Structural Evolution of Q-Carbon and Nanodiamonds
Structural Evolution of Q-Carbon and Nanodiamonds
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DOI：
10.1007/s11837-017-2714-y
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发表时间：
2018-04-01
期刊：
影响因子：
2.6
通讯作者：
Narayan, Jagdish
中科院分区：
文献类型：
--
作者：
Gupta, Siddharth;Bhaumik, Anagh;Narayan, Jagdish
本文深入探讨了通过纳秒激光熔化和淬火类金刚石碳（DLC）薄膜来生长致密堆积的Q - 碳和纳米金刚石所涉及的一级相变。具有不同sp³含量的DLC薄膜在过冷状态下以可控方式快速熔化并淬火，从而形成了不同的纳米结构，即纳米金刚石、Q - 碳和Q - 碳纳米复合材料。这一分析为过冷度对Q - 碳结构演变的依赖性提供了直接证据。有限元热流计算表明，过冷度随sp³含量单调变化。详细研究了从熔化状态定向凝固过程中固 - 液界面不稳定性现象。由此产生的横向偏析导致了胞状丝状Q - 碳纳米结构的形成。基于微扰理论，对不稳定性开始时的胞尺寸和波长对DLC薄膜sp³含量的依赖性进行了建模。
This article provides insights pertaining to the first-order phase transformation involved in the growth of densely packed Q-carbon and nanodiamonds by nanosecond laser melting and quenching of diamond-like carbon (DLC) thin films. DLC films with different sp 3 content were melted rapidly in a controlled way in super-undercooled state and quenched, leading to formation of distinct nanostructures, i. e., nanodiamonds, Q-carbon, and Q-carbon nanocomposites. This analysis provides direct evidence of the dependence of the super-undercooling on the structural evolution of Q-carbon. Finite element heat flow calculations showed that the super-undercooling varies monotonically with the sp 3 content. The phenomenon of solid-liquid interfacial instability during directional solidification from the melt state is studied in detail. The resulting lateral segregation leads to formation of cellular filamentary Q-carbon nanostructures. The dependence of the cell size and wavelength at the onset of instability on the sp 3 content of DLC thin films was modeled based on perturbation theory.