scholarly journals Carrier Depletion near the Grain Boundary of a SiC Bicrystal

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Young-Wook Kim ◽  
Eita Tochigi ◽  
Junichi Tatami ◽  
Yong-Hyeon Kim ◽  
Seung Hoon Jang ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Grain Boundary ◽  
Diffusion Bonding ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Depletion Layer ◽  
Native Oxide ◽  
Electrical Insulator ◽  
Dopant Profiling ◽  
Scanning Transmission

AbstractSilicon carbide (SiC) bicrystals were prepared by diffusion bonding, and their grain boundary was observed using scanning transmission electron microscopy. The n-type electrical conductivity of a SiC single crystal was confirmed by scanning nonlinear dielectric microscopy (SNDM). Dopant profiling of the sample by SNDM showed that the interface acted as an electrical insulator with a ~2-μm-thick carrier depletion layer. The carrier depletion layer contained a higher number of oxygen impurities than the bulk crystals due to the incorporation of oxygen from the native oxide film during diffusion bonding. Density functional theory calculations of the density of states as a function of the bandgap also supported these findings. The existence of a carrier depletion layer was also confirmed in a p-type polycrystalline SiC ceramic. These results suggest that the electrical conductivity of SiC ceramics was mostly affected by carrier depletion near the grain boundary rather than the grain boundary itself.

scholarly journals Atomic origin of spin-valve magnetoresistance at the SrRuO3 grain boundary

2020 ◽  
Vol 7 (4) ◽  
pp. 755-762 ◽  
Author(s):  
Xujing Li ◽  
Li Yin ◽  
Zhengxun Lai ◽  
Mei Wu ◽  
Yu Sheng ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Density Functional ◽  
Magnetic Moments ◽  
Spin Valve ◽  
Density Functional Theory Calculations ◽  
Precise Knowledge ◽  
Transmission Electron ◽  
Defect Control ◽  
Scanning Transmission ◽  
Low Dimensional

Abstract Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order.

scholarly journals Electrical Conductivities and Interactions in Binary Mixtures of Imidazolium-Based Ionic Liquids with Acetonitrile and Dimethyl Sulfoxide

2020 ◽  
Vol 71 (2) ◽  
pp. 392-402
Author(s):  
Oana Ciocirlan ◽  
Amalia Stefaniu
Keyword(s):  
Electrical Conductivity ◽  
Ionic Liquids ◽  
Dimethyl Sulfoxide ◽  
Binary Mixtures ◽  
Density Functional ◽  
Binary Systems ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Electrical Conductivities ◽  
Anion Type

This paper reports experimental electrical conductivities data of eight binary systems of four ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF4], 1-hexyl-3-methylimidazolium tetrafluoroborate, [Hmim][BF4], 1-butyl-3-methylimidazolium hexafluorophosphate, [Bmim][PF6] and 1-butyl-2,3-dimethyl-imidazolium tetrafluoroborate, [Bmmim][BF4] with the organic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN) at atmospheric pressure and temperatures from 298.15 to 328.15 K. It was found that conductivities in the investigated ionic liquids follow the order: [Bmim][BF4] ] [Bmim][PF6] ][Bmmim][BF4] ] [Hmim][BF4]. Experimental results demonstrate that the binary mixtures possess higher electrical conductivity compared with pure components. Electrical conductivity data were correlated using Casteel�Amis and Arrhenius equations. The molar conductivity was derived from experimental data and fitted to Walden rule. The influence of the cation structure and anion type on the conductivity was discussed, which help understanding the intermolecular interactions in the binary systems. A deeper understanding of the transport behavior of ILs is given by means of density functional theory calculations (DFT)

scholarly journals Layer-dependent topological phase in a two-dimensional quasicrystal and approximant

2020 ◽  
Vol 117 (42) ◽  
pp. 26135-26140
Author(s):  
Jeffrey D. Cain ◽  
Amin Azizi ◽  
Matthias Conrad ◽  
Sinéad M. Griffin ◽  
Alex Zettl
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Transition Metal Dichalcogenide ◽  
Material System ◽  
Two Dimensional ◽  
Topological Properties ◽  
Scanning Transmission ◽  
Layered Transition Metal ◽  
Low Dimensional ◽  
Physical Phenomena

The electronic and topological properties of materials are derived from the interplay between crystalline symmetry and dimensionality. Simultaneously introducing “forbidden” symmetries via quasiperiodic ordering with low dimensionality into a material system promises the emergence of new physical phenomena. Here, we isolate a two-dimensional (2D) chalcogenide quasicrystal and approximant, and investigate their electronic and topological properties. The 2D layers of the materials with a composition close to Ta1.6Te, derived from a layered transition metal dichalcogenide, are isolated with standard exfoliation techniques, and investigated with electron diffraction and atomic resolution scanning transmission electron microscopy. Density functional theory calculations and symmetry analysis of the large unit cell crystalline approximant of the quasicrystal, Ta21Te13, reveal the presence of symmetry-protected nodal crossings in the quasicrystalline and approximant phases, whose presence is tunable by layer number. Our study provides a platform for the exploration of physics in quasicrystalline, low-dimensional materials and the interconnected nature of topology, dimensionality, and symmetry in electronic systems.

