Lihong Liang

Size-dependent thermal conductivity of nanoscale semiconducting systems

We study the size dependence of thermal conductivity in nanoscale semiconducting systems. An analytical formula including the surface scattering and the size confinement effects of phonon transport is derived. The theoretical formula gives good agreements with the existing experimental data for Si and

Size-dependent elastic modulus of Cu and Au thin films

\mathrm{GaAs}

The size-dependent phonon frequency of semiconductor nanocrystals

nanowires and thin films.

Size-dependent melting depression and lattice contraction of Bi nanocrystals

Abstract A model for size-dependent elastic modulus of Cu and Au thin films is established based on consideration of size-dependent atomic distance and bond energy. The predictions of the model for the enhancement of the elastic modulus of Cu and Au thin films correspond to the results of computer simulations well.

Size-dependent interface energy

A model, without adjustable parameters, describing the size-dependent phonon frequency of semiconductor nanocrystals is established based on the size-dependent force constant and thus the size-dependent bond length and bond energy of nanocrystals. This model shows frequency shifts as the size of the crystals decreases. Our predictions agree with the results of experiments for the blue shift of TiO2 nanoparticles, Si and InP quantum dots. The model will be useful for understanding the origins of the phonon behaviour of nanocrystals and the effect of the thermodynamic parameters on the phonon frequency.

Melting enthalpy depression of nanocrystals based on surface effect

Abstract Several models, free of any adjustable parameters, for the size-dependent melting temperature and the size-dependent lattice contraction of nanocrystals and related solid–liquid interface energy are introduced and compared with the newest experimental results of Bi nanocrystals. It is found that the models may interpret the experimental results well.

Thermal conductivity of composites with nanoscale inclusions and size-dependent percolation

A universal and analytic thermodynamic model without any adjustable parameters was established to elucidate the interface energy of multilayers at the nanometer scale by taken the size effect, the interfacial orientation, and the interfacial mismatch into account. Theoretical predictions were consistent with the calculations of the modified analytical embedded atom method and the experimental data, implying that the proposed thermodynamic model could be expected to be a general approach on nanoscale to understand interface energy in binary systems.

Thermodynamic superheating of low-dimensional metals embedded in matrix

Takagi was the first to demonstrate that ultrafine metallic particles melt below their corresponding bulk melting temperature in 1954 [1]. Now it is known that the melting temperatures of all nanocrystals, including metals [2, 3], semiconductors [4, 5] and organic nanocrystals [6, 7], depend on their size and this has been explained in terms of various models related to interface energy [8]. This size effect is experimentally also observed on the melting enthalpy [2, 6]. However, none of the above models can interpret sizedependent melting enthalpy of nanocrystals directly [8]. Knowledge of thermodynamic parameter are important for complete understanding of melting transition of nanocrystals and will deepen our insight into the size effect on melting. Therefore, a direct consideration on the size-dependence of melting enthalpy is needed. In this contribution, a simple physical model for the size-dependent melting enthalpy of nanocrystals in terms of the effect of bond number and bond energy of surface atoms of nanocrystals and that of the corresponding liquids on the internal energy of the system is developed. Combining with Mott’s expression for the vibrational entropy of melting for metallic crystals, size-dependent melting temperature of metallic nanocrystals is also predicted. The model predictions correspond well to the latest experimental results of indium nanocrystals. We consider that size-dependent melting enthalpy H (r ) is additive where r denotes radius of nanoparticles and nanowires, or half thickness of thin films,

Size-dependent elastic modulus and vibration frequency of nanocrystals

An analytical model for thermal conductivity of composites with nanoparticles in a matrix is developed based on the effective medium theory by introducing the intrinsic size effect of thermal conductivity of nanoparticles and the interface thermal resistance effect between two phases. The model predicts the percolation of thermal conductivity with the volume fraction change of the second phase, and the percolation threshold depends on the size and the shape of the nanoparticles. The theoretical predictions are in agreement with the experimental results.

Size-dependent interface phonon transmission and thermal conductivity of nanolaminates

A simple model for size-dependent melting temperature and melting entropy of nanocrystals embedded in a matrix is introduced to interpret the superheating phenomenon. The model predicts not only melting temperature and the melting entropy increase for embedded nanocrystals as the size of the nanocrystals decreases, but also melting temperature and the melting entropy depression for free-standing nanocrystals with reducing size. The model is supported by available experimental results of nanoparticles and thin films.