Epitaxial Formation Mechanism of Multilayer TiO 2 Films with Ordered Accessible Vertical Nanopores by Evaporation-Driven Assembly
Surfactant-templated mesoporous titania (TiO2) films have excellent physical and electronic properties, but some potential applications require films thicker than the 100-200 nm typically prepared by sol-gel coating. In this paper, the mechanism of forming micron-thick TiO2 films with vertically oriented nanopore channels by a layer-by-layer deposition technique (up to eight 125 nm-thick layers) is investigated. In situ grazing incidence small angle x-ray scattering (GISAXS) performed on successive layers of Pluronic F127-templated films reveals if and how epitaxially oriented layers form during aging at 4 °C. At 78% relative humidity (RH), films cast onto substrates modified with crosslinked F127 maintain (011)-oriented $$Im\bar{3}m$$ cubic mesophase order, whereas micelles on unmodified glass lose their preferred orientation, leading to the observation of an arc in GISAXS attributed to an anisotropic micelle structure. A similar arc from randomly oriented domains is found at low RH (38%) regardless of substrate modification. Avrami model analysis shows that each oriented epitaxial layer followed formation kinetics with the same order (n=1.8±0.3) and half-life (10-20 min). Cross-sectional electron microscopy and impedance spectroscopy of the films after calcination at 400 °C show the formation of continuous, accessible vertical pore channels by micelle fusion for mesophases properly oriented by initial substrate modification.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States); Univ. of Kentucky, Lexington, KY (United States)
- Sponsoring Organization:
- National Science Foundation (NSF), Washington, DC (United States); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
- Contributing Organization:
- Advanced Photon Source, Argonne National Laboratory
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1580579
- Journal Information:
- Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 3 Vol. 124; ISSN 1932-7447
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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