Analyses of local burnout in a sub-scale test coil for the 32 T magnet after spontaneous quenches during fast ramping

2022 ◽  
Author(s):  
Xinbo Hu ◽  
Anatolii A Polyanskii ◽  
Dmytro Abraimov ◽  
Andrey V. Gavrilin ◽  
Hubertus W Weijers ◽  
...  
Keyword(s):  
Hot Spot ◽  
Chemical Vapor ◽  
Superconducting Magnet ◽  
Growth Conditions ◽  
Vortex Pinning ◽  
Coated Conductors ◽  
Careful Examination ◽  
Organic Chemical ◽  
Damaged Zone ◽  
Edge Defects

Abstract Industrial production of REBa2Cu3O7-δ (REBCO) coated conductors made it possible to construct the 32 T magnet, the first successful all-superconducting user magnet to exceed 30 T, which now serves users as SCM4 (Superconducting Magnet) at the NHMFL. Here we present an analysis of the damage that occurred in late-stage proof testing of the 32 T prototype coil after many essential facets of the design had been proven through more than 100 intentionally triggered quenches at fields up to 24 T. This prototype coil was then subjected to accelerated charge-discharge cycles at a rate 44 times faster than its design ramp rate to attempt to address its fatigue tolerance. The extra hysteresis loss of the fast ramps led to heating of the end pancakes which induced, after 55 fatigue cycles, 3 spontaneous quenches at progressively lower currents. Recognizing that the coil was damaged, the pancakes were then unwound and their REBCO tapes run through our continuous in-field transport Ic and remnant-field magnetization monitoring device, YateStar, which revealed 3 highly localized zones of low Ic in the end pancake that induced quench. Careful examination of these zones, especially the most intensely damaged one, revealed that the worst hot spot reached at least 779C during the quenches. Magneto-optical imaging showed that this damaged zone was about 5 mm in diameter and indeed the perpendicular damage length induced in neighboring turns by this localized quench heating was almost as great. Although there is much present concern about fatigue crack propagation from edge defects, we actually attribute this damage not to fatigue but to fluctuations in vortex pinning density due to imperfect BaZrO3 (BZO) nanorod growth that locally reduced the critical current Ic. These localized low-Ic regions then had to shed their excess current into the copper stabilizer, producing intense heating. We provide transmission and scanning electron microscopy evidence for local fluctuations of the BZO pinning structure and relate it to recent work that shows significant variations of 4 K, high field Ic values due to apparent production fluctuations of the growth conditions of the Zr-doped Metal-Organic Chemical Vapor Deposition (MOCVD) REBCO used for this test magnet.

TEM study of very thin InGaAsP layers grown by liquid-phase epitaxy

1990 ◽  
Vol 48 (4) ◽  
pp. 672-673
Author(s):  
N.A. Bert ◽  
A.O. Kosogov
Keyword(s):  
Liquid Phase ◽  
Liquid Phase Epitaxy ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Dark Field ◽  
Organic Chemical ◽  
Simple Liquid ◽  
Cross Sectional ◽  
Conventional Procedure ◽  
Double Heterostructures

The very thin (<100 Å) InGaAsP layers were grown not only by molecular beam epitaxy and metal-organic chemical vapor deposition but recently also by simple liquid phase epitaxy (LPE) technique. Characterization of their thickness, interfase abruptness and lattice defects is important and requires TEM methods to be used.The samples were InGaAsP/InGaP double heterostructures grown on (111)A GaAs substrate. The exact growth conditions are described in Ref.1. The salient points are that the quarternary layers were being grown at 750°C during a fast movement of substrate and a convection caused in the melt by that movement was eliminated. TEM cross-section specimens were prepared by means of conventional procedure. The studies were conducted in EM 420T and JEM 4000EX instruments.The (200) dark-field cross-sectional imaging is the most appropriate TEM technique to distinguish between individual layers in 111-v semiconductor heterostructures.

Observations on the Growth of YBa2Cu3O7 Thin Films at Very High Laser Fluences

1995 ◽  
Vol 388 ◽  
Author(s):  
Rand R. Biggers. ◽  
M. Grant Norton ◽  
I. Maartense ◽  
T.L. Peterson ◽  
E. K. Moser ◽  
...  
Keyword(s):  
Thin Films ◽  
Substrate Surface ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
High Fluences ◽  
Laser Fluences ◽  
High Laser ◽  
High Laser Fluences ◽  
Very High

