Molecular Dynamics Simulation Study On The Structure And Thermal Properties Of Platinum Nanowires

As an important member of nanomaterials，noble metal nanowires possess uniquephysical properties,which are very different from bulk materials or the othernanomaterials. Owing to the excellent electrical, optical, magnetic and thermalproperties, noble metal nanowires have drawn great interests from the Scientists indifferent countries because of the potential applications of nanostructure in sensors,catalysts and microelectronic device. Nowadays, For the experimentation, one of themost challenging works is to control the size and morphology of the nanowires, whichthe thermal stability are also studied a lot in applications. The nanowires’ propertieswere highly related to their own size and geometries. For example, the meltingtemperatures of nanowires are decreased with the reduction of their diameters, leadingto strong size effects. And novel helical cylindrical multishell structures have beenidentified both theoretically and experimentally. Therefore， to study the thermalproperties of noble metal nanowires and the effects of size and structures are essentialfor the preparation and fabrication in their various areas of applications.In this paper, we will employ molecular dynamics simulations with an embeddedatom potential to investigate the structural and thermal properties of Pt nanowires as atype of noble metal nanowires. The works mainly contain the following three aspects:The first part is to study the dependence of the solidification behavior behaviors of Ptnanowires on the cooling rate; the second is to study the thermal stability and thestructural evolution of Pt nanowires along the [100],[110]and[111] crystallographicorientations during the solution annealing; the third is to study the novel structures andthermal stability of Pt nanowires under the critical diameter size.The results of simulation mainly involve as following:â‘´We found that the cooling rate has great effect on the final structure of thegoldnanowires during solidification from liquid. At the very fast cooling rate, the Ptnanowires exhibit amorphous structure. With the decrease of cooling rates, the finalstructure of the Pt nanowires changes from amorphous to crystalline via helicalmulti-shelled structure.⑵Through analyzing the radial distribution function of Pt nanowires at300Kcooled at the different cooling rates. It is found that this novel helical multi-shelledstructure possesses the short-range ordering and long-range disordering of amorphous structure. At the cooling rate of k₅=5×10¹²ks, The results of simulation indicate thatthe ordering degree of Pt nanowires increases while the temperature decreasing, as theobvious jump implies the structural transition.⑶To employ simulated annealing algorithm to process the Pt nanowires orientedin the [100],[110],and [111]directions, it is found that the final nanowires have thesimilar microstructure，and the [110] nanowires have the better structure stability andthermal stability than the others.â‘·To adopt molecular dynamic simulation to study the structure characteristics andmelting behavior of Pt nanowires, the stable helical multishell structures are obtained.Then we calculate their melting temperatures, which show clear dependence on wiresizes and structures. The melting temperatures generally decrease accompanied withdiameter reduced.⑸In order to further describe the thermal stability and melting behavior of Ptnanowires, we employ the Lindemann index to scale the properties quantitatively. Oursimulated results verify that inhomogeneous premelting behavior starts in the interior ofhelical structures and expands gradually outside. But the bulk-like structures performthe opposite direction.