Research On The Cross-scale Integrate Fabrication Of Carbon Nanotube Field Emission Microelectrodes For X-ray Generation

One-dimensional nanomaterials have unique properties and future pragmatization.One-dimensional nanomaterials are easily intertwined and their morphology is complex and variable because of their high aspect ratio.It is difficult to operate a large number of one-dimensional nanomaterials one by one directly during large scale fabrication process.It is urgent to develop a novel fabrication technology to promote one-dimensional nanomaterials to be widely used in the development of high-performance devices.Aiming at the problems in the large-scale controllable preparation of one-dimensional nanomaterials,this paper proposes a composite preparation technology.With the help of dispersion media,one-dimensional nanomaterials can be integrated into microprocessing technology to achieve large-scale and controllable fabrication.Here large-scale refers to the use of micro-machining platforms for taping out,while controlled preparation means that the density of one-dimensional nanomaterial and the surface morphology of the sample can be controlled by adjusting the fabrication parameters.The composite fabrication technology is based on the structural characteristics of high aspect ratio of one-dimensional nanomaterials,and has wide applicability to the controlled preparation of one-dimensional nanomaterials.Carbon nanotubes are typical representatives of one-dimensional nanomaterials,which attract great academic attention due to its unique structure and excellent physical and chemical properties.In this research,carbon nanotubes are taken as an example,inorganic compound(sodium silicate)and organic medium(polyimide)were used to verify the composite fabrication technology.According to the unique application of the field emission X-ray tube electrode,two kinds of electrodes were designed,fabricated and tested.The main research contents and conclusions are as follows:(1)Aiming at the technical problems of the poor bonding between the carbon nanotubes and the flexible substrate in the traditional flexible carbon nanotube field emission electrode,we are trying to solve this problem by inserting CNT into metal substrate.By using micromachining technology,we could implant nano-scale materials into micro-scale metal substrate at room temperature.Thanks to the effective direct contact and the strong interactions between CNTs and the substrate,field emission current of 1.11mA(current density is 22.2 mA/cm~2)could be achieved from the micro wire.Moreover,the wire shows excellent mechanical properties for large amplitude bending,which is beneficial for geometric designing.To check the practical application of the wire,a simplified X-ray imaging system was set up by modifying a conventional tube.The X-ray generation test was operated at 4.5 KV,and the emission current is around 307?A.The grey shade that appears on the sensitive film after being exposed to the radiation confirms the X-ray generation.(2)The inorganic paste also would not break device vacuum during high temperature operation due to volatile components out-gassing that would seriously impact the field emission property of the electron source.By using inorganic binder,the cathode could resist high temperature annealing up to 400?.Our novel emitter showed relatively good field emission properties such as low turn on field(reduced from 1.52 V/?m to 1.25 V/?m),high current density,and good stability(applied electric field 2.3 V/?m,emission current reduced from 344?A to 233?A after 40 hours).The emitter showed great field emission properties(with applied field 4.63 V/?m,emission current could be 1.97 mA,work for 40h continuously;with the applied voltage 781 V,emission current could be 3.08 mA,emission current could be 241 mA/cm~2).We ascribed the improved emission properties after the annealing process to the oxygen desorption induced decrease of work function,and defect annealing which could stabilize the emitter.To check the application of the emitter,the fabricated emitter was sealed in a conventional X-ray tube.The X-ray generation test was operated at 5.0 KV,and the emission current is around 84?A.The blackened shade on the sensitive film confirmed the X-ray generation,which demonstrated that our emitter successfully survived the high temperature processing steps of the X-ray source fabrication.