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Hf_0.5Zr_0.5O₂‐based materials have garnered significant attention for applications requiring ferroelectricity at the nanoscale. This behavior arises due to the stabilization of metastable phases at room temperature. However, the synthesis of phase pure Hf_0.5Zr_0.5O₂remains a challenging problem in both thin films and nanoparticles. Herein, the crystallization of Hf_0.5Zr_0.5O₂nanoparticles from an as‐synthesized amorphous phase is studied. By tailoring the aggregate nature of the intermediate amorphous nanoparticles via different drying processes, the crystallization pathway can be altered, resulting in significant differences in crystal structure, crystallite size, and crystallite morphology after calcination. X‐ray diffraction (XRD) and Rietveld refinement show the dominant crystallographic phase changes from a monoclinic structure to a cubic structure for samples with decreased aggregation. Samples prepared via freeze drying exhibit the most aggregation control and correspond with the observation of single‐crystalline particle aggregates and branching structures attributed to a crystallization by particle attachment mechanism. Herein, differing crystallization pathways lead to unique crystal morphologies that stabilize the traditionally high‐temperature phases of Hf_0.5Zr_0.5O₂‐based materials that are necessary for functional applications.

 

Nanomaterials have unique properties, functionalities, and excellent performance, and as a result have gained significant interest across disciplines and industries. However, currently, there is a lack of techniques that can assemble as-synthesized nanomaterials in a scalable manner. Electrophoretic deposition (EPD) is a promising method for the scalable assembly of colloidally stable nanomaterials into thick films and arrays. In EPD, an electric field is used to assemble charged colloidal particles onto an oppositely charged substrate. However, in constant voltage EPD the deposition rate decreases with increasing deposition time, which has been attributed in part to the fact that the electric field in the suspension decreases with time. This decreasing electric field has been attributed to two probable causes, (i) increased resistance of the particle film and/or (ii) the growth of an ion-depletion region at the substrate. Here, to increase EPD yield and scalability we sought to distinguish between these two effects and found that the growth of the ion-depletion region plays the most significant role in the increase of the deposit resistance. Here, we also demonstrate a method to maintain constant deposit resistance in EPD by periodic replenishing of suspension, thereby improving EPD’s scalability. 

Inductors and transformers (here referred to as power components) for modern AC/DC switching power supplies require magnetic materials that have high power density and efficiency at high frequencies, with high magnetic saturation, low coercivity, and multi‐micrometer thicknesses to increase magnetic energy storage and power handling. Rather than using a single‐phase magnetic material in a polymer‐based composite, a composite formed from two magnetic phases (such as a 0‐3 nanocomposite) can simultaneously achieve all of the listed requirements and benefit from contributions by both the zero‐ and three‐dimensional phases to the magnetic properties. The fabrication of 0‐3 magnetic nanocomposites for power component applications requires a method to deposit magnetic nanoparticles into thick, physically stable yet porous films, and a subsequent method for infiltrating the magnetic nanoparticle film with another magnetic material. Here, the deposition of magnetic nanoparticles into micron‐thick films using electrophoretic deposition (EPD) is discussed. This is described along with a new method, to improve upon traditional EPD methods by increasing film–substrate interactions with chelating agents, therefore increasing film stability. Next, the use of electro‐infiltration for fully incorporating a secondary magnetic material within the nanoparticle film is presented, showing the cumulative fabrication process with the addition of a multilayered nanocomposite fabrication technique for increasing overall nanocomposite thickness. The subsequent cross‐sectional and magnetic characterization of the fabricated 0‐3 nanocomposites is also shown. Finally, future directions for 0‐3 magnetic nanocomposites are offered, with emphasis on potential materials synthesis techniques and on translating knowledge beyond power component applications.

 

Incorporating nanoparticles into devices for a wide range of applications often requires the formation of thick films, which is particularly necessary for improving magnetic power storage, microwave properties, and sensor performance. One approach to assembling nanoparticles into films is the use of electrophoretic deposition (EPD). This work seeks to develop methods to increase film thickness and stability in EPD by increasing film-substrate interactions via functionalizing conductive substrates with various chelating agents. Here, we deposited iron oxide nanoparticles onto conductive substrates functionalized with three chelating agents with different functional moieties and differing chelating strengths. We show that increasing chelating strength can increase film-substrate interactions, resulting in thicker films when compared to traditional EPD. Results will also be presented on how the chelating strength relates to film formation as a function of deposition conditions. Yield for EPD is influenced by deposition conditions including applied electric field, particle concentration, and deposition time. This work shows that the functionalization of substrates with chelating agents that coordinate strongly with nanoparticles (phosphonic acid and dopamine) overcome parameters that traditionally hinder the deposition of thicker and more stable films, such as applied electric field and high particle concentration. We show that functionalizing substrates with chelating agents is a promising method to fabricate thick, stable films of nanoparticles deposited via EPD over a larger processing space by increasing film-substrate interactions. 

The fabrication and characterization of the first magnetoelectric sensors utilizing arrays of Janus magnetoelectric composite nanowires composed of barium titanate and cobalt ferrite are presented. By utilizing magnetoelectric nanowires suspended across electrodes above the substrate, substrate clamping is reduced when compared to layered thin-film architectures; this results in enhanced magnetoelectric coupling. Janus magnetoelectric nanowires are fabricated by sol–gel electrospinning, and their length is controlled through the electrospinning and calcination conditions. Using a directed nanomanufacturing approach, the nanowires are then assembled onto pre-patterned metal electrodes on a silicon substrate using dielectrophoresis. Using this process, functional magnetic field sensors are formed by connecting many nanowires in parallel. The observed magnetic field sensitivity from the parallel array of nanowires is 0.514 ± .027 mV Oe⁻¹at 1 kHz, which translates to a magnetoelectric coefficient of 514 ± 27 mV cm⁻¹ Oe⁻¹.