Binary And Ternary Transition Metal Pnictide Nanoparticles And Their Three-Dimensional Assemblies: Towards Promising Magnetic Refrigeration Materials

BINARY AND TERNARY TRANSITION METAL PNICTIDES NANOPARTICLES AND THEIR THREE DIMENSIONAL ASSEMBLIES: TOWARDS PROMISING MAGNETIC REFRIGERATION MATERIALS by MALSHA ANURADHI HETTIARACHCHI May 2019 Advisor: Dr. Stephanie L. Brock Major : Chemistry Degree : Doctor of Philosophy Bulk MnAs has been recognized as a potential MR material with large MCE. However, the magnetic transition of bulk MnAs suffers from a large thermal hysteresis of 6 K precluding efficient MR cycling, and the magnetic entropy change associated with the phase transition is limited to a narrow temperature range, making the temperature control window very small. Solid solutions of MnAs, synthesized by both cation and anion doping, are reported to reduce the hysteresis, enabling tuning of the optimal temperature range. Reducing the materials’ dimensions to the nano scale has the potential to enable formation of nano 3-dimensional graded macrostructures thereby greatly expanding the temperature window. This dissertation research was focused on: (1) synthesis, characterization, and magnetic property evaluation of MnAsxSb1-x (x=0.1-0.9) nanoparticles, (2) three-dimensional assembly of discrete nanoparticles of well-established system Fe1.2Ni0.8P. As a sub-goal of objective (1), MnSb nanoparticle synthesis was carried out employing two strategies in solution-phase. The slow heating approach yielded phase-pure, spherical shape MnSb nanoparticles ca. 13 nm in diameter with an amorphous manganese oxide shell around the MnSb core, which suppresses the saturation magnetization up to 0.04 BM/mol Mn. The NaBH4 addition method produced elongated head-tail MnSb nanoparticles with increased saturation magnetization that was twenty times higher than the former case. MnAsxSb1-x nanoparticles of over all x were synthesized by slight modification of the protocol developed for MnSb nanoparticle synthesis. The target compositions of x=0.1-0.9 appeared phase-pure in PXRD, but almost all the compositions were As deficient as revealed by elemental compositional analysis by XRF. In order to achieve objective (2), at the outset, compositions of Fe1.2Ni0.8P discrete nanoparticles were selected. These nanoparticles were assembled into three-dimensional networks by oxidation-induced gelation, after functionalized by 11-MUA or 1-DDT. Discrete nanoparticle compositions of Fe1.2Ni0.8P were capable of forming solid, black monoliths after supercritical drying. All the assembled compositions were capable of upholding the initial crystallinity and morphology even after the gelation, and most importantly, most of these composites exhibit no significant alternation in the crystallinity and the morphology after the post-heat treatment. Magnetic properties of these composites were evaluated as a function of different heating conditions

Zeolites and ordered porous solids: fundamentals and applications

Pérez Pariente, J.; Martínez Sánchez, MC. (2011). Zeolites and ordered porous solids: fundamentals and applications. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/11205Archivo delegad

CO Gas Sensor for Consumer Electronic Applications

Gas sensors in smartphones and other mobile devices have the potential to contribute to improving the quality of life and security. This calls for a high degree of miniaturization and a reduction in power consumption. In this work, various aspects of miniaturized, resistive CO gas sensors based on metal oxides (MOX) were investigated. Deposition took place through pulsed laser deposition (PLD) on structures of platinum that were patterned using a lift-off process. The influence of the resist geometry on the metal structures was demonstrated by experiment and simulation. With regard to the MOX thin films, the focus was set on SnO2. Both its electrical and gas-sensing properties were highly influenced by the deposition parameters: Higher deposition pressures (>10 Pa) are leading to higher base resistances and to a higher sensor signal for CO in dry air. These properties correlated with the nanoporous morphology of the material. For measurements in humid air, the response to CO was reduced compared to dry air. Different noble metal additives, in particular Pd, were introduced by sputtering, thereby significantly improving properties. CO-sensitivity in humid air was also demonstrated for highly porous WO3. In a parameter study, the impact of the heated membrane geometry on the power consumption of the sensor was further investigated in simulation and experiment.Gassensoren in Smartphones und anderen mobilen Geräten haben das Potential, zukünftig Lebensqualität und Sicherheit zu verbessern. Dafür ist ein hoher Grad an Miniaturisierung und die Reduzierung der Leistungsaufnahme notwendig. In dieser Arbeit wurden verschiedene Aspekte miniaturisierter, resistiver COSensoren auf Basis von Metalloxiden (MOX) untersucht. Herstellung erfolgte mit gepulster Laserabscheidung (PLD) auf Platinstrukturen, die mit einem Lift-Off-Prozess strukturiert wurden. Per Simulation und Experiment wurden Einflüsse der Lackgeometrie auf die Metallstruktur aufgezeigt. Bei den untersuchten MOX-Dünnschichten lag der Fokus auf SnO2. Dessen elektrische und gassensitive Eigenschaften hängen stark von den Abscheidungsbedingungen ab:Höhere Abscheidungsdrücke (>10 Pa) führen zu höheren Grundwiderständen sowie zu einem höheren Signal für CO in trockener Luft. Diese Eigenschaften korrelieren mit der nanoporösen Morphologie des Materials. Bei Messungen in feuchter Luft reduzierte sich das CO-Signal im Vergleich zu trockener Luft. Durch den per Sputtern aufgebrachten Zusatz von Edelmetallen, insbesondere von Palladium (Pd), konnten die Eigenschaften deutlich verbessert werden. COSensitivität in feuchter Luft konnte für hochporöses WO3 ebenfalls gezeigt werden. In einer Parameterstudie wurde in Experiment und Simulation zudem der Einfluss der geheizten Membrangeometrie auf die Leistungsaufnahme des Sensors untersucht

