Investigation of phonon modes in 2H-TaX2 (X = S/Se) flakes with electrostatic doping

Abstract

Electrostatic doping-assisted phonon softening has been intensively investigated in semiconducting transition metal dichalcogenides (TMDCs), in which strong electron–phonon interactions can be achieved in thin layers. Though electron–phonon coupling plays an important role in structure phase transitions for metallic 2H-TaX2 (X = S, Se), it has been rarely studied under electrostatic doping. Here, the effect of electrostatic doping on the vibrational phonon modes of 2H-TaSe2 and 2H-TaS2 thin films is studied with ionic liquid gating by the electric-double-layer gating technique. Under a gate bias (VG) of 1.5 V, 2H-TaSe2 has a blue shift of 7 cm−1 and a red shift of 3 cm−1 for the in-plane (E2g) and out-of-plane vibration (A1g) modes, respectively, indicating a strong electron–phonon interaction in both intralayer and interlayer. By varying the thickness of the flakes, it has been found that there exists a threshold VG value for the stiffening of the E2g mode and the softening of the A1g mode because of the strong electrostatic screening effect at lower doping density. As the intensity of the E2g mode decreases with VG, an anomalous enhancement of the A1g phonons can be achieved, which is further convinced in TaS2. The asymmetric phonon evolution behavior is very different with that in the semiconducting TMDCs, which may provide useful information for understanding electron–phonon interplay in metallic layer materials.

Hard Ferromagnetism Down to the Thinnest Limit of Iron-Intercalated Tantalum Disulfide

“…These data demonstrate that chemical intercalation is a viable method for accessing Fe x TaS 2 in the few-layer limit with the potential to vary the stoichiometry and homogeneity. We find that all Raman spectra in Figure e–g display a red shift in the A 1g mode by 8–10 cm –1 from the expected value for 2 H -TaS 2 . , This shift is consistent with electron transfer from Fe to the host lattice, , in agreement with our DFT calculations. For all calculated structures and magnetic configurations, we found that Fe converges to a +2 oxidation state, matching our electron energy loss spectroscopy results (Figure S12) and published experimental data on bulk Fe x TaS 2 . − We note that without annealing these chemically intercalated materials, we observe neither superlattice spots in NBED data nor significant changes to the Raman spectra (Figure S5).…”

“…We find that all Raman spectra in Figure 1e−g display a red shift in the A 1g mode by 8−10 cm −1 from the expected value for 2H-TaS 2 . 34,35 This shift is consistent with electron transfer from Fe to the host lattice, 36,37 in agreement with our DFT calculations. For all calculated structures and magnetic configurations, we found that Fe converges to a +2 oxidation state, matching our electron energy loss spectroscopy results (Figure S12) and published experimental data on bulk Fe x TaS 2 .…”

“…Finally, the bilayer sample exhibits a substantially broad feature in the low-frequency region, pointing to a high level of intercalant disorder. Although sharp Fe-related modes are absent in this sample, the red-shifted A 1 mode reveals that the TaS 2 lattice has been electrondoped, 36,37 and STEM-EDS confirms the substantial intercalation of Fe. Taken together, we suggest that structural disorder, which is encouraged by reduced dimensionality, likely promotes the observed broadened magnetic responses in ultrathin Fe x TaS 2 .…”

Facile synthesis of cardanol‐based reactive diluents and application for anti‐shrinkage UV‐curable resins

“…Cardanol is the main component of renewable resources from cardanol shell liquid, and there are rigid benzene ring and flexible C15 unsaturated chain in its structure, 18,19 which was used to preparation of cardanol‐based softener, surfactant, diluent 20–26 . Cardanol was utilized to fabricate UV‐curable resins, which endow UV‐curing resin with good flexibility, hydrophobicity, heat resistance, and other excellent properties 27–31 .…”