Study On The Structure And Properties Of Transition Metal Dichalcogenides Under High Pressure

Both the lattice and electronic structure of layered Transition Metal Dichalcogenides(TMDs)are strongly dependent on thickness,thus,TMDs show a wide range of optical,electronic,photoelectronic properties,whicn have been widely used in field-effect transistors(FETs),solar cells,photoelectric detectors,electroluminescent devices,and so on.Pressure can effectively modify the optoelectronic properties of TMDs through control of the lattice and electronic structures.In this way,it is necessary to systematically investigate the structure and properties of TMDs under high pressure,which will profoundly impact the fabrication of optoelectronic devices.In this paper,by combining the Raman spectra measurements,photoluminescence(PL)spectra measurements and first-principles calculations,the lattice and electronic structural evolutions of ultrathin Mo S2,multilayer Re S2,monolayer Re S2 and multilayer Zr S3 under high pressure were systematically studied to reveal the fundamental regulation of pressure-tuned structure and properties of TMDs.The results are as follows:1.For Mo S2,the interlayered interaction grows as the layer number increases.To reveal the fundamental regulation of interlayered interaction-tuned behaviors of ultrathin Mo S2 under high pressure,we contrast the high-pressure Raman spectra of trilayer and quadlayer Mo S2.Our experimental results suggested that the Raman responses to pressure in trilayer Mo S2 are quite different from that in quadlayer Mo S2.Furthermore,combining the experimental results with first-principles calculations,we demonstrated that the quadlayer Mo S2 transforms into an AB' stacking configuration above 8.6 GPa,while the trilayer Mo S2 possesses a distorted 2H structure within our studied pressure range.Our study demonstrated that interlayer coupling plays an important role in modifying the lattice structure of compressed ultrathin Mo S2.2.Distinct from Mo S2,multilayer Re S2 is an anisotropic layered TMDs.It has been reported that adjacent layers in Re S2 are only weakly coupled to each other,with a coupling energy no more than 8% of that of Mo S2.Combining Raman spectra,PL spectra and first-principles calculations,we systematically investigated the lattice and electronic structural evolutions of multilayer Re S2 under high pressure.Our Raman spectra measurements and first-principles calculations suggested the occurrence of an intralayer phase transition followed by an interlayer transition in compressed multilayer Re S2.Meanwhile,a transition from one indirect to another indirect bandgap at 2.7 GPa was revealed by both high-pressure photoluminescence(PL)measurements and first-principles calculations.Furthermore,by contrasting the high-pressure behaviors of Mo S2 with that of Re S2,we demonstrated interlayer coupling plays an important role in modifying the lattice and electronic structures in compressed TMDs.3.To explore the effect of substrate on compressed TMDs with different thickness,we contrast the high-pressure Raman spectra of supported monolayer and multilayer Re S2 on Si substrate.After 1.7 GPa,the splitting of Eg-3 mode was observed in compressed monolayer Re S2.Further first-principles calculations suggested that monolayer Re S2 is much more compressible than Si substrate,thus,strain should exist in compressed monolayer Re S2,which will result in the split of Eg-3 mode after 1.7 GPa.However,the high-pressure behaviors of multilayer Re S2 are quite different from that of monolayer Re S2,Eg-3 mode in multilayer Re S2 remains well-symmetric up to 4.2 GPa,our first-principles calculations suggested that the compressibility of multilayer Re S2 falls in between monolayer Re S2 and Si substrate,in this way,the strain in multilayer Re S2 should be weaker than that in monolayer Re S2,which will result in the well-symmetric Eg-3 mode up to 4.2 GPa.Our study suggested that substrate can effectively tuned the lattice structure of supported monolayer Re S2 under high pressure.4.Zr S3 is another novel layered TMDs which possess a pseudo-1D structure.Combining Raman spectra and first-principles calculations,we systematically investigated the lattice and electronic structural evolutions of multilayer Zr S3 under high pressure.Both our experimental results and first-principle calculations suggested that the compression on a-axis is more effective when compared to b-axis,which can be attributed to its pseudo-1D structure.Furthermore,according to the high-pressure Raman spectra,distinct inflection points were observed at around 11.4 GPa,which may indicate the occurrence of phase transition in multilayer Zr S3 after 11.4 GPa.Moreover,our first-principles calculations confirmed a transition from one indirect to another indirect bandgap at 10.0 GPa in multilayer Zr S3.In addition,our study suggested that the electronic structural evolution of multilayer Zr S3 is closely related to its lattice structural evolution.