Real-Time Visualization of Convective Transportation of Solid Materials at Nanoscale

Abstract

Convective transportation of materials in the solid state occurring in a prototype solid bilayer system of Al and Si with negligible mutual solubility has been directly imaged in real time at nanoscale using a valence energy-filtered transmission electron microscope. Such solid-state convection is driven by the stress gradient developing in the bilayer system due to the amorphous to crystalline phase transformation of the Si sublayer. The process is characterized by compression experienced in the Si phase crystallizing within the Al sublayer, as well as by the development of mushroom-shaped "plumes" of Al nanocrystals in the Si sublayer as a result of compressive stress relaxation and discrete, new nucleation of crystalline Al. The real-time, atomistic observation and the thus-obtained fundamental understanding of solid-state convection enable highly sophisticated applications of such a complex process in advanced fabrication and processing of nanomaterials and solid-state devices.

Direct synthesis of multilayer graphene on an insulator by Ni-induced layer exchange growth of amorphous carbon

“…In the field of group-IV semiconductors including Si, [27][28][29][30][31] Ge, [32][33][34][35] and SiGe, 36,37 metal-induced layer exchange (MILE) allows large-grained (>30 lm) highly oriented thin films to be formed on insulators. In MILE, an amorphous semiconductor layer crystallizes by "layer exchange" between the amorphous layer and a catalyst metal layer.…”

- Introduction to Metal-Induced Crystallization

“…As a result of both effects, Al tends to migrate toward the free-volumerich, tensilely stressed Si layer (in situ XRD stress measurements have indicated [12,15], indeed, the relaxation of the compressive stress in the Al phase during MIC). Thus, the Al layer is gradually "replaced" by the c-Si grains growing inside it, and the Al migrates to the original location of the a-Si layer, as revealed by the development of convective Al "plumes" comprising many Al nanocrystals (see Fig.…”

“…Amorphous semiconductors such as silicon and germanium can crystallize at a temperature much lower than their "bulk" crystallization temperatures when they are put in direct contact with a metal, such as Al [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], Au [18][19][20][21][22], Ag [23][24][25], Ni [26][27][28][29][30][31][32][33], Cu [34][35][36], and Pd [37,38]. This phenomenon, which was firstly observed more than 40 years ago for amorphous germanium [39], is now commonly referred to as metal-induced crystallization (MIC) [40][41][42][43].…”

“…On the one hand theoretical modeling of the (interface) thermodynamics was performed by employing the macroscopic atom approach [10,11,44]. On the other hand dedicated, in particular in situ heating high-resolution transmission electron microscopy (HRTEM) and valence energyfiltered transmission electron microscopy (VEFTEM), experiments were performed to reveal the operating atomistic mechanisms [14,15]. It has been found that MIC is in general an interface-controlled phenomenon [10,11,14,40].…”

Effects of gold‐induced crystallization process on the structural and electrical properties of germanium thin films

“…Therefore, MIC method is the most promising method to obtain high quality poly‐Ge films at temperatures much lower than those required in the absence of a metal catalyst. In MIC, Al, Au, and Ag have been used as the catalyst metals for crystallizing α ‐Ge films. These metals can lower the crystallization temperature of α ‐Ge films by forming eutectic alloy during thermal annealing .…”