Improved Ordering of Quasi-Two-Dimensional MoS₂ via an Amorphous-to-Crystal Transition Initiated from Amorphous Sulfur-Rich MoS_2+x

Abstract

The synthesis of stoichiometric two-dimensional (2D) transition-metal dichalcogenides (TMDC) over large areas remains challenging. Using a combination of X-ray diffraction and X-ray absorption spectroscopy, we demonstrate the advantages of using a thin amorphous layer of S-rich MoS2 (MoS4 in this paper) for the growth of well-ordered crystalline MoS2 films via annealing at 900 °C. In contrast to the crystallization of stoichiometric amorphous MoS2, the crystallization of the as-deposited amorphous MoS4 phase shows the strong preferred ordering of layered MoS2 on a Si/SiO x nontemplating substrate with the dominant (002) crystallographic plane and accompanying Kiessig fringes, which indicate the improved crystallinity of the MoS2 layers. A similar effect can only be achieved by the templated crystallization of an amorphous MoS2 thin film deposited on a c-plane sapphire substrate. We suggest that the crystal growth improvement originates from the lower coordination number (CN) of the Mo atoms in the MoS4 amorphous phase (CN = 4) in comparison with that of amorphous MoS2 (CN = 6) and the gradual release of free sulfur atoms from the thin film during crystallization.

Self-Constructing 100% Water-Resistant Metal Sulfides through In Situ Acid Etching for Effective Elemental Mercury (Hg0) Capture

“…Figure S1 shows the X-ray diffraction (XRD) patterns of CoS x as prepared in the presence of different concentrations of sulfuric acid (H 2 SO 4 ). Pristine CoS x as synthesized in the absence of H 2 SO 4 exhibited no obvious diffraction peak, indicating the amorphous nature of the synthetic CoS x via a precipitation method at room temperature. , Increasing the H 2 SO 4 concentration from 0.092 to 0.368 mol L –1 during the in situ acid-etching process did not significantly increase the crystallinity of CoS x . Only several isolated diffraction peaks probably belonging to cattierite (CoS 2 ), linnaeite (Co 3 S 4 ), tricobalt tetroxide (Co 3 O 4 ), and elemental sulfur (S 8 ) were observed.…”

Memory Effect on the Synthesis of Perovskite-Type Li-Ion Conductor LixLa2/3–x/3TiO3 (LLTO)

“…Epitaxial synthesis methods have been used to produce desired polymorphs, whereby depositing layers of atoms, metastable phases can be formed by limiting the kinetics. These include chemical vapor deposition to grow 2D WSe 2 /Bi 2 Te 3 and WS 2 /MoS 2 heterostructures, pulsed laser deposition (PLD) to form metastable MoS 2 , and selectively synthesizing brookite using PLD …”

NbTe4 Phase‐Change Material: Breaking the Phase‐Change Temperature Balance in 2D Van der Waals Transition‐Metal Binary Chalcogenide

“…[3,[6][7][8][9][10][11] As a result, MoTe 2 has been extensively studied as a switching layer in nextgeneration non-volatile memories (NVMs), such as resistive random access memory (ReRAM) and phase-change random access memory (PCRAM), due to the large changes in electrical properties ranging from metallic to semiconducting accessable by switching between phases. Zhang et al reported an electric-field-induced structural transition from a 2H semiconducting to a distorted transient [11,15,[29][30][31] the T c and T m values of NbTe 4 were defined by the onset temperature of crystallization and melting peaks in this study; B) XRD curves of NbTe 4 thin films annealed at various temperatures; C) cross-sectional TEM image of 350 °C annealed NbTe 4 thin film; D) zoomed in image of the white-box area in (C); E) the FFT pattern taken from the area of (D).…”

“…Recently, this technique has been applied for the large-area growth of TMDs such as MoTe 2 and MoS 2 . [11,15,16] Interestingly, as-deposited sputtered TMDs are typically amorphous; the layered crystalline structure can be formed by post-annealing at elevated temperature. Such an amorphousto-crystalline phase transition is often observed for chalcogenidebased phase-change materials (PCMs) such as Ge 2 Sb 2 Te 5 (GST) used in rewritable optical discs and PCRAM devices.…”

“…Figure 1. A) Comparison of T c and T m values of various 2D TM chalcogenides;[11,15,[29][30][31] the T c and T m values of NbTe 4 were defined by the onset temperature of crystallization and melting peaks in this study; B) XRD curves of NbTe 4 thin films annealed at various temperatures; C) cross-sectional TEM image of 350 °C annealed NbTe 4 thin film; D) zoomed in image of the white-box area in (C); E) the FFT pattern taken from the area of (D).…”