Build-up Of Low-temperature Low Pressure And Atmospheric Pressure Plasma Systems,as Well As Investigations On Their Applications

As the fourth state of matter,artificially-generated low-temperature plasma contains many electrons and radicals,so it is widely used in microelectronics,materials,automobiles,and medical industries.Low-temperature plasma can be divided into two categories,namely low-pressure and atmospheric pressure plasmas according to its working pressure.Currently,all marketed artificial low-temperature low-pressure plasma(whether capacitively coupled or inductively coupled plasma)will cause certain damage to the material during material processing,because of the inevitable bombardment of the positive ions onto the material surface,due to high plasma density and uncontrollable plasma electric field.Two-dimensional semiconductor materials are very thin,for example,graphene and molybdenum disulfide are only one or a few atomic layers thick.The plasma bombardment effect is very obvious and fatal for such materials when we adopt plasma to make surface modifications like doping and phase control.Therefore,it is of great importance to develop a gentle plasma treatment technology with low plasma density,controllable plasma electric field and less damage to the material surface.In addition,low-temperature atmospheric pressure plasma has great potential and research significance in biomedicine and other aspects.While triple-negative breast cancer is currently the only breast cancer with no reliable treatment method,it has a high degree of malignancy,high mortality and poor prognosis.Therefore,there is an urgent need to explore a new treatment option,and low-temperature atmospheric pressure plasma is a very promising one.In this thesis,a set of low-pressure plasma device namely capacitively coupled electrodeless plasma(CCEP)and a set of cold atmospheric pressure plasma(CAP)device are designed and built to meet the above requirements.The former isapplied to the layer-by-layer thinning of two-dimensional semiconductors and the latter the treatment of triple negative breast cancer.The main research work carried out is as follows.1.Independently developed CCEP technology based on inductively coupled plasma(ICP)technology,designed and built a planar coil-shaped inductor coil.Based on the measured values of inductance,capacitance,and resistance of the coil,the frequency of the RF power supply in CCEP mode was determined through RF matching principle calculation.The corresponding tuning capacitor(1-10 nF)and matching capacitor(20-56 nF)were built to realize stable discharge in CCEP(capacitive discharge)mode and ICP(inductive discharge)modes.The Langmuir probe method was used to detect the characteristics of CCEP.The electron concentration and temperature in the capacitive discharge mode,inductive discharge mode and the transition stage between capacitive and inductive discharge mode were measured and compared.CCEP can realize capacitive discharge at low input power.The plasma has an extremely low electron density(?10⁹ cm^-3)as well as low average electron temperature(0.4?0.5eV),and the plasma electric field is parallel to the substrate surface,so that the movement of positive ions can be constrained in the direction parallel to the substrate,greatly suppressing the plasma ion bombardment effect.As a result,we achieved gentle,controllable and low-damage etching of two-dimensional semiconductor materials like WSe₂.The experimental results show that CCEP can not only achieve the layer-by-layer etching of WSe₂,but also greatly reduce the damage caused by plasma bombardment.2.A dielectric barrier discharge(DBD)-like discharge structure device was built,it can meet the requirements of daily laboratory cell experiments,but with the increase in experimental requirements,this device cannot meet the requirements of animal experiments.Therefore,the DBD-like discharge structure is improved and converted into a DBD discharge structure.The electrode and quartz tube structure is optimized,which can reduce the ignition voltage of the device and make the discharge more stable.We connected the optimized CAP jet onto the human body impedance simulation circuit to detect voltage and current flowing through the human body,and the temperature of CAP jet.All these electrical parameters meet the safety requirements of animal experiments,so that the device can meet the requirements of daily laboratory cell experiments and live animal experiments.We finally measured the composition of the CAP jet by optical emission spectroscopy(OES),which lays the foundation for the follow-up study of the mechanism of how plasma killing tumor cells.3.The proliferation of SUM149 cells before and after CAP treatment was studied to determine the inhibitory effect of CAP on SUM149 cells.Through the detection of cell inclusions and the characterization of transmission electron microscopy,it was found that the cell morphology treated by CAP did not fully conform to the early characteristics of apoptosis.We detected iron death characteristic proteins and found that cells incubated with iron death inhibitors were able to resist the killing of cells by CAP,and confirmed that the form of CAP causing SUM149 cells death is ferroptosis.