Epitaxial Formation Mechanism of Multilayer TiO2 Films with Ordered Accessible Vertical Nanopores by Evaporation-Driven Assembly

M. Arif Khan, Syed Z. Islam, Suraj Nagpure, Yuxin He, Namal Wanninayake, Rebecca L. Palmer, Joseph Strzalka, Doo Young Kim, Barbara L. Knutson, Stephen E. Rankin

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

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. Here, the mechanism of forming micrometer 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 cross-linked F127 maintain a (011)-oriented Im3 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 relative humidity (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.

Original languageEnglish
Pages (from-to)1958-1972
Number of pages15
JournalJournal of Physical Chemistry C
Volume124
Issue number3
DOIs
StatePublished - Jan 23 2020

Bibliographical note

Funding Information:
Film synthesis, characterization, and detailed electron microscopy were supported by the U.S. National Science Foundation (NSF) under an EPSCoR Research Infrastructure Initiative Track-1 Project (Grant IIA-13355438) and Grant CBET-1604491. Resources of the Advanced Photon Source at Argonne National Laboratory were used for X-ray scattering experiments, supported by U.S. Department of Energy (DOE) Office of Science User Facility operated under Contract DE-AC02-06CH11357.

Publisher Copyright:
Copyright © 2019 American Chemical Society.

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy (all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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