硅量子点结合能的尺寸和形状效应

Size and Shape Effects of Silicon Quantum Dot Cohesive Energy

【目的】分析硅量子点的尺寸和形状对其结合能的影响。【方法】采用密度泛函理论第一性原理的方法,计算了不同尺寸、形状的硅量子点结合能。【结果】随着体系内原子数的增多,硅量子点结合能基本上呈现增大的趋势,这与纳米材料结合能的尺寸效应一致。然而,这种尺寸效应也会受到形状的影响。引入形状因子λ,研究发现在等尺寸的情况下,四面体形状(TH)的硅量子点结合能总是小于中心四面体对称(TC)的硅量子点,二者的结合能也都小于八面体形状(OT)的硅量子点。在一些硅量子点上出现原子数小的硅量子点其结合能反而大于原子数大的硅量子点,其原因是因为原子数小的硅量子点具有较大的形状因子。另外,硅量子点体系中氢硅比(氢原子与硅原子的比值),即n(H)/n(Si),能够同时反映硅量子点的尺寸、形状参数,硅量子点结合能与氢硅比的线性关系进一步证明了硅量子点的尺寸、形状效应。

【Purposes】It aims to analyze the effect of the size and shape of silicon quantum dots on their binding energy.【Methods】The cohesive energy of silicon quantum dots with different sizes and shapes is calculated by using the method of density functional theory first principles.【Findings】The calculation results show that the cohesive energy of silicon quantum dots basically exhibits shows an increasing trend with the increase of atom number in the system,which is consistent with the size effect of the cohesive energy of nanomaterials.However,this size effect is also influenced by shape.By introducing a shape factorλ,it is found that the cohesive energy of tetrahedron(TH)silicon quantum dots is always smaller than that of tetrahedron-centered symmetric(TC)silicon quantum dots at equal sizes,and the cohesive energy of both is also smaller than that of octahedron(OT)silicon quantum dots.In some silicon quantum dots,the cohesive energy of silicon quantum dots with smaller atomic number is larger than that of silicon quantum dots with larger atomic number because the silicon quantum dots with smaller atomic number have larger shape factor.In addition,the ratio of hydrogen atoms to silicon atoms in the silicon quantum dot system,i.e.,n(H)/n(Si),can reflect the size and shape parameters of silicon quantum dots at the same time.The linear relationship between the cohesive energy of silicon quantum dots and the ratio of hydrogen atoms to silicon atoms further proves the size and shape effects of silicon quantum dots.