Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2023)
Achieving control over the motion of dissolved particles in liquid metals is of importance for the meticulous realization of hierarchical particle assemblies in a variety of nanofabrication processes. Brownian forces can impede the motion of such particles, impacting the degree of perfection that can be realized in assembled structures. Here, we show that light-induced Marangoni flow in liquid metals (i.e., liquid-gallium) with Laguerre-Gaussian (LGpl) lasers as heating sources is an effective approach to overcome Brownian forces on particles, giving rise to predictable assemblies with a high degree of order. We show that by carefully engineering surface tension gradients in liquid-gallium using non-Gaussian LGpl lasers, the Marangoni and convective flow that develops in the fluid drives the trajectory of randomly dispersed particles to assemble into 100 μm wide ring-shaped particle assemblies. Careful control over the parameters of the LGpl laser (i.e., laser mode, spot size, and intensity of the electric field) can tune the temperature and fluid dynamics of the liquid-gallium as well as the balance of forces on the particle. This in turn can tune the structure of the ring-shaped particle assembly with a high degree of fidelity. The use of light to control the motion of particles in liquid metals represents a tunable and rapidly reconfigurable approach to spatially design surface tension gradients in fluids for more complex assembly of particles and small-scale solutes. This work can be extended to a variety of liquid metals, complementary to what has been realized in particle assembly out of ferrofluids using magnetic fields.
    Cover page: Light-Induced Surface Tension Gradients for Hierarchical Assembly of Particles from Liquid Metals.
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2024)

    This dissertation explored the innovative avenues for the confinement growth of materials, leveraging both space-confined and area-selective synthesis strategies through a variety of interface engineering approaches. It highlighted the multifaceted roles of the interface during the synthesis process, acting not only as a nanoreactor and/or a physical scaffold to constrain the geometry of the resulting materials, but also setting a specific chemical microenvironment. This environment is instrumental in facilitating the confined nucleation, growth, and stabilization of intermediates or final products, a process pivotal to area-selective synthesis. Towards it, we first focused on the intercalation of large molecules, such as P2O5, through the basal plane of graphene. This process yielded a confined P2O5 and/or metal phosphate structure within the graphene/Ge (110) heterointerface, following a two-step mechanism. This mechanism involved the dissociation of P2O5 and the subsequent intercalation of its fragments, as corroborated with density functional theory (DFT). The focus was then turned to area-selective synthesis of materials by engineering the surface energy profile at the vacuum-liquid and/or graphene/diamond like carbon (DLC) interface. In one study, a complex surface energy profile was achieved at liquid metal-vacuum interface using Laguerre-gaussian (????) lasers as the heat source, which induced novel Marangoni flow pattern. Marangoni surface flow, and convective flow in bulk liquid metal directed the movement of microparticles within the liquid, demonstrating that careful tuning over the parameters of the ???? laser (i.e., laser mode, spot size, and intensity of the electric field) allowed for precise control over the structure of the ring-shaped particle assemblies at solid-liquid interface. Finally, this dissertation presented a novel method for tuning the work function of monolayer graphene across a broad temperature range. This was achieved through engineering the graphene-Ga implanted DLC heterointerface, allowing for bipolar tuning (either increase or decrease) of the local work function landscape of graphene up to 500°C. This comprehensive study established a clear link between interface engineering and the confinement growth capabilities of materials, offering new strategies and advanced understanding for confinement materials synthesis.

      • Article
      • Peer Reviewed
      LBL Publications (2023)
      Intercalation is the process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on the intercalation of metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains challenging. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5 at the graphene-substrate heterointerface using various techniques. Density functional theory (DFT) corroborates the experimental results and reveals the intercalation mechanism, whereby P2O5 dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5 intercalation, the possibility of intercalation from predissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This in-depth study advances our understanding of intercalation routes of large molecules via the basal plane of graphene as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds.
        Cover page: Elucidating the Mechanism of Large Phosphate Molecule Intercalation Through Graphene-Substrate Heterointerfaces.
        Top