Kumari Satchi, Singh Dilip K, Giri P K
Department of Physics, Indian Institute of Technology, Guwahati 781039, India.
J Nanosci Nanotechnol. 2009 Sep;9(9):5231-6. doi: 10.1166/jnn.2009.1138.
Although embedded Ge nanocrystals (NCs) have been grown by variety of techniques and its properties have been studied extensively, intrinsic properties of isolated Ge NCs have not been studied properly due to lack of proper synthesis technique. Here we report on the synthesis of freestanding Ge nanoparticles (NPs) down to approximately 7 nm using ball milling technique and study its structural evolution as a function of milling time. Morphology and microstructure of the freestanding Ge NPs are studied using atomic force microscopy, transmission electron microscopy and X-ray diffraction (XRD) analysis. A systematic study of the XRD line profile using Williamson-Hall method reveals presence of anisotropic strain in the milled NPs. Strain anisotropy factor is calculated using a modified Williamson-Hall method by taking into consideration a dislocation contrast factor, assuming that dislocations are main contributors to the strain in these NPs. Our calculations suggest that screw type dislocations are main contributors to the strain anisotropy in the Ge NPs. We find that for milling time up to 40 hrs, NPs size monotonically goes down to approximately 7.3 nm and then almost saturates, while the dislocation density first increases from 1.64 x 10(16) m(-2) to 11.62 x 10(17) m(-2) for milling time up to 20 hrs and then decreases drastically during further milling. We have monitored a low temperature heat release at approximately 310 degrees C from the milled NPs using differential scanning calorimetry, clearly indicating a kind of structural relaxation of the strained NPs.
尽管通过多种技术已经生长出了嵌入式锗纳米晶体（NCs），并且对其性质进行了广泛研究，但由于缺乏合适的合成技术，孤立锗纳米晶体的固有性质尚未得到恰当研究。在此，我们报告了使用球磨技术合成出尺寸低至约7纳米的独立锗纳米颗粒（NPs），并研究了其作为球磨时间函数的结构演变。使用原子力显微镜、透射电子显微镜和X射线衍射（XRD）分析对独立锗纳米颗粒的形态和微观结构进行了研究。使用威廉姆森 - 霍尔方法对XRD线轮廓进行的系统研究揭示了研磨后纳米颗粒中存在各向异性应变。通过考虑位错对比度因子，采用改进的威廉姆森 - 霍尔方法计算应变各向异性因子，假设位错是这些纳米颗粒中应变的主要贡献者。我们的计算表明，螺旋型位错是锗纳米颗粒中应变各向异性的主要贡献者。我们发现，对于长达40小时的球磨时间，纳米颗粒尺寸单调下降至约7.3纳米，然后几乎饱和，而位错密度在长达20小时的球磨时间内首先从1.64×10¹⁶ m⁻²增加到11.62×10¹⁷ m⁻²，然后在进一步球磨过程中急剧下降。我们使用差示扫描量热法监测到研磨后的纳米颗粒在约310℃有低温热释放，清楚地表明了应变纳米颗粒的一种结构弛豫。
