Preparation And Optoelectronic Properties Of Novel Two-Dimensional Materials Quantum Dots(2D QDs)

It has been drawing widespread attention to novel two-dimensional materials,since the discovery of graphene.Meanwhile,explored the research objects to a series of new materials,such as functional graphene,hexagonal boron nitride?h-BN?,transition-metal dichalcogenides?TMDs?and black phosphorus?BP?.Novel two-dimensional materials quantum dots?2D QDs?have been obtained when the size of two-dimensional materials discreased to under the exciton Bohr radius(?6?.2D QDs showing numerous low-dimensional physical properties which different from the bulk materials,caused by a series of quantum effects in the quantum scale space.In particular,the structure of energy gap would change a lot,possessing unique optoelectronic properties.In the researches of this thesis,we adopt liquid phase ultrasonic exfoliation technology,respectively exfoliated 2D QDs with particle size around 5 nm from bulk materials:fluorine doped graphene quantum dots?F-GQDs?and transition-metal dichalcogenides QDs of Ti?TiSe₂ QDs,TiTe₂ QDs?.We fully characterized and investigated as-prepared2D QDs by modern analytical characterization testing technology,using transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,atomic force microscopy?AFM?,X-ray diffraction?XRD?,Raman spectra,Fourier transform infrared?FTIR?spectra,Ultraviolet-Visible absorption?UV-Vis?spectral,photoluminescence?PL?spectra,photoluminescence excitation?PLE?spectra,X-ray photoelectron spectroscopy?XPS?,also discussed the optoelectronic properties.The applications of the three kinds of QDs had been explored in photodetector field and tested the performances of detectors.The main contents and conclusions are as follows:?1?Take degreasing cotton as raw material,through high temperature carbonization forming carbon fibers and futher hydrothermal reaction with HF,obtained precursor fluorinated carbon fibers?F-CFs?.F-GQDs with an average diameter of 3.25 nm were prepared after F-CFs liquid phase ultrasonic exfoliated in N-methyl pyrrolidone?NMP?solution.Because of the introducing of F,forming C-F bond,adding surface functional groups,increasing crystal defects of GQDs,resulting Raman peak?D peak?widen and intensified,increasing the electron transition energy level,which makes the F-GQDs obsess good optical absorption and photoluminescence properties.We also analyzed the forming mechanisms of F-GQDs.?2?Using the improved liquid phase tip sonication combined with bath sonication exfoliation technology,we respectively exfolinated TiSe₂ QDs with an average diameter of 3.78 nm and TiTe₂ QDs with an average diameter of 3.24 nm from the TiSe₂ and TiTe₂bulk materials.Both TiSe₂ QDs and TiTe₂ QDs have good dispersion and the crystallinity.Through Raman characterization,it was found that A_1gg vibration mode played a leading role in TiSe2 QDs,while the predominance in TiTe₂ QDs was E_g vibration mode.TiSe₂QDs and TiTe₂ QDs have strong absorption in UV region,but showed different photoluminescence properties,indicating with different ways of electrobic transitions.?3?The vertical structure UV detector based on F-GQDs has a ratio of photocurrent to dark current of magnitude¹0⁵ and its detectivity?D*?could stablize at¹0¹22 Jones under?=365 nm UV light irradiation.It has favorable photoelectric detection performance and stability,expected to apply in the field of UV detection.Photodetectors based on TiSe₂ QDs and TiTe₂ QDs with interdigital electrodes structure showed“negative photocurrent”in I-V test,which caused by the generation of photoinduced charge traps hindered the photocurrent transport.Generally speaking,the D*of these two photodetectors in the ultraviolet detection(?=365 nm,D*?TiSe₂ QDs?¹0¹⁰ Jones,D*?TiTe₂ QDs?¹0¹¹ Jones)is always going to be an order of magnitude higher than infrared waveband??=850 nm?.Although the corresponding responsitivity(R¹0^-1–10^-2 A·W^-1)is small,both showed preferable performances of photoelectric detection,possessing the basic qualities as photoelectric detecting materials.