Study On The Growth Of Single-Wall Carbon Nanotubes Promoted By Chalcogens

Single-wall carbon nanotube(SWCNT)can be imagined to be a seamless hollow cylinder that is rolled up from a graphene sheet.SWCNTs show excellent physical and chemical properties and wide-range application prospects.Bulk preparation of highquality SWCNTs with controllable structures is essential for their real applications.Floating catalyst chemical vapor deposition(FCCVD)is one of the most efficient techniques for obtaining SWCNTs in large scale,where growth promoter plays an important role.In this thesis,the working mechanism of chalcogen growth promoters,including oxygen(O),sulfur(S),selenium(Se)and tellurium(Te)are studied.And the structural characteristics of the SWCNTs obtained using these promoters are compared and analyzed.Isolated,high purity semiconducting SWCNTs(s-SWCNTs)were selectively grown using S and O as co-promoters.The main results obtained are as follows:(1)Controllable synthesis of SWCNTs using Se as a growth promoter and its working mechanism.High purity,high quality SWCNTs with a narrow diameter distribution(1.7-1.9 nm)were prepared using Se as a growth promoter.The amount of Se required was only about a quarter of S,and the carbon conversion efficiency can be as high as 24.9%.In situ transmission electron microscopy(TEM)study showed that Se-doped iron(Fe)was the high-temperature stable phase.Combined with theoretical simulations,the working mechanism of Se was proposed as:① increasing carbon diffusion rate;②promoting C-C bond formation;③ reducing the bonding energy between SWCNTs and catalysts.A high-performance SWCNT/germanium(Ge)heterojunction photodetector was constructed by using the prepared SWCNTs with a narrow diameter distribution.(2)Controlled growth of SWCNTs promoted by O and Te and analysis on the working mechanism of chalcogen promoters.Under optimized conditions,isolated,short SWCNTs were prepared using O as a growth promoter;while large diameter SWCNTs were obtained when Te was used as a promoter.The distributions of O,S,Se and Te elements in iron catalyst was investigated.In addition,the structural characteristics of the SWCNTs obtained were compared and analyzed,based on which the working mechanisms of chalcogen elements were proposed.(3)Growth of isolated s-SWCNTs by using S and O as growth promoters.We developed a FCCVD technique using S and O as co-growth promoters.Thanks to the synergetic effect of S and O,high-quality isolated s-SWCNTs were prepared under optimized growth condition.The working mechanisms of S and O were elucidated:S has a strong ability to promote the growth of SWCNT,while O inhibits the aggregation of catalyst nanoparticles and selectively etches m-SWCNT.A thin film field effect transistor was constructed using the as-prepared isolated s-SWCNT network as a channel material.