Shanghai Applied Radiation Institute, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, People's Republic of China.
Inorg Chem. 2012 Aug 6;51(15):8473-8. doi: 10.1021/ic301046z. Epub 2012 Jul 17.
Results on Al-induced crystallization of amorphous Ge (a-Ge) deposited by vacuum thermal evaporation techniques under thermal annealing in N(2) atmosphere are presented in detail. The a-Ge crystallization and fractal Ge pattern formation on the free surface of annealed Al/Ge bilayer films deposited on single-crystal Si (100) substrates were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive X-ray spectrometry (EDS), and Raman spectra. It is found that the temperature field effects play an extremely crucial role in a-Ge crystallization and fractal Ge formation process. The open branched structure of fractal Ge clusters in Al/Ge bilayer films was effectively prepared by Al-induced crystallization when they were annealed at 400 °C for 60 min. These films with fractal Ge clusters exhibit charming noninteger dimensional nanostructures, which differ from those of conventional integer dimensional materials such as one-dimensional nanowires/nanorods, nanotubes, nanobelts/nanoribbons, two-dimensional heterojunctions, thin films, and zero-dimensional nanoparticles. The SEM image shows that a big Al grain was found located near the center of a fractal Ge cluster after the films were annealed at 400 and 500 °C for 60 min. This suggests that the grain boundaries of polycrystalline Al films are the initial nucleation sites of a-Ge. It also validates the preferred nucleation theory of a-Ge at triple-point grain boundaries of polycrystalline Al at the interface. This discovery may be explained by the metal-induced nucleation (MIN) mechanism.
详细介绍了在氮气气氛下热退火时，通过真空热蒸发技术沉积的非晶锗(a-Ge)的铝诱导结晶的结果。通过扫描电子显微镜 (SEM)、X 射线衍射 (XRD)、原子力显微镜 (AFM)、能谱 (EDS) 和拉曼光谱研究了单晶 Si (100) 衬底上沉积的退火 Al/Ge 双层膜自由表面上的 a-Ge 结晶和分形 Ge 图案形成。结果发现，温度场效应对 a-Ge 结晶和分形 Ge 形成过程起着至关重要的作用。当在 400°C 下退火 60 分钟时，通过铝诱导结晶可以有效地制备双层膜中的分形 Ge 簇的开叉分支结构。这些具有分形 Ge 簇的薄膜具有迷人的非整数维纳米结构，与传统的整数维材料（如一维纳米线/纳米棒、纳米管、纳米带/纳米带、二维异质结、薄膜和零维纳米颗粒）不同。SEM 图像显示，在薄膜退火 400 和 500°C 60 分钟后，在分形 Ge 簇的中心附近发现了一个大的 Al 晶粒。这表明多晶 Al 薄膜的晶界是非晶态 a-Ge 的初始形核部位。这也验证了界面处多晶 Al 三点晶界处 a-Ge 的优先形核理论。这一发现可以用金属诱导形核（MIN）机制来解释。
