The Synthesis and Superconducting Behavior of Crystalline Superlattices: (TiSe2)m(NbSe2)n

1996 ◽  
Vol 441 ◽  
Author(s):  
Myungkeun Noh ◽  
David C. Johnson
Keyword(s):  
Annealing Temperature ◽  
Substrate Surface ◽  
Domain Size ◽  
Bragg Diffraction ◽  
Conductivity Measurements ◽  
High Quality ◽  
Rocking Curve ◽  
Integral Number ◽  
Controlled Crystallization ◽  
Diffraction Peaks

AbstractA series of kinetically stable, crystalline superlattices containing an integral number of intergrown TiSe2 and NbSe2 layers have been synthesized by controlled crystallization of elementally modulated reactants. Theta-theta and rocking curve data were collected to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Nucleation of the dichalcogenide structure occurs upon annealing at temperatures above 200°C with the c-axis oriented perpendicular to the substrate surface. The [00l] diffraction linewidths decrease with increased annealing time and temperature suggesting growth of the c-axis domain size. High quality c-axis oriented dichalcogenide crystalline superlattices result from extended annealing at the relatively low annealing temperature of 500°C. The large number of well resolved [00l] Bragg diffraction peaks confirm the well developed crystal structure of the product superlattices in this direction. Four probe electrical conductivity measurements were used to determine the variation of the superconducting critical temperature as a function of the number of TiSe2 and NbSe2 layers in the superlattice.

The Preparation of Crystalline NbSe2/TiSe2 Superlattices from Modulated Elemental Reactants

1995 ◽  
Vol 382 ◽  
Author(s):  
Myungkeun Noh ◽  
James Thiel ◽  
David C. Johnson
Keyword(s):  
Diffraction Data ◽  
Substrate Surface ◽  
Domain Size ◽  
High Angle ◽  
High Quality ◽  
Rocking Curve ◽  
Modulated Elemental Reactants ◽  
Unit Cells ◽  
Controlled Crystallization ◽  
Elemental Reactants

ABSTRACTThree new crystalline NbSe2/TiSe2 superlattice compounds with 43.472±0.005A, 80.66±0.03A and 117.9±0.1Å unit cells in thec direction were prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants with different compositional layer thicknesses. Theta-theta and rocking curve data were collected using a theta-theta diffractometer to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Low angle diffraction data demonstrates that the initial layered reactant contracts in the c-axis direction upon initial annealing and suggests that the interfaces become smoother during this initial interdiffusion. High angle rocking curve diffraction data shows the development of caxis oriented NbSe2fTiSe2 crystal growth perpendicular to the substrate surface. Theta-theta scans show a gradual decrease of the (001) diffraction linewidths of the growing compound as a function of annealing time and temperature indicating an increase in the c-axis domain size. High quality caxis oriented TiSe2/NbSe2 crystalline superlattices result from annealing at the relatively low temperature of 500ºC. The rational synthesis of intergrowth compounds from superlattice reactants as described herein will permit the tailoring of physical properties as a function of compositional layer thicknesses and nativeproperties of the parent compounds.

Growth of SnS van der Waals Epitaxies on Layered Substrates

2013 ◽  
Vol 1493 ◽  
pp. 213-217 ◽  
Author(s):  
S.F. Wang ◽  
W.K. Fong ◽  
W. Wang ◽  
K.K. Leung ◽  
C. Surya
Keyword(s):  
Molecular Beam ◽  
Crystal Size ◽  
Substrate Surface ◽  
Van Der Waals ◽  
Layered Materials ◽  
Substantial Improvement ◽  
High Quality ◽  
Rocking Curve ◽  
Large Lattice ◽  
Unit Layer

ABSTRACTIn this paper we present systematic investigations on the growth of SnS van der Waals epitaxies (vdWEs) on different substrates, including crystalline and layered substrates, by molecular beam epitaxy (MBE). Experimental growth of SnS on conventional 3D substrates, such as GaAs, indicates strong interaction between the SnS layer and the substrate resulting in poor crystallinity in general. Substantial improvement in the film crystallinity can be obtained when the deposition is made on layered substrates, with saturated surface bonds, as observed in SnS films deposited on mica and crystalline substrates with a graphene buffer layer. Crystal size as large as one micron and rocking curve FWHM of 0.118° was observed despite the large lattice mismatches. This represents significant improvement over the reported value of ∼3°. Several symmetric growth orientations are observed for films grown on mica substrates. The results indicate that weak vdW interactions between the saturated bonds of the substrate surface and the SnS unit layer which is an important factor for achieving high quality epitaxy layered materials.

