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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2019)

The advent of spintronics in 1988 represents a step forward in the development of high efficiency electronics. Adding the spin degree of freedom allows the design of new technologies that do not require charge motion in a device, which translates in lower energy dissipation, for this reason ferromagnetic insulators have played an important role in the research of new spintronic applications.

Rare earth iron garnets are a type of ferromagnetic insulators which physical and chemical characteristics make them the ideal candidates for their use in spintronic research, for this reason is of great importance to understand their properties to exploit them to their full potential.

The first chapter covers an introduction to spintronics and iron garnets as candidates for their application on the development of new technologies, the basic concepts of spintronics are covered in this section.

In chapter two it is covered the concept of magnetic anisotropy and its control by thickness dependence in iron garnet thin films. Here, it is demonstrated that by exerting an adequate strain in the lattice structure of the iron garnet it is possible to align its magnetization perpendicular to the sample plane, and that the magnitude of this effect can be systematically tuned by the thickness of the iron garnet thin film. The obtention of this perpendicular magnetic anisotropy is an important requirement for the study of physical phenomena such as Quantum Anomalous Hall Effect.

In chapter three the effect of lattice strain in the dynamic magnetic properties of europium iron garnet are analyzed. The strain on the films is applied by lattice mismatch by the use of different garnet substrates, and then subsequently studied by ferromagnetic resonance technique, which provides important information about the dynamics of spin wave propagation. In this experiment, it was found that the intrinsic damping, which is associated to the energy dissipation of a spin wave, is independent of the lattice strain.

Finally, in chapter four the use of iron garnets as a source of pure spin-current is examined. By setting up spin Seebeck effect and spin pumping experiments, the spin wave transmission through different configurations and posterior charge conversion on materials with large spin-orbit coupling are studied.

    Cover page: Experimental Study and Development of Rare Earth Iron Garnets as Pure Spin-Current SourcesCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Merced Previously Published Works (2023)
    Complex 3D geometry and high conductivity have generally been mutually exclusive characteristics for conducting polymers. For instance, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a benchmark conducting polymer, typically exhibits conductivity 1 to 2 orders of magnitude lower in 3D-printed forms compared to 2D-processed thin films, due to its sensitivity to processing conditions. Here, we investigate the main causes of this reduced conductivity, which are found to be (1) the ink formulation strategy and (2) the strong lateral phase separation of the printed filaments. Processing approaches that overcome these factors have produced significant conductivity enhancement to 1200 S/cm, higher than the typical 2D-processed PEDOT:PSS. Our study also unveils a set of guiding principles for optimizing the conductivity of direct ink writing (DIW)-printed PEDOT:PSS, including printing orientation, print bed temperature, and nozzle diameter. With the combination of high conductivity and 3D geometric freedom, potential applications such as omnidirectionally deformable LED devices with strain-independent electrical behavior and bespoke electronics that replicate the shape of human body parts have been demonstrated.
      Cover page: Imparting High Conductivity to 3D Printed PEDOT:PSS
      • Article
      • Peer Reviewed
      UC Merced Previously Published Works (2021)
      Conducting polymer hydrogels combine electrical conductivity and tunable water content, rendering them strong candidates for a range of applications including biosensors, cell culture platforms, and energy storage devices. However, these hydrogels are mechanically brittle and prone to damage, prohibiting their use in emerging applications involving dynamic movement and large mechanical deformation. Here, we demonstrate that applying the concept of architecture to conducting polymer hydrogels can circumvent these impediments. A stereolithography 3D printing method is developed to successfully fabricate such hydrogels in complex lattice structures. The resulting hydrogels exhibit elastic compressibility, high fracture strain, enhanced cycling stability, and damage-tolerant properties despite their chemical composition being identical to their brittle, solid counterparts. Furthermore, concentrating the deformation to the 3D geometry, rather than polymer microstructure, effectively decouples the mechanical and electrical properties of the hydrogel lattices from their intrinsic properties associated with their chemical composition. The confluence of these new physical properties for conducting polymer hydrogels opens broad opportunities for a myriad of dynamic applications.
        Cover page: 3D printed architected conducting polymer hydrogels
        • Article
        • Peer Reviewed
        UC Merced Previously Published Works (2023)
        Materials are more easily damaged during accidents that involve rapid deformation. Here, a design strategy is described for electronic materials comprised of conducting polymers that defies this orthodox property, making their extensibility and toughness dynamically adaptive to deformation rates. This counterintuitive property is achieved through a morphology of interconnected nanoscopic core-shell micelles, where the chemical interactions are stronger within the shells than the cores. As a result, the interlinked shells retain material integrity under strain, while the rate of dissociation of the cores controls the extent of micelle elongation, which is a process that adapts to deformation rates. A prototype based on polyaniline shows a 7.5-fold increase in ultimate elongation and a 163-fold increase in toughness when deformed at increasing rates from 2.5 to 10 000% min-1 . This concept can be generalized to other conducting polymers and highly conductive composites to create "self-protective" soft electronic materials with enhanced durability under dynamic movement or deformation.
          Cover page: Deformation Rate‐Adaptive Conducting Polymers and Composites
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2020)
          Eukaryotes have evolved various quality control mechanisms to promote proteostasis in the endoplasmic reticulum (ER). Selective removal of certain ER domains via autophagy (termed as ER-phagy) has emerged as a major quality control mechanism. However, the degree to which ER-phagy is employed by other branches of ER-quality control remains largely elusive. Here, we identify a cytosolic protein, C53, that is specifically recruited to autophagosomes during ER-stress, in both plant and mammalian cells. C53 interacts with ATG8 via a distinct binding epitope, featuring a shuffled ATG8 interacting motif (sAIM). C53 senses proteotoxic stress in the ER lumen by forming a tripartite receptor complex with the ER-associated ufmylation ligase UFL1 and its membrane adaptor DDRGK1. The C53/UFL1/DDRGK1 receptor complex is activated by stalled ribosomes and induces the degradation of internal or passenger proteins in the ER. Consistently, the C53 receptor complex and ufmylation mutants are highly susceptible to ER stress. Thus, C53 forms an ancient quality control pathway that bridges selective autophagy with ribosome-associated quality control in the ER.
            Cover page: A cross-kingdom conserved ER-phagy receptor maintains endoplasmic reticulum homeostasis during stress.
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2024)
            The chemokine CCL28 is highly expressed in mucosal tissues, but its role during infection is not well understood. Here, we show that CCL28 promotes neutrophil accumulation in the gut of mice infected with Salmonella and in the lung of mice infected with Acinetobacter. Neutrophils isolated from the infected mucosa expressed the CCL28 receptors CCR3 and, to a lesser extent, CCR10, on their surface. The functional consequences of CCL28 deficiency varied between the two infections: Ccl28-/- mice were highly susceptible to Salmonella gut infection but highly resistant to otherwise lethal Acinetobacter lung infection. In vitro, unstimulated neutrophils harbored pre-formed intracellular CCR3 that was rapidly mobilized to the cell surface following phagocytosis or inflammatory stimuli. Moreover, CCL28 stimulation enhanced neutrophil antimicrobial activity, production of reactive oxygen species, and formation of extracellular traps, all processes largely dependent on CCR3. Consistent with the different outcomes in the two infection models, neutrophil stimulation with CCL28 boosted the killing of Salmonella but not Acinetobacter. CCL28 thus plays a critical role in the immune response to mucosal pathogens by increasing neutrophil accumulation and activation, which can enhance pathogen clearance but also exacerbate disease depending on the mucosal site and the infectious agent.
              Cover page: CCL28 modulates neutrophil responses during infection with mucosal pathogens
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