Matching Items (31)

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Fabrication of highly spin-polarized Co2FeAl0.5Si0.5 thin-films

Description

Ferromagnetic Heusler Co[subscript 2]FeAl[subscript 0.5]Si[subscript 0.5] epitaxial thin-films have been fabricated in the L2[subscript 1] structure with saturation magnetizations over 1200 emu/cm[superscript 3]. Andreev reflection measurements show that the spin

Ferromagnetic Heusler Co[subscript 2]FeAl[subscript 0.5]Si[subscript 0.5] epitaxial thin-films have been fabricated in the L2[subscript 1] structure with saturation magnetizations over 1200 emu/cm[superscript 3]. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100) substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.

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Created

Date Created
  • 2014-04-15

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Developing a Framework for the in-situ Analysis of Artists’ Prints and Paintings via Hyperspectral Imaging

Description

Hyperspectral imaging is a novel technology which allows for the collection of reflectance spectra of a sample in-situ and at a distance. A rapidly developing technology, hyperspectral imaging has been

Hyperspectral imaging is a novel technology which allows for the collection of reflectance spectra of a sample in-situ and at a distance. A rapidly developing technology, hyperspectral imaging has been of particular interest in the field of art characterization, authentication, and conservation as it avoids the pitfalls of traditional characterization techniques and allows for the rapid and wide collection of data never before possible. It is hypothesized that by combining the power of hyperspectral imaging with machine learning, a new framework for the in-situ and automated characterization and authentication of artworks can be developed. This project, using the CMYK set of inks, began the preliminary development of such a framework. It was found that hyperspectral imaging and machine learning as a combination show significant potential as an avenue for art authentication, though further progress and research is needed to match the reliability of status quo techniques.

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Created

Date Created
  • 2020-05

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Market Research for Titanium Rifle Barrel

Description

There is a growing market for lightweight firearm barrels. Currently this market is dominated by Aluminum and Carbon fiber barrels, however, Gunwright, LLC proposes an innovative new way to manufacture

There is a growing market for lightweight firearm barrels. Currently this market is dominated by Aluminum and Carbon fiber barrels, however, Gunwright, LLC proposes an innovative new way to manufacture Titanium firearm barrels. This report offers insight into potential customers and existing competitors.

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Agent

Created

Date Created
  • 2014-05

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Lateral Programmable Metallization Cells: Materials, Devices and Mechanisms

Description

Lateral programmable metallization cells (PMC) utilize the properties of electrodeposits grown over a solid electrolyte channel. Such devices have an active anode and an inert cathode separated by a long

Lateral programmable metallization cells (PMC) utilize the properties of electrodeposits grown over a solid electrolyte channel. Such devices have an active anode and an inert cathode separated by a long electrodeposit channel in a coplanar arrangement. The ability to transport large amount of metallic mass across the channel makes these devices attractive for various More-Than-Moore applications. Existing literature lacks a comprehensive study of electrodeposit growth kinetics in lateral PMCs. Moreover, the morphology of electrodeposit growth in larger, planar devices is also not understood. Despite the variety of applications, lateral PMCs are not embraced by the semiconductor industry due to incompatible materials and high operating voltages needed for such devices. In this work, a numerical model based on the basic processes in PMCs – cation drift and redox reactions – is proposed, and the effect of various materials parameters on the electrodeposit growth kinetics is reported. The morphology of the electrodeposit growth and kinetics of the electrodeposition process are also studied in devices based on Ag-Ge30Se70 materials system. It was observed that the electrodeposition process mainly consists of two regimes of growth – cation drift limited regime and mixed regime. The electrodeposition starts in cation drift limited regime at low electric fields and transitions into mixed regime as the field increases. The onset of mixed regime can be controlled by applied voltage which also affects the morphology of electrodeposit growth. The numerical model was then used to successfully predict the device kinetics and onset of mixed regime. The problem of materials incompatibility with semiconductor manufacturing was solved by proposing a novel device structure. A bilayer structure using semiconductor foundry friendly materials was suggested as a candidate for solid electrolyte. The bilayer structure consists of a low resistivity oxide shunt layer on top of a high resistivity ion carrying oxide layer. Devices using Cu2O as the low resistivity shunt on top of Cu doped WO3 oxide were fabricated. The bilayer devices provided orders of magnitude improvement in device performance in the context of operating voltage and switching time. Electrical and materials characterization revealed the structure of bilayers and the mechanism of electrodeposition in these devices.

