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Bulk vs nanoscale WS2: Finite size effects and solid-state lubrication

机译:批量与纳米级WS2:有限的尺寸效应和固态润滑

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摘要

To investigate phonon confinement in nanoscale metal dichalcogenides, we measured the low-temperature specific heat of layered and nanoparticle WS2. Below 9 K, the specific heat of the nanoparticles deviates from that of the bulk counterpart. Further, it deviates from the usual T (3) dependence below 4 K due to finite size effects that eliminate long wavelength acoustic phonons and interparticle-motion entropy. This separation of nanoscale effects from T-3 dependence can be modeled by assuming that the phonon density of states is flexible, changing with size and shape. We invoke relationships between the low-temperature T (3) phonon term, Young's modulus, and friction coefficient to assess the difference in the tribological properties. On the basis of this analysis, we conclude that the improved lubrication properties of the nanoparticles are extrinsic.
机译:为了研究声子限制在纳米级金属二卤化物中,我们测量了层状纳米颗粒WS2的低温比热。低于9 K,纳米粒子的比热与本体的比热有所偏差。此外,由于消除了长波长声子和粒子间运动熵的有限尺寸效应,它偏离了4 K以下通常的T(3)依赖性。可以通过假设状态的声子密度是灵活的,随尺寸和形状变化而建模的,从而将纳米级效应与T-3依赖性隔离开来。我们调用低温T(3)声子项,杨氏模量和摩擦系数之间的关系,以评估摩擦学性质的差异。基于该分析,我们得出结论,纳米颗粒的改善的润滑性能是非固有的。

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