Preparation Of One-Dimensional MoS₂ Nanostructures And Research Into Their Photoelectric And Gas Sensing Performance

Transition metal dichalcogenides(TMDCs),represented by molybdenum disulfide(MoS₂),have attracted intense researchers'attention since the first time they were reported due to their unique low-dimensional property and electronic structure.There are a lot of works which focus on the planar structure MoS₂,yet the research on one-dimensional(1-D)MoS₂ is far away from what has been achieved on the planar structure.The reason can be attributed to the fact that the 1-D MoS₂ is still quite challenging in synthesis or inadequate for device fabrication.This work originates from the synthesis and morphological control of MoS₂ nanotubes(NTs),and obtains the solid characterization of the structure and composition of MoS₂ NTs through electron microscopy and micro-Raman spectroscopy.Afterwards,the electrical property is studied based on a single NT field effect transistor(FET).Later,the MoS₂ NTs'response to ultraviolet light(UV)and nitrogen dioxide(NO₂)are respectively studied under the premise of gas adsorbance on semiconductor surface.Finally,the synthesis route is extended to MoS₂ based core-shell nanowires as well.The details are as follows:(1)A silicon dioxide(SiO₂)nanowire(NW)sacrificial template assisted chemical vapor deposition(CVD)synthesis route is designed.The MoS₂ layers are deposited on the surface of SiO₂ NWs and the SiO₂@MoS₂ core-shell NWs are obtained at first.After treating with hydrofluoric(HF)solution,hollow and tubular structured MoS₂ with high integrity is obtained through characterization.By respectively controlling the diameter of SiO₂ NWs and the vapor phase reaction time,MoS₂ NTs with controllable diameter and layer number are obtained.The electrical property is investigated by fabricating a single NT based FET device,and an n-type enhancement mode behavior is observed.(2)The device based on MoS₂ NTs is designed and successfully fabricated to study the response to UV light with the wavelength of 254 nm and 365 nm,respectively.Under the same or approximate intensity,the sensitivity to 365 nm is 3.5-4.7 times that of 254 nm.The Kelvin Probe Force Microscopy(KPFM)study is conducted,and a surface potential enhancement of MoS₂ NT can be observed under UV illumination of both wavelengths.According to the measurement results,the surface potential enhancement caused by 365 nm is greater than 254 nm,which indicates that the distance decrease between Fermi level and conduction band under 365 nm is greater than 254nm.Thus,365 nm UV illumination is more effective in the n-type doping to MoS₂which is closed related to the desorption of oxygen molecules.(3)MoS₂ NTs based room-temperature NO₂ sensor is fabricated by introducing365 nm UV illumination.The NO₂ sensor exhibits a high-sensitivity and full-recovery response to NO₂ with concentration ranging from 0.5-100 ppm.Among them,the sensitivity to 100 ppm reaches 132.31,which is higher than the previously reported values obtained through the MoS₂ based NO₂ sensor.By comparing the sensitivity to SiO₂@MoS₂ NWs based sensor,a model based on the specific surface area induced depletion layer variation is proposed to explain the sensitivity enhancement.At the same time,the Wolkenstein model is applied to explain the significance of UV illumination to the gas sensor.The gas sensor we fabricated exhibits good selectivity among the tested gases as well as good stability in the repeatability test under the same NO₂ concentration.(4)Utilizing the same synthesis route with replacing the template NW to zirconium oxide(Zr O₂)NWs and rutile titanium oxide(Ti O₂)NWs respectively,the Zr O₂@MoS₂ and rutile Ti O₂@MoS₂ core-shell NWs are obtained.Besides,the Zn S@MoS₂ core-shell NWs are synthesized with Zn O NWs being templated.These syntheses prove the adaptability of the proposed route to prepare MoS₂ based 1-D heterojunctions.