| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Wednesday Sessions |
| Session TF1-WeM |
| Session: | Vapor Deposition of Functional Polymer Thin Films and Composites |
| Presenter: | Darrin Liau, University of Maryland, College Park |
| Authors: | D. Liau, University of Maryland, College Park G.W. Rubloff, University of Maryland, College Park S.B. Lee, University of Maryland, College Park K. Gregorczyk, University of Maryland, College Park |
| Correspondent: | Click to Email |
Ion transport in materials and at their interfaces plays a profound role in a wide spectrum of applications. These include: energy generation (solar-driven water splitting and fuel cells); energy storage (batteries and capacitors); environmental management (water desalination and purification, and nuclear waste management and remediation); solid-state ionic devices (neuromorphic computing); and a variety of biological systems (ion channels). Here we present an MLD synthesis route to incorporating ion-selective moieties into a thin film, concentrating on the crown ether (CE) family of molecules for their well understood and characterized affinity to selectively bind metal cations in the electron-rich center of the molecule.
Two commercially available crown-ether materials (CE), 1,4,10-Trioxa-7, 13-diazacyclopentadecane(2A15C5) and for 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (2A18C6), were measured using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to assess their suitability as precursors. The results for both molecules show that vaporization begins at ~100-150C in both cases, leading to evaporation of essentially all the material by ~200-250C. The DSC curves for both materials show heat flow indicative of phase changes in the range of the vaporization temperatures ~100-150°C. Malonyl chloride (MC) was used as an organic linker precursor. In-situ spectroscopic ellipsometry (SE) was used to probe the MLD process parameters, showing a wide temperature window between 75°C-150°C with a linear growth rate ~5-6 Å/cycle. Detailed cycle-by-cycle SE show step-wise growth corresponding to the discrete precursor pulses for the CE and the MC. This allows estimates of thickness added per precursor dose, which include an increase in thickness of ~0.295 nm during the MC pulse and ~0.343 for the 2A15C5 CE pulse, for a total thickness added of ~0.622 nm for a full MLD cycle.
Chemical analysis of the as-grown MLD films was conducted by in-vacuo X-ray photoelectron spectroscopy (XPS). The presumed molecular configuration of CE and MC film is confirmed by the presence of all expected elements in the expected ratios. The O 1s spectrum indicates the presence of two species, consistent with expectations based on the presence of both C-O-C oxygen in the CE ring and C=O oxygen in the MC. The N 1s spectrum shows a single species of N in the film, as predicted from the CE moiety. The C 1s spectrum is more complex but consistent with the structure: on the higher binding energy side, we see a peak associated with N-C=O at ~290 eV, an overlapping C-N and C-O at ~288 eV, and a C-C peaks at ~285eV.