Study On The Thermal Conductivity And Thermal Rectification Of MoS₂ Films

The control and management of heat transfer is a key goal and direction in energy utilization,and a important research in the thermal management of solid-state devices is the thermal rectification phenomenon.In this paper,the experimental measurement and comparison of the thermal conductivity of single-layer and multi-layer MoS2 films are focused.The two-phase transition,their thermal conductivity and the thermal rectification effect of MoS2 films are also discussed.Firstly,in order to measure the thermal conductivity of the MoS2 films,this work conducted a research on experimental instruments for the measurement of thermal conductivity of low-dimensional materials,and set up a related experimental system.Then standard micron platinum wire was used to verify this system by suspended microelectrodes.Moreover,a bamboo-like polymer nanotube was measured with this system.Its extremely low thermal conductivity indicates that the material is a novel thermal insulation material,and the synthesis method can be used to fabricate thermal insulation nanotubes.Through theoretical calculations,the ratio of the outer diameter of the polymer nanotube to the hole is the key factor in determining the thermal insulation performance.The smaller outer diameter and larger hole ratio result in smaller thermal conductivity and better thermal insulation performance.Combined with theoretical calculation and experimental analysis,the applicability of the system to the thermal conductivity of micro-nano materials is verified.Secondly,the single-layer MoS2 sample was successfully transferred to the suspended microelectrode by PMMA approach Then,the suspended microelectrode supporting the single-layer MoS2 sample was further energized and heated,and the thermal conductivity of the sample was obtained through experiments.The thermal rectification coefficient of the single-layer MoS2 was obtained.The rectification coefficients of the single-layer MoS2 with three different geometric structure were 10%～13%,11%～14%and 69～70%,respectively.In addition,theoretical models were used to discuss the dependence of thermal rectification on geometric asymmetry(angle and spacing).The results show that the thermal rectification effect of single layer MoS2 is positively correlated with its structural asymmetry.The greater the angle is,the greater the thermal rectification coefficient will be.Next,this article conducted a comparative study of thermal conductivity on the single-layer and multi-layer MoS2 samples.The suspended microelectrodes were used to measure the thermal conductivity of MoS2 films,and the thermal rectification coefficient was obtained.Combined with calculations,the difference between the thermal conductivity and thermal rectification effect of single-layer and multi-layer MoS2 films were studied.In addition,the samples were cut by focused ion beam technology to obtain three samples with the same layer and different angles.The relationship between the thermal rectification coefficient and geometric asymmetry was studied on the samples with three different angles.The results demonstrated that the thermal conductivity of the single-layer film was greater than that of the multilayer film,and both of them decreased with the increasing temperature and the number of layers.While the thermal rectification coefficient increased with the increasing angle,and is almost independent of the temperature and the number of layers.Finally,this paper studies the thermal conductivity and thermal rectification effect of the two phases based on the phase transition of MoS2.Herein,suspended microelectrodes were used to measure the thermal conductivity of the 1T and 2H phases of the same sample.The thermal rectification effect of two-phase MoS2 was also obtained according to the thermal conductivity in the opposite directions.The results show that as the temperature increases,the thermal conductivity of both IT and 2H MoS2 decreases,and the thermal conductivity of the 1T phase is slightly greater than that of the 2H phase.It is also found that the thermal rectification coefficient had no obvious correlation with the phase transition,but is related to their asymmetric structure.In addition,this paper proposes a design method of thermal rectifier and thermal transistor,and gives the corresponding heat flow output characteristic curve.By adjusting the phase,size,and structural asymmetry of different samples,the direction of the heat flow can be effectively controlled,and the directional management and control of the heat flow can also be realized.