Crystalline structure, electronic and lattice-dynamics properties of NbTe2

Abstract

Layered-structure materials are currently relevant given their quasi-2D nature. Knowledge of their physical properties is currently of major interest. Niobium ditelluride possesses a monoclinic layered-structure with a distortion in the tellurium planes. This structural complexity has hindered the determination of its fundamental physical properties. In this work, NbTe2 crystals were used to elucidate its structural, compositional, electronic and vibrational properties. These findings have been compared with calculations based on density functional theory. The chemical composition and elemental distribution at the nanoscale were obtained through atom probe tomography. Ultraviolet photoelectron spectroscopy allowed the first determination of the work function of NbTe2. Its high value, 5.32 eV, and chemical stability allow foreseeing applications such as contact in optoelectronics. Raman spectra were obtained using different excitation laser lines: 488, 633, and 785 nm. The vibrational frequencies were in agreement with those determined through density functional theory. It was possible to detect a theoretically-predicted, low-frequency, low-intensity Raman active mode not previously observed. The dispersion curves and electronic band structure were calculated, along with their corresponding density of states. The electrical properties, as well as a pseudo-gap in the density of states around the Fermi energy are characteristics proper of a semi metal.

Evolution of Structural and Electronic Properties in NbTe2 under High Pressure

“…The B g modes represent the atomic vibrations parallel to the b axis. Barajas-Aguilar et al calculated the position of these Raman peaks using density functional theory (DFT), 25 which conforms well to our measurement at the ambient pressure (see the comparison in Table 1). When the external pressure is applied, all Raman peaks shift to the high wavenumber direction.…”

Ultrafast Carrier Dynamics in 2D NbTe2 Thin Films

“…Characteristic peaks at ∼55 cm −1 , ∼83 cm −1 , ∼121 cm −1 , ∼140 cm −1 , ∼157 cm −1 , ∼168 cm −1 , ∼219 cm −1 , and ∼262 cm −1 can be observed, which correspond to the phonon modes of Ag 1 , Ag 2 , Ag 4 , Ag 5 , Ag 6 , Bg 4 , Ag 7 , and Ag 8 in NbTe2, respectively. [33][34] These results indicate the high crystal quality of the samples. Optical absorption spectra (from 400 nm to 900 nm) of NbTe2 flakes with different thicknesses were measured by using a UV-vis spectrometer, as shown in Figure 1(e).…”

Few-Layer NbTe2 Nanosheets as Substrates for Surface-Enhanced Raman Scattering Analysis

“…Apart from the C element (285 eV), six peaks including 44.1 (Te 4d), 576.1 (Te O2), 586.1 (Te 3d3), 822.1 (Te 3p3), 873.1 (Te 3p1), 1009.1 (Te 3s) were considered as the Te element, and three peaks including 206.1 (Nb 3d3), 365.1 (Nb 3p3), and 380.1 (Nb 3p1) belonged to the Nb element. The Raman spectrum of FL NTNs showed a slight difference from that of bulk NbTe 2 (Figure c), where characteristic peaks at 55, 95, 122, 168, 217, and 263 cm –1 belonged to the models of A g 1 , B g 2 , A g 4 , B g 4 , A g 7 , and A g 8 , respectively . Besides, the light absorption properties of NTNs (aqueous solution) were also investigated by a UV–vis–NIR absorbance spectrometer (Figure d), where a red-shift was observed on the absorption peak of FL NTNs (242 nm) compared with that of bulk NbTe 2 (223 nm).…”

“…Besides, 1T-phase MoS 2 , 2H-phase MoS 2 , and NbS 2 are also used for SERS analysis but with limited Raman enhancement compared to the noble metal structure. , 2D-layered niobium ditelluride (NbTe 2 ) has been demonstrated with charge density wave characteristics, strong electron coupling, superconductivity, electrocatalytic activity, the quantum spin Hall effect, and so on . Besides, there are strong covalent bonds between niobium and tellurium atoms within layers of NbTe 2 , while the weak van der Waals (VDW) interactions between layers ensure its strippable character . Up to now, NbTe 2 is basically synthesized by chemical vapor deposition (CVD), which had high quality but with the low deposition rate, harsh reaction conditions, a complicated process, and poor controllability …”