New light shed on the origin of plasticity in nanostructured silicon
How does nanostructured silicon deform has been the subject of a long-standing debate over the past decade. Now recent research from a team of scientists led by Dr. Zhidan Zeng from HPSTAR clarifies that pressure-induced phase transitions play a key role in the plastic deformation of compressed silicon nanoparticles. Their findings are reported in Physical Review Letters (DOI: 10.1103/PhysRevLett.124.185701).
Caption: A schematic diagram showing the experimental setup and the different mechanisms of plasticity in relative large and small silicon nanoparticles.
硅材料是微电子产业最重要的基础材料，也是整个现代信息社会的基石。随着集成电路的特征线宽不断降低，对硅材料的高精度加工早已从宏观尺寸跨入了纳米尺寸。因此，硅在纳米尺度的机械性能对于集成电路工业具有越来越重要的意义, 在过去十几年吸引了大量的理论和实验研究。众所周知，晶体硅是一种典型的脆性材料。有趣的是，科学家却在各种硅纳米材料中观察到了明显的压应力诱导塑性形变, 但是过去的研究对于这种塑形形变的机理却长期存在争议。最近，北京高压科学中心的研究小组利用高压原位同步辐射径向X射线衍射技术精确测定了硅纳米颗粒发生塑性形变过程中的应力、应变和原子结构变化, 从而澄清了其塑性的微观机理，相关成果以“Origin of Plasticity in Nanostructured Silicon”为题发表于近期的《物理评论快报》（DOI: 10.1103/PhysRevLett.124.185701）上。
Diamond can be amorphous: from scenario to reality
AUGUST 22, 2017 — A team led by HPSTAR scientist, Dr. Zhidan Zeng synthesizes a new form of carbon—“amorphous diamond”—under high pressure and temperature (HPHT). This bulk amorphous diamond obtained under HPHT can be maintained to ambient conditions for potential applications, realizing possible the hardest amorphous (glass) material ever discovered. This work is recently published as an article by Nature Communications (Synthesis of quenchable amorphous diamond. Nature Communications, 2017).
金刚石是天然存在的硬度最高的材料，同时还具有最高的弹性模量（体模量），最高的原子密度、最高的热导率等优异性质。这些优异性能和其特殊结构有关。本研究采用玻璃碳（glassy carbon）作为起始材料，利用高压原位激光加温技术首次成功合成了块体状的100% sp3 共价键的新型非晶态碳材料。通过同步辐射x 射线衍射、高分辨电子显微镜及电子能量损失谱等多种实验手段，一致证明这种新型碳材料具有典型非晶态结构，且材料内部所有碳原子间的共价键都是sp3 键，因而是真正的“非晶态金刚石”。非晶态金刚石的合成说明金刚石并不是唯一的全部碳原子都以sp3 键结合的碳材料，改变了我们对碳材料的传统认知。“非晶态金刚石”由于其无序的原子结构而具备非晶材料各向同性的特点，且材料内部不存在晶界、位错等传统晶体缺陷，又因高强度sp3 共价键的存在而很可能具备接近甚至超越单晶金刚石的优异性能（高压原位同步辐射x 射线衍射实验已经证实其体模量高于金刚石），作为一种新型的超硬材料，可能在众多科学技术领域取得重要应用。
Lithiation-inducedstress in Li-ion batteries from micro-Raman Spectroscopy
Stress is along standing challenge for the applications of silicon(Si) anodesin lithium(Li)ion batteries. Using in situ micro Raman spectroscopy, a team ofscientists led by Dr. Zhidan Zeng at the Center for High Pressure Science &Technology Advanced Research (HPSTAR) measured the stress in siliconnanoparticles in a working Li-ion battery for the first time. This new studywould be helpful in understanding how the nanostructured silicon anodesfracture during battery operation, and therefore provide guidance for theirfuture design.
