Atomic‐Scale Edge Morphology, Stability, and Oxidation of Single‐Layer 2H‐TaS₂

Abstract

Tantalum disulphide belongs to the group of transition metal dichalcogenides (TMDs) and has attracted attention for its unique structural, electronic, and catalytic properties. Herein, we report the edge properties of single-layer 2H-TaS 2 studied by using density functional theory calculations, because the knowledge of the edge morphology, stability, and surface energy is essential for the determination of nanoparticle shapes and understanding the nature of catalytically active sites. We calculate the grand canonical potential of TaS 2 clusters having various edge morphologies to evaluate the edge energies of the Ta-edge and S-edge terminated surfaces. Under S-rich conditions, the most likely shape of TaS 2 is a deformed hexagon dominated by the Ta-edge covered by S monomers, while the triangular shape is preferred under S-poor conditions. Exposed edges of the single-layer TaS 2 are susceptible to oxidation in air because both oxygen adsorption and substitution at the edge are strongly exothermic, À 0.96 and À 2.20 eV for single O atom, respectively. The XPS calculation shows that specific initial steps of oxidative process (adsorption, vacancy creation, substitution) are unlikely to be distinguished in the XPS spectra due to small shift of respective binding energies, but initial edge oxidation of TaS 2 should be observable by an asymmetry of the Ta 4f doublet towards higher binding energies.

Unidirectional growth of epitaxial tantalum disulfide triangle crystals grown on sapphire by chemical vapour deposition with a separate-flow system

“…Furthermore, all the (0 0 0 l ) diffraction peaks are sharp and intense, meaning the considerable good crystallinity of the films. The oxide phase is not seen in the XRD patterns, indicating that the surface oxide layer was scarcely present, 47–51 consistent with the XPS spectra shown later. A TEM image and electron diffraction pattern were also obtained to confirm the crystallinity of the triangle domains as shown in Fig.…”

Effect of Oxygen Poisoning on the Bidirectional Hydrogen Electrocatalysis in TaS2 Nanosheets

“…Theoretical modeling of the first step of the oxidation of 2H-TaS 2 indicates a preference for the oxygen atoms to be absorbed on the edge of the nanosheets at the bridge position between edge S and Ta atoms. Hence, the oxygen is in direct contact with both the Ta and the S atoms through new covalent bonds . Another theoretical study supports that 1T-TaS 2 is oxidized at their edges upon exposure to oxygen/air .…”

“…Hence, the oxygen is in direct contact with both the Ta and the S atoms through new covalent bonds. 22 Another theoretical study supports that 1T-TaS 2 is oxidized at their edges upon exposure to oxygen/air. 23 Note that the valence band feature of intercalated TaS 2 in UPS (Figure 2B) was completely suppressed after 5 days of air exposure indicating the opening of the band gap since the formed tantalum oxide or tantalum sulfur oxide is an insulator and that explains the decrease in conductivity.…”

“…In the literature, the thermally oxidized 2D layer of TaS 2 can be transformed into Ta 2 O 5 as identified by the Ta4f of the doublet at 26 and 28 eV. 21 The situation of the spontaneously oxidized HAintercalated TaS 2 is certainly not giving the pure Ta 2 O 5 but rather another complex composition with sulfur oxide groups (possibly with SO 2 groups as proposed in the theoretical study 22 ) since the Ta4f doublet is shifted by 1 eV toward high energy. After 30 days of exposure, the Ta4f feature from intercalated TaS 2 is close to almost completely suppressed; instead, the oxidized Ta is dominant because of the oxidation of intercalated TaS 2 in air.…”

Computational Methods for Charge Density Waves in 2D Materials

“…Regarding 2D TaS 2 , several groups use computational methods to answer questions involving this CDW material and its structures. For instance, Lazar et al, analyzed the structure of thin TaS 2 , focusing on the 1 T and 2 H phases [ 114 , 115 ]. A commensurate charge density wave phase was derived from first principles, and both the vdW interaction and electron–electron interactions were included by using the exact exchange approximation (EXX) as well as the random phase approximation (RPA).…”