AbstractThe pulsed-laser deposition (PLD) technique utilizes one of the most energetic beams available to form thin films of the superconducting oxide YBa2Cu3O7 (YBCO). IN this study we examine the growth of YBCO at very high laser fluences (25 to 40 J/cm2); a more typical fluence for PLD would be nearer to 3 J/cm2. the use of high fluences leads to unique film microstructures which, in some cases, appear to be related to the correspondingly higher moveabilities of the adatoms. Films grown on vicinal substrates, using high laser fluences, exhibited well-defined elongated granular morphologies (with excellent transition temperature, Tc, and critical current density, Jc). Films grown on vicinal substrates using off-axis magnetron sputtering, plasma-enhanced metal organic chemical vapor deposition (PE-MOCVD), or PLD at more typical laser fluences showed some similar morphologies, but less well-defined. Under certain growth conditions, using high laser fluences with (001) oriented substrates, the YBCO films can exhibit a mixture of a- and c-axis growth where both crystallographic orientations nucleate on the substrate surface at the same time, and grow in concert. the ratio of a-axis oriented to c-axis oriented grains is strongly affected by the pulse repetition rate of the laser.

Novel Design of MOCVD Reactor with Three Radial Inward Flows for Epitaxial Growth of GaN Thin Films

2011 ◽  
Vol 308-310 ◽  
pp. 1037-1040
Author(s):  
Liao Qiao Yang ◽  
Jian Zheng Hu ◽  
Zun Miao Chen ◽  
Jian Hua Zhang ◽  
Alan G. Li
Keyword(s):  
Gas Flow ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Operating Pressure ◽  
Axisymmetric Mode ◽  
Mocvd Reactor ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition ◽  
D Model

In this paper, a novel super large metal organic chemical vapor deposition (MOCVD) reactor with three inlets located on the periphery of reactor was proposed and numerical evaluation of growth conditions for GaN thin film was characterized. In this design, the converging effects of gas flow in the radial direction could counterbalance the dissipation of metal organics source. CFD was used for the mathematical solution of the fluid flow, temperature and concentration fields. A 2-D model utilizing axisymmetric mode to simulate the gas flow in a MOCVD has been developed. The growth of GaN films using TMGa as a precursor, hydrogen as carrier gas was investigated. The effects of flow rates, mass fraction of various species, operating pressure, and gravity were analyzed and discussed, respectively. The numerical simulation results show all the fields distributions were in an acceptable range.

scholarly journals Investigation of AlGaN/GaN Heterostructures Grown on Sputtered AlN Templates with Different Nucleation Layers

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4050 ◽  
Author(s):  
Chuan-Yang Liu ◽  
Ya-Chao Zhang ◽  
Sheng-Rui Xu ◽  
Li Jiang ◽  
Jin-Cheng Zhang ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Optimal Growth ◽  
Growth Conditions ◽  
Layer Growth ◽  
Organic Chemical ◽  
Propagation Mechanism ◽  
Nucleation Layer ◽  
Low Dislocation Density ◽  
Structural And Electrical Properties ◽  
Metal Organic

In this work, a sputtered AlN template is employed to grow high-quality AlGaN/GaN heterostructures, and the effects of AlN nucleation layer growth conditions on the structural and electrical properties of heterostructures are investigated in detail. The optimal growth condition is obtained with composited AlN nucleation layers grown on a sputtered AlN template, resulting in the smooth surface morphology and superior transport properties of the heterostructures. Moreover, high crystal quality GaN material with low dislocation density has been achieved under the optimal condition. The dislocation propagation mechanism, stress relief effect in the GaN grown on sputtered AlN, and metal organic chemical vapor deposition AlN nucleation layers are revealed based on the test results. The results in this work demonstrate the great potential of AlGaN/GaN heterostructures grown on sputtered AlN and composited AlN nucleation layers for microelectronic applications.

scholarly journals The Optimization of Interfaces in InAsSb/InGaAs Strained-Layer Superlattices grown by Metal-Organic Chemical Vapor Deposition

1994 ◽  
Vol 340 ◽  
Author(s):  
R. M. Biefeld ◽  
K. C. Baucom ◽  
S. R. Kurtz
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Interface Layer ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Strained Layer ◽  
Strained Layer Superlattice ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition

ABSTRACTWe have prepared InAsSb/InGaAs strained-layer superlattice (SLS) semiconductors by metal-organic chemical vapor deposition (MOCVD) using a variety of growth conditions. The presence of an InGaAsSb interface layer is indicated by the x-ray diffraction patterns. The optimized growth conditions involved the use of low pressure, short purge times between the growth of the layers, and no reactant flow during the purges. We used MOCVD to prepare an optically pumped, single heterostructure InAsSb/InGaAs SLS / InPSb laser which emitted at 3.9 μm with a maximum operating temperature of approximately 100 K.

