Intermolecular Interactions in Self-Assembly Process of Sodium Dodecyl Sulfate by Vertically Polarized Raman Spectra

Molecular self-assembly is extremely important in many fields, but the characterization of their corresponding intermolecular interactions is still lacking. The C-H stretching Raman band can reflect the hydrophobic interactions during the self-assembly process of sodium dodecyl sulfate （SDS） in aqueous solutions. However, the Raman spectra in this region are seriously overlapped by the OH stretching band of water. In this work, vertically polarized Raman spectra were used to improve the detection sensitivity of spectra of C-H region for the first time. The spectral results showed that the first critical micelle concentration and the second critical micelle concentration of SDS in water were 8.5 and 69 mmol/L, respectively, which were consistent with the results given by surface tension measurements. Because of the high sensitivity of vertically polarized Raman spectra, the critical micelle concentration of SDS in a relatively high concentration of salt solution could be obtained in our experiment. The two critical concentrations of SDS in 100 mmol/L NaCl solution were recorded to be 1.8 and 16.5 mmol/L, respectively. Through comparing the spectra and surface tension of SDS in water and in NaCl solution, the self-assembly process in bulk phase and at interface were discussed. The interactions among salt ions, SDS and water molecules were also analyzed. These results demonstrated the vertically polarized Raman spectra could be employed to study the self-assembly process of SDS in water.

Different angle-resolved polarization configurations of Raman spectroscopy: A case on the basal and edge plane of two-dimensional materials

Angle-resolved polarized Raman（ARPR） spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials.However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations： 1） to change the polarization of the incident laser, 2） to rotate the sample, and 3） to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite（HOPG） exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of twodimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.

Polarization Raman spectra of graphene nanoribbons

The on-surface synthesis method allows the fabrication of atomically precise narrow graphene nanoribbons(GNRs),which bears great potential in electronic applications.Here,we synthesize armchair graphene nanoribbons(AGNRs)and chevron-type graphene nanoribbons(CGNRs)array on a vicinal Au(111112)surface using 10,10′-dibromo-9,9′-bianthracene(DBBA)and 6,12-dibromochrysene(DBCh)as precursors,respectively.This process creates spatially wellaligned GNRs,as characterized by scanning tunneling microscopy.AGNRs show strong Raman linear polarizability for application in optical modulation devices.Different from the distinct polarization of AGNRs,only weak polarization exists in CGNRs polarized Raman spectrum,which suggests that the presence of the zigzag boundary in the nanoribbon attenuates the polarization rate as an important factor affecting the polarization.We analyze the Raman activation mode of CGNRs using the peak polarization to expand the application of the polarization Raman spectroscopy in nanoarray analysis.

Visualization of Ferroelectric Domains in Thin Films of Molecular Materials Using Confocal Micro-Raman Spectroscopy

Ferroelectrics are an important class of functional materials.Among all their unique properties,the study of their ferroelectric domains and domain walls is of great interest due to their importance in ferroelectric applications.There are many methods to characterize ferroelectric domains,namely,scanning probe microscopy,optical microscopy,electron microscopy,etc.Currently,newly emerged molecular ferroelectrics are attracting much attention from chemists,physicists and researchers in material sciences due to their structural flexibility,light mass,simple fabrication,etc.However,for the characterization of molecular ferroelectric domains,most conventional methods require either a complicated preparation process or direct contact between physical probes and material surfaces,limiting the development of molecular ferroelectric materials.In this report,we have demonstrated that confocal micro-Raman spectroscopy,as a nondestructive and noncontact in-situ method,is very suitable for studying the ferroelectric polarization and structures of domains in molecular ferroelectrics.Taking recently reported molecular ferroelectric trimethylchloromethyl ammonium trichlorocadmium(II)(TMCM-CdCl_(3))as an example,the non-180°domains have been characterized and visualized at different temperatures.Such a simple and extendable method requires minimum sample preparation,which would further benefit the research of molecular ferroelectric domain engineering and promote the miniaturization and integration of molecular ferroelectric films.

Identification of vibrational mode symmetry and phonon anharmonicity in SbCrSe_(3)single crystal using Raman spectroscopy

Developing an understanding of the physics underlying vibrational phonon modes,which are strongly related to thermal transport,has attracted significant research interest.Herein,we report the successful synthesis of bulk SbCrSe_(3)single crystal and its thermal transport property over the temperature range from 2 to 300 K.Using angle-resolved polarized Raman spectroscopy(ARPRS)and group theory calculation,the vibrational symmetry of each observed Raman mode in the cleaved(001)crystal plane of SbCrSe_(3)is identified for the first time,and then further verified through firstprinciples calculations.The ARPRS results of some Raman modes(e.g.,Ag2~64 cm-1 and Ag 7~185 cm-1)can be adopted to determine the crystalline orientation.More importantly,the temperature dependence of the lattice thermal conductivity(κL)is revealed to be more accurately depicted by the three-phonon scattering processes throughout the measured temperature range,substantiated by in-situ Raman spectroscopy analysis and the model-predictedκL.These results reveal the fundamental physics of thermal transport for SbCrSe_(3)from a completely new perspective and should thus ignite research interest in the thermal properties of other lowdimensional materials using the same strategy.

Unravelling the anisotropic light-matter interaction in strainengineered trihalide MoCl_(3)

Layered trihalides exhibit distinctive band structures and physical properties due to the sixfold coordinated 3d or 4d transition metal site and partially occupied d orbitals,holding great potential in condensed matter physics and advanced electronic applications.Prior research focused on trihalides with highly symmetric honeycomb-like structures,such as CrI3 andα-RuCl_(3),while the role of crystal anisotropy in trihalides remains elusive.In particular,the trihalide MoCl_(3) manifests strong in-plane crystal anisotropy with the largest difference in Mo–Mo interatomic distances.Research on such material is imperative to address the lack of investigations on the effect of anisotropy on the properties of trihalides.Herein,we demonstrated the anisotropy of MoCl_(3) through polarized Raman spectroscopy and further tuned the phonon frequency via strain engineering.We showed the Raman intensity exhibits twofold symmetry under parallel configuration and fourfold symmetry under perpendicular configuration with changing the polarization angle of incident light.Furthermore,we found that the phonon frequencies of MoCl_(3) decrease gradually and linearly with applying uniaxial tensile strain along the axis of symmetry in the MoCl_(3) crystal,while those frequencies increase with uniaxial tensile strain applied perpendicularly.Our results shed light on the manipulation of anisotropic light-matter interactions via strain engineering,and lay a foundation for further exploration of the anisotropy of trihalides and the modulation of their electronic,optical,and magnetic properties.