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Agent

Created

Date Created
  • 2020

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Growth and characterization of pyrite thin films for photovoltaic applications

Description

A series of pyrite thin films were synthesized using a novel sequential evaporation

technique to study the effects of substrate temperature on deposition rate and micro-structure of

the deposited material. Pyrite was

A series of pyrite thin films were synthesized using a novel sequential evaporation

technique to study the effects of substrate temperature on deposition rate and micro-structure of

the deposited material. Pyrite was deposited in a monolayer-by-monolayer fashion using

sequential evaporation of Fe under high vacuum, followed by sulfidation at high S pressures

(typically > 1 mTorr to 1 Torr). Thin films were synthesized using two different growth processes; a

one-step process in which a constant growth temperature is maintained throughout growth, and a

three-step process in which an initial low temperature seed layer is deposited, followed by a high

temperature layer, and then finished with a low temperature capping layer. Analysis methods to

analyze the properties of the films included Glancing Angle X-Ray Diffraction (GAXRD),

Rutherford Back-scattering Spectroscopy (RBS), Transmission Electron Microscopy (TEM),

Secondary Ion Mass Spectroscopy (SIMS), 2-point IV measurements, and Hall effect

measurements. Our results show that crystallinity of the pyrite thin film improves and grain size

increases with increasing substrate temperature. The sticking coefficient of Fe was found to

increase with increasing growth temperature, indicating that the Fe incorporation into the growing

film is a thermally activated process.

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Agent

Created

Date Created
  • 2014

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Growth and characterization of novel thin films for microelectronic applications

Description

I studied the properties of novel Co2FeAl0.5Si0.5 (CFAS), ZnGeAs2, and FeS2 (pyrite) thin films for microelectronic applications ranging from spintronic to photovoltaic. CFAS is a half metal with theoretical spin

I studied the properties of novel Co2FeAl0.5Si0.5 (CFAS), ZnGeAs2, and FeS2 (pyrite) thin films for microelectronic applications ranging from spintronic to photovoltaic. CFAS is a half metal with theoretical spin polarization of 100%. I investigated its potential as a spin injector, for spintronic applications, by studying the critical steps involved in the injection of spin polarized electron populations from tunnel junctions containing CFAS electrodes. Epitaxial CFAS thin films with L21 structure and saturation magnetizations of over 1200 emu/cm3 were produced by optimization of the sputtering growth conditions. Point contact Andreev reflection measurements show that the spin polarization at the CFAS electrode surface exceeds 70%. Analyses of the electrical properties of tunnel junctions with a superconducting Pb counter-electrode indicate that transport through native Al oxide barriers is mostly from direct tunneling, while that through the native CFAS oxide barriers is not. ZnGeAs2 is a semiconductor comprised of only inexpensive and earth-abundant elements. The electronic structure and defect properties are similar in many ways to GaAs. Thus, in theory, efficient solar cells could be made with ZnGeAs2 if similar quality material to that of GaAs could be produced. To understand the thermochemistry and determine the rate limiting steps of ZnGeAs2 thin-film synthesis, the (a) thermal decomposition rate and (b) elemental composition and deposition rate of films were measured. It is concluded that the ZnGeAs2 thin film synthesis is a metastable process with an activation energy of 1.08±0.05 eV for the kinetically-limited decomposition rate and an evaporation coefficient of ~10-3. The thermochemical analysis presented here can be used to predict optimal conditions of ZnGeAs2 physical vapor deposition and thermal processing. Pyrite (FeS2) is another semiconductor that has tremendous potential for use in photovoltaic applications if high quality materials could be made. Here, I present the layer-by-layer growth of single-phase pyrite thin-films on heated substrates using sequential evaporation of Fe under high-vacuum followed by sulfidation at S pressures between 1 mTorr and 1 Torr. High-resolution transmission electron microscopy reveals high-quality, defect-free pyrite grains were produces by this method. It is demonstrated that epitaxial pyrite layer was produced on natural pyrite substrates with this method.

