Research on Boron Nitride Nanotube’s Doping and Its Thermoelectric Properties

Author:Zhuang Zuo Zuo

Supervisor:liu xiao wei


Degree Year:2019





As a Ⅲ-Ⅴnaomaterial,boron nitride nanotubes(BNNTs)have unique physical and chemical properties,which enable them to become one of the most widely studied nanomaterials in recent years.In addition to excellent high temperature thermal stability and high chemical stability,researches show that BNNTs have a high Seebeck coefficient,adjustable electrical properties and lower thermal conductivity than that of CNTs,which makes BNNTs have great application prospects in the fields of nanoelectronics,thermoelectricity and composite materials.However,BNNTs as a wide band gap semiconductor need to be doped to adjust the electrical characteristics.In terms of the doping of BNNTs,there are several problems,for example,the synthesis technology is complex and low yields;the doping amount can’t be controlled.Both the theoretical analysis and the experimental study of thermoelectric characteristics for BNNT are in a blank state.Therefore,it is of great significance to carry out research on BNNT doping and thermoelectric properties.In this paper,the theoretical modeling related to the thermoelectric properties of BNNT is carried out.Based on this,the thermoelectric properties of BNNT films are adjusted by doping method,which is used to verify The theoretical model.And the thermoelectric properties of BNNTs based composites are studied.The thermoelectric theoretical model of BNNT thin film is established.Since BNNT and contact junction between nanotubes is the two main factors that makes up the thin film,the influences of these two factors on Seebeck coefficient and conductivity are considered respectively.And the contribution of contact junction and BNNT to the thermoelectric parameters of the film is comprehensively analyzed.The effects of doping concentration on thermoelectric parameters were studied.The results show that with the increase of carbon content,the Seebeck coefficient of BNNT films decreases,and the conductivity increases.Based on the preparation of BNNTs by ball milling,the growth mechanism of BNNTs prepared by ball milling was studied.The effect of catalyst mass ratio,gas flow rate,reaction time and reaction temperature on the yield and morphology of BNNTs were analyzed.The experimental results show that the catalyst mass ratio mainly affects the quality and yield of BNNTs;the reaction gas flow rate mainly affects the morphology of the nanotubes;and the annealing time has little effect on the size and morphology of the nanotubes,while the reaction gas flow rate mainly affects the morphology of the nanotubes.Annealing temperature mainly affects the diameter distribution range of nanotubes.The doping of BNNTs is achieved by thermal annealing.The effects of process parameters,such as input time of dopant source,annealing temperature and type of dopant source,on the morphology and doping content of BNNTs were studied.The results show that the thermal annealing post-treatment method improves the doping efficiency and the yield of doped BNNTs,and can achieve carbon or silicon doping and carbon/silicon co-doping.Different concentrations of doping can be achieved by controlling process parameters.Theversatility of the method is verificated by multi-element doping.The study results of electrical properties show that the doped BNNTs are p-type semiconductors.In view of the problem that the thermoelectric properties of BNNT and its composites are still in the blank state,the thermoelectric properties of BNNT films and their composites are studied in this paper.The c-doped and si-doped BNNT films are taken as the research objects,respectively.The influence of doping concentration on the thermoelectric parameters of nanotube films is analyzed and the correctness of the thermoelectric theoretical model of bnnt thin films is verified by experiments.In order to improve the thermoelectric properties,the composites constructed by BNNT/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid(PEDOT:PSS)were prepared.And their thermoelectric properties were studied.The results show that with the increase of BNNT content,the conductivity increases at initially and decreases afterwards,while the Seebeck coefficient increases monotonously,but the trend of increase gradually becomes lower.When the content of BNNT is 14.7wt%,the Seebeck coefficient is the largest,up to 38.67μV/K,which is 93.35% higher than that of the untreated PEDOT:PSS film(20.0μV/K).The Seebeck coefficient of the composite membrane decreases as the carbon content of the BNNTs increases.In this paper,the research results provide guidance for further research on the thermoelectric property of BNNTs,and lay a foundation for the application of BNNTs in a foundation nanodevices research and thermoelectric fields.