Experimental Study On Field Emission Ion Source Based On Quadrupole Mass Spectrometer

Cold cathode field emission provides a clean,low-pollution,low-power ionizing ion source for quadrupole mass spectrometers.The traditional hot cathode ion source has a widely application in various mass spectrometers due to its relatively low manufacturing cost.Since the hot cathode ion source usually by heating filament and generates hot electron emission,so it needs high operating power,and when the filament is heated,a part of the gas is released from the filament,and when working in high vacuum and ultra-high vacuum,these gases are easily pollute the background;in addition,in the MEMS process,the hot cathode ion source cannot be dissipated due to thermal load,which is disadvantageous for miniaturization.In contrast,cold cathode field emission ion sources have a low power consumption,fast operation speed,and consume less power when operating at lower temperatures.In this paper,carbon nanotubes are used as ion sources to research the emission properties,ionization properties,ion energy,ion source voltage distribution and quadrupole matching,and the analysis of its preliminary spectra.In this paper,the preliminary results of ionization performance of ion source are obtained by CST simulation.The effects of different decelerating pole size,different accelerating pole structure and accelerating height on electron energy and electron trajectory are simulated.the electronic simulation figures show the aperture size of the deceleration pole has a great influence on electron speed.The acceleration pole structure mainly affects the motion trajectory and electron energy of the electrons in the ionization region.Then through experimental tests,the effects of different deceleration polar apertures,accelerating pole structures and electrode spacing on ion current concentration and ion energy dispersion were obtained.then we get an optimized ion source model.in this model,the ion current of this structure was measured at-8A~-9A magnitude.The experiment changes the magnitude of the accelerating pole voltage and measures the distribution of ion energy.When the accelerating pole voltage is 60 V,the average ion energy is about 3.6eV.Finally,according to the voltage distribution of the quadrupole,calculating the voltage applied by the field emission ion source,and match it with the quadrupole.the CNT is 5V,the gate is 1200 V,the deceleration pole is 30 V,and the acceleration pole is 80 V.When the pole potential is 70 V,a preliminary spectrum of the field emission ion source and the quadrupole is obtained.Through the matching test of the field emission ion source and the quadrupole,the hydrogen peak,the water peak and the nitrogen peak were successfully emerged,which proved that the field emission ion source can be used in the quadrupole mass spectrometer system.However,there are still problems such as low resolution and low sensitivity of the quadrupole need to solve.