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Degradation of superconducting Nb/NbN films by atmospheric oxidation

IEEE Transactions on Applied Superconductivity

Henry, Michael D.; Wolfley, Steven L.; Young, Travis R.; Monson, Todd M.; Pearce, Charles J.; Lewis, Rupert; Clark, Blythe C.; Brunke, Lyle B.; Missert, Nancy A.

Niobium and niobium nitride thin films are transitioning from fundamental research toward wafer scale manufacturing with technology drivers that include superconducting circuits and electronics, optical single photon detectors, logic, and memory. Successful microfabrication requires precise control over the properties of sputtered superconducting films, including oxidation. Previous work has demonstrated the mechanism in oxidation of Nb and how film structure could have deleterious effects upon the superconducting properties. This study provides an examination of atmospheric oxidation of NbN films. By examination of the room temperature sheet resistance of NbN bulk oxidation was identified and confirmed by secondary ion mass spectrometry. As a result, Meissner magnetic measurements confirmed the bulk oxidation not observed with simple cryogenic resistivity measurements.

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High pressure FAST of nanocrystalline barium titanate

Ceramics International

Fraga, Martin B.; Delplanque, Jean P.; Yang, Nancy Y.; Lavernia, Enrique J.; Monson, Todd M.

This work studies the microstructural evolution of nanocrystalline (<1 µm) barium titanate (BaTiO3), and presents high pressure in field-assisted sintering (FAST) as a robust methodology to obtain >100 nm BaTiO3 compacts. Using FAST, two commercial ~50 nm powders were consolidated into compacts of varying densities and grain sizes. Microstructural inhomogeneities were investigated for each case, and an interpretation is developed using a modified Monte Carlo Potts (MCP) simulation. Two recurrent microstructural inhomogeneities are highlighted, heterogeneous grain growth and low-density regions, both ubiqutously present in all samples to varying degrees. In the worst cases, HGG presents an area coverage of 52%. Because HGG is sporadic but homogenous throughout a sample, the catalyst (e.g., the local segregation of species) must be, correspondingly, distributed in a homogenous manner. MCP demonstrates that in such a case, a large distance between nucleating abnormal grains is required—otherwise abnormal grains prematurely impinge on each other, and their size is not distinguishable from that of normal grains. Compacts sintered with a pressure of 300 MPa and temperatures of 900 °C, were 99.5% dense and had a grain size of 90±24 nm. These are unprecedented results for commercial BaTiO3 powders or any starting powder of 50 nm particle size—other authors have used 16 nm lab-produced powder to obtain similar results.

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Magnetic Smart Tags (MaST) for Arms Control and Treaty Verification

Langlois, Eric L.; Pillars, Jamin R.; Monson, Todd M.; Arrington, Christian L.; Finnegan, Patrick S.; St John, Christopher S.; Smartt, Heidi A.

The ability to track nuclear material is a challenge for resiliency of complex systems, e.g., harsh environments. RF tags, frequently used in national security applications, cannot be used for technological, operational, or safety reasons. Magnetic Smart Tags (MaST) is a novel tag technology based on magnetoelastic sensing that circumvents these issues. This technology is enabled by a new, cost-effective, batch manufacturing electrochemical deposition (ECD) process. This new advancement in fabrication enables multi-frequency tags capable of providing millions of possible codes for tag identification unlike existing theft deterrent tags that can convey only a single bit of information. Magnetostrictive 70% Co: 30% Fe was developed as the base alloy comprising the magnetoelastic resonator transduction element. Saturation magnetostriction, S , has been externally measured by the Naval Research Laboratory to be as high as 78 ppm. Description of a novel MEMS variable capacitive test structure is described for future measurements of this parameter.

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Results 51–75 of 167
Results 51–75 of 167