scholarly journals High-Density Well-Aligned Dislocations Introduced by Plastic Deformation in Bi1−xSbx Topological Insulator Single Crystals

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 317 ◽  
Author(s):  
Yuki Tokumoto ◽  
Riku Fujiwara ◽  
Keiichi Edagawa
Keyword(s):  
Single Crystals ◽  
Surface States ◽  
Zone Melting ◽  
High Density ◽  
Experimental Investigations ◽  
Dirac Fermions ◽  
Fundamental Study ◽  
Transmission Electron ◽  
Spin Polarized ◽  
Device Applications

Topological insulators (TIs) have a bulk bandgap and gapless edge or surface states that host helically spin-polarized Dirac fermions. Theoretically, it has been predicted that gapless states could also be formed along dislocations in TIs. Recently, conductivity measurements on plastically deformed bismuth antimony (Bi1−xSbx) TIs have revealed excess conductivity owing to dislocation conduction. For further application of them, fundamental study on dislocations in TIs is indispensable. Dislocations controlled based on fundamental studies could potentially be useful not only for experimental investigations of the dislocation properties but also for diverse device applications. In the present study, Bi1−xSbx TI single crystals were fabricated by a zone-melting method. The crystals were plastically deformed at room temperature. The resultant dislocations were observed by transmission electron microscopy (TEM). It was found that high-density dislocations with the Burgers vector satisfying the condition for the formation of gapless states were successfully introduced. The dislocations were mostly of edge type with lengths on the order of more than a few micrometers.

scholarly journals Optical and Thermoelectric Properties of Surface-Oxidation Sensitive Layered Zirconium Dichalcogenides ZrS2−xSex (x = 0, 1, 2) Crystals Grown by Chemical Vapor Transport

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 327
Author(s):  
Thalita Maysha Herninda ◽  
Ching-Hwa Ho
Keyword(s):  
Single Crystals ◽  
Thermoelectric Properties ◽  
Surface States ◽  
Chemical Vapor ◽  
Surface Oxidation ◽  
Vapor Transport ◽  
Chemical Vapor Transport ◽  
X Ray ◽  
Transmission Electron ◽  
Work Structure

In this work, structure, optical, and thermoelectric properties of layered ZrS2−xSex single crystals with selenium composition of x = 0, 1, and 2 were examined. Single crystals of zirconium dichalcogenides layer compounds were grown by chemical vapor transport method using I2 as the transport agent. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) results indicated that ZrS2−xSex (x = 0, 1, and 2) were crystalized in hexagonal CdI2 structure with one-layer trigonal (1T) stacking type. X-ray photoelectron and energy dispersive X-ray measurements revealed oxidation sensitive behavior of the chalcogenides series. Transmittance and optical absorption showed an indirect optical gap of about 1.78 eV, 1.32 eV, and 1.12 eV for the ZrS2−xSex with x = 0, 1, and 2, respectively. From the result of thermoelectric experiment, ZrSe2 owns the highest figure-of merit (ZT) of ~0.085 among the surface-oxidized ZrS2−xSex series layer crystals at 300 K. The ZT values of the ZrS2−xSex (x = 0, 1, and 2) series also reveal increase with the increase of Se content owing to the increase of carrier concentration and mobility in the highly Se-incorporated zirconium dichalcogenides with surface states.

scholarly journals Generation of spin-polarized hot electrons at topological insulators surfaces by scattering from collective charge excitations

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Khalil Zakeri ◽  
Janek Wettstein ◽  
Christoph Sürgers
Keyword(s):  
Topological Insulators ◽  
Spin Asymmetry ◽  
Surface States ◽  
Inelastic Channel ◽  
Dirac Fermions ◽  
Elastic Channel ◽  
Fundamental Physics ◽  
Spintronic Devices ◽  
Spin Polarized ◽  
New Ideas

