Examination of peak stress dependence for tantalum spall when shocked near the spall strength
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McCoy, Chad August [Sandia National Laboratories (↗
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Oxide morphology and spalling model for NiAl
A scanning electron microscope equipped with an energy dispersive spectrographic unit was used to study in detail the Al2O3 oxide morphology and oxide-metal interface of a nickel-rich NiAl alloy (Ni-42 at% Al) with a view toward providing information relevant to spalling theories in the MCrAlY system. In addition, the kinetics of spalling was studied for critical evaluation of one of the step-process spall models and for collection of pertinent experimental data. Cyclic oxidation tests were run in 1-atm air at about 1100 C, and isothermal specimens were examined from 2 min to 200 hr of exposure. It is shown that oxide spalling occurs primarily at the oxide-metal interface in an intergranular mode, that crystallographic Kirkendall voids arise as a result of oxidation, and that the fractional area of spalled oxide varies widely in cyclic tests but increases with the square of oxide thickness for isothermal tests. A spall model is developed in the form of a summation series.
Smialek, J. L.↗
Controlled Spalling of 4H Silicon Carbide with Investigated Spin Coherence for Quantum Engineering Integration
We detail scientific and engineering advances which enable the controlled spalling and layer transfer of single crystal 4H silicon carbide (4H-SiC) from bulk substrates. 4HSiC’s properties, including high thermal conductivity and a wide bandgap, make it an ideal semiconductor for power electronics. Moreover, 4H-SiC is an excellent host of solid-state atomic defect qubits for quantum computing and quantum networking. Because 4H-SiC substrates are expensive (due to long growth times and limited yield), techniques for removal and transfer of bulk-quality films are desirable for substrate reuse and integration of the separated films. In this work, we utilize updated approaches for stressor layer thickness control and spalling crack initiation to demonstrate controlled spalling of 4H-SiC, the highest fracture toughness crystal spalled to date. We achieve coherent spin control of neutral divacancy (VV 0 ) qubit ensembles and measure a quasi-bulk spin T 2 of 79.7 μs in the spalled films.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Spall velocity measurements from laboratory impact craters
Spall velocities were measured for a series of impacts into San Marcos gabbro. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles varied in material and size with a maximum mass of 4g for a lead bullet to a minimum of 0.04 g for an aluminum sphere. The spall velocities were calculated both from measurements taken from films of the events and from estimates based on range measurements of the spall fragments. The maximum spall velocity observed was 27 m/sec, or 0.5 percent of the impact velocity. The measured spall velocities were within the range predicted by the Melosh (1984) spallation model for the given experimental parameters. The compatability between the Melosh model for large planetary impacts and the results of these small scale experiments is considered in detail. The targets were also bisected to observe the internal fractures. A series of fractures were observed whose location coincided with the boundary of the theoretical near surface zone predicted by Melosh. Above this boundary the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
Polanskey, Carol A.↗
A Deterministic Interfacial Cyclic Oxidation Spalling Model: Model Development and Parametric Response - Part 1
An equation has been developed to model the iterative scale growth and spalling process that occurs during cyclic oxidation of high temperature materials. Parabolic scale growth and spalling of a constant surface area fraction have been assumed. Interfacial spallation of the only the thickest segments was also postulated. This simplicity allowed for representation by a simple deterministic summation series. Inputs are the parabolic growth rate constant, the spall area fraction, oxide stoichiometry, and cycle duration. Outputs include the net weight change behavior, as well as the total amount of oxygen and metal consumed, the total amount of oxide spalled, and the mass fraction of oxide spalled. The outputs all follow typical well-behaved trends with the inputs and are in good agreement with previous interfacial models.
Smialek, James L.↗
Planarizing Spalled GaAs(100) Surfaces by MOVPE Growth
III-V photovoltaic devices have demonstrated exceptional performance across various applications, with controlled crystal fracturing, known as controlled spalling, emerging as a promising method to reduce costs by enabling substrate reuse. Spalling GaAs(100) substrates, a commonly used substrate in III-V photovoltaics, results in faceted ridges that must be planarized to grow high-quality photovoltaic devices. Here, in this study, we demonstrate that a GaAs(100) wafer offcut toward [$0\bar{11}$] and spalled toward [$011$] can be efficiently planarized by growing C:GaAs by metal-organic vapor phase epitaxy (MOVPE) on the surface, with up to 95% of the nominally deposited material used to fill the valleys between ridges. We find that reducing the offcut to 2° enhances the planarizing capability of C:GaAs. A surface morphology model indicates that the density of surface dangling bonds significantly influences the growth evolution of undoped GaAs surfaces. In contrast, the model suggests that the effectiveness of C:GaAs as a smoothing layer stems from modifying the atomic surface structure and, consequently, the associated sticking coefficients of the facets, which can alter the evolution of surface morphology. Our findings provide guidelines for the epitaxial planarization of semiconductor surfaces and improve the understanding of MOVPE growth on nonplanar surfaces.
