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TiO 2 has been extensively studied in many fields including photocatalysis, electrochemistry, optics, etc. Understanding the mechanism of the anatase–rutile phase transition (ART) process is critical for the design of TiO 2 -based high-activity photocatalysts and tuning its properties for other applications. In this work, the ART process using individual anatase micro-particles with a large percentage of (001) facets was monitored and studied. Phase concentration evolution obtained via Raman microscopy was correlated with the morphological evolution observed in scanning electron microscope (SEM) images. The ART of anatase microcrystals is dominated by surface nucleation and growth, but the ART processes of individual anatase particles are distinctive and depend on the various rutile nucleation sites. Two types of transformation pathways are observed. In one type of ART pathway, the rutile phase nucleated at a corner of an anatase microcrystal and grew in one direction along the edge of the crystal firstly followed by propagation over the rest of the microcrystal in the orthogonal direction on the surface and to the bulk of the crystal. The kinetics of the ART follows the first-order model with two distinct rate constants. The fast reaction rate is from the surface nucleation and growth, and the slow rate is from the bulk nucleation and growth. In the other type of ART pathway, multiple rutile nucleation sites formed simultaneously on different edges and corners of the microcrystal. The rutile phase spread over the whole crystal from these nucleation sites with a small contribution of bulk nucleation. Our study on the ART of individual micro-sized crystals bridges the material gap between bulk crystals and nano-sized TiO 2 particles. The anatase/rutile co-existing particle will provide a perfect platform to study the synergistic effect between the anatase phase and the rutile phase in their catalytic performances.
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Influence of Furil Dioxime on Cobalt Electrochemical Nucleation and Growth
The nucleation and growth of cobalt (Co) on blanket Si with extremely thin Co seed was studied in the presence of furil dioxime (FD). Cyclic voltammetry (CV), chronoamperometry, and galvanostatic nucleation studies were conducted to understand the effects of FD on Co nucleation process. A potential dependent suppression effect was observed at low potential with a breakdown of the suppression at high potential, resulting in a hysteresis in CV. The potentiostatic current transient experiments showed that side reactions and adsorption process both greatly affected Co nucleation. A well-established model, which deconvolutes the individual contributions to the total current transient, was applied to fit the experimental curves. Progressive and instantaneous Co nucleation were observed across different FD concentrations and applied potentials. Galvanostatic studies further proved the suppression effect of FD and the effects on film morphology were studied at different conditions.
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- Award ID(s):
- 1662332
- PAR ID:
- 10302513
- Publisher / Repository:
- The Electrochemical Society
- Date Published:
- Journal Name:
- Journal of The Electrochemical Society
- Volume:
- 167
- Issue:
- 2
- ISSN:
- 0013-4651
- Page Range / eLocation ID:
- Article No. 022509
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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