Research On The Preparation And Properties Of Molybdenum Disulfide Films And Their Optoelectronic Devices

Two-dimensional layered nanomaterials represented by graphene and molybdenum disulfide?MoS₂?have shown wide applications in many fields,such as electronic,photoelectric devices and sensors,due to their good stability,abundant structure and excellent physical and chemical properties.And it has gradually become the focus of research in many fields,such as physics,chemistry,material science and so on.The MoS₂ nanomaterials have adjustable band gap which are different from zero band gap of graphene.The special band gap of MoS₂ makes it have a wide application prospect in all kinds of functional devices.High quality and few layered MoS₂ films and MoS₂/WS₂ heterostructure composites were prepared by mechanical exfoliation and chemical vapor deposition?CVD?in our research.The morphology,composition and optical properties of the materials were characterized and analyzed.A back gate field effect transistor?FET?based on MoS₂ film of different layers and its heterostructure was successfully prepared.And the devices are applied to photodetection with high sensitivity and micro glucose biosensors with ultra low concentration.The main contents are as follows:?1?The researches on the preparation and optical properties of few layered MoS₂films was carried out.High quality and few layered MoS₂ films were prepared by CVD and mechanical exfoliation.The crystal structure,morphology,thickness and optical properties of the materials were also characterized.According to the contrastive analysis of the morphology of the samples prepared by the CVD method at different reaction time during the growth process,the growth mechanism of MoS₂films was discussed.During the formation of S-Mo-S bonds,the growth speed of different crystal planes was different,resulting in the growth of hexagonal MoS₂crystals in three directions.And finally the triangulated thin MoS₂ film structure appeared.It was also found that the other TMDs films have the same morphological evolution during the growth process.The researches content of this part establish a foundation for the growth of MoS₂ heterostructure and the application of MoS₂ thin films in functional devices.?2?The research on the preparation and electrical properties of few layered MoS₂films FET was carried out.A back gate field effect transistor based on MoS₂ films of different layers was prepared.And the electrical properties of the devices were compared and analyzed.The output characteristic curve of the devices reflected the good control effect of gate voltage on the device.Moreover,a good ohmic contact was formed between the source and the drain electrode and the MoS₂ channel layer,which was beneficial to the injection of the carriers.The transfer characteristics of the device showed that the carrier mobility of bilayer to five layer MoS₂ films based FETs were 31.7,12.8,4.1 and 3.2 cm²/V·s,respectively,under V_ds of 0.5 V.?3?The photoelectric characteristics of MoS₂ based FET was studied.In consideration of the incident light irradiating the top of the device from top to bottom,a back gate phototransistor based on few-layered MoS₂ films was designed and prepared.The effect of optical power and gate voltage on the photoelectric performance of the device was discussed by contrast experiments.The experimental results showed that,under the fixed gate voltage,photocurrent and photoresponse of the devices increases gradually with the increase of optical power.At the same optical power,the greater the gate voltage was,the greater the photoresponse was achieved.?4?The preparation and photoelectrical properties of MoS₂ heterostructure based FET were studied.First,large area and high quality MoS₂/WS₂ heterostructures were prepared by CVD method,and the morphology,composition and optical properties of the heterostructures were characterized and analyzed.In the study,we discussed the morphological differences in different regions of heterostructure samples and the evolution process between different regions.By comparing the optical properties of the heterostructure with the MoS₂ film,the motion of the carrier at the heterostructure interface was revealed.Then the photoelectric properties of FET based on the MoS₂heterostructure were studied and compared with MoS₂ devices.Under 20 mW illumination,the photoresponse of MoS2/WS2 heterostructure based phototransistors increased by 50 times.The photoresponse of MoS2/MoO3 heterostructure devices formed by the composite high work function MoO₃ material increased by nearly 100times.The results showed that the MoS₂ heterostructure can enhance the performance of device effectively.Nanomaterials with high work function induced the charge transfer process at the heterostructure surface to produce the built-in electric field.Furthermore,it can effectively promote the separation of photogenerated electron hole pairs in MoS₂.A good photoelectric modulation effect on MoS₂ film phototransistors was achieved.From the theoretical analysis of energy band,we know that the main reason for the improvement of photoelectric performance is the difference of the band location of two kinds of materials in heterostructure,resulting in the effective separation of photoelectron hole pairs at the interface.The hole was captured by the defects at the heterostructure interface,while the electronic was moved to the external circuit to participate in the electrical conductivity,which effectively improved the photoelectric performance of the device.?5?The performance of glucose biosensor based on MoS₂ FET was studied.The results showed that,under the same gate voltage and drain voltage,the Ids increased with the increase of glucose concentration,so that the detection of unknown glucose solution was realized.In our research,we used the MoS₂ FET for the first time to realize the ultra sensitive detection of an extremely low concentration of glucose solution.The sensitivity of the glucose biosensor was as high as 269.71 mA/mM.The detection limit was as low as 300 nM and the linear range was 300 nM³0 mM.In addition,the device we prepared also had the advantages of short response time?<1s?,good stability,and micro detection.This part of the study shown that few-layered MoS₂ based FET had a wide development space in the field of the application of new functional devices.