Electrochemical Synthesis and Characterization of La2CuO4+δ Single Crystals

1999 ◽  
Vol 14 (4) ◽  
pp. 1221-1226 ◽  
Author(s):  
D. P. Scarfe ◽  
X. Xiong ◽  
W. J. Zhu ◽  
P. H. Hor ◽  
S. C. Moss ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Single Crystals ◽  
Oxidation Process ◽  
Synthesis And Characterization ◽  
High Quality ◽  
Rocking Curve ◽  
X Ray ◽  
Diffraction Peaks ◽  
Flowing Oxygen

An electrochemical oxidation technique was used to obtain bulk oxidized La2CuO4+δ single crystals from the as-grown crystals. Samples were prepared by galvanostatic oxidation with currents in the range 5–10 μA and with different charging times. Some samples were annealed at 110 °C in flowing oxygen. Small high-quality crystals were obtained from electrochemically oxidized larger crystals that contained microcracks. Transmission x-ray Laue photography and rocking curve measurements for several fundamental diffraction peaks were used to confirm the crystal quality. The Tc and bulk magnetic properties of samples at different stages in the oxidation process are reported. After annealing at 110 °C, a 15 K transition was observed.

Computerized simulation of shortened ingots with a controlled crystallization for manufacturing of high-quality forgings

2019 ◽  
Vol 103 (5-8) ◽  
pp. 3057-3065 ◽  
Author(s):  
Oleg E. Markov ◽  
Oleksiy V. Gerasimenko ◽  
Alexander A. Shapoval ◽  
Oleksandr R. Abdulov ◽  
Roman U. Zhytnikov
Keyword(s):  
High Quality ◽  
Controlled Crystallization ◽  
Computerized Simulation

scholarly journals Structural and magnetic study of metallo-organic YIG powder using 2-ethylhexanoate carboxylate-based precursors

2019 ◽  
Vol 33 (09) ◽  
pp. 1950100 ◽  
Author(s):  
S. Hosseinzadeh ◽  
P. Elahi ◽  
M. Behboudnia ◽  
M. H. Sheikhi ◽  
S. M. Mohseni
Keyword(s):  
Saturation Magnetization ◽  
Annealing Temperature ◽  
Sintering Temperature ◽  
Magnetic Behavior ◽  
Yttrium Iron ◽  
Organic Precursor ◽  
Maximum Value ◽  
Diffraction Peaks ◽  
Iron Garnet ◽  
Organic Decomposition

The crystallization and magnetic behavior of yttrium iron garnet (YIG) prepared by metallo-organic decomposition (MOD) method are discussed. The chemistry and physics related to synthesis of iron and yttrium carboxylates based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found which elucidates synthesis of metallo-organic precursor of YIG in spite of the literatures of doped YIG samples such as Bi-YIG. Typically, the metal carboxylates used in preparation of ceramic oxide materials are 2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and solubility of yttrium and iron 2EH used in synthesis of YIG powder by MOD are reported. The crystallization and magnetic parameters, including saturation magnetization and coercivity of these samples, smoothly change as a function of the annealing temperature. It is observed that high sintering temperature of [Formula: see text] to [Formula: see text] promotes the diffraction peaks of YIG, therefore, we can conclude that the formation of YIG in MOD method increases the crystallization temperature. The maximum value of saturation magnetization and minimum value of coercivity and remanence are observed for the sample sintered at [Formula: see text] which are 13.7 emu/g, 10.38 Oe and 1.5 emu/g, respectively. This study cites the drawbacks in chemical synthesis of metallo-organic-based YIG production.

scholarly journals Growth of Ordered Graphene Ribbons by Sublimation Epitaxy

Crystals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 449
Author(s):  
Shuxian Cai ◽  
Xingfang Liu ◽  
Xin Zheng ◽  
Zhonghua Liu
Keyword(s):  
Substrate Surface ◽  
Graphene Film ◽  
Graphene Ribbon ◽  
High Quality ◽  
Graphene Layers ◽  
Force Microscopy ◽  
Layer Graphene ◽  
Micro Raman Spectroscopy ◽  
Atomic Force ◽  
Few Layer Graphene

Ordered graphene ribbons were grown on the surface of 4° off-axis 4H-SiC wafers by sublimation epitaxy, and characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM) and micro-Raman spectroscopy (μ-Raman). SEM showed that there were gray and dark ribbons on the substrate surface, and AFM further revealed that these ordered graphene ribbons had clear stepped morphologies due to surface step-bunching. It was shown by μ-Raman that the numbers of graphene layers of these two types of regions were different. The gray region was composed of mono- or bilayer ordered graphene ribbon, while the dark region was of tri- or few-layer ribbon. Meanwhile, ribbons were all homogeneous and had a width up to 40 μm and a length up to 1000 μm, without micro defects such as grain boundaries, ridges, or mono- and few-layer graphene mixtures. The results of this study are useful for optimized growth of high-quality graphene film on silicon carbide crystal.

scholarly journals Study of Detector-Grade CdMnTe:In Crystals Obtained by a Multi-Step Post-Growth Annealing Method

