De Deb Sankar, Behara Dilip Kumar, Saha Sulay, Kumar Arun, Subramaniam Anandh, Sivakumar Sri, Pala Raj Ganesh S
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP-208016, India.
Phys Chem Chem Phys. 2020 Nov 21;22(43):25366-25379. doi: 10.1039/d0cp01300e. Epub 2020 Nov 3.
Stabilization of different morphologies of iso-material native/non-native heterostructures is important for electron-hole separation in the context of photo-electrochemical and opto-electronic devices. In this regard, we explore the stabilities of different morphologies of rutile ("native", ground state phase) and anatase ("non-native" phase) TiO heterostructures through (1) seed-mediated growth and (2) a thermally induced arrested phase transition synthesis protocol. Furthermore, the experimental results are analyzed through a combination of Density Functional Tight Binding (DFTB) and Finite Element Model (FEM) methods. During the seed-mediated growth, anatase is grown over a polydispersed and polycrystalline rutile core through thermal treatment yielding core-shell, Janus and yolk-shell iso-material heterostructures as observed from HRTEM. The arrested phase transition of anatase to rutile at different annealing temperatures yields rutile crystals in the subsurface region of the anatase and rutile/core-thin anatase/shell heterostructures but does not yield a Janus structure. Small particles that can be modeled via DFTB computations suggest that: (1) a heterostructure of the rutile/core-anatase/shell is energetically more stable than the anatase/core-rutile/shell or any other Janus configuration, (2) the off-centered rutile/core-anatase shell is more favorable to the mid-centered rutile/core-anatase shell and (3) Janus heterostructures can be stabilized when the mass ratio of the rutile seed to anatase overgrowth is high. FEM simulations, performed to evaluate the importance of stress relaxation in bicrystalline materials without defects, suggest that Janus structures can be stabilized in larger particles. The present studies add to the heuristics available for synthesizing iso-material heterostructures.
在光电化学和光电器件的背景下，稳定不同形态的同材料本征/非本征异质结构对于电子-空穴分离至关重要。在这方面，我们通过（1）种子介导生长和（2）热诱导的相变停滞合成方案，探索了金红石（“本征”，基态相）和锐钛矿（“非本征”相）TiO异质结构不同形态的稳定性。此外，通过密度泛函紧束缚（DFTB）和有限元模型（FEM）方法相结合来分析实验结果。在种子介导生长过程中，通过热处理使锐钛矿在多分散和多晶的金红石核上生长，从高分辨透射电子显微镜（HRTEM）观察到产生了核壳、双面和蛋黄壳同材料异质结构。在不同退火温度下锐钛矿向金红石的相变停滞在锐钛矿和金红石/核-薄锐钛矿/壳异质结构的亚表面区域产生了金红石晶体，但没有产生双面结构。可以通过DFTB计算建模的小颗粒表明：（1）金红石/核-锐钛矿/壳的异质结构在能量上比锐钛矿/核-金红石/壳或任何其他双面构型更稳定，（2）偏心的金红石/核-锐钛矿壳比中心的金红石/核-锐钛矿壳更有利，（3）当金红石种子与锐钛矿过生长的质量比很高时，双面异质结构可以稳定。为评估无缺陷双晶材料中应力松弛的重要性而进行的有限元模拟表明，双面结构可以在较大颗粒中稳定。本研究增加了可用于合成同材料异质结构的启发式方法。
