Vapor Phase Infiltration: The Key To Oksana Yurkevich's Self-Healing Semiconductors [new thesis]
Oksana Yurkevich, a former Marie Curie fellow, has recently defended her Ph.D. thesis regarding “Electronic and Self-healing Properties of Polymer-Inorganic Hybrids Enabled by Vapor Phase Infiltration”.
Self-healing materials are artificial or synthetically created substances that can automatically repair damages to themselves without any external diagnosis of the problem or human intervention. This kind of material has been used by humans from ancient times, such as roman structures, to technological applications, such as aerospace structures and components, including fuselage, engines, and coatings.
Oksana focused her research on self-healing polymer-hybrid materials using metal oxides (MeO). The self-healing material was based on a polymer matrix with dispersed metal oxide nanoparticles. To get metal oxides inside polymers, she used vapor phase infiltration.
In that manner, when the metal oxide thin film layer gets broken, it is restored by diffusion of the same metal oxide to the surface. In this dynamics, the polymer is used as a reservoir for the metal oxide repair agent.
Atomic Layer Deposition and Vapor Phase Infiltration
Similarly to atomic layer deposition (ALD), VPI involves sequential, separated gas phase reactions (Fig. 1). Chemical reactants, or precursors, are never present in the reactor at the same time (Fig. 1). Reaction paths can be controlled reasonably, avoiding unwanted side reactions in the gas phase. The exposure time can be made very long, minutes, hours, depending on the desired depth of diffusion and the spaces between the polymer chains (porosity).
Figure 1: Schematic of typical pressure profiles for ALD and VPI processes. The pink, blue and green lines represent the partial pressure of the 1st and 2nd precursors and a carrier/purge gas, respectively. The gas flow is usually kept constant even during exposure unless the reactor is hermetically sealed between the pulse and purge sequences. From thesis.
Oksana showed that the hybrid material, i.e., the polymer matrix with dispersed nanoparticles, can serve as a reservoir with healing agents to repair a cracked Metal-Oxide film (Fig. 2.). This was done without the use of liquid and reactive healing agents but through the growth of well-dispersed metal oxide nanoparticles inside polymers, enabling their diffusion and aggregation.
Figure 2 shows the healing scheme of the VPI-grown hybrid structure. Once the coating on the surface has a defect (Fig. 2, section 2), the particles move to the defect site and form a capping of the defect (Fig. 2, section 3).
Using indium, she developed and studied a novel semiconductor comprised of indium oxide nanoparticles distributed inside the polymer ParyleneC.
Using Zinc, ParyleneC/ZnO hybrids were obtained after VPI of Diethyl Zinc/H2O or Diethyl Zinc/H2O2 in a wide range of processing temperatures.
Oksana also revealed that the morphology and electrical properties of Indium-Tin Oxides could be largely restored upon healing.
Therefore, Oksana presented an expansion of the pool of self-healing materials to semiconductors such as indium, zinc, indium tin, and zinc indium oxides, thereby increasing the reliability and sustainability of future functional materials. Moreover, morphology and electrical properties are of immediate interest for further developing transparent flexible electrodes, which can be applied in modern electronics.
You can read her complete thesis directly on our website, here.
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Entropy-Driven Self-Healing of Metal Oxides Assisted by Polymer–Inorganic Hybrid Materials Oksana Yurkevich, Evgeny Modin, Iva Šarić, Mladen Petravić, Mato Knez. First published: 31 May 2022 https://doi.org/10.1002/adma.202202989
Electronic and Self-healing Properties of Polymer-Inorganic Hybrids Enabled by Vapor Phase Infiltration. by Oksana Yurkevich, 2022, Ph.D. thesis.