HEAT TRANSFER THROUGH HYDROGENATED GRAPHENE SUPERLATTICE NANORIBBONS: A COMPUTATIONAL STUDY

Optimization of thermal conductivity of nanomaterials enables the fabrication of tailor-made nanodevices for thermoelectric applications. Superlattice nanostructures are correspondingly introduced to minimize the thermal conductivity of nanomaterials. Herein we computationally estimate the effect of total length and superlattice period ( lp ) on the thermal conductivity of graphene/ graphane superlattice nanoribbons using molecular dynamics simulation. The intrinsic thermal conductivity ( ) is demonstrated to be dependent on lp . The of the superlattice, nanoribbons decreased by approximately 96% and 88% compared to that of pristine graphene and graphane, respectively. By modifying the overall length of the developed structure, we identified the ballisticdiffusive transition regime at 120 nm. Further study of the superlattice periods yielded a minimal thermal conductivity value of 144 W m− 1 k− 1 at lp = 3.4 nm. This superlattice characteristic is connected to the phonon coherent length, specifically, the length of the turning point at which the wave-like behavior of phonons starts to dominate the particle-like behavior. Our results highlight a roadmap for thermal conductivity value control via appropriate adjustments of the superlattice period

Model for melting transition of twisted DNA in a thermal bath

We investigated the melting transition of deoxyribonucleic acid (DNA) embedded in a Langevin fluctuation–dissipation thermal bath. Torsional effects were taken into consideration by introducing a twist angle $$\varphi$$ between neighboring base pairs stacked along the molecule backbone. We use the Barbi–Cocco–Payrard model to numerically study the impact of the twist angle on the melting temperature, considering four different sequences composed of 69 base pairs. According to the outcomes of our simulation, for all heterogeneous sequences, an increase in twist angle leads to a linear rise in melting temperature with a positive slope. For angles greater than the so-called equilibrium angle, the DNA chain becomes very rigid against opening and accordingly high temperatures are required to initiate the melting process. We also investigate the opening probability of bubbles, the bubble lifetime profiles and bubble length along the different DNA sequences

Thermal rectification in polytelescopic Ge nanowires

Herein we served non-equilibrium molecular dynamics (NEMD) approach to simulate thermal rectification in the mono- and polytelescopic Ge nanowires (GeNWs). We considered mono-telescopic structures with different Fat-Thin configurations (15-10 nm-nm or Type (I); 15-5 nm-nm or Type (II); and 10–5 or Type (III) nm-nm) as generic models. We simulated the variation of thermal conductivity against interfacial cross-sectional temperature as well as the direction of heat transfer, where a higher thermal conductivity correlating to thicker nanowires, and a more significant drop (or discontinuity) in the average interface temperature in the positive (or negative) direction were detected. Noticeably, interfacial thermal resistance followed the order of Type (II) (48 K/μW, maximal) ˃ Type (III) ˃ Type (I) (5 K/μW, minimal). In the second stage, a series of polytelescopic nanostructures of GeNWs were born with consecutive cross-sectional interfaces. Surprisingly, larger interfacial cross-sectional areas equivalent to smaller diameter changes along the GeNWs were responsible for higher temperature rectification. This led to a very limited thermal conductivity loss or a very high unidirectional heat transfer along the polytelescopic structures - the key for manufacturing next generation high-performance thermal diodes.24 month embargo; available online: 13 June 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

AN INSIGHT INTO THERMAL PROPERTIES OF BC3-GRAPHENE HETERO-NANOSHEETS: A MOLECULAR DYNAMICS STUDY

Simulation of thermal properties of graphene hetero-nanosheets is a key step in understanding their performance in nano-electronics where thermal loads and shocks are highly likely. Herein we combine graphene and boron-carbide nanosheets (BC3N) heterogeneous structures to obtain BC3N-graphene hetero-nanosheet (BC3GrHs) as a model semiconductor with tunable properties. Poor thermal properties of such heterostructures would curb their long-term practice. BC3GrHs may be imperfect with grain boundaries comprising non-hexagonal rings, heptagons, and pentagons as topological defects. Therefore, a realistic picture of the thermal properties of BC3GrHs necessitates consideration of grain boundaries of heptagon-pentagon defect pairs. Herein thermal properties of BC3GrHs with various defects were evaluated applying molecular dynamic (MD) simulation. First, temperature profles along BC3GrHs interface with symmetric and asymmetric pentagon-heptagon pairs at 300 K, ΔT= 40 K, and zero strain were compared. Next, the efect of temperature, strain, and temperature gradient (ΔT) on Kaptiza resistance (interfacial thermal resistance at the grain boundary) was visualized. It was found that Kapitza resistance increases upon an increase of defect density in the grain boundary. Besides, among symmetric grain boundaries, 5–7–6–6 and 5–7–5–7 defect pairs showed the lowest (2 × ­10–10 m2 K ­W−1) and highest (4.9× ­10–10 m2 K ­W−1) values of Kapitza resistance, respectively. Regarding parameters afecting Kapitza resistance, increased temperature and strain caused the rise and drop in Kaptiza thermal resistance, respectively. However, lengthier nanosheets had lower Kapitza thermal resistance. Moreover, changes in temperature gradient had a negligible efect on the Kapitza resistanc