First Principles Study Of Carbon Nanotube Gas Adsorption And Low Pressure Sensing Mechanism

Carbon nanotubes?CNTs?have excellent electronic,optical and mechanical properties,and their gas adsorption properties have great application potential in gas storage,sensing,field emission and other fields.In this thesis,a first-principles calculation was used to study the adsorption on the capped,open-tip,capped with defect,non-defective,and defective tube wall of armchair?5,5?CNTs,and analyze the characteristics of structure,adsorption energy,work function,density of states,and charge transfer for CNTs adsorption.Field emission experiments related to gas adsorption of carbon nanotubes were carried out in vacuum environment.The conclusion is as follows:The non-defective capped structure exhibits semiconductor property,and the defective capped structure shows semi-metallic property.Chemisorption of hydrogen,oxygen,and nitrogen gas molecules at the defect site can convert semi-metallic property to semiconducting property.Oxygen and nitrogen can be physically adsorbed at the single vacancy defect site on the capped CNT,while the physisorption of hydrogen is unstable.These gas molecules can be chemically adsorbed at the defect site.Chemisorption of hydrogen molecule and atom reduces the work function of carbon nanotube,while chemisorption of oxygen molecule and atom increases the work function.Chemisorption of nitrogen is able to prevent the chemisorption of oxygen and carbon nanotubes,and protect the defects of carbon nanotubes.The chemisorption of atomic nitrogen can fill in the missing carbon atom at the defect site,form a nitrogen-doped CNT,and reduce the work function significantly.The different locations of the defects at the capped end could affect the work function of CNTs.Defects in the tube wall can increase the conductivity of the CNTs bundle.The external electric field can increase the physisorption energy of gas molecules,affect the adsorption form of H₂O and change the adsorption site of argon.