AbstractTopological insulators (TIs) are materials which exhibit topologically protected electronic surface states, acting as mass-less Dirac fermions. Beside their fascinating fundamental physics, TIs are also promising candidates for future spintronic devices. In this regard, generation of spin-polarized currents in TIs is the first and most important step towards their application in spin-based devices. Here we demonstrate that when electrons are scattered from the surface of bismuth selenide, a prototype TI, not only the elastic channel but also the inelastic channel is strongly spin dependent. In particular collective charge excitations (plasmons) excited at such surfaces show a large spin-dependent electron scattering. Electrons scattered by these excitations exhibit a high spin asymmetry, as high as 40%. The observed effect opens up new possibilities to generate spin-polarized currents at the surface of TIs or utilize the collective charge excitations to analyze the electrons’ spin. The results are also important to understand the spin polarization of the photo-excited electrons excited at TIs surfaces. Moreover, our finding will inspire new ideas for using these plasmonic excitations in the field of spin-plasmonics.

scholarly journals Dimensional crossover and band topology evolution in ultrathin semimetallic NiTe2 films

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Joseph A. Hlevyack ◽  
Liang-Ying Feng ◽  
Meng-Kai Lin ◽  
Rovi Angelo B. Villaos ◽  
Ro-Ya Liu ◽  
...  
Keyword(s):  
Film Thickness ◽  
Ultrathin Films ◽  
Molecular Beam ◽  
Surface States ◽  
Single Layer ◽  
Dirac Fermions ◽  
Dirac Semimetal ◽  
Emergent Phenomena ◽  
Device Applications ◽  
Topological Surface

AbstractNickel ditelluride (NiTe2), a recently discovered Type-II Dirac semimetal with topological Dirac fermions near the Fermi energy, is expected to exhibit strong thickness-mediated electronic tunability and intrinsic two-gap superconductivity in the single-layer limit. Realizing such intriguing phenomena requires the fabrication of ultrathin NiTe2 films and an understanding of the underlying physics that is still under debate. By conducting experimental band mappings of ultrathin films prepared with molecular beam epitaxy, we reveal spectroscopic evidence for the dimensionality crossover of single-crystalline ultrathin NiTe2 films as a function of film thickness. As the film thickness increases from one to five layers, the gap in the conical topological surface states closes. Comparisons of experimental to first-principles results also highlight difficulties in fabricating atomically smooth single-layer NiTe2 films. Our results not only provide further impetus for studying emergent phenomena in NiTe2 but also underscore the limitations of fabricating NiTe2 films for device applications.

Dislocation Substructure in NiAl Single Crystals Deformed at Ambient Temperature

1996 ◽  
Vol 460 ◽  
Author(s):  
X. Shi ◽  
T. M. Pollock ◽  
S. Mahajan ◽  
V. S. Arunachalam
Keyword(s):  
Ambient Temperature ◽  
Single Crystals ◽  
Dislocation Substructure ◽  
High Density ◽  
Weak Beam ◽  
Transmission Electron ◽  
Beam Transmission ◽  
Edge Dislocations ◽  
Double Cross

ABSTRACTDislocation substructure in NiAI single crystals oriented for single slip and deformed at ambient temperature has been studied using weak-beam transmission electron microscopy. Deformation is localized in bands that consists mostly of near-edge dislocations, with an interspersion of a high density of elongated prismatic loops. Pure screw dislocations are not observed, but dislocations having “zigzag” configurations that are near-screw in orientation are present. A high density of jogs is observed on both near-edge and zigzag dislocation segments. The mechanisms for the development of this substructure are discussed, emphasizing the role of double cross slip and resulting glissile and sessile jogs of varying heights.

TEM and cathodoluminescence of precipitates in II-VI semiconductors

1988 ◽  
Vol 46 ◽  
pp. 488-489
Author(s):  
Joanna L. Batstone
Keyword(s):  
Crystal Growth ◽  
Band Gap ◽  
Local Strain ◽  
Wide Band ◽  
Optoelectronic Device ◽  
Wide Band Gap ◽  
Bulk Crystal Growth ◽  
Transmission Electron ◽  
Device Applications ◽  
Stoichiometry Control

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-x Te are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.