Crystals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 387 ◽  
Author(s):  
Pengfei Yu ◽  
Yongren Chen ◽  
Wei Li ◽  
Wenfei Liu ◽  
Bin Liu ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Crystal Quality ◽  
High Resistivity ◽  
Detector Performance ◽  
Rocking Curve ◽  
X Ray ◽  
Annealing Step ◽  
Subsequent Step ◽  
Te Inclusions ◽  
Annealing Method

A multi-step annealing method was successfully applied to inclusions reduction and resistivity improvement of CdMnTe:In (CMT:In) single crystals with high resistivity, including a Cd atmosphere annealing step followed by a Te atmosphere annealing step. After the Cd atmosphere annealing step, the density of Te inclusions was reduced distinctly, and it could be also decreased in the subsequent step of re-annealing under Te atmosphere. Both the resistivity and IR transmittance decreased notably after Cd atmosphere annealing, whereas they increased tremendously after re-annealing under a Te atmosphere. The reduction of full-width at-half-maximum (FWHM) and the increase of the intensity of the X-ray rocking curve indicated an improvement of the crystal quality. Meanwhile, after Cd atmosphere annealing, the increase of the intensity of the (D0,X) peak and the disappearance of the (A0,X) peak in photoluminescence (PL) measurements suggested further that the crystal quality was improved. The detector performance was enhanced obviously after annealing. The higher the annealing temperature, the better the performance was. The detector fabricated by CMT:In slice (Cd atmosphere annealing at 1073 K for 240 h and Te atmosphere re-annealing at 773 K for 120 h) with 9.43% energy resolution and 1.25 × 10−3 cm2/V μτ value had the best detector performance.

Fabrication of Ultrathin Bragg Beam Splitter by Plasma Chemical Vaporization Machining

2012 ◽  
Vol 523-524 ◽  
pp. 40-45 ◽  
Author(s):  
Taito Osaka ◽  
Makina Yabashi ◽  
Yasuhisa Sano ◽  
Kensuke Tono ◽  
Yuichi Inubushi ◽  
...  
Keyword(s):  
Beam Splitter ◽  
Bragg Reflection ◽  
Free Electron Lasers ◽  
Crystalline Perfection ◽  
Plasma Chemical ◽  
High Quality ◽  
Rocking Curve ◽  
Mechanical Process ◽  
X Ray ◽  
Beam Splitters

A novel fabrication process was proposed to produce high-quality Bragg beam splitters for hard X-ray free-electron lasers (XFELs), which should consist of thin, bend-free, and robust Bragg-case crystals without any defects. A combination of a mechanical process and plasma chemical vaporization machining was employed. High crystalline perfection of the fabricated Si(110) crystal was verified with X-ray topography and rocking curve measurements. In addition, the thickness was evaluated to be 4.4 μm from the fringe period of the measured rocking curve. The crystal can be employed in Bragg beam splitters using the (220) Bragg reflection for X-ray pump-X-ray probe experiments with XFEL sources.

scholarly journals Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SiC by MBE

1999 ◽  
Vol 4 (S1) ◽  
pp. 310-315 ◽  
Author(s):  
R. Lantier ◽  
A. Rizzi ◽  
D. Guggi ◽  
H. Lüth ◽  
B. Neubauer ◽  
...  
Keyword(s):  
Substrate Surface ◽  
Free Exciton ◽  
Near Band Edge ◽  
Band Edge Emission ◽  
Edge Emission ◽  
Rocking Curve ◽  
A Value ◽  
Dislocations Density ◽  
Aln Buffer ◽  
Atomically Flat

The Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550oC on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AlN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations.

X-Ray Diffraction Analysis on Crystallite Development of Nanostructured Aluminium

2006 ◽  
Vol 118 ◽  
pp. 53-58
Author(s):  
Elisabeth Meijer ◽  
Nicholas Armstrong ◽  
Wing Yiu Yeung
Keyword(s):  
Crystallite Size ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Equal Channel Angular Extrusion ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Integral Breadth ◽  
X Ray ◽  
Heat Treated ◽  
Diffraction Peaks

This study is to investigate the crystallite development in nanostructured aluminium using x-ray line broadening analysis. Nanostructured aluminium was produced by equal channel angular extrusion at room temperature to a total deformation strain of ~17. Samples of the extruded metal were then heat treated at temperatures up to 300oC. High order diffraction peaks were obtained using Mo radiation and the integral breadth was determined. It was found that as the annealing temperature increased, the integral breadth of the peak reflections decreased. By establishing the modified Williamson-Hall plots (integral breadth vs contract factor) after instrumental correction, it was determined that the crystallite size of the metal was maintained ~80 nm at 100oC. As the annealing temperature increased to 200oC, the crystallite size increased to ~118 nm. With increasing annealing temperature, the hardness of the metal decreased from ~60 HV to ~45 HV.

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