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Agent

Created

Date Created
  • 2013

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Study of doped magnetic systems

Description

Doping and alloying agents are commonly used to engineer the properties of magnetic materials. This study investigates the effects of doping manganese in thin films of Ni80Fe20 (permalloy) and Ni65Fe15Co20

Doping and alloying agents are commonly used to engineer the properties of magnetic materials. This study investigates the effects of doping manganese in thin films of Ni80Fe20 (permalloy) and Ni65Fe15Co20 magnetic systems for low power memory technologies, including those that operate at low temperature.

Elemental manganese is anti-ferromagnetic with a Neel temperature of 100 K. When used as a dopant in a magnetic material, it is found to often align its moment in an antiferromagnetic direction. Thus, the addition of manganese might be expected to reduce the overall saturation magnetization (MS) of the magnetic system. In this study, we show that the use of manganese dopants in Ni80Fe20 (permalloy) and Ni65Fe15Co20 thin films can reduce their saturation magnetization and still retain excellent switching properties.

Magnetic properties and transport properties were determined using Vibrating Sample Magnetometer. A 19% decrease in the MS of (Ni80Fe20)1-xMnx thin films and a 36% decrease for (Ni65Fe15Co20)1-xMnx thin films for dopant levels of x = 30%. The impact of depositing a ruthenium (Ru) under-layer for (Ni65Fe15Co20)1-xMnx system was also studied.

The structural (lattice parameters and phases), surface (roughness and topography) and electrical properties (resistivity and mean free path) of the Mn-doped Ni65Fe15Co20 films were determined with X-Ray Diffraction, Atomic Force Microscopy and Four-Point probe technique respectively.

The properties were analyzed and Ni65Fe15Co20 system with Ru- under-layer with 20 at. % Mn content was found to exhibit the following low-field switching properties at 10 K; MS~700 emu.cm-3, easy axis coercivity ~10 Oe and hard axis coercivity ~5 Oe, easy axis squareness ~0.9 and anisotropy field ~12 Oe, that are deemed useful for low-power memory applications that could be used at cryogenic temperatures.

To determine the transport properties thought these magnetic layers for use in superconductor/ferromagnetic memory structures, a study of the oxidation conditions of Al films was performed in order to produce a reliable aluminum oxide tunnel barrier on top of these films. The production of N-I-F-S (Normal metal-Insulator-Ferromagnet-Superconductor) tunnel junctions will allow for the investigation of the tunneling density of states as a function of ferromagnetic layer thickness, allowing for the determination of important transport parameters relevant to magnetic barrier Josephson junction devices.

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Agent

Created

Date Created
  • 2018

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Synthesis, Characterization, and Optimization of Superconductor-Dielectric Interfaces

Description

The chemical, structural, and electrical properties of niobium-silicon, niobium-germanium, and YBCO-dielectric interfaces are characterized. Reduction in the concentration of interfacial defects in these structures can improve the performance of (i)

The chemical, structural, and electrical properties of niobium-silicon, niobium-germanium, and YBCO-dielectric interfaces are characterized. Reduction in the concentration of interfacial defects in these structures can improve the performance of (i) many devices including low-loss coplanar, microstrip, and stripline microwave resonators used in next-generation cryogenic communication, sensor, and quantum information technologies and (ii) layers used in device isolation, inter-wiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication.

Methods were developed to synthesize amorphous-Ge (a-Ge) and homoepitaxial-Si dielectric thin-films with loss tangents of 1–2×10 -6 and 0.6–2×10 -5 at near single-photon powers and sub-Kelvin temperatures (≈40 mK), making them potentially a better choice over undoped silicon and sapphire substrates used in quantum devices. The Nb/Ge interface has 20 nm of chemical intermixing, which is reduced by a factor of four using 10 nm Ta diffusion layers. Niobium coplanar resonators using this structure exhibit reduced microwave losses.

The nature and concentration of defects near Nb-Si interfaces prepared with commonly-used Si surface treatments were characterized. All samples have H, C, O, F, and Cl in the Si within 50 nm of the interface, and electrically active defects with activation energies of 0.147, 0.194, 0.247, 0.339, and 0.556 eV above the valence band maximum (E vbm ), with concentrations dominated by a hole trap at E vbm +0.556 eV (presumably Nb Si ). The optimum surface treatment is an HF etch followed by an in-situ 100 eV Ar ion mill. RCA etches, and higher energy ion milling processes increase the concentration of electrically active defects.