Thin films for superconducting electronics: Precursor performance issues, deposition mechanisms, and superconducting phase formation-processing strategies in the growth of Tl2Ba2CaCu2O8 films by metal-organic chemical vapor deposition

1997 ◽  
Vol 12 (5) ◽  
pp. 1214-1236 ◽  
Author(s):  
Bruce J. Hinds ◽  
Richard J. McNeely ◽  
Daniel B. Studebaker ◽  
Tobin J. Marks ◽  
Timothy P. Hogan ◽  
...  
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Vapor Pressure ◽  
Vapor Deposition ◽  
Film Growth ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Metal Organic ◽  
Organic Chemical Vapor Deposition

Epitaxial Tl2Ba2CaCu2O8 thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followed by a postanneal in the presence of Tl2O vapor. Vapor pressure characteristics of the recently developed liquid metal-organic precursors Ba(hfa)2 • mep (hfa = hexafluoroacetylacetonate, mep = methylethylpentaglyme), Ca(hfa)2 • tet (tet = tetraglyme), and the solid precursor Cu(dpm)2 (dpm = dipivaloylmethanate) are characterized by low pressure thermogravimetric analysis. Under typical film growth conditions, transport is shown to be diffusion limited. The transport rate of Ba(hfa)2 • mep is demonstrated to be stable for over 85 h at typical MOCVD temperatures (120 °C). In contrast, the vapor pressure stability of the commonly used Ba precursor, Ba(dpm)2, deteriorates rapidly at typical growth temperatures, and the decrease in vapor pressure is approximately exponential with a half-life of ∼9.4 h. These precursors are employed in a low pressure (5 Torr) horizontal, hot-wall, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO3 substrates. From the dependence of film deposition rate on substrate temperature and precursor partial pressure, the kinetics of deposition are shown to be mass-transport limited over the temperature range 350–650 °C at a 20 nm/min deposition rate. A ligand exchange process which yields volatile Cu(hfa)2 and Cu(hfa) (dpm) is also observed under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl2Ba2CaCu2O8 at temperatures of 720–890 °C in flowing atmospheres ranging from 0–100% O2. The resulting Tl2Ba2CaCu2O8 films are shown to be epitaxial by x-ray diffraction and transmission electron microscopic (TEM) analysis with the c-axis normal to the substrate surface, with in-plane alignment, and with abrupt film-substrate interfaces. The best films exhibit a Tc = 105 K, transport-measured Jc= 1.2 × 105 A/cm2 at 77 K, and surface resistances as low as 0.4 mΩ (40 K, 10 GHz).

Comparison of the Incorporation of Various Transition Metals into GaN by MOCVD

2006 ◽  
Vol 955 ◽  
Author(s):  
Matthew H Kane ◽  
William Fenwick ◽  
Nola Li ◽  
Shalini Gupta ◽  
Eun Hyun Park ◽  
...  
Keyword(s):  
Transition Metals ◽  
Room Temperature ◽  
Room Temperature Ferromagnetism ◽  
Magnetic Hysteresis ◽  
Chemical Vapor ◽  
Magnetic Ordering ◽  
Growth Conditions ◽  
Shallow Donor ◽  
Organic Chemical ◽  
Secondary Phases

ABSTRACTThe incorporation of transition metals in GaN has long been of interest in spintronics due to theoretical predictions of room temperature ferromagnetism in these materials. However, the mechanism of the observed ferromagnetism of the nitride-based DMS is still controversial, and may originate from a carrier-mediated, defect-related or nanoscale clustering mechanism. In this work, we present a comparative study of the incorporation of various transition metals and their effect on the optical, structural, and magnetic properties of GaN. Metal-organic chemical vapor deposition (MOCVD) has been employed to produce epitaxial films of varying thickness and manganese and iron doping using bis-cyclopentyldienyl(magnanese,iron) as the transition metal sources. High-resolution X-ray diffraction reveals no secondary phases under optimized growth conditions. Magnetic hysteresis is observed at room temperature in both GaMnN and GaFeN, though the strength of the magnetic ordering is roughly an order of magnitude weaker in the Fe-alloyed samples. Increasing Mn concentrations significantly affect long-range lattice ordering, and the observation of local vibrational modes (LVMs) supports the formation of nitrogen vacancies, even under optimized MOCVD growth conditions. Such vacancies form shallow donor complexes and thus contribute to self-compensation. A disorder-induced mode at 300 cm−1 and a LVM due to vacancies at 669 cm-1 were revealed by Raman spectroscopy.

