Si/$_x$/Ge $_{1-x}$纳米线中Al的可逆传播
Reversible Al Propagation in Si$_x$Ge$_{1-x}$ Nanowires
摘要：
虽然可逆性是热力学中的一个基本概念，但大多数反应都不容易可逆，特别是在固态物理学中。例如，热扩散是一种广为人知的概念，尤其用于将掺杂剂原子注入基质中的取代位置并改善器件特性。通常，这种扩散过程将产生在越来越大的区域上延伸的浓度梯度，而不可能逆转这种效应。另一方面，虽然半导体纳米线的自底向上生长是有趣的，但仍然难以制造具有高度控制的轴向异质结构。在本文中，我们报告了一个可逆的热扩散过程中发生的固态交换反应之间的Al金属垫和Si $_x$ Ge $_{1-x}$合金纳米线的原位透射电子显微镜观察。热辅助反应导致产生夹在反应的Al和未反应的SixGe 1-x部分之间的富Si区域，形成轴向Al/Si/Si $_x$ Ge $_{1-x}$异质结构。在加热或（缓慢）冷却时，Al金属可重复地移入和移出Si $_x$ Ge $_{1-x}$合金纳米线，同时保持棒状几何形状和结晶度，从而允许在单个工艺步骤中以可逆方式制造和接触纳米线异质结构，与当前的基于Si的技术兼容。这个有趣的系统是有前途的各种应用，如相变存储器中的全晶体系统与集成的接触，以及Si/Si $_x$ Ge $_{1-x}$ /Si异质结构的近红外传感应用。
英文摘要：
While reversibility is a fundamental concept in thermodynamics, most reactions are not readily reversible, especially in solid state physics. For example, thermal diffusion is a widely known concept, used among others to inject dopant atoms into the substitutional positions in the matrix and improve the device properties. Typically, such a diffusion process will create a concentration gradient extending over increasingly large regions, without possibility to reverse this effect. On the other hand, while the bottom up growth of semiconducting nanowires is interesting, it can still be difficult to fabricate axial heterostructures with high control. In this paper, we report a reversible thermal diffusion process occurring in the solid-state exchange reaction between an Al metal pad and a Si$_x$Ge$_{1-x}$ alloy nanowire observed by in-situ transmission electron microscopy. The thermally assisted reaction results in the creation of a Si-rich region sandwiched between the reacted Al and unreacted SixGe1-x part, forming an axial Al/Si/Si$_x$Ge$_{1-x}$ heterostructure. Upon heating or (slow) cooling, the Al metal can repeatably move in and out of the Si$_x$Ge$_{1-x}$ alloy nanowire while maintaining the rod-like geometry and crystallinity, allowing to fabricate and contact nanowire heterostructures in a reversible way in a single process step, compatible with current Si based technology. This interesting system is promising for various applications, such as phase change memories in an all crystalline system with integrated contacts, as well as Si/Si$_x$Ge$_{1-x}$/Si heterostructures for near-infrared sensing applications.
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