Stress-Tuned Optical Transitions in Layered 1T-MX2 (M=Hf, Zr, Sn; X=S, Se) Crystals

Abstract

Optical measurements under externally applied stresses allow us to study the materials’ electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX2 compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX2 materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke–Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS2 and HfSe2 absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.

First-principles study on tunable optoelectronic properties of monolayer Mo1−xWxSe2 alloys and defect engineered electronic properties of Mo1−xWxSe2 alloys

“…Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDs) have been a widely established class of materials with various features that make them tremendously appealing for fundamental studies of nanophotonic and nanoelectronic applications [1]. Some intriguing schemes including 2D superconductivity [2][3][4], valley polarization [5], piezoelectric properties [6], optical transition [7], photocatalysis [8], electrocatalysis [9], thermoelectric properties [10], quantum spin Hall effect [11], supercapacitance [12], energy conversion [13], electromagnetic shielding [14] etc can occur in TMD monolayers. In recent years, they have been extensively studied in flexible devices [15], nanoelectronics [16], energy storage devices [17], biosensors [18], and light detecting devices [19].…”

Excitons and Phonons in Two-Dimensional Materials: From Fundamental to Applications

“…The purpose of this Special Issue entitled "Excitons and Phonons in Two-Dimensional Materials: From Fundamental to Applications" is to provide a unique international forum and to cover the entire range of fundamental and applied research associated with excitonic complexes and phonon modes in two-dimensional layered materials. This Special Issue is composed of nine published papers [6][7][8][9][10][11][12][13][14] devoted to investigations of different 2D materials, such as S-TMDs, perovskites, and the multilayered structure of thin films, with theoretical [7,9,11,13] and experimental [10] approaches, as well as their combination [6,8,12,14].…”

“…In Ref. [8], the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX 2 compounds (M = Hf, Zr, Sn; X = S, Se) are determined using the density functional theory. The studied transitions are optically active and exhibit in-plane polarisation of light with negative pressure coefficients.…”