14 SOLAR ENERGY↗
Cryogenic hybrid magnonic circuits based on spalled YIG thin films
Yttrium iron garnet (YIG) magnonics has garnered significant research interest because of the unique properties of magnons (quasiparticles of collective spin excitation) for signal processing. In particular, hybrid systems based on YIG magnonics show great promise for quantum information science due to their broad frequency tunability and strong compatibility with other platforms. However, their broad applications have been severely constrained by substantial microwave loss in the gadolinium gallium garnet (GGG) substrate at cryogenic temperatures. In this study, we demonstrate that YIG thin films can be spalled from YIG/GGG samples. Our approach is validated by measuring hybrid devices comprising superconducting resonators and spalled YIG films, which exhibit anti-crossing features that indicate strong coupling between magnons and microwave photons. Such new capability of separating YIG thin films from GGG substrates via spalling and the integrated superconductor-YIG devices represent a significant advancement for integrated magnonic devices, paving the way for advanced magnon-based coherent information processing.
36 MATERIALS SCIENCE↗
In Situ MOVPE Smoothing of Acoustically Spalled GaAs for Substrate Reuse
High material costs, especially for substrates, have limited the widespread adoption of III-V photovoltaics. A potential to reduce this cost is to reuse the III-V substrate via acoustic spalling, however this technique can leave a rough surface, hindering subsequent device performance. This research investigates the potential of using metalorganic vapor-phase epitaxy growth as a buffer layer to smooth the surface of acoustically spalled germanium and gallium arsenide (GaAs) substrates for improved III-V photovoltaic cell yield and performance, while retaining the maximum number of reuses of a substrate. Three potential smoothing layers were explored: lightly doped C:GaAs, highly doped Se:GaInP, and lightly doped Se:GaInP. C:GaAs showed the most promise as a smoothing layer, while Se:GaInP tended to conform to the underlying morphology, potentially increasing roughness in some areas. Utilizing 5 ..mu..m of C:GaAs as a planarizing buffer increased the average efficiency (without an antireflection coating) from an as-spalled baseline from 2.1% to 4.9% and performing a 5-min 30 degrees C 8:1:1 H2SO4:H2O2:H2O etch prior to a 5 ..mu..m of C:GaAs as a planarizing buffer further increased efficiency to 11.1%.
14 SOLAR ENERGY↗
Planarizing Spalled GaAs(100) Surfaces by MOVPE Growth
III-V photovoltaic devices have demonstrated remarkable performance in many applications, and spalling is a promising technique for reducing device costs by recovering the substrate for reuse. In this study, we investigate the in situ planarization of A-directionally spalled GaAs(100) substrates using metal-organic vapor phase epitaxy (MOVPE) grown C:GaAs with CCl4 as the carbon source. We have characterized the (100)-oriented growth for various CCl4 flow rates and observed that the CCl4 or its by-products promote material diffusion from the facet tops to the underlying valleys. For facets with a height of 5 ..mu..m on a substrate with an A-spall and 6 degreesB -offcut, it took 7 ..mu..m of C:GaAs to planarize the substrate. For a similar sample, with a 6 degreesA -offcut, it required 2 ..mu..m of growth to fill the valleys but there were remnant facets.
III-V↗
A Path to III-V Photovoltaic Cost Reduction Combining GaAs (211) Spalling with Halide Vapor Phase Epitaxy
This presentation is an overview of the following, Spalling on 211 oriented wafers produces flat surface without faceting: 1) Demonstrated spall on entire 2" wafer; 2) GaAs and GaInP grown on 211 wafers by HVPE; and 3) Promising cell with VOC=1.02 V and IQE-1. Next steps: 1) Grow cell on spalled wafer and 2) Growth studies to improve material and cell on 211 substrates.
14 SOLAR ENERGY↗
Analysis of rolling contact spall life in 440 C steel bearing rims
The results of a two year study of the mechanisms of spall failure in the HPOTP bearings are described. The objective was to build a foundation for detailed analyses of the contact life in terms of: cyclic plasticity, contact mechanics, spall nucleation, and spall growth. Since the laboratory rolling contact testing is carried out in the 3 ball/rod contact fatigue testing machine, the analysis of the contacts and contact lives produced in this machine received attention. The results from the experimentally observed growth lives are compared with calculated predictions derived from the fracture mechanics calculations.
