Growth Of Two Dimensional Cadmium Iodide Nanoplates,heterostructures And Heterostructures Arrays

The one-atom-thick layer carbon--graphene has fantastic properties and have attracted tremendous interests in recent years,there many other inorganic two dimensional materials?2DMs?beyond graphene which promise rich physical and chemical properties,having potential applications in electronics,photonics,energy harvesting,flexible electronics,transparent electrodes,and sensing.Layered materials in which the atomic layers are weakly bonded together by van der Waals interactions can be readily isolated into single or few-layer nanosheets through mechanical exfoliation or liquid exfoliation processes and often exhibit sheet morphology in CVD synthesis progress.These atomic sheets with few dangling-bonds often exhibit extraordinary electronic and optical properties,in contrast to typical nanostructures that are plagued by dangling bonds and trap states at the surface.Additionally,2DMs in which adjacent layers combine without direct chemical bonds allow the integration of different 2DMs without the constraints of crystal lattice matching to create diverse van der Waals heterostructures?vdWHs?.These vdWHs possess functions and properties that not previously possible.n this study,growth of Cadmium Iodide?CdI₂?nanoplates,Cadmium Iodide-Transitional Metal Dichalcogenides?TMDCs?vdWHs,heterostructures arrays are reported.The main contents of this work are as follows:?1?Growth of Cadmium Iodide?CdI₂?NanoplatesThe synthesis of two-dimensional layered CdI₂ nanoplates using a vapor transport and deposition approach is realized.CdI₂ nanoplates were characterized by optical microscope?OM?,atomic force microscope?AFM?,laser co-focusing Raman spectrometer,scanning electron microscope?SEM?,X-ray diffraction?XRD?,transmission electron microscope?TEM?.OM studies show that the resulted CdI₂nanoplates predominantly adopt hexagonal and triangular morphologies with the lateral dimension in range of²-10?m.AFM studies show that the resulted nanoplates exhibit a thickness in range of 5-220 nm with relatively smooth surface.Selected area electron diffraction?SAED?reveals that the resulting CdI₂ nanoplates are single-crystals.The high-resolution TEM image shows the recognizable lattice fringe without defects clearly,confirming the high quality crystalline structure.Different thickness of CdI₂ nanoplates were characterized by Raman and Photoluminescence.Raman studies show that the Raman peaks intensities increase with increasing thickness.However,the Raman peak at?110 cm^-1 does not show any change.Raman mapping shows highly uniform contrast throughout the entire nanoplate,suggesting highly uniform composition and high quality crystalline structure.In addition,photoluminescence studies show that peak position red-shift with decreasing thickness.?2?Growth of CdI₂-Transitional Metal Dichalcogenides van der Waals HeterostructuresThe monolayer,double or few-layers of WS₂,WSe₂ and MoS₂ nanosheets synthesized using CVD approach were characterized by OM,AFM and Raman.The lateral dimension of WS₂,WSe₂ and MoS₂ is about 50?m,20?m and 5?m respectively.Three types of 2D-TMD?WS₂,WSe₂ and MoS₂?nanosheets synthesized on SiO₂/Si substrate were used as the substrate for the subsequent growth of CdI₂nanoplates and CdI₂-MoS₂,CdI₂-WS₂ and CdI₂-WSe₂ vdWHs were obtained.OM images show that the underlying 2D-TMD substrate can not only guide the nucleation location,but also guide the growth and determine the final morphology of the resulted CdI₂ nanoplates.We also find that the CdI₂ nanosheets grow on the 2D-TMD show a certain preferred orientation through studying the microscopy images of the three kinds of vdWHs.?3?Growth of CdI₂-WS₂ Heterostructures ArraysLarge area of WS₂ nanosheets were synthesized using a new CVD approach and were characterized by OM,AFM,Raman,SEM and TEM.The obtained WS₂nanosheets are monolayer or few-layer and show large lateral dimension Raman studies show characteristic A_1g band red-shift slightly with decreasing the thickness,and photoluminescence studies show PL peaks around 630 nm and red shift with increasing thickness.SAED and high resolution scanning transmission microscope reveals that the resulting WS₂ nanosheets are single-crystals.Applying electron beam lithography and O₂ plasma etching process on pre-grown WS₂,we obtained square WS₂ nanosheets array.Using such square WS₂ array as the template in the physical vapor deposition process,the CdI₂ nanoplates selectively nucleate and grow on the WS₂ monolayer squares,forming a regular CdI₂-WS₂ vertical heterostructures array.Raman mapping images clearly confirm that the CdI₂ nanoplates grow on the top of the squareWS₂ nanosheets.It is also noted that the CdI₂ hexagons typically adopts two orientations on the squareWS₂ nanosheets:the edges of a few CdI₂ hexagons are parallel to the edges of bottom WS₂ templates and most have a angle of 30^o to the edges of bottom square WS₂ templates.