Paper TF-TuP7
Synthesis of High-quality MoS₂ Atomic Layers with Inorganic Seeding Promoters by Chemical Vapor Deposition

Tuesday, December 13, 2016, 4:00 pm, Room Mauka

Molybdenum disulfide (MoS₂) is highlighted due to their unique physical and electrical properties such as ultrathin layered structure, high on/off ratio, and high mobility. The Band gap of layered-semiconductor MoS₂ is changed from 1.2 eV to 1. 9 eV depending on the layered thickness. Monolayer MoS₂ with direct band gap is an optimal material to develop novel optoelectronic devices. There are many method to prepare monolayer MoS₂ such as mechanically, chemically exfoliation, and chemical vapor deposition (CVD) method. Among them, the CVD method is inexpensive and easy to synthesize MoS₂ films with large scale and uniform thickness. In the CVD process, the absorption of vapor phase molybdenum and sulfur on the substrate is a problem for laterally layered growth of MoS₂. Recently, organic aromatic molecules helps the nucleation of MoS₂ in the CVD process. However, the organic materials are easily decomposed due to their thermal instability at the growth temperature. Herein, we first report the inorganic seeding promoter including alkali metal ions to grow high quality MoS₂ flakes. The size of the grown flakes was up to 200 um. The crystalline quality and the thickness of the MoS₂ were confirmed by AFM, Raman, and PL. The difference of typical Raman peaks of E_2g and A_1g is lower than ~19 cm^-1 with full width half maximum values of 3.8 cm^-1 and 4.5 cm^-1, respectively. This high quality is similar with mechanically exfoliated MoS₂. In addition, the size of the grown MoS₂ flakes can be tuned by concentration of the seeding promoters. The growth process with seeding promoters will be suggested in terms of surface reaction and nucleation of participating atoms and promoters on the surface. Our suggested inorganic seeding promoter will open the way to grow high quality monolayer MoS₂ flakes with scalable size.