Phase Engineering of Transition Metal Dichalcogenides via a Thermodynamically Designed Gas-Solid Reaction

Polymorph conversion of transition metal dichalcogenides (TMDs) offers intriguing material phenomena that can be applied for tuning the intrinsic properties of 2D materials. In general, group VIB TMDs can have thermodynamically stable 2H phases and metastable 1T/T' phases. Herein, we report key principles to apply carbon monoxide (CO)-based gas-solid reactions for a universal polymorph conversion of group VIB TMDs without forming undesirable compounds. We found that the process conditions are strongly dependent on the reaction chemical potential of cations in the TMDs, which can be predicted by thermodynamic calculations, and that polymorphic conversion is triggered by S vacancy (V-S) formation. Furthermore, we conducted DFT calculations for the reaction barriers of V-S formation and S diffusion to reveal the polymorph conversion mechanism of WS2 and compared it with that of MoS2. We believe that phase engineering 2D materials via thermodynamically designed gas-solid reactions could be functionally used to achieve defect-related nanomaterials.1

Robust Co alloy design for Co interconnects using a self-forming barrier layer

Abstract With recent rapid increases in Cu resistivity, RC delay has become an important issue again. Co, which has a low electron mean free path, is being studied as beyond Cu metal and is expected to minimize this increase in resistivity. However, extrinsic time-dependent dielectric breakdown has been reported for Co interconnects. Therefore, it is necessary to apply a diffusion barrier, such as the Ta/TaN system, to increase interconnect lifetimes. In addition, an ultrathin diffusion barrier should be formed to occupy as little area as possible. This study provides a thermodynamic design for a self-forming barrier that provides reliability with Co interconnects. Since Cr, Mn, Sn, and Zn dopants exhibited surface diffusion or interfacial stable phases, the model constituted an effective alloy design. In the Co-Cr alloy, Cr diffused into the dielectric interface and reacted with oxygen to provide a self-forming diffusion barrier comprising Cr2O3. In a breakdown voltage test, the Co-Cr alloy showed a breakdown voltage more than 200% higher than that of pure Co. The 1.2 nm ultrathin Cr2O3 self-forming barrier will replace the current bilayer barrier system and contribute greatly to lowering the RC delay. It will realize high-performance Co interconnects with robust reliability in the future

Selective hydrocarbon or oxygenate production in CO2 electroreduction over metallurgical alloy catalysts

Alloying of metals can be used to optimize intermediate binding during electrocatalysis but challenges remain in overcoming thermodynamic atomic miscibility in alloys. Here we report a coordination-controlled metal alloy in which copper clusters are spatially dispersed in a crystalline silver lattice to promote the electrochemical reduction of CO2 to ethanol. The synergistic interactions between Cu–Cu sites and Cu–Ag interfaces achieve highly selective hydrocarbon and oxygenate production by strengthening and diversifying the binding of *CO intermediates on terrace and defect sites. To control atomic coordinates beyond the miscibility limit and optimize the catalyst microstructure, sacrificial elements are incorporated with thermodynamically guided compositions to form intermetallic compounds. The sacrificial elements are then selectively dealloyed. Using a membrane electrode assembly, ethylene-selective production on copper catalysts (Faradaic efficiency, 69.6 ± 1.3%; full cell efficiency, 23.5%) is steered to ethanol-selective production on the supersaturated Ag–Cu solid-solution catalyst (Faradaic efficiency, 40.4 ± 2.4%; full cell efficiency, 14.4%). Metallurgy-designed catalyst fabrication enables the efficient chemical manufacturing of either hydrocarbons or oxygenates and offers guidelines for catalyst design principles. [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to Springer Nature Limited.FALS