Temperature-dependent Raman spectroscopy and thermal conductivity of TiS2 hexagonal nanodiscs

Explaining Mysterious “Shoulder” Raman Band in TiS2 by Temperature-dependent Anharmonicity and Defects

“…15,16 The presence of the shoulder has been reported for multiple laser wavelengths in the range of 488−633 nm (1.95−2.54 eV) with similar relative intensities of the A 1g and "Sh" features. [13][14][15][16][17][18][19][20]24 To date, the most often stated hypotheses of the origin of the A 1g band's shoulder involve phonon stiffening due to the presence of excess titanium atoms in the interlayer gaps [14][15][16]20,24,28 and the overtone (or summation) processes. 15,16,18,24 None of them has yet been fully confirmed.…”

“…Although many results have been reported regarding phonons in TiS 2 including Raman spectra at room temperature – and low temperatures (below 100 K), – infrared reflectance measurements, , neutron scattering, and theoretical works considering phonons in TiS 2 within the harmonic approximation ,,– phonon structure of this material is still poorly understood. There are two major concerns, yet unexplained, regarding typically reported Raman spectra in TiS 2 : According to the symmetry of the pristine TiS 2 crystalthermodynamically stable in the trigonal phase ( P 3̅ m 1, CdI 2 -type structure) , often denoted as 1 T precisely two phonon modes are expected to affect the polarizability of the material and lead to Raman scattering: in-plane E g (∼235 cm –1 at the room temperature) and out-of-plane A 1g (∼335 cm –1 ). – However, the majority of reported Raman spectra also reveal the existence of an additional band at about 370–390 cm –1 , in the high-energy vicinity of the A 1g mode (Figure a)commonly called “shoulder” or “Sh” mode. , The presence of the shoulder has been reported for multiple laser wavelengths in the range of 488–633 nm (1.95–2.54 eV) with similar relative intensities of the A 1g and “Sh” features. – , To date, the most often stated hypotheses of the origin of the A 1g band’s shoulder involve phonon stiffening due to the presence of excess titanium atoms in the interlayer gaps – ,,, and the overtone (or summation) processes. ,,, None of them has yet been fully confirmed. The temperature evolution of the phonon frequencies evaluated within Raman experiments is intriguing. First, the measured temperature dependence of the out-of-plane A 1g and “Sh” bands’ positions significantly depends on the sample preparationleading to different slopes dω/d T in representative reports – (see...…”

“…According to the symmetry of the pristine TiS 2 crystalthermodynamically stable in the trigonal phase ( P 3̅ m 1, CdI 2 -type structure) , often denoted as 1 T precisely two phonon modes are expected to affect the polarizability of the material and lead to Raman scattering: in-plane E g (∼235 cm –1 at the room temperature) and out-of-plane A 1g (∼335 cm –1 ). – However, the majority of reported Raman spectra also reveal the existence of an additional band at about 370–390 cm –1 , in the high-energy vicinity of the A 1g mode (Figure a)commonly called “shoulder” or “Sh” mode. , The presence of the shoulder has been reported for multiple laser wavelengths in the range of 488–633 nm (1.95–2.54 eV) with similar relative intensities of the A 1g and “Sh” features. – , To date, the most often stated hypotheses of the origin of the A 1g band’s shoulder involve phonon stiffening due to the presence of excess titanium atoms in the interlayer gaps – ,,, and the overtone (or summation) processes. ,,, None of them has yet been fully confirmed.…”

Investigation of Temperature-Dependent Phonon Anharmonicity and Thermal Transport in SnS Single Crystals

“…However, a comprehensive and careful analysis of the origin of its intrinsically low κ L is still relatively rare. TDRS, a fast, accurate, and nondestructive method, is a powerful means to study the phonon anharmonicity. − Therefore, it is necessary to utilize Raman spectroscopy, combined with theoretical calculations, to reveal the phonon scattering mechanism of SnS crystals.…”