Strain-induced vibrational properties of few layer black phosphorus and MoTe₂ via Raman spectroscopy

Abstract

We studied and compared the effect of tensile strain on the Raman spectra of black phosphorus (BP) and molybdenum ditelluride (MoTe2) crystals by using a simple custom strain device. In-situ Raman spectroscopy on BP revealed clear red shifting of all three phonon modes, A1 g, B2g and A2 g, under tensile stress. From our theoretical analyses, we found that such red shifting strongly depends on the direction of the strain exerted on the system even within the elastic deformation limit (i.e. strain ≤ 1 %). In particular, calculated results for the strain along the armchair direction are consistent with our experimental data, confirming that the strain applied to the sample acts effectively along the armchair direction. In a comparative study, we found that the effect of strain on the Raman shifting is larger for BP than that for MoTe2, presumably due to the smaller Young’s modulus of BP. We also see a remarkable resemblance between donor-type intercalation induced vibrational properties and tensile stress-induced vibrational properties in BP. We anticipate that our method of in-situ Raman spectroscopy can be an effective tool that can allow observation of strain effect directly which is critical for future flexible electronic devices.

Mechanistic Investigation of the Formation of Nickel Nanocrystallites Embedded in Amorphous Silicon Nitride Nanocomposites

“…Feshin et al reported that the coordination of N(CH 3 ) 3 to GeCl 4 causes the electron density redistribution to elongate the Ge-Cl bond length and increase the polarity of the Ge-Cl bond [ 41 ]. It is generally accepted that the red-shifts of Raman peaks can be interpreted as a decrease in the force constant of chemical bonds, since the frequency is proportional to the square root of the force constant [ 42 ]. Therefore, it could be analogically assumed that the N:→Ni dative bond formation makes the Ni-Cl bond of NiCl 2 weaker and more polar and, hence, more reactive.…”

Review of Anisotropic 2D Materials: Controlled Growth, Optical Anisotropy Modulation, and Photonic Applications

“…[ 191 ] The strain‐induced Raman shift is less in 1T‐MoTe 2 and 2H‐MoTe 2 than BP, possibly due to the relatively smaller Young's modulus. [ 192 ] An experimental study by our group has shown that under an off‐axis tensile strain, the Raman intensity of GaSe flake is suppressed in the strain direction. [ 193 ] The intrinsic fourfold‐symmetry of the E 2g 1 mode in angle‐dependent Raman spectra is tuned to a twofold‐symmetry (Figure 8e).…”

“…[191] The strain-induced Raman shift is less in 1T-MoTe 2 and 2H-MoTe 2 than BP, possibly due to the relatively smaller Young's modulus. [192] An experimental study by our group has shown that under an off-axis [199] Copyright 2018, American Physical Society. b) Schematic of the patterned BP nanoribbon and c) its optical absorption spectrum for x-and y-polarized light.…”

Symmetry induced phonon renormalization in few layers of 2H-MoTe2 transistors: Raman and first-principles studies

“…As Raman spectroscopy does not require any sample preparation, it has been extensively used as a non-invasive, contact-less, fast and accurate tool to determine strain [43], doping effects [13], layer number [17,44], crystal orientation [45], structural transitions between different polytypes [9,[11][12][13][14][46][47][48] in fewlayer MoTe 2 devices in ambient as well as different sample environments. Furthermore, Raman scattering has been employed in various 2D materials to measure electron-phonon coupling (EPC) that governs electronic transport properties [31,32].…”