Thermally Activated Optical Absorption into Polaronic States in Hematite
Thermally Activated Optical Absorption into Polaronic States in Hematite
复制标题
赤铁矿中极化状态的热激活光学吸收
DOI：
10.1021/acs.jpclett.0c03751
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Knowles, Kathryn E.
中科院分区：
文献类型：
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作者：
Shelton, Jacob L.;Knowles, Kathryn E.
极化子的形成，即电子或空穴与晶格畸变强烈耦合，抑制了许多第一行过渡金属氧化物半导体的载流子迁移率。最近报道的赤铁矿 (α-Fe2O3) 的 XUV 瞬态吸收测量表明，在光激发时形成电子小极化子，形成不扭曲的电荷转移状态，然后进行亚皮秒晶格重组。在这里，我们证明赤铁矿的极化子态可以通过热激活晶格中基态的光学跃迁直接访问。从 30 到 573 K 收集的热差光谱与斯托克斯共振拉曼光谱相结合，表明带边缘 (2.1–2.3 eV) 附近的光学跃迁与区域中心 a1g 和纵向 (LO) 光学声子之间存在强耦合。对原始和极化子畸变赤铁矿晶格的电子和振动结构的密度泛函理论计算证实，与电子小极化子形成相对应的几何畸变位于28-meV a1g和81-meV LO声子坐标上，并再现了在实验热差和共振拉曼光谱中观察到的特征。
Polaron formation, whereby an electron or hole strongly couples to a lattice distortion, inhibits the carrier mobility of many first-row transition metal oxide semiconductors. Recently reported XUV transient absorption measurements of hematite (α-Fe2O3) demonstrate formation of electron small polarons upon photoexcitation into an undistorted charge-transfer state followed by subpicosecond lattice reorganization. Here, we show that polaronic states of hematite can be accessed directly via optical transitions from the ground state in a thermally activated lattice. Thermal difference spectra collected from 30 to 573 K combined with Stokes resonance Raman spectra indicate strong coupling between optical transitions near the band-edge (2.1–2.3 eV) and zone-center a1gand longitudinal (LO) optical phonons. Density functional theory calculations of the electronic and vibrational structures of pristine and polaron-distorted hematite lattices confirm that the geometric distortion corresponding to electron small polaron formation lies along the 28-meV a1gand 81-meV LO phonon coordinates and reproduce the features observed in the experimental thermal difference and resonance Raman spectra.