Temperature and rate-dependent formation of metastable silicon- Dr. Chuanlong Lin

OCTOBER 10, 2020

New work from a team of scientists led by Dr. Chuanlong Lin from HPSTAR revealed two distinctive transition pathways, a thermally-activated crystal-crystal transition and a mechanically-driven amorphization, in the structural evolution of high-pressure metallic β-Sn silicon (Si-II) under rapid decompression at various temperatures. The study is published in the recent issue of Physical Review Letters.

Metastable silicon also has shown promising electrical properties as its ambient stable form for using as semiconductors. These metastable allotropes can be synthesized from its high-pressure metallic phase via decompression, depending on temperature, decompression rate (or strain rate), stress, etc. However, the underlying mechanisms governing the different transformation paths still remain unclear.

The team utilized in situ time-resolved x-ray diffraction to probe the structure evolution of Si-II toward the metastable silicon under decompression. The researchers found that under slow decompression, Si-II transformed to a metastable crystalline phase in the pressure range of 4.3-9.2 GPa, while Si-II collapsed mechanically to an amorphous form at around 4.3 GPa when the volume expansion approaches a critical strain via rapid decompression beyond a threshold rate.

Caption:  Temperature- and decompression rate-dependent transtion pathways in Si-II.

"The thermophysical factors including decompression rate, activation barrier and temperature coupled together to affect the transformation paths and the end products,” explained Dr. Lin.

"Our study provides deep insight into understanding the formation conditions and is of fundamental significance in controlled synthesis of the desirable metastable silicon phases for practical use.”

近日，由北京高压科学研究中心林传龙研究员带领的国际研究小组利用时间分辨X射衍射技术提示了Si-II的两种不同的相变动力学过程和转变机理：一是在缓慢卸压过程中由热激发引起的晶体到晶体相变；另一种是在快速卸载过程由晶格发生机械坍塌引起的高压金属硅的非晶化。相关研究以“Temperature-and Rate-Dependent Pathways in Formation of Metastable Silicon Phases under Rapid Decompression”发表在近日的《物理评论快报》上。