Study of the hydrostatic pressure dependence of the Raman spectrum of W/WS₂ fullerene-like nanosphere with core–shell structure

Abstract

The structural behavior of a W/WS2 fullerene-like nanosphere with a core–shell structure has been studied in the hydrostatic pressure range from atmospheric pressure to 18 GPa by Raman spectroscopy using a methanol–ethanol–water mixture (16:3:1) as the pressure transmitting medium (PTM). We found that it is interesting that the intensity ratio of the LA+TA mode and the A1g mode changes with increasing pressure. We attribute this change to the shape transformation of an inorganic fullerene-like IF-W/WS2 nanosphere under high hydrostatic pressure. By comparing the Raman spectra of an IF-W/WS2 nanosphere released from high pressure with that of the original one, we found that the change in morphology is reversible. This indicates that the spherical shape of the IF-W/WS2 has excellent behavior in resisting compression.

Correlatively Dependent Lattice and Electronic Structural Evolutions in Compressed Monolayer Tungsten Disulfide

“…All Raman peaks show blue shifts with pressure. An unknown phonon mode appearing on the lower wavenumber side of A 1 ′ at 0.87 GPa is denoted as B mode, which is first discovered in our monolayer WS 2 after comparing to previous reports on WS 2 bulk or nanotubes (Supporting Information, Section 8, for discussion). − This Raman-inactive B mode, that is, Raman-inactive vibration, is activated by structural disorder. Upon further compression, the Raman spectra with fitted curves present tiny shoulders emerging on the right side of B (∼424 cm –1 ) at 1.93 GPa and on the right side of A 1 ′ (around 448 cm –1 ) at 4.46 GPa (Figure a).…”

“…could be a qualitative indicator for the severity of structural disorder. 29 Because of the comparatively large curvature and hollow core, compressed WS 2 nanotubes in DAC has the intensity of B 1u even higher than A 1g . 30 For monolayer WS 2 on Si/SiO 2 substrate here, is ∼0.33 at 0.87 GPa, reaches the maximum 0.7 at 2.42 GPa, and then fluctuates around 0.6 afterward (Figure S4).…”

“…Given the noncoherent character of Raman scattering light, symmetry is vital to Raman intensity in that it directly influences matrix elements of polarizability tensors . Therefore, the intensity ratio could be a qualitative indicator for the severity of structural disorder . Because of the comparatively large curvature and hollow core, compressed WS 2 nanotubes in DAC has the intensity of B 1u even higher than A 1g .…”

Splitting of monolayer out-of-planeA1′Raman mode in few-layerWS2

“…The in-phase and outof-phase vibrational pattern of the A 1g /B 1u pair in bulk WS 2 finds its counterpart in the variety of in-and outof-phase vibrations observed in FL-WS 2 . In WS 2 nanomaterials, the B 1u mode gains in Raman intensity and its evolvement can be followed in WS 2 nanomaterials under pressure [29,36], in different layer orientation in thin films [37] and in different diameter WS 2 nanotubes [29,38]. In these cases, a strong resonance behavior is observed as well, much like in FL-WS 2 : the modes not allowed in a first-order Raman process appear most strongly when the excitation energy is in or close to resonance with the optical transitions.…”

Raman spectroscopic investigations on transition‐metal dichalcogenides MX2 (M = Mo, W; X = S, Se) at high pressures and low temperature

“…By mechanical exfoliation technique, indirect band gap of bulk MoS 2 was found to increase gradually with the decreasing number of layers resulting in the direct band gap in a single‐layer sample. These sizeable band gaps make single layer semiconducting TMDCs such as MoS 2 , WS 2 , MoSe 2 and WSe 2 well suited for electronic applications such as transistors, photodetectors and electroluminescent devices . Apart from this, considering interest has also been shown by the researchers in high‐pressure and low‐temperature studies to explore the chemical and structural information of the materials.…”