通过同位素研究揭示立方方铁锰矿 In$_2$O$_3$ 中氧对拉曼活性声子模式的影响
Unravelling the oxygen influence in cubic bixbyite In$_2$O$_3$ on Raman active phonon modes by isotope studies
AI总结：
本研究通过同位素实验与理论计算，揭示了立方 In$_2$O$_3$ 中氧对拉曼声子模式的影响，并推测氧空位会导致特定模式红移。
摘要：
在本研究中，我们对立方方铁锰矿 In$_2$O$_3$（一种重要的氧化物基宽带隙半导体）中的拉曼活性声子模式进行了全面研究。通过密度泛函微扰理论计算，确定了所有模式及其频率的原子贡献，从而揭示了晶格动力学的基本见解。这些模拟针对 $^{16}$O 和 $^{18}$O 同位素比的不同组成（包括其纯态）进行。结果显示，随着 $^{18}$O 含量的增加，所有模式的频率均出现红移，这是由于原子质量增加所致。对于七个最低能量模式，这种相对位移低于 1%，而对于其余 15 个较高能量模式，位移约为 5.5%。除一个模式对应于纯氧振动状态外，所有模式都有铟和氧晶格位点的能量贡献。通过拉曼光谱，这些结果得到了实验验证，且吻合度极佳。研究的样品包括一个含 $^{16}$O 同位素的块体单晶和一个作为 $^{18}$O 样品的分子束外延（MBE）生长的薄膜。飞行时间二次离子质谱法确认了样品中氧同位素的纯度。这些同位素类似物研究使得通过拉曼光谱直接实验获取立方 In$_2$O$_3$ 的基本材料性质成为可能。例如，我们推测，In$_2$O$_3$ 中氧空位的存在将导致以氧振动为主的模式（如 $E_{g}^{(4)}$ 或 $A_{g}^{(4)}$）向低频移动。
英文摘要：
In this study, we performed comprehensive investigations on the Raman active phonon modes in cubic bixbyite In$_2$O$_3$, an important oxide based, wide-bandgap semiconductor. Fundamental insights into the lattice dynamics are revealed, by determining the atomistic contribution to all modes and their frequencies by density functional perturbation theory calculations. Those simulations were performed for different compositions of $^{16}$O and $^{18}$O isotope ratios, including their pure states. An increasing red-shift of the mode frequencies with increasing $^{18}$O content for all modes, due to the increased atomic mass, is revealed. For the seven lowest energy modes, this relative shift is below 1%, whereas for the remaining 15 higher energetic modes a shift of about 5.5% was identified. All modes have energy contributions of both indium and oxygen lattice sites, except for one, which corresponds to a pure oxygen vibrational state. Applying Raman spectroscopy, those results could be verified experimentally with excellent agreement. Investigated samples consisted of a bulk single crystal with $^{16}$O isotopes and a MBE grown thin film as the $^{18}$O sample. Time-of-flight secondary ion mass spectrometry confirms the purity of the oxygen isotope in the sample. These isotopologue studies allow for a direct experimental access to fundamental material properties in cubic In$_2$O$_3$ by means of Raman spectroscopy. For example, we speculate, that the presence of oxygen vacancies in In$_2$O$_3$ would result in a shift of modes that are dominated by O-vibrations, e. g., $E_{g}^{(4)}$ or $A_{g}^{(4)}$, towards lower frequencies.
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