Hafnium oxides‐based ferroelectric materials are promising for applications in nonvolatile memory devices. To control the ferroelectricity of such materials, it is necessary to tune their polymorphism, interfacial features, and defect (oxygen vacancy) distribution. A strategy is described for enhancing the ferroelectric properties of polycrystalline hafnium zirconium oxide (HZO) ultrathin films by modifying the oxygen pressure during the device preparation stage, which involves thermal annealing of TiN electrodes that serve as oxygen reservoirs. Microstructural and chemical characterizations along with theoretical analysis reveal that interfacial layers of TiO2−x (or TiOxNy) can characteristically form between the TiN electrode and the HZO thin film, depending on the oxygen treatment conditions. These interfacial layers directly affect the polymorphic distribution of the as‐deposited HZO. In particular, the engineered interfacial TiO2−x layer facilitates the generation and stabilization of ferroelectric orthorhombic phase HZO by promoting the uniform distribution of oxygen vacancies. Electric field cycling tests further highlight the enhanced ferroelectric polarization and coercive voltage following interfacial engineering. The results presented herein demonstrate successful tuning of the structural and interfacial properties of polycrystalline HZO devices, thus enabling control over their ferroelectric characteristics, which is critical for the fabrication of devices with designed functionality.
Photoelectrochemical (PEC) water splitting using photo-active nanomaterials is a promising technique to generate hydrogen in a sustainable way. The charge-transfer and charge separation in photoelectrode are important factors in determining the performance of PECs. Here, we utilize single layer graphene as a photocatalyst on WO3 thin film / Nb:SrTiO3 (100) structure to enhance oxygen evolution reaction in alkaline electrolyte. The graphene-decorated photoelectrodes exhibit efficient charge transfer due to electronic and electrochemical properties of graphene edges, which leads to decreasing onset potential and increasing photo current density from 237 μA/cm2 to 763 μA/cm2 at 1.23 V vs RHE. In addition, such extremely thin layer can protect the photoelectrode from chemical corrosion without disturbing the light absorption. We discuss the role of graphene edges for photoelectrochemical water oxidation. Thus, these results can provide a new route for advanced designs of nanomaterial-based PECs devices.
Acknowledgments This research was supported by next generation engineering researcher program of national research foundation of Korea (NRF) funded by the Ministry of Science, ICT (NRF-2019H1D8A2106002).
Cellulose nanocrystals (CNCs) have emerged as a promising templating material due to unique features, such as high surface area, surface hydroxyl groups and rod-like shape, which allow for sustainable nanoscale control of advanced functional materials. Especially, such high surface functionality and specific morphology can be imparted on the resultant nanomaterials with beneficial properties during templating. Here, we present synthesis of one-dimensional (1D) nanostructured vanadium oxides (NVOs), such as VO2(B) and V2O5‧nH2O nanobelts (NBs), with single- crystalline by hydrothermal treatment using CNCs as a sacrificial template. Importantly, the single-crystal vanadium oxide nanobelts exhibits the enhanced electrochemical performance of Li ion batteries with high specific capacity (>300 mAh/g) and long lifespan (>244 mAh/g at 50 cycles) compared to the polycrystalline nanoflakes (NFs) counterpart. Furthermore, we suggest that during hydrothermal treatment the sacrificial CNCs template-derived carbon is beneficial for electron transfer in cathode materials. Thus, we demonstrate that the utilization of CNCs templating to develop novel single-crystalline oxide cathode nanomaterials can provide a fruitful pathway for extraordinary electrochemical performance of next-generation alkaline batteries.
To protect the active layer, which are inter layer dielectrics (ILD) and metal lines, from being damaged by UV laser during the etching process, etch stop layers (ESL) are used in patterning process of the integrated circuits (ICs) fabrication in back end of line (BEOL). The ESL material should have a higher etch selectivity than the active layer. Therefore, it must have a low dielectric constant and high chemical resistance. Aluminum oxide compounds (AlOx, AlOC, AlON, etc.) are highly suitable for use as ESL due to the low dielectric constant between about 4 and 9, high etch selectivity, high density (2.5-3.8 g/cm3) and pattern transfer capability. We focused on lowering the dielectric permittivity and increasing the density by controlling the precursor/reactant pulsed time of atomic layer deposition (ALD).
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