Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA, USA.
Nanotechnology. 2010 Dec 17;21(50):505707. doi: 10.1088/0957-4484/21/50/505707. Epub 2010 Nov 23.
The amorphous to crystalline phase transformation process is typically known to take place at very high temperatures and facilitated by very high compressive stresses. In this study, we demonstrate crystallization of amorphous ultra-thin platinum films at room temperature under tensile stresses. Using a micro-electro-mechanical device, we applied up to 3% uniaxial tensile strain in 3-5 nm thick focused ion beam deposited platinum films supported by another 3-5 nm thick amorphous carbon film. The experiments were performed in situ inside a transmission electron microscope to acquire the bright field and selected area diffraction patterns. The platinum films were observed to crystallize irreversibly from an amorphous phase to face-centered cubic nanocrystals with average grain size of about 10 nm. Measurement of crystal spacing from electron diffraction patterns confirms large tensile residual stress in the platinum specimens. We propose that addition of the externally applied stress provides the activation energy needed to nucleate crystallization, while subsequent grain growth takes place through enhanced atomic and vacancy diffusion as an energetically favorable route towards stress relaxation at the nanoscale.
非晶相向晶相的转变过程通常发生在非常高的温度下，并在非常高的压缩应力下得到促进。在这项研究中，我们证明了在拉伸应力下，室温下非晶态超薄铂膜的结晶。使用微机电设备，我们在由另一个 3-5nm 厚的非晶碳膜支撑的 3-5nm 厚的聚焦离子束沉积的铂膜中施加高达 3%的单轴拉伸应变。实验是在透射电子显微镜内原位进行的，以获得明场和选区衍射图案。铂膜从非晶态不可逆地结晶为面心立方纳米晶体，平均晶粒尺寸约为 10nm。从电子衍射图谱测量晶体间距证实了铂样品中存在大的拉伸残余应力。我们提出，外加应力的施加提供了形核结晶所需的激活能，而随后的晶粒生长则通过增强原子和空位扩散来进行，这是纳米尺度下应力松弛的能量有利途径。
