Molecular Simulation For The Thermal Transport Properties Of Low-dimensional Nanomaterials

The development of new nanomaterials and devices is an important part andtarget of nanotechnology. Nowadays, the low-dimensional nanomaterials such as:silicon nanowires, nanotubes and graphene, etc., have been attracting much attentionfor their unique structures and excellent compatibility with traditional technologies.Furthermore, they also exhibit great potential for application in the field of sensors,solar cells and recyclable energy storage system. However, the micro/nano devicesgenerally have the compact structure and the characteristics of high-performance,this will lead to more serious problem of heat transfer and heat radiation. Therefore,it is necessory to investigate the thermal transport properties of nanomaterials andobtain the heat transport mechanism in micro/nano materials to realize the control ofthermal transport properties of nanomaterials in the future. In this article, themolecular dynamics simulations are used to investigate the thermal transportproperties of low-dimensional nanomaterials in atomic scale, the conclusion of thisarticle will provide some reference values to slove the problem of heat radiation inthe future.Firstly, the structure of nanotubes are chosen to analyze the influence of somebasic factors on the thermal transport properties of low-dimensional nanomaterials.The results show that: under the effect of length, the thermal conductivities ofnanotubes increase with the increasing length, but the increasing trend is graduallyweakened. At low-temperature section, the molecular dynamics is invalid, thequantum corrections should been taken on it. Under the effect of temperature, thethermal conductivities of boron nitride nanotubes increases linearly firstly and thenbegins to drop obviously with the increase of temperature. Under the action ofstrain, the thermal conductivities of boron nitride nanotubes decreases with thegrowth of tensile or compressive strain respectively, but the decreasing mechanismsof two periods are different.Then, in order to analyze the influence of amorphization on the thermaltransport properties, the structure of nanowires is chosen for the investigation.Firstly, the effect of crystal oriention on the thermal transport properties of siliconnanowires is studied, the simulation results show that the thermal conductivities ofcrystal silicon nanowires show anisotropy. The order of the thermal conductivitiesof silicon nanowires with different crystal orientions is K_[110]> K_[111]> K_[112]> K_[100].Further, the structure of Si/a-Si core-shell nanowires which contain partlyamorphous structure is established, by analyzing the thermal transport properties ofSi/a-Si core-shell nanowires, the effect of amorphous silicon shell and core/shell interface is investigated: the amorphous silicon shell and the interface betweencrystal silicon core and amorphous silicon shell will reduce the thermalconductivities obviously and play a weaken role to the ballistic characteristics ofsilicon nanowires. Under the action of both amorphous silicon shell and core/shellinterface, Si/a-Si core-shell nanowires express significant non-propagation,diffusion thermal transport properties. At last, the thermal transport properties ofC/a-Si core-shell nanowires are studied to compare to the properties of Si/a-Sicore-shell nanowires: similar to that of Si/a-Si core-shell nanowires, the amorphoussilicon shell and core/shell interface in C/a-Si core-shell nanowires also play anegative role to the thermal conductivities and an enhance role to the diffusioncharacteristic, but the degree of change is weakened.Subsequently, the thermal transport properties of graphene and graphynenanoribbons which attracting much attention are investigated, the effect of length,width and chirality are respectively analyzed. The investigation on graphenenanoribbons shows that: the chirality play an important influence on the thermalconductivities of nanoribbons, the thermal conductivities of Armchair graphenenanoribbons are higher than that of Zigzag graphene nanoribbons. Bonding betweentwo graphene nanoribbons will play a weaken role to the thermal conductivities ofdouble graphene and the weaking degree is obvious. There are remarkabledifferences between thermal transport properties of graphyne and graphenenanoribbons, the investigations show that: the thermal conductivities of graphynenanoribbons are obviously lower than that of graphene nanoribbons. The thermalconductivities of graphyne nanoribbons decrease with the increasing atoms in carbonline. In contrast to graphene nanoribbons, the thermal conductivities of Zigzaggraphyne nanoribbons are higher than that of Armchair graphyne nanoribbons, andthere are some differences between the thermal conductivities trends with width ofgraphene and graphyne nanoribbons.Finally, for the thermal and mechanical properties of silicon nanofilm are poor,we use graphene which express excellent thermal and mechanical properties toenhance the properties of silicon nanofilm. By analyzing the thermal transportproperties of Gr/Si/Gr composite material, the effect of plusing other structure to themodel on the thermal transport properties of nanomaterials is investigated. Firstly,the properties of silicon nanofilm is changed by covering both sides with grapheneand the stable structure Gr/Si/Gr composite material is achieved. Then, byinvestigating the thermal transport properties of Gr/Si/Gr composite material, it isfound that: graphene can enhance the thermal transport properties and weaken theballistic characteristics of silicon nanofilm with small thickness. In this section,graphene play a decisive role to the thermal transport properties of Gr/Si/Grcomposite material. With the increase of the thickness of silicon nanofilm, the decisive role of graphene in Gr/Si/Gr composite material is weakened. When thethickness is large, graphene will play a weaken role to the thermal conductivities ofGr/Si/Gr composite material for the presence of interface between graphene andsilicon nanofilm.