Precipitation of NiHfsi phase in NiAl single crystals containing Hf

1995 ◽  
Vol 53 ◽  
pp. 532-533
Author(s):  
A. Garg ◽  
R. D. Noebe ◽  
R. Darolia
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
High Temperature Strength ◽  
Bridgman Technique ◽  
Shell Mold ◽  
Third Phase ◽  
Unknown Phase ◽  
Transmission Electron ◽  
Two Phases ◽  
Nial Matrix

Small additions of Hf to NiAl produce a significant increase in the high-temperature strength of single crystals. Hf has a very limited solubility in NiAl and in the presence of Si, results in a high density of G-phase (Ni16Hf6Si7) cuboidal precipitates and some G-platelets in a NiAl matrix. These precipitates have a F.C.C structure and nucleate on {100}NiAl planes with almost perfect coherency and a cube-on-cube orientation-relationship (O.R.). However, G-phase is metastable and after prolonged aging at high temperature dissolves at the expense of a more stable Heusler (β'-Ni2AlHf) phase. In addition to these two phases, a third phase was shown to be present in a NiAl-0.3at. % Hf alloy, but was not previously identified (Fig. 4 of ref. 2 ). In this work, we report the morphology, crystal-structure, O.R., and stability of this unknown phase, which were determined using conventional and analytical transmission electron microscopy (TEM).Single crystals of NiAl containing 0.5at. % Hf were grown by a Bridgman technique. Chemical analysis indicated that these crystals also contained Si, which was not an intentional alloying addition but was picked up from the shell mold during directional solidification.

Transmission Electron Microscopy study of Bi-based superconducting phases

1990 ◽  
Vol 48 (4) ◽  
pp. 50-51
Author(s):  
J.G. Wen ◽  
K.K. Fung
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Single Crystals ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Space Groups ◽  
Superconducting Phases ◽  
Ceramic Samples ◽  
Transmission Electron ◽  
Modulated Structures

Bi-based superconducting phases have been found to be members of a structural series represented by Bi2Sr2Can−1Cun−1On+4, n=1,2,3, and are referred to as 2201, 2212, 2223 phases. All these phases are incommensurate modulated structures. The super space groups are P2/b, NBbmb 2201, 2212 phases respectively. Pb-doped ceramic samples and single crystals and Y-doped single crystals have been studied by transmission electron microscopy.Modulated structures of all Bi-based superconducting phases are in b-c plane, therefore, it is the best way to determine modulated structure and c parameter in diffraction pattern. FIG. 1,2,3 show diffraction patterns of three kinds of modulations in Pb-doped ceramic samples. Energy dispersive X-ray analysis (EDAX) confirms the presence of Pb in the three modulated structures. Parameters c are 3 0.06, 38.29, 30.24Å, ie 2212, 2223, 2212 phases for FIG. 1,2,3 respectively. Their average space groups are all Bbmb.

An Overview of Cu Wire Intermetallic Compound Formation and a Corrosion Failure Mechanism

2012 ◽  
Author(s):  
Dongmei Meng ◽  
Laura Buck ◽  
James Cargo
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Corrosion Mechanism ◽  
Fundamental Study ◽  
Corrosion Failure ◽  
Transmission Electron ◽  
Intermetallic Compound Formation ◽  
Scanning Transmission ◽  
Low K

Abstract Cu needs a higher level of ultrasound combined with bonding force to be bonded to the Al pad properly, not just because Cu is harder than Au, but it is also harder to initiate intermetallic compounds (IMC) formation during bonding. This increases the chances of damaging the metal/low k stack under the bondpad. This paper presents a fundamental study of IMC as well as one example of a failure mode of Cu/Al bonded devices, all based on detailed analysis using scanning electron microscopy, scanning transmission electron microscopy, energy dispersive spectrometers, and transmission electron microscopy. It presents a case study showing a corrosion mechanism of Cu/Al ballbond after 168hr UHAST stress. It is observed that all Cu9Al4 was consumed, while very little copper aluminide remained after 168 hours of UHAST stressing.

ε-InSe single crystals grown by a horizontal gradient freeze method

CrystEngComm ◽  
2020 ◽  
Vol 22 (45) ◽  
pp. 7864-7869
Author(s):  
Maojun Sun ◽  
Wei Wang ◽  
Qinghua Zhao ◽  
Xuetao Gan ◽  
Yuanhui Sun ◽  
...  
Keyword(s):  
Single Crystals ◽  
Optoelectronic Device ◽  
Indium Selenide ◽  
Horizontal Gradient ◽  
Device Applications

Indium selenide (InSe) single crystals have been considered as promising candidates for future optical, electrical, and optoelectronic device applications.

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