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Typical titanium oxide (TiO2) films are transparent in the visible range, allowing for their index of refraction and thickness to be extracted by single-angle spectroscopic ellipsometry (SE) using a Cauchy model. However, TiO2 films grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (IV) (TDMAT) and H2O at 350 °C absorb in the visible range due to the formation of Ti-O-N/Ti-N bonds. Single-angle SE is inadequate for extracting the optical constants of these films, as there are more unknowns (n, k, d) than measurable parameters (ψ, Δ). To overcome this limitation, we combined SE with transmission (T) measurements, a method known as SE + T. In the process, we developed an approach to prevent backside deposition on quartz substrates during ALD deposition. When applying a B-spline model to SE + T data, the film thicknesses on the quartz substrates closely matched those on companion Si samples measured via standard lithography. The resulting optical constants indicate a reduced refractive index, n, and increased extinction coefficient, k, when compared to purer TiO2 thin films deposited via a physical vapor deposition (PVD) method, reflecting the influence of nitrogen incorporation on the optical properties.
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Interfacial Engineering of Conformal Titanium Oxide Nanofilms on Porous Carbon Supercapacitor Electrodes Via Atomic Layer Deposition
Atomic layer deposition (ALD) has been gaining in popularity as a powerful deposition technique and have been shown to be a promising interfacial engineering method to boost the electrochemical performance of supercapacitors, bridging the gap in energy density. In that regard, we developed an ALD technique to deposit titanium dioxide (TiO2) nanofilms onto porous activated carbon (AC) electrodes. This study focused on the critical aspects of the ALD process that were still unexplored by previous relevant works, including the effects of precursor pulse duration and film thickness on the complex porous structures of AC. In particular, these comprehensive investigations pave the way towards uniform distribution and excellent conformity of the TiO2 nanofilms across the AC surface. Moreover, the deposited films were found to be amorphous and resulted in increased amounts of oxygen-containing surface functional groups. The enhanced electrochemical behavior from the TiO2 nanofilms were found to be optimal at 60 ALD cycles with an estimated film thickness of 2.3 nm. The assembled supercapacitor device coated with this ALD technique exhibited higher specific capacitance compared to the bare AC. The key findings of this work provide the foundation of an effective strategy using ALD for fabricating new electrode materials for high-performance supercapacitors.
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- Award ID(s):
- 2235385
- PAR ID:
- 10615720
- Publisher / Repository:
- Materials Research Society
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Posted Content:
- https://doi.org/10.2139/ssrn.5224571
