Preparation Of Carbon Nanotube/Metal Composite Materials By Magnetron Sputtering And Investigation Of Their Mechanical And Electrical Properties

During the past few decades,carbon nanotube(CNT)/metal composite materials have fascinated the worldwide research community and researchers with their phenomenal mechanical,electrical and thermal properties,and CNT/metal composites have become a booming candidate for the next generation of conductor materials.However,the preparation of CNT/metal composites with excellent comprehensive properties had encountered many major challenges,such as the effective stress transmission within the composite material,the transportation of electrons,the peeling of the interface between the metal and the CNT and other scientific problems.These problems showed a dependence on the interface structure.Therefore,through design the interface between CNT and metal,it becomed one of the reliable ways to prepare CNT/metal composites with excellent comprehensive properties.In this paper,different metals were deposited on the surface of the CNT to study the nucleation model and influencing factors,and establish the nucleation of metals on the surface of CNT.Then the CNT/Cu composite films and CNT/Al-Cu composite fibers with excellent properties were prepared though interface design and regulation.Subsequently,the microstructure of the composite was characterized by X-ray diffractometer,scanning electron microscope and transmission electron microscope,and its conductivity,tensile strength and fatigue properties were analyzed and tested.Finally,the effects of different interface structures on the properties of composites and their strengthening mechanism were systematically studied.The detailed research contents and the main outcomes were summarized as follows:(1)Study on the interface between CNT and metals:The effects of metal types,deposition rates,deposition thickness,CNT diameter and alloying on the nucleation of the metal on the CNT surface were systematically studied.It is found that there were mainly three nucleation modes:particle growth,island growth and film growth.There are three factors that affect the metal nucleation:the energy of metal atoms before they were deposited on the CNT surface(E_v),the binding energy between metal and CNT(E_b),and the diffusion energy of metal atoms on the CNT surface(E_diff).The E_v was mainly determined by deposition process,which can be changed by process selection and parameter adjustment.The E_b was determined by the type of metal,and different metals have different Eb,which can be improved by alloying.The E_diff was directly proportional to E_b,generally about 1/4 of E_b(E_b/4?E_diff).In the metal nucleation mode,with the E_b+E_v gradual increased,the nucleation model changed from particle growth to film growth.During the deposition process,the nucleation of metal on the CNT surface can be improved by adjust the deposition rate,deposition time and alloying.(2)CNT/Cu composite films:The effects of interface microstructure and annealing temperature on the electrical properties of CNT/Cu composite films were systematically studied.The results showed that the stability and the resistivity of the CNT/Cu film was better than pure Cu film,its resistivity reach 4.15??·cm after600?annealing.The stability and low resistivity of CNT/Cu films were better than that of pure Cu films.The CNT/Cu films reached to lowest resistivity of 6??·cm after annealed at 600°C,and keeps low resistivity after annealed at 700°C.This is mainly due to two kinds of interface structure formed between CNT and Cu.The first kind is(111)planes of Cu parallel to(002)planes of the CNT,the other type is a covetic interface structure formed by C atoms diffusing into Cu grains.These epitaxial interfaces reduce the contact resistance and promote the formation of a local ballistic conductor between CNT and Cu with low electron scattering,resulting in a reduced electrical resistivity.Then the flexible composite films were prepared with layered composite structure and cyclic bending tests were carried out.It was found that CNT/Cu composite films have very high fatigue properties and.exhibited history-independent cyclic bending response.The high dense wrinkling of composite film becomed the dominant cyclic deformation behavior.The cracks initiation and formation were voided by the wrinkling process releasing the bending stress.The resistivity of composite film no longer increase even if the number of cycle reached as high as 10⁵.This result provided us a novel insight to design nanoscale metal films with ultrahigh fatigue resistance and superior service ability.(3)CNT/Al-Cu composite fiber:In order to improve the interface bonding force between CNT fiber and Cu layer,an ultra-thin Al layer was introduced between CNT fiber and Cu layer as a transition layer.After annealing,the Al atoms and Cu atoms diffused into the carbon nanotube fiber to form diffuse interface and chemical reaction interface,leading to the sliding resistance increase and contact resistance decrease between CNT.It achieved a simultaneous improving in conductivity and strength.Subsequently,the CNT/Al-Cu composite fiber was densified,and the CNT/Al-Cu-R fiber with ultra-high strength and electrical conductivity.The strength and elasticity modulus of composite reached as high as 6.6 and 500 GPa,respectively,while a high conductivity of 1.8×10⁷ S/m was maintained.This can be attributed to the diffusion of Cu and Al atoms into the carbon nanotube fiber,which enhances friction between the CNT by“pinning”and“bridging”.This structure provided us with novel insights into the design of CNT/metal nanocomposites with ultrahigh strength and conductivity.