Growth Characteristics of AlGaN/GaN HEMTs on Patterned Si (111) Substrates Using Double AlN Interlayers by MOCVD

2011 ◽  
Vol 396-398 ◽  
pp. 372-375 ◽  
Author(s):  
Yong Wang ◽  
Nai Sen Yu ◽  
Cong Shun Wang ◽  
Kei May Lau
Keyword(s):  
Chemical Vapor ◽  
High Electron Mobility Transistors ◽  
Growth Conditions ◽  
Growth Characteristics ◽  
Organic Chemical ◽  
High Electron ◽  
Si Substrates ◽  
Electron Mobility Transistors ◽  
Thermal Expansion Coefficients ◽  
Gan Hemts

AlGaN/GaN high electron mobility transistors (HEMTs) were grown on un-patterned, patterned without mask, and patterned with mask Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The patterns on the Si substrates were fabricated by SiO2 masks and wet etching. Double AlN interlayers grown at high temperature were employed to relax the tensile stress induced by the large mismatches in the lattice constants and the thermal expansion coefficients. Growth characteristics of AlGaN/GaN HEMTs were discussed and analyzed. Before achieving optimized growth conditions, more cracking lines were observed on patterns along the [1-100] orientation than along the [11-20] orientation, resulted from more stable GaN (1-100) facets than GaN (11-20) facets. It is suggested that long patterns should be made along the [11-20] orientation. Micro-Raman measurements showed that Raman shifts at the concave corners are bigger than those at the convex corners, indicating the presence of the larger stress at the concave corners.

scholarly journals Highly Conductive n-Al0.65Ga0.35N Grown by MOCVD Using Low V/III Ratio

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1006
Author(s):  
Christian J. Zollner ◽  
Yifan Yao ◽  
Michael Wang ◽  
Feng Wu ◽  
Michael Iza ◽  
...  
Keyword(s):  
Electron Concentration ◽  
Ohmic Contacts ◽  
Chemical Vapor ◽  
Growth Conditions ◽  
Organic Chemical ◽  
Operating Voltage ◽  
Metal Organic ◽  
Silicon Doped ◽  
Uv Leds ◽  
Organic Chemical Vapor Deposition

Highly conductive silicon-doped AlGaN and ohmic contacts are needed for deep-UV LEDs and ultrawide bandgap electronics. We demonstrate improved n-Al0.65Ga0.35N films grown by metal–organic chemical vapor deposition (MOCVD) on sapphire substrates using a low V/III ratio (V/III = 10). A reduced V/III ratio improves repeatability and uniformity by allowing a wider range of silicon precursor flow conditions. AlxGa1−xN:Si with x > 0.5 typically has an electron concentration vs. silicon concentration trend that peaks at a particular “knee” value before dropping sharply as [Si] continues to increase (self-compensation). The Al0.65Ga0.35N:Si grown under the lowest V/III conditions in this study does not show the typical knee behavior, and instead, it has a flat electron concentration trend for [Si] > 3 × 1019 cm−3. Resistivities as low as 4 mΩ-cm were achieved, with corresponding electron mobility of 40 cm2/Vs. AFM and TEM confirm that surface morphology and dislocation density are not degraded by these growth conditions. Furthermore, we report vanadium-based ohmic contacts with a resistivity of 7 × 10−5 Ω-cm2 to AlGaN films grown using a low V/III ratio. Lastly, we use these highly conductive silicon-doped layers to demonstrate a 284 nm UV LED with an operating voltage of 7.99 V at 20 A/cm2, with peak EQE and WPE of 3.5% and 2.7%, respectively.

MOCVD Growth of Ga(Al)N/InGaN/Ga(Al)N-Heterostructures: Influence of the Buffer Layer Al-Concentration and Growth Duration on the In-Incorporation in InGaN

2001 ◽  
Vol 680 ◽  
Author(s):  
Marco Schowalter ◽  
Brigitte Neubauer ◽  
Andreas Rosenauer ◽  
Dagmar Gerthsen ◽  
Oliver Schön ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Growth Conditions ◽  
Buffer Layers ◽  
Organic Chemical ◽  
Growth Duration ◽  
Mocvd Growth ◽  
Transmission Electron ◽  
Metal Organic ◽  
Composition Fluctuations ◽  
Organic Chemical Vapor Deposition

ABSTRACTTransmission electron microscopy (TEM) has been applied to analyze the thickness and the In-concentration of InGaN layers in GaN/InGaN/GaN- and AlGaN/InGaN/AlGaN-quantum well (QW) structures. Two series of samples were grown by metal organic chemical vapor deposition varying either only the growth duration for the InGaN QW or by changing the Al- concentration in the buffer layers at unaltered InGaN growth conditions. A rising average In- concentration from 6.5 to 15.4 % and a decreasing growth rate are observed with increasing growth duration. The increase of the Al-concentration in the buffer layers from 0 to 36 % strongly affects the In-incorporation during the InGaN growth, which decreases from 17.5 to 2.5 %. All samples are characterized by an inhomogeneous In-distribution containing In-rich agglomerates with a size of only a few nanometers and less pronounced composition fluctuations on a scale of 100 nm.

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