Discovery, properties and applications of tungsten and its inorganic compounds

Origins of Fermi Level Pinning for Ni and Ag Metal Contacts on Tungsten Dichalcogenides

Tungsten transition metal dichalcogenides (W-TMDs) are intriguing due to their properties and potential for application in next-generation electronic devices. However, strong Fermi level (EF) pinning manifests at the metal/W-TMD interfaces, which could tremendously restrain the carrier injection into the channel. In this work, we illustrate the origins of EF pinning for Ni and Ag contacts on W-TMDs by considering interface chemistry, band alignment, impurities, and imperfections of W-TMDs, contact metal adsorption mechanism, and the resultant electronic structure. We conclude that the origins of EF pinning at a covalent contact metal/W-TMD interface, such as Ni/W-TMDs, can be attributed to defects, impurities, and interface reaction products. In contrast, for a van der Waals contact metal/TMD system such as Ag/W-TMDs, the primary factor responsible for EF pinning is the electronic modification of the TMDs resulting from the defects and impurities with the minor impact of metal-induced gap states. The potential strategies for carefully engineering the metal deposition approach are also discussed. This work unveils the origins of EF pinning at metal/TMD interfaces experimentally and theoretically and provides guidance on further enhancing and improving the device performance.

In Situ X-ray Diffraction Studies on the Reduction of V2 O5 and WO3 by Using Hydrogen

The reduction of metal oxides with hydrogen is widely used for the production of fine chemicals and metals both on the laboratory and industry scale. In situ methods can help to elucidate reaction pathways and to gain control over such synthesis reactions. In this study, the reduction of WO₃ and V₂ O₅ with hydrogen was investigated by in situ X-ray powder diffraction with regard to intermediates and the influence of heating rates and hydrogen flow rates. Mixtures of V₄ O₉ , V₆ O₁₃ and VO₂ in two modifications were identified as intermediates on the way to phase-pure V₂ O₃ . None of the intermediates occurs in a single phase and therefore cannot be prepared this way. In contrast, the intermediates of the WO₃ reduction, H_0.23 WO₃ and W₁₀ O₂₉ , appear consecutively and can be isolated. For both reactions, the heating and flow rates have little influence on the formation of intermediates.

Bi-functional hydrogen and coordination bonding surfactant: A novel and promising collector for improving the separation of calcium minerals

Mono-functional chelating collectors exhibit limited selectivity in the flotation of minerals. In particular, the selective separation of calcium minerals presents a significant challenge because mono-functional chelating collectors, such as fatty acid, indistinguishably adsorb onto mineral surfaces by coordinating with the same metal cation (Ca²⁺). Thus, there is an urgent need to develop new-mode-functional collectors to separate calcium minerals and a need to understand the underlying chemoselectivity. Given the difference of the hydrogen bonding ability of anions with fluorite, calcite and scheelite surfaces, the introduction of additional hydrogen bonding functional groups into collector molecules is a novel strategy to improve selectivity. In this study, a hydrogen and coordination bonding (bi-functional) collector, 2-cyano-N-ethylcarbamoyl acetamide (CEA) was developed, which could form coordination bonds with the Ca²⁺ ions (by carbonyl groups) and hydrogen bonds with the anions (by amino groups) on calcium mineral surfaces. The results of flotation tests showed that CEA can selectively separate fluorite and calcite from scheelite at pH 7. The promising selectivity of CEA lies in both the electrical properties and the anions' hydrogen bonding ability with the three calcium minerals. The negatively charged scheelite surfaces are not conducive to coordination bonding with CEA while the positively charged fluorite and calcite surfaces are. Besides, the hydrogen bonding ability of fluorite (F^-) and calcite (CO₃^2-) with carbamido in CEA is higher than that of scheelite (WO₄^2-), and this also plays an essential role. This coordination and hydrogen bonding based surfactant design protocol has a great potential in the development of tail-made collectors/depressants for the separation of other oxidized minerals.