Bastias, P. C.↗
A Deterministic Interfacial Cyclic Oxidation Spalling Model: Algebraic Approximation, Descriptive Parameters, and Normalized Universal Curve - Part 2
A cyclic oxidation interfacial spalling model has been developed in Part 1. The governing equations have been simplified here by substituting a new algebraic expression for the series (Good-Smialek approximation). This produced a direct relationship between cyclic oxidation weight change and model input parameters. It also allowed for the mathematical derivation of various descriptive parameters as a function of the inputs. It is shown that the maximum in weight change varies directly with the parabolic rate constant and cycle duration and inversely with the spall fraction, all to the 1/2 power. The number of cycles to reach maximum and zero weight change vary inversely with the spall fraction, and the ratio of these cycles is exactly 1:3 for most oxides. By suitably normalizing the weight change and cycle number, it is shown that all cyclic oxidation weight change model curves can be represented by one universal expression for a given oxide scale.
Smialek, James L.↗
Demonstration of GaAs-Based Photovoltaics on Acoustically Spalled Surfaces Grown by MOCVD
This study demonstrates the potential of sonic lift-off (SLO) technology for repeatable substrate reuse in gallium arsenide (GaAs)–based photovoltaics (PVs), offering a pathway toward cost effective production for terrestrial PV applications. Single-junction GaAs solar cells fabricated on acoustically spalled substrates achieved performance metrics comparable with those grown on standard commercial substrates, exhibiting short-circuit current densities (J sc ) of approximately 26.2–26.4 mA/cm 2 , open-circuit voltages (V oc ) around 1001 mV, fill factors (FFs) of 84%, and AM1.5G efficiencies near 22%. These results confirm that one reuse cycle can be realized without a performance penalty, offering a direct pathway to reducing substrate cost in fabrication. Furthermore, subsequent reuse of the substrates highlighted critical challenges, as devices fabricated from reused substrates showed significant degradation in performance (J sc of 15.5 mA/cm 2 , V oc of 748 mV, FF of 72%, and efficiency of 8%), primarily due to degradation of the epitaxial structure resulting from repeated spalling cycles.
Acoustic Spalling↗
Micrometeorite craters on lunar glass particles - The relationship between radial fracture zones and spall zones.
Discussion of the microimpact-crater morphology observed by scanning electron microscopy on a glass bead (nearly 580 microns in maximum diameter) recovered from zone A of the Luna 16 sample. The microcrater has a diameter of approximately 200 microns and a centrally located melted region or pit that is slightly elevated above the surrounding area. Around the pit is a radial fracture zone half of which has spalled off. The spall zone is more than half again as large as the radial fracture zone.
Glass, B. P.↗
Solutions for discharge chamber sputtering and anode deposit spalling in small mercury ion thrusters
Proposed solutions to the problems of sputter erosion and sputtered material spalling in the discharge chamber of small mercury ion thrusters are presented. The accelerated life test evaluated three such proposed solutions: (1) the use of tantalum as a single low sputter yield material for the exposed surfaces of the discharge chamber components subject to sputtering, (2) the use of a severely roughened anode surface to improve the adhesion of the sputter-deposited coating, and (3) the use of a wire cloth anode surface in order to limit the size of any coating flakes which might spall from it. Because of the promising results obtained in the accelerated life test with anode surfaces roughened by grit-blasting, experiments were carried out to optimize the grit-blasting procedure. The experimental results and an optimal grit-blasting procedure are presented.
Power, J. L.↗
Accelerated life test of sputtering and anode deposit spalling in a small mercury ion thruster
Tantalum and molybdenum sputtered from discharge chamber components during operation of a 5 centimeter diameter mercury ion thruster adhered much more strongly to coarsely grit blasted anode surfaces than to standard surfaces. Spalling of the sputtered coating did occur from a coarse screen anode surface but only in flakes less than a mesh unit long. The results were obtained in a 200 hour accelerated life test conducted at an elevated discharge potential of 64.6 volts. The test approximately reproduced the major sputter erosion and deposition effects that occur under normal operation but at approximately 75 times the normal rate. No discharge chamber component suffered sufficient erosion in the test to threaten its structural integrity or further serviceability. The test indicated that the use of tantalum-surfaced discharge chamber components in conjunction with a fine wire screen anode surface should cure the problems of sputter erosion and sputtered deposits spalling in long term operation of small mercury ion thrusters.
Power, J. L.↗
Impact cratering and spall failure at gabbro
Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the - 9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m)of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejectra resides in a few large fragments.
Lange, M. A.↗
Impact cratering and spall failure of gabbro
Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2 g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the -9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80 percent) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m) of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments.
Lange, M. A.↗