A thin SrTiO 3 buffer layer used in YBa 2 Cu 3 O 7-δ superconductor/high-performance Ba(Zn 1/3 Ta 2/3 )O 3 and Ba(Cd 1/3 Ta 2/3 )O 3 microwave dielectric trilayers improves the structural quality of the layers and results in 90 K superconductor critical temperatures. This advance enables the production of more compact high-temperature superconductor capacitors, inductors, and microwave microstrip and stripline devices.

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Created

Date Created
  • 2020

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Effect of helium ion irradiation on the tunneling behavior in niobium/aluminum/aluminum oxide/niobium Josephson junctions

Description

The study of high energy particle irradiation effect on Josephson junction tri-layers is relevant to applications in space and radioactive environments. It also allows us to investigate the influence of

The study of high energy particle irradiation effect on Josephson junction tri-layers is relevant to applications in space and radioactive environments. It also allows us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this work, we studied the influence of 2MeV Helium ion irradiation with doses up to 5.2×1016 ions/cm2 on the tunneling behavior of Nb/Al/AlOx/Nb Josephson junctions. Structural and analytical TEM characterization, combined with SRIM modeling, indicates that over 4nm of intermixing occurred at the interfaces. EDX analysis after irradiation, suggests that the Al and O compositions from the barrier are collectively distributed together over a few nanometers. Surprisingly, the IV characteristics were largely unchanged. The normal resistance, Rn, increased slightly (<20%) after the initial dose of 3.5×1015 ions/cm2 and remained constant after that. This suggests that tunnel barrier electrical properties were not affected much, despite the significant changes in the chemical distribution of the barrier's Al and O shown in SRIM modeling and TEM pictures. The onset of quasi-particle current, sum of energy gaps (2Δ), dropped systematically from 2.8meV to 2.6meV with increasing dosage. Similarly, the temperature onset of the Josephson current dropped from 9.2K to 9.0K. This suggests that the order parameter at the barrier interface has decreased as a result of a reduced mean free path in the Al proximity layer and a reduction in the transition temperature of the Nb electrode near the barrier. The dependence of Josephson current on the magnetic field and temperature does not change significantly with irradiation, suggesting that intermixing into the Nb electrode is significantly less than the penetration depth.

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Agent

Created

Date Created
  • 2012

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Synthesis, structures and properties of thermoelectric materials in the Zn-Sb-In system

Description

The challenging search for clean, reliable and environmentally friendly energy sources has fueled increased research in thermoelectric materials, which are capable of recovering waste heat. Among the state-of-the-art thermoelectric materials

The challenging search for clean, reliable and environmentally friendly energy sources has fueled increased research in thermoelectric materials, which are capable of recovering waste heat. Among the state-of-the-art thermoelectric materials β-Zn4Sb3 is outstanding because of its ultra-low glass-like thermal conductivity. Attempts to explore ternary phases in the Zn-Sb-In system resulted in the discovery of the new intermetallic compounds, stable Zn5Sb4In2-δ (δ=0.15) and metastable Zn9Sb6In2. Millimeter-sized crystals were grown from molten metal fluxes, where indium metal was employed as a reactive flux medium.Zn5Sb4In2-δ and Zn9Sb6In2 crystallize in new structure types featuring complex framework and the presence of structural disorder (defects and split atomic positions). The structure and phase relations between ternary Zn5Sb4In2-δ, Zn9Sb6In2 and binary Zn4Sb3 are discussed. To establish and understand structure-property relationships, thermoelectric properties measurements were carried out. The measurements suggested that Zn5Sb4In2-δ and Zn9Sb6In2 are narrow band gap semiconductors, similar to β-Zn4Sb3. Also, the peculiar low thermal conductivity of Zn4Sb3 (1 W/mK) is preserved. In the investigated temperature range 10 to 350 K Zn5Sb4In2-δ displays higher thermoelectric figure of merits than Zn4Sb3, indicating a potential significance in thermoelectric applications. Finally, the glass-like thermal conductivities of binary and ternary antimonides with complex structures are compared and the mechanism behind their low thermal conductivities is briefly discussed.

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Agent

Created

Date Created
  • 2011