Electron Charging and Discharging in Double Layer Mechanically Exfoliated MoS₂ Flakes

Molybdenum disulphide (MoS₂) is a transition metal dichalcogenide (TMD) 2D material that has unique optical and electronic properties making it attractive for future electronic and photonic devices. Due to the quantum confinement effect in 2D MoS₂, it has a tuneable band gap which increases as the size decreases. MoS₂ can transition from bulk MoS₂ that has an indirect band gap of ~1.2eV to having direct band gap of ~1.8eV making, when it is as monolayer 2D MoS₂ [1]. Moreover, moving from bulk to MoS₂nanoparticles makes the quantum size effects noticeable [2]. In this work, we use MoS₂ flakes from mechanical exfoliation to fabricate a MOS-like device to study the electron charging and discharging effect.<br/><br/>Mechanical exfoliation was used to prepare the MoS₂ flakes, with a simple exfoliation approach involving scotch tape to exfoliate the crystal MoS₂. The flakes were transferred and bonded to an silicon wafer caped with thermal oxide. To ensure a uniform distribution of nanoflakes across the p-Si substrate, the MoS₂ flakes were taped and removed at different areas on the Si wafer. The produced flakes were then characterized using different tools to check its morphology and structure at which SEM and AFM images were generated showing mechanically exfoliated flakes with thicknesses ranging from 2 to 8 nm and a variety of shapes and structures.<br/><br/>Furthermore, the charging device have been fabricated with the structure MoS₂ on SiO₂/n-Si. This device is electrically characterized using conductive AFM. The IV results showed a large hysteresis effect indicating charging within the MoS₂ flake. The charge retention test also showed a stable and reproducible charging and discharging processes within the MoS₂ flake. Morever, these results show that MoS₂ flakes have interesting memory features and can be a viable charge storage element for future memory cells.<br/><br/>References<br/>[1] E. Zhang, W. Wang, C. Zhang, Y. Jin, G. Zhu, Q. Sun, D. W. Zhang, P. Zhou, and F. Xiu, “Tunable charge-trap memory based on few-layer MOS2,” ACS Nano, vol. 9, no. 1, pp. 612–619, 2014.<br/><br/>[2] L. Muscuso, S. Cravanzola, F. Cesano, D. Scarano, and A. Zecchina, “Optical, vibrational, and structural properties of MoS2 nanoparticles obtained by exfoliation and fragmentation via ultrasound cavitation in isopropyl alcohol,” The Journal of Physical Chemistry C, vol. 119, no. 7, pp. 3791–3801, 2015.