Fractal Germanium Patterns: Annealing Strategies and Perspectives of Metal-Induced Crystallization

Abstract

Semiconductor germanium (Ge) in contact with some metals, such as Al, Pd, and Au, etc., is a class of distinctive materials with non-integer dimensions (D) that differ from integer dimensional materials, such as nanoparticles (0D), nanowires/nanorods//nanotubes/nanoribbons (1D), and thin films (2D). In this article, we describe our efforts toward understanding the annealing strategies and perspectives of metal-induced crystallization for the amorphous Ge embedded in Al, Pd, and Au matrices prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the Al-induced crystallization of amorphous Ge and formation processes of fractal Ge patterns. In addition, the fractal Ge patterns induced by Pd nanoparticles with solid-state reactions will be summarized in detail. Temperature-dependent properties of resistance and fractal dimension in Pd/Ge bilayer films will be expounded. In particular, the nonlinear optical properties are discussed in detail. Finally, we will emphasize the in situ observations by transmission electron microscopy and multi-fractal analysis for the fractal Ge patterns induced by Au nanoparticles. Moreover, the polycondensation-type fractal Ge patterns with non-integer dimensions, thick branches and smooth edges, and metastable gamma-Au_0.6Ge_0.4 are further investigated. The computer simulation indicated that the experimental results are good agreement with the simulation patterns, which were carried out by a ripening mechanism of non uniform grains. This review may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices.

Keywords:

• germanium
• amorphous
• annealing
• metal-induced crystallization
• fractal pattern
• aluminum
• palladium
• gold
• microstructure
• nanostructure

FUNDING

The work described in this article was financially supported by the National Natural Science Foundation of China (Project Numbers: 11074161, 11025526 and 41073073), Shanghai Pujiang Program (Project Number: 10PJ1404100), Key Innovation Fund of Shanghai Municipal Education Commission (Project Number: 10ZZ64), Science and Technology Commission of Shanghai Municipality (Project Numbers: 10JC1405400, 09530501200), and Shanghai Leading Academic Discipline Project (Project Number: S30109). This work was also supported by a grant from City University of Hong Kong (Grant Number: 9667074).