RESUMO
A fundamental understanding of the transition metal dichalcogenide (TMDC)-metal interface is critical for their utilization in a broad range of applications. We investigate how the deposition of palladium (Pd), as a model metal, on WTe2(001), leads to the assembly of Pd into clusters and nanoparticles. Using X-ray photoemission spectroscopy, scanning tunneling microscopy imaging, and ab initio simulations, we find that Pd nucleation is driven by the interaction with and the availability of mobile excess tellurium (Te) leading to the formation of Pd-Te clusters at room temperature. Surprisingly, the nucleation of Pd-Te clusters is not affected by intrinsic surface defects, even at elevated temperatures. Upon annealing, the Pd-Te nanoclusters adopt an identical nanostructure and are stable up to â¼523â K. Density functional theory calculations provide a foundation for our understanding of the mobility of Pd and Te atoms, preferential nucleation of Pd-Te clusters, and the origin of their annealing-induced monodispersity. These results highlight the role the excess chalcogenide atoms may play in the metal deposition process. More broadly, the discoveries of synthetic pathways yielding thermally robust monodispersed nanostructures on TMDCs are critical to the manufacturing of novel quantum and microelectronics devices and catalytically active nano-alloy centers.
RESUMO
Homogenous single-layer MoS2films coated with sub-single layer amounts of gold are found to isolate the reaction of methanol with carbon monoxide, the fundamental step toward higher alcohols, from an array of possible surface reactions. Active surfaces were prepared from homogenous single-layer MoS2films coated with sub-single layer amounts of gold. These gold atoms formed clusters on the MoS2surface. A gas mixture of carbon monoxide (CO) and methanol (CH3OH) was partially converted to acetaldehyde (CH3CHO) under mild process conditions (308 kPa and 393 K). This carbonylation of methanol to a C2species is a critical step toward the formation of higher alcohols. Density functional theory modeling of critical steps of the catalytic process identify a viable reaction pathway. Imaging and spectroscopic methods revealed that the single layer of MoS2facilitated formation of nanoscale gold islands, which appear to sinter through Ostwald ripening. The formation of acetaldehyde by the catalytic carbonylation of methanol over supported gold clusters is an important step toward realizing controlled production of useful molecules from low carbon-count precursors.
RESUMO
The band structures of the transition metal dichalcogenides (TMD's) 2H-MoS2(0001) and 2H-WSe2(0001), before and after palladium adsorption, were investigated through angle-resolved photoemission. Palladium adsorption on 2H-MoS2(0001) is seen to result in very different band shifts than seen for palladium on 2H-WSe2(0001). The angle resolved photoemission results of palladium adsorbed on WSe2(0001) indicate that palladium accepts electron density from substrate. The resulting band shift will lead to a decrease in the barriers to the hole injection. The opposite band shifts occur upon palladium adsorption between 2H-MoS2(0001). The overall trend is consistent with the deposition of other metals deposited on TMD's, except that for palladium adsorption on MoS2(0001), there is an increase in the MoS2(0001) substrate band gap with palladium adsorption, as is evident from the combination of photoemission and inverse photoemission.
