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Indium-based amorphous metal oxides (AMOs) are important materials that enable a wide range of electronic and optoelectronic applications. The metal cations that substitute for In are known to effectively tune the material properties as well as to retain the desirable amorphous state when subjected to high operating temperatures. While much attention focuses on property tuning, there is less focus on those fundamental factors that enhance thermal stability. Hence, in this paper, we employ in situX-ray scattering and ab initiomolecular dynamics (MD) to systematically study the effects of secondary cations on the crystallization process. A series of amorphous (In1–xMx)2O3thin films (M = Sn, Zn, and Ga; x= 5, 10, 20, and 30%) are grown by pulsed laser deposition (PLD) under identical deposition conditions. The films are then annealed isochronally, and the degree of crystallinity, crystallization temperature (Tc), and crystallization time (τc) are determined by a quantitative analysis of the time-evolved X-ray scattering patterns. All doped films have a Tchigher than the corresponding undoped films, and significantly higher Tcvalues (>400 °C) are found at the higher degrees of Zn and Ga substitution (20 and 30%). For the same level of substitution, Tcincreases in the order Sn > Zn > Ga, suggesting increasing crystallization barriers and local structural disorder. All crystallized films are in the common cubic phase except for IZO-20%, where an additional rhombohedral phase is observed throughout the crystallization process. The pole figure analysis reveals the detailed preferred orientations buried in postannealed crystalline films. Complementary ab initiomolecular dynamics (MD) simulations of the as-deposited AMOs provide an informative theoretical perspective. The medium-range structures characterized by the value and variance of effective coordination numbers around metal and oxygen atoms are found to play an important role in explaining the observed crystallization dynamics in these oxides.

Anion doping of transparent amorphous metal oxide (a-MO) semiconductors is virtually unexplored but offers the possibility of creating unique optoelectronic materials owing to the chemical tuning, modified crystal structures, and unusual charge-transport properties that added anions may impart. We report here the effects of fluoride (F–) doping by combustion synthesis, in an archetypical metal oxide semiconductor, indium oxide (In–O). Optimized fluoride-doped In–O (F:In–O) thin films are characterized in depth by grazing incidence X-ray diffraction, X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure (EXAFS). Charge-transport properties are investigated in thin-film transistors (TFTs), revealing that increasing fluoride content (0.0 → 1.57 atom %) slightly lowers the on-current (Ion) and electron mobility due to scattering from loosely bound F–centers but enhances important TFT performance parameters such as the Ion/Ioffratio, subthreshold swing, and bias stress stability, yielding superior TFT switching versus undoped In–O. These results are convincingly explained by ab initio molecular dynamics simulations and density functional theory electronic structure calculations. Combined with the EXAFS data, the experimental and theoretical results show that F–hinders crystallization by enhancing the local and medium-range disorder, promotes a uniform film morphology, and favors the formation of deeper, more localized trap states as compared to F–-free In–O. These data also show that the local organization and electronic structure of amorphous F–-doped oxide semiconductors are significantly different from those of F–-doped crystalline oxide semiconductors and suggest new avenues to further modify a-MOs for enhanced optoelectronic properties.

Copper cobalt selenide, CuCo2Se4, has been identified as an efficient catalyst for electrocatalytic CO2reduction, exhibiting high selectivity for carbon-rich and value-added products. Achieving product selectivity is one of the primary challenges for CO2reduction reactions, and the catalyst surface plays a pivotal role in determining the reaction pathway and, more importantly, the intermediate adsorption kinetics leading to C1- or C2+-based products. In this research, the catalyst surface was designed to optimize the adsorption of the intermediate CO (carbonyl) group on the catalytic site such that its dwell time on the surface was long enough for further reduction to carbon-rich products but not strong enough for surface passivation and poisoning. CuCo2Se4was synthesized through hydrothermal method, and the assembled electrode showed the electrocatalytic reduction of CO2at various applied potentials ranging from −0.1 to −0.9 V vs RHE. More importantly, it was observed that the CuCo2Se4-modified electrode could produce exclusive C2 products such as acetic acid and ethanol with 100% faradaic efficiency at a lower applied potential (−0.1 to −0.3 V), while C1 products such as formic acid and methanol were obtained at higher applied potentials (−0.9 V). Such high selectivity and preference for acetic acid and ethanol formation highlight the novelty of this catalyst. The catalyst surface was also probed through density functional theory (DFT) calculations, and the high selectivity for C2 product formation could be attributed to the optimal CO adsorption energy on the catalytic site. It was further estimated that the Cu site showed a better catalytic activity than Co; however, the presence of neighboring Co atoms with the residual magnetic moment on the surface and subsurface layers influenced the charge density redistribution on the catalytic site after intermediate CO adsorption. In addition to CO2reduction, this catalytic site was also active for alcohol oxidation producing formic or acetic acid from methanol or ethanol, respectively, in the anodic chamber. This report not only illustrates the highly efficient catalytic activity of CuCo2Se4for CO2reduction with high product selectivity but also offers a proper insight of the catalyst surface design and how to obtain such high selectivity, thereby providing knowledge that can be transformative for the field.