Design for low‐temperature microwave‐assisted crystallization of ceramic thin films

Abstract

We designed experiments to determine optimized values for input parameters such as temperature, solution concentration, and power input for synthesizing ceramic materials, specifically titanium dioxide (TiO2) thin films using microwave radiation, which permits crystallization of these films at significantly lower temperatures (150‐160 °C) compared to conventional techniques (>450 °C). The advantage of using lower temperatures is both reduced energy requirements, and in expanding the set of substrates (e.g., plastics) on which the thin film materials can be deposited. Low temperature crystallization permits ceramic thin film materials to be directly grown on delicate plastic substrates (which melt at temperatures over 200°C) and thus would have important applications in the emerging flexible electronics industry.Using a linear regression with quadratic terms, we found estimated optimal settings for the reaction parameters. When tried experimentally, these optimal settings produced better results (% coverage with film) than any of the data used in estimation. This approach allows fine tuning of the input parameters and can lead to reliable synthesis of films in a low‐temperature environment. It may also be an important step in understanding the fundamental mechanisms underlying the growth of these films in the presence of electromagnetic fields like microwave radiation. Copyright © 2017 John Wiley & Sons, Ltd.

Defect‐Mediated Anisotropic Lattice Expansion in Ceramics as Evidence for Nonthermal Coupling between Electromagnetic Fields and Matter

“…During MWR‐assisted heating of anatase powders, we track the change in lattice parameters while the powder is being heated. For MWR‐assisted synthesis experiments, the diffraction peaks of anatase appear only after a sufficient amount of the powder has nucleated in the solution, i.e., when the solution temperature reaches 150 °C (see Experimental Section for details). As the diffraction spectrum also includes scattering from the glass vial and the solution, a large amorphous hump is also detected as background.…”

“…The solution was stirred at 650 rpm to avoid hotspot formation. For the synthesis experiment, a sol–gel solution based on tetrabutyl‐orthotitanate was used as a TiO 2 precursor . The sol–gel was mixed with TEG in the ratio of 1:4.…”

Linking far-from-equilibrium defect structures in ceramics to electromagnetic driving forces

“…Details regarding sol-gel preparation and thin lm growth using this experimental setup have been reported previously. 22,23 MWRassisted reactions were performed at a solution temperature of 225 C and MWR input powers of 40, 80, and 120 W. All reactions were held at the prescribed temperature for 60 minutes.…”

Far-from-equilibrium effects of electric and electromagnetic fields in ceramics synthesis and processing

“…58 in response to the electric field resulting in ohmic heating, which can be several times stronger in intensity than dielectric effects. 76 It is, however, unclear if these interactions alone can explain how microwaves catalyze chemical reactions at low temperatures 17,74,77 and drive structural changes in a variety of materials. 4,22,56,75 In an example for the latter, discussed next, microwave fields induce disorder in local atomic arrangements that subsequently leads to crystallization of ceramic oxides such as TiO 2 at temperatures as low as 150-160°C.…”