Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Department of Physics, Hunan Normal University, Changsha 410081, Hunan, P. R. China.
Nanoscale. 2012 Apr 21;4(8):2748-53. doi: 10.1039/c2nr30095h. Epub 2012 Mar 15.
Surface energies of nanostructures are of considerable interest, and thermodynamic methods have provided valuable insight into the physics and chemistry of these systems. Although the effect of surface energy on melting behaviors of nanostructures has been widely investigated in theoretical calculations and simulations, from the thermodynamics at the nanometer scale point of view, the comprehensive understanding of the fundamental physical and chemical issues involved in nanostructures' melting is still lacking. For instance, nanostructures with negative curvature, such as nanotubes, show different melting behaviors compared with the nanostructures with positive curvature such as nanowires, and both nanotubes and nanowires exhibit abnormal melting temperature compared with that of the bulk counterparts. Herein, we put forward a general model to elucidate the melting temperature of the nanostructures with positive and negative curvatures based on the surface energy at the nanometer. Further, the surface mean square relative atomic displacement (MSRD) of these nanostructures has been studied from the perspective of the size-dependent cohesive energy consideration, which can provide the atomic understanding of the nanostructures' melting. Theoretical analyses indicate that both melting temperatures of the nanostructures with the positive and negative curvatures decrease with decreasing dimensionality, and the surface MSRDs show different size effects in the systems with the positive and negative curvatures, respectively. The melting temperature of the surface with the negative curvature is higher than that of the surface with the positive curvature, and both melting temperatures are smaller than that of the bulk counterpart when the size of nanostructures is less than a threshold value. The unique melting behaviors of nanostructures are attributed to the size- and curvature-dependent surface energy of nanostructures. These results provide new insight into the fundamental understanding of the melting temperature of nanostructures.
纳米结构的表面能具有重要意义，热力学方法为这些系统的物理和化学提供了有价值的见解。尽管表面能对纳米结构熔化行为的影响在理论计算和模拟中得到了广泛研究，但从纳米尺度的热力学角度来看，对涉及纳米结构熔化的基本物理和化学问题的综合理解仍然缺乏。例如，具有负曲率的纳米结构，如纳米管，与具有正曲率的纳米结构，如纳米线，表现出不同的熔化行为，并且纳米管和纳米线都表现出与体相比异常的熔化温度。在此，我们提出了一个基于纳米表面能的一般模型来阐明具有正曲率和负曲率的纳米结构的熔化温度。此外，还从尺寸相关的结合能考虑的角度研究了这些纳米结构的表面均方根相对原子位移（MSRD），这可以提供对纳米结构熔化的原子理解。理论分析表明，具有正曲率和负曲率的纳米结构的熔化温度都随维度的降低而降低，并且在具有正曲率和负曲率的系统中，表面 MSRD 分别表现出不同的尺寸效应。具有负曲率的表面的熔化温度高于具有正曲率的表面的熔化温度，并且当纳米结构的尺寸小于阈值时，两者的熔化温度都小于体的熔化温度。纳米结构的独特熔化行为归因于纳米结构的尺寸和曲率依赖的表面能。这些结果为理解纳米结构的熔化温度提供了新的见解。