scholarly journals Investigation of Charge-Transfer Interactions Induced by Encapsulating Fullerene in a Mesoporous Tetrathiafulvalene-Based Metal-Organic Framework

2019 ◽  
Author(s):  
Manuel Souto ◽  
Joaquín Calbo ◽  
Samuel Mañas-Valero ◽  
Aron Walsh ◽  
Guillermo Minguez Espallargas
Keyword(s):  
Electrical Conductivity ◽  
Charge Transfer ◽  
Density Functional ◽  
Metal Organic Framework ◽  
Metal Organic Frameworks ◽  
Density Functional Theory Calculations ◽  
Spectroscopic Techniques ◽  
Functional Theory ◽  
Guest Molecules ◽  
Metal Organic

<p>The design of Metal-Organic Frameworks (MOFs) incorporating electroactive guest molecules in the pores has become a subject of great interest in order to install additional electrical functionalities within the framework while maintaining porosity. In this direction, understanding the charge-transfer (CT) process between the framework and the guest molecules is crucial towards the design of new electroactive MOFs. Herein, we present the encapsulation of fullerenes (C<sub>60</sub>) in a mesoporous tetrathiafulvalene(TTF)-based MOF. The CT process between the electron-acceptor C<sub>60 </sub>guest and the electron-donor TTF ligand is studied in detail by means of different spectroscopic techniques and density functional theory calculations. Importantly, gas sorption measurements demonstrate that sorption capacity is maintained after encapsulation of fullerenes, whereas the electrical conductivity is increased by two orders of magnitude due to the CT interactions between C<sub>60</sub>and the TTF-based framework. </p>

scholarly journals Aluminum depletion induced by co-segregation of carbon and boron in a bcc-iron grain boundary

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Ahmadian ◽  
D. Scheiber ◽  
X. Zhou ◽  
B. Gault ◽  
C. H. Liebscher ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Atom Probe Tomography ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Local Variation ◽  
Atom Probe ◽  
Atomic Scale ◽  
Polycrystalline Materials ◽  
Repulsive Interaction ◽  
Structural Units

AbstractThe local variation of grain boundary atomic structure and chemistry caused by segregation of impurities influences the macroscopic properties of polycrystalline materials. Here, the effect of co-segregation of carbon and boron on the depletion of aluminum at a Σ5 (3 1 0 )[0 0 1] tilt grain boundary in a α − Fe-4 at%Al bicrystal is studied by combining atomic resolution scanning transmission electron microscopy, atom probe tomography and density functional theory calculations. The atomic grain boundary structural units mostly resemble kite-type motifs and the structure appears disrupted by atomic scale defects. Atom probe tomography reveals that carbon and boron impurities are co-segregating to the grain boundary reaching levels of >1.5 at%, whereas aluminum is locally depleted by approx. 2 at.%. First-principles calculations indicate that carbon and boron exhibit the strongest segregation tendency and their repulsive interaction with aluminum promotes its depletion from the grain boundary. It is also predicted that substitutional segregation of boron atoms may contribute to local distortions of the kite-type structural units. These results suggest that the co-segregation and interaction of interstitial impurities with substitutional solutes strongly influences grain boundary composition and with this the properties of the interface.

scholarly journals An antisite defect mechanism for room temperature ferroelectricity in orthoferrites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shuai Ning ◽  
Abinash Kumar ◽  
Konstantin Klyukin ◽  
Eunsoo Cho ◽  
Jong Heon Kim ◽  
...  
Keyword(s):  
Rare Earth ◽  
Density Functional ◽  
Room Temperature ◽  
Magnetic Ordering ◽  
Density Functional Theory Calculations ◽  
Piezoresponse Force Microscopy ◽  
Antisite Defect ◽  
Scanning Transmission ◽  
Antisite Defects ◽  
Defect Mechanism

AbstractSingle-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of YFe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.

scholarly journals Ab Initio Study of the Combined Effects of Alloying Elements and H on Grain Boundary Cohesion in Ferritic Steels

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 291 ◽  
Author(s):  
Aparna P. A. Subramanyam ◽  
Abril Azócar Guzmán ◽  
Smobin Vincent ◽  
Alexander Hartmaier ◽  
Rebecca Janisch
Keyword(s):  
Grain Boundary ◽  
Density Functional ◽  
Detrimental Effect ◽  
Density Functional Theory Calculations ◽  
Alloying Elements ◽  
Ferritic Steels ◽  
Functional Theory ◽  
Substitutional Element ◽  
Spin Polarized ◽  
Interstitial Elements

