-assembly of the BODIPY derivative could enhance the understanding of surface assembly mechanism.

scholarly journals Defect-Induced π-Magnetism into Non-Benzenoid Nanographenes

Nanomaterials ◽  
2022 ◽  
Vol 12 (2) ◽  
pp. 224
Author(s):  
Kalyan Biswas ◽  
Lin Yang ◽  
Ji Ma ◽  
Ana Sánchez-Grande ◽  
Qifan Chen ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Open Shell ◽  
Scanning Tunneling Spectroscopy ◽  
Membered Ring ◽  
Structural Defects ◽  
Scanning Tunneling ◽  
Honeycomb Lattice ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force

The synthesis of nanographenes (NGs) with open-shell ground states have recently attained increasing attention in view of their interesting physicochemical properties and great prospects in manifold applications as suitable materials within the rising field of carbon-based magnetism. A potential route to induce magnetism in NGs is the introduction of structural defects, for instance non-benzenoid rings, in their honeycomb lattice. Here, we report the on-surface synthesis of three open-shell non-benzenoid NGs (A1, A2 and A3) on the Au(111) surface. A1 and A2 contain two five- and one seven-membered rings within their benzenoid backbone, while A3 incorporates one five-membered ring. Their structures and electronic properties have been investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy and scanning tunneling spectroscopy complemented with theoretical calculations. Our results provide access to open-shell NGs with a combination of non-benzenoid topologies previously precluded by conventional synthetic procedures.

scholarly journals Atomic-scale intermolecular interaction of hydrogen with a single VOPc molecule on the Au(111) surface

RSC Advances ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 6240-6245
Author(s):  
Jinoh Jung ◽  
Shinjae Nam ◽  
Christoph Wolf ◽  
Andreas J. Heinrich ◽  
Jungseok Chae
Keyword(s):  
Molecular Dynamics ◽  
Atomic Force Microscopy ◽  
Intermolecular Interaction ◽  
Scanning Tunneling Spectroscopy ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Force Microscopy ◽  
Hydrogen Molecules ◽  
Atomic Force ◽  
Micro Cavity

Molecular dynamics of hydrogen molecules trapped in micro-cavity between atomic-scale tip and VOPc molecules on surface and intermolecular interactions have been studied by using scanning tunneling spectroscopy and atomic force microscopy at atomic-scale.

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