ABSTRACT
We theoretically investigate the full thermal transport and optoelectronic features of two estab- lished van der Waals (vdW) heterostructures based on the recently synthesized monolayer of C 3 N using the machinery of the Boltzmann transport and GW+BSE calculations. Among the structures, C 3 N/hBN tends to exhibit a small indirect gap semiconducting nature with an admixture of com- paratively higher 'flat-and-dispersiveness' and band degeneracy in the conduction band minima. A nearly comparable high thermoelectric power factor is observed for both the charge carriers at 300 K and 900 K at specific concentrations. The other material, C 3 N/graphene however maintains a low Seebeck coefficient with large electrical conductivity which correctly manifests its metallic character. A combination of low atomic mass, higher anharmonicity and longer lifetime of acous- tic phonons in C 3 N/hBN results in an intermediate lattice thermal conductivity (196 Wm -1 K -1 ) at room temperature as compared to its constituent monolayers. Under heavy n-type doping, C 3 N/hBN hetero-bilayer displays a figure of merit value of 0.13 (and 0.36) at room temperature (and at 900 K). As per the optical signatures are concerned, C 3 N/hBN reveals two distinct absorp- tion peaks with a high electron-hole quasiparticle interaction energy correction. Besides both the structures display a much better absorption throughout the spectrum compared to graphene. We expect these findings will motivate future research in designing thermoelectric and optoelectronic materials made of light mass, earth-abundant and non-toxic elements.
ABSTRACT
Two dimensional transition metal trihalides have drawn attention over the years due to their intrinsic ferromagnetism and associated large anisotropy at nanoscale. The interactions involved in these layered structures are of van der Waals types which are important for exfoliation to different thin samples. This enables one to compare the journey of physical properties from bulk structures to monolayer counterpart. In this topical review, the modulation of electronic, magnetic and optical properties by strain engineering, alloying, doping, defect engineering etc have been discussed extensively. The results obtained by first principle density functional theory calculations are verified by recent experimental observations. The relevant experimental synthesis of different morphological transition metal trihalides are highlighted. The feasibility of such routes may indicate other possible heterostructures. Apart from spintronics based applications, transition metal trihalides are potential candidates in sensing and data storage. Moreover, high thermoelectric figure of merit of chromium trihalides at higher temperatures leads to the possibility of multi-purpose applications. We hope this review will give important directions to further research in transition metal trihalide systems having tunable band gap with reduced dimensionalities.
