Dhara Soumen, Imakita Kenji, Giri P K, Fujii Minoru
Opt Lett. 2014 Jul 1;39(13):3833-6. doi: 10.1364/OL.39.003833.
We report on the lattice strain dependence of the nonlinear optical (NLO) parameters of strained Si nanoparticles (NPs), which are prepared in a controlled way by a mechanical ball milling process. X-ray diffraction analysis shows that the nature of strain is compressive and is primarily caused by milling-induced lattice dislocations, which is further supported by high-resolution transmission electron microscopy imaging. It is found that the nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) are strongly influenced by the associated lattice strain present in Si NPs. With the increase of lattice strain, the β gradually decreases while n₂ increases slowly. The strain-dependent observed changes in the NLO parameters of Si NPs are found to be advantageous for application purpose, and it is explained on the basis of strain-induced modification in the electronic structure of the highest occupied molecular orbital and lowest unoccupied molecular orbital states of Si NPs. These results demonstrate the potential of strain-dependent enhancement of nonlinearities for silicon photonics applications.
我们报道了通过机械球磨工艺以可控方式制备的应变硅纳米颗粒（NPs）的非线性光学（NLO）参数与晶格应变的关系。X射线衍射分析表明，应变的性质是压缩性的，主要由研磨诱导的晶格位错引起，高分辨率透射电子显微镜成像进一步证实了这一点。研究发现，非线性折射率（n₂）和非线性吸收系数（β）受到硅纳米颗粒中相关晶格应变的强烈影响。随着晶格应变的增加，β逐渐减小，而n₂缓慢增加。发现硅纳米颗粒NLO参数中与应变相关的观测变化对于应用目的是有利的，并基于应变诱导的硅纳米颗粒最高占据分子轨道和最低未占据分子轨道状态的电子结构变化进行了解释。这些结果证明了应变依赖性增强非线性特性在硅光子学应用中的潜力。
