Thermal conductivity of two-dimensional (2D) materials has gained prominence due to the attractive applications in thermal management and thermoelectric devices. In this work, we present a new member of bilayer 2D boron allotropes, denoted as bilayer β₁₂ borophene, and study the thermal transport properties by solving phonon Boltzmann transport equation based on density functional theory. Based on quantitative chemical bonding analysis, we identify large degrees of covalent bonding of the interlayer interaction. In comparison to its monolayer counterpart, the bilayer exhibits much higher in-plane thermal conductivity despite the lower phonon group velocity and buckling structure, inferring a new physical mechanism. The thermal conductivity (κ) of bilayer β₁₂ borophene at 300 K is 140.5 (86.3) W·m⁻¹·K⁻¹ along armchair (zigzag) direction, and κ_armchair is about 52.7% higher than that of monolayer β₁₂ borophene. The abnormal enhancement is attributed to the suppressed phonon scattering possibility and elongation of phonon lifetime. More interesting, after forming bilayer β₁₂ borophene through interlayer covalent bonding, the dominated phonon branch to thermal conductivity changes to transverse acoustic phonons from out-of-plane flexural acoustic (ZA) phonons in the monolayer borophene. Our study elucidates the rich thermal transport characteristics in bilayer covalently bonded 2D materials, and injects fresh insights into the phonon engineering of 2D borophene relevant for emergent thermal management applications.

Recent studies have indicated that two-dimensional (2D) MoS₂ exhibits low in-plane and inter-plane thermal conductivities. This poses a significant challenge to heat management in MoS₂-based electronic devices. To address this challenge, we have designed MoS₂-graphene interfaces that fully utilize graphene, a 2D material that exhibits very high thermal conductivity. First, we performed ab initio atomistic simulations to understand bonding and structural stability at the interfaces. The interfaces that we designed, which were connected via strong covalent bonds between Mo and C atoms, were energetically stable. We then performed molecular dynamics simulations to investigate interfacial thermal conductance in these materials. Surprisingly, the interfacial thermal conductance was high and comparable to those of covalently bonded graphene-metal interfaces. Importantly, each interfacial Mo–C bond served as an independent thermal channel, enabling modulation of the interfacial thermal conductance by controlling the Mo vacancy concentration at the interface. The present work provides a viable heat management strategy for MoS₂-based electronic devices.

The thermal conductance across the one-dimensional (1D) interface between a MoS₂ monolayer and Au electrode (edge-contact) has been investigated using molecular dynamics simulations. Although the thermal conductivity of monolayer MoS₂ is 2–3 orders of magnitude lower than that of graphene, the covalent bonds formed at the interface enable interfacial thermal conductance (ITC) that is comparable to that of a graphene–metal interface. Each covalent bond at the interface serves as an independent channel for thermal conduction, allowing ITC to be tuned linearly by changing the interfacial bond density (controlling S vacancies). In addition, different Au surfaces form different bonding configurations, causing large ITC variations. Interestingly, the S vacancies in the central region of MoS₂ only slightly affect the ITC, which can be explained by a mismatch of the phonon vibration spectra. Further, at room temperature, ITC is primarily dominated by phonon transport, and electron–phonon coupling plays a negligible role. These results not only shed light on the phonon transport mechanisms across 1D metal–MoS₂ interfaces, but also provide guidelines for the design and optimization of such interfaces for thermal management in MoS₂-based electronic devices.

The quest for materials and devices that are capable of controlling heat flux continues to fuel research on thermal controlling devices. In this letter, using molecular dynamics simulations, we demonstrate that a partially clamped single-layer graphene can serve as a thermal modulator. The mismatch in phonon dispersion between the unclamped and clamped graphene sections results in phonon interface scattering, and the strength of interface scattering is tunable by controlling the clamp-graphene distance via applying the external pressure. Owing to the ultra-thin structure of graphene and its highly sensitive phonon dispersion to external physical interaction, the modulation efficiency—which is defined as the ratio of the highest to lowest heat flux—can reach as high as 150% at a moderate pressure of 50 GPa. This modulation efficiency can be further enhanced by arranging a number of clamps in series along the direction of the heat flux.

Using density functional theory calculations, we have investigated the mechanical properties and strain effects on the electronic structure and transport properties of molybdenum disulfide (MoS₂) nanotubes. At a similar diameter, an armchair nanotube has a higher Young's modulus and Poisson ratio than its zigzag counterpart due to the different orientations of Mo-S bond topologies. An increase in axial tensile strain leads to a progressive decrease in the band gap for both armchair and zigzag nanotubes. For armchair nanotube, however, there is a semiconductor-to-metal transition at the tensile strain of about 8%. For both armchair and zigzag nanotubes, the effective mass of a hole is uniformly larger than its electron counterpart, and is more sensitive to strain. Based on deformation potential theory, we have calculated the carrier mobilities of MoS₂ nanotubes. It is found that the hole mobility is higher than its electron counterpart for armchair (6, 6) nanotube while the electron mobility is higher than its hole counterpart for zigzag (10, 0) nanotube. Our results highlight the tunable electronic properties of MoS₂ nanotubes, promising for interesting applications in nanodevices, such as opto-electronics, photoluminescence, electronic switch and nanoscale strain sensor.