Institute for Physical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany.
Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, 85748 Garching by Munich, Germany.
ACS Nano. 2023 Jun 13;17(11):10423-10430. doi: 10.1021/acsnano.3c01119. Epub 2023 May 23.
Antiferromagnets are promising materials for future opto-spintronic applications since they show spin dynamics in the THz range and no net magnetization. Recently, layered van der Waals (vdW) antiferromagnets have been reported, which combine low-dimensional excitonic properties with complex spin-structure. While various methods for the fabrication of vdW 2D crystals exist, formation of large area and continuous thin films is challenging because of either limited scalability, synthetic complexity, or low opto-spintronic quality of the final material. Here, we fabricate centimeter-scale thin films of the van der Waals 2D antiferromagnetic material NiPS, which we prepare using a crystal ink made from liquid phase exfoliation (LPE). We perform statistical atomic force microscopy (AFM) and scanning electron microscopy (SEM) to characterize and control the lateral size and number of layers through this ink-based fabrication. Using ultrafast optical spectroscopy at cryogenic temperatures, we resolve the dynamics of photoexcited excitons. We find antiferromagnetic spin arrangement and spin-entangled Zhang-Rice multiplet excitons with lifetimes in the nanosecond range, as well as ultranarrow emission line widths, despite the disordered nature of our films. Thus, our findings demonstrate scalable thin-film fabrication of high-quality NiPS, which is crucial for translating this 2D antiferromagnetic material into spintronic and nanoscale memory devices and further exploring its complex spin-light coupled states.
反铁磁体是未来光自旋电子应用的有前途的材料，因为它们在太赫兹范围内显示自旋动力学，且没有净磁化强度。最近，已经报道了层状范德华（vdW）反铁磁体，它们将低维激子特性与复杂的自旋结构结合在一起。虽然存在各种用于制造 vdW 2D 晶体的方法，但由于可扩展性有限、合成复杂性或最终材料的光自旋电子质量低，因此很难形成大面积和连续的薄膜。在这里，我们使用液相剥离（LPE）制成的晶体制备了范德华 2D 反铁磁材料 NiPS 的厘米级薄膜。我们通过这种基于油墨的制造来进行统计原子力显微镜（AFM）和扫描电子显微镜（SEM）来进行特性和控制横向尺寸和层数。使用低温超快光学光谱学，我们解析了光激发激子的动力学。我们发现反铁磁自旋排列和纠缠的 Zhang-Rice 多重激子，其寿命在纳秒范围内，尽管我们的薄膜具有无序性质，但发射线宽度非常窄。因此，我们的发现证明了高质量 NiPS 的可扩展薄膜制造，这对于将这种二维反铁磁材料转化为自旋电子学和纳米级存储设备以及进一步探索其复杂的自旋-光耦合状态至关重要。
