Studies On IR And Raman Spectra Of Bi-O-X(X=S,Se,Te)materials

The development of semiconductors is significant to the progress of information age.Nowadays,the improvement in the properties of traditional 3D semiconductors has been approaching the limit,while the rise of layered semiconductors is breaking the deadlock.However,almost each kind of typical layered semiconductors have its shortage,which obstructs them from being put into application.To make it closed,it's important to search new high-property 2D semiconductors.In the recent decade,the researches on Bi2O2Se show that it is a layered material with various interesting properties.Bi2P2Se has a suitable band gap,high carrier mobility and air stability simultaneously.At the same time,the other bismuth oxychalcogenide layered materials have been discovered and researched gradually,which have huge potential in thermoelectrical,photoelectrical and photocatalytic fields.Considering that the theoretical researches on this series of materials are not enough yet at present,we plan to do some researches on the IR and Raman spectra of bismuth oxychalcogenide layered materials to provide some references for later theoretical or experimental researches.We calculated the IR and Raman frequency,irreducible representations,polarized configurations,vibrational vectors and intensities of six Bi-O-X(X?S,Se,Te)materials by density functional theory(DFT).What's more,we measured the Raman spectra of Bi202Se with single crystalline and polycrystalline,respectively.The main results include:1.Structure optimization on Bi2O2X and Bi2OX2 layered materials based on DFT shows that Van de Waals(VdW)interaction plays an important role in these materials.One can only obtain the accurate lattice consntants with the VdW interactions.2.There are four Raman modes of Bi2O2Se in theory,including two Eg(with frequencies of about 67 and 433 cm-1),one Alg(163 cm-1)and one B1g(354 cm-1)modes.However,only two peaks of A1g and B,g can be detected in our temperature dependent Raman measurements,in which we observed the B,g mode at room pressure for the first time.Theoretically,B1g mode has the highest Raman intensity.But experiment found the A/g mode has the highest intensity.This is possibly due to the phonon damping effect caused by the high carrier concentration in Bi2O2Se crystal.3.Bi2O2Te and Bi2O2Se have the same structure,so their Raman spectra are similar.Our calculated Raman frequencies are consistent with other theoretical and experimental works.In addition,the IR spectra of Bi2O2Se and Bi2O2Te have never been reported yet.4.Bi2O2S has twelve IR and twelve Raman modes.There are three Ag Raman modes with the highest intensity,which are located at about 171,285 and 368 cm-1 respectively.While,the rest three materials,Bi2OX2(X=S,Se,Te)all have the same symmetry and,they all have eight IR and ten Raman modes respectively.For Bi2OS2,there are two A1g modes with the highest Raman intensity,which are located at about 132 and 346 cm-1.For Bi2OSe2,there are also two A1g modes with the highest Raman intensity,which are located at about 89 and 218 cm-1.For Bi2OTe2,only one A1g mode at about 163 cm-1 has the highest intensity.The IR and Raman spectra of the above-mentioned four materials have not been reported yet.In conclusion,we calculated the IR and Raman spectra of 6 Bi-O-X(X=S,Se,Te)layered materials by DFT.Combined with others' work,we find that both Bi2O2Se and Bi2O2Te have four Raman peaks theoretically but only two of them have been detected in experiments.Meanwhile,the other four materials have no report on Raman specta and,all of the six materials have no report on IR spectra yet.Our work provides some meaningful and important information for future studies about these layered materials.