School of Mechanical Engineering and Materials and Nanotechnologies Program, Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
Nanotechnology. 2012 Dec 14;23(49):495603. doi: 10.1088/0957-4484/23/49/495603. Epub 2012 Nov 16.
Self-assembled α-FeSi(2) nanoislands were formed using solid-phase epitaxy of low (1.2 ML) and high (21 ML) Fe coverages onto vicinal Si(111) surfaces followed by thermal annealing. At a resulting low Fe-covered Si(111) surface, we observed in situ, by real-time scanning tunneling microscopy and surface electron diffraction, the entire sequence of Fe-silicide formation and transformation from the initially two-dimensional (2 × 2)-reconstructed layer at 300 °C into (2 × 2)-reconstructed nanoislands decorating the vicinal step-bunch edges in a self-ordered fashion at higher temperatures. In contrast, the silicide nanoislands at a high Fe-covered surface were noticeably larger, more three-dimensional, and randomly distributed all over the surface. Ex situ x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy indicated the formation of an α-FeSi(2) island phase, in an α-FeSi(2){112} // Si{111} orientation. Superconducting quantum interference device magnetometry showed considerable superparamagnetism, with ~1.9 μ(B)/Fe atom at 4 K for the low Fe-coverage, indicating stronger ferromagnetic coupling of individual magnetic moments, as compared to high Fe-coverage, where the calculated moments were only ~0.8 μ(B)/Fe atom. Such anomalous magnetic behavior, particularly for the low Fe-coverage case, is radically different from the non-magnetic bulk α-FeSi(2) phase, and may open new pathways to high-density magnetic memory storage devices.
使用固相外延技术，在晶向为（111）的硅表面分别以低（1.2 ML）和高（21 ML）的铁覆盖度生长，然后进行退火处理，形成了自组装的α-FeSi(2)纳米岛。在低铁覆盖的 Si(111)表面，我们通过实时扫描隧道显微镜和表面电子衍射原位观察到，在 300°C 时，最初二维（2×2）重构层的整个 Fe 硅化物形成和转变序列，以及在较高温度下以自组装方式装饰倾斜阶跃堆边缘的（2×2）重构纳米岛。相比之下，在高铁覆盖的表面上，硅化物纳米岛明显更大、更三维、且随机分布在整个表面。非原位 X 射线光电子能谱和高分辨率透射电子显微镜表明形成了一个α-FeSi(2)岛相，具有α-FeSi(2){112} // Si{111}取向。超导量子干涉仪磁强计显示出相当大的超顺磁性，在 4 K 时低铁覆盖的情况下每个 Fe 原子约有 1.9 μB，表明单个磁矩的铁磁耦合更强，而高铁覆盖的情况下，计算出的磁矩仅为每个 Fe 原子约 0.8 μB。这种异常的磁行为，特别是在低铁覆盖的情况下，与非磁性体相α-FeSi(2)截然不同，可能为高密度磁性存储器件开辟新途径。