Near-Field Radiative Thermal Transport and Energy Conversion

Thermal radiation occurs when electromagnetic energy is emitted from one body and absorbed by another body. The net energy transferred between bodies, called radiative heat transfer, is well-understood when the distance between them is large compared to the wavelength of the electromagnetic waves. However, a question of fundamental interest is: what happens when the distance between the radiating bodies is smaller than or comparable to the wavelength of the radiation? That is, what happens when the bodies are brought into the “near-field?” Countless theoretical treatments now exist in the literature indicating that the radiative heat transfer can increase by orders of magnitude when the spacing between bodies is reduced to tens or hundreds of nanometers, and these predictions are largely supported by a handful of experimental studies. Moreover, computational work suggests that near-field radiation between parallel plates can have important, novel applications. However, their realization has thus far been prohibited by the technical difficulty in positioning parallel plates across nanoscale gaps. My first research objective was to measure near-field radiative heat transfer between parallel plates separated by less than a single micrometer, a goal which had eluded researchers for nearly half a century. Using a pair of microscale devices and a custom-built nanopositioner, we systematically demonstrated heat flux enhancements of 100-fold compared to the far-field by decreasing the inter-plate distance between parallel silica plates from 10 μm to approximately 60 nm. I then modified this approach to utilize a single planar microdevice situated across a vacuum gap from a macroscopic planar surface. By using devices with lesser curvature and higher mechanical stiffness, I reduced the minimum attainable gap size between silica plates to approximately 25 nanometers and measured a near-field heat flow 1,200 times higher than that of the far field, representing a significant improvement over the previous demonstration. Most importantly, replacing one of the microdevices with a macroscopic surface enabled a greater degree of flexibility in materials processing, opening up new opportunities for novel measurements. My second objective was to use this new technique to demonstrate novel near-field-enabled thermal diode using a doped silicon microdevice and an extended vanadium dioxide thin film. Because the emissive and absorptive properties of vanadium dioxide change dramatically when it undergoes an insulator-metal transition at 68 degrees Celsius, the radiative heat flow can change depending on the direction of the temperature difference. For a vacuum gap size of approximately 140 nanometers, I measured that the heat flow from metallic vanadium dioxide to doped silicon exceeds the heat flow from doped silicon to insulating vanadium dioxide by a factor of approximately two. Computational modeling showed that this rectification could be further improved by decreasing the thickness of the vanadium dioxide film. Finally, I demonstrated the first near-field power output enhancement in a thermophotovoltaic system. For a doped silicon emitter at 655 kelvin radiating at an indium arsenide-based cell, I measured a 40-fold increase in the electrical output power from the cell by reducing the vacuum gap spacing from 10 micrometers to approximately 60 nanometers. Additional experiments were carried out with a cell having a different bandgap energy, and its performance was compared to the first cell. Moreover, a detailed mathematical model was developed to identify ways to improve the device efficiency in the future. These studies represent an important milestone in near-field-enabled energy conversion.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146129/1/fiorino_1.pd

Institute of Ion Beam Physics and Materials Research; Annual Report 1999

Summary of the Scientific Activities of the Institute in 1999: Highlight Reports / Short Contributions / Statistic

The Electrochemistry of Two-Dimensional Materials and Their Heterostructures for Energy Applications

Meeting the growing energy demands of the 21st century is one of the greatest problems facing humanity, which has led to intense research into improving energy generation, storage, and transportation. To meet this challenge, many researchers have focused on nanomaterials, which offer unique opportunities for property modulation, attractive kinetics, and increased surface area. Two-dimensional (2D) materials are a class of nanomaterial consisting of atomically thin sheets with a wide range of attractive properties and the weak interlayer van der Waals interactions in these compounds can be exploited to stack layers of different materials with an atomically smooth interface to form a hybrid material called a heterostructure. Despite recent advances in identifying promising 2D materials and heterostructures for potential applications for energy technology, there is a significant need for the development of mechanistic understandings of these materials. In this dissertation, 2D materials are integrated into a nanodevice architecture to systematically probe the mechanisms of 2D electrochemical energy materials. We investigate the synthesis of high-quality monolayer crystals of MoS2, and highlight the role of elevated sulfur concentration in suppressing the formation of unwanted suboxide and oxysulfide intermediate products during the stepwise sulfurization of MoO3 to MoS2. Using these high-quality crystals of MoS2, we investigate the electrocatalytic production of hydrogen with MoS2/WTe2 heterostructures, and demonstrate that enhanced charge injection through the heterointerface optimizes the catalytic performance of MoS2. Our investigation of the electrochemical intercalation of lithium into heterostructures of hexagonal boron nitride, graphene, and MoS2 demonstrates the key role that heterointerfaces play in controlling both the kinetics and thermodynamics of the lithium-induced structural phase transition in MoS2. We further probe the staging of intercalated lithium within graphene, and the effect of mechanical strain on this ordering. Finally, we investigate the influence of the thickness of MoS2 flakes on the kinetics of its lithium-induced structural phase transition. The nanodevice approach in this dissertation seeks to systematically probe the factors that can affect the electrochemistry of 2D energy materials. We demonstrate the importance of charge injection upon the performance of 2D electrocatalysts and how heterointerfaces, support substrates, and mechanical strain can modify the phase stability and intercalation dynamics of 2D materials. These findings have implications for the production of renewable fuels, nanostructuring metal-ion battery and supercapacitor electrodes, and for many other device applications utilizing 2D nanomaterials. Our aim is to inform future materials engineering and energy device architecture for the next generation of nanostructured energy technology

Nanomaterials by severe plastic deformation: review of historical developments and recent advances

International audienceSevere plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity