arXiv subjects

H. F. Feng

Publications and source records attributed to H. F. Feng.

6 recordsLinked to original sources

arXiv2025

Realization of Phonon FETs in 2D material through Engineered Acoustic Mismatch

Field-effect transistors (FETs) predominantly utilize electrons for signal processing in modern electronics. In contrast, phonon-based field-effect transistors (PFETs)-which employ phonons for active thermal management-remain markedly underdeveloped, with effectively reversible thermal conductivity modulation posing a significant challenge. Herein, we propose a novel PFET architecture enabling reversible thermal conductivity modulation. This design integrates a substrate in the central region with a two-dimensional (2D) material to form an engineered junction, exploiting differences in out-of-plane acoustic phonon properties to regulate heat flow. Molecular dynamics simulations of a graphene (Gr)/hexagonal boron nitride (h-BN) junction demonstrate a substantial thermal conductivity reduction up to 44-fold at 100 K. The effect is maintained at room temperature and across diverse substrates, confirming robustness. This work establishes a new strategy for dynamic thermal management in electronics.

physics.comp-ph↗

arXiv2025

Unusually Strong Four-Phonon Scattering Effects on Low-Temperature Thermal Conductivity in Two-Dimensional Materials

First principles-based predictions of lattice thermal conductivity (TC) from perturbation theory have achieved significant success. Usually, it only included three-phonon (3ph) scattering processes, only recently four-phonon (4ph) scattering processes were found to have a comparable impact as 3ph scattering at medium and high temperatures in various materials. While the influence of 4ph scattering on TC at low temperatures was generally believed to be insignificant. By combining the first-principles calculations, machine learning techniques, and Boltzmann transport equation (BTE), we find that there are unusually strong 4ph processes even in the low-frequency range of two-dimensional (2D) materials such as h-XN (X = B, Al, Ga), which have a remarkable influence on the low-temperature TC. Such strong 4ph processes originated from the out-of-plane acoustic (ZA) phonon mode of 2D materials. Furthermore, we find that the intensity of 4ph scattering and thus TC can be effectively manipulated by changing the dispersion of ZA phonon mode, which can be easily achieved through strain engineering. The present study provides new insights into low-temperature phonon transport and its manipulation in 2D materials.

cond-mat.mtrl-sci↗

arXiv2024

Exotic thermoelectric properties of coronene-cyclobutadienoid graphene nanoribbons

Thermoelectric materials traditionally incorporate heavy metals to achieve low lattice thermal conductivity. However, elements such as Te, Bi, and Pb are costly and pose environmental hazards. In this study, we introduce a novel design strategy for thermoelectric materials, focusing on room-temperature, light-element, and high-ZT materials such as coronene-cyclobutadienoid graphene nanoribbons (cor4GNRs). This material demonstrates a ZT value exceeding 2.1, attributed to its exceptionally low phonon thermal conductivity resulting from its unique edge structure. Importantly, its electrical conductance and Seebeck coefficient remain relatively high and nearly unaffected by the edge structure. This distinct behavior in phonon and electronic transport properties leads to a remarkably high ZT value. Additionally, we discover that applying strain can significantly reduce phonon thermal conductivity, potentially increasing the ZT value to over 3.0. Our findings provide innovative insights for the design and application of advanced thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2024

Nontrivial impact of interlayer coupling on thermal conductivity: opposing trends in in-plane and out-of-plane phonons

