Plasma synthesis and processing of nanostructured quantum materials

Low-temperature plasmas (LTPs) have long been recognized as effective in enhancing physical and chemical processes during materials synthesis. The emergence of quantum materials has renewed the interest in processing using LTPs, with the goal of engineering systems that exhibit quantum coherence, electronic wave function topology, quantum entanglement, and quantum fluctuation effects. There are vast opportunities for control, enhancement, and discovery of new phenomena when these materials are synthesized as thin films and heterostructures. A now-classic example is the interface-enhanced superconductivity of monolayer β-FeSe on (001)-oriented SrTiO₃. LTPs generated by laser ablation are of particular interest in this regard because of their rich chemistry and spatiotemporal phenomena. These plasmas can produce reactivity, temperature, and stress profiles to induce chemo-thermo-mechanical materials transformations at interfaces that are not accessible by other approaches. The kinetic energy of ions can be readily tuned in the ~1-100 eV range and ion densities controlled between 10⁹ and 10¹⁵ cm^-3. Compressive stress (kPa to tens of GPa) and temperature pulses (hundreds to thousands of kelvin) can be delivered by the leading edge of the plasma expansion. The sequence and timing of these conditions are adjustable, allowing new types of nonequilibrium processing. In this talk, I will review the state of plasma synthesis and processing of quantum materials, such as graphene, transition metal dichalcogenides, and atomic-monolayer epitaxial quantum materials. I will show how Langmuir probe, optical emission spectroscopy, and gated-intensified CCD imaging diagnostics can be used in conjunction with plasma fluid simulations to probe the plasma flow dynamics, distinguish the various components, and control the plasma parameters of the multi-species laser-generated plasma used for growth of FeSe/SrTiO₃ quantum heterointerfaces.