Femtosecond Laser Direct Writing Of Molybdenum Sulfide Patterns And Micro/nanoscale Sensors

In the past decades,functional devices with characters of miniaturization and integration are continuously developed to improve the performance and reduce the volume.There are many kinds of functional materials involved in integrated devices,however,silicon-based materials are still the main materials with high resolution in micro nano scale.Mature silicon-based semiconductor technology requires hundreds of complex processes,but it is difficult to realize the preparation and processing of other functional materials.Therefore,it is urgent to develop an efficient micro-scale material synthesis and patterning process suitable for more kinds of materials to further improve the performance and integration of micro nano functional devices.In recent years,two-dimensional materials have been widely concerned by scholars at home and abroad.Due to their unique structure,they show their excellent physical and chemical properties in many aspects.Molybdenum disulfide（MoS₂）is one of the representatives of two-dimensional materials.With its excellent photoelectric properties,abundant edge active sites,controllable band gap and excellent physical and chemical stability,nanoscale MoS₂ nanosheets are widely used in miniature gas / biological detection unit,battery technology,hydrogen evolution catalysis,supercapacitor fields and so on.However,the existing MoS₂ fabrication process still has some intractable problems,such as harsh processing environment,various processes and difficult to achieve specific location patterning,which limit the application of MoS₂ materials in the field of integrated micro nano devices.With the development of ultrafast pulsed laser,laser micromachining technology has developed rapidly,which makes it possible to directly write high-precision miniature functional devices.Femtosecond laser has unique advantages in the field of micro nano fabrication due to its high peak power（1015 w）and power density（1021 w / cm2）,short operation time and nonlinear absorption.In this work,MoS₂ will be taken as a representative to research a single-step synthesis and patterning method by using femtosecond laser-induced multiphoton absorption on any substrate at atmospheric temperature,so as to enhance its application potential in the field of micro nano functional devices.The research will be carried out in the following orders: research and development of suitable precursors,analysis of chemical and photochemical mechanism in the process of processing,discussion of product characterization and influencing factors of molding,practical application of the technology and performance test.The main contents are as follows1.A suitable precursor for femtosecond laser direct writing MoS₂ has been explored,which using molybdenum acetylacetonate as molybdenum source,carbon disulfide and sulfur powder as sulfur source,oleylamine as complexing agent,isopropanol as solvent,and optimizing the composition of the precursor.On the premise of meeting the synthesis of molybdenum sulfide,the precursor ensures good spinnability,and avoids the bubble pinning phenomenon in the laser direct writing process.These characteristics help to improve the continuity,uniformity and repeatability of the final product.Using femtosecond laser processing platform,MoS₂ material was prepared on silica substrate uniformly,continuously and rapidly.The composition and crystallinity of the product were confirmed by laser Raman spectroscopy,and the product was confirmed to be MoS₂ by X-ray spectrum analysis.2.The chemical synthesis mechanism of femtosecond laser processing technology and the product molding process has been explored.The chemical reaction in the process of precursor configuration was determined by liquid chromatography mass spectrometry,and the solute composition in the precursor before laser processing was determined,so as to infer the chemical reaction in the process of laser processing.The two-photon absorption effect in the reaction process was confirmed by UV absorption spectrum,and the verification experiments were carried out by using femtosecond laser with different wavelengths,which furtherly proved that the MoS₂ material was synthesized by photo-induced synthesis in the femtosecond laser direct writing process rather than just relying on the thermal effect of laser.The effects of laser power,laser processing speed and laser focus position on the product forming process were analyzed by laser processing parameter gradient experiment,and the parameters were optimized to improve the uniformity and continuity of the product.3.Further,making full use of the structural characteristics of the product with high edge active site density,the MoS₂ miniature gas detector was fabricated by maskless lithography and electron beam evaporation on the basis of femtosecond laser direct writing MoS₂ micro nano array.The electrical performance and gas sensing response of the device were tested.The test results show that the gas sensing response to 0.5 ppm nitrogen dioxide（NO2）gas is achieved at room temperature.In addition to NO2 gas,other harmful gases were also tested,such as ammonia and hydrogen sulfide,and the devices showed obvious gas sensitivity,which proves the application potential of the device in chemical industry,environment,agriculture and other fields.In this work,femtosecond laser-induced photochemical synthesis of molybdenum sulfide is proposed for the first time,which significantly improves the efficiency and flexibility of microscale patterning of molybdenum sulfide,and promotes its application in functional devices such as micro nano gas detectors.At the same time,this work also provides new ideas for other functional nano materials to achieve high precision,high efficiency and high designability in micro nano scale.