Hydrogen enhanced decohesion is expected to play a major role in ferritic steels, especially at grain boundaries. Here, we address the effects of some common alloying elements C, V, Cr, and Mn on the H segregation behaviour and the decohesion mechanism at a Σ 5 ( 310 ) [ 001 ] 36.9 ∘ grain boundary in bcc Fe using spin polarized density functional theory calculations. We find that V, Cr, and Mn enhance grain boundary cohesion. Furthermore, all elements have an influence on the segregation energies of the interstitial elements as well as on these elements’ impact on grain boundary cohesion. V slightly promotes segregation of the cohesion enhancing element C. However, none of the elements increase the cohesion enhancing effect of C and reduce the detrimental effect of H on interfacial cohesion at the same time. At an interface which is co-segregated with C, H, and a substitutional element, C and H show only weak interaction, and the highest work of separation is obtained when the substitute is Mn.

scholarly journals Ultra-small rhenium clusters supported on graphene

2015 ◽  
Vol 17 (12) ◽  
pp. 7898-7906 ◽  
Author(s):  
Orlando Miramontes ◽  
Franco Bonafé ◽  
Ulises Santiago ◽  
Eduardo Larios-Rodriguez ◽  
Jesús J. Velázquez-Salazar ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Dark Field ◽  
High Angle ◽  
Functional Theory ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

In this work, the adsorption of very small rhenium clusters (2–13 atoms) supported on graphene was studied by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) in combination with density functional theory calculations.

Investigation of Charge-Transfer Interactions Induced by Encapsulating Fullerene in a Mesoporous Tetrathiafulvalene-Based Metal-Organic Framework

2019 ◽  
Author(s):  
Manuel Souto ◽  
Joaquín Calbo ◽  
Samuel Mañas-Valero ◽  
Aron Walsh ◽  
Guillermo Minguez Espallargas
Keyword(s):  
Electrical Conductivity ◽  
Charge Transfer ◽  
Density Functional ◽  
Metal Organic Framework ◽  
Metal Organic Frameworks ◽  
Density Functional Theory Calculations ◽  
Spectroscopic Techniques ◽  
Functional Theory ◽  
Guest Molecules ◽  
Metal Organic

<p>The design of Metal-Organic Frameworks (MOFs) incorporating electroactive guest molecules in the pores has become a subject of great interest in order to install additional electrical functionalities within the framework while maintaining porosity. In this direction, understanding the charge-transfer (CT) process between the framework and the guest molecules is crucial towards the design of new electroactive MOFs. Herein, we present the encapsulation of fullerenes (C<sub>60</sub>) in a mesoporous tetrathiafulvalene(TTF)-based MOF. The CT process between the electron-acceptor C<sub>60 </sub>guest and the electron-donor TTF ligand is studied in detail by means of different spectroscopic techniques and density functional theory calculations. Importantly, gas sorption measurements demonstrate that sorption capacity is maintained after encapsulation of fullerenes, whereas the electrical conductivity is increased by two orders of magnitude due to the CT interactions between C<sub>60</sub>and the TTF-based framework. </p>

scholarly journals Single-atom doping of MoS2 with manganese enables ultrasensitive detection of dopamine: Experimental and computational approach

2020 ◽  
Vol 6 (32) ◽  
pp. eabc4250 ◽  
Author(s):  
Yu Lei ◽  
Derrick Butler ◽  
Michael C. Lucking ◽  
Fu Zhang ◽  
Tunan Xia ◽  
...  
Keyword(s):  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Density Functional Theory Calculations ◽  
Single Atom ◽  
Buffer Solution ◽  
Dopamine Detection ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Metal Dichalcogenides ◽  
Metal Doped

Two-dimensional transition metal dichalcogenides (TMDs) emerged as a promising platform to construct sensitive biosensors. We report an ultrasensitive electrochemical dopamine sensor based on manganese-doped MoS2 synthesized via a scalable two-step approach (with Mn ~2.15 atomic %). Selective dopamine detection is achieved with a detection limit of 50 pM in buffer solution, 5 nM in 10% serum, and 50 nM in artificial sweat. Density functional theory calculations and scanning transmission electron microscopy show that two types of Mn defects are dominant: Mn on top of a Mo atom (MntopMo) and Mn substituting a Mo atom (MnMo). At low dopamine concentrations, physisorption on MnMo dominates. At higher concentrations, dopamine chemisorbs on MntopMo, which is consistent with calculations of the dopamine binding energy (2.91 eV for MntopMo versus 0.65 eV for MnMo). Our results demonstrate that metal-doped layered materials, such as TMDs, constitute an emergent platform to construct ultrasensitive and tunable biosensors.

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