Study On The Modification Of Graphene Gas Sensor Induced By Highly Charged Ion Irradiation

Gas sensors play an irreplaceable role in industrial production and daily life by responding to various toxic and harmful gases.The traditional metal-oxide gas sensor has a fast response and low economic costs,but the metal oxide gas sensor has worse selectivity and high operating temperature,which causes a certain amount of energy consumption and easily become the ignition point of flammable and explosive gases.Accordingly,it is crucial to develop new and efficient room-temperature gas sensors.The discovery of two-dimensional materials represented by graphene provides new possibilities for the development of various electronic devices.Graphene has a very high specific surface area and electron mobility,which can theoretically realize single-molecule detection,and has a good response to a variety of gases at room temperature,which can meet the development demands of low energy consumption,higher sensitivity,and integration,smaller size,and flexible sensors,etc.Through density functional theory calculations,scholars found that the adsorption capacity of perfect lattice graphene to gas molecules was significantly lower than that of graphene with defects.Scholars’theoretical calculations results proved that graphene with defects has a significantly better ability to adsorb gas molecules than graphene with complete lattice.Some current literatures showed that the response of graphene gas sensors has been improved to a certain extent by the irradiation of low energy heavy ions and swift heavy ions.However,there are few related reports at present,and the mechanism remains unclear.There is also a lack of studies on the correlation between irradiation conditions and gas response enhancement.In addition,high charge ions are a kind of unique low energy ion,which produces defects similar to swift heavy ion irradiation.However,the related research is rarely reported.Based on the current status of research,highly charged ions were used to the research the modification of graphene gas sensors.Firstly,the monolayer graphene gas sensors were fabricated,the graphene samples were characterized by Raman spectroscopy,and the gas response tests of the unirradiated sensors were measured.Secondly,the sensors were irradiated with highly charged ions(⁵⁴Xe²⁰⁺,⁵⁴Xe¹⁷⁺),the irradiated graphene samples were characterized by a Raman spectrometer,and the gas response tests of the irradiated sensors were measured.The experimental results show that:（1）Raman spectrums of pristine graphene sensors have shown that the peak intensity ratio of G peak and 2D peak is about 2:1,and the D peak is undiscovered.Spectrograms indicate that within the detection limit of the Raman spectrometer,there is a perfect lattice in each monolayer graphene sample.The sensors have certain response values to single-concentration and multi-concentration cycle gas,and the phenomenon of adsorption saturation does not appear,but the response value is at a low level.（2）With the increase of irradiation fluence,the D peak in the Raman spectrum began to appear.When the irradiation fluence reaches 1×10¹³ ions/cm²,the peak intensity ratio of D peak and G peak also reaches the highest value.The full width at half maximum of the D and G peaks are on the rising trend,which indicates the onset of amorphization.The 1×10¹³ions/cm² to 1×10¹⁴ ions/cm² induced defects started to transform from sp³hybridization-associated defects to vacancy-like defects.When the irradiation fluence exceeds 1×10¹⁵ ions/cm²,the graphene becomes completely amorphous.In the single-concentration and multi-concentration cycle gas tests,the response values have been significantly improved after irradiation,the gas response values of some sensors are higher and the gas response improvement multipliers caused by the irradiation of high-charged ions were also at a high level.The response value of the graphene gas sensor to 1 ppm NO₂under the irradiation fluence of 1×10¹⁴ ions/cm² is 12.17%,and the improvement multiplier is 27 times;the graphene gas sensor under the irradiation fluence of 5×10¹⁴ ions/cm² has a response value of 6.25%to 50 ppb NO₂,and the improvement multiplier is 12 times.These data are superior to some previous results.After comparing the gas responses before and after irradiation,it is found that the response values of the pristine graphene gas sensors to NO₂ are very limited,and the reason for the improvement of gas response is that irradiation defects provide more gas adsorption sites.By exploring the relationship between the gas response improvement and irradiation fluence,it is found that the low and medium irradiation fluences do not provide enough adsorption sites for gas adsorption.The optimum irradiation fluence range is from 1×10¹³ ions/cm² to 7×10¹⁴ ions/cm²,which is attributed to the that the amount of adsorption sites and electrical properties induced by irradiation defects are two key factors that determine the optimum irradiation fluence.At the same time,for different concentrations of gas,the required optimum irradiation fluence is also different.This work not only proves the advantages of highly charged ion irradiation to modify the performance of gas sensors,but also provides new research ideas for improving the responsivity and low-concentration detection performance of two-dimensional material gas sensors.