Department of Mechanical and Aerospace Engineering, Rutgers University , Piscataway, New Jersey 08854, United States.
ACS Nano. 2016 Nov 22;10(11):10563-10572. doi: 10.1021/acsnano.6b06583. Epub 2016 Nov 8.
The relative stability and melting of cubic boron nitride (c-BN) nanoparticles of varying shapes and sizes are studied using classical molecular dynamics (MD) simulation. Focusing on the melting of octahedral c-BN nanoparticles, which consist solely of the most stable {111} facets, decomposition is observed to occur during melting, along with the formation of phase segregated boron clusters inside the c-BN nanoparticles, concurrent with vaporization of surface nitrogen atoms. To assess this MD prediction, a laser-heating experiment of c-BN powders is conducted, manifesting boron clusters for the post-treated powders. A general analysis of the geometrical and surface dependence of the nanoparticle ground-state energy using a Stillinger-Weber potential determines the relative stability of cube-shaped, octahedral, cuboctahedral, and truncated-octahedral c-BN nanoparticles. This stability is further examined using transient MD simulations of the melting behavior of the differently shaped nanoparticles, providing insights and revealing the key roles played by corner and edge initiated disorder as well as surface reconstruction from {100} to the more stable {111} facets in the melting process. Finally, the size dependence of the melting point of octahedral c-BN nanoparticles is investigated, showing the well-known qualitative trend of depression of melting temperature with decreasing size, albeit with different quantitative behavior from that predicted by existing analytical models.
采用经典分子动力学（MD）模拟研究了不同形状和尺寸的立方氮化硼（c-BN）纳米粒子的相对稳定性和熔化。重点研究了由最稳定的{111}面组成的八面体 c-BN 纳米粒子的熔化，在熔化过程中观察到分解，同时在 c-BN 纳米粒子内部形成了相分离的硼簇，伴随着表面氮原子的蒸发。为了评估 MD 预测，对 c-BN 粉末进行了激光加热实验，在经过后处理的粉末中表现出硼簇。使用 Stillinger-Weber 势对纳米粒子基态能量的几何形状和表面依赖性进行的一般分析确定了立方体形、八面体形、十二面体形和截角八面体形 c-BN 纳米粒子的相对稳定性。通过对不同形状的纳米粒子熔化行为的瞬态 MD 模拟进一步研究了这种稳定性，提供了见解，并揭示了在熔化过程中，由角和边缘引发的无序以及从{100}到更稳定{111}面的表面重构在熔化过程中起着关键作用。最后，研究了八面体 c-BN 纳米粒子的熔点随尺寸的依赖性，表现出与现有分析模型预测的不同的定量行为，但具有已知的定性趋势，即随尺寸减小而降低熔点。
