Abstract

The high-pressure, α-PbO₂-structured polymorph of titanium dioxide (TiO₂-II) was recently identified in micrometer-sized grains recovered from four Neoarchean spherule layers deposited between ∼2.65 and ∼2.54 billion years ago. Several lines of evidence support the interpretation that these layers represent distal impact ejecta layers. The presence of shock-induced TiO₂-II provides physical evidence to further support an impact origin for these spherule layers. Detailed characterization of the distribution of TiO₂-II in these grains may be useful for correlating the layers, estimating the paleodistances of the layers from their source craters, and providing insight into the formation of the TiO₂-II. Here we report the investigation of TiO₂-II-bearing grains from these four spherule layers using multivariate curve resolution–alternating least squares (MCR-ALS) applied to Raman microspectroscopic mapping. Raman spectra provide evidence of grains consisting primarily of rutile (TiO₂) and TiO₂-II, as shown by Raman bands at 174 cm^–1 (TiO₂-II), 426 cm^–1 (TiO₂-II), 443 cm^–1 (rutile), and 610 cm^–1 (rutile). Principal component analysis (PCA) yielded a predominantly three-phase system comprised of rutile, TiO₂-II, and substrate-adhesive epoxy. Scanning electron microscopy (SEM) suggests heterogeneous grains containing polydispersed micrometer- and submicrometer-sized particles. Multivariate curve resolution–alternating least squares applied to the Raman microspectroscopic mapping yielded up to five distinct chemical components: three phases of TiO₂ (rutile, TiO₂-II, and anatase), quartz (SiO₂), and substrate-adhesive epoxy. Spectral profiles and spatially resolved chemical maps of the pure chemical components were generated using MCR-ALS applied to the Raman microspectroscopic maps. The spatial resolution of the Raman microspectroscopic maps was enhanced in comparable, cost-effective analysis times by limiting spectral resolution and optimizing spectral acquisition parameters. Using the resolved spectra of TiO₂-II generated from MCR-ALS analysis, a Raman spectrum for pure TiO₂-II was estimated to further facilitate its identification.

© 2017 The Author(s)

Raman spectral analysis of TiO₂ thin films doped with rare-earth samarium

Chang-Hu Yang and Zhong-Quan Ma
Appl. Opt. 51(22) 5438-5441 (2012)

Fabrication of TiO₂ thin films with both anatase and rutile structures together using the ion-implantation method

Yu-Jie Ma, Fei Lu, Bing-Xi Xiang, Jin-Lai Zhao, and Shuang-Chen Ruan
Opt. Mater. Express 8(3) 532-540 (2018)

Laser-induced high-pressure and high-temperature conditions at the titanium–water interface and their implication on TiO₂ nanoparticles

Arpita Nath and Alika Khare
J. Opt. Soc. Am. B 29(3) 351-356 (2012)

Photonic crystal structures in titanium dioxide (TiO₂) and their optimal design

X. Wang, M. Fujimaki, and K. Awazu
Opt. Express 13(5) 1486-1497 (2005)

Micro fiber with cladding of titanium dioxide (TiO₂) nanoparticles and its violet light sensing

Donghui He, Yang Hu, Jun Tao, Xiaojie Zheng, Huaan Liu, Guangyin Jing, Huihui Lu, Heyuan Guan, Jianhui Yu, Jun Zhang, Jieyuan Tang, Yunhan Luo, and Zhe Chen
Opt. Mater. Express 7(1) 264-272 (2017)