Ke-Min Li

Acoustic phonon transport in a four-channel quantum structure

The acoustic phonon transport in a four-channel quantum structure is investigated by use of the scattering matrix method. It is found that different acoustic phonon modes transport selectively into different channels, standing waves can be formed owning to acoustic phonons interfering with each other in the quantum structure, the transmission coefficients of acoustic phonon through different channels depend sensitively on the parameters of the structure, and the channels all exhibit the noninteger quantized thermal conductance at very low temperatures due to the splitting of the quantum structure. The structure may be used as a split device for acoustic phonon modes and controlling the acoustic phonon transport.

Ballistic thermal transport in a cylindrical semiconductor nanowire modulated with bridge contacts

Using the scattering-matrix method, we studied ballistic phonon transmission and thermal conductance at low temperatures in a cylindrical quantum wire with bridge contacts. The transmission coefficient exhibited a stepped profile, which became more evident as the bridge radius increased. When the dimensions of the bridge are identical to those of main wires, we observed a quantum platform of the thermal conductance, even in the presence of interface scattering. When the dimensions of the bridge are smaller than those of main wires, however, we could not observe the quantum platform. We also revealed other interesting physical properties, such as universal quantum thermal conductance and resonant transmission. A brief analysis of these results is given.

Ballistic thermal conductance by phonons through superlattice quantum-waveguides

Ballistic thermal conductances (BTCs) by phonons through superlattice quantum-waveguides are investigated by using the scattering-matrix method and the elastic continuum theory. A comparison for the cylindrical model (CM) and the rectangular model (RM) is addressed. We find that for these two models, the quantum thermal conductance can be observed even when the superlattices exist in quantum-waveguides. At low temperature, BTCs for the CM and the RM present almost the same behaviors regardless of the periodic length of superlattices. However, at higher temperature, BTCs for the RM are larger than those for the CM stemming from lower cutoff frequencies of high order modes for the RM. We also find that BTCs undergo a noticeable transformation from the monotonic decrease to constant with increasing the periodic number of superlattices. A brief analysis of these results is given.

Tunability of acoustic phonon transmission and thermal conductance in three dimensional quasi-periodically stubbed waveguides

We investigate acoustic phonon transmission and thermal conductance in three dimensional (3D) quasi-periodically stubbed waveguides according to the Fibonacci sequence. Results show that the transmission coefficient exhibits the periodic oscillation upon varying the length of stub/waveguide at low frequency, and the period of such oscillation is tunably decreased with increasing the Fibonacci number N. Interestingly, there also exist some anti-resonant dips that gradually develop into wide stop-frequency gaps with increasing N. As the temperature goes up, a transition of the thermal conductance from the decrease to the increase occurs in these systems. When N is increased, the thermal conductance is approximately decreased with a linear trend. Moreover, the decreasing degree sensitively depends on the variation of temperature. A brief analysis of these results is given.

Gibbs free energy approach to the prediction of melting points of isolated, supported, and embedded nanoparticles

By means of the thermodynamic and thermophysical properties of bulk materials, the Gibbs free energies for isolated, supported, and embedded nanoparticles were obtained and used to elucidate the sized-dependent melting phenomenon of the nanoparticles. To account for the substrate effect upon the melting point of nanoparticles, the interfacial energy of binary immiscible systems was studied in detail. It was found that the interfacial energy of a binary immiscible system including carbon can be replaced almost entirely by the contribution from carbon; thus, the reason why the melting model of isolated nanoparticles can be applied to research the melting of the supported nanoparticles was clarified. Moreover, a new approach to achieving the diameter of the smallest crystalline nanoparticles was proposed based on the melting behavior of embedded nanoparticles.

Ballistic thermal transport by phonons in three dimensional periodic nanostructures.

Ballistic thermal transport properties by phonons in three dimensional (3D) periodic nanostructures is investigated. Results show that thermal transport properties in 3D periodic nanostructures can be efficiently tuned by modulating structural parameters of systems. When the incident frequency is below the first cutoff frequency, the quasi/formal-periodic oscillations of the transmission coefficient versus the periodic number/length can be observed. When the incident frequency is above the first cutoff frequency, however, these quasi/formal-periodic oscillations cannot be observed. As the periodic number is increased, the thermal conductance undergoes a prominent transition from the decrease to the constant. We also observe other intriguing physics properties such as stop-frequency gaps and quantum thermal conductance in 3D periodic nanostructures. Some similarities and differences between 2D and 3D periodic systems are identified.