Facile Preparation And Field Emission Properties Of Vertical Graphene Nanosheets And Nanodiamond Films

In recent years,carbon nanomaterials/nanostructures have been widely used in electronic devices,new energy applications,new materials and bio-medicine,due to their abundant and unique physical properties,chemical properties and favorable biological compatibility.As two representative kinds of carbon nanomaterials/nanostructures,vertical graphene nanosheets?VGNs?and nanodiamond films both have good field emission performance owing to the high height width ratio of VGNs and low/negative electron affinity of nanodiamond films.Therefore,it can be applied as a new generation of cold cathode field emission display.Vertical graphene nanosheets and nanodiamond films are synthesized by plasma enhanced chemical vapor deposition system?CVD?or hot filament CVD normally employing carbon?C?-containing gases as precursors.However,these methods exist many problems,such as the relatively complicated operation,and high cost especially for the PECVD system,the usage and storing of the precursor gases normally with hazardous natures,and poor scalability of growth.To solve the above problems,we develop a thermal chemical growth technology that are capable of growing vertical graphene nanosheets and/or nanodiamond films through adjusting precursor components and various experimental parameters.In this thesis,the main contents are as follows:1.The research background and status of VGNs and nanodiamond films were briefly introduced.The main preparation methods and functional properties of these two carbon nanomaterials/nanostructures were summarized.The research significance,contents,testing and characterization methods of this work were also described.2.Synthesis of VGNs using methane?CH₄?as the precursor was developed by thermal CVD.Through optimizing the experimental parameters including the pretreatment temperature of catalyst films,growth temperature and pressure,the well aligned VGNs with uniform morphologies on nickel-coated stainless steel were realized and the growth mechanism was discussed.In addition,the field emission measurement indicated that the VGNs exhibited relatively good field emission properties and stable field emission with a turn-on electric field strength of⁴.5 V/?m?defined at the current density of 10?A/cm²?,and a field enhancement factor of¹802.3.In order to further optimize the preparation of VGNs,glucose and urea were respectively used as carbon source and dopant.Through optimizing the experimental parameters including the surface roughness of SS,growth temperature and time,the patterned nitrogen?N?-doped VGNs with uniform morphologies on stainless steel were realized.It was interesting that VGNs mainly grown on the roughened regions,which can be attributed to the more nucleation and catalyzing sites on such regions than smooth SS.Meanwhile,the field emission measurement indicated that the appropriate N doping?¹.86 at.%?significantly improved the field emission properties of VGNs.The obtained N-doped VGNs exhibited excellent field emission properties with a relatively low turn-on electric field strength of².6 V/?m?defined at the current density of 10?A/cm²?,a large field enhancement factor of⁹428,and a stable field emission of more than 6.5 h at electric field strength of 7.0 V/?m.4.Through optimizing the experimental parameters including thickness of the catalyst films,growth temperature and time,intrinsic and N-doped nanodiamond films were successfully grown on nickel-coated stainless steel just by thermal chemical growth in a resistance-heating furnace using glucose as carbon source and urea as dopant.Moreover,compared with the traditional preparation methods,such as PECVD,this method not only has the aforementioned merits above,but also possess merit with no need of pre-seeding.It was found that when the thickness of the catalyst film was 10 nm,the obtained nanodiamond films had the highest crystallinity.The field emission measurement indicated that compared with the field emission properties of intrinsic nanodiamond films,the appropriate N doping?¹.95 at.%?can improve the field emission properties of nanodiamond films.The obtained N-doped nanodiamond films exhibited relatively good field emission properties with a low turn-on electric field strength of 3.6 V/?m?defined at a current density of 0.01 mA/cm²?,and a stable field emission of more than 6.5 h at electric field strength of 6.0 V/?m.5.The main research contents and related results were summarized,and the future development of VGNs and nanodiamond films was prospected.