Liu Shang, Covian Alejandra Cuervo, Wang Xiaoxin, Cline Cory T, Akey Austin, Dong Weiling, Yu Shui-Qing, Liu Jifeng
Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.
Center for Nanoscale Systems, Harvard University, Cambridge, MA, 02138, USA.
Small Methods. 2022 May;6(5):e2200029. doi: 10.1002/smtd.202200029. Epub 2022 Apr 3.
GeSn on Si has attracted much research interest due to its tunable direct bandgap for mid-infrared applications. Recently, short-range order (SRO) in GeSn alloys has been theoretically predicted, which profoundly impacts the band structure. However, characterizing SRO in GeSn is challenging. Guided by physics-informed Poisson statistical analyses of k-nearest neighbors (KNN) in atom probe tomography (APT), a new approach is demonstrated here for 3D nanoscale SRO mapping and semi-quantitative strain mapping in GeSn. For GeSn with ≈14 at. % Sn, the SRO parameters of Sn-Sn 1NN in 10 × 10 × 10 nm nanocubes can deviate from that of the random alloys by ±15 %. The relatively large fluctuation of the SRO parameters contributes to band-edge softening observed optically. Sn-Sn 1NN also tends to be more favored toward the surface, less favored under strain relaxation or tensile strain, while almost independent of local Sn composition. An algorithm based on least square fit of atomic positions further verifies this Poisson-KNN statistical method. Compared to existing macroscopic spectroscopy or electron microscopy techniques, this new APT statistical analysis uniquely offers 3D SRO mapping at nanoscale resolution in a relatively large volume with millions of atoms. It can also be extended to investigate SRO in other alloy systems.
由于其可调节的直接带隙适用于中红外应用，硅上锗锡（GeSn）已引起了众多研究兴趣。最近，理论上预测了GeSn合金中的短程有序（SRO），这对能带结构有深远影响。然而，表征GeSn中的SRO具有挑战性。在此，以原子探针断层扫描（APT）中k近邻（KNN）的物理信息泊松统计分析为指导，展示了一种用于GeSn中三维纳米尺度SRO映射和半定量应变映射的新方法。对于含≈14原子百分比锡的GeSn，10×10×10纳米立方体中Sn-Sn第一近邻（1NN）的SRO参数可能会与随机无序参数与随机合金的相比偏差±15%。SRO参数的相对较大波动导致了光学上观察到的带边软化。Sn-Sn 1NN也倾向于更偏向表面，在应变弛豫或拉伸应变下不太有利，而几乎与局部锡成分无关。一种基于原子位置最小二乘拟合的算法进一步验证了这种泊松-KNN统计方法。与现有的宏观光谱或电子显微镜技术相比，这种新的APT统计分析独特地提供了在相对较大体积中具有数百万原子的纳米级分辨率的三维SRO映射。它还可以扩展到研究其他合金系统中的SRO。
