Investigation Of Interference Effect And Interfacial Thermal Conductance Of 2D Materials By Raman Spectroscopy

In recent years,Two-dimension（2D）materials have attracted a lot of research interest,2D layered transition metal dichalcogenides（TMDs）are now playing increasingly important roles in both fundamental studies and technological applications due to their tunable electronic structure,large exciton binding energy and extraordinary sunlight absorption property.It is known that the interference effect of light in multilayer systems can effectively improve the Raman signal intensities of 2D materials,the first part of the work is to systematically study the effect of interference on the Raman signal intensities of 1-200 layers 2D HfS₂ by Raman spectroscopy.In addition,interfacial thermal conductance plays an important role in affecting the stability of devices based on 2D materials.The other part of the work is to measure the interfacial thermal conductance between 2D MoS₂ and different substrates by Raman spectroscopy.New emerging 2D materials HfS₂ has received considerable attention recently due to its ultrahigh photoresponsivity,well-balanced carrier mobility and appropriate band gap,which offer potential in electronic and optoelectronic devices.It is believed that HfS₂ has the potential to be an ideal material for the preparation of low-power devices in the future.In this work,HfS₂ flakes up to 200 layers with varying color contrasts are fabricated by mechanical exfoliation method and transferred on SiO₂/Si substrate.The effects of main experimental factors:thickness of SiO₂,excitation wavelength and layer number on Raman intensities of HfS₂ flakes and molecules adsorbed on HfS₂ flakes are quantitatively studied both theoretically and experimentally by considering optical interference effect.Due to the low absorption of HfS₂,many strong high-order interference-induced enhancement peaks are observed which are different from high absorption materials like graphene and MoS₂,in which only 2-4 interference-induced enhancement peaks exist.For the first time,we found the surface enhanced Raman scattering（SERS）effect of HfS₂.Due to the environmental instability of single layer HfS₂ under ambient conditions,multi-layer HfS₂ is a better choice than single layer HfS₂ as a Raman scattering enhanced substrate which has a stronger SERS effect and a better environmental stability.The discovery here will expand the application of HfS₂flakes in molecular detection.2D materials MoS₂ is emerging as a desired material in the design and preparation of advanced devices in the future,and the thermal stability of devices is strongly related to the interfacial thermal conductance.It is of great significance to probe interfacial thermal conductance between MoS₂ flake and different substrates.Raman spectroscopy has been regarded as an effective tool to measure the interfacial thermal conductance of two-dimensional materials due to its excellent material selectivity and extremely high resolution,and optical heating Raman technology is also considered as one of the most successful method to detect the interfacial thermal conductance of two-dimensional materials.In this work,we prepared few-layer MoS₂ and graphene flakes by mechanical exfoliation method,and transferred MoS₂ on top of grapheme by dry transfer method.Interfacial thermal conductance of 5-layer（5L）MoS₂ supported on SiO₂/Si and on 3L graphene substrates are obtained by combing temperature and laser power-dependent Raman spectroscopy studies,which are 1.73±0.07 MWm^-2K^-11 and 2.56±0.08 MWm^-2K^-1,individually.The result shows that the high thermal conductance material graphene is used as a substrate for MoS₂ compared with SiO₂/Si,which could increase the interfacial thermal conductance value by 47.9%.In addition,we further explored the influence of absorption coefficient and in-plane thermal conductance of MoS₂ on the interface thermal conductance,and found the latter has a greater impact.Therefore,selecting the appropriate material graphene as the supporting substrate of MoS₂ can significantly improve the thermal stability of devices based on MoS₂,and the results here will shed light on experimentally probing interfacial thermal conductance between MoS₂ flake and different substrates.