The study of heat transport in two-dimensional (2D) materials reveals novel behaviors due to quantum confinement effects, where in-plane and out-of-plane phonons play crucial roles. In 2D materials like graphene, it is widely recognized that the out-of-plane vibrational mode is the primary contributor to thermal conductivity owing to the mirror symmetry. Based on this perspective, the introduction of interlayer coupling, which breaks this symmetry, is expected to induce a significant reduction in thermal conductivity within 2D materials. Nevertheless, recent studies have presented unexpected findings, indicating that interlayer coupling can actually increase thermal conductivity of 2D materials. This controversial result suggests a nontrivial underlying mechanism governing the effects of interlayer coupling on thermal conductivity in 2D materials, necessitating further exploration. In our work, we investigate the modulation of thermal conductivity through interlayer coupling in a sandwich structure composed of hexagonal boron nitride (h-BN) and bilayer graphene (BG), specifically a h- BN/BG/h-BN system. Through molecular dynamics simulations, we find that the thermal conductivity from out-of-plane phonons can be significantly reduced, while that from in-plane phonons can be significantly increased, as the interlayer coupling strength increases. This results in a nontrivial, coupling-strength-dependent overall thermal conductivity. The phonon spectrum analysis conducted using our modified package reveals that the upshift and flattening of the out-of-plane (ZA and ZO) phonon modes are mainly responsible for these variations, and the extent of the upshift and flattening is proportional to the strength of interlayer coupling. This work offers new insights into manipulating the thermal conductivity of 2D materials.

cond-mat.mes-hall↗

arXiv2023

Stacking and Thickness Effects on Cross-Plane Thermal Conductivity of Hexagonal Boron Nitride

Recently, the in-plane thermal transport in van der Waals (vdW) materials such as graphene, hexagonal boron nitride (h-BN), and transition metal dichalcogenides (TMDs) has been widely studied. Whereas, the cross-plane one is far from sufficient. Based on the non-equilibrium molecular dynamics simulations and Boltzmann transport equation, here we reveal the stacking and thickness effects on the cross-plane thermal conductivity (K) of h-BN. We find that K can be significantly modulated by both the stacking structure and thickness (d) of h-BN, which is unexpected from the viewpoint of its smooth in-plane structure and weak interlayer interaction. In the small thickness region (d<6 nm), K of h-BN at room temperature significantly increases with thickness, following a power law of K ~ d^b with b=0.84, 0.66, and 0.92 for AA', AB, and AB' stacking structures, respectively. Moreover, K of AB' structure reaches up to 60% larger than that of AA' and AB structures with d=5.3 nm, showing the remarkable stacking effect. We also find that the stacking effect on K changes dramatically with d increasing, where AA' stacking has the largest K with d > 200 nm. We finally clarify that such exotic stacking and thickness dependence of K is owing to the competing effect of excited number of phonons and phonon relaxation time, both of which directly affect the thermal conductivity. Our findings may provide new insights into the cross-plane thermal management in vdW materials.

cond-mat.mtrl-sci↗

arXiv2023

Giant twist-angle dependence of thermal conductivity in bilayer graphene originating from strong interlayer coupling

Recently, the twist-angle effect on 2D van der Walls (vdW) materials, such as bilayer graphene, has attracted great attention. Many novel electronic, magnetic and even optical properties induced by such effect have been discovered. However, the twist-angle effect on phononic property is not so remarkable. By investigating the thermal conductivity of twist bilayer graphene (TBG), here we reveal that the trivial twist-angle effect on phononic property observed in previous studies is owing to the non-localization nature of phonons. This characteristic makes phonons hardly trapped by the weak interlayer potentials induced by the twist-angle dependent Moiré pattern. We propose that the twist-angle effect can be effectively enhanced by increasing the interface coupling. In use of a sandwich structure composed of h-BN and TBG, we demonstrate that the thermal conductivity of TBG can be either significantly increased or dramatically decreased, under the synergistic modulation of interlayer coupling strength and twist angle. Particularly, the twist-angle effect can lead to a nontrivial reduction of thermal conductivity up to 78% when a strong interlayer coupling is applied. The reduction is several times larger than that observed in the freestanding TBG where the reduction is attributed to the twist-angle dependent phonon scatterings induced by the edge phonons. The underlying mechanism for the giant twist-angle dependence of thermal conductivity is further revealed on the basis of phonon transport theory. Our findings provide a platform for achieving efficient twist-angle modulation on phonon transport property of vdW materials.

cond-mat.mes-hall↗