Spin-states in MoS2 thin-film transistors distinguished by operando electron spin resonance

Abstract

Transition metal dichalcogenide MoS2 is a two-dimensional material, attracting much attention for next-generation applications thanks to rich functionalities stemming from its crystal structure. Many experimental and theoretical works have focused on the spin-orbit interaction which couples the valley and spin degrees of freedom so that the spin-states can be electrically controllable. However, the spin-states of charge carriers and atomic vacancies in devices have not been yet elucidated directly from a microscopic viewpoint. Here, we report the spin-states in thin-film transistors using operando electron spin resonance spectroscopy. We have observed clearly different electron spin resonance signals of the conduction electrons and atomic vacancies, and distinguished the corresponding spin-states from the signals and theoretical calculations, evaluating the gate-voltage dependence and the spin-susceptibility and g-factor temperature dependence. This analysis gives deep insight into the MoS2 magnetism and clearly indicates different spin-scattering mechanisms compared to graphene, which will be useful for improvements of the device characteristics and new applications.

High Charge Transfer from C60 Pyrrolidine Tris-Acid to SnO2 Electron Transport Layer Directly Observed by ESR Spectroscopy

“…The consistency of ESR parameters indicates that the observed signal of the SnO 2 –CPTA is from the CPTA. The Δ H pp is a parameter indicating the environment of the spin, − while the constant Δ H pp parameter of the ESR signal of the CPTA and SnO 2 –CPTA implies that the spins of CPTA are not affected by SnO 2 . Thus, it can be inferred that the charges of CPTA are accumulated in the bulk area of CPTA (Figure a).…”

“…Researchers reported that the signal of PC 61 BM cannot be observed at room temperature even with the use of the thick polymer/fullerene blend layers due to the short spin–lattice relaxation time, which is the time it takes for the absorbed microwave energy to be transferred to the lattice vibration. − This is why almost no signals were observed in the PC 61 BM thin film (Figure d) under dark and light irradiation conditions. Researchers reported that when PC 61 BM is layered with ZnO, the anion signal of PC 61 BM can be observed at room temperature and obtained a slightly larger g factor of PC 61 BM ( g = 2.0004) than that in bulk heterojunction ( g = 1.999) at low temperature due to a mixing of wave functions between PC 61 BM and ZnO. ,, The reported ESR parameters of the anion signal of PC 61 BM ( g = 2.0004) are consistent with the observed ESR signal of SnO 2 –PC 61 BM ( g = 2.0003). , Thus, it can be inferred that the anion signal of PC 61 BM was observed for the SnO 2 –PC 61 BM layered film.…”

“…Perovskite solar cells (PSCs) attracted much attention because of their advantage in solution processability, bandgap tunability, large absorption coefficient, and long diffusion lengths over the other solar cells. − Fullerene-passivated SnO 2 electron transport layers (ETLs) have been widely investigated recently. − Passivating the SnO 2 ETL with a C 60 pyrrolidine tris-acid (CPTA) (Figure a) or a [6,6]-phenyl C 61 -butyric acid methyl ester (PC 61 BM) (Figure b) improves the device performance of PSCs because these fullerene modified SnO 2 ETLs demonstrate a smaller trap state density and a higher interfacial charge transfer. − , Furthermore, the SnO 2 passivated using the CPTA yields a higher device performance than that passivated using the PC 61 BM in the PSCs because the chemical bonding between CPTA and SnO 2 enhanced the electron injection and reduced recombination rates in the PSCs, while the PC 61 BM only exhibits a physical coating with SnO 2 . , However, a lack of a thorough knowledge of charge transfer and accumulation still exists, which prevents the development of more efficient fullerene derivatives for high-performance PSCs. Electron spin resonance (ESR) is an effective method for studying the charge accumulation states in a material by directly observing unpaired electrons. − Studying the difference in charge accumulation states between different fullerene-passivated SnO 2 ETLs from a microscopic viewpoint is very interesting.…”

Spin-Valley Locking for In-Gap Quantum Dots in a MoS2 Transistor

“…Out-of-plane Zeeman shifts have been demonstrated, , in transport through both defects and electrostatically defined quantum dots, reporting out-of-plane g -factors ranging from 3.4 to 15.8 and 0.8–2.4, respectively. While we cannot fully exclude the possibility that the out-of-plane g -factor of D 1 could represent a pure spin state without any valley-Zeeman contribution, the large g -factor observed for D 2 , and the pronounced g -factor anisotropy observed in both transitions, can only be explained by a combination of spin and valley Zeeman effects. Further extracting the respective contributions of spin- and valley g -factors to the total effective g -factor would require knowledge of the precise charge occupation and spin-valley eigenspectrum, neither of which is known with certainty.…”

Constructing Reactive Micro‐Environment in Basal Plane of MoS2 for pH‐Universal Hydrogen Evolution Catalysis

“…Figure 2c exhibits a robust signal in the spectrum of MoS 2 -S V at the g value of 2.002, which is originated from unpaired electrons of sulfur vacancies. [52,53] However, the signal is lessened by cobalt doping, signifying cobalt atoms can fill up the sulfur vacancies.…”