Homogeneity and tolerance to heat of monolayer MoS₂ on SiO₂ and h-BN

Abstract

We investigated the homogeneity and tolerance to heat of monolayer MoS2 using photoluminescence (PL) spectroscopy.

Changes in the Raman spectra of monolayer MoS2 upon thermal annealing

“…On the other hand, both E 1 2g and A 1g peaks of the basal plane and edge of the MoS 2 on h‐BN appear at approximately the same positions, respectively, although foreign molecules are also considered to be chemisorbed on the edge. That is, charge transfer between the electron‐depleted MoS 2 and the electron‐accepting molecules, such as O 2 molecules, is insufficient to shift the A 1g peak; as a result, monolayer MoS 2 on h‐BN has a homogeneous Raman spectra over the entire area, which is consistent with the results of PL measurements …”

“…On the other hand, thick (over quadlayer) MoS 2 on SiO 2 , as well as monolayer MoS 2 on h‐BN, was well preserved even after annealing up to 550°C and consecutive optical mappings. Optical microscopy images demonstrate that monolayer MoS 2 on h‐BN has enhanced tolerance to heat involving thermal annealing and laser irradiation compared with that on SiO 2 , which is due to the strong adhesion of MoS 2 on the atomically flat h‐BN …”

“…Thermal annealing above 450°C and consecutive optical mappings caused monolayer MoS 2 on SiO 2 to decompose and eventually disappear. However, monolayer MoS 2 on h‐BN showed an enhanced tolerance to heat due to its stronger interfacial adhesion compared with that between MoS 2 and SiO 2 , so that no noticeable changes in the optical images and Raman spectra were observed upon annealing up to 550°C. Figure plots the electrical measurement results of monolayer MoS 2 field effect transistors to investigate whether or not defects are created on MoS 2 on h‐BN during thermal annealing.…”

“…Acquisition times varied depending on the samples; otherwise, all other measurement parameters were fixed. Details of the sample preparation and optical measurements have been described in a previous report …”

Development of the Applications of Palladium on Charcoal in Organic Synthesis

“…Palladium is the most frequently used metal in catalysis, and heterogeneous palladium catalysts are most commonly used as efficient catalysts. They have indeed been largely applied to redox reactions including oxidation and hydrogenation, alkenylation, C−H bond functionalization, asymmetric synthesis and carbon‐carbon coupling reactions . In addition, they are of interest in the synthesis of natural products (such as γ‐lactams and γ‐lactones) and often employed in total syntheses .…”