Angle resolved vibrational properties of anisotropic transition metal trichalcogenide nanosheets

Abstract

Layered transition metal trichalcogenides (TMTCs) are a new class of anisotropic two-dimensional materials that exhibit quasi-1D behavior. This property stems from their unique highly anisotropic crystal structure where vastly different material properties can be attained from different crystal directions. Here, we employ density functional theory predictions, atomic force microscopy, and angle-resolved Raman spectroscopy to investigate their fundamental vibrational properties which differ significantly from other 2D systems and to establish a method in identifying anisotropy direction of different types of TMTCs. We find that the intensity of certain Raman peaks of TiS, ZrS, and HfS have strong polarization dependence in such a way that intensity is at its maximum when the polarization direction is parallel to the anisotropic b-axis. This allows us to readily identify the Raman peaks that are representative of the vibrations along the b-axis direction. Interestingly, similar angle resolved studies on the novel TiNbS TMTC alloy reveal that determination of anisotropy/crystalline direction is rather difficult possibly due to loss of anisotropy by randomization distribution of quasi-1D MX chains by the presence of defects which are commonly found in 2D alloys and also due to the complex Raman tensor of TMTC alloys. Overall, the experimental and theoretical results establish non-destructive methods used to identify the direction of anisotropy in TMTCs and reveal their vibrational characteristics which are necessary to gain insight into potential applications that utilize direction dependent thermal response, optical polarization, and linear dichroism.

Emerging in‐plane anisotropic two‐dimensional materials

“…25,26 Since then, the polarizationdependent absorption, [26][27][28][29][30][31] Raman spectroscopy, [32][33][34] photoluminescence, [35][36][37] and the in-plane anisotropic electronic, 26,38,39 thermal, 40,41 and mechanical 42 properties of BP have been intensively studied. Ignited by BP, other inplane anisotropic 2D materials, from semimetals (T d WTe 2 , 43 1 T' MoTe 2,44,45 and ZrTe 5 46 TaIrTe 4 , 47,48 ) to semiconductors (group IV monochalcogenides, 49 Ta 2 NiS 5 , 50 GaTe, 51 group IVB trichalcogenides, 52 group IV-group V compounds, 53 70 TlSe, 71 ) (Table 1) and so on were explored. After developing for few years, the in-plane anisotropic 2D materials have becoming one of the most attractive research interests in the scientific field.…”

Electronics and optoelectronics of quasi-1D layered transition metal trichalcogenides

“…This character gives the TMTC class of materials strong anisotropies in their electrical and optical properties. [25][26][27][28][29][30][31] This anisotropy lends an additional degree of freedom in the fabrication of next generation electronics such as high mobility transistors benefiting from reduced backscattering from hot electrons [32][33][34] and novel integrated digital inverters 35 . More than this, these materials have great potential in electronics that rely on the generation and detection of polarized light, i.e, on-chip polarizers [36][37][38][39] , polarization sensitive photodetectors [40][41][42] , and polarized light emission 28,43,44 .…”

Quantum Effects Allow the Construction of Two‐Dimensional Co3O4‐Embedded Nitrogen‐Doped Porous Carbon Nanosheet Arrays from Bimetallic MOFs as Bifunctional Oxygen Electrocatalysts

“…Two-dimensional (2D) inorganicm aterials possess unique structuralf eatures, such as high anisotropy,e xpanded surface area, macroscopic ultra-thinness,a nd flexibility, [10][11][12][13] which not only allow ah igh density of surfacea ctive sites but also endows excellent mechanical and electronic properties. [14][15][16] Among 2D materials, carbon-based 2D materials display superior electrical conductivity,h igh carrierm obility,a nd strong structures tability,a nd have great potentials as electrocatalysts. [17][18][19][20][21][22] For example, phosphorus-doped ordered mesoporous carbons, [23] polyaniline-derived N-and O-doped mesoporous carbons, [24] and metal-free electrocatalysts assembled from carbon nanotubes andg raphene [25] have been reported to promote ORR activities.…”