Development Of Array X-ray Source Based On Carbon Nanotube Field Emission Cathode

X-ray detection is playing a more and more important role in modern medicine,biological science and industrial testing.It also puts forward higher requirements for the performance and preparation technology of X-ray source.Conventional devices that use hot cathode X-ray CT tubes for detection has some weakness such as slow response,high delay,high energy consumption,short life and large volume.Moreover,high-precision rotational motion around the target object is required when a single tube is used for CT imaging,in this case X-ray image information of multiple angles can be obtained to perform the CT image reconstruction,which mechanical motion is more likely to cause imaging blur.Risks such as increased geometric errors have gradually failed to meet existing demand conditions.The new field emission X-ray source array developed in this paper can greatly avoid these problems mentioned above.The X-ray source array can complete CT reconstruction without high-precision rotary motion,and realize static scanning as well.The power consumption of a single X-ray source is greatly reduced.Moreover the X-ray source can be quickly switched by the gate control to image high-speed moving objects,as a result,the motion blur is greatly reduced during the CT imaging process.Thirdly,the X-ray source can be quickly turned off when the angle is switched,so that the invalid dose is greatly reduced and the motion blur is effectively reduced together.The core of this paper is to fabricate an array X-ray source based on carbon nanotubes.The X-ray source is a triode structure with pulse control.The pulse current of a single source can reach 300mA,and the anode working current can reach 200mA..After optimizing the electron gun,its effective focal spot area is only about 0.1mm2,which enables faster CT detection.The main contents of this paper are as follows:1.Growth and transfer of carbon nanotubes vertical arrays1)The photolithography parameter was optimized to solve the problems of lithographic pattern blur,pattern shedding,pattern line width discomfort,etc.The entire silicon wafer is lithographically patterned with an inverted edge in an inverted pattern.2)Multi-layer metal film with different functions as catalyst stack was fabricated by vapor deposition,and microwave plasma chemical vapor deposition method is used to grow CNTs to overcome the problem of uneven growth length of carbon nanotubes,poor bonding with substrate,and unsuitable density.The total field emission current of more than 300mA and current density of 5.7A/cm2 was reached from the as-prepared carbon nanotube arrays.3)The carbon nanotube arrays oriented on the silicon substratewas transferred to molybdenum sheet by using two different transfer methods of solder and binder.The transferred carbon tube realizes a very strong bond with the substrate,and has more strong resistance.4)The morphology and analysis of the carbon nanotube film were observed under scanning electron microscopy,and the problems in the preparation of carbon nanotube array by various methods were found and improved.The test mainly includes the detection of the field emission threshold,the magnitude of the cathode emission current,the current density and the I-V curve.2.Structural design and simulation of X-ray tubesAccording to the requirements,the structures of the cathode,gate and anode of the triode tube X-ray tube are accurately modeled,and the model is solved and simulated by the electromagnetic simulation software using the finite element method.Finally,the ray tube structure model with a focal area of only about 0.1 mm2 was obtained by continuously optimizing the structure,and the model X-ray source was further modeled and simulated.3.Fabrication and imaging test of array X-ray sourceAccording to the designed structure,the high-precision assembly of various parts into a whole structure,the array carbon nanotube X-ray source was successfully prepared by ultra-high vacuum baking and exhausting.There are 21 independent X-ray sources contained within an array of X-ray sources.Then,through the built test system,the relevant performance of the radiation source is tested.The anode working current can reach more than 200mA.The imaging test results show that compared with the traditional hot cathode ray tube,the developed carbon nanotube field emission array X-ray source has a faster swith speed,higher imaging resolution,faster scanning speed and more stable imaging effect.A clear CT image was successfully achieved firstly.It is a major supplement to the relevant technical fields at home and abroad.